Diffractively coupled Fabry-Perot resonator with power-recycling.

We demonstrate the optical coupling of two cavities without light transmission through a substrate. As the all-reflective coupling component, we use a dielectric low-efficiency 3-port diffraction grating. In contrast to a conventional transmissive coupling component, such an all-reflective coupler avoids all thermal effects that are associated with light absorption in the substrate.

Waveguide grating mirror in a fully suspended 10 meter Fabry-Perot cavity.

We report on the first demonstration of a fully suspended 10 m Fabry-Perot cavity incorporating a waveguide grating as the coupling mirror. The cavity was kept on resonance by reading out the length fluctuations via the Pound-Drever-Hall method and employing feedback to the laser frequency. From the achieved finesse of 790 the grating reflectivity was determined to exceed 99.

Pound-Drever-Hall error signals for the length control of three-port grating coupled cavities.

Gratings enable light coupling into an optical cavity without transmission through any substrate. This concept reduces light absorption and substrate heating and was suggested for light coupling into the arm cavities of future gravitational wave detectors. One particularly interesting approach is based on all-reflective gratings with low diffraction efficiencies and three diffraction orders (three ports).

All-reflective coupling of two optical cavities with 3-port diffraction gratings.

The shot-noise limited sensitivity of Michelson-type laser interferometers with Fabry-Perot arm cavities can be increased by the so-called power-recycling technique. In such a scheme the power-recycling cavity is optically coupled with the interferometer's arm cavities. A problem arises because the central coupling mirror transmits a rather high laser power and may show thermal lensing, thermo-refractive noise and photo-thermo-refractive noise.

Realization of a monolithic high-reflectivity cavity mirror from a single silicon crystal.

We report on the first experimental realization of a high-reflectivity cavity mirror that solely consists of a single silicon crystal. Since no material was added to the crystal, the urgent problem of "coating thermal noise" that currently limits classical as well as quantum measurements is avoided. Our mirror is based on a surface nanostructure that creates a resonant surface waveguide.

Encapsulated subwavelength grating as a quasi-monolithic resonant reflector.

For a variety of laser interferometric experiments, the thermal noise of high-reflectivity multilayer dielectric coatings limits the measurement sensitivity. Recently, monolithic high-reflection waveguide mirrors with nanostructured surfaces have been proposed to reduce the thermal noise in interferometric measurements. Drawbacks of this approach are a highly complicated fabrication process and the high susceptibility of the nanostructured surfaces to damage and pollution.

Demonstration of a cavity coupler based on a resonant waveguide grating.

Thermal noise in multilayer optical coatings may not only limit the sensitivity of future gravitational wave detectors in their most sensitive frequency band but is also a major impediment for experiments that aim to reach the standard quantum limit or to cool mechanical systems to their quantum ground state. Here, we present the experimental realization and characterization of a cavity coupler, which is based on a surface relief guided ode resonant grating. Since the required thickness of the dielectric coating is dramatically decreased compared to conventional mirrors, it is expected to provide low mechanical loss and, thus, low thermal noise.