Systems and methods for optical demodulation in a depth-sensing device
An exemplary imaging device includes an optical sensor having an optical axis, a lens positioned to focus light from a scene onto the optical sensor, a matrix of variable-phase optical elements that are dimensioned to introduce at least two different phase delays into a wavefront of a light signal received from the scene through the lens, a housing that secures the matrix of variable-phase optical elements between the optical sensor and the lens, and a processing subsystem programmed to determine a phase difference associated with the light signal based on the at least two different phase delays. Related systems and methods are also provided.
1. An imaging device comprising:
an optical sensor having an optical axis;
a lens positioned to focus light from a scene onto the optical sensor;
a matrix of variable-phase optical elements that are dimensioned to introduce at least two different phase delays into a light signal received from the scene through the lens, the matrix of variable-phase optical elements:
directing, when in a first position, a portion of the light signal having a first phase delay of the at least two different phase delays to a first pixel of the optical sensor; and
directing, when at least one optical component of the imaging device is shifted laterally relative to another optical component of the imaging device, a portion of the light signal having a second phase delay of the at least two different phase delays to the first pixel of the optical sensor;
a housing that secures the matrix of variable-phase optical elements between the optical sensor and the lens; and
a processing subsystem programmed to determine a phase difference associated with the light signal based on the at least two different phase delays.
2. The imaging device of claim 1 , wherein the matrix of variable-phase optical elements comprises a diffractive optical element that directs the portion of the light signal having the first phase delay of the at least two different phase delays to the first pixel of the optical sensor and that directs the portion of the light signal having the second phase delay of the at least two different phase delays to a second pixel of the optical sensor.
3. The imaging device of claim 2 , wherein, when the at least one optical component of the imaging device is shifted laterally relative to the other optical component of the imaging device, the matrix of variable-phase optical elements directs a portion of the light signal having a third phase delay to the first pixel of the optical sensor and directs a portion of the light signal having a fourth phase delay to the second pixel of the optical sensor.
4. The imaging device of claim 2 , wherein the second phase delay of the at least two different phase delays is separated from the first phase delay of the at least two different phase delays by a predetermined fraction of a wavelength of the light carrying the light signal.
5. The imaging device of claim 1 , wherein an optical component of the imaging device directs:
a third portion of the light signal having a third phase delay of the at least two different phase delays to a third pixel of the optical sensor; and
a fourth portion of the light signal having a fourth phase delay of the at least two different phase delays to a fourth pixel of the optical sensor, the optical component comprising at least one of the lens, the optical sensor, or the matrix of variable-phase optical elements.
6. The imaging device of claim 5 , wherein:
the first phase delay of the at least two different phase delays is 90° out of phase from the second phase delay of the at least two different phase delays;
the second phase delay of the at least two different phase delays is 90° out of phase from the third phase delay of the at least two different phase delays; and
the third phase delay of the at least two different phase delays is 90° out of phase from the fourth phase delay of the at least two different phase delays, the first, second, third, and fourth phase delays producing signals that permit optical quadrature demodulation.
7. The imaging device of claim 1 , wherein the matrix of variable-phase optical elements comprises:
a first diffractive optical element (DOE) disposed between the lens and the optical sensor; and
a second DOE disposed between the lens and the first DOE, the first and second DOEs producing the at least two different phase delays.
8. The imaging device of claim 7 , wherein:
the first DOE comprises a first substrate having a first pattern of protruding features; and
the second DOE comprises a second substrate having a second pattern of protruding features, the first and second patterns of protruding features having different periodicities.
9. The imaging device of claim 8 , further comprising a positioning system that couples the first DOE and the second DOE to the housing, wherein the positioning system independently positions the first and second DOEs to alter a phase delay associated with a pixel of the optical sensor.
10. The imaging device of claim 1 , further comprising a light projector that projects the light signal as a pulsed light signal onto the scene to be imaged, the pulse light signal being reflected from objects in the scene and directed by the lens toward the optical sensor.
11. The imaging device of claim 1 , wherein:
the processing subsystem is programmed to perform a calibration of the delays of the at least two different phase delays; and
the processing subsystem is programmed to determine the phase difference associated with the light signal based on the calibration of the delays of the at least two different phase delays.
12. A depth imaging system comprising:
an imaging device comprising:
an optical sensor having an optical axis and an array of photosensitive pixels;
a lens positioned to focus light from a scene onto the optical sensor;
a diffractive optical element (DOE) having features that are dimensioned to introduce at least two different phase delays into a wavefront of a light signal received from the scene through the lens to at least partially optically demodulate the light signal, a width of at least one of the features of the DOE being substantially the same as a width of a first pixel of the array of photosensitive pixels;
a housing that secures the DOE between the optical sensor and the lens; and
a processing subsystem programmed to determine a phase difference associated with the light signal based on at least partially optically demodulated light received by the optical sensor from the DOE.
13. The depth imaging system of claim 12 , wherein:
the processing subsystem is programmed to perform a calibration of the delays of the at least two different phase delays; and
the processing subsystem determines the phase difference associated with the light signal based on the calibration of the delays of the at least two different phase delays.
14. The depth imaging system of claim 12 , wherein the DOE:
directs a first portion of the light signal having a first phase delay of the at least two different phase delays to the first pixel of the array of photosensitive pixels; and
directs a second portion of the light signal having a second phase delay of the at least two different phase delays to a second pixel of the array of photosensitive pixels.
15. The depth imaging system of claim 14 , wherein the DOE:
directs a third portion of the light signal having a third phase delay of the at least two different phase delays to a third pixel of the array of photosensitive pixels; and
directs a fourth portion of the light signal having a fourth phase delay of the at least two different phase delays to a fourth pixel of the array of photosensitive pixels.
16. The depth imaging system of claim 12 , wherein:
the optical sensor, the lens, and the DOE comprise optical components of the imaging device; and
when at least one of the optical components of the imaging device is shifted laterally relative to another of the optical components of the imaging device, the DOE:
directs a portion of the light signal having a first phase delay of the at least two different phase delays to the first pixel of the array of photosensitive pixels; and
directs a portion of the light signal having a second phase delay of the at least two different phase delays to a second pixel of the array of photosensitive pixels.
17. The depth imaging system of claim 12 , wherein a first phase delay of the at least two different phase delays is separated from a second phase delay of the at least two different phase delays by a predetermined fraction of a wavelength of the light carrying the light signal.
18. An imaging device comprising:
an optical sensor having an optical axis and an array of photosensitive pixels;
a lens positioned to focus light from a scene onto the optical sensor;
a diffractive optical element (DOE) having features that are dimensioned to introduce at least two different phase delays into a wavefront of a light signal received from the scene through the lens to at least partially optically demodulate the light signal;
a housing that secures the DOE between the optical sensor and the lens; and
a processing subsystem programmed to:
perform a calibration of the delays of the at least two different phase delays; and
determine a phase difference associated with the light signal based on the calibration of the delays of the at least two different phase delays and based on the at least partially optically demodulated light signal received by the optical sensor from the DOE.
19. The imaging device of claim 18 , wherein a width of at least one of the features of the DOE is substantially the same as a width of a first pixel of the array of photosensitive pixels.