CN108226936B - Time division sharing window laser radar system based on micro-mirror - Google Patents
Time division sharing window laser radar system based on micro-mirror Download PDFInfo
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- CN108226936B CN108226936B CN201711106256.0A CN201711106256A CN108226936B CN 108226936 B CN108226936 B CN 108226936B CN 201711106256 A CN201711106256 A CN 201711106256A CN 108226936 B CN108226936 B CN 108226936B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4811—Constructional features, e.g. arrangements of optical elements common to transmitter and receiver
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4818—Constructional features, e.g. arrangements of optical elements using optical fibres
Abstract
The invention discloses a time division sharing window laser radar system based on a micro mirror.A first single-sided reflector is provided with a first through hole; a second through hole is formed in the second single-sided reflector; the laser beam generated by the laser is divided into two paths, and one path of laser beam is emitted to the micro mirror through the first through hole and then is emitted to a detection target through the micro mirror; the other path of laser beam is emitted to a second single-sided reflector after passing through the delay fiber, is emitted to a micromirror through a second through hole, and is emitted to a detection target through the micromirror; the echo light beam reflected from the detection target is reflected to the first single-sided reflector and the second single-sided reflector by the micro mirror and then is converged to the optical detector by the converging lens. The invention adopts the time delay optical fiber to separate the echo beams of the two beams of emergent laser on the time domain, realizes that two paths of echo beams can be simultaneously detected by adopting one group of detectors, further simplifies the system structure, reduces the system volume and the number of devices, saves the cost and reduces the assembly precision of the system.
Description
Technical Field
The invention relates to a laser radar, in particular to a time division sharing window laser radar system based on a micro mirror.
Background
Lidar is a high precision distance measuring device. As an active detection device, the laser radar is not influenced by the daytime and the night, and has strong anti-interference capability. In addition to applications in the fields of topographic mapping and the like, great attention has been drawn in recent years also in the fields of autopilot and unmanned aerial vehicles. The traditional laser radar adopts the design of combining multi-path laser with a mechanical rotating structure, so that the speed is low, the volume is large, the energy consumption is high, and the cost is high. The micromirror is used for replacing a mechanical rotating structure, so that the volume of the equipment can be greatly reduced, the scanning frequency is improved, and the energy consumption is less. In addition, the micro mirror can form a one-dimensional scanning mirror surface and can scan in a two-dimensional plane, and the whole observation surface can be detected only by one path of laser. Due to the compact structure design, the laser radar based on the micro mirror can be easily embedded into portable equipment, and the application range of the laser radar is greatly expanded.
The existing laser radar system mainly uses a scheme of combining a mechanical rotating structure with multiple paths of laser. The equipment volume and the cost are difficult to reduce. Chinese patent publication No. CN 206331115U discloses a laser radar solution combining a rotating motor and a one-dimensional micromirror, but the existence of the rotating motor makes further reduction of the system size difficult. In addition, the scheme uses a light detector with a light sensitive surface of 3 mm, is expensive and has slow time domain response, and cannot measure short pulse laser with higher precision. Chinese patent publication No. CN 106707289a proposes an electromagnetically driven galvanometer, but the size of the mirror surface is centimeter level, which is much larger than that of the conventional MEMS micromirror, so that it is difficult to obtain a larger scanning frequency. Nor does this patent describe the specific construction of its lidar system. Lidar systems based entirely on MEMS micro-mirrors are subject to further research and demonstration. Existing MEMS micro-mirror based lidar still mainly uses a scheme where the transmission and reception windows are separated. The laser radar system with separate receiving and transmitting devices has the disadvantages that the direction distribution of the echo light field is wide, so that the receiving light path is complicated, the system volume and the cost are increased, and the laser radar system is difficult to apply to portable equipment.
Disclosure of Invention
In order to solve the above problems, the present invention provides a micromirror-based time division shared window lidar system, comprising: the device comprises a laser, an optical fiber beam splitter, a first single-sided reflector, a micromirror, a time-delay optical fiber, a second single-sided reflector, a converging lens and an optical detector;
the first single-sided reflector is provided with a first through hole; a second through hole is formed in the second single-sided reflector;
the laser beam generated by the laser is divided into two paths by the optical fiber beam splitter, and one path of laser beam is emitted to the micro mirror through the first through hole and then is emitted to a detection target through the micro mirror; the other path of laser beam is emitted to a second single-sided reflector after passing through the delay fiber, is emitted to the micromirror through the second through hole, and is emitted to a detection target through the micromirror; the laser beam emitted to the micro mirror through the first through hole and the second through hole has a first included angle theta which is larger than 0;
and the echo light beams reflected from the detection target are reflected to the first single-sided reflector and the second single-sided reflector by the micromirrors and then are converged to the optical detector by the converging lens.
