Optical network virtualization

With the deepening of SDON technology research, industry and gradually discover Optical Network virtualization is a major part of the basis and premise-based open control SDON also SDON inside the controller can not be missing. For SDON technology, network virtualization is an important part of the support network of diverse structures, network architecture supports simultaneous multi-carrier presence. It supports a range of open programmable network interface and create a virtual abstraction layer for the network physical layer device. Abstraction layer allows the user to control and change the appropriate network status, and shields the user from the physical layer of the network operation and use complex, allowing users to deploy new applications more easily on an abstract level, thereby enhancing application flexibility.

The main difference SDON in network virtualization and broad network virtualization is the ability to virtualize the subject. Often, people think SDN data network capabilities from a single, isolated disparate hardware platforms, and in the form of a virtual machine to manage these components. The SDON Network virtualization will make these simplifications, generalization. For example: Shielded physical plane details and automate planning, configuration, management, optimization and protection and restoration. Manual processes and planning processes also to the evolution of virtualization, automation and increased flexibility enables operators to reduce high-level workloads, placing the lower level, including optoelectronics levels.

In SDON architecture system, optical network virtualization main aims: the physical layer of optical network infrastructure virtualization, and then complete the optical network services abstraction and encapsulation, services and physical layer network infrastructure will provide separation , for the upper user programmable, definable virtual layer optical networks. Can have a profound impact on the future development of optical networks, operators can pass to an open application layer user interface, the optical network infrastructure control to the application layer user. According to the user's level of competence, some or all of the network resources open virtual layer optical networks, allowing users to virtual optical network resources available on the basis, according to their need for access and control - allows users to integrate their own definition of network resources to achieve "The optical network resources as a service" technology concept OAAS of.

SDON technology advantages and characteristics

SDON technology has three major advantages. First, it can effectively solve the interconnection between heterogeneous networks. Through OpenFlow and other related agreements to expand the development of object-oriented interactive control interface enables heterogeneous network information abstraction and cross-layer network control integration, resulting in the access network and the core network, data networks and optical networks, cable networks and between the radio network set up with a unified control system of the new heterogeneous network architectures. Second, the arrangement of optical network to meet user needs. For flexibility in the use of network equipment, operations and sales, and it enables users to faster achieve the desired services. Third, SDON can bring optical network resource virtualization management. It can cover the entire range of network equipment OTN products to better play the advantages of network infrastructure resources, through open unified resource management platform that allows the use of network resources optimized. It features multi-domain SDON aspect of hierarchical control architecture mainly as follows:

1, the whole structure is divided into four levels: APP application layer, Orchestrator total control layer, single domain controller layer, and Optical Network device layer.

2, NBI focus APP application layer interfaces with Orchestrator total controller uses Restful interface mechanism. Restful mechanism architectural style draws WEB services, with no state, to achieve simple and efficient, loosely coupled, scalable and other technical advantages, so as to achieve open control SDON of NBI, programmable, definable and other technical characteristics, provides a natural technology support.

3, SBI interfaces single domain controller layer and between the layers of optical networking equipment and OTN networks as much as possible compatible WASON earlier deployed to ensure network interoperability SDON these network devices, better meet the smooth deployment of business operators upgrade, gradual evolution of ideas.

MPO Connector and MTP connector

With the rapid development of data centers, cloud computing, cloud storage and other applications gradually penetrated the bandwidth requirements of each industry, network communication also will increase rapidly, while the high speed, high capacity, high-bandwidth often requires more space and higher costs, which exist this long-term contradiction, MTP/MPO fiber optic wiring standard has become the best solution for the current density and high bandwidth. MTP and MPO market today exist two kinds of fiber optic connection system, they are very similar to some extent, mutually compatible, and that they really tell the difference.

MPO connector

MPO (Multi-fiber Pull Off) is Japan's NTT Communications designed the first generation of shrapnel clamping type multi-core optical fiber connector, is the name of several companies now produce a multi-pin connector head. The MTP, by the United States USConec company registered the brand, specifically refers to the production of unique MPO connector type.

internal components comparison

What is the MPO connector?

MPO is a "multi-fiber pull off" the abbreviation. This connector ferrule has more than one core, by mechanical means snaps into place.
Now various manufacturers on a market multiple MPO design, different types of connectivity products, its performance and cost are very different. Some of the performance characteristics of the product to make it more prominent, and some MPO connector can be matched with many different brands of products, but some are not, this depends on how close the interworking of these connector design with standard products. MPO connector complete definition, refer to the implementation of IEC-61754-7 and EIA / TIA-604-5 (aka FOCIS 5).

What is a MTP connector?

MTP connector is an innovative design with multiple high performance MPO connector with respect to the average for the MPO connector, MTP fiber optic connector on the optical and mechanical properties have been strengthened. MTP connectors are fully compliant with all MPO connector professional standards, including EIA / TIA-604-5 FOCIS 5 and IEC-61754-7.

MPO connector is consistent with industry standards mutual pairable MTP connector, which means replacing the MPO connector with MTP connector for better performance is possible. Most follow the MPO connector of old design performance is quite limited, it can not provide the same high performance with MTP connector.

Why MTP connector is described as a high performance MPO connector?

Through a specially designed MTP connector performance and availability were improved compared with MPO connectors. This design feature MTP is unique and protected by patents. The main features are as follows:

1, MTP fiber optic connector sleeve frame parts can be easily removed.

MT ferrule design can be reworked and re-grinding in the production of energy to ensure that performance is not lost. Yin and Yang in the field even after assembly flexible to change, ferrule assembly can be over after interference detection.

2, MTP fiber optic connector ferrule float to improve transmission performance when mechanical docking. It allows two connectors under the influence of external forces make matched ferrule to maintain good physical contact.

3, MTP fiber optic connector elliptical guide pin is used in stainless steel, oval docking guide pin can improve the accuracy and reduce the wear of the guide hole, such that the optical fiber connector MTP more durable to maintain high performance transmission.

4, in the MTP fiber optic connector has a metal clip for fixing the push pin ring. Specific features:

Prevent the loss of the guide pin;

Concentrated pressure generated by the spring;

Prevent the spring from touching the fiber friction in the mechanical expansion process caused damage to the optical fiber;

5, MTP fiber optic connector spring design maximizes ribbon clearance 12 core and multi-core optical fiber ribbon applications to prevent damage.

6, MTP fiber optic connector having at least four standard matching parts, can be adapted to different types of cable, more practical, including:

Round cable loose tube structure;

Oval coat of ribbon cable;

Strip bare fiber;

Short tail cuff connector parts, very suitable for use in a small space, reduction of 45% of the volume.

Software-defined optical transport network make the network should be the need to change

Last year, China established the broadband strategy released two milestones: the 2015 basic realization of urban fiber-to-floor home in rural broadband into the village into the village, urban and rural households broadband access basic to 20Mbps and 4Mbps, some developed cities met 100Mbps; to 2020, a comprehensive broadband network covering urban and rural, urban and rural households to broadband access, respectively, 50Mbps and 12Mbps, the developed part of the city home users up to 1Gbps. This means that in the next few years, operators must continue to upgrade optical networks to achieve these goals. It is worth noting that the network bandwidth is growing at the same time, an endless stream of new broadband services, intelligent optical network flexibility and put forward higher requirements. Promotion of software-defined optical transport network (SD-OTN) to achieve network virtualization to maximize the use of network resources, so that an effective means of networks should the need to change.

Expansion and intelligent optical networks are two main trends of development. Cisco predicts that global data traffic in the next few years will show explosive growth. The next five years, the compound annual growth rate of global traffic will reach 66 percent, the growth rate in Asia as much as 76%. Nokia Communications released a research report pointed out that by 2020, the daily per capita consumption of personalized traffic will reach 1GB. Huawei predicts that the next three years, China backbone network traffic growth rate of up to 70% of the total bandwidth of backbone transmission network will reach 150Tbps, there may even exceed 200Tbps. In anticipation of traffic turmoil, carriers and communications companies are actively studying and deploying 100G and ultra-100G technologies. Single-carrier technology has been difficult to meet the needs of rapid development of traffic, the use of multi-carrier technology to improve spectral efficiency has become the focus of attention of the industry.

