JPH0284605A - Photodetector - Google Patents

Abstract

PURPOSE:To enhance the utilization rate of the light from a light source by reflecting the radial light emitted from a photoconductor in the mirror part of a holed mirror and making this reflected light incident to a light receiving element by an optical system. CONSTITUTION:The incident diffracted light is reflected by the mirror part 53 and is made incident to the mirror 102 of a reflector 100; thereafter, the light progresses along an optical axis 72a and is condensed to the center of the light receiving face of the light receiving element 70. The light receiving element 70, therefore, provides the effect of detecting the light by conduction of a photodiode arising from the photodetection of the element. The beam light from the light emitting element 30 is hardly lost at the time of the passage through the central hole 52 of the holed mirror 50, the reflection by the holed mirror 50 and the reflection by the mirror 102. The holed mirror 50, a planoconvex lens 40 and the mirror 102 are disposed into the optical route between the light emitting element 30, the optical fiber 90 and the light receiving element 70 in this way, by which the utilization rate of the beam light from the light emitting element 30 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Industrial Application] The present invention relates to a photodetection device, and particularly to a photodetection device suitable for employing an optical waveguide such as an optical fiber optical waveguide.

[Prior art]

Conventionally, in this type of photodetection device, for example, a beam splitter is disposed between a laser light source and an optical fiber, and the laser light from the laser light source is incident on the optical fiber through the beam splitter. The reflected laser light that is reflected by the object to be detected after being emitted from the fiber is made to enter the optical fiber again, and then the laser light that is emitted from the same optical fiber is reflected by a beam splitter and made to enter the photodetector. (Refer to p. 139 of "Optical Fiber Sensors" edited by Takataka Okoshi and published by Ohmsha, 1986).

[Problem to be solved by the invention]

However, although this type of configuration has the advantage of having a high degree of freedom in detecting the object to be detected because it uses a single optical fiber, it also uses a beam splitter, so the laser beam from the laser light source is There is a problem in that the light utilization rate until the light reaches the photodetector is low.

Incidentally, when a beam splitter is used, the light utilization rate is 25% even in an ideal case (when there is no surface reflection or internal absorption at the beam splitter).

Therefore, in order to cope with this problem, the present invention aims to provide a photodetecting device that increases the light utilization rate by effectively utilizing a mirror with a hole.

[Means to solve the problem]

In solving this problem, the configuration of the present invention includes a light source,
between the light source and the optical waveguide, the optical waveguide comprising a light-receiving element, the light from the light source entering the object to be detected, and the reflected light from the object to be detected being emitted as radial light; a mirror with a hole, the mirror having a hole disposed in the hole for passing the light from the light source to the optical waveguide, and a mirror portion for receiving and reflecting radial light from the optical waveguide; The present invention further includes an optical system that converges the reflected light from the mirror portion and makes it incident on the light receiving element.

[Effect]

In the present invention configured as described above, by employing a mirror with a hole in the optical system, the light from the light source is directly incident on the optical waveguide through the hole of the mirror with a hole, and the radial light emitted from the optical waveguide is The light of be able to. As a result, the light utilization efficiency of the light from the light source of this type of photodetection device can be significantly increased.

Further, if the spherical center of the mirror portion of the mirror with a hole is positioned offset from the output axis of the optical waveguide, and the mirror portion is positioned at an angle with respect to the output axis, the optical waveguide can be However, a sufficient amount of light incident on the mirror portion can be ensured while minimizing the size and shape of the mirror with holes, so that the light utilization rate can be further increased.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.
The figure shows an example of a photodetection device according to the present invention. This photodetecting device includes a housing 10 consisting of a pair of housing members 10a and 10b.
0a is coaxially assembled to the housing member 10b by bonding its opening to the opening of the housing member 10b with an adhesive. On the bottom wall of the housing member 10a,
A pair of holding holes 11 and 12 are bored vertically so as to have axes parallel to the axis of the housing member 10a. 11 and screw 20.
It is attached by a.

