JPH03274426A - Highly directive photodetector - Google Patents

Abstract

PURPOSE:To obtain a bright detector using a bright optical element which is able to take out nearly the whole energy of the 0-order Fraunhofer diffraction by providing a two-dimensional photodetector at the projecting side of a multi- luminous-flux highly-directive optical system. CONSTITUTION:A highly-directive optical element comprising a convex lens OB and a pin hole P at the focus of the lens OB is two dimensionally arranged, whereby a multi-luminous- flux highly-directive optical system is constituted. That is, many distributed index lenses GL are regularly arranged within a frame and bonded each other with use of a black silicone resin bonding agent B so that the light does not leak from a gap of the lenses. An array PA of pin holes are tightly attached to the rear face of an array GA of the distributed index lenses. Since each pin hole P of the array PA is aligned with the axis of the array GA, the intensity of the light passing through each pin hole of the array PA is changed in accordance with the distribution of a plane wave when the plane wave having the two-dimensional distribution of intensity enters the lens array GA. Therefore, if a two-dimensional photodetector is provided behind the pin hole array PA, the two-dimensional distribution of intensity of the plane wave can be measured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a highly directional photodetector capable of separating and detecting a plane wave having a two-dimensional intensity distribution incident from a predetermined direction. For example, the present invention relates to a highly directional photodetector suitable for detecting absorption distribution in a scattering body such as a living body.

[Conventional technology]

Since the discovery of X-rays, technology for observing the inside of living organisms (human bodies) from the outside without causing damage (non-invasive or non-invasive measurement methods) has been strongly sought after and developed in the field of biology, especially medicine. I've been doing it. This technology uses gamma rays and X-rays, which have the shortest wavelengths of electromagnetic waves, and radio waves, which have the longest wavelengths. The former is xwACT, the latter is NMR-CT
(Magnetic Re5onance 1m
aging%MRI).

On the other hand, spectroscopy in the ultraviolet-visible, near-infrared, and infrared regions, which are widely used in the fields of physics and chemistry, can be applied to the entire living body (i.e.
There have been relatively few attempts to apply it to n vivo. This is because many problems regarding the most basic "quantitativeness" remain unsolved in biological measurements that use light, especially those that utilize absorption and luminescence processes. Currently, reflection spectrum measurement devices using solid-state elements and high-sensitivity TVs are currently available.
This is the reason why measurements using cameras and the like have been attempted, but the reliability of the reproducibility and absolute values obtained is low.

When light is irradiated onto a scatterer such as a living tissue, it is possible to extract a certain amount of straight light if the light is received 180 degrees facing the object, but so far the spatial resolution cannot be said to be very good.

The difference in spatial resolution between X-rays and light cannot currently be bridged. However, using light, particularly near-infrared light, it should be possible to image tissue oxygen levels from hemoglobin in the blood. These will provide information different from other NMRCT or X-ray CT.

If the tissue is 3 to 5 thick, we can detect the light that passes through it. This means that "optical radiography" can be used for diagnosis. The tissue of the female breast is relatively uniform, allowing light to easily pass through it, and its shape makes it easy to detect transmitted light (thickness: ~3 cm).
It has been used under the name phy (Lightscanning).

Under such circumstances, the present inventors disclosed
No. 98 and Japanese Patent Application Laid-open No. 1-250034, in order to separate and extract the plane wave mixed with the scattered light and observe it, the zero-order spectrum (Airy disk) of the Franphofer diffraction image (Airy disk) of the plane wave is used. - It is sufficient to observe only the portion within the first dark ring of the disk), and it has been shown that by doing so, it is possible to eliminate most of the scattered components. As one of the highly directional optical elements that realizes such fin observation, we have proposed an optical element consisting of two pinholes P and P2 separated from each other as shown in Fig. 42. This optical element is for detecting zero-order light by the detector 23 through the pinhole P2. Further, as shown in FIG. 43, a highly directional optical element is made of a linear, elongated hollow glass fiber 35, and its inner wall surface is coated with a light absorbing material, such as an absorbing material 35 such as carbon. proposed. In such optical elements,
If the aperture diameter and length are set appropriately according to the measurement target and the optical element is made sufficiently long compared to the entrance aperture diameter, only plane waves parallel to the optical axis will be detected among the light incident on the highly directional optical element. It can be taken out from the exit surface. And, the above-mentioned Unexamined Patent Publication No. 1-
In No. 62898 and Japanese Unexamined Patent Publication No. 1-250034,
A one-dimensional or two-dimensional photodetector is combined on the output side of a multi-beam high-directivity optical system constructed by bundling a plurality of these highly directional optical elements to detect a two-dimensional intensity distribution incident from a predetermined direction. We have proposed a highly directional photodetector that separates and detects the plane waves that contain the waves.

Problems to be solved by C. However, in highly directional optical elements such as those shown in FIGS. The next diffraction image (the first dark ring of the Airy disk) is larger than the aperture diameter on the entrance side, and if an extraction aperture with the same size as the aperture diameter on the entrance side is used, it will be a part of the 0th order diffraction image. Furthermore, it was found that the further the observation point is moved away, the larger the first dark ring becomes, and the smaller the energy extracted from the extraction aperture becomes. Therefore, a multi-beam high-directivity optical system is constructed by closely arranging such highly directional optical elements, and a one-dimensional or two-dimensional photodetector is attached to the output side of the optical system to detect two or more beams incident from a predetermined direction. When attempting to separate and detect a plane wave with a dimensional intensity distribution, the plane wave that is actually detected is considerably attenuated, making it impossible to obtain a sharp, highly directional photodetector.

