Optical system for collecting distance information within a field

An optical system for collecting distance information within a field is provided. The optical system may include lenses for collecting photons from a field and may include lenses for distributing photons to a field. The optical system may include lenses that collimate photons passed by an aperture, optical filters that reject normally incident light outside of the operating wavelength, and pixels that detect incident photons. The optical system may further include illumination sources that output photons at an operating wavelength.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to the field of optical sensors and more specifically to a new and useful optical system for collecting distance information in the field of optical sensors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIG. 1, a one-dimensional optical system100for collecting distance information within a field includes: a set of illumination sources110arranged along a first axis, each illumination source in the set of illumination sources110configured to output an illuminating beam of an operating wavelength toward a discrete spot in the field ahead of the illumination source; a bulk imaging optic130characterized by a focal plane opposite the field; an aperture layer140coincident the focal plane, defining a set of apertures144in a line array parallel to the first axis, and defining a stop region146around the set of apertures144, each aperture in the set of apertures144defining a field of view in the field coincident a discrete spot output by a corresponding illumination source in the set of illumination sources110, the stop region146absorbing light rays reflected from surfaces in the field outside of fields of view defined by the set of apertures144and passing through the bulk imaging optic130; a set of lenses150, each lens in the set of lenses150characterized by a second focal length, offset from the focal plane opposite the bulk imaging optic130by the second focal length, aligned with an aperture in the set of apertures144, and configured to collimate light rays passed by the aperture; an optical filter160adjacent the set of lenses150opposite the aperture layer140and configured to pass light rays at the operating wavelength; a set of pixels170adjacent the optical filter160opposite the set of lenses150, each pixel in the set of pixels170corresponding to a lens in the set of lenses150and including a set of subpixels arranged along a second axis non-parallel to the first axis; and a diffuser180interposed between the optical filter160and the set of pixels170and configured to spread collimated light output from each lens in the set of lenses150across a set of subpixels of a corresponding pixel in the set of pixels170.

Generally, the one-dimensional optical system100(the “system”) functions as an image sensor that, when rotated about an axis parallel to a column of apertures, collects three-dimensional distance data of a volume occupied by the system. Specifically, the one-dimensional optical system100can scan a volume to collect three-dimensional distance data that can then be reconstructed into a virtual three-dimensional representation of the volume, such as based on recorded times between transmission of illuminating beams from the illumination sources and detection of photons—likely originating from the illumination sources—incident on the set of pixels170, based on phase-based measurements techniques, or based on any other suitable distance measurement technique. The system100includes: a column of offset apertures arranged behind a bulk imaging optic130and defining discrete fields of view in a field ahead of the bulk imaging optic130(that is non-overlapping fields of view beyond a threshold distance from the system); a set of illumination sources110that project discrete illuminating beams at an operating wavelength into (and substantially only into) the fields of view defined by the apertures; a column of lenses that collimate light rays passed by corresponding apertures; and an optical filter160that selectively passes a narrow band of wavelengths of light (i.e., electromagnetic radiation) including the operating wavelength; and a set of pixels170that detect incident photons (e.g., count incident photons, tracks times between consecutive incident photons). The system can therefore selectively project illuminating beams into a field ahead of the system according to an illumination pattern that substantially matches—in size and geometry across a range of distances from the system—the fields of view of the apertures. In particular, the illumination sources are configured to illuminate substantially only surfaces in the field ahead of the system that can be detected by pixels in the system such that minimal power output by the system (via the illumination sources) is wasted by illuminating surfaces in the field for which the pixels are blind. The system can therefore achieve a relatively high ratio of output signal (i.e., illuminating beam power) to input signal (i.e., photons passed to an incident on the pixel array). Furthermore, the set of lenses150can collimate light rays passed by adjacent apertures such that light rays incident on the optical filter160meet the optical filter160at an angle of incidence of approximately 0°, thereby maintaining a relatively narrow band of wavelengths of light passed by the optical filter160and achieving a relatively high signal-to-noise ratio (“SNR”) for light rays reaching the set of pixels170.

The system includes pixels arranged in a column and aligned with the apertures, and each pixel can be non-square in geometry (e.g., short and wide) to extend the sensing area of the system for a fixed aperture pitch and pixel column height. The system also includes a diffuser180that spreads light rays passed from an aperture through the optical filter160across the area of a corresponding pixel such that the pixel can detect incident photons across its full width and height thereby increasing the dynamic range of the system.

The system is described herein as projecting electromagnetic radiation into a field and detecting electromagnetic radiation reflected from a surface in the field back to bulk receiver optic. Terms “illumination beam,” “light,” “light rays,” and “photons” recited herein refer to such electromagnetic radiation. The term “channel” recited herein refers to one aperture in the aperture layer140, a corresponding lens in the set of lenses150, and a corresponding pixel in the set of pixels170.

1.2 Bulk Imaging Optic

The system includes a bulk imaging optic130characterized by a focal plane opposite the field. Generally, the bulk imaging optic130functions to project incident light rays from outside the system toward the focal plane where light rays incident on a stop region146of the aperture layer140are rejected (e.g., mirrored or absorbed) and where light rays incident on apertures in the aperture layer140are passed into a lens characterized by a focal length and offset from the focal plane by the focal length.

In one implementation, the bulk imaging optic130includes a converging lens, such as a bi-convex lens (shown inFIG. 2) or a plano-convex lens, characterized by a particular focal length at the operating wavelength of the system. The bulk imaging optic130can also include multiple discrete lens that cooperate to project light rays toward the aperture layer140and that are characterized by a composite focal plane opposite the field, as shown inFIG. 11. However, the bulk imaging optic130can be any other suitable type of lens or combination of lenses of any other type or geometry.

