JP2024061876A - Light-emitting device and manufacturing method thereof - Google Patents

Abstract

To provide a light-emitting device that can continuously emit light with stable brightness by improving detection accuracy of monitor light.SOLUTION: A light-emitting device 10 includes a light-emitting element 12, a radiation angle conversion element 14 that converts a radiation angle of incident light IL from the light-emitting element 12 and irradiates with incident light IL, a light receiving element 15 that receives reflected light RL of the radiation angle conversion element 14 with respect to the incident light IL, and a control unit 17 that controls light output of the light-emitting element 12 on the basis of the detected value of the light receiving element 15. The radiation angle conversion element 14 includes a substrate 16 and a plurality of microlenses 20 arranged two-dimensionally on the substrate. The microlens 20 is formed such that intensity of the reflected light RL in a predetermined direction increases more specifically than in other directions. The light receiving element 15 is arranged to receive the reflected light RL in a predetermined direction.SELECTED DRAWING: Figure 1

Description

The present invention relates to light-emitting devices, lighting devices, display devices, screens, etc., and in particular to optical devices that use radiation angle conversion elements with uneven structures on the surface, such as microlens arrays.

Radiation angle conversion elements that scatter or change the angle of incident light in various directions are used in display devices and screens, and are also widely used in a wide variety of devices such as lighting devices to obtain uniform lighting intensity. In general, they are often used to expand the radiation angle of light emitted from a light-emitting element.

In recent years, there has been a demand for more advanced performance, such as uniformity of the light emission angle and intensity distribution per angle, or uniformity of the in-plane intensity when projecting diffused light. For example, there is a need to diffuse light emitted at a specified angle from an array of vertical cavity surface emitting lasers (VCSELs) over a wider angular range and to impart anisotropy to the diffusion angle.

There are several types of elements that convert light by diffusing it or expanding its radiation angle. For example, there are elements that have a structure in which minute spaces are dispersed inside a flat plate, or in which fine particles are dispersed (e.g., a translucent resin plate), elements that have minute irregularities randomly applied to the surface of a substrate (e.g., glass whose surface has been roughened by etching, etc.), elements that have designed irregularities formed by processing the surface of a substrate (e.g., a diffraction type element), and elements that have many lenses arranged on the surface of a substrate (e.g., a microlens array).

Among these, radiation angle conversion elements using microlens arrays have high transmittance and are easy to control the diffusion angle, and are therefore used when a high level of diffusion performance is required (see, for example, Patent Documents 1 and 2).

JP 2009-42772 A JP 2017-9669 A

The intensity of light emitted from a light-emitting element is controlled by increasing or decreasing the current flowing through the light-emitting element (constant current control). However, with a control method that flows a constant current, the light output changes over time, for example, depending on the ambient temperature of the light-emitting element, or the light output changes as the light-emitting element deteriorates depending on the time of use. For this reason, a control method that installs a light-receiving element (such as a photodiode) near the light-emitting element, monitors the light output of the light-emitting element, and keeps the monitored light output constant (constant output control). In this case, the light detected by the light-receiving element (monitor light) is scattered light emitted from the light-emitting element into the surroundings, or light scattered by a cover glass installed on the outside of the light-emitting element, a radiation angle conversion element formed on the cover glass, a housing, etc.

When a part of the optical output from a light-emitting element is detected by a light-receiving element and the monitoring result is used for control, it is naturally desirable to have a larger power of light detected by the light-receiving element, because it is easier to distinguish it from noise and background light, and it is advantageous for detecting signals with a high signal-to-noise ratio (S/N), so that the detection accuracy can be improved and the detection circuit can be simplified. However, in conventional technology, the light-receiving element is usually placed in a position that does not obstruct the optical path of the light to be used, or in a position that is convenient in terms of the physical structure. As a result, because a part of scattered light, which does not necessarily have a high S/N ratio, is used as the monitor light, the power of the light detected by the light-receiving element is small, and it is difficult to improve the detection sensitivity when the optical output from the light-emitting element fluctuates. This can cause cases where the fluctuation in the optical output from the light-emitting element cannot be suppressed within a specified range of precision and accuracy, which can be problematic depending on the application.

The present invention was made in consideration of these circumstances, and its purpose is to provide a light-emitting device that uses a radiation angle conversion element and that can continuously irradiate light with a stable brightness by improving the detection accuracy of the monitor light and suppressing fluctuations in the light output.

In order to solve the above problems, a light emitting device according to one aspect of the present invention includes a light emitting element, a radiation angle conversion element that converts the radiation angle of incident light from the light emitting element and irradiates the light, a light receiving element that receives the reflected light of the radiation angle conversion element relative to the incident light, and a control unit that controls the light output of the light emitting element based on the detection value of the light receiving element. The radiation angle conversion element includes a substrate and a plurality of microlenses that are two-dimensionally arranged on one main surface of the substrate. The microlenses are formed so that the intensity of the reflected light in a specific direction is specifically increased compared to other directions, and the light receiving element is positioned to receive the reflected light in the specific direction.

The surface of the microlens may include a curved surface with a tangent plane angle of 45° or more.

The microlenses may be approximately rectangular in plan view.

The microlens may include a curved surface with a tangent plane angle of 45° or more in the direction of the long side.

