Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-01-25
2001-09-04
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06285476
ABSTRACT:
A portion of this disclosure contains material in which copyright is claimed by the applicant. The applicant has no objection to the copying of this material in the course of making copies of the application file or any patents that may issue on the application, but all other rights whatsoever in the copyrighted material are reserved.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to structures and techniques which are useful in high bandwidth laser communications equipment, laser radar, visible and infrared remote sensing equipment, long range, and to methods of making and using such systems.
2. Related Art
Wideband (high-speed) data transfer at rates in excess of 1.5 Megabits-per-second (Mbps) is expensive for dedicated bandwidth (e.g., leased lines) over the existing telecommunications infrastructure. Over modest ranges where an unobstructed line of sight exists, a laser communication link can provide an alternative means of obtaining dedicated bandwidth at high data rates.
For this and other reasons, wireless information transmission systems in general are increasingly desirable as alternatives to costly wired installations and high telecommunications rates which prevail even for short distance communications. Radio frequency communications systems have the disadvantage of requiring that carrier frequency and communications bandwidth be assigned to an application, since the much wider beamwidths and sidelobes can interfere with each other. Thus, there is an increasing need for communications systems, such as those using light frequencies, that transmit large quantities of information in a line-of-sight application without creating interference problems.
Microwave systems are also line of sight, but the majority of such systems on the market are not capable of the desired data rates in excess of 10 Mbps (e.g., 45, 100 and 155 Mbps). The higher-bandwidth microwave systems (i.e. >10 Mbps) generally require Federal Communication Commission licensing, and are susceptible to terrain and building reflections, typically requiring tall towers which add significantly to the expense.
Free space laser communication within the atmosphere has been a realizable technology for many years, although commercially available laser communication systems are few in number. Manufacturers include Laser Communications Inc. (LCI) of Lancaster, Penn. (recently acquired by Jolt, Ltd. of Jerusalem, Israel), Proteon (formerly SilCom Technology) in Ontario, Canada, Canon USA in Englewood Cliffs, N.H. (Canobeam™), and AstroTerra Corp. in San Diego, Calif. (TerraLink™terminals). Each of these systems includes a basic set of subsystems: diode laser, beam-forming optics, receiver (telescope plus detector), electronics, and a mechanical housing.
The AstroTerra™ terminals, so far as the inventors are aware, are the longest range terminals commercially available at this time. The range of such competing systems is less than the range provided by the present invention, and because of their design systems of this type are inherently less reliable and more costly to manufacture than the system developed by the inventors which is described in more detail herein.
U.S Pat. No. 5,347,387 to Rice discloses a duplex optical transceiver wherein received light energy entering the system is initially reflected from a paraboloidal mirror onto a beam expander mirror. The light reflected from the beam expander then passes through a light baffle and a polarized beam rotating device. Next, the recollimated beam is multiplexed through a cube beamsplitter and re-imaged onto an avalanche photodiode detector. In the transmit path, the semiconductor laser emission is circularized and collimated to the desired beam divergence before being multiplexed through a cube beamsplitter and transmitted out the transceiver. Because Rice uses polarization to multiplex incoming and outgoing light beams, his system is limited as to the bandwidth of transmitted data.
U.S. Pat. No. 5,390,040 to Mayeux discloses an optical transceiver that employs a Cassegrain receiver for receiving an incoming beam reflected from a field of view onto the central portion of a primary mirror, and a transmitter for transmitting an outgoing beam of a different wavelength into the atmosphere. In Mayeux, the transmitted and received beams travel along two separate paths inside the transceiver.
U.S. Pat. No. 5,422,900 to Reele et al. discloses an optical compact disk writer with an integrated laser module wherein a laser driver circuit connected to the input of a laser is completely shielded from electromagnetic interference (EMI) from the rest of the system. The reference also discloses a lower housing formed of metal to act as the laser's main heat sink. U.S. Pat. No. 5,640,407 to Freyman et al. discloses a temperature regulating laser diode assembly wherein a laser diode is mounted directly on a compact thermoelectric cooler, which is then mounted on a heat sink.
Other references, such as U.S. Pat. Nos. 5,264,955 to Sakanaka et al., 5,424,860 to Mihara, 5,506,716 to Mihara et al., 5,535,034 to Tanaguchi, 5,142,400 to Solinsky, and 5,659,413 to Carlson show other communications technology applications.
None of these prior systems provides an optimal solution to the problem of establishing useful and reliable laser information transmission systems with significant range and bandwidth. Therefore, there is a need in the field for improved systems and methods which meet these needs.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved laser communications system.
It is a further object of the invention to provide a laser communications system with increased range.
It is a further object of the invention to provide a laser communications system with increased bandwidth.
It is a further object of the invention to provide a laser communications system with improved reliability.
It is a further object of the invention to provide a laser communications system which is less costly to manufacture.
In a preferred embodiment of the invention, an optical transceiver employs a Cassegrain receiver for receiving an incoming beam from a field of view reflected off a primary mirror and focused through an aperture stop, and a transmitter for directing an outgoing beam of a different wavelength using the same primary and secondary mirrors. Received light energy entering the system is initially reflected onto a primary mirror which then focuses the beam onto a secondary mirror. The light reflected from the secondary mirror next encounters a protruding snout light baffle and a field stop to filter out unwanted background light and off-axis light sources. The received energy passing through the field stop is collimated, wavelength multiplexed through a beamsplitter, optically filtered and then focused onto an avalanche photodiode detector.
In the transmit path, the semiconductor laser emission is circularized and adjusted to the desired beam divergence and passed through a narrowband dichroic optical filter. This laser transmitter energy is then dichroically multiplexed through a beamsplitter and transmitted out the transceiver. The laser driver assembly is thermoelectrically cooled and EMI shielded.
The transceiver internal optics in the preferred embodiment comprise a parabolic primary mirror and integral aluminum mount, and a secondary mirror. The transceiver is packaged in a cylindrical aluminum casting that includes an integral cast hood to shield the transmit/receive window from rain and snow, a cast mount for a sighting scope, and an integral cast heat sink. The exterior surface of the transmit/receive window is cold-mirror coated to reflect visible light and the majority of incident solar energy, and the interior surface utilizes an electrically conductive film as a thermally controlled resistive heater for defogging and deicing. The interior surface of the transmit/receive window provides a flat mounting surface for the secondary mirror.
The invention provides a cost-effective imp
Booker Jesse W.
Cabato Alvin
Carlson Robert T.
Driscoll David
Hamilton Scott
LSA, Inc.
Pascal Leslie
Phan Hanh
Reed Smith Hazel & Thomas LLP
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