Long wavelength photodetector

Abstract

To provide an infrared photodetector capable of detecting an image represented by infrared light by converting infrared light into visible light.SOLUTION: An infrared photodetector (1) provided herein comprises a plurality of columnar crystals (2) arranged in an array for converting infrared light (10) into visible light (11), and a light receiver (3) configured to receive visible light (11) converted by the plurality of columnar crystals (2), where the columnar crystals (2) contain a rare earth element.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a long wavelength photodetector that detects long wavelength light by upconverting the long wavelength light to short wavelength light. [Background technology]

[0002] As a method for detecting radiation, a scintillator is known which comprises a first crystalline phase having a plurality of unidirectional columnar crystals and a second crystalline phase covering the side surfaces of the first crystalline phase, the first crystalline phase containing an alkaline earth metal fluoride, and which emits light when excited by radiation (Patent Document 1, Patent Document 2).

[0003] A practical method for detecting infrared light is to use quantum infrared sensors made of InGaAs or InSb. Because of their high sensitivity, quantum infrared sensors are being used in the space field for environmental measurement and meteorological observation from artificial satellites.

[0004] However, quantum infrared light sensors are susceptible to the effects of Brownian motion within materials and simultaneously detect heat emitted by the image sensor itself, so the image sensor must be kept at a temperature sufficiently lower than that of the subject. Therefore, in order to use a quantum infrared light sensor as a detector, the image sensor must be cooled to an extremely low temperature, which results in the problem of a long time required for the quantum infrared light sensor to operate.

[0005] This problem was solved by improving the thin-film structure of the quantum infrared light sensor, enabling it to operate at room temperature, and successfully commercializing a small, thin, resin-packaged quantum infrared light sensor.

[0006] However, the In and Ga used in this quantum infrared sensor are rare metals, so the cost cannot be reduced and they are expensive.

[0007] Another method of detecting infrared light is two-photon absorption, a nonlinear phenomenon that occurs in proportion to the square of the intensity. Two-photon absorption is an excitation process in which two photons are absorbed simultaneously.

[0008] For example, an infrared laser (1550 nm) and Nd 3+ A technology is known in which an infrared laser is upconverted to visible light by two-photon absorption using a conversion material while maintaining the pattern of an infrared QR Code (registered trademark) by using sum frequency mixing (SFM) with a YVO4 laser (1064 nm) (Non-Patent Document 1). A bulk nonlinear optical crystal (KTP crystal) is used as the material for this upconversion. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-111107 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-149883 [Non-patent literature]

[0010] [Non-Patent Document 1] Adrian J. Torregrosa et. al., “Up-Conversion Sensing of 2D Spatially-Modulated Infrared Information-Carrying Beams with Si-Based Cameras”, Sensors 2020, 20, 3610; doi:10.3390 / s20123610 Summary of the Invention [Problem to be solved by the invention]

[0011] However, the above-mentioned Patent Documents 1 and 2 disclose scintillators that detect radiation, and do not suggest any findings relating to the detection of infrared light.

[0012] The nonlinear phenomenon of two-photon absorption uses photons with half the energy of the transition energy, so it can be excited with near-infrared light. However, mid-infrared and far-infrared light have low energy and do not excite photons, preventing practical application.

[0013] The above-mentioned Non-Patent Document 1 uses the nonlinear operation of a nonlinear optical crystal, which is proportional to the square of the intensity, to upconvert infrared light to visible light, and therefore has the problem of low conversion efficiency in converting weak infrared light to visible light.

[0014] Furthermore, in Non-Patent Document 1, the nonlinear optical crystal that up-converts infrared light to visible light is configured in bulk, and therefore there is a problem that images expressed by infrared light cannot be detected.

[0015] An object of one aspect of the present invention is to provide a long-wavelength light detector that can convert long-wavelength light into short-wavelength light and detect an image represented by the long-wavelength light.

