JP2007150902A - Light receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light receiving device for receiving axial deviation incident light within a wide angle range with respect to the incident light in a three-dimensional optical system. <P>SOLUTION: The light receiving device comprises a photodetector 4 separated from a light source 1 by a free space 2; and a condenser 10 which is arranged near the input end of the photodetector 4, where the opposing interval of a side surface having a reflecting function is reduced toward the photodetector 4, and which internally includes a reflection surface 7 including an optical axis 3 substantially facing the side surface within the range from an incident side surface 5 to a light emission side surface 6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light receiving device used for optical space transmission, for example.

  Ideally, the optical axes of the transmitter and receiver are aligned in space optical transmission, but in reality, static axis misalignment due to improper alignment between the fixed transmitter and fixed receiver, or the transmitter and receiver. There is a dynamic axis shift when at least one of the parts is a moving (movable) body. When the axis shift occurs, problems such as SN degradation due to a decrease in received light level, a decrease in transmission rate due to an increase in error rate, and an increase in transmission power occur. Furthermore, since the light receiving area becomes smaller as the light receiving element responds at a higher speed, the influence of the axial deviation becomes remarkable. The axis deviation includes both positional deviation and angle deviation. In the case of optical space transmission, since the beam diameter is expanded to some extent during propagation in free space, the angle shift is more problematic than the position shift. However, a conventional lens or the like for condensing on a light receiving element having a small area has a fixed dispersion surface, so that the condensing position changes sensitively due to a change in incident angle, resulting in a deterioration in gain.

As a method of receiving the incident light with the angle deviation at a wide angle, by providing a reflecting mirror on the side surface of the conical lens whose cross section decreases in the direction of the light receiving element, the light that does not directly enter the light receiving element is also reflected on the side surface. In some cases, the light is incident on the light receiving element (see, for example, Patent Document 1).
In addition, there is a lens in which the conical shape of Patent Document 1 is changed to a trumpet-shaped lens to increase the allowable directivity angle, and the refractive index in the lens is increased in the propagation direction to further increase the allowable directivity angle (for example, Patent Document). 2).

Further, the coupling element is a surface inclined with respect to the incident side surface, and reflects the signal light incident on the incident side surface within a predetermined propagation angle range with respect to the incident direction to the incident side surface, and cooperates with the incident side surface. In some cases, there is an emission side surface that guides the signal light in a direction in which the distance from the incident side surface is wide (see, for example, Patent Document 3).
JP-A-8-62039 (for example, FIG. 1) Japanese Patent Laying-Open No. 2005-218102 (for example, FIG. 1) Japanese Laid-Open Patent Publication No. 2000-111754 (for example, FIG. 1)

However, in the case of the conical collector having the constant refractive index of the conical shape of Patent Document 1 and the trumpet shape of Patent Document 2, the light having a small incident angle α (that is, the refraction angle α ₁ on the incident side surface) is reflected by the side surface. Although it can be coupled to the light receiving element, as shown in FIG. 5, light having a large incident angle (refractive angle α ₁ > 3 / 2π-2θ ₁ −θ ₂ ) is reflected on the incident side surface by reflection on the collector side surface. And cannot be coupled to the light receiving element. FIG. 5 is an explanatory diagram of a locus of incident light due to multiple reflection of two reflecting surfaces approaching a general propagation direction.

  In order to improve it, in Patent Document 2, a refractive index distribution is provided so that the refractive index increases in the propagation direction, and the incident angle to the reflecting surface on the side surface of the collector increases, that is, progresses according to propagation. The allowable light receiving angle is widened by reducing the angle between the direction and the optical axis.

  However, it is not only technically difficult to form a refractive index distribution in the light collector, but also has a problem that it is very disadvantageous in terms of cost.

  On the other hand, the conventional method of Patent Document 3 is effective for propagation of two-dimensional light, but has a problem that it is not effective for light incident three-dimensionally.

  An object of the present invention is to provide a light receiving device that can receive axially shifted incident light in a wider angle range with respect to incident light in a three-dimensional optical system in consideration of such problems of conventional apparatuses.

