Noise Suppression on the Tunable Laser for Precise Cavity Length Displacement Measurement

Abstract

The absolute distance between the mirrors of a Fabry-Perot cavity with a spacer from an ultra low expansion material was measured by an ultra wide tunable laser diode. The DFB laser diode working at 1542 nm with 1.5 MHz linewidth and 2 nm tuning range has been suppressed with an unbalanced heterodyne fiber interferometer. The frequency noise of laser has been suppressed by 40 dB across the Fourier frequency range 30–300 Hz and by 20 dB up to 4 kHz and the linewidth of the laser below 300 kHz. The relative resolution of the measurement was 10−9 that corresponds to 0.3 nm (sub-nm) for 0.178 m long cavity with ability of displacement measurement of 0.5 mm.

Noise cancellation in distributed feedback laser based interrogation system for twin grating accelerometer

“…Most significant components were at 150 Hz and 300 Hz, while there were other significant components up to 4000 Hz (figures 6(a)-(b)). This kind of noise originating from the power supply of a DFB laser has been reported in [14]. The noise spectrum of PD S and PD R was of the same nature.…”

“…In [10], laser frequency stabilization based on feedback mechanisms using a HCN gas cell, and laser frequency locking and beating frequency have been reported. In [14], a complex stabilization mechanism for a DFB laser diode, based on injection current feedback has been reported.…”