The spectral range of the optical frequency comb (OFC) generated by electro-optic modulators (EOMs) is limited by the modulation depth. In this paper, an on-chip system based on a Si3N4 waveguide is built to broaden a 12.5 GHz electrooptic comb (EO-comb). A numerical simulation is carried out to demonstrate the nonlinearities of self-phase modulation (SPM), Raman soliton self-frequency shift, and dispersive wave generation dominating the spectral broadening of the EO-comb in the waveguide.
We demonstrated the application of optical frequency combs in the realization of programmable microwave photonic filters. A reconfigurable high-order PF filter based on a wide-bandwidth optical frequency comb was designed, and the increasing of the tap (comb tooth) numbers results in the increasing of the order of the microwave photonic filter. In this article, the repetition frequency of the optical frequency comb is 12.5 GHz, and the optical spectral coverage reaches 25.6 nm. The order of the RF filter obtained in the experiment reaches 256, the free spectrum range (FSR) reaches 11 GHz, the 3dB-passband width is from 300 MHz to 2.6 GHz, and the sidelobe suppression is as high as 26 dB. A progressive optical pulse shaper was used to program the tap weights, which allow us to shape the bandpass of the filter. In addition, by adjusting the spectral distribution of the optical frequency comb, two types of RF filters with different passband shapes can be realized, namely, Gaussian and Sinc filters.
Signal to noise ratio (SNR) is one of the key parameters in the communication, radar and spectrum perception systems. In this paper, we propose and demonstrate a SNR enhancement receiver with wide processing bandwidth and tunability, where two coherent optical frequency combs (OFCs) based on multi-channel microwave source and electro-optic modulators are incorporated to accomplish simultaneous frequency down-conversion and channelization. By exploiting a dual frequency microwave source as a comb driver, the FSR tunable OFC is demonstrated. The FSR of the laser can be tuned flexibly from 8 GHz to 12 GHz by controlling the controlling the frequency of the microwave source. Multifrequency microwave signal is generated from a 0-10GHz microwave signal source and cloned to the optical domain by a carrier suppressed single sideband modulator (CS-SS) and then down-converted and channelized to the same IF. The IF signals are digitalized and then added in the digital domain. With the proposed receiver a 7.2 dB SNR enhancement has been achieved.
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