Readout Method Of Transient Pulse Signal Based On Optical Phase Modulation

In nuclear data measurement experiments,the front-end electronics usually use high-bandwidth amplifiers to match and amplify the weak transient pulse signals,and send them to the back-end electronics through analog cables.However,due to the limitation of bandwidth,attenuation,interference and other factors,it is becoming more and more difficult to transmit transient pulse signals through cables.One way is to place the back-end readout electronics near the detectors.However,the forward-moving digital circuits not only bring high-frequency interference to front-end analog circuits,but also increase the difficulties of design,installation,power supply,and heat dissipation.Especially,when detectors are in an extremely harsh environment such as strong electric field,strong magnetic field and strong radiation,traditional readout methods will face enormous challenges.Optical fibers is widely used in data transmission because of its high bandwidth,low cost,and ease of use.At this time,the optical fiber exists as a medium for digital signal transmission.In addition,optical fibers are also used to fabricate various sensors to transmit analog signals imposed on light waves.It is widely used for the detection of acoustic signals,optical signals,electrical signals and magnetic signals.Among them,the analog signal transmission system based on optical phase modulation technology has the advantages of high bandwidth,high sensitivity,high dynamic range,no electromagnetic radiation,strong anti-interference ability,and so on.Therefore,this thesis proposes an analog signal readout method based on the optical phase modulation.The proposed system use the electro-optic phase modulator to impose the transient pulse signal on the phase of the light wave.The modulated light wave is transmitted to the back-end readout system through the long optical fiber,and then interferes with the reference light.The interference signal is converted into electrical signal by the photodetector,and then sampled by the waveform digitization module.The real-time demodulation algorithm is implemented in the FPGA to restore the waveform of the original signal.The research work of this thesis is mainly divided into two parts,including optical phase modulation method and demodulation algorithm.In this thesis,the lithium niobate phase modulator is used to impose the original signal and carrier signal into light wave.A multiplexing array is also constructed based on time division multiplexing and space division multiplexing.The prototype circuits are implemented,including modulator driver module,signal conditioning module and digital demodulation module.And the readout electronics system based on the PXIe platform is set up to verify the performance of the proposed method.The amplitude and phase distortion of the cable has become one of the bottlenecks restricting the transmission of transient pulse signals.This thesis will use optical fiber to transmit analog signals,which can avoid the problems of high loss and high distortion caused by analog cables.It has the advantages of high sensitivity,large dynamic range,good linearity,strong anti-interference ability,and so on.It can be applied to the readout of transient pulse signals and provides a new method for the readout of detector signals.