Absolute distance meter with optical switch

• US 8,659,749 B2
• Filed: 08/03/2010
• Issued: 02/25/2014
• Est. Priority Date: 08/07/2009
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Bridges, Robert E.
• Primary Examiner(s): Alsomiri, Isam
• Assistant Examiner(s): RODRIGUEZ, VICENTE M
• Application Number:
  US12/849,065
• Publication Number:
  US 20110032509A1
• Time in Patent Office: 1,302 Days
• Field of Search: 356/5.13
• US Class Current: 356/5.13
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

An absolute distance meter (ADM) that determines a distance to a target includes a light source that emits an emitted light beam. The ADM also includes a fiber switching network having at least one optical switch that switches between at least two positions in response to a switch control signal, a first one of the positions enabling a measure mode in which the emitted light beam is emitted from the fiber switching network towards the target and is reflected back as a measure light beam into the fiber switching network, a second one of the positions enabling a reference mode in which the light beam comprises a reference light beam within the fiber switching network. The ADM further includes a single channel detector that detects the measure and reference light beams in a temporally spaced multiplexed manner and provides an electrical signal which corresponds to the detected measure and reflected light beams. Also, the ADM includes a single channel signal processor that processes the electrical signal and provides a conditioned electrical signal in response thereto, and a data processor that processes the conditioned electrical signal to determine the distance to the target.

Claims

1. An absolute distance meter that determines a distance to a target, comprising:

a light source that emits a light beam;

a fiber switching network having at least one optical switch that switches between at least two routes in response to a switch control signal, a first one of the routes enabling a measure mode in which the light beam is emitted from the fiber switching network through an end of an optical fiber towards the target and is reflected back through the end of the optical fiber as a measure light beam and back into the fiber switching network, a second one of the routes enabling a reference mode in which the light beam comprises a reference light beam within the fiber switching network;

a single channel detector that detects the measure and reference light beams in a temporally spaced multiplexed manner and provides an electrical signal which corresponds to the detected measure and reference light beams;

a single channel signal processor that processes the electrical signal and provides a conditioned electrical signal in response thereto;

electronics that controls timing of the switch control signal; and

a data processor that processes the conditioned electrical signal to determine the distance to the target.

2. The absolute distance meter of claim 1, wherein the light source comprises a laser or superluminescent diode and wherein the light beam is a laser light beam or a superluminescent diode light beam.

3. The absolute distance meter of claim 1, wherein the single channel signal processor provides a modulation signal to the light source to modulate the light beam power, polarization, wavelength, phase, or combinations thereof in a manner that is sinusoidal, pulsed, chirped, or combinations thereof.

4. The absolute distance meter of claim 1, wherein the single channel signal processor provides the switch control signal to control the switching of the at least one optical switch between the measure mode route and the reference mode route.

5. The absolute distance meter of claim 1, wherein the absolute distance meter is for use within a laser tracker, total station, laser scanner, or handheld device.

6. The absolute distance meter of claim 1, wherein the fiber switching network further comprises:

at least one fiber optic coupler through which the emitted light beam and the measure and reference light beams pass; and

a partial fiber retroreflector;

wherein the at least one fiber optic coupler is optically connected to the single channel detector, to the light source, and to the at least one optical switch;

wherein in the measure mode the emitted light beam is sent from the light source through the at least one fiber optic coupler to the at least one optical switch that is in the measure mode route and to the target, and wherein the measure light beam from the target passes through the at least one optical switch that is in the measure mode route and through the at least one fiber optic coupler and to the single channel detector; and

wherein in the reference mode the emitted light beam is sent from the light source through the at least one fiber optic coupler to the at least one optical switch that is in the reference mode route and to the partial fiber retroreflector, and wherein the reference light beam reflected from the partial fiber retroreflector passes through the at least one optical switch that is in the reference mode route and through the at least one fiber optic coupler and to the single channel detector.

7. The absolute distance meter of claim 1, wherein the fiber switching network further comprises:

an optical circulator through which the emitted light beam and the measure and reference light beams pass; and

a partial fiber retroreflector;

wherein the optical circulator is optically connected to the single channel detector, to the light source, and to the at least one optical switch;

wherein in the measure mode the emitted light beam is sent from the light source through the optical circulator to the at least one optical switch that is in the measure mode route and to the target, and wherein the measure light beam from the target passes through the at least one optical switch that is in the measure mode route and through the optical circulator and to the single channel detector; and

wherein in the reference mode the emitted light beam is sent from the light source through the optical circulator to the at least one optical switch that is in the reference mode route and to the partial fiber retroreflector, and wherein the reference light beam reflected from the partial fiber retroreflector passes through the at least one optical switch that is in the reference mode route and through the optical circulator and to the single channel detector.

