WO2017187609A1 - 平行光発生装置 - Google Patents
平行光発生装置 Download PDFInfo
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- WO2017187609A1 WO2017187609A1 PCT/JP2016/063398 JP2016063398W WO2017187609A1 WO 2017187609 A1 WO2017187609 A1 WO 2017187609A1 JP 2016063398 W JP2016063398 W JP 2016063398W WO 2017187609 A1 WO2017187609 A1 WO 2017187609A1
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- light source
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/30—Collimators
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
- G02B19/0004—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed
- G02B19/0009—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having refractive surfaces only
- G02B19/0014—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having refractive surfaces only at least one surface having optical power
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
- G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
- G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
- G02B19/0052—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a laser diode
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B3/00—Simple or compound lenses
- G02B3/02—Simple or compound lenses with non-spherical faces
- G02B3/06—Simple or compound lenses with non-spherical faces with cylindrical or toric faces
Definitions
- the present invention includes a light source that emits light having an asymmetric spread angle in a biaxial direction included in a plane perpendicular to the optical axis, and a conversion optical system that reduces the spread angle of output light from the light source.
- the present invention relates to a parallel light generator.
- the configuration disclosed in Patent Document 1 uses an aspherical single lens and arranges a light source at the focal position of the lens, thereby making light having a large divergence angle substantially parallel light.
- the actual light source is not a point light source, but has a finite light emission point size.
- the spread half angles ⁇ ho and ⁇ vo after collimation in the horizontal direction and the vertical direction are expressed by the following formula (1) using the focal length f of the lens used for collimation and the light emission half widths wh and wv in each direction of the light source.
- ⁇ ho Tan ⁇ 1 (wh / f)
- ⁇ vo Tan ⁇ 1 (wv / f) (1) It becomes.
- the spread half angles ⁇ ho and ⁇ vo after collimation increase as the light emission half widths wh and wv increase. Since the light emission width of the light source is generally not freely changeable by the user, it is necessary to increase the focal length f of the lens in order to reduce the divergence angle. At this time, since the light source is disposed at the focal position on the incident surface side of the lens, the distance between the light source and the lens increases as the focal length f increases.
- the effective diameter of the lens is determined so that no loss occurs with respect to light rays with a large divergence angle. It is preferable from the viewpoint of efficiency.
- the focal length f, the effective diameter ⁇ of the lens, and the spread half angles ⁇ ho and ⁇ vo after collimation are determined independently for a light source having emission half widths wh and wv. It is not possible to trade off. That is, in order to reduce the divergence angle, it is necessary to increase the focal length f, and it is necessary to place a large lens away from the lens. If a lens with a short focal length f is used, the spread angle cannot be reduced. For this reason, there is a problem that it is difficult to satisfy the conditions of downsizing, a small divergence angle, and high light utilization efficiency.
- the present invention has been made to solve this problem, and an object of the present invention is to obtain a parallel light generator capable of satisfying the conditions of downsizing, a small divergence angle and high light utilization efficiency.
- a parallel light generator includes a lens having a cylindrical and concave incident surface, and an exit surface that is convex with respect to the optical axis, and one direction in a plane perpendicular to the optical axis. And a light source having a different divergence angle with the other direction that is 90 degrees different from the one direction, the light source is disposed at the position of the focal distance on the incident surface side in the other direction of the lens, and the one direction of the light source Are arranged in the direction of curvature of the cylindrical shape of the lens.
- the parallel light generation device has a lens having a cylindrical incident surface having a concave shape and an exit surface having a convex shape with respect to the optical axis, and different spread angles in one direction and the other direction. Is arranged at the position of the focal length on the incident surface side in the other direction of the lens, and arranged so that one direction is the direction of curvature of the cylindrical shape of the lens.
- FIG. 1A is a plan view of a parallel light generator according to Embodiment 1 of the present invention, and FIG. 1B is a side view thereof.
- FIG. 2A is a plan view of a light source in the parallel light generator according to Embodiment 1 of the present invention, and FIG. 2B is a side view thereof.
- 3A is a plan view for explaining the optical path of the parallel light generator according to Embodiment 1 of the present invention, and FIG. 3B is a side view. It is explanatory drawing which shows the relationship between the spreading half angles (theta) ho and (theta) vo after the collimation of a horizontal direction and a vertical direction, and the focal distance f.
- FIG. 6A is a plan view of a parallel light generator according to Embodiment 2 of the present invention
- FIG. 6B is a side view thereof
- FIG. 7A is a plan view of a light source in the parallel light generator according to Embodiment 3 of the present invention
- FIG. 7B is a side view.
- FIG. 1A and 1B are explanatory diagrams of a parallel light generator according to Embodiment 1, in which FIG. 1A is a plan view and FIG. 1B is a side view.
