Optical stack

Abstract

An optical stack includes a reflective polarizer, an absorptive polarizer, and a half-wave delayer. The half-wave delayer is disposed between the reflective polarizer and the absorptive polarizer. For approximately normal incident light and a first polarization state, the reflective polarizer reflects at least about 60% of the incident light of at least a first wavelength less than the cutoff wavelength and transmits at least about 50% of the incident light of at least a second wavelength greater than the cutoff wavelength. For approximately normal incident light, the half-wave delayer has a first delay of less than about 250 nanometers (nm) at the first wavelength and a second delay at the second wavelength. The deviation of the first delay from the first half-wave delay corresponding to the first wavelength is less than the deviation of the second delay from the second half-wave delay corresponding to the second wavelength.

Description

Technical Field

[0001] This disclosure relates in general to optical stacks, and more particularly to optical stacks for backlights. Background Technology

[0002] In backlights, reflective polarizers are commonly used to recirculate light and enhance the final efficiency and brightness of the display. Additionally, absorptive polarizers, among others, are used in conjunction with liquid crystal modules to polarize light for appropriate adjustment by the liquid crystal module. In some manufacturing processes, roll-to-roll reflective polarizers may have a reflective axis (i.e., a blocking axis or slow axis) in the transverse direction (i.e., the width direction of the roll). Roll-to-roll absorptive polarizers may have an absorption axis along the length of the roll. In some cases, it may be desirable to align the reflective axis of the reflective polarizer with the absorption axis of the absorptive polarizer within the optical stack. In conventional manufacturing processes, one or both rolls of the polarizer are cut and rotated, increasing manufacturing time and process costs. Summary of the Invention

[0003] In a first aspect, this disclosure provides an optical stack. The optical stack includes a reflective polarizer, an absorptive polarizer, and a half-wave delayer. The reflective polarizer includes a transmission axis and a reflection axis that are orthogonal to each other. The half-wave delayer is disposed between the reflective polarizer and the absorptive polarizer. For approximately normal incident light and a first polarization state, the reflective polarizer includes a transmission band having a cutoff wavelength. The reflective polarizer reflects at least about 60% of incident light of at least a first wavelength less than the cutoff wavelength and transmits at least about 50% of incident light of at least a second wavelength greater than the cutoff wavelength. For approximately normal incident light and an orthogonal second polarization state, the reflective polarizer transmits at least 70% of incident light of at least the first wavelength and at least the second wavelength. For approximately normal incident light, the half-wave delayer has a first delay of less than about 250 nanometers (nm) at the first wavelength and a second delay at the second wavelength. The deviation of the first delay from the first half-wave delay corresponding to the first wavelength is less than the deviation of the second delay from the second half-wave delay corresponding to the second wavelength. For approximately normal incident light and a first polarization state, the absorbing polarizer has a first transmittance at a first wavelength and a larger second transmittance at a second wavelength.

[0004] In a second aspect, this disclosure provides another optical stack. The optical stack includes a display panel, a reflective polarizer, an absorptive polarizer, and a half-wave delayer. The display panel is configured to emit display light comprising a blue emission spectrum having a full width at half maximum (FWHM) defined between a minimum wavelength and a maximum wavelength. The reflective polarizer is configured to receive and reflect a portion of the display light from the display panel as reflected polarized light. The reflective polarizer includes mutually orthogonal transmission and reflection axes. The half-wave delayer is disposed between the reflective polarizer and the absorptive polarizer. For substantially normal incident light and a first polarization state, the reflective polarizer includes a transmission band having a cutoff wavelength greater than the minimum wavelength of the blue emission spectrum of the display panel. The reflective polarizer reflects at least about 60% of the incident light of at least a first wavelength less than the cutoff wavelength and transmits at least about 50% of the incident light of at least a second wavelength greater than the cutoff wavelength. For substantially normal incident light and an orthogonal second polarization state, the reflective polarizer transmits at least 70% of the incident light of at least the first wavelength and at least the second wavelength. For approximately normal incident light, the half-wave delayer has a first delay of less than about 250 nm at a first wavelength and a second delay at a second wavelength. The deviation of the first delay from the first half-wave delay corresponding to the first wavelength is smaller than the deviation of the second delay from the second half-wave delay corresponding to the second wavelength. For approximately normal incident light and a first polarization state, the absorbing polarizer has a first transmittance at the first wavelength and a larger second transmittance at the second wavelength. Attached Figure Description

[0005] The exemplary embodiments disclosed herein can be more fully understood in light of the following detailed description taken in conjunction with the accompanying drawings. The drawings are not necessarily drawn to scale. Similar numbers used in the drawings refer to similar parts. However, it should be understood that the use of numbers to refer to parts in a given drawing is not intended to limit parts labeled with the same numbers in another drawing.