The light emitting element may emit light of a predetermined wavelength, and the radiation angle conversion element may further include a dielectric multilayer film formed on the other main surface of the substrate. The dielectric multilayer film may have a transmittance spectrum in which the transmittance at the predetermined wavelength when the incident angle is equal to or greater than the predetermined angle is smaller than the transmittance at the predetermined wavelength when the incident angle is 0°.

The dielectric multilayer film may have a transmittance of 70% or more at a specified wavelength when the angle of incidence is 0°, and a transmittance of 30% or less at a specified wavelength when the angle of incidence is 45°.

In addition, any combination of the above components, and any conversion of the present invention into a method, device, system, etc., are also valid aspects of the present invention.

According to the present invention, in a light-emitting device using a radiation angle conversion element, by improving the detection accuracy of the monitor light, it is possible to provide a light-emitting device that can suppress fluctuations in light output and continuously irradiate light with a stable brightness.

1 is a schematic cross-sectional view showing a light-emitting device according to an embodiment of the present invention. 2A to 2C are diagrams showing a radiation angle conversion element. 3A to 3C are diagrams showing a microlens. FIG. 2 is a schematic enlarged cross-sectional view of a radiation angle conversion element. FIG. 2 is a diagram showing an example of the mathematical shape of a microlens in a microlens array. 1 is a diagram showing the relationship between the arrangement of light-emitting elements and radiation angle conversion elements and a portion where the intensity of reflected light increases in a specific direction. 7A to 7C are diagrams showing the relationship between the arrangement of light emitting elements and radiation angle conversion elements and the areas where the intensity of reflected light increases in a specific direction. This is a diagram showing the intensity distribution of reflected light two-dimensionally, with the horizontal axis representing longitude and the vertical axis representing latitude. FIG. 9 is a diagram showing the reflected light intensity at longitude 90° in FIG. 8 . FIG. 9 is a diagram showing the reflected light intensity at a latitude of 33° in FIG. 8 . 11A and 11B are diagrams for explaining the mechanism by which a portion with increased reflected light intensity appears in the long side direction of a microlens. FIG. 12 is an enlarged view of a portion of FIG. 11A and 11B are diagrams for explaining the mechanism by which a reflected light intensity increase portion does not appear in the short side direction of a microlens. 13A and 13B are diagrams for explaining an experiment for confirming a reflected light intensity increase portion. FIG. 13 is a schematic diagram showing a case where a reference beam is incident from the long side direction of a microlens. FIG. 16 is an observation diagram of reflected light when a reference light is incident as shown in FIG. 15 . 11A and 11B are diagrams showing the observed reflected light when the conditions of the radiation angle conversion element are changed. FIG. 13 is a schematic diagram showing a case where a reference beam is incident from the short side direction of a microlens. FIG. 19 is an observation diagram of reflected light when a reference light is incident as shown in FIG. 18. 13A and 13B are diagrams for explaining a radiation angle conversion element according to a modified example. 13 is a diagram showing a transmittance spectrum of a dielectric multilayer film in a radiation angle conversion element according to a modified example. FIG.

Below, an embodiment of the present invention will be described. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and duplicated explanations will be omitted as appropriate. Furthermore, the embodiment does not limit the invention but is merely an example, and all of the features and combinations thereof described in the embodiment are not necessarily essential to the invention.

Figure 1 is a schematic cross-sectional view showing a light-emitting device 10 according to an embodiment of the present invention. This light-emitting device 10 includes a light-emitting element 12, a radiation angle conversion element 14 that converts the radiation angle of incident light IL from the light-emitting element 12 and irradiates it as outgoing light OL, at least one light-receiving element 15 that receives reflected light RL of the radiation angle conversion element 14 with respect to the incident light IL, and a control unit 17 that controls the light output of the light-emitting element 12 based on the detection value of the light-receiving element 15.

In this embodiment, the light-emitting element 12 is a VCSEL array. In other embodiments, the light-emitting element 12 may be a FP type semiconductor laser, a light-emitting diode (LED), or an array thereof.

Figures 2(a) to (c) show schematic diagrams of the radiation angle conversion element 14. Figure 2(a) is a plan view of the radiation angle conversion element 14. Figure 2(b) is a side view of the radiation angle conversion element 14 in the long side direction. Figure 2(c) is a side view of the radiation angle conversion element 14 in the short side direction.

The radiation angle conversion element 14 comprises a substrate 16 and a microlens array 18 formed on one of the main surfaces of the substrate 16.

From the viewpoint of increasing the efficiency of light utilization, it is desirable that the substrate 16 is transparent within the applicable wavelength range. The material of the substrate 16 may be selected from quartz, glass, and transparent resin. As the glass, but is not limited to these, soda lime glass, white plate glass, borosilicate glass, aluminoborosilicate glass, phosphate glass, fluorophosphate glass, etc. can be used, and by function, low dielectric constant glass, alkali-free glass, high refractive index glass, multi-component glass such as optical glass, reinforced glass, etc. can be used. As the transparent resin, but is not limited to these, cyclic (poly)olefin resin, aromatic polyether resin, polyimide resin, epoxy resin, acrylic resin, polyester resin, polyamide resin, polycarbonate resin, polyether resin, silicone resin, etc. can be used.

