This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2022-085148, filed on May 25, 2022, the entire contents of which are incorporated herein by reference.
The present invention relates to a micro lens array, a diffuser plate, and an illumination apparatus.
For example, a known micro lens array has a plurality of lens elements arranged and is used for an apparatus for illumination, measurement, facial recognition, spatial recognition, and the like (see for example, Patent Document 1). When such a micro lens array is used for the purpose of optically making light from a light source uniform, and if a pitch between the lens elements is too small, interference fringes due to interference of light transmitted between the lens elements becomes obvious and may hinder the uniformity of light-source light. On the other hand, when the pitch between the lens elements is too large, the light irradiated from the light source is non-uniformly incident on the micro lens array, which cause moire fringes and may result in non-uniform irradiation distribution. As a result, when a screen or the like is irradiated with light from the light source using the micro lens array, the illuminance distribution in the irradiation pattern may become non-uniform.
To suppress the non-uniformity of the illuminance distribution in the irradiation pattern due to the interference fringes described above, a countermeasure of randomly distributing the position, shape, and the like of each lens element has been considered (for example, see Patent Document 2, Patent Document 3, and the like). Unfortunately, excessive randomization may not provide desired light distribution characteristics, and in particular, may make it difficult to sharpen an edge of an irradiation profile. Furthermore, a complicated array of the lens elements may cause disadvantages such as a long production time and a high production cost.
In addition, as a measure for suppressing the non-uniformity of the illuminance distribution in the irradiation pattern due to the interference fringes while the array of the lens elements is made regular, a measure in which hexagonal lens elements are arrayed in a honeycomb shape is considered. A technique itself of arraying hexagonal lens elements in a honeycomb shape is known (for example, Patent Literature 4).
However, in a case where the hexagonal lens elements are arrayed in a honeycomb shape, an outer shape of an irradiation pattern of irradiation light by the micro lens array also becomes a hexagonal shape, and when light is received by a normal light receiving element, there is a case where a decrease in efficiency or peripheral dimming is promoted.
The technique of the present disclosure is invented in view of the above, and an advantage of some aspects of the invention is to provide a technique of obtaining a more uniform and highly efficient illuminance distribution by a micro lens array.
Solution to Problem
To solve the above problems, a micro lens array according to the present disclosure is a micro lens array in which a plurality of lens elements are arranged on at least one surface of a planar member, the micro lens array including a honeycomb structure including columns of the lens elements alternately arrayed, each of the lens elements having a shape of a hexagon in a plan view and being linearly arranged such that sides of the hexagon in a predetermined direction are in contact with each other, wherein a mathematical expression indicating a SAG of the lens element includes a term of AxmynXmYn (m and n are integers except 0), in a case where, when an optical axis of the lens element is an origin, Y is a coordinate in an arrangement direction of the lens elements in the columns of the lens elements, X is a coordinate in an array direction in which the columns of the lens elements are alternately arrayed, and A is a predetermined coefficient.
Thus, the SAG can be controlled for each (X, Y) coordinate in the lens element by making the mathematical expression indicating SAG of the lens element include the term of AxmynXmYn (m and n are integers except 0) and appropriately determining the coefficient Axmyn. Then, it makes it possible to control the aspherical shape in the oblique direction having an angle with respect to the arrangement direction of the lens elements in the columns of the lens elements in each lens shape. This makes it possible to control the outer shape of the irradiation pattern of the irradiation light that has passed through the micro lens array. As a result, the outer shape of the irradiation pattern can be adjusted in accordance with the shape of the light receiving surface of the light receiving element, the efficiency of the optical system can be increased, or the peripheral dimming of the light receiving surface can be suppressed. In other words, the outer shape of the irradiation pattern in the present disclosure can also be referred to as an illuminance distribution in the irradiation pattern.
In addition, in the present disclosure, a mathematical expression indicating the SAG of the lens element is represented by
According to this, by appropriately determining the coefficient Axmyn, the arrangement direction of the lens elements in the columns of the lens elements and the SAG in the array direction of the columns of the lens elements can independently be determined, and the lens shape as the non-rotating body shape with respect to the optical axis can more easily be defined.
In the above description, m and n may be even numbers. According to this configuration, it is easy to configure a lens shape which is point-symmetric about the optical axis in each lens element. Further, the mathematical expression indicating the SAG of the lens elements may include the term of Ax2y2X2Y2. According to this, by changing the coefficient Axmyn, the lens shape in the vicinity of the optical axis can be changed more greatly, and the lens shape can be controlled more efficiently.
