The development trend of optical communication technology

With the proposal of the concept of Internet +, the demand for transmission bandwidth of emerging businesses represented by the Internet service industry has increased sharply, and the capacity of the man transmission system also needs to be improved.

Man transmission technology is a transmission technology between backbone network and access network. This technology needs to take into account the high performance of backbone network and the low cost of access network.At present, the coherent transmission technology has been commercially available in the long-distance transmission system of the backbone network, whose transmission distance is greater than 1000 kilometers, and the transmission rate of a single wavelength can reach 100-Gb/s.In MAN, the transmission distance is usually less than 300 km. Although coherent transmission technology can provide high transmission performance, it is very complex and high cost, and cannot meet the requirements of low cost transmission in MAN.The current access network mainly adopts the low-cost modulation scheme of OOK signal direct modulation laser.Due to the limitations of the modulation mode and the modulation format, the transmission rate can only reach 10-Gb/s and the transmission distance is within 20 km.

According to the current development of optical devices and electric chips, the technical scheme of direct modulation and direct detection is the best in the current man-area network transmission.The structure of direct adjustment and direct inspection of access network is adopted on the optical fiber link, and the digital signal processing (DSP) technology of backbone network transmission is introduced in the receiving end, so that the transmission performance and cost can be achieved.

For the direct inspection and transmission technology of man, the industry can start from the following aspects:

1. Considering the limitations of the bandwidth and sampling rate of the current analog (ADC) and digital-analog (DAC) converter, the multi-dimensional modulation of the optical signal should be fully utilized, including amplitude, phase and polarization state, to improve the spectral efficiency of the signal.

2. Nyquist single-carrier orthogonal amplitude modulation (QAM) signals and multi-carrier orthogonal frequency division multiplexing (OFDM) are both alternatives that can be considered.The QAM signal is slightly better in transmission performance than the OFDM due to its high nonlinear tolerance.While OFDM signals have the advantage of low complexity in signal processing and can be designed flexibly specifically for different network environments

3. In the selection of the optical device, the optical device can have a higher tolerance compared to the coherent transmission system because it is directly detected and recovered with DSP at the receiving end. For example, in the direct inspection system, the phase noise of the laser has a low impact on the performance of the signal. Therefore, the low-cost distributed feedback (DFB) laser and the vertical cavity surface emission (VCSEL) lasers can be considered as lasers at the emitting end.

4. Polarization multiplexing technology can also be applied to the direct inspection and transmission system of man. However, how to maintain the low cost of optical fiber collector and distribution in this case is a problem worth exploring deeply.

Overall, with the continuous progress of silicon photonic integration and electric chip technology, as well as the further improvement of market demand for transmission rate, man man transmission technology will have greater development.