[0006] Figure 1 This is a schematic exploded top perspective view of an optical stack according to one embodiment of the present disclosure;

[0007] Figure 2 yes Figure 1 A schematic front view of the optical stack;

[0008] Figure 3 This is a schematic diagram of an optical stacked half-wave delayer according to one embodiment of the present disclosure;

[0009] Figure 4 This is a detailed schematic diagram of a reflective polarizer according to one embodiment of the present disclosure;

[0010] Figure 5This is a graph showing the transmittance versus wavelength of a reflective polarizer with a transmission band according to one embodiment of the present disclosure;

[0011] Figure 6 This is another graph showing the transmittance versus wavelength of a reflective polarizer with other transmission bands according to another embodiment of the present disclosure;

[0012] Figure 7 This is a schematic diagram of an optical stacked half-wave delayer according to one embodiment of the present disclosure;

[0013] Figure 8 This is a graph showing the delay versus wavelength of a half-wave delayer according to one embodiment of the present disclosure;

[0014] Figure 9 This is a graph showing the delay deviation versus wavelength of a half-wave delayer according to one embodiment of the present disclosure;

[0015] Figure 10 This is a schematic diagram of an optically stacked absorption polarizer according to one embodiment of the present disclosure; and

[0016] Figure 11 This is a graph showing the transmittance versus wavelength of an absorbing polarizer according to one embodiment of the present disclosure. Detailed Implementation

[0017] In the following description, reference is made to the accompanying drawings, which form a part thereof, and various embodiments are illustrated therein. It should be understood that other embodiments can be conceived and made without departing from the scope or spirit of this disclosure. Therefore, the following detailed description should not be considered limiting.

[0018] This invention relates to optical stacks. These optical stacks can be used in the backlights of electronic devices with displays, such as computer monitors, televisions, mobile phones, personal digital assistants (PDAs), wearable devices, and other portable devices. Typical optical stacks include reflective polarizers and absorptive polarizers.

[0019] In conventional manufacturing processes and using conventional material selection, reflective polarizers are stretched such that the reflection axis (parallel to the axis of the polarization state preferentially reflected by the reflective polarizer) is along the width direction of the reflective polarizer. Furthermore, conventional absorptive polarizers are typically aligned longitudinally, resulting in an absorption axis approximately along the length of the absorptive polarizer. Therefore, conventional manufacturing processes result in the rolls of reflective and absorptive polarizers having transmission axes orthogonally oriented to each other. Consequently, providing sheets with absorptive and reflective polarizers with transmission axis alignment may require costly conversion steps. Typically, in sheet-to-roll lamination processes, reflective polarizers are cut and rotated 90 degrees to align with the transmission axis. This process is time-consuming and expensive, and the conversion step can sometimes increase the chance of introducing defects, which can reduce the yield or usable portion of the optical stack. Therefore, it may be desirable to align the reflection axis of the reflective polarizer with the absorption axis of the absorptive polarizer within the optical stack to save additional manufacturing time and process costs.

[0020] In some designs, a half-wave delayer is positioned between a reflecting polarizer and an absorbing polarizer. The half-wave delayer may have a slow axis oriented approximately 45 degrees to the transmission axis of the reflecting polarizer. The half-wave delayer rotates the linearly polarized light between the reflecting and absorbing polarizers by 90 degrees, aligning the reflection axis of the reflecting polarizer with the absorption axis of the absorbing polarizer. However, the incorporation of a half-wave delayer can pose challenges to uniformly rotating linearly polarized light across all visible wavelengths to minimize color shift or other artifacts at various viewing angles in the optical stack. Color shift can be due to nonlinear wavelength-dependent modulation of light in conventional half-wave delayers. In some of these cases, achromatic half-wave delayers are fabricated using special materials to reduce color shift. However, even achromatic half-wave delayers may exhibit some chromatic aberration during the conversion of linearly polarized light. Furthermore, utilizing achromatic half-wave delayers can significantly increase the overall cost of the optical stack.

