FSO laser communication system based on MEMS micromirror and control method thereof
By integrating electrostatically driven MEMS micromirrors and a variable divergence angle optical module, combined with intelligent feedback control, the problems of directivity deviation and attenuation in the atmospheric channel of the FSO system were solved, achieving efficient beam adjustment and improved communication stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-24
- Publication Date
- 2026-03-10
AI Technical Summary
In atmospheric channels, FSO systems are affected by directivity deviations and atmospheric attenuation. Existing technologies struggle to achieve fast, precise beam pointing control and intelligent adjustment, resulting in insufficient communication stability and reliability.
High-precision beam pointing adjustment is achieved by using electrostatically driven MEMS micromirror components combined with gear/linkage mechanisms. Through a variable divergence angle optical module and intelligent feedback control, the source of link attenuation is distinguished according to the trend of optical power change, and the beam pointing and divergence angle are dynamically adjusted to compensate for deviation and attenuation.
It effectively maintains the stability and reliability of communication links in complex atmospheric environments, improves the ability to resist pointing errors and atmospheric attenuation, and enhances the system's response speed and control accuracy.
Smart Images
Figure CN121643902A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of wireless communication, in particular to a FSO laser communication system based on MEMS micro mirror and a control method thereof. BACKGROUND
[0002] Free-Space Optical Communication (FSO) is a high-speed wireless communication technology that utilizes laser beams to transmit data in the atmosphere. Compared with traditional radio frequency communication, it has significant advantages such as high bandwidth, good security, resistance to electromagnetic interference, and no need for spectrum license, etc., and shows broad prospects in the fields of metropolitan access, backbone network backup, inter-satellite communication, and military applications. However, the reliability and stability of FSO systems are severely affected by the atmospheric channel. The main technical challenges are as follows: On the one hand, pointing deviation and disturbance. To achieve high-speed data transmission, FSO systems usually use highly collimated narrow beams, which puts extremely high requirements on the aiming and tracking accuracy between the transmitting and receiving ends. In actual deployment, especially between ground fixed stations or on mobile platforms, factors such as the slight sway of buildings, thermal expansion and contraction effects, wind loads, and slight ground vibrations can cause micro-radian or even milliradian level pointing deviations in the communication terminal. Such deviations can cause the transmitted light beam to deviate from the receiving aperture, resulting in a dramatic fluctuation in received optical power or even the interruption of the communication link. Traditional mechanical gimbals or voice coil motor driven beam steering mechanisms, although they can provide a wide range of adjustments, have slow response speed, large volume, high power consumption, and are difficult to compensate for high-frequency micro-vibrations in real time and accurately.
[0003] On the other hand, atmospheric attenuation and channel variation: when laser passes through the atmosphere, it will be attenuated by environmental factors such as fog, rain, snow, and turbulence. Among them, thick fog causes the most significant scattering loss due to its particle size being comparable to the wavelength of the laser, which can cause link attenuation to exceed 300 dB / km. In the face of such a wide range of overall signal attenuation, simply relying on increasing the transmission power is not only inefficient, but also increases system power consumption and cost, and in extreme cases still cannot meet the communication requirements. In the existing technology, there is a lack of an intelligent mechanism that can dynamically adjust the beam shape according to the channel attenuation characteristics. Although some systems try to use adaptive optics or multiple transmitters to form an array to cope with turbulence, the system is complex, costly, and has limited effect on uniform attenuation (such as thick fog).
[0004] To address pointing deviations, microelectromechanical systems (MEMS) micromirrors have been introduced into the field of freeform surface mirror (FSO). MEMS micromirrors offer advantages such as small size, low power consumption, fast response speed, and ease of integration. However, existing MEMS micromirrors based on electromagnetic or piezoelectric actuation often struggle to balance deflection angle and accuracy, and face technical bottlenecks in high-precision, large-angle out-of-plane motion control.
