WO2021205248A1

WO2021205248A1 - Optical systems including collimating films

Info

Publication number: WO2021205248A1
Application number: PCT/IB2021/051778
Authority: WO
Inventors: Kundapur Raveesh SHENOY; Tri D. Pham; Charles J. Studiner Iv; Zhaohui Yang; Corey D. Balts; Przemyslaw P. Markowicz; Mark A. Roehrig; Michelle L. Toy; Judith M. Invie
Original assignee: 3M Innovative Properties Company
Priority date: 2020-04-08
Filing date: 2021-03-03
Publication date: 2021-10-14

Abstract

An optical construction includes a lens film having opposing first and second major surfaces. The first major surface includes a plurality of microlenses arranged along orthogonal directions. An optically opaque mask layer including a UV-cured polymer material is disposed on the second major surface of the lens film and defines a plurality of laser-ablated through openings therein. The openings are aligned to the microlenses in a one-to-one correspondence. For a substantially collimated light incident on the first major surface along an incident direction, an optical transmittance of the optical construction as a function of a transmitted angle includes a first transmitted peak having a first transmittance T1 at a first transmitted angle within about 10 degrees of the incident direction, and a second transmitted peak having a second transmittance T2 at a second transmitted angle between about 30 to 60 degrees of the incident direction, wherein T2/T1 ≥ 0.01.

Description

OPTICAL SYSTEMS INCLUDING COLLIMATING FILMS

Technical field

The present disclosure generally relates to optical systems including collimating films.

Background

Display devices may include a fingerprint sensor which detects light reflected by the fingerprint. Such display devices commonly use a backlight arrangement, where a light-diffusing film is placed between a light source and a display panel, say, a liquid crystal display panel.

Summary

Some aspects of the disclosure relate to an optical construction including a lens film including an outermost structured first major surface and an opposing outermost substantially planar second major surface. The structured first major surface includes a plurality of microlenses arranged along orthogonal first and second directions. The optical construction includes an optically opaque mask layer including a UV-cured polymer material. The optically opaque mask layer is disposed on the second major surface of the lens film and defines a plurality of laser-ablated through openings therein arranged along the first and second directions. The openings are aligned to the microlenses in a one-to-one correspondence. For a substantially collimated light incident on the structured first major surface side of the optical construction along an incident direction substantially orthogonal to the first and second directions, an optical transmittance of the optical construction as a function of a transmitted angle includes a first transmitted peak having a first transmittance T1 at a first transmitted angle within about 10 degrees of the incident direction, and includes a second transmitted peak having a second transmittance T2 at a second transmitted angle between about 30 to 60 degrees of the incident direction, wherein T2/T1 > 0.01.

Other aspects of the disclosure relate to an optical system including a display extending along the first and second directions. An optical sensor is disposed opposite the display. The optical system includes an optical construction described in at least one aspect of the disclosure disposed between the display and the optical sensor.

These and other aspects of the present application will be apparent from the detailed description below. In no event, however, should the above summaries be construed as limitations on the claimed subject matter, which subject matter is defined solely by the attached claims.

Brief Description of Drawings

The various aspects of the disclosure will be discussed in greater detail with reference to the accompanying figures where, Fig. 1 schematically shows an optical system in accordance with some embodiments;

Fig. 2 schematically shows an emissive display in accordance with some embodiment;

Fig. 3 schematically shows an optical construction of an optical system in accordance with some embodiments;

Fig. 4 shows a microscopic image of a microlens;

Fig. 5 shows a microscopic image of a laser ablated optically opaque mask layer in accordance with some aspects of the disclosure; and

Fig. 6 graphically represents optical transmittance of the optical construction as a function of transmitted angle according to some aspects of the disclosure.

The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

Detailed Description of Illustrative embodiments

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure.

