WO2023225834A1

WO2023225834A1 - Laser radar using light interference

Info

Publication number: WO2023225834A1
Application number: PCT/CN2022/094601
Authority: WO
Inventors: Peiyan CAO; Yurun LIU
Original assignee: Shenzhen Genorivision Technology Co., Ltd.
Priority date: 2022-05-24
Filing date: 2022-05-24
Publication date: 2023-11-30
Also published as: TW202346897A

Abstract

A method and an apparatus (100) for 3D scan of an object in proximity. Light from a light source (150) is split into an external path and an internal path. The light on the external path bounces back from the object (290) and interferes with the light on the internal path. The interference may be used to determine an accurate time of flight of the light on the external path.

Description

LASER RADAR USING LIGHT INTERFERENCE

Background

A laser radar (also called LIDAR, LiDAR and LADAR) is a device that measures distance to a target by illuminating that target with a laser (e.g., ultraviolet, visible, or near infrared) . A laser radar may be used to image objects, which may include a wide range of materials, including non-metallic objects, rocks, rain, chemical compounds, aerosols, clouds and even single molecules.

A laser radar may include a laser (e.g., a laser with a wavelength between 500 nm and 1600 nm) . The laser may be pulsed or continuous. A laser radar may include a mechanism that scans and controls the laser. The mechanism may scan the laser mechanically (e.g., oscillating plane mirrors, polygon mirrors) or electronically (e.g., phased array) . A laser radar may also have a detector configured to detect light reflected by the objects being imaged.

The vertical-cavity surface-emitting laser (VCSEL) , is a type of semiconductor laser diode with laser beam emission perpendicular from the top surface, contrary to conventional edge-emitting semiconductor lasers (also in-plane lasers) which emit from surfaces formed by cleaving the individual chip out of a wafer. A VCSEL may have an active region sandwiched between upper and lower Bragg reflectors (e.g., formed by epitaxial growth on a substrate) . A VCSEL may be formed from materials such as GaAs, InGaAs, or AlGaAs.

Summary

Disclosed herein is a method, comprising: for i=1, …, M, generating an original laser pulse (i) toward a same object, wherein M is a positive integer; for each value of i, splitting the original laser pulse (i) into first laser pulses (i, j) , j=1, …, Ni and a second laser pulse (i) in terms of propagation directions, wherein Ni, i=1, …, M are positive integers; for each value of i and j, guiding the first laser pulse (i, j) and a backscattered laser pulse (i, j) to a light detector (i, j) , resulting in an interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) , wherein the backscattered laser pulse (i, j) results from the second laser pulse (i) scattering at a spot (i, j) of the object; and for each value of i and j, determining a final time of flight (i, j) based on (A) a time when the original laser pulse (i) is generated, (B) a time when the backscattered laser pulse (i, j) reaches the light detector (i, j) , and (C) the interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) .

In an aspect, the original laser pulses (i) , i=1, …, M are generated one by one.

In an aspect, the object is inside a human mouth.

In an aspect, for each value of i, the original laser pulse (i) comprises visible lights.

In an aspect, for each value of i, said splitting the original laser pulse (i) is performed using one or more beam splitters.

In an aspect, said determining the final time of flight (i, j) comprises: determining a preliminary time of flight (i, j) from a time when the original laser pulse (i) is generated to a time when the backscattered laser pulse (i, j) reaches the light detector (i, j) ; and calculating the final time of flight (i, j) based on (A) the preliminary time of flight (i, j) and (B) a phase difference between the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) .

In an aspect, said calculating the final time of flight (i, j) comprises determining the phase difference between the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) based on (A) an intensity of a combined wave resulting from the interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) , (B) an intensity of the first laser pulse (i, j) , and (C) an intensity of the backscattered laser pulse (i, j) .

In an aspect, all Ni, i=1, …, M are 1.

In an aspect, all Ni, i=1, …, M are greater than 1.

In an aspect, the method further comprises, after said generating, said splitting, and said guiding are performed: rotating the light detectors (i, j) , i=1, …, M, and j=1, …, Ni collectively; and then repeating said generating, said splitting, and said guiding.

