Study On Optical Signal Processing Technology And Application Based On Twin-Core Fiber

The term "optical signal processing" can refer to a broad range of techniques that operate on optical data signals. Compare with electrical signal processing, it has many advantages and is one of the key techniques for optical communications networks. Optical signal processing include wide research field such as modulation format conversion, optical logic gates, all optical wavelength conversion, optical calculations, and various areas of microwave photonics. Under the supports of the National Nature Science Foundation of China, this dissertation is devoted to investigate the optical temporal differentiator (OTD), optical single sideband (OSSB) modulation for radio over fiber system (RoF), and photonic generation of ultrawideband (UWB) signals. The main innovative research efforts are summarized as follows:(1) An optical temporal differentiator based on twin-core fiber (TCF) has been analyzed and verified. When the two cores have the same structure parameters (radius and refractive index), the transmission spectrum of TCF matches with the features of the first-order temporal differentiation. Hence, TCF can be used as an OTD. Furthermore, one of the cores should be cut in N sections with the same length for achieving high-order OTD, which can be considered to consist of N cascaded first-order OTDs based on TCF. Due to the comb-spectrum of TCF, an OTD implemented based on TCF for wavelength-division multiplexed (WDM) system, which is satisfied ITU-T G.692recommendation, can be achieved by properly setting the parameters of TCF. Simulation results show that16-channel first-order OTD is with channel spacing of100GHz, bandwidth of33.5GHz, and the maximum difference between actual central frequency and nominal central frequency for16-channels of4.2GHz. The differentiation results for the TCF based first-order, high-order, and WDM system OTD have been verified by inputting Gaussian pulses. Results show that the three OTDs have a good accuracy. The performances also have been analyzed by deviation factor, energetic efficiency, and3dB bandwidth. At last, as an application of TCF based OTD, a technique for recovering phase profile from intensity measurements at the input and output of OTD is presented.(2) An OSSB modulation for WDM-RoF systems using a TCF have been analyzed and verified. Due to the slope of the TCF transmission spectrum, the carrier, upper-sideband, and lower-sideband experience different attenuation and the optical double sideband (ODSB) modulation to OSSB modulation conversion can be realized with optimized optical carrier-to-sideband ratio (OCSR) and the performance of optical links can be improved. Single-sideband modulated radio-over-fiber system based on long period fiber grating has been presented. OCSR can be optimized.(3) Optical single sideband modulation RoF system with tunable OCSR based on LPFG has been verified. This system mainly consists of polarization controllers, polarization beam splitter, two parallelized LPFGs, and polarization beam combiner. By tuning the polarization controller, continuously tunable OCSR can be obtained with the range of from10dB to-5dB.(4) An approach for photonic multi-channel UWB pulse generation and modulation based on TCF has been proposed and verified. The TCF serves as a multi-wavelength optical frequency discriminator. By using phase-modulation to intensity-modulation (PM-IM) conversion, positive and negative Gaussian monocycle pulses have been obtained. Furthermore, multiple modulation formats such as on-off keying (OOK), pulse position modulation (PPM) and binary phase shift keying (BPSK) are implemented.(5) A structure of UWB pulse photonic generation based on paralleled Mach-Zehnder modulators (MZMs) by pulse shape construction has been analyzed and verified. Electrical Gaussian pulse chains modulate the lightwave via two paralleled MZMs and two optical pulses with special waveform can be obtained at the output of MZMs. By adjusting the relative time delay between the two optical pulses, Guassian doublet, positive, and negative Gaussian monocycle pulses can be obtained.