Semiconductor laser wavelength stabilization using a gas cell

Abstract

Optical wavelength stabilization is very important in gas sensing application. However, current tunable diode absorption spectroscopy roughly detects the wavelength of gas. It cannot tell an accurate wavelength in gas detection due to limited resolution of optical spectrum analyzer. Wavelength drift in the gas detection occurs because of fluctuations in lasers. A feedback control is necessary for wavelength stabilization. This project aims to demonstrate stabilization of the wavelength of a semiconductor laser by building a feedback through a stable gas cell. The gas cell provides a stable resonance as an absolute wavelength reference. Amplified spontaneous emission from an Erbium doped fiber amplifier (a broadband optical signal) injects into an 800 mm gas cell with 100μg hydrogen cyanide at 10 Torr to find out the corresponding absorption spectrum. The result shows that an absorption peak is located at 1547.372 nm with about 1.1 dB losses. To detect the gas with a higher resolution, an InGaAsP/InP distributed feedback laser is preferred, which has a narrow bandwidth from 1546.8 nm to 1549.2 nm. We apply side locking method via a simple locking circuit to reduce the fluctuation of laser and the results are monitored by oscilloscopes and a power meter. The locking performance of side locking is around 20 pm. Possibility of using Pound-Drever-Hall stabilization is considered.