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Free keywords:
Physics, Optics, physics.optics
Abstract:
Reflection gratings enable light coupling to optical cavities without
transmission through substrates. Gratings that have three ports and are mounted
in second-order Littrow configuration even allow the coupling to high-finesse
cavities using low diffraction efficiencies. In contrast to conventional
transmissive cavity couplers, however, the phase of the diffracted light
depends on the lateral position of the grating, which introduces an additional
noise coupling. Here we experimentally demonstrate that this kind of noise
cancels out once both diffracted output ports of the grating are combined. We
achieve the same signal-to-shot-noise ratio as for a conventional coupler. From
this perspective, 3-port grating couplers in second-order Littrow configuration
remain a valuable approach to reducing optical absorption of cavity coupler
substrates in future gravitational wave detectors.