At the same time, with the growing number of broadband users, the type of intelligent terminal has become even more rich, cloud computing, big data, networking and other applications rise and gradually becoming more mature. Optical network support broadband services rendered dynamic trends. Traffic Storm is not evenly distributed, network traffic is often at different times are not the same, monthly, daily and even hourly flow situation is different. Such as big game day might have compared with the usual more users watch online live video; and if in the neighborhood during the day tend to be less traffic, more traffic at night, but during the day in the office area in general is more traffic, less traffic at night. If we can achieve dynamic network resource management and scheduling will undoubtedly maximize the use of network resources, thereby reducing overall costs. The conventional automatic switched optical network, generalized multi-protocol label switching architecture has been unable to meet this demand, an urgent need to introduce new technologies like software-defined optical transport network.

Software-defined optical transport network is the direction of the development of next generation optical transport networks, its design ideas from computing software-defined network (SDN). SDN is a new network architecture, network control plane and data forwarding plane will be separated, and programmable control. SDN architecture typical of three layers, the top layer of the application, including a variety of services and applications; middle control layer is mainly responsible for handling data plane resource scheduling, maintenance of network topology and status information; the underlying infrastructure layer is responsible for data processing based on the flow table, forwarding and status collector. Its main advantages as follows: standardization of hardware, reducing system hardware requirements, in order to achieve cost reductions; intelligent network management fully realized by the software to improve the ease of operation; simplifies network configuration process can rapid opening of new business.

SDN application in the main operators in the field of IP data networks, data centers and optical transmission network of the three scenarios. Among them, the software-defined OTN flexible pipes, dynamic bandwidth and programmable three characteristics, it is possible to achieve flexible scheduling hardware, network software dynamically adjust resources will help operators to manage network resources fine. Software-defined optical transport network of programmable optical network transmission controllers and programmable resource virtualization technology to provide efficient, flexible, open network services for different applications. It requires flexible optical, electrical function modules, programmable light system that supports OpenFlow standard control interface, providing an open API.

Currently, SDN standardization work is still in its infancy, software-defined optical transport networks need to overcome software programming optical path flexible switching, software-driven optical transmission adjustment key technology software extensions of optical automatic networking, as it continues to mature and widely applications, broadband network is expected to usher in a new round of changes.

Gigabit broadband killer application call

CIO website recently published a signed Steven Max Patterson's article "Gigabit Internet out of the small market." The article said that Google Fiber Gigabit Internet can be verified attractive prices to win market. Now, users have, the next step is to find the killer application.

Since 2011, Google launched the $70 per month gigabit fiber-optic broadband service in Kansas City since, according to market research firm, principal analyst Michael Render of RVA LLC company data, the United States currently has 83 ISP learning Google started to provide gigabit broadband services , prices are between $50 to $150. Over the past few years, the average annual growth rate gigabit broadband users reached 480%. From the third quarter of last year to the second quarter of this year, the number of users Gigabit to 174,000 from 40,000. Moreover, Comcast and other companies have even launched a 2Gbps of broadband services.

Optical devices as well as optical equipment, continuous improvement and falling prices of fiber optic cable technology led directly to the decline in the price of broadband services. According to data DrPeering website, since 1998, the price per Mbps broadband services has remained slow down more than 30% annually. (This will be another of Moore's Law it?)

internet transit pricing

Broadband service prices continue to decline, the direct driving force behind the competition. Google such companies seem unattainable with conventional prices provide gigabit broadband services. Traditional telecommunications operators have been complaining endlessly. Broadband is no longer able to become an effective telecom operator revenue sources, like the previous voice services, SMS same. Now more like a Gigabit broadband internet. With Patterson to the article, as iPhone has just launched the era, the real significance App, few users are few, and the platform to wait until there are more applications and users increase came in.

By the US government as well as Juniper, Cisco, Verizon, Google, Comcast and other non-profit organization jointly sponsored US Ignite now are trying to play a gigabit broadband era of application incubator to help developers and researchers to showcase their Gigabit applications. HD video, remote meetings, remote education, remote industrial control, virtual reality, telemedicine, etc., may be the opportunity to show their talents gigabit broadband. HD and low latency Gigabit broadband two advantages. It has been through the use of Gigabit broadband demonstration halfway across the globe violin ensemble. No ultra-wideband, this trio is not possible.

Editing in the Dabie Mountain area travel these days, a particularly deep feeling is that there's a beautiful, if we can take advantage of broadband networks configure remote education, health care and other resources, there is a remote meeting to address the business office, plus high-speed rail will attract more more people settle in their hometowns, and even stranger to pioneering, for the construction of China's urbanization significance. Editing years have seen a Cisco's video conferencing system, which went to the site of feeling is very strong. But that system was very expensive, now can reach that level conference system is not cheap. Editing was wondering if we can use to launch a low-cost Gigabit broadband or even free desktop video conferencing system, the enterprise will be very attractive. SDN and cloud now appears to promote all software-based, cloud-based, but with Gigabit broadband can truly cloud-based.

Telecommuting is one aspect of telemedicine is one thing more interested in editing recently. Fiber broadband will focus decentralized medical resources, work best thing. A few days ago in Denver, is there a summit on health IT, which has a lot of discussion on telemedicine. HCI (Health care informatics) website gives a detailed report. The article said that the United States might is at a turning point in telemedicine. The US government has introduced subsidies telemedicine development policy. The meeting room, 40 percent of the audience said they had begun telemedicine attempt.

With telemedicine, distance education, and so on, Chinese people still have to go to Beijing, Shanghai, Guangzhou and Shenzhen to focus it? Gigabit fiber era to come quickly.

What is the SDN?

Software-defined networking (Software Defined Network, SDN), is a new kind of network innovation Emulex network architecture, network virtualization is an implementation of its core technology OpenFlow network devices through the control and data planes separated, in order to achieve the flexible control of network traffic, the network as a conduit to become more intelligent.


SDN architecture typical of three layers. The upper one is the application layer, including a variety of services and applications; middle control layer, is responsible for processing the data plane resource scheduling, maintaining the network topology and status information; the underlying infrastructure layer, is responsible for the data stream based on the table processing, forwarding and status collector.

The main advantage of SDN as follows: standardization of hardware, reducing system hardware requirements, in order to achieve cost reductions; intelligent network management fully realized by the software to improve the ease of operation; simplifies network configuration process can rapid opening of new business.

POL - Passive Optical LAN

Shanghai Bell POL program uses GPON passive optical LAN technology, based 7360 ISAM FX optical access products, can provide FTTD, WIFI backhaul, video surveillance, LTE small base station backhaul (MBH) and other diverse businesses POL deployment scenarios and flexible to meet the diverse corporate office network deployment requirements.

For enterprise network deployment features, Shanghai Bell POL Passive Optical LAN solution provides a variety of ONU equipment for business users to choose. For example, voice, data needs, the user can select I-240G-D voice and data coverage for WIFI backhaul, the user can choose to WIFI AP 040P support POE power supply or SFP ONT supports direct access to the new generation 802.11ac AP.

In order to meet the security needs of enterprise users, Shanghai Bell POL resolve outstanding security program implemented security enhancements made in the dimension of the physical layer, the Ethernet layer, IP layer, and management levels, etc., to solve the user's worries.

The overall design of CFP optical module system

40Gbit/s CFP overall design of the optical module is mainly to solve the transmitting unit, the receiving unit implementation issues and control unit. Specific design methods are introduced each unit below.