[0005] Therefore, there is an urgent need in this field for an FSO system solution that can simultaneously overcome the dual challenges of pointing deviation and atmospheric attenuation. This system needs to integrate a beam pointing control mechanism with fast response and high control precision, capable of intelligently distinguishing the sources of link attenuation and collaboratively adjusting beam pointing, beam shape, and even transmit power to maintain link stability and reliability in complex and variable atmospheric environments. Summary of the Invention
[0006] To address the shortcomings of existing technologies, this invention proposes an FSO laser communication system and its control method based on MEMS micromirrors. The aim is to optimize the system to effectively combat the impact of complex and variable atmospheric environments and improve the stability and reliability of wireless optical communication systems.
[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an FSO laser communication system based on MEMS micromirrors, the system comprising an optical emitting unit, an optical receiving unit, and a control and feedback unit; The optical emitting unit includes: a laser emitter for generating a communication laser beam; a MEMS micromirror assembly disposed on the output optical path of the laser emitter for adjusting the directionality of the communication laser beam; the MEMS micromirror assembly is electrostatically driven and uses a gear and linkage mechanism to convert in-plane driving motion into out-of-plane motion of the micromirror to achieve high-precision angle adjustment; and a variable divergence angle optical module disposed on the output optical path of the laser emitter for dynamically adjusting the divergence angle of the communication laser beam. The optical receiving unit includes: a photodetector for receiving communication optical signals from the peer and converting them into electrical signals; an optical power monitoring module for real-time monitoring and acquiring received optical power data; and a data reporting module for sending the received optical power data or link quality indicators derived therefrom to the transmitting end through a reverse communication channel. The control and feedback unit is communicatively connected to the optical emitting unit and the optical receiving unit, and is used to: receive feedback information from the data reporting module; determine, based on the changes in the feedback information, whether the main source of link attenuation is pointing error or atmospheric attenuation; and generate control commands according to the determination result to drive the MEMS micromirror assembly to perform pointing compensation, and / or drive the variable divergence angle optical module to adjust the beam divergence angle.
[0008] Preferably, the logic for the control and feedback unit to determine the source of link attenuation includes: if the received optical power data shows periodic fluctuations, then the main source of the link attenuation is determined to be pointing error, and the MEMS micromirror assembly is preferentially controlled to perform angle fine-tuning; if the received optical power data shows an overall decrease, then the main source of the link attenuation is determined to be atmospheric attenuation, and the variable divergence angle optical module is preferentially controlled to increase the beam divergence angle.
[0009] Preferably, the control and feedback unit is further configured to execute a power boosting mode: when atmospheric attenuation is determined and the beam divergence angle is increased, if the received optical power data is still lower than a preset threshold, the laser transmitter is controlled to increase its emission power.
[0010] Preferably, the MEMS micromirror assembly includes a comb-shaped interdigitated electrode and a gear transmission mechanism and a linkage mechanism connected between the comb-shaped interdigitated electrode and the micromirror; the comb-shaped interdigitated electrode generates linear or rotational motion under electrostatic drive, and transmits and converts the motion through the gear transmission mechanism and the linkage mechanism, ultimately realizing the precise control of the continuous lifting and deflection angle of the micromirror.
[0011] Preferably, the derived link quality indicators sent by the data reporting module include signal-to-noise ratio or bit error rate.
[0012] Preferably, the control and feedback unit employs a PID controller or a fuzzy controller, using the received optical power data or link quality indicators as feedback signals to form a closed-loop control of the MEMS micromirror assembly and / or the variable divergence angle optical module.