In an aspect, a number of the light detectors (i, j) , i=1, …, M, and j=1, …, Ni is greater than 1, and the light detectors (i, j) , i=1, …, M, and j=1, …, Ni are arranged in a row.

In an aspect, said rotating the light detectors (i, j) , i=1, …, M, and j=1, …, Ni collectively is about an axis that intersects all the light detectors (i, j) , i=1, …, M, and j=1, …, Ni.

Disclosed herein is an apparatus, comprising: laser sources (i) , i=1, …, M, wherein M is a positive integer; and light detectors (i, j) , i=1, …, M and j=1, …, Ni, wherein Ni, i=1, …, M are positive integers, wherein for each value of i, the laser source (i) is configured to generate an original laser pulse (i) toward a same object, wherein for each value of i, the apparatus is configured to split the original laser pulse (i) into first laser pulses (i, j) , j=1, …, Ni and a second laser pulse (i) in terms of propagation directions, wherein for each value of i and j, the apparatus is configured to guide the first laser pulse (i, j) and a backscattered laser pulse (i, j) to a light detector (i, j) of the apparatus, resulting in an interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) , wherein the backscattered laser pulse (i, j) results from the second laser pulse (i) scattering at a spot (i, j) of the object, and wherein for each value of i and j, the apparatus is configured to determine a final time of flight (i, j) based on (A) a time when the original laser pulse (i) is generated, (B) a time when the backscattered laser pulse (i, j) reaches the light detector (i, j) , and (C) the interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) .

In an aspect, the laser sources (i) , i=1, …, M are configured to generate the original laser pulses (i) , i=1, …, M one by one.

In an aspect, the object is inside a human mouth.

In an aspect, for each value of i, the apparatus further comprises one or more beam splitters configured to split the original laser pulse (i) into the first laser pulses (i, j) , j=1, …, Ni and the second laser pulse (i) .

In an aspect, all Ni, i=1, …, M are 1.

In an aspect, all Ni, i=1, …, M are greater than 1.

In an aspect, the apparatus is configured to, after said generating, said splitting, and said guiding are performed, rotate and then repeat said generating, said splitting, and said guiding.

In an aspect, said rotating is about an axis that intersects all the light detectors (i, j) , i=1, …, M, and j=1, …, Ni.

Brief Description of Figures

Fig. 1A and Fig. 1B schematically show an apparatus, according to an embodiment.

Fig. 2 schematically shows a cross-sectional view of the apparatus of Fig. 1A and Fig. 1B, according to an embodiment.

Fig. 3 shows a plot illustrating the operation of the apparatus of Fig. 2, according to an embodiment.

Fig. 4 is a flowchart generalizing the operation of the apparatus of Fig. 1A –Fig. 2, according to an embodiment.

Detailed Description

APPARATUS FOR LIDAR OPERATION

Fig. 1A and Fig. 1B schematically show an apparatus 100, according to an embodiment. The apparatus 100 comprises a first substrate 110 and a second substrate 120. The first substrate 110 may comprise GaAs. The second substrate 120 may comprise silicon.

As shown in Fig. 1A, the first substrate 110 comprises an array of VCSELs 150. The VCSEL 150 has a first electric contact 152 and a second electric contact 155 (not shown here but shown in Fig. 2) . The first electric contact 152 and the second electric contact 155 are configured to power the VCSEL 150. The VCSEL 150 has an aperture 158, from which laser may be emitted. The first electric contact 152 may be positioned to surround the aperture 158. The VCSEL 150 may have a via 151 through the entire thickness of the first substrate 110, for electrical connect to the second substrate 120. The via 151 and the first electric contact 152 are electrically connected.

The first substrate 110 may have a plurality of windows 153 positioned to allow the laser beams emitted by the VCSELs 150 and backscattered by an object to transmit through the first substrate 110 and reach detectors on the substrate 120. The windows 153 may simply be void space or may be a material that is not opaque to the laser beams from the VCSELs 150. In an embodiment, the first substrate 110 itself may be not opaque to the laser beam from the VCSELs 150 and the windows 153 may be omitted. For example, GaAs is not opaque to light with a wavelength from about 900 nm to about 18 μm. In another example, a wavelength converter is used with the apparatus 100 to convert the laser emitted by VCSELs 150 into a laser with a wavelength to which the first substrate 110 is not opaque.

