Large dynamic range extremely weak light high-precision optical power attenuator

Abstract

The application provides a large dynamic range extremely weak light high-precision optical power attenuator, which comprises a sealed constant-temperature aluminum alloy optical dark box, a coarse adjustment attenuating sheet combination module, a double reverse optical wedge continuous fine adjustment module, a two-dimensional angle adjustable honeycomb light extinction system, a global temperature monitoring and light source stable power module, a double-channel real-time optical path monitoring module and a closed-loop control unit; the coarse adjustment attenuating sheet combination module realizes stepped coarse attenuation; the double reverse optical wedge continuous fine adjustment module realizes continuous linear adjustment of optical density OD; the two-dimensional angle adjustable honeycomb light extinction system realizes dissipation and absorption of scattered light; the global temperature monitoring and light source stable power module realizes global temperature closed-loop temperature control of the dark box; the double-channel real-time optical path monitoring module realizes real-time calculation of actual attenuation ratio and completes error correction. The honeycomb plate can adjust the light absorption angle in real time according to the working condition of the optical path, and the absorption attenuating sheet and the double optical wedge continuously adjust the scattered stray light, so as to solve the defects of fixed light absorption efficiency of the fixed honeycomb and fluctuation of stray light with the ratio.

Description

Technical Field

[0001] This invention belongs to the fields of precision optical metrology, single-photon detection calibration, and extremely weak light radiation measurement technology. In particular, it relates to a high-precision optical power attenuator with a large dynamic range for extremely weak light, which is specifically applicable to high-precision metrology scenarios such as single-photon detector (SPD) detection efficiency traceability calibration and laser weak light calibration. Background Technology

[0002] Single-photon detectors (SPDs) are highly sensitive photoelectric detection devices capable of resolving and detecting extremely weak light signals at the single-photon level. Due to their superior weak light detection capabilities, SPDs have been widely used in fields such as extremely weak light measurement, photon counting analysis, precision optical testing, laser remote sensing, biofluorescence detection, single-photon spectral analysis, and advanced imaging. Detection efficiency (DE), as a core parameter measuring the photoelectric conversion performance of a single-photon detector, directly determines the measurement accuracy and operational reliability of the detection system. The accuracy and traceability of its value are crucial for the consistency, reliability, and comparability of experimental data and engineering measurement results. Therefore, achieving high-precision, traceable calibration of single-photon detector detection efficiency is a vital foundation for establishing unified measurement standards, ensuring accurate and reliable measurement results, and promoting the application of advanced photoelectric detection technologies.

[0003] Currently, standardized calibration methods for single-photon detector detection efficiency in the industry mainly fall into two categories: the correlation photon method and the standard detector method. Each method has its own characteristics and applicable scenarios. The correlation photon method has a relatively simple measurement process and does not rely on a high-precision standard light source, making it one of the important means of measuring detection efficiency. However, this method is essentially a relative measurement method and does not possess complete metrological traceability capabilities. It typically requires calibration and verification using an absolute radiometer standard detector system to ensure the accuracy and reliability of the measurement results.

[0004] In actual calibration, the power levels of the detector light used in the correlated photon method and the standard detector method differ significantly, typically by about 3 to 6 orders of magnitude, forming a dynamic power range that spans a wide area. To achieve effective connection and accurate comparison between the two measurement systems, it is necessary to use a high-precision optical attenuation device to attenuate the high-power optical signal by a large factor, converting it to the linear response range within which the single-photon detector can operate stably.

[0005] However, existing traditional optical attenuation schemes and commercially available attenuation devices are insufficient to meet the requirements of high-precision calibration applications for single-photon detectors. During attenuation over ultra-wide dynamic ranges, existing equipment generally suffers from insufficient attenuation linearity, limited attenuation accuracy, weak suppression of stray and reflected light, and poor long-term stability. These issues easily introduce additional measurement errors during extremely weak light measurements, affecting the accuracy and repeatability of detection efficiency calibration results. These problems have become significant technical bottlenecks restricting the improvement of high-precision traceability and calibration capabilities for single-photon detectors.

[0006] Specifically, this is reflected in the following aspects:

[0007] 1. Simple structure for eliminating stray light

[0008] At high attenuation rates, light needs to be attenuated to near the photon level, requiring an extremely low stray light environment. Conventional attenuators rely on simple light shields or black plates, resulting in low absorption rates. Reflected light from the device surface and scattered light from the cavity walls can easily be superimposed on the effective signal, leading to significantly higher measurement errors and making it difficult to achieve near-photon level stray light suppression.

[0009] 2. Lack of stray light suppression measures due to reflection effects between attenuators. At high attenuation rates, the light needs to be attenuated to near the photon level. If multiple attenuators are used simultaneously in the optical path, the attenuated signal is very weak and falls within the nonlinear measurement region of the measuring instrument. To eliminate the influence of instrument nonlinearity on the measurement results, multiple attenuators are usually combined to produce transmittance at different magnifications. The total transmittance is expressed as the product of the transmittances of all individual attenuators. Attenuators are typically mounted vertically, but when multiple attenuators are used in series, stray light due to reflection effects between attenuators occurs. The reflected light from later attenuators is reflected back to earlier attenuators, creating multiple reflections and crosstalk. This results in a deviation between the total transmittance of the filter and the product of the transmittances of all individual attenuators, leading to transmittance equivalence issues.