The present disclosure may be a micro lens array in which a plurality of lens elements are arranged on at least one surface of a planar member, the micro lens array including
According to this configuration, the SAG on the lens surface can be set to be greater or less than the SAG in the X direction and the Y direction in the direction of the predetermined angle range between the X direction and the Y direction when viewed from the origin in each lens shape. This makes it possible to appropriately control the aspherical shape of the lens shape of each lens element in a direction oblique to the X direction and the Y direction.
In addition, a micro lens array according to the present disclosure may be a micro lens array in which a plurality of lens elements are arranged on at least one surface of a planar member, the micro lens array including
Here, it has been found that the irradiation pattern in the micro lens array having the honeycomb structure can be changed by changing the numerical value of a described above. It has been found by experiment or simulation that when the value of the parameter a is relatively great, the irradiation pattern has an outer shape approximate to a hexagon, and when the value of the parameter a is less, the irradiation pattern changes from a rectangular shape to a quadrilateral shape such that each side is curved inward. If the outer shape of the irradiation pattern is approximate to a hexagon, the irradiation pattern protrudes from the light receiving surface of the light receiving element, or promotes peripheral dimming.
On the other hand, when the irradiation pattern has a rectangular shape or a quadrilateral shape such that each side is curved inward, the amount of light with which the irradiation pattern protrudes from the light receiving surface of the light receiving element can be reduced, and the amount of light with which the four corners of the light receiving element are irradiated can relatively be increased. According to this configuration, by controlling the lens shape such that the value of one parameter falls within a target range, the shape of the irradiation pattern of the micro lens array having the honeycomb structure can be controlled, and the light receiving efficiency on the light receiving surface of the light receiving element and the peripheral dimming on the light receiving surface can be controlled. More specifically, in a case where the irradiation pattern is approximated to a rectangular shape, the light receiving efficiency on the light receiving surface of the light receiving element can be improved and the peripheral dimming on the light receiving surface can be controlled. In addition, when the irradiation pattern is approximated to a quadrilateral shape such that each side is curved inward, the peripheral dimming particularly on the light receiving surface can remarkably be suppressed.
In addition, in the present disclosure, a second pitch which is a pitch in an array direction in which the columns of the lens elements are alternately arrayed may be larger than a first pitch which is a pitch of the plurality of lens elements in the arrangement direction of the lens elements in the columns of the lens elements. According to this configuration, the shape of the lens element can be made more horizontally long, and the aspect ratio k can be increased. As a result, the value of the parameter a can be made relatively less, the shape of the irradiation pattern of the micro lens array can be easily formed into a rectangular shape or a quadrilateral shape such that each side is curved inward, and the light receiving efficiency on the light receiving surface of the light receiving element and the peripheral dimming on the light receiving surface can be easily controlled.
In addition, in the present disclosure, in the shape of the hexagon, an apex angle of two sides which are not in contact with front and rear lens elements in the columns of the lens elements may be 125 degrees or less. According to this configuration, the value of the apex angle α can be made relatively less. As a result, the value of the parameter a can be made relatively less, the shape of the irradiation pattern of the micro lens array can be changed from a rectangular shape to a quadrilateral shape such that each side is curved inward, and the light receiving efficiency on the light receiving surface of the light receiving element and the peripheral dimming on the light receiving surface can be controlled.
In addition, in the present disclosure, an intensity pattern of light transmitted through the micro lens array may have a substantially rectangular shape or a substantially quadrilateral shape such that each side is curved inward. According to this configuration, for the above-described reason, the light receiving efficiency on the light receiving surface of the light receiving element and the peripheral dimming on the light receiving surface can be controlled.
In addition, the present disclosure may be a diffuser plate using the micro lens array described above.
In addition, the present disclosure may be an illumination apparatus including: the micro lens array described above; and a light source configured to emit light incident on the micro lens array. In this case, the lens elements in the micro lens array may be arrayed on a surface on the light source side. The directivity of the light source may be ±20° or less. The light source may be a laser light source that emits near-infrared light.
The illumination apparatus may be used in distance measuring equipment. Further, the present invention may be used in distance measuring equipment using a Time Of Flight system.
Note that, in the present invention, wherever possible, the techniques for solving the above-described problem can be used in combination.
According to the present disclosure, a more uniform and highly efficient illuminance distribution can be obtained by the micro lens array.
A micro lens array according to an embodiment of the present disclosure will be described below with reference to the drawings. Note that each of the configurations, combinations thereof, and the like in the embodiment are an example, and various additions, omissions, substitutions, and other changes may be made as appropriate without departing from the spirit of the present disclosure. The present disclosure is not limited by the embodiment and is limited only by the claims.