[0016] Another aspect of the present invention aims to provide a long-wavelength photodetector that has excellent conversion efficiency for converting long-wavelength light into short-wavelength light. [Means for solving the problem]

[0017] In order to solve the above problems, a long-wavelength photodetector according to one aspect of the present invention comprises a plurality of crystals arranged in an array that convert long-wavelength light into short-wavelength light, and a photodetector that receives the short-wavelength light converted by the plurality of crystals, wherein the crystals contain a rare earth element.

[0018] According to this feature, the rare earth elements contained in the plurality of crystals arranged in an array convert long wavelength light into short wavelength light, and the light receiver receives the short wavelength light converted from the long wavelength light by the rare earth elements of the plurality of crystals arranged in an array. Thus, the long wavelength light is converted into short wavelength light by the rare earth elements of the plurality of crystals arranged in an array. As a result, a long wavelength light detector can be realized that can convert long wavelength light into short wavelength light and detect an image represented by long wavelength light.

[0019] In the long-wavelength photodetector according to one aspect of the present invention, it is preferable that the long-wavelength light includes infrared light and the short-wavelength light includes visible light.

[0020] According to the above configuration, infrared light can be converted into visible light and an image represented by the infrared light can be detected.

[0021] In the long-wavelength photodetector according to one aspect of the present invention, the crystal is preferably a columnar crystal having one directionality.

[0022] According to the above configuration, the configuration of the plurality of crystals arranged in an array that converts long wavelength light into short wavelength light is simple and compact.

[0023] In the long wavelength photodetector according to one aspect of the present invention, the rare earth element preferably includes at least one of Nd, Er, Ho, Dy, Tm, and Sm.

[0024] According to the above configuration, an image expressed by long wavelength light can be detected by a crystal containing at least one of Nd, Er, Ho, Dy, Tm, and Sm.

[0025] In the long-wavelength photodetector according to one aspect of the present invention, it is preferable that the pitch of the plurality of crystals is shorter than the wavelength of the long-wavelength light.

[0026] According to the above configuration, the spatial resolution of the plurality of crystals arranged in an array is improved, and the resolution of image data based on the short wavelength light converted from the long wavelength light by the crystals can be improved.

[0027] In the long wavelength photodetector according to one aspect of the present invention, it is preferable that the long wavelength light is incident on one end face of the columnar crystal, and the short wavelength light is emitted from the other end face of the columnar crystal.

[0028] According to the above configuration, short-wavelength light converted from long-wavelength light at one end face of the columnar crystal can be made to travel through the interior of the columnar crystal while being totally reflected, and can be emitted from the other end face of the columnar crystal toward the photodetector.

[0029] In a long-wavelength photodetector according to one aspect of the present invention, it is preferable that the crystal has an intermediate level between a first level and a second level higher than the first level, the long-wavelength light causes the energy level of the crystal to transition from the first level to the intermediate level or from the intermediate level to the second level, and the crystal emits the short-wavelength light by transitioning from the second level to the first level.

[0030] According to the above configuration, it is possible to realize a linear operation in which the energy level of the rare earth element is excited stepwise from the first level to the second level via the intermediate level.

[0031] Preferably, the long-wavelength photodetector according to one aspect of the present invention further includes an illuminator that irradiates the crystal with pump light to improve the efficiency of conversion from the long-wavelength light to the short-wavelength light by the crystal.

[0032] According to the above configuration, the energy levels of the rare earth element can be excited stepwise by the pump light.

[0033] Preferably, the long-wavelength photodetector according to one aspect of the present invention further includes an image data generator that generates image data based on the visible light received by the photoreceiver.

[0034] According to the above configuration, infrared light can be converted into visible light to obtain image data representing an infrared light image.

