Research On High-precision Microwave Frequency Measurement Based On Photonic Methods

Microwave frequency measurement technology has important applications in military electronic warfare,radar,civilian wireless communications,traffic vehicle control and many other fields.The traditional electronics microwave frequency measurement method has not been able to meet the demand for greater bandwidth and higher speed of frequency measurement technology due to the “electronic bottleneck” limitations.Microwave photonics technology combines the advantages of microwave technology and photonic technology,with large bandwidth,high speed,low loss,small size,light weight,antielectromagnetic interference and many other advantages.At present,a lot of photonics microwave frequency measurement solutions have been reported,not only in the direction of wide measurement range and high measurement accuracy,but also gradually showing the trend of integration and miniaturization.This thesis focuses on the high-precision microwave frequency measurement technology based on photonic methods,and the main research contents and results can be summarized as follows.(1)A high-accuracy multiple microwave frequencies measurement is achieved by double-pumped stimulated Brillouin scattering(SBS).Using the frequency-amplitude mapping between the sweeping reference frequency and the output optical power monitored by a low-speed optical power meter,in combination with the different amplification to the optical signal of different wavelengths by double-pumped SBS,the precise measurement of multiple microwave frequencies is accomplished by the number of optical power peaks appeared in the mapping and their respective positions.The narrow gain bandwidth of the double-pumped SBS effectively reduces the measurement error of the proposed system.The system is experimentally verified to have a measurement error as low as 5 MHz and a wide measurement range from 0 to 21.42 GHz.Then,a nonlinear fitting data processing method is introduced to reduce the minimum distinguishable frequency difference from 30 MHz to18 MHz for multiple frequencies measurement,thus the resolution of the system is substantially improved.The proposed system achieves simultaneous detection of multiple frequencies with low error and wide range,and it only requires a low-speed optical power meter to monitor the optical signal power,making the whole system low-cost and highly practical.(2)A high-precision microwave frequency measurement scheme based on apodized fiber Bragg grating(AFBG)combined with SBS is proposed.Utilizing the complementary filtering characteristics of the transmission and reflection ports of the AFBG and by selecting a suitable optical carrier wavelength,the upper and lower sidebands of the optical carrier modulated by the mixed signals from the microwave frequency to be measured and the sweeping reference frequency can be separated and propagated in the upper and lower optical paths to participate in the SBS process as pump light and probe light,respectively.Similarly,a low-speed optical power meter is used to establish the frequency-amplitude mapping between the sweeping reference frequency and the output optical power to determine the value of the microwave frequency to be measured.The participation of the AFBG greatly simplifies the configuration of the scheme and reduces the number of active devices required in the form of electro-optic modulator,improving the stability and practicality of the scheme.The experimentally built scheme achieves an error of less than 1MHz and a wide measurement range of 10.68-20 GHz.This scheme can also achieve dualfrequency simultaneous measurement with high resolution,and the experiment has verified that the measurement error of dual-frequency measurement is also less than 1 MHz,with the minimum distinguishable frequency difference as low as 8 MHz.(3)A silicon-based integrated notch filter with a narrow filtering bandwidth is designed and fabricated,and a range-tunable microwave frequency measurement system is proposed and built using the integrated device.By embedding a vertically coupled double micro-ring resonator into a Fabry-Perot cavity consisting of two circular Bragg grating mirrors,the coherent interference within the cavity can reconstruct the output spectral shape,thus a integrated notch filter with a simulated filtering bandwidth as low as 6.972 pm is obtained.Using the notch filtering characteristic of the integrated device,the range-tunable measurement of the microwave frequency is completed by coupling the optical signal,which is modulated by the microwave frequency to be measured and the sweeping reference frequency,into the integrated device and establishing the frequency-amplitude mapping between the sweeping reference frequency and the output optical power from the integrated device.The measurement range is determined by the frequency difference between the optical carrier and the lowest point of the notch filtering of the integrated device.Therefore,the tuning of the measurement range can be simply achieved by changing the wavelength of the optical carrier.The silicon-based integrated notch filter is fabricated on silicon-oninsulator platform and is tested with a filtering bandwidtn of 0.0368 nm.The frequency measurement system based on the integrated device has a measurement error of less than0.25 GHz within ranges of 0-22.37 GHz and 0-26.62 GHz.This system combines a silicon integrated device of narrow filtering bandwidth with optical fiber devices,achieving microwave frequency measurement of low error and adjustable range.