Study On Tunable Laser Based On Reconstruction-equivalent-chirp Technique

In today’s society, the requirements on the transmission capacity and rate of optical communication system continue to improve, especially in dense wavelength division multiplexing system (DWDM) which includes hundreds of wavelengths. If fixed wavelength optical modules are still used, it will make the laser number increase exponentially and the usage rate decrease. Meanwhile, the maintenance costs and the energy consumption grow dramatically. To solve these problems, the large range tunable semiconductor laser is a good choice. It has a lot of advantages, such as low cost, narrow linewidth, low threshold and so on. It can also support dynamic wavelength allocation in optical networks. Thereby the flexibility and bandwidth utilization of the laser are greatly improved.In view of the research on reconstruction equivalent chirp (REC) technique, this paper presents the simulation of tunable laser and a low cost, high performance micro-motor tunable laser.First, this paper reviews the development of optical fiber communication and semiconductor lasers, with the final conclusion that tunable laser in optical communication system becomes more and more important. Then, the background and principle of tunable laser are discussed. Secondly, this paper introduces the chirped grating and apodized grating. The principles and methods of the reconstruction equivalent chirp (REC) technique are also introduced. Thirdly, it makes s brief introduction of the basic theory of laser simulation--coupled mode theory and transfer matrix theory. Any grating structure can be calculated through the theory. Forth, we simulate widely tunable semiconductor laser based on REC technique, which consists of step-chirped sampled gratings. The step-chirped SBG serves as a comb-like reflector with flat envelop. Then two multi-channel SBGs in the laser with slightly different channel spacing will lead to vernier effect in their reflection spectra. In order to simplify the fabrication of complex structures, REC technique and equivalent apodization are introduced to design step-chirped DBR tunable laser. Therefore, only uniform grating with nonuniform sampling pattern is required which can be fabricated by standard holographic exposure. As a result, the fabrication is cheap and fast. High yield lasers with precise wavelength spacing can be easily fabricated. It has a promising future.Last but not least, we design a mirco-motor tunable laser using REC array chips. It is tuned by temperature combined with machine. After repeated tests, finally the laser can be tuned finely. It is low cost and high performance. Apart from those, the tuning range can be easily extended. It has a wide application prospect.