Research On Low-cost Optical Transmission Technology Based On Delta-Sigma Modulation

In short-distance optical transmission,cost becomes an important issue.Compared with the complex structure and high cost of coherent receiver,direct modulation and direct detection structure is more popular.There are dispersion compensation and SSBN problems in direct detection.How to eliminate the effects of dispersion and SSBN has become a hot research topic in recent years.On the other hand,in the mobile fronthaul network,Delta-Sigma modulation technology is applied to wireless signal transmitters,which greatly reduces the cost and complexity of digital fronthaul network.Aiming at the problems of system cost and direct detection,this paper studies the low-cost direct detection,the main contents include:(1)The principle of Delta-Sigma modulator is analyzed,and its quantization noise source and noise distribution are analyzed by using linear simplified model.Taking the single frequency signal as an example,the signal-to-noise ratio of the output signals of Delta-Sigma modulators with different orders is theoretically derived.(2)To solve the problem of high computational complexity in the parameter search of high-order stable Delta-Sigma modulator,genetic algorithm(GA)is proposed to optimize the structural parameters of high-order Delta-Sigma modulator,which greatly increases the search efficiency.(3)Aiming at the limited signal-to-noise ratio of analog signals output by Delta-Sigma architectures with 1-bit and 2-bit quantization,a new system architecture is proposed to eliminate the in-band noise after Delta-Sigma modulation,and achieve ultra-high signal-tonoise ratio output,so as to support the ultra-high spectral efficiency of radio-over-fiber fronthaul network.(4)Aiming at the dispersion compensation and ultra-low cost requirements in direct modulation and direct detection,a self-coherent detection system based on Delta-Sigma modulator and block phase switching technology is proposed.The low-cost I/O port is used instead of DAC port,and only a single PD is used for signal detection,thus realizing the experiment of transmitting 1200 km of QPSK signal with a single channel rate of 32Gb/s on standard single-mode fiber.(5)To solve the problem that SSBN is difficult to eliminate in direct detection,a SSBN elimination algorithm is proposed,which realizes the transmission of 16 QAM signal with112Gb/s rate for 240 km on standard single-mode fiber.