[0021] This disclosure relates to an optical stack comprising a reflective polarizer, an absorptive polarizer, and a half-wave delayer. The reflective polarizer of this disclosure has mutually orthogonal transmission and reflection axes. A half-wave delayer is disposed between the reflective polarizer and the absorptive polarizer. For substantially normal incident light and a first polarization state, the reflective polarizer of this disclosure includes a transmission band having a cutoff wavelength. For the first polarization state, the reflective polarizer reflects at least about 60% of incident light of at least a first wavelength less than the cutoff wavelength and transmits at least about 50% of incident light of at least a second wavelength greater than the cutoff wavelength. For substantially normal incident light and an orthogonal second polarization state, the reflective polarizer transmits at least 70% of incident light of at least the first wavelength and at least the second wavelength.

[0022] Furthermore, the half-wave delay of the present invention is designed such that, for approximately normal incident light, the half-wave delay has a first delay of less than about 250 nanometers (nm) at a first wavelength and a second delay at a second wavelength. The deviation of the first delay from the first half-wave delay corresponding to the first wavelength is less than the deviation of the second delay from the second half-wave delay corresponding to the second wavelength.

[0023] Such optimization of the half-wave retarder at wavelengths smaller than the cutoff wavelength of the transmission band of the reflective polarizer can reduce optical artifacts, such as color shift. Specifically, the combination of the reflective polarizer and the half-wave retarder disclosed herein exhibits improved performance in reducing color shift. Furthermore, the half-wave retarder optimized in this manner is easier and cheaper to manufacture than conventional achromatic half-wave retarders.

[0024] Now for reference Figure 1 and Figure 2 The image illustrates an optical stack 100 according to an embodiment of the present disclosure. The optical stack 100 includes a reflective polarizer 102, a half-wave delayer 104, an absorptive polarizer 106, and a display panel 108. In some embodiments, the reflective polarizer 102, the half-wave delayer 104, the absorptive polarizer 106, and the display panel 108 are substantially co-linear with each other or have the same in-plane dimensions (i.e., length and width).

[0025] The optical stack 100 defines mutually orthogonal x-axis, y-axis, and z-axis. The x-axis and y-axis are in-plane axes of the optical stack 100, while the z-axis is a transverse axis set along the thickness of the optical stack 100. In other words, the x-axis and y-axis are set along the plane of the optical stack 100, while the z-axis is perpendicular to the plane of the optical stack 100. The reflective polarizer 102, the half-wave delayer 104, the absorptive polarizer 106, and the display panel 108 are arranged adjacent to each other along the z-axis of the optical stack 100.

[0026] In some embodiments, the reflective polarizer 102, half-wave delayer 104, and absorptive polarizer 106 of the optical stack 100 may be in optical contact with each other. In some embodiments, the reflective polarizer 102, half-wave delayer 104, and absorptive polarizer 106 of the optical stack 100 are attached using one or more of the following: pressure-sensitive adhesive, optically transparent adhesive, ultraviolet (UV) curable adhesive or polyvinyl alcohol-based adhesive, laminate, or any other attachment mechanism.

[0027] The reflective polarizer 102 includes a transmission axis 122 and a reflection axis 124 that are orthogonal to each other. The reflective polarizer 102 may be a notch-type reflective polarizer with one or more notches or bands. The reflective polarizer 102 may be any suitable reflective polarizer, including a wire-grid polarizer or a multilayer birefringent reflective polarizer. In an exemplary embodiment, the reflective polarizer 102 may have a transmission axis 122 generally along the x-axis of the reflective polarizer 102 and a reflection axis 124 generally along the y-axis. The reflective polarizer 102 also includes a first primary surface 112 and a second primary surface 114 opposite to the first primary surface 112. In some embodiments, each of the first primary surface 112 and the second primary surface 114 of the reflective polarizer 102 may be generally flat and disposed along the xy-plane.

