  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. Cryogenic
cooling of this mirror is also challenging, and thus thermal noise becomes a
general problem. Here, we theoretically investigate an all-reflective coupling
scheme of two optical cavities based on a 3-port diffraction grating. We show
that power-recycling of a high-finesse arm cavity is possible without
transmitting any laser power through a substrate material. The power splitting
ratio of the three output ports of the grating is, surprisingly, noncritical.

Optics