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.
An ultrafast high-repetition-rate mode-locked fiber laser based on a semiconductor saturable absorption mirror is reported in this paper. The repetition rate is as high as 1 GHz. A piece of single-mode EDF is used as the gain medium and a linear cavity is built. The central wavelength of the mode-locked fiber laser is 1561 nm, the spectral width is 10.10 nm, the pulse interval is 1ns, the RF signal-to-noise ratio is greater than 68 dB, and the pulse width is 247 fs. The experimental results show that the stable high repetition rate mode-locked pulse can be obtained through this simple and compact structure, and the application of the mode-locked laser in optical sub-sampling is verified.
In this paper, a broadband microwave photonic channelized receiver based on optical frequency comb (OFC) injection locking technology is illustrated. The simulation results show that, with more than 80 comb lines generated from OFC, this receiver enables channelized scanning and reception of broadband signal up to 40 GHz with instantaneous bandwidth of 1 GHz. Meanwhile, the channels selected using optical injection locking (OIL) technology, perform high gain and low phase noise with suppression ratio between the selected comb line and other comb lines is 28.7 dB. Due to OIL technology, the wideband tunability of this receiver would not depend on the optical filter or demultiplexer, and the band limitation and operation resolution introduced by optical components are broken through. The OIL technology also lead to the architecture of receiver more compact and feasible in practical.
In this paper, we illustrate a discrete Fourier processor based on dual optical frequency combs (OFCs). The simulation verified the DFT calculation with the frequency coverage of 0.2 GHz to 3 GHz and the resolution is 200 MHz. Meanwhile, demodulation of standard OFDM signal in time domain is simulated. This scheme avoids the problem of "electronic bottleneck" in current all-electronic processors. It is superior to the existing photon-assisted Fourier transform schemes in flexibility and accuracy, and has the characteristics of low power consumption, high throughput and high precision.
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.
In this paper, we illustrate a radio-frequency (RF) channelization scheme based on dual optical frequency combs (OFCs). Modulated by two sets of cascaded electro-optic (EO) modulators, dual coherent OFCs with different free spectrum ranges (FSRs), namely 10 GHz and 11 GHz, are generated. Based on OFCs, a channelizer with six channels, 1 GHz channel spacing is experimentally demonstrated, covering frequency range from 1 GHz to 7 GHz. The input RF signal is impressed onto the signal comb by a Dual-Parallel Mach-Zander modulator (DPMZM). At the same time, balance detection methods and I/Q demodulation are used to achieve high-precision reception and the processing of RF signals. Selecting the corresponding channel with a waveshaper, the performance of six channels is shown and the spectra at different stages are also demonstrated.
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