JP2008008671A - Light receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light receiving device with a wide allowable incident angle range capable of securing the lowest gain. <P>SOLUTION: The light receiving device comprises: an input surface 5 on which the light is incident; an output surface 6 opposite to the incident surface 5 and smaller than the input surface 5; a light collector 10, provided with the side surface along the input surface 5 to the output surface 6, an internal peripheral surface 8 of which is made to reflect the light incident on the input surface 5; and a detection part 4 for receiving the light emitted from the output surface 6. The shape of the internal peripheral surface 8 of the light collector 10 is such that the part of the inclination angle 11 of the internal peripheral surface 8 to the central axial line 3 of the output surface 6, where is simply decreasing as approaching from output surface 6 toward input surface 5, is arranged at least nearer to the input surface 5 than to the output surface 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  Recently, attempts have been made to perform cordless signal transmission between AV devices. As the means, optical transmission using infrared rays is used exclusively, such as infrared communication using a mobile phone.

  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. When at least one of the parts is a moving (movable) body, for example, when the mobile phone is used while being held or transmitted to a moving automobile, there is a dynamic axis shift. 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, since the conventional lens for condensing light receiving elements with a small area has a fixed dispersion surface, the condensing position changes sensitively due to fluctuations in the incident angle, resulting in a deterioration in gain.

  As a method of receiving the incident light with the angle deviation at a wide angle, there is a method using a reflecting mirror provided on the side surface of the lens (for example, see Patent Document 1).

  FIG. 11 shows a side sectional view of the light receiving device proposed in Patent Document 1. In FIG.

  A frustoconical lens 81 whose cross section decreases toward the light receiving element 82 is provided. The reflecting mirror 83 is attached without a spatial gap so as to cover the side surface of the lens 81.

  With this configuration, the light that has not directly entered the light receiving element is also reflected by the reflecting mirror 83 and is incident on the light receiving element 82 so that the incident light efficiently reaches the light receiving element 82. Yes.

  In addition, there is one using total reflection on the side surface of the collector (see, for example, Patent Document 2).

  FIG. 12 shows a side sectional view of the dielectric total internal reflection collector proposed in Patent Document 2.

  The dielectric total internal reflection collector includes a receiving surface 91 bent in a convex shape, a concave side surface 92 that is axisymmetric, and a circular detection surface 93. An optical sensor 94 is incorporated in the detection surface 93 and is covered with a flat thin film optical filter 95.

By adopting such a configuration, a light beam that has passed through the receiving surface 91 and has not directly entered the detection surface 93 is totally reflected by the side surface 92 and is received by the detection surface 93, thereby receiving incident light at a wide angle. I can do it.
JP-A-8-62039 (for example, FIG. 1) Japanese translation of PCT publication No. 2004-508733 (for example, FIG. 1)

  However, in the light receiving devices described in Patent Document 1 and Patent Document 2, due to the shape of the side surfaces, even if light that is incident with a wide angle misalignment can be received, the gain is high. There was a problem of becoming smaller.

  In order for the received data to be processed as valid data, it must be received with a gain greater than the minimum necessary gain value (hereinafter referred to as the minimum gain value). That is, even if light that is incident with an axial deviation can be received, only the range in which a gain value equal to or greater than the minimum gain value is obtained is an allowable axial deviation light receiving angle range.

  In the shape of the side surface of the conventional light receiving device described in Patent Document 1 or Patent Document 2, the gain value decreases greatly as the axial misalignment angle of incident light increases, so that the axial misalignment light receiving that can guarantee the minimum gain value. There was also a limit to increasing the angular range. That is, with the shape of the side surface of the conventional light receiving device, it is not possible to effectively receive the incident light with the axis shifted at a wide angle.

  In the following, the fact that the gain value greatly decreases as the axial misalignment angle of the incident light increases in the shape of the side surface of the conventional light receiving device described above will be described using mathematical expressions.

In the collector that guides the incident light passing through the input surface to the output surface by reflection of the side surface as shown in FIGS. 11 and 12, the incident angle β _m and the reflection angle γ _{m to the mth} reflection point on the side surface are These are represented by Equation 3 and Equation 4, respectively. Where α ₁ is the angle of refraction of the incident light at the input surface, θ _m is the inclination angle of the mth reflection point, and the angle code is based on the input surface direction from the output surface. The inclination angle refers to an angle formed by a center line connecting the center points of the input surface and the output surface and a tangent line on the side surface in the direction from the input surface to the output surface.

数３および数４より、図１１の反射鏡８３のように側面に金属などの反射率の高い反射材料を使用する場合、数５となる光線は、側面での反射により入力面方向へ反射されて最終的には入力面から外部へ出射されてしまい、受光素子８２で受光できない。

From Equation 3 and Equation 4, when a reflective material such as metal is used on the side surface as in the reflector 83 of FIG. 11, the light beam represented by Equation 5 is reflected toward the input surface by reflection on the side surface. Finally, the light is emitted from the input surface to the outside and cannot be received by the light receiving element 82.