In order to achieve this object, the present invention provides the first invention, comprising: a concentrator for collecting and emitting the light emitted from the light source; and a light receiving element for receiving the light emitted from the light collector. A light receiving device,
The concentrator has an incident side surface and an exit side surface at both ends, and the inside of the side surface having a reflection function for reflecting light incident from the incident side surface becomes substantially narrower as it goes from the incident side surface to the exit side surface. In the light collecting device, a reflection surface that substantially faces the side surface is provided in the whole or a part of the range from the incident side surface to the emission side surface.

  The second aspect of the present invention is the light receiving device according to the first aspect of the present invention, wherein the reflecting surface includes the optical axis of the condenser.

  The third aspect of the present invention is the light receiving device according to the first aspect of the present invention, wherein there are a plurality of the reflecting surfaces, and there are intersecting lines between the reflecting surfaces.

  The fourth aspect of the present invention is the light receiving device according to the third aspect of the present invention, wherein the intersecting lines of the plurality of reflecting surfaces are parallel to the optical axis of the condenser.

  The fifth aspect of the present invention is the light receiving device according to the first aspect of the present invention, wherein there are a plurality of the reflecting surfaces, and no line of intersection exists between the reflecting surfaces.

  A sixth aspect of the present invention is the light receiving device according to the fifth aspect of the present invention, wherein the degree of inclination of the reflecting surface with respect to the optical axis of the condenser is reduced as it goes from the incident side surface to the emission side surface.

  The seventh aspect of the present invention is the light receiving device according to the first aspect of the present invention, wherein the reflecting surface is formed of a metal surface.

  The eighth aspect of the present invention is the light receiving device according to the first aspect of the present invention, wherein the reflecting surface is formed with a periodic structure that causes Bragg reflection.

  The ninth aspect of the present invention is the light receiving device according to the first aspect of the present invention, wherein the reflecting surface is formed at an interface that causes total reflection between the light collector and a material having a different refractive index.

  The tenth aspect of the present invention is the light receiving device according to any one of the first to ninth aspects, wherein at least one of the incident side surface and the emission side surface of the condenser is a curved surface.

  Further, an eleventh aspect of the present invention is any one of the first to tenth aspects, further comprising a filter that transmits only a specific wavelength on the incident side surface of the collector or between the emission side surface and the light receiving element. This is the light receiving device of the present invention.

  The present invention exhibits an effect that it is possible to provide a light receiving device having a larger allowable reception angle than conventional ones.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1A is a light receiving device according to an embodiment of the present invention, and includes a lens concentrator 10 in which two light guides 9 are in contact via a reflecting surface including an optical axis. FIG. 1A is a diagram schematically illustrating a longitudinal section of the light receiving device, and FIG. 1B illustrates a ray trajectory viewed from a section perpendicular to the optical axis of the light receiving device. It is a schematic diagram for. The configuration of the present embodiment will be described with reference to FIG.

  As shown in FIGS. 1A and 1B, the light receiving device according to the embodiment of the present application is separated from the light source 1 by a free space 2, and the light receiving element 4 on the optical axis 3 and the incident side surface 5 have curved surfaces. The exit side surface 6 is in contact with the light receiving element 4, and the distance between the side reflecting surfaces 8 facing the surface decreases toward the light receiving element 4. The incident side surface and the exit side surface are divided to include the reflecting surface 7 including the optical axis inside. The lens concentrator 10 is provided.

  However, the reflecting surface 7 may be a flat surface or a curved surface. Further, it is not necessary to strictly include the optical axis if slight characteristic deterioration can be allowed.

  Next, using the lens concentrator having the reflecting surface 7 including the optical axis of the present embodiment, Pin-PD (Pin Photo Diode) or APD (Avalanche Photodiode) having a small light-receiving area with respect to the axially shifted parallel incident light. A mechanism for focusing on a light receiving element such as the above will be described using a ray trajectory.

  First, the trajectory of light rays will be described using a two-dimensional model of a conventional type lens concentrator 110 of multiple reflection at opposing reflecting surfaces shown in FIG.

