Optical waveguides – Optical fiber bundle – Imaging
Reexamination Certificate
1999-05-18
2001-06-12
Ullah, Akm E. (Department: 2874)
Optical waveguides
Optical fiber bundle
Imaging
Reexamination Certificate
active
06246822
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to receivers and, more particularly, to fiber-coupled receivers and associated methods for receiving an image.
BACKGROUND OF THE INVENTION
Fiber-coupled receivers are commonly employed to detect two-dimensional images. A fiber-coupled receiver generally includes a plurality of bundled optical fibers of equal length extending between opposed first and second ends. The first ends of the optical fibers are typically tightly packaged to receive the image information in parallel. In this regard, each optical fiber defines one pixel of the resulting image.
The fiber-coupled receiver also typically includes a lens for focusing the image upon the first ends of the optical fibers. While fiber-coupled receivers can detect two-dimensional images, fiber-coupled receivers can also be utilized to detect three-dimensional images. In this regard, the image information from a pulse-illuminated object would be received by the first ends of the optical fiber at slightly different times. As known to those skilled in the art, the initial signals that arrive at the first ends of the optical fibers will represent those portions of the object that is being imaged that are closest to the receiver, while signals that are received at progressively later times represent those portions of the object that are increasingly further from the receiver. By analyzing the times at which the signals are received by the first ends of the optical fibers, a three-dimensional image of the object can be reconstructed.
Conventional fiber-coupled receivers also include a detector having a plurality of array elements, one of which is generally associated with each optical fiber. In particular, each array element is generally positioned to receive the signals emitted by the second end of a respective optical fiber. Since each of the optical fibers has an equal length, the array elements receive and process the signals in parallel. In addition to detecting the signals provided by the second ends of the optical fibers, the detector generally amplifies the detected signals prior to further processing of the signals. As such, a typical detector can comprise a photo-multiplier tube having a plurality of anodes, each of which both detects and amplifies the signals emitted by the second end of a respective optical fiber.
A conventional fiber-coupled receiver also generally includes a digitizer for receiving the amplified signals from the detector and for creating a digital representation of the signals. In addition, a conventional fiber-coupled receiver typically includes a signal processor for receiving the digitized representations of the signals and for reconstructing the image. In this regard, each optical fiber corresponds to a respective pixel of the resulting image with the position of the pixel based upon the position of the first end of the respective optical fibers relative to the first ends of the other optical fibers. For a receiver designed to detect three-dimensional images, the signal processor will also analyze the differences in time at which the signals were received by the receiver, as described above.
While conventional fiber-coupled receivers can effectively detect two- and three-dimensional images, conventional fiber-coupled receivers are quite expensive and surprisingly heavy. In this regard, the requirement that conventional fiber-coupled receivers include a detector, a signal amplifier and a signal processor associated with each optical fiber significantly increases the overall cost of the receiver. As such, conventional fiber-coupled receivers may not be employed in cost-sensitive or weight-constrained imaging applications in view of their substantial costs and weight penalty.
SUMMARY OF THE INVENTION
A fiber-coupled receiver and associated method are therefore provided according to the present invention for detecting two-dimensional and three-dimensional images of an object illuminated by a modulated source in a cost-effective manner. In this regard, the fiber-coupled receiver utilizes a plurality of optical fibers as signal delay line elements extending between respective first and second ends. According to the present invention, at least some of the optical fibers impose different optical delays such that signals that are received in parallel by the first ends of the optical fibers are emitted at different times from the second ends of the optical fibers. To impose different optical delays, at least some of the optical fibers can have different lengths. The fiber-coupled receiver also includes at least one detector for receiving the signals emitted at different times from the second ends of the optical fibers such that the signals that are received in parallel by the first ends of the optical fibers are received in series by the detector. By presenting the signals in series to the detector, the fiber-coupled receiver of the present invention need not include either a detector having separate array elements for each optical fiber or a separate detector for each optical fiber. Instead, the fiber-coupled receiver of the present invention includes a significantly fewer number of detectors than the number of optical fibers since each detector can receive signals in series from a number of optical fibers. By reducing the number of detectors, the fiber-coupled receiver and associated method of the present invention are significantly less expensive than conventional fiber-coupled receivers and are therefore particularly useful in cost-sensitive applications.
The fiber-coupled receiver can also include a digitizer for receiving the signals from the detector and for digitizing the signals. The fiber-coupled receiver can also include a signal processor for receiving the digitized signals and for reconstructing the corresponding image, either in two dimensions or in three dimensions as described below.
According to one advantageous embodiment, the fiber-coupled receiver is designed to detect a three-dimensional image of an object illuminated by a pulsed source. Since the image information relates to a three-dimensional image, the image information is received by the first ends of the optical fibers, not at the same time, but over a predetermined period of time. In order to retain the array element position information provided by the differences in time at which the image information is received by the first ends of the optical fibers, the differences in length of the optical fibers should be sufficiently long to introduce an optical delay relative to the other optical fibers that separates the image signals from each other. As such, the differences in time at which the image information signal is received by the first ends of the optical fiber can be readily distinguished from the much longer optical delays imposed upon the signals as a result of the differences in length of the optical fibers. By analyzing the differences in time at which the image information was received by the first ends of the optical fibers, the signal processor of the fiber-coupled receiver of the present invention can reconstruct a three-dimensional image.
According to one embodiment, the fiber-coupled receiver includes a plurality of detectors for receiving the signals emitted from the second ends of respective subsets of the plurality of optical fibers. Since each optical fiber of a respective subset of optical fibers imposes a different optical delay, such as by having a different length, the signals are presented in series to each detector. Although the fiber-coupled receiver of this embodiment includes a plurality of detectors, the fiber-coupled receiver still need not include the same number of detectors as optical fibers since a single detector can receive the signals emitted in series by a plurality of optical fibers.
Since the fiber-coupled receiver and associated method of the present invention need not include either a detector having at least as many array elements as optical fibers or the same number of detectors as optical fibers, the fiber-coupled receiver of
Caswell Robert Lynn
Hayes Cecil Leon
Kim Kyung Joon
Alston & Bird LLP
The Boeing Company
Ullah Akm E.
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