また、図１２のように側面９２での全反射を利用する場合は、数６となる光線は、側面９２で全反射されず透過するので、やはり検知面９３で受光できない。ただし、ｎ：集光器の屈折率（＞１）であり、図１２の全反射の方が図１１の場合よりも受光条件が厳しい。

When using the total reflection on the side surface 92 as shown in FIG. 12, the light beam represented by Equation 6 passes through the side surface 92 without being totally reflected, and therefore cannot be received by the detection surface 93. However, n is the refractive index (> 1) of the condenser, and the light receiving conditions are more severe in the case of total reflection in FIG. 12 than in the case of FIG.

次に、入力面と出力面の大きさの差が大きく、集光器の長さが短い、開口角が大きい場合を考える。

Next, consider a case where the difference in size between the input surface and the output surface is large, the collector is short, and the aperture angle is large.

For ease of explanation, assuming a centrally symmetric collector with circular input surfaces and output surfaces (respective radii D ₀ and D ₁ ) and straight side surfaces, the tilt angle θ is at the reflection position. Regardless, it is expressed by Equation 7. Where h is the distance between the input surface and the output surface (the length of the condenser).

数３、数４、および数７より、利得と正の相関関係にある入力面と出力面の大きさの差が大きく、集光器の長さが短いほど、反射点への入射角β_ｍおよび反射角γ_ｍが大きくなるので受光が困難となる。したがって、図１１に示した特許文献１や図１２に示した特許文献２の形状の集光器を使用する場合、集光器の長さが短くなると、入射光が軸ズレするにしたがって利得が急激に低下してしまう。つまり、従来の側面形状の集光器では、軸ズレに対する利得の低下を抑えながら集光器の長さを短くすること、すなわち、小型化をするにも限度があった。

From Equations 3, 4, and 7, the larger the difference in size between the input surface and the output surface that are positively correlated with the gain, and the shorter the collector length, the incident angle β _m to the reflection point. Further, since the reflection angle γ _m becomes large, it becomes difficult to receive light. Therefore, when using the collector of the shape of Patent Document 1 shown in FIG. 11 or Patent Document 2 shown in FIG. 12, when the length of the collector is shortened, the gain increases as the incident light is axially displaced. It drops rapidly. In other words, in the conventional side-shaped collector, there is a limit to shortening the length of the collector, that is, downsizing, while suppressing a decrease in gain with respect to axial deviation.

For example, in the case of a small shape in which the ratio of the input surface diameter and the output surface diameter at which the maximum gain is 20 dB is 10: 1, D ₀ = 5 mm, D ₁ = 0.5 mm, and the collector length is 10 mm, Since it has an inclination angle of θ = 24.2 °, the incident angle and reflection angle to the mth reflection point on the side surface are β _m = α ₁ −24.2 ° + 48.5 ° m, and γ, respectively. _m = α ₁ + 48.5 ° m, and no light can be received unless m <2.

  However, in order to obtain a high gain at m <2, the first arrival position after refraction at the input surface is the vicinity including the output surface regardless of the incident position on the input surface, regardless of the presence or absence of axial misalignment. Must be. With the conventional configuration as shown in FIG. 11, it is impossible to configure such an input surface in a wide directivity angle range of ± 15 °. In the case of a trumpet shape in which the inclination angle monotonously increases from the output surface to the input surface as shown in FIG. 12, the inclination angle of the side surface on the input surface side is larger than that in the case of a straight line, which is even more difficult.

  As described above, when the length of the condenser is shortened, the gain rapidly decreases with respect to a slight axial shift of the incident light, and the gain of the incident light shifted in a wide angle cannot be guaranteed.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a light receiving device having a wider axis misalignment incident angle range that can guarantee the minimum gain for incident light in a three-dimensional optical system. .

In order to solve the above-described problem, the first aspect of the present invention provides:
An input surface on which light is incident, an output surface facing the input surface and having an area smaller than the input surface, and provided from the input surface to the output surface, and an inner peripheral surface thereof is incident from the input surface A light collector having a side surface for reflecting light;
A detector that receives light emitted from the output surface;
The shape of the inner peripheral surface of the light collector is at least a portion where the inclination angle of the inner peripheral surface with respect to the center line of the output surface monotonously decreases from the output surface toward the input surface. A light receiving device having a shape closer to the input surface than the input surface.

The second aspect of the present invention
The inclination angle of the inner peripheral surface is a tangent to the inner peripheral surface included in the plane and the center line at each point on a line where the plane including the center line of the output surface intersects the inner peripheral surface. 1 is a light receiving device according to the first aspect of the present invention.

The third aspect of the present invention
In the light receiving device according to the first aspect of the present invention, the reflection of the light incident from the input surface on the inner peripheral surface is a metal reflection.

The fourth aspect of the present invention is
The shape of a portion of the inner peripheral surface other than the portion where the inclination angle monotonously decreases is the light receiving device according to the third aspect of the present invention, in which the inclination angle is constant or monotonously increases.

The fifth aspect of the present invention provides
The shape of the inner peripheral surface is a shape in which the distance r in the vertical direction from the center line is expressed by the formula 1 at the position z of the distance from the output surface on the center line. It is a device.