[0010] 3. The system has poor stability and repeatability.

[0011] For high-rate attenuation, since the attenuation ratio of a single filter is limited, multiple filters are usually combined to meet the requirements of different attenuation ratios. Traditional optical attenuation is built on an optical platform, which is significantly affected by ambient light and vibration. At the same time, there are mechanical positioning errors when multiple filters are combined, and there is a lack of high-precision reset and positioning mechanisms, making it difficult to ensure the high stability and repeatability of the system for long-term operation, and thus failing to meet the requirements of metrological-grade high-precision measurement. Summary of the Invention

[0012] To address the above technical problems, this invention provides a high-precision optical power attenuator with a large dynamic range for extremely weak light. The specific technical solution is as follows: A high-precision optical power attenuator with a large dynamic range for extremely weak light includes a sealed, temperature-controlled aluminum alloy optical dark box, a coarse-adjustment attenuator assembly module, a dual-reverse optical wedge continuous fine-adjustment module, a two-dimensional angle-adjustable honeycomb extinction system, a global temperature monitoring and light source power stabilization module, a dual-channel real-time optical path monitoring module, and a closed-loop control unit;

[0013] The coarse attenuator assembly module includes multiple independent neutral density attenuators, which are driven by independent linear motors to cut into the optical path to achieve stepped coarse attenuation.

[0014] The dual-reverse optical wedge continuous fine adjustment module is connected in series at the rear end of the optical path of the coarse adjustment attenuator combination module. It includes a pair of optical wedges with the same wedge angle and refractive index. Two sets of synchronous linear motors drive the two optical wedges to move in opposite directions, so as to realize continuous linear adjustment of optical density OD, and the center of the transmitted light spot coincides with the main optical axis without offset throughout the entire process.

[0015] The two-dimensional angle-adjustable honeycomb extinction system includes multiple sets of distributed honeycomb light-absorbing units. Each set of honeycomb light-absorbing units includes a honeycomb light-absorbing plate and a two-dimensional rotary servo motor and an angle closed-loop feedback sensor mounted on its back. These are respectively arranged on the attenuator reflected light emission side and on both sides of the double light wedge scattered light. The two-dimensional rotary servo motor and the double light wedge drive motor establish a millisecond-level linkage closed loop. The pitch and horizontal angle of the honeycomb plate are dynamically adjusted according to the real-time displacement of the double light wedges, so that the attenuator reflected light and the light wedge scattered light are perpendicularly incident on the honeycomb channel to achieve dissipation and absorption.

[0016] The full-range temperature monitoring and light source power stabilization module includes a distributed platinum resistance temperature sensor array and a cavity constant temperature liner, which realizes closed-loop temperature control of the entire dark box, real-time voltage stabilization of the output power of the incident laser light source, and temperature drift compensation for attenuation ratio based on temperature data.

[0017] The dual-channel real-time optical path monitoring module includes an input reference beam splitter and an output trap standard detector. It synchronously collects the input raw optical power and the attenuated transmitted optical power, calculates the actual attenuation ratio in real time and compares it with the theoretical calibration value. When the deviation exceeds the threshold, it automatically drives the motor and the cellular extinction system to complete the error correction.

[0018] The coarse adjustment attenuator combination module, the dual reverse optical wedge continuous fine adjustment module, the two-dimensional angle adjustable honeycomb extinction system, the full-range temperature monitoring and light source power stabilization module, and the dual-channel real-time optical path monitoring module are all housed in a sealed constant temperature aluminum alloy optical dark box.

[0019] The closed-loop control unit is electrically connected to all the above modules to realize integrated closed-loop operation of automatic attenuation ratio combination, continuous fine adjustment, stray light adaptive suppression, constant temperature light stabilization, and real-time attenuation ratio verification.

[0020] The present invention has the following beneficial effects:

[0021] 1. Adaptive dynamic stray light suppression significantly reduces background noise.

[0022] The two-dimensional rotating honeycomb panel can adjust the light absorption angle in real time according to the optical path conditions, fully absorbing the reflected light from the attenuator and the scattered stray light generated by the continuous adjustment of the dual optical wedges, solving the defects of the traditional fixed honeycomb panel with fixed light absorption efficiency and stray light fluctuation with magnification; combined with the original three-level extinction system, the stray light suppression capability of the system is further improved by 1 to 2 orders of magnitude, which is suitable for ultra-low background requirements of single photon fW~pW extremely weak light measurement.

[0023] 2. Integrated coarse and fine attenuation with continuously adjustable attenuation, no optical axis shift, and excellent linearity.