[0035] In order to solve the above problem, another long-wavelength photodetector according to one aspect of the present invention comprises a crystal that converts long-wavelength light into short-wavelength light, an illuminator that irradiates the crystal with pump light to improve the conversion efficiency of the long-wavelength light to the short-wavelength light by the crystal, and a photodetector that receives the short-wavelength light converted by the crystal, wherein the crystal contains a rare earth element.

[0036] According to this feature, the energy levels of the rare earth element contained in the crystal are excited stepwise by pump light and long-wavelength light, resulting in a linear operation in which the rare earth element emits short-wavelength light. Therefore, long-wavelength light can be converted to short-wavelength light without using two-photon absorption, which is a nonlinear phenomenon. As a result, a long-wavelength photodetector with excellent conversion efficiency for converting long-wavelength light to short-wavelength light can be realized.

[0037] In a long-wavelength photodetector according to one aspect of the present invention, it is preferable that the pump light excites the energy level of the crystal from a first level to an intermediate level, the long-wavelength light excites the energy level of the crystal, which has transitioned to the intermediate level by the pump light, to a second level, and the crystal transitions from the second level to the first level by emitting the short-wavelength light.

[0038] According to the above configuration, a linear operation of stepwise exciting the energy level of the rare earth element from the first level to the second level via the intermediate level can be realized by the pump light and the long wavelength light.

[0039] In a long-wavelength photodetector according to one aspect of the present invention, it is preferable that the long-wavelength light excites the energy level of the crystal from a first level to an intermediate level, the pump light excites the energy level of the crystal, which has transitioned to the intermediate level by the long-wavelength light, to a second level, and the crystal transitions from the second level to the first level by emitting the short-wavelength light.

[0040] According to the above configuration, a linear operation in which the energy level of the rare earth element is excited stepwise from the first level to the second level via the intermediate level can be realized by the long wavelength light and the pump light.

[0041] In the long wavelength photodetector according to one aspect of the present invention, it is preferable that the pump light is laser light.

[0042] According to the above configuration, the energy levels of the rare earth elements contained in the crystal can be excited stepwise by the laser light and the long wavelength light.

[0043] In the long-wavelength photodetector according to one aspect of the present invention, it is preferable that the pump light is irradiated onto the incident side of the crystal for the long-wavelength light.

[0044] According to the above configuration, the energy levels of the rare earth elements can be excited in stages on the side of the crystal where long wavelength light is incident, thereby converting the long wavelength light into short wavelength light.

[0045] In a long-wavelength photodetector according to one aspect of the present invention, it is preferable that the crystal is a columnar crystal having one directionality, and the pump light is irradiated onto an end face of the columnar crystal on the incident side of the long-wavelength light.

[0046] According to the above configuration, the energy levels of the rare earth elements can be excited in stages at the end face of the columnar crystal on the side where long wavelength light is incident, thereby converting long wavelength light into short wavelength light.

[0047] In the long-wavelength photodetector according to one aspect of the present invention, it is preferable that the illuminator irradiates the crystal with the pump light from a plurality of directions.

[0048] According to the above configuration, the energy levels of the rare earth element can be excited stepwise at multiple locations in the crystal by the pump light and the long wavelength light.

[0049] In the long-wavelength photodetector according to one aspect of the present invention, it is preferable that the crystals are a plurality of crystals arranged in an array, and the crystals are columnar crystals having one directionality.

[0050] According to the above configuration, long wavelength light is converted into short wavelength light by the rare earth elements of the plurality of crystals arranged in an array, and as a result, it is possible to convert the long wavelength light into short wavelength light and detect an image represented by the long wavelength light. [Effects of the Invention]

[0051] According to one aspect of the present invention, it is possible to provide a long-wavelength light detector that can convert long-wavelength light into short-wavelength light and detect an image represented by the long-wavelength light.

