Ranging system which compares an object-reflected component of a light beam to a reference component of the light beam

• US 4,533,242 A
• Filed: 09/28/1982
• Issued: 08/06/1985
• Est. Priority Date: 09/28/1982
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Psaltis, Demetri, Goss, Willis C., McLauchlan, John M., Tubbs, Eldred F., AuYeung, John
• Primary Examiner(s): BUCZINSKI, STEPHEN C
• Application Number:
  US06/425,202
• Time in Patent Office: 1,043 Days
• Field of Search: 356/5, 343/13 R
• US Class Current: 356/5.07
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32

Abstract

A system is described for measuring the distance to an object by comparing a first component (18) of a light pulse that is reflected off the object (14), with a second component (20) of the light pulse that passes along a reference path (26) of known length, which provides great accuracy with a relatively simple and rugged design. The reference path (26) can be changed in precise steps so that is has an equivalent length approximately equal to the path length of the light pulse component that is reflected from the object. The resulting small difference in path lengths can be precisely determined by directing the light pulse components into opposite ends of a detector (70) formed of a material that emits a second harmonic light output at the locations where the opposite-going pulses pass simultaneously across one another.

Claims

1. A distance measuring system comprising:

means for generating a pair of components of a pulse of light, including an object component and a reference component;

a detector assembly including a detector with opposite ends and a side, said detector formed of a material that produces a harmonic light output that can be detected at a side of the detector when components of a light pulse that are directed into the opposite ends of the detector pass simultaneously in opposite directions through at least a portion of the detector, said assembly also including means for indicating the position of harmonic light output from the detector;

means for directing the object component toward an object and directing light reflected from the object into a first end of the detector; and

means for directing the reference component along a reference path of known length and into the second end of the detector to determine the length of the object component path by the precise position at which it crosses the reference component path.

2. The apparatus described in claim 1 wherein:

said means for directing the reference component includes means for varying the reference path length in precisely known steps.

3. In a ranging system which includes a source that generates object and reference components of a brief light pulse, a first optical system that reflects the object component off an object-to-be-ranged and directs the reflected light to a comparing apparatus, and a second optical system that passes the reference component along a reference path of known equivalent length to the comparing apparatus, the improvement wherein:

said second optical system includes means for varying the reference optical path to an equivalent length almost equal to the path of the object beam component, whereby the comparing apparatus has to measure only slight differences in the beam component path lengths;

said means for varying the reference path includes a plurality of light transmitting elements, each having two delay paths along which light can pass, including a short length delay path and a longer length delay path, and also includes switch means operable to pass light along either of the delay paths, said light transmitting elements being connected in series.

4. The improvement described in claim 3 wherein:

the second delay paths of said devices vary in length in a geometric progression with each of a plurality of second delay paths having a length twice that of a next shorter second delay path.

5. In a ranging system which includes a source that generates object and reference components of a brief light pulse, a first optical system that reflects the object component off an object-to-be-ranged and directs the reflected light to a comparing apparatus, and a second optical system that passes the reference component along a reference path of known equivalent length to the comparing apparatus, the improvement wherein:

said second optical system includes means for varying the reference optical path to an equivalent length almost equal to the path of the object beam component, whereby the comparing apparatus has to measure only slight differences in the beam component path lengths;

said comparing apparatus includes a detector with opposite ends of a material that generates a second harmonic light output from light beams that pass simultaneously in opposite directions through the material and means for detecting said second harmonic light at a side of said material;

said first and second optical systems are positioned to direct said beam components into the opposite ends of said detector; and

said means for detecting said second harmonic light includes a linear array of photodetectors for detecting light at all locations along said detector where the components pass simultaneously across each other to enable determination of the center or other point of the area of second harmonic emission.