Noise suppression for the precise measurement of Fabry-Perot cavity with wide tunable range

We present the method to suppress the frequency noise on a laser diode working at 1540 nm with wide tunable range (up to 2 nm). The noise suppression is made by an unbalanced heterodyne fiber interferometer. The frequency noise in our experiment has been suppressed by -20 dBc at Fourrier frequencies of 0-20 kHz and by more than 40 dB up to 300 Hz while the tunability range stayed untouched. The linewidth measurements show the decrease from 1.5 kHz to 300 Hz. By this method we were able to reach 10-12 uncertainty corresponding to 0.1 fm in cavity length and the tunable range of 100s of GHz corresponding to 1000s nm cavity length changes.