Study on narrow linewidth randomly distributed weak feedback external-cavity diode laser

A narrow linewidth randomly distributed weak feedback external-cavity diode laser (RDWF-ECDL) is investigated and experimentally demonstrated. This laser configuration consists of a single longitudinal mode (SLM) laser and a series of randomly distributed feedback mirrors. The Lang-Kobayashi laser rate equations are generalized to arbitrary number and arbitrary distribution of external feedback points for the first time. The influence of external cavity parameters on the output characteristics of RDWF-ECDL has also been theoretically analyzed and experimentally verified. Three different fiber Bragg grating arrays (FBGAs) were used to construct the proposed RDWF-ECDL. With the feedback from FBGA20, we achieve a SLM laser output with an OSNR of 78 dB, a linewidth of 100 Hz and the white frequency noise of 15 Hz²/Hz. The proposed theoretical model can guide the design and optimization of RDWF-ECDLs and the proposed RDWF-ECDL has the advantage of narrow linewidth, which is promising for the applications that demand high coherence source.