As shown in Fig. 1B, the second substrate 120 has an array of detectors 143, configured to detect laser beams emitted by the VCSELs 150 and backscattered by an object. The first substrate 110 is mounted to the second substrate 120. The detectors 143 are positioned such that the laser beams emitted by the VCSELs 150 and backscattered by an object can transmit through the windows 153 of the first substrate 110 and reach the detectors 143.

The second substrate 120 can be a printed circuit board (PCB) , a silicon substrate, or any other suitable form. In the case that the second substrate 120 is a PCB, the detectors 143 and the circuitry 160 may be chips mounted on or embedded in the PCB. In the case that the second substrate 120 is a silicon substrate, the detectors 143 and the circuitry 160 may be formed by a CMOS process.

The apparatus 100 may have circuitry 160 configured to drive the VCSELs 150 and the detectors 143. For example, the circuitry 160 may be integrated on the second substrate 120. The first substrate 110 may be bonded to the second substrate 120 such that the VCSELs 150 are electrically connected to the circuitry 160. The circuitry 160 may have an electric contact 141 that electrically connects to the via 151. The circuitry 160 may have an electric contact 149 that electrically connects to the second electric contact 155 of the VCSELs 150. The circuitry 160 may be configured to control the detectors 143, or process or interpret signals from the detectors 143.

The electrical connection between VCSELs 150 and the circuitry 160 may be made by ways. One example is wire bonding. Another example is by conductive adhesive (e.g., benzocyclobuene (BCB) ) .

Fig. 2 schematically shows a cross-sectional view of the apparatus 100, according to an embodiment. In this example, the VCSEL 150 may comprise an active layer 154, which may include a quantum well, sandwiched between an upper Bragg reflector 156 and a lower Bragg reflector 157. The upper Bragg reflector 156, the active layer 154, and the lower Bragg reflector 157 may be epitaxially formed on the first substrate 110.

The detectors 143 may be any suitable detectors. In an example, the detectors 143 include photomultipliers. A photomultiplier is able to multiply the current produced by incident light by many times, and thus allowing detection of low incident flux of photons. A photomultiplier may be in a form of a vacuum phototube that includes a housing containing a photocathode, several dynodes and an electron collector. Light entering the housing and incident on the photocathode causes electrons to be emitted by the photocathode, as a consequence of the photoelectric effect. The electrons impinge on the successive dynodes, causing electron multiplication by secondary emission. After impingement on the last dynode, the electrons are collected by the collector and used for detection of the incident light.

In an example, the detectors 143 include single photon avalanche diode (SPAD) (also known as a Geiger-mode APD or G-APD) . A SPAD is an avalanche photodiode (APD) working under a reverse bias above the breakdown voltage. Here the word “above” means that absolute value of the reverse bias is greater than the absolute value of the breakdown voltage. When a photon incidents on a SPAD, it may generate charge carriers (electrons and holes) . Some of the charge carriers are accelerated by an electric field in the SPAD and may trigger an avalanche current by impact ionization. Impact ionization is a process in a material by which one energetic charge carrier can lose energy by the creation of other charge carriers. For example, in semiconductors, an electron (or hole) with enough kinetic energy can knock a bound electron out of its bound state (in the valence band) and promote it to a state in the conduction band, creating an electron-hole pair. A SPAD may be used to detect low intensity light (e.g., down to a single photon) and to signal the arrival times of the photons with a jitter of a few tens of picoseconds. A SPAD may be in a form of a p-n junction under a reverse bias (i.e., the p-type region of the p-n junction is biased at a lower electric potential than the n-type region) above the breakdown voltage of the p-n junction. The breakdown voltage of a p-n junction is a reverse bias, above which exponential increase in the electric current in the p-n junction occurs.

