Increasing of the frequency stability of the 760nm wavelength DFB laser diode for laser interferometry

Abstract

The linewidth of the emission spectrum and the mode-hop free tuning range of the wavelength are crucial parameters for laser sources in laser interferometry, especially absolute laser interferometry. At present time the DFB (Distributed FeedBack), laser diodes are the most suitable laser sources from semiconductor laser sources for using in laser interferometry. We present our set-up of the optical fiber based laser interferometer where these laser diodes can be used. 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.