In the transmitting unit, the selection of 10Gbit/s DML (directly modulated laser) as TOSA (light emitting component), laser driver integrated circuit chips within the drive. Laser driver receives a differential input data and provide a laser bias and modulation currents. Since the semiconductor laser slope efficiency will vary with changes in temperature, it is necessary to APC and extinction ratio compensation circuitry to achieve a stable laser average optical power. Lasers PD (photodiode) Monitoring LD optical output power and the output value of the feedback monitor PD to MCU (microcontroller), MCU by detecting feedback IBias values ​​to control the bias current output, thereby adjusting the bias Set circuit causes LD remains constant optical power output. Meanwhile, in order to avoid high-speed PCB (printed circuit board) on the other line interference on signal lines in the wiring of the signal differential signal transmission lines.

The receiving unit is mainly composed of PIN (photodiode) and TIA (transimpedance amplifier) ​​package together photodetector and limiting amplifier, thus completing the optical / electrical conversion. Four different wavelengths of light signals from each detector receives the appropriate wavelength and converts it into an electrical signal having a certain level, and then after the limiting amplifier signal power progressively larger, simultaneous extraction and recovery by the CDR circuit clock signal The signal received decision value dynamically created to allow data recovery and output.

The control unit uses MCU chip, through the acquisition of digital information for each of the corresponding port real-time monitoring of each channel voltage, temperature, laser bias current, input optical power and received optical power and reporting, in order to achieve the following three major functions: (1 ) communicate with the host computer system; (2) extracting module internal analog and digital information, testing, reporting and alerting; (3) modules within the various parameter settings intelligent control.

The basic principle of SDH

The basic principle of SDH
The basic principle of SDH
SDH level information structure is referred to as Synchronous Transport Module using STM-N (Synchronous Transport Mode, N = 1,4, 16,64), the basic module STM-1, four STM-1 synchronous multiplexing constitute STM- 4, sixteen STM-1 or four STM-4 synchronous multiplexing constitute STM-16, four STM-16 synchronous multiplexing constitute STM-64, or even four STM-64 synchronous multiplexing constitute STM-256; SDH using massive frame structure to carry information, each frame consists of longitudinal and transverse row 9 column 270 × N bytes, each byte containing 8bit, the entire frame structure is divided into a section overhead (Section OverHead, SOH) area, STM-N payload area and a management unit pointer (AU PTR) three regional areas, where section overhead area is mainly for network operation, management, maintenance and finger together to ensure that information can be transmitted properly flexible, it is divided into regenerator section overhead ( Regenerator Section OverHead, RSOH) and multiplex section overhead (Multiplex Section OverHead, MSOH); with a snap-pointer; payload area used to store bits of real information for business and a small amount of overhead bytes for channel maintenance channel management to indicate when the message payload area at the exact location of the first byte of STM-N frame so that the reception can correctly extract payload. SDH frame transmission when the press from left to right, arranged in order clusters of type stream from top to bottom sequentially transmitted every frame transmission time is 125μs, transmitted per second 1/125 × 1,000,000 frame of STM-1 in terms of per frame bit number 8bit × (9 × 270 × 1) = 19440bit, the STM-1 transfer rate is 19,440 × 8,000 = 155.520Mbit/s; STM-4 and the transfer rate is 4 × 155.520Mbit/s = 622.080Mbit/s; the transmission rate of STM-16 is 16 × 155.520 (or 4 × 622.080) = 2488.320Mbit/s.

When the SDH transmission traffic signal traffic signal to enter a variety of SDH frames to go through mapping, positioning and multiplexing three steps. ITU-T G.707 standard recommendations multiplex mapping structure as shown.
ITU-T G.707 standard recommendations multiplex mapping structure
ITU-T G.707 standard recommendations multiplex mapping structure

Mapping is the signal to go through a variety of rate justification loaded into the appropriate standard containers (C), then add the path overhead (POH) forming a virtual container (VC) of the process, the frame phase deviation occurs is called frame offset.

Positioning the frame offset information that is incorporated into the tributary unit (TU) or management unit (AU) process, through tributary unit pointer (TU PTR) or administrative unit pointer (AU PTR) function to achieve.

The concept is relatively simple reuse, reuse is a plurality of signal adaptation into the lower-order channel layer order path layer, or a plurality of higher-order channel layer signal into the multiplexing process of adaptation by layer. Multiplexing is staggered by byte interleaving manner TU organized into higher order VC or the AU organized into STM-N process, since TU and AU pointer after each VC signal processing branch has phase synchronization, so that the complex process is synchronous with string theory and data multiplexing and conversion are similar.

OTN is the best choice for the development of transport network technology

OTN for the application of new technology, but its development has been years of history, has matured. ITU-T from 1998 started the OTN series of standards development, by 2003 the main standard is basically sound, logical interface such as OTN G.709, OTN physical interfaces G.959.1, equipment standards G.798, jitter standard G.8251 protection switching standards G.873.1 and so on. In addition, for OTN-based control plane and management plane, ITU-T has completed the development of appropriate primary specification.

In addition to improving the standard addition, in recent years, OTN technology equipment and testing instruments, it is also rapid progress. Mainstream transmission equipment manufacturers are generally supportive of one or more types of OTN equipment. In addition, the mainstream delivery instrument firms generally can support OTN functionality of the instrument.

With powered and OTN technology business achieved rapid development and growing maturity, OTN test technology has been applied topically or business network. In the United States and Europe, a relatively large network operators such as Verizon, Deutsche Telekom and so has established a G.709 OTN network, as a new generation delivery platform. Expected in the next few years, OTN will usher in large-scale development.

Foreign operators the ability to support the OTN transmission network interface is generally clear demand has been proposed, but the actual network applications ROADM equipment which form the main places, mainly the cost and maintenance of network size and other factors closely associated with network management. Domestic carriers for the development and application of OTN technology is also quite concerned about, from the beginning of 2007, China Telecom, China Netcom and former China Mobile Group and so has undertaken applied research and test validation OTN technology, but the network is also part of the province Local deployed by cross-layer based on OTN equipment OTN-based transport pilot network technology, network node, there ROADM-based OTN equipment. Due to the high cost of ROADM relative to the current maintenance system for maintenance, so ROADM just some operators were using small-scale experiments, and based on cross-layer OTN equipment has been used commercially in large scale China Mobile, China Telecom, China Unicom, radio and television and other major carriers, as well as Southern Power, China Petrochemical and other large private networks.

As the best choice for the development of transport network technology, can be expected in the near future, OTN technology will be more widely used as carriers to create a superior network platform to expand business market the technology of choice.

PMC metro OTN help China achieve 400G and OTN switching technology

Recently, PMC has released its newest DIGI-G4-- latest generation of OTN chip. PMC Chinese R & D Center for Communication Products Division Director Zhang Tianyu introduced to, DIGI-G4 is the first industry's highest density single-chip, can support 400G. Further integration of a large number of equipment manufacturers put the device on the board, resulting in a large power cost increases, while DIGI-G4 to peripheral devices incorporate internal, so that each port 100G power by 50%.

Interview, PMC DIGI-G4 product line manager Kevin representation, PMC developed this chip is completely respond to the needs of the market, that the rapid growth of bandwidth, the bandwidth will double every two years, which in the world are Such a trend. On the other hand, 100G become the standard has become a trend, this standard mainly in the backbone network, including China Mobile, China Telecom is largely concentrated in such a network backbone, certainly in terms of the operators to the metro, these bandwidth from the metro to the demand increase network access, metro bottleneck is additionally backbone.

In addition to bandwidth requirements, is the data center needs. Kevin stressed that large scale data centers, they are to complete the interconnection between the data centers. DIGI-G4 chip design at the beginning of this just like Google, AMAZON have conducted technical exchanges, they are particularly urgent need is encrypted. Light layer of encryption is not enough, mainly because we have to have encryption in the business layer, we DIGI-G4 chip encryption can be done in the 100G OTN, not only in 100G encryption, I can rate the operational level in my son's entire 100G You can be encrypted.

