Wide-angle, high-speed, free-space optical communications system

• US 5,606,444 A
• Filed: 10/20/1994
• Issued: 02/25/1997
• Est. Priority Date: 09/10/1992
• Status: Expired due to Fees

• Current Assignee: Eldec Corporation (Crane Company)
• Original Assignee: Eldec Corporation (Crane Company)
• Inventors: Lindsay, Thomas A., Johnson, Bruce E., Regnier, Mark A., Brodeur, David L., Morton, deceased, Randall E.
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US08/325,965
• Time in Patent Office: 859 Days
• Field of Search: 359/113, 359/129, 359/143, 359/152-154, 359/159, 359/161, 359/164, 359/167, 359/172, 359/194
• US Class Current: 398/125
• CPC Class Codes: H04B 10/1143 Bidirectional transmission
• CPC Class Codes: H04B 10/40 Transceivers

Abstract

A free-space optical communications system for transmitting data between an aircraft computer system (14) and a ground-based computer system (12). The system includes a pair of corresponding optical transmitters (36) and optical receivers (38) that transmit and receive optical signals transmitted between the two computer systems. Included within each optical transmitter is one or more light-emitting diodes (42) that produce optical signals corresponding to the data to be transmitted. A beam-forming horn (44) is bonded directly to the light-emitting diodes to direct the optical signal uniformly over a target area. The optical receiver includes one or more infrared windows (50) to reduce the mount of ambient light received by the optical receiver. A compound parabolic concentrator (64) collects light transmitted from the optical transmitter and directs the light onto an avalanche photodiode (66), which includes thermal bias compensation. An AC network couples the output signal of the photodiode to a transimpedance amplifier (70). An optional optical shroud (34) surrounds the optical transmitters and receivers to further reduce the amount of ambient light that is received by the optical receivers.

Claims

1. A free-space optical communications system for transmitting data from an aircraft computer system to a ground-based computer system, comprising:

an optical transmitter coupled to the aircraft computer system for producing optical signals that correspond to the data to be transmitted between the aircraft computer system and the ground-based computer system, wherein the optical transmitter includes;

(a) a light source that produces optical signals corresponding to the data to be transmitted;

(b) means for gathering the optical signals produced by the light source and for distributing the optical signals uniformly over a target area;

an optical receiver coupled to the ground-based computer system, for receiving the optical signals produced by the optical transmitter, wherein the optical receiver includes;

(a) optoelectronic means for producing an output signal that corresponds to the data transmitted; and

(b) a compound parabolic concentrator coupled to the optoelectronic means, for gathering a portion of the optical signals produced by the light source and for directing the portion of the optical signals gathered to the optoelectronic means.

2. The free-space optical communications system of claim 1, further comprising:

an optical shroud that extends between the optical transmitter and the optical receiver for reducing the amount of ambient light that is received by the optical receiver coupled to ground-based computer system; and

light-filtering means disposed in front of the optoelectronic means for reducing the mount of ambient light directed to the optoelectronic means.

3. The free-space optical communications system of claim 1, wherein the optical receiver further includes means for removing a portion of the output signal due to ambient light received by the optical receiver.

4. The free-space optical communications system of claim 1, further comprising:

gain control means coupled to the optoelectronic means, for regulating the magnitude of the output signal produced by the optoelectronic means.

5. The free-space optical communications system of claim 1, further including:

a temperature-compensated biasing means for providing a bias voltage to the optoelectronic means.

6. The free-space optical communications system of claim 1, wherein the means for gathering the optical signals produced by the light source and for distributing the optical signals uniformly over a target area comprises a hollow horn having a reflective interior coating.

7. The free-space optical communications system of claim 1, wherein the means for gathering the optical signals produced by the light source and for distributing the optical signals uniformly over a target area comprises a solid horn-shaped prism made of a substantially transparent material.

8. The free space optical communications system of claim 7 wherein the means for gathering the optical signals produced by the light source and for distributing the optical signals uniformly over a target area comprises a compound parabolic concentrator.

9. The free-space optical communications system of claim 1, wherein the means for gathering the optical signals produced by the light source and for distributing the optical signals uniformly over a target area comprises a lens disposed in front of the light source.

10. A free-space optical communications system for transmitting data bidirectionally between an aircraft computer system and a ground-based computer system, comprising:

a first optical transmitter coupled to the aircraft computer system and a second optical transmitter coupled to the ground-based computer system, each transmitter including;

(a) a light source that produces optical signals corresponding to the data to be transmitted between the aircraft computer system and the ground-based computer system;

(b) means for collecting the optical signals produced by the light source and distributing the optical signals uniformly over a target area; and

a first optical receiver coupled to the ground-based computer system and a second optical receiver coupled to the aircraft computer system that receive the optical signals transmitted from a corresponding optical transmitter, wherein each optical receiver includes;

(a) a photodiode that produces an output signal that is proportional to a received optical signal;

(b) a compound parabolic concentrator bonded to the photodiode that collects the optical signals transmitted from the optical transmitter and directs the optical signals onto the photodiode;

(c) current shunt means coupled to an output of the photodiode for shunting away a portion of the output signal that is due to ambient light collected by the compound parabolic concentrator.

