Infrared detector and measurement and control method thereof

Abstract

The invention provides an infrared detector and a measurement and control method thereof. The infrared detector comprises a concave optical fiber; the first fixing block is slidably arranged at the first end of the concave surface optical fiber in a sleeving mode, and the middle of the first side surface of the first fixing block sinks towards the second side surface to form a mounting groove; the trampoline type resonator is arranged in the mounting groove and is flush with the groove edge of the mounting groove, so that a Fabry-Perot resonant cavity is defined between the trampoline type resonator and the first end face of the concave optical fiber; the piezoelectric ceramic is arranged on the concave optical fiber in a sleeving manner and is adjacent to the second side surface of the first fixing block so as to excite the trampoline type resonator in a resonance manner; the trampoline type resonator periodically changes the resonant frequency under the irradiation of infrared light with periodically changing radiation intensity, and the concave optical fiber transmits the detection laser to the Fabry-Perot resonant cavity, so that the detection laser forms first reflected light after passing through the Fabry-Perot resonant cavity. And the intensity change of the first reflected light carries the change amplitude of the resonance frequency of the trampoline type resonator so as to represent the radiation intensity of the infrared light.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of infrared detection, and in particular to an infrared detector and a measurement and control method thereof. BACKGROUND

[0002] The measurement principle of the uncooled infrared detector is to convert the energy of infrared radiation into heat by using infrared absorption material, and to realize the detection of the change of infrared radiation intensity by measuring the temperature change of the infrared absorption material. Since the measurement sensitivity of the uncooled infrared detector is inversely proportional to the thermal conductivity of the device, it is required to reduce the thermal conductivity of the device as much as possible to enable a greater temperature change caused by unit intensity of infrared radiation in order to realize the detection of high sensitivity of the change of infrared radiation intensity. However, if the thermal conductivity of the device is reduced, the time for the device to reach temperature equilibrium through the heat transfer process will also be lengthened, which reduces the response rate of the device.

[0003] The inventors have found in the implementation of the present application that by reducing the size of the device of the uncooled infrared detector, the thermal capacity of the device can be reduced, so that a greater temperature change caused by unit intensity of infrared radiation and the time for the device to reach temperature equilibrium through the heat transfer process are shortened, thereby realizing the simultaneous improvement of the measurement sensitivity and the response rate of the infrared detector. However, due to the limitation of the contact measurement method of the uncooled infrared detector, the uncooled infrared detector of the prior art usually needs to be provided with electrodes on the device, so that the size of the device is difficult to effectively reduce, and therefore there is an urgent need to provide an infrared detector capable of simultaneously improving its measurement sensitivity and response rate. SUMMARY

[0004] The present application provides an infrared detector and a measurement and control method thereof to solve the problem that the uncooled infrared detector of the related art usually needs to be provided with electrodes on the device, so that the size of the device is difficult to effectively reduce, resulting in the inability to simultaneously improve the measurement sensitivity and the response rate of the infrared detector.

[0005] The first aspect of the present application provides an infrared detector, comprising:

[0006] a concave optical fiber;

[0007] a first fixing block slidably sleeved on a first end of the concave optical fiber, a middle part of a first side surface of the first fixing block is recessed toward a second side surface to form a mounting groove, and a groove edge of the mounting groove protrudes from a first end surface of the concave optical fiber;

[0008] a trampoline type resonator arranged in the mounting groove and flush with the groove edge of the mounting groove, so as to define a Fabry-Perot resonant cavity between the trampoline type resonator and the first end surface of the concave optical fiber;

[0009] The piezoelectric ceramic is sleeved on the concave optical fiber and arranged adjacent to the second side surface of the first fixing block to resonantly excite the trampoline resonator under the action of alternating voltage;

[0010] The trampoline resonator is used to periodically change the resonance frequency under the irradiation of infrared light with periodically changed intensity; the concave optical fiber is used to transmit the probe laser into the Fabry-Perot resonant cavity, so that the probe laser interferes in the Fabry-Perot resonant cavity and forms the first reflected light, so as to convert the vibration displacement of the trampoline resonator into the intensity change of the first reflected light, and the change amplitude of the resonance frequency of the trampoline resonator represents the intensity of the infrared light.

[0011] In an embodiment, the trampoline resonator comprises:

[0012] A sensing region;

[0013] A fixed region located at the periphery of the sensing region;

[0014] A plurality of suspension regions arranged at intervals along the periphery of the sensing region, each of which is connected between the sensing region and the fixed region.

[0015] In an embodiment, the sensing region of the trampoline resonator has a photonic crystal structure, the lattice of the photonic crystal structure is a two-dimensional hexagon, and a through hole is arranged at the vertex of the lattice, wherein the radius of the through hole is 549.6 nm and the distance between adjacent two through holes is 1542.8 nm, so that the probe laser with a wavelength of 1550 nm is reflected by the surface of the sensing region on the side facing the concave optical fiber.

[0016] In an embodiment, the radius of curvature of the first end surface of the concave optical fiber ranges from 70 μm to 200 μm, and the length of the Fabry-Perot resonant cavity ranges from 40 μm to 150 μm.

