Investigation Of All-Optical Signal Processing Based On AlGaAs Optical Nonlinear Effects

With the development of human society, people’s demand for information is boomingday by day, and communication and network has penetrated into every corner of humansociety. The rapid development of the various services, such as voice, data and multimedia,has boosted the communication technology, especially optical fiber communicationtechnology. The all-optical network with data and information exchange based on usingall-optical methods hopefully solves the bottlenecks of O-E-O in traditional optical network,which has become an inevitable trend and consensus in the optical network field. Theconstruction of all-optical network is required various signal processings, such aswavelength conversion, format conversion, logic switches, routing selection and3Rregeneration and so on, all of which can be achieved by using all-optical methods.All-optical signal processing can be obtained using optical nonlinear effects in thenonlinear materials. The all-optical signal processing based on optical nonlinear effects hasdistinct advantages of ultra-fast response, high-capacity communication. Meanwhile, withthe development of semiconductor technology, optoelectronic devices are developingtowards miniaturization and integration. AlGaAs, with characteristic of great second-orderand third-order nonlinearity effects, mature production technology and easy to be integratedwith other semiconductor devices, makes itself as an ideal material for all-optical signalprocessing devices. In nonlinearity application, there is a positive correspondence betweennonlinearity conversion efficiency and the light intensity in optical devices. Microringresonator can increase the time of interaction between the light and matter with the increaseof the light intensity, which has greatly improved the nonlinearity conversion efficiency.All-optical signal processing, such as all-optical wavelength conversion, all-opticallogic gates, all-optical computing, all-optical UWB signal generation and so on, can beobtained with the help of microring resonator and the second-order or third-ordernonlinearity effects based on AlGaAs, the detailed contents can be found as follows:(1) The material properties and nonlinear characteristics of AlGaAs are discussed indetails; nonlinearity effect expression equation has been derived based on Maxwellequation. For second-order nonlinearity effect, various current methods of phase matchingin isotropy media are presented. Considering the design of most devices in this thesis is based on microring resonator, details about microring resonator are theorecticallyinvestigated. Microring resonator transfer functions and other related functions at stablestate are derived. Evaluation parameters for microring resonator performance are alsointroduced and explained. Here focus on phase transfer functions of microring resonator,analyze phase shift characteristics with different coupling coefficient and the amplitude ofvibration, finally, and discuss the manufacture technology of AlGaAs devices.(2) AQPM matching conditions are theorectically derived based on the process ofnonlinear polarization generation. To avoid too small bending radius in AQPM withAlGaAs bend waveguide, we propose to use in combining the form birefringence andAQPM in microring resonator to realize effective Second-Harmonic Generation (SHG),analyze the impacts of coupling coefficient, waveguide losses, input power, microring Qfactor on the conversion efficiency, present the theoretical conversion efficiency in differentconditions, as well as provide the possibilities for making birefringence microring resonator.On that basis, we further analyze to utilize AQPM and form birefringence to realize theeffective wavelength conversion in bent waveguide.(3) We propose to use a method of combining of cross phase modulation (XPM) inAlGaAs with microring resonator to obtain large phase modulation in the conditions oflower power input. And this dissertation puts forward to realize all-optical XOR、XNOR、NOT logical operation based on microring resonators cascade，and then a deformable MZIis used in combination with microring resonators to obtain all of the seven logicaloperations: AND、NAND、OR、NOR、NOT、XOR and XNOR. On this basis, a devicedesigned to combine AlGaAs microring resonators with waveguide to obtain four basiclogical computation (half adder, half subtracter，full adder，full subtracter) is presented inthis dissertation. The switching between the above mentioned logical computation isdepends on the use of different signal input ports and input intensity.(4) DPSK has been widely used in optical communications, but to correctly transmitsignals, it needs to pre-code the transmitting information. It is known that traditional DPSKpre-coding is completed in the electrical domain. In this dissertation, we propose to useall-optical XOR logical operation to achieve DPSK pre-coding in the optical domain basedon the fact that the realization of DPSK pre-coding depends on XOR logical operation. (5) Based on the discussion of using XPM in AlGaAs microring resonator to obtainphase modulation in a wide range for the probe light, we propose to combine microringresonator with MZI to obtain UWB generation, utilize two ring cascade to achieveMonocycle and Doublet UWB signal generation, and use single microring, in combinationwith MZI to obtain Doublet UWB pulse signal generating. The impacts of device timedelay, input power, the pump pulse width on the UWB spectrum distribution are analyzedin details.(6) A scheme of using phase shift characteristic in microring resonator is presented inthis thesis, and the phase shift here, essentially, is caused by the effective refractive indexchanges in microring resonator. The effective refractive index changes can be achievedthrough the electro-optics effect, two-photon absorption, self phase modulation and crossphase modulation. We describe this in brief and analyze using SHG and single photonabsorptiometry (SPA) to generate free charge carriers, so as to achieve the possibility on thecontrol of effective refractive index changes in microring resonator.