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High Speed All-optical Signal Processing Based On Semiconductor Optical Amplifiers And Optial Filtering

Posted on:2009-09-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:J J DongFull Text:PDF
GTID:1118360275970862Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
As the bit rate of one wavelength channel and the number of channels continue increasing in the telecommunication networks thanks to the advancement of optical transmission technologies, switching is experiencing the transition from the electrical domain to the optical domain. All-optical signal processing, including wavelength conversion, optical logic gates and signal 3R regeneration, etc, is one of the most important enabling technologies to realize optical switching, including optical circuit switching, optical burst switching and optical packet switching.Semiconductor optical amplifiers (SOAs) are very promising in all-optical signal processing because of their high nonlinearities, low power consumption, high power efficiency, small footprint, low cost, and ease to be integrated with other semiconductor optoelectronic devices. In this dissertation, some all-optical signal processing techniques based on SOAs which are related with the 40Gbit/s optical communication system, such as all-optical wavelength conversion, all-optical format conversion, all-optical logic gates, and all-optical ultrawideband (UWB) pulse generation, have been demonstrated. Several research achievements and contributions are summarized as the followings:Firstly, the basic principle for SOA-based all-optical signal processing is investigated. The propagation equation for the optical field and the rate equation for the carrier density in SOA are derived. And the principle and applications for nonlinearities of SOA are discussed. Different SOA models and their applications are summarized. A novel ultrafast SOA model is presented and the numerical arithmetic is provided.Secondly, an analytical formula for wavelength conversion of transient cross phase modulation (T-XPM) is deduced from the viewpoint of impulse response function. The analytical formula can interpret accordingly the polarity evolution of wavelength conversion. The calculated detuning of the filter by the formula is found to agree well with the published experiment results. We experimentally demonstrate both inverted wavelength conversion and non-inverted wavelength conversion at 10Gbit/s and 40Gbit/s. In the inverted wavelength conversion, the filter detuning is small and it is useful to accelerate the amplitude recovery, where the XGM dominates this process. However, in the non-inverted wavelength conversion, the filter detuning is relatively large, and it acts as frequency- amplitude conversion. And the XPM is dominant. Thirdly, a variety of format conversion schemes are presented using single SOA and a detuning filter. NRZ-to-RZ format conversion by T-XPM effect is theoretically demonstrated. Some important parameters are analyzed. NRZ-to-PRZ and inverted wavelength conversion of NRZ signal have been demonstrated with the same structure. At last, simultaneous SOA-based NRZ-to-PRZ conversion and 2R regeneration of amplified NRZ signal using self phase modulation (SPM) are investigated. The blue shifted filter can suppress the distortion of NRZ signals, and obtain 2R regeneration. Conversely, the red shifted filter can extract the frequency chirp and suppress the direction current components. Hence the NRZ-to-PRZ format conversion is obtained.Fourthly, a variety of SOA-based logic gates and the advanced logic circuits are investigated. Both logic NOR and OR gates at 40Gitb/s based on T-XPM effect are presented for the first time to our knowledge. The impact of linewidth enhancement factor and input pulsewidth on output performances is analyzed. Then multifunctional logic gates at 40Gbit/s, including NOR, OR, NOT, AND, and XNOR, are demonstrated based on single SOA and optical filtering by considering the four-wave mixing (FWM) effect. At last, optical half /full adders based on single SOA and several optical bandpass filter are theoretically proposed. Different logic functions are realized by different filter detuning. Fifthly, the optical UWB pulse generation based on SOAs is systematically studied. We propose a scheme for optical UWB monocycle generation based on T-XPM effect. A pair of polarity-reversed UWB monocycle pulses is achieved by locating the probe carrier at the positive and negative linear slope of the filter, respectively. Then we demonstrate a simple and compact scheme to generate UWB monocycle pulses utilizing gain saturation of the dark RZ signal in an SOA. The UWB frequency spectra at different injected currents, different input pulsewidth, and different input wavelengths are analyzed. Later, a filter-free scheme for UWB generation by XGM of single SOA is proposed and demonstrated. The system shows good stability when the input probe power varies from -10dBm to 6dBm and the probe wavelength varies in the whole C-band. At last, a simple method to generate UWB doublet and triplet pulses from NRZ-DPSK signals is experimentally demonstrated by the dispersion of single mode fiber.Sixthly, all-optical signal processing based on FWM effect of SOAs is investigated. A typical SOA FWM model is presented. And we propose all-optical bit error monitoring system (BEMS) based on the FWM model. The BEMS is realized by cascaded SOAs, which implement logic NOT and logic AND, respectively. The results show this scheme is competent for 40Gbit/s RZ format and 10Gbit/s NRZ format. Then wavelength conversion based on FWM in an SOA for various bit rate and various data formats is experimentally investigated. Especially, for 40Gbit/s NRZ signals, multi-wavelength conversion from single channel to triple channels is obtained. At last, all-optical single-to-dual channel format conversion from NRZ to RZ using FWM in single SOA is demonstrated. Based on FWM, two sideband components are generated and both channels are RZ formats. And all the converted RZ signals have a Q factor larger than 6.
Keywords/Search Tags:All-optical signal processing, Semiconductor optical amplifier, Transient cross phase modulation, Four-wave mixing, Ultrawideband generation
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