また、第６の本発明は、
前記内周面の形状は、前記中心線上の前記出力面からの距離ｚの位置における、前記中心線から垂直方向の距離ｒが数２で表される形状であり、
前記中心線を含む断面における、前記入力面の円周上の点と前記出力面の円周上の点とを結ぶ直線の、前記中心線となす角度が２７°以上の形状である、第３の本発明の受光デバイスである。

The sixth aspect of the present invention provides
The shape of the inner peripheral surface is a shape in which the distance r in the vertical direction from the center line at the position of the distance z from the output surface on the center line is expressed by Formula 2,
In a cross section including the center line, a straight line connecting a point on the circumference of the input surface and a point on the circumference of the output surface is a shape having an angle of 27 ° or more with the center line, This is a light receiving device of the present invention.

また、第７の本発明は、
前記内周面の形状は、前記出力面の中心線に対して回転対称の形状である、第１の本発明の受光デバイスである。

The seventh aspect of the present invention
The shape of the inner peripheral surface is the light receiving device according to the first aspect of the present invention, which is a rotationally symmetric shape with respect to the center line of the output surface.

In addition, the eighth aspect of the present invention
In the light receiving device according to the first aspect of the present invention, the focal length of the input surface is larger than the distance between the input surface and the output surface.

The ninth aspect of the present invention provides
The inner peripheral surface is the light receiving device according to the first aspect of the present invention, which is made of a highly reflective material.

The tenth aspect of the present invention is
The inner peripheral surface is the light receiving device of the first aspect of the present invention having a periodic structure that causes Bragg reflection.

  According to the present invention, it is possible to provide a light receiving device having a wider axis misalignment incident angle range that can guarantee a minimum gain with respect to incident light in a three-dimensional optical system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
1 and 2 are side cross-sectional views showing light ray trajectories of the light receiving device having the first side surface shape according to the first embodiment of the present invention. FIG. 1 shows a ray trajectory when the incident light has no axial misalignment, and FIG. 2 shows a ray trajectory when the incident light has an axial misalignment.

  As shown in FIG. 1, the light receiving device according to the first embodiment includes a light collector 10 and a light receiving element 4, and is separated from the light source 1 by a free space 2.

The condenser 10 includes an output surface 6 and an input surface 5 that faces the output surface 6 and has a larger area than the output surface 6. The input surface 5 is a convex surface, and its focal position is farther from the output surface 6. A reflective side surface 8 is provided from the input surface 5 to the output surface 6. The portion of the reflective side surface 8 that is biased toward the input surface 5 side rather than the output surface 6 side has a shape in which the inclination angle (θ _m ) 11 monotonously decreases from the output surface 6 toward the input surface 5. And the part of the reflective side surface 8 other than the part where the inclination angle 11 decreases monotonously has a shape in which the inclination angle 11 is constant.

  In addition, the condenser 10 includes a light guide unit 9 having a constant refractive index inside the area surrounded by the input surface 5, the output surface 6, and the reflective side surface 8. The concentrator 10 has an axisymmetric shape with respect to the central axis 3 connecting the center points of the input surface 5 and the output surface 6.

  And the light receiving element 4 is arrange | positioned in the position which receives the light radiate | emitted from the output surface 6 of the collector 10. FIG. A ray trajectory 12 indicates a ray trajectory in the light collector 10 after the light incident from the input surface 5 enters the light collector 10.

  Note that the focal position of the input surface 5 is farther than the output surface 6 means that the incident light 7 with no axial deviation intersects the central axis 3 after refraction on the input surface 5. Regardless of the position, it is far from the output surface 6 position. Note that the intersections of the light rays incident on the respective positions on the input surface 5 with the central axis 3 do not necessarily coincide with each other.

  Further, the inclination angle referred to here is an angle formed by the tangent line of the reflective side surface 8 included in the plane and the central axis 3 at each point on the line where the plane including the central axis 3 and the reflective side surface 8 intersect. To tell. For example, the plan view shown in FIG. 1 is an example of a plane including the central axis 3. In this case, the tangent line at the intersection (reflection point (P) 13) with the outer shape of the reflective side surface 8 in FIG. The angle formed (tilt angle 11) is the tilt angle at the reflection point (P) 13.

  The reflective side surface 8 corresponds to an example of the inner peripheral surface of the present invention. The light collector 10 and the light receiving element 4 correspond to examples of the light collector and the detection unit of the present invention, respectively. The center axis 3 corresponds to an example of the center line of the output surface of the present invention.

  Next, assuming that all the light rays reaching the output surface 6 are received by the light receiving element 4, the light receiving state of the light incident on the input surface 5 will be described by ray tracing of the light incident on the input surface 5. .

  First, the case where the incident light 7 with no axial deviation enters the condenser 10 will be described with reference to FIG.

  The light beam 30 incident on the center of the input surface 5 travels on the central axis 3 and directly reaches the center of the output surface 6. Since the focal position of the input surface 5 is farther than the output surface 6, the point reached after refraction at the input surface 5 with respect to the central axis 3 as the incident point on the input surface 5 moves away from the central axis 3. The distance from the center of the output surface 6 is the same as the incident position on the input surface 5. Further, the point reached after the refraction is that after leaving the output surface 6, the inclination angle 11 moves to a part on the reflection side surface 8, but the output surface is reflected by the reflection side surface 8 like the light beam 31. Reach 6 The arrival point on the output surface 6 at that time moves in the direction opposite to the incident position on the input surface 5 with respect to the central axis 3.