A light emitting element 30 is assembled into the large diameter part 22a of the stepped hole 22 bored in the holder 20 through the auxiliary plate 13, and this light emitting element 30 emits light generated by conduction from the built-in light emitting diode. is emitted as a beam of light through the light emitting surface 31 along the optical axis 31a. Medium diameter portion 22b of stepped hole 22
A plano-convex lens 40 is assembled in the , and this plano-convex lens 40 combines the beam light from the light emitting element 30 with parallel light.
7, the light is emitted into the small diameter portion 22c of the stepped hole 22 along the optical axis 31a. Further, on the annular inner end surface 23 formed at a predetermined acute angle θ with respect to the optical axis 31a in the holder 20, a holed mirror 5o is bonded with adhesive at its back surface 51, and this holed mirror 5o is attached at the center thereof. The parallel light from the plano-convex lens 4o is passed through the hole 52 along the optical axis 31a toward the housing member 10b.

In this case, the axis of the central hole 52 is inclined downward by a predetermined acute angle θ with respect to the optical axis 31a, and the inner diameter of the central hole 52 allows all of the parallel light from the plano-convex lens 4o to pass through the central hole 52 along the optical axis 31a. It is determined that it will pass. Further, the mirror portion 53 of the mirror with a hole 5o is formed of a concave mirror having a predetermined radius of curvature, and the spherical center of this mirror portion 53 is located on the optical axis 31a. Note that the auxiliary plate 13 is attached to the bottom wall of the housing member 10a by screws 13a, 13a. Holding hole 1 of housing member 10a
2, a cylindrical holder 60 is assembled with screws 62 with its inner end 61 locked to the inner end flange 12a of the holding hole 12, and a light receiving element 70 is installed in the holder 60. are attached with adhesive. The light-receiving element 70 receives, through the light-receiving surface 72, light traveling along the optical axis 72a as will be described later, using its built-in photodiode.

A pair of retaining holes 14. are provided in the bottom wall of the housing member 10b.
15 is coaxially bored with each of the holding holes 11 and 12, and a holder 80 is fitted with a stepped cylindrical portion 80a and a flange portion 80b attached to the bottom wall of the housing 10b. An optical fiber 90 is installed coaxially with the optical axis 31a at its inner end 90a in the zero-stage cylindrical part 80a which is abutted and assembled by screws 81 and 82. The optical fiber 90 allows the parallel light from the center hole 52 of the holed mirror 50 to enter and propagate along the optical axis 31a at the inner end 90a.
The light is made incident on the object to be detected from its outer end (not shown).

Further, this optical fiber 90 receives reflected light from the object to be detected at its outer end and propagates it, and diffracts the light from its inner end 90a to the mirror section 50 of the mirror with hole 50.
3. In this case, the numerical aperture NA of the aperture end surface 91 of the inner end 90a of the optical fiber 90 is selected to ensure a sufficient opening of the diffracted light incident on the mirror section 53. In order to increase the proportion of the beam light from the element 30 guided to the light receiving element 70 (hereinafter referred to as light utilization rate), the cross-sectional area of the plane specified on the mirror part 53 by the spread of the incident diffracted light is set as Sa. When the cross-sectional area of parallel light passing through the central hole 52 of the mirror 50 with a hole is sb, Sa is made to be sufficiently larger than sb. Note that the light utilization rate is (S a −S
b) / S a.

A reflector 10 is provided in the holding hole 15 of the housing member 10b.
0 is coaxially assembled at its cylindrical base 101 with screws 103. Further, the reflector 100 is a mirror 102
The mirror 102 is bonded to the inclined inner end surface of the cylindrical base 101. In such a case, mirror 10
The angle of inclination of the second axis with respect to the optical axis 72a is such that the reflected and diffracted light from the mirror section 53 is focused by the mirror 102 and the optical axis 72a is
The light is directed toward the light receiving element 70 along the direction a so as to be reflected.

In this embodiment configured as described above, the light emitting element 30
When a light beam is generated from the plane, this light beam passes through the plano-convex lens 4
0, the light becomes parallel light, passes through the center hole 52 of the mirror with a hole 50, and enters the inner end 90a of the optical fiber 90. In such a case, even if the axis of the central hole 52 is inclined downward with respect to the optical axis 31a, most of the parallel light from the plano-convex lens 40 will be directed to the central hole 5 because the inner diameter of the central hole 52 is appropriately determined as described above.
Pass 2. The parallel light that has entered the optical fiber 90 as described above propagates along the optical fiber 90, exits from its outer end, and enters the object to be detected.

