Low divergence angle dependent photodetectors and calibration systems

Abstract

This invention relates to the field of optical instrument technology, providing a low-divergence-angle-dependent photodetector and calibration system. The low-divergence-angle-dependent photodetector includes a first photodiode, a second photodiode, and a concave mirror. The first photodiode has a first photosensitive plane; the second photodiode has a second photosensitive plane; the concave mirror has a rear plane and a front concave surface that are opposite to each other, with the front concave surface facing the second photodiode. The first and second photosensitive planes are set at an angle to each other, and the rear plane is set at an angle to the second photosensitive plane, thereby forming a light trap between the first photodiode, the second photodiode, and the concave mirror. This application enables the detector to be applied to optical measurement scenarios with different divergence angles by achieving collimated light responsivity with a single calibration.

Description

Technical Field

[0001] This invention relates to the field of optical instrument technology, and in particular to a low divergence angle-dependent photodetector and calibration system. Background Technology

[0002] Photodetectors are widely used components in various sectors of the national economy. The response characteristics of a detector are its most important basic parameters, and accurate responsivity enables accurate measurement of optical signals with different characteristics.

[0003] In related technical fields, most broadcast detectors consist of single or multiple photodiodes. These photodiodes can only be used to measure collimated light or light signals with a specific divergence angle at a specific distance. Once the divergence angle or the incident angle changes, the detector's responsivity will change drastically, thus failing to guarantee a constant responsivity and leading to significant measurement errors in the power measurement of the light signal. Summary of the Invention

[0004] This invention provides a low divergence angle-dependent photodetector and calibration system to solve the problem that the responsivity of existing photodetectors is not constant when the divergence angle or the incident angle changes, resulting in large measurement errors in the power measurement of optical signals. The invention enables the photodetector to be applied to optical measurement scenarios with different divergence angles by calibrating the responsivity of collimated light in a single step.

[0005] This invention provides a photodetector with low divergence angle dependence, comprising:

[0006] A first photodiode, the first photodiode having a first photosensitive plane;

[0007] A second photodiode, the second photodiode having a second photosensitive plane;

[0008] A concave mirror has a rear plane and a front concave surface that are opposite to each other. The front concave surface faces the second photodiode. The first photosensitive plane and the second photosensitive plane are set at an angle to each other. The rear plane is set at an angle to the second photosensitive plane, so as to form a light trap between the first photodiode, the second photodiode and the concave mirror.

[0009] According to the present invention, a low divergence angle dependent photodetector is provided, wherein the first photosensitive plane, the second photosensitive plane, and the rear plane are arranged perpendicularly to each other.

[0010] According to the present invention, a photodetector with low divergence angle dependence is provided, wherein the optical center axis of the incident light is at 45° to the first photosensitive plane, the optical center axis of the light reflected after absorption by the first photosensitive plane is at 45° to the second photosensitive plane, and the optical center axis of the light reflected after absorption by the second photosensitive plane is perpendicular to the rear plane.

[0011] According to the present invention, a photodetector with low divergence angle dependence is provided, wherein the first photosensitive plane and the second photosensitive plane are opposite to each other and arranged in a staggered parallel manner, and the front concave surface is arranged opposite to the second photosensitive plane.

[0012] According to the present invention, a low divergence angle dependent photodetector is provided, wherein the distance between the first photodiode and the second photodiode is less than or equal to 10 mm.

[0013] According to the present invention, a low divergence angle dependent photodetector is provided, wherein the distance between the second photodiode and the concave mirror is less than or equal to 10 mm.

[0014] According to the present invention, a low divergence angle dependent photodetector further includes an entrance port, wherein the plane containing the entrance port is parallel to the rear plane, and the entrance port is correspondingly disposed to the first photosensitive plane.

[0015] According to the present invention, a low divergence angle dependent photodetector includes a housing, the housing having a mounting cavity, an entrance port being opened on the housing and communicating with the mounting cavity, and a first photodiode, a second photodiode and a concave mirror being disposed within the mounting cavity.

