Research On Semiconductor-Fiber Composite Cavity Tunable Lasers

Nowadays, semiconductor laser technology has become more and more mature, their application in optical communication networks gradually increases, but with the new emerging technology, especially wavelength division multiplexing (WDM) optical communication technology used in wide areas. This makes people propose a higher demand for the source of optical communication.In this paper, a new type of semiconductor-fiber composite cavity (SFCC) tunable laser will be introduced and its principle will be analyzed. This tunable laser uses a Fabry-Perot Laser Diode (FPLD) to be the core, with fiber, filter and so on to construct a ring shape cavity. This structure can achieve a narrow bandwidth of light output and a wide range of broadband by adjusting the filter. So it can meet the capacity and speed of data transmission requirements for optical communication system, and it will have a very good development prospects.In this paper we firstly make an analysis about the basic theory of FPLD, and then explain how it works. On this basis, a one-dimensional model on SFCC laser is established, and a more in-depth study of its characteristics in time domain and frequency domain is also taken by the numerical method. The detail as follows:1.First, show the basic theory of the semiconductor, and make an analysis about the materials gain and the spontaneous radiation. Then the structure and working principle of FPLD laser are described, furthermore, the traveling wave equation and carrier rate equation which base on cavity electromagnetic field are also deduced.2.The basic components of SFCC laser structure and its working mechanism are described. Meanwhile, something about the related devices such as filter and their affects to the whole system are also introduced.3.Use the time domain distribution to make a numerical simulation for the one-dimensional wave equation of SFCC laser, get the numerical solution (by matlab programming).And then the dynamic characteristics such as carrier density in time and space variation and so on are studied.4.Make a frequency domain analysis about the spectral characteristics of SFCC laser output with the results of dynamic simulation in time domain as initial values, use extended matrix method to do essential research. The reason why not make a direct frequency domain analysis is that it is relatively difficult. After that, use sampled grating to achieve filter function of SFCC laser, it can get a better output spectrum and a better tuning characteristics. This paper will form a combination tunable narrow-band filter with two different sampled gratings.We first deduce the Bragg conditions and the coupled mode theory of uniform grating. Then the principle about sampling gratings is introduced, especially amplitude sampling gratings. At last, the combination tunable narrowband filter formed by two different sampled gratings is applied to the SFCC laser, and a comparison on wavelength selection and tuning characteristics is made according to the simulation results.