Discussion on the effect of an optical phase-locked loop on the coherence properties of a laser

Abstract

The statistical characteristics of laser phase noise are analyzed in detail. To restrain the phase noise, an optical phase-locked loop (OPLL) is employed to achieve phase locking of a laser. The working mechanism of OPLL is discussed. By calculating the cross-correlation function between a phase-locked laser and an ideal laser, the feasibility of laser phase locking by means of an OPLL has been certified. Furthermore, the autocorrelation of a phase-locked laser and the cross correlation between an ordinary laser and an ideal laser are compared to show the performance of the OPLL. The quantitative analysis results show that if the linewidth of a laser is about 2 MHz, the time constant of an OPLL should be less than 50 ns to meet the needs of coherent beam combining.