Research On All-optical Quantization Based On Optical Nonlinear Effects

Analog-to-digital converter(ADC)plays an important role in signal processing and communication systems.Therefore,ADC with large analog bandwidths,high sampling rates and high quantization resolutions has also become widely researched.Due to the difficulty in balancing the sampling rate and quantization resolution,the traditional electronic ADC is difficult to achieve the high performance.Optical sampling technology can provide femtosecond time jitter and achieve a rate of more than 100 GSas-1.In order to achieve a high-performance ADC,how to obtain a high quantization resolutions scheme is particularly important.The all-optical quantization scheme using high-order nonlinear effects not only avoids the bottleneck problem of electronic devices,but also can obtain large analog bandwidth and high quantization resolution,so it has important research significance.This dissertation mainly explores two methods to achieve all-optical quantization based on nonlinear effects.The main research contents and innovation points are listed below:1.The generation of near-mid infrared and high-coherence supercontinuum in Micro-nano waveguide is studied.Based on the As2S3 material with high refractive index and high nonlinear coefficient,a ridge waveguide with a suspended structure is designed to generate the supercontinuum.Air and Si3N4 are used as the upper and lower cladding layers,AS2S3 as the ridge core,and the width and height of the ridge core are optimized.The spectral width at-40 dB can be broadened from 1.0?m to 5.6 ?m,which spans 2 octaves.The supercontinuum broadenings are simulated numerically when the pump wavelength,peak power and waveguide length change.Then,the influence of noises on the coherence of the spectrum is analyzed.These studies will be widely used in the fields of biomedical detection and high-precision measurement.2.The self-phase modulation(SPM)effect in Highly Nonlinear Fiber(HNLF)is studied.An all-optical quantization scheme by slicing supercontinuum,which is generated in a 310 m normal dispersion HNLF is proposed.The spectrum broadening of femtosecond pulse with nonlinear effect is analyzed by numerical simulation.The HNLF with normal dispersion can produce flat and coherent supercontinuum.The wavelength division multiplexing device is used to slice the supercontinuum.The feasibility of the scheme is proved by simulation.The all-optical quantization experiment platform is built,and 3 bit and 5 bit all-optical quantizer are implemented.The maximum value of the differential nonlinear error and integral nonlinear error are 0.471 LSB and 0.519 LSB,which is further proved the effectiveness of the scheme.3.The all-optical quantization approaches using the non-linear effects in a silicon waveguide is studied.A quantization scheme by slicing supercontinuum in a Si3N4 ridge waveguide is proposed.An all normal dispersion in the communication band is achieved by optimizing the structure parameters.The numerical simulation show that an integration all-optical quantizer with 5.996 bit is implemented in a 1 cm Si3N4 ridge waveguide with the range of peak power from 130 to 440 W.This scheme can realize optical quantization with lower power and achieve on-chip optical interconnection with other silicon-based devices,which provide a research foundation for the realization of low power and integratable all-optical ADCs.4.The soliton self-frequency shift(SSFS)effect in HNLF is studied.An all-optical quantization scheme is proposed by the SSFS effect that is generated in 310 m anomalous dispersion HNLF,is proposed.The Raman frequency shift is generated with the non-linear effects by numerical simulation.An all-optical quantization experiment platform is set up to achieve quantization resolution of 2.74 bit.In order to obtain higher quantization resolution,a cascaded single-mode fiber(SMF)and HNLF method for spectrum compression are proposed.Simulation results show that the spectrum width is compressed from 15 nm to 1.95 nm and the quantization resolution is improved from 2.13 bit to 5.36 bit.5.An all-optical quantization scheme using the SSFS effect in photonic crystal fiber(PCF)is proposed.A 5 m-long CS2 liquid core PCF is designed,which ensure the SSFS and spectrum compression are realized simultaneously in this fiber.When the input peak power is 15.3 W,the 36.07 nm spectrum width is compressed to 7.33 nm.The spectral compression factor is 4.92 and the wavelength shift is as high as 190 nm.Then the PCF is used to an all-optical quantization system,which achieve a 4-bit quantization resolution.Compared with fibers cascaded,this scheme has the integration and reliability,and reduces the complexity of the quantization system,which has advantages for low-power and integrated optical signal processing systems.In this dissertation,the related theories of all-optical frequency quantization methods are studied,and the feasibilities of the quantization scheme are verified by building experimental platforms based on different HNLFs.In order to achieve low power and integrated all-optical quantization,high nonlinear coefficients media such as waveguides and PCF are designed to replace traditional optical fibers.The works in this thesis lay the research foundation for subsequent all-optical quantification,which is expected to be widely used in the fields of optical communication and high-speed information processing in the future.