  Further, as the incident point on the input surface 5 moves away from the central axis 3 and approaches the end, the point on the reflection side surface 8 that reaches first after refraction further moves from the output surface 6 side to the input surface 5 side. However, the point on the reflective side surface 8 that reaches first because of refraction at the input surface 5 does not reach the region where the inclination angle 11 near the input surface 5 monotonously decreases, or even if it reaches, the inclination angle Since 11 is a region that is not significantly different from a certain region, the point reached on the output surface 6 after being reflected by the reflective side surface 8 continues to be opposite to the incident position on the input surface 5 with respect to the central axis 3. It moves to the end of the output surface 6. Then, after reaching the output surface 6, the reaching point moves to the reflection side surface 8 in the direction opposite to the incident position on the input surface 5 with respect to the central axis 3 to form a second reflection point.

  As shown in Expression 3, the incident angle β to the reflection point on the side surface is such that the inclination angle at each reflection point is accumulated in the refraction angle for each reflection on the side surface. The closer to the end, the more the number of reflections between the reflecting surfaces facing each other increases, and the light receiving condition of Equation 5 cannot be satisfied. Accordingly, when the focal point of the input surface 5 is farther from the output surface 6 as in the collector 10 of the first embodiment shown in FIG. 1, a light ray (light ray 32) incident near the end of the input surface 5 is used. ) The gain for the amount of light decreases.

  Next, the case where the incident light 14 with an axial shift enters the condenser 10 will be described with reference to FIG.

As shown in FIG. 2, the case where the light emitted from the light source 1 is incident on the input surface 5 of the condenser 10 from a direction shifted in the axial deviation direction will be described. In this case, light rays 34 incident on the center axis 3 of the input surface 5, progresses the refracted light guide portion 9 with refraction angle alpha ₁ 14 at an incident angle alpha 13.

  The reflection point on the reflective side surface 8 of the light ray 35 incident near the end in the direction opposite to the axial deviation of the input surface 5 reaches the first after the refraction at the input surface 5 is a region where the inclination angle 11 decreases monotonously. Since it is near the input surface 5, the absolute value of the inclination angle 11 at the reflection point is minimum on the reflection side surface 8 and is very small. According to Equation 3, the incident angle (= reflection angle) is the value at the input surface 5. Near the refraction angle, the reflected light reaches and is received near the end in the direction opposite to the axial deviation of the output surface 6 with respect to the central axis 3.

  Here, if the inclination angle 11 at the point on the reflective side surface 8 that reaches first is further reduced, the second reflective point on the reflective side surface 8 on the same side as the first reflective point with respect to the central axis 3 is reached. However, since the incident angle at the second reflection point is very small, the reflected light at the second reflection point also reaches the output surface 6 and is received.

  Next, as the incident point approaches the central axis 3 from the end opposite to the axis shift of the input surface 5 (upper side in FIG. 2), the reflection point that first reaches the reflection side surface 8 after being refracted on the input surface 5. Is moving from the input surface 5 side to the output surface 6 side, the inclination angle 11 at the reflection point on the reflection side surface 8 gradually increases, and the point reaching the output surface 6 after reflection is in the axial deviation direction. Move. Then, after reaching the end of the output surface 6, the point reached after the reflection moves to the reflection side surface 8 in the direction opposite to the incident position on the input surface 5 with respect to the central axis 3 to move to the second reflection point. Can do.

  Since the incident beam (= reflection angle) of the second reflection point is large, the ray 34 of the axially shifted light 14 incident near the center on the input surface 5 is reflected in the direction of the input surface 5 as shown in FIG. Even if a third reflection point is formed on the reflection side surface 8 which is reflected in the direction of the output surface 6 and is opposed, the incident angle to the third reflection point is very large, and finally it is reflected in the direction of the input surface 5. The light receiving element 4 cannot receive light.

  Then, as the incident position on the input surface 5 approaches the end of the axial deviation direction from the central axis 3, the first reflection point on the reflective side surface 8 after refraction at the input surface 5 moves in the direction of the output surface 6. As a result, the second reflection point on the opposing reflection side surface 8 also moves in the direction of the output surface 6, reaches the output surface 6, and can receive light like the light beam 33.

  Next, the light receiving device of the present invention having a configuration different from that in FIGS. 1 and 2 will be described.

  3 and 4 are side cross-sectional views showing light ray traces of the light receiving device having the second side surface shape according to the first embodiment of the present invention. FIG. 3 shows a ray trajectory when the incident light has no axial deviation, and FIG. 4 shows a ray trajectory when the incident light has an axial deviation.

  As shown in FIG. 3, the light receiving device having the second side surface shape according to the first embodiment includes a light collector 20 and a light receiving element 24, and is arranged separated from the light source 1 by a free space 2. ing.

The condenser 20 includes an output surface 26 and an input surface 25 that faces the output surface 26 and has a larger area than the output surface 26. The input surface 25 is a convex surface, and its focal position is farther from the output surface 26. A reflective side surface 28 is provided from the input surface 25 to the output surface 26. The portion of the reflective side surface 28 that is biased toward the input surface 25 side rather than the output surface 26 side has a shape in which the inclination angle (θ _m ) 21 monotonously decreases from the output surface 26 toward the input surface 25. And the part of the reflective side surface 28 other than the part where the inclination angle 21 monotonously decreases has a shape in which the inclination angle 21 monotonously increases toward the input surface 25.