[0024] The figure-eight tilt attenuator provides ultra-large dynamic step coarse adjustment, while the dual reverse optical wedges enable continuous and smooth fine adjustment throughout the entire range. The reverse movement of the dual optical wedges completely cancels the translational offset of the single wedge beam, resulting in zero optical axis drift throughout the entire adjustment range and a strictly linear change in total OD with displacement. At the same time, it is equipped with a synchronous linkage honeycomb structure to solve the problem of severe stray light fluctuation inherent in continuously adjustable attenuators, taking into account the triple advantages of large dynamic range, continuous adjustability, and low stray light.

[0025] 3. Global constant temperature control and closed-loop power management of the light source eliminate temperature drift system errors.

[0026] Distributed multi-point temperature measurement + cavity constant temperature liner suppresses temperature deformation of optical components and mechanical structure; real-time voltage stabilization of input light source power eliminates attenuation drift caused by temperature and light source fluctuations, enabling the equipment to perform continuous measurement and testing for a long time, greatly improving measurement repeatability and long-term stability.

[0027] 4. Dual-channel real-time monitoring and closed-loop verification ensures traceable measurement and real-time error correction.

[0028] The input and output dual-channel detectors synchronously monitor the optical path, verify the attenuation ratio and output optical power in real time, and automatically compensate for deviations caused by positioning, stray light, and temperature drift. It can be directly compared and calibrated synchronously with the single-photon detector under test, ensuring accurate and controllable attenuation throughout the process. The measurement results have complete metrological traceability, and the indicators are superior to existing domestic similar equipment, reaching the international advanced level.

[0029] 5. The project has significant industrialization value.

[0030] This invention can be widely used in scenarios such as single-photon detector metrology and calibration, quantum communication optical power attenuation testing, biological extremely weak fluorescence detection, supercontinuum weak light calibration, and laser remote sensing weak signal simulation; the modular and automated design supports hot-swapping and automatic calibration, reducing equipment maintenance costs and is suitable for mass industrialization in metrology institutes, quantum technology laboratories, and optoelectronic testing companies. Attached Figure Description

[0031] Figure 1 The honeycomb panel structure of the present invention;

[0032] Figure 2 This is a schematic diagram illustrating the absorption of light by trapping within a honeycomb structure according to the present invention.

[0033] Figure 3 This is a schematic diagram of the three levels of stray light in this invention;

[0034] Figure 4 This is a general block diagram of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0036] This invention, based on a sealed aluminum alloy optical dark box, a figure-eight tilted modular attenuator, a honeycomb three-stage stray light elimination system, and a micron-level linear motor positioning mechanism, adds four core innovative modules to form an angle-adjustable honeycomb stray light adaptive suppression system, an integrated optical path for fixed-rate attenuation coarse adjustment and dual-reverse optical wedge continuous fine adjustment, a global distributed temperature closed-loop monitoring and light source power stabilization system, and an input / output dual-channel real-time optical path monitoring and calibration closed-loop system. It achieves discrete point and continuous rate adjustable attenuation, dynamic adaptive stray light suppression, constant temperature power stabilization, and real-time online rate calibration, solving the four major technical pain points of traditional attenuators: stray light fluctuation, optical axis offset, temperature drift, and inability to calibrate the rate in real time.

[0037] This invention provides a high-precision optical power attenuator with a large dynamic range for extremely weak light, such as... Figure 3 , 4 As shown, it includes: a sealed constant temperature aluminum alloy optical dark box, a coarse adjustment attenuator combination module, a dual reverse optical wedge continuous fine adjustment module, a two-dimensional angle adjustable honeycomb extinction system, a full-range temperature monitoring and light source power stabilization module, a dual-channel real-time optical path monitoring module, and a closed-loop control unit.

[0038] The coarse attenuator assembly module includes multiple independent neutral density attenuators, which are installed at a 4.5-degree figure-eight angle or vertically, and are driven by an independent linear motor to cut into the optical path to achieve stepped coarse attenuation.

[0039] The dual-reverse optical wedge continuous fine adjustment module is connected in series at the rear end of the optical path of the coarse adjustment attenuator combination module. It includes a pair of optical wedges with the same wedge angle and refractive index. Two sets of synchronous linear motors drive the two optical wedges to move in opposite directions, so as to realize continuous linear adjustment of optical density OD, and the center of the transmitted light spot coincides with the main optical axis without offset throughout the entire process.

[0040] The two-dimensional angle-adjustable honeycomb extinction system includes multiple sets of distributed honeycomb light-absorbing units. Each set of honeycomb light-absorbing units includes a honeycomb light-absorbing plate and a two-dimensional rotary servo motor and an angle closed-loop feedback sensor mounted on its back. These are respectively arranged on the attenuator reflected light emission side and on both sides of the double light wedge scattered light. The two-dimensional rotary motor and the double light wedge drive motor establish a millisecond-level linkage closed loop, dynamically adjusting the pitch and horizontal angle of the honeycomb plate according to the real-time displacement of the double light wedges, so that the attenuator reflected light and the light wedge scattered light are perpendicularly incident on the honeycomb channel to achieve dissipation and absorption.