The present invention was made in view of this situation, and
The purpose of this is to make a highly directional optical element, which is an element of a multi-beam highly directional optical system used with a one-dimensional or two-dimensional photodetector, even if the diameter of the extraction aperture is the same as the diameter of the entrance side aperture. A bright optical element that can extract almost all the energy of the 0th-order diffraction image of Forfar diffraction is used, and a plurality of such bright elementary optical elements are bundled to form a bright multi-beam highly directional optical system. Another object of the present invention is to provide a bright, highly directional photodetector comprising such a multi-beam, highly directional optical system and a one-dimensional or two-dimensional photodetector.

[Means to solve the problem]

The first highly directional photodetector of the present invention has a convex lens and a pinhole arranged at its focal plane, and the pinhole is a first part of the Franphofer diffraction image formed by the convex lens.
A multi-beam highly directional optical system configured by bundling a plurality of highly directional optical elements each having a diameter equal to or smaller than a dark ring and extracting only a plane wave component incident on the convex lens from a predetermined direction; It is equipped with a one-dimensional or two-dimensional photodetector placed on the output side of the directional optical system.
The present invention is characterized in that it is configured to extract and detect only plane waves having a two-dimensional or second-order sea-like intensity distribution.

In this case, the highly directional optical element disposes a second convex lens substantially the same as the convex lens on the exit side of the pinhole, and the front focal plane of the second convex lens coincides with the pinhole surface. If the optical system is arranged so that the light component passing through the pinhole is converted into a plane wave and emitted, the light emitted from the multi-beam highly directional optical system becomes a plane wave, and 1 Even if the dimensional or two-dimensional photodetector is placed a certain distance from the multi-beam highly directional optical system, the intensity distribution of the incident plane wave can be resolved and detected.

A second highly directional photodetector of the present invention includes a convex lens and an optical fiber disposed on its focal plane, and the core of the optical fiber has a diameter equal to or less than the first dark ring of the Franphofer diffraction image formed by the convex lens. a multi-beam highly directional optical system configured by bundling a plurality of highly directional optical elements that extract only plane wave components incident on the convex lens from a predetermined direction; and an output side of the multi-beam highly directional optical system. A one-dimensional or two-dimensional photodetector arranged in a predetermined direction, and configured to extract and detect only light beams incident from a predetermined direction and a plane wave having an original or two-dimensional intensity distribution. be.

In this case as well, the highly directional optical element arranges a second convex lens substantially the same as the convex lens on the exit side of the optical fiber, and the front focal plane of the second convex lens is the exit surface of the optical fiber. If the optical fibers are arranged so that they match, and the light component that has passed through the optical fiber is converted into a plane wave and then emitted, the light emitted from the multi-beam highly directional optical system becomes a plane wave, and 1 Even if the dimensional or two-dimensional photodetector is placed a certain distance from the multi-beam highly directional optical system, the intensity distribution of the incident plane wave can be resolved and detected.

A third highly directional photodetector of the present invention includes a one-dimensional or two-dimensional convex lens array and a one-dimensional or two-dimensional photodetector arranged on the focal plane of the one-dimensional or two-dimensional convex lens array, and the photodetector includes each convex lens. It is configured to sample and separate and read out only the zero-order diffraction image of Framphofer diffraction due to the method, and to extract and detect only plane waves with a one-dimensional or two-dimensional intensity distribution incident from a predetermined direction. It is characterized by the following structure.

Note that the convex lens is an objective lens, a gradient index lens,
It may be constructed from any flat plate microlens.

[Function] In the first and second highly directional photodetectors of the present invention, the highly directional optical element is composed of a convex lens and a pinhole or an optical fiber arranged in the focal plane of the convex lens. Since the core has a diameter less than or equal to the first dark ring of the Franphofer diffraction image produced by the convex lens, most of the energy of the plane wave component incident on the convex lens from a predetermined direction can be extracted, but energy from a direction different from that direction can be extracted. Most of the stray components and scattered components can be removed. Therefore, a multi-beam high-directivity optical system configured by bundling a plurality of such high-directivity optical elements can also extract only a plane wave having a one-dimensional or two-dimensional intensity distribution incident from a predetermined direction with sufficient resolution. By combining this with a one-dimensional or two-dimensional photodetector, a highly directional photodetector with high directivity, resolution, and sensitivity can be obtained. It becomes a highly directional photodetector suitable for detection.

Further, in the third highly directional photodetector of the present invention, the one-dimensional or two-dimensional photodetector arranged on the focal plane of the one-dimensional or two-dimensional convex lens array has zero Franphofer diffraction due to each convex lens. Since it is configured to sample only the diffraction image and read it out separately, only the plane J having a one-dimensional or two-dimensional intensity distribution incident from a predetermined direction can be separated from surrounding scattered light, etc. Since it can detect with high resolution, it is also a highly directional photodetector suitable for detecting the absorption distribution inside a scattering body such as a living body.

〔Example〕

Before explaining the highly directional photodetector of the present invention, the highly directional optical element, which is an element of the multi-beam highly directional optical system that constitutes the main part of this photodetector, will first be explained.

