Frequency stabilization technology of HCN absorption in 1.5 μm DFB semiconductor laser

A distributed feedback laser diode (DFB-LD) has become the key light source, in which a narrow linewidth and short-term frequency stability are highly demanded, in the far-distance coherent measurement systems due to the characteristics of high-speed direct modulation, low cost, and mass production. To improve frequency stability of a DFB-LD, a new method of frequency locking was proposed. The frequency of the DFB-LD was locked to an absorption line of H¹³C¹⁴N gas at the wavelength of 1548.956 nm by a photoelectric feedback loop based on the principle of side frequency locking. The photodetection module, subsequent error signal generation and processing module and the laser drive module were integrated on the same analog circuit board to minimize the noise of the system. The frequency discrimination signal was generated by using a divider instead of a subtractor to increase the system sensibility and precision of frequency stability significantly. The second-level frequency stability of the DFB-LD was improved by more than two orders of magnitude from 3.67×10⁻⁸ to 2.34×10⁻¹⁰ by using two techniques. The experimental results show that the frequency stability scheme of DFB-LD has high precision frequency stability, in addition to the features of simple structure, low cost, mass production and suitable for UAV applications. The DFB-LD is an ideal light source for far-distance coherent measurement.