An optical waveguide is constructed so as to comprise a non-solid core surrounded by a solid-state material. The non-solid core has an index of refraction which is lower than the index of refraction of the surrounding solid state material, and light can be transmitted with a low loss through the non-solid core. The non-solid core can extend through at least one of multiple layers of the solid state material, wherein the non-solid core is elevated on a substrate material above at least one topmost layer of the multiple solid state layers lateral to the non-solid core. In an exemplary application, the non-solid core comprises a sample material whose light transmission, absorption, and/or interference characteristics are to be measured.