The axially shifted parallel incident light 11 having the incident angle 12 (α) is first refracted in the α ₁ direction on the incident side surface 5 of the lens concentrator 110 and reflected by the first reflection point 17 on the first reflection surface 15. The reflection angle at the first reflection point is β ₁ (first reflection angle β ₁ = π / 2 −θ ₁ −α ₁ ), the angle between the first reflection surface 15 and the optical axis 3 is θ ₁ , Assuming that the angle formed between the second reflection surface 16 facing the first reflection surface 15 and the optical axis 3 is θ ₂ , the second reflection angle β ₂ (β ₂ = β ₂₎ at the second reflection point 18 on the second reflection side surface 16. (θ ₁ + θ ₂ −β ₁ −π) is expressed by the following equation.

  That is, α calculated from α1 (formula 2) where β2 = 0 is the maximum light receiving angle.

However, α is derived from Snell's law of the following equation, and α and α ₁ have a monotonically increasing relationship in the assumed incident angle range, and therefore the maximum light receiving angle is substituted with the maximum refraction angle α _1max .

  The above results also hold for a three-dimensional optical system that is optically symmetric.

  Next, the case of Embodiment 1 of the present application shown in FIG. 1 will be described using a ray trajectory.

  Consider axially shifted parallel incident light 11 having an incident angle exceeding the allowable light receiving angle range in a conventional example (see FIG. 5) in which no reflecting surface including the optical axis exists. In the case where the first reflection point is the side surface of the conventional lens concentrator 110 having no reflection surface including the optical axis, the first reflection point is compared with the first embodiment of the present application in which the reflection surface 7 including the optical axis is present. There is no difference in the trajectory up to one reflection point.

However, the locus after reflection at the first reflection point of the light beam having the refraction angle α ₁ satisfying the following expression 2 ′ is the side surface facing the side surface including the first reflection point of the lens concentrator 110 in the conventional example. It proceeds to the upper second reflection point and is then reflected out of the incident side of the lens collector.
That is, the refraction angle α ₁ satisfies the relationship of Expression 2 ′ derived from Expression 2.

Here, α _1max ′ indicates the maximum refraction angle in the conventional lens concentrator 110.

On the other hand, since the locus after reflection at the first reflection point in Embodiment 1 of the present application has the second reflection point on the reflection surface including the optical axis, the first reflection point after reflection at the second reflection point. Proceed toward the third reflection point on the side surface of the lens concentrator having, and finally coupled to the light receiving element. That is, in the case of the first embodiment of the present application, θ ₂ = 0 in equation 2, so that equation 4 holds.

From this equation 4, it can be seen that the maximum refraction angle α _1max of the lens concentrator 10 of Embodiment 1 of the present application is larger than the conventional maximum refraction angle α _1max ′. It can be said that it has a wider acceptance angle than before.

  In the case of the conventional lens concentrator 110 having no reflecting surface including the optical axis, all the reflection points are on the side surfaces of the lens concentrator, so it is sufficient to consider only the above case. In this case, the first reflection point may be on the reflection surface 7 including the optical axis.

Therefore, the ray trajectory in that case will be described next. That is, the ray trajectory in that case is reflected at the second reflection point on the side surface of the lens concentrator after reflection at the first reflection point on the reflection surface 7 including the first optical axis, and includes the optical axis. Multiple reflection between the reflecting surface and the side surface of the lens concentrator including the second reflecting point finally couples to the light receiving element. In this case, since θ ₁ = 0 in Equation 2, the relationship of the following Equation 4 ′ holds.

  Therefore, it can be seen from Equation 4 'that even when the first reflection point is on the reflection surface 7 including the optical axis, the allowable light receiving range is wider than in the conventional case where there is no reflection surface including the optical axis.

  FIGS. 1A and 1B show the case where the ray trajectory of the axially shifted parallel incident light 11 is reflected by the reflecting surface 7 and proceeds to the exit side surface 6 side. A conventional ray trajectory 14 emanating from the side is also shown.