[0028] A half-wave delayer 104 is disposed between the reflective polarizer 102 and the absorptive polarizer 106. The half-wave delayer 104 includes a first primary surface 116 and a second primary surface 118 opposite to the first primary surface 116. In some embodiments, each of the first primary surface 116 and the second primary surface 118 of the half-wave delayer 104 may be substantially flat and disposed along the xy-plane. Figure 2 In an exemplary embodiment, the absorbing polarizer 106 is disposed adjacent to the first principal surface 116 of the half-wave delayer 104. Furthermore, the second principal surface 118 of the half-wave delayer 104 is disposed adjacent to the first principal surface 112 of the reflecting polarizer 102. Typically, the half-wave delayer 104 includes a layer of birefringent material. In some embodiments, the half-wave delayer 104 includes a half-wave cyclic olefin polymer (COP) delayer. In some embodiments, the half-wave delayer 104 may include two layers of birefringent material. In some embodiments, the half-wave delayer 104 may be a mixture of two materials, namely a positive birefringent material and a negative birefringent material. In some embodiments, the half-wave delayer 104 may include two layers such that one layer can rotate linearly polarized light by approximately 15 degrees, while the other layer can rotate linearly polarized light by approximately 75 degrees. In some embodiments, the half-wave delayer 104 is a non-achromatic half-wave delay, i.e., the delay of the half-wave delayer 104 deviates substantially from an ideal half-wave delay over at least a portion of the visible wavelength range. Typically, the delay of an achromatic half-wave retarder deviates less from that of an ideal half-wave retarder than that of a non-achromatic retarder. Furthermore, compared to its delay at lower wavelengths, a non-achromatic half-wave retarder usually has the same or smaller delay at higher wavelengths. On the other hand, the delay of an achromatic half-wave retarder typically increases at higher wavelengths.

[0029] The half-wave delayer 104 includes a slow axis 126 oriented at approximately 45 degrees relative to the transmission axis 122 of the reflective polarizer 102. For the purposes of this patent application, given the bidirectional nature of the transmission axis 122, orientations of approximately 45 degrees and approximately 135 degrees can be considered substantially equivalent. Approximately 45 degrees can also be understood as not being limited to a precise 45 degrees; rather, the alignment of the axis can be within 10 degrees, 5 degrees, or 1 degree of 45 degrees. In some cases, alignment can be a trade-off between manufacturability (e.g., tolerance) and optical performance, with the appropriate balance depending on the application attributes.

[0030] The display panel 108 is positioned below the reflective polarizer 102, opposite to the half-wave delayer 104. Figure 2 In some exemplary embodiments, the display panel 108 is disposed adjacent to the second primary surface 114 of the reflective polarizer 102. In some embodiments, the display panel 108 includes an organic light-emitting diode (OLED) display panel. In some embodiments, a quarter-wavelength retarder (not shown) may be disposed between the reflective polarizer 102 and the display panel 108. The quarter-wavelength retarder can be used to generate circular polarization to reduce ambient reflections from the display panel 108. In some other embodiments, the display panel 108 includes a liquid crystal display (LCD) panel.

[0031] The absorptive polarizer 106 can be disposed on the half-wave delayer 104, opposite to the reflective polarizer 102. Figure 2 In an exemplary embodiment, the bottom surface 120 of the absorbing polarizer 106 is disposed on the first primary surface 116 of the half-wave delayer 104. The absorbing polarizer 106 includes a transmission axis 128 oriented approximately 90 degrees relative to the transmission axis 122 of the reflecting polarizer 102 and approximately 45 degrees (or 135 degrees) relative to the slow axis 126 of the half-wave delayer 104. In an exemplary embodiment, the transmission axis 128 of the absorbing polarizer 106 is disposed approximately along the y-axis. The absorbing polarizer 106 may comprise any suitable material, such as a polymer material. In some embodiments, the absorbing polarizer 106 may comprise polyvinyl alcohol. In some embodiments, the absorbing polarizer 106 may comprise a polarizing element, including a polarizing or dichroic dye.