As shown in FIG. 2(a), the microlens array 18 is a two-dimensional array of multiple microlenses 20 on one of the main surfaces of the substrate 16. The microlens array 18 may be formed in the form of a layer on one of the main surfaces of the substrate 16, using the same material as the substrate 16 or a different material from the substrate 16. Note that multiple concentric circles are drawn within the roughly defined rectangle in FIG. 2(a), but this is a flat representation of the contour line of a convex or concave surface, and it should be noted that such concentric circles are not actually drawn. The same is true for the other drawings.

The material forming the microlens array 18 is preferably one with high transparency from the viewpoint of light utilization efficiency, and may be a transparent resin or a transparent organic-inorganic hybrid material when moldability is also taken into consideration. The material constituting the microlens array 18 is not limited to these, but includes curable resins that can be cured by heating or irradiation with light such as ultraviolet light, and resins that can be cured by the action of a curing agent or catalyst, and may include epoxy resins, (unsaturated) polyester resins, silicone resins, alkyd resins, and acrylic resins. Furthermore, thermoplastic resins may include polyacetal resins, polycarbonate resins, polyester resins, (cyclic) polyolefin resins, and polyamide resins. Furthermore, organic-inorganic hybrid materials may include sol-gel cured materials obtained by hydrolyzing and condensation-polymerizing alkoxides of Si (silicon).

Of the above materials, in the 2P (two-piece) molding method, which involves forming a coating of uncured resin on one main surface of the substrate 16 and then transferring the desired shape using a mold, it is desirable to use curable resins such as, but not limited to, epoxy and acrylic resins. On the other hand, when the microlens array 18 is manufactured by an injection molding method, a thermoplastic resin may also be used.

Figures 3(a) to (c) show the microlens 20. Figure 3(a) is a plan view of the microlens 20. Figure 3(b) is a side view of the microlens 20 in the long side direction. Figure 3(c) is a side view of the microlens 20 in the short side direction.

In this embodiment, the microlens 20 has a convex curved surface and a shape symmetrical with respect to the central axis Ax. In other embodiments, the microlens may have a concave curved surface as long as the effects of the present invention are achieved. Specific shapes may be a spherical shape consisting of a part of a sphere, or other aspheric shapes. The aspheric shape may have a paraxial radius of curvature that is approximated to a sphere in a range close to the central axis Ax, and is expressed by a certain mathematical formula having an appropriate high-order coefficient based on the required optical specifications and ease of formation. The aspheric shape has a curvature that varies according to the distance from the central axis Ax, and has a very high degree of freedom in design, but on the other hand, it is highly complex. In other embodiments, the microlens may have a spherical shape as long as the effects of the present invention are achieved. Although the degree of freedom in design and specification selection is low, there is an advantage in that the curvature is constant and therefore it is easy to manufacture, including using a mold. In addition, as long as the effects of the present invention are achieved, the microlens may have a curved surface or lens that is not symmetrical with respect to the central axis.

The microlenses 20 have different effective ranges in two orthogonal directions within the plane on which they are arranged, with the effective range in the long side direction being larger than the effective range in the short side direction, and the effective range in the diagonal direction being larger than the effective range in the long side direction. Each microlens 20 of the microlens array 18 used in this embodiment is approximately rectangular in plan view.

In the microlens 20 shown in Figures 3(a) to (c), the convex curved surface is the "lens surface 20a", the intersection of the central axis Ax of the microlens 20 and the lens surface 20a is the "microlens apex 20b", the periphery of the approximately rectangular microlens 20 is the "microlens peripheral edge 20c", the imaginary line on the lens surface 20a that runs from the microlens apex 20b along the lens surface 20a to the microlens peripheral edge 20c and is perpendicular to the contour line of the lens surface 20a is the "microlens generatrix 20d", and the distance (variable) from the central axis Ax to the lens surface 20a is "r".

Figure 4 is a schematic enlarged cross-sectional view of the radiation angle conversion element 14. As shown in Figure 4, the angle θ between a plane VP perpendicular to the central axis Ax of the microlens 20 having an axially symmetric surface and a tangent plane TP at a point on the lens surface 20a is defined as the "tangent plane angle θ". In this embodiment, the microlens array 18 is formed on one main surface of the parallel plate-shaped substrate 16, and the other main surface is a flat surface. When the microlens array 18 is arranged so that its central axis Ax is parallel to the traveling direction of the light IL emitted from the light emitting element 12, the flat main surface on which the microlens array 18 is not formed corresponds to the plane VP perpendicular to the central axis Ax of the microlens 20.

Figure 5 shows an example of the mathematical shape of a microlens 20 in the microlens array 18. In Figure 5, the solid line represents the coordinate (Z [mm]) of the lens surface with respect to the distance r [mm]. The dashed line represents the tangent angle θ [°] with respect to the distance r. r = 0 corresponds to the central axis Ax of the microlens 20. As can be seen from Figure 5, the tangent angle θ increases with distance from the central axis Ax. In the microlens 20 having a convex shape symmetrical with respect to the central axis Ax and having a substantially rectangular shape in a plan view, a curved surface with a larger tangent angle θ appears in the long side direction and further in the diagonal direction. Figure 5 shows the range of the microlens 20 in the short side direction, long side direction, and diagonal direction.

