Terahertz detector based on microcavity enhanced non-degenerate two-photon absorption

Abstract

The invention belongs to the technical field of infrared / terahertz detection, provides a terahertz detector based on microcavity enhanced non-degenerate two-photon absorption, solves the problem that a traditional high-sensitivity terahertz detector needs ultralow-temperature refrigeration, and adopts the technical scheme that the input end of a polarization controller is connected with a pump laser used for generating pump light; the input end of the optical fiber taper is connected with the output end of a polarization controller for adjusting the polarization characteristic of the pump light; the surface of the echo wall mode microcavity is coated with a fluorescent material of quantum dot perovskite, and a terahertz signal to be detected is focused on the fluorescent material through a terahertz focusing lens used for gathering field energy; optically coupling the optical fiber taper and the echo wall mode microcavity; the input end of the optical filter is connected with the output end of the optical fiber taper, and the output end of the optical filter after the non-fluorescent wave band is filtered is connected with a photoelectric detector used for converting light field intensity information generated by fluorescent light waves into electric signals. Terahertz high-sensitivity detection at normal temperature becomes possible.

Description

Technical Field

[0001] The present invention belongs to the technical field of infrared / terahertz detection, and particularly relates to a terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption. Background Art

[0002] The statements in this part merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] A terahertz detector is a device used to detect terahertz-band signals and is widely applied in fields such as imaging, communication, security detection, and biomedicine. Currently, the main terahertz detector technologies include two types: thermal detectors and photodetectors. Although thermal detectors have a wide response range for terahertz signals, their response speed is slow, the sensitivity is relatively low, and they are easily interfered by the ambient temperature; although photodetectors have high sensitivity and fast response capabilities, achieving high sensitivity requires working in a low-temperature environment, which increases the complexity and cost of the system, and the dependence on the refrigeration system limits the portability of such detectors. Summary of the Invention

[0004] To solve at least one of the technical problems existing in the above background art, the first aspect of the present invention provides a terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption, which can not only achieve room-temperature high-sensitivity detection of terahertz waves, but also has the advantages of strong integratability and a wide detection frequency band.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption includes:

[0007] A polarization controller, whose input end is connected to a pump laser for generating pump light;

[0008] An optical fiber taper, whose input end is connected to the output end of the polarization controller for adjusting the polarization characteristics of the pump light;

[0009] A whispering-gallery-mode microcavity, whose surface is coated with a fluorescent material of quantum dot perovskite, and the terahertz signal to be measured is focused onto the fluorescent material through a terahertz focusing lens for aggregating field energy;

[0010] Optical coupling between the optical fiber taper and the whispering-gallery-mode microcavity;

[0011] A terahertz focusing lens, which focuses the terahertz signal light to be measured onto the microcavity;

[0012] An optical filter, whose input end is connected to the output end of the optical fiber taper, and the output end after filtering out non-fluorescent bands is connected to a photodetector for converting the optical field intensity information generated by the fluorescent light wave into an electrical signal.

[0013] As an implementation manner, the pump light is single-frequency continuous light, and the wavelength of the pump light is determined according to the frequency of the measured terahertz wave, and the wavelength range is between 524 - 630 nm.

[0014] As an implementation manner, the whispering gallery mode microcavity adopts a microsphere cavity structure, and the diameter of the microsphere cavity is 50 μm to 500 μm.

[0015] As an implementation manner, the fluorescent material is MAPbBr3 quantum dot perovskite fluorescent material.

[0016] As an implementation manner, the preparation process of the perovskite fluorescent material MAPbBr3 quantum dots includes:

[0017] First step, mix 75 mg of lead bromide, 5 ml of octadecene, 2 ml of oleic acid, 2 ml of oleylamine with 90 mg of zinc bromide, heat to 120 °C, and keep for 30 minutes;

[0018] Second step, raise the temperature to 140 °C and keep for 10 minutes;

[0019] Third step, inject 0.4 ml of cesium oleate, and cool with ice water after reacting for 20 seconds;

[0020] Fourth step, centrifuge at a speed of 3500 rpm for 10 minutes and discard the precipitate;

[0021] Fifth step, add 4 ml of acetone to the supernatant;

[0022] Sixth step, centrifuge at a speed of 3500 rpm for 3 minutes, collect the precipitate, and disperse it with 2 ml of n-hexane.

[0023] As an implementation manner, the optical filter adopts a fiber Bragg grating.

