Measurement Of Photodetectors' Frequency Response Based On Mode-locked Light Source

As the rate of information transmission raising,the bandwidth of optoelectronic devices is also increased.The photodetector is the core device in optoelectronic links to convert optical signal into electrical signal.Therefore,accurate measurement of photodetector's frequency response contributes to the optimization of optoelectronic links.In this thesis,measurement methods for measuring frequency response of photodetectors are studied in depth.This thesis firstly analyzes two kinds of sweep frequency methods for measuring frequency response of photodetectors.Based on these two sweep frequency methods,this thesis proposes a new measurement method which achieves ultra-wideband measurement range and self-calibration by segmenting the photodetector in frequency domain.Firstly,two kinds of sweep frequency measurement methods are introduced and verified,which are based on vector network analysis and based on two-tone modulation heterodyne respectively.The method based on vector network analysis gets measurement results from scatter parameters directly.But this method needs an extra calibration process to the frequency response of electro-optical conversion devices and the measurement range is limited by the bandwidth of VNA.The method based on two-tone modulation heterodyne gets the photodetector's frequency response from the relative intensity of photocurrent's amplitudes.Thus,this method does not require an additional calibration process.However,the measurement range of this method is still limited by the bandwidth of microwave devices.Because the measurement range of sweep frequency methods is limited,a method for measuring the frequency response of photodetectors based on mode-locked laser is proposed to achieve ultra-wide measurement range.This method is verified in simulation and experiment.Because the optical frequency comb from the mode-locked laser is used as optical stimulus,the photodetector can be divided into several segments in frequency domain for measuring.The measurement can be completed by microwave sources only sweeping in the segment's frequency range,so that the measurement range is not limited by the bandwidth of microwave devices.Besides,this method inherits the advantage of the two-tone modulation heterodyne method,in which the frequency response gets from the relative intensity of photocurrent's amplitudes to avoid extra calibration process.At the end of this thesis,a measurement method based on three-tone modulation heterodyne is proposed and verified in simulation and experiment.In this method,the photodetector is segmented in frequency domain and segments' frequency range is determined by the frequency of microwave source,so that this method can achieve ultrawide measurement range.Because the frequency range of each segment is adjustable,segments can be accurately spliced by taking the microwave sources' frequency configuration method.Besides,this method also gets photodetector's frequency response from photocurrent relatively amplitudes,from which it can achieve self-calibration.