JP5606720B2 - Photodetector - Google Patents

Description

 The present invention relates to a light detection device. The light detection apparatus of the present invention can be applied to, for example, an endoscope or a microscope that performs image observation of a living body or the like.

 In general, in various systems using light such as image observation, sensors, security, and laser radar, a technique for detecting desired light is a fundamental and important factor that greatly affects the performance. In particular, the need for high-speed and high-sensitivity detection technology is high.

 For example, when viewing living body observation using light in image observation, the state and shape of the living body change from moment to moment, so that accurate detection requires high-speed light detection. Moreover, since a living body is easily damaged by light irradiation, there is an upper limit to the amount of illumination light and excitation light that can be irradiated to a biological sample. Therefore, the optical signal obtained from a living body is usually weak. In addition, when detecting light energy such as self-emission emitted from a detection target such as a living body without irradiating light, extremely weak light must be detected. In addition to biological samples, when the distance from the detection means to the detection target is long, when there is a substance that interferes with detection due to scattering, absorption, etc., the detection signal decreases when the detection target is very small or very small. It is reduced by doing and is weak. For these reasons, in various detection systems such as living body observation using light, a high-speed and high-sensitivity light detection technique is strongly demanded.

 Typical photodetection elements currently used include PMT (Photo multiplier tube), APD (Avalanche photo diode), and PD (Photo diode). Since PMT and APD perform electron multiplication in the detection element, highly sensitive light detection can be realized. On the other hand, although the PD can realize a very high response speed, it does not have an electron multiplication function in the detection element, and therefore usually a signal is amplified using an electric amplifier. In other words, the PMT, APD, and PD all perform signal amplification at the electrical stage to improve sensitivity.

 Typical two-dimensional photodetectors include CCD (Charged Coupled Device), CMOS (Complementary Metal Oxide Semiconductor), EM-CCD (Electron multiplying-CCD), EB-CCD (Electron Bombardment-CCD), I- There is a CCD (Intensified-CCD). When weak light is detected using a CCD or CMOS, it is necessary to arrange an electric amplifier at the subsequent stage in the same manner as the PD in order to improve sensitivity. EM-CCD and EB-CCD have an electron multiplication function in the detection element like APD, and realize high sensitivity. The I-CCD has a configuration in which an optical amplifier (Image Intensifier, hereinafter referred to as II) is disposed in front of the CCD. I. I. Converts the incident light signal into an electrical signal once. I. After the electron multiplication is performed in an MCP (Micro channel plate) built in the light, the multiplied electron signal is again converted into light by colliding the multiplied electron with the fluorescent plate. That is, the I-CCD also realizes highly sensitive light detection by performing signal amplification at the electrical stage.

 However, there is a trade-off relationship between detection sensitivity and detection speed in the conventional photodetection technology using signal amplification in the electrical stage described above. That is, when detection is performed using these detection techniques, it is very difficult to achieve both high speed and high sensitivity. Therefore, at present, light detection must be performed at the expense of either the detection speed or the detection sensitivity.

 On the other hand, development of an optical amplifier using an optical fiber as an optical transmission means has been actively promoted mainly in the field of long-distance optical communication. Compared with an electric amplifier, an optical amplifier can operate at a very high speed and in a wide band, and has a characteristic that optical amplification with very low noise and high gain is possible depending on the configuration. Therefore, it is expected that such an optical amplifier can be detected at high speed and with high sensitivity by arranging the optical amplifier in front of the high-speed photoelectric conversion element (see, for example, Patent Document 1).

   The gist of this patent document 1 is that light is emitted from one of two optical fibers arranged at a predetermined angle, and light is detected from the other fiber, so that the resolution in the depth direction of the object to be observed (axial resolution). Has been proposed to improve.

 On the other hand, ASE (Amplified spontaneous emission) is generated from the optical amplifier, and this becomes a dominant noise cause at the time of light detection when the optical amplifier is used. Therefore, in order to realize high-speed and high-sensitivity light detection using an optical amplifier, it is essential that the optical amplifier has low noise. In the optical amplifier, the higher the input signal light intensity, the higher the signal-to-noise ratio (hereinafter referred to as SNR) after optical amplification, and the light detection sensitivity.

 A low noise optical amplifier used in the long-distance optical communication field is composed of a single mode optical fiber. The reason why this single mode optical fiber configuration is used is that the matching with the transmission line is excellent, and the noise of the optical amplifier increases in proportion to the propagation mode of the gain fiber constituting the optical amplifier. There is. For this reason, in the long-distance optical communication field, the use of a single mode optical fiber as the gain fiber greatly contributes to the low noise performance of the optical amplifier.

 However, even a low-noise optical amplifier for long-distance optical communication composed of such a single mode optical fiber has the following problems to be used in the preceding stage of the photoelectric conversion element. That is, signal light detected in fields such as living body observation, sensors, security, and laser radar is mostly scattered light or light with a disturbed wavefront. Such light has a very low coupling efficiency to a single mode fiber, and the optical signal that can be taken into the optical amplifier is a weak signal in a limited portion of the whole. For this reason, since the SNR deteriorates, high light receiving sensitivity cannot be obtained.

 On the other hand, in order to collect scattered light and light with a disturbed wavefront with high efficiency, it is conceivable to arrange a multimode optical fiber amplifier having a large core diameter immediately before the photoelectric conversion element. However, as the number of spatial modes increases due to the increase in the core diameter, optical noise generated in the optical amplifier increases. In this case as well, the SNR deteriorates, so that high light receiving sensitivity cannot be obtained.

 In the above description, the case where light is detected has been described as an example. However, when detecting electromagnetic waves other than light such as millimeter waves and microwaves, it is considered that the same problem is encountered.

US Pat. No. 6,423,956

Therefore, the object of the present invention made by paying attention to these points is that detection light can be detected at high speed and with high sensitivity even if the light to be detected is light scattered by a living body or the like, or light whose wavefront is disturbed. An object of the present invention is to provide a light detection method, a light detection device, a living body observation method, a microscope, and an endoscope. Another object of the present invention is to provide a low-noise detection signal with high efficiency even in a scene where it is desired to minimize damage due to an increase in electromagnetic energy such as the amount of light, or in a scene where the detection signal reaching the target is weak. An object of the present invention is to provide a light detection method and a light detection device that can be collected, a living body observation method, a microscope, and an endoscope.