[0024] As an implementation manner, the working band of the photodetector is the visible light band, and the detectable wavelength covers 450 - 520 nm.

[0025] As an implementation manner, the fiber taper generates an evanescent field through an extremely thin taper region, and optical coupling is performed between the fiber taper and the whispering gallery mode microcavity in the way of evanescent field coupling.

[0026] As an implementation manner, when the optical field intensity information generated by the fluorescent light wave is converted into an electrical signal, the conversion is performed according to the set ratio.

[0027] To solve the above problems, the second aspect of the present invention provides a terahertz detection method, which can not only achieve high-sensitivity detection of terahertz waves at room temperature, but also has the advantages of strong integratability and wide detection frequency band.

[0028] To achieve the above object, the present invention adopts the following technical solutions:

[0029] A terahertz detection method, which is based on the terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption described in the first aspect, is used to detect the terahertz signal to be measured.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. The present invention adopts a scheme that combines the fluorescence up-conversion technology based on two-photon absorption with a highly sensitive visible light detector, making it possible to perform highly sensitive terahertz detection at room temperature. This method of the present invention avoids the problem that traditional highly sensitive terahertz detectors require cryogenic cooling, eliminates large-volume temperature control and cooling devices, thereby reducing costs.

[0032] 2. The present invention uses a whispering gallery mode microcavity as an attachment platform for perovskite fluorescent materials. Its ultra-high Q value and extremely large optical field energy density have significantly reduced the power threshold required for the non-degenerate two-photon absorption effect to occur. The present invention can perform conversion with a lower-power pump light, without optical amplification or using a pulsed light source, and the system complexity is significantly reduced.

[0033] 3. Different from the traditional terahertz detection technology based on parametric up-conversion of optical nonlinear effects, non-degenerate two-photon absorption does not need to consider the phase matching relationship in the optical field conversion process, thereby enabling the detection of broadband terahertz waves.

[0034] The advantages of the additional aspects of the present invention will be partially given in the following description, partially will become obvious from the following description, or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0036] Figure 1 is a schematic structural diagram of a terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption provided by an embodiment of the present invention;

[0037] Figure 2 is a structural diagram of a perovskite fluorescent material MAPbBr3 quantum dot provided by an embodiment of the present invention

[0038] Figure 3 is a scanning electron microscope physical diagram of a perovskite fluorescent material MAPbBr3 quantum dot provided by an embodiment of the present invention;

[0039] Figure 4 is a fluorescence spectrum generated by non-degenerate two-photon absorption measured by an embodiment of the present invention;

[0040] Among them, 1 is a pump laser, 2 is a polarization controller, 3 is a whispering gallery mode microcavity, 4 is an optical fiber taper, 5 is an optical filter, 6 is a photodetector, and 7 is a focusing lens. Specific implementation manners

[0041] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0042] It should be noted that the following detailed description is illustrative and is intended to provide further description of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0043] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0044] In the present invention, terms such as "connected" and "coupled" should be understood in a broad sense, which may mean a fixed connection, an integral connection or a detachable connection; it may be directly connected or indirectly connected through an intermediate medium. For those relevant scientific research or technical personnel in the field, the specific meanings of the above terms in the present invention can be determined according to specific circumstances, and should not be construed as a limitation to the present invention.

[0045] As mentioned in the background art, the current main terahertz detector technologies include two types: thermal detectors and photodetectors. Although thermal detectors have a wide response range to terahertz signals, their response speed is slow, the sensitivity is relatively low, and they are easily affected by the ambient temperature; although photodetectors have high sensitivity and fast response capabilities, achieving high sensitivity requires working in a low-temperature environment, which increases the complexity and cost of the system, and the dependence on the refrigeration system limits the portability of such detectors.

[0046] Non-degenerate Two-Photon Absorption (NTPA) refers to the absorption of two photons with different energies (pump light and signal light photons) by the same material at the same time, resulting in the transition of electrons in the material. When two photons irradiate the material simultaneously, they can excite the electrons in the material through different energy paths, prompting the electrons to transition from the ground state to the excited state. This process is non-linear and depends on the matching of photon energies. The photons in the excited state will radiate fluorescent photons with a higher frequency than the pump light and signal light during the process of returning to the ground state. The fluorescent photons can be received and detected by a highly sensitive detector in the high-frequency light band, thereby characterizing the intensity of the signal light in the terahertz band through the fluorescence intensity and realizing the detection of terahertz waves. By combining the NTPA material with a whispering-gallery-mode microcavity, the response ability of the detector to terahertz signals can be greatly improved. The high Q value of the microcavity can effectively enhance the interaction between light and matter, increase the residence time of photons in the material, thereby increasing the probability of two-photon absorption, and further improving the sensitivity and response speed of the detector.

