Monolithic dielectric surfaces as new low-loss light-matter interfaces

Abstract

We propose a new mirror architecture, which is solely based upon structuring of the surface of a monolithic, possibly monocrystalline, bulk material. We found that a structure of T-shaped ridges of a subwavelength grating can theoretically provide 100% reflectivity. Since no material needs to be added to the mirror device, lowest mechanical loss can also be expected. [5,6] this interface needs to provide outstanding low optical and mechanical losses. High reflectivity is demanded as lost photons result in decoherence of the light-matter quantum state. High mechanical quality factors of the test mass vibrational modes are required to reduce the influence of thermal noise [7] and to reach the quantum mechanical ground state [8]. In current approaches the surface of the mechanical device is composed of a multilayer dielectric coating. Reflectivities of up to 99.9998% have been demonstrated [9]. To achieve high mechanical quality factors, monocrystalline materials such as quartz or silicon are used. Quality factors above 10 9 were measured [10]. However, recent theoretical and experimental research revealed that multilayer dielectric coatings result in a significant reduction of quality factors [7], and that the simultaneous realization of high optical and mechanical quality is a nontrivial problem.

Demonstration of a cavity coupler based on a resonant waveguide grating

“…However, Bunkowski et al [19] theoretically investigated such a device and found parameters for a high-reflection waveguide mirror with broad spectral response. Recent theoretical research showed that even the remaining high-index layer can be avoided and that a monolithic high-reflection mirror is possible by applying an appropriate grating structure to the substrate's surface without the need for adding any other material [20]. This new approach does not imply suspended microstructures [21], which had been reported before and, therefore, overcomes the limitation to very small grating areas.…”

Development of Mirror Coatings for Gravitational Wave Detectors

“…These include diffractively-coupled mirrors [81,82], the use of corner reflectors [83], or the use of waveguide (macro-structured) surfaces [84,85]. These coating-free solutions still require significant development.…”

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

“…This property is, for instance, widely investigated for use in narrowband filter applications [21]. However, broadband designs under normal incidence as investigated in [10,11,22,23] are favourable for the purpose of highly reflective surface mirrors in high-precision interferometric experiments, since they are less sensitive to parameter deviations. The basic principle of a waveguide grating mirror under normal incidence is shown in Fig.…”