[0017] In an embodiment, the reflectivity of the first end surface of the concave optical fiber is less than the reflectivity of the surface of the sensing region of the trampoline resonator on the side facing the first end surface of the concave optical fiber, and the difference therebetween ranges from 5% to 10% of the reflectivity of the surface of the sensing region of the trampoline resonator on the side facing the first end surface of the concave optical fiber.

[0018] In an embodiment, the infrared detector further comprises:

[0019] A second fixing block sleeved on the second end of the concave optical fiber;

[0020] A first ceramic gasket and a second ceramic gasket, both of which are sleeved on the concave optical fiber, the first ceramic gasket is located between the first fixing block and the piezoelectric ceramic, and the second ceramic gasket is located between the piezoelectric ceramic and the second fixing block;

[0021] A base fixedly connected with the bottom of the second fixing block.

[0022] The second aspect of the present application provides an infrared detection device, comprising:

[0023] The infrared detector of any one of the above embodiments;

[0024] An infrared lens for focusing the infrared light to be detected onto the infrared detector;

[0025] An optical chopper arranged between the infrared lens and the infrared detector and located on the light path of the infrared light to be detected, for modulating the radiation intensity of the infrared light to be detected, so that the radiation intensity of the infrared light to be detected is periodically changed to irradiate the sensing area of the trampoline-type resonator away from the side of the concave optical fiber;

[0026] A laser for emitting a detection laser;

[0027] A fiber adapter, a fiber circulator and a single-mode optical fiber connected in sequence between the laser and the second end of the concave optical fiber, to transmit the detection laser into the Fabry-Perot resonant cavity, so that the detection laser forms a first reflected light after interference in the Fabry-Perot resonant cavity; the first reflected light is reflected back into the fiber circulator through the concave optical fiber;

[0028] A photodetector connected with the fiber circulator, for detecting the intensity change of the first reflected light;

[0029] A demodulation module for analyzing the intensity change of the first reflected light to obtain the change amplitude of the resonance frequency of the trampoline-type resonator;

[0030] A calculation module for calculating the radiation intensity of the infrared light to be detected according to the following formula :

[0031]

[0032] Wherein, represents the change amplitude of the resonance frequency of the trampoline-type resonator, represents the infrared radiation absorption coefficient of the material of the trampoline-type resonator, represents the infrared responsivity of the trampoline-type resonator, represents the resonance frequency of the trampoline-type resonator, represents the modulation frequency of the optical chopper, represents the infrared thermal response time of the trampoline-type resonator.

[0033] In an embodiment, the laser is also used to emit an adjusting laser when no infrared detection is performed, the adjusting laser forms a second reflected light after being transmitted into the Fabry-Perot resonant cavity, and the photodetector is also used to detect the intensity of the second reflected light; the infrared detection device further comprises:

[0034] a PI controller and an adder, the PI controller being connected with the piezoelectric ceramic through the adder to apply a direct current voltage to the piezoelectric ceramic and adjust a voltage value of the direct current voltage, so as to make the length of the Fabry-Perot resonant cavity increase or decrease and make the photodetector detect the intensity of the reflected light;

[0035] a PI controller connected with the photodetector to lock the length of the Fabry-Perot resonant cavity to the length corresponding to the maximum slope of the second reflected light intensity change when the length of the Fabry-Perot resonant cavity increases or decreases.

[0036] In an embodiment, the demodulation module comprises:

[0037] a phase-locked loop connected with the photodetector and the adder respectively;

[0038] a phase-locked amplifier connected with the phase-locked loop and the calculation module respectively;

[0039] the phase-locked loop is used to analyze the intensity change of the first reflected light to obtain the change of the resonance frequency of the trampoline resonator;

[0040] the phase-locked amplifier is used to amplitude demodulate the change of the resonance frequency of the trampoline resonator to obtain the amplitude of the change of the resonance frequency of the trampoline resonator;

[0041] the phase-locked loop is also used to apply an alternating current voltage to the piezoelectric ceramic through the adder and lock the frequency of the alternating current voltage to the resonance frequency of the trampoline resonator.

[0042] In an embodiment, the infrared detection device further comprises:

[0043] a vacuum chamber, a light-transmitting window, a fiber flange, a wiring flange and a vacuum valve are arranged on the side wall of the vacuum chamber, the light-transmitting window is located between the optical chopper and the infrared detector and on the light path of the infrared light to be detected, the fiber flange is used for the single-mode optical fiber to pass through, and the wiring flange is used for the electric connecting wire connected to the piezoelectric ceramic to pass through;

[0044] a vacuum pump connected with the vacuum valve through a vacuum pipe to vacuumize the inside of the vacuum chamber.

[0045] The third aspect of the present application provides a measurement and control method, which uses the infrared detector of any one of the above embodiments or the infrared detection device of any one of the above embodiments to detect the radiation intensity of the infrared light to be detected.

