Instantaneous frequency measurement scheme employing dual-parallel phase modulation

Area of Science:

• Photonics and Optical Engineering
• Microwave Engineering
• Signal Processing

Background:

• Accurate and instantaneous frequency measurement is crucial for various applications, including radar, communications, and electronic warfare.
• Traditional frequency measurement techniques often face limitations in terms of speed, range, or accuracy.

Purpose of the Study:

• To propose and validate a novel scheme for instantaneous frequency measurement over a wide frequency range.
• To convert frequency information into a measurable phase shift using phase modulators and electrical time delay.
• To establish an amplitude comparison function for accurate frequency determination.

Main Methods:

• Utilizing two parallel phase modulators (PMs) to modulate an unknown signal with a tunable electrical time delay.
• Employing a 2x2 optical coupler and two photodetectors to detect phase shifts introduced by the time delay.
• Establishing an amplitude comparison function based on the output power ratio of the photodetectors to determine microwave frequency.

Main Results:

• Achieved an instantaneous frequency measurement range from 0.25 GHz to 21 GHz.
• Demonstrated a measurement error of less than 60 MHz.
• Showcased the ability to shift the measurement range by adjusting the electrical time delay.

Conclusions:

• The proposed scheme enables wide-range, instantaneous frequency measurement with high accuracy.
• The adjustable electrical time delay allows for flexible range shifting and optimization.
• A two-step measurement approach combining rough and precise measurements enhances overall performance.