Research On Photonics-assisted Frequency Measurement Technology

In the complex and changeable electromagnetic environment,frequency measurement is a prerequisite for signal identification.Faced with the increasing use of frequency spectrum resources,it is difficult for conventional electronical method to cope with frequency measurement over a large bandwidth due to its limited working bandwidth of electronic devices.Microwave photonics technology,which uses the advantages of large bandwidth of spectrum resources and integrates with microwave technology,has become a hot solution in the field of instantaneous frequency measurement with its advantages of large bandwidth,low loss and anti electromagnetic interference.The common method in the single-frequency measurement scheme is to map the measured frequency with parameters such as power,time,and space.Among them,the frequency-power mapping scheme is the most widely studied.In the multi-frequency measurement scheme,the commonly used methods are down conversion,optical sampling,frequency scanning and so on.The main work of this paper is as follows.1.The key components and basic theories commonly used in microwave photonic frequency measurement systems are introduced,and the related modulation formats,photoelectric detection principles,etc.are derived and analyzed.The periodic power fading effect caused by fiber dispersion and its application in frequency measurement are deduced,and the expression of polarized light and the devices related to polarization are briefly explained.2.A frequency-microwave power mapping scheme based on dual-polarization Mach-Zehnder modulator(DPol-MZM)is studied.This solution introduces power attenuation through the fiber dispersion,and uses the polarization beam splitter(PBS)to construct an amplitude comparison function(ACF).The frequency measurement range can be adjusted by adjusting the phase shift between polarization states and the fiber length.The simulation verifies that the system has a frequency measurement capability with an error of less than 0.2GHz in the bandwidth of 5.7 ~ 14.2GHz.3.A frequency-optical power mapping frequency measurement scheme based on wavelength division multiplexer(WDM)is studied.In this scheme,two lasers with different wavelengths are used,and the ACF function is established through two different WDM channels by using the filtering characteristics of wide bandwidth and flat power attenuation of WDM.The simulation verifies that the frequency measurement scheme can achieve frequency measurement with an error less than 0.2 GHz over the bandwidth of 0 to 26 GHz.4.A frequency measurement scheme using the time-domain characteristics of the signal based on 90 ° Hybrid Coupler(90 ° HC)is studied.The time delay is introduced through the variable optical delay line(VODL).The signals with different frequencies will produce different phase shifts.Finally,90 ° HC is used to extract the phase information and convert it to DC power.The frequency measurement range of this scheme can be flexibly adjusted by VODL.The simulation results show that the frequency measurement range of the scheme is 2 ~ 23 GHz,and the frequency measurement error is kept within 0.3GHz.5.A multi-frequency measurement scheme based on a three-optical comb down-conversion is studied.Due to the slight difference of the spacing between the three optical combs,the down converted signal will show a certain rule.The original signal frequency is estimated by ADC and frequency calculation algorithm.Simulation results show that the scheme has the ability of multi-frequency measurement.The frequency range is 0 ~ 40 GHz,and the frequency measurement accuracy can reach the MHz level.