DELAYED-SELF-HETERODYNE MEASUREMENT OF LASER FREQUENCY FLUCTUATIONS

The two-sample (or Allan) variance of frequency fluctuations is used for laser frequency-noise characterization at Fourier frequencies below 1 MHz. The delayed self-heterodyne technique is employed for the variance measurement; analytical calculations ensure that just twice the variance values are observed at tau < 0.3-tau-d, where tau is the averaging time for the frequency measurement and tau-d is the delay time. The variance measurements of 1.5-mu-m DBR and DFB laser diodes (LD's) are demonstrated at 6.0 x 10(-7) less-than-or-equal-to tau less-than-or-equal-to 1.0 x 10(-4) [s] by using an 81.5-km fiber delay line; observed flicker fluctuations (or 1/f noise) are summarized.