As shown inFIGS. 1 and 2, the system includes an aperture layer140coincident the focal plane, defining a set of apertures144in a line array parallel to the axes of the illumination sources, and defining a stop region146around the set of apertures144, wherein each aperture in the set of apertures144defines a field of view in the field coincident a discrete spot output by a corresponding illumination source in the set of illumination sources110, and wherein the stop region146absorbs and/or reflects light rays reflected from surfaces in the field outside of fields of view defined by the set of apertures144and passing through the bulk imaging optic130. Generally, the aperture layer140defines an array of open regions (i.e., apertures, including one aperture per lens) and closed regions (“stop regions”) between adjacent opens. Each aperture in the aperture layer140defines a “pinhole” that defines a field of view for its corresponding sense channel and passes light rights reflected from an external surface within its field of the view into its corresponding lens, and each stop region146can block light rays incident on select regions of the focal plane from passing into the lens array, as shown inFIG. 6.

The aperture layer140includes a relatively thin opaque structure coinciding with (e.g., arranged along) the focal plane of the bulk imaging optic130, as shown inFIGS. 1 and 2. For example, the aperture layer140can include a 10 micrometer-thick copper, silver, or nickel film deposited (e.g., plated) over a photocurable transparent polymer and then selectively etched to form the array of apertures. In a similar example, a reflective metalized layer or a light-absorbing photopolymer (e.g., a photopolymer mixed with a light absorbing dye) can be deposited onto a glass wafer and selectively cured with a photomask to form the aperture layer140and the set of apertures144. Alternatively, the aperture layer140can include a discrete metallic film that is mechanically or chemically perforated to form the array of apertures, bonded to the lens array, and then installed over the bulk imaging optic130along the focal plane. However, the aperture layer140can include any other reflective (e.g., mirrored) or light-absorbing material formed in any other way to define the array of apertures along the focal plane of the bulk imaging optic130.

In the one-dimensional optical system100, the aperture layer140can define a single column of multiple discrete circular apertures of substantially uniform diameter, wherein each aperture defines an axis substantially parallel to and aligned with one lens in the lens array, as shown inFIG. 3. Adjacent apertures are offset by an aperture pitch distance greater than the aperture diameter and substantially similar to the lens pitch distance, and the aperture layer140defines a stop region146(i.e., an opaque or reflecting region) between adjacent apertures such that the apertures define discrete, non-overlapping fields of view for their corresponding sense channels. At increasingly smaller diameters up to a diffraction-limited diameter—which is a function of wavelength of incident light and numeric aperture of the bulk imaging lens—an aperture defines a narrower field of view (i.e., a field of view of smaller diameter) and passes a sharper but lower-intensity (attenuated) signal from the bulk imaging optic130into its corresponding lens. The aperture layer140can therefore define apertures of diameter: greater than the diffraction-limited diameter for the wavelength of light output by the illumination sources (e.g., 900 nm); substantially greater than the thickness of the aperture layer140; and less than the aperture pitch distance, which is substantially equivalent to the lens pitch distance and the pixel pitch distance. In one example, aperture layer140can define apertures of diameters approaching the diffraction-limited diameter to maximize geometrical selectivity of the field of view of each sense channel. Alternatively, the apertures can be of diameter less that the diffraction-limited diameter for the wavelength of light output by the illumination sources. In one example, the aperture layer140can define apertures of diameters matched to a power output of illumination sources in the system and to a number and photon detection capacity of subpixel photodetectors in each pixel in the set of pixels170to achieve a target number of photons incident on each pixel within each sampling period. In this example, each aperture can define a particular diameter that achieves target attenuation range for pixels originating from a corresponding illumination source and incident on the bulk imaging optic130during a sampling period. In particular, because an aperture in the aperture layer140attenuates a signal passed to its corresponding lens and on to its corresponding pixel, the diameter of the aperture can be matched to the dynamic range of its corresponding pixel.

In one implementation, a first aperture141in the aperture layer140passes light rays—reflected from a discrete region of a surface in the field (the field of view of the sense channel) ahead of the bulk imaging optic130—into its corresponding lens; a stop region146interposed between the first aperture141and adjacent apertures in the aperture layer140blocks light rays—reflected from a region of the surface outside of the field of view of the first aperture141—from passing into the lens corresponding to the first aperture141. In the one-dimensional optical system100, the aperture layer140therefore defines a column of apertures that define multiple discrete, non-overlapping fields of view of substantially infinite depth of field, as shown inFIG. 2.

In this implementation, a first aperture141in the aperture layer140defines a field of view that is distinct and that does not intersect a field of view defined by another aperture in the aperture layer140, as shown inFIG. 2. The set of illumination sources110includes a first illumination source111paired with the first aperture141and configured to project an illuminating beam substantially aligned with (i.e., overlapping) the field of view of the first aperture141in the field ahead of the bulk imaging optic130. Furthermore, the first illumination source111and a bulk transmitting optic120can cooperate to project an illuminating beam of a cross-section substantially similar to (and slightly larger than) the cross section of the field of view of the first aperture141as various distances from the bulk imaging optic130. Therefore light output by the first illumination source111—paired with the first aperture141—and projected into the field of view of the first aperture141can remain substantially outside the fields of view of other apertures in the aperture layer140.

