A MEMS micromirror reinforcing structure

Abstract

The application provides a MEMS micromirror reinforcing structure. The MEMS micromirror reinforcing structure comprises a support base and a frame arranged on the upper surface of the support base, the frame is a hollow structure arranged in an open manner; in a first direction, a mirror surface is sequentially connected with the frame through a first elastic structure and a first actuator cantilever; in a second direction, the mirror surface is sequentially connected with the frame through a second elastic structure and a second actuator cantilever; the upper surface of the support base is provided with a stopper, and the stopper is located directly below the mirror surface. By arranging the stopper, the large displacement of the MEMS micromirror in a third direction can be limited, and mechanical damage caused by large-amplitude vibration and impact can be avoided.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS), and particularly to a MEMS micromirror reinforcement structure. Background Technology

[0002] With the rapid development of space technology, space laser communication technology, with its unique advantages such as low transmission loss, high communication rate, large information capacity, and strong anti-interference performance, has gradually become a research hotspot and important application direction in the field of aerospace communication. In space laser communication systems, precise pointing and stable transmission of light are crucial for achieving efficient communication. Therefore, quasi-static micromirrors, capable of rapidly and precisely adjusting the direction of light, have become a core component in this field.

[0003] Traditionally, quasi-static micromirrors are primarily driven by voice coil motors and piezoelectric ceramics. However, with the increasing demands for miniaturization, integration, and lightweighting in spacecraft, these two traditional driving methods are gradually revealing limitations in terms of size, weight, and power consumption. In contrast, microelectromechanical systems (MEMS) micromirrors, with their extremely small size, extremely light weight, and extremely low power consumption, demonstrate significant advantages in aerospace applications, particularly showing broad application prospects in scenarios such as space laser communication.

[0004] However, quasi-static micromirrors in MEMS face severe challenges in practical applications. Due to their underdamped structural design and low shock resistance, micromirrors are highly susceptible to environmental vibrations, shocks, and high-frequency resonances, leading to excessive deflection angles and failure. Furthermore, the resonant frequency of the micromirrors is easily affected by ambient temperature and lifespan, causing drift, which further increases the reliability issues of MEMS micromirror feedforward control.

[0005] To improve the performance and on-orbit stability of MEMS quasi-static micromirrors, this application provides a MEMS micromirror reinforcement structure. Summary of the Invention

[0006] In view of the defects and shortcomings of existing MEMS micromirrors, this application provides a MEMS micromirror reinforcement structure. This MEMS micromirror reinforcement structure includes a support base and a frame disposed on the upper surface of the support base. The frame is an open, hollow structure. In a first direction, the mirror surface is connected to the frame sequentially via a first elastic structure and a first actuator cantilever. In a second direction, the mirror surface is connected to the frame sequentially via a second elastic structure and a second actuator cantilever. A stopper is disposed on the upper surface of the support base, and the stopper is located directly below the mirror surface. By setting the stopper, large-amplitude displacement of the MEMS micromirror in a third direction can be limited, avoiding mechanical damage caused by large-range vibrations and impacts.

[0007] One embodiment of this application provides a MEMS micromirror reinforcement structure, comprising:

[0008] Support base;

[0009] A frame, which is a hollow structure, is fixedly disposed on the upper surface of the support base around the support base;

[0010] The centerline of the frame coincides with the centerline of the mirror surface along a third direction.

[0011] A first actuator cantilever and a second actuator cantilever are symmetrically arranged on both sides of the mirror surface along a first direction, with the mirror surface as the center of symmetry. One end of each first actuator cantilever is connected to the mirror surface, and the other end is connected to the frame. Along a second direction, with the mirror surface as the center of symmetry, two second actuator cantilever arms are symmetrically arranged on both sides of the mirror surface. One end of each second actuator cantilever is connected to the mirror surface, and the other end is connected to the frame. Along a third direction, the first actuator cantilever, the second actuator cantilever, and the mirror surface are all spaced apart from the upper surface of the support base. The first direction, the second direction, and the third direction are perpendicular to each other.

[0012] A first elastic structure and a second elastic structure, wherein the first elastic structure is disposed between the mirror surface and the first actuator cantilever; and the second elastic structure is disposed between the mirror surface and the second actuator cantilever.