The invention of the photodetection device according to claim 1 that achieves the above object is as follows:
Mode adjusting means for adjusting the mode state of the multi-mode incident light;
Control means for controlling mode adjustment conditions of the mode adjustment means in accordance with the spatial distribution state of the incident light;
Amplifying means for amplifying the light having the adjusted mode state output from the mode adjusting means;
Conversion means for converting the amplified light output from the amplification means into an electrical signal, and the mode adjustment means adjusts the mode distribution of the energy of incident light, and the amplification spatial mode by the amplification means The present invention is characterized in that it is configured to adjust to a mode that substantially matches.

The invention according to claim 2 is the light detection device according to claim 1,
The control means is controlled to increase the output signal level from the conversion means.

The invention according to claim 3 is the light detection device according to claim 1,
The mode adjusting means is a fiber Bragg grating or a tapered fiber.

According to a fourth aspect of the present invention, in the light detection device according to the second aspect, the control means has a function of applying mechanical extension, bending, or stress to the mode adjustment means. .

The invention according to claim 5 is the light detection apparatus according to claim 2, wherein the control means has a function of giving a temperature change to the mode adjustment means.

The invention according to claim 6 is the optical detection apparatus according to claim 1, characterized in that the mode adjusting means is a tapered fiber constituted by a graded index fiber.

According to the first aspect of the present invention, the mode adjusting means for adjusting the mode distribution of the energy of the incident light so as to adjust the mode substantially coincides with the amplification spatial mode of the amplifying means is provided before the amplifying means and the converting means. Since the mode adjustment condition of the mode adjustment means is controlled according to the spatial distribution state of the incident light, even if the detected light is scattered light or the wave front is disturbed Even if the mode state of the incident light changes, the light to be detected can be collected with high efficiency, and light detection with high speed and high sensitivity becomes possible.

According to the invention described in claim 2, in addition to the effect of the invention described in claim 1, there is an effect that the configuration of the light detection device can be simplified most. In the present invention, since the output level of the conversion means is monitored and the mode adjustment condition of the mode adjustment means is changed so that the output level of the conversion means becomes high, the spatial distribution state of incident light can be known indirectly and simply. it can. That is, there is no need for a special part to be added to know the spatial distribution state of incident light. Therefore, the number of parts constituting the light detection device can be minimized.

 According to the invention described in claim 3, in addition to the effect of the invention described in claim 1, by using an optical fiber element such as a fiber Bragg grating or a tapered fiber for the mode adjusting means, external vibration such as mechanical vibration is obtained. There is an effect that it is possible to realize a photodetector that is resistant to environmental fluctuations.

 According to the invention described in claim 4, in addition to the effect of the invention described in claim 3, a control means having a function of giving a mechanical extension or bending function to a fiber Bragg grating or tapered fiber is used. Thus, the mode state can be controlled at high speed. This makes it possible to detect light with high speed and high sensitivity even when the mode state of incident light fluctuates at high speed.

According to the invention described in claim 5, in addition to the effect of the invention described in claim 3, the controller has a function of giving a temperature change to an optical fiber element such as a fiber Bragg grating or a tapered fiber. By using it, the mode can be adjusted without impairing the mechanical stability of the optical fiber element itself. This effect is particularly useful for applications that require long-term stability.

 According to the invention described in claim 6, in addition to the effect of the invention described in claim 1, a graded index fiber whose refractive index gradually decreases from the core central part to the peripheral part is used as the mode adjusting means. Thus, mode adjustment with low loss becomes possible.

1 is a block diagram showing a schematic configuration of a photodetection device according to a first embodiment of the present invention. It is a figure explaining the adjustment of the mode in a mode adjustment means. It is a figure which shows schematic structure of the rigid endoscope type blood vessel imaging apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows the schematic shape of the core part longitudinal cross-section of a tapered fiber. It is a schematic block diagram of an Er addition fluoride fiber type optical amplifier. It is a block diagram which shows schematic structure of the photon detection apparatus which concerns on 3rd Embodiment of this invention. It is a figure which shows schematic structure of the rigid endoscope type blood vessel imaging apparatus which concerns on 4th Embodiment of this invention. It is a block diagram which shows schematic structure of the photon detection apparatus which concerns on 5th Embodiment of this invention. It is a figure which shows schematic structure of the highly sensitive endoscope which concerns on 6th Embodiment of this invention. It is a block diagram which shows schematic structure of the photon detection apparatus which concerns on 7th Embodiment of this invention. It is a figure which shows schematic structure of the rigid endoscope type blood-vessel imaging device which concerns on 8th Embodiment of this invention. It is a figure which shows schematic structure of the laser scanning type | mold multiphoton fluorescence microscope using the photon detection apparatus based on 9th Embodiment of this invention. It is a block diagram which shows schematic structure of the photon detection apparatus which concerns on 10th Embodiment of this invention. It is a figure which shows schematic structure of the rigid endoscope type blood vessel imaging apparatus concerning 11th Embodiment of this invention. It is a block diagram which shows schematic structure of the photon detection apparatus which concerns on 12th Embodiment of this invention. It is a figure which shows schematic structure of the rigid endoscope type blood-vessel imaging device which concerns on 13th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of the photodetection device according to the first embodiment of the present invention. This photodetection device is for amplifying detected light emitted from a sample to be observed and delivering it as an electrical signal to a signal processing system.

The light detection apparatus according to the present embodiment includes a mode adjustment unit 10 that adjusts the mode state of incident multimode light to be detected, and an amplification unit 20 that amplifies the light whose mode state is adjusted by the mode adjustment unit 10. And a converting means 30 for converting the light amplified by the amplifying means 20 into an electric signal and outputting it to a signal processing system. The amplifying unit 20 has an amplification characteristic with an excellent SNR for a specific amplification spatial mode, and the mode adjusting unit 10 adjusts the mode distribution of the energy of the multimode incident electromagnetic wave by the amplifying unit 20. The mode is adjusted to substantially match the amplification space mode.