In this embodiment, the microlens 20 is a convex aspheric lens in which the coordinate Z of the lens surface decreases as the distance r increases, the material constituting the microlens is sufficiently transparent, the area in the short side direction is 0.0081 mm x 2 = 0.0162 mm, the area in the long side direction is 0.0125 mm x 2 = 0.025 mm, and the area in the diagonal direction is 0.0149 mm x 2 = 0.0298 mm.

In the microlens array 18 used in this embodiment, in the area of the microlenses 20 in the short side direction, long side direction, and diagonal direction, a curved surface and its range where the tangential plane angle θ is 45° or more appears in all directions. In this embodiment, the distance from the central axis Ax where the tangential plane angle θ is 45° is 0.0048 mm, so if the ranges where the angle θ is 45° or more in the short side direction, long side direction, and diagonal direction are r _th ^(S) , r _th ^(L) , and r _th ^(D) , respectively, the values are r _th ^(S) = 0.0033 mm, r _th ^(L) = 0.0077 mm, and r _th ^(D) = 0.0101 mm.

The 2P (two-piece) molding method can be used as a manufacturing method for the microlens array 18. In the 2P molding method, a mold with an inverted shape of the microlens array 18 is pressed against uncured resin spread on one main surface of the substrate 16, and the shape of the mold is transferred to the resin while curing by heating or irradiating with light such as ultraviolet light. The mold is then released to obtain the microlens array 18 integrated with the substrate 16. Furthermore, post-curing may be performed by heating. In this case, the curing is further promoted, and it is expected that the rigidity, mechanical strength, weather resistance, etc. of the microlens array 18 will be improved. In such a molding method by transfer, a mold that forms all the microlenses 20 at once on a substrate 16 of a certain size can also be used.

As another manufacturing method, a step-and-repeat method can be used. In the step-and-repeat method, a mold corresponding to a size smaller than the desired substrate is used, and transfer is repeated several to several tens of times to form microlenses 20 on a substrate of a larger size than the desired size. In addition, a method for manufacturing the microlens array 18 using a mold includes an injection molding method. However, the manufacturing method of the microlens array 18 is not limited to these methods.

By combining the above-mentioned radiation angle conversion element 14 with a light emitting element 12 (VCSEL array), a light emitting device 10 is constructed that converts light IL emitted from the light emitting element 12 as shown in FIG. 1 into light OL having a predetermined radiation angle or diffusion angle and irradiates it forward. Converting the radiation angle of light means that the light emitted from the microlens 20 is expanded or diffused over a predetermined angle due to refraction, scattering, etc., and light with little large deviation or distribution of light intensity regardless of the direction or location is effective for applications such as uniform lighting.

The inventor has found that when the light emitting device 10 is constructed by combining the radiation angle conversion element 14 and the light emitting element 12 in this way, the intensity of the reflected light RL in a specific direction increases specifically with respect to the arrangement of the light emitting element 12 and the radiation angle conversion element 14. The inventor has further come up with the idea that the detection accuracy of the monitor light can be improved by arranging a light receiving element 15 such as a PD (Photo Diode) or APD (Avalanche Photo Diode) to receive the reflected light RL as monitor light.

As shown in FIG. 1, the control unit 17 is connected to the light-emitting element 12 and the light-receiving element 15. The control unit 17 performs control (constant output control) to keep the light output of the light-emitting element 12 constant by feeding back the detection value of the light-receiving element 15 to the drive current of the light-emitting element 12. In this embodiment, the reflected light RL monitored by the light-receiving element 15 has a high intensity and a high signal-to-noise ratio, so that a light-emitting device 10 can be realized that can continuously irradiate light with a stable brightness.

Figures 6 and 7 (a) to (c) are diagrams showing the relationship between the arrangement of the light emitting element 12 and the radiation angle conversion element 14 and the part where the intensity of the reflected light RL increases in a specific direction. The part where the intensity of the reflected light RL increases specifically is called the "reflected light intensity increasing part 60". In this case, to represent the arrangement of each element and the position of the reflected light intensity increasing part 60, the position on the surface of the sphere S is represented using polar coordinates (spherical coordinates) and, in part, the concept of longitude and latitude.

The center Os of the light-emitting element, the center M of the radiation angle conversion element 14, and the line segment OsM connecting them are on the axis A of the sphere S. The axis A passes through the center O of the sphere S. The center of the light-emitting element 12 or the radiation angle conversion element 14 may be near the intersection of the diagonals of the light-emitting element 12 or the radiation angle conversion element 14 in a planar view, or may be an appropriately determined point in the central part of the light-emitting element 12 or the radiation angle conversion element 14, or may be another optically or geometrically determined center. Here, the center of the light-emitting element 12 or the radiation angle conversion element 14 is on the light emission surface of the light-emitting element 12 or the surface of the radiation angle conversion element 14, and is the intersection of the diagonals of the light emission surface or the surface of the radiation angle conversion element 14 in a planar view.

