The present invention is concerned with an imaging system for the self-imaging of objects, using optical waveguides comprising reflecting boundary surfaces, and satisfying the imaging condition L.lambda. = 4hN.sub..mu. W.sup.2.sub.eq, wherein L is the axial distance between the object and the self-image, W.sub.eg is a typical transverse dimension of the waveguide having an effective refractive index N.sub..mu., and .lambda. is the operational wavelength, and h is an integer for single imaging and not an integer for multiple imaging. Many embodiments of dielectric thin film waveguides are described which have the purpose of self-imaging very small objects with good levels of resolution. Magnification or reduction by means of the imaging system are also provided for.

An optical waveguide device (30) that limits the peak optical intensity applied to an optical absorbing device (36), such as a photodetector or electro-absorption modulator. The optical waveguide device (30) includes a single mode input waveguide (34) coupled to a multi-mode, waveguide interference coupler (32). A single mode output waveguide (38) collects the light from the interference coupler (32). The absorbing device (36) is defined in the waveguide coupler (32) by a reverse-biased p-i-n diode structure. A voltage potential applied to the diode structure creates an electric field across the waveguide coupler (32) that causes the waveguide coupler (32) to absorb. Light entering the interference coupler (32) from the single mode waveguide (34) expands into other propagation modes that interact to constructively and destructively interfere. Because the light expands in the coupler (32), the amplitude of the light decreases even though the overall power remains substantially the same. When the light recombines as it approaches the output waveguide (38), the amplitude of the light returns to the input amplitude. The absorbing device (36) is defined in the waveguide coupler (32) between the area of interference (24) and the output waveguide (38). The absorption in the absorbing device (36) is exponential; the most light is absorbed at first and then progressively less light along the device.

The present invention relates to an optical system for providing uniform illumination of a light valve. The light source is an extended source generally emitting a non-uniform spatial distribution of light power. Source light is focused into the entrance end of a light transmitting tunnel having reflecting interior wall surfaces and having cross sectional and length dimensions chosen to deliver, at the exit end of the tunnel, light which is substantially uniform in power distribution over the surface area of the exit end. This is caused by multiple reflections from the tunnel walls. The exiting light is advantageously used to illuminate uniformly a light valve. The tunnel may be tapered to alter the exit angular aperture. The tunnel may be hollow or filled with a transparent material. In addition, the tunnel may be segmented and folded to provide a joint which conforms tunnel geometry to given spatial limitations between source and valve. The joint also provides a convenient way of directing heat out of the tunnel structure. One embodiment of the present invention includes a compound light transmitting tunnel with a plurality of segments and exit ends. A joint between adjacent segments divides light into a transmitted range of wavelengths and a reflected range of wavelengths.

A lens comprising a plurality of identical straight optical fibers arranged in a bundle with at least a portion of each fiber treated to suppress internal reflections, so that each fiber transmits only rays which enter the end of the fiber substantially parallel to its axis at that point, the angle between adjacent fibers of the bundle of optical fibers being adjustable to provide a lens for a range of solid angles, with a field of any shape and an image adjustable in size which may be altered in location and plane, by extending the optical fibers by flexible sections with internal reflections permitting transmission of rays on curved paths.

An optical device (10) incorporates a rectangular multimode waveguide (14) with an input aperture (22), and two output optical fibres (26 and 28) with respective input apertures (30 and 32). An input light beam (34) of Gaussian transverse intensity profile is focused to a beam waist (36) at the center of the aperture (22). The beam phase and waist radius w are arranged such that the light beam (34) excites symmetric modes in the waveguide (14). Modal dispersion along the waveguide (14) producestwo electric field intensittlVxima of similar magnitude centered on the fibre input apertures (30 and 32). This provides the beamsplitter function of division of input radiation into two similar intensity outputs. Devices of the invention may be arranged to divide input beams into more than two output beams. The invention may also provide a light beam combiner.