The basic principle of the highly directional optical element, which is an element of the multi-beam highly directional optical system used in the present invention, is as shown in FIG. A pinhole P2 having a diameter approximately equal to the first dark ring of the diffraction image is placed above to extract most of the 0th order diffraction image.In particular, the diameter of the pinhole P2 is set to the diameter of the entrance aperture. The following shall be done. In this case,
The entrance aperture P1 is the aperture P of the lens L. (You can even be yourself). 7. First, the relationship between the size of the zero-order diffraction image and the aperture P is determined. The diameter of the first dark ring of the Airy disk in the diffraction image by the lens is D = 2.44λ・f/Dr (1
). Here, Dr is the diameter of the aperture P1, and f is the focal length of the lens L. When determining the conditions under which the aperture diameter Dr is equal to or larger than the first dark ring diameter, D%≧244λ·f (2) is obtained. It is extremely easy to construct a highly directional optical element that satisfies these conditions using a convex lens. To give a numerical example, for example, when using light with a wavelength λ of 500 nm, the focal length f is 5 c for an aperture diameter of 1 mm.
If a convex lens of m is used, the diameter of the first dark ring of the Airy disk is 6. I X I L”mm, focal length f is 1
When using a 0cm convex lens, the number 1111! It can be seen that the diameter of the ring is 1.22 x 10"mm, which satisfies the condition of formula (2). If a highly directional optical element that satisfies the condition of formula (2) is used as a unit, Even when a large number of highly directional optical elements are closely arranged next to each other to capture all the incident plane waves, the adjacent ones do not interfere with each other, and the two-dimensional plane waves whose intensity differs depending on the location are used. For example, absorption images can be detected with high resolution.

Next, a specific example of a highly directional optical element will be explained. Second
What is shown in the figure is composed of an objective lens Ob made of, for example, a microscope objective lens that satisfies the relationship of formula (2) above, and a pinhole P placed in its focal plane. This allows only the 0th order diffraction image of the phasic diffraction to pass through. Also, Figure 3(a)
shows another form of convex lens GL. This is known under the trade name "Selfoc Lens" and is also called a gradient index lens. This lens has a refractive index that gradually decreases from the central axis to the periphery, and has a light condensing effect similar to a convex lens. By appropriately selecting the length,
The focal plane can be made to coincide with the end face of the cylinder. As shown in FIG. 3(b), a pinhole P similar to the case in FIG. It is also possible to allow only images to pass through.

By the way, among optical fibers, there are multimode fibers, graded index fibers, single mode fibers, etc. Among these, single mode fibers have extremely small core diameters, and when the light is input to the core end face at the input end. It has the property of only allowing light to pass through, and not allowing light that passes at a large angle to the axis, as shown in Figures 2 to 3.
It can be used in place of the pinhole P shown in Fig.

Moreover, since the aperture of the single mode fiber has a value that matches the first dark ring of Franhofer diffraction of the objective lens ob or the gradient index lens GL, only the 0th-order diffraction image of Franhofer diffraction is efficiently combined. It is convenient for conveying information. Furthermore, since an optical fiber is used for the extraction part, the light can be guided to any desired location, which is advantageous in terms of arrangement.

Fig. 4 shows an example in which a single mode fiber SM is arranged at the focal point of the objective lens ob to configure a highly directional optical element, and Fig. 5 shows an example in which a single mode fiber SM is arranged at the focal point of one end of the gradient index lens GL. An example in which a highly directional optical element is constructed is shown below.

In the case of an eyepiece, etc., the first dark ring of Franhofer diffraction can be made to be the same as the aperture of the multimode fiber. For example, a small aperture can be placed in front of the lens so that the first dark ring matches the aperture of the multimode fiber. In such cases, multimode fibers can also be used.

The hexagonal plane wave passing through the highly directional optical element as described above is
It leaves the element as a spherical wave that diverges.

For example, when a photodetector is placed behind the pinhole P to measure the absorption rate, the emitted light may diverge in this way, but for example, if a large number of highly directional optical elements are bundled, When detecting the distribution image of an absorbing object using
It is desirable that the light be configured to exit as a plane wave from the highly directional optical element. Several such configurations are illustrated in FIGS. 6-9. In the case of Fig. 6, an objective lens Ob2, which is similar to the objective lens Obl on the input side, is placed on the exit side so that its focal point coincides with a pinhole P placed in the middle, so that the 0th order diffraction image is in focus. The wave passes through the hole P, becomes a spherical wave, and is converted back into a plane wave by the objective lens Ob2. In the case of the seventh surface, the gradient index lens GL is placed after and in front of the pinhole P in Figure 3b).
A gradient index lens GL2 similar to I is arranged confocally. The one shown in FIG. 8(a) uses a single mode fiber SM in place of the pinhole P in FIG. 6. Furthermore, as shown in Fig. 1), a gradient index lens G is used instead of one of the objective lenses Obl or Ob2.
L may also be used. In this case, the first dark ring of Franhofer diffraction of the gradient index lens GL and the objective lens ○b1
Alternatively, it is necessary that it approximately coincide with the first dark ring of Ob2.

The one shown in FIG. 9 uses a single mode fiber SM instead of the pinhole P shown in FIG.

None of the highly directional optical elements described above can simultaneously detect plane waves having a two-dimensional distribution.

