JPS62200308A - Photodetector - Google Patents

Abstract

PURPOSE:To efficiently lead a signal light to a photodetector and to detect the signal of good SN ratio by providing a means which intercepts the external light, close around the exit face of a photoconductor which transmits optical information and the detecting face of the photodetector. CONSTITUTION:Optical information is emitted at a prescribed angle from an e it face 1a of a photoconductor 1 to a photodetecting face 2b of a photodetecor 2. A filter 7 is slightly inclined to the optical axis and is arranged to eliminate noise light mixed in the signal light. A light shielding means 8 is provided on th outside of the exit range between the exit face 1a and the detector 2 to intercept the light from the external, and gaps among the phtotoconductor 1, the filter 7, the detector 2, and the light shielding means 8 are closed with a filler 9. Thus, the noise light from the external is cut off to detect the signal light with a good SN ratio.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention efficiently converts light emitted from the end face of a light-transmitting light guide made of an optical fiber, an optical fiber bundle, resin, glass, or the like. Disgrace to the detector (related to the device)

[Prior art]

In recent years, reflecting the information society, optical communication systems that transmit information using light have developed rapidly.

Among these, optical fibers, which are light guides for information communication, are attracting attention as innovative materials that guide light to the output end while reflecting it internally. Furthermore, this optical fiber is gradually beginning to be used in communication lines and various devices because it can be easily converted into an electrical signal by arranging a photodetector opposite the output end face.

However, when converting optical information from an optical fiber into an electrical signal, the S/N ratio of photodetection is naturally affected by optical loss at the end face of the optical fiber, scattering on the light receiving surface of the photodetector, intrusion of noise light, etc. decreases. In particular, when the light-receiving surface of a light guide is used as a sensor end for light detection, the light that should serve as a signal is weak, but there is a large amount of light that becomes noise (very often there is), making it very difficult to detect signal light. Met.

[Purpose of the invention]

The purpose of the present invention is to
It is an object of the present invention to provide a photodetection device that can efficiently guide signal light to a photodetector and perform signal detection with a good S/N ratio.

[Structure of the invention]

For this purpose, the present invention is configured by providing a light shielding means for blocking external light around the output surface of the light guide and the light detection surface of the photodetector.

〔Example〕

Examples of the present invention will be described below. First, FIG. 1 is a diagram showing the relationship between the light guide 1 and the photodetector 2, and the light 3 emitted from the light exit surface 1a including the circular end face of the light guide 1 with a radius r is A constant angle θ from a line 4 passing through the center of the light body 1. The light is emitted toward the light receiving element 2a of the photodetector 2 at the following angles. After this light 3 is incident on a point 2c within the light detection surface 2b of the light receiving element 2a, it becomes an electric signal and is extracted from the signal line 5.

Note that the constant angle θ here. is uniquely given by the numerical aperture NA inherent to a light guide such as a fiber, NA=(nl ” + nz ”)”2θ.=sin
−' (NA). n, , and nz are the core material of the light guide, respectively;
It is the refractive index of the coating material.

FIG. 2 shows how light is actually emitted from the emission surface 1a, and 6 is the emission range.

This output range 6 has a truncated cone shape with the output surface 1a as the upper base and the axis coaxial with the center line 4 of the light guide 1, and the angle between the side line 6a of the range and the center line 4 is θ. It becomes. Hereinafter, the space of this cone will be referred to as the emission range.

FIG. 3 shows the relationship between the emission range 6 and the photodetector 2. Note that the light guide 1 is omitted in this figure. A circle 6b indicates the intersection boundary between the emission range 6 and the light detection surface 2b of the light receiving element 2a of the photodetector 2, and optical information is detected from inside this circle 6b. The output range 6 is such that the axis 4 is located at the light detection surface 2 as shown in this figure.
It is preferable to be substantially perpendicular to the substantially center of b. Also,
Although it is preferable that the circle 6b is somewhat apart from the edge 2d of the photodetection surface 2b, it may overlap as long as it does not have any influence. The photodetector 2 arranged in this way has a light guide 1
Since all of the light from the photodetecting surface 2b hits the photodetecting surface 2b, the signal light is incident accurately and quantitatively.

