Retro detector system

• US 7,649,617 B2
• Filed: 09/10/2007
• Issued: 01/19/2010
• Est. Priority Date: 09/22/2006
• Status: Active Grant

• Current Assignee: Leica Geosystems AG (Hexagon AB)
• Original Assignee: Leica Geosystems AG (Hexagon AB)
• Inventors: Walsh, Gregory C.
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Ratcliffe; Luke D
• Application Number:
  US11/900,063
• Publication Number:
  US 20090128797A1
• Time in Patent Office: 862 Days
• Field of Search: 356 301- 22
• US Class Current: 356/5.01
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

A light detection system duplicates the dynamic range of low intensity non-cooperative targets for high intensity cooperative targets. Both dynamic ranges of return light pulses are supported at the same time. In one embodiment, two beam splitters are used to reduce the intensity of reflected light that is received from high intensity sources to levels that can be accurately ranged. Ambiguity between the two paths is resolved by using an additional detector. Alternatively, one beam splitter is used to reduce the intensity of reflected light that is received from high intensity sources to levels that can be accurately ranged. The beam splitter system increases the effective dynamic range of the detection and ranging system passively without any need to reconfigure the system.

Claims

1. A light detection system for detecting return light energy reflected from a target object, the light detection system comprising:

a first optical beam splitter that splits the return light energy into a first splitter large light energy portion and a first splitter small light energy portion;

a second optical beam splitter that splits the first splitter small light energy portion into a second splitter large light energy portion and a second splitter small light energy portion;

a first light energy detector that receives the first splitter large light energy portion via a long optical path and the second splitter small light energy portion via a short optical path such that the second splitter small light energy portion arrives at the first light energy detector before the first splitter large light energy portion, and in the event that the second splitter small light energy portion exceeds a first threshold light energy level of the first light energy detector, generates a stop signal; and

a second light energy detector that receives the second splitter large light energy portion and, in the event that the second splitter large light energy portion exceeds a threshold energy level of the second detector generates a latch signal or integrates to sufficient level, whereby, when the first light energy detector has generated the stop signal, the latch or integrator voltage level signal indicates that the stop signal was generated by the first light energy detector in response to the second splitter small light energy portion.

2. A light detection system for detecting a return laser light signal reflected from a target object, the light detection system comprising:

a first optical beam splitter that splits the return laser light signal into a primary laser light portion that comprises about 99% of the light energy of the return laser light signal and a secondary laser light portion that comprises about 1% of the light energy of the return laser light signal;

a second optical beam splitter that splits the secondary laser light portion into a low attenuation laser light portion that comprises about 90-99% of the light energy of the secondary laser light portion and a high attenuation laser light portion that comprises about 1-10% of the light energy of the secondary laser light portion;

a first photodetector having a first light energy threshold and that receives the low attenuation laser light portion from the second optical beam splitter and that, in the event that the low attenuation laser light portion exceeds the first light energy threshold, generates a latch signal or intensity level through integration; and

a second photodetector having a second light energy threshold and that receives the high attenuation laser light portion from the second optical beam splitter and the primary laser light portion from the first optical beam splitter and that generates a stop signal when light energy received by the second photodetector exceeds the second light energy threshold,

the latch signal generated by the first photodetector indicating that the stop signal generated by the second photodetector was generated in response to the high attenuation laser light portion received by the second photodetector from the second optical beam splitter.

3. A light detection system comprising:

a first optical beam splitter that splits light energy received by the first optical beam splitter into a large light energy portion and a small light energy portion;

a stop signal generator that generates a stop signal if light energy received by the stop signal generator exceeds a stop signal threshold level;

a long optical path connected between the first optical beam splitter and the stop signal generator to provide the large light energy portion to the stop signal generator at a first time;

a short optical path connected between the first optical beam splitter and the stop signal generator, the short optical path including a second optical beam splitter that splits the small light energy portion from the first optical beam splitter into a low attenuation light energy portion and a high attenuation light energy portion, the high attenuation light energy portion being provided to the stop signal generator in a second time that is shorter than the first time; and

a latch signal generator or signal integrator connected to receive the low attenuation light energy portion, and that generates a latch signal if the low attenuation light energy portion exceeds a latch signal threshold level, the latch signal indicating that a stop signal generated by the stop signal generator is in response to the high attenuation light energy portion.

4. A light detection system comprising:

a first optical beam splitter that splits light energy received by the first optical beam splitter into a large light energy portion and a small light energy portion;

a stop signal generator that generates a stop signal if light energy received by the stop signal generator exceeds a stop signal threshold level;

a long optical path connected between the first optical beam splitter and the stop signal generator to provide the large light energy portion to the stop signal generator at a first time;

a short optical path connected between the first optical beam splitter and the stop signal generator to provide the small light energy portion to the stop signal generator at a second time that is shorter than the first time; and

a latch signal generator or signal integrator connected to the stop signal generator which is armed for a fixed time period after the stop signal is generated to detect the presence of a second pulse, which, if detected, indicates that the response of the detector was from a high intensity received light energy signal.