[0032] In some implementations, the optical stack 100 may include additional or intermediate films, layers, or components, such as a diffuse layer, a redirecting layer, or a substrate layer. The optical stack 100 may have any suitable thickness overall, depending on the desired application properties.

[0033] Display panel 108 is configured to emit display light 10. Reflective polarizer 102 is configured to receive and reflect a portion of the display light 10 from display panel 108 as reflected polarized light 12. Display light 10 is generally unpolarized. However, in some cases, display light 10 may be at least partially polarized light. For illustrative purposes, display light 10 may be considered as light having an unknown or arbitrary polarization state or polarization state distribution. Reflected polarized light 12 is generally polarized along the reflection axis 124 (i.e., the y-axis) of reflective polarizer 102. Reflected polarized light 12 may therefore have a first polarization state along the y-axis. Reflective polarizer 102 transmits a first transmitted light 14 having an orthogonal second polarization state parallel to the transmission axis 122 (i.e., the x-axis) of reflective polarizer 102.

[0034] Half-wave delay 104 receives first transmitted light 14 from reflective polarizer 102. Half-wave delay 104 is configured to rotate or modulate at least a portion of the polarization of the first transmitted polarized light 14 into orthogonally polarized second transmitted light 16. Therefore, the second transmitted light 16 may have a first polarization state. Absorbing polarizer 106 receives the second transmitted light 16 from half-wave delay 104 and emits at least a portion of the second transmitted light 16 as output light 18 having the first polarization state.

[0035] Figure 3 and Figure 4 A reflective polarizer 102 is shown. The reflective polarizer 102 may include one or more of the following: a polymer reflective polarizer, a wire-grid reflective polarizer, and a diffuse reflective polarizer. Figure 4 As shown, the reflective polarizer 102 includes a plurality of alternating first polymer layers 302 and second polymer layers 304. In some embodiments, the total number of the plurality of alternating first polymer layers 302 and second polymer layers 304 is at least 40. In some other embodiments, the total number of the plurality of alternating first polymer layers 302 and second polymer layers 304 is at least 50, at least 75, at least 90, at least 95, or at least 100. Each of the first polymer layers 302 and second polymer layers 304 defines an average thickness “T” along the z-axis. In some embodiments, each of the first polymer layers 302 and second polymer layers 304 has an average thickness “T” of less than about 350 nm. In some embodiments, each of the first polymer layers 302 and second polymer layers 304 may have an average thickness “T” of less than about 400 nm. In some other embodiments, the average thickness “T” of each of the first polymer layers 302 and second polymer layers 304 may be less than about 500 nm, less than about 600 nm, or less than about 700 nm. In some embodiments, the reflective polarizer 102 may further include a protective layer 306 disposed on each main side of a plurality of alternating first polymer layers 302 and second polymer layers 304.

[0036] Figure 5 and Figure 6 Exemplary graphs 400 and 500 are shown respectively. Graphs 400 and 500 depict the relationship between the transmission percentage of different transmission bands of the reflective polarizer 102 and the wavelength. The wavelength is expressed in nanometers (nm) in the visible light wavelength range. Figure 5 and Figure 6 In this context, transmittance is expressed as the percentage of transmission on the left vertical axis. Figure 5 In the diagram, reflectance is expressed as the percentage of reflection on the right vertical axis. The percentage of reflection is complementary to the percentage of transmission, i.e., percentage of reflection = (100 - percentage of transmission).

[0037] refer to Figure 1 , Figure 5 and Figure 6 The display panel 108 is configured to emit display light 10 comprising a blue emission spectrum 402 having a full width at half maximum (FWHM) 410 defined between a minimum wavelength 406 and a maximum wavelength 407. Any suitable energy unit can be used to illustrate the blue emission spectrum 402 of the display panel 108 in graphs 400, 500. In some embodiments, the minimum wavelength 406 is greater than about 430 nm, and the maximum wavelength 407 is less than about 480 nm. In some other embodiments, the minimum wavelength 406 may be greater than about 400 nm, and the maximum wavelength 407 may be less than about 500 nm.