Generally, photons projected into the field by the first illumination source111illuminate a particular region of a surface (or multiple surfaces) in the field within the field of view of the first sense channel and are reflected (e.g., scattered) by the surface(s); at least some of these photons reflected by the particular region of a surface may reach the bulk imaging optic130, which directs these photons toward the focal plane. Because these photons were reflected by a region of a surface within the field of view of the first aperture141, the bulk imaging optic130may project these photons into the first aperture141, and the first aperture141may pass these photons into the first lens151(or a subset of these photons incident at an angle relative to the axis of the first aperture141below a threshold angle). However, because a second aperture142in the aperture layer140is offset from the first aperture141and because the particular region of the surface in the field illuminated via the first illumination source111does not (substantially) coincide with the field of view of the second aperture142, photons reflected by the particular region of the surface and reaching the bulk imaging optic130are projected into the second aperture142and passed to a second lens152behind the second aperture142, and vice versa, as shown inFIG. 2. Furthermore, a stop region146between the first and second apertures142can block photons directed toward the focal plane between the first and second apertures142reflected by the bulk imaging optic130, thereby reducing crosstalk between the first and second sense channels.

For a first aperture141in the aperture layer140paired with a first illumination source111in the set of illumination sources110, the first aperture141in the aperture layer140defines a first field of view and passes—into the first lens151—incident light rays originating at or reflected from a surface in the field coinciding with the first field of view. Because the first illumination source111projects an illuminating beam that is substantially coincident (and substantially the same size as or minimally larger than) the field of view defined by the first aperture141(as shown inFIG. 4), a signal passed into the first lens151by the first aperture141in the aperture layer140can exhibit a relatively high ratio of light rays originating from the first illumination source111to light rays originating from other illumination sources in the system. Generally, because various illumination sources in the system may output illuminating beams at different frequencies, duty cycles, and/or power levels, etc. at a particular time during operation, light rays passed from the bulk imaging optic130into a first pixel171in the set of pixels170but originating from an illumination source other than the first illumination source111paired with the first pixel171constitute noise at the first pixel171. Though the relatively small diameters of apertures in the aperture layer140may attenuate a total light signal passed from the bulk imaging optic130into the set of lenses150, each aperture in the aperture layer140may pass a relatively high proportion of photons originating from its corresponding illumination source than from other illumination sources in the system; that is, due to the geometry of a particular aperture and its corresponding illumination source, a particular aperture may pass a signal exhibiting a relatively high SNR to its corresponding lens and thus into its corresponding pixel. Furthermore, at smaller aperture diameters in the aperture layer140—and therefore smaller fields of view of corresponding channels—the system can pass less noise from solar radiation or other ambient light sources to the set of pixels170.

In one variation, the system includes a second aperture layer interposed between the lens array and the optical filter160, wherein the second aperture layer defines a second set of apertures144, each aligned with a corresponding lens in the set of lenses150, as described above. In this variation, an aperture in the second aperture layer140can absorb or reflect errant light rays passed by a corresponding lens, as described above, to further reduce crosstalk between channels, thereby improving SNR within the system. Similarly, the system can additionally or alternatively include a third aperture layer interposed between the optical filter160and the diffuser(s)180, wherein the third aperture layer defines a third set of apertures144, each aligned with a corresponding lens in the set of lenses150, as described above. In this variation, an aperture in the third aperture layer can absorb or reflect errant light rays passed by the light filter, as described above, to again reduce crosstalk between channels, thereby improving SNR within the system.

1.4 Lens Array

The system includes a set of lenses150, wherein each lens in the set of lenses150is characterized by a second focal length, is offset from the focal plane opposite the bulk imaging optic130by the second focal length, is aligned with a corresponding aperture in the set of apertures144, and is configured to collimate light rays passed by the corresponding aperture. Generally, a lens in the set of lenses150functions to collimate lights rays passed by its corresponding aperture and to pass these collimated light rays into the optical filter160.

In the one-dimensional optical system100, the lenses are arranged in a single column, and adjacent lenses are offset by a uniform lens pitch distance (i.e., a center-to-center-distance between adjacent pixels), as shown inFIG. 3. The set of lenses150is interposed between the aperture layer and the optical filter160. In particular, each lens can include a converging lens characterized by a second focal length and can be offset from the focal plane of the bulk imaging optic130—opposite the bulk imaging optic130—by the second focal length to preserve the aperture of the bulk imaging optic130and to collimate light incident on the bulk imaging optic130and passed by a corresponding aperture. Each lens in the set of lens can be characterized by a relatively short focal length (i.e., less than a focal length of the bulk imaging optic130) and a relatively large marginal ray angle (e.g., a relatively high numeric aperture lens) such that the lens can capture highly-angled light rays projected toward the lens by the extent of the bulk imaging optic130. That is, each lens in the set of lens can be characterized by a ray cone substantially matched to a ray cone of the bulk imaging optic130.

Lenses in the set of lenses150can be substantially similar. A lens in the set of lenses150is configured to collimate light rays focused into its corresponding aperture by the bulk imaging optic130. For example, a lens in the set of lenses150can include a bi-convex or plano-convex lens characterized by a focal length selected based on the size (e.g., diameter) of its corresponding aperture and the operating wavelength of the system. In this example, the focal length (f) of a lens in the set of lenses150can be calculated according to the formula:

f=d22⁢λ
where d is the diameter of the corresponding aperture in the aperture layer and A is the operating wavelength of light output by the illumination source (e.g., 900 nm). The geometry of a lens in the set of lenses150can therefore be matched to the geometry of a corresponding aperture in the aperture layer such that the lens passes a substantially sharp image of light rays—at or near the operating wavelength—into the optical filter160and thus on to the pixel array.