Further, the aperture of the first through hole is not smaller than the diameter of the laser beam incident to the first single-sided reflector; the aperture of the second through hole is not smaller than the diameter of the laser beam incident to the second single-sided reflector.
Further, the splitting ratio of the optical fiber splitter is 1: 1.
Further, the first included angle θ satisfies the following relationship: theta is more than 0 and less than or equal to 45 degrees.
Further, the laser is a pulsed laser. The micro mirror is a dynamically deformable and controllable micro mirror.
Further, the micromirror is a one-dimensional micromirror.
Further, the micromirror is a two-dimensional micromirror.
Further, the mirror surfaces of the first single-sided reflecting mirror and the second single-sided beam splitter are of micro-nano structures.
Further, the micromirror is electrostatically driven, electromagnetically driven, electrically and thermally driven, or piezoelectrically driven.
Further, the light detector is a PN/PIN photodetector, an avalanche photodiode, a photomultiplier tube, a CCD or CMOS detector.
In summary, the invention provides a micromirror-based time division shared window laser radar system, wherein a first through hole is formed on a first single-sided reflector; a second through hole is formed in the second single-sided reflector; laser beams generated by the laser are divided into two paths by the optical fiber beam splitter, and one path of laser beams is emitted to the micro mirror through the first through hole and then is emitted to a detection target through the micro mirror; the other path of laser beam is emitted to a second single-sided reflector after passing through the delay fiber, is emitted to a micromirror through a second through hole, and is emitted to a detection target through the micromirror; the laser beam emitted to the micro mirror through the first through hole and the second through hole has a first included angle theta which is larger than 0; the echo light beam reflected from the detection target is reflected to the first single-sided reflector and the second single-sided reflector by the micro mirror and then is converged to the optical detector by the converging lens. The invention adopts the time delay optical fiber to separate the echo beams of the two beams of emergent laser on the time domain, realizes that two paths of echo beams can be simultaneously detected by adopting one group of detectors, further simplifies the system structure, reduces the system volume and the number of devices, saves the cost and reduces the assembly precision of the system.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions and advantages of the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a schematic structural diagram of a micromirror-based time division shared window lidar system according to the present invention.
FIG. 2 is a schematic diagram of a micromirror structure according to an embodiment of the invention.
FIG. 3 is a schematic diagram of a micromirror structure according to an embodiment of the invention.
FIG. 4(a) is a schematic diagram of a micromirror structure according to an embodiment of the invention.
FIG. 4(b) is a schematic diagram of a micromirror structure according to an embodiment of the invention.
FIG. 5 is a schematic diagram of a micro mirror structure according to an embodiment of the invention.
FIG. 6 is a schematic diagram of a micro mirror structure according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
The first embodiment is as follows:
as shown in fig. 1, the present invention provides a micromirror-based time division shared window lidar system, comprising: the device comprises a laser 1, an optical fiber beam splitter 2, a first single-sided reflector 5, a micro-mirror 3, a second single-sided reflector 6, a converging lens 8, a light detector 9 and a delay optical fiber 4.
The first single-sided reflector 5 is provided with a first through hole; a second through hole is formed in the second single-sided reflector 6;
the laser beam generated by the laser 1 is divided into two paths by the optical fiber beam splitter 2, and one path of laser beam is emitted to the micro mirror 3 through the first through hole and then emitted to the detection target 7 through the micro mirror 3; the other path of laser beam is emitted to a second single-sided reflector 6 after passing through a delay optical fiber 4, is emitted to the micro mirror 3 through the second through hole, and is emitted to a detection target 7 through the micro mirror 3; the laser beam emitted to the micro mirror 3 through the first through hole and the second through hole has a first included angle theta which is larger than 0;
the echo light beam reflected from the detection target 7 is reflected by the micro mirror 3 to the first single-sided mirror 5 and the second single-sided mirror 6, and then is converged to the optical detector 9 by the converging lens 8.