[0046] The advantages or beneficial effects of the above technical solutions at least include: by slidably sleeving the first fixed block on the first end of the concave optical fiber, recessing the middle part of the first side surface of the first fixed block towards the second side surface to form a mounting groove, and arranging the trampoline type resonator in the mounting groove and flush with the groove edge of the mounting groove, the trampoline type resonator and the first end surface of the concave optical fiber define a Fabry-Perot resonant cavity; and since the trampoline type resonator periodically changes the resonance frequency due to the photothermal effect under the irradiation of infrared light with periodically changing intensity, and the concave optical fiber is also used to transmit probe laser into the Fabry-Perot resonant cavity, the probe laser can interfere in the Fabry-Perot resonant cavity and form first reflected light, so as to convert the vibration displacement of the trampoline type resonator into the intensity change of the first reflected light, and the change amplitude of the resonance frequency of the trampoline type resonator represents the radiation intensity of the infrared light. Compared with the prior art non-cooled infrared detector, the detection method of detecting the radiation intensity change of the infrared light by using the optical interference of the Fabry-Perot resonant cavity is a completely non-contact detection method, which can avoid the restriction of the electrode and other electrical measurement structures on the measurement sensitivity and response rate of the infrared detector, and is beneficial to simultaneously improving the measurement sensitivity and response rate of the infrared detector by reducing the size of the infrared detector. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0048] Figure 1 A structure schematic diagram of an infrared detector according to an embodiment of the present application is shown.

[0049] Figure 2 An exploded view of a mid-infrared detector is shown. Figure 1 An exploded view of a mid-infrared detector is shown.

[0050] Figure 3A An effect schematic diagram of a Fabry-Perot resonant cavity according to an embodiment of the present application is shown.

[0051] Figure 3B A cross-sectional structure schematic diagram of a mid-infrared Fabry-Perot resonant cavity is shown. Figure 3A A cross-sectional structure schematic diagram of a mid-infrared Fabry-Perot resonant cavity is shown.

[0052] Figure 4 An analysis result schematic diagram of the noise equivalent power of the infrared detector of the prior art and the infrared detector of the present application is shown.

[0053] Figure 5 A structure schematic diagram of a trampoline type resonator is shown.

[0054] Figure 6 The structure of the middle photonic crystal is shown. Figure 4 The structure of the middle photonic crystal is shown.

[0055] Figure 7 The reflectivity analysis results of the sensing area of the trampoline type resonator under two conditions of no photonic crystal structure and the photonic crystal structure are shown.

[0056] Figure 8 The structure of the infrared detection device of the embodiment of the present application is shown.

[0057] Figure 9 The Allan variance curve of the infrared detection device of the prior art and the infrared detection device of the present application is shown.

[0058] Figure 10 The corresponding relationship between the length of the Fabry-Perot resonant cavity and the reflectivity of the embodiment of the present application is shown. DETAILED DESCRIPTION

[0059] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0060] Figure 1 The structure of the infrared detector according to the embodiment of the present application is shown. Figure 2 The structure of the middle photonic crystal is shown. Figure 1 The exploded view of the middle infrared detector is shown. Figure 3A The effect of the Fabry-Perot resonant cavity of the embodiment of the present application is shown. Figure 3B The structure of the middle photonic crystal is shown. Figure 3A The cross-sectional structure of the middle Fabry-Perot resonant cavity is shown.

[0061] Please refer to Figures 1 to 3BThe infrared detector 11 comprises a concave optical fiber 111, a first fixing block 112, a trampoline resonator 113 and a piezoelectric ceramic 114. The first fixing block 112 is sleeved on the first end of the concave optical fiber 111 in a slidable manner. The middle part of the first side surface of the first fixing block 112 is recessed towards the second side surface to form a mounting groove 112a. The groove edge of the mounting groove 112a is protruded from the first end surface 111a of the concave optical fiber 111. The trampoline resonator 113 is arranged in the mounting groove 112a and flush with the groove edge of the mounting groove 112a, so as to define a Fabry-Perot resonant cavity (not labeled in the figure) between the trampoline resonator 113 and the first end surface 111a of the concave optical fiber 111. The piezoelectric ceramic 114 is sleeved on the concave optical fiber 111 and arranged adjacent to the second side surface of the first fixing block 112, so as to resonantly excite the trampoline resonator 113 under the action of an alternating voltage. The trampoline resonator 113 is used to periodically change the resonance frequency under the irradiation of infrared light with periodically changed radiation intensity, so as to convert the radiation intensity of the infrared light into the change amplitude of the resonance frequency of the trampoline resonator 113. The concave optical fiber 111 is used to transmit a detection laser into the Fabry-Perot resonant cavity, so that the detection laser interferes in the Fabry-Perot resonant cavity and forms a first reflected light. The vibration displacement of the trampoline resonator 113 is converted into the intensity change of the first reflected light, so that the intensity change of the first reflected light carries the change amplitude of the resonance frequency of the trampoline resonator 113, so as to represent the radiation intensity of the infrared light by using the change amplitude of the resonance frequency of the trampoline resonator 113.