[0016] The present invention also provides a calibration system, comprising:

[0017] A light source, which is used to emit a beam of controllable power in a preset direction;

[0018] A power stabilization system is disposed in the preset direction and is used to modulate the beam to obtain a collimated beam.

[0019] A one-dimensional displacement stage is disposed behind the power stabilization system along the preset direction, and the one-dimensional displacement stage has a measurement position corresponding to the preset direction.

[0020] A cryogenic radiometer is mounted on the one-dimensional displacement stage, and the cryogenic radiometer can be movably switched to the measurement position.

[0021] As described above, the low divergence angle dependent photodetector is mounted on the one-dimensional displacement stage, and the low divergence angle dependent photodetector can be movably switched to the measurement position.

[0022] This invention provides a low-divergence-angle-dependent photodetector. By setting a first photosensitive plane and a second photosensitive plane at an angle to each other, and setting a rear plane at an angle to the second photosensitive plane, a light trap is formed between a first photodiode, a second photodiode, and a concave mirror. Under the condition of divergent beam incident, a small portion of the beam reflected after absorption by the first photosensitive plane is incident on the second photosensitive plane. The remaining reflected beam, after absorption by the second photosensitive plane, is incident perpendicularly on the concave mirror. The spot size increases progressively under this divergence angle condition. After convergence and reflection by the concave mirror, a small-divergence-angle or parallel beam is obtained. This beam then returns to the incident port after absorption and a small portion of reflection by the second and first photosensitive planes, respectively. This ensures that within this divergence angle, whether the incident beam is parallel or divergent, its reflected beam is fully received by the first and second photosensitive planes, with only a very small portion returning to the incident port. This achieves a divergence-angle-independent receiving system, enabling the detector to be applied to optical measurement scenarios with different divergence angles by achieving collimated light with a single calibration of the responsivity. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of an embodiment of the low divergence angle dependent photodetector provided by the present invention;

[0025] Figure 2 This is a schematic diagram of another embodiment of the low divergence angle dependent photodetector provided by the present invention;

[0026] Figure 3 This is a schematic diagram of the calibration system provided by the present invention.

[0027] Figure label:

[0028] 10. Calibration system;

[0029] 100. Low divergence angle dependent photodetector; 110. First photodiode; 111. First photosensitive plane; 120. Second photodiode; 121. Second photosensitive plane; 130. Concave mirror; 131. Front concave surface; 132. Rear plane; 140. Inlet; 150. Housing;

[0030] 200. Light source;

[0031] 300. Power stabilization system;

[0032] 400. One-dimensional displacement stage;

[0033] 500. Low-temperature radiometer. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0035] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0037] This invention proposes a photodetector and calibration system with low divergence angle dependence.

[0038] In embodiments of the present invention, such as Figure 1As shown, a photodetector 100 with low divergence angle dependence is provided, including a first photodiode 110, a second photodiode 120, and a concave mirror 130. The first photodiode 110 has a first photosensitive plane 111; the second photodiode 120 has a second photosensitive plane 121; the concave mirror 130 has a rear plane 132 and a front concave surface 131 that are opposite to each other, with the front concave surface 131 facing the second photodiode 120. The first photosensitive plane 111 and the second photosensitive plane 121 are set at an angle to each other, and the rear plane 132 is set at an angle to the second photosensitive plane 121, so as to form a light trap between the first photodiode 110, the second photodiode 120, and the concave mirror 130.

[0039] The first photodiode 110 has a first photosensitive plane 111, whose main function is to receive and convert optical signals into electrical signals. When light shines on the first photosensitive plane 111, the photon energy is absorbed, and electrons are excited to form a photocurrent.

[0040] The second photodiode 120 has a second photosensitive plane 121, which is set at an angle to the first photosensitive plane 111. The function of the second photodiode 120 is to receive the residual light signal reflected from the first photodiode 110 and perform photoelectric conversion again.

[0041] The concave mirror 130 has a front concave surface 131 facing the second photodiode 120. Its main function is to converge and reflect the light signal reflected from the second photodiode 120. This helps to reduce the divergence angle of the light signal and improve the sensitivity of the detector.

