Laser Wavelength Measurement using a Fabry-Perot Interferometer

Wavelength measurement is required in many laser applications, in this paper, we built a precise Fabry-Perot interferometer for near infrared cavity ring-down spectroscopy. The interferometer is formed by a 2mm thick etalon of Schott Zerodur glass, providing a free spectral range of about 50GHz, and two InGaAs amplified photodetectors with maximum bandwidths up to 5MHz. The experimental results showed a good linearity in narrow frequency windows of 18.5GHz, which nearly covers the entire gas absorption linewidth. By using the ratio of the reflected signal to the transmitted signal of the etalon, the fine wavelength could be determined from a DFB laser with a 3σ detection limit of 27MHz. And the interferometer accuracy was measured about 125MHz compared with a commercial wavelength meter. Besides it has fast response, simple structure, and can be used to deduce the exact quantity of the trace gases.