Study On The Output Characteristics Of Fiber Grating External Cavity Semiconductor Lasers

It is a fact that dense wavelength division multiplexing (DWDM) is a developing trend of optical fiber communication system. The laser source, as the important portion of DWDM optical fiber communication system, must satisfy some strict requirements such as stable lasing wavelength, and narrow line-width, etc. Fiber grating external cavity semiconductor laser (FGESL) has received considerable attention as a promising source to satisfy these strict requirements.In this paper, a novel theoretical model about the output characteristics of FGESL has been established. After considering the gain distribution with wavelength, the expression formula of the output spectrum of the FGSEL has been deduced by ray trace method. Combing with rate equation about carrier, the fine structure of output spectrum has been investigated. The results show that, in the reflective band width of grating, fiber grating external cavity will result in energy distribution to vary seriously, there exist many peaks and the number of peak is related to the lengths of external cavity; With the increase of the bias current, the output power and side-mode suppression ratio of FGSEL tend to increase accompanying with fluctuation, whose amplitude and frequency will decrease with the decrease of the reflectivity of the front facet.On the other hand, the influences of the reflectivity of the front facet of the diode on the output characteristics of the FGESL have been investigated. The numerical simulation results show that, with the increase of the reflectivity of the front facet of the diode, the action of the fiber grating is more powerful, the external cavity mode is more obvious, and the side mode suppression ratio increases accompanied by an oscillation. The above results can provide an instructive insight into the output characteristics of FGESL.