[0052] According to another aspect of the present invention, it is possible to provide a long wavelength photodetector that has excellent conversion efficiency for converting long wavelength light into short wavelength light. [Brief explanation of the drawings]

[0053] [Figure 1] 1A and 1B are diagrams illustrating the principle of an infrared photodetector according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing a configuration of the infrared light detector. [Figure 3] 3 is a diagram showing transitions of energy levels of columnar crystals provided in the infrared photodetector. FIG. [Figure 4] 1 is an image showing the appearance of a fiber array provided in the infrared photodetector. [Figure 5] 10 is a magnified image of the end and side surfaces of the fiber array. [Figure 6] 6 is an enlarged image of part A shown in FIG. 5. [Figure 7] FIG. 2 is a diagram showing transitions of energy levels when the columnar crystal contains Nd. [Figure 8] FIG. 2 is a diagram showing transitions of energy levels when the columnar crystal contains Nd. [Figure 9] FIG. 2 is a diagram showing transitions of energy levels when the columnar crystals contain Er. [Figure 10] FIG. 2 is a diagram showing transitions of energy levels when the columnar crystal contains Ho. DETAILED DESCRIPTION OF THE INVENTION

[0054] Hereinafter, one embodiment of the present invention will be described in detail.

[0055] (overview) This embodiment is a system and method for irradiating a micrometer-scale fiber array crystal doped with rare earth element ions with laser light, converting infrared light into visible light through linear upconversion emission, and detecting the infrared light. Using a fiber array crystal reduces transmission loss of the converted visible light and improves detection sensitivity. Furthermore, by appropriately selecting the composition of rare earth elements used in the material, it is possible to efficiently induce the upconversion phenomenon and improve detection sensitivity. This embodiment also has the economic effect of reducing the cost of expensive, high-end infrared cameras and infrared detectors.

[0056] (Configuration of infrared photodetector 1) Fig. 1 is a diagram showing the principle of an infrared photodetector 1 (long wavelength photodetector) according to an embodiment. Fig. 2 is a perspective view showing the configuration of the infrared photodetector 1. Fig. 3 is a diagram showing the transition of energy levels of a columnar crystal 2 (crystal) provided in the infrared photodetector 1.

[0057] The infrared light detector 1 includes a fiber array 6 including a plurality of unidirectional columnar crystals 2 (crystals) arranged in an array that convert infrared light 10 (long wavelength light) into visible light 11 (short wavelength light), and a photodetector 3 that receives the visible light 11 converted by the plurality of columnar crystals 2. The columnar crystals 2 contain a rare earth element. The infrared light detector 1 is not limited to converting infrared light, and may also convert long wavelength light into short wavelength light with a wavelength shorter than that of the long wavelength light. The photodetector 3 has a plurality of pixels.

[0058] The rare earth element of the columnar crystals 2 includes at least one of Nd (neodymium), Er (erbium), Ho (holmium), Dy (dysprosium), Tm (thulium), and Sm (samarium).

[0059] The infrared light detector 1 further includes an illuminator 4 that irradiates the columnar crystals 2 with laser light 12 (pump light) to improve the efficiency of conversion from infrared light 10 to visible light 11 by the columnar crystals 2. The light receiver 3 may include a cut filter that cuts the infrared light 10 and the laser light 12 so as not to receive the infrared light 10 and the laser light 12. Alternatively, the infrared light 10 may be converted into visible light 11 by multiphoton absorption by a plurality of columnar crystals 2 arranged in an array, without providing the illuminator 4.

[0060] Infrared light wavelength λ MIR The wavelength λ of the visible light 11 converted from the infrared light 10 by the columnar crystal 2 is, for example, 1550 nm or 2700 nm. σ The wavelength λ of the laser light 12 generated from a titanium-sapphire laser or an LD (laser diode) is, for example, 500-700 nm. pump is, for example, 690-990 nm.

[0061] The laser light 12 excites the energy level of the columnar crystals 2 from the first level EL1 to the intermediate level ELM. Then, the infrared light 10 excites the energy level of the columnar crystals 2, which has transitioned to the intermediate level ELM by the laser light 12, to the second level EL2. The columnar crystals 2 emit visible light 11, causing the energy level to transition from the second level EL2 to the first level EL1.