[0042] The concave mirror 130 has a rear plane 132 that is angled to the second photosensitive plane 121, ensuring that the reflected light can be effectively captured and converged by the front concave surface 131 of the concave mirror 130.

[0043] The first photosensitive plane 111 and the second photosensitive plane 121 are set at an angle to each other to allow the light signal to be reflected multiple times between the two photodiodes, thereby increasing the light signal capture efficiency.

[0044] The angle between the rear plane 132 and the second photosensitive plane 121 ensures that the light beam reflected from the second photodiode 120 can be effectively focused by the concave mirror 130, further improving the performance of the detector.

[0045] The specific angular arrangement of the first photosensitive plane 111, the second photosensitive plane 121, and the concave mirror 130 forms a light trap. This light trap can capture and reflect light signals multiple times, ensuring efficient absorption and conversion of light signals within a specific divergence angle range. This allows the detector to receive and measure light signals independently of the divergence angle. In other words, whether the light is parallel or divergent, as long as its divergence angle is within the detector's design range, it can be effectively detected and measured.

[0046] The photodetector's minimum detectable power is reduced by the specific angular arrangement of the first photosensitive plane 111, the second photosensitive plane 121, and the concave mirror 130 to form a light trap. This allows the detector to detect lower-intensity light signals, improving its sensitivity. Due to the reduced laser divergence angle and the light trap effect, the detector's detection range is increased. This means the detector can detect light signals at greater distances.

[0047] This application sets the first photosensitive plane 111 and the second photosensitive plane 121 at an angle to each other, and the rear plane 132 is set at an angle to the second photosensitive plane 121, so as to form a light trap between the first photodiode 110, the second photodiode 120 and the concave mirror 130. Under the condition of divergent beam incident, a small part of the light beam after being absorbed by the first photosensitive plane 111 is incident on the second photosensitive plane 121. The part of the reflected light after being absorbed by the second photosensitive plane 121 is incident perpendicularly on the concave mirror 130. The size of the light spot becomes larger and larger under this divergence angle condition. After being converged and reflected by the concave mirror 130, a small divergence angle or parallel beam is obtained. After being absorbed and partially reflected by the second photosensitive plane 121 and the first photosensitive plane 111 respectively, it returns to the entrance port 140. This ensures that the incident beam within this divergence angle, whether parallel or divergent, has its reflected beam fully received by the first photosensitive plane 111 and the second photosensitive plane 121, with only a very small portion returning to the incident light port. This achieves a receiving system independent of the divergence angle, and thus enables the detector to be applied to optical measurement scenarios with different divergence angles by achieving a single calibration response of the collimated light.

[0048] Reference Figure 1 According to the present invention, a photodetector 100 with low divergence angle dependence is provided, wherein a first photosensitive plane 111, a second photosensitive plane 121 and a rear plane 132 are arranged perpendicularly to each other.

[0049] Understandably, because the three planes are perpendicular to each other, the transmission path of the optical signal between the photodiode and the concave mirror 130 is more defined and efficient. This helps reduce the loss of the optical signal during transmission and improves the sensitivity of the detector. The optical signal will undergo multiple reflections between the photodiode and the concave mirror 130, forming a certain optical trapping effect. This helps to capture and converge the optical signal, improving the detection efficiency of the detector. The perpendicular arrangement may help reduce the impact of background noise on the detector performance. Due to the definition of the optical signal on the transmission path, the detector can more easily distinguish the target signal from background noise, thereby improving the signal-to-noise ratio. The mutually perpendicular arrangement makes the detector structure relatively simple, facilitating manufacturing and assembly. This helps to reduce manufacturing costs and improve the reliability and stability of the detector. Since the perpendicular arrangement is insensitive to the divergence angle of the optical signal, it can be applied to optical measurement scenarios with different divergence angles. This makes the detector have a wider range of applications.

