Research On The Generation And Application Of Optical Frequency Comb

As an interdiscipline, Microwave Photonics combines the broad bandwidth of optical communication and the flexibility of microwave wireless communication, which is of great potential in application. It focuses on the interaction of optical signal and microwave signal. Multi-carrier Modulation is applied to optical communication as Multi-carrier Optical Communication, which is of great use for building more simple, stable and costless system. As one of the key technologies in both Microwave Photonics and Multi-carrier Optical Communication, Optical Frequency Comb(OFC) becomes the hotspot of current study, and is of great value in applications; Large number of laser is saved when the OFC is used as multi-carrier optical source, and the source is more stable, which means a lot to the Multi-carrier Optical Communication; By using all-optical frequency down-conversion based on OFC, the optical carrier and the signal in the adjacent channel are filtered out and beaten directly, the system is more simple and cheaper, and the non-linear loss and the demand for bandwidth are reduced; The ideal Nyquist pulse, which is generated by OFC and can be closely arranged in time domain, is of great value in decreasing inter-symbol interference and increasing the efficiency of spectrum. How to generate optical frequency comb with high quality is always difficult. This article focuses on the generation of Optical Frequency Comb based on the electro-optic modulator.The operating principle of electro-optic modulator is first analyzed and some frequently used electro-optic modulator, such as intensity modulator, phase modulator, polarization modulator and Dual-Parallel Mach-Zehnder Modulator, are discussed. Then two schemes to generate OFC based on electro-optic modulator are proposed. Scheme one generates a high quality and tunable OFC with 3, 5, 9, 15 and 25 lines by setting the driving voltage of two cascaded modulators, and it is proved to be correct and tunable by theoretical derivation, simulation and experiment. Besides, the factors which affect the performance of OFC, such as modulation index, DC bias voltage and initial phase, are pointed out. Scheme two generates OFC by bi-direction use of intensity modulator in a fiber Sagnac loop. Optical signal splits into two optical signal at the input port of the Sagnac loop and travel in opposite directions, one is clockwise and modulated, the other is counter-clockwise and unmodulated. They are coupled at the output port of Sagnac loop and sent to the polarizer. By adjusting the polarization state of the coupled optical signal, OFC with 5 lines is obtained. Furthermore, the effect of polarization controller on the performance of OFC is analyzed.