The light emitting element 12 is arranged so that its center Os is on the surface of the sphere S. The radiation angle conversion element 14 is arranged so that its center M coincides with the center O of the sphere S. As described above, the radiation angle conversion element 14 is formed by arranging a plurality of microlenses 20 on at least one of the main surfaces of the substrate 16 having parallel main surfaces, and the microlenses 20 face the light emitting element 12, and the optical axis Ax of the microlenses 20 is parallel to the axis A. The light emitted from the light emitting element 12 proceeds approximately symmetrically with respect to the axis A and is incident on the surface ML1, which is the surface on which the microlens array 18 of the radiation angle conversion element 14 is formed. The other surface ML2 of the radiation angle conversion element 14 is a plane, and the light is emitted from the surface ML2 (see FIG. 1). The surface ML2 is parallel to the equatorial plane Eq described later and perpendicular to the axis A. Also, the point on the axis A that is symmetrical to the point Os with respect to the point O is defined as point R.

Let us consider a case where the microlenses 20 of the microlens array 18 are roughly rectangular in plan view (perspective viewed vertically from point O) and are densely arranged two-dimensionally. Here, let points As and Bs be the points where a straight line passing through point M and parallel to the long side of the microlens 20 intersects with the sphere S, and points Cs and Ds be the points where a straight line passing through point M and parallel to the short side of the microlens 20 intersects with the sphere S.

Longitude 0° is the meridian connecting Os-Ds-R, longitude 90° is the meridian connecting Os-As-R, longitude 180° is the meridian connecting Os-Cs-R, and longitude 270° is the meridian connecting Os-Bs-R.

Latitude 0° is represented by a line that connects As-Cs-Bs-Ds around the sphere S. This notionally corresponds to the equator. Latitude 90° corresponds to point Os. This notionally corresponds to one of the poles. The center M of the radiation angle conversion element 14 is on the equatorial plane Eq that is bounded by As-Cs-Bs-Ds.

Light emitted at a predetermined angle from the light-emitting element 12 with center Os ideally travels symmetrically about axis A and is incident on surface ML1 of radiation angle conversion element 14 arranged on the equatorial plane Eq. The radiation angle of the light incident on radiation angle conversion element 14 is converted (enlarged) by the action of microlenses 20 on the surface, and the light is emitted from surface ML2 of radiation angle conversion element 14. The light emitted from radiation angle conversion element 14 travels in the direction of point R at a predetermined radiation angle.

In the radiation angle conversion element 14 according to one embodiment, the microlens 20 is formed by 2P molding using ultraviolet-curable acrylic resin on a glass substrate (D263 T eco) of 2.8 mm × 2.3 mm × thickness 0.3 mm. The microlens 20 has an axially symmetric convex aspheric shape whose curved shape is expressed by Z [mm] = 0.0231 - 104.43 × r ² + 7735.5 × r ⁴ , where r [mm] is the distance from the central axis.

Each microlens 20 of the microlens array 18 is rectangular in plan view with a long side length of 0.025 mm, a short side length of 0.0162 mm, and a diagonal length of 0.0298 mm, and the maximum value of Sag is 0.0161 mm in the long side direction, 0.0068 mm in the short side direction, and 0.0231 mm in the diagonal direction. In the microlens array 18, 12,000 microlenses 20 (100 in the long side direction and 120 in the short side direction) are arranged without gaps on the glass substrate.

The BRDF (bidirectional reflectance distribution function) was measured for such a microlens array 18. The BRDF was measured using an IS-SA manufactured by Radiant Zemax. BRDF was measured by irradiating the microlens array 18 with parallel light from a direction perpendicular to the main surface (e.g., surface ML2) of the substrate 16, and measuring the intensity of the reflected light projected onto a hemispherical dome arranged around the microlens array 18. BRDF measurements were performed for three types of light source including wavelengths of 445 nm, 555 nm, and 595 nm. The above concept of spherical coordinates will be linked to the measurement results for explanation.

Figures 8, 9, and 10 show the measurement results using BRDF. Figures 8, 9, and 10 show the measurement results when light containing a wavelength of 555 nm was irradiated in particular, but the measurement results were almost the same even when light with wavelengths of 445 nm and 595 nm was irradiated.

Figure 8 is a two-dimensional diagram showing the intensity distribution of reflected light, with the horizontal axis representing longitude and the vertical axis representing latitude. In Figure 8, the light intensity was measured in a longitude range of 0° to 180°, but an almost symmetrical intensity distribution also appears in the longitude range of 180° to 360° (Cs-Bs-Ds).

Figure 9 shows the reflected light intensity at longitude 90° for Figure 8, with the horizontal axis representing latitude and the vertical axis representing light intensity (arbitrary units).

Figure 10 shows the reflected light intensity at latitude 33° for Figure 8, with the horizontal axis representing longitude and the vertical axis representing light intensity.

From Figures 8 to 10, it can be seen that when light from the light-emitting element 12 is diffused or the like by a radiation angle conversion element 14 having predetermined shape parameters, there may be a singular point (i.e., a reflected light intensity increasing section 60) where the reflected light intensity is increased in a predetermined direction for the arrangement of each element. In this embodiment, the reflected light intensity increasing section 60 appears near longitudes of 90° and 270° (note that this direction coincides with the long side direction of the radiation angle conversion element 14 when viewed from the center M of the radiation angle conversion element 14) and near latitudes of 33°.

Therefore, by arranging a light receiving element 15 such as a PD or APD in the reflected light intensity increasing section 60 as in the light emitting device 10 of this embodiment, it is possible to obtain monitor light with a good signal-to-noise ratio without adding extra parts or elements, and it is possible to realize a light emitting device 10 that can continuously provide stable brightness.