OPERATION OF APPARATUS 100

In an embodiment, with reference to Fig. 1A –Fig. 2, in the apparatus 100, the number of the VCSELs 150 may be the same as the number of the detectors 143. For example, as shown in Fig. 1A and Fig. 1B, the number of VCSELs 150 and the number of detectors 143 are both 16.

In an embodiment, the apparatus 100 may include LIDAR units each of which includes a VCSEL 150 and a detector 143. Fig. 2 shows such a LIDAR unit. For illustration, the apparatus 100 may include 16 LIDAR units as shown in Fig. 1A and Fig. 1B.

In an embodiment, with reference to Fig. 2, the operation of a LIDAR unit of the apparatus 100 may be as follows. The VCSEL 150 of the LIDAR unit may generate an original laser pulse 250 toward an object 290.

In an embodiment, the LIDAR unit may include a beam splitter 260 positioned on the way the original laser pulse 250 travels toward the object 290. In an embodiment, the beam splitter 260 may split the original laser pulse 250 into a first laser pulse 251 and a second laser pulse 252 in terms of propagation direction (i.e., the first laser pulse 251 and the second laser pulse 252 leave the beam splitter 260 in different propagation directions) .

In an embodiment, the first laser pulse 251 leaving the beam splitter 260 may be guided to the detector 143 of the LIDAR unit. In an embodiment, the LIDAR unit may include a mirror 270 that reflects and guides the first laser pulse 251 from the beam splitter 260 to the detector 143 as shown.

In an embodiment, the second laser pulse 252 may hit a spot 290s of the object 290 and scatter back as a backscattered laser pulse 252b. In an embodiment, the apparatus 100 may include an optical system (not shown for simplicity) that guides the backscattered laser pulse 252b to the detector 143 of the LIDAR unit.

In an embodiment, the first laser pulse 251 and the backscattered laser pulse 252b may interfere with each other at the detector 143 of the LIDAR unit.

PRELIMINARY TIME OF FLIGHT

In an embodiment, a preliminary time of flight (ToF _p) from the time when the original laser pulse 250 is generated to the time when the backscattered laser pulse 252b reaches the detector 143 may be determined. In an embodiment, the determination of the preliminary time of flight ToF _p may include starting a ToF counter (not shown) of the LIDAR unit when the original laser pulse 250 is generated, and then stopping the ToF counter when the light intensity detected by the detector 143 exceeds a pre-specified threshold value Y _th (e.g., Y _th may be 40 as shown in Fig. 3) . In an embodiment, the value of the ToF counter after the ToF counter is stopped may be used to determine the preliminary time of flight ToF _p.

LIGHT INTENSITY DETECTED BY DETECTOR 143

Fig. 3 shows a plot of the light intensity Y as detected by the detector 143 of the LIDAR unit of Fig. 2 over time t. With reference to Fig. 2 and Fig. 3, as an example, assume that at time t=t ₀, the original laser pulse 250 is generated at the VCSEL 150.

Assume further that at time t=t ₁, the first laser pulse 251 arrives at the detector 143 causing the light intensity detected by the detector 143 to rise from Y=0 to Y=Y ₁.

Assume further that at time t=t ₂, the backscattered laser pulse 252b arrives at the detector 143 thereby contributing with the first laser pulse 251 to cause the light intensity detected by the detector 143 to change from Y=Y ₁ to Y=Y _1+2b. Note that Y _th should be different (e.g., greater as shown) than Y ₁ so that the ToF counter described above is stopped at time t=t ₂. As mentioned above, the value of the stopped ToF counter can be used to determine the preliminary time of flight ToF _p.

Assume further that at the detector 143, the first laser pulse 251 ends at time t=t ₃ (i.e., the duration of the first laser pulse 251 at the detector 143 is t ₃-t ₁) leaving the backscattered laser pulse 252b alone bombarding the detector 143, thereby causing the light intensity detected by the detector 143 to change (increase or decrease) from Y=Y _1+2b to Y=Y _2b.

Assume further that at the detector 143, the backscattered laser pulse 252b ends at time t=t ₄ (i.e., the duration of the backscattered laser pulse 252b at the detector 143 is t ₄-t ₂) causing the light intensity detected by the detector 143 to fall from Y=Y _2b to Y=0.