 FIG. 2 is a diagram for explaining mode adjustment in the mode adjustment means 10. The mode adjusting unit 10 allows the incidence of multimode light on the incident side, and on the output side, the mode adjusting unit 10 substantially matches the amplification spatial mode of the subsequent amplification unit 20, that is, has a highly consistent energy mode distribution. It is comprised so that adjustment may be performed. FIG. 2A shows an example of the mode distribution of the energy of incident light on the incident side of the mode adjusting means. In this example, energy is distributed in a basic mode indicated by mode number 1 and higher-order modes indicated by mode numbers 2 to 7. FIGS. 2B and 2C are diagrams showing the mode distribution of light energy on the emission side of the mode adjusting means 10 in different cases. In FIG. 2B, only the two modes indicated by mode numbers 1 and 2 are allowed, and the energy of each mode on the incident side of the mode adjusting means 10 is converted into these two modes with low loss. Is done. Further, FIG. 2C shows that the mode distribution of energy on the exit side of the mode adjusting means is allowed to have the same mode numbers 1 to 7 as those on the incident side, but the mode distribution of energy changes, An example in which the distribution of the two modes of mode numbers 1 and 2 is particularly high is shown. That is, in FIG. 2C, the number of spatial modes is reduced in a pseudo manner. The mode adjustment means 10 may be either one that reduces the number of modes itself as shown in FIG. 2B or one that changes the energy distribution as shown in FIG.

  With the schematic configuration of FIG. 1, the detected light that is a scattered wave or a wave whose wavefront is disturbed enters the mode adjusting unit 10 according to a mode allowed on the incident side of the mode adjusting unit 10. At this time, the coupling efficiency between the detected light and the mode adjusting means 10 increases as more higher-order modes are allowed. Thereafter, the detected light undergoes mode adjustment by the mode adjustment unit 10 and is emitted to the amplification unit 20. At this time, the mode distribution of the energy of the light to be detected emitted from the mode adjusting unit 10 and the amplification spatial mode by the amplification unit 20 substantially coincide with each other, so that energy loss due to mode mismatch is reduced. Further, the detected light is amplified by the amplifying unit 20 and emitted to the converting unit 30, and is converted into an electric signal by the converting unit 30. The electrical signal output from the conversion means 30 is converted into desired data by a signal processing system following the subsequent stage.

  As described above, according to the present embodiment, the mode adjustment unit 10 that adjusts the mode distribution of energy to a mode that substantially matches the amplification spatial mode of the amplification unit 20 by adjusting the mode distribution of energy. Because it is arranged in front of the amplifying means and the converting means, even if the detected light is scattered light or the light whose wave front is distorted, the detected light can be collected with high efficiency, and it is fast and sensitive. Light detection is possible.

In addition, when the spatial distribution state of the detected light input to the mode adjusting unit 10 changes according to time, the mode adjusting unit 10 can adjust the mode suitable for the spatial distribution state of the detected light. Control means for changing the characteristics is used. By checking the voltage level output from the conversion unit 30, it is possible to determine whether the spatial distribution state of the detected light input to the mode adjustment unit 10 matches the characteristics of the mode adjustment unit 10. Accordingly, the control means is used so that the voltage level output from the conversion means 30 is increased, and the characteristics of the mode adjustment means 10 are changed, so that the spatial distribution state and mode of the detected light input to the mode adjustment means 10 are changed. The characteristics of the adjusting means 10 can be adapted. By doing so, even when the spatial distribution state of the light to be detected changes with time, high-speed and high-sensitivity light detection becomes possible.

Furthermore, by combining the light detection device described in this embodiment with a configuration that performs synchronous detection with a wavelength tunable light source as described in JP-A-2009-153654, high-speed, high-sensitivity, and high-contrast light Detection can also be realized.

(Second Embodiment)
FIG. 3 is a diagram showing a schematic configuration of a rigid endoscope blood vessel imaging device according to the second embodiment of the present invention. This apparatus detects a detected signal light obtained by irradiating a laser beam and visualizes a blood vessel position existing under fat.

  This rigid endoscope blood vessel imaging apparatus irradiates laser light for illumination while scanning the biological sample 100, and the light reflected or scattered on the surface and inside of the biological sample 100 has the configuration shown in FIG. It is configured so as to be detected and converted into an electric signal by an optical detection device, and to display an image by processing the electric signal by a signal processing system.

  This rigid endoscope type blood vessel imaging apparatus has a single mode fiber (SMF) output type Er-doped fluoride fiber laser 61 having a wavelength of 543 nm and an output of 2 mW, an isolator 62, a single mode fiber: SMF) 63 and a collimator 64 are provided as an illumination optical system, and the laser light emitted from the Er-added fluoride fiber laser 61 is substantially collimated by the collimator 64 via the isolator 62 and the SMF 63 to a desired observation position of the biological sample 100. It is configured to be irradiated.

 Further, a laser driver 66 for driving the Er-doped fluoride fiber laser 61 is provided, and the Er-doped fluoride fiber laser 61 controls the entire rigid endoscope blood vessel imaging apparatus via the laser driver 66. The output state is controlled by control from a computer 69 described later.

 Further, in order to detect the signal light from the biological sample 100, the rigid endoscope blood vessel imaging apparatus shown in FIG. 3 includes the mode adjustment means 10, the amplification means 20 and the conversion means 30 of the light detection apparatus shown in FIG. As a configuration corresponding to each, a tapered fiber 11, an Er-doped fluoride fiber type optical amplifier 21, and a silicon PIN-PD (PIN photo diode) 31 are provided. Further, an electrical amplifier 67 that amplifies the electrical signal output from the PIN-PD 31 and an analog-to-digital (analog-to-digital) that converts the analog electrical signal amplified by the electrical amplifier 67 into a digital signal. A digital (AD) converter 68 is provided.

 A tapered fiber is an optical fiber having a structure in which the diameter of a core portion through which light is guided varies from the input side to the output side. The incident surface of the tapered fiber 11 faces the biological sample 100 and is disposed at a position close to the collimator 64, and is fixed on the scanning mount 65 together with the collimator 64. As shown in the schematic shape of the longitudinal section of the core portion in FIG. 4, the tapered fiber 11 has a tapered shape in which the core diameter on the input side is larger than the core diameter on the output side. In this embodiment, the core diameters on the input side and output side are 50 μm and 4 μm, respectively, and the length is 1.0 m.

