Research On Key Technologies Of High Speed Optical Communication Systems

With the quick development of high speed and larger capacity busesiness, such as4G mobile communication, high-definition video, real-time games, telemedicine, Internet of Things, and so on, they propose great demand for high-speed backbone network. There are several ways to increase the capacity of optical communication system, such as:to increase the single-channel rate, add more wavelengths, improve the spectrum efficiency, and manufacture new types of fiber etc. These methods can be achieved through optical time optical time division multiplexing(OTDM), wavelength division multiplexing(WDM), orthogonal frequency division multiplexing and using high order modulation format. The content of this thesis is mainly focused on the high speed ultra-short optical pulse generation; demultiplexion technique;160GBaud differential quadrature phase shift keying (DQPSK) OTDM signal transmission; the generation of frequency comb and high speed signals.The main achievements and innovations are summarized as follows:1. A traveling wave electrode model of electro-absorption modulator (EAM) is proposed. Then, pulse generation based on a single EAM or cascaded EAMs are experimentally demonstrated. It is found that pulses with full width at half maximum (FWHM) of5ps can be generated using one EAM while3ps can be achived through cascaded EAMs, but the signal-noise ratio (SNR) is degraded seriously. To this end, three different generation methods are proposed to obtain short pulses with high quality. Firstly, based on the modulation function of the lithium niobate modulator, Mach-Zehnder modulator(MZM) and two phase modulators (PM) are used to generate ultra-short pulses. On this basis, using an EAM or a dual parallel MZM (DPMZM) cascaded with two PMs to generate ultra-short pulses is proposed and experimentally demonstrated. The generated40GHz ultra-short pulses are all with FWHM of～2ps, time jitter less than100fs, the extinction ratio (ER) larger than20dB and SNR larger than25dB. The phase stability is verified through DQPSK modulation and demodulation. At last, the advantanges and disavantages of the proposed methods are analyzed.2.160GBaud DQPSK signal to40GBaud de-multiplexing using EAM or DPMZM or polarization modulator are proposed and experimentally demonstrated. Firstly,2.7ps optical window is generated through self-cascaded EAM, and then it is used in160GBaud DQPSK signal to40GBaud de-multiplexing system. The measured demultiplexing power penalty is less than2dB. Second, the characteristics of the optical switch generated from the DPMZM are analyzed in detail. Then, the generated5.7ps window is used in160GBaud DQPSK system, and error free performance is achieved with only0.2dB power penalty. Thirdly, a polarization modulator is used to generate the optical switch with FWHM of5.4ps, ER larger than15dB and SNR exceeds28dB. The demultiplexing power penalty is less than1.8dB. The three approaches have their own strengths and weaknesses, which lead to different application scenarios.3. We have built up the high speed transmission platform and investigate the different signals transmission performance.The generated40GHz ultra-short pulse after DQPSK modulation is multiplexed to160GBaud and error free performance is achieved after410km G.657fiber transmission. Then, DPMZMs are used to generate pulse width tunable CSRZ-DQPSK signals. Error free performance is achieved after320km transmission for different width puses.The results show that12ps signal achieves the best performace.4. Ultra-flat phase and frequency locked frequency comb is generated using two cascaded DPMZMs. Based on frequency comb and programmable optical processor, high frequency-purity and low phase noise millimeter wave or terahertz wave signals with frequency from40GHz to as high as440GHz are successfully generated. Also,2,3,4,5,6,7,8times of the40GHz pulses are generated based on programmable optical processor and frequency comb.The generated pulses are with almost the constant pulse width of1.9ps, good ER and improved SNR over26dB.Finally,160GHz50%CSRZ signal generation only using a DPMZM driven by a40GHz sinusoidal signal is proposed and experimentally demonstrated.