Detection of an electromagnetic signal

• US 7,792,431 B2
• Filed: 11/01/2004
• Issued: 09/07/2010
• Est. Priority Date: 11/05/2003
• Status: Expired due to Fees

• Current Assignee: MBDA UK Ltd. (MBDA SAS)
• Original Assignee: MBDA UK Ltd. (MBDA SAS)
• Inventors: Richards, Thomas J, Jennings, Martyn R
• Primary Examiner(s): Liu; Li
• Application Number:
  US10/518,032
• Publication Number:
  US 20050254826A1
• Time in Patent Office: 2,136 Days
• Field of Search: 398158-159, 398/161, 398/208, 398/214, 356/5, 356/5.06, 356/141, 356/141.1, 359/349, 385/31
• US Class Current: 398/161
• CPC Class Codes: G01S 3/783 using amplitude comparison of signals derived from static detectors or detector systems
• CPC Class Codes: G01S 7/4804 Auxiliary means for detecting or identifying lidar signals or the like, e.g. laser illuminators
• CPC Class Codes: G01S 7/4818 using optical fibres

Abstract

A signal detector system (10) comprises a single signal detector (11) having a limited on-time during which any received electromagnetic signal can be assessed. The signal detector (11) receives electromagnetic signals from a single direction in space (D) through a single optical fibre (12), a signal splitter 13 which splits the collected signal between three optical paths (20, 30 and 40), and a signal combiner (14) which combines the portions of the signal transmitted by the three optical paths (20, 30 and 40) and transmits the combined signal to a signal detector input (15). Each of the optical paths (20, 30 and 40) includes a respective optical delay (21, 31 and 41) designed to delay transmission of any received signal towards the signal detector (11). In this manner the signal detector (11) will receive any signals that arrived at the optical fibre (12) during three separate periods of time.

Claims

1. A signal detection system comprising:

an electromagnetic signal detector having a limited duty cycle on-time for detecting receipt of electromagnetic signals,

at least two optical paths each arranged to receive an electromagnetic signal from a same nominal direction in space and to transmit any received signal towards said signal detector, and

a first optical time delay within one of said optical paths for delaying transmission of said received signal towards said signal detector, wherein at least one of said optical paths is arranged to transmit a signal, received during a first time period, to said signal detector during a duty cycle on-time, and said first optical time delay is selected to transmit a signal received during a second time period, earlier than said first time period and before said duty cycle on-time, to said signal detector within said duty cycle on-time, extending the operational range of said signal detector by compressing the real time during which a signal can be received by one of said at least two optical paths into the same duty cycle on-time of said signal detector.

2. A signal detection system, according to claim 1, in which said at least one of said optical paths is arranged to transmit a signal received during said duty cycle on time to said signal detector within the same duty cycle on-time.

3. A signal detection system, according to claim 1, in which a further optical path is arranged to receive an electromagnetic signal from said same nominal direction in space and to transmit said received signal towards said signal detector, said further optical path including a second optical time delay which is longer than said first optical time delay.

4. A signal detection system, according to claim 1, in which each of said optical paths is defined by a separate optical fibre and said optical fibres are closely packed on a focal plane to collect electromagnetic signals from approximately said same nominal direction in space.

5. A signal detection system, according to claim 1, in which a single optical fibre is positioned to collect electromagnetic signals from said same nominal direction in space, and a signal splitter is arranged to split any collected signal between said optical paths.

6. A signal detection system, according to claim 1, in which a lens system is arranged to focus said received signal transmitted by said optical paths onto said signal detector.

7. A signal detection system, according to claim 1, in which a signal combiner is arranged to combine said received signals transmitted by said optical paths and to transmit the combined signal to said signal detector.

8. A signal detection system, according to claim 1, including tagging means arranged to identify which of said optical paths has transmitted a received signal to said signal detector.

9. A signal detection system, according to claim 8, in which said tagging means comprises a tagger arranged in each of said optical paths and arranged to identify a signal transmitted by that optical path.

10. A signal detection system, according to claim 1, in which each of said optical paths includes a processing element to process a signal transmitted by that path.

11. A signal detection system, according to claim 1, in the form of an active system, in which said optical time delay is selected to define a series of ranges over which said received signal might have traveled to said signal detection system, and said signal detector is arranged to identify the range of a source of said signal by identifying the optical path through which said signal was transmitted.

12. A signal detection system, according to claim 1, in the form of a passive system in which said optical time delay is selected to enable said signal detector during a single duty cycle on-time to average the value of said received signal.

13. A signal detection system, according to claim 1, in the form of an active system including an electromagnetic energy transmitter, in which said received signal comprises a reflection of part of the electromagnetic energy by an object, and said optical time delay is selected to define a series of ranges over which said reflection might have traveled to said signal detection system, and said signal detector is arranged to identify the range of said object by identifying the optical path through which said reflection was transmitted.

14. A signal detection system, according to claim 13, which is mounted for scanning in small increments to receive said reflected signal from different directions, said transmitter is arranged to emit multiple bursts of electromagnetic energy to illuminate a volume in space, and said signal detector is arranged to have a series of duty cycle on-times coordinated with the bursts to detect any said reflection from said object.

15. A signal detection system, according to claim 13, comprising a plurality of signal detection systems arranged as a matrix of optical fibres, each of said optical fibres pointing in a different nominal direction, to receive reflections from said object and said signal detectors are arranged to form an image of said object.

16. A signal detection system, according to claim 13, comprising a plurality of signal detection systems arranged as a matrix of optical fibres, each of said optical fibres pointing in a different nominal direction, to receive reflections, an optical system arranged to focus any reflection from the object into the optical paths of said signal detectors, and said signal detectors are arranged to form an image of said object.

17. A method of detecting an electromagnetic signal travelling from a nominal direction in space using an electromagnetic signal detector having a limited duty cycle on-time for detecting receipt of electromagnetic signals, said method comprising the steps of:

receiving the signal in different time periods,

splitting the signal into portions and transmitting said portions along a plurality of paths,

delaying the passage of the split signal along some of said paths with respective optical delays,

detecting the portion of the signal that leaves each of said paths during said duty cycle on-time, and

extending the operational range of said signal detector by compressing the different time periods during which a signal can be received into the same duty cycle on-time of said signal detector.

18. A method, according to claim 17, including identifying the path through which the signal was received.

19. A method, according to claim 17, including averaging the signal leaving the paths.

20. A signal detection system comprising:

an electromagnetic signal detector having a limited on-time for detecting receipt of electromagnetic signals,

at least two optical paths each arranged to receive an electromagnetic signal from the same nominal direction in space and to transmit any received signal towards said signal detector,

an optical time delay operative within one of said optical paths to delay transmission of said received signal towards said signal detector, and said optical time delay is selected to extend the operational range of said signal detector by compressing the real time during which said received signal can be received into the shorter on-time of said signal detector, and

an electromagnetic energy transmitter, wherein said received signal comprises a reflection by an object of part of the electromagnetic energy transmitted by said transmitter, and said optical time delay is selected to define a series of ranges over which said reflection might have traveled to said signal detection system, and said signal detector is arranged to identify the range of said object by identifying the optical path through which said reflection was transmitted, wherein said signal detection system is mounted for scanning in small increments to receive said reflected signal from different directions, said transmitter is arranged to emit multiple bursts of electromagnetic energy to illuminate a volume in space, and said signal detector is arranged to have a series of on-times coordinated with the bursts to detect any said reflection from said object.