8. The absolute distance meter of claim 1, wherein the fiber switching network further comprises:

first and second fiber optic couplers through which the emitted light beam and the measure and reference light beams pass;

wherein the first fiber optic coupler is optically connected to the light source, to the at least one optical switch, and to the second fiber optic coupler;

wherein the second fiber optic coupler is optically connected to the first fiber optic coupler, to the at least one optical switch, and to the light source;

wherein in the measure mode the emitted light beam is sent from the light source through the first fiber optic coupler, through the second fiber optic coupler and to the target, and wherein the measure light beam from the target passes through the second fiber optic coupler and to the least one optical switch that is in the measure mode route and to the single channel detector; and

wherein in the reference mode the emitted light beam is sent from the light source through the first fiber optic coupler and to the at least one optical switch that is in the reference mode route, and to the single channel detector as the reference light beam.

9. The absolute distance meter of claim 1, wherein the fiber switching network further comprises:

at least one fiber optic coupler through which the emitted light beam and the measure and reference light beams pass;

second and third optical switches; and

a partial fiber retroreflector;

wherein the at least one fiber optic coupler is optically connected to the single channel detector, to the light source, and to the at least one optical switch;

wherein in the measure mode the emitted light beam is sent from the light source through the at least one fiber optic coupler to the at least one optical switch that is in the measure mode route, to the second optical switch that is in the measure mode route, and to the target, and wherein the measure light beam from the target passes through the second optical switch that is in the measure mode, through at least one optical switch that is in the measure mode route and through the at least one fiber optic coupler and to the single channel detector; and

wherein in the reference mode the emitted light beam is sent from the light source through the at least one fiber optic coupler to the at least one optical switch that is in the reference mode route, to the third optical switch that is in the reference mode route, and to the partial fiber retroreflector, and wherein the reference light beam reflected from the partial fiber retroreflector passes through the third optical switch that is in the reference mode route, through at least one optical switch that is in the reference mode route, and through the at least one fiber optic coupler and to the single channel detector.

10. The absolute distance meter of claim 1, wherein the fiber switching network further comprises:

at least one fiber optic coupler through which the emitted light beam and the measure and reference light beams pass;

a second optical switch; and

a partial fiber retroreflector;

wherein the at least one fiber optic coupler is optically connected to the single channel detector, to the light source, to the at least one optical switch, and to the second optical switch;

wherein in the measure mode the emitted light beam is sent from the light source through the at least one fiber optic coupler to the at least one optical switch that is in the measure mode route and to the target, and wherein the measure light beam from the target passes through the at least one optical switch that is in the measure mode route and through the at least one fiber optic coupler and to the single channel detector; and

wherein in the reference mode the emitted light beam is sent from the light source through the at least one fiber optic coupler to the second optical switch that is in the reference mode route and to the partial fiber retroreflector, and wherein the reference light beam reflected from the partial fiber retroreflector passes through the at least one optical switch that is in the reference mode route and through the at least one fiber optic coupler and to the single channel detector.

11. The absolute distance meter of claim 10, wherein the at least one optical switch and the second optical switch each comprises an optical modulator or attenuator that is driven between a first minimum level and a second maximum level in which the at least one optical switch and the second optical switch act as switches.

12. The absolute distance meter of claim 1, further comprising an optical assembly that receives the emitted light beam from the fiber switching network and transmits the emitted light beam towards the target, and that receives the measure light beam from the target and transmits the measure light beam toward the fiber switching network.

13. The absolute distance meter of claim 12, further comprising a visible laser light source that emits a visible laser, wherein the optical assembly includes optics that merges the emitted visible laser with the emitted light beam from the fiber switching network to form a composite emitted light beam and transmits the composite emitted light beam towards the target.

14. The absolute distance meter of claim 1, wherein the target is a retroreflector.

15. The absolute distance meter of claim 1, wherein the at least one optical switch comprises a second optical fiber that terminates in a low reflection termination.

16. The absolute distance meter of claim 1, wherein the light beam passes through the at least one optical switch in a first direction and the measure light beam passes through the at least one optical switch in a second direction opposite to the first direction.

17. The absolute distance meter of claim 1, wherein a second optical switch is cascaded with the at least one optical switch to increase isolation between the two routes.

18. An absolute distance meter that determines a distance to a target, comprising:

a laser that emits a laser beam;

a fiber switching network having an optical switch that switches between two routes in response to a switch control signal, a first route being a measure mode route in which the laser beam is emitted from the fiber switching network through an end of an optical fiber towards the target and is reflected back through the end of the optical fiber as a measure light beam into the fiber switching network, a second route being a reference mode route in which the light beam comprises a reference light beam within the fiber switching network;

a single channel detector that detects the measure and reference light beams in a multiplexed manner and provides an electrical signal which corresponds to the detected measure and reference light beams;

electronics that controls timing of the switch control signal; and

a processor that processes the electrical signal to determine the distance to the target.

19. The absolute distance meter of claim 18, wherein the processor provides a modulation signal to the laser to modulate the laser.

20. The absolute distance meter of claim 18, wherein the processor provides the switch control signal to control the switching of the optical switch between the measure mode route and the reference mode route.

21. The absolute distance meter of claim 18, wherein the absolute distance meter is for use within a laser tracker, total station, laser scanner, or handheld device, and wherein the target comprises a retroreflector.

22. The absolute distance meter of claim 18, further comprising an optical assembly that receives the emitted light beam from the fiber switching network and transmits the emitted light beam towards the target, and that receives the measure light beam from the target and transmits the reference light beam towards the fiber switching network.