Abstract: The thermo-optic behavior of an optical path over a range of temperatures &Dgr;T is controlled by determining a figure-of-merit (FOM) for the optical path and including in the path a body of crystalline material that enables the conditions specified by the FOM to be satisfied. The crystalline material is highly transparent at a wavelength &lgr; of radiation propagating in the path, and it has a coefficient of thermal expansion (CTE) and a refractive index n such that the CTE and dn/dT are mutually adapted to satisfy the FOM over the range &Dgr;T. In one embodiment, the CTE and dn/dT of an etalon compensate one another so as to perform frequency discrimination that is essentially temperature insensitive over the range &Dgr;T. In a preferred embodiment of the optical etalon the crystalline material comprises LiCaAlF6.

Abstract: Waveguides according to this invention have a chalcogenide glass core that comprises Se and one or both of As and Ge, and further comprises one or more dopant elements selected from the elements that cause a change in optical energy gap Eg of the glass core. The amount of dopant is selected such that Eg is equal to or less than a 2-photon energy 2h&ngr;, where h is Planck's constant and &ngr;=c/&lgr;, where c is the speed of light in vacuum and &lgr; is an operating wavelength. The dopant elements furthermore are selected such that the chalcogenide glass core has a nonlinear refractive index n2 greater than 200n2 (SiO2), where n2 (SiO2) is the nonlinear index of silica at &lgr;. Typically, &lgr; is about 1.55 &mgr;m. Exemplary, the dopant elements are selected from Sb, Bi, Sn, Pb, In, Tl, Cu, Ag and S. Currently preferred dopants are Te, Sb, Tl, Cu and Ag.