By introducing an asymmetry in the effective refractive index profile of a waveguide, wave energy can be extracted from the waveguide by radiation at wavelengths greater than a critical wavelength, where the latter is a function of the effective index distribution. This technique is employed to develop a variety of optical wavelength filters.
A symmetrical waveguide coupler having two signal channels for coupling a first signal having a wavelength .lambda..sub.1 and a second signal having a wavelength .lambda..sub.2 which is longer than .lambda..sub.1. The coupler includes a carrier substrate and first and second dielectric strips embedded in the substrate to form two identical dielectric waveguides which together with the substrate define a coupling region. The first waveguide has first and second arms connected to the coupling region and the second waveguide has a third arm connected to the coupling region. The second and third arms are oriented in a direction facing away from the first arm. The dielectric strips are so dimensioned and arranged within the substrate as to present an effective coupling length c.sub.1 L.sub.1 equal to .pi./.sub.2 at a wavelength of .lambda..sub.1 for coupling the first signal between the first and third arms and an effective coupling length c.sub.1 L.sub.1 equal to .pi. at a wavelength of .lambda..sub.2 for coupling the second signal between the first and second arms, with c.sub.1 being the coupling coefficient between the fundamental modes of the signals in the strips and a function of wavelength, and L.sub.1 being the length of the coupling region.
An optical coupling device comprising an electrooptical substrate, a pair of optical waveguides formed in the surface of the substrate and a grating electrode is provided. The grating electrode is so disposed to extend along one of the pair of optical waveguides at least partially. Thus, when a suitable voltage is applied to the grating electrode, a periodically changing structure of refractive index is formed within the one of the paired optical waveguides to couple the paired optical waveguides, thereby allowing to transfer a light signal from one waveguide to the other.
The invention introduces the concept of very low cost, fully integrated, large scale planar polymer light guide networks. These networks are intended primarily for automotive applications, including data communication, multiplex, sensor, switch and display networks. However, the concept is also applicable in other areas where the length of the network does not exceed a few meters. The basic idea is to `cut` a thin sheet of clear plastic (polymethylmetacrylate polycarbonate, or polystyrene) into a whole network consisting of optical links, couplers, sensors, etc. . . . In addition to being low cost, planar polymer light guide networks extend the one dimensional geometry of fiber optics into two dimensions, adding tremendous design capability and versatility.
In an optical device such as, e.g., an optical communications coupler or an optical gyroscope, a substrate-supported waveguide is aligned with a device component such as, e.g., an optical fiber or a photodetector. Optical alignment of such component relative to the waveguide is facilitated as the component is located in a preferentially etched groove in the substrate supporting the waveguide. In the case of an optical fiber connection, optical coupling is facilitated by a ledge structure overhanging a sloping etched wall of a groove holding the fiber. In the case of a photodetector, an etched groove may be essentially perpendicular to the direction of light propagation.