[0062] The above scheme can define a Fabry-Perot resonant cavity between the trampoline resonator 113 and the first end surface 111a of the concave optical fiber 111 by slidably sleeving the first fixed block 112 on the first end of the concave optical fiber 111, recessing the middle part of the first side surface of the first fixed block 112 towards the second side surface to form a mounting groove 112a, and arranging the trampoline resonator 113 in the mounting groove 112a and flush with the groove edge of the mounting groove 112a; and since the trampoline resonator 113 is used to periodically change its resonance frequency under the irradiation of infrared light with periodically changing radiation intensity, the concave optical fiber 111 is used to transmit the probe laser into the Fabry-Perot resonant cavity, so that the probe laser interferes in the Fabry-Perot resonant cavity and forms the first reflected light, so as to convert the vibration displacement of the trampoline resonator 113 into the intensity change of the first reflected light, so that the intensity change of the first reflected light carries the change amplitude of the resonance frequency of the trampoline resonator 113, so as to use the change amplitude of the resonance frequency of the trampoline resonator 113 to represent the radiation intensity of the infrared light, so that the detection of the radiation intensity change of the infrared light can be realized. Compared with the non-cooled infrared detector 11 of the prior art, the detection method for detecting the radiation intensity change of the infrared light by using the optical interference of the Fabry-Perot resonant cavity is a completely non-contact detection method, which can avoid the restriction of the electrode and other electrical measurement structures on the measurement sensitivity and response rate of the infrared detector 11, and is beneficial to simultaneously improving the measurement sensitivity and response rate of the infrared detector 11 by reducing the size of the infrared detector 11. For example, as shown in Figure 4 Fig. 8 is a schematic diagram of the analysis results of the noise equivalent power of the infrared detector of the prior art and the infrared detector 11 of the present application, wherein the gray line represents the size of the noise equivalent power of the infrared detector of the prior art with the change of the noise frequency, and the blue line represents the size of the noise equivalent power of the infrared detector 11 of the present application with the change of the noise frequency. Figure 4 As can be seen from

[0063] In one embodiment, as Figure 5As shown, the trampoline resonator 113 includes a sensing region 113a, a fixed region 113b and a plurality of suspension regions 113c. The fixed region 113b is located at the periphery of the sensing region 113a, and the plurality of suspension regions 113c are arranged at intervals along the periphery of the sensing region 113a, each of which is connected between the sensing region 113a and the fixed region 113b. When the infrared light with periodically changing intensity is irradiated to the sensing region 113a, the resonance frequency of the trampoline resonator 113 is periodically changed due to the photothermal effect, so as to realize the conversion of the intensity of the infrared light into the change amplitude of the resonance frequency of the trampoline resonator 113.

[0064] The plurality of periodically arranged circular through holes 1131 can be obtained by etching the sensing region 113a through a photolithography process.

[0065] Exemplarily, the sensing region 113a can be a rectangular region with a side length L1 of 50 μm, the length L2 of the suspension region 113c can be 44 μm, and the width (not labeled in the figure) of the suspension region 113c can be 2.5 μm.

[0066] In an embodiment, referring to Figure 5 and Figure 6 , the structure of the sensing region 113a of the trampoline resonator 113 is a photonic crystal, the lattice structure of the photonic crystal is a two-dimensional hexagon, and the through hole 1131 is arranged at the vertex of the lattice; wherein the radius of the through hole is 549.6 nm and the distance L3 between two adjacent through holes is 1542.8 nm, so that the probe laser with a wavelength of 1550 nm is reflected by the surface of the sensing region 113a towards the side of the concave fiber 111.

[0067] The through hole 1131 can be obtained by etching the vertex of the lattice structure through a photolithography process.

[0068] In the above scheme, since the photonic crystal is a kind of artificial periodic structure with periodic variation of refractive index, and the lattice structure thereof is two-dimensional hexagonal, the through holes 1131 can be arranged in a periodic array structure in the sensing area 113a by arranging the through holes 1131 at the vertices of the lattice structure of the photonic crystal. When the distance L3 between two adjacent through holes 1131 in the array structure is controlled to be in the order of the wavelength of light, a photonic band gap occurs, making it difficult for light waves in the corresponding wavelength range to propagate. Specifically, by arranging the radius of the through holes 1131 to be 549.6 nm and the distance L3 between two adjacent through holes 1131 to be 1542.8 nm, the detection laser with a wavelength of 1550 nm is difficult to propagate and is reflected from the sensing area 113a of the trampoline resonator 113 to the surface of the concave optical fiber 111 toward the first end surface 111a of the concave optical fiber 111, so that the reflectivity of the sensing area 113a of the trampoline resonator 113 toward the surface of the concave optical fiber 111 is improved. For example, as shown in Figure 7 , when the sensing area 113a is not arranged with a plurality of periodically arranged circular through holes 1131, the reflectivity of the sensing area 113a of the trampoline resonator 113 to the detection laser with a wavelength of 1550 nm (the gray line in Figure 7 ) is 42.6%; when the thickness of the sensing area 113a of the trampoline resonator 113 is arranged to be 200 nm, the radius of the plurality of periodically arranged circular through holes 1131 arranged in the sensing area 113a is arranged to be 549.6 nm, and the distance L3 between two adjacent through holes 1131 is arranged to be 1542.8 nm, the reflectivity of the sensing area 113a of the trampoline resonator 113 to the detection laser with a wavelength of 1550 nm (the blue line in Figure 7 ) can reach 98.7%, almost achieving total reflection of the detection laser with a wavelength of 1550 nm.

[0069] Preferably, referring to Figure 5 and Figure 6 , the material of the trampoline resonator 113 is silicon nitride.

[0070] In an embodiment, referring to Figures 1 to 3B , the radius of curvature of the curve of the first end surface 111a of the concave optical fiber 111 ranges from 70 μm to 200 μm (including the end point value), and the length d of the Fabry-Perot resonant cavity ranges from 40 μm to 150 μm (including the end point value). The length d of the Fabry-Perot resonant cavity is the shortest distance between the center of the first end surface 111 of the concave optical fiber 111 and the sensing area 113a of the trampoline resonator 113.