[0013] A stopper is provided on the upper surface of the support base and within the frame, and the stopper is located below the mirror surface.

[0014] In one embodiment, along the third direction, the projection of the stop on the upper surface of the support is smaller than the projection of the mirror on the upper surface of the support.

[0015] In one implementation, along the third direction, the centerline of the stop coincides with the centerline of the mirror.

[0016] In one implementation, along the third direction, the maximum distance between the upper surface of the stop and the lower surface of the mirror is equal to 80% of the relative displacement of the fracture strength of the MEMS micromirror.

[0017] In one embodiment, the material of the stopper is selected from metal, ceramic, glass or plastic.

[0018] In one embodiment, the frame is made of a material selected from metal, ceramic, glass, or plastic.

[0019] In one embodiment, the MEMS micromirror reinforcement structure further includes a laser and a photodetector disposed on the upper surface of the support base. The laser and the photodetector are respectively disposed on both sides of the stop. The laser is used to emit a light beam toward the lower surface of the mirror, and the photodetector is used to receive the light beam reflected from the lower surface of the mirror.

[0020] In one embodiment, the MEMS micromirror ruggedization structure further includes a drive controller, which is electrically or wirelessly connected to the photodetector.

[0021] In one embodiment, the laser includes a gas laser, a solid-state laser, or a semiconductor laser; the wavelength of the beam emitted by the laser includes the visible light band or the invisible light band.

[0022] In one implementation, the photodetector includes a photodiode, a PIN photodiode, a photomultiplier tube, a four-quadrant detector, or an infrared detector.

[0023] As described above, the MEMS micromirror reinforcement structure of this application has the following beneficial effects:

[0024] The MEMS micromirror reinforcement structure of this application includes a support base and a frame disposed on the upper surface of the support base. The frame is an open, hollow structure. In a first direction, the mirror surface is connected to the frame sequentially via a first elastic structure and a first actuator cantilever. In a second direction, the mirror surface is connected to the frame sequentially via a second elastic structure and a second actuator cantilever. A stopper is disposed on the upper surface of the support base, and the stopper is located directly below the mirror surface. By setting the stopper, large displacements of the MEMS micromirror in the third direction can be limited, thereby improving the impact resistance of the MEMS micromirror in the third direction and reducing mechanical damage to the MEMS micromirror caused by high-frequency resonance in the third direction.

[0025] The MEMS micromirror reinforcement structure of this application also acquires the deflection angle of the MEMS micromirror in real time by setting lasers and photodetectors on both sides of the stop. On the one hand, it can be directly fed back to the limit signal of the drive controller for large-angle alarm; on the other hand, it can acquire the resonant frequency required by the feedforward control algorithm through the step response signal, and calibrate the parameters of the feedforward control of the MEMS micromirror caused by factors such as temperature changes, thereby realizing the reliability reinforcement of the MEMS micromirror from the perspective of electrical control. Attached Figure Description

[0026] Figure 1 The diagram shown is a three-dimensional structural schematic of the MEMS micromirror reinforcement structure provided in the embodiments of this application.

[0027] Figure 2 Displayed as Figure 1A schematic diagram of the cross-sectional structure along the AA direction.

[0028] Figure 3 The image shown is a second-order dynamic equivalent model of a MEMS micromirror provided in an embodiment of this application.

[0029] Figure 4 The diagram shown is a schematic of the MEMS micromirror limit alarm and parameter calibration provided in the embodiment of this application.

[0030] Figure 5 The diagram shows the two-step driving algorithm and its effect for the MEMS micromirror provided in the embodiments of this application.

[0031] Component designation explanation

[0032] 100, support base; 200, frame; 300, mirror; 410, first actuator cantilever; 420, first elastic structure; 510, second actuator cantilever; 520, second elastic structure; 600, stop; 700, laser; 800, photodetector. Detailed Implementation

[0033] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] With the rapid development of space laser communication technology, the reliability requirements for MEMS micromirrors are becoming increasingly stringent. As core components in space laser communication, the performance of MEMS micromirrors directly impacts the overall stability and efficiency of the communication system. However, due to their structural characteristics, MEMS micromirrors are prone to performance degradation or even failure when exposed to complex space environments such as vibration, shock, and temperature variations. Especially during the transportation, launch, and on-orbit operation phases of spacecraft, the reliability of micromirrors is crucial. Therefore, robust design for MEMS micromirrors to improve their survivability in harsh environments has become a research hotspot and challenge in this field.