[0047] Compared with degenerate two-photon absorption, NTPA can utilize two photons with different energies for absorption, which means that transitions can be achieved in a relatively wide wavelength range. In addition, compared with parametric up-conversion infrared / terahertz detection based on optical non-linear effects, this process does not need to consider the phase matching condition between the converted optical frequencies, thereby realizing wide-spectrum signal light detection. Therefore, the inventive solution can achieve a terahertz detection device with room temperature, wide spectrum, high sensitivity, and miniaturization, and is expected to further expand the application scope of terahertz technology.

[0048] The present invention provides a terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption, which can not only achieve room-temperature high-sensitivity detection of terahertz waves, but also has the advantages of strong integratability and wide detection frequency band.

[0049] As Figure 1 shown, the present invention provides a terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption, including:

[0050] A polarization controller 2, the input end of which is connected to a pump laser 1 for generating pump light;

[0051] An optical fiber taper 4, the input end of which is connected to the output end of the polarization controller 2 for adjusting the polarization characteristics of the pump light;

[0052] A whispering-gallery-mode microcavity 3, the surface of which is coated with a fluorescent material of quantum dot perovskite, and the terahertz signal to be measured is focused on the fluorescent material through a terahertz focusing lens 7 for concentrating field energy;

[0053] Optical coupling between the optical fiber taper 4 and the whispering-gallery-mode microcavity 3;

[0054] The optical filter 5 is connected to the output end of the fiber taper 4 at the input end. After filtering out the non-fluorescent wavelength band, the output end is connected to the photodetector 6 for converting the optical field intensity information generated by the fluorescent light wave into an electrical signal.

[0055] With the solution of combining the fluorescence up-conversion technology based on two-photon absorption with a highly sensitive visible light detector, the present invention makes it possible to perform highly sensitive terahertz detection at room temperature. This method avoids the problem that traditional highly sensitive terahertz detectors require cryogenic cooling, eliminates large-volume temperature control and cooling devices, and thus reduces the cost.

[0056] Among them, the pump laser 1 is connected to the input end of the polarization controller 2 through an optical fiber and is used to output pump light.

[0057] In this embodiment, the output laser of the pump laser 1 is a single-frequency continuous light with a wavelength in the visible light band, and preferably the output wavelength range is 524 - 630 nm. Among them, the polarization controller 2 is used to adjust the polarization characteristics of the pump light, achieve high-efficiency resonance between the pump light and the cavity mode, and deliver the adjusted light wave into the fiber taper 4.

[0058] Among them, the whispering gallery mode microcavity 3 is coated with a fluorescent material of quantum dot perovskite on the surface and is used to enhance the interaction between the optical field and the fluorescent material.

[0059] In this embodiment, the whispering gallery mode microcavity 3 adopts a microsphere cavity structure. The whispering gallery mode micro-ring cavity is preferably designed as a SiO2 microsphere cavity with a diameter of 50 μm to 500 μm, and can be prepared by heating the tip of a communication optical fiber with a hydrogen-oxygen flame.

[0060] It should be noted that in other embodiments, the wavelength of the output laser of the pump laser and the diameter of the microsphere cavity can also be selected according to actual situations.

[0061] The present invention uses the whispering gallery mode microcavity as an attachment platform for the perovskite fluorescent material. Its ultra-high Q value and extremely high optical field energy density significantly reduce the power threshold required for the non-degenerate two-photon absorption effect to occur. This solution can perform conversion with a lower-power pump light, without optical amplification or using a pulsed light source, and the system complexity is significantly reduced.

[0062] In this embodiment, preferably, the perovskite fluorescent material is MAPbBr3 quantum dots. Figure 2 is the structural diagram of the MAPbBr3 quantum dots of the perovskite fluorescent material. Figure 3 is the SEM physical diagram of the MAPbBr3 quantum dots of the perovskite fluorescent material, and its preparation process includes:

[0063] First step: Mix 75 mg (0.2 mmol) of lead bromide, 5 mL of octadecene, 2 mL of oleic acid, 2 mL of oleylamine with 90 mg (0.4 mmol) of zinc bromide, heat to 120 °C, and keep for 30 minutes;

[0064] Second step: Raise the temperature to 140 °C and keep for 10 minutes;

[0065] Third step: Inject 0.4 mL of cesium oleate, cool with ice water after reacting for 20 seconds;

[0066] Fourth step: Centrifuge at 3500 rpm for 10 minutes and discard the precipitate;

[0067] Fifth step: Add 4 mL of acetone to the supernatant;

[0068] Sixth step: Centrifuge at 3500 rpm for 3 minutes, collect the precipitate, and disperse it with 2 mL of n - hexane.

