Frequency stability of the 760 nm DFB laser diodes for laser metrology

Abstract

At present time the DFB (Distributed FeedBack), laser diodes are the most suitable laser sources from semiconductor laser sources for using in laser interferometry. The DFB laser diodes have narrow frequency linewidth, mode hop free tuning range up to 2 nm and sufficient optical power. In addition to the other types of laser diodes are available in the package with optical fiber at the output and the DFB laser diodes with 1541 nm wavelength has optical isolator inside. Unfortunately the DFB laser diodes with 760 nm wavelength have no optical isolator inside package. This induces a back reflection from the fiber connections at the output to the laser chip. Than the mode hop free tuning range is decreasing rapidly. We present our experience with adaptation of the DFB laser diodes to laser interferometer and methods to decrease back reflection. We used frequency stabilization by frequency lock to F-P (Fabry – Perot) resonator for VCSEL laser diode but the DFB laser diodes can be better frequency stabilized using absorption to absorption spectrum of gases (760 nm, 1542 nm, 1552 nm) to compare achieved frequency stability of the 760 nm DFB laser diodes.