Multiple synchronized optical sources for time-of-flight range finding systems

• US 8,891,067 B2
• Filed: 01/31/2011
• Issued: 11/18/2014
• Est. Priority Date: 02/01/2010
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Bamji, Cyrus
• Primary Examiner(s): RODRIGUEZ, VICENTE M
• Application Number:
  US13/018,293
• Publication Number:
  US 20110188027A1
• Time in Patent Office: 1,387 Days
• Field of Search: 356/5.01, 356/5.1
• US Class Current: 356/5.01
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/4815 using multiple transmitters
• CPC Class Codes: G01S 7/4911 Transmitters

Abstract

TOF system optical power is augmented using auxiliary optical emitter unit(s) that may be a wireless (WOE), or a plug-wired (PWOE). WOE units sense emitted TOF system optical energy S_out and emit optical energy S_out-n preferably dynamically synchronized in frequency and in phase to S_out as received by the WOE. Each WOE includes at least one optical sensor to detect S_out, and internal feedback ensuring that frequency and phase of the WOE emitted S_out-n optical energy are dynamically synchronized with frequency and phase of the TOF emitted S_out optical energy. PWOE units need no internal feedback but are calibrated by the TOF system to cause a close match between frequency and phase of the PWOE-emitted optical energy with what would be emitted by the TOF system primary optical source. If PWOE(s) are used in isolation, delay difference between PWOE and the TOF primary optical energy source can be software-compensated.

Claims

1. A phase-based time-of-flight (TOF) system that includes a primary optical source that emits optical energy S_out having a modulation frequency ω

and a phase φ and

a time of flight sensor which detects S_in, which is at least a fraction of emitted said optical energy that is reflected-back by a target object a distance Z away, and determines said distance Z from a shift in said phase φ

in S_in, said TOF system further including;

at least one auxiliary optical emitting unit whose output optical energy is substantially indistinguishable to said time of flight sensor from optical energy emitted by said primary optical source;

said auxiliary optical emitting unit including at least one of a wireless optical emitting (WOE) unit, and a plug-wired optical emitting (PWOE) unit;

wherein optical energy emitted by each said auxiliary optical emitting unit is substantially indistinguishable to said time of flight sensor in modulation frequency and phase as optical energy S_out emitted by said TOF system when reflected by said target object.

2. The TOF system of claim 1, wherein said at least one auxiliary optical emitting unit is a WOE unit disposed to receive a portion of emitted said optical energy S_out output by said TOF system, said S_out having a modulation frequency and a phase shift as received by said WOE unit, said WOE unit generating output optical energy S_out-n dynamically locked to at least one of modulation frequency and phase cp relative to optical energy received by said WOE unit;

wherein operation of said at least one WOE unit increases effective power of optical energy reflected back toward said TOF system by said target object.

3. The TOF system of claim 1, wherein said at least one WOE unit is disposed in at least one location selected from a group consisting of (a) disposing external to said TOF system, and (b) disposing a distance from said target object less than said distance Z.

4. The TOF system of claim 1, wherein said at least one WOE unit includes:

means for receiving a fraction of emitted said S_out optical energy; and

means for generating optical energy S_out-n synchronizable with at least one of modulation frequency and phase with TOF generated said S_out optical energy, as received by said WOE.

5. The TOF system of claim 1, wherein said at least one WOE unit includes:

a voltage controlled oscillator (VCO);

a phase-lock-loop (PLL) unit that generates an error signal representing at least one of error in said modulation frequency and error in said phase between said S_out and S_out-n, said error signal coupled in close loop feedback to said means for generating to lock at least one of modulation frequency and phase of S_out-n to modulation frequency and phase of said S_out.

6. The TOF system of claim 1, wherein said at least one WOE includes means for repositioning said WOE unit relative to said TOF system so as to increase at least one of amount of incoming optical energy from S_out received by said WOE, and amount of said S_now-n optical energy emitted by said WOE falling upon said target object.

7. The TOF system of claim 1, wherein:

said at least one auxiliary optical emitting unit is a PWOE unit, removably coupleable to said TOF system adjacent said primary optical source; and

said TOF system includes means for calibrating said PWOE unit for delay relative to said primary optical source.

8. The TOF system of claim 7, wherein said means for calibrating includes:

means for acquiring a primary depth image of said target object using only optical energy S_out emitted by said primary optical source;

means for acquiring a depth image of said target object using only optical energy emitted by each said PWOE unit, one unit at a time;

means for comparing, one at a time, said primary depth image with depth images acquired using optical energy emitted by each said PWOE unit; and

means for compensating delay associated with each said PWOE unit to minimize a difference between said primary depth image and a depth image acquired with optical energy emitted by each said PWOE unit after said compensation;

said means compensating using software without adjusting a delay of a PWOE unit.

9. The TOF system of claim 7, wherein said means for calibrating includes:

means for acquiring a primary depth image of said target object using only optical energy S_out emitted by said primary optical source;

means for acquiring a depth image of said target object using only optical energy emitted by each said PWOE unit, one unit at a time;

means for comparing said primary depth image with depth images acquired using optical energy emitted by each said PWOE unit; and

means for changing the delay of said PWOE unit such that a difference in depth data between at least one pixel in each acquired depth image is minimized.