[0069] Among them, the fiber taper 4 generates an evanescent field through an extremely thin taper region, realizes the optical coupling between the fiber taper and the micro - cavity, and its output end is connected to the input end of the optical filter;

[0070] Among them, the optical filter 5 filters out the interference signals in non - fluorescence bands, improves the signal - to - noise ratio of detection, and its output end is connected to the photodetector;

[0071] Preferably, the optical filter 5 adopts a fiber Bragg grating.

[0072] It can be understood that in other embodiments, those skilled in the art can set according to specific working conditions, which will not be elaborated here.

[0073] Among them, the photodetector is used to receive the optical field intensity information of fluorescence and convert it into an electrical signal proportional to it;

[0074] In this embodiment, the working band of the photodetector is the visible light band, and the detectable wavelength covers 450 - 520 nm.

[0075] The terahertz focusing lens 7 is used to focus the terahertz signal light to be measured on the micro - cavity to improve the signal light energy density.

[0076] There are two optical paths, namely the fiber waveguide and free space, in the system of the present invention:

[0077] The light source in the fiber waveguide path is the pump laser 1, which is sequentially connected to the polarization controller 2, the fiber taper 4, the whispering - gallery - mode micro - cavity coated with fluorescent material, the optical filter 5, and the photodetector 6 through the optical fiber;

[0078] The free-space path is the terahertz signal light to be detected. This signal light focuses the field energy on the fluorescent material coated on the surface of the whispering-gallery mode microcavity through the focusing lens 7. There is pump light with a high energy density in the fluorescent material, but the pump light power is slightly lower than the threshold power of degenerate two-photon absorption. After receiving the terahertz wave to be measured, when the power condition for non-degenerate two-photon absorption is met, the perovskite fluorescent material emits fluorescence.

[0079] Among them, the pump and fluorescence optical fields are coupled in and out of the whispering-gallery mode microcavity through the fiber taper 4. This detector uses the perovskite fluorescent material as the material for non-degenerate two-photon absorption and the whispering-gallery mode microcavity 3 as a platform to enhance the interaction between light and matter. The pump light is coupled in and out of the whispering-gallery mode microcavity through the fiber taper 4, improving the power density of the pump light field and thus significantly reducing the pump light power condition.

[0080] Then, the terahertz wave to be measured is focused on the perovskite fluorescent material coated on the surface of the microcavity through the focusing lens 7. The fluorescent material generates fluorescence with a higher optical frequency than the pump light and the terahertz wave through non-degenerate two-photon absorption. The generated fluorescence is coupled out of the whispering-gallery mode microcavity through the fiber taper 4, and then undergoes filtering processing. The intensity of the fluorescence is obtained using the photodetector 6, thereby characterizing the intensity of the terahertz wave to be measured.

[0081] The present invention also provides a terahertz detection method for detecting a terahertz signal to be measured based on the above-mentioned terahertz detector with microcavity-enhanced non-degenerate two-photon absorption.

[0082] The specific detection principle is as follows:

[0083] The terahertz signal light to be detected focuses the field energy on the fluorescent material coated on the surface of the microcavity through the focusing lens. There is pump light with a high energy density in the fluorescent material, but the pump light power is slightly lower than the threshold power of degenerate two-photon absorption. After receiving the terahertz wave to be measured, when the power condition for non-degenerate two-photon absorption is met, the perovskite fluorescent material emits fluorescence. Among them, the pump and fluorescence optical fields are coupled in and out of the microcavity through the fiber taper. This detector uses the perovskite fluorescent material as the material for non-degenerate two-photon absorption and the whispering-gallery mode microcavity as a platform to enhance the interaction between light and matter. The pump light is coupled in and out of the microcavity through the fiber taper, improving the power density of the pump light field and thus significantly reducing the pump light power condition.

