Light source system capable of continuously adjusting attenuation ratio

Abstract

The invention discloses a light source system capable of continuously adjusting an attenuation ratio, and belongs to the technical field of optical radiation measurement and photoelectric detection. In order to solve the problems of wavelength dependence, discontinuous adjustment, spectrum distortion and the like existing in an existing light intensity adjusting scheme, a combined structure of an integrating sphere and a diaphragm cylinder is adopted, and the device comprises a light source, the integrating sphere with the high-reflection inner wall, a front-end adjustable diaphragm, the diaphragm cylinder with the extinction inner wall and a rear-end adjustable diaphragm. Continuous attenuation of output light intensity in a predetermined dynamic range is realized by adjusting the apertures of the front and rear diaphragms, the lower limit of attenuation ratio meets the requirement, and the dynamic range can reach more than three orders of magnitude. The system uses the integrating sphere to form a stable Lambert light source, the attenuation process depends on geometric parameters, spectral distribution and spatial uniformity basically remain unchanged, and the non-uniformity of a light-emitting surface is not greater than 5%. The invention further provides a calibration method, high-precision attenuation prediction is achieved through detector measurement and view factor model fitting, and the calibration method is suitable for weak cursor calibration, detector linearity testing and other applications.

Description

Technical Field

[0001] This invention relates to the field of optical radiation measurement and photoelectric detection technology, specifically to a light source system with a continuously adjustable attenuation ratio. Background Technology

[0002] In weak light measurement, photodetector calibration, and extremely weak radiance experiments, a light source system with stable spectral distribution, controllable spatial distribution, and continuously adjustable light intensity or radiance within a large dynamic range is usually required.

[0003] In existing technologies, commonly used light intensity modulation schemes include:

[0004] (1) Neutral density filter or variable neutral density filter:

[0005] Light intensity attenuation is achieved by changing the optical density. This type of approach has a significant wavelength dependence, is prone to introducing spectral distortion, and the adjustment is mostly limited to a limited range, with restricted dynamic range and repeatability.

[0006] (2) Multi-position fixed aperture or bore wheel:

[0007] Approximate intensity attenuation is achieved by switching between different apertures. However, this method involves discontinuous adjustment, making it difficult to achieve fine and repeatable control over a large attenuation range.

[0008] (3) Directly adjust the light source drive current:

[0009] Light intensity is varied by changing the current of the light source. This method often results in significant changes in spectral distribution and brightness stability, making it unsuitable for use as a high-stability calibration light source.

[0010] Furthermore, while existing technologies employ methods such as using an integrating sphere as a stable Lambertian light source and using an aperture tube or Gershun tube to define the field of view and obtain an approximate radiance beam, these technologies suffer from the following shortcomings: intensity adjustment is mostly discrete, resulting in a limited dynamic range; spectral and spatial distributions are prone to change during adjustment; and the attenuation ratio is difficult to predict and accurately calibrate using geometric parameters. This invention proposes a continuously adjustable attenuation ratio light source system and its calibration method based on a combination of an integrating sphere and an aperture tube. This system achieves: continuously adjustable attenuation of output light intensity or radiance within a predetermined dynamic range; the attenuation ratio is primarily determined by the geometric parameters of the adjustable aperture, and can be represented by analytical or approximate analytical models; during adjustment, the spectral distribution and spatial uniformity of the output light remain essentially stable, making it suitable as a weak, calibrated light source.

[0011] Therefore, it is necessary to provide a light source system that is simple in structure, stable in spectral and spatial characteristics, continuously adjustable in attenuation ratio over a wide range, and traceable and calibrated. Summary of the Invention

[0012] To overcome the above technical problems, this invention provides a light source system with a continuously adjustable attenuation ratio. Based on an integrating sphere and aperture tube combination structure, this invention is suitable for calibration of weak light radiance / irradiance, testing of photodetector linearity, and calibration of large dynamic range optical measurement systems. The specific technical solution is as follows:

[0013] A light source system with a continuously adjustable attenuation ratio includes:

[0014] A light source, used to generate luminous flux;

[0015] An integrating sphere with a high-reflectivity diffuse reflection coating on its inner wall; the integrating sphere has a first opening and a second opening, the first opening being used to connect to the light source, and the second opening being a light outlet.

