Patent Publication Number: US-2023161088-A1

Title: Optical construction and optical system

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to an optical construction and an optical system, and in particular, to an optical construction and an optical system for a display. 
     BACKGROUND 
     Devices, such as cell phones and tablets, can be equipped with biometric authentication features, such as fingerprint sensors. In some cases, the fingerprint sensors are incorporated under a display of the devices, and are referred to as under-the-display fingerprint sensors. The under-the-display fingerprint sensors turn a defined area of the display into a fingerprint sensor, thereby eliminating the need for a separate physical fingerprint sensor. 
     SUMMARY 
     In a first aspect, the present disclosure provides an optical construction. The optical construction includes 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 further includes a multilayer optically opaque mask layer disposed on the second major surface of the lens film opposite the structured first major surface. The multilayer optically opaque mask layer includes a first layer including a first metal and a second layer including a second metal. The multilayer optically opaque mask layer further includes a third layer disposed between the first and second layers. Each of the first, second and third layers has an average thickness less than about 200 nanometers (nm). The first layer is disposed between the second major surface of the lens film and the third layer, such that for substantially normally incident light and for at least one wavelength in a visible wavelength range extending from about 400 nm to about 600 nm, each of the first and second layers has an optical reflectance of greater than about 5%, the third layer has an optical transmittance of greater than about 70%, and the mask layer has an optical reflectance of less than about 20%. The mask layer defines a plurality of through openings therein extending through at least the first, second and third layers and arranged along the first and second directions. The through openings are aligned to the microlenses in a one-to-one correspondence. 
     In a second aspect, the present disclosure provides an optical system including a display including a plurality of light emitting pixels arranged along the first and second directions. The optical system further includes an optical sensor disposed proximate the display. The optical system further includes the optical construction of the first aspect disposed between the display and the optical sensor. 
     In a third aspect, the present disclosure provides an optical construction for absorbing visible light and transmitting infrared light. The optical construction includes a plurality of microlenses disposed on a substantially light absorbing optical cavity system and arranged along orthogonal first and second directions. The optical cavity system includes opposing first and second reflectors defining an optical cavity therebetween. The optical cavity has a length less than 200 nm, such that for substantially normally incident light and a visible wavelength range extending from about 400 nm to about 600 nm, for at least one wavelength in the visible wavelength range, the optical cavity system reflects less than about 20% of the incident light, and transmits less than 2% of the incident light and for at least one wavelength in the visible wavelength range, the optical construction transmits at least 10% of the incident light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments disclosed herein may be more completely understood in consideration of the following detailed description in connection with the following figures. The figures are not necessarily drawn 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. 
         FIG.  1    is a schematic view of an optical system according to one embodiment of the present disclosure; 
         FIG.  2 A  is a schematic view of a multilayer optically opaque mask layer according to one embodiment of the present disclosure; 
         FIG.  2 B  is a schematic view of a first layer of the multilayer optically opaque mask layer according to one embodiment of the present disclosure; 
         FIG.  2 C  is a schematic view of a second layer of the multilayer optically opaque mask layer according to one embodiment of the present disclosure; 
         FIG.  2 D  is a schematic view of a third layer of the multilayer optically opaque mask layer according to one embodiment of the present disclosure; 
         FIG.  3 A  is a graph illustrating exemplary variations of a transmittance and a reflectance of a light blocking layer with a wavelength of incident light; 
         FIG.  3 B  is a graph illustrating exemplary variations of a transmittance and a reflectance of another light blocking layer with a wavelength of incident light; and 
         FIG.  4    is a graph illustrating exemplary variations of an absorption, a transmittance and a reflectance of the multilayer optically opaque mask layer with a wavelength of incident light. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. 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. The following detailed description, therefore, is not to be taken in a limiting sense. 
     A display with an under-the-display fingerprint sensor may include a display panel, collimation optics, a light blocking layer with holes, and an image sensor. The light blocking layer may have low reflectance and low transmittance in visible range of light in order to improve overall display ambient contrast in a dark state. Conventional displays with the under-the-display fingerprint sensor use black paint as the light blocking layer. However, the black paint may be incompatible with the display fabrication process. Moreover, it may also be difficult to provide holes in the black paint to enable a fingerprint signal to pass through. According to some aspects of the present disclosure, multilayer optically opaque mask layers are provided that address these and other issues with conventional light blocking layers. 
     The present disclosure relates to an optical system and an optical construction. The optical system includes a display, an optical sensor, and the optical construction. The optical system and the optical construction may be used in electronic devices that include displays, such as computer monitors, televisions, mobile phones, personal digital assistants (PDAs), wearable devices and other portable devices. 