Regarding the first laser pulse 251 and the backscattered laser pulse 252b with respect to the detector 143 of the LIDAR unit, during the time period (t ₁, t ₂) , only the first laser pulse 251 bombards the detector 143. Then, during the time period (t ₂, t ₃) , both the first laser pulse 251 and the backscattered laser pulse 252b bombard the detector 143. Then, during the time period (t ₃, t ₄) , only the backscattered laser pulse 252b bombards the detector 143.

PHASE DIFFERENCE AND FINAL TIME OF FLIGHT

Continuing the example above, with reference to Fig. 2, let T ₁ be the time duration that starts when the original laser pulse 250 is generated at the VCSEL 150 and ends when the first laser pulse 251 reaches the detector 143. Assume that ToF _p= 805 ps, and that T ₁=2 ps. Note that the specific values used in the present patent application are not necessarily realistic.

With reference to Fig. 2 and Fig. 3, assume further that Y ₁ = 20, Y _1+2b = 120, and Y _2b = 100. As a result, Y _1+2b = Y ₁ + Y _2b (i.e., 120=20+100) . This means that the phase difference between the two interfering

laser pulses

251 and 252b at the detector 143 is J×2π (with J being an integer) .

As a result, in an embodiment, a final time of flight ToF _f from the time when the original laser pulse 250 is generated to the time when the backscattered laser pulse 252b reaches the detector 143 may be determined such that (A) the difference between ToF _f and T ₁ is an integer multiple of the period T of the original laser pulse 250, and (B) the magnitude of the difference between ToF _f and ToF _p is minimum (i.e., the smallest) .

Assume that T=100 ps. As a result, with ToF _p= 805 ps and T ₁=2 ps as assumed above, ToF _f can be determined to be 802 ps. This is because ToF _f =802 ps satisfies both conditions (A) and (B) above. Specifically, an indefinite number of values of ToF _f satisfy condition (A) (e.g., 502 ps, 602 ps, 702 ps, 802 ps, 902 ps, 1002 ps, etc) . However, among these values of ToF _f, only ToF _f =802 ps satisfies condition (B) ; that is the magnitude of the difference between 802 ps and 805 ps (i.e., 3 ps) is minimum.

As another example, with reference to Fig. 2 and Fig. 3, assume that Y _1+2b = 80, and ToF _p= 847 ps, whereas other parameters remain unchanged. As a result, Y _1+2b = Y _2b -Y ₁ (i.e., 80=100-20) . This means that the phase difference between the two interfering

laser pulses

251 and 252b is (K+0.5) ×2π (K is an integer) .

As a result, in an embodiment, the final time of flight ToF _f may be determined such that (i) the difference between ToF _f and T ₁ is (L+0.5) ×T (with L being an integer) , and (ii) the magnitude of the difference between ToF _f and ToF _p is minimum (i.e., the smallest) .

With T=100 ps as assumed above, and with ToF _p= 847 ps and T ₁=2 ps as assumed above, ToF _f can be determined to be 852 ps. This is because ToF _f =852 ps satisfies both conditions (i) and (ii) above. Specifically, an indefinite number of values of ToF _f satisfy condition (i) (e.g., 552 ps, 652 ps, 752 ps, 852 ps, 952 ps, 1052 ps, etc) . However, among these values of ToF _f, only ToF _f =852 ps satisfies condition (ii) ; that is the magnitude of the difference between 852 ps and 847 ps (i.e., 5 ps) is minimum.

In short, to determine the final time of flight ToF _f, the preliminary time of flight ToF _p may be determined (e.g., by using the ToF counter as described above) , and then the values of Y ₁, Y _2b, and Y _1+2b may be compared to determine the phase difference between the 2 interfering

laser pulses

251 and 252b at the detector 143. Then, this phase difference may be used to fine-tune the preliminary time of flight ToF _p so as to determine the final time of flight ToF _f.

In an embodiment, the final time of flight ToF _f may be determined by the apparatus 100.

