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

• US 10,113,868 B2
• Filed: 10/16/2014
• Issued: 10/30/2018
• Est. Priority Date: 02/01/2010
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Inventors: Bamji, Cyrus
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US14/516,352
• Publication Number:
  US 20150036119A1
• Time in Patent Office: 1,475 Days
• Field of Search: 356 501
• 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 including a primary output source adapted to emit first energy S_out having a modulation frequency ω

and a phase φ

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

in S_in, said TOF system comprising;

at least one auxiliary wireless optical emitting (WOE) unit that includes at least one optical sensor for receiving a portion of S_out and is adapted to output second energy S_out-n at a frequency and phase derived from the received portion of S_out;

wherein said first energy and second optical energy are adapted to be received by said time of flight sensor in replicated modulation frequency and phase as optical energy S_out emitted by said TOF system when reflected by said target object.

2. The system of claim 1 wherein S_out-n is locked in frequency ω

and phase φ

with S_out.

3. The TOF system of claim 1, wherein the at least one WOE unit is configured to generate output optical energy S_out-n dynamically locked to at least one of modulation frequency and phase φ

of optical energy received by said WOE unit.

4. The TOF system of claim 3, wherein said at least one WOE unit includes:

a phase lock loop adapted to receive a fraction of emitted said S_out optical energy; and

adapted to generate optical energy S_out-n synchronizable with at least one of modulation frequency and phase of 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 adapted to generate 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 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 5, wherein the at least one WOE unit includes a processor operable to form a depth image using data acquired by at least a first sensor and a second sensor within said WOE unit, and identify from an output signal from each said sensor, which sensor output to use in driving said PLL.

7. The TOF system of claim 6, wherein said at least one WOE further includes memory storing best lock data for using in synchronizing said PLL.

8. 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 incoming signal 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;

transmitting optical energy S_out having a modulation frequency ω and

a phase φ

to illuminate a target object imaged by the system;

receiving a portion of optical energy S_out that the TOF system transmits to illuminate the target object;

synchronizing modulation of output optical energy from at least one auxiliary optical emitting unit to frequency and phase of the received portion of optical energy S_out transmitted by the TOF system;

using the synchronized optical energy output from the at least one auxiliary optical emitting unit to illuminate the target object; and

receiving optical energy reflected by the target object from the synchronized optical energy output of the at least one auxiliary optical emitting unit to determine distance Z.

9. The method of claim 8, and comprising:

receiving at least a fraction of optical energy S_out on each of

at least a first sensor and a second sensor within said at least one auxiliary optical emitter;

generating a depth image based on the optical energy received by the at least first and second sensors;

based on the depth image determining from which of the at least first and second sensors to use an output signal

to synchronize the modulation of output optical energy from the at least one auxiliary optical emitting unit.

10. The method of claim 8, further including positioning said at least one auxiliary optical emitting unit relative to said TOF system so as to increase at least one of amount of incoming optical energy from S_out received by the at least one auxiliary optical emitting unit, and amount of an optical energy S_out-n emitted by the at least one auxiliary optical emitting unit illuminating said target object.

11. The method of claim 8, further including determining a phase delay relative to S_out at which to synchronize modulation of output optical energy from the at least one auxiliary optical emitting unit.

12. The method of claim 11, wherein determining the phase delay comprises:

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

acquiring a respective depth image of said target object for each of the at least one auxiliary optical emitting unit using only optical energy emitted by the auxiliary optical emitting unit;

comparing said primary depth image with each of the respective depth images; and

determining the phase delay relative to S_out to be a phase delay that minimizes a difference in depth data between the primary depth image and the respective depth image.