[0050] Specifically, the optical center axis of the incident light is at 45° to the first photosensitive plane 111, the optical center axis of the light reflected after absorption by the first photosensitive plane 111 is at 45° to the second photosensitive plane 121, and the optical center axis of the light reflected after absorption by the second photosensitive plane 121 is perpendicular to the rear plane 132.

[0051] Understandably, when incident light strikes the first photosensitive plane 111 at a 45° angle, part of the optical signal is absorbed and converted into an electrical signal, while the remaining optical signal is reflected at the same 45° angle to the second photosensitive plane 121. On the second photosensitive plane 121, part of the optical signal is again absorbed and converted into an electrical signal, while the remaining optical signal is reflected in a direction perpendicular to the rear plane 132. The reflected optical signal directly strikes the rear plane 132 of the concave mirror 130, is then converged by its front concave surface 131, and may be reflected back to the photodiode system, forming a light trapping effect. This ensures the effective transmission and reflection of the optical signal between the photodiodes, improving the utilization rate of the optical signal and the performance of the detector.

[0052] Reference Figure 2 According to the present invention, a photodetector 100 with low divergence angle dependence is provided, wherein a first photosensitive plane 111 and a second photosensitive plane 121 are arranged opposite to and offset parallel to each other, and a front concave surface 131 is arranged opposite to the second photosensitive plane 121.

[0053] Understandably, the first photosensitive plane 111 and the second photosensitive plane 121 are arranged opposite each other and offset parallel to each other. This allows for effective transmission and reflection of optical signals between the two photosensitive planes, while maintaining a certain offset to avoid direct optical path interference. The concave surface 131 is arranged opposite to the second photosensitive plane 121, so that the optical signal reflected by the second photosensitive plane 121 can directly illuminate the concave surface 131, thereby being effectively converged or reflected. Since optical signals diverge during propagation, this arrangement reduces the dependence on the optical signal divergence angle, ensuring that even with a small divergence angle, the optical signal can be effectively received and processed.

[0054] When a light signal shines onto the first photosensitive plane 111, part of the light signal is absorbed and converted into an electrical signal, while the remaining light signal is reflected at a specific angle onto the second photosensitive plane 121. On the second photosensitive plane 121, a similar process occurs again: part of the light signal is absorbed, and the remaining light signal is reflected onto the concave surface 131. The concave surface 131 converges or reflects the reflected light signal again to achieve specific optical effects or detection purposes. The staggered parallel arrangement of the photosensitive planes reduces the possibility of optical path interference and improves the efficiency of light signal reception.

[0055] According to the present invention, a low divergence angle dependent photodetector 100 is provided, wherein the distance between the first photodiode 110 and the second photodiode 120 is less than or equal to 10 mm.

[0056] Understandably, the distance between the first photodiode 110 and the second photodiode 120 is less than or equal to 10 mm. This ensures that when the optical signal is transmitted between the two photodiodes, the divergence of the optical signal is relatively low due to the short distance, thereby improving the optical signal reception efficiency and detector performance. The photodetector design takes into account the divergence angle of the optical signal. Because optical signals diverge during propagation, especially over long distances, the divergence angle increases, leading to weakened signal strength and limited detection distance. However, due to the small distance between the first photodiode 110 and the second photodiode 120, even with a small divergence angle, the optical signal can be effectively received and processed, thus reducing dependence on the optical signal divergence angle. The reduced photodiode spacing allows the detector to receive and process optical signals more effectively, improving detection sensitivity and accuracy.

[0057] According to the present invention, a low divergence angle dependent photodetector 100 is provided, wherein the distance between the second photodiode 120 and the concave mirror 130 is less than or equal to 10 mm.

[0058] Understandably, the distance between the second photodiode 120 and the concave mirror 130 is less than or equal to 10 mm. This ensures that the light signal reflected or emitted from the second photodiode 120 can directly and efficiently illuminate the concave mirror 130, reducing light signal loss during propagation. Since light signals diverge during propagation, especially after multiple reflections or refractions, the divergence angle increases, leading to weakened light signal intensity and limited detection distance. However, due to the small distance between the second photodiode 120 and the concave mirror 130, even with a small divergence angle, the light signal can be effectively converged or reflected by the concave mirror 130, thus reducing dependence on the light signal divergence angle. Because of the small distance between the second photodiode 120 and the concave mirror 130, the detector can more effectively receive and process light signals, improving detection sensitivity and accuracy.

