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United States Patent m
 WAVELENGTH MULTIPLEXED TWO
DIMENSIONAL IMAGE TRANSMISSION
THROUGH SINGLE MODE OPTICAL FIBER
 Inventor: John H. Hong, Moorpark, Calif.
 Assignee: Rockwell International Corporation, Seal Beach, Calif.
 Appl. No.: 837,019
 Filed: Feb. 18,1992
 Int. CI.' H04J 14/00; H04J 14/02
 U.S. CI 359/124; 359/130;
359/117; 385/27; 385/132
 Field of Search 359/115, 124, 125, 129,
359/130, 131, 117, 127, 154; 385/317, 132
 References Cited
U.S. PATENT DOCUMENTS
3,755,676 8/1973 Kinsel 359/117
3,845,294 10/1974 Indig et al 359/129
3,924,931 12/1975 Cheo 385/37
4,557,563 12/1985 Sprague 350/162.12
4,857,726 8/1989 Kinney et al 359/130
5,121,231 6/1992 Jenkins et al 35/127
5,129,058 7/1992 Mifune et al 395/162
Hiroichi Yoshida, Optical Communication Type Digital Data Transmission, Feb. 9, 1989.
Primary Examiner—Richard E. Chilcot, Jr.
Assistant Examiner—Rafael Bacares
Attorney, Agent, or Firm—John C. McFarren
An apparatus and method are provided for transmitting two-dimensional images through a single mode optical fiber. Light from a broadband source is dispersed into component wavelengths, spatially modulated to contain an image, collected for multiplexing in a single mode optical transmission fiber, transmitted through the single mode fiber, and demultiplexed into its component wavelengths to reproduce the transmitted image. The two-dimensional dispersing and collecting elements may be realized using thin film channel waveguides having arrays of optical gratings. Because the dispersive element at the receiving (output) end of the transmission fiber must reproduce the dispersal pattern used at the source, the information transmitting device may be used for data encryption and decryption.
5 Claims, 2 Drawing Sheets
U.S. Patent May 24, 1994 Sheet 2 of 2 5,315,423
WAVELENGTH MULTIPLEXED TWO DIMENSIONAL IMAGE TRANSMISSION THROUGH SINGLE MODE OPTICAL FIBER
The present invention relates to the transmission of infonnation through optical fibers and, in particular, to the parallel transmission of two-dimensional images through a single mode optical fiber.
BACKGROUND OF THE INVENTION
Optical fibers have greatly enhanced the capabilities of modern telecommunication systems by vastly increasing communication bandwidths, reducing costs, and improving reliability. Because of the limits of fiber technology and state-of-the-art input/output devices, however, current photonic communication links operate at bandwidths far below those that are theoretically possible.
Wavelength division multiplexing devices, such as the prior art apparatus illustrated schematically in FIG. 1, have been investigated for transmission of images through single mode fibers. Wavelength division multiplexing device 10 couples a plurality of input fibers to a single mode optical transmission fiber 11. The input fibers provide input light from a collection of modulated optical sources, such as semiconductor laser diodes, each emitting at a unique wavelength, such as Xi, X2, X3, X4, and X5, for example. The input light is coupled to single mode transmission fiber 11 by means of a collective array of grating couplers 12, 14, 16, and 18. At the receiving end of transmission fiber 11, a dispersive array of grating couplers 13,15,17, and 19 separate the light into its wavelength components Xi, X2, X3, X4, and X5, which are output on separate optical fibers as illustrated.
Although the bandwidth capabilities of single mode optical transmission fibers can be realized by the foregoing technique, wavelength division multiplexing device 10 does not fully address the possible relationships among the information being transmitted over the parallel wavelength channels, which is an important aspect 4J of parallel communication channels. Therefore, an improved single mode optical fiber image transmission system is needed to operate at high bandwidths with low attenuation while exploiting the parallel nature of the information being transmitted.
SUMMARY OF THE INVENTION
The present invention comprises an apparatus and method of transmitting two-dimensional images through a single mode optical fiber. Light from a broadband source is dispersed into predetermined component wavelengths (or wavelength bands). The dispersed light is spatially modulated to contain an image, collected and multiplexed for transmission in a single mode optical fiber, transmitted through the single mode fiber, and demultiplexed into its component wavelengths to reproduce the transmitted image. The two-dimensional dispersing and collecting elements may be realized using multiplexed volume holograms generated in photorefractive media or thin film channel waveguides having arrays of optical gratings. Because the dispersive element at the receiving (output) end of the transmission fiber must be similar to that used at the source, the data
transmitting device may include data encryption and decryption as an additional function.
A principal object of the invention is the parallel transmission of two-dimensional data through a single mode optical fiber. A feature of the invention is the use of thin film channel waveguides for dispersing and collecting the component wavelengths of a broadband light source. An advantage of the invention is the optical transmission of a large number of parallel channels of data at high bandwidths with low attenuation.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and for further advantages thereof, the following Detailed Description of the preferred Embodiment, makes reference to the accompanying Drawings, wherein like reference numerals refer to the same or similar components throughout the several figures in which:
FIG. 1 is a schematic diagram of a prior art optical fiber array of spectral filters arranged to collect and disperse light according to its component wavelengths;
FIG. 2 is a schematic diagram illustrating the basic method of transmitting an image through a single mode optical fiber;
FIG. 3 is a plan view of a thin film channel waveguide of the present invention for dispersing and collecting component wavelengths of light to be transmitted through a single mode optical fiber; and
FIG. 4 is an expanded schematic diagram of a multilayered embodiment of the system of FIG. 2 incorporating thin film waveguides as illustrated in FIG. 3.
DETAILED DESCRIPTION OF THE
Referring to FIG. 2, a schematic diagram of a single mode optical fiber image transmission system 20 is illustrated. In system 20, broadband light source 21 provides an appropriate mix of broadband light, either coherent or incoherent, into a spectrally dispersive device 22. Unlike one-dimensional devices such as gratings and prisms found in monochromators, dispersive device 22 is an apparatus for separating the broadband light from source 21 into its spectral components across a two-dimensional area. Dispersive device 22 may comprise a multiplexed volume hologram written in a photorefractive medium, as is known in the prior art, or a thin film channel waveguide as described below. In either embodiment, the function of device 22 is to display the spectral components of the broadband light across a two-dimensional plane, as illustrated in FIG. 2, so that, for example, the shortest wavelength appears at the upper left corner and the longest wavelength appears at the lower right corner.
A spatial light modulator 23, or an image containing film, for example, is placed in the plane where the spectral components of the light have been separated. Spatial light modulator 23 (or the image film) locally modulates the light intensity to define the two-dimensional information or image to be transmitted. A second twodimensional spectrally dispersive device 24, which may comprise a photographic medium having a multiplexed volume hologram or a thin film channel waveguide similar to device 22 but used in a reversed mode, is situated to collect and recombine the modulated spectral components of the light from spatial light modulator 23. Device 24 recombines the image-containing light