Next, a method for manufacturing the lens concentrator 10 of Embodiment 1 of the present application will be described.
That is, a conventional lens concentrator 110 having the same shape as that obtained by dividing the lens concentrator 110 into two along the surface including the optical axis 3 may be prepared, and may be bonded or fixed with the reflecting surface 8 interposed therebetween. You may hold with a jig. The reflective surface 8 is a metal surface, a periodic structure of refractive index using Bragg reflection, or a boundary surface between the refractive index material different from the refractive index of the light guide portion 9 of the lens concentrator 10 and the light guide portion 9. And a total reflection structure.

  In addition, when the output surface of the lens concentrator reaches the sensing portion of the light receiving element, for example, the active layer of the semiconductor, high efficiency can be achieved.

  Further, a filter that transmits only a specific wavelength may be provided in contact with the incident side surface of the lens concentrator or between the emission side surface and the light receiving element.

Thus, by forming the reflecting surface 7 not only on the side surface of the lens concentrator whose cross section decreases in the direction of the light receiving element, but also on the surface including the optical axis, Since the incident angle can be made larger, light reception at a wider angle is possible.
(Embodiment 2)
FIG. 2 is a light receiving device according to another embodiment of the present invention, and includes a lens concentrator 50 in which four light guides 59 are in contact with each other through two reflecting surfaces including an optical axis. It is a schematic diagram which shows the structure of a device. 2A is a diagram schematically illustrating a longitudinal section of the light receiving device, and FIG. 2B illustrates a ray trajectory viewed from a section perpendicular to the optical axis of the light receiving device. It is a schematic diagram for. The configuration of the present embodiment will be described with reference to the same drawing, focusing on the differences from the above embodiment.

  As shown in FIG. 2B, the light receiving device according to the embodiment of the present application has a second reflecting surface 7 according to the first embodiment of the present application and a line of intersection between the reflecting surface 7 and the optical axis 3. 1 is different from the configuration of FIG. 1 in that a reflecting surface 19 is provided and a lens concentrator 50 including four light guides 59 is provided.

  In the first embodiment, an incident side surface that includes incident light and transmitted light (this surface is defined as an incident surface, hereinafter referred to as an incident surface) is not far from the optical axis 3. Since either one of the first reflection point and the second reflection point is necessarily on the reflection surfaces 7 and 19 including the optical axis, even if there is one reflection surface 7 including the optical axis (see FIG. 1B), It can be said that the acceptance angle is wider than that.

  However, in the configuration of FIG. 1, incident light whose incident surface on the incident side surface is far from the optical axis 3 may be emitted from the lens collector 10 toward the incident side surface. This will be described with reference to FIG.

  That is, the configuration of the lens concentrator 10 in FIG. 1 is equivalent to, for example, the case where the second reflecting surface 19 does not exist in the configuration in FIG. If the ray trajectory 20 when there is no light is shown in FIG. 2B, the light beam reflected by the first reflection point 30 on the side surface of the lens concentrator 50 is the lens of the same light guide 59 as shown by the broken line. The second reflection point 31 is provided on the side surface of the condenser 50. Then, this light beam returns from the second reflection point 31 to the incident side surface 5 side. Therefore, in this case, the allowable light receiving angle is the same as that of the conventional lens concentrator 110.

  Therefore, even if the incident surface on the incident side is far from the optical axis, the reflection including the optical axis is performed so that the second reflection point does not come on the side surface of the lens concentrator of the same light guide unit as the first reflection point. In the second embodiment, a plurality of surfaces 7 and 19 are provided.

  The larger the number of reflection surfaces including the optical axis, the better. However, if the number of the light guide portions 59 of the lens concentrator 50 is four as shown in FIG. 2, the number of reflection surfaces including the optical axis is one. Even incident light that cannot be received by the configuration can be coupled to the light receiving element 4 because the second reflection point 32 is on the reflection surface 19 including the optical axis as shown in FIG. The arrangement of the reflecting surfaces 7 and 19 including the optical axis is preferably symmetric with respect to the optical axis 3.

  Thus, by using a plurality of reflecting surfaces including the optical axis, it is possible to receive light at a wider angle than the configuration of the first embodiment, even for incident light whose incident surface on the incident side surface is far from the optical axis. .