- the spread angle is different between the horizontal direction which is one direction in the plane perpendicular to the optical axis and the vertical direction which is the other direction 90 degrees different from the one direction.
- a semiconductor laser is used as the light source 20 having the following.
- the horizontal ray 20a has the smallest spread half angle, typically 2 to 15 ° (half angle 1 / e2).
- the internal position 21a is a virtual emission point of the horizontal light beam 20a.
- the vertical light ray 20b has the largest spread half angle, typically 15 to 45 ° (half angle 1 / e2).
- the emission point of the light beam 20 b in the vertical direction is the end face 21 b of the light source 20.
- the light source 20 has finite emission widths 20c and 20d in the horizontal and vertical directions.
- the light emission width 20c in the horizontal direction is usually in the range of several ⁇ m to several 100 ⁇ m.
- the light emission width 20d in the vertical direction is usually in the range of 1 ⁇ m to several ⁇ m.
- the semiconductor laser that is the light source 20 generally has an astigmatic difference of about several ⁇ m to 20 ⁇ m, and the virtual emission point differs between the horizontal direction and the vertical direction.
- the horizontal direction behaves as if it is emitted from the inside from the end face of the semiconductor laser. That is, the internal position 21a is a virtual emission point.
- the lens 10 is an optical element having a center thickness d having an entrance surface 11 and an exit surface 12, and is made of glass having a refractive index n.
- the lens 10 is usually produced by a method for producing a lens, such as polishing or molding.
- an antireflection film for the light source wavelength is formed on the incident surface 11 and the emission surface 12.
- the incident surface 11 is configured as a concave shape that is cylindrical with respect to the horizontal light beam 20 a of the light source 20, and the output surface 12 has a convex shape that is rotationally symmetric with respect to the optical axis 10 a of the lens 10.
- the entrance surface 11 has a curvature with a curvature radius R h1 in the horizontal direction and a curvature radius R v1 (plane) in the vertical direction, and the exit surface 12 has a curvature with a curvature radius R v2 in both the horizontal and vertical directions.
- the signs of the curvature radii R h1 and R h2 are based on the intersections of the entrance surface 11 and the exit surface 12 and the optical axis 10a as a reference when the position of the center of curvature is on the light source side and on the opposite side. Define as negative.
- the vertical focal length f and the front (light source side) focal length FFLv with respect to the vertical light ray 20b are the vertical curvature radius R v1 of the incident surface 11 and the vertical curvature radius R v2 of the output surface 12.
- h1 is the front (light source side) principal point position in the vertical direction of the lens 10
- the sign is defined as positive from the intersection of the incident surface 11 and the optical axis 10a toward the inside of the lens.
- Equations (3) and (5) are related.
- the light source 20 is installed so that the end surface 21b is located at the focal length FFLv with respect to the vertical direction of the lens 10.
- FIG. 3A is a plan view and FIG. 3B is a side view.
- the light beam emitted from the light source 20 enters the incident surface 11 of the lens 10 while spreading, propagates through the lens from the incident surface 11 to the output surface 12, and exits from the output surface 12. Since the incident surface 11 has a cylindrical shape, the horizontal light beam 20 a and the vertical light beam 20 b are affected differently depending on the shape of the incident surface 11. In order to simplify the description, only the light beam 20a in the horizontal direction is considered as the light beam from the light source 20, and only the light beam 20b in the vertical direction is considered in the vertical direction.
- Ray 20a in the horizontal direction behaves like emitted from internal position 21a of the semiconductor laser, concave and the curvature radius R h1, the convex surface of curvature radius R h2, the beam diameter is enlarged.
- the operation of the above light rays will be described with a light ray matrix (for example, see: Lasers, AE Siegman, University Science Books, Mill Valley California, 1986.).
- a horizontal light beam 20 a from the light source 20 propagates a distance (focal length FFLv) from the light source 20 to the incident surface 11 of the lens 10 and enters the lens 10.
- the operation of the lens 10 is as follows: propagation through a dielectric boundary surface (incident surface 11) having a radius of curvature R h1 and a refractive index n, a dielectric having a thickness d and a refractive index n, and a radius of curvature R h2 and a refractive index n.
- This can be explained as an action received by the horizontal light beam 20a by each optical element on the dielectric interface (outgoing surface 12).
- the action that each optical element gives to the horizontal light beam 20a described by the column vector can be described by a matrix of 2 rows and 2 columns, and the expressions (6), (7), (8), and ( 9).
- r is the optical axis height of the light beam incident on each optical element
- ⁇ is the angle of the light beam incident on each optical element with respect to the optical axis
- r ′ is the optical axis height of the light beam emitted from each optical element.
- ⁇ ′ is the angle of the light beam emitted from each optical element.