The present inventor has studied the mechanism by which such a reflected light intensity increased portion 60 occurs, and has obtained the following findings from various experiments.
1) The reflected light intensity increase portion 60 appears in the hemisphere including the light emitting element 12 in spherical coordinates.
2) There is no contribution from the light directly reflected from the surface ML1 of the radiation angle conversion element 14. The intensity of the regular reflection from the surface of the microlens array 18 made of a transparent dielectric material is small.
3) The reflected light intensity increased portion 60 is not directly formed by scattering from the gaps between the microlenses 20 of the microlens array 18. This is because the same result was obtained even if the gaps were dyed black to eliminate the optical contribution of reflected light.
4) As the tangent plane angle θ of the microlens 20 increases, the reflected light intensity increase portion 60 becomes more prominent. This occurs when the microlens 20 includes a surface with a steep gradient.
5) The reflected light intensity increase portion 60 occurs in a distributed manner centered on the points on the meridians Os-As-R and Os-Bs-R. Conversely, the reflected light intensity increase portion 60 does not overlap with the meridians Os-Ds-R and Os-Cs-R.

The microlens 20 has an aspheric shape, has a radius of curvature r near the center and higher-order terms, and is mathematically symmetric about the central axis Ax. The tangent plane angle θ increases with distance from the central axis Ax. As described above, the microlens 20 is rectangular in plan view, so the distance from the central axis Ax of the microlens 20 to the edge in the short side direction is shorter than the distance from the central axis Ax to the edge in the long side direction. Therefore, the tangent plane angle θ is larger in the long side direction of the microlens and also in the diagonal direction.

Figure 11 is a diagram for explaining the mechanism by which a reflected light intensity increase portion 60 appears in the long side direction of the microlens 20. Figure 11 shows a cross section passing through the central axis of the microlens 20 and parallel to the long side direction of the microlens 20. Figure 12 is an enlarged view of a portion of Figure 11.

When the light IL1 incident on the microlens array 18 is near the base of the first microlens 20(1) (a portion relatively far from the central axis), it is reflected with an intensity close to total reflection and enters the adjacent second microlens 20(2) if the angle of incidence with respect to the tangent plane TP(1) is large. In this case, the angle of incidence with respect to the tangent plane TP(2) of the second microlens 20(2) is small, so it enters and propagates inside the microlens array 18 with only slight reflection loss. The light IL1 is reflected by the surface ML2 and heads toward the microlens. The light IL1 then reaches the curved surface of the microlens, passes through the third microlens 20(3), and exits the microlens array 18 again, proceeding to the hemispherical area including the light emitting element 12.

Assuming the above mechanism, the surface of the microlens 20 must include a curved surface with a tangential angle θ of 45° or more. In the case of a microlens that does not include a curved surface with a tangential angle θ of 45° or more, the light reflected on the surface of the first microlens 20(1) travels directly to the area of the upper hemisphere including the light-emitting element 12 shown in FIG. 6, but because the light intensity is small, it is difficult to form a unique area with high reflected light intensity.

The surface of the microlens 20 preferably includes a curved surface with a tangential plane angle θ of 50° or more, more preferably includes a curved surface with a tangential plane angle θ of 55° or more, and even more preferably includes a curved surface with a tangential plane angle θ of 60° or more. When the surface of the microlens 20 includes such a curved surface, the intensity of the light reflected by the surface of the first microlens 20(1) increases, and the intensity of the reflected light that enters from the second microlens 20(2), propagates inside the microlens array 18, is reflected, and is emitted from the third microlens 20(3) also increases. Thus, a reflected light intensity increasing portion 60 is formed.

The contribution of surface ML2 of radiation angle conversion element 14 to the formation of reflected light intensity increasing section 60 was found by the fact that by directly painting surface ML2 with a matte black color, i.e., by making the incidence on surface ML2 essentially zero, the reflected light intensity increasing section 60 was not formed.

In addition, the intensity (reflectance) of reflected light from an interface such as a surface is approximately 4% when the angle of incidence is zero (perpendicular incidence), but due to the principle of Fresnel reflection, it is well known that as the angle of incidence increases, particularly when the angle exceeds 50°, the reflectance exceeds 10%. For this reason, the reflected light intensity tends to increase when the angle of incidence of the light that is the source of the formation of the reflected light intensity increasing portion 60 on surface ML2 is larger. Therefore, the angle of incidence on surface ML2 is 45° or more, preferably 50° or more, and more preferably 55° or more.

The direction in which the reflected light intensity increasing portion 60 is formed can vary depending on the shape and actual density of the microlenses 20, the thickness of the microlens array 18, the thickness of the substrate 16, etc.

The above is the situation in the long side direction of a microlens 20 having a curved surface with a tangent plane angle θ of 45° or more. In the short side direction of a microlens 20 where the area having such a curved surface is small or not provided, such a reflected light intensity increased portion 60 is not formed. Figure 13 is a diagram for explaining the mechanism by which the reflected light intensity increased portion 60 does not appear in the short side direction of the microlens 20. Figure 13 shows a cross section passing through the central axis of the microlens 20 and parallel to the short side direction of the microlens 20.

