Switchable Instantaneous Frequency Measurement by Optical Power Monitoring Based on DP-QPSK Modulator

We propose and analyze an instantaneous frequency measurement system using optical power monitoring technique with improved resolution. The primary component employed in the proposal is a DP-QPSK modulator which is used to modulate the microwave signal with a designed time delay and phase shifting. Then the generated optical signal is sent to polarization beam splitter (PBS) via polarization controller (PC). Thanks to the complementary transmission nature of polarization interference introduced by PBS, the frequency information is converted to the optical power and the relationship between the amplitude comparison function (ACF) and microwave frequency to be measured is established. Thus, the frequency of the microwave signal could be easily measured through monitoring the optical powers of the two output ports of the PBS. Furthermore, by adjusting the DC biases of the DP-QPSK modulator instead of changing the electrical delay, the measurement range and resolution can be switched. In this paper, the basic principle of the instantaneous frequency measurement system is derived in detail, and simulation has been performed to investigate the resolution, the measurement range and the impact of imperfection devices. The proposed scheme is wavelength independent and measurement range switchable, which can avoid the laser wavelength drifting problem and greatly increase the system flexibility.

MODEL OF INSTANTANEOUS FREQUENCY MEASUREMENT RECEIVER WITH PRELIMINARY FREQUENCY MULTIPLICATION AND AUXILIARY CHANNEL BASED ON NONLINEAR SCATTERING PARAMETERS

The article deals with instantaneous frequency measurement (IFM) receiver model. Proposed receiver exploits preliminary frequency multiplication of input signal and auxiliary microwave detector channel. Article goal is investigation of microwave transfer coefficient irregularity compensation method. Another goal is investigation and reduction of measurement error sources. Research goals are reached by mathematical model construction and it further investigation. Mathematical model is based on the nonlinear large signal scattering parameters. Model demonstrates that preliminary frequency multiplication allows reduction of required group delay time of delay line. It is showed that measurement result affected by transfer coefficient irregularity, transfer coefficient instability of receiver chain elements and multiply reflected from irregularities waves. Auxiliary measurement channel and measurement function in the form of voltage ratio at basic channel detector and auxiliary channel detector provide a way to reduce influence of input signal amplitude, instabilities and irregularities of transfer coefficient on the frequency measurement result. It is showed that full reduction of aforementioned factors prevented by parasitic harmonics and multiply reflected waves. Required suppression level of parasitic harmonic are presented. Obtained results can find applications in sphere of electronic warfare and measurement theory and techniques.