ALTERNATIVE EMBODIMENTS

In the embodiments described above, with reference to Fig. 1A –Fig. 2, each of the 16 LIDAR units of the apparatus 100 includes a VCSEL 150 and a detector 143. In other words, each detector 143 has its own VCSEL 150. Alternatively, multiple detectors 143 may share a same VCSEL 150. In other words, multiple LIDAR units share a same VCSEL 150 (so, these multiple LIDAR units may be called sharing LIDAR units) .

In an embodiment, the operation of a sharing LIDAR unit may be similar to the operation of a regular LIDAR unit (Fig. 2) as described above. Note that in a regular LIDAR unit, the detector 143 has its own VCSEL 150 (as shown in Fig. 2) .

Specifically, in an embodiment, the operation of P sharing LIDAR units sharing a same VCSEL 150 may be as follows (P is an integer greater than 1) . An original laser pulse 250 may be generated by the shared VCSEL 150 and then split by one or more beam splitters (like the beam splitter 260) into P first laser pulses 251 and a second laser pulse 252. The P first laser pulses 251 may be guided respectively to the P detectors 143 of the P sharing LIDAR units. The second laser pulse 252 may scatter at P spots of the object 290 and return to the apparatus 100 as P backscattered laser pulses 252b respectively. The P backscattered laser pulses 252b may be guided by the optical system of the apparatus 100 to the P detectors 143 respectively, resulting in interferences with the P first laser pulses 251 at the P detectors 143. Then, P final times of flight may be individually determined for the P sharing LIDAR units as described above.

FLOWCHART GENERALIZING OPERATION OF APPARATUS 100

Fig. 4 shows a flowchart 400 generalizing the operation of the apparatus 100 of Fig. 1A –Fig. 2, according to an embodiment. In step 410, the operation includes, for i=1, …, M, generating an original laser pulse (i) toward a same object, wherein M is a positive integer. For example, in the embodiments described above, with reference to Fig. 1A -Fig. 2, each of the 16 VCSEL 150 of the apparatus 100 generates an original laser pulse 250 toward the same object 290 (here, M=16) .

In step 420, the operation includes, for each value of i, splitting the original laser pulse (i) into first laser pulses (i, j) , j=1, …, Ni and a second laser pulse (i) in terms of propagation directions, wherein Ni, i=1, …, M are positive integers. For example, in the embodiments described above, with reference to Fig. 1A -Fig. 2, for each of the 16 VCSELs 150 of the apparatus 100, the original laser pulse 250 generated by said each VCSEL 150 is split into the first laser pulse 251 and the second laser pulse 252 traveling in 2 different propagation directions. Here, M=16, and N1=N2=…=N16=1.

In step 430, the operation includes, for each value of i and j, guiding the first laser pulse (i, j) and a backscattered laser pulse (i, j) to a light detector (i, j) , resulting in an interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) , wherein the backscattered laser pulse (i, j) results from the second laser pulse (i) scattering at a spot (i, j) of the object. For example, in the embodiments described above, with reference to Fig. 1A -Fig. 2, for each LIDAR unit (sharing or regular) of the apparatus 100, the first laser pulse 251 and the backscattered laser pulse 252b are guided to the detector 143 of said each LIDAR unit, resulting in the interference of the first laser pulse 251 and the backscattered laser pulse 252b at the detector 143, wherein the backscattered laser pulse 252b results from the second laser pulse 252 scattering at the spot 290s of the object 290.

In step 440, the operation includes, for each value of i and j, determining a final time of flight (i, j) based on (A) a time when the original laser pulse (i) is generated, (B) a time when the backscattered laser pulse (i, j) reaches the light detector (i, j) , and (C) the interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) . For example, in the embodiments described above, with reference to Fig. 1A –Fig. 2, for each LIDAR unit (sharing or regular) of the apparatus 100, the final time of flight ToF _f is determined based on (1) the preliminary time of flight ToF _p of said each LIDAR unit, and (2) the interference of the first laser pulse 251 and the backscattered laser pulse 252b at the detector 143 of said each LIDAR unit. In other words, the final time of flight ToF _f for said each LIDAR unit is determined based on (A) the time when the original laser pulse 250 is generated in said each LIDAR unit, (B) the time when the backscattered laser pulse 252b reaches the detector 143 of said each LIDAR unit, and (C) the interference of the first laser pulse 251 and the backscattered laser pulse 252b at the detector 143 of said each LIDAR unit.