[0071] If the curvature radius is too large, the focusing ability is insufficient, and the photons will be dispersed outside the Fabry-Perot resonant cavity. If the curvature radius is too small, the focusing point deviates from the center of the Fabry-Perot cavity, and the photons are easy to escape. This range can ensure that the photons are effectively constrained in the effective action area of the Fabry-Perot cavity. If the length of the Fabry-Perot resonant cavity is too large, the optical path difference is difficult to meet the resonance condition, and the photons are easy to escape. If the length of the Fabry-Perot resonant cavity is too small, the number of reflections of the photons in the Fabry-Perot resonant cavity is insufficient, the residence time of the photons is short, and the binding effect is poor. By setting the curvature radius of the first end face 111a of the concave optical fiber 111 to be between 70 μm and 200 μm, and setting the length of the Fabry-Perot resonant cavity to be between 40 μm and 150 μm, more photons can be continuously interfered and back and forth in the cavity, thereby being effectively bound, which is conducive to improving the coupling efficiency of the probe laser, thereby reducing the detection noise of the probe laser and improving the sensitivity of the detection.

[0072] In an embodiment, referring to Figures 1 to 3B , the reflectivity of the first end face 111a of the concave optical fiber 111 is less than the reflectivity of the surface of the sensing area 113a of the trampoline-type resonator 113 facing the first end face 111a of the concave optical fiber 111, and the difference between them is in the range of 5% to 10% (including the end value) of the reflectivity of the surface of the sensing area 113a of the trampoline-type resonator 113 facing the first end face 111a of the concave optical fiber 111. For example, the reflectivity of the first end face 111a of the concave optical fiber 111 to the probe laser is in the range of 85% to 95%, and the reflectivity of the surface of the sensing area 113a of the trampoline-type resonator 113 facing the first end face 111a of the concave optical fiber 111 to the probe laser is in the range of 5% to 98.7%, and the difference between them is in the range of 5% to 10%, so that the difference between them is small. In this way, the interfered probe laser can be emitted from the first end face 111a of the concave optical fiber 111, and the energy loss of the probe laser during the interference process is small.

[0073] In an embodiment, referring to Figure 1 and Figure 2 , the infrared detector 11 further comprises a second fixing block 115, a first ceramic gasket 116, a second ceramic gasket 117, and a base 118. The second fixing block 115 is sleeved on the second end of the concave optical fiber 111. The first ceramic gasket 116 and the second ceramic gasket 117 are both sleeved on the concave optical fiber 111, the first ceramic gasket 116 is located between the first fixing block 112 and the piezoelectric ceramic 114, and the second ceramic gasket 117 is located between the piezoelectric ceramic 114 and the second fixing block 115, so as to protect the piezoelectric ceramic 114. The base 118 is fixedly connected with the bottom of the second fixing block 115 to support the second fixing block 115.

[0074] The base 118 comprises, from bottom to top, a circular base disc 118a, a first support column 118b, a second support column 118c and a screw rod 118d which are coaxially arranged in sequence and the diameters of the circular base disc 118a, the first support column 118b, the second support column 118c and the screw rod 118d gradually decrease, and the screw rod 118d is screwed with the bottom of the second fixing block 115. The structure of the base 118 can not only support the second fixing block 115, but also support more stably.

[0075] As shown in Figure 8 The embodiment of the present application also provides an infrared detection device 10, which comprises the infrared detector 11, the infrared lens 12, the optical chopper 13, the laser 14, the optical fiber adapter 15, the optical fiber circulator 16, the single-mode optical fiber 17, the demodulation module 22 and the calculation module 23 of any of the above embodiments.

[0076] The infrared lens 12 is used for focusing the infrared light to be detected on the infrared detector 11.

[0077] The optical chopper 13 is arranged between the infrared lens 12 and the infrared detector 11 and located on the light path of the infrared light to be detected, and is used for modulating the radiation intensity of the infrared light to be detected, so that the radiation intensity of the infrared light to be detected is periodically changed and irradiated to the side of the trampoline-type resonator 113 away from the concave optical fiber 111. The duty cycle of the optical chopper 13 can be 50%, and the modulation frequency of the optical chopper 13 is The modulation frequency of the optical chopper 13 can be expressed by the following formula (1):

[0078] Formula (1)

[0079] Wherein, is the thermal response time of the trampoline-type resonator 113.

[0080] The laser 14 is used for emitting a detection laser. Optionally, the laser 14 can be a narrowband laser 14, the wavelength of the detection laser can be 1550nm, and the power of the detection laser can be 1-10 mu W (including the end value). By selecting the power of the detection laser between 1 mu W and 10 mu W, the interference of the photo-thermal effect caused by the trampoline-type resonator 113 absorbing the detection laser on the detection of the infrared radiation intensity can be reduced.

[0081] The optical fiber adapter 15, the optical fiber circulator 16 and the single-mode optical fiber 17 are sequentially connected between the laser 14 and the second end of the concave optical fiber 111, so as to transmit the detection laser into the Fabry-Perot resonant cavity, so that the detection laser forms a first reflected light after interference in the Fabry-Perot resonant cavity; and the first reflected light is reflected back into the optical fiber circulator 16 through the concave optical fiber 111.