  In addition, the light collector 20 includes a light guide unit 29 having a constant refractive index inside the area surrounded by the input surface 25, the output surface 26, and the reflective side surface 28. The condenser 20 has an axisymmetric shape with respect to a central axis 23 that connects the center points of the input surface 25 and the output surface 26.

  The light receiving element 24 is arranged at a position for receiving light emitted from the output surface 26 of the condenser 20. The ray trajectory 22 indicates the ray trajectory in the light collector 20 after the light incident from the input surface 25 enters the light collector 20.

  3 and FIG. 4, the light receiving mechanism of the light receiving device having the second side surface shape is configured so that the input surface 25 at the time of axial misalignment is compared with the light receiving device having the first side surface shape described above. The light receiving device having the first side shape is the same as that of the light receiving device having the first side surface shape except that the amount of incident light near the center decreases.

  As described above, the light receiving device according to the first embodiment increases the ratio of reflection on the reflection side surface after refraction at the input surface regardless of whether it has the first side surface shape or the second side surface shape. In this way, the input surface has a focal point position farther than the output surface, and the portion where the inclination angle monotonously decreases from the output surface toward the input surface is located on the input surface side rather than the output surface side. By adopting the side surface shape, incident light near the edge on the input surface is prevented from receiving reflected light when there is no axial misalignment. When there is no deviation, direct light reception and reflection light reception are promoted, and when there is an axis deviation, reflection light reception is suppressed.

  Next, referring to FIGS. 5 to 9, the gain in each of the case where the shape of the reflection side surface of the light receiving device of the first embodiment is used and the case where the typical shape of the conventional reflection side surface is used are shown as follows. The comparison will be described.

  FIG. 5 shows side sectional views of various reflecting side surface shapes of the condenser, which are expressed by the functions shown in Table 1.

  The shape of each reflective side surface shown in FIG. 5 and the function of Table 1 is as follows: (i) straight line, (ii) inclination angle monotonically increases, (iii) inclination angle changes from monotonic increase to constant, and (iv) inclination angle is constant (Vi) Inclination angle has a turning point from monotonic increase to monotonic decrease, (vi) Inclination angle monotonously increases from 0, then turns monotonically to return to 0, (vii) Inclination angle Have the inflection point from monotonic decrease to monotonic increase. Note that these changes in the inclination angle are shown in the direction from the output surface to the input surface.

図６は、表１の関数で示す集光器の反射側面の各形状(i)〜(vii)がわかりやすいように、それらの側断面を誇張して示した模式図である。図１および図２に示した第１の側面形状を有する反射側面８の形状は、表１の(iv)の関数で表される形状であり、図６(iv)の模式図が相当する。また、図３および図４に示した第２の側面形状を有する反射側面２８の形状は、表１の(v)の関数で表される形状であり、図６(v)の模式図が相当する。また、特許文献１および特許文献２の集光器の部分の形状は、それぞれ、表１の(i)および(ii)の形状に相当する。

FIG. 6 is a schematic diagram showing exaggerated side cross sections so that the shapes (i) to (vii) of the reflecting side surfaces of the concentrator indicated by the functions in Table 1 are easy to understand. The shape of the reflective side surface 8 having the first side surface shape shown in FIGS. 1 and 2 is a shape represented by the function (iv) of Table 1, and corresponds to the schematic diagram of FIG. 6 (iv). The shape of the reflective side surface 28 having the second side shape shown in FIGS. 3 and 4 is a shape represented by the function (v) in Table 1, and the schematic diagram in FIG. To do. Moreover, the shape of the part of the concentrator of patent document 1 and patent document 2 is corresponded to the shape of (i) and (ii) of Table 1, respectively.

In Table 1, the central axis of the condenser is the z-axis (the output surface is the origin), the radii between the input surface and the output surface are D ₀ and D ₁ , and the distance between the input surface and the output surface is h. When the surface is a spherical surface, the radial distance r from the central axis is shown.

  For each function in Table 1, gains were calculated when the average tilt angle was changed and when the incident light had no axial deviation and 15 ° axial deviation, and the changes in the minimum gains were compared.

  FIG. 7 is a diagram for explaining the set values of the respective side shapes targeted when calculating the respective gains. The average inclination angle is the inclination angle when the side surface shape is assumed to be a straight line, that is, the point on the circumference of the input surface and the point on the circumference of the output surface in the cross section including the center line of the output surface. The angle formed by the straight line and the center line.

Specifically, in each function of (i) to (vii) in Table 1, the output surface radius D ₁ = 0.5 mm, and the distance h between the output surface and the input surface is set as a fixed value h = 10 mm. at 0.25mm increments in the range of the radius _{D 0} from 0.5mm to 13 mm, the center position X0 of the input spherical, the center line of the output surface, at the position of 0.2mm increments between the output surface and the input surface, In all cases when each was changed, the gain with respect to the incident light without axial misalignment and the gain with respect to the incident light with 15 ° axial misalignment were obtained.

