Studying The Instability Of The Lasing Wave Of Fiber Grating External Cavity Semiconductor Lasers

With the rapid development of information technology, data transmission capacity is increasing steadily. At present, dense wavelength division multiplexing (DWDM) is the most effective method of raising the capacity of optical fiber communications. The laser source, as the most important portion of DWDM optical fiber communication system, must satisfy some strict requirements such as stable lasing wavelength, and narrow line-width, etc. As a promising source to satisfy these strict requirements, fiber grating external cavity semiconductor lasers (FGECSLS) have been received considerable attention. Despite FGECSL have many advantages, because of its nature of the external cavity laser, it still has the common phenomenon such as lasing wavelength instability, mode hopping and output instability, etc. In this paper, the instability of the lasing wavelength of FGECSL have been analyzed deeply.After determining the mode distribution of FGECSL based on the phase condition, the influence of the air gap length between the head of fiber and front face of FP-LD on the lasing wavelength of FGECSL has been investigated theoretically. Numerical simulations show that the variation of the air gap length will result in the lasing wavelength rippling around the Bragg wavelength of fiber grating (FG), and the amplitude of fluctuation becomes smaller with the increase of the external cavity length. For a fixed length of external cavity, the lasing wavelength can be accurately located at the Bragg wavelength of FG through adjusting the air gap length carefully.On the other hand, the influences of the temperature variation on the lasing wavelength of FGECSL have been investigated under the determined air gap length and different external cavity lengths. Numerical simulations show that, the lasing wavelength of the FGECSL has a shift tendency to longer wavelengths with the increase of the temperature; the mode hopping happens for a short external cavity and disappears for a long external cavity. The above results of the study are helpful for the optimization package design of FGECSL device.