[0013] Secondly, the present invention provides a control method for an FSO laser communication system based on MEMS micromirrors, comprising the following steps: Optical power detection steps: Detect the received optical power in real time at the receiving end; Feedback reporting step: The received optical power or the link quality index derived therefrom is sent to the transmitting end through the reverse communication channel; Adaptive decision-making steps: The controller at the transmitting end determines, based on the trend of the received optical power change, whether the main source of link attenuation is pointing error or atmospheric attenuation; Beam control steps: If the error is determined to be a pointing error, the MEMS micromirror assembly is driven to compensate for the pointing of the emitted beam. If atmospheric attenuation is determined, the variable divergence angle optical module is driven to adjust the divergence angle of the emitted beam.
[0014] Preferably, in the adaptive decision-making step: pointing error is identified by analyzing the fluctuation periodicity and directionality of the received optical power; atmospheric attenuation is identified by analyzing the overall decrease magnitude and rate of change of the received optical power.
[0015] Preferably, in the beam control step, when atmospheric attenuation is determined, if the link quality is still not up to standard while or after driving the variable divergence angle optical module to increase the beam divergence angle, the laser transmitter is controlled to increase the emission power.
[0016] Preferably, the method includes three switchable operating modes: power tracking mode: when there is a weak high-frequency pointing error, the MEMS micromirror assembly is prioritized for dynamic angle tracking; divergence angle adjustment mode: when there is uniform atmospheric attenuation, the variable divergence angle optical module is controlled to expand the light spot to compensate for link loss; power enhancement mode: under extreme attenuation conditions, the transmission power is increased in tandem and supplemented by angle compensation.
[0017] This invention discloses an FSO laser communication system based on MEMS micromirrors and its control method. The system includes an optical transmitting unit, an optical receiving unit, and a control and feedback unit. The optical transmitting unit integrates a MEMS micromirror assembly that uses electrostatic drive and a gear / linkage mechanism to achieve high-precision off-plane angle adjustment, as well as a variable divergence angle optical module. The optical receiving unit monitors the received optical power in real time and reports it through a reverse channel. The control and feedback unit analyzes the changing trend of the received optical power to intelligently distinguish between two different causes of link degradation: pointing error and atmospheric attenuation. When pointing error caused by vibration is identified, the MEMS micromirror is controlled to perform rapid and accurate beam pointing compensation. When atmospheric attenuation caused by fog, rain, etc., is identified, the variable divergence angle optical module is controlled to expand the beam divergence angle to cover the receiving end and can also collaboratively increase the transmitting power, effectively improving the stability and reliability of the link in complex and variable atmospheric environments. Attached Figure Description
[0018] Figure 1 A schematic diagram of an FSO laser communication system based on MEMS micromirrors provided for this invention; Figure 2 This is a schematic diagram of the MEMS micromirror assembly structure provided by the present invention. Detailed Implementation
[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0020] Example 1 Figure 1 A schematic diagram of an FSO laser communication system based on MEMS micromirrors is provided for this invention. (Refer to...) Figure 1 The free-space laser communication system based on MEMS micromirrors provided in this embodiment includes three main parts: an optical emitting unit 100, an optical receiving unit 200, and a control and feedback unit 300. The optical emitting unit 100 and the optical receiving unit 200 are respectively deployed at both ends of the communication link, constituting bidirectional communication. For simplicity, the following description uses communication in one direction as an example.
[0021] The optical emitting unit 100 mainly includes a laser emitter 101, a MEMS micromirror assembly 102, and a variable divergence angle optical module 103. The laser emitter 101 can be a distributed feedback laser or an electro-absorption modulated laser to generate a laser beam for carrying communication signals. Its operating wavelength can be selected as the 1550nm communication band, which is safe for the human eye and has good transmission characteristics in the atmosphere.
[0022] The MEMS micromirror assembly 102 is one of the key components of this embodiment. Figure 2 This is a schematic diagram of the MEMS micromirror assembly structure provided by the present invention, with reference to... Figure 2 ,in Figure 2 (a) in the diagram is a schematic of a MEMS micromirror assembly without angle adjustment. Figure 2 (b) is a schematic diagram of a MEMS micromirror assembly that performs angle adjustment. This MEMS micromirror assembly is manufactured using surface micromachining technology, specifically based on a multilayer polycrystalline silicon process. The assembly includes an electrostatic comb actuator 1021, a gear transmission mechanism 1022, and a micromirror 1023.