In one example, the laser 1 is a pulsed laser.
In one example, the laser 1 may be a semiconductor edge-emitting laser, a vertical surface cavity emitting semiconductor laser, a fiber laser, or the like.
The micromirror 3 may be a micromirror 3 with controllable dynamic deformation, and according to different specific designs, the micromirror may be a one-dimensional or two-dimensional scanning micromirror, and the driving manner may be electrostatic driving, electromagnetic driving, electrothermal driving, or piezoelectric driving.
Specifically, in order to realize that the laser emission and the signal reception share one window, a single-sided mirror assembly is inserted between the laser 1 and the micromirror 3, and the single-sided mirror assembly has the function of enabling most or all energy of laser beams emitted by the laser 1 to smoothly pass through to reach the micromirror 3 and ensuring that most energy of echo beams is emitted to the convergent lens 8. In order to achieve a multiplication of the scan field of view, the single-sided mirror assembly comprises a first single-sided mirror 5 and a second single-sided mirror 6; the first single-sided reflector 5 and the second single-sided reflector 6 respectively correspond to two paths of light beams emitted by the optical fiber beam splitter.
The first single-sided mirror 5 and the second single-sided mirror 6 may be prepared by perforating, slotting in the center of the total reflection mirrors. The first single-sided reflector 5 is provided with a first through hole 51, and preferably, the first through hole 51 is located at the center of the first single-sided reflector 5. Of course, the first through hole may be formed in another position of the first single-sided reflecting mirror 5. The area of the first through hole 51 is larger than the laser spot size but much smaller than the total mirror surface area of the first single-sided mirror 5. Similarly, the second single-sided reflector 6 is provided with a second through hole 61, and preferably, the second through hole 61 is located at the center of the single-sided reflector 6. Of course, the second through hole 61 may be opened at another position of the second single-sided reflecting mirror 6. The area of the second through hole 61 is larger than the laser spot size but much smaller than the total mirror surface area of the second single-sided mirror 6.
The aperture of the first through hole 51 is not smaller than the diameter of the laser beam incident on the first single-sided reflecting mirror 5; the aperture of the second through hole 61 is not smaller than the diameter of the laser beam incident on the second single-sided reflecting mirror 6. When the aperture (diameter) of the first through hole 51 is not smaller than the diameter of the laser beam incident on the first single-sided reflecting mirror 5, it is possible to ensure that all or almost all of the laser beam passes through the first single-sided reflecting mirror 5. In addition, in order to ensure that all or almost all of the laser beam passes through the first single-sided mirror 5, one beam emitted from the fiber splitter 2 is directed to the first through hole 51. When the aperture (diameter) of the second through hole 61 is not smaller than the diameter of the laser beam incident on the second single-sided reflecting mirror 6, it is possible to ensure that all or almost all of the laser beam passes through the second single-sided reflecting mirror 6. In addition, in order to ensure that all or almost all laser beams pass through the second single-sided mirror 6, the other beam emitted from the fiber beam splitter 2 is reflected by the mirror and then directed to the second through hole 61.
When the aperture of the first through hole 51 is equal to the diameter of the laser beam incident on the first single-sided reflector 5, it can be ensured that the laser beam emitted from the laser 1 just passes through the first through hole 51, and the echo beam is incident on the converging lens 8 through the first single-sided reflector 5 to the maximum extent, thereby improving the detection efficiency.
Similarly, when the aperture of the second through hole 61 is equal to the diameter of the laser beam incident on the second single-sided reflector 6, it can be ensured that the laser beam emitted from the laser 1 just passes through the second through hole 61, and the echo beam is incident on the converging lens 8 through the second single-sided reflector 6 to the maximum extent, thereby improving the detection efficiency.
In order to ensure that the echo beams reflected by the first single-sided mirror 5 and the second single-sided mirror 6, respectively, can enter the condenser lens 8, the first single-sided mirror 5 and the second single-sided mirror 6 are offset with respect to the condenser lens 8. That is, the lower end of the first single-sided mirror 5 is higher than the lower end of the condenser lens 8, and the echo beam reflected from the upper end of the second single-sided mirror 6 is not blocked by the first single-sided mirror.
