Multiwavelength optical signal processing for reconfigurable fiber-optic communication systems 構成可変光ファイバ通信システムのための多波長光信号処理機能
Multiwavelength optical signal processing for reconfigurable fiber-optic communication systems
Nguyen Tan Hung
グエン タン フン
With the continuing emergence of high-bandwidth and on-demand applications, next-generation optical network will require significant improvements in terms of capacity, reconfigurability, and energy efficiency. These challenges call for developing optical networks capable of flexibly handling a higher capacity while consuming even less power than present. In searching for solutions of providing very high capacity and reconfigurability and energy efficiency, optical signal processing appear to be one of the enabling technologies due to its possibility for high-bandwidth applications and better scalability than electronics. This thesis concentrates on realizing multiwavelength signal processing architectures, providing key functionalities in wavelength division multiplexed (WDM) and optical time division multiplexed (OTDM) systems and networks. To implement desired optical functions for multiple channels, various optical nonlinearities in fibers and/or semiconductor optical amplifier (SOA) such as self-phase modulation (SPM), cross-phase modulation (XPM), cross-gain modulation (XGM), four wave mixing (FWM), and stimulated Raman scattering (SRS) are utilized selectively. Since the nonlinear e ects often occur at the same time, while a nonlinear e ect is in action, techniques to suppress the others are applied. Work of this thesis can be divided into three parts, addressing important issues for realization of reconfigurable WDM/OTDM networks. In the first part, a multiwavelength optical signal processor performing wavelength-waveform conversions, pulsewidth tunability, and signal regeneration is realized simultaneously through AND logic gate based on fiber-based parametric processing. The provided functions are desirable at WDM network nodes. It is necessary to implement optical switching of a group of wavelengths, at the same time, requires to mitigate the e ect of changes in transmission parameters of links before and after switching since the lightpaths are changed from time to time. Therefore, it is particularly desirable to integrate more functionalities into a single processing scheme, the socalled multi-channel multi-function optical signal processor (MCMF-OPS). It will be indicated that while switching multiple wavelengths to di erent wavelengths, the proposed MCMF-OPS presents large regenerations against timing jitter and signal distortions due to fiber dispersion and narrow filtering e ect for the incoming signals. Meanwhile, the pulsewidth tunability significantly improves the transmission performance for the outgoing signals via pulsewidth mani agement. The second part, on the other hand, focuses on inline multiwavelength processing with possibility of providing good channel quality even under the dynamic environment of optical paths while maintaining path wavelengths. The processing systems demonstrated in this part are based on a semiconductor optical amplifier (SOA) due to its distinctive properties compared to other photonic materials. Using SOA for multiwavelength systems faces some challenges due to the overwhelming influence of nonlinear crosstalks, especially as the number of channels increase. To overcome the problem, we introduce a technique of holding beam to suppress the e ect of interactions amongWDMchannels, leading to an enhanced input power dynamic range (IPDR) for SOA-based multiwavelength systems including optical amplification and optical signal processing based on XGM, and XPM. A more important aspect of optical signal processing is parallel multiwavelength processing which is capable of providing controllability into individual WDM channels. Parallel multiwavelength processing opens way for inline path processing at network nodes through which there may exist di erent lightpaths with di erent modulation format originating from and departing to di erent nodes without the need of wavelength conversion. To realize such a signal processor, we propose a multiple switching-window optical gate (MWOG), which is a compatible version of the conventional Sagnac interferometric switch. MW-OG o ers independent tunability of switching windows in wide range from 20% to 80% duty ratio at di erent wavelengths. The use of MW-OG for inline signal processing in a mixed NRZ and RZ data format transmission network shows significant improvement in transmission performance of optical paths due to regeneration and inline pulsewidth management by the proposed MW-OG. Finally, the third part is devoted to realization of a photonic gateway between a WDM network and an ultrafast OTDM LAN. It is still a technical challenge, yet immense importance, to construct an OTDM LAN o ering ultrahigh speed connections among users without any opticalelectronic-optical (O/E/O) devices that coexisted with conventional LANs. A emphasis is placed on providing a flexible transmultiplexing between OTDM and WDM networks. We will see that key to the success of such a gateway are a reconfigurable multiwavelength pulse compressor performing as a central synchronization controlling system responsible for the operation of the whole gateway. Nonlinear pulse compression techniques based on Raman amplifier or/and SPM are used to compress multiwavelenth clock and data pulses down to picosecond and subpicosecond ranges, o ering a compression factor up to 40 fold. Then, the compressed pulse source plays an active role for demonstrations of OTDM-to-WDM and WDM-to-OTDM conversions using multiwavelength sampling in fiber. The proposed converters provide an increased degree of flexible for channel arrangement into WDM/OTDM grids which in other others, represent for functions of routing and wavelength assignment in optical networks.