[0082] The fiber adapter 15 can be an FC / APC fiber adapter, and the fiber circulator 16 has an input end, a first output end and a second output end. The laser 14 is connected with the input end of the fiber circulator 16 through the fiber adapter 15, and the first output end of the fiber circulator 16 is connected with the second end of the concave fiber 111 through the single-mode fiber 17 to transmit the probe laser into the Fabry-Perot resonant cavity to form the first reflected light after interference, and the first reflected light is reflected back into the fiber circulator 16 through the concave fiber 111, the single-mode fiber 17 and the first output end of the fiber circulator 16 in turn.

[0083] The photodetector 21 is connected with the fiber circulator 16 to detect the intensity change of the first reflected light. Specifically, the photodetector 21 is connected with the second output end of the fiber circulator 16 to detect the intensity change of the first reflected light.

[0084] The demodulation module 22 is used to analyze the intensity change of the first reflected light to obtain the change amplitude of the resonance frequency of the trampoline resonator 113.

[0085] The calculation module 23 is used to calculate the radiation intensity of the to-be-detected infrared light according to the change amplitude of the resonance frequency of the trampoline resonator 113, the preset resonance frequency of the trampoline resonator 113 and the infrared thermal response time thereof, the infrared radiation absorption coefficient of the material of the trampoline resonator 113 and the infrared response rate thereof.

[0086] Specifically, the calculation module 23 can calculate the radiation intensity of the to-be-detected infrared light through the following formula (2) :

[0087] Formula (2)

[0088] wherein, represents the change amplitude of the resonance frequency of the trampoline resonator 113, represents the infrared radiation absorption coefficient of the material of the trampoline resonator 113, represents the infrared response rate of the trampoline resonator 113, represents the resonance frequency of the trampoline resonator 113, represents the modulation frequency of the optical chopper 13, represents the infrared thermal response time of the trampoline resonator 113.

[0089] The above scheme, on the one hand, modulates the radiation intensity of the infrared light to be detected by the optical chopper 13, so that the radiation intensity of the infrared light to be detected is periodically varied when it irradiates the trampoline resonator 113, which causes the resonant frequency of the trampoline resonator 113 to change periodically due to the photothermal effect; on the other hand, the laser 14 transmits the detection laser to the second end of the concave fiber 111 through the fiber optic adapter 15, the fiber optic circulator 16 and the single-mode fiber 17, so that the detection laser can be transmitted to the Fabry-Perot resonator cavity, where it interferes and forms the first reflected light. The first reflected light is reflected back into the fiber optic circulator 16 via the concave optical fiber 111, enabling the photodetector 21 to detect the intensity change of the first reflected light. This converts the resonant frequency change of the trampoline resonator 113 into an intensity change of the first reflected light. The demodulation module 22 then analyzes this intensity change to obtain the amplitude of the resonant frequency change of the trampoline resonator 113. The calculation module 23 then substitutes this amplitude into a preset formula to obtain the radiation intensity of the infrared light to be detected, thus achieving infrared radiation intensity detection. This modulation-demodulation detection method measures the relative change rather than the absolute value of the resonant frequency of the trampoline resonator 113, making it insensitive to fluctuations in ambient temperature. This avoids the influence of ambient temperature fluctuations on the resonant frequency measurement of the trampoline resonator 113, improving the stability of the infrared detection device 10. For example, as... Figure 9 As shown, comparing the infrared radiation intensity of the infrared light to be detected measured using the modulation-demodulation detection method in this application with that measured using the non-modulation detection method, the maximum Allan variance of the former is ( Figure 9 The maximum value of the blue line is close to The latter's maximum Allan variance ( Figure 9 The maximum value of the medium gray line is close to The maximum Allan variance of the former is about one order of magnitude smaller than that of the latter, which indicates that the stability of the infrared detection device 10 for measuring the infrared light to be detected using the modulation-demodulation detection method in this application is improved by about one order of magnitude.

[0090] In one implementation, please refer to the following: Figure 3A , Figure 3B and Figure 8 Laser 14 is also used to emit modulated laser without infrared detection. After the modulated laser is transmitted into the Fabry-Perot resonant cavity, it forms a second reflected light. Photodetector 21 is also used to detect the intensity change of the second reflected light.

[0091] The infrared detection device 10 also includes a PI controller 24 and an adder 25. The PI controller 24 is connected to the piezoelectric ceramic 114 through the adder 25 to apply a DC voltage to the piezoelectric ceramic 114 and adjust the voltage value of the DC voltage to increase or decrease the length d of the Fabry-Perot resonant cavity, and to enable the photodetector 21 to detect the intensity change of the second reflected light.

[0092] The PI controller 24 is connected to the photodetector 21 to lock the length d of the Fabry-Perot resonator to the length corresponding to the maximum slope of the change in reflected light intensity, as the length of the Fabry-Perot resonator increases or decreases.

[0093] like Figure 10 As shown, due to the relationship between the length d of the Fabry-Perot resonator and the intensity of the laser incident on the Fabry-Perot resonator... The intensity of its reflected light (i.e., the second reflected light). Calculated reflectance There is a corresponding relationship between them, and the intensity of the modulated laser incident into the Fabry-Perot resonator is... Typically a fixed value, the PI controller 24 controls the length d of the Fabry-Perot resonator by applying a DC voltage to the piezoelectric ceramic 114 and adjusting the voltage value, thereby increasing or decreasing the length d of the resonator and adjusting the intensity of the reflected light after the laser is transmitted into the Fabry-Perot resonator. A corresponding change occurs, and the intensity of the reflected light is then detected by photodetector 21. The changes.

