Wang Xiaochan, Ma Jianxin, Zhang Qi, Xin Xiangjun
Appl Opt. 2019 Apr 20;58(12):3222-3228. doi: 10.1364/AO.58.003222.
A generation scheme for the linear frequency-modulated (LFM) signals with tunable carrier frequency and improved time-bandwidth product (TBWP) using an optical frequency comb (OFC) and a fiber Bragg grating (FBG) time delay line is proposed and demonstrated by simulation. In the scheme, intensity modulation is used to convert the continuous time-domain waveform to an optical pulse with a duty cycle of one-sixteenth, and two cascaded polarization modulators driven by two different radio frequency signals are used to generate 16-line OFC without an optical filter. Then the 16-line OFC is injected into the FBG time delay line, which consists of 16 discrete FBGs, and each spectral line is reflected by the specific FBG after different time delays. By properly designing the position of the FBGs, the 16 spectral lines of the 16-line OFC are separated in the time domain. The time-separated OFC is then modulated by a phase modulator driven by a periodic parabolic signal for introducing parabolic phase modulation. Subsequently, after the heterodyne beating between the phase-modulated optical signal and the local oscillator light wave emitted from a tunable laser source (TLS) in a photodiode, an electrical LFM signal with improved TBWP is generated. Simulation results show that the generated LFM signal has the bandwidth of 31.78 GHz and TBWP of 1365.33, and its center frequency can be tuned by varying the wavelength of the TLS.
提出了一种利用光学频率梳（OFC）和光纤布拉格光栅（FBG）时延线生成具有可调载波频率和改进时间带宽积（TBWP）的线性调频（LFM）信号的方案，并通过仿真进行了演示。在该方案中，强度调制用于将连续的时域波形转换为占空比为十六分之一的光脉冲，并且由两个不同射频信号驱动的两个级联偏振调制器用于在无需光学滤波器的情况下生成16线OFC。然后将16线OFC注入由16个离散FBG组成的FBG时延线中，每条谱线在经过不同时延之后被特定的FBG反射。通过合理设计FBG的位置，16线OFC的16条谱线在时域中被分离。然后，由周期性抛物线信号驱动的相位调制器对时间分离的OFC进行调制，以引入抛物线相位调制。随后，在光电二极管中，经过相位调制的光信号与可调谐激光源（TLS）发射的本地振荡光波之间进行外差拍频后，生成具有改进TBWP的电LFM信号。仿真结果表明，生成的LFM信号带宽为31.78 GHz，TBWP为1365.33，并且其中心频率可以通过改变TLS的波长进行调谐。