Since the average inclination angle is determined by the radius D _{0 of} the input surface, the radius D _{1 of} the output surface, and the distance h between the output surface and the input surface, the average inclination angle changes as the radius D _{0 of the} input surface is changed. .

  8 and 9 are graphs showing changes in the minimum gain value with respect to the average inclination angle obtained as described above for each function (i) to (vii) in Table 1. FIG. Here, the lower gain value of the two gains at the time of no axis deviation and 15 ° axis deviation is used as the minimum gain value. FIG. 8 shows changes in the minimum gain when the center position X0 of the input spherical surface is 4.2 mm, and FIG. 9 shows changes in the respective minimum gains when X0 is 0 mm. In addition, each code | symbol (i)-(vii) shown in FIG. 8 and FIG. 9 respond | corresponds to the reflective side surface shape represented by each numerical formula of (i)-(vii) of Table 1. FIG. Further, here, the gain value in the case where the reflection side surface is metal reflection is shown.

  From FIG. 8, in the case of the side shape of (iv), that is, in the case of the first side shape of the first embodiment, the same average inclination angle is obtained in the solid angle range where the average inclination angle is 27 ° or more. It can be seen that the minimum gain value is greater than in any other shape.

  Further, in the case of the side shape of (v), that is, in the case of the second side shape of the first embodiment, the conventional average having the same average inclination angle in the solid angle range where the average inclination angle is 47 ° or more. The minimum gain value is larger than that of the side shape ((i), (ii), (iii), (vi), (vii)). Further, in the case of the side shape (v), the minimum gain value is larger than that in the case of the conventional side shape having the same average inclination angle even when the average inclination angle is in the range of 35 ° to 41 °.

  From FIG. 9 in which X0 is 0 mm, it can be seen that there is a tendency similar to FIG.

  That is, in the case of the side shape (iv), the minimum gain value is larger in the solid angle range where the average inclination angle is 24 ° or more than in the conventional shape having the same average inclination angle.

  In the case of the side shape (v), the minimum gain value is larger in the solid angle range where the average inclination angle is 47 ° or more than in the case of the conventional side shape having the same average inclination angle. Further, in the case of the side shape (v), the minimum gain value is larger than that in the case of the conventional side shape having the same average inclination angle even in the angle range where the average inclination angle is 27 ° to 43 °.

  From these results, using the side shape represented by the formulas (iv) and (v), when the solid angle is large, the minimum gain value should be increased compared to other shapes with the same average inclination angle. You can see that If the minimum gain value can be increased, the allowable axis deviation angle range can be increased.

  This is because the focal position of the input surface is more than the output surface so that the ratio of reflection on the reflective side surface after refraction on the input surface, which is common to the reflective side surface shapes expressed by the formulas (iv) and (v), is increased. By adopting an input surface shape that is farther away and a side surface shape that has a portion whose inclination angle monotonously decreases as it goes from the output surface to the input surface. Incident light near the edge of the light is suppressed when there is no axial misalignment, and reflected light reception is promoted when there is an axial misalignment, while incident light near the center of the input surface promotes direct and reflected light reception when there is no axial misalignment. This is because reflected light reception is suppressed when the axis is displaced. Therefore, since a gain decrease when the axis is shifted can be suppressed, a relatively high gain can be maintained in a wide directivity angle range where the average inclination angle is 47 ° or more. Therefore, it is possible to manufacture a light-receiving device having a wider axial incident angle range that can guarantee the minimum gain than the conventional one.

  If the condensing body is enlarged in a similar shape, the gain increases. Therefore, if each shape is similarly increased in a similar shape, each gain is increased while maintaining the magnitude relationship of the respective gains. That is, if the side surface shape represented by the formulas (iv) and (v) is used regardless of the size of the same size, if the solid angle is large, other sizes with the same average inclination angle may be used. The minimum gain value can be increased compared to the shape.

  The shapes of the reflecting side surface 8 of the collector 10 of the first embodiment and the shape of the reflecting side surface 28 of the collector 20 including the similar shapes are shown in Table 1 (iv), (v ) Can be expressed as in Equation 1.

例えば、平均傾斜角が広い範囲（例えば、２７°以上の範囲）で、数１で表される反射側面形状を前提とすることにより、許容できる軸ズレ角度範囲の大きい受光デバイスを容易に設計できる。

For example, it is possible to easily design a light receiving device having a large allowable axial deviation angle range by assuming a reflective side surface shape expressed by Equation 1 in a wide average inclination angle range (for example, a range of 27 ° or more). .

  Further, in FIGS. 8 and 9, focusing on the reflective side surface shape expressed by the formula (iv), in the range where the average inclination angle is 27 ° or more, the conventional reflective side surface shape having the same average inclination angle is used. It can also be seen that the minimum gain can be reliably increased. In other words, a light receiving device having a large allowable axial deviation angle range can be obtained by assuming a reflective side surface shape represented by Formula 2 indicating a similar shape of the function (iv) in the range where the average inclination angle is 27 ° or more. It can be designed more easily.

次に、軸ズレ無し時と軸ズレ有り時の各入射光の利得差が小さい場合の反射側面形状を最適構成として、表１の各関数毎に最適構成の反射側面形状を抽出し、それらの各最適構成の反射側面形状における利得を対比した。

Next, the reflective side surface shape when the gain difference of each incident light when there is no axial misalignment and when there is an axial misalignment is taken as the optimal configuration, and the reflective side surface shape of the optimal configuration is extracted for each function in Table 1, The gain in the reflective side surface shape of each optimum configuration was compared.

