Fiber Grating Laser

With the coming of information society, the need for communication is rapidly increasing. Meanwhile, the developing integrated services require larger and larger communication capacity. Optical wavelength multiplexing technology is an available way to resolve this problem, which have became a research hot-spot in field of modern optical fiber communication. In Dense Wavelength Division Multiplexing (DWDM) networks, for avoiding serious crosstalk between adjacent channels, we demand that the spectrum width of laser is less than 1e-10m and the work wavelength must be very stable and easy tuning. However, normal semiconductor lasers are inadequate for this application. By using the special characteristics of grating, we can make a fiber grating laser (FGL), which has many special characteristics, such as high gain, small frequency chirp, stable output power, resistance electromagnetic disturbance and so on. In the future DWDM networks, semiconductor laser may be instead by FGL. The achievements include in this paper are as follows: 1. The development and characteristics of FGL have been reviewed. 2. Detailed coupled-mode equations of periodic dielectric waveguides are deduced from Maxwell equations. A transmit matrix method to analyze the characters of irregular refractive index grating are provided. For the first time, the transformation of refractive index and phase are united in an equation to avoid analyzing different type gratings by different methods, and the transmit matrix are used to numerically calculate the reflective spectrum of uniform, chirped, phased shift and sampled grating. The interval between two reflective peaks of sampled grating is related to the period of grating only instead of sampling rate. However, in some papers, the sampling rate is required to be less than 10%. 3. The development of fiber gratings writing technology is summarized. The photosensitive mechanism, in-grating sources and fabricated methods of fiber grating have been reviewed as well. 4. The fundamental principles of FGL are discussed. The structures and achieved methods of single wavelength FGL and multi-wavelength FGL are summarized. Moreover, the advantages and disadvantages of FGL are compared. 5. A feasible approach is put forward to devise a big tuning range FGL based on sampled gratings. By analyzing the spectrum characteristics of grating and laser rate equations, we obtained not only the relationships between output power, threshold pump power, erbium-doped fiber length and fiber grating refractive index but also the linear relationships between FGL wavelength shift with pressure, temperature, and strain as well. Furthermore, we give a suggestion to improve DBR laser. This approach adopts two different period sampled gratings to make Fabry-Perot resonators of DBR laser. The stimulated wavelength is decided by the overlapping refractive peaks of the two gratings. We can tune the wavelength discretely by tuning one of grating merely as well as tune the wavelength continuously by tuning two gratings at the same time. The tuning range is relative to the period of two gratings. So, this approach can achieve the output of fixture or random wavelength, which enlarges the tuning range adequate for optical fiber communication and sensor system. If the two gratings are the same one, this approach can also achieve multi-wavelength laser output.