JP2780300B2 - Photodetector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector, and more particularly to a photodetector suitable for employing an optical waveguide such as an optical fiber or an optical waveguide.

(Prior art)

Conventionally, in this type of light detection device, for example, a beam splitter is disposed between a laser light source and an optical fiber, and laser light from the laser light source is made to enter the optical fiber through the beam splitter. The reflected laser light emitted from the fiber and reflected by the object to be detected is again incident on the optical fiber, and then the laser light emitted from the optical fiber is reflected by a beam splitter and incident on a photodetector. (Optical fiber sensor No. 139, edited by Takataka Ohkoshi, published by Ohmsha in 1986)
Page).

[Problems to be solved by the invention]

However, although such a configuration has the advantage that a single optical fiber is employed and thus has a high degree of freedom for detection of an object to be detected, the use of a beam splitter allows the laser beam from the laser light source to be used. There is a problem that the light utilization rate until the light reaches the light detector is low. Incidentally, when the beam splitter is employed, for example, even in an ideal case (when there is no surface reflection or internal absorption by the beam splitter), the light utilization rate is 25%.

In view of the above, an object of the present invention is to provide a photodetecting device in which the light utilization factor is increased by effectively utilizing a mirror with a light transmitting portion.

[Means for solving the problem]

In order to solve the above problem, according to the present invention, there is provided a light source and a light receiving element, and an optical waveguide that introduces light from the light source and emits the light toward a detection target, and the emitted light is reflected by the detection target. An optical waveguide that introduces this reflected light and emits as radial light, and a mirror with a light-transmitting portion disposed between the light source and the optical waveguide, from the light source to the optical waveguide. A mirror having a light-transmitting portion having a light-transmitting portion that transmits light and a mirror portion that receives and reflects the radial light from the optical waveguide, and reflected light from the mirror portion converges on the light-receiving element. A light detection device including an optical system configured to be incident.

[Function and effect of the invention]

In the present invention thus configured, the light-transmitting mirror is disposed between the light source and the optical waveguide, and light from the light source is introduced into the light waveguide through the light-transmitting portion of the light-transmitting mirror. Then, the light is emitted toward the object to be detected. Then, when the detection target reflects light from the optical waveguide, the reflected light is introduced by the optical waveguide, emitted as radial light, and reflected by the mirror portion of the mirror with the light transmitting portion.

Here, the optical system is configured so that the reflected light of the mirror unit converges and enters the light receiving element. Therefore, the reflected light from the mirror section converges and enters the light receiving element.

As described above, the light from the light source can be made incident on the light receiving element while reducing the loss in the optical system. As a result, the light utilization of the light source of this type of photodetector can be greatly increased.

In addition, if the mirror portion of the mirror with the light transmitting portion is positioned at an angle with respect to the emission axis with its sphere shifted from the emission axis of the optical waveguide, the light from the optical waveguide enters the mirror portion. The amount of light is minimized while minimizing the shape and dimensions of the mirror with the translucent part.
We can secure enough. Therefore, the light utilization rate of the light source can be further increased.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a photodetector according to the present invention. This light detection device includes a housing 10 including a pair of housing members 10a and 10b.
The opening is adhered to the opening of the housing member 10b with an adhesive, and is assembled coaxially to the housing member 10b. The bottom wall of the housing member 10a has a pair of holding holes 11,
12 is vertically drilled so as to have an axis parallel to the axis of the housing member 10a, and the holding hole 11 has a cylindrical holder.
20 is attached with a screw 20a so that the outer end step 21 is engaged with the outer end flange 11a of the holding hole 11.

In the large diameter portion 22a of the stepped hole 22 drilled in the holder 20,
The light emitting element 30 is assembled through the auxiliary plate 13, and the light emitting element 30 emits light generated by conduction from the built-in light emitting diode through the light emitting surface 31 as light beam along the optical axis 31a. In the middle diameter portion 22b of the stepped hole 22, a plano-convex lens 40
The plano-convex lens 40 has a light emitting element 30
Beam light from the laser beam as parallel light along the optical axis 31a
Out of the small diameter portion 22c. Further, a mirror 50 with a hole is adhered to the annular inner end face 23 of the holder 20 formed at a predetermined acute angle θ with respect to the optical axis 31a with an adhesive at a back surface 51 thereof. The parallel light from the plano-convex lens 40 passes through the central hole 52 as an optical part and passes along the optical axis 31a toward the housing member 10b.