In order to improve the detection efficiency, the first single-sided reflector 5 and/or the second single-sided reflector 6 may also be a micro-nano structure, or the first single-sided reflector and/or the second single-sided reflector may have a mirror surface designed by a special micro-nano structure, so as to implement the required functions. Since the time for the laser emergent beam to reach the detection target 7 and return is so short that the micromirror 3 does not rotate significantly when compared with the pulse emergent, the direction of the echo beam (dotted line in fig. 1) is just opposite to that of the emergent beam (solid line in fig. 1), and one path of the echo beam of the approximately parallel light is reflected to the converging lens 8 through the first single-sided reflector 5 and then is incident on the light receiving surface of the light detector 9, and can be received by the single light detector 9; the other echo beam of the approximately parallel light is reflected to the converging lens 8 by the second single-sided reflector 6, then enters the light receiving surface of the light detector 9, and can be received by the single light detector 9.
In one example, the laser 1 is a fiber laser; the laser 1 and the optical fiber beam splitter 2 are connected through an optical fiber.
In one example, the splitting ratio of the fiber splitter 2 is 1: 1. In order to increase the scanning field of view, after being emitted, the laser is equally divided into two beams of laser with equivalent energy through the optical fiber beam splitter 2, wherein one beam of laser is incident to the first single-sided reflector 5 and is incident to the micro mirror 3 through the first single-sided reflector 5; and the other beam of laser is incident to a second single-sided reflector 6 after passing through the delay optical fiber 4, and is incident to the mirror surface of the micro mirror 3 through the second through hole at an included angle relative to the first beam of laser theta.
In one example, the first included angle θ satisfies the following relationship: theta is more than 0 and less than or equal to 45 degrees. Wherein the angle θ may be a scanning range of the single light beam in the direction when the field of view of the direction is increased to 2 θ; the angle θ may also be any angle smaller than the scanning range of the single beam in this direction. Due to the adoption of the delay optical fiber 4, two laser beams are separated and can be distinguished in a time domain, and echo light beams are received by a single optical detector 9 after passing through the first single-sided reflector 5 and the second single-sided reflector 6 respectively. Of course, the first angle θ is not limited to the above angle, as long as it is possible to receive the echo light beams returned from the first single-sided mirror 5 and the second single-sided mirror 6 by the single photodetector 9.
In one example, the photodetector 9 is a PN/PIN photodetector, avalanche photodiode, photomultiplier tube, CCD or CMOS detector.
(1) The invention uses the micromirror to replace a mechanical rotating structure, can greatly reduce the volume of equipment, improves the scanning frequency and consumes less energy. In addition, the micro mirror can form a one-dimensional scanning mirror surface and can scan in a two-dimensional plane, and the whole observation surface can be detected only by one path of laser. Due to the compact structure design, the laser radar based on the micro mirror can be easily embedded into portable equipment, and the application range of the laser radar is greatly expanded.
(2) The invention is especially suitable for short-distance detection and application scenes of portable equipment, adopts a laser radar scheme of sharing a transmitting window and a receiving window, in the scheme, a micro mirror simultaneously serves as a scanning reflecting mirror for emitting laser beams and echo light beams, and the size of the mirror surface of the micro mirror determines the light receiving area and the capacity of receiving a light field. By introducing a single-sided mirror with a through-hole between the laser and the micromirror, it passes most of the outgoing laser energy while reflecting most of the echo energy. The echo is reflected by the micro mirror and returns to the single-sided reflector, the direction is unchanged, and the phenomenon that the echo direction is widely distributed does not exist, so that the echo can be received by a single optical detector after being focused by the lens. According to the design scheme of the invention, the complete laser radar system can mainly comprise a laser, a micro mirror, a single-sided reflector and a light detector, thereby greatly reducing the number of elements and the complexity of the system.
(3) The invention uses a laser beam splitter to scan the field of view doubly, and the emergent laser is divided into two beams of laser with equal energy after passing through the beam splitter. Respectively pass through the corresponding single-sided reflecting mirrors and enter the micro-mirror surfaces with the angle difference of theta. The angle theta can be the scanning range of a single light beam in the direction, and under the scanning of two laser beams, the field of view in the direction is increased to 2 theta; the angle θ may also be any angle smaller than the scanning range of the single beam in this direction. By adopting the scheme of the invention, the multiplication of the scanning field of view can be realized. The laser radar system can realize a large enough scanning angle, and is particularly suitable for full-automatic driving and other applications with high requirements on scanning view fields.