[0041] The full-range temperature monitoring and light source power stabilization module includes a distributed platinum resistance temperature sensor array and a cavity constant temperature liner, which realizes closed-loop temperature control of the entire dark box, real-time voltage stabilization of the output power of the incident laser light source, and temperature drift compensation for attenuation ratio based on temperature data.

[0042] The dual-channel real-time optical path monitoring module includes an input reference beam splitter and an output trap standard detector. It synchronously collects the input raw optical power and the attenuated transmitted optical power, calculates the actual attenuation ratio in real time and compares it with the theoretical calibration value. When the deviation exceeds the threshold, it automatically drives the motor and the cellular extinction system to complete the error correction.

[0043] The closed-loop control unit is electrically connected to all the above modules to realize integrated closed-loop operation of automatic attenuation ratio combination, continuous fine adjustment, stray light adaptive suppression, constant temperature light stabilization, and real-time attenuation ratio verification.

[0044] Furthermore, the inner wall of the honeycomb light-absorbing panel is coated with an ultra-low reflection matte paint with an absorption rate of ≥99.6%, and the honeycomb adopts a hexagonal deep hole structure; the two-dimensional rotary servo motor has independent horizontal and pitch dual-axis adjustment functions, and a built-in micro grating collects the real-time rotation angle.

[0045] Furthermore, the synchronous counter-movement of the two optical wedges cancels out the lateral beam offset, and the total optical density OD changes linearly with the wedge displacement; the scattered stray light generated by the sliding of the two optical wedges is synchronously adjusted by a linkage two-dimensional rotating honeycomb motor to dynamically absorb the newly scattered light from the wedges, eliminating the defect of drastic fluctuations in stray light intensity with attenuation ratio during continuous adjustment; the wedge angle of the two optical wedges is 2°, the maximum stroke is 20mm, and the overall attenuation coverage is (1~10). -7 ).

[0046] Furthermore, distributed platinum resistance temperature sensors are attached to the attenuator, double optical wedges, guide rail, and heat-sensitive areas of the light source window, respectively; a semiconductor cooling and heating constant temperature liner is arranged in the optical dark box interlayer to control the cavity temperature fluctuation within ±0.1℃; the input reference beam splitter monitors the laser power in real time, and adjusts the light source driving current through negative feedback to stabilize the incident reference light power, while compensating for the transmittance error caused by temperature drift in real time based on the temperature coefficient database of each optical element.

[0047] Furthermore, the input reference beam splitter collects the unattenuated raw laser power as the calculation benchmark, and the output trap standard detector and the back-end single-photon detector under test sample synchronously; the main control compares the theoretical attenuation ratio with the measured ratio in real time, and automatically executes the following triple correction operations when deviation occurs: attenuator / dual optical wedge repositioning and reset, secondary optimization of the cellular absorption angle, and temperature drift error compensation, to ensure the accuracy of output optical power and attenuation ratio in real time.

[0048] Furthermore, the coarse adjustment attenuator is installed at a 4.5-degree angle, with the reflected light deviating from the main light path and incident on the corresponding honeycomb light-absorbing unit; multiple attenuators are independently traceable and calibrated, and the total transmittance of the combination is equal to the product of the transmittance of the individual attenuators, with the measured relative equivalent difference being less than one ten-thousandth.

[0049] In this invention, multiple distributed honeycomb light-absorbing units equipped with two-dimensional angle rotation motors adaptively adjust the incident angle of reflected light, dynamically maximizing stray light absorption and reducing system background noise. Inside the optical dark box, each reflected and scattered light emission side is independently equipped with a honeycomb light-absorbing unit, which includes a light-absorbing plate. Each honeycomb light-absorbing plate is backed by a two-dimensional angle rotation servo motor, which integrates independent horizontal and vertical dual-axis adjustment functions and incorporates a built-in micro-grating angle closed-loop feedback sensor. Figure 1 As shown in Figure 2, the substrate of the honeycomb light-absorbing panel is aluminum alloy, and the inner wall is sprayed with ultra-low reflection matte paint with an absorption rate of ≥99.6%. The honeycomb adopts a hexagonal structure with a side length of 5mm and a deep hole of 20mm to extend the optical path.

[0050] When switching attenuator combinations or adjusting the attenuation ratio of the dual wedges, the closed-loop control unit retrieves the theoretical emission angle of the reflected light based on the current optical path wavelength and attenuation ratio, and drives the two-dimensional servo rotary motor to adjust the pitch and horizontal angles of the honeycomb panel in real time. This ensures that the reflected light from the attenuator interface and the scattered light from the dual wedges are perpendicularly incident into the honeycomb channel, preventing the light from directly reflecting off the honeycomb surface at an angle and escaping. When the switching of the optical path wavelength and attenuation ratio causes the angle of the reflected light to shift, the motor dynamically fine-tunes the honeycomb attitude in milliseconds to ensure that all stray light enters the honeycomb cavity and is dissipated through multiple reflections.