[0059] Reference Figure 1 and Figure 2 According to the present invention, a low divergence angle dependent photodetector 100 is provided, which further includes an entrance port 140. The plane where the entrance port 140 is located is parallel to the rear plane 132, and the entrance port 140 is correspondingly arranged with the first photosensitive plane 111.

[0060] Understandably, the photodetector has an entrance port 140, the plane of which is parallel to the rear plane 132 of the detector. This ensures that the light signal can enter the detector perpendicularly or nearly perpendicularly, reducing light signal loss and scattering during the incident process. It also allows for better design placement of its optical elements. The entrance port 140 corresponds to the first photosensitive plane 111 of the detector. After passing through the entrance port 140, the incident light can directly illuminate the first photosensitive plane 111, reducing the propagation distance and possible scattering of the light signal inside the detector. Due to the corresponding arrangement of the entrance port 140 and the first photosensitive plane 111, and the parallel relationship between the entrance port 140 and the rear plane 132, the photodetector has a low dependence on the divergence angle of the light signal. Even if the light signal has a certain divergence angle, it can be effectively received by the detector and converted into an electrical signal. This improves the sensitivity and detection efficiency of the photodetector. Because the light signal can directly and efficiently illuminate the photosensitive plane, reducing light signal loss and scattering, the accuracy and reliability of the detection are improved.

[0061] Meanwhile, the layout and parameter settings of optical components can be more reasonable, enabling efficient reception, processing and conversion of optical signals, thus miniaturizing the size of the photodetector.

[0062] Reference Figure 2According to the present invention, a low divergence angle dependent photodetector 100 is provided. The low divergence angle dependent photodetector 100 includes a housing 150, the housing 150 having a mounting cavity, an entrance port 140 being opened on the housing 150 and communicating with the mounting cavity, and a first photodiode 110, a second photodiode 120 and a concave mirror 130 being disposed in the mounting cavity.

[0063] Understandably, the housing 150, as the main body of the detector, is typically made of robust and corrosion-resistant materials to provide necessary mechanical protection and electromagnetic shielding. An internal mounting cavity is provided within the housing 150 to house the detector's critical components. An entrance 140 is formed on the housing 150 and communicates with the mounting cavity. The entrance 140 is designed to allow external light to enter the detector's interior, and its position and size are designed to ensure that only light within a specific divergence angle range can enter.

[0064] The mounting cavity is used to mount the main components of the detector. The interior of the mounting cavity is usually specially treated to reduce light loss and scattering as it propagates inside.

[0065] The first photodiode 110 and the second photodiode 120 are the core photoelectric conversion elements of the detector. They are placed inside the mounting cavity and positioned appropriately between the entrance port 140 and the concave mirror 130. The first photodiode 110 and the second photodiode 120 are used to receive light signals from different angles or different portions, and the incident angle of the light is determined by comparing their output signals.

[0066] The concave mirror 130 is located within the mounting cavity, near the entrance port 140. The function of the concave mirror 130 is to focus or reflect incoming light to improve the energy density and detection efficiency of the optical signal. Through the carefully designed concave mirror 130, efficient reception and processing of low-divergence-angle optical signals can be achieved.