- the (1,1) component of the 2-by-2 matrix representing the action of the optical element is A
- the (1,2) component is B
- the (2,1) component is C
- (2, 2) component is defined as D.
- C in the formula (7) represents (n ⁇ 1) / (nR h1 ).
- the horizontal beam radius wh1 becomes approximately R h2 / R h1 fold exit surface 12
- the horizontal direction of the light beam 20a incident on the incident surface 11 at the incident surface 11
- the spread half angle ⁇ h1 becomes R h1 / R h2 times on the exit surface.
- the spread angle in the horizontal direction can be reduced by the ratio of the curvature radii R h1 and R h2 .
- the horizontal direction is not a collimator but an enlargement system, and the horizontal spread angle can be determined independently of the relationship between the light emission half widths wh and wv and the focal length f shown in Equation (1). Is shown.
- Equation (12) is obtained from the product of the matrixes of Equation (6) and Equation (11).
- Equation (12) the propagation from the light source 20 to the incident surface 11 only increased the beam diameter at the incident surface 11 from r to r + FFLv ⁇ ⁇ . It can be seen that the rate of change in the beam diameter and divergence angle between the surfaces 12 does not change. It is clear from Equation (12) that this is not limited to the case where the propagation distance is FFLv. From the above, in the parallel light generator of the present invention, it is clear that the horizontal spread angle does not depend on the distance between the light source 20 and the lens 10 in the optical axis direction.
- light 20b in the vertical direction since the arranged end face 21b of the semiconductor laser to the position of the focal length FFLv, the plane of the entrance face 11 and by a convex radius of curvature R v2, is collimated.
- the operation of the above light rays will be described using a light ray matrix as in the horizontal direction.
- the light beam 20 b emitted from the light source propagates a distance (focal length FFLv) from the light source to the incident surface 11 of the lens 10 and enters the lens 10.
- the operation of the lens 10 is as follows: propagation through a dielectric boundary surface (incident surface 11) having a radius of curvature Rv1 and a refractive index n, a dielectric material having a thickness d and a refractive index n, and a curvature radius Rv2 and a refractive index n.
- This can be explained as an effect of the light beam 20b in the vertical direction received by each optical element on the dielectric interface (outgoing surface 12).
- the action given to each optical element with respect to the light beam 20b in the vertical direction described by the column vector can be described by a matrix of 2 rows and 2 columns, and is expressed by equations (15), (16), and (17), respectively.
- equations (15), (16), and (17) the action received by the light beam 20b in the vertical direction from the entrance surface 11 to the exit surface 12 is expressed by the following equation (18) as a product of these.
- the focal length f in the vertical direction that is, the radius of curvature R v2 and the refractive index n of the lens are determined in accordance with the required value of the vertical spread angle.
- the radius of curvature R h1 and the thickness d can be selected in accordance with the required value of the spread angle in the horizontal direction.
- a semiconductor laser manufactured by EAGLEYARD (model number: EYP-BAL-0808-08000-4020-CMT-0000) having a wavelength of 808 nm is collimated using a rotationally symmetric plano-convex lens. think of.
- the semiconductor laser has a horizontal spreading half angle of 8.5 °, a vertical spreading half angle of 25.5 °, a horizontal emission width of 200 ⁇ m, and a vertical emission width of 1 ⁇ m.
- the spread angle after collimation is set to 1 ° in both the horizontal and vertical directions.
- FIG. 4 shows the relationship between the spread half-angles ⁇ ho 401 and ⁇ vo 402 after collimation in the horizontal direction and the vertical direction and the focal length f, and FIG. Is shown.
- Expressions (1) and (2) are used, as shown in FIGS. 4 and 5, a lens having a focal length of 5.7 mm and an effective aperture of 5.5 mm is required.
- a radius of curvature R h1 0.2 mm
- a radius of curvature R h2 Rv2: 1.7 mm
- a thickness of 3.4 mm a refractive index of 1.8
- a vertical focal length 2 .1 mm
- light source side focal position 0.25 mm
- effective diameter 2 mm lens can be used, and the lens can be significantly reduced in diameter while satisfying a small divergence angle and high light utilization efficiency.
- values of the radius of curvature and the like are not limited to this configuration, and the size can be further reduced by reducing the vertical focal length and scaling.
- the incident surface 11 having a cylindrical shape and a concave shape, and a convex surface having a rotationally symmetric shape on the optical axis 10a
- the lens 10 having the shape of the emission surface 12 is arranged so that the horizontal direction of the light source 20 is the direction of curvature of the cylindrical shape of the lens 10, and the end surface of the light source 20 is positioned at the incident surface side focal length FFLv in the vertical direction.