When the incident light is reflected by the object to be detected and enters the optical fiber 90 again from its outer end, the incident light propagates along the inside of the optical fiber 90 and enters the inner end 90.
The diffracted light is output from a and enters the mirror portion 53 of the mirror 50 with holes. In this case, since the numerical aperture NA of the inner end 91 of the optical fiber 90 is appropriately determined as described above, the diffracted light passes through the holed mirror 5 with a sufficient spread.
The light is incident on the mirror section 53 of 0.

The diffracted light incident as described above is reflected by the mirror portion 53, enters the mirror 102 of the reflector 100, is reflected, travels along the optical axis 72a, and is focused at the center of the light-receiving surface of the light-receiving element 70. Therefore, the light-receiving element 70 performs a light-detecting function by conducting the photodiode as the light-receiving element 70 receives light. In such a case, the beam light from the light emitting element 30 passes through the holed mirror 5.
Since there is almost no loss when passing through the center hole 52 of 0, when reflected by the mirror 50 with a hole, and when reflected by the mirror 102, the optical path between the light emitting element 30, the optical fiber 90, and the light receiving element 70 is The light emitting element 30 can be created by simply arranging the mirror 50 with a hole, the plano-convex lens 40, and the mirror 102.
It is possible to significantly improve the light utilization efficiency of the beam light from. In addition, since the mirror part 53 of the mirror with hole 50 is a concave mirror,
Helps reduce the number of optical parts. In addition, each screw 13a, 2
0a.

The position of each component can be finely adjusted by adjusting the degree of screwing such as 62, 81, 82, etc. In such a case, if precision machining is performed, it is possible to fix with adhesive instead of these screws. Further, the predetermined acute angle θ in the mirror with hole 50
By setting the angle to about 60' to 80°, the mirror with hole 50
It is possible to reduce the size of the mirror part 53, and to suppress spherical aberration of the mirror part 53.

In carrying out the present invention, as shown in FIG. 2, a biconvex lens 40A is used instead of the plano-convex lens 40, and the center hole 52 of the mirror with hole 50 is located at the center along the same axis as the optical axis 31a. It may be formed and implemented as a hole 52a.

Further, in implementing the present invention, the light from the plano-convex lens 40 is not limited to parallel light, but may be convergent light.

Furthermore, in carrying out the present invention, as shown in FIG. 3, a holed mirror 50A having a plate-shaped mirror portion 53a and a convex lens 50B are used in place of the holed mirror 50, and the light receiving element 70 and the mirror 102 are connected to each other. A convex lens 100A may be placed between the two.

Further, in implementing the present invention, a mirror with holes 50C arranged as shown in FIG. 4 may be used instead of the mirror with holes 50 shown in FIG. 1. Mirror with hole 50C
has almost the same configuration as the mirror with holes 50 shown in FIG. It is maintained at a rotated position such that the spherical center 0 of the portion 53c is located below the optical axis 31a. In this case, the mirror portion 53c is formed as a concave mirror having the same radius of curvature as the mirror portion 53 of the mirror with a hole 50, and the spherical surface of the mirror portion 53c is aligned with the optical axis 31a.
The inner end 9 of the optical fiber 90 is centered at the intersection 01 with
It has the minimum necessary surface area so as to symmetrically receive all the diffracted light emitted from 0a at the aperture angle θNA (corresponding to the numerical aperture NA). Note that the center hole 52 of the holed mirror 50C (same as the center hole 52 of the holed mirror 50) is deviated downward as it deviates downward from the intersection 0 of the spherical center 0.

However, if the mirror with hole 50C is arranged like this,
This holed mirror 50C has its central hole 52 as the optical axis 31a.
All the diffracted light from the optical fiber 90 is received in a state where the optical fiber 90 is shifted downward. As shown in FIG.
As in the case where 0C is arranged with the spherical center 0 aligned with the optical axis 31a, the optical fiber 9
The lower part of the diffracted light from the optical fiber 90 cannot enter the mirror 50C with a hole, or the central part of the diffracted light from the optical fiber 90 (which has high intensity) passes through the center hole 52 of the mirror 50C with a hole. The efficiency of the amount of reflected light at the mirror portion 53c can be maximized while suppressing the dimensions and shape of the mirror with holes 50C to the necessary minimum without causing problems such as storage.