Therefore, a large number of these highly directional optical elements are two-dimensionally arranged to form a multi-beam highly directional optical system. First, examples of cases in which the emitted light becomes diffused light are shown in Figures 10 to 13.
This will be explained with reference to the drawings. The multi-beam high-directivity optical system shown in FIG. 10 corresponds to one in which a large number of high-directivity optical elements of FIG. 3 and others are arranged in parallel. First, a large number of similar graded refractive index lenses GL are arranged in a stacked pattern in a regular manner within a frame, and they are adhered to each other using adhesive strips made of black silicone resin, for example, and light leaks backward through the gaps. Make sure not to. A pinhole array PA is closely attached to the rear surface of the gradient index lens array GA thus formed.

Each pinhole of the pinhole array PA is provided so as to coincide with the axis of each gradient index lens GL. Therefore, when a plane wave having a two-dimensional intensity distribution enters the gradient index lens array GA from the front of the gradient index lens array GA, the intensity of the light passing through each pinhole of the pinhole array PA will follow the distribution. different. Therefore, by placing a separate photodetector behind each pinhole or by placing a two-dimensional photodetector behind the pinhole array PA, the two-dimensional intensity distribution of the plane wave can be measured. Furthermore, the multi-beam high-directivity optical system shown in FIG. 11 corresponds to a system in which a large number of high-directivity optical elements shown in FIG. is used. A flat plate microlens PM is produced by, for example, producing a regular array of minute lenses on a transparent plate using the IJ sophistic method, or by creating a gradient index lens regularly using methods such as ion exchange or ion implantation. It was created in the form of an array. By arranging a pinhole array PA having pinholes corresponding to the focal position of each microlens on the focal plane of the flat microlens PM, a multi-beam array similar to the multi-beam highly directional optical system shown in FIG. A highly directional optical system can be constructed. Furthermore, the multi-beam high-directivity optical system shown in FIG. 12 corresponds to one in which a large number of high-directivity optical elements shown in FIG. 5 are arranged in parallel.

That is, on the rear surface of the gradient index lens array GA explained in FIG. array SA
A single-mode fiber array SA is used in place of the pinhole array PA shown in FIG. 10 to provide a temporary effect. moreover,
The one in FIG. 13 uses an array SH of single mode fibers SM similar to the single mode fiber array SA in place of the pinhole array PA in FIG. 11. This array SH is provided with supports S on both sides,
Each support S is a single mode fiber S centered on the focal point of each microlens of the flat microlens PM.
A large number of openings equal to the diameter of M are provided, and the input and output ends of single mode fibers SM are inserted into each opening, and the single mode fibers SM are regularly arranged.

By the way, in the multi-beam high-directivity optical systems shown in FIGS. 10 to 13, the emitted light becomes diverging light, as described above. If the emitted light comes out as diverging light from the emitting point on the back surface of the pinhole array PA, etc., the detectors such as the two-dimensional photodetector cannot be placed too far apart (if they are too far apart, the adjacent channels (The two may interfere with each other, making it impossible to measure the intensity distribution.) Therefore, it is possible to construct a multi-beam highly directional optical system in which the emitted light is also emitted as a plane wave having a distribution similar to that of the incident light. Examples are shown in FIGS. 14 to 17. The multi-beam high-directivity optical system shown in FIG. 14 corresponds to one in which a large number of high-directivity optical elements shown in FIG. 7 are arranged in parallel.

To configure this optical system, a pinhole array PA is placed between the two gradient index lens arrays GAI and GA2 explained in connection with FIG. 10, and the axis of each gradient index lens is The pinholes of the pinhole array PA are aligned and brought into close contact. With this configuration, scattered light from an incident plane wave with a two-dimensional intensity distribution is removed by this multi-beam highly directional optical system and output as a plane wave with a two-dimensional intensity distribution as well. Even if a detector such as a two-dimensional photodetector is arranged to some extent from this multi-beam highly directional optical system, the intensity distribution can be measured two-dimensionally. The multi-beam highly directional optical system shown in FIG. 15 has a confocal second plate microlens PM2 arranged behind the multi-beam highly directional optical system shown in FIG. 11. Also, the first
The multi-beam high-directivity optical system shown in FIG. 6 corresponds to one in which a large number of high-directivity optical elements shown in FIG. 9 are arranged in parallel. A detailed explanation is not necessary. Furthermore, the multi-beam highly directional optical system shown in FIG. 17 includes a second flat microlens at the core of the output end of each single mode fiber of the array SH, behind the multi-beam highly directional optical system shown in FIG. 13. They are arranged so that the front focal points of PM2 coincide.

Now, by combining a multi-beam highly directional optical system and a two-dimensional photodetector as shown in Figures 10 to 17 above, plane waves with a two-dimensional intensity distribution that are incident from a predetermined direction can be detected. It is possible to construct a bright, highly directional photodetector that can separate and detect background light such as diffused light with high sensitivity.

That is, the highly directional photodetector shown in FIG.
A two-dimensional photodetector 20 is arranged on the output side of the multi-beam high-directivity optical system 11 shown in FIG. The highly directional photodetector shown in FIG. 19 has a two-dimensional photodetector 20 disposed on the output side of the multi-beam highly directional optical system 12 shown in FIG. In FIG. 20, a two-dimensional photodetector 20 is arranged on the output side of the multi-beam highly directional optical system 13 shown in FIG. In FIG. 21, a two-dimensional photodetector 20 is arranged on the output side of the multi-beam highly directional optical system 14 shown in FIG. These figures 18 to 21
In the highly directional photodetector shown in the figure, the light emitted from the multi-beam highly directional optical systems 11 to 13 diverges from each pinhole of the pinhole array PA or the output end of the single mode fiber as shown in the figure. Therefore, if the photoelectric conversion surface 21 of the two-dimensional photodetector 20 is placed too far from the output surface of the multi-beam highly directional optical systems 11 to 13, adjacent channels will interfere with each other and the intensity distribution will change. It becomes impossible to measure accurately.