It may be desired to use a collimating optical element in display devices to transmit light to an optical sensor in order to improve the resolution of the optical sensor. Suitable collimating optical elements may include a microlens array and a mask with holes where the microlenses have a focus at the holes. One approach involves ablating holes in sub-micron metal layers coated on a substrate of the microlens fdm using laser processing. It may be desirable to reduce back reflection and cross talk, in order to improve resolution, for instance, for efficient fingerprint detection in a display device having fingerprint sensors. The embodiments disclosed herein addresses these and other challenges.

Some embodiments of the disclosure, as shown in Fig. 1, relate to an optical system (200) including an optical construction (100). The optical construction (100) in some aspects includes a lens film (10). The lens film (10) includes an outermost structured first major surface (11) and an outermost substantially planar second major surface (12) disposed opposite the structured first major surface (11). In some aspects, the lens film includes a substrate layer (14) and a lens layer (15) disposed thereon. The lens layer (15) may include the outermost structured first major surface (11), and the substrate layer (14) may include the outermost substantially planar second major surface (12). The substrate layer (14) may be made from PET, although polycarbonate and acrylic can also be used. In some aspects, it may be desirable to have a higher refractive index for the substrate layer (14), for instance greater than 1.50, so that the angular width of the cone of light within the substrate layer (14) is minimized. The structured first major surface (11) includes a plurality of microlenses (13). The microlenses (13) may be arranged as amicrolens array along orthogonal first (x-axis) and second (y-axis) directions.

A microlens is a lens having at least one lateral dimension (e.g., diameter) less than 1 mm. In some embodiments, the average diameter of the microlenses may be in a range of 5 micrometers to 1000 micrometers. In some embodiments, the microlenses may be curved about the orthogonal first (x-axis) and second (y-axis) directions. In other embodiments, the microlenses may be lenticular microlenses. In some instances, the array of microlenses, can have any suitable geometry. For instance, the array can be regular (e.g., square or hexagonal lattice) or irregular (e.g., random or pseudorandom). The microlenses used in any of the embodiments described herein can be any suitable type of microlenses. In some embodiments, an array of microlenses includes at least one of refractive lenses, diffractive lenses, metalenses (e.g., surface using nanostructures to focus light), Fresnel lenses, spherical lenses, aspherical lenses, symmetric lenses (e.g., rotationally symmetric about an optical axis), asymmetric lenses (e.g., not rotationally symmetric about an optical axis), or combinations thereof. Fig. 4 shows the microscopic image of a microlens (13) in the lens film (10) arranged in the cross web and down web directions.

In some aspects, the optical construction (100) includes an optically opaque mask layer (20) disposed on the second major surface (12) of the lens film (10). The mask layer (20) may include a plurality of through openings (21), or pinholes, arranged in an array along the first (x-axis) and second (y-axis) directions. In some aspects, the openings (21) may be aligned to the microlenses (13) in a one-to-one correspondence. In some cases, the microlenses (13) may be lenticular microlenses and the openings (21) may be slits (optically or physically) having a width substantially smaller than a width of the lenticular microlenses and having a length extending in a direction along the length of the lenticular microlenses. The openings (21) formed in any of the embodiments described herein can have any suitable shape. In some embodiments, an array of openings (21) may include at least one of elliptical pinholes, circular pinholes, rectangular pinholes, square pinholes, triangular pinholes, and irregular pinholes. An array of openings may include any combinations of these pinhole shapes.

The through openings (21) in the optically opaque mask layer (20) may be formed by laser ablation through the microlenses (13), for example. Suitable lasers may include fiber lasers such as a 40W pulsed fiber laser operating a wavelength of 1070 nm, for example. Creating openings in a layer using a laser through a microlens array is generally described in US2007/0258149 (Gardner et ak), for example. An absorption overcoat can optionally be applied to the optical construction (100) to increase the absorption of energy from the laser. A microscopic image of an optically opaque mask layer (20) with laser-ablated through openings (21) is shown in Fig. 5. As shown in Fig. 1, the optical system (200) includes a display (40) extending along the first (x- axis) and second (y-axis) directions. In some instances, the display (40) may be an emissive display including a plurality of pixels (42) configured to generate and emit light as schematically represented in Fig. 2. In other embodiments, the display may be an organic light emitting diode (OLED) display, or a liquid crystal display (LCD). In some aspects, the display (40) may be a semi-transparent display panel which allows at least some light to be transmitted through the display panel. In some aspects, the optical construction (100) may be bonded to the display (40) using a first adhesive layer (60) ((e.g., optical clear adhesive layer). The first adhesive layer (60), in some instances, may have an index of refraction of less than about 1.3 for at least one visible wavelength.

