Frequency Measurement Technique Based On Microwave Photonics

Instantaneous frequency measurement technology is a very critical technology in the modern electronic warfare.Through the rapid frequency measurement,the enemy’s electromagnetic information can be captured accurately,and then we can achieve the investigation,defense,attack and other purposes.As the signal rate increases,the traditional electronic frequency measurement technology is gradually unable to adapt to the complicated measurement.Microwave photonics combines the advantages of microwave and photon,with anti-electromagnetic interference,large bandwidth,small loss,relatively simple system structure and so on.It has great potential for development.The frequency measurement technique based on microwave photonics can overcome many bottlenecks in the traditional frequency measurement technology,with low loss,wide bandwidth,anti-electromagnetic interference,small size,etc.It has become one of the popular direction of current research.This paper mainly discusses frequency-microwave power mapping technology and multi-frequency measurement technology.Two schemes are proposed for frequencymicrowave power mapping.For scheme one,the optical signal is modulated by the microwave signal through the polarization modulator(Pol M),and then we use the polarization controller to introduce a fixed phase shift.After introducing the dispersion to the downstream optical signal by optical fiber,we can obtain an ACF function.Through matlab,the relationship among the ACF curve,optical fiber length and optical carrier wavelength is verified.Through VPI simulation,when using low loss fiber and the measurement range from 29 GHz to 36 GHz,the frequency measurement error is ±0.4 GHz.When using loss compensation and the measurement range from 22 GHz to 36 GHz,the frequency measurement error is ±0.25 GHz.For scheme two,two optical signals,which are orthogonal to each other,propagate in different directions in the Sagnac ring.Affected by rate matching for microwave and photon,one optical signal completes phase modulation,another optical signal is not modulated.After introducing the dispersion to the both optical signals by the same optical fiber,we can obtain an ACF function Through matlab,it is verified that the ACF curve is not only related to the fiber length and optical carrier wavelength,but also to the angle of the polarization controller,which can improve the flexibility and reconfigurability for system.Through VPI simulation,the frequency measurement range from 21 GHz to 39 GHz with the error of ±0.2GHz is achieved.For multi-frequency measurement technology,we use optical frequency comb as a multi-carrier light source in a multi-frequency measurement scheme.This can reduce the system requirement for the number of lasers,and improve the stability of the light source.Firstly,an generation scheme of optical frequency comb based on the dual-polarization Mach-Zehnder modulator is proposed.By setting the RF voltage and the DC bias reasonably,we can get a 9-line flat optical frequency comb.VPI simulation verifies the feasibility of the scheme.Then the optical frequency comb is modulated by the signal that need to be measured through the Mach-Zehnder modulator(MZM).Through the Fabry-Perot(F-P)etalon and the wavelength division multiplexer(WDM),we can complete multi-frequency measurement by measuring the power of each output port of the WDM.The consistency of theoretical analysis and simulation is proved by VPI.Finally,the major factors influencing the measurement accuracy and range are analyzed,which verifies that the whole system has good flexibility and some practical value.