The lens concentrator 50 according to the present embodiment can be manufactured by preparing a lens concentrator 110 having the same shape as the conventional lens concentrator 110 divided into four along the plane including the optical axis 3. Subsequent steps are basically the same as those described in the first embodiment.
(Embodiment 3)
FIG. 3 shows a light receiving device according to another embodiment of the present invention, in which four light guides 69 are arranged via a finite reflection surface 21 composed of parallel reflection surfaces facing the optical axis as a center. It is a structure schematic diagram of the light receiving device which comprises the lens concentrator 60 which touches. 3A is a diagram schematically showing a cross section taken along line AA ′ including the optical axis 3 of the light receiving device (see FIG. 3B). FIG. 3B is a diagram illustrating the light receiving device. It is the figure which showed typically the light ray locus in the cross section perpendicular | vertical to an optical axis. The configuration of the present embodiment will be described with reference to the same drawing, focusing on the differences from the above embodiment.

  As shown in FIG. 3, the light receiving device according to the embodiment of the present application is equivalent to the configuration having the light guide portion of the waveguide structure inside the reflecting surfaces 7 and 19 described in the second embodiment. In this configuration, the reflecting surfaces 7 and 19 are replaced with a finite reflecting surface 21 configured with opposing reflecting surfaces and a light guide portion 22 within the finite reflecting surface.

  The manufacturing method of the lens concentrator 60 of the present embodiment is basically the same as that of the second embodiment described above except for the light guide portion 22 in the finite reflection surface.

  The light guide portion 22 in the finite reflection surface may be manufactured by controlling the thickness of the adhesive layer used in the above-described manufacturing method to be thick, or formed by a mold using a glass material or a resin material. May be made to be sandwiched between four lens concentrators. The molding material may be the same as or different from that of the light guide unit 69. Alternatively, an air layer may be simply provided.

Thus, in addition to the light guide portion 69 of the lens concentrator 60 having the same allowable light receiving angle as that of the above embodiment, the relationship is equivalent to the case where θ ₁ = θ ₂ = 0 is substituted in Equation ₂ . A light guide portion 22 in the finite reflection surface including the optical axis is configured. Since this light guide portion 22 does not exist in the configuration of the above embodiment, the light incident on the light guide portion 22 in the finite reflection surface near the optical axis has a wider light receiving angle than the above embodiment. It will be.

As the cross section of the light guide portion 22 in the finite reflection surface increases, the ratio of the portion having a larger light reception angle than the allowable light reception angle of the above-described embodiment increases, so that the allowable light reception angle of the entire lens condenser 60 increases. . FIG. 3B shows the ray trajectory. Here, the broken line portion in FIG. 3B represents that the light beam repeats reflection, and finally reaches the light receiving element 4 by repeating the reflection.
(Embodiment 4)
FIG. 4 shows a light receiving device according to another embodiment of the present invention, in which four light guides 79 are arranged via a finite reflection surface 121 formed of a curved reflection surface facing the optical axis as a center. It is a structure schematic diagram of the light receiving device which comprises the lens concentrator 70 which touches. The configuration of the present embodiment will be described with reference to the same drawing, focusing on the differences from the above embodiment.

  Embodiment 4 of the present application is an example in which the area of the cross section perpendicular to the optical axis 3 of the light guide portion 22 in the finite reflection surface of Embodiment 3 is made smaller toward the light receiving element 4 (FIG. 4B). ) And (c)).

  Here, FIG. 4A is a diagram schematically showing an AA ′ cross section (see FIG. 3B) including the optical axis 3 of the light receiving device, and FIG. It is the figure which showed typically the light ray locus in the cross section perpendicular | vertical to the optical axis. FIG. 4C shows a cross section perpendicular to the optical axis 3 at a position closer to the light receiving element 4 than in FIG. 4B in order to explain the change in the cross section of the light guide portion 122 in the finite reflection surface. It is a schematic diagram.

In the case of the present embodiment, the allowable light receiving angle of the light guide portion 122 in the finite reflection surface is smaller than that in the third embodiment, but the light guide portion 79 constituting the lens concentrator 70 is Since the 2 tilt angle θ ₂ has a negative value, the allowable light receiving angle is larger than those in the first to third embodiments in which the second tilt angle θ ₂ = 0. The reason will be described below.

