High return loss receiving scheme to improve the transmission performance of the optical module 10G LTE

The rapid development of mobile Internet, the rapid application of intelligent terminals holdings of explosive growth, driven by substantial growth in global data traffic.

Up to now, 422 operators in 143 countries launched a commercial LTE network. Last year alone, there are 106 operators to launch commercial LTE services. Terminal, the TD industrial chain have become more sophisticated, the market began to face the ultimate force.

China Mobile LTE construction in the module is 6G and 10G of SFP+ optical module, the surge in market demand and mature industry chain light module products technology innovation, as well as the cost pressure from operators transfer to the optical module manufacturers through equipment manufacturers. About LTE 10G optical module receiver technology, currently the industry there are two solutions: high return loss program and receives regular reception program, differences between these two programs receiving device is mainly reflected in the module optical return loss design.

After receiving the conventional scheme, LC connector into the receiving device, the air between PIN dies its flat end and the gap within the device, and most of the light in the optical fiber transmission perpendicular to the flat face, when they occur, specular light will all return in the core, the reflectivity can usually return Rf=(nf-1)2/(nf+1)2 is calculated by, nf is the refractive index of the fiber material, take nf=1.47, too Rf=3.6%(-14.4dB), another study suggests that the fiber end after the grinding and polishing, will produce a thin layer at the fiber end face deterioration. Its refractive index of about 1.6, higher than the refractive index of the fiber core, this case, Rf =5.3%(-12.7dB), that is, return loss of -12.7dB, and lower standards -12dB 10G Ethernet is very close, almost No margin.

Compared with conventional receiving scheme, high return loss LC connector receiving scheme between PIN die and adds a miter ceramic pin, as shown in Figure 2. Pin angled end fiber mandrels not at right angles, although there is an air gap, but after launching inclined surface angle of the reflected light propagates in the optical fiber is smaller than the total reflection critical angle, therefore, from pins inclined surface reflected light , does not spread in the core, but all through the cladding dissipation occurs and eventually leak out to 8°oblique pin, for example, return loss measured according to statistics, generally better than -27dB. Therefore, in the optical return loss index, regular reception program receives far and high return loss program.

Figure 1 regular reception device Schematic diagram
Figure 2 high return loss Schematic receiving device of FIG.
Figure 3 pin flat end surface reflectance in
Figure 4 pin inclined surface reflectance in

Optical return loss is defined as the ratio of the reflected light power and the incident power, the worse the show return loss fiber link light reflecting stronger, and in the optical fiber transmission systems, connectors, fiber end faces, optical and detector surface will caused by Fresnel reflection. The light reflected back to the impact of the system include:

1) so that the optical signal transmission is weakened;

2) the incident signal interference;

3) reduce signal noise in a digital transmission system.

Since the reflected light will return after emission sources, the impact caused by the light source include:

1) cause the center wavelength of the emitted light fluctuations;

2) cause strong fluctuations in the light emission of the light source;

3) permanently damage the light.

Even FP light source, although the retroreflective little effect on the spectral characteristics, but retroreflected light into the light amplification cavity after the active region, to join the mainstream, resulting in light intensity fluctuations of light intensity fluctuations resulting in RIN, RIN is the transmitter and not related to the receiver noise will limit the maximum signal to noise ratio is possible to obtain the optical fiber link, thereby affecting receiver sensitivity. Moreover, a broadband noise RIN essence, it reflects the relative signal power, the impact of intensity fluctuation of the light source and the receiving end of the system electrical noise generated by the formula is as follows:

RIN =<ΔP>2/(P2*BW)

<ΔP> is the average noise power, P is the average optical power, BW is the bandwidth of the receiver and system link.

Thus, the system, the higher the rate, the more bandwidth link noise, the greater the noise power, the lower the signal to noise ratio, the higher the error rate. Therefore, optical modules for 10G LTE, to ensure the reliability and stability of the optical transmission system emission spectrum of the light source and power, it is necessary to receive a high return loss devices designed to minimize reflection link. Despite regular reception program module can use the transmitter optical isolator programs to protect the light source and the influence of the reflected return loss caused by the system still exists, while isolating the price than the high return loss program in the price of optical fiber pins much more expensive.

Despite facing increasingly fierce price competition and cost pressures, but has always been to uphold the quality first philosophy, in the development of the module Accelink Technology Co., Ltd. (ACCELINK) SZ002281's Wuhan Telecommunication Devices Co., Ltd. (WTD) and adhere to the production of high-performance principle, without compromising product performance for the price to reduce costs. But through continuous R & D investment to master the core technology, innovative technology and lean manufacturing, and other initiatives to design cost control programs, and technical innovation WTD's LTE 10G optical module receives high return loss programs, compared to the conventional reception scheme, the light return loss better indicators of the impact of emission sources is small so that the stability of the system is greatly improved.

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