Research On Superimposed Sampled Fiber Bragg Grating Based En/Decoding Technology Of Optical Code Division Multiple Access Systems

Compared with the mature communication technology such as Wavelength Division Multiple Access (WDMA), Optical Code Division Multiple Access (OCDMA) technology has many advantages the anti interference capacity, inherent safety, low cost, asynchronous random access and so on, have the ideal prospect for the application in future optical networks with physical layer security and all optical high-speed access networks. En/decoder is the key device of the whole OCDMA system and it has the important function that encode multi-channel signals to share the common transmission medium and select signal among the coupled signals so that it become the core task of the research of OCDMA technology. And it becomes the decisive factor for the system’s performance. With its powerful and flexible signal-processing capability, the Fiber Bragg Grating (FBG) stands out of many other candidate materials for the En/decoder and greatly enhance the practicability of the En/decoder. The OCDMA technology is still in the practical development process and apparatus and techniques is an important negative factor.Obviously, solving the existing problems established in the matured instruments and craftwork is an effective choice to reducing the operation cost. In this paper, We implement the innovative investigations on En/decoders based on FBG, aiming to solve the existing problems.Firstly, the advantages of OCDMA technology are discussed. We introduce the research situation and tendency of the optical fiber communication especially the OCDMA technology, followed with the systematic structure of OCDMA and its emblematical schemes of en/decoding.And the advantages and disadvantages of various schemes are summarized.Then we summarize the optical signal-processing function of FBG based on its fundamental principles and numerical methods. FBG becomes the best choice for En/decoder with its powerful and flexible capacity. The principles of FBG’s appliance to the emblematical en/decoders and each one’s drawbacks are analyzed.In order to solve the problem that traditional FBG requires production platform with high degree of accuracy and complexity, The SI-SFBG technology is presented in this paper. According to the principle of equivalent chirp and the equivalent phase, SI-SFBG has the same en/decoding function with the traditional FBG, but act better in production method and price compared with the traditional ones, through the theoretical analysis. Based on a single uniform phase mask and sub-micrometer production platform, we can make the SI-SFBG with compact structure and multiple wavelengths to meet the need of various types of En/decoder.The feasibility of En/decoder based on SI-SFBG is discussed theoretically. We design a SI-SFBG used in SAE OCDMA system and complete the 4-user,40GHz-transmission rate system simulation, the results confirm the applicability of SI-SFBG in the SAE system. Aiming at the dispersion problem which is common in traditional multi-wavelength coding system, we propose the total-dispersion-compensating en/decoding technology according to the principle of equivalent chirp. We successful design a SI-SFBG applicable to the SAE system and complete a 4-user system simulation, whose transmission rate is 5GHz, transmission distance is 10km. Based on the designed En/decoder, no dispersion exists after 10km-transmission.No extra dispersion-compensating device is used and the signal we receive equals the results of back-to-back (BTB) with the traditional en/decoder. It proves the ideal way to solve the dispersion problem.