Note that here, a light receiving element 2 having a square light detection surface 2b is used.
Although the example using the light receiving element a has been given, the present invention is not limited to this, and other light receiving elements may be used as long as they have the light detection surface 2b including the circle 6b.

The noise light is mixed with the signal light and guided from the light guide l through a first path, and a second path which enters the light detection surface 2b from between the exit surface 1a and the edge 2d of the light detection surface 2b in FIG. It invades from two routes:

Noise light entering from the first path is detected through the signal light transmission path and cannot be removed by a light shielding member, but it can be removed by providing a filter in the emission range 6. . At this time, it is preferable to arrange a filter having signal light transmission characteristics so as to cross any optical path in the emission range 6.

This situation is shown in FIG. 7 is a plate-shaped filter;
The intersection line 7a with the emission range 6 is arranged to form a smooth closed curve such as an ellipse, and the light emitted from the emission surface 1a always hits the filter, and only the signal light reaches the photodetector 2. .

Note that here, the filter 7 is arranged slightly diagonally with respect to the center line 4, but doing so has the effect of reducing reflected light from the filter surface from entering the light guide 1 again. .

Noise light entering from the second path can be removed by providing a light shielding means between the output range from the output surface 1a to the photodetector 2 and the outside.

FIG. 5 shows an example of light shielding. (a) to ((a) in this figure 5)
C) all show cross sections along a plane including the center line 4 in FIG. 4, and the same reference numerals are given to the same parts as those described above.

As shown in FIG. 5(a), when a light shielding member 8 is provided and this light shielding member 8 is fixed to the light guide 1, the filter 7, and the photodetector 2 with adhesive, noise light from the outside can be detected by photodetection. Vessel 2
It will no longer be incident on .

Note that when the detection light is weak, the gaps Gl, G2,
Since light leakage from G3 also has an effect, this gap is closed with fillers 9a to 9°, as shown in FIG. 5(b). Thereby, light leakage can be prevented between the light guide 1 and the light shielding member 8, between the filter 7 and the light shielding member 8, and between the photodetector 2 and the light shielding member 8. As a filler,
It is preferable to use a black material that absorbs as much light as possible and is easy to adhere to. For example, it is effective to use carbon-mixed rubber, black malt plain, or the like.

Figure 5 (C) shows a photomultiplier tube (hereinafter referred to as P) as a photodetector.
It is called MT. )2' is shown below. In this example, a fiber bundle bound by a jig 10 is used for the light guide 1. The PMT 2' is fitted into a socket 11 and surrounded by a light shielding material 12 and a magnetic shielding material 13. The filter 7 is fixed to the filter jig 14 with a stopper 17 so as to be sandwiched between the ring-shaped close contact light shielding members 15 and 16, and the filter jig 14 is fixed to the magnetic shielding material 13 and the jig 10, and the filter jig 14 is fixed to the magnetic shielding material 13 and the jig 10. The fixed part is filled with filling material 18,
It is shielded by a light-shielding material 19 to prevent light leakage from the outside.

With this configuration, only the light that has passed through the filter 7 out of the light emitted from the light guide 1 reaches the photocathode 2a' of the PMT 2', so that optical information can be detected extremely well.

FIG. 6 shows the distance between the output surface 1a of the light guide 1 and the light detection surface 2b of the photodetector 2. Output surface 1 with radius r,
When the photodetection surfaces 2b with radius a and radius r are placed apart from each other by a distance d, in order for light to be detected without loss, if the photodetection range boundary line 6a intersects with the photodetection surface 2b, good. That is, when the relationship r,+d-tan θ0≦r3 is satisfied, light can be detected without loss. However, in order to satisfy the above equation, r should not be increased unnecessarily (it is preferable to set it close to θ so that the equality holds as much as possible.This may depend on the characteristics of the photodetector 2, but θ. In the range of ≦45°, d≦4r,
It is desirable that the following conditions are met.

In addition, the diameter φ. When using a light guide made of bundled fibers, φ. An arrangement where d is less than d is preferable, and d≧10φ. It is even more preferable.

This is the optical detection surface 2b on one fiber facing east.
When light enters at a level that degrades the optical fiber, if the fiber is in close contact with or very close to the optical detection surface 2b, the optical detection surface 2b will be locally damaged, but d=nφ (n
is a positive number), the optical power density on the photodetecting surface 2b decreases by 1/n'' times, and the optical power density on the photodetecting surface 2b
It becomes possible to prevent the deterioration of. n is 10
The above values are preferable.