     The optical construction includes a lens film and a multilayer optically opaque mask layer. The lens film includes an outermost structured first major surface and an opposing outermost substantially planar second major surface. The structured first surface includes a plurality of microlenses arranged along orthogonal first and second directions. The multilayer optically opaque mask layer is disposed on the second major surface of the lens film and includes a first layer, a second layer and a third layer. Each of the first, the second and the third layers has an average thickness less than about 200 nanometers (nm). For a substantially normal incident light with a wavelength in a visible wavelength range, each of the first and the second layers has an optical reflectance of greater than about 5%, and the third layer has an optical transmittance of greater than about 70%. The multilayer optically opaque mask layer has an optical reflectance of less than about 20%. The multilayer optically opaque mask layer defines a plurality of through openings therein extending through at least the first, second and third layers and arranged along the first and second directions. The through openings are aligned to the microlenses in a one-to-one correspondence. 
     The mask layer may be directly coated on the planar second major surface of the lens film by vacuum coating process, such as electron beam evaporation, thermal evaporation, physical vapor deposition, and chemical vapor deposition or sputtering, thereby simplifying the display fabrication process. By selecting the right combination of materials for different layers and controlling the layer thickness of each layer, the multilayer optically opaque mask layer may achieve low reflectance and low transmittance in visible range of light, and hence may improve overall display ambient contrast in a dark state. Moreover, as the mask layer is thin, the process of drilling the through openings in the mask layer is further simplified and may be carried out by laser ablation. 
     Referring now to the Figures,  FIG.  1    illustrates an optical system  300  including a display  110 , and an optical sensor  50  disposed proximate the display  110 . The optical system  300  further includes an optical construction  200  for absorbing visible light and transmitting infrared light. The optical construction  200  is disposed between the display  110  and the optical sensor  50 . 
     The optical system  300  defines mutually orthogonal x, y and z-axes. The x and y-axes are in-plane axes of the optical system  300 , while the z-axis is a transverse axis disposed along a thickness of the optical system  300 . In other words, the x and y-axes are disposed along a plane of the optical system  300 , while the z-axis is perpendicular to the plane of the optical system  300 . The display  110 , the optical construction  200 , and the optical sensor  50  of the optical system  300  are disposed adjacent to each other along the z-axis. 
     In some embodiments, the optical system  300  further includes a first adhesive layer  60 . The first adhesive layer  60  bonds the optical construction  200  to the display  110 . The first adhesive layer  60  has an index of refraction of less than about 1.3 for at least one wavelength in a visible wavelength range extending from about 400 nm to about 600 nm. In some embodiments, the optical system  300  may further include a second adhesive layer  70 . The second adhesive layer  70  bonds the optical construction  200  to the optical sensor  50 . 
     The display  110  includes a plurality of light emitting pixels  111  arrange along first and second directions. The first and second directions are orthogonal to each other. The first direction may be defined along the x-axis and the second direction may be defined along the y-axis. The light emitting pixels  111  may emit light in response to an electric current. The light emitting pixels  111  may include any suitable sub-pixel arrangement, for example, a pentile matrix or an RGB matrix, as per application attributes. 
     The optical construction  200  includes a lens film  10  and a multilayer optically opaque mask layer  20  or a substantially light absorbing optical cavity system  90 . In some embodiments, the optical construction  200  includes the multilayer optically opaque mask layer  20 . In some other embodiments, the optical construction  200  includes the optical cavity system  90 . 
     The lens film  10  includes an outermost structured first major surface  11  and an opposing outermost substantially planar second major surface  12 . The structured first major surface  11  includes a plurality of microlenses  13  arranged along the orthogonal first and second directions. The plurality of microlenses  13  may be disposed on the optical cavity system  90  and arranged along the first and second directions. Specifically, the lens film  10  including the microlenses  13  is disposed on the optical cavity system  90 . The microlenses  13  may have at least one lateral dimension (e.g., diameter) less than 1 millimeter (mm) and any suitable geometry. In some embodiments, the microlenses  13  may include 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. 
     The mask layer  20  is disposed on the second major surface  12  of the lens film  10 , opposite the structured first major surface  11 . The mask layer  20  includes a first layer  21 , a second layer  22 , and a third layer  23  disposed between the first and second layers  21 ,  22 . 
     The mask layer  20  defines a plurality of through openings  40  therein extending through at least the first, second and third layers  21 ,  22 ,  23  and arranged along the first and second directions. The through openings  40  are aligned to the microlenses  13  in a one-to-one correspondence. 