However, the set of lenses150can include lenses of any other geometry and arranged in any other way adjacent the aperture layer.

1.5 Optical Filter

As shown inFIG. 3, the system includes an optical filter160adjacent the set of lenses150opposite the aperture layer and configured to pass light rays at the operating wavelength. Generally, the optical filter160receives electromagnetic radiation across a spectrum from the set of lenses150, passes a relatively narrow band of electromagnetic radiation—including radiation at the operating wavelength—to the pixel array, and blocks electromagnetic radiation outside of the band. In particular, electromagnetic radiation other than electromagnetic radiation output by the illumination source—such as ambient light—incident on a pixel in the set of pixels170constitutes noise in the system. The optical filter160therefore functions to reject electromagnetic radiation outside of the operating wavelength or, more pragmatically, outside of a narrow wavelength band, thereby reducing noise in the system and increasing SNR.

In one implementation, the optical filter160includes an optical bandpass filter that passes a narrow band of electromagnetic radiation substantially centered at the operating wavelength of the system. In one example, the illumination sources output light (predominantly) at an operating wavelength of 900 nm, and the optical filter160is configured to pass light between 899.95 nm and 900.05 nm and to block light outside of this band.

The optical filter160may selectively pass and reject wavelengths of light as a function of angle of incidence on the optical filter160. Generally, optical bandpass filters may pass wavelengths of light inversely proportional to their angle of incidence on the light optical bandpass filter. For example, for an optical filter160including a 0.5 nm-wide optical bandpass filter, the optical filter160may pass over 95% of electromagnetic radiation over a sharp band from 899.75 nm to 900.25 nm and reject approximately 100% of electromagnetic radiation below 899.70 nm and above 900.30 nm for light rays incident on the optical filter160at an angle of incidence of approximately 0°. However, in this example, the optical filter160may pass over 95% of electromagnetic radiation over a narrow band from 899.5 nm to 900.00 nm and reject approximately 100% of electromagnetic radiation over a much wider band below 899.50 nm and above 900.30 nm for light rays incident on the optical filter160at an angle of incidence of approximately 15°. Therefore, the incidence plane of the optical filter160can be substantially normal to the axes of the lenses, and the set of lenses150can collimate light rays received through a corresponding aperture and output these light rays substantially normal to the incidence plane of the optical filter160(i.e., at an angle of incidence of approximately 0° on the optical filter). Specifically, the set of lenses150can output light rays toward the optical filter160at angles of incidence approximating 0° such that substantially all electromagnetic radiation passed by the optical filter160is at or very near the operating wavelength of the system.

In the one-dimensional optical system100, the system can include a single optical filter160that spans the column of lens in the set of lenses150. Alternatively, the system can include multiple optical filters160, each adjacent a single lens or a subset of lenses in the set of lenses150. However, the optical filter160can define any other geometry and can function in any other way to pass only a limited band of wavelengths of light.

1.6 Pixel Array and Diffuser

The system includes a set of pixels170adjacent the optical filter160opposite the set of lenses150, each pixel in the set of pixels170corresponding to a lens in the set of lenses150and including a set of subpixels arranged along a second axis non-parallel to the first axis. Generally, the set of pixels170are offset from the optical filter160opposite the set of lenses150, and each pixel in the set of pixels170functions to output a single signal or stream of signals corresponding to the count of photons incident on the pixel within one or more sampling periods, wherein each sampling period may be picoseconds, nanoseconds, microseconds, or milliseconds in duration.

The system also includes a diffuser180interposed between the optical filter160and the set of pixels170and configured to spread collimated light output from each lens in the set of lenses150across a set of subpixels of a single corresponding pixel in the set of pixels170. Generally, for each lens in the set of lenses150, the diffuser180functions to spread light rays—previously collimated by the lens and passed by the optical filter160—across the width and height of a sensing area within a corresponding pixel. The diffuser180can define a single optic element spanning the set of lenses150, or the diffuser180can include multiple discrete optical elements, such as including one optical diffuser element aligned with each channel in the system.

In one implementation, a first pixel171in the set of pixels170includes an array of single-photon avalanche diode detectors (hereinafter “SPADs”), and the diffuser180spreads lights rays—previously passed by a corresponding first aperture141, collimated by a corresponding first lens151, and passed by the optical filter160—across the area of the first pixel171, as shown inFIGS. 3, 5, and 6. Generally, adjacent apertures can be aligned and offset vertically by an aperture pitch distance, adjacent lenses can be aligned and offset vertically by a lens pitch distance substantially identical to the aperture pitch distance, and adjacent pixels can be aligned and offset vertically by a pixel pitch distance substantially identical to the lens and aperture pitch distances. However, the pixel pitch distance may accommodate only a relatively small number of (e.g., two) vertically-stacked SPADs. Each pixel in the set of pixels170can therefore define an aspect ratio greater than 1:1, and the diffuser180can spread light rays passed by the optical filter160according to the geometry of a corresponding pixel in order to accommodate a larger sensing area per pixel.