 In addition, as shown in FIG. 5, the Er-doped fluoride fiber type optical amplifier 21 includes isolators 73a and 73b, a wavelength division multiplexing (WDM) coupler 74, an Er-doped fluoride fiber 75, and an optical filter. 76, including a laser diode (LD) 77;

 Isolators 73a and 73b are disposed on the input side and output side of the Er-doped fluoride fiber optical amplifier 21, and suppress return light. The LD 77 is an excitation light source for the Er-doped fluoride fiber 75 and uses a semiconductor laser having a wavelength of 975 nm and an output of 100 mW. Further, a driver 72 for driving the LD 77 connected to the LD 77 is provided. The WDM coupler 74 is configured to multiplex the excitation light from the LD 77 and the signal light emitted from the incident-side isolator 73 a and output the resultant light to the Er-doped fluoride fiber 75. The Er-doped fluoride fiber 75 is a single-mode Er-doped fluoride fiber having a core diameter of 4 μm, amplifies the signal light with the pump light, and outputs residual pump light and ASE. The optical filter 76 is provided on the emission side of the Er-doped fluoride fiber 75, and removes residual excitation light and ASE and emits only signal light. This signal light is emitted from the Er-doped fluoride fiber amplifier 21 via the isolator 73b. The Er-doped fluoride fiber type optical amplifier 21 can amplify the output of the tapered fiber 11 by about 15 dB.

 Further, as shown in FIG. 3, the rigid endoscope blood vessel imaging apparatus according to the present embodiment includes a computer 69 that controls each part of the apparatus and processes a digital signal output from the AD converter 68. The computer 69 is connected to the laser driver 66, the driver 71, and the driver 72, and controls the Er-doped fluoride fiber laser 61, the Er-doped fluoride fiber optical amplifier 21, and the scanning mount 65, respectively, and an AD converter 68. The signal processing is performed by associating each output signal with the output signal of the Er-doped fluoride fiber laser 61, the amplification factor of the Er-doped fluoride fiber optical amplifier 21, and the position of the scanning mount 65, and the result is displayed on the display monitor 70. Configured to display.

 With the configuration as described above, in the rigid endoscope blood vessel imaging apparatus according to the present embodiment, when observing a biological sample, the computer 69 scans the scanning mount 65 via the driver 71 and the laser driver. The Er-added fluoride fiber laser 61 is driven through 66 to irradiate the biological sample 100 with laser light from the collimator 64. This laser light is reflected or scattered on the surface and inside of the biological sample 100 and enters the tapered fiber 11 as signal light having a wavelength of 543 nm.

 Here, since the core diameter on the incident side of the tapered fiber 11 is 50 μm, the area of the incident surface is large compared to a fiber with a core diameter of 4 μm, and a wide range of signals can be collected. Higher order modes can be incident. On the other hand, on the exit side of the tapered fiber, the core diameter is as small as 4 μm, and the energy distribution between modes is adjusted to concentrate on the fundamental mode.

 The signal light that has undergone mode adjustment enters the Er-doped fluoride fiber optical amplifier 21 and enters the single-mode Er-doped fluoride fiber 75 having a core diameter of 4 μm whose fundamental mode is the amplification spatial mode shown in FIG. To do. Since the mode distribution on the emission side of the tapered fiber and the amplification spatial mode of the Er-doped fluoride fiber 75 substantially coincide with each other, the coupling efficiency at the junction between the two becomes high. For this reason, the loss of energy of the signal light incident on the tapered fiber 11 can be suppressed, and the Er-doped fluoride fiber optical amplifier 21 can perform amplification in a substantially single mode, so that the generation of ASE can be suppressed. , Signal light having a high SNR can be obtained.

 Further, as shown in FIG. 3, the signal light emitted from the Er-doped fluoride fiber optical amplifier 21 is converted into an electric signal by the PIN-PD 31, amplified by the electric amplifier 67, and converted into a digital signal by the AD converter 68. It is converted and transmitted to the computer 69. The computer 69 performs signal processing by associating this electrical signal with the scanning position information obtained from the driver 71, generates a blood vessel image, and displays it on the monitor 70. In this way, the blood vessel position existing under fat can be imaged at high speed.

 As described above, according to the present embodiment, the light receiving surface can be widened by arranging the tapered fiber 11 in front of the Er-doped fluoride fiber type optical amplifier 21. Since the number of spatial modes is large, a large amount of signal light can be incident even if the signal light to be detected is scattered light or light with a disturbed wavefront. In addition, since the mode distribution of energy is adjusted to a mode that substantially matches the amplification spatial mode of the Er-doped fluoride fiber optical amplifier 21 with a small number of amplification spatial modes by the tapered fiber 11, ASE can be reduced. , Optical amplification with high SNR becomes possible. Furthermore, mode adjustment can be performed with little energy loss by using the tapered fiber 11. Therefore, even if the detected signal light is scattered light or light with a disturbed wavefront, it is possible to amplify light with high signal light intensity and low noise light intensity. Therefore, by arranging this optical amplifier in front of the PIN-PD 31, it becomes possible to detect light with high speed and high sensitivity.

 Further, by using a tapered fiber 11 which is a kind of optical fiber as the mode adjusting means 10, a long spatial mode adjusting waveguide can be stably realized. By making the length longer, adiabatic spatial mode adjustment becomes possible, and lower-loss spatial mode adjustment can be realized. In addition, the use of the optical fiber eliminates the need for fine adjustment of the spatial optical system, thereby improving the degree of freedom in use. Furthermore, since the tapered fiber 11 has a very high degree of design freedom, it is possible to realize a mode adjusting means suitable for the state of the detection light. Further, since the tapered fiber 11 can be manufactured relatively easily, an inexpensive photodetection device can be provided.

 Further, since the Er-doped fluoride fiber type optical amplifier 21 is used as the amplifying means 20, it is possible to perform amplification with high gain and low noise and high amplification efficiency. Furthermore, optical amplification is possible even in a wavelength band that cannot be operated with a silica-based fiber optical amplifier, and in particular, efficient optical amplification in the visible band is possible.