  FIG. 10 shows the correlation between the reflection side surface shape and the gain of the optimum configuration extracted for each function of (i) to (vii) in Table 1.

Each optimal configuration was extracted based on the total data obtained by changing the center position X0 of the radius D ₀ and the input spherical input surface above. First, for each function of (i) to (vii), a configuration was extracted in which the difference between the gain for light incident without axis deviation and the gain for light incident with a 15 ° axis deviation was minimized. When a plurality of configurations having the same gain difference are extracted, the configuration having the largest gain value is extracted as the optimal configuration.

The values of the input surface radius D ₀ and the input spherical center position X ₀ of the configuration extracted as each optimal configuration are (i) 7.25 mm and 5.4 mm, (ii) 8.5 mm and 7.4 mm, respectively. (Iii) is 11.25 mm and 10.0 mm, (iv) is 11.25 mm and 4.2 mm, (v) is 13.0 mm and 0 mm, (vi) is 12.5 mm and 3.0 mm, (vii) Are 4.75 mm and 2.4 mm.

  Each gain shown in FIG. 10 indicates the gain in the case where the reflection side surface shape having the optimum configuration represented by each function is used. Therefore, in the case of the shape represented by any function, the gains when there is an axial deviation and when there is no axial deviation are substantially equal.

  As described in (iv) at the time of metal reflection in FIG. 10, the gain difference between the absence of axial deviation and the presence of axial deviation is equal to the optimum configuration, but the gain value is low, or the gain difference is Some are big. Also in the case of (iv) at the time of metal reflection in FIG. 10, only a part is described other than the optimal configuration, and descriptions other than the optimal configuration are omitted for other shapes.

  From FIG. 10, the angle dependency of the gain when the reflection side surface is changed to the shapes of (i) to (vii) is the highest in the case of (iv) used in the first embodiment, and the angle dependency. It turns out that the nature is small.

  Compared with the gain (25 dB) under the assumption that all light received on the input surface is received, the gain for the shape (iv) is low regardless of the presence or absence of axial misalignment. This is because the change in the angle of the gain is compensated so that the light incident on the end of the input surface can be received when there is no axial deviation, and can be received when there is no axial deviation. Specifically, in (iv) shown in FIG. 10, a high gain of about 20 dB is obtained in the directivity angle range of ± 15 °.

  FIG. 5 shows the case of metal reflection (using a material with high reflectivity) and the case of total reflection. As can be seen from the comparison of Equations 5 and 6, the case of metal reflection has a higher gain. Is obtained.

  In actual use, a light receiving device used for optical space transmission is required to have a gain of at least about 20 dB. From FIG. 10, it can be said that a light-receiving device having a concentrator having a reflection side surface having an optimal configuration represented by the function (iv) can be used in practical use even with a small one having a length of about 10 mm. I can say that.

  Increasing the size of the concentrator with a similar shape increases the gain while maintaining the same gain difference ratio from the axial misalignment. That is, even when the optimally shaped concentrators represented by the functions shown in FIG. 10 are changed in the same ratio with similar shapes, the magnitude relationship between the shapes does not change. Therefore, for example, when using a concentrator having an optimal reflection side surface represented by the function (v), the gain is about 16 dB at the size shown in FIG. 10, so that the gain is about 20 dB. If it is a large shape with a similar shape, it will be practical.

  Further, as described above, the optimum shape of the reflective side surface represented by each function obtained in FIG. 10 is the same distance between the input surface and the output surface, and the input surface diameter is changed within the same range. Since each of the shapes has the largest gain, it can be said that the optimum configuration shown by the function (iv) can achieve the highest gain within the same limited space. In other words, as long as the same gain is obtained, the size can be reduced to the smallest when the shape of the reflective side surface (similar shape) of the optimum configuration shown by the function (iv) is used. Further, from FIG. 5, similarly to the function (iv), in the case of the optimum configuration indicated by the function (v) having a shape in which the inclination angle monotonously decreases toward the input surface on the input surface side, In the case of metal reflection, it can be said that it can be made smaller than in the case of other conventional reflective side surface shapes.

  Therefore, when a higher gain is required, the desired gain can be obtained with the smallest size by increasing the shape of the reflective side surface of the optimal configuration indicated by the function (iv) with a similar shape. .

  Although the light receiving element 4 has been described as an example of the detection unit of the present invention, not only a photoelectric converter such as a photodiode as a light receiving element, but also an optical transmission line is connected to the output surface to transmit the light as far as it is. Also good. In the case of receiving wavelength-multiplexed light, an optical filter or the like may be arranged before being coupled to the light receiving element, and the light may be received after wavelength separation. The optical filter may be used for the purpose of removing unnecessary wavelengths.

  In the first embodiment, the input surfaces 5 and 25 are convex. However, the same effect can be obtained even if the input surface has a shape other than that, for example, a flat surface or a concave surface.