In one example, each pixel in the set of pixels170is arranged on an image sensor, and a first pixel171in the set of pixels170includes a single row of 16 SPADs spaced along a lateral axis perpendicular to a vertical axis bisecting the column of apertures and lenses. In this example, the height of a single SPAD in the first pixel171can be less than the height (e.g., diameter) of the first lens151, but the total length of the 16 SPADs can be greater than the width (e.g., diameter) of the first lens151; the diffuser180can therefore converge light rays output from the first lens151to a height corresponding to the height of a SPAD at the plane of the first pixel171and can diverge light rays output from the first lens151to a width corresponding to the width of the 16 SPADs at the plane of the first pixel171. In this example, the remaining pixels in the set of pixels170can include similar rows of SPADs, and the diffuser180can similarly converge and diverge light rays passed by corresponding apertures onto corresponding pixels.

In the foregoing example, the aperture layer can include a column of 16 like apertures, the set of lenses150can include a column of 16 like lenses arranged behind the aperture layer, and the set of pixels170can include a set of 16 like pixels—each including a similar array of SPADs—arranged behind the set of lenses150. For a 6.4 mm-wide, 6.4 mm-tall image sensor, each pixel can include a single row of 16 SPADs, wherein each SPAD is electrically coupled to a remote analog front-end processing electronics/digital processing electronics circuit240. Each SPAD can be arranged in a 400 μm-wide, 400 μm-tall SPAD area and can define an active sensing area approaching 400 μm in diameter. Adjacent SPADs can be offset by a SPAD pitch distance of 400 μm. In this example, the aperture pitch distance along the vertical column of apertures, the lens pitch distance along the vertical column of lenses, and the pixel pitch distance along the vertical column of pixels can each be approximately 400 μm accordingly. For the first sense channel in the system (i.e., the first aperture141, the first lens151, and the first pixel171, etc.), a first diffuser180can diverge a cylindrical column of light rays passed from the first lens151through the optical filter160—such as a column of light approximately 100 μm in diameter for an aperture layer aspect ratio of 1:4—to a height of approximately 400 μm aligned vertically with the row of SPADs in the first pixel171. The first diffuser can similarly diverge the cylindrical column of light rays passed from the first lens151through the optical filter160to a width of approximately 6.4 μm centered horizontally across the row of SPADs in the first pixel171. Other diffusers180in the system can similarly diverge (or converge) collimated light passed by corresponding lenses across corresponding pixels in the set of pixels170. Therefore, in this example, by connecting each SPAD (or each pixel) to a remote analog front-end processing electronics/digital processing electronics circuit240and by incorporating diffusers180that spread light passed by the optical filter160across the breadths and heights of corresponding pixels, the system can achieve a relatively high sensing area fill factor across the imaging sensor.

Therefore, in the one-dimensional optical system100, pixels in the set of pixels170can include an array of multiple SPADS arranged in aspect ratio exceeding 1:1, and the diffuser180can spread light rays across corresponding non-square pixels that enables a relatively large numbers of SPADs to be tiled across a single pixel to achieve a greater dynamic range across the image sensor than an image sensor with a single SPAD per pixel, as shown inFIG. 3. In particular, by incorporating multiple SPADs per pixel (i.e., per sense channel), a first sense channel in the system can detect multiple incident photons—originating from a surface in the field bound by a field of view defined by the first aperture141—within the span of the dead time characteristic of the SPADs. The first sense channel can therefore detect a “brighter” surface in its field of view. Additionally or alternatively, the first pixel171in the first sense channel can be sampled faster than the dead time characteristic of SPADs in the first pixel171because, though a first subset of SPADs in the first pixel171may be down (or “dead”) during a first sampling period due to collection of incident photons during the first sampling period, other SPADs in the first pixel171remain on (or “alive”) and can therefore collect incident photons during a subsequent sampling period. Furthermore, by incorporating pixels characterized by relatively high aspect ratios of photodetectors, the image sensor can include pixels offset by a relatively small pixel pitch, but the system100can still achieve a relatively high dynamic range pixel.

However, pixels in the set of pixels170can include any other number of SPADs arranged in any other arrays, such as in a 64-by-1 grid array (as described above), in a 32-by-2 grid array, or in a 16-by-4 grid array, and the diffuser180can converge and/or diverge collimated light rays onto corresponding pixels accordingly in any other suitable way. Furthermore, rather than (or in addition to) SPADs, each pixel in the set of pixels170can include one or more linear avalanche photodiodes, Geiger mode avalanche photodiodes, photomultipliers, resonant cavity photodiodes, QUANTUM DOT detectors, or other types of photodetectors arranged as described above, and the diffuser(s)180can similarly converge and diverge signals passed by the optical filter(s)160across corresponding pixels, as described herein.

The system includes a set of illumination sources110arranged along a first axis, each illumination source in the set of illumination sources110configured to output an illuminating beam of an operating wavelength toward a discrete spot in a field ahead of the illumination source. Generally, each illumination source functions to output an illuminating beam coincident a field of view defined by a corresponding aperture in the set of apertures144, as shown inFIGS. 1 and 2.

In one implementation, the set of illumination sources110includes a bulk transmitter optic and one discrete emitter per sense channel. For example, the set of illumination sources110can include a monolithic VCSEL arrays including a set of discrete emitters. In this implementation, the bulk transmitter optic can be substantially identical to the bulk imaging optic130in material, geometry (e.g., focal length), thermal isolation, etc., and the bulk transmitter optic is adjacent and offset laterally and/or vertically from the bulk imaging optic130. In a first example, set of illumination sources110includes a laser array including discrete emitters arranged in a column with adjacent emitters offset by an emitter pitch distance substantially identical to the aperture pitch distance. In this first example, each emitter outputs an illuminating beam of diameter substantially identical to or slightly greater than the diameter of a corresponding aperture in the apertures layer, and the column of emitters is arranged along the focal plane of the bulk transmitter optic such that each illuminating beam projected from the bulk transmitter optic into the field intersects and is of substantially the same size and geometry as the field of view of the corresponding sense channel, as shown inFIG. 4. Therefore, substantially all power output by each emitter in the set of illumination sources110can be projected into the field of view of its corresponding sense channel with relatively minimal power wasted illuminating surfaces in the field outside of the fields of view of the sense channels.

