Abstract: A first out-coupled light spot is produced on a first detector surface, from a first region of varying refractive index formed in an optical waveguide. A second out-coupled light spot is produced on a second detector surface different than the first, from a second region of varying refractive index formed in the waveguide. The light spots are produced in response to a forward propagating communications signal in the waveguide. A signal from the first surface is compared to a signal from the second surface, and this comparison is used to discriminate between a wavelength shift and a change in power in the communication signal. Other embodiments are also described and claimed.

Abstract: A refractive index grating is formed in an optical waveguide. A detector has an incident light surface that is oriented at about a right angle to a longitudinal axis of the waveguide. The surface is positioned upstream of the grating and outside of the waveguide to receive reflected light from the grating. An index matching material fills essentially the entirety of the light path for the reflected light, from an outside surface of the waveguide to the detector's incident light surface. Other embodiments are also described and claimed.

Abstract: A tomographic interferometer device in which a spectral light source lights an object to create an object beam originating from that object. A stepped optical block is also exposed to the source to create a plurality of individual reference beams having different path lengths. The object beam and reference beams are made to interfere and the resulting light is sent to an array of side by side photodetectors.

Abstract: The apparatus for measuring the thickness of transparent objects (1) has a radiation source (3) of short coherence length and a Michelson interferometer (5), wherein the object (1) to be measured can be arranged in its measuring arm (11), and path length variation element (15), which has an optical path length that changes periodically due to its own rotation, is arranged in the reference arm (13). The cross-sectional surface (34) of the element (15) wherein the reference beam comes to rest has at least four corners so that the reference radiation path in the element (15) has at least two reflections on the inner surfaces of the element. The reference beam (41e) coming out of the element (15) is reflected back by means of a fixed reflector (30) into the element (15), preferably into itself.