When the irradiation light source 102 emits pulsed light based on a drive signal from the light source control unit 101, the pulsed light passes through the irradiation optical system 103 and is emitted onto the measurement target O. The reflected light reflected on the surface of the measurement target O passes through the light receiving optical system 104, is received by the light receiving element 105, and then is converted into an appropriate electrical signal by the signal processing circuit 106. Then, a calculation unit (not illustrated) measures the distance to each location on the measurement target O by measuring the time from when the irradiation light is emitted from the irradiation light source 102 until the light receiving element 105 receives the reflected light, that is, the time-of-flight of the light.
For the irradiation optical system 103 or the light receiving optical system 104 in the distance measuring equipment 100 using the TOF system, a micro lens array may be used. The micro lens array is a lens array formed by the group consisting of micro lens elements having a diameter in a range of about 10 μm to several millimeters. In general, the function and accuracy of the micro lens array vary depending on characteristics such as the shape (spherical, aspherical, cylindrical, hexagonal, or the like) of each lens element constituting the lens array, the size of the lens element, the arrangement of the lens elements, and the pitch between the lens elements.
When the micro lens array is used for the distance measuring equipment 100 using the TOF system described above, the measurement target O is required to be irradiated with light with a uniform intensity distribution. That is, the angle of view θFOI (FOI: Field of Illumination) that is a usable divergence angle of light that has passed through the micro lens array is determined according to the size of the measurement target O or the measurement distance, but in the range of the angle of view θFOI, the uniformity of the irradiance distribution of the light that has passed through the micro lens array may be required. As described above, the micro lens array is required to have characteristics corresponding to the purpose of use.
Next, as illustrated in
Here, as illustrated in
On the other hand, in the present embodiment, by controlling the aspherical shape of the lens surface of each hexagonal lens element, the irradiation pattern can be controlled to have a rectangular shape as illustrated in
More specifically, as an expression indicating the SAG on the lens surface of the lens element, an aspheric expression (1) as illustrated in the middle part of
Here, Y is the coordinate in the vertical direction in
Here, the mathematical expression describing the SAG on the lens surface of the lens element 1a is not limited to the above expression (1). For example, the mathematical expression describing the SAG may include the term of AxmynXmYn (m and n are integers except 0). Thus, SAG can be controlled for each (X, Y) coordinate in the lens element 1a by making the mathematical expression indicating SAG of the lens element 1a include the term of AxmynXmYn (m and n are integers except 0) and appropriately determining the coefficient Axmyn. Then, the aspherical shape in the oblique direction having an angle with respect to the arrangement direction of the lens elements in the columns of the lens elements can be controlled in each lens shape. Thus, the irradiation pattern can be controlled to have a rectangular shape as illustrated in
Note that in the term of AxmynXmYn, m and n may be even numbers. According to this configuration, it is easy to configure a lens shape which is point-symmetric about the optical axis in each lens element. Further, the mathematical expression describing the SAG of the lens element 1a may include the term of Ax2y2X2Y2. According to this configuration, by changing the coefficient Ax2y2, the lens shape in the vicinity of the optical axis can be changed more greatly. Thus, the lens shape can be controlled more efficiently, and the shape of the irradiation pattern can be controlled more efficiently.
As a result of controlling the SAG in the oblique direction with respect to the X direction and the Y direction in the lens shape of the lens element 1a as described above, the SAG on the lens surface may deviate from the range between the SAG in the X direction and the SAG in the Y direction at the same distance r from the optical axis as illustrated in
On the other hand, in the present disclosure, the SAG on the lens surface deviates from the range between the SAG in the X direction and the SAG in the Y direction at the same distance r from the optical axis in the direction of the predetermined angle range between the X direction and the Y direction when viewed from the origin of the lens element 1a. As a result, for example, in the θ direction in
More specifically, in the case where the light receiving surface of the light receiving element is quadrangular and the irradiation pattern by the micro lens array 1 is hexagonal, when the entire irradiation pattern is emitted on the light receiving surface, light is not emitted on the four corners of the light receiving surface, and peripheral dimming is promoted. On the other hand, when sufficient light is emitted to the four corners of the light receiving surface, the ratio of the irradiation light emitted to the outside of the light receiving surface increases, and the efficiency decreases. On the other hand, by making the outer shape of the irradiation pattern approximate to a rectangular shape, the efficiency can be improved and the peripheral dimming can be suppressed.
Next, another index of the above-described aspherical surface expression (1), which characterizes the irradiation pattern shape of the micro lens array having the honeycomb structure, will be described.
When an apex angle between two sides where the lens elements 5a are not in contact with each other in the columns 5b of the lens elements 5a is a (hereinafter, simply referred to as an apex angle α in the X direction), a pitch of the lens elements in the Y direction is Py, and a pitch of the lens elements 5a in the X direction is Px, it is assumed that the following relationship
α=a·k+90(deg) (2)
is satisfied between an aspect ratio k=Px/Py and the apex angle α in the X direction (a is a parameter defined in the present embodiment). In the present embodiment, the parameter a is used as an index to evaluate the characteristics of the irradiation pattern of the micro lens array 5.
a=(α−90)/k (3)
In
Next,
Next,
From the results of
In the embodiment described above, the light emitted from the light source 2 passes through the micro lens array 5 and is projected onto the screen 3. Alternatively, the micro lens array 5 may be used in such a manner that the light emitted from the light source 2 is reflected on the micro lens array 1 and projected onto the screen 3.