[0094] As the length d of the Fabry-Perot resonator increases or decreases, the PI controller 24 measures the intensity of the second reflected light as a function of the length d of the Fabry-Perot resonator via the photodetector 21, as shown in the figure. Figure 7 The slope A of the intensity change of the second reflected light is the maximum, which makes the length corresponding to that point the optimal value of the Fabry-Perot resonator length d. Therefore, by locking the length d of the Fabry-Perot resonator to the length corresponding to the maximum slope of the intensity change of the second reflected light, the Fabry-Perot resonator can be in its optimal working state.

[0095] In one implementation, please refer to the following: Figure 8The demodulation module 22 comprises a phase-locked loop 221 and a phase-locked amplifier 222, the phase-locked loop 221 is connected with the photodetector 21 and the adder 25 respectively, and the phase-locked amplifier 222 is connected with the phase-locked loop 221 and the calculation module 23 respectively. The phase-locked loop 221 is used for analyzing the intensity variation of the second reflected light to obtain the variation of the resonance frequency of the trampoline resonator 113, and the phase-locked amplifier 222 is used for amplitude demodulation of the variation of the resonance frequency of the trampoline resonator 113 to obtain the amplitude of the variation of the resonance frequency of the trampoline resonator 113. In this way, the amplitude demodulation of the variation of the resonance frequency of the trampoline resonator 113 can be realized.

[0096] Further, please refer to Figure 8 The phase-locked loop 221 is also used for applying an alternating voltage to the piezoelectric ceramic 114 through the adder 25 and locking the frequency of the alternating voltage to the resonance frequency of the trampoline resonator 113, so as to ensure that the vibration frequency of the piezoelectric ceramic 114 is always the same as the resonance frequency of the trampoline resonator 113. Preferably, the loop bandwidth of the phase-locked loop 221 is set to 3 times of the modulation frequency of the optical chopper 13, so as to quickly realize frequency locking.

[0097] In an embodiment, as shown in Figure 8 The infrared detection device 10 further comprises a vacuum chamber 31 and a vacuum pump 32. The side wall of the vacuum chamber 31 is provided with a light transmission window 311, a fiber flange 312, a wiring flange 313 and a vacuum valve 314. The light transmission window 311 is located between the optical chopper 13 and the infrared detector 11 and on the light path of the to-be-detected infrared light. The fiber flange 312 is used for allowing the single-mode optical fiber 17 to pass through. The wiring flange 313 is used for allowing the electrical connecting wire connected to the piezoelectric ceramic 114 to pass through. The vacuum pump 32 is connected with the vacuum valve 314 through a vacuum pipe 315, so as to vacuumize the inside of the vacuum chamber 31. In this way, the vacuum chamber 31 and the vacuum pump 32 can be used to construct a high-vacuum environment around the infrared detector 11, which is conducive to reducing environmental heat convection and improving the quality factor of the trampoline resonator 113, thereby improving the detection accuracy of the infrared detector 11.

[0098] The present application also provides a measurement and control method, which uses the infrared detector 11 of any one of the above embodiments or the infrared detection device 10 of any one of the above embodiments to detect the radiation intensity of the to-be-detected infrared light. Since the specific structure of the infrared detector 11 or the infrared detection device 10 used in the measurement and control method refers to the above embodiments, the measurement and control method at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0099] The above-described embodiments are merely illustrative of several embodiments of the present application, which are described in more detail and in a specific and detailed manner, but should not be construed as limiting the scope of the patent of the present application. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. An infrared detector, characterized in that, include: Concave optical fiber; A first fixing block is slidably sleeved on the first end of the concave optical fiber. The middle part of the first side surface of the first fixing block is recessed towards the second side surface to form a mounting groove, and the groove edge of the mounting groove protrudes from the first end face of the concave optical fiber. A trampoline-type resonator is disposed in the mounting groove and flush with the edge of the mounting groove, so that a Fabry-Perot resonant cavity is defined between the trampoline-type resonator and the first end face of the concave optical fiber. A piezoelectric ceramic is sleeved on the concave optical fiber and disposed adjacent to the second side surface of the first fixing block, so as to resonate and excite the trampoline resonator under the action of AC voltage; The trampoline-type resonator is used to periodically change its resonant frequency under infrared light irradiation with periodically varying radiation intensity; the concave optical fiber is used to transmit the probe laser into the Fabry-Perot resonant cavity, so that the probe laser interferes in the Fabry-Perot resonant cavity and forms a first reflected light, so as to convert the vibration displacement of the trampoline-type resonator into the intensity change of the first reflected light, and the intensity change of the first reflected light carries the amplitude of the change in the resonant frequency of the trampoline-type resonator. The variation amplitude of the resonant frequency of the trampoline-type resonator is used to characterize the radiation intensity of the infrared light.