[0051] Traditional fixed honeycomb panels can only adapt to a single reflection angle, resulting in a large amount of stray light escaping and high background noise when operating conditions change. This invention, through two-dimensional angle adaptive adjustment, ensures that the honeycomb light-absorbing structure always maintains the optimal light absorption posture, further reducing the overall stray light of the system by 1 to 2 orders of magnitude, and significantly reducing the background noise of single-photon level measurements. The honeycomb unit and attenuator are matched with a 4.5-degree figure-eight tilt optical path, combined with a three-level stray light suppression system of "metal shell shielding - honeycomb geometric dissipation - matte varnish energy absorption", forming an adaptive angle control and three-level physical extinction composite stray light suppression network.

[0052] In this invention, an integrated optical path of "fixed attenuation coarse adjustment and dual reverse optical wedge continuous fine adjustment" is adopted, with zero offset of the optical axis throughout the entire process; synchronous linkage of the cellular extinction unit close-loop suppresses the addition of stray light from the optical wedge, solving the problem of severe fluctuation of stray light when switching the continuous attenuation ratio.

[0053] 1. Coarse adjustment unit: Figure-eight tilt modular attenuation chip group

[0054] Multiple independent neutral density attenuators are retained, and they are installed at a 4.5-degree figure-eight angle. An independent linear motor drives the modular entry optical path to achieve… Stepped coarse attenuation; each attenuator element is independently traceable and calibrated at the factory, and the total transmittance meets the following requirements: N is the total number of attenuators. Let be the transmittance of the i-th attenuator. The equivalent relative difference is controlled within the range of one ten-thousandth to eliminate inter-attenuator reflection crosstalk error.

[0055] 2. Fine-tuning unit: Double reverse symmetrical optical wedge continuous attenuation structure

[0056] A set of reverse-paired optical wedges is connected in series at the rear end of the coarse adjustment optical path. The two wedges have the same refractive index, wedge angle, and thickness, and are driven by two sets of synchronous precision linear motors in reverse linkage.

[0057] To counteract beam shift defects: Single beam wedge adjustment causes the transmitted beam spot to shift laterally, resulting in optical axis drift and transmittance drift; double beam wedges move in opposite directions and synchronously, and the beam shift cancels each other out. The center of the beam spot always coincides with the main optical axis in the entire continuous adjustment range, with zero optical axis shift, thus completely eliminating the measurement drift caused by beam shift.

[0058] Advantages of linear attenuation: The total optical density OD changes strictly linearly with the synchronous displacement of the two optical wedges. The linearity is improved by an order of magnitude with continuous adjustment, which can realize continuous and smooth fine-tuning of OD and fill the gap in the step attenuation of fixed filters.

[0059] 3. Synchronous closed-loop stray light linkage suppression mechanism

[0060] The sliding and angle changes of the dual optical wedges generate interface scattering stray light, and the scattering intensity changes drastically with the wedge displacement (attenuation factor). This invention establishes a millisecond-level linkage closed loop between the dual optical wedge drive motor and the two-dimensional rotary honeycomb motor:

[0061] The control unit collects the current displacement and transmission attenuation ratio of the dual optical wedges in real time, calculates the emission angle of the scattered light from the optical wedges in real time, and synchronously drives the corresponding two-dimensional rotating honeycomb motor to adjust the light absorption angle, dynamically matching the propagation direction of the scattered light from the optical wedges, and introducing the newly added scattered stray light from the optical wedges into the honeycomb channel for absorption in real time; thus, during the continuous change of the attenuation ratio, the scattered stray light is synchronously and dynamically suppressed, eliminating the inherent defect of stray light fluctuating drastically with the attenuation ratio.

[0062] Fixed filter coarse adjustment provides an ultra-wide attenuation range, dual optical wedges enable continuous fine tuning within any range, and the entire unit can achieve... Wide dynamic range with continuously adjustable attenuation, balancing a large dynamic range with continuous and smooth adjustment capability.

[0063] In this invention, a global distributed temperature monitoring and laser source power closed-loop stabilization system are used to suppress the attenuation factor and output optical power drift caused by temperature drift.

[0064] 1. Global Distributed Temperature Monitoring Structure

[0065] Multiple sets of miniature high-precision platinum resistance temperature sensors are arranged inside the optical dark box, respectively attached to five key heat-sensitive areas: the attenuator substrate, the double-wedge optical surface, the honeycomb light-absorbing wall, the motor rail, and the light source input window. The sensor sampling frequency is 1Hz, and the temperature data of each point is collected in real time and uploaded to the main control unit. The outside of the dark box is equipped with a semiconductor cooling and heating constant temperature liner to form a sealed constant temperature cavity.

[0066] 2. Temperature drift compensation algorithm

[0067] The main controller has a built-in temperature coefficient calibration database for each optical component: based on real-time multi-point temperature data, it corrects the OD error caused by the theoretical transmittance of the attenuator and the refractive index offset of the double wedge in real time; at the same time, it performs temperature compensation on the positioning coordinates of the linear motor to offset the positioning deviation caused by the thermal expansion and contraction of the metal guide rail.