     The optical cavity system  90  includes opposing first and second reflectors  21 ,  22  defining an optical cavity  91  therebetween. The first layer  21  may be interchangeably referred to as the first reflector  21 . The second layer  22  may be interchangeably referred to as the second reflector  22 . The optical cavity  91  has a length less than 200 nm. 
     Each of the first and second reflectors  21 ,  22  defines the plurality of through openings  40  therein. The through openings  40  are arranged along the first and second directions and aligned to the microlenses  13  in a one-to-one correspondence. 
     The through openings  40  may be of any suitable diameter. In some embodiments, each of the through openings  40  may have a diameter from about 1 micron (μm) to about 5 μm. In some other embodiments, each of the through openings  40  may have a diameter of about 3 μm. The through openings  40  may be provided by any suitable process, for example, by laser ablation. 
     In some embodiments, the optical sensor  50  incudes a plurality of sensor pixels  51  aligned to the microlenses  13  and the through openings  40  in a one-to-one correspondence. 
     The first layer  21  includes a first metal, and the second layer  22  includes a second metal. In some embodiments, at least one of the first and second layers  21 ,  22  includes one or more of titanium, chromium, nickel, copper, platinum, cobalt, tungsten, and manganese. In some embodiments, the second layer  22  includes one or more of aluminum, gold and silver. In some embodiments, the first layer  21  includes titanium and the second layer  22  includes aluminum. In some embodiments, the third layer  23  includes an optically transparent dielectric material. In some embodiments, the third layer  23  includes silicon dioxide (SiO 2 ). Selection of the materials of the first, second and third layers  21 ,  22 ,  23  may depend on desired optical transmissive and reflective properties of the materials. In some embodiments, the optical construction  200  may trap light by repeated reflections from the first and the second layers  21 ,  22 . The third layer  23  may transmit light to enable such reflections from the first and second layers  21 ,  22 . 
     In some embodiments, selection of materials of the first and second and third layers  21 ,  22 ,  23  may depend upon factors, such as adhesion to a Polyethylene Terephthalate (PET) film, laser ablation feasibility, and material cost. 
     The first, second and third layers  21 ,  22 ,  23  may be directly coated on the second major surface  12  of the lens film  10  by vacuum coating process, such as electron beam evaporation, thermal evaporation, physical vapor deposition, chemical vapor deposition or sputtering, and thereby simplify the fabrication process. Further, by selecting the right combination of materials for the first, second and third layers  21 ,  22 ,  23 , the mask layer  20  may achieve low reflectance and low transmittance in visible range of light, and hence may improve overall display ambient contrast in a dark state. Moreover, the first, second and third layers  21 ,  22 ,  23  may further simplify the process of drilling the through openings  40  in the mask layer  20 . 
     In some embodiments, the first layer  21  has an average thickness t of about 5 nm to about 50 nm, or about 5 nm to about 40 nm, or about 5 nm to about 30 nm, or about 5 nm to about 20 nm. In some embodiments, the second layer  22  has an average thickness t of about 5 nm to about 70 nm, or about 5 nm to about 60 nm, or about 5 nm to about 50 nm, or about 5 nm to about 40 nm. In some embodiments, the third layer  23  has an average thickness t of about 20 nm to about 200 nm, or about 30 nm to about 150 nm, or about 40 nm to about 120 nm, or about 50 nm to about 100 nm. 
     By optimizing the average thickness t of each of the first, second and third layers  21 ,  22 ,  23  for different wavelengths, both low reflectance and low transmittance may be achieved. 
     Now referring to  FIGS.  1  and  2 A , the first layer  21  is disposed between the second major surface  12  of the lens film  10  and the third layer  23 , such that for substantially normally incident light  30  and for at least one wavelength in a visible wavelength range extending from about 400 nm to about 600 nm, each of the first and second layers  21 ,  22  has an optical reflectance of greater than about 5%. In some embodiments, for the at least one wavelength in the visible wavelength range, at least one of the first and second layers  21 ,  22  has an optical reflectance of greater than about 10%, or 15%, or 20%. In some embodiments, for the at least one wavelength in the visible wavelength range, each of the first and second layers  21 ,  22  has an optical reflectance of greater than about 10%, or 15%. For the at least one wavelength in the visible wavelength range, the third layer  23  has an optical transmittance of greater than about 70%, and the mask layer  20  has an optical reflectance of less than about 20%. In some embodiments, for the at least one wavelength in the visible wavelength range, the mask layer  20  has an optical reflectance of less than about 15%, or 10%. In some embodiments, mask layer  20  may include more than three layers. More than three layers may further reduce the optical reflectance of the mask layer  20 . 