11. The free-space optical communications system of claim 10, wherein the first and second optical receiver each includes:

an optical filter disposed between the corresponding optical transmitter and the photodiode.

12. The free-space optical communications system of claim 10, wherein the first and second optical receivers each include:

a temperature-compensated voltage supply that provides a temperature-compensated biasing voltage to the photodiode.

13. The free-space optical communications system of claim 10, wherein the first and second optical receivers each include:

means for extracting a time varying portion of the output signal produced by the photodiode.

14. A free-space optical communications system for transmitting data bidirectionally between an aircraft computer system and a ground-based computer system, comprising:

a pair of optical transmitters, one of which is coupled to the aircraft computer system and another of which is coupled to the ground-based computer system, wherein each of the optical transmitters includes;

(a) one or more light-emitting diodes (LEDs) that produce optical signals that correspond to data to be transmitted;

(b) a hollow horn having a reflective interior surface that surrounds the one or more LEDs for uniformly distributing optical signals produced by the LEDs over a target area, and

a pair of optical receivers, one of which is coupled to the aircraft computer system and another of which is coupled to the ground-based computer system, wherein each optical receiver includes;

(a) means for gathering light that impinges upon the optical receiver;

(b) a photodiode bonded to the means for gathering light, the photodiode producing an electrical signal that is proportional to the amount of light gathered; and

(c) filter means disposed in front of the means for gathering light for reducing the amount of ambient light received by the photodiode.

15. The free space, optical communications system of claim 14, wherein the means for gathering light comprises a compound parabolic concentrator.

16. A method of optically transmitting data between an aircraft computer system and a ground-based computer system, comprising the steps of:

producing an infrared optical signal that corresponds to the data to be transmitted;

directing the infrared optical signal through light distributing means so that the optical signal is evenly distributed within a target area in which an optical receiver is positioned;

gathering light at the optical receiver using a compound parabolic concentrator that is bonded to a photodiode, the photodiode producing an electrical signal proportional to the amount of light gathered;

removing a component of the electrical signal produced by the photodiode due to ambient light gathered by the compound parabolic concentrator; and

coupling an AC component of the electrical signal produced by the photodiode to an amplifier, wherein a magnitude of the AC component of the electrical signal is proportional to the data transmitted between the aircraft computer system and the ground-based computer system.

17. An optical transceiver adapted to be coupled to an exterior of an aircraft for transmitting and receiving data between an aircraft computer system and a ground-based computer system comprising:

an optical transmitter for producing optical signals that correspond to data to be transmitted from the aircraft computer system to the ground-based computer system, including;

(a) one or more light sources coupled to the aircraft computer system for producing the optical signals corresponding to data that is transmitted from the aircraft computer system to the ground-based computer system;

(b) light distributing means for gathering the optical signals and distributing the optical signals uniformly over a target area;

an optical receiver for receiving optical signals that are transmitted from a second optical transmitter coupled to the ground-based computer system, including;

(a) a photodiode that produces an output signal that is proportional to a received optical signal;

(b) a compound parabolic concentrator bonded to the photodiode that collects optical signals and directs the collected optical signals onto the photodiode; and

(c) a current shunt coupled to the output signal produced by the photodiode that shunts a portion of the output signal due to ambient light collected by the light-collecting means.

18. An optical communications system for transmitting data bidirectionally between a first computer system and a second computer system, comprising:

an optical transmitter coupled to the first computer system for producing optical signals that correspond to the data to be transmitted between the first computer system and the second computer system, wherein the optical transmitter includes;

(a) light-producing means for producing optical signals corresponding to the data to be transmitted;

(b) light distributing means for gathering the optical signals produced by the light-producing means and for distributing the optical signals uniformly over a target area;

an optical receiver coupled to the second computer system for receiving the optical signals produced by the optical transmitter, wherein the optical receiver includes;

(a) a photodiode for producing an output signal that is proportional to a received optical signal, the output signal of the photodiode being coupled to the second computer system for producing an output signal that corresponds to the data transmitted;

(b) a compound parabolic concentrator bonded to the photodiode for gathering a portion of the optical signals produced by the light-producing means and for directing the portion of the optical signals gathered to the photodiode; and

(c) light-filtering means disposed in front of the compound parabolic concentrator for reducing the amount of ambient light received by the photodiode.

19. The optical communications system of claim 18, wherein the optical receiver further includes current shunt means coupled to the photodiode for removing a portion of the output signal due to ambient light received by the optical receiver.

20. The optical communications system of claim 18, further comprising:

gain control means coupled to the photodiode for regulating the magnitude of the output signal produced by the photodiode.

21. The optical communications system of claim 18, further including:

a temperature-compensated biasing means for providing a bias voltage to the photodiode.