Design And Analysis Of OCDMA Optical En/decoder Based On The Micro Ring Resonator

Optical Code Division Multiple Access(OCDMA) technology with the advantages of electric CDMA and bandwidth of optical fiber communication has become one of the most important technologies to realize all-optical communication. Optical en/decoder as the key device in OCDMA system has a demand of higher degree of integration, easier tuning, more user accommodated.As the basic structure of the large-scale integrated optical circuits, the micro-ring resonator(MRR) has a series of advantages including small size, superior frequency selective characteristics, supporting multi tuning manner, scalability performance as well as the compatibility with microelectronics batch processing. These merits make the MRR a promising implementation scheme for the en/decoder above mentioned. Currently, there are three problems in the international researches of the MRR-based en/decoder. Firstly, partial en/decoding schemes are not good enough, which limits the system capacity due to the one-dimensional manner. Secondly the codec performance is not well, which behaves as a low auto-correlation/ cross-correlation peak value in en/decoding process. Thirdly the user capacity cannot be extended easily, which means a low utilization rate of the channel band. Aiming at these problems, this paper carried out the following research work on the theoretical analysis, parameter design, numerical calculation and performance optimization.1. By combining the reflection spectrum from the download port of the MRR array with the phase conversion from the phase shifter, a novel en/decoder structure is proposed by using the MRR array as the core unit. The transfer matrix equation of the MRR array is established based on the optical waveguide coupling mode theory and the transmission theory. In addition, the reflection spectrum characters is researched respectively for the parallel-coupled-double-rings and tandem-coupled-three-rings en/decoder structures. In the two types of en/decoding structures, moreover, the relationship between the coupling coefficients, the processing tolerance, the loss coefficient, the chip rate, the channel spacing and the autocorrelation peak side lobe ratio, cross-correlation peak value are analyzed. Based on the above researches, the en/decoder parameters selection range is conformed. Through numerical simulation, the correlation peak ratio and the time/frequency domain output spectrum of the wavelength/phase two-dimensional coherent decoding for the two kinds of structures are obtained, verifying the feasibility of the MRR array based en/decoder.2. In order to optimize the en/decoder, several methods are proposed including the best coupling coefficient method, the coupling coefficient of Gauss and Planarization flattened distribution optimization method and the radius optimization method. Aiming at the two kinds of en/decoding structure(parallel-coupled double-rings and tandem-coupled three-rings), the en/decoding performance before and after the optimization are contrasted. Theoretical calculation shows that, the correlation peak ratio performance of the en/decoder after optimization is enhanced.3. In order to enlarge the user capacity of the system, the MRR based en/decoder structure is further improved according to the Vernier effect which can easily expand the MRR free spectral range. Based on the transfer matrix equation, the 3dB bandwidth, the rectangular factor, the peak reflectivity and the spurious mode suppression characteristics of the improved tandem en/decoder structure are analyzed in detail, which helps to obtain the reasonable range of the en/decoder parameters. Moreover, the wavelength hopping/phase en/decoding of such structure is realized in design and simulation. In addition, by using the coupling coefficient of Planarization flattened distribution optimization method and the radius optimization method, the performance is further improved. The results shows that, the improved en/decoder based on the tandem MRR can obtain high correlation peak ratio, and the user capacity is enhanced exponentially.4. In order to satisfy the needs of signals transmission through relative rotating interfaces in OCDMA, we propose and realize a novel single-channel SI plastic optical fiber rotary joint(PFORJ) by using a pair of upside down taper lens(UDTLs). Then based on the ray tracing method, structure parameters were simulated and analysed in detail. The fabrication of the UDTLs and the measurement of this PFORJ performance were carried out.