The optical system (200) may include an optical sensor (50) disposed opposite the display. The optical construction (100) of at least one or more embodiments of the disclosure may be disposed between the display (40) and the optical sensor (50). In some aspects, the optical construction (100) may be bonded to the optical sensor (50) using a second adhesive layer (70) (e.g., optical clear adhesive layer). In some aspects, the optical sensor (50) may include a plurality of sensor pixels (51) aligned to the microlenses (13) and the through openings (21) in a one-to-one correspondence.

In some embodiments, the optical system (200) may be a bioanalytic device (e g., optically determines hemoglobin concentration), and/or a molecular analysis device (e.g., optically determines blood glucose levels). In some embodiments, the optical sensor (50) may be configured to detect a fingerprint and the optical system (200) including the optical construction (100) may be configured to determine if a detected fingerprint matches a fingerprint of an authorized user.

The optical system according to an embodiment may include an infrared light source (80) disposed to emit light (81) toward a front surface (41) of the display. The infrared light source, for instance, may be infrared light from the sun, or room heaters that emit infrared lights, etc.

In some embodiments, the optically opaque mask layer (20) disposed on the second major surface (12) of the lens film (10) may include a material having a transmission of less than 10%, or less than 5%, for normally incident unpolarized light in a predetermined wavelength range in the near-ultraviolet (e.g., less than 400 nm and at least 350 nm), visible (e.g., 400 nm to 700 nm) and/or infrared (greater than 700 nm and no more than 2500 nm). The transmission may depend on material properties (e.g., absorbance) and material thickness. In some embodiments, the mask layer (20) may be substantially optically opaque between adjacent openings in the array of openings (21). In some cases, the optically opaque mask layer (20) may substantially block (e.g., blocks at least 70% of light by absorption, reflection, or a combination thereof) light incident on the layer between openings (21) for at least one wavelength and for at least one polarization state. In some embodiments, the mask layer (20) may be formed by applying a wavelength selective multilayer optical fdm onto the second major surface (12) and physical or optical openings (21) can then be formed therein. In some embodiments, for at least one polarization state (and in some embodiments, for each of two orthogonal polarization states), the wavelength selective multilayer optical film may have regions between adjacent openings (21) that transmit at least 60% of normally incident light in a predetermined first wavelength range (e.g., a near ultraviolet, a visible, or a near infrared range) and blocks at least 60% of normally incident light in a predetermined second wavelength range (e.g., a different near ultraviolet, a visible, or a near infrared range).

In some embodiments, the optically opaque mask layer (20) disposed on the second major surface (12) of the lens film (10) may include a UV-cured polymer material and the plurality of laser-ablated through openings (21) may be formed therein. It may be desirable that the UV-cured polymer material has sufficiently high absorption of the laser to be ablated to form the opening. After ablation, it may be desirable that the optically opaque mask layer (20) including the UV-cured polymer material blocks visible light (OUED emission spectrum) to a sufficiently high degree to meet the light blocking metrics (FWHM, cross talk etc.). For example, the mask layer (20) may include carbon black coated polymer material, which absorbs visible light and infrared light of the laser. For instance, various carbon black loadings may be used to strike a balance between ablation/absorption properties and processability. A roll coating process may be used to coat the carbon black-loaded material on the lens film. UV lights (Fusion D lamps) may be employed to cure the coating.

In some aspects, the optically opaque mask layer (20) may have an average thickness t and the laser-ablated through openings (21) may have an average lateral opening d, wherein t/d < 3. In some cases, t/d < 2, or 1.5, or 1, or 0.75, or 0.5. In some cases, the optically opaque mask layer (20) may have an average thickness t of less than about 10 microns, or less than 7 microns, or less than 5 microns. In some cases, the laser-ablated through openings (21) may have an average lateral opening d of less than about 10 microns, or less than 7 microns, or less than 5 microns.

