Research On Microwave Signal Processing Based On Optical Delay

Microwave technology has become the key in modern communication systems,radar systems,and satellite positioning systems.Microwave signal processing with advantages of broadband,high speed,and high precision has become the focus of studying.However,the electronic microwave signal processing is challenging in terms of processing speed,transmission loss,bandwidth,and electromagnetic interference.Thanks to the advantages of high efficiency,broadband,low loss,and strong anti-interference ability,microwave photonic technology will be an all-round improvement of the microwave signal processing.In this thesis,the microwave photonic signal processing technology was studied,especially the all-optical Digital-to-Analogue Conversion(DAC)and the optoelectronic hybrid analog-to-digital conversion(ADC).The main research contents are as follows:Firstly,the existing technologies of all-optical DAC and optoelectronic hybrid DAC were studied in detail,and their advantages and disadvantages were analyzed.The principle and critical technology of microwave photonic signal processing were described,as well as the principle and characteristics of the core optoelectronic devices,especially the principle,measurement,and control method of optical delay.The basic principles of DAC and ADC were analyzed,and the indexes were also discussed.Secondly,an all-optical serial DAC based on optical delay was proposed to solve the problem on the conversion speed limitation of the traditional DAC.Optical carriers with different quantized weights from several wavelength-independent semiconductor lasers are multiplexed,and the multiplexed optical carriers are modulated by a serial digital signal to be converted.Optical fiber dispersion is used to realize the isometric delay between multiple wavelength components so that the optical signals with different bit weights are incoherent superposition in the same time window.The superimposed optical signal in the time window is cut out by using an optical decision gate with synchronous clock at last,and the signal power represents the analog amplitude.The experimental system of a 4-bit all-optical serial DAC based on optical delay was built,and the conversion rate was 3.125GS/s.The measured integral nonlinearity and the difference nonlinearity were measured to be 0.108 and 0.479,respectively,by traversing the 16 patterns of 4-bit digital signal.Meanwhile,the DAC was used to generate a sine wave,a triangle wave,and sawtooth wave,the generated sine wave has a frequency of 195.3 MHz,and the effective bit is 3.46 bit.The theoretical analysis and the experimental demonstration show that the proposed DAC is feasible,and excellent technical indexes have been implemented.Besides,the performance of the proposed DAC will be affected by the delay precision,the speed of optical decision gate,and the extinction ratio.Thirdly,an optoelectronic hybrid DAC based on optical delay and interpolation was proposed to solve the problem on the quantization precision,which depends on the power precision of the light source,in the last proposed method.The results of multi-channel electrical DACs modulate the optical carriers with different wavelengths,and the modulated optical carriers are multiplexed.The light intensity information of different wavelength components in each byte time window is then intercepted by the clock-synchronous optical decision gate.At last,the optical fiber dispersion is used to introduce an isometric optical delay between different wavelength components,so that the components of each wavelength with corresponding analog quantity are uniformly expanded in the time domain.The interpolation based on optical delay is completed,and the analog signal is finally output.The experimental system with an 8-wavelength channel and a conversion precision of 16 bits was built.A conversion rate of 8.33 GSa/s was realized.A sine wave,a triangular wave,a square wave,and a sawtooth wave were generated,the sine wave has a frequency of 260.4 MHz,and the effective bit was 5.05.The theoretical analysis and the experimental demonstration show that the proposed DAC is feasible,and excellent technical indexes have been implemented.The parallel conversion of multi-channel electronic DAC was realized by using optical delay and interpolation,and thus the conversion rate was much improved.The mismatch of multi-channel amplitude and delay is the primary source of error.Lastly,an optoelectronic hybrid ADC was proposed based on optical delay.A sampled light pulse is generated by a broad-spectrum light source modulated by a narrow electrical pulse.The sampled light pulse is divided into multiple channels,and an isometric optical delay is introduced to form a multi-channel parallel sampling pulse train to improve the sampling rate.The analog signal is sampled by multi-channel intensity modulation.The sampled light pulse is then broadened by using the dispersion effect in an optical fiber,and an electrical DAC array implements the electrical quantization.The influences of the consistency of power and delay of multi-channel and the nonlinearity of the modulation on the conversion precision were derived theoretically.A multi-channel consistency precorrection method and a nonlinear post-processing scheme for the modulation were proposed to improve the performance of the ADC.The consistency error of multi-channel delay was controlled within 1ps based on the high-precision optical delay measurement and the fabrication technology.The effective number of bits can be increased by using the nonlinearity correction method.The experimental system of a 4-channel optoelectronic hybrid ADC based on optical delay was built.A sampling rate of 12GS/s was realized,and the effective bit was measured to be 5.84 when a 1.992-GHz sine wave was tested.The theoretical analysis and the experimental demonstration show that the proposed ADC is feasible,the high speed and wideband were realized,and the experimental system has practical worth.In summary,the all-optical DAC and the optoelectronic hybrid ADC of microwave signals are proposed and experimentally demonstrated based on microwave photonics,especially the optical delay.The proposed DAC and ADC have high practicability.