[0068] 3. Light source power closed-loop stabilization unit

[0069] A laser source power monitoring detector is integrated at the front end of the device's optical input to collect the incident raw laser power in real time. When the output power of the source drifts with temperature, the main controller synchronously adjusts the source drive current to form a power negative feedback closed loop, ensuring that the incident reference light power entering the attenuation system remains stable over a long period of time.

[0070] This invention eliminates the triple errors caused by temperature changes: temperature drift of filter transmittance, drift of attenuation linearity of double wedges, and thermal expansion and contraction error of mechanical positioning; the power fluctuation of the incident light source is suppressed by real-time voltage stabilization, and the stability of the attenuation ratio and output optical power of the whole machine for long-term continuous measurement is greatly improved, meeting the long-term repeatability requirements of metrology.

[0071] This invention employs a dual-channel real-time monitoring system that synchronizes input-side reference monitoring and output-side single-photon detector to verify the accuracy of attenuation ratio and output optical power in real time.

[0072] 1. Dual-channel monitoring hardware architecture

[0073] Input reference monitoring channel: A beam-splitting monitoring detector is set between the light source and the coarse adjustment attenuation module to collect the original unattenuated laser power in real time, which serves as the reference for calculating the theoretical attenuation ratio;

[0074] Output synchronous monitoring channel: A low-noise trap standard detector is set at the light output port of the attenuator to synchronously collect transmitted light signals in parallel with the single-photon detector under test at the back end.

[0075] 2. Real-time rate verification logic

[0076] The closed-loop control unit reads the input reference optical power and the output measured transmitted optical power in real time. It calculates the actual real-time attenuation ratio by combining the current attenuator combination and the double optical wedge displacement, and compares the difference with the theoretical pre-calibrated ratio. If the deviation between the two exceeds the set threshold, the system automatically performs three-level correction: ① Re-drives the positioning motor to reset and correct the position of the attenuator and double optical wedge; ② Links the two-dimensional cellular motor to optimize the stray light suppression angle; ③ Retrieves multi-point temperature data to correct temperature drift error.

[0077] 3. Single-photon detector collaborative calibration logic

[0078] The output monitoring detector samples synchronously with the SPD under test, converts the measured optical power of the standard detector into the equivalent photon count, compares it with the SPD photon count in real time, and dynamically corrects the SPD detection efficiency calibration parameters. The accuracy of the output optical power after attenuation is verified in real time throughout the process, avoiding magnification distortion caused by filter aging, optical path offset, and stray light abrupt change, and ensuring the accuracy of metrological traceability.

[0079] like Figure 4 As shown, the main optical path includes: incident light passing through attenuator 1, attenuator 2, and attenuator 3 before exiting through a double optical wedge. The incident light passes through attenuator 2 and attenuator 3 at a 45-degree angle and the double optical wedge to form primary scattered light, which is absorbed by the honeycomb light-absorbing unit.

[0080] The present invention provides a high-precision optical power attenuator with a large dynamic range for extremely weak light, the complete structure of which is detailed as follows:

[0081] Sealed constant temperature aluminum alloy optical dark box: Double-layer sealed aluminum alloy cavity, with a semiconductor heating and cooling constant temperature liner in the middle, and full gap sealing to block external stray light; the inner wall is fully covered with honeycomb light-absorbing panels, and each honeycomb panel is equipped with an independent two-dimensional rotary servo motor.

[0082] Coarse adjustment attenuator assembly module: 3 attenuators with different OD figure-eight tilt neutral density, driven by independent high-precision linear motors, and micron-level grating closed-loop positioning;

[0083] Dual-reverse optical wedge continuous fine-tuning module: a pair of optical wedges of the same specification, two sets of synchronous reverse linear drive mechanisms, displacement grating closed-loop feedback; and independent two-dimensional adjustable honeycomb light absorption units on both sides.

[0084] Two-dimensional angle-adjustable honeycomb extinction system: multiple sets of distributed honeycomb light-absorbing components, dual-axis rotary motor and angle grating, and millisecond-level linkage closed loop with attenuator and dual optical wedge drive system;

[0085] Full-range temperature monitoring and light source power stabilization module: distributed platinum resistance temperature measurement array, light source input spectrometer, and light source drive power negative feedback circuit;

[0086] Dual-channel real-time optical path monitoring module: input reference spectrometer, output trap standard detector;

[0087] Closed-loop control unit for the whole machine: an integrated main control board that integrates motion control, angle adjustment, temperature compensation, and real-time magnification verification, and is equipped with human-machine interaction and automatic calibration programs.

[0088] The following provides more specific embodiments:

[0089] Example 1: Engineering Example of a Two-Dimensional Angle Adjustable Honeycomb Extinction System (divided into two groups: basic assembly and multi-condition testing)

[0090] The optical dark box contains a total of 5 independent honeycomb light-absorbing units: 3 sets correspond to the reflection light paths of three figure-eight tilted attenuators, and 2 sets are arranged at the left and right scattering exits of the double reverse light wedges;

[0091] The single honeycomb light-absorbing panel has an external dimension of 80mm×80mm, a honeycomb side length of 5mm, a thickness of 0.1mm, a hole depth of 20mm, and a hexagonal array arrangement; the honeycomb substrate is formed by stamping aluminum alloy, and the inner and outer walls are coated with black matte paint with an absorption rate of 98.8%.