[0016] An adjustable aperture at the front end, located at or connected to the second opening of the integrating sphere, is used to adjust the effective light-passing area emitted from the integrating sphere and entering the subsequent optical path. The aperture radius of the adjustable aperture at the front end is... and Continuously adjustable between;

[0017] The aperture tube is a hollow cylindrical structure with an extinct inner wall. One end of it is connected to the adjustable aperture at the front end, and its length is [length missing]. ;

[0018] A rear adjustable aperture, located at the other end of the aperture tube, is used to define the system's output aperture and field of view. The aperture radius of the rear adjustable aperture is within... and Continuously adjustable between;

[0019] Specifically, by adjusting the apertures of the front adjustable aperture and the rear adjustable aperture, the output light intensity of the light source system can be continuously and adjustablely attenuated within a predetermined dynamic range, and the adjustable range of the apertures of the front adjustable aperture and the rear adjustable aperture satisfies the following:

[0020] ;

[0021] Where M is the preset lower limit of the attenuation ratio.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] By combining an integrating sphere, an aperture tube, and two adjustable apertures (front and rear), this invention achieves continuously adjustable attenuation of light intensity or radiance under a predetermined light source operating state. The dynamic range is mainly determined by the adjustable aperture ratio. The decision can be designed to be at least three orders of magnitude larger, or even higher.

[0024] This invention uses a geometric model to describe the integrating sphere extraction factor and the aperture tube apparent factor, and corrects the model parameters through a calibration method, so that the attenuation ratio can be predicted through structural parameters and high-precision calibration can be achieved, with good traceability.

[0025] The light source emits light from the Lambertian surface inside the integrating sphere. The attenuation process mainly depends on geometric factors and does not depend on changing the driving current of the light source, thus maintaining a basically unchanged spectral distribution throughout the attenuation range.

[0026] By constraining the aperture ratio of the integrating sphere, applying small-angle conditions to the aperture tube, and designing the extinction effect on the inner wall, this invention can maintain the non-uniformity of the light-emitting surface within the entire attenuation range at a preset threshold, for example, no more than 5%, preferably no more than 2%, making it suitable as a high-uniformity calibration light source.

[0027] The system has a relatively simple structure. The front and rear adjustable apertures can be driven by an electric structure to realize the automatic and continuous adjustment of the attenuation ratio, which makes it easy to integrate into instrument systems such as photodetector linearity testing and extremely weak light radiance calibration. Attached Figure Description

[0028] Figure 1 is a schematic diagram of the overall structure of the light source system of the present invention;

[0029] Figure 2 is a schematic diagram of the geometric structure of the aperture tube and the front and rear adjustable apertures;

[0030] Figure 3 shows the attenuation ratio as a function of... A schematic diagram of the changing attenuation ratio curve. Detailed Implementation

[0031] 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.

[0032] like Figure 1 , Figure 2 As shown, the present invention provides a light source system with a continuously adjustable attenuation ratio, comprising:

[0033] The light source is used to generate luminous flux, preferably a halogen tungsten lamp with a constant current power supply, but other continuous spectrum light sources can also be used.

[0034] An integrating sphere is a hollow sphere with a high-reflectivity diffuse reflection coating on its inner wall. The integrating sphere has at least a first opening and a second opening: the first opening is used to connect a light source, allowing the light flux output by the light source to enter the interior of the integrating sphere; the second opening serves as a light outlet for coupling subsequent geometric attenuation components.

[0035] The adjustable front aperture, located at or connected to the second opening of the integrating sphere, is used to adjust the effective light-transmitting area exiting the integrating sphere and entering the aperture tube. The aperture radius of the adjustable front aperture is... to The range is continuously adjustable.

[0036] The aperture tube is a hollow cylindrical structure with an extinct inner wall. One end is connected to the front adjustable aperture, and the other end is connected to the rear adjustable aperture. It is used to limit the system's field of view and suppress stray light inside the tube. The length of the aperture tube is L.

[0037] A rear-end adjustable aperture, located at the exit end of the aperture tube, is used to limit the system's output aperture and field of view, achieving further geometric attenuation. The aperture radius of the rear-end adjustable aperture is... and The range is continuously adjustable.

