単一もしくは混合フォーマット光ネットワークのための光ファイバの四光波混合を用いた光信号処理

摘要

As data rates in broadband optical networks continue to grow, all optical signal processing technologies are expected to become important for future high bit-rate communication systems to address the growing demand for network flexibility, low cost and high bandwidth. Along the line of the capacity increased, many new modulation formats have been introduced. The most straightforward format is on-off-keying (OOK) modulation format. The state of art reveals that the differential phase-shift keying (DPSK)modulation format is the best candidate for high-speed long haul network segment, while OOK is suitable for short reach network segment. However, the next generation transmission systems will more likely employ mixed modulation formats. Thus, the shift towards these changes to be applied in many applications is necessary. Hence, it is worth investigating several signal processing, not only by using a single modulation format but also mixed modulation formats. In order to realize such systems, the scheme requirement must be transparent to modulation format and bit-rate. One of the promising candidates is based on the third-order nonlinear susceptibility x(3) in a nonlinear fiber, which is also called four-wave mixing (FWM). Fiber-based FWM, in a highly nonlinear fiber (HNLF) is a preferable choice due to its fast nonlinear response and high conversion efficiency. FWM technique can be also be used as an all-optical AND logic gates and signal regenerator. In optical fiber communication systems, signal distortions due to chromatic dispersion in fiber dominantly limit transmission length and bit-rate. An improvement in the distorted signal is crucially needed, as the processed signal will become more degraded after some distance of transmission. Optical phase conjugation (OPC) and tunable dispersion compensation modulator (TDCM) are two attractive schemes used to increase the signal robustness in transmission systems. It is also desirable if a practical function such as flexible picosecond width-tunability can be accomplished. The advantageous of flexible converted pulse width are for the creation of higher bit-rate signals and the ability to support wider bandwidth requirements. In this thesis, the experimental demonstration using compressed RZ clock from Raman adiabatic-soliton compressor (RASC) and continuous wave (CW) signal as a pump signals in all-optical fiber-based FWM AND-gate using singleand mixed OOK-DPSK modulation formats in many applications can be realised. The applications including: all-optical nonreturn-to-zero(NRZ)-to-return-to-zero(RZ) wavelength-waveform conversions, all optical wave-length multicasting, all channel OTDM demultiplexing, and transmission performance between the midspan of OPC and TDCM. We experimentally demonstrated an all-optical NRZ-DPSK-to-RZ-DPSK waveform-wavelength conversion with flexible picosecond width-tunability and signal regeneration with reshaping functionality. The scheme is based on a RASC and a fiber-based AND-gate. In the first demonstration, we demonstrate waveform-wavelength conversion of a 10-Gb/s DPSK signal without input signal degradation over wide input-output wavelength ranges. The measurement results of the converted RZ-DPSK signal are pedestal-free, and its converted pulse width can be adjusted by tuning the Raman pump power in RASC. Further investigation of the regenerative properties due to chromatic dispersion is conducted at several Raman pump power settings over 40-km standard single-mode fibers (SSMFs) without dispersion compensation. Also, low power penalty with an error-free operation is obtained for the RZ-DPSK regenerated converted signal. Next, an all-optical 1-to-6 wavelength multicasting of a 10-Gb/s picosecond-tunable-width converted OOK data signal using a parametric pulse source from a RASC is experimentally demonstrated. Width-tunable wavelength multicasting within the C-band with approximately 40.6-nm of separation with various compressed RZ data signal inputs has been proposed and demonstrated. The converted multicast pulse widths can be flexibly controlled down by tuning the Raman pump powers of the RASC. Nearly equal pulse widths at all multicast wavelengths are obtained. Furthermore, wide open eye patterns and low power penalties at the 10??9 BER level are found. An all-optical demultiplexing of 40-Gb/s hybrid OTDM mixed format channels by using RASC-flexible control-window is also demonstrated. Error-free operations with less than 1.3-dB power penalties were obtained and this scheme is expected to be scalable toward higher bit-rates. Further demonstration related to NRZ-to-RZ waveform-wavelength conversion for 4 x 10-Gb/s multichannel mixed OOK-DPSK data formats, deploying a single FWM and RASC has been done. The fiber-based switch in HNLF based on parametric process between mixed data signals and the compressed RZ clock from RASC. By flexibly tuning the Raman pump power from RASC in between 0.20 and 0.90 W, high quality converted signal can be achieved. Bit-error-rate measurements show negative power penalties for the obtained RZ signals with pedestal-free pulses. Finally, we demonstrated the transmission performance between the midspan of TDCM and OPC schemes with specialty using multichannel-mixed OOK and DPSK format. The OPC scheme has the advantage over the penalties performance compared to TDCM scheme.