- the light in the horizontal direction of the light source 20 is expanded on the incident surface 11 and the exit surface 12 of the lens 10, and the light in the vertical direction of the light source 20 is converted into substantially parallel light on the exit surface 12 of the lens 10. Therefore, it is possible to realize a parallel light generator that satisfies both the small divergence angle, the high light utilization efficiency, and the miniaturization condition.
- the light source 20 is a semiconductor laser.
- the same effect can be obtained for other types of lasers and light sources that are not lasers.
- the semiconductor laser is more suitable when applied.
- the spread angle does not increase due to the astigmatic difference.
- lenses having different focal lengths in the horizontal direction and the vertical direction are used, the horizontal focus position is made to coincide with the internal position 21a of the semiconductor laser, and the vertical focus position is set to the semiconductor laser.
- Another effect is that the positioning accuracy in the horizontal direction of the light source 20 and the lens 10 can be relaxed.
- the conventional collimating method when a positional shift occurs in the horizontal and vertical directions, there is a problem that the emission direction of the light beam is inclined with respect to the ideal emission direction, as can be seen from the equation (20).
- the lens 10 In order to suppress the inclination of the light beam, the lens 10 is required to be accurately positioned with respect to the light source 20, and typically, installation accuracy of about several ⁇ m to several tens of ⁇ m is required.
- the positional accuracy of the light emitting point with respect to the chip outline of the semiconductor laser has high accuracy in the vertical direction, but is low in the horizontal direction.
- the thickness in the vertical direction is strictly controlled, while the horizontal direction depends on the accuracy of cutting from the wafer to the chip, and the horizontal direction is usually cut out from several ⁇ m to several tens of ⁇ m. It becomes accuracy. For this reason, the position of the light emitting point in the horizontal direction varies with respect to the outer shape of the chip.For example, even when the chip and the lens are assembled with high accuracy on the basis of the outer shape, the relative position of the light emitting point in the horizontal direction and the lens varies. End up. On the other hand, in the present embodiment, even if a horizontal position shift due to a variation in the chip cutout position occurs, the influence on the inclination of the light emission direction is small, and assembly based on the outer shape is facilitated. It has the effect of being able to.
- the shape of the entrance surface 11 of the lens 10 is a cylindrical shape on the concave surface in the horizontal direction
- the concave surface shape may be a spherical surface or an aspherical surface.
- an aspherical surface it can be expected that aberrations generated in the optical system will be corrected better.
- the horizontal operation of the present invention is equivalent to collimating the light source image at the focal position of the dielectric boundary surface of the incident surface 11 at the dielectric boundary surface of the output surface 12. This is different from conventional collimating lenses, including those that are not axially symmetric, that collimate the light source image at the imaging position by the dielectric boundary surface of the incident surface at the dielectric boundary surface of the output surface.
- the focal position of the dielectric boundary surface of the exit surface 12 is the light source 20 by the dielectric boundary surface of the incident surface 11. This is effective when it is located in a range close to the focal plane instead of the image forming position.
- the shape in the vertical direction is a simple flat surface, but it is not necessary to be a complete flat surface, and the effect of the present invention can be obtained even with a concave surface or a convex surface. For example, by making the surface concave, it is possible to make the incident angle of the light ray gentler, so that it can be expected to reduce the aberration.
- the shape of the emission surface 12 is a rotationally symmetric convex surface, but does not have to be strictly rotationally symmetric.
- the degree of freedom in design can be increased, so it can be expected that the aberration will be corrected well. Becomes easier.
- the material of the lens 10 does not need to be glass, but may be plastic or crystal. It is clear that the focal length FFLv of the lens 10 and the installation position of the light source 20 do not need to be exactly matched, and there is no problem even if they deviate back and forth as long as they are within the required range of the spread angle in the vertical direction.
- a cylindrical lens having a concave incident surface and a light emitting surface having a convex shape with respect to the optical axis, and the optical axis.
- a light source having a different divergence angle between one direction in the plane perpendicular to the other and 90 degrees different from the other direction, and the light source is disposed at the focal plane side focal length in the other direction of the lens.
- the parallel light generator can satisfy the conditions of downsizing, a small divergence angle, and high light utilization efficiency.
- the light emission point width in one direction of the light source is set to be larger than the light emission point width in the other direction, so that a light source having a different spread angle can be realized. it can.
- the light source is a light source having an astigmatic difference, which can contribute to the realization of light sources having different divergence angles.
- the parallel light generation device of the first embodiment since the light source is a semiconductor laser, it is possible to realize a parallel light generation device that can satisfy the conditions of downsizing, a small divergence angle, and high light utilization efficiency. Can do.
- FIG. 6A and 6B are explanatory views of the parallel light generation apparatus according to the second embodiment.
- FIG. 6A is a plan view thereof
- FIG. 6B is a side view thereof.