[0035] To address the above-mentioned shortcomings, this application provides a MEMS micromirror reinforcement structure. The following embodiments will provide a detailed description.

[0036] This embodiment provides a MEMS micromirror reinforcement structure, such as Figure 1 and Figure 2As shown, the MEMS micromirror reinforcement structure includes a support base 100, a frame 200, a mirror 300, a first actuator cantilever 410, a first elastic structure 420, a second actuator cantilever 510, a second elastic structure 520, and a stop 600. The frame 200 is a hollow structure with open upper and lower surfaces. The lower surface of the frame 200 surrounds and is fixed to the upper surface of the support base 100. Along a third direction, the centerline of the frame 200 coincides with the centerline of the mirror 300. Along a first direction, with the mirror 300 as the center of symmetry, two first actuator cantilever 410s are symmetrically arranged on both sides of the mirror 300. One end of each first actuator cantilever 410 is fixedly connected to the frame 200, and the other end is connected to the mirror 300 through the first elastic structure 420. The first actuator cantilever 410 is connected to the first actuator cantilever 510 through the second elastic structure 420. An elastic structure 420 drives the mirror 300 to deflect along a first direction. Along a second direction, with the mirror 300 as the center of symmetry, two second actuator cantilever arms 510 are symmetrically arranged on both sides of the mirror 300. One end of each second actuator cantilever arm 510 is fixedly connected to the frame 200, and the other end is connected to the mirror 300 via a second elastic structure 520. The second actuator cantilever arm 510 drives the mirror 300 to deflect along the second direction via the second elastic structure 520. Along a third direction, the first actuator cantilever arm 410, the second actuator cantilever arm 510, and the mirror 300 are all spaced from the upper surface of the support base 100. The first direction, the second direction, and the third direction are perpendicular to each other. As one implementation, the first direction can be parallel to the X-axis, the second direction can be parallel to the Y-axis, and the third direction can be parallel to the Z-axis.

[0037] like Figure 1 and Figure 2 As shown, the stopper 600 is disposed on the upper surface of the support base 100, located within the hollow structure of the frame 200, and below the mirror 300. Without affecting the rotation angle of the MEMS micromirror, the stopper 600 can effectively limit the large displacement of the mirror 300, avoiding mechanical damage such as free structure fracture caused by random vibration of the MEMS micromirror in the third direction (Z-axis direction), thereby improving the reliability and strengthening of the MEMS micromirror.

[0038] In optional embodiments, such as Figure 1 and Figure 2 As shown, along the third direction, the projection of the stop 600 on the upper surface of the support 100 is smaller than the projection of the mirror 300 on the upper surface of the support 100. In order to avoid the deformation of the first elastic structure 420 and the second elastic structure 520 causing an accidental collision between the first elastic structure 420 or the second elastic structure 520 and the stop 600, the support area of ​​the stop 600 should be as small as possible.

[0039] In optional embodiments, such as Figure 1 and Figure 2 As shown, along the third direction, the center line of the stop 600 coincides with the center line of the mirror 300, which facilitates the determination of the position of the stop 600. The shape of the stop 600 can be, for example, cylindrical, cuboid, or hexagonal prism. The actual shape of the stop 600 used can be based on ease of manufacturing.

[0040] In an optional embodiment, along the third direction, the maximum distance between the upper surface of the stop 600 and the lower surface of the mirror 300 is equal to 80% of the relative displacement of the fracture strength of the MEMS micromirror. Setting the relative distance between the upper surface of the stop 600 and the lower surface of the mirror 300 can be based on the premise that the mirror 300 of the MEMS micromirror has sufficient motion margin in the third direction (Z-axis direction). For example, the lengths of the first actuator cantilever 410 and the second actuator cantilever 510 in the MEMS micromirror are both 14.12 mm, and the out-of-plane displacement distance required to achieve a 3.5 mrad rotation angle is 50 μm. Considering factors such as processing errors, installation accuracy, and margin, the relative distance between the upper surface of the stop 600 and the lower surface of the mirror 300 is ultimately set to 100 μm.

