Instantaneous Microwave Frequency Measurement Using Programmable Differential Group Delay (DGD) Modules

We propose and experimentally demonstrate a photonic approach for the measurement of microwave frequencies with adjustable measurement range and resolution. After an unknown microwave signal is modulated onto an optical carrier by a Mach-Zehnder modulator (MZM), the optical output of the MZM is sent to two programmable differential group delay (DGD) modules to introduce different microwave power fading effects, respectively. When the microwave powers of the two channels are measured with two photodetectors separately, a fixed relationship between the microwave power ratio and the microwave frequency is established. The frequency measurement range and resolution can be tuned by electrically varying the DGD values. Frequency measurement with good accuracy for the microwave signals is experimentally realized. When the input power of a continuous-wave microwave signal is within the range of 15 to 3 dBm, the measured errors remain within 0.04 GHz for a measurement range of 4.5-6.5 GHz.