Therefore, these multi-beam highly directional optical systems 11 to 13
The two-dimensional photodetector 20 used in combination with the two-dimensional photodetector 20 must be such that these optical systems 11 to 13 and the photoelectric conversion surface 21 can be brought into close contact with each other. In addition, the two-dimensional photodetector 20
As a method for reading light intensity at dimensional positions, if only the detected intensity at the position corresponding to the center of the output end of each highly directional optical element is read out, plane waves from a predetermined direction and other scattered light, etc. can be read out. It can be separated and detected with high resolution.

Furthermore, the highly directional photodetector shown in FIGS. 22 to 25 is
A two-dimensional photodetector 20 is arranged on the output side of the multi-beam high-directivity optical systems 15 to 18 shown in FIGS. 14 to 17, respectively. These multi-beam highly directional optical systems 15~
18, as mentioned above, an incident plane wave with a two-dimensional intensity distribution has scattered light removed by this multi-beam highly directional optical system, and thus has a two-dimensional intensity distribution as well. Since it is emitted as a plane wave, even if the photoelectric conversion surface 21 of the two-dimensional photodetector 2o is placed at a certain distance from the output surface of these multi-beam highly directional optical systems 15 to 18, the intensity distribution cannot be determined two-dimensionally. It has the characteristics of being able to measure accurately.

By the way, the highly directional photodetector shown in FIGS. 18 to 25 above uses multi-beam highly directional optical systems 11 to 18. However, the multi-beam high-directivity optical system 11-1
4 pinhole array PA.

The two-dimensional photodetector 2 detects the effect of the single-mode fiber array SA and the single-mode fiber array SH, which extracts only the zero-order diffraction image of Franhofer diffraction caused by each objective lens or gradient index lens.
These pinhole arrays PA, single mode fiber arrays SA,
Alternatively, the single mode fiber array SH can be omitted. That is, as shown in FIGS. 26 and 27, the highly directional photodetector is constructed using a convex lens array such as a flat plate microlens PM or a refractive index lens array GA, and a photoelectric conversion surface 21 arranged on its focal plane. It consists of a dimensional photodetector 20. With this configuration, the plane waves incident on these highly directional photodetectors are transmitted to the focal plane by each unit convex lens LU of the lens array as shown in FIG. F diffraction image FD
Therefore, in order to read out only the zero-order diffraction image, if we sample and read out the intensity only at the ○ mark position in (C) of the figure, this sampling becomes the first
It has the same effect as the Vinhol array PA shown in FIG. 8 or FIG. 19. Therefore, it is also possible to omit the pinhole array PA and configure the highly directional photodetector of the present invention only from the convex lens array and the two-dimensional photodetector arranged on its focal plane.

Now, as mentioned above, the multi-beam high-directivity optical systems 11 to 18,
Or, flat plate microlens PM, refractive index lens array G
The two-dimensional photodetector used in combination with the convex lens array such as A is not particularly limited, but any existing two-dimensional photodetector can be used. An example is shown below.

A two-dimensional photodetector converts the two-dimensional intensity distribution of light into an electrical image signal, and the configuration of the photodetector can be roughly divided into solid-state image sensors and photoelectric conversion image sensors. be. Examples of solid-state image sensors include a parallel independent processing photodiode array shown in FIG. 29, a charge-coupled device (CCD) type image sensor 1 shown in FIG. 30, and a field-effect transistor (MOS) shown in FIG. ) type image sensor.

The parallel independent processing photodiode array is one in which photodiodes 100 having a photovoltaic effect are arranged in an array as shown in FIG. 29, and wired so that the output of each photodiode can be taken out directly. Since the signal can be extracted independently from each photodiode, it is possible to access a specific photodiode as needed, and to separate the signal with background light removed (AC component signal) and the signal without background light removed (DC component signal). It is possible to perform parallel and independent processing of the signals from each photodiode, such as switching between the two photodiodes.

As shown in FIG. 30, a CCD type image sensor is a p-type layer formed by diffusion or epitaxial growth on an n-type silicon wafer, and on top of which a p-type layer is formed by forming a picture element 110 on which three electrodes form one unit. The electrodes are arranged so that they are arranged in a matrix. By sequentially and selectively switching the voltage applied to the three electrodes that make up the picture element, a video signal is extracted while signal charges (e.g., holes) generated by incident light are sequentially transferred in one direction. has been done. Furthermore, by cooling the CCD, dark current and fixed noise at room temperature can be reduced.

As shown in FIG. 31, the M, O3 type image sensor has picture elements 120 in which two electrodes corresponding to It consists of a scanning circuit and a switch circuit made of MOS type field effect transistors. To extract a video signal from the sensor, a scanning pulse is applied to each pixel by the X and Y axis scanning signal generator shown in FIG. 31, and the signal charge generated in the pixel by the incident light is
A signal current is extracted from the picture element whose voltage on the Y-axis electrode becomes O.

