Amplitude-Independent Photonic Instantaneous Frequency Measurement With Improved Sensitivity

A technique for improving the sensitivity of a class of broadband RF photonic instantaneous frequency measurement (IFM) systems is proposed and practically demonstrated. The technique utilizes lock-in amplification to isolate the desired signal from background noise. The demonstration is conducted on a dual orthogonal measurement IFM system utilizing multiple wavelengths and a transversal Hilbert transform achieving independent amplitude and frequency measurements over a multioctave bandwidth with a sensitivity of $-$ 37 dBm. This performance is comparable with traditional electronic IFM receivers. The successful application of this lock-in approach to this multichannel photonic system illustrates its flexibility and indicates that it should be applicable to even more sophisticated systems.