(4) The invention adopts the time delay optical fiber to separate the echo beams of the two beams of emergent laser on the time domain, realizes that two paths of echo beams can be simultaneously detected by adopting one group of detectors, further simplifies the system structure, reduces the system volume and the number of devices, saves the cost and reduces the assembly precision of the system.
Example two:
in the lidar system described in the first embodiment, the micromirror 3 is an important optical relay component and scanning device in the optical path. On the one hand, the size of the reflective surface of the micromirror 3 defines the maximum reflective area, and on the other hand, the micromirror 3 realizes scanning of the light beam based on its own scanning structure.
Further, the micromirror 3 is a micromirror with controllable dynamic deformation.
In the second embodiment, the basic structure of the mirror surface of the micromirror 3 is shown in fig. 2, and includes an outer mirror 10 and an inner mirror 11, wherein the inner mirror 11 is connected to the outer mirror 10 via a connecting mechanism 12, and the outer mirror 10 is connected to an external fixed anchor point via a torsion shaft 13. The outer mirror 10, the inner mirror 11 and the connecting mechanism 12 form a whole body and rotate around the rotating shaft, and the connecting mechanism 12 is symmetrically distributed around the rotating shaft of the micro mirror.
The outer mirror 10, inner mirror 11, connection mechanism 12, and torsion shaft 13 are formed on an SOI wafer. The SOI wafer is composed of a top monocrystalline silicon device layer, a middle silicon dioxide buried layer and a bottom monocrystalline silicon substrate layer. The forming process comprises the following steps: the overall structure of the micromirror is defined by selectively etching the top device layer, including forming the outer mirror, the inner mirror, the connecting mechanism, and the torsion axis. The division of the inner mirror and the outer mirror and the formation of the connecting mechanism are realized by selectively etching the designated area.
In the structure shown in fig. 2, two semicircular grooves symmetrical to each other are etched on the SOI with a straight line of the torsion axis 13 as a symmetry axis, the semicircular grooves have a first width (H1) and a first radius (R1), a line connecting two end points of a single semicircular groove is parallel to the symmetry axis, and a first distance (L1) is formed between the two semicircular grooves, and the first width (H1), the first radius (R1) and the first distance (R1) define the basic shape and size of the micromirror mirror structure. Wherein the first radius (R1) defines a dimension of the endoscope 11; the first width (H1) and the first distance (L1) define the length and width of the attachment mechanism 12. The dimensions of the outer mirror 10 are determined by the dimensions of the outer mirror defined by the selective etching process. After the etching is finished, the inner mirror and the outer mirror are simultaneously plated with the high-reflectivity mirror layer. The high-reflectivity mirror layer can be realized by evaporation plating or ion reactive sputtering plating, the plating metal can be gold, silver or aluminum, and the flatness of the mirror layer is ensured by controlling the plating process so as to ensure that the micro mirror is in mirror reflection in the scanning process. In one example, the mirror flatness is within 20 nm. The mirror flatness can be verified based on AFM measurements and the like.
Example three:
in fig. 2, a configuration of the micromirror 3 is shown, in which the inner mirror 11 rotates around a rotation axis. The natural rotational frequency of the micromirror as a whole during the rotational wobbling is determined by the total moment of inertia of the micromirror and the stiffness coefficient of the torsion axis 13. Therefore, by adjusting the shape and size of the connecting mechanism 12, the rotating frequency of the whole micro mirror is ensured to be far less than the natural frequency of the vibrator formed by the connecting mechanism 12 and the inner mirror 11. The size of the connection mechanism 12 may be adjusted by adjusting the first width (H1) and the first distance (L1), and the shape of the connection mechanism 12 may be formed by changing the etched pattern.