In some embodiments, as best seen in Fig. 3, the optically opaque mask layer (20) may include a first optically opaque mask sublayer (22) having a UV-cured first polymer material disposed on a second optically opaque mask sublayer (23) having a UV-cured second polymer material. The first and second sublayers (22, 23), in some instances, may be thin UV cured polymer layers that can be combined together to form a single, fully cured, thick optically opaque mask layer (20), which absorbs normally incident unpolarized light in a visible and infrared wavelength range. Each opening (21) in the plurality of laser- ablated through openings extends through both sublayers (22, 23). A larger thickness of the optically opaque mask layer (20) may be chosen to reduce cross-talk (i.e., light from one microlens incident on a through opening aligned with a different microlens), for example, or a smaller thickness of the optically opaque mask layer (20) may be chosen to increase the light transmitted through the openings (21). Figs. 1 and 3 show schematic cross-sectional views of the optical construction (100) including an array of microlenses (13) and an array of through openings (21). In some embodiments, the optical system may include at least one light source or at least one light source array. The light source(s) may include one or more light emitting diodes (LEDs), one or more lasers, or one or more laser diodes (e g., vertical cavity surface emitting laser (VCSEL), for example. In some embodiments the light may be partially or substantially collimated. In some aspects, collimated light (30) in the array of microlenses (13) directs light (30) primarily to a corresponding opening (21) in the array of openings (21). In some aspects, substantially collimated light (30) may be incident on the structured first major surface (11) side of the optical construction (100) along an incident direction (31) substantially orthogonal to the first and second directions.

In some aspects, for a substantially normally incident light extending across and covering at least 20 of the microlenses (13) in the array of microlenses, the optical construction (100) may have a total optical transmittance (T) of at least 30%, or at least 40%, or at least 50%, or at least 60%.

Fig. 6 graphically represents optical transmittance of the optical construction as a function of transmitted angle according to some aspects of the disclosure. In some aspects, as shown in Fig. 6, the optical transmittance (T) of the optical construction (100) of the substantially collimated light (30) as a function of a transmitted angle (Q) includes a first transmitted peak (PI) having a first transmittance T1 at a first transmitted angle (01) within about 10 degrees of the incident direction. In some instances, the first transmittance T1 > 10%, or > 15%, or > 20%, or > 25% for the incident light having a wavelength of about 550 nm.

The optical transmittance (T) of the optical construction (100) of the substantially collimated light (30) as a function of a transmitted angle (Q) may include a second transmitted peak (P2) having a second transmittance T2 at a second transmitted angle (02) between about 30 to 60 degrees of the incident direction. In some instances, the second transmittance T2 > 1%, or > 1.5%, or > 2%, or > 2.5%, or > 3% for the incident light having a wavelength of about 550 nm. In some such instances, the second transmittance T2 < 10%, or < 8%, or < 6%, or < 5% for the incident light having a wavelength of about 550 nm. In some embodiments, T2/T1 > 0.01. In some other instances, T2/T1 > 0.02, or > 0.03, or > 0.04, or > 0.05, or > 0.06, or > 0.07, or > 0.08, or > 0.09, or > 0.1. In other instances, T2/T1 < 0.5, or < 0.4, or < 0.3, or < 0.2.

The different curves shown in Fig. 6 represent the optical transmittance of different laser-ablated samples. The below table (Table 1) shows the summary of the optics analysis, including maximum transmission, and maximum crosstalk, in the down web (DW) direction of the laser-ablated samples. Table 1

The samples may differ in their carbon black loading percentages (say, 15% or 20%), thickness t of the mask layer (20), average lateral opening d of the through openings (21), acrylate monomer additives, etc.

