Development of a wavelength stabilized optical source with a laser diode

Optical sensing technology with laser interferometry have been used in industrial metrology. Usually, frequency stabilized lasers have been used for the accurate measurement of length or surface roughness. (1’ However, the length reference of the laser inter-ferometer is the wavelength of light, so optical measurements with a frequency stabilized laser have the disadvantage that the error induced by fluctuations in the refractive index of air must be compensated for. A wavelength stabilized optical source with a laser diode(LD) is proposed for distance measurements, and a compact, precise light source developed using an air-gap etalon as a length reference (wavelength reference). (2) A new and simple method to control the wavelength has been devised, and spectral linewidth reduced simultaneously using this method. Important characteristics of the optical source are wavelength stability and narrow spectral linewidth. Experimental results for wavelength stability were 3x10^-9 estimated from the square root of the Allan variance(integration time T is 10 sec). Experimental results for spectral linewidth were 700KHz(with feedback) and 10 MHz(free running). Satisfactory results were obtained for the other characteristics(output power and point stability).