Furthermore, in the second embodiment shown in FIG. 3, when the spatial distribution state of the detected light changes depending on time, measurement position, etc., high-speed and high-sensitivity light detection can be achieved by using the following configuration. Is possible. First, the tapered fiber 11 in FIG. 3 is bonded to the piezo element. By changing the current passed through the piezo element, the piezo element, and consequently the tapered fiber 11, can be expanded or contracted. By doing so, the mode adjustment characteristic of the tapered fiber 11 can be changed. At this time, the current flowing in the piezo element is controlled by the computer 69 so that the output voltage from the PIN-PD 31 is increased.

(Third embodiment)
FIG. 6 is a block diagram showing a schematic configuration of a photodetection device according to the third embodiment of the present invention. This photodetection device is provided with a plurality of mode adjustment means 10 and a multiplexing means 40 between the mode adjustment means 10 and the amplification means 20 in the configuration of the photodetection apparatus shown in FIG.

 With this configuration, the detected light is input to the plurality of mode adjusting units 10, and the spatial mode adjustment is performed in each mode adjusting unit 10. Thereafter, the output lights from the plurality of mode adjusting means 10 are input to the multiplexing means 40 and are combined. The detected signal light output from the multiplexing unit 40 is amplified by the amplification unit 20 and further converted into an electric signal by the conversion unit 30. The electrical signal output from the conversion means 30 is converted into desired data by a signal processing system following the subsequent stage.

 According to the present embodiment, in addition to the effects of the first embodiment, a plurality of mode adjustment means 10 for performing mode adjustment of multi-mode incident light incident in parallel are provided in front of the amplification means 20 and the conversion means 30. Since they are arranged, signal waves can be collected with high efficiency even if the detected signal light is scattered light or light whose wavefront is disturbed, and light detection with high speed and high sensitivity becomes possible. In addition, since it includes a multiplexing unit 40 that combines a plurality of lights output from the plurality of mode adjusting units 10, the operation stability of the entire apparatus is further improved by combining the incident light with a reduced number of modes. Can be improved.

(Fourth embodiment)
FIG. 7 is a diagram showing a schematic configuration of a rigid endoscope blood vessel imaging apparatus according to the fourth embodiment of the present invention using the light detection apparatus shown in FIG. This rigid endoscope blood vessel imaging apparatus uses an illumination lens 64b instead of the collimator 64a in the rigid endoscope blood vessel imaging apparatus shown in FIG. 3, and a plurality of tapered fibers 11 are provided in parallel. A fiber coupler 41 is provided as a multiplexing means 40 on the emission side. Further, the illumination lens 64 b and the incident surfaces of the plurality of tapered fibers 11 are fixed to the scanning mount 65 so as to face the biological sample 100.

 Unlike the collimator 64 a shown in FIG. 3, the illumination lens 64 b diffuses the laser light propagated through the SMF 63 and irradiates the region of the biological sample 100 facing the incident surface of the tapered fiber 11. The laser light is reflected or scattered on the surface and inside of the biological sample 100 and is incident on the plurality of tapered fibers 11 as multimode light. After the energy distribution between modes is adjusted, the signal light incident on each tapered fiber 11 is incident on the fiber coupler 41 and multiplexed as light having a small number of modes including the fundamental mode. Thereafter, the signal light combined by the fiber coupler 41 enters the Er-doped fluoride fiber type optical amplifier 21. Since other configurations and operations are the same as those of the second embodiment, the same components are denoted by the same reference numerals, and description thereof is omitted.

 As described above, according to the present embodiment, in addition to the effects of the second embodiment, more signal light can be collected by having a plurality of tapered fibers 11. Also, since the operation is generally more stable with an element having a smaller number of spatial modes, the operation stability of the entire apparatus can be further improved by reducing the number of spatial modes of the signal light and using the multiplexing means. Can be improved.

(Fifth embodiment)
FIG. 8 is a block diagram showing a schematic configuration of the photodetecting device according to the fifth embodiment of the present invention. In the configuration of the photodetecting device shown in FIG. 1, this photodetecting device is provided with a plurality of mode adjusting means 10 and amplifying means 20 in parallel, one each as a set, and the output from each amplifying means 20 Are configured to be input to the conversion means 30 that can process these outputs in parallel.

 In the above configuration, the detected light is input to the plurality of mode adjusting units 10, and the spatial mode adjustment is performed in each mode adjusting unit 10. Thereafter, the output light from the plurality of mode adjusting means 10 is input to the corresponding amplifying means 20 and amplified, and further converted into electric signals in parallel by the converting means 30. The electrical signal output from the conversion means 30 is converted into desired data by a signal processing system following the subsequent stage.

 According to the present embodiment, the plurality of mode adjusting means 10 for adjusting the multimode incident light incident in parallel to the mode substantially matching the amplification spatial mode by the amplifying means 20 by adjusting the mode distribution of energy. Since each of the signal light to be detected is scattered light or light with a distorted wavefront, it can be collected with high efficiency, at a high speed. Highly sensitive light detection is possible. Furthermore, it has a plurality of mode adjusting means 10 and a plurality of amplifying means 20 corresponding thereto, and converts the light output from each of the amplifying means 20 into an electrical signal in parallel, so that a plurality of information such as image information can be simultaneously obtained Can be obtained.

(Sixth embodiment)
FIG. 9 is a diagram showing a schematic configuration of a high-sensitivity endoscope according to the sixth embodiment of the present invention using the light detection device shown in FIG. This high-sensitivity endoscope irradiates a laser beam for illumination, detects the light reflected or scattered on the surface and inside of the biological sample 100 by the photodetection device in FIG. An electric signal is processed by a signal processing system to display an endoscopic image.

 As an optical system for irradiating the biological sample 100 with laser light for illumination, this high-sensitivity endoscope uses an LD80 having a wavelength of 635 nm and an output of 20 mW, an isolator 81, a multi-mode fiber (MMF) 82a, and The illumination lens 83 is provided, and the output of the LD 80 as the light source is output to the space from the illumination lens 83 via the isolator 81 and the MMF 82a, and is irradiated to the biological sample 100.

