ELECTRO-OPTICAL TELEMETRY SYSTEM RECEIVER UTILIZING NEGATIVE FEEDBACK TO ELIMINATE ATMOSPHERICALLY INDUCED LOW FREQUENCY LIGHT BEAM INTENSITY VARIATIONS

• US 3,569,715 A
• Filed: 09/05/1968
• Issued: 03/09/1971
• Est. Priority Date: 09/05/1968
• Status: Expired due to Term

• Current Assignee: Robert R. Horning
• Original Assignee: Robert R. Horning
• Inventors: Horning, Robert R.
• Application Number:
  US04/757,657
• Time in Patent Office: 915 Days
• US Class Current: 398/119
• CPC Class Codes: G08C 23/04 using light waves, e.g. infrared
• CPC Class Codes: H04B 10/60 Receivers

Abstract

An electro-optical telemetry system wherein a light beam is modulated with high frequency information signals for transmission to a receiver that includes a photodetector for transducing the modulated light beam to electric information signals, a frequency filter connected to the output of the photodetector for extraction of low frequencies that are induced in the transmitted beam by atmospheric turbulence, and a light modulator at the receiver input to which the extracted low frequencies are negatively fed back to substantially eliminate the atmospherically induced variations in the received light beam.

Claims

1. In an electro-optical telemetry system including a source of light that is information-modulated at a high frequency and transmitted in a beam through an atmosphere subject to variable optical inhomogeneities that induce low frequency intensity variations in said beam, the combination of:

a. means for transducing said information-modulated light beam to electric information signals;

b. a frequency filter connected to the output of said transducing means for extracting low frequency electrical variations from said information signals;

c. modulating means interposed in the path of said beam between said source and said transducing means said modulating means being arranged to transmit said beam therethrough to said transducing means in a condition of information modulation that retains the information content of the beam during passage of the beam through said modulating means;

d. means for negatively feeding back to said modulating means said extracted low frequency electrical variations for inverse control of said modulating means for substantially eliminating said low frequency intensity variations induced in said transmitted light beam; and

e. wherein said modulating means includes;

a modulator responsive to said low frequency electrical variations to effect corresponding inverse polarization modulation of said beam within said modulator; and

means for converting said inverse polarization modulation of said beam into inverse intensity variations.

2. The combination of claim 1, further including biasing means coupled to said beam for providing said modulating means with an operating point around which said modulating means can be driven.

3. The combination of claim 2, wherein said biasing means is a source of DC voltage that is applied to said modulating means.

4. The combination of claim 1, further including means coupled to said beam for imposing information on said transmitted beam by polarizatiOn modulation, and modulation conversion means interposed between said source and said modulating means for converting the information modulation of the beam from polarization modulation to intensity modulation.

5. The combination of claim 4, wherein said transducing means is a photodetector, and said modulating means includes an electro-optical polarization modulator, and an optical analyzer interposed between said modulator and photodetector for transducing polarization modulation of said beam by said electro-optical polarization modulator to intensity modulation.