System and method for providing an eye safe laser communication system

• US 6,594,043 B1
• Filed: 12/28/1999
• Issued: 07/15/2003
• Est. Priority Date: 12/28/1999
• Status: Expired due to Term

• Current Assignee: Xylon LLC (Intellectual Ventures LLC)
• Original Assignee: Air Filters, Inc. (Rensa Filtration, Inc.)
• Inventors: Dunn, James E., Bloom, Scott H., Acampora, Anthony
• Primary Examiner(s): Pascal; Leslie
• Assistant Examiner(s): SEDIGHIAN, REZA
• Application Number:
  US09/473,076
• Time in Patent Office: 1,295 Days
• Field of Search: 359/110,111,155,161,169,177,170 250/205,221,169,170
• US Class Current: 398/15
• CPC Class Codes: H04B 10/1149 Arrangements for indoor wireless networking of information
• CPC Class Codes: H04B 10/40 Transceivers

Abstract

A system and method for producing an eye safe laser communication system. The system and method detects an interfering object in the optical path and cuts off or reduces the power in the communication beam to safe levels. In one embodiment, a second laser diode transmitter and receiver is installed in each network node. The laser transmitter is pointed at a corresponding network node and the pulses travel in parallel with the communication beam. The pulses are reflected back to the transmitting node where they are detected. Their flight time is measured. When an interfering object is present, in one scenario, the pulses bounce of the interfering object and return to the receiver in the transmitting node, resulting in a reduced flight time. This reduced flight time is interpreted as an interfering object and the beam is shut down or reduced to a safe level. In a second scenario, the interfering object absorbs the detection beam. In another embodiment, a CCD camera is used to capture a reflection from an object in the path of the communication link. In this embodiment the CCD has an overlapping field of view with the communication transceiver'"'"'s transmit laser. The laser'"'"'s transmission beam forms a baseline pattern on the CCD. Any pixel to pixel variation from the baseline pattern indicates an interference, thus triggering the system to shut down or reduce the power of the communication link. Another embodiment uses retroreflection of the human eye to detect interference by the human eye and an optical magnification device. In this embodiment, a CCD is used to detect signals bent back by retroreflection of the human eye. When such a signal is detected, the link is immediately shut down. Another embodiment utilizes the communication link itself and a detector in the receiver to detect instantaneous power drops caused by an interfering object. When an interfering object is detected, the system shuts down or reduces the power of the communication beam to an eye safe level.

Claims

1. A system for producing an eye safe laser communication system having a first network node in data communications with a second network node via a communication beam generated by a communication transmitter, the system comprising:

a detect transmitter for transmitting a detect signal from the first network node to the second network node;

a detect receiver at the first network node for detecting a reflection of the detect signal;

a timing device at the first network node for determining the flight time of the reflected detect signal; and

a control device coupled to said timing device for reducing the communication beam to an eye safe level, if the flight time is less than a predetermined threshold value in accordance with said timing device.

2. The system of claim 1, wherein said predetermined threshold value is a pre-calculated flight time of a non-interfering communication beam.

3. The system of claim 1, wherein said detect transmitter is a pulse laser device that generates a stream of pulses at fixed intervals.

4. The system of claim 3, wherein said timing device is a timer started concurrently with one of said pulses and stopped when said reflected detect signal is received by said detect receiver.

5. The system of claim 4, wherein said control device is a microprocessor.

6. The system of claim 5, wherein reducing the communication beam to an eye safe level is accomplished by sending a signal from the microprocessor to the communication transmitter.

7. The system of claim 6, wherein the signal from the microprocessor to the communication transmitter causes the communication transmitter to shut down.

8. A method for producing an eye safe laser communication system having a first network node in data communications with a second network node via a communication beam generated by a communication transmitter, the method comprising the steps of:

transmitting an interference detection signal from the first network node to the second network node;

receiving a reflection of the interference detection signal at the first network node;

starting a timer simultaneously with said transmitting step;

stopping the timer simultaneously with said receiving step;

reading a value from the time to determine a flight time of the interference detection signal;

comparing the flight time with a predetermined flight time associated with an interference detection signal having no interference;

determining that interference is present if said flight time is less than said predetermined flight time; and

reducing power of the communication beam if interference is present in accordance with said examining step.

9. A method for producing an eye safe laser communication system having a first network node in data communications with a second network node via a communication beam generated by a communication transmitter, the method comprising the steps of:

transmitting an interference detection signal from the first network node to the second network node;

starting a timer coincident with said transmitting step;

stopping the timer upon receipt of a reflected signal or upon expiration of a predetermined window of expectation associated with a known round trip flight time of the detection signal;

determining if an interference is present in accordance with a value retrieved from the timer, wherein interference is present if the value is within the window of expectation; and

reducing power of the communication beam if interference is present in accordance with said determining step.