Here, in the light guide unit 79 in FIG. 4, θ ₁ > 0 and θ ₂ <0. However, since the curvature of the facing surface of the light guide portion 122 in the finite reflection surface is different, θ ₁ > 0, θ ₂ > 0. This is because in FIG. 5, the case of spreading in a trumpet is defined as the same sign with θ ₁ > 0 and θ ₂ > 0.

That is, in the case of the light guide portion 122 of the finite reflection surface of the fourth embodiment, θ ₁ > 0 and θ ₂ > 0, so that the maximum refraction angle of the light guide portion 22 described in FIG. If the maximum refraction angles of the light guide portion 122 are _expressed as α _{1max (22)} and α _{1max (122)} , respectively, the following equation can be derived from Equation 2.

Therefore, since the relationship of α _{1max (122)} <α _{1max (22)} is _established from Expression 5, the allowable light receiving angle of the light guide portion 122 of the present embodiment is the allowable value of the light guide portion 22 of the third embodiment. It can be seen that it is smaller than the light receiving angle.

  Therefore, when the cross-sectional shape of the light guide portion 122 in the finite reflection surface of the present embodiment is small, the influence of the light guide portion 122 is small, and the proportion of the entire light guide portion 79 is the same as that of the third embodiment. Since it can be larger than the case, the allowable light receiving angle can be increased more effectively than in the third embodiment.

  In this way, the reflecting surface is formed not only on the side surface of the lens concentrator whose cross section is reduced in the direction of the light receiving element but also on the surface including the optical axis, so that the incident light is incident on the reflecting surface on the side surface of the lens concentrator Since the angle can be made larger, light can be received at a wider angle.

  As described above, the present invention is arranged, for example, in the vicinity of the light receiving element separated from the light source in free space and the input end of the light receiving element, and the distance between the opposing side surfaces having the reflecting function is directed toward the light receiving element. The lens concentrator is made smaller and includes at least one reflecting surface that divides the incident side surface and the output side surface.

  In this way, by forming a reflection surface that divides the incident side surface and the output side surface not only on the side surface of the lens concentrator but also inside the lens concentrator, the incident angle to the lens concentrator can be further increased. As a result, it is possible to receive light at a wider angle and to provide an optical system capable of high-speed optical space transmission in a wider light reception angle range.

  In the above-described embodiment, a reflecting surface (for example, the reflecting surface 7 including the optical axis in FIG. 1) that substantially faces the reflecting surface of the side surface in the entire range from the incident side surface to the exit side surface is provided inside the lens concentrator. However, the present invention is not limited to this. For example, the reflective surface of the present invention may be provided in a range excluding the vicinity of the incident side surface and / or the vicinity of the output side surface. In short, as long as the angle of incidence on the lens concentrator can be increased, a reflecting surface that substantially faces the side surface having a reflecting function in a part of the range from the incident side surface to the output side surface within the concentrator. May be provided.

  In the above-described embodiment, the case where the emission side surface and the light receiving element are in contact with each other has been described. However, the present invention is not limited to this. For example, a space may exist between the two.

  Moreover, although the said embodiment demonstrated the case where the entrance side surface of a lens concentrator is a curved surface and the output side surface is a plane, it is not restricted to this, For example, an exit side surface may be a curved surface.

  Further, in the above embodiment, the explanation has been made mainly on the case where glass or resin is used as the material of the light guide part or the light guide part in the finite reflection surface, but not limited thereto, for example, in the light collector, Adds erbium (Er), Yb (yttrium), etc. like an optical fiber amplifier (amplifier), or amplifies the incident light to the light receiving element by causing stimulated emission from the outside using the Raman amplification effect. May be.

  Further, in the above-described embodiment, a configuration example in which a reflective surface that substantially faces the reflective surface of the side surface is provided in the whole or a part of the range from the incident side surface to the output side surface inside the lens concentrator is described. In addition to the example (for example, the reflecting surface 7 including the optical axis in FIG. 1), for example, a configuration in which the distance from the side surface of the lens concentrator facing in a ring shape becomes smaller toward the light receiving element is also conceivable. It is done. Specifically, a reflecting surface (not shown) concentric with the side surface of the lens concentrator can be mentioned, but a surface including incident light on the incident side surface and transmitted light entering the lens concentrator. The incident light that is away from the optical axis has a ratio that both the first reflection point and the second reflection point are on the side surface of the lens concentrator than in the case where the cross section does not have a ring shape as in the above embodiment. Since it is large, the effect of expanding the light receiving angle is not so great.