FIGS. 7(a) to 7(d) show still another embodiment, in which the light guide 1 and the photodetector 20 have the same or different outer diameters.
In between, the outer diameter is the same as that of the light guide 1 or the photodetector 20.
Alternatively, a larger filter 21 is interposed, and the outside of their joint portion is covered with a light-shielding material 22.

Note that the above system can also be applied to reading weak optical information from a phosphor. A phosphor is a material that, when irradiated with light of a certain wavelength, is triggered by the energy of that light and emits light of a different wavelength.At this time, the power of the emitted light is proportional to the power of the irradiated light. Several orders of magnitude weaker. The present invention is extremely effective for detecting weak optical information buried in such noise.

Next, an example of application to a device using a storage type phosphor will be described with reference to FIG. This device emits photostimulating excitation light 25 from a laser light source 24 while moving (sub-scanning) a radiation image conversion panel 23 (hereinafter referred to as conversion panel) having a photostimulable phosphor layer in the direction of arrow y. When the conversion panel 23 is scanned in the direction of the arrow X, the scanning line becomes like 24a. ), the conversion panel 2
This is to read the radiation image recorded in 3.

When a photostimulable phosphor is irradiated with radiation, such as X-rays or ultraviolet rays, a part of the energy of this radiation is accumulated, and if it is then irradiated with photostimulable excitation light, it will emit light according to the accumulated energy. Stimulated luminescence occurs.

Therefore, a conversion panel was formed using this photostimulable phosphor, and an X-ray image of a human body, etc. was recorded on the conversion panel, and then this was scanned with photostimulation excitation light to generate stimulated luminescence. When detected by a photodetector, the radiation image formed on the panel can be read.

In this device, the stimulated excitation light becomes noise light and the stimulated emission light becomes signal light. Therefore, if the condenser and detector are configured as shown in FIG. 5(C) and a filter that transmits stimulated emission light and blocks stimulated excitation light is used as a noise light cut filter, S Image reading with a good /N ratio can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, since the light shielding means for blocking external light is provided around the output surface of the light guide and the light detection surface of the photodetector, there is no possibility of being affected by noise light from the outside. , signal light can be detected with a good S/N ratio.

[Brief explanation of drawings]

Fig. 1 shows the relationship between the light guide and the photodetector, Fig. 2 shows the state of the light emitted from the light guide, and Fig. 3 shows the light emitted from the light guide to the photodetector. FIG. 4 is a diagram showing a filter interposed on the incident side of the photodetector, FIGS. 5(a) to (C) are explanatory diagrams for blocking noise light from the outside, and FIG. The figure is an explanatory diagram of the distance setting between the light guide and the photodetector, and Figures 7+al to (d) are explanatory diagrams of the filter and light shielding material loaded in the part between the light guide and the photodetector. FIG. 8 is a diagram showing an example in which the present invention is applied to image reading of a radiation image conversion panel. DESCRIPTION OF SYMBOLS 1... Light guide, 1a... Light emission surface, 2... Photodetector, 2a... Light receiving element, 2b... Light detection surface, 3...
- Light, 4... Center line, 5... Signal line, 6... Output range, 7... Filter, 8... Light shielding member, 9a to 9
c... filler, 10... jig, 11... socket, 12... light shielding material, 13... magnetic shielding material, 14
... Filter jig, 15.16 ... Adhesive light-shielding material,
17... Stopper, 18... Filler, 19... Light shielding material, 20... Photodetector, 21... Filter, 22
... Light shielding material, 23 ... Conversion panel, 24 ... Laser light source, 25 ... Stimulated excitation light, 26 ... Light collector,
27...PMT. Agent Patent Attorney Tsuneaki Nagao Figure 5

Claims (2)

[Claims] (1) In a photodetection device that transmits optical information through a light guide and guides it to a photodetector, external light is blocked around the exit surface of the light guide and the photodetection surface of the photodetector. A photodetecting device characterized by being provided with a light blocking means. (2) The photodetection device according to claim 1, wherein the light shielding means is substantially in close contact with the boundary between both surfaces of the emission surface and the photodetection surface.