[0084] Then, the terahertz wave to be measured is focused on the perovskite fluorescent material coated on the surface of the microcavity through the focusing lens. The fluorescent material generates fluorescence with a higher optical frequency than the pump light and the terahertz wave through non-degenerate two-photon absorption. The generated fluorescence is coupled out of the microcavity through the fiber taper, and then undergoes filtering processing. The intensity of the fluorescence is obtained using the photodetector, thereby characterizing the intensity of the terahertz wave to be measured.

[0085] To verify the effectiveness of the proposed solution of the present invention, the following simulation experiment was conducted.

[0086] MAPbBr3 quantum dot perovskite was coated on a SiO2 microsphere cavity with a diameter of about 300 nm. Figure 1 The terahertz detection experimental device based on microcavity-enhanced non-degenerate two-photon absorption was set up. A continuous laser (Oxxius, LPX-532L) was used to output a pump beam with a wavelength of 532 nm. The resonance between the pump beam and the cavity mode was achieved by adjusting the polarization controller and the cavity temperature. A terahertz wave to be measured with a frequency of 10 THz was output by a quantum cascade laser and focused on the microsphere cavity through a silicon lens. The emitted two-photon absorption fluorescence was connected to a spectrometer (Ocean Insight, QEPro) through an optical fiber after passing through an optical filter, and the fluorescence spectrum was measured and obtained. As Figure 4 shown, the spectrum of non-degenerate two-photon absorption measured is presented. The peak of the fluorescence intensity appears near 522.85 nm. This simulation experiment fully demonstrates the effectiveness of the proposed solution of the present invention.

[0087] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption, characterized in that, Including: A polarization controller, with its input end connected to a pump laser for generating pump light; An optical fiber taper, with its input end connected to the output end of the polarization controller for adjusting the polarization characteristics of the pump light; A whispering gallery mode microcavity, whose surface is coated with a fluorescent material of quantum dot perovskite, and the terahertz signal to be measured is focused onto the fluorescent material through a terahertz focusing lens for aggregating field energy; Optical coupling between the optical fiber taper and the whispering gallery mode microcavity; An optical filter, with its input end connected to the output end of the optical fiber taper, and the output end after filtering out non-fluorescent bands is connected to a photodetector for converting the optical field intensity information generated by the fluorescent light wave into an electrical signal.

2. The terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption according to claim 1, wherein The pump light is single-frequency continuous light, and the wavelength of the pump light is determined according to the frequency of the terahertz wave to be measured, and the wavelength range is between 524 - 630 nm.

3. The terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption according to claim 1, characterized in that, The whispering gallery mode microcavity adopts a microsphere cavity structure, and the diameter of the microsphere cavity is 50 μm to 500 μm.

4. The terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption according to claim 1, wherein The fluorescent material is MAPbBr3 quantum dot perovskite fluorescent material.

5. The terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption according to claim 4, wherein The preparation process of the perovskite fluorescent material of MAPbBr3 quantum dots includes: The first step: Mix 75 mg of lead bromide, 5 ml of octadecene, 2 ml of oleic acid, 2 ml of oleylamine with 90 mg of zinc bromide, heat to 120 °C, and keep for 30 minutes; The second step: Raise the temperature to 140 °C and keep for 10 minutes; The third step: Inject 0.4 ml of cesium oleate, cool with ice water after reacting for 20 seconds; The fourth step: Centrifuge at a speed of 3500 rpm for 10 minutes and discard the precipitate; The fifth step: Add 4 ml of acetone to the supernatant; The sixth step: Centrifuge at a speed of 3500 rpm for 3 minutes, collect the precipitate, and disperse it with 2 ml of n-hexane.

6. The terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption according to claim 1, characterized in that, The optical filter adopts a fiber Bragg grating.

7. The terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption according to claim 1, characterized in that, The working band of the photodetector is the visible light band, and the detectable wavelength covers 450 - 520 nm.

8. The terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption according to claim 1, characterized in that The optical fiber taper generates an evanescent field through an extremely thin tapered region, and the optical coupling between the optical fiber taper and the whispering gallery mode microcavity is carried out in the way of evanescent field coupling.

9. The terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption according to claim 1, wherein When the optical field intensity information generated by the fluorescent light wave is converted into an electrical signal, the conversion is carried out according to the set proportional relationship.

10. A terahertz detection method, characterized in that, Detect the terahertz signal to be measured by the terahertz detector based on microcavity-enhanced non-degenerate two-photon absorption according to any one of claims 1 - 9.

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