In the micromirror structure shown in fig. 3, four arc-shaped grooves are etched on the same circumference with the center of the inner mirror as a symmetry point on the SOI, the four arc-shaped grooves are divided into two groups, the two arc-shaped grooves in each group are symmetrical with respect to the symmetry point of the center of the inner mirror, and the connection mechanism 14 is formed between the adjacent arc-shaped grooves. The arc-shaped grooves have a second width (H2) and a second radius (R2), and a second distance (L2) is arranged between two adjacent arc-shaped grooves, and the second width (H2), the second radius (R2) and the second distance (R2) define the basic shape and the size of the micromirror mirror structure. Wherein the second radius (R2) defines a dimension of the endoscope; the second width (H2) and the second distance (L2) define the length and width of the attachment mechanism 14. The size of the outer mirror is determined by the outer mirror size defined by the selective etching process.
In the embodiment of fig. 3, the four arc-shaped slots are named as a first arc-shaped slot, a second arc-shaped slot, a third arc-shaped slot and a fourth arc-shaped slot in sequence according to a clockwise order. The distances between two of the four arc-shaped grooves can be equal to the second distance (L2) or unequal (L21, L22, L23 and L24) according to the requirements of the rotational inertia.
In the above embodiment, the four arc-shaped grooves are on one circle, and for the purpose of suppressing dynamic deformation, the four arc-shaped grooves are shaped to be joined into one circle whose actual positions are spaced from each other by being developed in the form of an exploded view.
In the micromirror structure shown in fig. 4(a), the first and second grooves symmetrical to each other, and the third and fourth groove structures symmetrical to each other are etched on the SOI with the inner mirror center as a point of symmetry.
As shown in fig. 4(b), the first groove structure has the following shape: arranging a circular ring, wherein the circle center of the circular ring can coincide with the center of the endoscope, or can deviate from the center of the endoscope by a unit distance according to a structure dynamic deformation value, the outer diameter of the circular ring is RA, the inner diameter of the circular ring is RB, the circular ring is cut by using a circular arc with the radius of RC, the cutting circular arc and the circular ring form two parts in a surrounding manner, and the part where a minor arc section is located is a first groove; the second groove is mirror symmetric with the first groove about the endoscope center.
Of course, according to a specific dynamic deformation suppression situation, the concentric circles may be cut in a parabolic structure, a portion of a minor arc surrounded by the parabolic structure and the concentric circles forms a first groove, and the second groove and the first groove are in mirror symmetry with respect to the center of the endoscope.
The third groove has the following structure: and setting a parabola y as ax2+ b, setting a circle center on a symmetry axis of the parabola on the focus side of the parabola on the symmetry axis of the parabola, setting a circle with the radius RD, and forming a third groove by a graph formed by the circle and the part where the vertex of the parabola is located. The third groove and the fourth groove are in mirror symmetry about the center of the endoscope.
Example four:
in this embodiment, in order to minimize the dynamic deformation of the endoscope 11, the following steps are adopted:
after the dimensions of the outer mirror 10, inner mirror 11 and torsion shaft 13 are determined, finite element computational analysis of the structure is performed. Based on finite element analysis, the dynamic deformation distribution of the edge of the central hole of the outer mirror 10 is obtained, and then one end of the connecting mechanism 12 close to the outer mirror 10 is arranged at the position with the minimum deformation.
And then, carrying out integral dynamic deformation calculation, further checking the dynamic deformation distribution near one end of the connecting mechanism close to the outer mirror, and moving the connecting mechanism to be near a new minimum value.
This is repeated several times until the desired deformation value is reached.
The results obtained based on finite element experiments are not the same for different endoscope configurations. Fig. 2 shows a single rectangular connecting shaft 12, which is arranged at the edge of the outer mirror 10 in a position in line with the torsion axis, whereby the lowest dynamic deformation for axial rotation is achieved.
Fig. 3 shows that the connecting mechanism 14 is composed of 4 beams which are respectively connected at 4 different positions of the edge of the inner mirror and the outer mirror, and the structural scheme is suitable for the condition that the minimum value of the dynamic deformation of the outer mirror is not at the center of the edge.
Figure 4 shows that the attachment means 15 consist of two C-shaped attachment means, which are attached at two central positions at the edge of the outer mirror and at 4 different positions at the edge of the inner mirror. The design scheme is suitable for the condition that the minimum value of the dynamic deformation of the outer mirror is positioned in the center of the edge.
In the structure shown in fig. 3 and 4, the number of the four contact points between the endoscope and the outer mirror is more, and the reasonable selection of the four contact points is also beneficial to further suppressing the dynamic deformation of the endoscope.