- the parallel light generating apparatus of the second embodiment is different from the light source 20 of the first embodiment in that a semiconductor laser array having a plurality of light emitting points in the horizontal direction is used as the light source 30. Since the other points are the same as those of the first embodiment, the same reference numerals are given to the corresponding parts, and the description thereof is omitted.
- the end face 31 of the light source 30 that is a semiconductor laser array is installed at the position of the focal length FFLv in the vertical direction of the lens 10.
- Ray 30a in the horizontal direction from the light source 30, a convex concave and the curvature radius R h2 of the lens 10 in the radius of curvature R h1 the beam diameter of each light beam emitted from the light emitting points is increased.
- Ray 30b in the vertical direction from the light source 30, since using a light source 30 to the position of the focal length FFLv, is collimated by the convex surface of the plane and the curvature radius R v2 of the entrance surface 11 of the lens 10.
- the light in the horizontal direction of the light source 30 is expanded on the incident surface 11 and the exit surface 12 of the lens 10, and the light in the vertical direction of the light source 30 is substantially parallel on the exit surface 12 of the lens 10. Since it is converted into light, it becomes possible to realize a parallel light generator that satisfies both the small divergence angle, high light utilization efficiency, and miniaturization conditions.
- the beam pattern after the lens is in an array shape, and spatial uniformity is low.
- a lens 10 having an incident surface 11 having a cylindrical and concave shape and a light exit surface 12 having a rotationally symmetrical shape and a convex shape on the optical axis 10a is used.
- a spatially uniform beam is particularly useful when used for direct illumination without using a uniform optical system. Furthermore, since the beams of a plurality of light emitting points are overlapped, there is an effect that speckles which are problems when the laser is used for illumination can be reduced without adding a uniform optical system.
- the astigmatic difference is affected by the temperature distribution inside the semiconductor laser. Since the semiconductor laser array has different heat generation densities at the center and the end of the semiconductor laser array, the internal temperature distribution changes at the center and the end, and the astigmatic difference becomes a factor that varies from one light emitting point to another. . However, in this embodiment, even if there is a variation in astigmatism at each light emitting point, an increase in the spread angle can be suppressed, and stable parallel light can be obtained.
- the same effect can be obtained in combination with the lens 10 of the present invention even when the light source 30 is an array light source in which the light emission width or the cycle of the light emission points varies depending on the position in the horizontal direction. There is no.
- the configuration of the second embodiment is simple and inexpensive, and the configuration of the second embodiment is also used when the emission width and the period of the emission point change statically and dynamically in the horizontal direction. Then, there is an effect that a small divergence angle, high light utilization efficiency and miniaturization conditions can be satisfied.
- the light source has a plurality of light emitting points in one direction.
- the condition of high light use efficiency can be satisfied.
- the light source is a semiconductor laser array, a spatially uniform beam can be obtained.
- FIG. 7 is an explanatory diagram illustrating the definition of the light source 30 according to the third embodiment.
- the light source 30 comprising a semiconductor laser array is characterized by its emission width W and the period P of the emission point.
- F. F. W / P (22)
- the parallel light generator has a fill factor F.V. F. 0.5 ⁇ F. F. This is particularly suitable when the semiconductor laser array in the range ⁇ 1 is used as the light source 30.
- description here is abbreviate
- the horizontal spread angle from the light source 30 and the spread angle after the arrayed lens are the fill factor F. of the light source 30. F. Limited by. From formula (25), fill factor F.R. F. In the case of an array light source having an aperture of 0.5 or more, collimation is performed with a conventional rotationally symmetric lens. Therefore, when the light source is arranged at the front focal position, there is no vignetting for a beam within a certain spread angle ⁇ . It can be seen that the horizontal spread angle cannot be reduced.
- the horizontal divergence angle can be reduced, and a parallel light generator capable of satisfying the conditions of small divergence angle, high light utilization efficiency, and miniaturization can be realized.
- the horizontal spread angle is determined by the magnification which is the ratio of the beam diameters on the entrance surface and the exit surface, as described above.
- the beam diameter at the entrance surface does not become smaller than the emission width W, and the vignetting does not occur inside the lens and at the exit surface, the beam diameter at the exit surface cannot be larger than the period P of the emission point.
- the divergence angle in the horizontal direction after the lens is the fill factor of the original divergence angle.
- F. Will be limited to twice. From the above results, the fill factor F.E. F.
- the semiconductor laser array in the range of 0.5 to 1 is used as the light source 30, the parallel light generator of the third embodiment is particularly suitable.
- the light source is a fill factor F.D determined from the light emission width W of the plurality of light emission points and the period P of the light emission points.