Photoelectric conversion image sensors include an electrostatic focusing MCP diode array as shown in Figure 32, which is a combination of a microchannel plate (MCP) and a diode array, and a proximity type MCP diode array as shown in Figure 33.
In addition, the image orthicon shown in Fig. 34, the vidicon shown in Fig. 35, and the 36th image orthicon that combines MCP and bidicon
Photonic microscope system (V
IM system), and a photo-counting image acquisition system (PIAS system) as shown in FIG. 37, which combines an MCP and a semiconductor device detection element.

In the electrostatic focusing MCP diode array, as shown in FIG. 32, incident light causes a photocathode 130 to emit photoelectrons 136, which are accelerated and imaged by an electron lens system 131 and then enter an MCP 132. The electrons are multiplied by the MCP 132, enter the phosphor screen 133, and emit light. The light emitted from the phosphor screen is configured to pass through an optical fiber 134 and enter a diode array 135 to output a video signal.

In the proximity type MCP diode array, as shown in FIG. 33, incident light causes photocathode 140 to emit photoelectrons, which are directly incident on MCP 141. Electrons are multiplied by the MCP 141, enter the phosphor screen 142, and emit light. The light from the fluorescent screen 142 is configured to pass through an optical fiber 143 and enter a diode array 144 to output a video signal.

In the image orthicon, as shown in FIG. 34, photoelectrons 151 are emitted from a photocathode 150 in response to incident light, and the photoelectrons are accelerated and pass through a target mesh 152 to a target (with a low resistance of about several μm thick). glass plate)
Collision with 153. As a result, target 153 to 2
Next, electrons are emitted, and the emitted electrons are collected on the target mesh, and a positive charge image corresponding to the incident light is formed on the target. When the target surface is scanned by the electron beam 154 in this state, a decelerating electric field is created near the target surface, which neutralizes the positive charges on the target surface. The electrons remaining after neutralization are density-modulated by the positive charge of the target, and further reach the vicinity of the electron gun 155 via an orbit almost the same as the original electron orbit. There are 2 near the electron gun.
A secondary electron multiplier 156 is arranged, which amplifies the returned electrons and outputs a video signal.

In the vidicon, as shown in FIG. 35, the target has a configuration in which a transparent conductive film 161 and a high resistivity photoconductive film 162 are stacked on a transparent face plate 160, and after scanning with an electron beam 163, the incident light is When there is a pair of electrons and holes, the electrons pass through the transparent conductive film 161 and reach the signal electrode 16.
4, but the holes move to the surface of the photoconductive film on the scanning section side. Next, when the surface of the photoelectric film is scanned again by the electron beam, the electron beam flows into the target according to the magnitude of the surface potential due to the holes, passes through the signal electrode 164, and becomes a video signal.

The VIM system is a combination of a two-dimensional photon counter 170 and a low-afterimage vidicon 171, as shown in FIG. The light incident on the two-dimensional photon counter 171 generates photoelectrons on the photocathode 172, and these photoelectrons pass through the mesh 17.
3. The light enters an MCP (two-stage connected MCP in FIG. 36) 175 through an electron lens 174, is amplified, and hits a fluorescent screen 176 on the output surface to form a bright spot. This bright spot is imaged by the lens 177 on the photocathode of the vidicon with low afterimage, and a video signal corresponding to the incident light is obtained from the output of the vidicon.

The PIAS system, as shown in FIG. 37, is a combination of an MCP (in FIG. 37, a three-stage connected MCP) and a silicon semiconductor detector 181.

The multiplied and accelerated photoelectrons from the MCP 182 enter the semiconductor device detection element, are further multiplied by the electron impact effect upon incidence, and pass through the resistance layer of the detection element 181 to the four electrodes around the element. 183 outputs it as a current. By inputting these four outputs to a position calculation device (not shown), a position signal corresponding to the incident light can be obtained.

Although typical two-dimensional photodetectors have been described above, photodetectors that can be used in combination with the multi-beam highly directional optical system of the present invention are not limited to those described here; Alternatively, any device that can detect light one-dimensionally is applicable. When applying the multi-beam highly directional optical system of the present invention to the two-dimensional detector, the light passing through the multi-beam highly directional optical system is sent to the detector instead of the incident light of the two-dimensional photodetector. Let it enter VIM
The two-dimensional photon counter 180 used in the system may be used. The conventional two-dimensional photodetectors shown in Figs. 29 to 37 use an optical fiber plate on the incident surface to brighten the screen and flatten the screen. Of course, the multi-beam, highly directional optical system of the present invention may be used instead of the plate.

Next, an application example of the above-described highly directional photodetector will be described.

FIG. 38 and FIG. 39 show conceptual diagrams when applied to biological laser sensing tomography (laser optical tomography). In the case of FIG. 38, the highly directional light from the laser 200 is introduced into the living body 403 by, for example, a highly directional optical element 201 as shown in FIG. However, the introduction is not limited to this, for example, it may be introduced through the anus or the like. )
, irradiates highly directional light from inside the body. The light that has passed through without being absorbed or scattered by the living body 403 is detected by the highly directional photodetector 202 according to the present invention to obtain an optical tomographic image of the living body 403. The image is displayed on a monitor 203, for example. In the case of FIG. 39, contrary to the case of FIG. 38, highly directional light is irradiated from outside the body and detected inside the body.

