Frequency-Modulated Continuous-Wave Laser Source Based on Four-Wave Mixing Process in a Silicon Integrated Waveguide Doped With Reverse-Biased P-i-N Junction

We propose and demonstrate a Frequency Modulated Continuous Wave (FMCW) laser source realized through sideband modulation and four-wave mixing (FWM). A silicon waveguide, featuring a reverse-biased P-i-N junction, is designed to excite FWM process. With the increase of the applied bias voltage, the efficiency of the FWM effect in the silicon waveguide is improved due to more effective removal of free-carriers. The silicon integrated waveguide enables a high conversion efficiency of −12 dB. In the experiment, the radio frequency (RF) signal swept over a range of 9 GHz to 11 GHz. A laser was modulated by a Mach-Zehnder modulator to generate a first-order sideband. Meanwhile, the FWM process in silicon waveguide expand threefold frequency sweeping span to 6 GHz, thereby enhancing spatial resolution to 2.5 cm. The original tuning range of 2 GHz and tuning rate of 0.2 GHz/s is multiplied by 3 times to 6 GHz and 0.6 GHz/μs respectively. The results show that FMCW laser source has a wider frequency bandwidth of 6 GHz, a high linearity of 11.5×10^-5, and a fast chirp rate of 0.6 GHz/μs. The frequency-modulated light source exhibits excellent linearity, low noise, narrow linewidth, and fast tuning rates, which are critical attributes for modern electrical systems such as FMCW light detection and ranging (LiDAR) system. Additionally, the system obviates the need for intricate linearization algorithms, offering the advantages of simplicity in structure, high precision and easy to integrate.