An integrated optical wavelength demultiplexer has deposited on a waveguide layer a pair of Luneburg lenses, the first for collimating light from an optical fiber, the second for focussing light at an array of photodetectors formed under the waveguide layer. Between the lenses is the dispersive element, a thin-film prism of a highly dispersive low-loss material such as arsenic trisulfide. A known integrated optical demultiplexer, which uses a chirped diffraction grating to spatially disperse (rather than angularly disperse) the optical wavelengths, would suffer a greater insertion loss particularly for wavelengths coupled out at a later point in the grating. Demultiplexing with a thin-film prism should also result in the capability to handle a larger number of channels, for a given channel isolation and substrate area.
Channel separation of wavelength multi/demultiplexers using a grating structure in a planar multimode slab waveguide is improved by choosing the thickness of the slab waveguide to be greater than the input diameter at least in the area of the grating structure. The aperture of the radiation incident upon the grating structure is chosen to be correspondingly smaller than the input aperture.
A wavelength division method and system employing a radiation transmissive planar waveguide provided with collimating and focusing lenses and with a periodic radiation transmissive diffraction grating incorporating radiation reflecting elements in spaced array, preselected, in demultiplexing service, to separate into individual entities an optical signal input constituting a multiplicity of coherent radiation signals of different characteristic wavelengths transmitted simultaneously via the waveguide and, in multiplexing service, to consolidate a multiplicity of coherent radiation signals individually introduced to the grating via the waveguide along angular courses substantially coincident with the angular courses taken by individual radiation signals of corresponding wavelengths exiting the grating during demultiplexing service, and means directing the signals to dedicated receptors.
A photodetector comprises a waveguide layer to propagate lights, a clad layer which is laminated onto the waveguide layer and has a refractive index smaller than that of the waveguide layer, the clad layer having at least two portions having different thicknesses, and photoelectric converting devices which are respectively provided on the surfaces of the different thickness portions of the clad layer on the side opposite to the side which faces the waveguide layer.
A spectral filter for an integrated optic application, such as in an optical demultiplexer (14), is provided and includes a common input waveguide (20) integrally connected to a pair of optical output waveguides (22, 24). The material selected for the output waveguides (22, 24) can be semiconductor material that provides a low index of refraction for a specific wavelength in one output waveguide and a relatively higher index of refraction for the same wavelengths in the other output waveguide, the output waveguide materials being interrelated in that they have a common index of refraction for at least one wavelength across the spectrum of radiation. An incident spectrum of radiation (16) can be split into at least a pair of bandwidths of radiation to provide a spectral filter function.
Integrated optic devices incorporating echelon gratings suitable for use in performing multi/demultiplexing functions in optical communications systems. The echelon gratings can be either reflection or transmissive types and are conveniently formed using conventional photolithographic techniques.