     In some embodiments, the first and second reflectors  21 ,  22  define the optical cavity  91  such that for substantially normally incident light  30  and a visible wavelength range extending from about 400 nm to about 600 nm, for at least one wavelength in the visible wavelength range, the optical cavity system  90  reflects less than about 20% of the incident light, and transmits less than 2% of the incident light. Further, for at least one wavelength in the visible wavelength range, the optical construction  200  transmits at least 10% of the incident light  30 . 
     In some embodiments, the optical cavity  91  includes an air gap which has relatively high optical transmittance as compared to the first and second reflectors  21 ,  22 . Repeated reflections of light from the first and second reflectors  21 ,  22  across the optical cavity  91  may trap light within the optical cavity system  90 . Therefore, the optical cavity system  90  may have high optical absorption. 
     It may be noted that by selecting right combination of materials of the first, second and third layers  21 ,  22 ,  23 , as well as the optimization of the average thickness t of each of the first, second and third layers  21 ,  22 ,  23 , low optical transmittance and low optical reflectance of the mask layer  20  may be achieved. For example, a larger average thickness t may be chosen to reduce cross-talk (light from one microlens incident on the through openings  40  aligned with a different microlens), or a smaller average thickness t may be chosen to increase light transmitted through the through openings  40 . Similarly, a light absorption of the optical cavity system  90  may be increased by optimizing materials and dimensions of the first and second reflectors  21 ,  22  and the optical cavity  91 . 
     The optical sensor  50  may be configured to detect a fingerprint and a display device (e.g., a mobile phone) including the display  110  may be configured to determine if the detected fingerprint matches a fingerprint of an authorized user. In some embodiments, the optical system  300  further includes an infrared light source  80  disposed to emit light  81  toward a front side  42  of the display  110 . The infrared light source  80  may aid the optical sensor  50  in detecting a fingerprint on the display  110 . The infrared light source  80  may be positioned such that the infrared light source  80  emit light  81  towards a suitable direction. Light  81  emitted by the infrared light source  80  may have a wavelength range extending from about 700 nm to about 1 mm. 
     When a finger is placed on the display  110  of the optical system  300 , the finger reflects a light emitted by the display  110  and/or the infrared light source  80 . The reflected light travels through the display  110  before reaching the optical construction  200  and the optical sensor  50 . The mask layer  20  of the optical construction  200  with the through openings  40  may allow a portion of the reflected light to reach the optical sensor  50  for signal detection. The other portion of the reflected light from the finger, and the light emitted by the display  110  and/or the infrared light source  80  may be absorbed by the mask layer  20 . 
     Now referring to  FIG.  2 A , the mask layer  20  or the optical cavity system  90  is illustrated. The substantially normally incident light  30  is also illustrated. The mask layer  20  includes the first, second and third layers  21 ,  22 ,  23 . The incident light  30  may be reflected and transmitted according to one more materials chosen for each of the first, second and third layers  21 ,  22 ,  23 . The combination of the first, second and third layers  21 ,  22 ,  23  may substantially absorb the incident light  30 . 
     The optical cavity system  90  includes the first and second reflectors  21 ,  22 . The incident light  30  may be at least partially reflected by the first and second reflectors  21 ,  22 . The optical cavity system  90  further includes the optical cavity  91  disposed between the first and second reflectors  21 ,  22 . The optical cavity  91  may allow the incident light  30  to circulate in a closed path due to repeated reflections from the first and second reflectors  21 ,  22 . The optical cavity system  90  and the mask layer  20  may trap the incident light  30 , and a portion of reflected light from the second layer  22 . 
       FIG.  2 B  illustrates the first layer  21  of the mask layer  20 . In some embodiments, the first layer  21  includes one or more of titanium, chromium, nickel, copper, platinum, cobalt, tungsten, and manganese. In some embodiments, the first layer  21  may include one or more of aluminum, gold and silver. In some embodiments, the first layer  21  has an average thickness of about 5 nm to about 50 nm, or about 5 nm to about 40 nm, or about 5 nm to about 30 nm, or about 5 nm to about 20 nm. 
       FIG.  2 C  illustrates the third layer  23  of the mask layer  20 . In some embodiments, the third layer  23  includes an optically transparent dielectric material. In some embodiments, the third layer  23  includes SiO 2 . In some embodiments, the third layer  23  has an average thickness of about 20 nm to about 200 nm, or about 30 nm to about 150 nm, or about 40 nm to about 120 nm, or about 50 nm to about 100 nm. 