Example five:
the micromirror mirrors in the above embodiments can be driven by different principles, including but not limited to electrostatic, electromagnetic, electrothermal, and piezoelectric driving.
Fig. 5 shows a driving structure of a one-dimensional electrostatically-driven micromirror, the micromirror surface is fixed on the anchor point 16 via the torsion axis and connected to an external power source.
The movable comb teeth 18 are positioned at two sides of the external mirror and are distributed with the static comb teeth 17 in a crossed way, and the static comb teeth 17 are connected with the other pole of the external power supply through a welding area 19. When the external power supply applies periodic voltage to excite, the micro mirror can rotate in one dimension.
In one example, the moving and static comb teeth are planar comb teeth.
In one example, the moving and static comb teeth are vertical comb teeth.
Based on the comb structure, the micromirror can work in both a resonant mode and a quasi-static mode.
In this embodiment, the moving combs 18 are directly disposed on both sides of the mirror surface of the outer mirror, which increases the dynamic deformation of the outer mirror. With the foregoing embodiment, the separation of the endoscope and the outer mirror, and the placement of the attachment mechanism 12 at a minimum dynamic deformation design, effectively attenuates the transmission of dynamic deformation to the endoscope.
Example six:
as shown in fig. 6, a two-dimensional electrostatically driven micromirror is constructed by coupling a mirror surface to a rotatable gimbal structure 23 and providing two pairs of comb tooth arrays 20 and 22. Wherein the second pair of comb arrays 22 is perpendicular to the arrangement direction of the first pair of comb arrays 20. Due to the presence of the isolation grooves 24 and 25, the two-dimensional micromirror is controlled by three microelectrodes 21, 26 and 27, thereby achieving independent deflection in two mutually perpendicular directions. Comb array 20/22 may be planar or vertical, corresponding to lissajous scan mode and progressive scan mode, respectively.
Example seven:
the present embodiment will specifically describe the feature sizes of the micromirror structures in the first to sixth embodiments. As described above, in the embodiment of the present invention, the inner mirror and the outer mirror are separated from each other, and the characteristic size of the micromirror is defined by the size of the outer mirror, so that the total size of the mirror surface of the micromirror is several times that of a common product, which can provide a sufficiently large echo beam receiving area.
In a specific series of micromirror structures, the outer mirror feature size is selected from the size between 2 mm-20 mm, and the inner mirror feature size is selected from the size between 0.5 mm-4 mm. The outer mirror is larger in size and is only used for receiving the echo light beam, and the inner mirror is smaller in size and is used for deflecting the emergent laser light beam and receiving a part of the echo light beam.
Through the mode described in the previous embodiment, the connecting mechanism with a specific shape and size is arranged between the endoscope and the outer endoscope, and the end, close to the outer endoscope, of the connecting mechanism is arranged at the position where the dynamic deformation of the outer endoscope is smaller, so that the transmission of the dynamic deformation of the outer endoscope to the endoscope is weakened. Thereby ensuring that the dynamic deformation of the endoscope is smaller and suppressing the spot distortion of the emergent laser. The dynamic deformation of the outer mirror is relatively large, but because the distance from the micro mirror to the photoelectric detector is very short, the spot distortion absolute value of the echo light beam is very small, and the loss of the echo energy can be ignored.
In terms of micromirror size, a larger mirror size increases the moment of inertia of the micromirror, thereby reducing the natural rotational frequency and the maximum rotational angle, which can be reduced by using thinner device layers. In one specific example, the characteristic thickness of the micromirror is thinned to 10-80 microns.
Example eight:
in the above embodiments, the comb structure of the scanning mirror is mentioned, and the present embodiment focuses on the micromirror with the vertical comb structure and describes the processing method thereof.
The micro-mirror structure is arranged on an SOI wafer, and the SOI wafer sequentially comprises a first layer of single crystal silicon device layer, a first layer of silicon oxide insulating layer, a second layer of single crystal silicon device layer, a second layer of silicon oxide insulating layer and a single crystal silicon substrate layer from top to bottom. The comb tooth structure of the edge of the micromirror is fabricated as follows:
And 2, sequentially etching and penetrating the first layer of single crystal silicon device layer, the first layer of silicon oxide insulating layer and the second layer of single crystal silicon device layer by a dry etching process, and stopping on the surface of the second layer of silicon oxide insulating layer.