In such a 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 passes all the parallel light from the plano-convex lens 40 along the optical axis 31a to the central hole 52. It is set to pass. In addition, mirror 50 with hole
The mirror portion 53 is formed by a concave mirror having a predetermined radius of curvature, and the spherical center of the mirror portion 53 is located on the optical axis 31a. The auxiliary plate 13 is attached to the bottom wall of the housing member 10a by the screws 13a, 13a. A cylindrical holder 60 is attached to the holding hole 12 of the housing member 10a with a screw 62 by locking an inner end 61 of the holder 60 to an inner end flange 12a of the holding hole 12, and is attached by a screw 62. In
The light receiving element 70 is adhered by an adhesive. Then
The light-receiving element 70 has a built-in photodiode,
Light traveling along the optical axis 72a as described later is received through the light receiving surface 72.

On the bottom wall of the housing member 10b, a pair of holding holes 14, 15 are formed coaxially with the holding holes 11, 12, respectively.In the holding hole 14, a holder 80 is provided with a stepped cylindrical portion 80a. And the flange portion 80b is brought into contact with the bottom wall of the housing 10b, and assembled with the screws 81 and 82. In the stepped cylindrical portion 80a, the optical fiber 90 has an inner end 90a,
The optical fiber 9 is mounted coaxially with the optical axis 31a.
0 indicates that the parallel light from the central hole 52 of the perforated mirror 50 is incident along the optical axis 31a at the inner end portion 90a and propagated, and is incident on the object from the outer end portion (not shown). Let it. The optical fiber 90 receives the reflected light from the object to be detected at the outer end thereof, propagates the reflected light, and makes the reflected light from the inner end 90a incident on the mirror portion 53 of the perforated mirror 50 as diffracted light. In such a case, the numerical aperture NA of the opening end face 91 of the inner end 90a of the optical fiber 90 is selected so as to ensure a sufficient opening of the diffracted light incident on the mirror 53. In this embodiment, in order to increase the ratio of the light beam emitted from the light emitting element 30 to the light receiving element 70 (hereinafter, referred to as light utilization rate), the light beam is specified on the mirror section 53 by the spread of the incident diffracted light. Assuming that the cross-sectional area of the plane is Sa and the cross-sectional area of the parallel light passing through the central hole 52 of the perforated mirror 50 is Sb, Sa is sufficiently larger than Sb. The light utilization rate is represented by (Sa-Sb) / Sa.

In the holding hole 15 of the housing member 10b, a reflector 100 is mounted coaxially with a screw 103 at a cylindrical base 101 thereof. The reflector 100 has a mirror 102, and the mirror 102 is bonded to the inclined inner end surface of the cylindrical base 101. In such a case, the inclination angle of the axis of the mirror 102 with respect to the optical axis 72a is determined so that the diffracted light reflected from the mirror unit 53 is condensed by the mirror 102 and reflected toward the light receiving element 70 along the optical axis 72a. .

In the present embodiment configured as described above, the light emitting element 30
When a light beam is generated from the
Through the center hole 52 of the perforated mirror 50 and enters the inner end 90a of the optical fiber 90. In this case, even if the axis of the central hole 52 is inclined downward with respect to the optical axis 31a, the central hole 52
Since the inside diameter of the lens is appropriately determined as described above, almost all of the parallel light from the plano-convex lens 40 passes through the central hole 52. As described above, the parallel light entering the optical fiber 90 propagates along the light 90, exits from the outer end thereof, and enters the object to be detected.

When the light thus incident is reflected by the object to be detected and enters the optical fiber 90 again from the outer end thereof, the incident light propagates along the optical fiber 90 and becomes diffracted light from the inner end 90a. Then, the light exits and enters the mirror section 53 of the mirror 50 with holes. In such a case, the numerical aperture of the inner end 91 of the optical fiber 90
Since the NA is appropriately determined as described above, the diffracted light enters the mirror section 53 of the mirror 50 with a sufficient spread.

