This paper presents a study on the issue of current-driven distributed feedback (DFB) semiconductor lasers (LD) experiencing nonlinear laser frequency variation in the course of linear frequency modulation. A theoretical model of the linear frequency modulation process of DFB semiconductor lasers is established. On this basis, the relationship between injection current and laser frequency is analyzed and a correction method has been put forward, to improve the linearity of the laser frequency variation. It was eventually verified that the proposed correction method can greatly improve the linearity of the linear frequency modulation (LFM) output laser signal.
In this review, methane absorption characteristics mainly in the near-infrared region and typical types of currently available semiconductor lasers are described. Wavelength modulation spectroscopy (WMS), frequency modulation spectroscopy (FMS), and two-tone frequency modulation spectroscopy (TTFMS), as major techniques in modulation spectroscopy, are presented in combination with the application of methane detection.
Recent Developments in Modulation Spectroscopy for Methane Detection Based on Tunable Diode Laser