As shown in FIG. 13, unlike the case of the long side direction of the microlens 20 described above, the light IL2 incident near the bottom of the first microlens 20(1) enters the microlens array 18 from the surface ML1 of the first microlens 20(1) and exits from the surface ML2. Therefore, in the short side direction of the microlens 20, no light travels to the hemispherical area including the light-emitting element 12 as occurs in the long side direction, or even if it does, it is very little, so the reflected light intensity increase portion 60 is not formed.

The inventor confirmed the above circumstances experimentally. Figure 14 is a diagram for explaining an experiment to confirm the reflected light intensity increased portion. For the radiation angle conversion element 14 used in the above BRDF measurement, as shown in Figure 14, light was incident from the surface ML1 side at an incident angle of 60° with respect to the main surface (surface ML2) of the substrate 16, and the light emitted vertically upward from the microlens array 18 was observed with a metallurgical microscope. This explains the existence of a portion where the reflected light intensity increases specifically due to the reversibility of light, by understanding the optical characteristics when reflected light with a specifically increased intensity is formed and when light is incident on the reverse optical path.

Figure 15 is a schematic diagram of when reference light is incident from the long side direction of the microlens 20. Figure 16 is an observation diagram of reflected light when reference light is incident as shown in Figure 15. In Figure 16, an arrangement of concentric "shadows 72" can be confirmed, which is the distribution of reference light reflected in a vertical direction from the microlens 20. In Figure 16, a crescent-shaped area 70 of high light intensity can be observed in the long side direction of the microlens 20, which is approximately rectangular in plan view, and away from the central axis. From the perspective of the reversibility of light, it can be understood that the reflected light intensity increase area is formed due to light incident on the long side direction of the microlens 20 and away from the central axis.

Figure 17 shows the observed reflected light when the conditions of the radiation angle conversion element 14 are changed. Here, the surface ML2 of the radiation angle conversion element 14 was painted matte black, and the reflected light was observed using the same observation method as in Figure 15. As a result, unlike the observation diagram shown in Figure 16, no crescent-moon-shaped areas of high light intensity were observed in the long side direction of the microlens 20, away from the central axis. This confirms that the reflection from the planar surface ML2 of the radiation angle conversion element 14 contributes to the formation of the reflected light intensity increase area formed in a specific direction.

Figure 18 is a schematic diagram of when reference light is incident from the short side direction of the microlens 20. Figure 19 is an observation diagram of reflected light when reference light is incident as shown in Figure 18. As can be seen from Figure 19, a distribution (shadow 72) of reflected light reflected in a vertical direction from the microlens 20 can be seen, but no areas of high intensity of reflected light are observed. From these experimental results, it was confirmed that no areas of increased reflected light intensity are formed in the short side direction of the microlens 20.

As described above, in the light emitting device 10 according to this embodiment, the microlens 20 is formed so that the intensity of the reflected light RL in a specific direction is specifically increased compared to other directions. The light receiving element 15 is then positioned so as to receive the reflected light RL in the specific direction as monitor light. This improves the detection accuracy of the monitor light, thereby realizing a light emitting device 10 that can continuously provide stable brightness.

In addition, the light emitting device 10 according to this embodiment does not require the installation of a component (for example, a dispersing element such as a half mirror) for efficiently directing the monitor light to the light receiving element. Therefore, since there is no need to add extra components or elements, an inexpensive light emitting device 10 can be realized.

Figure 20 is a diagram for explaining a radiation angle conversion element 114 according to a modified example. The radiation angle conversion element 114 shown in Figure 20 includes a substrate 16, a microlens array 18 formed on one main surface of the substrate 16, and a dielectric multilayer film 19 formed on the other main surface ML2 of the substrate 16.

Figure 21 shows the transmittance spectrum of the dielectric multilayer film 19 in the radiation angle conversion element 114 according to the modified example. In Figure 21, the solid line represents the transmittance spectrum when the incident angle to the dielectric multilayer film 19 is 0°, and the dashed line represents the transmittance spectrum when the incident angle to the dielectric multilayer film 19 is a predetermined angle (greater than 0°). In this modified example, the dielectric multilayer film 19 has a transmittance spectrum in which the transmittance at a predetermined wavelength λo when the incident angle is equal to or greater than the predetermined angle is smaller than the transmittance at the predetermined wavelength λo when the incident angle is 0° (synonymous with an increase in reflectance). For example, the dielectric multilayer film 19 has a transmittance of 70% or more at a predetermined wavelength λo when the incident angle is 0°, and a transmittance of 30% or less at a predetermined wavelength λo when the incident angle is 45°.

The light beams constituting the reflected light intensity increasing section 60 described above are light beams whose angle of incidence on the surface ML2 is equal to or greater than a predetermined angle (45° in the above embodiment). On the other hand, the dielectric multilayer film 19 has a characteristic that the entire transmittance spectrum shifts toward shorter wavelengths as the angle of incidence increases. Therefore, by providing a dielectric multilayer film 19 on the surface ML2 that has a small transmittance (large reflectance) at the wavelength λo of the light used in the transmittance spectrum at angles equal to or greater than a predetermined angle, the light intensity in the reflected light intensity increasing section 60 formed in a specific direction can be further increased. The angle of incidence and reflectance at which an increase in reflectance at wavelength λo is expected may be appropriately determined according to the desired optical characteristics.