The diffracted light incident as described above is reflected by the mirror unit 53, is incident on the mirror 102 of the reflector 100, is reflected, travels along the optical axis 72a, and is condensed at the center of the light receiving surface of the light receiving element 70. For this reason, the light receiving element 70 performs the light detecting function by the conduction of the photodiode accompanying the light reception. In such a case, the beam light from the light emitting element 30 has almost no loss when passing through the central hole 52 of the perforated mirror 50, at the time of reflection by the perforated mirror 50, and at the time of reflection by the mirror 102.
0, the light utilization of the light beam from the light emitting element 30 can be greatly improved only by disposing the mirror 50 with a hole, the plano-convex lens 40 and the mirror 102 in the optical path between the optical fiber 90 and the light receiving element 70. . In addition, since the mirror portion 53 of the perforated mirror 50 is a concave mirror, the number of optical components is reduced. Further, fine adjustment of the position and the like of each component can be made by adjusting the degree of screwing of each screw 13a, 20a, 62, 81, 82 and the like. In such a case, if precision processing is performed, fixing with an adhesive is possible without using these screws. In addition, a predetermined acute angle θ
By setting the angle to about 60 ° to 80 °, the size of the mirror 50 with a hole can be reduced and the spherical aberration of the mirror section 53 can be suppressed.

In practicing the present invention, a biconvex lens 40A is used instead of the plano-convex lens 4 as shown in FIG.
In addition, the central hole 52 of the holed mirror 50 may be formed and implemented as a central hole 52a coaxial with the optical axis 31a.

In the embodiment of the present invention, the light from the plano-convex lens 40 is not limited to parallel light, but may be convergent light.

In the embodiment of the present invention, as shown in FIG. 3, instead of the mirror 50 having a hole, a mirror 50A having a plate-like mirror portion 53a and a convex lens 50B are employed, and the light receiving element 70 is provided.
The convex lens 100 </ b> A may be disposed between the mirror 102 and the mirror 102.

Further, in practicing the present invention, instead of the mirror 50 having a hole shown in FIG. 1, a mirror 50C having a hole provided as shown in FIG. 4 may be employed. The perforated mirror 50C has substantially the same configuration as the perforated mirror 50 of FIG. 1. The perforated mirror 50C has a center of curvature C (corresponding to the center of curvature of the mirror 53) of its mirror 53c. Mirror part 53 as the center
The spherical center 0 of c is maintained at a rotated position so as to be positioned below the optical axis 31a. In such a case, the mirror unit 53c
It is formed as a concave mirror having the same radius of curvature as the mirror portion 53 of the hole-provided mirror 50, spherical surface of the mirror unit 53c and around the intersection O ₁ with its optical axis 31a, the optical fiber 9
It has a minimum necessary surface area so as to symmetrically receive all of the diffracted light emitted from the inner end portion 90a of 0 at an aperture angle θ _NA (corresponding to the numerical aperture NA). The center hole 52 of the perforated mirror 50C (the same as the center hole 52 of the perforated mirror 50)
It is displaced downwardly with the displacement downward from the intersection O ₁ of the spherical center O.

Then, if the mirror 50C with a hole is arranged in this way,
The mirror with holes 50C receives all the diffracted light from the optical fiber 90 in a state where the center hole 52 is shifted downward from the optical axis 31a. As shown in FIG. 5, the spherical center O of the mirror 50C with a hole is shown.
Is aligned with the optical axis 31a, the lower part of the diffracted light from the optical fiber 90 cannot enter the holed mirror 50C due to the inclination of the holed mirror 50C, or Minimizing the size and shape of the perforated mirror 50C without causing the problem that the central part (with high intensity) of the diffracted light from 90 passes through the central hole 52 of the perforated mirror 50C. In addition, the efficiency of the amount of light reflected by the mirror 53c can be maximized.

Incidentally, NA = 0.57 (θ _NA = 34.81 °), the distance between the intersection O ₁ and the opening end surface 91 of the optical fiber 90 is 6.5 (mm), and the radius of curvature of the holed mirror 50C is 10 (mm). , And ∠O
₁ CO when (see FIG. 4) to 4 °, all around the intersection O ₁ of the diffracted light from the optical fiber 90 with respect to the mirror unit 53c that is incident on the mirror portion 53c was confirmed.