Zhang Tianyu said, OTN switching is actually OTN electrical cross concept think back 45 years ago when the mainstream use in backbone OTN, or one of the technical support line, in fact, a few years ago that is electrically OTN Cross into the mainstream over the past few years, we can see that a carrier is a strategy they deploy the branch line from the previous one turned into OTN switching, China at the forefront, China's leading OTN deployment in the world, We see in the world is a very clear trend in the world's top ten operators have nine full deployment of OTN electrical cross-based network, see the full flexibility of this technology to operators on services.

Currently, the chip supplier in terms of providing light to the equipment manufacturers a chip is not enough, cost pressures down the pressure from the operator level, for equipment operators in terms of R & D investment is controlled, previously invested heavily in software research and development team We do such a transmission device is unrealistic, so a lot depends on chip manufacturers, can have a complete package in the release of the chip at the same time available to them so that they can be completed within a short period of their development.

Zhang Tianyu finally said, PMC continues to invest in software, accounting for the company's software engineers than hardware engineers now, we offer a very complete package, and after the actual deployment verification, to reduce secondary research equipment manufacturers.

Ultra-narrow linewidth laser spectroscopy measurement solution

Spectral linewidth measurements are to laser spectroscopy components. Different types of lasers, its value will have a width of several orders of magnitude difference: After continuous laser frequency stabilization especially its spectral linewidth can achieve 1Hz or less, and some lasers can cover a wide range of a few THz spectrum, such as femtosecond lasers.

Original value spectrum by Shawlow-Townes linewidth given expression, it shows essentially the width is a phase change caused by the spontaneous emission process caused. For the rare-earth doped lasers, such as erbium-doped fiber laser, Shawlow-Townes linewidth at mHz range value.

Generally, real narrow linewidth laser linewidth is difficult to measure: All measurements are subject to limited limited measurement time, and frequency caused by different noise sources during this period by the width of the laser light source Jitter, such as pump laser noise, acoustic noise, vibration noise. Narrow linewidth laser, for example, the measured linewidth can be seen as an integrated frequency jitter measurement system within the integration time due to technical noise source.

Linewidth measurement method

Self-heterodyne method:
Under normal circumstances, the use of self-heterodyne beat frequency measurement laser spectral linewidth. In this method, the signal via a two-way unbalanced Mach - Zehnder fiber interferometer, the way in which there is AOM frequency shifter, another way to delay fiber (Figure 1). For the measurement of narrow linewidth lasers, delay fiber length is usually 25km, corresponding to a time delay of about 120us. Two optical interference signal to produce a shape and width of the spectrum associated with the laser linewidth.

Self-heterodyne method
Self-heterodyne method

The measurement of spectral analysis, there are two cases: one is smaller than the coherence length of the laser interferometer arms or near poor, one is laser has a longer coherence length (the sub-coherent domain). Less than the coherence length of the laser interferometer arms difference under ideal conditions will produce a half-height, half-width equal to the width of the laser spectrum Lorentz spectrum (Figure 2).

Strictly speaking, the herein "ideally" refers only to the laser light having a white noise spectrum (corresponding to the coherence time of the exponential decay). Most very narrow spectral linewidth lasers contain a large amount of Gaussian noise (such as pump noise, vibration and noise, acoustic noise). This leads to a more complex Voigt line, it is a Gaussian and Lorentzian line linear convolution. For the rare-earth doped fiber laser, Lorentzian linewidth values ​​are generally small which is a linear function predominantly Gaussian line. This corresponds to the frequency of the noise spectrum in 1 / f function is presented in the form until the high frequency band (> MHz). Spectrum does not show the white noise floor, it's just by a trend / f function extends until the shot noise and ASE bands appear obvious. However, for the Lorentz line width, laser manufacturers are still often take a conservative measure, that measure since heterodyne linear 20dB below the peak point of the spectrum width, Gaussian influence here is not significant from the corresponding Lorentzian half-width also easily calculated, about 20dB 10% width.

Figure 3 illustrates the self-heterodyne laser linewidth measurement of C15: from heterodyne linewidth measured half-value width of approximately 32kHz, and 120kHz 20dB at half-width. Graphic display, the corresponding half width Gaussian curve 32 kHz, Lorentzian line function 20dB at half width 120kHz, corresponding Lorentzian line width of 12kHz; either Gaussian or Lorentzian line functions are not well matched and measured. Lorentzian values ​​intersect at only -20dB at Match difference clearly illustrates, using traditional methods and only this value as a Lorentzian laser linewidth measurement, because measured linewidth significantly narrower. As a comparison, the figure shows the fitted curve Voigt's.

For the coherence length is significantly greater than the difference between the laser interferometer arms, from the outside with a clear difference between the linear function linear function Lorentzian deviating. This is due to the coherent interference of light from the two paths of the interferometer. Figure 4 illustrates a case where the optical linewidth of 700Hz. Linear function of AOM by the frequency-dependent Dirac function and interferometer transfer function Δ composition is determined by the depth of the ripples of the laser linewidth. Measurement noise and limited system bandwidth and linear measurements will function theory and real ripples depth biased.

However, this type of linear function itself shows a line width of less than 1kHz, the best way to get the width of the measured data is a linear function fitting. Figure 5 illustrates the measurement of E15 laser linewidth (sub-coherent linewidth measurement), the corresponding value of the linear function corresponding to the line width is 200Hz.

Phase noise integration
Another method based on the measured linewidth frequency noise Score:
Frequency noise spectral density function

Here, S_Δθ (f) is the frequency noise spectral density function (press Hz2 / Hz basis). Although this method, at least in theory by the 1 / f noise is dominated by laser is effective, but only for the actual integration of the frequency range is known to be meaningful. And the use of optical fiber delay 25km from the outside compared to the beat frequency method, which should range from approximately 10kHz points until the upper frequency limit of the device. E15, frequency X15 (E15 frequency stabilized version) and C15 noise fiber laser shown in Figure 6:

Heterodyne beat linewidth

"Heterodyne beat linewidth" substantially covers the technical noise and frequency jitter caused by the width of the narrow-linewidth laser, the technology is the use of noise from the above described 25km delay fibers from the outer beat frequency kHz linewidth measurement value when due. Exact width measurement of these linewidth is very difficult, but is calculated based on the basic principles of the rare earth-doped fiber laser laser parameters showed that the value in the mHz range. Straightforward measurement method for obtaining these values ​​(as the name mentioned) is a laser with a stable measured narrow-linewidth laser light source or the like do beat. If you can use a sufficient resolution to capture the beat, the line width can be measured. Typical measurement obtained with the technical challenge of noise: Measurement sub-Hz line width desired value during the measurement can not drift out of the beat frequency range measurement window. For most lasers, this is a strictly limited, unless they can have very high stability. For example, the ORS1500 Menlo lasers, is an ultra-stable low thermal expansion locked fiber laser interferometer, which it produces a line width of less than 0.3Hz of the beat as possible (Figure 7, Figure 8). The disadvantage is that due to the size and complexity of the system, it is only for special applications only practical. 

For compact and stable laser X15 residual frequency drift suppression heterodyne measurement of having such a low value of the beat linewidth, but it was able to get only a few Hz linewidth values.

NOTE: coherence

Ideally, the coherence time of the laser linewidth is inversely proportional relationship between Δθ = 1/ (π ∙ τ_coh). This relationship only under strict conditions Lorentzian linewidth accurate. As mentioned earlier, for narrow linewidth laser, such as rare-earth doped fiber laser, the best measure of the line width can be seen as a more narrow linewidth integrated frequency jitter. Thus, if the measured line width is used, its coherence time (and the coherence length) is often much larger than the value obtained by the inverse relationship.