[0023] In this embodiment, the electrostatic comb actuator 1021 consists of two rows of interlocking interdigitated fingers, one of which is a fixed comb tooth and the other is a movable comb tooth. The fixed and movable comb teeth are arranged in a comb-like staggered pattern. After applying a driving voltage, a strong electrostatic force perpendicular to the mirror surface is generated, outputting a precise linear displacement in the plane. The magnitude of the displacement is proportional to the rate of change of capacitance between the comb teeth. Affected by factors such as voltage, number of comb teeth, and gap, the movable comb tooth is connected to the MEMS micromirror through a drive rod structure, which amplifies the minute displacement of the comb tooth and transmits it to the micromirror, thereby realizing the angle adjustment of the micromirror and ultimately achieving precise control of the beam.
[0024] In this embodiment, the gear transmission mechanism 1022 includes a drive rod 1024, a pinion 1025, and a large gear 1026 connected to the micromirror base. One side of the drive rod is provided with a toothed structure that meshes with the pinion. The meshing of the pinion and the large gear converts the linear displacement of the moving comb teeth into a rotational motion with amplified torque.
[0025] In this embodiment, the micromirror 1023 is connected to the output end of the large gear of the gear transmission mechanism via a vertical torsion arm hinge. Driven by the gear mechanism, the micromirror 1023 can achieve out-of-plane, continuous deflection around its axis. This design can achieve optical deflection angles exceeding ±5 degrees, with positioning accuracy down to the microradian level.
[0026] The variable divergence angle optical module 103 is located in the optical path after the MEMS micromirror assembly 102. In a preferred embodiment, this module is an electro-controlled liquid crystal lens. By applying different control voltages, the arrangement of liquid crystal molecules can be changed, thereby dynamically altering its equivalent focal length. When combined with a fixed collimating lens, continuous adjustment of the outgoing beam divergence angle can be achieved, for example, from 0.5 milliradians to 5 milliradians, to cope with atmospheric attenuation of varying intensities.
[0027] The optical receiving unit 200 mainly includes a photodetector 201, an optical power monitoring module 202, and a data reporting module 203.
[0028] The photodetector 201 employs an avalanche photodiode, which efficiently converts the received optical signal into an electrical signal and amplifies it.
[0029] The optical power monitoring module 202 samples the average current output by the APD in real time through a low-noise amplifier and an ADC converter, and converts it into a digital form of the received optical power value p(t).
[0030] The data reporting module 203 is integrated into the communication FPGA of the system. It packages the p(t) data or the calculated signal-to-noise ratio into the reverse overhead of the communication protocol and sends it to the control and feedback unit 300 at the other end through an independent reverse wireless link (such as Wi-Fi or 4G / 5G) or the return optical channel of the main FSO link.
[0031] The control and feedback unit 300 is implemented with a high-performance MCU or FPGA as its core, and its internal control logic includes: The p(t) data is received from the data reporting module 203 and digitally filtered to eliminate noise.
[0032] Calculate the rate of change dp(t) / dt and spectral characteristics of p(t) within a certain time window. If periodic fluctuations are found in p(t) that correspond to the building sway frequency (e.g., 0.1-10 Hz) and the fluctuation amplitude is significant, then the main cause of the current link degradation is determined to be pointing error.
[0033] Monitor the moving average of p(t). If this average shows a smooth and continuous downward trend within a few seconds, without a significant increase in volatility, then the main cause of the current link degradation is atmospheric attenuation (such as fog or rain).