In a second example, the discrete emitters are similarly arranged in a column with adjacent emitters offset by an emitter pitch distance twice the aperture pitch distance, as shown inFIG. 2. In this second example, each emitter is characterized by an illuminating active area (or aperture) of diameter approximately (or slightly greater than) twice the diameter of a corresponding aperture in the apertures layer, and the column of emitters is offset behind the bulk transmitter optic by twice the focal length of the bulk transmitter optic such that each illuminating beam projected from the bulk transmitter optic into the field intersects and is of substantially the same size and geometry as the field of view of the corresponding sense channel, as described above. Furthermore, for the same illumination beam power density, an illuminating beam output by an emitter in this second example may contain four times the power of an illuminating beam output by an emitter in the first example described above. The system can therefore include a set of emitter arranged according to an emitter pitch distance, configured to output illuminating beams of diameter, and offset behind the bulk transmitter optic by an offset distance as a function of a scale factor (e.g., 2.0 or 3.0) and 1) the aperture pitch distance in the aperture layer, 2) the diameter of apertures in the aperture layer, and 3) the focal length of bulk transmitter optic, respectively. The system can therefore include an illuminating subsystem that is proportionally larger than a corresponding receiver subsystem to achieve greater total output illumination power within the same beam angles and fields of view of corresponding channels in the receiver subsystem.

The system can also include multiple discrete sets of illumination sources, each set of illumination sources110paired with a discrete bulk transmitter optic adjacent the bulk imaging optic130. For example, the system can include a first bulk transmitter optic, a second bulk transmitter optic, and a third bulk transmitter optic patterned radially about the bulk imaging optic130at a uniform radial distance from the center of the bulk imaging optic130and spaced apart by an angular distance of 120°. In this example, the system can include a laser array with one emitter—as described above—behind each of the first, second, and third bulk transmitter optics. Each discrete laser array and its corresponding bulk transmitter optic can thus project a set of illuminating beams into the fields of view of defined by corresponding in the apertures in the aperture layer. Therefore, in this example, the three discrete laser arrays and the three corresponding bulk transmitter optics can cooperate to project three times the power onto the fields of view of the sense channels in the system, as compared to a single laser array and one bulk transmitter optic. Additionally or alternatively, the system can include multiple discrete layer arrays and bulk transmitter optics to both: 1) achieve a target illumination power output into the field of view of each sensing channel in the receiver subsystem with multiple lower-power emitters per sensing channel; and 2) distribute optical energy over a larger area in the near-field to achieve an optical energy density less than a threshold allowable optical energy density for the human eye.

However, the system can include any other number and configuration of illumination source sets and bulk transmitter optics configured to illuminate fields of view defined by the sense channels. The set of illumination sources110can also include any other suitable type of optical transmitter, such as a 1×16 optical splitter powered by a single laser diode, a side-emitting laser diode array, an LED array, or a quantum dot LED array, etc.

In one implementation, the bulk receiver lens, the aperture layer, the set of lenses150, the optical filter160, and the diffuser180are fabricated and then aligned with and mounted onto an image sensor. For example, the optical filter160can be fabricated by coating a fused silica substrate. Photoactive optical polymer can then be deposited over the optical filter160, and a lens mold can be placed over the photoactive optical polymer and a UV light source activated to cure the photoactive optical polymer in the form of lenses patterned across the optical filter160. Standoffs can be similarly molded or formed across the optical filter160via photolithography techniques, and an aperture layer defined by a selectively-cured, metallized glass wafer can then be bonded or otherwise mounted to the standoffs to form the aperture layer. The assembly can then be inverted, and a set of discrete diffusers and standoffs can be similarly fabricated across the opposite side of the optical filter160. A discrete image sensor can then be aligned with and bonded to the standoffs, and a bulk imaging optic130can be similarly mounted over the aperture layer.

Alternatively, photolithography and wafer level bonding techniques can be implemented to fabricate the bulk imaging optics, the aperture layer, the set of lenses150, the optical filter160, and the diffuser180directly on to the un-diced semiconductor wafer containing the detector chips in order to simplify manufacturing, reduce cost, and reduce optical stack height for decreased pixel crosstalk.

One variation of the system includes: a set of illumination sources110arranged along a first axis, each illumination source in the set of illumination sources110configured to output an illuminating beam of an operating wavelength toward a discrete spot in a field ahead of the illumination source; a bulk imaging optic130characterized by a focal plane opposite the field; a set of lens tubes210arranged in a line array parallel to the first axis, each lens tube in the set of lens tubes210including: a lens characterized by a focal length, offset from the focal plane by the focal length, and configured to collimate light rays reflected into the bulk imaging optic130from a discrete spot in the field illuminated by a corresponding illumination source in the set of optics into the bulk imaging optic130; and a cylindrical wall218extending from the lens opposite the focal plane, defining a long axis substantially perpendicular to the first axis, and configured to absorb incident light rays reflected into the bulk imaging optic130from a region in the field outside the discrete spot illuminated by the corresponding illumination source. In this variation, the system also includes: an optical filter160adjacent the set of lens tubes210opposite the focal plane and configured to pass light rays at the operating wavelength; a set of pixels170adjacent the optical filter160opposite the set of lenses150, each pixel in the set of pixels170corresponding to a lens in the set of lenses150and including a set of subpixels aligned along a third axis perpendicular to the first axis; and a diffuser180interposed between the optical filter160and the set of pixels170and configured to spread collimated light output from each lens in the set of lenses150across a set of subpixels of a corresponding pixel in the set of pixels170.