Laser linewidth summary

Laser linewidth summary
Laser linewidth summary

SDH Background

Birth SDH technology has its inevitability, with the development of communications, information transfer requires not only a voice, as well as text, data, images and video. Coupled with the development of digital communications and computer technology in the 1970s and 1980s, has been found in the T1 (DS1) / E1 carrier systems (1.544 / 2.048Mbps), X.25 frame relay, ISDN (Integrated Services Digital Network) and FDDI ( Fiber Distributed Data Interface) and other network technologies. With the advent of the information society, people want modern information transmission network quickly and cost-effectively provide a variety of circuits and services, and the complexity of the bandwidth limitations of the above-mentioned network technology because of its monotony of business, expanded only in the original modify or improve within a frame has been of no avail. SDH is in this context to develop. In a variety of broadband fiber access network technologies, using SDH technology access network system is the most common. SDH solve the birth home due to bandwidth limitations behind the development of the medium and the backbone network and customers' business needs, and user generated between the access and core network "bottleneck" problem, while improving the lot of bandwidth transmission line utilization. SDH technology since the introduction of the 1990s, it has been a mature, standard technology, the backbone network is widely used, and the price is getting lower and lower, application SDH technology in the access network can be enormous bandwidth in the core network and technology advantages into access networks and take advantage of SDH synchronous multiplexing, standardized optical interface, a powerful network management capabilities, flexible network topology capability and high reliability benefits, benefit from long-term construction and development of the access network .

Optical interconnects: follow "actinic" trend lifeline

If the light sensor is to support all interconnected neural networks, the optical interconnection is supporting all interconnected lifeline.

We know that broadband Internet, on the one hand depends on the broadband high-speed backbone network, on the other hand relies on large volumes of data center, and the data center is needed in the short-distance high-capacity dense data exchange and transfer.

The traditional use of copper electrical interconnect data centers which have been difficult to meet the demand for high-speed bulk data transfer and exchange. Then the high-capacity data center, how to meet such high-speed short-range intensive data exchange and transfer it?

Now widely recognized by the scientific community is the use of active optical cable (AOC). AOC applications first, data centers and high-performance computers, both have to use a lot of servers connected to each other (computing unit), routers (switching unit) and memory (storage unit), "In the world ranking of the Milky Way computer for example, it has thousands of computing units and switching units, requiring high-speed low-power interconnect, and AOC can satisfy these needs. "

With the advent of the era of big data development and application scenarios, AOC will become the main form of ultra-wideband interconnection, the market will gradually grow.

Because the technology development and background, from communications to interconnected world, is forming a "actinic" trend: the long-distance backbone network, to the access network, fiber to the home, to the LAN and between racks connection, which is already the world of light; and from between machines, between the circuit board, and then between the integrated circuit chip, have gradually become electrically connected by optical interconnects.

In this "actinic" trend in active optical cable (AOC) with its high transfer rate, low energy consumption, high mounting density, low crosstalk, long connection distance or time delay, anti-electromagnetic interference and other prominent advantages , will play an increasingly important role in the interconnection between the racks, between the machine and the circuit board in between.

Four evolutionary stage of optical network

Future trends optical networking should be further enhanced by network intelligence and automation to ensure a more accurate resource data, fault location more quickly and reduce the costs of maintenance personnel, thus achieving the purpose of reducing OPEX. Based on the current technical studies of the evolution of the optical fiber network should go through four stages.

Port intelligent. Automated data acquisition via fiber ports visualization and data to achieve more accurate optical network resources, the process is more optimized. Including electronic work order closed-loop operation, the port information is automatically collected and guidance of field operations and so on. This technique has started from 2011, it is also already gradually applied in the bearer network and access network outside of the fiber.

Link intelligent. Through centralized remote fiber test and performance data analysis, to achieve fast fault location, in order to protect the normal operation of fiber optic networks. Including analysis and other online OTDR monitoring to establish the link test, optical performance and network fault early warning mechanism for content, this technology research from 2014, there are some small-scale applications.

Node intelligent. The concept of intelligent peripherals to expand optical wiring nodes, thus completing the process from the point to the surface, and process optimization intelligent fiber optic network as a whole. Including environmental monitoring passive node has permission to manage passive electronic lock, you can trace the route covers the management of fiber optic lighting and fiber content on the route. This technology is expected to start in 2016.

Reconfigurable networks. The ultimate status of the fiber-based network should be an unmaintained network, automation technology will be fully applied in the fiber-based networks. Including user resources automatically assigned, remote device Automatic defibrillators, automatic routing failure repair. Fiber-based value-added features while sensing characteristics will emerge, such as energy, oil pipeline monitoring, electronic security fence program, based on optical fiber vibration of ammunition safety monitoring. At this time the fiber has not limited communication capabilities, but provides more room for imagination as other industry applications. This technology is expected to gradually start from 2018.

OTN development process

Through a new generation OTN G.872, G.709, G.798 ITU-T recommendations are canonical "digital transmission system" and "light delivery system." OTN will solve the traditional WDM networks without wavelength / sub-wavelength service dispatch capability, network capacity is weak, weak protection and other issues.

Optical transport network for IP services, IP transport requirements adaptation service has become an important issue in the further development of optical communication. Optical transport network from a variety of angles and provide a solution compatible with the existing technology in the premise, because the large number of applications SDH equipment, in order to solve the processing and transmission of data services, based on SDH technology developed MSTP equipment and has a large number of applications in the network, it is well compatible with existing technology, but also to meet the transfer function data services. But with the increasing processing power and requires more detailed data services particles, business demand for transport network presented two aspects: on the one hand the transmission network to provide a large pipeline, then generalized OTN technology (in the electric field is OTH, in the optical domain ROADM) provides a new solution that solves the SDH-based cross particles VC-12 / VC4 is small, scheduling more complex issues not meet service delivery needs of large particles, in part, to overcome the WDM System fault location difficult to point to point connection-oriented networking, network capacity is weak, network survivability and ability to provide a means shortcomings weak; on the other hand service optical transport network to propose a more detailed processing requirements, the industry also made a packet transport network solution, the main technologies involved include T-MPLS and PBB-TE and the like.

OTN Network

As network traffic growing demand for bandwidth, operators and system manufacturers have been constantly consider ways to improve service delivery technology issues.

Digital transmission network evolution from the original based T1 / E1 of the first generation of digital transmission network, experienced-based SONET / SDH second generation digital transmission network, to the development in the third generation of OTN-based digital transmission network. First and second generation transport network was originally designed for voice services specifically designed, though can also be used to transmit data and video services, but the transmission efficiency is not high. In contrast, the third-generation transport network technology, from the design to support voice, data and video services to support the bandwidth on demand (BOD) when with other protocols, quality cut of service (QoS) and optical virtual private net (OVPN) and other functions.

In 1998, the ITU Telecommunication Standardization Sector (ITU-T) formally proposed the concept of OTN. From the functional point of view, OTN can be transmitted in the form of all-optical subnet, and the use of light at the boundary of sub - electricity - light conversion. Thus, each subnet can 3R regenerator coupled to constitute a large optical network, as shown in FIG. Therefore, OTN transport network can be seen as the all-optical network evolution process of a transition application.

In the OTN functional description, the optical signal is wavelength (or center wavelength) to characterize. Optical signal processing may be based on a single wavelength, or based on a WDM group. (Based on other optical multiplexing, time division multiplexing, optical time division multiplexing, or optical code division multiplexing OTN, remains to be studied.) OTN can be achieved in the optical domain transfer service signals, multiplexing, routing, monitoring, and to ensure its performance and survivability. OTN can support a variety of top business or protocols, such as SONE / SDH, ATM, Ethernet, IP, PDH, Fibre Channel, GFP, MPLS, OTN virtual concatenation, ODU multiplexing, is the ideal foundation for future network evolution. More and more operators worldwide start constructing a new generation of OTN-based transport networks, systems manufacturers have also introduced a more OTN features of the product to support building the next generation transport network.

Nufern Introduces New erbium ytterbium co-doped fiber

Nufern Inc. today announced the expansion of its fiber optic EyeSAFE product line by introducing two new erbium ytterbium co-doped fiber. These new products provide the most advanced erbium ytterbium co-doped glass component technology and proprietary NuCOAT-FA Nufern low refractive index coating technology.