[0041] In an alternative embodiment, the material of the stopper 600 is selected from metal, ceramic, glass, or plastic.

[0042] In an alternative embodiment, the material of the frame 200 is selected from metal, ceramic, glass, or plastic.

[0043] In optional embodiments, such as Figure 1 and Figure 2 As shown, the MEMS micromirror reinforcement structure also includes a laser 700 and a photodetector 800. The laser 700 and photodetector 800 are respectively disposed on both sides of the stop 600, and both are located on the upper surface of the support 100. The laser 700 emits a light beam towards the lower surface of the mirror 300, and the photodetector 800 receives the light beam reflected from the lower surface of the mirror. When the mirror 300 deflects, the photodetector 800 receives the reflected light of different intensities from the lower surface of the mirror 300 in real time. Therefore, the position of the laser 700 on the upper surface of the support 100 should be such that it can emit a light beam towards the lower surface of the mirror 300, and the position of the photodetector 800 on the upper surface of the support 100 should be such that it can receive the reflected light from the lower surface of the mirror 300.

[0044] like Figure 3 As shown, the deflection of the mirror 300 of the MEMS micromirror is achieved through the torsional torque generated by two pairs of elastic structures (the first elastic structure 420 and the second elastic structure 520). This motion can be modeled as a dual-mass spring-damped system. and Represents the mass of the two blocks. and This represents the spring stiffness at each end. and This represents the damping coefficient at both ends. Two pairs of elastic structures (first elastic structure 420 and second elastic structure 520) are fixed to the frame 200 via two pairs of actuator cantilevers (first actuator cantilevers 410 and second actuator cantilevers 510) to control the deflection of the mirror 300. The two mass blocks are interconnected. and These represent the spring stiffness and damping coefficient of the section connecting the two mass blocks, respectively. and These are the displacements of the two mass blocks. Assume... and The driving force is the force between the two masses. According to Newton's second law, the dynamic equation of the two masses can be expressed as:

[0045] (1)

[0046] (2)

[0047] and These are the first and second derivatives of displacement with respect to time, namely velocity and acceleration.

[0048] The natural oscillation frequency of a MEMS micromirror system is defined as Where k is the spring stiffness and m is the mass of the mass block; the damping ratio is defined as... ,in, It is the damping coefficient. The system input is the voltage V, and the output is the deflection angle of the MEMS micromirror. K is the input-output system, i.e., the voltage-angle gain. Therefore, the differential equation of the single-axis system can be expressed as follows:

[0049] (3)

[0050] Equation (3) above describes the system output (the deflection angle of the mirror) under a given input voltage V. The dynamic behavior of ), where, This represents the first derivative of the deflection angle with respect to time, i.e., the angular velocity of the mirror. This represents the second derivative of the deflection angle with respect to time, i.e., the angular acceleration of the mirror.

[0051] The mirror 300, frame 200, first actuator cantilever 410, first elastic structure 420, second actuator cantilever 510, and second elastic structure 520 in a MEMS micromirror generally adopt an underdamped structure design, which has a high resonant frequency and a low damping coefficient. The MEMS micromirror itself is equivalent to a second-order system damped by a spring-mass block, and its transfer function model is as follows:

[0052] .

[0053] in, It is the system gain; It is the resonant frequency of the system; It is a complex frequency variable in the Laplace variation; The damping ratio is denoted as .

[0054] When the resonant frequency of a MEMS micromirror is high and the damping coefficient is low, the system will have a large quality factor. The size of the quality factor represents the rate of energy loss in the system. This determines that the mirror 300, frame 200, first actuator cantilever 410, first elastic structure 420, second actuator cantilever 510, and second elastic structure 520 in the MEMS micromirror will generate large-amplitude high-frequency resonance when excited by a step signal. When the resonance amplitude exceeds the maximum safe range of the device, the actuator cantilever (first actuator cantilever 410 and second actuator cantilever 510) and elastic structure (first elastic structure 420 and second elastic structure 520) are very prone to breakage, resulting in device damage.