Generally, in this variation, the system includes a lens tube in replacement of (or in addition to) each aperture and lens pair described above. In this variation, each lens tube can be characterized by a second (short) focal length and can be offset from the focal plane of the bulk imaging optic130by the second focal length to preserve the aperture of the bulk imaging optic130and to collimate incident light received from the bulk imaging optic130, as described above and as shown inFIGS. 5 and 7.

Each lens tube also defines an opaque cylindrical wall218defining an axis normal to the incidence plane of the adjacent optical filter160and configured to absorb incident light rays, as shown inFIG. 5. Generally, at greater axial lengths, the cylindrical wall218of a lens tube may absorb light rays passing through the lens tube at shallower angles to the axis of the lens tube, thereby reducing the field of view of the lens tube (which may be similar to decreasing the diameter of an aperture in the aperture layer up to the diffraction-limited diameter, as described above) and yielding an output signal of collimated light rays nearer to perpendicular to the incidence plane of the optical filter160. Each lens tube can therefore define an elongated cylindrical wall218of length sufficient to achieve a target field of view and to pass collimated light rays at maximum angles to the axis of the lens tube less than a threshold angle. In this variation, a lens tube can thus function as an aperture-sense pair described above to define a narrow field of view and to output substantially collimated light to the adjacent optical filter160.

The cylindrical wall218of a lens tube can define a coarse or patterned opaque interface about a transparent (or translucent) lens material, as shown inFIG. 5, to increase absorption and decrease reflection of light rays incident on the cylindrical wall218. Each lens tube (and each lens described above) can also be coated with an anti-reflective coating.

As shown inFIG. 9, in this variation, the set of lens tubes210can be fabricated by implementing photolithography techniques to pattern a photoactive optical polymer (e.g., SU8) onto the optical filter160(e.g., on a silicon wafer defining the optical filter). A light-absorbing polymer can then be poured between the lens tubes and cured. A set of lenses150can then be fabricated (e.g., molded) separately and then bonded over the lens tubes. Alternatively, lenses can be fabricated directly onto the lens tubes by photolithography techniques. Yet alternatively, a mold for lenses can be cast directly onto the lens tubes by injecting polymer into a mold arranged over the lens tubes. A singular diffuser180or multiple discrete diffusers180can be similarly fabricated and/or assembled on the optical filter160opposite the lens tubes. Standoffs extending from the optical filter160can be similarly fabricated or installed around the diffuser(s)180, and the image sensor can be aligned with and bonded to the standoffs opposite the optical filter160. Other optical elements within the system (e.g., the bulk imaging lens, the bulk transmitting lens, etc.) can be fabricated according to similar techniques and with similar materials.

Another variation of the system includes: a set of illumination sources110arranged in a first rectilinear grid array, each illumination source in the set of illumination sources110configured to output an illuminating beam of an operating wavelength toward a discrete spot in a field ahead of the illumination source; a bulk imaging optic130characterized by a focal plane opposite the field; an aperture layer coincident the focal plane, defining a set of apertures144in a second rectilinear grid array proportional to the first rectilinear grid array, and defining a stop region146around the set of apertures144, each aperture in the set of apertures144defining a field of view in the field coincident a discrete spot output by a corresponding illumination source in the set of illumination sources110, the stop region146absorbing light rays reflected from surfaces in the field outside of fields of view defined by the set of apertures144and passing through the bulk imaging optic130; a set of lenses150, each lens in the set of lenses150characterized by a second focal length, offset from the focal plane opposite the bulk imaging optic130by the second focal length, aligned with an aperture in the set of apertures144, and configured to collimate light rays passed by the aperture; an optical filter160adjacent the set of lenses150opposite the aperture layer and configured to pass light rays at the operating wavelength; a set of pixels170adjacent the optical filter160opposite the set of lenses150, each pixel in the set of pixels170aligned with a subset of lenses in the set of lenses150; and a diffuser180interposed between the optical filter160and the set of pixels170and configured to spread collimated light output from each lens in the set of lenses150across a corresponding pixel in the set of pixels170.

Generally, in this variation, the system includes a two-dimensional grid array of channels (i.e., aperture, lens, and pixel sets or lens tube and pixel sets) and is configured to image a volume occupied by the system in two dimensions. The system can collect one-dimensional distance data—such as counts of incident photons within a sampling period and/or times between consecutive photons incident on pixels of known position corresponding to known fields of view in the field—across a two-dimensional field. The one-dimensional distance data can then be merged with known positions of the fields of view for each channel in the system to reconstruct a virtual three-dimensional representation of the field ahead of the system.