 Further, a laser driver 79 for driving the LD 80 is provided, and the LD 80 is configured such that the output is controlled by the computer 69 that controls the entire high-sensitivity endoscope via the laser driver 79.

 In addition, the light detection device for detecting the light to be detected from the biological sample 100 includes 128 × 128 tapered fibers 11 as the mode adjusting means 10 and 128 × 128 semiconductors corresponding to the tapered fibers 11 as the amplifying means 20. An optical amplifier (semiconductor optical amplifier: SOA) 22 and a CCD camera 32 having 128 × 128 pixels are used as the conversion means 30, respectively. Further, an isolator 84a is provided between each tapered fiber 11 and the corresponding SOA 22, and an isolator 84b and an ASE-removing optical band-pass filter (BPF) are provided between each SOA 22 and the CCD camera 32. ) 85 is provided. An analog-to-digital (AD) converter 68 that converts an analog electric signal into a digital signal is provided at the subsequent stage of the CCD camera 32.

 The tapered fiber 11 has a core diameter of 50 μm and 9 μm on the input side and the output side, and a length of 1.0 m. The incident surface faces the biological sample 100 and the illumination lens 83. Are arranged so that signal light from different positions of the biological sample 100 is incident, and is fixed to the housing 78 together with the illumination lens 83. The SOA 22 is configured to be controlled by a computer 69 via a driver 86.

 As a result, the signal light having a wavelength of 635 nm reflected or scattered on the surface and inside of the biological sample 100 is input to each tapered fiber 11 and the mode is adjusted. Each output of the tapered fiber 11 is input to the corresponding SOA 22 via the isolator 84 and amplified by about 18 dB. The output of each SOA 22 enters the corresponding BPF 85 via the corresponding isolator 84, and the ASE is removed. The output of each BPF 85 is input so as to correspond to each pixel of the 128 × 128 pixel CCD camera 32 and is converted into an electrical signal. Further, the signal output converted into an electrical signal by the CCD camera 32 is converted into a digital signal by the AD converter 68.

 In addition, the high-sensitivity endoscope according to the present embodiment is provided with a computer 69 that controls each part of the apparatus and processes a digital signal output from the AD converter 68. The computer 69 is connected to the laser driver 79 and the driver 86, respectively, to control the LD 80 and the SOA 22, and performs signal processing by associating the output signal of the AD converter 68 with the output of the LD 80 and the amplification factor of the SOA 21. The result is displayed on the display monitor 70 as, for example, an endoscopic image.

 As described above, according to the present embodiment, the same effects as those of the second embodiment can be obtained, and an endoscopic image can be obtained with higher speed and higher sensitivity than in the past. In the present embodiment, a plurality of tapered fibers 11 and a plurality of SOAs 22 corresponding to the plurality of tapered fibers 11 are provided, and the optical output from each SOA 22 is converted into an electrical signal in parallel. Can be obtained. Therefore, this is particularly effective when generating a two-dimensional image or the like.

 Further, by using the SOA 22 as the amplification means 20, it becomes possible to construct a compact and low-cost photodetection system and to integrate with other semiconductor elements such as a plurality of semiconductor optical amplifiers and photodiodes (PD). It becomes possible. It also has the advantage of requiring less power supply. Furthermore, since the SOA has a wider operating wavelength band than the fiber-type optical amplifier, it can cope with various detected lights.

(Seventh embodiment)
FIG. 10 is a block diagram showing a schematic configuration of the photodetecting device according to the seventh embodiment of the present invention. In the configuration of the photodetecting device shown in FIG. 1, this photodetecting device is provided with a wave collecting means 50 for collecting the detected light before the mode adjusting means 10. As a result, in addition to the effect of the first aspect of the invention, the amount of signal light that can be detected can be further increased.

(Eighth embodiment)
FIG. 11 is a diagram showing a schematic configuration of a rigid endoscope blood vessel imaging apparatus according to the eighth embodiment of the present invention using the light detection apparatus shown in FIG. This rigid endoscope blood vessel imaging apparatus is a rigid endoscope blood vessel imaging apparatus shown in FIG. 3 in which a condensing lens 51 is provided in front of the incident surface of the tapered fiber 11. By providing the condensing lens 51 in front of the tapered fiber 11, a larger portion of the light reflected or scattered on the surface and inside of the biological sample 100 can be taken into the tapered fiber 11. In addition, there is an advantage that it is possible to detect with high sensitivity and high SNR even for a test substance existing in a deep part or a distant part of the detection target.

(Ninth embodiment)
FIG. 12 is a diagram showing a schematic configuration of a laser scanning multiphoton microscope according to the ninth embodiment of the present invention. In this embodiment, in the laser scanning multiphoton microscope, the light detection apparatus shown in FIG. 10 is used for detection of signal light from a living cell sample.

 As shown in FIG. 12, the laser scanning multiphoton microscope according to the present embodiment includes a titanium sapphire laser 87, an intensity modulator 88, an XY galvanometer mirror 89, a pupil projection lens 90, an imaging lens 91, and a dichroic. A mirror 92, an objective lens 93 constituting an objective optical system, an isolator 102, a condensing lens 52, a tapered waveguide 12, an SOA 23, a PIN-PD 33, an electric amplifier 67, an AD converter 68, and an amplification factor control means 103 are provided. It is configured to include.

 The titanium sapphire laser 87 is a light source that generates an ultrashort optical pulse having a repetition frequency of 80 MHz, a pulse width of 150 fs, and an oscillation wavelength of 1060 nm. The ultrashort light pulse from the titanium sapphire laser 87 is adjusted to an average light intensity of 100 mW by a light intensity adjusting device 88, and an XY galvanometer mirror 89, a pupil projection lens 90, an imaging lens 91, a dichroic mirror 92, and Via the objective lens 93, the living cell sample 101 to be examined is condensed and irradiated. At that time, the XY galvanometer mirror 89 is driven to scan the irradiation position of the laser beam on the sample. Thereby, in a desired region in the living cell sample 101, for example, red fluorescent protein (DsRed) can be excited by multiphoton excitation (for example, two-photon excitation) to generate fluorescence.

