Multi-mode frequency sweeping interferometer and method of using same

• US 9,857,160 B1
• Filed: 09/24/2014
• Issued: 01/02/2018
• Est. Priority Date: 09/24/2013
• Status: Active Grant

• Current Assignee: TVS Holdings, LLC (Safariland LLC)
• Original Assignee: TVS Holdings, LLC (Safariland LLC)
• Inventors: Hoffer, Jr., John M
• Primary Examiner(s): Barbee, Manuel L
• Application Number:
  US14/494,878
• Time in Patent Office: 1,196 Days
• CPC Class Codes: G01B 2290/25 Fabry-Perot in interferometer, e.g. etalon, cavity
• CPC Class Codes: G01B 9/02004 using frequency scans
• CPC Class Codes: G01B 9/02028 Two or more reference or object arms in one interferometer
• CPC Class Codes: G01B 9/0207 Error reduction by correction of the measurement signal based on independently determined error sources, e.g. using a reference interferometer
• CPC Class Codes: G01B 9/02075 of particular errors
• CPC Class Codes: G01B 9/02077 of the object
• CPC Class Codes: G01B 9/02081 simultaneous quadrature detection, e.g. by spatial phase shifting

Abstract

A multi-mode frequency sweeping interferometer has a single measurement light producing device configured to produce a coherent light source consisting of a single light beam. The single measurement light producing device transitions the single light beam between a fixed light beam and a scanning wavelength light beam. A primary beam splitter produces a first reference beam and a first measurement beam from said single light beam. The first reference beam is configured to travel a fixed path length to a primary reference reflector and the first measurement beam is configured to travel to and from a moveable reflective target over an unknown path length. A first interferometer is created by interfering the first reference beam with the first measurement beam and one or more optoelectronic devices may be configured to determine a measured distance to the movable reflective target.

Claims

1. A multi-mode frequency sweeping interferometer comprising:

a) a single measurement light producing device that produces a coherent light source consisting of a single outgoing light beam;

whereby said single measurement light producing device is configured to transition said single light beam between a fixed light beam to a scanning wavelength light beam;

b) a first distance measurement interferometer comprising;

one or more optics;

whereby said single outgoing light beam is split by a first beam splitter to produce a first reference beam and a first measurement beam;

whereby said first reference beam is configured to travel a path of fixed distance to and from a first reference reflector;

whereby said first measurement beam is configured to travel to a moveable reflective target of unknown distance and reflect back from said moveable reflective target as a return beam;

whereby said first reference beam and said return beam are combined by an interference optics to produce an interference beam;

c) one or more optoelectronic components that convert said interference beam into one or more first electrical signals;

d) a digitizing electronic feature that produces one or more first digital values from said first electrical signals;

e) a processor coupled to said digitizing electronics feature and said single measurement light producing device;

whereby said processor receives said one or more first digital values and calculates a distance to said moveable reflective target;

whereby said processor sends frequency control instructions to said single measurement light producing device to change the frequency of said scanning wavelength light beam;

whereby said multi-mode frequency sweeping interferometer operates in an absolute distance mode to provide an absolute distance measurement to said moveable reflective target using frequency scanning interferometry;

whereby said multi-mode frequency sweeping interferometer operates a in a relative distance mode to provide a relative distance measurement using fixed frequency interferometry;

whereby said multi-mode frequency sweeping interferometer is configured to transition between the absolute distance measurement mode and the relative distance measurement mode to determine a measured distance to said moveable reflective target; and

f) an interface to communicate said measured distance; and

g) an algorithm that controls the transition between the absolute distance measurement mode and the relative distance measurement mode as a function of the first electrical signals

wherein the multi-mode frequency sweeping interferometer automatically transitions between the absolute distance measurement mode and the relative distance measurement mode to determine a measured distance to the moveable reflective target.

2. The multi-mode frequency sweeping interferometer of claim 1, wherein the single light beam is a laser beam.

3. The multi-mode frequency sweeping interferometer of claim 1, further comprising an outgoing frequency measurement interferometer comprising:

a) one or more optics configured in the path of the single light beam before it reaches the moveable reflective target to derive a frequency measurement beam single light beam;

b) one or more optics configured in the path of said frequency measurement beam whereby an outgoing frequency interference beam is created;

c) one or more optoelectronic devices that convert said outgoing frequency interference beam into one or more second electrical signals; and

d) digitizing electronics that produce second digital values of said second electrical signals;

whereby the change in the optical frequency is measured and used to calculate the wavelength during a frequency scan; and

whereby the change in optical frequency is used as a feedback to control the frequency to a fixed value.

4. The multi-mode frequency interferometer of claim 3 wherein the one of more optics to create an outgoing frequency interference beam comprises a Fabry-Perot etalon.

5. The multi-mode frequency sweeping interferometer of claim 1, further comprising a second distance measurement interferometer comprising:

a) a second beam splitter configured between the first beam splitter and the first reference reflector that creates a second reference beam;

b) a third beam splitter configured between the first beam splitter and the movable reflective target to produce a second measurement beam;

c) a second combining optics that combines the second reference beam and second measurement beam into a second interference beam;

d) one or more optoelectronic devices that convert the second interference beam into a second electrical signal;

e) a digitizing electronic feature that produces a one or more of second digital values of said second electrical signals;

whereby the difference in distance as measured by the first distance measurement interferometer and the second distance measurement interferometer creates a reference distance that can be used to calculate the optical frequency;

whereby the calculated optical frequency is used to calculate an absolute distance to the target

whereby the calculated optical frequency can be used to control the laser to a fixed frequency.