[0055] In an optional embodiment, the MEMS micromirror hardening structure further includes a drive controller, which is electrically or wirelessly connected to the photodetector 800. The laser 700 emits a beam of light onto the lower surface of the mirror 300. As the mirror 300 deflects, the photodetector 800 receives reflected light of varying intensities from the lower surface of the mirror 300 in real time. When the mirror 300 deflects too much due to impact or high-frequency resonance, the photodetector 800 sends a limit signal to the drive controller as a large-angle alarm. The drive controller then controls the excitation signal of the MEMS micromirror.

[0056] like Figure 4As shown, the laser 700 emits a beam of light onto the lower surface of the mirror 300. When the mirror 300 deflects, the photodetector 800 receives the reflected light from the mirror 300 in real time, thereby detecting the deflection angle of the mirror 300. When the mirror 300 deflects beyond the maximum limit due to vibration or impact and produces continuous large-amplitude oscillations, the photodetector 800 can send a feedback signal to the drive controller when high-frequency resonance occurs. The drive controller drives the MEMS micromirror (the mirror 300, frame 200, first actuator cantilever 410, first elastic structure 420, second actuator cantilever 510, and second elastic structure 520 of the MEMS micromirror cooperate) to reduce the deflection angle, suppress the high-frequency resonance of the device, thereby reducing the resonance time of the device near the maximum limit, reducing the risk of breakage of the actuator cantilever (first actuator cantilever 410 and second actuator cantilever 510) and elastic structure (first elastic structure 420 and second elastic structure 520), and strengthening the reliability of the device.

[0057] In an optional embodiment, the laser 700 emits a beam of light to the lower surface of the mirror 300. When the mirror 300 deflects, the photodetector 800 receives the reflected light from the lower surface of the mirror 300 with different intensities in real time. The resonant frequency required by the feedforward control algorithm is obtained through the step response signal, and the parameters of the MEMS micromirror feedforward control caused by factors such as temperature changes are calibrated to improve the reliability of the feedforward control.

[0058] For MEMS micromirrors with low damping and high resonant frequency, a feedforward two-step drive algorithm can be selected. The effect of using the feedforward two-step drive algorithm is as follows: Figure 5 As shown ( Figure 5 (a) is an open-loop diagram. Figure 5 (b) is a schematic diagram of the feedforward two-step drive. It can be seen that the algorithm can quickly suppress high-frequency resonance and stabilize the device quickly within the target angle. The key parameter of the drive algorithm is the resonant frequency of the MEMS micromirror. Damping ratio The parameters are determined as follows:

[0059] .

[0060] When the temperature of the working environment changes significantly and / or the device operates for a long time, the device's resonant frequency will drift significantly; when the resonant frequency drifts, the control effect of the device control algorithm will decrease significantly.

[0061] When the inherent resonant frequency of a MEMS micromirror changes, the device is no longer effectively controlled by the control algorithm and will vibrate. The MEMS micromirror reinforcement structure provided in this embodiment uses a laser 700 and a photodetector 800. The laser 700 emits a beam of light to the lower surface of the mirror 300, and the photodetector 800 detects the oscillation of the device by receiving the reflected light from the lower surface of the mirror 300. Based on the frequency of the oscillation, the device feeds back the current resonant frequency to the drive controller, thereby enabling the drive controller to correct the control algorithm parameters and achieve self-calibration of the MEMS micromirror control.

[0062] In an optional embodiment, the laser 700 is selected from a gas laser, a solid-state laser, or a semiconductor laser. The wavelength of the beam emitted by the laser 700 can be either visible or invisible.

[0063] In an optional embodiment, the photodetector 800 is selected from a photodiode, a PIN photodiode, a photomultiplier tube, a four-quadrant detector, or an infrared detector.

[0064] In optional embodiments, the actuation mechanism of the actuation structure in the MEMS micromirror hardening structure can be electrostatically driven, thermoelectrically driven, electromagnetically driven, or piezoelectrically driven. The piezoelectric material for piezoelectric actuation is selected from scandium-doped aluminum nitride, lithium niobate, lead zirconate titanate, or lithium tantalate.

