Abstract
We report on a novel cancellation technique, for reducing the nonlinearity associated with the tracking phase-modulator in recently proposed phase-locked coherent demodulator for phase modulated analog optical links. The proposed cancellation technique is input RF signal power and frequency independent leading to a significant increase in dynamic range of the coherent demodulator. Furthermore, this technique demonstrates that large values of the signal-to-intermodulation ratio of the demodulated signal can be obtained even though the tracking phase modulator is fairly nonlinear, and thereby relaxing the linearity requirements for the tracking phase modulator. A new model is developed and the calculated results are in good agreement with measurements.
Highlights
The use of optical links for the transmission of RF signals is a subject of considerable interest for future commercial and military systems [1, 2]
In the proposed receiver, both the signal and the noise swings are reduced by the same factor, retaining the signal-to-noise ratio (SNR) while improving the Spurious Free Dynamic Range (SFDR) as shown in [4, 6]
We propose a method to cancel out nonlinearities associated with the tracking phase modulator and inherently nonlinear response of the balanced detector
Summary
The use of optical links for the transmission of RF signals is a subject of considerable interest for future commercial and military systems [1, 2]. Theoretically investigated and experimentally demonstrated a novel coherent optical phase-locked demodulator with feedback [4, 5, 6, 7] resulting in 15 dB of SFDR improvement compared to the traditional approach. To achieve a high bandwidth phase-locked receiver, compact semiconductor phase modulators have to be used to keep loop delay sufficiently low These modulators can have fairly nonlinear response significantly limiting the dynamic range of the receiver [9]. We propose a method to cancel out nonlinearities associated with the tracking phase modulator and inherently nonlinear response of the balanced detector
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