[0034] When a pointing error is detected, a control signal is generated to drive the MEMS micromirror assembly 102. This control is based on a PID algorithm, using p(t) as the feedback quantity, to dynamically adjust the voltage applied to the comb driver 1021, causing the micromirror 1023 to generate a reverse compensation angle, thereby pulling the beam back to the center of the receiving aperture.
[0035] When atmospheric attenuation is detected, a control signal is generated to drive the variable divergence angle optical module 103. For example, the voltage applied to the liquid crystal lens is increased to shorten its focal length, thereby expanding the divergence angle of the emitted beam and making the spot size at the receiving end larger. This ensures that the receiving aperture can still be covered even when the beam has a certain degree of drift, thus improving link redundancy.
[0036] In power boost mode, if the average value of p(t) is still lower than the minimum communication threshold after increasing the divergence angle, the control module will send a command to the drive circuit of the laser emitter 101 to increase its output power by a preset step value within the safety specifications.
[0037] Assume the system is deployed between two high-rise buildings, and crosswinds cause the towers to sway periodically. Step 1: The optical power monitoring module 202 at the receiver detects that p(t) fluctuates around the standard value by approximately 10dB at a frequency of about 1Hz. Step 2: The data reporting module 203 sends this information to the control and feedback unit 300 in real time. Step 3: The attenuation source judgment module of the control and feedback unit 300 identifies this periodic characteristic and determines it to be a pointing error. Step 4: The control unit enters power tracking mode and initiates PID closed-loop control for the MEMS micromirror assembly 102. Its control command is out of phase with the p(t) fluctuation, successfully suppressing the fluctuation amplitude of the received optical power within 2dB and maintaining link stability. Subsequently, the weather turns cloudy, and a light fog spreads. Step 1: The average value of p(t) at the receiver begins to decrease slowly and continuously, and the periodic fluctuation disappears. Step 2: The control and feedback unit 300 determines this to be atmospheric attenuation. Step 3. Subsequently, the control unit switches to the divergence angle adjustment mode and controls the variable divergence angle optical module 103 to gradually increase the beam divergence angle from 1 milliradian to 3 milliradian. Step 4. After this operation, the downward trend of p(t) is curbed and recovers, and the link is maintained at a low bit error rate.
[0038] This invention provides an FSO laser communication system based on MEMS micromirrors. The system includes an optical transmitting unit, an optical receiving unit, and a control and feedback unit. The optical transmitting unit integrates a MEMS micromirror assembly that uses electrostatic drive and a gear / linkage mechanism to achieve high-precision off-plane angle adjustment, as well as a variable divergence angle optical module. The optical receiving unit monitors the received optical power in real time and reports it via a reverse channel. The control and feedback unit analyzes the changing trend of the received optical power to intelligently distinguish between two different causes of link degradation: pointing error and atmospheric attenuation. When pointing error caused by vibration is identified, the MEMS micromirror is controlled to perform rapid and accurate beam pointing compensation. When atmospheric attenuation caused by fog, rain, etc., is identified, the variable divergence angle optical module is controlled to expand the beam divergence angle to cover the receiver and can also collaboratively increase the transmitting power, effectively improving the stability and reliability of the link in complex and variable atmospheric environments.