That is, highly directional light from the laser 200 is expanded by the beam expander 204 and irradiated onto the living body 403 from the outside. For example, a highly directional optical system 205 as shown in FIG. 13 is inserted into the body, and its tip is configured so that it can be controlled from outside the body. A two-dimensional photodetector 20 is closely attached to the rear end of the highly directional optical system 205, forming a highly directional photodetector 206 as shown in FIG. , the image is displayed on a monitor 203, for example. In this case, the highly directional optical system 2
05 may be replaced by a highly directional optical element as shown in FIG. 9, and the two-dimensional photodetector 20 may be replaced by a single photodetector. As described above, an optical CT image of the living body 403 can be obtained using the highly directional photodetector of the present invention.

Next, a case where the highly directional photodetector of the present invention is applied to a conventionally known apparatus for diagnosing female breast cancer will be described with reference to a diagram showing the configuration of FIG. 40.

In the figure, 401 is a scan head, 403 is a human body, and 405
is a video camera, 407 is an A/D converter, 409 is a near-infrared light frame memory, 411 is a red light frame memory, 413 is a processor, 415 is a color conversion processing unit,
417 is an encoder keyboard, 419 is a D/A converter, 421 is a printer, 423 is a TV monitor, 42
5 is a video tape recorder. Red light (strongly absorbed mainly by hemoglobin in the blood) and near-infrared light (absorbed by blood, water, fat, etc.) are alternately transmitted through the light guide by the scan head 401 to the measured area of the human body.
For example, the breast is irradiated and scanned.

In the figure, light is emitted from the bottom upwards. As a result, the entire breast shines brightly, and this transmitted image is captured by a video camera 405, converted to a digital signal by an A/D converter 407, and the near-infrared light and red light are stored in frame memories 409 and 411 respectively via a digital switch. From the data in both frame memories, the processor 413 calculates the intensity ratio of near-infrared light and red light, and then performs color conversion processing to convert it into an analog signal, which is then used as a light absorption distribution image on a printer, television monitor, or videotape. Observe. In this conventional device, the light from the scan head 401 is not parallel light, but spreads across the tissue (breast) in the same way as if it were illuminated with a flashlight, and this is detected by two-dimensional detection such as a video camera. The resolution is not very good because it is received by a device.

Therefore, in the event of a misfire, the resolution can be improved by using, for example, a highly directional photodetector as shown in FIGS. 18 to 27 instead of the video camera 405.

Furthermore, FIG. 41 shows a conventional apparatus configuration for obtaining a light absorption distribution image using a collimated irradiation-receiving system. In this example, a laser beam is used as a light source, and an optical fiber 43
3, the laser beam is guided and irradiated onto the measurement target 435, and the transmitted light is captured by the fiber collimator 437 and sent to the detector 443.
The signal is converted into an electrical signal by the computer 451 via the preprocessing circuit 445, A/D converter 447, and interface 449. In this case, the optical fiber 433 for irradiation and the fiber collimator 437 for detection are scanned synchronously by a motor 439 to obtain a light absorption distribution image of each part to be measured, which is observed on a monitor 453. The light source is 633 nm He-Ne as red light.
An 830 nm semiconductor laser is used as the near-infrared light.

In 1977, Jobsis et al. successfully used this diagnostic device to detect the transmitted light by irradiating the heads of cats and humans with near-infrared light, and reported that the amount of transmitted light varied depending on the breathing state of the animal. Near-infrared light with a wavelength of 700 to 1,500 nm can be detected in a tissue as large as a cat's head with an irradiation amount of about 5 m"vV, which exceeds the current laser safety standards. It is about 1150 or less.It is also about 1/10 of the near-infrared light that we are exposed to on the coast, making it very safe.This device also uses optical fiber 4
33. By replacing the fiber collimator 437 with a highly directional optical element or multi-beam highly directional optical system according to the present invention, and changing the detector 443 to use a single photodetector or a two-dimensional photodetector, Resolution can be further improved.

Various embodiments of the highly directional photodetector of the present invention have been described above, but the photodetector does not necessarily have to be a two-dimensional photodetector;
It may also be a dimensional photodetector. Moreover, the present invention is not limited to the above-described embodiments, and can be modified in various ways.

Note that the resolution of the multi-beam high-directivity optical system shown in Figures 10 to 17 is determined by the diameter of each high-directivity optical element, so if you use the thinnest elements possible, you can achieve higher resolution. Plane waves with two-dimensional intensity distribution can be detected.

〔Effect of the invention〕

In the first and second highly directional photodetectors of the present invention,
The highly directional optical element consists of a convex lens and a pinhole or optical fiber arranged on its focal plane, and the core of the pinhole or optical fiber has a diameter less than or equal to the first dark ring of the Franphaux core diffraction image formed by the front 8-convex lens. Therefore, most of the energy of the plane wave component incident on the convex lens from a predetermined direction can be extracted, but most of the components and scattered components coming from a direction different from that direction can be removed. Therefore, a multi-beam high-directivity optical system configured by bundling a plurality of such high-directivity optical elements can also extract only a plane wave having a one-dimensional or two-dimensional intensity distribution incident from a predetermined direction with good resolution. By combining this with a one-dimensional or two-dimensional photodetector, a highly directional photodetector with high directivity, resolution, and sensitivity can be obtained. It becomes a highly directional photodetector suitable for detection.

