Performance Improvement Of Quantum Well Semiconductor Optical Amplifiers For All-optical Signal Processing

Optical communication networks have a rather fast development.Nowadays,the capacity in transmission network has reached the order of Pb/s.However,in order to process the Pb/s capacity at the network nodes,traditional O/E/O conversion becomes more and more difficult because of the huge power consumption and bottleneck of O/E conversion,and is not suitable for the development requirements of ultrahigh bit rate and huge capacity of optical communication networks.On the other hand,all-optical signal processing avoids the O/E/O conversion,reduces the power consumption,improves the processing bit rate and paves a new way for the optical signal switching at the network nodes.Generally,all-optical signal processing is based on the nonlinear effects of devices.Among the various devices,semiconductor optical amplifiers(SOAs)are continued to be focused and widely investigated,due to the advantages of high nonlinear coefficient,small footprint,easy to integrate with other semiconductor optoelectronic devices,and various nonlinear effects.Especially,the quantum well SOA are also widely used in all kinds of nonlinear application.On one hand,the nonlinear effects can easily controlled by energy-band engineering.On the other hand,the devices can also be large-scale commercial produced using metal organic chemical vapor deposition(MOCVD).In this dissertation,we select the quantum well SOA for all-optical signal processing as our main study object,and obtain the best output performance for all optical signal processing of wavelength conversion,format conversion and signal regeneration,by combining the energy band optimizing with operating condition improvement to enhance the different nonlinear effects.The major research achievements and contributions are summarized as follows:Firstly,the theory and model of quantum well SOA for all-optical signal processing are investigated.We modify the band structure algorithms.The solving time is reduced to 1/103 and the solving memory consumption is decreased to 1/333 at the same solving accuracy.Then we combine the band structure solving with the energy density matrix equation and give the relationship of the energy band design with the material susceptibility control.We further construct the material model of quantum well SOA based on the modular programming ideas,which can solve the band structure and susceptibility of main?-? materials quantum well.Next,we combine the band structure solving,susceptibility calculation with the SOA dynamic model to construct the carrier heating model and ultrafast polarization model for different applications.Finally,we comprehensively analyze the characterized parameters of quantum well SOA,including material gain,differential material gain,refractive index change,differential refractive index change,linewidth enhancement factor,polarization dependent gain and third order susceptibility,which is helpful to design the quantum well SOA for all-optical signal processing.Secondly,wavelength conversions based on cross gain modulation(XGM),cross phase modulation(XPM),transient cross phase modulation(T-XPM),and four wave mixing(FWM)are theoretically investigated.We analyze the key problems and propose the schemes to improve the performance.For the wavelength conversion using XGM effect,XGM effect is enhanced and the carrier recovery time is also accelerated by controlling the carrier injection process to quantum well.For the wavelength conversion using XPM effect,by using the difference of the bidirectional propagation between pump signal and probe signal to suppress the slow interband effect,better wavelength conversion is obtained.For the wavelength conversion using T-XPM effect,we propose the scheme using the pump signal with amplitude dips to control the strength of the intraband effects and the interband effects.We firstly obtain recovery process of a few picoseconds without the help of detuning bandpass filter and the operating bit rate can reach to 640 Gb/s.For the wavelength conversion using FWM effect,we enhance the third order nonlinear effects by optimizing the quantum well structure of the SOA and the value of the third order susceptibility can be enhanced 2.3 times.Thirdly,the schemes of different modulation format conversions in the optical communication network are theoretically and experimentally investigated.For the format conversion from phase-shift keying(PSK)to on-off keying(OOK),we firstly experimentally demonstrate 40Gb/s regenerative and wavelength-converting format conversion from non-return-to-zero(NRZ)differential phase-shift keying(DPSK)to return-to-zero(RZ)OOK.Then using the half bit delay delay interferometer(DI)or detuning bandpass filter to preprocess the RZ-DPSK,NRZ quadrature phase shift keying(NRZ-QPSK),and RZ-QPSK signal,we further demonstrate the regenerative and wavelength-converting format conversion from RZ-DPSK/NRZ-QPSK/RZ-QPSK to RZ-OOK.In order to further improve the performance of the format conversion,we optimize the quantum well structure of the SOA,enhance nonlinear effect and improve the operating performance and the conversion efficiency.For the format conversion from NRZ to RZ,we propose a novel scheme using the XGM effect in contrast to the former schemes using XPM effect.The experiment demonstrates the performance of format conversion using XGM effect is much better than that using XPM effect.Finally,we experimentally demonstrate the 2 × 80 Gb/s format conversion from polarization division multiplexing(PDM)NRZ-QPSK to PDM RZ-QPSK.Fourthly,the regeneration of phase modulated signals based on cross gain compression(XGC)effect is theoretically and experimentally investigated.We experimentally demonstrate the amplitude regeneration of one NRZ-DPSK signal using two commercial SOAs and obtain 2.77dB power penalty at bit error ratio of 1×10-9.As the nonlinear effects and requirements of the two experimental SOA are completely different,we optimize the quantum well structure to control the nonlinear effects and make each SOA get the best operating performance.Then we further simplify the setup of the XGC effect and use only one commercial SOA to realize amplitude regeneration of two RZ-DPSK signals.Finally,we investigate the amplitude regeneration of time interleaved PDM RZ-QPSK signals and design the optimized quantum well SOA.The polarization dependent gain(PDG)in the C band is less than 0.2dB and the device can operate at 856Gb/s.