[0062] Alternatively, the infrared light 10 may excite the energy level of the columnar crystals 2 from the first level EL1 to the intermediate level ELM, the laser light 12 may excite the energy level of the columnar crystals 2, which has transitioned to the intermediate level ELM by the infrared light 10, to the second level EL2, and the columnar crystals 2 may emit visible light 11, thereby transitioning the energy level of the columnar crystals 2 from the second level EL2 to the first level EL1.

[0063] The laser beam 12 is preferably irradiated onto the incident side of the columnar crystal 2 on which the infrared light 10 is incident, and more preferably onto the end face 8 of the columnar crystal 2. The laser beam 12 may be irradiated from the lens 13 side of the columnar crystal 2 or from the lens 14 side. The laser beam 12 may also be irradiated toward the side face 15.

[0064] The laser beam 12 may be irradiated onto the columnar crystals 2 from multiple directions. For example, if the irradiator 4 that irradiates the laser beam 12 is configured to surround or encase the fiber array 6, the laser beam 12 can be uniformly irradiated onto the columnar crystals 2 from multiple directions.

[0065] Instead of the laser light 12, light or light emitted by an LED (Light Emitting Diode) may be used.

[0066] The pitch of the plurality of columnar crystals 2 is preferably shorter than the wavelength of the infrared light 10. However, whether the pitch is longer or shorter than the wavelength of the infrared light 10, image detection of the infrared light 10 is possible.

[0067] Infrared light 10 passes through a lens 13 and enters one end face 8 of the columnar crystal 2. Visible light 11 converted from the infrared light 10 by the columnar crystal 2 is emitted from the other end face 9 of the columnar crystal 2 through a lens 14 toward the photodetector 3.

[0068] The infrared light detector 1 further includes an image data generator 5 that generates image data based on the visible light 11 received by the light receiver 3.

[0069] The infrared photodetector 1 according to this embodiment is based on a two-step linear phenomenon using the transition levels of rare earth elements, rather than on a nonlinear phenomenon such as SFG (sum frequency mixing) or two-photon absorption as in the aforementioned Non-Patent Document 1. Therefore, the infrared photodetector 1 can convert even weak infrared light that is difficult to observe into visible light.

[0070] The rare earth elements doped into the columnar crystals 2 of the fiber array 6 include Nd, Er, Ho, Dy, Tm, and Sm, and each rare earth element has a different wavelength of the laser light 12, the wavelength of the infrared light 10 to be observed, and the wavelength of the visible light 11 to be converted.

[0071] Fig. 4 is an image showing the appearance of the fiber array 6 provided in the infrared photodetector 1. Fig. 5 is an enlarged image of the surface and side of the fiber array 6. Fig. 6 is an enlarged image of part A shown in Fig. 5.

[0072] The fiber array 6 has dimensions on the order of several millimeters, as shown in Fig. 4. The fiber array 6 has a plurality of cylindrical columnar crystals 2, each about 1 µm in diameter and about 1 mm in length, arranged in parallel to one another in an array.

[0073] (Nd 3+ (transition of energy levels of 7 and 8 are diagrams showing transitions of energy levels when the columnar crystals 2 contain Nd.

[0074] As shown in the transition diagram on the left side of Figure 7, first, laser light 12 with a wavelength of 740 nm changes the energy level of Nd. 4 I 9 / 2 from 4 F 5 / 2 Then, infrared light with a wavelength of 1.3 μm excites the energy level of Nd. 4 F 5 / 2 from 4 G 5 / 2 to be excited.

[0075] Or, laser light 12 with a wavelength of 750 nm changes the energy level of Nd. 4 I 9 / 2 from 4 F 7 / 2 Then, infrared light with a wavelength of 1.9 μm excites the energy level of Nd. 4 F 7 / 2 from 4 G 5 / 2 to be excited.