[0038] The output beam is emitted from the adjustable aperture at the rear end, forming a beam with basically stable spectral and spatial characteristics and continuously adjustable light intensity or radiance over a large range, which is used for the calibration of external measured systems or detectors.

[0039] Optionally, a monitoring opening is also provided on the integrating sphere, and a reference detector is arranged at the monitoring opening to monitor the radiance inside the integrating sphere, thereby achieving auxiliary correction of the stability and attenuation ratio of the light source output.

[0040] The total attenuation ratio of the system of this invention is determined by the following three parts:

[0041] In the integrating sphere, the luminous flux output from the light source enters the integrating sphere and, due to diffuse reflection from the high reflectivity of the inner wall, forms an approximate Lambertian radiance field. (Radiance inside the integrating sphere) It can be represented as:

[0042] (1)

[0043] in, To output luminous flux from the light source. It is a coefficient related to the radius of the integrating sphere, the reflectivity of the inner wall, and the aperture ratio.

[0044] The front adjustable aperture extraction factor is [value missing], and the front adjustable aperture radius is [value missing]. At that time, its effective light transmission area for:

[0045] (2)

[0046] Corresponding extraction factor Follow The change shows a monotonically increasing trend.

[0047] The geometrical attenuation of the aperture tube and the adjustable aperture at the rear end, the length of the aperture tube is The radius of the adjustable aperture at the rear is Under the condition of small angle approximation. In the case of a smaller value, the apparent factor between the coaxial circular holes at both ends of the aperture tube can be expressed as about An approximate analytical function is obtained, thus yielding the partial attenuation factor of the aperture tube. .

[0048] Therefore, the total attenuation ratio of the system can be expressed as:

[0049] (3)

[0050] The current and rear adjustable apertures are respectively in the range and The maximum value of output light intensity or radiance when continuously varying within a range. and minimum value The ratio is mainly determined by the adjustable aperture ratio, and its dynamic range approximately satisfies:

[0051] (4)

[0052] In this invention, the adjustable aperture range preferably satisfies the following:

[0053] (5)

[0054] Where M is a preset lower limit of the attenuation ratio, preferably not less than 10. 3 More preferably not less than 10 4 To achieve a continuously adjustable attenuation dynamic range of no less than three orders of magnitude, preferably no less than four orders of magnitude.

[0055] Light emission characteristics constraints and non-uniformity indicators:

[0056] 1. To ensure that the light source system is suitable as a calibration light source, the present invention imposes the following constraints on the light emission characteristics:

[0057] Integral sphere opening ratio constraint, integral sphere opening ratio for:

[0058] (6)

[0059] Let be the area of ​​the i-th opening. The total inner surface area of ​​the integrating sphere is controlled within a preset range to ensure good spatial uniformity of the radiance field within the sphere. Preferably... Not greater than a certain threshold.

[0060] 2. Small angle approximation conditions:

[0061] Aperture tube length With front and rear adjustable aperture diameter satisfy:

[0062] η (7)

[0063] Where η is a preset small angle threshold, such as 0.1, to ensure that the apparent factor between the coaxial circular holes at both ends of the aperture tube meets the small angle approximation condition, thus forming a small field of view output beam.

[0064] 3. Inner wall extinction and stray light suppression:

[0065] The inner wall of the aperture tube is made of matte black paint, matte thread or flocked structure. If necessary, an intermediate light-blocking plate can be set to suppress stray light generated by multiple reflections inside the tube and ensure the effective dynamic range under high attenuation conditions.

[0066] 4. Non-uniformity index of the light-emitting surface:

[0067] Non-uniformity of the light-emitting surface is defined as: the maximum irradiance within a predetermined area of ​​the light-emitting surface. Minimum value ,average value satisfy:

[0068] (8)

[0069] The obtained non-uniformity index U. Preferably, the non-uniformity of the light-emitting surface of the light source system under a predetermined operating state is no greater than 5%, more preferably no greater than 2%, and even more preferably no greater than 1%.

[0070] With the above constraints, the present invention can maintain the spectral distribution of the output beam basically unchanged and the spatial non-uniformity within a predetermined range throughout the attenuation adjustment range, making it suitable as a calibration light source for weak radiance / irradiance.