6. The multi-mode frequency sweeping interferometer of claim 1 further comprising an index compensating feature that adjusts a measured distance value to a target as a function of a refractive index of air.

7. The multi-mode frequency sweeping interferometer of claim 1, further comprising a temperature compensating feature that adjusts a measured distance value to a target as a function of a temperature input.

8. The multi-mode frequency sweeping interferometer of claim 1, further comprising a frequency sweep rate algorithm that automatically adjust the frequency sweep rate.

9. The multi-mode frequency sweeping interferometer of claim 1, further comprising frequency sweep range algorithm that automatically adjust a frequency sweep range.

10. The multi-mode frequency sweeping interferometer of claim 1 further comprising a moveable platform;

wherein at least a portion of the optoelectronic components are coupled to the moveable platform,

whereby the single light beam can be directed by said moveable platform.

11. The multi-mode frequency sweeping interferometer of claim 10 wherein the measurement light producing device is mounted to the moveable platform.

12. The multi-mode frequency sweeping interferometer of claim 10, comprising a beam steering feature:

whereby the single light beam is directed by the beam steering feature.

13. The multi-mode frequency sweeping interferometer of claim 1, further comprising an outgoing frequency indicator comprising:

a) one or more optics configured in the path of the single light beam before it reaches the moveable reflective target to produce a frequency measurement beam;

b) one of more optics configured in the path of the frequency measurement beam to produce a frequency indicator beam;

c) one or more optoelectronic devices that convert said frequency indicator beam into an outgoing frequency electrical signal;

d) digitizing electronics that produce outing frequency digital values from said outgoing frequency electrical signal.

14. The multi-mode frequency sweeping interferometer of claim 13, wherein the one or more optics configured in the path of the frequency measurement beam comprises a Bragg reflector.

15. The multi-mode frequency sweeping interferometer of claim 1, further comprising a return frequency measurement interferometer comprising:

a) one or more optics configured in the path of the return beam to produce a return frequency measurement beam;

b) one or more optics configured in the path of said return frequency measurement beam whereby a return frequency interference beam is created;

c) one or more optoelectronic devices that convert said return frequency interference beam into one or more second electrical signals; and

d) digitizing electronics that produce second digital values of said second electrical signals;

whereby a change in the optical frequency between the single outgoing light beam and the return beam is measured and used to calculate the velocity of the moveable reflective target and;

whereby said process compensates for the calculated velocity to the moveable target in the calculated distance to said moveable reflective target.

16. The multi-mode frequency interferometer of claim 15 wherein the one of more optics to create a return frequency interference beam comprises a Fabry-Perot etalon.

17. The multi-mode frequency sweeping interferometer of claim 1, further comprising a return frequency indicator comprising:

a) one or more optics configured in the path of the return beam to produce a frequency measurement beam;

b) one or more optics configured in the path of the frequency measurement beam to produce a frequency indicator beam;

c) one or more optoelectronic devices that convert said frequency indicator beam into a return frequency electrical signal;

d) digitizing electronics that produce return frequency digital values from said outgoing frequency electrical signal

whereby a change in the optical frequency between the single outgoing light beam and the return beam is measured and used to calculate the velocity of the moveable reflective target; and

whereby said process compensates for the calculated velocity to the moveable target in the calculated distance to said moveable reflective target.

18. The multi-mode frequency sweeping interferometer of claim 17, wherein the one or more optics configured in the path of the frequency measurement beam comprises a Bragg reflector.

19. A multi-mode frequency sweeping interferometer comprising:

a) a single measurement light producing device that produces a coherent light source consisting of a single outgoing light beam;

whereby said single measurement light producing device is configured to transition said single light beam between a fixed light beam to a scanning wavelength light beam;

b) a first distance measurement interferometer comprising;

one or more optics;

whereby said single outgoing light beam is split by a first beam splitter to produce a first reference beam and a first measurement beam;

whereby said first reference beam is configured to travel a path of fixed distance to and from a first reference reflector;

whereby said first measurement beam is configured to travel to a moveable reflective target of unknown distance and reflect back from said moveable reflective target as a return beam;

whereby said first reference beam and said return beam are combined by an interference optics to produce an interference beam;

c) one or more optoelectronic components that convert said interference beam into one or more first electrical signals;

d) a digitizing electronic feature that produces one or more first digital values from said first electrical signals;

e) a processor coupled to said digitizing electronics feature and said single measurement light producing device;

whereby said processor receives said one or more first digital values and calculates a distance to said moveable reflective target;

whereby said processor sends frequency control instructions to said single measurement light producing device to change the frequency of said scanning wavelength light beam;

whereby said multi-mode frequency sweeping interferometer operates in an absolute distance mode to provide an absolute distance measurement to said moveable reflective target using frequency scanning interferometry;

whereby said multi-mode frequency sweeping interferometer operates in a relative distance mode to provide a relative distance measurement using fixed frequency interferometry;

whereby said multi-mode frequency sweeping interferometer is configured to transition between the absolute distance measurement mode and the relative distance measurement mode to determine a measured distance to said moveable reflective target,

f) an interface to communicate said measured distance;

g) a position sensing device that converts a positioning beam from a position sensing beam splitter to electrical signals; and

h) digitizing electronics that produce digital values of the position sensing device electrical signals;

wherein the position sensing device digital values are converted to a displacement value; and

whereby said position sensing device provides a transverse position the moveable target with respect to the measurement beam path.