Approaching the optimum phase measurement in the presence of amplifier noise

TL;DR

This paper introduces a phase measurement method combining heterodyne detection and Kalman filtering that approaches the quantum-limited spectral broadening in the presence of amplifier noise, significantly outperforming conventional techniques.

Contribution

The authors demonstrate a novel phase measurement approach that reduces amplifier noise impact, nearing the quantum limit, with practical experimental validation.

Findings

Achieves 5 dB numerical penalty and 15 dB experimental penalty relative to quantum limit.

Outperforms conventional phase measurement methods with penalties exceeding 30 dB.

Potential to enhance optical sensing distances by minimizing phase noise impact.

Abstract

In fundamental papers from 1962 [1, 2], Heffener and Haus showed that it is not possible to construct a linear noiseless amplifier. The implies that the amplifier intrinsic noise sources induce random perturbations on the phase of the incoming optical signal which translates into spectral broadening. To achieve the minimum (quantum noise limited) induced phase fluctuation, and the corresponding minimum spectral broadening, an optimum phase measurement method is needed. We demonstrate that a measurement method based on the heterodyne detection and the extended Kalman filtering approaches an optimum phase measurement in the presence of amplifier noise. A penalty of 5 dB (numerical) and 15 dB (experimental) compared to the quantum limited spectral broadening is achieved. For comparison, the conventional phase measurement method's penalty exceeds 30 dB for the measurements. Our results reveal new scientific insights by demonstrating that the impact of amplifier noise can be significantly reduced by using the proposed phase measurement method. An impact is envisioned for the phase-based optical sensing system, as optical amplification could increase sensing distance with the minimum impact on the phase.