[0071] The present invention also provides a calibration method for the above-mentioned light source system, comprising:

[0072] The detectors are arranged as follows: a first detector is placed at the entrance of the aperture tube or the monitoring port of the integrating sphere to measure the light intensity or radiance entering the aperture tube; a second detector is placed at the exit of the aperture tube to measure the light intensity or radiance output by the system.

[0073] With a stable light source, the radiance inside the integrating sphere remains stable over time under fixed driving conditions.

[0074] Collect calibration data and select several sets of front-end adjustable aperture radii. With the adjustable aperture radius at the rear The combination of the two detectors is used to adjust the front and rear adjustable apertures to the corresponding openings in sequence, and the output signals of the first and second detectors are recorded.

[0075] Calculate the experimental attenuation ratio:

[0076] For each group ( , ), calculate the experimental attenuation ratio:

[0077] (9)

[0078] Experimental attenuation ratio matrix By fitting the model with a small-angle approximation model based on the integral sphere extraction factor and the aperture tube apparent factor, structural correction parameters in the model are obtained, including but not limited to the effective length correction coefficient and the equivalent aperture correction coefficient.

[0079] Obtain the calibration attenuation function:

[0080] Based on the fitting results, the adjustable aperture at the front end was obtained. With adjustable aperture at the rear The calibration decay function of the independent variable In practical use, by reading the aperture dimensions of the two adjustable apertures, one can determine the appropriate aperture size based on the given information. Real-time calculation of the output light intensity or radiance of the light source system enables a continuously adjustable weak fixed light source without point-by-point measurement.

[0081] Example 1, Basic Structure:

[0082] The light source uses a halogen tungsten lamp with a color temperature of approximately 2856 K, equipped with a current stabilizer to ensure stable output luminous flux. The inner diameter of the integrating sphere is selected from 50 to 150 mm, and the inner wall is coated with a diffuse reflection coating with a reflectivity of not less than 0.95. Light source input port, system output port, and monitoring port are provided.

[0083] Install an adjustable aperture at the system output port, with an aperture radius of [missing information]. to Continuously adjustable within a certain range. The length of the diaphragm tube is selected from 50–200 mm, and its inner diameter is larger than the maximum aperture of the front and rear adjustable diaphragms. The inner wall is finished with matte black paint or a matte threaded structure. A rear adjustable diaphragm is installed at the outlet end of the diaphragm tube, with an aperture radius within... to Continuously adjustable within the range.

[0084] The adjustable aperture range design of the two adjustable apertures allows for:

[0085] (10)

[0086] Achieve a dynamic range of light intensity attenuation of no less than three orders of magnitude.

[0087] Example 2: Monitoring Detector and Calibration Process:

[0088] A silicon photodiode is installed at the monitoring port of the integrating sphere as a reference detector to monitor the radiance inside the integrating sphere in real time. A first detector is placed at the inlet of the aperture tube, and a second detector is placed at the outlet of the aperture tube.

[0089] Under fixed light source driving conditions, select multiple groups The signals from the two detectors were combined and recorded, and the experimental attenuation ratio matrix was calculated. A small-angle approximation model based on the integrating sphere and the apparent factor of the aperture tube was used to fit the experimental data, resulting in the corrected calibration attenuation function. In subsequent use, by reading the current front and rear adjustable aperture diameters, it is possible to utilize... Calculate the output light intensity or radiance.

[0090] Figure 3 The simulation results of the system attenuation ratio are shown. The light source power is 1W, the inner diameter of the integrating sphere is 60mm, the adjustable range of the front and rear apertures is from 1mm to 12mm, and the length of the aperture tube is 100mm. According to formula (3), the output light power of the system can be continuously adjusted from 0.89mW to 43nW, achieving light intensity attenuation of more than 5 orders of magnitude.