[0092] Two-dimensional rotary servo motor model: miniature precision dual-axis gimbal motor, horizontal adjustment range ±15°, pitch adjustment range ±10°, minimum angle adjustment resolution 0.01°, single angle adjustment response time ≤20ms;

[0093] The motor tail integrates a miniature grating encoder to transmit the attitude and angle of the honeycomb panel back to the main controller in real time; each honeycomb unit is equipped with an independent aluminum alloy light-shielding bracket to prevent stray light from leaking out during adjustment.

[0094] Example 2: Example of coarse attenuation adjustment + continuous fine adjustment of optical path using dual reverse optical wedges (mechanical assembly, linearity, and stray light linkage in three groups)

[0095] Example 2-1 Implementation of Optical Path Mechanical Assembly

[0096] The coarse adjustment module has three built-in neutral density attenuators with optical densities of OD1, OD2 and OD3, each driven by an independent linear motor, with a repeatability of ±0.06mm. The attenuators are uniformly tilted at a 4.5° V-shape with the main optical axis, and a 50mm space is reserved between the attenuators for the installation of honeycomb light traps.

[0097] Fine-tuning the parameters of the dual optical wedges in the optical path: quartz optical substrate, wedge angle 2°, light transmission diameter 25mm, refractive index n=1.45 in the visible light band; two sets of linear motors synchronously reverse-drive, maximum stroke of a single wedge 50mm, synchronous displacement error <6μm;

[0098] Optical path arrangement sequence: laser input port → input beam splitting monitoring detector → coarse adjustment attenuator module → dual reverse optical wedge fine adjustment module → output trap standard detector → single photon detector under test.

[0099] Example 2-2 Optical Axis Misalignment and Linearity Measurement Test

[0100] Continuously adjust the displacement of the dual optical wedges from 0 to 20 mm, and collect the center coordinates of the light spot and the measured OD value throughout the process.

[0101] 1) The maximum lateral offset of the light spot is 0.42μm, which meets the engineering "zero optical axis offset" index; compared with the single optical wedge scheme, the light spot offset is 128μm for the same stroke.

[0102] 2) Linear fitting between measured OD values ​​and displacement (R²) 2 =0.99994), linearity error <0.04%;

[0103] 3) The combination of coarse adjustment OD6 and dual optical wedges with maximum OD3 can achieve a total attenuation ratio of up to 10. -7 With multiple gear combinations, it can achieve a maximum speed of 10. -10 Attenuation, covering the single-photon fW~pW measurement range.

[0104] Example 3: Example of a system for global temperature monitoring and stable power of light source (two sets: temperature control assembly and long-term stability)

[0105] The optical dark box is filled with semiconductor cooling and heating elements, equipped with a PID temperature control module; the inner cavity is equipped with 8 PT1000 high-precision platinum resistance sensors, respectively attached with: OD1 attenuator, OD2 attenuator, OD3 attenuator, left optical wedge, right optical wedge, linear guide rail, honeycomb wall, and laser input window; temperature measurement accuracy ±0.01℃;

[0106] The machine is set to a standard operating temperature of 25℃, and the temperature control system automatically compensates for ambient temperature changes of 18~32℃.

[0107] Example 4: Application Implementation of Single Photon Detector (SPD) Detection Efficiency Calibration

[0108] Application scenario: Metrological traceability calibration of 670nm silicon-based SPD, with a target single-photon power range of 10. -10 ~10 -12 W;

[0109] Operating procedures:

[0110] 1) The control system automatically selects the coarse adjustment OD2+OD3 combination, and the dual optical wedges are continuously fine-tuned to the target photon flux;

[0111] 2) The input spectrophotometer collects the reference optical power, and the output traps the standard detector to sample synchronously with the SPD under test;

[0112] 3) The main controller compares the standard detector optical power with the SPD photon count every second and corrects the attenuation ratio in real time;

[0113] 4) Collect 30 sets of data continuously and calculate the combined standard uncertainty of SPD detection efficiency measurement.