- the parallel light generator according to the present invention includes a light source that emits light having an asymmetric spread angle in a biaxial direction included in a plane perpendicular to the optical axis, and the output light from the light source.
- the present invention relates to a configuration including a conversion optical system for reducing the divergence angle, and is suitable for use in solid-state illumination using an LED or a laser.
- 10 lens 10a optical axis, 11 entrance surface, 12 exit surface, 20, 30 light source, 20a, 30a horizontal light beam, 20b, 30b vertical light beam, 20c horizontal light emission width, 20d vertical light emission width, 21a internal position, 21b, 31 end face.
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Abstract
Description
光源から出射した光は、伝播に伴い広がっていくため、所望の光学系や照射面へ伝送するにあたり、広がり角を小さくし、平行光に近い光線とすることが求められている。光線を平行光とするためには、レンズを用いてレンズの入射面側焦点位置に光源を配置することでコリメートする技術が広く使われている。
θho=Tan-1(wh/f)
θvo=Tan-1(wv/f) (1)
となる。これより、焦点距離fのレンズでコリメートした場合、光源の発光半幅wh及びwvが大きくなるほど、コリメート後の広がり半角θho及びθvoが大きくなる。光源の発光幅は一般的に使用者が自由に変更できないため、広がり角を小さくするためには、レンズの焦点距離fを大きくする必要がある。このとき光源はレンズの入射面側焦点位置に配置するため、焦点距離fを大きくするにつれて、光源とレンズの距離が大きくなる。
wv1=wv+f×Tan(θvi) (2)
となる。これより、焦点距離fのレンズを用いる場合、広がり半角θvi内のエネルギーを効率よく利用するためには、レンズの有効径Φは、2×wv1以上とすることが好ましい。その結果、焦点距離fを大きくすると、fに比例して大きな有効径Φを有するレンズが必要となる。レンズの有効径が式(2)の値より小さい場合、広がり半角θvi内のエネルギーの一部はケラレにより失われる。
実施の形態1.
図1は、実施の形態1における平行光発生装置の説明図であり、図1Aは平面図、図1Bは側面図である。
実施の形態1の平行光発生装置では、光軸に対して垂直な面内における一方の方向である水平方向と、一方の方向とは90度異なる他方の方向である垂直方向とで異なる広がり角を有する光源20として半導体レーザを用いる。水平方向の光線20aが最小の広がり半角であり、典型的には、2~15°(半角1/e2)である。なお、内部位置21aは水平方向の光線20aの仮想的な出射点である。垂直方向の光線20bが最大の広がり半角であり、典型的には、15~45°(半角1/e2)である。垂直方向の光線20bの出射点は光源20の端面21bである。また、光源20は、水平、垂直方向に有限の発光幅20cと20dを有する。水平方向の発光幅20cは、通常数μmから数100μmの範囲である。垂直方向の発光幅20dは、通常1μmから数μmの範囲である。
なお、曲率半径Rh1とRh2の符号は、入射面11及び出射面12と光軸10aの交点を基準に、曲率中心の位置が光源側にある場合を正、対向する側にある場合を負として定義する。
ここで、h1はレンズ10の垂直方向の前側(光源側)主点位置であり、符号は、入射面11と光軸10aの交点からレンズ内部の方向に向かって正と定義する。曲率半径Rv1が無限大(平面)の場合、式(4)は簡略化され、次式(5)となる。
出射面12を回転対称とした場合、曲率半径Rh2=Rv2であり、式(3)と式(5)を関係付ける。光源20は、レンズ10の垂直方向に対する焦点距離FFLvにその端面21bが位置するように設置する。
光源20から出射した光線は、広がりながらレンズ10の入射面11に入射し、入射面11から出射面12までレンズ内部を伝播し、出射面12から出射する。入射面11は、シリンドリカル形状としているので、水平方向の光線20aと垂直方向の光線20bは、入射面11の形状により異なる作用を受ける。説明を簡略化するため、光源20からの光線として水平方向は水平方向の光線20a、垂直方向は垂直方向の光線20bのみを考える。
これより、入射面11から出射面12までに水平方向の光線20aが受ける作用は、各光学要素を表す行列の積として、次式(10)となる。