 The objective lens 93 guides fluorescence generated from the living cell sample 101 to the dichroic mirror 92. The dichroic mirror 92 is configured to transmit light having a wavelength of 1060 nm from the titanium sapphire laser 87 and to reflect light having a short wavelength of 700 nm or less. Thereby, the fluorescence having a wavelength of about 570 nm to 650 nm generated in the living cell sample 101 is reflected by the dichroic mirror 92.

 The condensing lens 52, the tapered waveguide 12, the SOA 23, and the PIN-PD 33 correspond to the wave collecting means 50, the mode adjusting means 10, the amplifying means 20, and the converting means 30 of the photodetector shown in FIG. The fluorescence reflected by the dichroic mirror 92 is condensed by the condenser lens 52 via the isolator 102 and input to the tapered waveguide 12. The tapered waveguide 12 has a spatial mode of 8 on the incident side, and is configured such that the number of modes on the output side is reduced to 2 by mode adjustment. The fluorescence output from the tapered waveguide 12 enters the SOA 23 controlled by the external computer 69 via the amplification factor control means 103, is amplified, and is converted into an electrical signal by the silicon PIN-PD33. The SOA 23 can be amplified with a high SNR while suppressing the generation of ASE by reducing the number of modes of the incident signal light.

 Further, the electrical signal output from the PIN-PD 33 is amplified by the electrical amplifier 67, converted into a digital signal by the AD converter 68, and transmitted to the external computer 69. The computer 69 performs signal processing by associating the signal received from the AD converter 68 with the scanning position information obtained from the XY galvanometer mirror 89 and displays the result on the monitor 70 as a microscope image.

 In the laser scanning multiphoton fluorescence microscope described above, for example, the fluorescence generated from the living cell sample 101 by two-photon excitation by the excitation light pulse from the titanium / sapphire laser 87 lasts for about several ns. That is, the fluorescence generated from the living cell sample 101 becomes pulse light synchronized with the excitation light pulse from the titanium / sapphire laser 87. Therefore, in the present embodiment, the computer 69 controls the amplification factor of the SOA 23 so as to increase at the timing at which the fluorescence enters in synchronization with the timing at which the pulsed fluorescence enters the SOA 23.

 According to the present embodiment, the fluorescence generated from the living cell sample 101 by the multi-photon excitation by the excitation light pulse from the titanium sapphire laser 87 is changed to a mode in which the number of spatial modes is reduced using the tapered waveguide 12. The signal obtained from the live cell sample 101 without excessively increasing the intensity of the laser light applied to the live cell sample 101 because the adjustment is performed and amplified by the SOA 23 and then photoelectrically converted by the silicon PIN-PD33. Even if the fluorescence which is light is weak, the fluorescence by two-photon excitation can be photoelectrically converted with high sensitivity.

 In addition, since the amplification factor of the SOA 23 is controlled in synchronization with the timing of the fluorescence incident on the SOA 23, it is possible to reduce the mixing of ASE generated by supplying power to the optical amplifier during the period when the fluorescence is not incident. And the SNR can be improved. Furthermore, the detection signal level can be easily adjusted by changing the amplification factor of the SOA 23.

(Tenth embodiment)
FIG. 13 is a block diagram showing a schematic configuration of the photodetection device according to the tenth embodiment of the present invention. In the configuration of the photodetecting device shown in FIG. 1, this photodetecting device combines a plurality of collecting means 50 and detection light from the plurality of collecting means 50 before the mode adjusting means 10. The wave means 40 is provided.

 In the above configuration, the detected light is collected by the plurality of collecting means 50 and input to the combining means 40. The multiplexing unit 40 multiplexes a plurality of input light to be detected and outputs the combined light to the mode adjusting unit 10. Other operations are the same as those of the photodetecting device of FIG.

 According to the present embodiment, in addition to the effect of the invention described in claim 1, by providing a plurality of wave collecting means 50, signal light from a plurality of locations can be acquired in a lump. By combining the signal light from the places with the multiplexing means 40, the energy of the signal light input to the amplifying means 20 can be increased and the SNR can be further improved.

(Eleventh embodiment)
FIG. 14 is a diagram showing a schematic configuration of a rigid endoscope blood vessel imaging device according to the eleventh embodiment of the present invention using the light detection device shown in FIG. This rigid endoscope blood vessel imaging device uses an illumination lens 64b instead of the collimator 64a in the rigid endoscope blood vessel imaging device shown in FIG. A condensing lens 51, a multi-mode fiber (MMF) 82 b coupled to the condensing lens 51, and a multimode fiber coupler 42 that combines signal light from each MMF 82 b are provided. The condensing lens 51 and the multimode fiber coupler 42 correspond to the collecting means 50 and the combining means 40 in FIG. 13, respectively.

 In addition, the illumination lens 64 b and each condensing lens 51 are fixed to the scanning mount 65 so as to face the sample 100. Further, unlike the collimator 64 a shown in FIG. 3, the illumination lens 64 b diffuses the laser light propagating through the SMF 63 and irradiates the region of the biological sample 100 facing the incident surface of each condensing lens 51. It is configured to let you.

 As a result, the laser light emitted from the illumination lens 64b is reflected or scattered on the surface and inside of the biological sample 100, and is collected by the plurality of condensing lenses 51, and is then collected by the multimode fiber coupler 42 via the MMF 82b. The light is combined and enters the tapered fiber 11 as multimode light. Since other configurations and operations are the same as those of the second embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

 As described above, according to the present embodiment, since a plurality of condensing lenses 51 are provided, signal light from a plurality of locations can be acquired at once, and the amount of signal light that can be detected is further increased. Is possible. Further, by combining the signal light from a plurality of places with the multi-mode fiber coupler 42, the number of the tapered fiber 11, the Er-doped fluoride fiber type optical amplifier 21, and the PIN-PD 31 following the subsequent stage can be reduced to one. it can. Moreover, the signal light energy input to the Er-doped fluoride fiber optical amplifier 21 can be increased by collecting the signal lights from a plurality of locations. Therefore, it is possible to obtain an endoscopic image at higher speed and higher sensitivity.