The values of the first and second transmittances T1 and T2 can be adjusted by suitable selection of the average thickness t, average lateral opening d and shape of the microlenses (13). For example, increasing the average lateral opening d generally increases Tl, but can also increase T2, while increasing t/d generally decreases T2, but can also decrease Tl. The shape of the microlenses (13) may be such that substantially collimated light (30) is substantially focused at the through openings (21) to provide a small T2/T1 or a different shape may be used to provide a larger T2/T1. For example, the microlenses (13) may include features or structures that direct a portion of the substantially collimated light (30) in a direction between about 30 to 60 degrees to the incident direction. Such features or structures can be provided by a replication tool (e.g., as engineered features or as artifacts of the process used to make the replication tool) used to make the microlenses (13). The replication tool can be made via diamond turning, for example.

According to at least one embodiment disclosed herein, the absorptive characteristics of the laser- ablated optically opaque mask layer (20) including a UV-cured polymer material reduces back reflection and cross talk. The optical construction (100) can be made by micro-replicating the array of microlenses using a cast and ultra-violet (UV) cure process, for example, where a resin is cast on a substrate and cured in contact with a replication tool surface. A solvent free formulation, for example, can enable coating on a micro-replication line to enable micro-replication of microlens and coating of ablation layer in one step on both sides of a substrate.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure.

Claims

1. An optical construction comprising: a lens film comprising an outermost structured first major surface and an opposing outermost substantially planar second major surface, the structured first major surface comprising a plurality of microlenses arranged along orthogonal first and second directions; and an optically opaque mask layer comprising a UV-cured polymer material and disposed on the second major surface of the lens film and defining a plurality of laser-ablated through openings therein arranged along the first and second directions, the openings aligned to the microlenses in a one-to-one correspondence, such that for a substantially collimated light incident on the structured first major surface side of the optical construction along an incident direction substantially orthogonal to the first and second directions, an optical transmittance of the optical construction as a function of a transmitted angle comprises a first transmitted peak having a first transmittance T1 at a first transmitted angle within about 10 degrees of the incident direction, and a second transmitted peak having a second transmittance T2 at a second transmitted angle between about 30 to 60 degrees of the incident direction, wherein T2/T1 > 0.01.

2. An optical system comprising: a display extending along the first and second directions; an optical sensor disposed opposite the display; and the optical construction of claim 1 disposed between the display and the optical sensor.

3. The optical system of claim 2, wherein the display is an emissive display comprising a plurality of pixels configured to generate and emit light, an organic light emitting diode (OLED) display, or a liquid crystal display.

4. The optical system of claim 2, wherein a first adhesive layer bonds the optical construction to the display, the first adhesive layer having an index of refraction of less than about 1.3 for at least one visible wavelength, and wherein a second adhesive layer bonds the optical construction to the optical sensor.

5. The optical system of claim 2, wherein the optical sensor comprises a plurality of sensor pixels aligned to the microlenses and the through openings in a one-to-one correspondence, and wherein the optical system further comprises an infrared light source disposed to emit light toward a front surface of the display.

6. The optical construction of claim 1, wherein the optically opaque mask layer has an average thickness t and wherein the laser-ablated through openings have an average lateral opening d, t/d < 3, and wherein the optically opaque mask layer has an average thickness of less than about 10 microns.

7. The optical construction of claim 1, wherein the laser-ablated through openings have an average lateral opening of less than about 10 microns.

8. The optical construction of claim 1, wherein T1 > 10% for the incident light having a wavelength of about 550 nm, wherein T2 > 1% for the incident light having a wavelength of about 550 nm, wherein

T2/T1 > 0.02, and wherein T2/T1 < 0.5.

9. The optical construction of claim 1, wherein the optically opaque mask layer comprises a first optically opaque mask sublayer comprising a UV-cured first polymer material disposed on a second optically opaque mask sublayer comprising a UV-cured second polymer material, wherein each opening in the plurality of laser-ablated through openings extends through both sublayers.

10. The optical construction of claim 1, wherein for a substantially normally incident light extending across and covering at least 20 of the microlenses, the optical construction has a total optical transmittance of at least 30%.