Research On Optical Frequency Comb Generation And Application In WDM System

Microwave photonics integrate the advantage of microwave wireless communication and optical communication. Photonic generation, processing, control and distribution of microwave signals can be realized by microwave photonics. Which has important applications in the next broadband wireless communication and military communication. And generation of optical frequency comb(OFC) is one of the key technologies. How to generate optical frequency comb with more lines, large spacing, high tone-to-noise, flatness and stability is the current hotspot. This article focuses on the generation of optical frequency comb and its application in WDM system.Based on the theory of electro-optic modulator, we propose two novel schemes for optical frequency comb generation by using intensity modulators. Scheme one generate an tunable optical frequency comb with 3, 5, 9, 15 and 25 lines, by setting the RF signals amplitude and DC voltage of two cascaded intensity modulators. While scheme two based on a single intensity modulator modulating two tone signals, set the amplitude, frequency and initial phase of which and adjust the DC voltage to realize 9 lines flat optical frequency comb. Analyse and discuss the influence of OFC flatness such as the modulation index, DC bias voltage and initial phase in the two schemes. In view of the bandwidth of the optical frequency comb is limited by the modulator working bandwidth, two schemes of extended optical frequency comb spectrum are proposed. One scheme obtains the odd or even optical sidebands by setting the different point of intensity modulator, realizing the expansion of the spectral interval and produced 15 or 20 lines optical frequency comb. The other scheme set the RF signal amplitude and DC voltage of dual-parallel Mach-Zehnder modulator(DPMZM) to realize optical carriers cancellation, and a broadband optical frequency comb with 50 lines is generated. The relationship between the modulation index and performance of OFC is analysed and discussed. The above schemes are verified by the VPI simulation and actual experiments. Finally, based on a single DPMZM produce 5 lines optical frequency comb as the light source of point-to-point WDM system, using VPI simulate 10 Gb/s digital information and the system BER is low after 30 km standard single-mode optical fiber transmission.