[0076] Or, the laser light 12 with a wavelength of 690 nm changes the energy level of Nd. 4 I 9 / 2 from 4 F 9 / 2 Then, infrared light with a wavelength of 2.5 μm excites the energy level of Nd. 4 F 9 / 2 from4 G 5 / 2 to be excited.

[0077] Next, Nd emits visible light11 with wavelengths of 568-578 nm, and the energy levels 4 G 5 / 2 from 4 I 9 / 2 Transition to.

[0078] In this way, the laser light 12 excites the energy level of the columnar crystal 2 from the first level to the intermediate level, and the infrared light 10 excites the energy level of the columnar crystal 2, which has transitioned to the intermediate level by the laser light 12, to the second level, and the columnar crystal 2 emits visible light 11, thereby transitioning its energy level from the second level to the first level.

[0079] As shown in the transition diagram on the right side of Figure 7, infrared light 10 with a wavelength of 2.5 μm changes the energy level of the columnar crystal 2. 4 I 9 / 2 from 4 I 13 / 2 Then, the laser light 12 with a wavelength of 1.06 μm excites the columnar crystal 2 to 4 I 13 / 2 from 4 F 7 / 2 The columnar crystal 2 emits visible light with a wavelength of 750 nm, and the energy level 4 F 7 / 2 from 4 I 9 / 2 Transition to.

[0080] In addition, infrared light 10 with a wavelength of 5.1 μm changes the energy level of the columnar crystal 2. 4 I 9 / 2 from 4 I 11 / 2 Then, the laser light 12 with a wavelength of 1.06 μm excites the columnar crystal 2 to 4 I 11 / 2 from 4 F 3 / 2 The columnar crystal 2 emits visible light with a wavelength of 880 nm, and the energy level 4 F 3 / 2 from 4 I9 / 2 Transition to.

[0081] In this way, the infrared light 10 excites the energy level of the columnar crystal 2 from the first level to the intermediate level, and the laser light 12 excites the energy level of the columnar crystal 2, which has transitioned to the intermediate level by the infrared light 10, to the second level, and the columnar crystal 2 emits visible light 11, thereby transitioning its energy level from the second level to the first level.

[0082] As shown in FIG. 8, the laser light 12 with a wavelength of 794-862 nm changes the energy level of the columnar crystal 2. 4 I 9 / 2 from 4 F 3 / 2 Then, infrared light 10 with a wavelength of 1550 nm excites the energy level of the columnar crystal 2. 4 F 3 / 2 from 4 G 5 / 2 Next, the columnar crystal 2 emits visible light with a wavelength of 568-578 nm, and the energy level 4 G 5 / 2 from 4 I 9 / 2 Transition to.

[0083] In addition, the laser light 12 with a wavelength of 741-793 nm changes the energy level of the columnar crystal 2. 4 I 9 / 2 from 2 H 9 / 2 Then, infrared light 10 with a wavelength of 1550 nm excites the energy level of the columnar crystal 2. 2 H 9 / 2 from 4 G 5 / 2 Next, the columnar crystal 2 emits visible light with a wavelength of 568-578 nm, and the energy level 4 G 5 / 2 from 4 I 9 / 2 Transition to.

[0084] The Nd in the columnar crystals 2 absorbs the laser light 12 and goes to the ground state ( 4 I 9 / 2 ) to intermediate level ( 2 H 9 / 2) (GSA (ground state absorption)). And Nd is excited to the intermediate level ( 2 H 9 / 2 ) to other intermediate levels ( 4 F 3 / 2 ) without emitting light (NR). Next, Nd undergoes a slow and gentle transition to another intermediate level ( 4 F 3 / 2 ) to the excited state ( 4 G 7 / 2 ) is excited (RET (Resonant Energy Transfer)).