       FIG.  2 D  illustrates the second layer  22  of the mask layer  20 . In some embodiments, the second layer  22  includes one or more of titanium, chromium, nickel, copper, platinum, cobalt, tungsten, and manganese. In some embodiments, the second layer  22  includes one or more of aluminum, gold and silver. In some embodiments, the second layer  22  has an average thickness of about 5 nm to about 70 nm, or about 5 nm to about 60 nm, or about 5 nm to about 50 nm, or about 5 nm to about 40 nm. 
     Now referring to  FIG.  3 A , a graph  300 A illustrates variations between optical transmittance and optical reflectance with wavelength of an incident light for a PET based collimation optics (e.g., a lens film) coated with a layer of aluminum of about 35 nm thickness. Aluminum was chosen as a light absorbing layer as it may provide ease in drilling micron sized through openings by laser ablation compared to other metals. The transmittance percentage and the reflectance percentage are plotted in the y-axis against the wavelength on the x-axis. Scale of the transmittance percentage is shown on the left y-axis. Scale of the reflectance percentage is shown on the right y-axis. The reflectance percentage is depicted by a curve  310 A and the transmittance percentage is depicted by a curve  320 A. As depicted by the graph  300 A, the transmittance percentage of the incident light is less than about 0.5% for wavelengths from about 400 nm to about 600 nm. However, the reflectance percentage of the incident light is about 87% for wavelengths from about 400 nm to about 600 nm. Therefore, there may be a need to further reduce the reflectance for improving the collimation optics. 
     Now referring to  FIG.  3 B , a graph  300 B illustrates variations between optical transmittance and optical reflectance with wavelength of an incident light for a PET based collimation optics (e.g., a lens film) coated with a layer of germanium of about 17 nm thickness and a layer of aluminum of about 35 nm thickness. The transmittance percentage and the reflectance percentage are plotted in the y-axis against the wavelength on the x-axis. Scale of the transmittance percentage is shown on the left y-axis. Scale of the reflectance percentage is shown on the right y-axis. The reflectance percentage is depicted by a curve  310 B and the transmittance percentage is depicted by a curve  320 B. As depicted by the graph  300 B, the transmittance percentage of the incident light is less than about 0.24% for wavelengths from about 400 nm to about 600 nm. Further, the reflectance percentage of the incident light is less than about 20% for wavelengths from about 400 nm to about 600 nm. Therefore, the collimation optics coated with the layer of germanium of about 17 nm thickness and the layer of aluminum of about 35 nm thickness has a lower transmittance and a lower reflectance as compared to the collimation optics with coated with a single layer of aluminum of about 35 nm thickness. However, there may be a need to further reduce the transmittance and the reflectance of the collimation optics. 
     Referring to  FIGS.  1  and  4   , a graph  400  illustrates variations between an optical absorption, an optical transmittance and an optical reflectance of an incident light with wavelength of the optical construction  200  in accordance to an embodiment of the present disclosure. The first layer  21  includes titanium. The average thickness t of the first layer  21  is about 13 nm. The second layer  22  includes aluminum. The average thickness t of the second layer  22  is about 29 nm. The third layer  23  includes SiO 2 . The average thickness t of the third layer  23  is about 84 nm. The absorption percentage, the transmittance percentage and the reflectance percentage are plotted in the y-axis against the wavelength on the x-axis. Scale of the absorption percentage is shown on the left y-axis. Scale of the transmittance percentage and the reflectance percentage is shown on the right y-axis. The absorption percentage is depicted by a curve  410 . The transmittance percentage is depicted by a curve  420 . The reflectance percentage is depicted by a curve  430 . It may be apparent from the graph  400  that the optical construction  200  exhibits a low reflectance percentage, a low transmittance percentage and a high absorption percentage. The absorption percentage may be equivalent to 100−(Reflectance percentage+Transmittance percentage). 
     As depicted in the graph  400 , the absorption percentage of the incident light is from about 94.5% to about 99.5% for wavelengths from about 400 nm to about 600 nm. The transmittance percentage of the incident light is less than about 0.5% for wavelengths from about 400 nm to about 600 nm. The reflectance percentage of the incident light is less than about 5.5% for wavelengths from about 400 nm to about 600 nm. The optical construction  200  may provide better optical characteristics than other optical configurations discussed above with reference to  FIGS.  3 A and  3 B . Specifically, the optical construction  200  may provide lower transmittance and lower reflectance. The three-layer configuration of the optical construction  200  may therefore provide improved light blocking performance than a single aluminum layer or a two-layer configuration including aluminum and germanium. 
     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. 
     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. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.