Further, in the present embodiment, the example in which the lens elements 5a in the micro lens array 5 are arrayed on one surface on the light sources 2 side has been described, but the lens elements 5a may be arrayed on one surface on the side opposite to the light sources 2. Furthermore, the lens elements may be arrayed on both sides.
In addition, the cross section of each of the lens elements 5a has a shape such that the curved surface shapes are discontinuously arranged, but may have a shape such that the curved surface shapes are continuously connected to each other by a smooth curve.
Further, as for the material of the micro lens array 5 in the present embodiment, the base material and the lens elements 5a may be formed of different materials, or may be integrally formed of the same material. When the base material and the lens element 5a are formed of different materials, one of the base material and the lens element 5a may be formed of a plastic material, and the other may be formed of a glass material. When the base material and the lens elements 5a are integrally formed of the same material, there is no refractive-index interface, and thus the transmittance can be increased. In addition, reliability without peeling between the base material and each of the lens elements 5a can be improved. In this case, the micro lens array 5 may be formed of a resin alone or a glass alone.
Further, as illustrated in
Further, as illustrated in
Further, a micro lens array having a function equivalent to that of the micro lens array 5 described in the present embodiment may be used as an optical system for image capturing, face authentication in a security device, or space authentication in a vehicle or a robot. Furthermore, the micro lens array 1 described in the present embodiment may be used in combination with other optical elements including diffraction optical elements and refractive optical elements. Additionally, any coating may be applied to the surface of the micro lens array 1.
Wiring containing a conductive substance may be provided on the surfaces of or inside the micro lens array 5 according to the present embodiment, and thus damage to the lens elements 5a can be detected by monitoring the energization state of the wiring. By doing so, damage such as cracking or peeling of each of the lens elements 5a can easily be detected, and thus damage due to malfunction or erroneous operation of the illumination apparatus or the distance measuring equipment caused by damage to the micro lens array 5 can be prevented. For example, by detecting the occurrence of a crack in each of the lens elements 5a based on the disconnection of the conductive substance and prohibiting the light sources from emitting light, the zero order light from the light sources can be prevented from directly passing through the micro lens array 5 via the crack and being emitted to the outside. As a result, the eye safety performance of the apparatus can be improved.
The wiring of the conductive substance may be provided around the micro lens array 5 or on each of the lens elements 5a. Further, it may be applied to any one of the surface on which the lens elements 5a are formed, the surface on the opposite side, and both surfaces. The electrically conductive substance is not particularly limited as long as it has electrical conductivity, and for example, metal, metal oxide, electrically conductive polymer, an electrically conductive carbon-based substance, or the like can be used.
More specifically, the metal include gold, silver, copper, chromium, nickel, palladium, aluminum, iron, platinum, molybdenum, tungsten, zinc, lead, cobalt, titanium, zirconium, indium, rhodium, ruthenium, alloys thereof, and the like. Examples of the metal oxide include chromium oxide, nickel oxide, copper oxide, titanium oxide, zirconium oxide, indium oxide, aluminum oxide, zinc oxide, tin oxide, or composite oxides thereof such as composite oxides of indium oxide and tin oxide (ITO) and complex oxides of tin oxide and phosphorus oxide (PTO). Examples of the electrically conductive polymer include polyacetylene, polyaniline, polypyrrole, and polythiophene. Examples of the electrically conductive carbon-based substance include carbon black, SAF, ISAF, HAF, FEF, GPF, SRF, FT, MT, pyrolytic carbon, natural graphite, and artificial graphite. These electrically conductive substances can be used alone, or two or more types thereof can be used in combination.
The conductive substance is preferably a metal or a metal oxide, which is excellent in conductivity and easy to form wiring, more preferably a metal, preferably gold, silver, copper, indium, or the like, and silver is preferable because silver is mutually fused at a temperature of about 100° C. and can form wiring excellent in conductivity even on the micro lens array 5 made of a resin. A pattern and a shape of the wiring of the conductive substance are not particularly limited. A pattern surrounding the micro lens array 1 may be used, or a pattern with a more complicated shape may be used for the sake of higher detectability for the crack or the like. Further, a pattern in which at least a part of the micro lens array 5 is covered with a transparent conductive substance may be used.
Number | Date | Country | Kind |
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2022-085148 | May 2022 | JP | national |