Frequency stabilization of FBG external cavity laser diode

In order to lock the frequency of the fiber Bragg grating external cavity laser diode to the vibrational rotational absorption of acetylene (C₂H₂) molecules, two problems must be solved: first, a large enough tuning range of the laser wavelength is required for sweeping the laser wavelength to locate the absorption line of acetylene; second, to acquire the error signal for feedback control, the laser should be frequency modulated. We present a technique to achieve frequency tuning and frequency modulation of the fiber Bragg grating external cavity laser diode by a structure of two piezoelectric transducers glued together, one for frequency tuning and the other for frequency modulation. Combining with this new structure, we use the method of extracting the third derivative signal of the absorption line as the error signal to realize frequency stabilization of the laser source successfully. The beat frequency experiment will be finished and reported in near future.