10. The TOF system of claim 5, wherein said system includes at least one WOE unit that includes sensors receiving at least a fraction of optical energy S_out, said WOE unit including:

means for forming a depth image using data acquiring by at least a first sensor and a second sensor within said WOE unit, and

means for identifying from an output signal from each said sensor, which sensor output to use in driving said PLL.

11. The TOF system of claim 10, wherein said at least one WOE further includes memory storing best lock data for using in synchronizing said PLL.

12. A method of dynamically enhancing detection performance of a phase-based time-of-flight (TOF) system that emits optical energy S_out having a modulation frequency ω

and a phase φ and

a sensor array which detects S_in, which is at least a fraction of emitted said optical energy that is reflected-back by a target object a distance Z away, and determines said distance Z from a shift in said phase φ

in S_in, the method including;

using optical energy from at least one auxiliary optical emitting unit whose output optical energy is indistinguishable to said sensor array from optical energy emitted by said TOF system;

said auxiliary optical emitting unit including at least one of a wireless optical emitting (WOE) unit, and a plug-wired optical emitting (PWOE) unit;

wherein optical energy emitted by each said auxiliary optical emitting unit is indistinguishable to said sensor array in modulation frequency and phase as optical energy S_out emitted by said TOF system when reflected by said target object.

13. The method of claim 12, including disposing said at least one auxiliary optical emitting (WOE) unit to receive a portion of emitted said optical energy S_out generated by said TOF system, said S_out having a modulation frequency and a phase shift as received by said WOE unit, said WOE unit generating output optical energy S_out-n dynamically locked to at least one of modulation frequency and phase φ

relative to optical energy received by said WOE unit;

wherein operation of said at least one WOE unit increases effective power of optical energy reflected back toward said TOF system by said target object.

14. The method of claim 12, further including disposing said at least one WOE unit in at least one location selected from a group consisting of (a) disposing external to said TOF system, and (b) disposing a distance from said target object less than said distance Z.

15. The method of claim 12, further including providing said at least one WOE unit with:

means for receiving a fraction of emitted said S_out optical energy; and

means for generating optical energy S_out-n synchronizable with at least one of modulation frequency and phase with TOF generated said S_out optical energy, as received by said WOE.

16. The method of claim 12, further including providing said at least one WOE unit with a closed-loop feedback system to force synchronization of at least one of modulation frequency and phase of S_out-n to modulation frequency and phase of said S_out.

17. The method of claim 16, wherein said closed-loop feedback system includes:

a voltage controlled oscillator (VCO);

a phase-lock-loop (PLL) unit that generates an error signal representing at least one of error in said modulation frequency and error in said phase between said S_out and S_out-n, said error signal coupled in close loop feedback to said means for generating to lock at least one of modulation frequency and phase of S_now-n to modulation frequency and phase of said S_out.

18. The method of claim 12, further including repositioning said WOE unit relative to said TOF system so as to increase at least one of amount of incoming optical energy from S_out received by said WOE, and amount of said S_now-n optical energy emitted by said WOE falling upon said target object.

19. The method of claim 12, wherein said at least one auxiliary optical emitting unit is a plug-wired optical emitting (PWOE) unit, removably coupleable to said TOF system adjacent said primary optical source;

and

providing said TOF system with means for calibrating said PWOE for delay relative to said primary optical source.

20. The method of claim 19, wherein said means for calibrating includes:

acquiring a primary depth image of said target object using only optical energy S_out emitted by said primary optical source;

acquiring a depth image of said target object using only optical energy emitted by each said PWOE unit, one unit at a time;

comparing said primary depth image with depth images acquired using optical energy emitted by each said PWOE unit; and

compensating delay associated with each said PWOE unit such that a difference in depth data between at least one pixel in each acquired depth image is minimized.

21. The method of claim 17, wherein said TOF system includes at least one WOE unit having sensors that receive at least a fraction of optical energy S_out, said WOE unit carrying out the following steps:

forming a depth image using data acquiring by at least a first sensor and a second sensor within said WOE unit; and

identifying from an output signal from each said sensor, which sensor output to use in driving said PLL.

22. The method of claim 19, wherein said means for calibrating carries out the following steps:

acquiring a primary depth image of said target object using only optical energy S_out emitted by said primary optical source;

acquiring a depth image of said target object using only optical energy emitted by each said PWOE unit, one unit at a time;

comparing said primary depth image with depth images acquired using optical energy emitted by each said PWOE unit; and

changing delay of said PWOE unit such that a difference in depth data between at least one pixel in each acquired depth image is minimized.

23. The method of claim 12, wherein said auxiliary optical emitting unit is at least one said PWOE unit, the method further including;

disabling said primary source from outputting optical energy; and

operating said TOF system so as to acquire data using solely optical energy output by at least one said PWOE unit.

24. The method of claim 17, wherein said TOF system includes at least one WOE unit that includes sensors receiving at least a fraction of optical energy S_out, the method further including:

forming, within said at least one WOE unit, a depth image using data acquiring by at least a first sensor and second sensor within said WOE unit; and

identifying, within said at least one WOE unit, from an output signal from each of said sensor, which sensor output to use in driving said PLL.

25. The method of claim 24, further including storing within each said WOE unit, best lock data for using in synchronizing said PLL.