[0039] It should be noted that the technical features in the above embodiments can be combined arbitrarily, and the resulting technical solutions all fall within the protection scope of this application. Furthermore, in this document, terms such as "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A free space laser communication system based on MEMS micromirror, characterized in that, The optical transmitting unit comprises a laser transmitter for generating a communication laser beam, a MEMS micro-mirror assembly arranged in the light path of the laser transmitter for adjusting the directionality of the communication laser beam, the MEMS micro-mirror assembly being electrostatically driven and converting the in-plane driving motion into the off-plane motion of the micro-mirror through a gear and linkage mechanism to achieve high-precision angle adjustment, and a variable divergence angle optical module arranged in the light path of the laser transmitter for dynamically adjusting the divergence angle of the communication laser beam. The optical receiving unit comprises a photodetector for receiving the communication optical signal from the opposite end and converting it into an electrical signal, an optical power monitoring module for monitoring and obtaining the received optical power data in real time, and a data reporting module for sending the received optical power data or the derived link quality indicators to the transmitting end through the reverse communication channel. The control and feedback unit is communicatively connected with the optical transmitting unit and the optical receiving unit, and is configured to receive the feedback information from the data reporting module, determine whether the main source of link attenuation is the pointing error or the atmospheric attenuation based on the change of the feedback information, and generate a control instruction to drive the MEMS micro-mirror assembly to perform pointing compensation and / or drive the variable divergence angle optical module to adjust the divergence angle of the light beam according to the determination result. The logic of the control and feedback unit for determining the source of link attenuation comprises:
2. The system of claim 1, wherein, If the received optical power data presents periodic fluctuations, it is determined that the main source of link attenuation is the pointing error, and the MEMS micro-mirror assembly is preferentially controlled to perform angle fine adjustment. If the received optical power data presents overall decline, it is determined that the main source of link attenuation is the atmospheric attenuation, and the variable divergence angle optical module is preferentially controlled to increase the divergence angle of the light beam. The control and feedback unit is further configured to perform a power boosting mode: when it is determined that the atmospheric attenuation increases the divergence angle of the light beam, and the received optical power data is still below the preset threshold, the laser transmitter is controlled to increase its transmission power.
3. The system of claim 2, wherein, The MEMS micro-mirror assembly comprises a comb-shaped interdigital electrode, and a gear transmission mechanism and a linkage mechanism connected between the comb-shaped interdigital electrode and the micro-mirror; the comb-shaped interdigital electrode generates linear or rotational motion under electrostatic driving and is transmitted and converted through the gear transmission mechanism and the linkage mechanism, finally realizing the precise control of the deflection angle of the micro-mirror.
4. The system of claim 1, wherein, The derived link quality indicators sent by the data reporting module include the signal-to-noise ratio or the bit error rate.
5. The system of claim 1, wherein, The control and feedback unit adopts a PID controller or a fuzzy controller to form a closed-loop control on the MEMS micro-mirror assembly and / or the variable divergence angle optical module with the received optical power data or the link quality indicators as the feedback signal.
6. The system of claim 1, wherein, The method comprises the following steps:
7. A method for controlling free space laser communication for the system according to any one of claims 1 to 6, characterized in that, optical power detection step: detecting the received optical power in real time at the receiving end; feedback reporting step: sending the received optical power or the derived link quality indicators to the transmitting end through the reverse communication channel; Adaptive decision step: the controller of the transmitting end determines whether the main source of link attenuation is pointing error or atmospheric attenuation according to the trend of the received optical power; Beam control step: If the determination is pointing error, the MEMS micromirror assembly is driven to compensate the pointing of the transmitting beam; If the determination is atmospheric attenuation, the variable divergence optical module is driven to adjust the divergence angle of the transmitting beam.
8. The method of claim 7, wherein, In the adaptive decision step: Pointing error is identified by analyzing the periodicity and directionality of the fluctuation of the received optical power; Atmospheric attenuation is identified by analyzing the overall amplitude and rate of change of the received optical power.
9. The method of claim 7, wherein, In the beam control step, when the determination is atmospheric attenuation, the laser transmitter is controlled to increase the transmitting power if the link quality is still not up to standard while or after the variable divergence optical module is driven to increase the divergence angle of the beam.
10. The method of claim 7, wherein, The method includes three switchable working modes: Power tracking mode: when there is high-frequency weak pointing error, the MEMS micromirror assembly is preferentially controlled to perform dynamic angle tracking; Divergence angle adjustment mode: when there is uniform atmospheric attenuation, the variable divergence optical module is controlled to expand the light spot to compensate for link loss; Power boost mode: under extreme attenuation conditions, the transmitting power is increased in conjunction with angle compensation.