式(10)を式(3)の関係から整理すると、次式(11)のようになる。
これより、曲率半径Rh1とRh2の比率により、水平方向の広がり角を小さくすることが可能となる。これは、水平方向をコリメートではなく拡大系としたことで、水平方向の広がり角が、式(1)に示した光源の発光半幅wh及びwvと焦点距離fの関係とは独立して決定できることを示している。
また、式(6)と式(11)の行列の積から、光源20から出射面12までに水平方向の光線20aが受ける作用を求めることができ、式(12)となる。
以上の光線の動作を水平方向と同様に光線行列で説明する。光源から出射した光線20bは、光源からレンズ10の入射面11までの距離(焦点距離FFLv)を伝播し、レンズ10に入射する。レンズ10の動作は、曲率半径Rv1、屈折率nの誘電体境界面(入射面11)と、厚さd、屈折率nの誘電体中の伝播と、曲率半径Rv2、屈折率nの誘電体境界面(出射面12)の各光学要素により垂直方向の光線20bが受ける作用として説明ができる。列ベクトルで記述される垂直方向の光線20bに対して各光学要素与える作用は、2行2列の行列で記述でき、それぞれ式(15)、式(16)、式(17)となる。
これより、入射面11から出射面12までに垂直方向の光線20bが受ける作用は、これらの積として、次式(18)となる。
前側(光源側)主点位置h1及び光源側(前側)焦点距離FFLvは、式(19)の(D-1)/C、及び(D-2)/Cであり、代入すると式(5)と同様となる。
また、式(6)と式(19)の行列の積から、光源20から出射面12までに垂直方向の光線20bが受ける作用を求めることができ、次式(20)となる。
式(20)より、光源20のある一点からの垂直方向の光線20bは、出射面12から出射後、平行光になることがわかる。また、有限の発光幅を有する場合、式(20)の入射光線の光軸高さrを発光半幅wv1と読み替えることで、式(1)に示した関係が得られる。
一つに、非点隔差による広がり角の増大が発生しないことがある。回転対称なレンズを用いる場合は、レンズの焦点位置を半導体レーザの端面21bに一致させると水平方向にフォーカスずれが発生し、広がり角が増大する。また、非点隔差を補正するために、水平方向と垂直方向で異なる焦点距離を有するレンズを用い、水平方向の焦点位置を半導体レーザの内部位置21aに一致させ、垂直方向の焦点位置を半導体レーザの端面21bに一致させるレンズを用いる手法も存在する。しかし、半導体レーザの水平方向の出射点位置である内部位置21aはばらつきがあり、またレーザ出力に依存して変化するため、複数の動作条件で非点隔差による広がり角の増大を抑制することは難しい。本実施の形態によれば、水平方向の広がり角は、光源20とレンズ10間の配置距離に依存しないため、垂直方向の焦点距離FFLvの位置に光源20の端面21bを配置することで、非点隔差が存在し、さらにばらつきやレーザの出力依存性があっても水平方向の広がり角が増大しないという効果を有する。
ところで、半導体レーザのチップ外形に対する発光点の位置精度は、垂直方向には高い精度を有するが、水平方向は精度が低い。これは、垂直方向は、厳密に厚さ制御がなされているのに対し、水平方向はウエハからチップに切出す際の精度に依存するからであり、水平方向は通常数μmから数10μmの切出し精度となる。このため、チップの外形に対して水平方向の発光点位置がばらついてしまい、例えば、チップとレンズを外形基準で高精度に組み立てた場合にも水平方向の発光点とレンズの相対位置はばらついてしまう。これに対して、本実施の形態においては、チップ切出し位置のばらつきによる水平方向の位置ずれが発生したとしても、光線の出射方向の傾きに与える影響が小さく、外形基準での組立てを容易にすることができるという効果を有する。
Rh1/Rh2×θh1=Δ/f×θv (21)
を満たす範囲で許容可能となる。ここでθvは光源20から垂直方向に出射した広がり角である。
図6は実施の形態2における平行光発生装置の説明図であり、図6Aはその平面図、図6Bはその側面図を示す。
実施の形態2の平行光発生装置は、光源30として、水平方向に複数の発光点を有する半導体レーザアレイを用いたことが実施の形態1の光源20とは異なる点である。その他の点については実施の形態1と同様であるため、対応する部分に同一符号を付してその説明を省略する。
実施の形態1と同様に、レンズ10の垂直方向の光源側焦点距離FFLvの位置に半導体レーザアレイである光源30の端面31を設置する。光源30からの水平方向の光線30aは、曲率半径Rh1のレンズ10の凹面及び曲率半径Rh2の凸面により、各発光点から出射した光線それぞれのビーム径が拡大される。光源30からの垂直方向の光線30bは、焦点距離FFLvの位置に光源30を配置しているので、レンズ10における入射面11の平面及び曲率半径Rv2の凸面によりコリメートされる。これにより、実施の形態1と同様に、光源30の水平方向の光はレンズ10の入射面11と出射面12で拡大され、光源30の垂直方向の光はレンズ10の出射面12で略平行光に変換されるので、小さな広がり角、高い光利用効率及び小型化の条件を共に満たす平行光発生装置を実現することが可能となる。
