Very precise phase/frequency control of confocal fabry-perot cavity coupled semiconductor laser

It is argued that ultra-narrow linewidth semiconductor lasers are attractive for the applications to precise measurements and high resolution spectroscopy, and coherent communication systems. The confocal Fabry-Perot cavity coupled semiconductor laser (CFP-LD) shows a wide band frequency noise suppression characteristics with natTllh linewidth. The FM characteristics of the CFP-LD had been reported elsewhere. The authors had carried out the experiment on the heterodyne optical phase-locked loop (OPLL) using two AlGaAs CFP-LDs of 10 kHz linewidths, with the phase error of 8.1 degrees and the frequency tracking error between two 1 asers of 0. ,lmHz at the integration time of 70sec [ 4]. The l inewidth of Uw het.erod~??ne signal under phase locking with PLL noise bandwidth of about 1 MHz 1.,ras less than 30 Hz, which was limited by the resolution bandwidth of the spectrum analyzer used in the measurement.