OTHER EMBODIMENTS

In an embodiment, with reference to Fig. 2 and step 410 of Fig. 4, the original laser pulses (i) , i=1, …, M may be generated one by one toward the object 290. For example, with reference to Fig. 1A -Fig. 2, the 16 VCSELs 150 of the apparatus 100 may respectively generate the 16 original laser pulses 250 one by one to the object 290. In an embodiment, the object 290 may be inside a human mouth. In an embodiment, each of the original laser pulses (i) , i=1, …, M may include visible lights. For example, with reference to Fig. 1A -Fig. 2, each of the 16 original laser pulses 250 respectively generated by the 16 VCSELs 150 may include visible lights.

In an embodiment, with reference to Fig. 1A -Fig. 2 and Fig. 4, all Ni, i=1, …, M may be 1. In other words, with reference to Fig. 1A –Fig. 2, each detector 143 of the apparatus 100 has its own VCSEL 150 (i.e., no sharing) . In yet other words, in the apparatus 100, the number of VCSELs 150 is equal to the number of detectors 143.

Alternatively, with reference to step 420 of Fig. 4, all Ni, i=1, …, M may be greater 1. In other words, each VCSEL 150 of the apparatus 100 is shared by multiple detectors 143.

ROTATION OF THE APPARATUS 100

In an embodiment, with reference to Fig. 2 and Fig. 4, after said generating (step 410) , said splitting (step 420) , and said guiding (step 430) are performed, all the detectors 143 of the apparatus 100 may be collectively rotated; and then said generating (step 410) , said splitting (step 420) , and said guiding (step 430) may be repeated so as to scan the object 290. In an embodiment, all the detectors 143 may be collectively rotated by rotating the entire apparatus 100 which includes all the detectors 143.

In an embodiment, with reference to Fig. 1A -Fig. 2, the number of all the detectors 143 of the apparatus 100 may be greater than 1, and all the detectors 143 of the apparatus 100 may be arranged in a row.

In an embodiment, with reference to Fig. 1A -Fig. 2 and Fig. 4, with all the detectors 143 of the apparatus 100 being in a row, the collective rotation of all the detectors 143 of the apparatus 100 described above may be about an axis (not shown) that intersects all the detectors 143 of the apparatus 100.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

A method, comprising:

for i=1, …, M, generating an original laser pulse (i) toward a same object, wherein M is a positive integer;

for each value of i, splitting the original laser pulse (i) into first laser pulses (i, j) , j=1, …, Ni and a second laser pulse (i) in terms of propagation directions, wherein Ni, i=1, …, M are positive integers;

for each value of i and j, guiding the first laser pulse (i, j) and a backscattered laser pulse (i, j) to a light detector (i, j) , resulting in an interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) , wherein the backscattered laser pulse (i, j) results from the second laser pulse (i) scattering at a spot (i, j) of the object; and

for each value of i and j, determining a final time of flight (i, j) based on (A) a time when the original laser pulse (i) is generated, (B) a time when the backscattered laser pulse (i, j) reaches the light detector (i, j) , and (C) the interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) .
The method of claim 1, wherein the original laser pulses (i) , i=1, …, M are generated one by one.
The method of claim 1, wherein the object is inside a human mouth.
The method of claim 1, wherein for each value of i, the original laser pulse (i) comprises visible lights.
The method of claim 1, wherein for each value of i, said splitting the original laser pulse (i) is performed using one or more beam splitters.
The method of claim 1, wherein said determining the final time of flight (i, j) comprises:

determining a preliminary time of flight (i, j) from a time when the original laser pulse (i) is generated to a time when the backscattered laser pulse (i, j) reaches the light detector (i, j) ; and