アレイ状光学素子を用いる場合と比較すると、単純な構成で安価であり、また、発光幅及び発光点の周期が水平方向に静的及び動的に変化する場合においても、実施の形態2の構成では小さな広がり角、高い光利用効率及び小型化の条件を満足させることができるという効果がある。
実施の形態3は、実施の形態2における光源30の複数の発光点の各発光幅Wと発光点の周期Pから決まるフィルファクタF.F.を定義したものである。
図7は、実施の形態3の光源30の定義を示す説明図である。半導体レーザアレイからなる光源30は、その発光幅Wと発光点の周期Pで特徴づけられ、フィルファクタF.F.を次式(22)で定義する。
F.F.=W/P (22)
本実施の形態では、平行光発生装置が式(22)に示すフィルファクタF.F.が0.5≦F.F.<1の範囲にある半導体レーザアレイを光源30とした場合に、特に好適である。なお、実施の形態3の平行光発生装置における全体の構成及び動作は実施の形態2と同様であるため、ここでの説明は省略する。
θho=2×TAN-1(W/2/f) (23)
となり、レンズ位置で各発光点の光が重ならないように焦点距離fを決めると、
f=(P―W)/(2×Tan(θhi/2)) (24)
となるので、式(23)と式(24)を整理すると、
Tan(θho/2)/Tan(θhi/2)
=F.F./(1-F.F.) (25)
となり、光源30からの水平方向広がり角とアレイ状レンズ後の広がり角は光源30のフィルファクタF.F.で制限される。式(25)より、フィルファクタF.F.が0.5以上のアレイ状光源は、従来の回転対称なレンズでコリメートするために、前側焦点位置に光源を配置した場合には、ある広がり角θ内のビームに対してケラレが無い条件で、水平方向の広がり角を小さくすることができないことがわかる。
また、各発光点の光軸に対して回転対称でないレンズをアレイ状に組み合わせたコリメータレンズを用いることも考えられるが、レンズの作製難度が高く、安価に作ることが難しい。また、光源とレンズの組立て難度も高くなる。
一方で、本発明のレンズ10と半導体レーザアレイからなる光源30との組み合わせにおいては、いかなるフィルファクタF.F.のアレイ状光源においても水平方向の広がり角を小さくすることが可能であり、小さな広がり角、高い光利用効率及び小型化の条件を満足させることのできる平行光発生装置が実現できる。
m=P/W=1/F.F. (26)
と制限される。これよりレンズ後の水平方向の広がり角は、元の広がり角のフィルファクタF.F.倍に制限されてしまう。
以上の結果から、式(22)に示すフィルファクタF.F.が0.5~1の範囲にある半導体レーザアレイを光源30とした場合に、実施の形態3の平行光発生装置は特に好適である。
Claims (7)
- シリンドリカル形状で凹面形状をなす入射面と光軸に対して凸面形状をなす出射面とを有するレンズと、
前記光軸に対して垂直な面内における一方の方向と、当該一方の方向とは90度異なる他方の方向との広がり角が異なる光源とを備え、
前記光源は前記レンズの前記他方の方向の入射面側焦点距離の位置に配置され、かつ、前記光源の一方の方向が前記レンズのシリンドリカル形状の曲率方向に配置されたことを特徴とする平行光発生装置。 - 前記光源の前記一方の方向の発光点幅が前記他方の方向の発光点幅より大きいことを特徴とする請求項1記載の平行光発生装置。
- 前記光源は非点隔差を有する光源であることを特徴とする請求項1記載の平行光発生装置。
- 前記光源は半導体レーザであることを特徴とする請求項3記載の平行光発生装置。
- 前記光源は、前記一方の方向に複数の発光点を有することを特徴とする請求項1記載の平行光発生装置。
- 前記光源は、前記複数の発光点の各発光幅Wと発光点の周期Pから決まるフィルファクタF.F.が0.5≦F.F.<1を満たすアレイ状光源であることを特徴とする請求項5記載の平行光発生装置。
- 前記光源は、半導体レーザアレイであることを特徴とする請求項5記載の平行光発生装置。
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CN108710167A (zh) * | 2018-07-27 | 2018-10-26 | 中国科学院光电研究院 | 一种校正元件 |
JP6696629B1 (ja) * | 2018-10-22 | 2020-05-20 | 三菱電機株式会社 | レーザ装置 |
Also Published As
Publication number | Publication date |
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CN109073908A (zh) | 2018-12-21 |
EP3435141B1 (en) | 2020-12-23 |
JPWO2017187609A1 (ja) | 2018-05-17 |
CN109073908B (zh) | 2020-12-15 |
JP6165366B1 (ja) | 2017-07-19 |
EP3435141A4 (en) | 2019-04-17 |
US20190391407A1 (en) | 2019-12-26 |
US11061244B2 (en) | 2021-07-13 |
EP3435141A1 (en) | 2019-01-30 |
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