Data processing: measuring – calibrating – or testing – Measurement system – Orientation or position
Reexamination Certificate
2001-05-11
2003-01-21
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Orientation or position
C359S199200, C356S614000, C342S417000
Reexamination Certificate
active
06510401
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to optics systems (including communication) and elements and, in particular, to optical transceiver with alignment between transmitter and receiver.
BACKGROUND OF THE INVENTION
Technological advances in semiconductor lasers, photo detectors, and semiconductor sensor arrays have led to laser communication systems being a viable alternative to conventional radio frequency (RF) systems. Free-space laser communication systems are expected to be a significant component of future communications, including terrestrial, airborne, and especially satellite applications.
The short wavelengths of the optical/infrared spectrum allow a transmission to be focused into a narrow beam. A narrow beam allows a great transmission distance. However, accurate pointing of a laser beam between communication terminals requires a spatial acquisition and tracking system. With the present usage of laser communication systems being low as compared to other types of communication systems, the present procedure of assuming that any laser beam received is the intended laser beam is reasonable. Therefore, present manufacturers of laser communication equipment have not seen a need to make any further improvements. Future laser communication usage is expected to be much greater than present usage, and applications may necessitate multiple co-located terminals. As a result, the present procedure could be unreliable and potentially disastrous.
Prior art methods of acquiring a laser beam include fixed mechanical pointing, transmit beam search, retro-reflector search, and use of a dedicated continuous beacon. Each prior art method fails to authenticate the received laser beam or beacon before applying pointing adjustments.
In the fixed pointing method, laser transmitters and receivers are rigidly mounted and manually aimed. Loss of communication in the fixed-pointing method often requires manually adjusting the spatial orientation of the transmitter and/or the receiver.
In the transmit beam search method, automated search and alignment methods are employed to acquire the communication laser beam over an angular search area and a tradeoff exists between search area and search time. The search process is more complex and lengthy when complementary receivers are searching simultaneously for non-stationary beams. Pointing of laser beams at incorrect (unauthenticated) targets will delay or prevent proper alignment.
In the retro-reflector search method, a passive reflector is used to reflect the transmitted laser beam that scans the search area until the reflection is detected. Reflected laser beams from multiple simple reflectors are indistinguishable and proper pointing is again delayed or prevented.
In the dedicated beacon method, a laser beacon is dedicated to the problem of aligning the transmitter and receiver. A laser beacon normally has a larger beam width than a communication laser beam and, therefore, requires fewer search steps, and less time, to align the receiver to the transmitter. Prior art methods employ continuous (unmodulated) beacons. Pointing of laser beams at incorrect (unauthenticated) targets will again delay or prevent proper alignment.
Several pointing alignment methods have been proposed. U.S. Pat. No. 4,401,886, entitled “ELECTROMAGNETIC BEAM ACQUISITION AND TRACKING SYSTEM,” discloses a device for scanning a laser beam over a field of view and use of a retro-reflector to return the beam to the transmitter that employs a photo multiplier detector. Dithering the beam around a central axis generates the pointing error employed in the steering process. The retro-reflector approach provides a useful beacon for short communication distances. However, reliable pointing demands that only the intended retro-reflector be in the field of view. Any source of reflection other than the reflector would interfere with operation. However, U.S. Pat. No. 4,401,886 does not disclose the present invention. U.S. Pat. No. 4,401,886 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 4,834,531, entitled “DEAD RECKONING OPTOELECTRONIC INTELLIGENT DOCKING SYSTEM,” discloses a device that uses independently triggered laser sources for illuminating and isolating a target. U. S. Pat. No. 4,834,531 does not disclose the present invention. U.S. Pat. No. 4,834,531 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 4,867,560, entitled “OPTICAL ALIGNMENT SYSTEM,” discloses a device for aligning two transceivers using two beams, where adjustments in alignment are made based on the difference in magnitude between respective quarters of the two beams from a reference value. However, U.S. Pat. No. 4,867,560 does not disclose the present invention. U.S. Pat. No. 4,867,560 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,062,150, entitled “FIBER-BASED FREE-SPACE OPTICAL SYSTEM,” discloses a device for coupling received and transmitted light over a physically nutating optical fiber. Modulation of the received signal caused by the nutation is used to make pointing adjustments of a steering mirror to align the transmit/receive beam. However, U.S. Pat. No. 5,062,150 does not disclose the present invention. U.S. Pat. No. 5,062,150 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,119,225, entitled “MULTIPLE ACCESS COMMUNICATION SYSTEM,” discloses a device for and a method of locating multiple terminals using a single narrow scanning beacon. However, U.S. Pat. No. 5,119,225 does not disclose the present invention. U.S. Pat. No. 5,119,225 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,142,400, entitled “METHOD AND APPARATUS FOR AUTOMATIC ACQUISITION AND ALIGNMENT OF AN OPTICAL BEAM COMMUNICATION LINK,” discloses a device for and method of establishing a communication link using a search mode, a stare mode, and retro-reflectors. However, U.S. Pat. No. 5,142,400 does not disclose the present invention. U.S. Pat. No. 5,142,400 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,390,040, entitled “OPTICAL TRANSCEIVER FOR FREE-SPACE COMMUNICATION LINKS,” discloses a device for acquiring a communication signal using the step-stare approach. However, U.S. Pat. No. 5,390,040 does not disclose the present invention. U.S. Pat. No. 5,390,040 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,465,170, entitled “ALIGNMENT ADJUSTING SYSTEM FOR USE IN OPTICAL SYSTEM OF OPTICAL TRANSCEIVER,” discloses a device for and method of for overcoming misalignment of optical systems due to thermal expansion. However, U.S. Pat. No. 5,465,170 does not disclose the present invention. U.S. Pat. No. 5,465,170 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,475,520 entitled “SATELLITE COMMUNICATIONS SYSTEM” discloses a device for communicating via an optical beam by a first transceiver transmitting a number of signals, each uniquely modulated, a second transceiver returning the signals it receives, and adjusting the transmission area to insure reception by the second transceiver of all the signals transmitted by the first transceiver. However, U.S. Pat. No. 5,475,520 does not disclose the present invention. U.S. Pat. No. 5,475,520 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,592,320, entitled “SATELLITE COMMUNICATIONS SYSTEM” discloses a device for communicating via an optical beam by a first transceiver scanning a first beam, a second transceiver scanning a second beam modulated by the time that the first beam was received, the first transceiver scanning modulating the first beam by the time that the second beam was received, and adjusting the scans of both transceivers to be in alignment. However, U.S. Pat. No. 5,592,320 does not disclose the method of
Martin Kenneth I.
Summers Kenneth E.
Hoff Marc S.
Morelli Robert D.
The United States of America as represented by the Director of t
West Jeffrey R
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