EyeSAFE product line includes Er-Yb operating band for the 1550 co-doped fiber, as well as the application of 2μm thulium and holmium-doped fiber. These latest dual-clad erbium ytterbium co-doped fiber to 1.0μm band spurious suppression ASE optimized to ensure the highest efficiency and output power of the pump. Nufern new single-mode erbium-ytterbium co-doped fiber has 6μm fiber core diameter, is used in low-power fiber amplifiers ideal fiber. The new multi-mode erbium-ytterbium co-doped fiber having a 10μm core diameter and a numerical aperture of 0.21, can achieve more than 10W of output power and extremely low 1.0μm of ASE.

Kanishka Tankala vice president fiber business statement to: "These new erbium ytterbium co-doped fiber has a very high efficiency, improve the level of power output while maintaining low 1.0μm ASE, it is the most outstanding of a commercial type of fiber optic products. These two fiber can help end users to develop the next generation of high-power fiber amplifier. combined NuCOAT-FA Nufern's proprietary coating technology, these fibers work in the eye-safe wavelength can bring better Reliability. "

The new erbium ytterbium co-doped fiber MM-EYDF-10/125-XP performance:



2016 China Telecom Solutions XG-PON1 interoperability

Currently, China Mobile added, broadband access market is highly competitive. China Telecom and China Unicom have copper resources are not willing to discard, so broadband network construction development should consider both asset protection. China Mobile is no copper "burden", and funded with strong competitiveness. Faced with the impact of China Mobile, China Telecom and China Unicom efforts to strengthen the construction of FTTH.

As the main force of China Telecom FTTH in the past few years, we have begun a gradual transition from the access technology G / EPON to 10G-EPON. Recent China Telecom's 2015 Central Purchasing PON equipment, including one million 10G EPON port, close to the G / EPON port level.

XG-PON is the next generation of GPON evolution of technology. Judgment based on practical needs and technology maturity, FSAN NG-PON evolution of the definition of planning is divided into two stages: XG-PON1 and NG-PON2. XG-PON1 medium-term evolution of PON, focusing on the study of both existing GPON ODN laying next generation standards.

10G EPON interoperability has been resolved, the current focus is to reduce equipment costs. XG-PON1 current focus is to promote interoperability, China Telecom will launch in the second half of 2015, 2016, respectively, and interoperability testing different vendors OLT ONU (SFU / HGU) devices, target solve interoperability in 2016, the scale of 2017 Commercial technical preparedness.

For China Telecom, XG-PON is insurmountable stage. Within three years, is expected to TWDM PON (NG-PON2) in standard equipment maturity, cost, interoperability and other aspects not yet reached the large-scale commercial level. China Telecom will organize XG-PON interoperability testing, as the Point XG-PON technology matures.

Technology of 400G optical modules

With the IEEE 100 Gbit/s (hereinafter referred to 100G) Ethernet standard-setting discussions with the end of the world's major manufacturers are promoting the global deployment of 100G and 400G focused its attention to even 1 Tbit/s system up. With 40G / 100G, like, 400G deployment should be a gradual manner. In order to make more effective use of existing DWDM (dense wavelength division multiplexing) line resources, reduce investment costs, operators can expect 400G deployment on existing networks, rather than re-design and build a new network to accommodate 400G of transmission. This means that you must adapt to the network design and planning 400G 100G / 40G or 10G to achieve a mixed deployment of 400G, 100G / 40G's.

1. Technical analysis 400G LAN Interface optical modules

400G LAN (Local Area Network) interface to optical modules may 100G Ethernet will continue to use proprietary parallel transmission. In February 2011, Finisar on "Beyond 100GE" seminar presented 400GE modules standard recommendation, primarily to support 400GE-LR16 and 400GE-SR16 two applications. Where 400GE-LR16 using 16×25G LAN WDM (1330,1310,1290 and 1270nm 4 waves channels) to achieve, and 400GE ~ SR16 is using a 16×25G multimode fiber interfaces. In addition, in the physical layer defines the CAUI (Attachment Unit Interface) -16, CPPI (parallel physical interface) -16 electrical interface standard. 16×25G 100GE just linear expansion, as long as the process to meet the requirements, there is no other technical difficulties. In contrast, the optical fiber parallel development will have more space, but supports higher densities needed photonic integration technology can make 400G commercially possible.

In addition, Finisar also proposed other possible ways 400G LAN applications: the first type is the use of already commercialization 4OG of EML (electro-absorption modulated laser) technology architecture composed of 10×40G; the second was that rely on technology to improve the EML, using 4-level amplitude modulation and DSP (digital signal processing) of dispersion compensation framework 8×50 G; third is 4×100G of architecture that must be complex amplitude phase modulation, such as PM-QPSK ( polarization multiplexing - Quadrature Phase Shift Keying), there is no possible commercialization of the technology demonstration.

NTT research report also pointed out that in the serial data transmission, 16×25G, 10×40G and 8X 50G of these types of architecture are possible. For 50G, modulation is also based MZ (Mach - Zehnder) the DQPSK (differential quadrature phase shift keying) modulation or OOK (on-off keying) modulation. Each architecture in size, cost, power consumption, etc. have their own advantages and disadvantages. From the current research point of view, DML (directly modulated laser) production process is simple, low power consumption, but the ER (extinction ratio) is small. EML complex production process, power consumption is relatively large, but the larger ER, you can get a very clear eye. Further, the quantum well EAM (electroabsorption modulator) InGaA1As based valence band offset is reduced due to a hole caused by accumulation in the modulation process, and therefore suitable for use as high-speed modulation. Figs. 1 to 3 are NTT in OFC 2011 show for the 400 GE of 1300nm, 50G EML spectrum, into the relationship between the current and the optical power and the transmission 10 and 40 km after the output eye diagram.

For 400GE systems, 50G of OOK modulation due to the physical size of the entire transmitter end, is a good compromise choice. In this modulation, DML comparison more difficult to implement. So we can predict, EML and 8×50G of OOK modulation prospects in 400GE systems.

2. Technical analysis 400G long-distance transmission optical modules

In the ITU-T / IEEE Joint seminars, Alcatel-Iucent report stated: interface cable OTU5 rate will reach 449.219 Gbit/s. With the increase rate, the system OSNR (optical signal to noise ratio), CD (chromatic dispersion), PMD (polarization mode dispersion) and nonlinear increasingly demanding. 400G signal dispersion tolerance of only 0.5 ps/nm, the 100G is 1 / 16.400G on OSNR also encountered a challenge, 6dB higher than the 100G. In particular, the use of higher than the current 7% FEC (forward error correction) after expenses, can achieve longer distances. The current discussion was more of a 25%. 400G 100G in PMD than the challenge faced bigger, 400G PMD tolerance of only 0.25ps, the 100G 1/4.

2.1 laser linewidth requirements

With the development of digital coherent receiver technology, the high-end multi-level modulation format because of its high spectral efficiency characteristics in DWDM systems are increasingly compelling. Phase noise characteristics of the laser transmitter and receiver optical local oscillator determines the bit error rate performance of the system. Table 1 lists the different modulation formats, 400G and 100G comparison with the laser line width requirements. Table, △fTX represents transmitter laser linewidth, △fLO represents wide receiver local oscillator light.

2.2 modulation formats and channel spacing feature

To meet the 400G DWDM transmission system in the current requirements and improves overall system capacity modulation pattern of the most important requirements are: to meet the SE (spectral efficiency) and OSNR sensitivity requirements, and have a very strong non-linear tolerance.

Theoretical capacity of single-mode fiber is 8 bit/s/Hz, the actual long-distance transmission equipment and optical fiber, a maximum of 4 bit/s/Hz. In modern optical communication systems, modulation format a great impact on system performance, in order to achieve with the existing network of 10G, 40G hybrid deployment, to achieve 80 wave 50 GHz spacing, it must meet high SE, which can be single-carrier high ary modulation or multi-carrier transmission is achieved. For 448G transmission system, consider the device frequency drift and R0ADM (reconfigurable OADM) non-ideal characteristics, requires practice must be 45G of 32QAM (quadrature amplitude modulation) modulation or 28G of PM ( polarization multiplexing) -256QAM. Electrical domain OFDM (Orthogonal Frequency Division Multiplexing) modulation of a single carrier can be substituted, as the complexity of both the DSP's, but due to the extra information OFDM cyclic prefix, preamble and training overhead symbols, etc., usually higher than the corresponding single-carrier format The SE is lower.