  The light receiving device of the present invention has an effect of receiving axially shifted incident light in a wider angle range, and is useful as a light receiving device used for optical space transmission or the like.

(A) The figure which represented typically the cross section of the vertical direction of the light receiving device of Embodiment 1, (b) For demonstrating the light ray locus seen from the cross section perpendicular | vertical to the optical axis of the light receiving device of the same embodiment Pattern diagram (A) The figure which represented typically the cross section of the vertical direction of the light receiving device of Embodiment 2, (b) For demonstrating the light ray locus seen from the cross section perpendicular | vertical to the optical axis of the light receiving device of the same embodiment Pattern diagram (A) The figure which represented typically the AA 'cross section containing the optical axis of the light receiving device of Embodiment 3, (b) Schematic of a light ray locus in the cross section perpendicular | vertical to the optical axis of the light receiving device of the same embodiment. Diagram (A) The figure which represented typically the AA 'cross section containing the optical axis of the light receiving device of Embodiment 4, (b) Schematic of a light ray locus in the cross section perpendicular | vertical to the optical axis of the light receiving device of the same embodiment. (C) The figure for demonstrating the change of the cross section of the light guide part in the finite reflection surface of the embodiment Explanatory drawing of ray trajectory due to multiple reflections at opposing reflecting surfaces in a conventional light receiving device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Free space 3 Optical axis 4 Light receiving element 5 Incident side surface 6 Outgoing side surface 7 Reflecting surface including an optical axis 8 Side reflecting surface 9, 59, 69, 79 Light guide part 10 Lens concentrator 11 Axis deviation (parallel) Incident light 12 Incident angle 13 Ray trajectory 14 Conventional ray trajectory 15 First reflecting surface 16 Second reflecting surface 17 First reflecting point 18 Second reflecting point 19 Second reflecting surface including optical axis 20 Second reflecting including optical axis Ray trajectory with no surface
21, 121 Finite reflective surface 22, 122 Light guiding part in the finite reflective surface

Claims (11)

A light receiving device comprising: a light collecting device that collects and emits light emitted from a light source; and a light receiving element that receives light emitted from the light collecting device,
The concentrator has an incident side surface and an exit side surface at both ends, and the inside of the side surface having a reflection function for reflecting light incident from the incident side surface becomes substantially narrower as it goes from the incident side surface to the exit side surface. The light receiving device is provided with a reflecting surface that substantially faces the side surface in the whole or a part of the range from the incident side surface to the emission side surface.   The light receiving device according to claim 1, wherein the reflecting surface includes an optical axis of the condenser.   The light receiving device according to claim 1, wherein there are a plurality of reflecting surfaces, and there are intersecting lines between the reflecting surfaces.   The light receiving device according to claim 3, wherein the intersecting line of the plurality of reflecting surfaces is parallel to an optical axis of the condenser.   The light receiving device according to claim 1, wherein there are a plurality of the reflecting surfaces, and there are no intersecting lines between the reflecting surfaces.   The light receiving device according to claim 5, wherein the degree of inclination of the reflecting surface with respect to the optical axis of the condenser decreases from the incident side surface toward the emitting side surface.   The light receiving device according to claim 1, wherein the reflecting surface is formed of a metal surface.   The light receiving device according to claim 1, wherein the reflecting surface is formed with a periodic structure that causes Bragg reflection. The light receiving device according to claim 1, wherein the reflection surface is formed at an interface that causes total reflection between the light collector and a material having a different refractive index.   The light receiving device according to claim 1, wherein at least one of the incident side surface and the emission side surface of the light collector is a curved surface.   The light receiving device according to claim 1, further comprising a filter that transmits only a specific wavelength on the incident side surface of the light collector or between the light emitting side surface and the light receiving element.

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