And 3, forming photoresist on the surface of the wafer after the etching process in the step 2 is finished, wherein the type and the thickness of the photoresist can cover gaps formed by dry etching. Specifically, the gluing process can be formed by one-time gluing, and the gap covering can be completed by multiple times of gluing.
And 4, depositing a layer of medium to seal the dry etching gap, and then gluing.
And step 5, photoetching and exposing the movable comb teeth and the mirror surface part, etching the first monocrystalline silicon device layer and the first silicon oxide insulating layer on the movable comb teeth and the mirror surface structure by taking photoresist as a mask, and removing the photoresist.
And 6, depositing a metal film to form a reflecting mirror surface and a bonding pad.
And 7, finally, etching the back cavity and releasing the movable structure of the micro mirror.
The micromirror formed by the above steps has two layers of static comb teeth, and thus the driving voltage is applied to at least three cases:
in the first case, voltage is applied between the upper layer static comb teeth and the moving comb teeth to realize resonant, quasi-static or digital scanning;
in the second situation, resonant scanning is realized between the lower layer of static comb teeth and the lower layer of moving comb teeth;
in the third situation, the upper and lower layers of static comb teeth apply driving voltage alternately, and electrostatic force is applied to the moving comb teeth uninterruptedly.
In the above driving method, a static bias may be applied to a part or the whole of one or both of the static comb teeth to adjust the resonance frequency and feed back the deflection angle. The vertical comb micro mirror provided by the invention has the advantages of simple process, controllable cost and rich functions, does not need to sacrifice the performance of devices, and is suitable for various application scenes.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. A micromirror-based time-division shared window lidar system comprising: the device comprises a laser, an optical fiber beam splitter, a first single-sided reflector, a micromirror, a time-delay optical fiber, a second single-sided reflector, a converging lens and an optical detector;
the first single-sided reflector is provided with a first through hole; a second through hole is formed in the second single-sided reflector;
the laser beam generated by the laser is divided into two paths by the optical fiber beam splitter, and one path of laser beam is emitted to the micro mirror through the first through hole and then is emitted to a detection target through the micro mirror; the other path of laser beam is emitted to a second single-sided reflector after passing through the delay fiber, is emitted to the micromirror through the second through hole, and is emitted to a detection target through the micromirror; the laser beam emitted to the micro mirror through the first through hole and the second through hole has a first included angle theta which is larger than 0;
the echo light beam reflected from the detection target is reflected to the first single-sided reflector and the second single-sided reflector by the micro mirror and then is converged to the optical detector by the converging lens;
the micromirror is controllable micromirror of dynamic deformation, the micromirror includes the movable part of micromirror mirror surface, movable part includes outer mirror and scope, the outer mirror with the scope passes through coupling mechanism and connects, the outer mirror passes through the torsion axis and links to each other with outside fixed anchor point, the outer mirror the scope with coupling mechanism constitutes a whole and rotates around the rotation axis, coupling mechanism about the rotation axis is symmetric distribution, the outer mirror with the scope surface has high reflectivity mirror surface layer.
2. The system of claim 1, wherein the aperture of the first via is not smaller than the diameter of the laser beam incident on the first single-sided mirror; the aperture of the second through hole is not smaller than the diameter of the laser beam incident to the second single-sided reflector.
3. The system of claim 1, wherein the fiber optic splitter has a splitting ratio of 1: 1.
4. The system of claim 1, wherein the first included angle θ satisfies the following relationship: theta is more than 0 and less than or equal to 45 degrees.
5. The system of claim 1, wherein the micromirrors are one-dimensional micromirrors.
6. The system of claim 1, wherein the micromirrors are two-dimensional micromirrors.
7. The system of claim 1, wherein the mirror surfaces of the first single-sided mirror and the second single-sided beam splitter are micro-nano structures.
8. The system of claim 1, wherein the micromirrors are electrostatically, electromagnetically, electro-thermally, or piezo-electrically driven.
9. The system of claim 1, wherein the light detector is a PN/PIN photodetector, an avalanche photodiode, a photomultiplier tube, a CCD, or a CMOS detector.
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| CN113031254A (en) * | 2019-12-09 | 2021-06-25 | 觉芯电子(无锡)有限公司 | Micro-mirror device, micro-mirror wafer level packaging method and optical window prototype manufacturing method |
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