In order to try to meet a 50GHz DWDM channel spacing, many theoretical studies in 2010 are based on multi-level amplitude modulation, which PM-256QAM, a total of 65,536 constellation points, compared to 100G PM-QPSK, the density increases 8 times, and noise and light XPM (cross-phase modulation) / SPM (self-phase modulation) is very sensitive to transmission distance is very short. From the current situation reported demonstration of single-carrier QAM speed opinion, short term 448G transmission, whether it is a single carrier OFDM PM ~ 256QAM or electricity of 32QAM, it is not yet commercialized.

The first one kind of relaxed solution required SE: abandon 50GHz spacing WDM mandatory requirements, such as a 16QAM using 56G PM and flexibility of 70 ~ 80 GHz spacing WDM, SE of 6 ~ 5 bit/s/Hz, and the need There are more than enough to support ROADM systems. Data center users tend to use this flexible solution, but with large-scale, multi-service mesh network carriers to stick with standard spacing to 50GHz. For compatibility with a 50GHz boundary conditions, the use of inverse multiplexing can channel into two 448G 224G wavelength. 28G PM-I6QAM modulation up to 4 bit/s/Hz net SE, compared to 100G PM-QPSK, doubling the capacity of each fiber is increased in WDM. In addition, in order to achieve 10G, 40G / 100G to 400G seamless upgrade deployment of WSS (wavelength selective switch) presents an adjustable bandwidth requirements.

The first two kinds of solutions: using higher order modulation 32QAM or low photon carrier orthogonal multiplexing to replace the single-carrier 448G signal. This method is called coherent WDM or coherent optical OFDM. It is with inverse multiplexing DWDM different nature, because it can be obtained at a specific single carrier modulation format and the same SE coherent reception OSNR tolerance. A 448G of the transmitter can be used 10 separate photons modulated quadrature carriers. The receiver can be divided into two groups (each five as a group) to detect the reception. From the above discussion it seems, in order to obtain the highest possible rate of subcarriers can be processed on the electric field parallel to maintain a minimum light the large ones would be a more practical and more economical solution. Table 2 lists the OFDM and single carrier 400G system performance comparison.

Due to high sensitivity compared to a single carrier and excellent CD / PMD tolerance, multi-polarization digital coherent receiving CO (g coherent light) -OFDM becoming more promising and began to receive widespread attention in the industry. In the future exploration of 400G optical modules based on OFDM modulation structure, the main three kinds of architecture: Based on the FFT (Fast Fourier Transform) OOFDM (optical orthogonal frequency division multiplexing), all-optical OFDM and electro-optical OFDM.

Traditional OOFDM based DSP / DAC of IFFT (Inverse Fast Fourier Transform) and FFT signal synthesizing demodulation, CD and PMD tolerance can be inserted by a cyclic prefix or a guard interval, promoted training symbols, but this will resulting in a 10% or 20% of the overhead, and increase line speed. Especially in need of period CD compensation transmission line, the transmission performance DSP-based multi-carrier OFDM will be limited fiber nonlinear characteristics. The use of silicon-based PLC (Planar Lightwave Circuit) and hybrid integration technology LN (lithium niobate) lightwave circuit, the two carriers have been able to make the QPSK (quadrature phase shift keying) modulator to achieve single polarization modulator 100G (25G) and dual polarization modulator 111G (13.9G). Taking into account the complexity of the transmitter, unlike conventional DSP-based OFDM, the number of sub-carriers must less (usually 2 to 4), because of less number of subcarriers can effectively reduce PAPR. In addition, the transmitter does not require DSP and DAC. The use of a small amount of carrier, loop overhead will lead to additional costs or limit the ability to compensate. Because we need a receiver using a linear filter based on CD / PMD compensation.

All-optical OFDM, must be inserted GI (guard interval) to improve, CD and PMD tolerance, and requires a long symbol periods (many sub-carriers) to offset the cost of GI caused by electro-optical OFDM therefore proposed architecture to solve issue, electro-optical OFDM architecture to meet the higher speed requirements. Table 3 presents a comparison of the performance of 400G systems in a variety of different modulation formats.

In summary, the use of fewer sub-carriers, all-optical OFDM has the following two advantages: no emission end of DSP / DAC, has a relatively low electrical, optical complexity; As a result of fewer subcarriers , thereby reducing the PAPR of the signal, there are in the CD or the low dispersion compensating optical fiber line, having good nonlinear suppression. Therefore, from the cost, performance and complexity, etc. to achieve the look, all-optical OFDM modulation technique (2SC-DP-16QAM format) and channel spacing flexible optical module vendors can attract attention, it will play an important in the early commercial 400G role.

3. 400G detection technology

3.1 micro-optics and hybrid integration technology

For coherent detection, the use of separate free space 90° balanced mixer and a light detector to build coherent receiver system, this complex configuration to achieve commercialization is difficult. From the 2009 ECOC, U2T and HHI demonstrates monolithic integrated PLC 90°. Mixers and two pairs of high-speed balance PD receiver, to the 2010 ECOC, U2T and HH1 once again demonstrated monolithic two-way PLC 90°. Mixer and eight high-speed balancing PD receivers. From the evolution and development trend in recent years, it seems 100G transmission technology, 400G line receiver technology is gradually moving towards integration.

The integrated use of monolithic integrated receiver and free space optics, there is no way to get satisfactory performance, reliability and low cost. In this regard, NTT PLC technology using a silicon PBS (polarizing beam splitter) and 90°as a monolithic integrated optical mixer DPOH (polarized light mixer). Another use of a new multi-channel collimator DPOH the coupling loss between the lower and the PD, and to suppress coupling deviation caused by temperature changes. In addition, NTT has developed a high-speed chip-level compact photoelectric conversion structure, and use these techniques to produce an integrated coherent receiver. Micro-optical alignment technology allows greatly improved sensitivity based PD matching and temperature performance PLC hybrid integrated devices.

Since the silicon-based microelectronics plane technology, optoelectronic devices is three-dimensional technology. Compared to hybrid integration, PIC (Photonic Integrated Circuit) can significantly reduce the size of the optical module, save packaging costs and flat connection allows the optical path to match and balance easier, thus effectively control deviation, it is the future mainstream. Currently Bell Labs has been research on monolithic silicon integrated coherent detection technology, but there are many technical difficulties to be a breakthrough. 400G early in the silicon PLC and free space optics hybrid integration will be more mature commercial programs.

3.2 with detection technology

Digital coherent reception technology in the field of high-speed transmission is generally regarded as a promising technology because it can increase the sensitivity of the system OSNR, CD and PMD compensation line transmission damage. Because electricity rates "bottleneck", ADC sampling rate will be limited to a very long period of time of less than 100 GS/s. In order to effectively address this issue in 400G even T bit/s channel transmission, the use of multi-carrier modulation format is an effective method.

The use of wavelength-independent detection, the receiver hardware complexity can bring lower by detecting a plurality of sub-carriers, not only from ADC sampling rate bottleneck constraints, and reduce the load on DSP. The structure shown in the block diagram of an optical transceiver module 4.

3.3 processing capabilities within power

Currently in 100G systems, most of the optical device has reached the extent of commercial, but in coherent receiver technology, the key to the biggest problem ADC and DSP chip production business is the processing power and power consumption. Although in 2010, Alcatel-Lucent has 112 G's long-distance system uses a 70M + door of 56 GS/s of ADC / DSP, but faces the same prediction in the 400G system bottleneck.