[0085] In both processes, visible light of the same wavelength is emitted when the energy levels of Nd are: 4 F 5 / 2 , 2 H 9 / 2 from 4 F 3 / 2 This is because the transition to

[0086] The energy level of Nd excited by the laser light 12 and the energy (cm) of the infrared light 10 to be detected by Nd are -1 The relationship between the wavelength (nm) of the infrared light 10 and the wavelength (nm) of the infrared light 10 is shown in Tables 1, 2, and 3 below.

[0087] [Table 1]

[0088] [Table 2]

[0089] [Table 3]

[0090] (Er 3+ (transition of energy levels of FIG. 9 is a diagram showing the transition of energy levels when the columnar crystals 2 contain Er.

[0091] As shown in FIG. 9, the laser light 12 with a wavelength of 806-970 nm changes the energy level of Er in the columnar crystal 2. 4 I 15 / 2 from 4 I 11 / 2 Then, infrared light 10 with a wavelength of 1550 nm excites the energy level of Er. 4 I 11 / 2 from 4 F 9 / 2 Next, Er emits visible light with a wavelength of 644-650 nm, and the energy level 4 F 9 / 2 from 4 I 15 / 2 Transition to.

[0092] In addition, laser light 12 with a wavelength of 690-805 nm changes the energy level of Er. 4 I 15 / 2 from 4 I 9 / 2 Then, infrared light 10 with a wavelength of 1550 nm excites the energy level of Er. 4 I 9 / 2 from 4 S 3 / 2 Next, Er emits visible light with a wavelength of 538-539 nm, and the energy level 4 S 3 / 2 from 4 I 15 / 2 Transition to.

[0093] In this way, the laser light 12 excites the energy level of Er from the first level to the intermediate level, and the infrared light 10 excites the energy level of Er, which has transitioned to the intermediate level by the laser light 12, to the second level, and Er emits visible light 11, thereby transitioning its energy level from the second level to the first level.

[0094] The energy level of Er excited by the laser light 12 and the energy (cm) of the infrared light 10 to be detected by Er are -1 The relationship between the wavelength (nm) of the infrared light 10 and the wavelength (nm) of the infrared light 10 is shown below (Table 4).

[0095] [Table 4]

[0096] (Ho 3+ (transition of energy levels of FIG. 10 is a diagram showing the transition of energy levels when the columnar crystals 2 contain Ho.

[0097] As shown in FIG. 10, the laser light 12 with a wavelength of 757-899 nm changes the energy level of Ho in the columnar crystal 2. 5 From I8 5 Then, infrared light with a wavelength of 1550 nm excites the energy level of Ho to 5 From I5 5 Then, Ho emits visible light with a wavelength of 649 nm, and the energy level 5 From F5 5 Transition to I8.

[0098] In addition, laser light 12 with a wavelength of 690-756 nm changes the energy level of Ho. 5 From I8 5 Then, infrared light with a wavelength of 1550 nm excites the energy level of Ho to 5 From I4 5 The Ho then undergoes excitation to the F4 level, emitting visible light11 at wavelengths of 540-544 nm. 5 From F4 5 Transition to I8.

[0099] In this way, the laser light 12 excites the energy level of Ho from the first level to the intermediate level, and the infrared light 10 excites the energy level of Ho, which has transitioned to the intermediate level by the laser light 12, to the second level, and the energy level of Ho transitions from the second level to the first level by emitting visible light 11.

[0100] The present inventors have 3+ For the first time, we have focused on the mechanism by which a single doped ZnO is excited at wavelengths less than 980 nm.

[0101] The energy level of Ho excited by the laser light 12 and the energy (cm) of the infrared light 10 to be detected by Ho are -1 The relationship between the wavelength (nm) of the infrared light 10 and the wavelength (nm) of the infrared light 10 is shown below (Table 5).

[0102] [Table 5]

[0103] (Energy levels of Dy, Tm, and Sm) The columnar crystals 2 may contain Dy, Tm, or Sm.

