The standard quantum limit of coherent beam combining

Abstract

Coherent beam combining refers to the process of generating a bright output beam by merging independent input beams of individually diffusing relative phases by locking them to each other. We report the first quantum mechanical noise limit calculations for coherent beam combining and compare our results to quantum-limited amplification. Our coherent beam combining scheme is based on an optical Fourier transformation which renders the scheme compatible with integrated optics combined with feed-back stabilization of the relative phases. The scheme can be layed out for an arbitrary number of input beams and approaches the shot noise limit for a large number of inputs.

Phase-locking an interferometer with single-photon detections

“…To resolve this, the MZIs may be locked directly with the weak signal that is detected on single-photon detectors at count rates of kHz to MHz [13,14]. Due to the gain-bandwidth product limit (connected to the fundamental Heisenberg number-phase uncertainty) [15,16], low count rates allow only for slow feedback. At count rates of few kHz in [13,14], the resulting feedback bandwidth is in the Hz range.…”

Quantum-limited measurements of intensity noise levels in Yb-doped fiber amplifiers

“…In this case multiple beams are amplified separately and then recombined to generate a high power output [15]. Recently, the noise performance of these systems has been theoretically investigated down to the quantum mechanical noise limit for the first time, showing that it can outperform the output noise variances of a linear amplifier under certain conditions [16]. A different attempt for optimizing the noise properties of amplifier systems is to reduce the noise level of its input state -the seed laser -as far as possible.…”