(Twelfth embodiment)
FIG. 15 is a block diagram showing a schematic configuration of the photodetection device according to the twelfth embodiment of the present invention. This photodetecting device has a configuration in which the collecting means 50 is provided in front of each mode adjusting means 10 in the configuration of the photodetecting device shown in FIG. As a result, in addition to the effects of the light detection device according to the fifth embodiment, it becomes possible to guide more detected light to the mode adjustment means 10.

(13th Embodiment)
FIG. 16 is a diagram showing a schematic configuration of a rigid endoscope blood vessel imaging apparatus according to the thirteenth embodiment of the present invention using the light detection apparatus shown in FIG. This rigid endoscope blood vessel imaging apparatus is a rigid endoscope blood vessel imaging apparatus according to the sixth embodiment shown in FIG. 9 in which a condensing lens 52 is provided in front of a plurality of tapered fibers 11. It is. By providing the condensing lens 52 in front of the tapered fiber 11, a larger portion of the light reflected or scattered on the surface and inside of the biological sample 100 can be taken into each tapered fiber 11. Since other configurations and operations are the same as those of the sixth embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

 As described above, according to the present embodiment, since the condensing lens 52 is provided in front of the tapered fiber 11, it is possible to further increase the amount of signal that can be detected. Therefore, it is possible to obtain an endoscopic image at higher speed and higher sensitivity.

 In addition, this invention is not limited only to the said embodiment, Many deformation | transformation or a change is possible. For example, although the tapered fiber 11 or the tapered waveguide 12 is used as the mode adjusting means, the invention is not limited to this, and a tapered photonic crystal waveguide, a long-period fiber Bragg grating, a refractive index modulation planar waveguide, or the like is used. Can do.

 For example, in the ninth embodiment, instead of the tapered waveguide 12, a graded index waveguide having a nonuniform refractive index distribution in the longitudinal direction of the waveguide is used, or in the longitudinal direction of the waveguide. Waveguides that provide a non-uniform stress distribution or a non-uniform temperature distribution can be used. In this case, energy exchange occurs between the spatial modes due to the refractive index, stress, or temperature fluctuation in the optical waveguide. By intentionally applying this refractive index, stress, or temperature fluctuation into the optical waveguide, a change in the energy ratio between the spatial modes can be induced.

 Further, as the amplifying means, an Er-doped fluoride fiber type optical amplifier or SOA is used, but it is not limited to this. For example, instead of these amplifiers, fiber-type optical amplifiers using the stimulated Raman scattering effect can be used. The operating wavelength band of rare-earth doped fiber optical amplifiers is very discrete, so there is a wavelength range where the optical amplification effect cannot be obtained, but the stimulated Raman scattering effect does not select the operating wavelength band, so use this Thus, optical amplification can be performed in an arbitrary wavelength region. Also, other fiber type optical amplifiers such as a fiber type Brillouin optical amplifier, a fiber type parametric optical amplifier, etc. can be used. In addition, dye amplifiers can be used. Compared with fiber-type optical amplifiers and semiconductor optical amplifiers, the dye amplification band is wide, and therefore, using a dye amplifier makes it possible to amplify a broadband signal. Furthermore, depending on the design of the dye, light amplification at various wavelengths becomes possible.

 Further, although the PIN-PD or CCD camera is used as the conversion means, the present invention is not limited to this. For example, an APD, PMT, CMOS, EM-CCD, or EB-CCD can be used.

 As the multiplexing means 40, a fiber coupler or a multi-mode fiber coupler is used, but is not limited to this. For example, a planar waveguide type optical coupler, a spatial beam combiner, a polarization combining coupler, a wavelength combining coupler, etc. You can also.

 As the wave collecting means, a condensing lens is used, but is not limited to this, and for example, a GRIN (Gradient Index) lens, a lensed fiber, or the like can be used.

DESCRIPTION OF SYMBOLS 10 Mode adjustment means 11 Tapered fiber 11a Tapered fiber core part 12 Tapered waveguide 20 Amplifying means 21 Er addition fluoride fiber type optical amplifier 22 Semiconductor optical amplifier (SOA)
23 Semiconductor Optical Amplifier (SOA)
30 Conversion means 31 PIN-PD
32 CCD camera 33 PIN-PD
40 Multiplexing means 41 Fiber coupler 42 Multimode fiber coupler 50 Condensing means 51 Condensing lens 52 Condensing lens 61 Er-doped fluoride fiber laser 62 Isolator 63 SMF
64a Collimator 64b Illumination lens 65 Scan mount 66 Laser driver 67 Electrical amplifier 68 AD converter 69 Computer 70 Display monitor 71 Driver 72 Driver 73a, 37b Isolator 74 WDM coupler 75 Er-doped fluoride fiber 76 Optical filter 77 LD
78 Housing 79 Laser driver 80 LD
81 Isolator 82a, 82b MMF
83 Illumination lenses 84a and 84b Isolator 85 BPF
86 Driver 87 Titanium sapphire laser 88 Light intensity adjusting device 89 XY galvanometer mirror 90 Pupil projection lens 91 Imaging lens 92 Dichroic mirror 93 Objective lens 100 Biological sample 101 Living cell sample 102 Isolator 103 Amplification rate control means

Claims (5)

Mode adjusting means for adjusting the mode state of the multi-mode incident light obtained as the detected light from the detection target;
The mode adjustment means has a fiber Bragg grating or tapered fiber as a control means for controlling mode adjustment conditions according to the spatial distribution state of the incident light,
Amplifying means for amplifying the light output from the mode adjusting means;
Conversion means for converting the light output from the amplification means into an electrical signal,
The photodetecting device, wherein the mode adjusting unit is configured to substantially match a mode distribution of the incident light and an amplification spatial mode of the amplifying unit. The light detection apparatus according to claim 1, wherein the control unit is controlled to increase an output signal level of the conversion unit. 2. The light detection apparatus according to claim 1, wherein the control unit has a function of applying a mechanical action (extension, bending, or stress) to the mode adjustment unit. The light detection apparatus according to claim 1, wherein the control unit has a function of giving a temperature change to the mode adjustment unit. 2. The photodetecting device according to claim 1, wherein the mode adjusting means is a tapered fiber made of a graded index fiber.

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