Claims

1. A continuously tunable attenuation ratio light source system, characterized by, The application relates to a light source system, comprising: a light source for generating light flux; an integrating sphere with a diffusely reflective coating on the inner wall, the integrating sphere being provided with a first opening for connecting the light source and a second opening as a light outlet; A front-end tunable aperture is arranged at the second opening of the integrating sphere and connected thereto, for adjusting the effective light passing area of light emitted from the integrating sphere and entering the subsequent light path, the aperture radius of the front-end tunable aperture is continuously adjustable between and . The diaphragm cylinder is a hollow cylindrical structure with an inner wall that absorbs light. One end of the diaphragm cylinder is connected to the front adjustable diaphragm, and the length is ; A rear-end adjustable diaphragm is arranged at the other end of the diaphragm cylinder, for defining the light aperture and the field angle, the aperture radius of the rear-end adjustable diaphragm is continuously adjustable between and ​ wherein the continuous adjustable attenuation of the output light intensity of the light source system in a predetermined dynamic range is realized by adjusting the aperture of the front adjustable diaphragm and the rear adjustable diaphragm, and the adjustable range of the aperture of the front adjustable diaphragm and the rear adjustable diaphragm satisfies: ； wherein M is a preset lower limit of the attenuation ratio.

2. The light source system of claim 1, wherein A monitoring opening is arranged on the integrating sphere, and a standard detector is arranged at the monitoring opening for monitoring the internal radiance of the integrating sphere and correcting the stability of the output of the light source system.

3. The light source system according to claim 1 or 2, characterized in that, Length of the diaphragm cylinder Diameter of the front and rear adjustable diaphragms , satisfies: η; wherein eta is a preset small-angle threshold.

4. The light source system of claim 1, wherein The inner wall of the diaphragm cylinder is provided with light-absorbing black paint, light-absorbing threads or flocked structure.

5. The light source system of claim 1, wherein In a predetermined working state, the non-uniformity of the light outlet surface of the light source system is not greater than a preset threshold, and the preset threshold is 5%.

6. The light source system of claim 1, wherein, The front adjustable diaphragm and / or the rear adjustable diaphragm is driven by a motor to realize the electric adjustment of the aperture.

7. The light source system of claim 1, wherein, Integral sphere opening ratio is: (6) A is the area of the ith opening, A is the total internal surface area of the integrating sphere, control is within a predetermined range.

8. The light source system of claim 1, wherein, The total attenuation ratio of the system is calculated as follows: The light source output light flux enters the integrating sphere, and a nearly Lambertian radiant intensity field is formed under the action of the internal wall diffuse reflection. The internal radiant intensity of the integrating sphere is represented as: (1) wherein, is the light source output luminous flux, is a coefficient related to the integral sphere radius, inner wall reflectivity, and opening ratio; Front end adjustable iris extraction factor , when the front end adjustable iris aperture radius is , its effective clear aperture is: (2) corresponding extraction factor with monotonically increases with The geometric attenuation of the diaphragm cylinder and the rear adjustable diaphragm is that the length of the diaphragm cylinder is , and the aperture radius of the rear adjustable diaphragm is ; in the case of satisfying the small-angle approximation condition , the view factor between the coaxial circular holes at both ends of the diaphragm cylinder can be expressed as an approximate analytical function about , so as to obtain the diaphragm cylinder partial attenuation factor ; Therefore, the total attenuation ratio of the system is expressed as: (3)。 9. The light source system of claim 1, wherein, The current and the rear adjustable diaphragm apertures are respectively in the interval And When the output light intensity or radiant brightness maximum value And minimum value The ratio is determined by the adjustable diaphragm aperture ratio, and the dynamic range approximately satisfies: (4)。 10. The light source system of claim 1, wherein, The calibration method of the light source system comprises the following steps: A standard detector is arranged as a first detector at the inlet of the diaphragm cylinder or the monitoring opening of the integrating sphere, and a second detector is arranged at the outlet of the diaphragm cylinder; In the case that the working condition of the light source is fixed, a plurality of combinations of the aperture radius of the front adjustable diaphragm and the aperture radius of the rear adjustable diaphragm are selected, the front adjustable diaphragm and the rear adjustable diaphragm are adjusted in sequence, and the output signals of the first detector and the second detector are recorded; The experimental attenuation ratio corresponding to each combination of the front and rear diaphragm opening degrees is calculated; The experimental attenuation ratio is fitted with a small-angle approximate model based on the extraction factor of the integrating sphere and the visual factor of the diaphragm cylinder, so that the correction parameters related to the structure are obtained; The calibration attenuation function with the aperture radius of the front adjustable diaphragm and the aperture radius of the rear adjustable diaphragm as the independent variables is obtained based on the correction parameters, and the output light intensity or radiance of the light source system is calculated from the calibration attenuation function according to the current diaphragm opening degree in actual use.

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