2. The infrared detector according to claim 1, characterized in that, The trampoline-type resonator includes a sensing region, a fixed region, and multiple suspension regions. The fixed region is located outside the sensing region, and the multiple suspension regions are spaced apart along the periphery of the sensing region. Each suspension region is connected between the sensing region and the fixed region. And / or, the radius of curvature of the first end face of the concave optical fiber ranges from 70μm to 200μm, and the length of the Fabry-Perot resonant cavity ranges from 40μm to 150μm.

3. The infrared detector according to claim 2, characterized in that, The sensing region is structured as a photonic crystal with a two-dimensional hexagonal lattice structure. A through-hole is formed at the vertices of the lattice, with a radius of 549.6 nm and a distance of 1542.8 nm between two adjacent through-holes, so that the detection laser with a wavelength of 1550 nm is reflected by the surface of the sensing region toward the concave optical fiber.

4. The infrared detector according to claim 1, characterized in that, The reflectivity of the first end face of the concave optical fiber is less than the reflectivity of the surface of the sensing area of ​​the trampoline resonator facing the first end face of the concave optical fiber, and the difference between the two is 5% to 10% of the reflectivity of the surface of the sensing area of ​​the trampoline resonator facing the first end face of the concave optical fiber.

5. The infrared detector according to claim 1, characterized in that, Also includes: The second fixing block is sleeved on the second end of the concave optical fiber; The first ceramic pad and the second ceramic pad are both sleeved on the concave optical fiber. The first ceramic pad is located between the first fixing block and the piezoelectric ceramic, and the second ceramic pad is located between the piezoelectric ceramic and the second fixing pad. The base is fixedly connected to the bottom of the second fixing block.

6. An infrared detection device, characterized in that, include: The infrared detector according to any one of claims 1 to 5; An infrared lens is used to focus the infrared light to be detected onto the infrared detector. An optical chopper is disposed between the infrared lens and the infrared detector and is located in the optical path of the infrared light to be detected. It is used to modulate the radiation intensity of the infrared light to be detected so that the radiation intensity of the infrared light to be detected is periodically varied and irradiates the side of the trampoline resonator away from the concave optical fiber. A laser for emitting the detection laser; An optical fiber adapter, an optical fiber circulator, and a single-mode optical fiber are sequentially connected between the laser and the second end of the concave optical fiber to transmit the probe laser to the Fabry-Perot resonator, where the probe laser interferes with the Fabry-Perot resonator to form a first reflected light; the first reflected light is reflected back to the optical fiber circulator via the concave optical fiber. A photodetector, connected to the fiber optic circulator, is used to detect the intensity change of the first reflected light; The demodulation module is used to analyze the intensity change of the first reflected light to obtain the amplitude of the change in the resonant frequency of the trampoline resonator; The calculation module is used to calculate the radiation intensity of the infrared light to be detected according to the following formula. : ， in, This indicates the amplitude of the change in the resonant frequency of the trampoline-type resonator. This represents the infrared radiation absorption coefficient of the trampoline-type resonator. This represents the infrared responsivity of the trampoline-type resonator. This indicates the resonant frequency of the trampoline-type resonator. This indicates the modulation frequency of the optical chopper. This indicates the infrared thermal response time of the trampoline-type resonator.

7. The infrared detection device according to claim 6, characterized in that, The laser is also used to emit modulated laser light without infrared detection. The modulated laser light is transmitted into the Fabry-Perot resonant cavity and forms a second reflected light. The photodetector is also used to detect the intensity change of the second reflected light. The infrared detection device also includes: A PI controller and an adder are provided. The PI controller is connected to the piezoelectric ceramic via the adder to apply a DC voltage to the piezoelectric ceramic and adjust the value of the DC voltage to increase or decrease the length of the Fabry-Perot resonant cavity, and to enable the photodetector to detect the intensity change of the second reflected light. The PI controller is connected to the photodetector to lock the length of the Fabry-Perot resonator to the length corresponding to the maximum slope of the second reflected light intensity change when the length of the Fabry-Perot resonator increases or decreases.

8. The infrared detection device according to claim 7, characterized in that, The demodulation module includes: A phase-locked loop is connected to the photodetector and the adder, respectively; A lock-in amplifier is connected to both the phase-locked loop and the computing module. The phase-locked loop is used to analyze the intensity change of the first reflected light to obtain the change in the resonant frequency of the trampoline resonator; The lock-in amplifier is used to demodulate the amplitude of the resonant frequency change of the trampoline resonator to obtain the amplitude of the resonant frequency change of the trampoline resonator. The phase-locked loop is also used to apply an AC voltage to the piezoelectric ceramic through the adder and lock the frequency of the AC voltage to the resonant frequency of the trampoline resonator.

9. The infrared detection device according to claim 6, characterized in that, Also includes: The vacuum chamber has a light-transmitting window, an optical fiber flange, a wiring flange, and a vacuum valve on its side wall. The light-transmitting window is located between the optical chopper and the infrared detector and is located in the optical path of the infrared light to be detected. The optical fiber flange is used for the single-mode optical fiber to pass through, and the wiring flange is used for the electrical connection wire connected to the piezoelectric ceramic to pass through. A vacuum pump, connected to the vacuum valve via a vacuum tube, is used to evacuate the interior of the vacuum chamber.

10. A measurement and control method, characterized in that, The infrared detector described in any one of claims 1 to 5 or the infrared detection device described in any one of claims 6 to 9 is used to detect the radiation intensity of the infrared light to be detected.

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