Furthermore, in the third highly directional photodetector of the present invention, 1
A one-dimensional or two-dimensional photodetector disposed at the focal plane of a two-dimensional or two-dimensional convex lens array is configured to sample and separate and read out only the zero-order diffraction image of Franhofer diffraction by each convex lens. Therefore, only plane waves with a one-dimensional or two-dimensional intensity distribution incident from a predetermined direction can be separated from surrounding scattered light, etc., and detected brightly and with good resolution. Similarly, the absorption distribution inside a scattering body such as a living body can be detected. This is a highly directional photodetector suitable for

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the basic principle of the highly directional optical element constituting the multi-beam highly directional optical system used in the highly directional photodetector of the present invention, and Figs. 2 to 9 are respectively Figures 10 to 17 are diagrams for explaining an embodiment of a highly directional optical element, and Figures 10 to 17 are diagrams for explaining an embodiment of a multi-beam highly directional optical system used in a highly directional photodetector of the present invention. 18 to 21 are diagrams for explaining some embodiments of the first highly directional photodetector according to the present invention, and FIGS. 22 to 25 are diagrams for explaining some embodiments of the first highly directional photodetector according to the present invention. 26 and 27 are diagrams for explaining two embodiments of the third highly directional photodetector according to the present invention, FIG. 28 shows the third embodiment according to the present invention.
Figure 29 for explaining the action of the highly directional photodetector.
37 is a diagram illustrating an example of a known two-dimensional photodetector, and FIGS. 38 and 39 show a case where the highly directional photodetector according to the present invention is applied to biological laser sensing tomography. 40 is a diagram showing the configuration when the highly directional photodetector according to the present invention is applied to a conventionally known breast cancer diagnostic device for female breasts, and FIG. 41 is a diagram showing a conventional method for obtaining a light absorption distribution image. Diagrams showing the configuration of the device, Figures 42 and 4
FIG. 3 is a diagram for explaining the highly directional optical element proposed in the previous application. L...Convex lens, Po...Lens opening %Pl...
Inlet opening, P2... pinhole, ○b, Obl, Ob
2...Objective lens, P...Binho Nobe GLSGL
I, GL2...Gradient index lens, SM...Single mode fiber, B...Adhesive, GASGAI,
GA2...gradient index lens array, P\...pinhole array, PM, PMI, PM2...flat plate microlens, SA...single mode fiber array, SH...single mode fiber array, S...
・Support, LU...Unit convex lens, FD...Franphaffer diffraction image, 11-18...Multi-beam highly directional optical system, 20...Two-dimensional photodetector, 21...Photoelectric Conversion surface, 200... Laser, 201... Highly directional optical element, 202.206... Highly directional photodetector, 203
...Monitor, 204...Beam expander, 205.
・Highly directional optical system, 403... Biological body

Claims (8)

[Claims] (1) Consisting of a convex lens and a pinhole placed on its focal plane, the pinhole has a diameter equal to or less than the first dark ring of the Franphofer diffraction image formed by the convex lens, and the plane wave incident on the convex lens from a predetermined direction A multi-beam highly directional optical system configured by bundling a plurality of highly directional optical elements that extract only components, and a one-dimensional or two-dimensional photodetector placed on the output side of the multi-beam highly directional optical system. 1. A highly directional photodetector comprising: a highly directional photodetector configured to extract and detect only a plane wave having a one-dimensional or two-dimensional intensity distribution incident from a predetermined direction. (2) In the highly directional optical element, a second convex lens substantially the same as the convex lens is arranged on the output side of the pinhole, and the front focal plane of the second convex lens is the pinhole surface. 2. The highly directional photodetector according to claim 1, wherein the highly directional photodetector is arranged so as to coincide with the pinhole, and the light component passing through the pinhole is converted into a plane wave and outputted. (3) Consisting of a convex lens and an optical fiber disposed on its focal plane, the core of the optical fiber has a diameter equal to or less than the first dark ring of the Franphofer diffraction image produced by the convex lens, and a plane wave incident on the convex lens from a predetermined direction A multi-beam highly directional optical system configured by bundling a plurality of highly directional optical elements that extract only components, and a one-dimensional or two-dimensional photodetector placed on the output side of the multi-beam highly directional optical system. 1. A highly directional photodetector comprising: a highly directional photodetector configured to extract and detect only a plane wave having a one-dimensional or two-dimensional intensity distribution incident from a predetermined direction. (4) In the highly directional optical element, a second convex lens substantially the same as the convex lens is arranged on the output side of the optical fiber, and the front focal plane of the second convex lens is the output surface of the optical fiber. 4. The highly directional photodetector according to claim 3, wherein the highly directional photodetector is arranged so as to coincide with the optical fiber and converts a light component passing through the optical fiber into a plane wave and outputs the plane wave. (5) Consisting of a one-dimensional or two-dimensional convex lens array and a one-dimensional or two-dimensional photodetector placed on its focal plane,
The photodetector is configured to sample and separate and read out only the zero-order diffraction image of Franphofer diffraction caused by each convex lens, and detects only a plane wave having a one-dimensional or two-dimensional intensity distribution incident from a predetermined direction. A highly directional photodetector characterized in that it is configured to extract and detect. (6) The highly directional photodetector according to any one of claims 1 to 5, wherein the convex lens is composed of an objective lens. (7) The highly directional photodetector according to any one of claims 1 to 5, wherein the convex lens is composed of a gradient index lens. (8) The highly directional photodetector according to any one of claims 1 to 5, wherein the convex lens is composed of a flat microlens.