[0104] The energy level of Dy excited by the laser light 12 and the energy (cm) of the infrared light 10 to be detected by Dy are -1 The relationship between the wavelength (nm) of the infrared light 10 and the wavelength (nm) of the infrared light 10 is shown below (Table 6).

[0105] [Table 6]

[0106] The energy level of Tm excited by the laser light 12 and the energy (cm) of the infrared light 10 to be detected by Tm -1 The relationship between the wavelength (nm) of the infrared light 10 and the wavelength (nm) of the infrared light 10 is shown below (Table 7).

[0107] [Table 7]

[0108] The energy level of Sm excited by the laser light 12 and the energy (cm) of the infrared light 10 to be detected by Sm are -1 The relationship between the wavelength (nm) of the infrared light 10 and the wavelength (nm) of the infrared light 10 is shown below (Table 8).

[0109] [Table 8]

[0110] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0111] 1. Infrared photodetector (long wavelength photodetector) 2 Columnar crystals (crystals) 3 Receiver 4 Irradiator 5 Image Data Generator 6 Fiber Array 8 End face 9 End face 10 Infrared light (long wavelength light) 11 Visible light (short wavelength light) 12 Laser light (pump light) EL1 1st level EL2 Second Level ELM Intermediate Level

Claims

1. a plurality of crystals arranged in an array that convert long wavelength light into short wavelength light; an illuminator that irradiates the crystal with pump light to improve the conversion efficiency of the crystal from the long wavelength light to the short wavelength light; a light receiver that receives the short wavelength light converted by the plurality of crystals, the crystal contains a rare earth element; the crystal has an intermediate level between a first level and a second level higher than the first level, the long wavelength light causes an energy level of the crystal to transition from the first level to the intermediate level or from the intermediate level to the second level; the crystal emits the short wavelength light by a transition from the second level to the first level; the crystals are unidirectional columnar crystals, the long wavelength light is incident on one end face of the columnar crystal, the short wavelength light is emitted from the other end face of the columnar crystal, The long-wavelength photodetector is characterized in that the illuminator is arranged to surround a fiber array having a plurality of the columnar crystals in order to uniformly irradiate the columnar crystals with the pump light from multiple directions.

2. the pump light excites the energy level of the crystal from a first level to an intermediate level; the long wavelength light excites the energy level of the crystal, which has transitioned to the intermediate level by the pump light, to a second level; 2. The long-wavelength photodetector according to claim 1, wherein the crystal emits the short-wavelength light, causing the energy level to transition from the second level to the first level.

3. the long wavelength light excites the energy level of the crystal from a first level to an intermediate level, the pump light excites the energy level of the crystal, which has transitioned to the intermediate level by the long wavelength light, to a second level; 2. The long-wavelength photodetector according to claim 1, wherein the crystal emits the short-wavelength light, causing the energy level to transition from the second level to the first level.

4. 2. The long wavelength photodetector of claim 1, wherein the pump light is laser light.

5. 2. The long wavelength photodetector according to claim 1, wherein the pump light is irradiated onto the crystal on the side where the long wavelength light is incident.

6. 2. The long wavelength photodetector according to claim 1, wherein the pump light is irradiated onto an end face of the columnar crystal on which the long wavelength light is incident.

7. the long wavelength light includes infrared light, 2. The long wavelength photodetector of claim 1, wherein the short wavelength light comprises visible light.

8. 2. The long-wavelength photodetector of claim 1, wherein the rare earth element comprises at least one of Nd, Er, Ho, Dy, Tm, and Sm.

9. 2. The long-wavelength photodetector according to claim 1, wherein the pitch of the plurality of crystals is shorter than the wavelength of the long-wavelength light.

10. The long wavelength light detector of claim 1 , further comprising an image data generator that generates image data based on the visible light received by the light receiver.

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