Optical Communication Systems technology trends - beyond 100G

With the progress of social information process, to video, cloud computing, networking and the representative of the emerging business demand for bandwidth surge, the existing backbone optical transmission system interconnection capacity can not meet the growing demand, an urgent requirement to further enhance transmission capacity.

In fact, as experienced from 2.5Gbit/s-> 10Gbit/s-> 40Gbit/s-> 100Gbit/s transmission capacity to enhance network surge in demand, its single channel optical transmission system transmission rate, is preparing the next generation Ultra 100G optical transmission systems. The optical transmission multiplexing dimension from a simple time division multiplex development, wavelength, frequency, polarization, multidimensional multiplex transmission mode, multi-pronged approach. Future demand for network capacity optical transmission, Pbit multi-core space division multiplexing as well as orbital angular momentum of photons reuse industry has become a hot topic. In the specific implementation, advanced quadrature amplitude modulation, coherent reception, digital signal processing, multi-carrier technology and optoelectronic integrated technology and other new technologies have been gradually introduced and continue to optimize and improve the optical transmission performance and reduce the cost of optical transmission.

Consider cost and compatibility, etc., based on full use of the fiber optic cable has been laid, the existing optical transmission systems by upgrading and transformation of the optical transceiver unit to raise a single wavelength channel transmission data rate of ways to enhance system capacity, it has the best cost and feasibility. Ultra 100G optical transmission will inherit design 100G optical transmission systems, the use of polarization multiplexing, multi-level modulation spectrum efficiency, increase the use of digital coherent reception receiver sensitivity and channel equalization capability.

Ultra 100G optical transmission is intended to further enhance the transmission capacity in a single fiber band resources available under the same circumstances, the key is to improve the efficiency of spectrum utilization and spectrum resources. For optical transmission systems, narrowband filtering effect of fiber loss caused by the window limits the available bandwidth of optical devices and optical transmission path caused by cascade claim maximize spectrum efficiency light transmission; non-linear effect of the optical transmission path optical transmission power requirement maximize efficiency. In addition, the level of light transmission symbol photovoltaic device baseband bandwidth also restricted.

In response to these super-100G optical transmission challenges, solve industry from the following aspects: ① full use of the optical signal can be modulated dimension (amplitude, phase, polarization) to carry data to improve spectral efficiency; ② multi-carrier orthogonal frequency division multiplexing technology to improve spectrum utilization and reduce the transmission rate to suppress symbol dispersion effect, reduce light, electrical parts bandwidth requirements; ③ using digital coherent receiver technology to improve the sensitivity and channel equalization capability of the receiver, using higher gain The error correction coding to improve the robustness of the system. ④ use of advanced optical integration technology to reduce size, lower power consumption and increase system reliability.

It should be noted that, despite the multi-dimensional multi-level modulation can improve spectral efficiency, to reduce the transmission channel and the photovoltaic device bandwidth requirements, but the minimum spacing will reduce the multilevel modulation symbol constellation between sensitivity and lower OSNR transmission damage tolerance capability. Therefore, the selection of higher-level QAM modulation may improve spectral efficiency and transmission rate over 100G, but since the strength of noise and phase noise tolerance diminished capacity, the transmission distance may be much lower than the current system 100G.

Optoelectronic devices integration technology is the basis for ultra-100G optical transmission to achieve. Although the multi-carrier transmission stages can reduce the bandwidth requirements of optical systems, electrical parts, the device power consumption is reduced by the square of the linear growth increase, but the bandwidth and power requirements are still alarming. Optoelectronic devices integrated technology is a key factor Ultra 100G optical transmission design feasibility and system performance.

Given the current business needs and optoelectronic devices technology level, 400Gbit/s optical transmission rate is the most feasible and cost-effective solution. Gemini carrier based on a flexible grid polarization multiplexing 16 quadrature amplitude modulation (2SC-PM-16-QAM) a 400G optical transmission is generally optimistic about the industry one of the options. The program for each transmission channel occupies 75GHz bandwidth and spectral efficiency can reach 5.3bit/s/Hz, compared with 100Gbit/s optical transmission 2bit/s/Hz spectral efficiency can be greatly improved. As a result of more intensive 16QAM modulation, 400G transmission damage tolerance capability (transmission distance) declined compared with 100G optical transmission system, expected to be the first application in the metro and data center interconnect applications.

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