[0067] The present invention also proposes a calibration system 10, which includes a low divergence angle dependent photodetector 100. The specific structure of the low divergence angle dependent photodetector 100 is as described in the above embodiments. Since the calibration system 10 adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0068] Reference Figure 3Specifically, the calibration system 10 includes a light source 200, a power stabilization system 300, a one-dimensional displacement stage 400, a cryogenic radiometer 500, and any one of the aforementioned low divergence angle-dependent photodetectors 100. The light source 200 is used to emit a power-controllable beam in a preset direction; the power stabilization system 300 is located in the preset direction, and the beam modulation system is used to modulate the beam to obtain a collimated beam; the one-dimensional displacement stage 400 is located behind the power stabilization system 300 along the preset direction, and the one-dimensional displacement stage 400 has a measurement position corresponding to the preset direction; the cryogenic radiometer 500 is mounted on the one-dimensional displacement stage 400, and the cryogenic radiometer 500 can be movably switched to the measurement position; the low divergence angle-dependent photodetector 100 is mounted on the one-dimensional displacement stage 400, and the low divergence angle-dependent photodetector 100 can be movably switched to the measurement position.

[0069] It is understandable that the light source 200 forms a stable collimated beam through the power stabilization system 300, and then the optical power P of the collimated beam is measured using the highest accuracy optical radiation measurement device - cryogenic radiometer 500. After that, the photodetector under test is switched to the position of the collimated beam using a one-dimensional translation stage, and the output photocurrent I of the photodetector under test is measured. Then the responsivity of the photodetector under test to the collimated light at this wavelength is I / P, with the unit being A / W.

[0070] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0071] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low divergence angle dependence photodetector, characterized in that, The low-divergence-angle-independent photodetector comprises a first photodiode, a second photodiode, and a concave mirror. The first photodiode has a first light-sensitive plane. The second photodiode has a second light-sensitive plane. The concave mirror has a rear plane and a front concave surface which are opposite to each other. The first light-sensitive plane and the second light-sensitive plane are arranged at an angle with each other. The rear plane is arranged at an angle with the second light-sensitive plane to form a light trap among the first photodiode, the second photodiode, and the concave mirror. The first light-sensitive plane is arranged opposite to the second light-sensitive plane and is misaligned with the second light-sensitive plane. The distance between the first photodiode and the second photodiode is less than or equal to 10 mm. The distance between the second photodiode and the concave mirror is less than or equal to 10 mm.

2. The low divergence angle dependence photodetector according to claim 1, wherein, The low-divergence-angle-independent photodetector further comprises an entrance port.

3. A calibration system, characterized by The plane on which the entrance port is located is parallel to the rear plane. The entrance port is arranged corresponding to the first light-sensitive plane. Under the condition of a divergent light beam, a small part of reflected light after the light beam is absorbed by the first light-sensitive plane is incident on the second light-sensitive plane. Part of the reflected light after the second light-sensitive plane absorbs the light is perpendicularly incident on the concave mirror. The size of the light spot is increasingly large under the condition of the divergence angle. After the light is converged and reflected by the concave mirror, a small divergence angle or a parallel light beam is obtained. The light beam is then absorbed by the second light-sensitive plane and the first light-sensitive plane and returns to the entrance port after a small part of the light is reflected. Therefore, under the condition of the divergence angle, the reflected light beam of the incident light beam, whether it is a parallel light or a divergent light, is fully received by the first light-sensitive plane and the second light-sensitive plane. Only a very small part of the light returns to the entrance port. Thus, a receiving system which is independent of the divergence angle is realized. The low-divergence-angle-independent photodetector comprises an outer shell. The outer shell has a mounting cavity. The entrance port is arranged on the outer shell and is in communication with the mounting cavity. The first photodiode, the second photodiode, and the concave mirror are arranged in the mounting cavity. The low-divergence-angle-independent photodetector comprises a light source, a power stabilization system, a one-dimensional displacement table, and a low-temperature radiation meter. The light source is used to emit a light beam with controllable power in a preset direction. The power stabilization system is arranged in the preset direction. The power stabilization system is used to modulate and process the light beam to obtain a collimated light beam. The one-dimensional displacement table is arranged behind the power stabilization system along the preset direction. The one-dimensional displacement table has a measurement position corresponding to the preset direction. The low-temperature radiation meter is mounted on the one-dimensional displacement table. The low-temperature radiation meter can be actively switched to the measurement position. The low-divergence-angle-independent photodetector is mounted on the one-dimensional displacement table. The low-divergence-angle-independent photodetector can be actively switched to the measurement position.

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