[0065] The MEMS micromirror reinforcement structure in this embodiment can acquire the deflection angle of the MEMS micromirror in real time by setting a laser 700 and a photodetector 800, and then extract the feedforward control parameters of the micromirror.

[0066] The MEMS micromirror reinforcement structure provided in this embodiment can enhance reliability in three directions. The first direction involves setting a stopper 600. By placing the stopper 600 on the upper surface of the support 100 below the mirror 300, the impact resistance of the MEMS micromirror in the third direction (which can be the Z-axis) is improved, reducing mechanical damage to the MEMS micromirror caused by high-frequency resonance in the third direction. The second direction involves setting a laser 700 and a photodetector 800. When the mirror 300 deflects excessively due to lateral impact or other reasons, generating high-frequency resonance, the photodetector 800 can quickly provide a feedback signal to reduce the deflection angle, suppress device oscillation, reduce the time of over-range deflection of the MEMS micromirror, and reduce the probability of device damage. The third direction utilizes the laser 700 and the photodetector 800. When the MEMS micromirror is affected by changes in ambient temperature, causing changes in the device's resonant frequency and affecting the MEMS micromirror's feedforward control effect, the photodetector calibrates the MEMS resonant frequency in real time, improving the reliability of the MEMS micromirror's feedforward control. The MEMS micromirror reinforcement structure provided in this embodiment strengthens the reliability of the MEMS micromirror from both mechanical stops and electrical control aspects.

[0067] The MEMS micromirror reinforcement structure in this embodiment effectively improves the reliability of MEMS micromirrors in extreme environments such as space laser communication, and has high industrial value.

[0068] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A MEMS micromirror reinforcement structure, characterized in that, include: Support base; A frame, which is a hollow structure, is fixedly disposed on the upper surface of the support base around the support base; The centerline of the frame coincides with the centerline of the mirror surface along a third direction. A first actuator cantilever and a second actuator cantilever are symmetrically arranged on both sides of the mirror surface along a first direction, with the mirror surface as the center of symmetry; one end of the first actuator cantilever is connected to the mirror surface, and the other end is connected to the frame. Similarly, along a second direction, two second actuator cantilever arms are symmetrically arranged on both sides of the mirror surface, with the mirror surface as the center of symmetry; one end of each second actuator cantilever arm is connected to the mirror surface, and the other end is connected to the frame. Along a third direction, the first actuator cantilever, the second actuator cantilever, and the mirror are all spaced apart from the upper surface of the support; the first direction, the second direction, and the third direction are perpendicular to each other; A first elastic structure and a second elastic structure, wherein the first elastic structure is disposed between the mirror surface and the first actuator cantilever; and the second elastic structure is disposed between the mirror surface and the second actuator cantilever. A stopper is provided on the upper surface of the support base and within the frame. The stopper is located below the mirror. The projection of the stopper on the upper surface of the support base is smaller than the projection of the mirror on the upper surface of the support base. The centerline of the stopper coincides with the centerline of the mirror. The maximum distance between the upper surface of the stopper and the lower surface of the mirror is equal to 80% of the relative displacement of the fracture strength of the MEMS micromirror. A laser and a photodetector are disposed on the upper surface of the support base and respectively on both sides of the stop. The laser is used to emit a light beam toward the lower surface of the mirror, and the photodetector is used to receive the light beam reflected from the lower surface of the mirror.

2. The MEMS micromirror reinforcement structure according to claim 1, characterized in that, The stopper is made of metal, ceramic, glass, or plastic.

3. The MEMS micromirror reinforcement structure according to claim 1, characterized in that, The frame is made of materials selected from metal, ceramic, glass, or plastic.

4. The MEMS micromirror reinforcement structure according to claim 1, characterized in that, It also includes a drive controller, which is electrically or wirelessly connected to the photodetector.

5. The MEMS micromirror reinforcement structure according to claim 1, characterized in that, The laser includes a gas laser, a solid-state laser, or a semiconductor laser; the wavelength of the beam emitted by the laser includes the visible light band or the invisible light band.

6. The MEMS micromirror reinforcement structure according to claim 1, characterized in that, The photodetector includes a photodiode, a PIN photodiode, a photomultiplier tube, a four-quadrant detector, or an infrared detector.

Images