calculating the final time of flight (i, j) based on (A) the preliminary time of flight (i, j) and (B) a phase difference between the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) .
The method of claim 6, wherein said calculating the final time of flight (i, j) comprises determining the phase difference between the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) based on (A) an intensity of a combined wave resulting from the interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) , (B) an intensity of the first laser pulse (i, j) , and (C) an intensity of the backscattered laser pulse (i, j) .
The method of claim 1, wherein all Ni, i=1, …, M are 1.
The method of claim 1, wherein all Ni, i=1, …, M are greater than 1.
The method of claim 1, further comprising, after said generating, said splitting, and said guiding are performed:

rotating the light detectors (i, j) , i=1, …, M, and j=1, …, Ni collectively; and then

repeating said generating, said splitting, and said guiding.
The method of claim 10,

wherein a number of the light detectors (i, j) , i=1, …, M, and j=1, …, Ni is greater than 1, and

wherein the light detectors (i, j) , i=1, …, M, and j=1, …, Ni are arranged in a row.
The method of claim 11, wherein said rotating the light detectors (i, j) , i=1, …, M, and j=1, …, Ni collectively is about an axis that intersects all the light detectors (i, j) , i=1, …, M, and j=1, …, Ni.
An apparatus, comprising:

laser sources (i) , i=1, …, M, wherein M is a positive integer; and

light detectors (i, j) , i=1, …, M and j=1, …, Ni, wherein Ni, i=1, …, M are positive integers,

wherein for each value of i, the laser source (i) is configured to generate an original laser pulse (i) toward a same object,

wherein for each value of i, the apparatus is configured to split the original laser pulse (i) into first laser pulses (i, j) , j=1, …, Ni and a second laser pulse (i) in terms of propagation directions,

wherein for each value of i and j, the apparatus is configured to guide the first laser pulse (i, j) and a backscattered laser pulse (i, j) to a light detector (i, j) of the apparatus, resulting in an interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) , wherein the backscattered laser pulse (i, j) results from the second laser pulse (i) scattering at a spot (i, j) of the object, and

wherein for each value of i and j, the apparatus is configured to determine a final time of flight (i, j) based on (A) a time when the original laser pulse (i) is generated, (B) a time when the backscattered laser pulse (i, j) reaches the light detector (i, j) , and (C) the interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) .
The apparatus of claim 13, wherein the laser sources (i) , i=1, …, M are configured to generate the original laser pulses (i) , i=1, …, M one by one.
The apparatus of claim 13, wherein the object is inside a human mouth.
The apparatus of claim 13, wherein for each value of i, the original laser pulse (i) comprises visible lights.
The apparatus of claim 13, wherein for each value of i, the apparatus further comprises one or more beam splitters configured to split the original laser pulse (i) into the first laser pulses (i, j) , j=1, …, Ni and the second laser pulse (i) .
The apparatus of claim 13, wherein said determining the final time of flight (i, j) comprises:

determining a preliminary time of flight (i, j) from a time when the original laser pulse (i) is generated to a time when the backscattered laser pulse (i, j) reaches the light detector (i, j) ; and

calculating the final time of flight (i, j) based on (A) the preliminary time of flight (i, j) and (B) a phase difference between the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) .
The apparatus of claim 18, wherein said calculating the final time of flight (i, j) comprises determining the phase difference between the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) based on (A) an intensity of a combined wave resulting from the interference of the first laser pulse (i, j) and the backscattered laser pulse (i, j) at the light detector (i, j) , (B) an intensity of the first laser pulse (i, j) , and (C) an intensity of the backscattered laser pulse (i, j) .
The apparatus of claim 13, wherein all Ni, i=1, …, M are 1.
The apparatus of claim 13, wherein all Ni, i=1, …, M are greater than 1.
The apparatus of claim 13, wherein the apparatus is configured to, after said generating, said splitting, and said guiding are performed, rotate and then repeat said generating, said splitting, and said guiding.
The apparatus of claim 22,

wherein a number of the light detectors (i, j) , i=1, …, M, and j=1, …, Ni is greater than 1, and

wherein the light detectors (i, j) , i=1, …, M, and j=1, …, Ni are arranged in a row.
The apparatus of claim 23, wherein said rotating is about an axis that intersects all the light detectors (i, j) , i=1, …, M, and j=1, …, Ni.