Implementation Of Optical Frequency Comb Based On Cascaded Dual-Drive Electro-Optic Modulator And Its Application In Optical Access Network

Optical frequency comb?OFC?is an optical source with a comb-like spectrum in the frequency domain.Owing to its high stability,simplicity,low cost,flexible tunability and many other good properties,it has been widely used and also attracts a large number of researchers'attention.The OFC can be used as precision optical frequency reference source,ultra-short pulse generation and arbitrary waveform generation.In the traditional optical communication system,a tunable laser array is used as the multicarrier light source,but this scheme has some shortcomings such as high cost and difficulty of synchronization between the respective carriers.It has been a trend to adopt the OFC rather than the tunable laser array as the multicarrier light source in large-capacity optical communication system,because the OFC has the advantages of low cost,tunable carrier spacing,high stability and carrier phase correlation.Using OFC as the multicarrier light source has a very broad application prospects in the optical communication system.There are many methods to generate OFC such as using a mode-locked laser,optical fiber nonlinear effect,recirculating frequency shifter based OFC and electro-optic modulator based OFC.The scheme of electro-optic modulator based OFC has some advantages such as simple structure,low cost and high stable carriers.Based on this,in this paper,a scheme based on cascaded dual-drive electro-optic LiNbO₃ modulator to generate OFC is proposed.And we also apply the generated OFC into a communication system and realize a new type passive optical network?PON?transmission system.The main content of the thesis includes:?1?We investigate the methods of generating OFC based on electro-optic modulator and put forward a new method to generate OFC.A scheme of OFC based on cascaded dual-drive electro-optic modulator is proposed,and the feasibility of the scheme is validated by theoretical simulation.We experimentally obtain a OFC whose wavelength spacing can be flexible adjusted from 6 GHz to 12.5 GHz.We can get 11 comb lines within 1.5 dB spectral ripple under single stage condition and 17 comb lines with 2 dB spectral ripple under cascaded condition.?2?We also design an auto-bias control system for the modulator to ensure the stability of the OFC.We adopt the technique based on dither tone and the radio of the 2^nd order harmonic signal to the fundamental 1^st order signal is used as the feedback parameter.The stable system operation is realized after completing the hardware circuit and control software.?3?We produce a 12 tones OFC with a 12 GHz channel spacing and a spectral ripple less than 1.5 dB as the light source of an ultra-dense wavelength division multiplexing?UDWDM?system.Combining with the spatial division multiplexing?SDM?technology,we experimentally demonstrate the feasibility of UDWDM-PON transmission through multicore fiber?MCF?.The MCF-based self-homodyne coherent detection?SHCD?scheme is adopted,and we transmit the pilot-tone through the central core of the 7-core MCF while the six outer core are used to transmit the 10 GBaud polarization division multiplexing quadrature phase-shift keying?PDM-QPSK?UDWDM-PON signals.We realize a SDM-UDWDM PON with 26 dB power budget,40 Gb/s single wavelength transmission rate and 2.88 Tb/s total transmission capacity after 37 km MCF transmission.Due to the application of the OFC and SHCD,there is no need to use the laser array as the light source,and at the receiver side,a narrow linewidth local oscillator laser is no longer necessary and the DSP complexity is reduced.So,the system cost is greatly reduced.