4. Conclusion

400G long-distance communication and transmission of the light entering a new era, the multi-carrier multi-level phase modulation and an array of optical communications is moving from single-carrier modulation with coherent detection of the polarization multiplexed coherent change detection. Photonic integration and electronic integration, ADC / DSP technology will be 400G optical communication modules and systems business of the key. With the urgent need for standardization of Ethernet, parallel light of the requirements of photonic integration technology will be a huge boost. In the next 2 to 3 years, 400G electro-optical OFDM-related technologies will gradually mature, although these devices have a certain distance from the commercial cost and power consumption, but as these technologies have matured and related standards of discussion and development, 400G commercial system is about to pull the curtain.

Data Center Why use AOC

The entire data center has begun global import 40G AOC, relative to 40G DAC copper, 40G AOC at 7 meters above data transmission environment with unparalleled advantages, including smaller, lighter, easier to bend and more easy management, signal transmission over longer distances and so on. AOC assemblies are full-duplex structure:
AOC system architecture diagram
AOC system architecture diagram
In the data center, if 40G SR4 optical modules can also obtain these goals.

Differences 40G AOC and SR4 module as follows:

1) Insert the return loss analysis: For the same distance, with the current technology and design, SR4 repeatability and interchangeability performance optical module interface inferior to 40G AOC. SR4 optical modules for different fiber jumpers plug the same module will have different insertion loss and return loss, this is basically a common problem. But insofar as the amount of change in line with the scope of the test and other related indicators of the eye will not be too significant change. And making good AOC this respect can be maintained basically stable, rocking performance better. SR4 repeatability test in the following table, showing the occurrence of a large volatility.
SR4 plug repeatability of test data
SR4 plug repeatability of test data

2) four-quadrant test: is the input voltage and signal amplitude measurements four combinations in order to ensure the lowest and highest voltage and temperature can maintain performance. AOC through a wide temperature range four quadrant tests to ensure the MPO connector and cable AOC will not melt at high temperatures. MPO interface itself changes in high and low temperature performance is to meet 0.3dB variation, materials used are also resistant to more than 120 degrees PEI material. As integrated molding products, integration tests to ensure product performance, this may appear to be more stable than using SR4 module optional uncertain performance of MPO jumpers. SR4 confirmed by mass relative to the optical eye diagram, AOC primarily by electric eye to judge the merits of indicators.

3) DDM monitor: SR4 have DDM monitoring function to see in real-time monitoring to determine the optimal size of the coupling receiving end ADC value when receiving coupling, so the reception sensitivity SR4 appear superior than some of the AOC. But SR4 optical modules and 40G AOC currently can not achieve real-time monitoring of optical power.

4) Transmission distance: not much difference between the two on OM3 fiber. But SR4 optical module can better control performance, if you want to achieve longer distances (> 300 m) of transport recommended SR4.

Summary: Based on the data within the data center connection, we recommend using active optical cable (AOC). The reason is that this AOC wiring consistency and repeatable, closed at both ends is easier to avoid environmental impact and vibration swing. If the failure can be directly replaced, without the need for on-site to do SR4 optical modules and MPO series termination jumper plug test cost savings.

SDN development of optical networks exist different technical route

Comparative data networks SDN different optical network SDN has its own unique characteristics. First, due to the characteristics of the physical layer, the optical network control architecture itself has control forwarding separation. Secondly, centralized control, optical network has a mature network management, the path calculation unit (PCE) and other centralized management and control systems. Third, the light has the characteristics of a connection-oriented network, all traffic using pre-configured, without the controller forward packets according to the following service packets instant hair flow, reducing the controller performance requirements, with better network scalability . We can say that the optical network already has some characteristics of SDN for evolution to SDN has laid a good foundation. But on the other hand, optical network physical layer device programmability weak, resource virtualization and sliced ​​more difficult to achieve, so that the light is introduced SDN network technology there are some difficulties.

SDN optical network based on the characteristics of the development of optical network SDN take the evolution of ideas and data networks SDN differ. Meanwhile, the optical network backbone, metro and access layer development needs and the technology used different, SDN also introduced different technical route.

(1) Route One: enhancement based on optical network control plane, stressed north to open interfaces.

Backbone OTN, DWDM optical network equipment and other support capabilities better control plane, based on the existing ASON / GMPLS control plane and centralized path computation unit PCE technology, to interface to achieve SDN centralized control by extending and enhancing management and control capabilities and open PCE North devices, applications and services and provide open programmable upper network and applications. This route can better protect existing technology investment, and facilitate smooth network evolution. Since the optical network physical layer private information more difficult to south standardized interface protocol is relatively large, south to the interface may allow multiple interface technologies.

(2) Route II: Introducing openflow agreement, stressing the south to open interfaces.

For packet transmission PTN and PON access network equipment, it does not have the intelligent control plane, can be introduced directly on the device openflow agreement to achieve south to an open and standardized interfaces. This route due to the realization of the South to interface standardization, equipment and services in favor of decoupling, simplify network node function, reduce equipment costs, ease of operators for metro and access massive multi-vendor sites centralized management control. For existing network equipment has been deployed, will consider implementing a centralized controller capacities through network upgrade approach.

Select SFF small fiber optic connector of a few tricks

In the mature markets, the clear winner with excellent technology, and also to promote the continuous development of competing technologies. In the optical fiber interconnection market, this situation will appear in a small form factor optical connectors in the field. Over the past three decades, many of the optical connector blossom, as short-lived, and LC and MTP * / MPO interconnection system will emerge as the clear leader in the global scope enables users, system designers and The optical component and transceiver designers become beneficiaries.

LC connector can provide optimal performance and ease of use on ceramic sleeve connector. MTP / MPO interconnect interface between the optical properties of the fiber port concentration to make a certain balance with optimal density. Although the original SC connectors for low-density patch panels and light modules, FC connector is designed for a more robust environment test equipment. In most applications, in view of the obvious advantages LC and MTP / MPO connector, the amount of ST, SC and FC connector is declining.

LC fiber optic interconnect system can support a variety of diameters, strain relief boots or limit benders. LC tab can help to achieve maximum density patch panel, while maintaining the ease of use. For single-mode applications, APC (angle polish) version to help achieve excellent back reflection performance. LC connector optional six rotating bushing tuning, when needed to provide the lowest insertion loss performance.

Despite the need for more high fiber density, the solution is usually based on the requirements of the transition from the ceramic sleeve is connected directly to the Precision Mold, MT-based multi-fiber connector ferrule. This makes the situation increasingly complex. Now let's step back and explain terms:

● MT Barrel - Precision Mold casing can support 2-72 fiber, used as MTP / MPO fiber optic connector on the device

● guide pin - pin hole MT sleeve utilized a part of the organization, can provide precise function of the plurality of optical fibers between two paired MT casing

● MPO connector - Rectangular industry standard multi-fiber push-pull connector interface, the public side (with guide pins) / female side (no guide pin) configuration can accommodate MT casing

● MTP connector - The optical and mechanical properties and vendor-specific versions of the MPO as a trademark connector interface, especially after pairing with optical module can be improved optical interface

According to the number of rays and specific applications, MTP / MPO interface supports both multimode and single-mode optical fiber having different numbers of optical fiber, optical cable construction and the cable diameter. The optical performance of the interface from the MT ferrule Precision Mold technology and polishing of glass fiber, these two processes in the past few years have been a large degree of improvement. Singlemode MT angle polished casing through improved return loss performance, multimode sleeve is through PC (plane) polished. For specific optical modules MTP / MPO, such as QSFP (eight functional fiber, four central fiber is not used) or CXP (24 fibers), there are a series of standards to promote the growth of the number of optical fibers. The new standard will be 16 and 32 to make the definition of fiber optic version.

Compared with the connector based on LC ceramic sleeve, MTP / MPO fiber optic technology at the level of the number of ports per significantly improved density. However, this requires designers, installers and end users to manage fiber careful assessment, so that during the life of the cable infrastructure of moves, adds and changes.

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