In this variation, the aperture layer can define a grid array of apertures, the set of lenses150can be arranged in a similar grid array with one lens aligned with one aperture in the aperture layer, and the set of pixels170can include one pixel per aperture and lens pair, as described above. For example, the aperture layer can define a 24-by-24 grid array of 200-μm-diameter apertures offset vertically and laterally by an aperture pitch distance of 300 μm, and the set of lenses150can similarly define a 24-by-24 grid array of lenses offset vertically and laterally by a lens pitch distance of 300 μm. In this example, the set of pixels170can include a 24-by-24 grid array of 300-μm-square pixels, wherein each pixel includes a 3×3 square array of nine 100-μm-square SPADs.

Alternatively, in this variation, the set of pixels170can include one pixel per group of multiple aperture and lens pairs. In the foregoing example, the set of pixels170can alternatively include a 12-by-12 grid array of 600-μm-square pixels, wherein each pixel includes a 6×6 square array of 36 100-μm-square SPADs and wherein each pixel is aligned with a group of four adjacent lenses in a square grid. In this example, for each group of four adjacent lenses, the diffuser180: can bias collimated light rays output from a lens in the (1,1) position in the square grid upward and to the right to spread light rays passing through the (1,1) lens across the full breadth and width of the corresponding pixel; can bias collimated light rays output from a lens in the (2,1) position in the square grid upward and to the left to spread light rays passing through the (2,1) lens across the full breadth and width of the corresponding pixel; can bias collimated light rays output from a lens in the (1,2) position in the square grid downward and to the right to spread light rays passing through the (1,2) lens across the full breadth and width of the corresponding pixel; and can bias collimated light rays output from a lens in the (2,2) position in the square grid downward and to the left to spread light rays passing through the (2,2) lens across the full breadth and width of the corresponding pixel, as shown inFIG. 8.

In the foregoing example, for each group of four illumination sources in a square grid and corresponding to one group of four lenses in a square grid, the system can actuate one illumination source in the group of four illumination sources at any given instance in time. In particular, for each group of four illumination sources in a square grid corresponding to one pixel in the set of pixels170, the system can actuate a first illumination source111in a (1,1) position during a first sampling period to illuminate a field of view defined by a first aperture141corresponding to a lens in the (1,1) position in the corresponding group of four lenses, and the system can sample all 36 SPADs in the corresponding pixel during the first sampling period. The system can then shut down the first illumination source111and actuate a second illumination source112in a (1,2) position during a subsequent second sampling period to illuminate a field of view defined by a second aperture142corresponding to a lens in the (1,2) position in the corresponding group of four lenses, and the system can sample all 36 SPADs in the corresponding pixel during the second sampling period. Subsequently, the system can then shut down the first and second illumination sources112and actuate a third illumination source in a (2,1) position during a subsequent third sampling period to illuminate a field of view defined by a third aperture corresponding to a lens in the (2,1) position in the corresponding group of four lenses, and the system can sample all 36 SPADs in the corresponding pixel during the third sampling period. Finally, the system can shut down the first, second, and third illumination sources and actuate a fourth illumination source in a (2,2) position during a fourth sampling period to illuminate a field of view defined by a fourth aperture corresponding to a lens in the (2,2) position in the corresponding group of four lenses, and the system can sample all 36 SPADs in the corresponding pixel during the fourth sampling period. The system can repeat this process throughout its operation.

Therefore, in the foregoing example, the system can include a set of pixels170arranged across an image sensor 7.2 mm in width and 7.2 mm in length and can implement a scanning schema such that each channel in the system can access (can project light rays onto) a number of SPADs otherwise necessitating a substantially larger image sensor (e.g., a 14.4 mm by 14.4 mm image sensor). In particular, the system can implement a serial scanning schema per group of illumination sources to achieve an exponential increase in the dynamic range of each channel in the system. In particular, in this variation, the system can implement the foregoing imaging techniques to increase imaging resolution of the system.

In the foregoing implementation, the system can also include a shutter182between each channel and the image sensor, and the system can selectively open and close each shutter182when the illumination source for the corresponding channel is actuated and deactivated, respectively. For example, the system can include one independently-operable electrochromic shutter182interposed between each lens, and the system can open the electrochromic shutter182over the (1,1) lens in the square-gridded group of four lenses and close electrochromic shutters182over the (1,2), (2,1), and (2,2) lens when the (1,1) illumination source is activated, thereby rejecting noise passing through the (1,2), (2,1), and (2,2) lens from reaching the corresponding pixel on the image sensor. The system can therefore selectively open and close shutters182between each channel and the image sensor to increase SNR per channel during operation. Alternatively, the system can include one independently-operable electrochromic shutter182arranged over select regions of each pixel, as shown inFIG. 8, wherein each electrochromic shutter182is aligned with a single channel (i.e., with a single lens in the set of lenses). The system can alternatively include MEMS mechanical shutters or any other suitable type of shutter interposed between the set of lenses150and the image sensor.

In this variation, the system can define two-dimension grid arrays of apertures, lenses, diffusers, and/or pixels characterized by a first pitch distance along a first (e.g., X) axis and a second pitch distance—different from the first pitch distance—along a second (e.g., Y) axis. For example, the image sensor can include pixels offset by a 25 μm horizontal pitch and a 300 μm vertical pitch, wherein each pixel includes a single row of twelve subpixels.

However, in this variation, the two-dimensional optical system can include an array of any other number and pattern of channels (e.g., apertures, lenses (or lens tubes), and diffusers) and pixels and can execute any other suitable scanning schema to achieve higher spatial resolutions per channel than the raw pixel resolution of the image sensor. The system can additionally or alternatively include a converging optic, a diverging optic, and/or any other suitable type of optical element to spread light rights passed from a channel across the breadth of a corresponding pixel.