Influences of Thermal Effect on the Performance of FMCW Signal Generated by Current-Modulated DFB-LDs

Abstract

A cost-effective linear chirp source is urgently needed in various commercial scenarios. Based on typical coupled mode theory (CMT) and a highly effective split-step time-domain model (SS-TDM) method, the influence of thermal effect on the performance of frequency-modulated continuous-wave (FMCW) signal generated by current-modulated distributed feedback laser diodes (CM-DFB-LDs) is numerically simulated. The results show that the thermal effect in DFB-LDs has a significant impact on the nonlinearity of the FMCW signal, and the increasing thermal effect leads to an enhancement in the nonlinearity of the FMCW signal. For a given thermal diffusion coefficient $D=2.0 \; \times 10^{-5}$ m2/s, with the increase of the thickness H between the active region and the substrate from $1.5 \; \mu $ m to $6 \; \mu $ m, both the bandwidth and the nonlinearity increase gradually at first and then tend towards saturation. For H fixed at $4.5 \; \mu $ m, with the increase of D from $1.5 \; \times 10^{-5}$ m2/s to $6 \; \times 10^{-5}$ m2/s, both the bandwidth and the nonlinearity show a downward trend. For $D = 6.0 \; \times 10.5$ m2/s and $H = 4.5 \; \mu $ m, a high-quality FMCW signal with a nonlinearity of $3.852 \; \times 10^{-5}$ and an root mean square (RMS) of 19.3 MHz under a bandwidth of 19.1 GHz can be obtained. Taking such FMCW signal as a transmitted signal, a 2 m distance ranging has been demonstrated, and the relative error is 0.340%.