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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 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 measurement probe is realized by standard optical fiber with reflection coated fiber optical connector.
First we used VCSEL laser diode to measurement with our fiber interferometer. The frequency linewidth, the mode hop free tuning range and the optical power is not sufficient for practical measurement outside of laboratory. The DFB laser diode has narrower frequency linewidth, wider mode hop free tuning range and more optical power. In addition to the opposite of VCSEL 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 package. One of the main problems in using of the DFB laser diodes with 760 nm wavelength is a back reflection from the fiber connections at the output. We present our experience with adaptation of both types of the DFB laser diodes to laser interferometer and methods to decrease back reflections from the connections of optical fibers.
We used stabilization by frequency lock to F-P (Fabry - Perot) resonator for VCSEL laser diode. The absorption in Krypton and Acetylen (760 nm, 1542 nm, 1552 nm) is used for the frequency stabilization of the DFB laser diodes.
We present comparison of our first measurement with frequency stabilization of these laser diodes with 760 nm and 1541 nm wavelength using absorption in Acetylene and Krypton and adaptation of these diodes to our laser interferometer.
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