The present invention has been described above based on an embodiment. This embodiment is merely an example, and those skilled in the art will understand that various modifications are possible in the combination of each component and each processing process, and that such modifications are also within the scope of the present invention.

In the above embodiment, a microlens that is approximately rectangular in plan view and has a curved surface only in the long side direction with a tangential plane angle θ of 45° or more has been described. However, what is required of the microlens of the present invention is that there is a specific direction in which the reflected light intensity increases with respect to the arrangement of the light emitting element and the radiation angle conversion element. Therefore, a microlens that is approximately rectangular in plan view may have a curved surface with a tangential plane angle θ of 45° or more in the short side direction in addition to the long side direction.

The shape of the microlenses is not limited to being approximately rectangular in plan view, but may be approximately square, trapezoidal, parallelogrammatic, diamond-shaped, etc. in plan view. Also, all of the microlenses included in the microlens array do not need to be the same shape.

As described above, the direction in which the reflected light intensity increases depends on the optical or geometric characteristics of the microlens. A microlens array may include multiple microlenses with different characteristics. In this case, a radiation angle conversion element can be configured in which multiple directions in which the reflected light intensity increases appear.

10 Light emitting device, 12 Light emitting element, 14 Radiation angle conversion element, 15 Light receiving element, 16 Substrate, 17 Control unit, 18 Microlens array, 19 Dielectric multilayer film, 20 Microlens, 20(1) First microlens, 20(2) Second microlens, 20(3) Third microlens, 60 Reflected light intensity increasing unit, 114 Radiation angle conversion element.

Claims (6)

A light-emitting element;
a radiation angle conversion element that expands the radiation angle of the incident light from the light emitting element and irradiates the light;
a light receiving element that receives reflected light of the radiation angle conversion element with respect to the incident light;
a control unit that controls the optical output of the light emitting element based on a detection value of the light receiving element;
A light emitting device comprising:
the radiation angle conversion element includes a substrate and a plurality of microlenses two-dimensionally arranged on one main surface of the substrate;
the microlens is formed so that the intensity of the reflected light in a predetermined direction has a maximum value;
the surface of the microlens includes a curved surface having a tangent plane angle of 45° or more;
a line segment OsM is a radius of a virtual circle C including a part of a straight line L that passes through a center M of the radiation angle conversion element in a planar view and is parallel to a direction in which the inclination of a tangent plane on the curved surface of the microlens is 45° or more, and a center Os of the light-emitting element, and a line segment OsM is a radius of the virtual circle C, a straight line Ls that passes through the center M and is perpendicular to the line segment OsM is an intersection point of the line Ls and the virtual circle C is an intersection point of the line segment MAs with a line segment connecting M and a point on the arc OsAs is an angle α [°], and in the relationship between the intensity of the reflected light and the angle α, the intensity of the reflected light has the maximum value when α=αM (αM=30° to 40°),
A light emitting device, characterized in that the light receiving element is disposed so as to receive the reflected light in a direction of α=αM. The light-emitting device according to claim 1, characterized in that the microlens is substantially rectangular in plan view. The light-emitting device according to claim 2, characterized in that the microlens includes a curved surface with a tangent plane angle of 45° or more in the long side direction. The light emitting element emits light of a predetermined wavelength,
the radiation angle conversion element further includes a dielectric multilayer film formed on the other main surface of the substrate,
4. The light-emitting device according to claim 1, wherein the dielectric multilayer film has a transmittance spectrum in which the transmittance at the specified wavelength when the incident angle is equal to or greater than a specified angle is smaller than the transmittance at the specified wavelength when the incident angle is 0°. The light-emitting device according to claim 4, characterized in that the dielectric multilayer film has a transmittance of 70% or more at the specified wavelength when the incident angle is 0°, and a transmittance of 30% or less at the specified wavelength when the incident angle is 45°. A light-emitting element;
a radiation angle conversion element for expanding a radiation angle of incident light from the light emitting element and irradiating the light, the radiation angle conversion element including a substrate and a plurality of microlenses two-dimensionally arranged on one main surface of the substrate;
a light receiving element that receives reflected light of the radiation angle conversion element with respect to the incident light;
a control unit that controls the optical output of the light emitting element based on a detection value of the light receiving element;
A method for manufacturing a light emitting device comprising:
a step of forming the microlens such that the intensity of the reflected light in a predetermined direction has a maximum value, the surface of the microlens includes a curved surface with a tangent plane angle of 45° or more, the surface of the microlens includes a part of a straight line L that passes through a center M of the radiation angle conversion element in a planar view and is parallel to a direction in which the inclination of the tangent plane on the curved surface of the microlens is 45° or more, and the center Os of the light-emitting element is included; in a virtual circle C having a radius of a line segment OsM, a straight line that passes through the center M and is perpendicular to the line segment OsM is defined as Ls, an intersection point between the line segment Ls and the virtual circle C is defined as As, an angle between the line segment MAs and a line segment connecting M and a point on the arc OsAs is defined as α [°], and in a relationship between the intensity of the reflected light and the angle α, the intensity of the reflected light has the maximum value when α = αM (αM = 30° to 40°);
positioning the light receiving element so as to receive the reflected light in a direction of α=αM;
A method for manufacturing a light emitting device, comprising:

Images