  Moreover, although the shape of the collectors 10 and 20 is an axially symmetric shape with respect to the central axes 3 and 23, the shape is not necessarily limited to the axially symmetric shape with respect to the central axes 3 and 23. For example, the cross-sectional shape perpendicular to the central axis may be an elliptical shape.

  Further, the reflection side surfaces 8 and 28 of the first embodiment only need to be able to reflect light only to the inner light guides 9 and 29 side. Therefore, for example, a light collector in which the light guide portions 9 and 29 are configured in close contact with the side surface portion having the reflection side surfaces 8 and 28 as inner peripheral surfaces may be used.

  In addition, it is desirable to use a material having high reflectivity for the reflection side surfaces 8 and 28 of the light receiving device of the first embodiment. A material having a reflectance of 70% or more is desirable, and for example, metal is suitable.

  Further, as the reflective side surface material, a periodic structure that realizes high reflectivity structurally, for example, causes Bragg reflection may be used.

  As is apparent from the above description, by using the light receiving device of the present invention, it is possible to provide an optical system that does not require a movable mechanism, provides a high gain in a wide light receiving angle range, and enables high-speed optical space transmission. .

  The light receiving device according to the present invention is small in size and has an effect that the axial misalignment incident angle range in which the minimum gain can be ensured with respect to the incident light in the three-dimensional optical system is wider than that of the conventional one. It is useful as a light receiving device that does not require optical axis adjustment, a high-speed transmission method, and the like.

Side sectional view of a light-receiving device having the first side surface shape according to Embodiment 1 of the present invention, showing a ray trajectory when incident light has no axial misalignment. Sectional side view which shows the light ray locus at the time of incident light misalignment of the light receiving device which has the 1st side surface shape of Embodiment 1 of this invention Side sectional view of a light-receiving device having the second side surface shape according to the first embodiment of the present invention, showing a ray trajectory when incident light has no axial misalignment. Sectional side view which shows the light ray locus at the time of incident light misalignment of the light receiving device which has the 2nd side surface shape of Embodiment 1 of this invention Cross-sectional side view of various shapes on the reflective side of the collector Schematic diagram showing exaggerated side sections of various shapes on the reflective side of the concentrator The figure explaining the setting value of each side shape made into object when calculating each gain The figure which showed the change of the minimum gain value with respect to the average inclination angle for each shape of the reflective side surface of the collector The figure which showed the change of the minimum gain value with respect to the average inclination angle for each shape of the reflective side surface of the collector The figure which shows the correlation of the shape of each optimal structure, and a gain among the various shapes of the reflective side surface of the collector shown in FIG. 3 and Table 1 Cross-sectional side view of a conventional light-receiving device that can receive incident light with a wide angle at a wide angle Side cross-sectional view of a conventional dielectric total internal reflection concentrator that can receive incident light with a wide angle at a wide angle

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Free space 3, 23 Center axis 4, 24 Light receiving element 5, 25 Input surface 6, 26 Output surface 7 Axis-free incident light 8, 28 Reflection side surface 9, 29 Light guide 10, 20, Light collector 11, 21 Side tilt angle 12, 22 Ray trajectory 13, 27 Reflection point 14 Axial incident light 30, 31, 32, 33, 34, 35 Ray

Claims (10)

An input surface on which light is incident, an output surface facing the input surface and having an area smaller than the input surface, and provided from the input surface to the output surface, and an inner peripheral surface thereof is incident from the input surface A light collector having a side surface for reflecting light;
A detector that receives light emitted from the output surface;
The shape of the inner peripheral surface of the light collector is at least a portion where the inclination angle of the inner peripheral surface with respect to the center line of the output surface monotonously decreases from the output surface toward the input surface. A light receiving device having a shape closer to the input surface than the input surface.   The inclination angle of the inner peripheral surface is a tangent to the inner peripheral surface included in the plane and the center line at each point on a line where the plane including the center line of the output surface intersects the inner peripheral surface. The light receiving device according to claim 1, wherein the light receiving device is an angle formed by.   The light receiving device according to claim 1, wherein the reflection of the light incident from the input surface on the inner peripheral surface is a metal reflection.   The light receiving device according to claim 3, wherein a shape of a portion of the inner peripheral surface other than a portion where the inclination angle monotonously decreases is a shape where the inclination angle is constant or monotonously increases. 4. The light receiving device according to claim 3, wherein the shape of the inner peripheral surface is a shape in which a distance r in the vertical direction from the center line is expressed by Formula 1 at a position of a distance z from the output surface on the center line. device.

The shape of the inner peripheral surface is a shape in which the distance r in the vertical direction from the center line at the position of the distance z from the output surface on the center line is expressed by Formula 2,
The angle between the straight line connecting the point on the circumference of the input surface and the point on the circumference of the output surface in a cross section including the center line is a shape of 27 ° or more. 4. The light receiving device according to 3.

  The light receiving device according to claim 1, wherein a shape of the inner peripheral surface is a rotationally symmetric shape with respect to a center line of the output surface.   The light receiving device according to claim 1, wherein a focal distance of the input surface is larger than a distance between the input surface and the output surface.   The light receiving device according to claim 1, wherein the inner peripheral surface is made of a highly reflective material. The light receiving device according to claim 1, wherein the inner peripheral surface has a periodic structure that causes Bragg reflection.

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