In practicing the present invention, as shown in FIG.
As shown in FIG. 6, the mirror 50C with the hole is translated downward as it is, and the light emitting element 30 and the spherical lens 40 are moved.
Even if the arrangement is changed so that the optical axis of B (corresponding to the plano-convex lens 40) (corresponding to the optical axis 31a) crosses the axis 90b of the optical fiber 90 at, for example, 4 °, the configuration shown in FIG. The same effect as in the case of can be secured. Note that {O ₁ CO is 4}.

In practicing the present invention, an optical system block 200 as shown in FIG. 7 is used instead of the optical system of the convex lens 40A, the mirror 50A with a hole, the convex lens 50B, the mirror 102, and the convex lens 100A in FIG. May be implemented. In such a case, the optical system block 200 includes the optical member 201 and the optical member 20.
The optical member 201 is joined to the joint surface of the optical member 202 at the joint surface. However, an optical transparent adhesive having the same refractive index as the refractive index of the two optical members 201 and 202 is applied to the portion including the optical axis 31a in the form of a film in each joint surface of the two optical members 201 and 202. A silver deposited film 202a forming a mirror surface is formed on the remaining portion of each bonding surface. Further, each optical member 201, 202 is, for example, BK
Since the optical member 202 is made of -7 glass, the critical angle δ (see FIG. 7) in the optical member 202 (wavelength input = 880 nm and δ = 41.
5 ゜) When the flat surface 202b is formed as described above, it is not necessary to provide a reflective film such as a silver deposition film on the flat surface 202b. In FIG. 7, the convex surface 201a of the optical member 201, the silver deposition film 202a, the optical member 2
The convex surface 202c, the flat surface 202b, and the convex surface 202d of the 02 are the left convex surface of the convex lens 40A in FIG.
a, which corresponds to the right convex surface of the convex lens 50B, the reflecting surface of the mirror 102, and the left convex surface of the convex lens 100A, respectively.

In practicing the present invention, as shown in FIG. 8, a cutout 202A having an air layer may be formed in place of the silver deposition film 202a in FIG. 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 central portions of the respective joining surfaces of the optical members 201 and 202.

In practicing the present invention, for example, a semiconductor laser may be used as the light emitting element 30, and a light receiving element 70 that incorporates, for example, a phototransistor may be used. The invention is not limited to this, and an optical waveguide may be generally used as the optical waveguide.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view of a main part showing a first partial modification of the embodiment, and FIG. 3 is a second partial modification of the embodiment. FIG. 4 is a sectional view of a principal part showing a third partial modification of the third embodiment, FIG. 5 is an explanatory view for comparison with the structure of FIG. 4, and FIG. FIGS. 7 and 8 are cross-sectional views of main parts in a case where each optical member in the embodiment is a single optical system block. is there. Explanation of reference numerals 30 …… Light-emitting element, 40 …… Plano-convex lens, 40A, 50B, 100A…
Convex lens, 50, 50A, 50C: Mirror with hole, 52, 52a: Central hole, 53, 53a, 53c: Mirror, 70: Light receiving element, 90:
Optical fiber, 102 ... Mirror, 200 ... Optical system block.

Claims (2)

(57) [Claims] 1. A light source and a light receiving element, and an optical waveguide that introduces light from the light source and emits the light toward a detected object, and introduces the reflected light when the emitted light is reflected by the detected object. An optical waveguide that emits as radial light; and a light-transmitting portion that is disposed between the light source and the optical waveguide, and that transmits light from the light source to the optical waveguide. And a mirror with a light transmitting unit having a mirror unit that receives and reflects the radial light from the optical waveguide,
An optical system configured so that light reflected from the mirror unit is converged and incident on the light receiving element. 2. The mirror portion of the mirror with a light-transmitting portion, wherein the mirror portion is inclined with respect to the emission axis of the optical waveguide while the spherical center thereof is shifted from the emission axis of the optical waveguide. 2. The photodetector according to claim 1, wherein