Incidentally, NA = 0.57 (θNA" 34.81°), the distance between the intersection 01 and the opening end surface 91 of the optical fiber 90 is 6.5 (mm), and the radius of curvature of the mirror with hole 50C is 5. (mm) and 10.C0 (see Figure 4) is 4 degrees, all of the diffracted light from the optical fiber 90 enters the mirror portion 53c centered at the intersection 0 with respect to the mirror portion 53C. was confirmed.

Further, in carrying out the present invention, the mirror 50C with a hole as shown in FIG. 5 is moved in parallel downward as shown in FIG. 6 in relation to the arrangement of the optical fiber 90, and at the same time, The optical axis (optical axis 3
Even if the arrangement is changed so that the optical fibers (coinciding with 1a) intersect at an angle of 4° with respect to the axis 90b of the optical fiber 90, the same effect as in the case of the configuration shown in FIG. 4 can be ensured.

Note that 10 and CO are 4''.

Furthermore, in implementing the present invention, an optical system block 200 as shown in FIG. 7 is adopted in place of the optical system of the convex lens 40A, mirror with hole 50A, convex lens 5OB, mirror 102, and convex lens 100A in FIG. It may also be carried out. In this case, the optical system block 200 is composed of an optical member 201 and an optical member 202, and the optical member 201 is joined to the joining surface of the optical member 202 at its joining surface. However, both optical members 201°20
A film of optically transparent adhesive having the same refractive index as that of both optical members 201 and 202 is coated on a portion of each bonding surface of 2 that includes the optical axis 31a. A silver vapor deposition film 202a forming a mirror surface is formed on the remaining portion. Moreover, since each optical member 201, 202 is formed of, for example, BK-7 glass, the critical angle δ (see FIG. 7) (wavelength input =
When the plane 202b is formed at an angle greater than δ=41.5° at 880 nm, there is no need to provide a reflective film such as a silver vapor deposited film on the plane 202b.In addition, in FIG. 202a, the convex surface 202c, the flat surface 202b, and the convex surface 202d of the optical member 202 are the left convex surface of the convex lens 40A in FIG. 3, and the mirror with hole 50A.
This corresponds to the mirror portion 53a, the right convex surface of the convex lens 50B, the reflective surface of the mirror 102, and the left convex surface of the convex lens 100A, respectively.

Furthermore, in implementing the present invention, a notch 202A having an air layer may be formed as shown in FIG. 8 instead of the silver vapor deposited film 202a in FIG. 7. In such a case, a spacer 202B is interposed at the outer edge of each notch 202A in order to supplement the adhesive strength of the transparent adhesive between the centers of the joint surfaces of both optical members 201 and 202.

Further, in carrying out the present invention, a semiconductor laser, for example, may be used as the light emitting element 30, a device having a built-in phototransistor, for example, may be used as the light receiving element 70, and an optical fiber 90 may be used as the light receiving element 70. However, in general, an optical waveguide may be used as the optical waveguide.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view of essential parts showing a first partial modification of the embodiment, and FIG. 3 is a sectional view showing a second partial modification of the embodiment. FIG. 4 is a cross-sectional view of the main part showing the third partial modification, FIG. 5 is an explanatory diagram for comparison with the configuration of FIG. 4, and FIG. 6 is the embodiment described above. A sectional view of a main part showing a fourth partial modification example, and FIGS. 7 and 8 are views showing a sectional view of a main part when each optical member in the above embodiment is made into a single optical system block. be. Explanation of symbols 30, . . . Light emitting element, 40. ,, plano-convex lens, 40A,
50B, 100A, , convex lens, 50° 50A, 50
C., mirror with hole 52.52a. Center hole, 53.53a, 53c, S near part, 7
0. , , light receiving element, 90. ,,optical fiber 102,,,
Mirror 200. ,,optics block. lυυA Figure 3

Claims (2)

[Claims] (1) An optical waveguide including a light source and a light receiving element, which allows the light from the light source to enter a detected object and emits reflected light from the detected object as radial light; A hole disposed between the light waveguide and the light waveguide to allow the light to pass from the light source to the light waveguide, and a mirror portion that receives and reflects the radial light from the light waveguide. A photodetecting device comprising: an optical system having a mirror to converge reflected light from the mirror section and to make the reflected light enter the light receiving element. (2) A first feature in which the mirror portion of the mirror with a hole is positioned with its spherical center offset from the output axis of the optical waveguide and at an angle with respect to the output axis. The photodetection device described in section.