Frequency Stabilization of Semiconductor Lasers

Abstract

Stability of laser frequency is one of the most important performances. The frequency stabilization involves basically three parts: a reference frequency, i.e., the target frequency the laser frequency is to be locked, a frequency discriminator, and a method of feedback to tune the laser. The absorption lines of atoms or molecules are mostly often used references, especially for applications of laser spectroscopy. The saturated absorption spectroscopy with Doppler broadening removed is an important step in spectroscopy and in laser’s frequency stabilization, which is introduced in Sect. 6.1. The wavelength modulation and the frequency modulation spectroscopic methods of the frequency stabilization are discussed in Sect. 6.2. Schemes with modulation-free are developed, as described in Sect. 6.3. Section 6.4 is engaged in explanation of Pound–Drever–Hall (PDH) method, which uses the resonant peaks of high precision Fabry–Perot cavity as reference frequencies. The last section introduces schemes of self-mixing interference, one of the methods of active noise reduction.