Swept-source heterodyne detection for interferometry in the H band

Abstract

It is well established that direct-detection interferometry outperforms heterodyne interferometry in terms of signal-to-noise ratio at optical wavelengths, not only because of the limited electronic bandwidth of photodetectors (typically <100 GHz), but also due to the shot-noise contribution of the optical local oscillator. The large-scale production of high-quality and cost-effective telecom components in the J+H band, and more recently in the K band, may open new schemes for the heterodyne signal detection and processing (e.g. correlation) as well as for the transport, distribution and control of the local oscillator. We describe how high-repetition-rate frequency-swept sources and telecom components could be exploited to parallelize, at reasonable cost, a large number of coherent detectors to expand the spectral coverage. We also present a first laboratory single-channel proof of concept that achieves a signal-to-noise ratio (SNR) probably sufficient for observing the brightest stars in the H band with telescopes of ~1 m2 at short integration time (<100 ms).