Claims

1. A high-precision optical power attenuator with a large dynamic range for extremely weak light, characterized in that, It includes a sealed constant temperature aluminum alloy optical dark box, a coarse adjustment attenuator combination module, a dual reverse optical wedge continuous fine adjustment module, a two-dimensional angle adjustable honeycomb extinction system, a full-range temperature monitoring and light source power stabilization module, a dual-channel real-time optical path monitoring module, and a closed-loop control unit. The coarse attenuator assembly module includes multiple independent neutral density attenuators, which are driven by independent linear motors to cut into the optical path to achieve stepped coarse attenuation. The dual-reverse optical wedge continuous fine adjustment module is connected in series at the rear end of the optical path of the coarse adjustment attenuator combination module. It includes a pair of optical wedges with the same wedge angle and refractive index. Two sets of synchronous linear motors drive the two optical wedges to move in opposite directions, so as to realize continuous linear adjustment of optical density OD, and the center of the transmitted light spot coincides with the main optical axis without offset throughout the entire process. The two-dimensional angle-adjustable honeycomb extinction system includes multiple sets of distributed honeycomb light-absorbing units. Each set of honeycomb light-absorbing units includes a honeycomb light-absorbing plate and a two-dimensional rotary servo motor and an angle closed-loop feedback sensor mounted on its back. These are respectively arranged on the attenuator reflected light emission side and on both sides of the double light wedge scattered light. The two-dimensional rotary servo motor and the double light wedge drive motor establish a millisecond-level linkage closed loop. The pitch and horizontal angle of the honeycomb plate are dynamically adjusted according to the real-time displacement of the double light wedges, so that the attenuator reflected light and the light wedge scattered light are perpendicularly incident on the honeycomb channel to achieve dissipation and absorption. The full-range temperature monitoring and light source power stabilization module includes a distributed platinum resistance temperature sensor array and a cavity constant temperature liner, which realizes closed-loop temperature control of the entire dark box, real-time voltage stabilization of the output power of the incident laser light source, and temperature drift compensation for attenuation ratio based on temperature data. The dual-channel real-time optical path monitoring module includes an input reference beam splitter and an output trap standard detector. It synchronously collects the input raw optical power and the attenuated transmitted optical power, calculates the actual attenuation ratio in real time and compares it with the theoretical calibration value. When the deviation exceeds the threshold, it automatically drives the motor and the cellular extinction system to complete the error correction. The coarse adjustment attenuator combination module, the dual reverse optical wedge continuous fine adjustment module, the two-dimensional angle adjustable honeycomb extinction system, the full-range temperature monitoring and light source power stabilization module, and the dual-channel real-time optical path monitoring module are all housed in a sealed constant temperature aluminum alloy optical dark box. The closed-loop control unit is electrically connected to all the above modules to realize integrated closed-loop operation of automatic attenuation ratio combination, continuous fine adjustment, stray light adaptive suppression, constant temperature light stabilization, and real-time attenuation ratio verification.

2. The attenuator according to claim 1, characterized in that, The inner wall of the honeycomb light-absorbing panel is coated with an ultra-low reflection matte paint with an absorption rate of ≥99.6%, and the honeycomb adopts a hexagonal deep hole structure; the two-dimensional rotary servo motor has independent horizontal and pitch dual-axis adjustment functions, and the angle closed-loop feedback sensor uses a built-in micro grating to collect the real-time rotation angle.

3. The attenuator according to claim 1, characterized in that, The synchronous and opposite movements of the two optical wedges cancel out the lateral deviation of the beam, and the total optical density OD changes linearly with the displacement of the optical wedges; the scattered stray light generated by the sliding of the two optical wedges is synchronously adjusted by the linkage two-dimensional rotating honeycomb motor to dynamically absorb the newly scattered light from the optical wedges, eliminating the defect of the stray light intensity fluctuating drastically with the attenuation ratio during continuous adjustment; the wedge angle of the two optical wedges is 2° and the maximum stroke is 20mm.

4. The attenuator according to claim 1, characterized in that, Distributed platinum resistance temperature sensors are attached to the attenuator, double optical wedges, and the heat-sensitive area of ​​the light source window, respectively; a semiconductor cooling and heating constant temperature liner is arranged in the optical dark box interlayer to control the temperature fluctuation of the cavity within ±0.1℃.

5. The attenuator according to claim 1, characterized in that, The input reference beam detector monitors the laser power in real time, and adjusts the light source drive current through negative feedback to stabilize the incident reference light power. At the same time, it compensates for the transmittance error caused by temperature drift in real time based on the temperature coefficient database of each optical element.

6. The attenuator according to claim 1, characterized in that, The input reference beam splitter collects the unattenuated raw laser power as the calculation benchmark, and the output trap standard detector and the back-end single-photon detector under test sample synchronously. The main control compares the theoretical attenuation ratio with the measured ratio in real time. When a deviation occurs, it automatically performs the following triple correction operations: repositioning and resetting the attenuator or double optical wedge, secondary optimization of the honeycomb absorption angle, and temperature drift error compensation, so as to ensure the accuracy of the output optical power and attenuation ratio in real time.

7. The attenuator according to claim 1, characterized in that, The coarse adjustment attenuator is installed at a 4.5-degree angle in a figure-eight pattern, so that the reflected light deviates from the main light path and enters the corresponding honeycomb light-absorbing unit.

8. The attenuator according to claim 1, characterized in that, The total transmittance of the attenuator meets the following requirements: N is the number of attenuators. Let be the transmittance of the i-th attenuator.

9. The attenuator according to claim 2, characterized in that, The substrate of the honeycomb light-absorbing panel is aluminum alloy.

10. The attenuator according to claim 2, characterized in that, The honeycomb structure uses hexagons with a side length of 5mm and a depth of 20mm.

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