[0038] refer to Figure 3 , Figure 4 and Figure 5 For approximately normal incident light 202 and a first polarization state, the reflective polarizer 102 includes a transmission band 404 with a cutoff wavelength 408. Specifically, for approximately normal incident light 202 and a first polarization state, the reflective polarizer 102 includes a transmission spectrum 403, which includes a transmission band 404 with a cutoff wavelength 408. The minimum wavelength 406 is smaller than the cutoff wavelength 408 of the transmission band 404 of the reflective polarizer 102. In other words, the reflective polarizer 102 includes a transmission band 404 with a cutoff wavelength 408, which is greater than the minimum wavelength 406 of the blue emission spectrum 402 of the display panel 108. Figure 5 In the exemplary embodiment, the maximum wavelength 407 is also less than the cutoff wavelength 408 of the transmission band 404 of the reflective polarizer 102. In other words, the cutoff wavelength 408 of the transmission band 404 of the reflective polarizer 102 is greater than the maximum wavelength 407 of the blue FWHM 410 of the display panel 108.

[0039] The cutoff wavelength 408 may correspond to the wavelength at which the transmittance is at its peak or half (50%) of the maximum transmittance. The cutoff wavelength 408 of the transmission band 404 of the reflective polarizer 102 is greater than about 500 nm. In some other embodiments, the cutoff wavelength 408 of the transmission band 404 of the reflective polarizer 102 is greater than about 525 nm. In some other embodiments, the cutoff wavelength 408 of the transmission band 404 of the reflective polarizer 102 is less than about 550 nm.

[0040] For a first polarization state, the reflective polarizer 102 reflects at least about 60% of the incident light 202 with a first wavelength W1 less than the cutoff wavelength 408, and transmits at least about 50% of the incident light 202 with a second wavelength W2 greater than the cutoff wavelength 408. In some other embodiments, for the first polarization state, the reflective polarizer 102 reflects at least about 70%, at least about 80%, at least about 90%, at least about 95%, or at least about 99% of the incident light 202 with a first wavelength W1 less than the cutoff wavelength 408. In some embodiments, for the first polarization state, the reflective polarizer 102 transmits at least about 55%, at least about 60%, at least about 70%, at least about 80%, or at least about 90% of the incident light 202 with a second wavelength W2 greater than the cutoff wavelength 408. The first wavelength W1 is located in the blue wavelength range. Therefore, for the first polarization state, the reflective polarizer 102 reflects at least a portion of the wavelengths in the blue wavelength range. In some embodiments, the first wavelength W1 is located in the range of about 400 nm to about 500 nm. In an illustrated embodiment, the first wavelength W1 is less than the minimum wavelength 406. In some other embodiments, the first wavelength W1 may be between the minimum wavelength 406 and the maximum wavelength 407. The second wavelength W2 may be located in the red wavelength range. In some embodiments, the second wavelength W2 is located in the range of about 600 nm to about 700 nm. In some embodiments, for a first polarization state, the reflective polarizer 102 may reflect at least about 60% of the incident light 202 of one or more wavelengths in the blue wavelength range and may transmit at least about 50% of the incident light 202 of each wavelength in subsequent wavelength ranges such as the green wavelength range and the red wavelength range.

[0041] For approximately normal incident light 202 and a second polarization state, the reflecting polarizer 102 transmits at least 70% of the incident light 202 at least of the first wavelength and at least of each of the second wavelengths W1 and W2. In some embodiments, for the second polarization state, the reflecting polarizer 102 transmits at least about 80%, at least about 85%, or at least about 90% of the incident light 202 at least of each of the first wavelength and the second wavelengths W1 and W2. Figure 5As shown, for generally normal incident light 202 and a second polarization state, the reflective polarizer 102 includes a transmission spectrum 420. In some embodiments, for the second polarization state, the reflective polarizer 102 can transmit at least 70% of the incident light 202 for each wavelength in the visible wavelength range of about 400 nm to about 700 nm. In some other embodiments, for the second polarization state, the reflective polarizer 102 can transmit at least 80%, at least 85%, or at least 90% of the incident light 202 for each wavelength in the visible wavelength range.

[0042] In some embodiments, the first polarization state is an S-polarization state and the second polarization state is a P-polarization state. In some other embodiments, the first polarization state is a P-polarization state and the second polarization state is an S-polarization state. The first polarization state is approximately along the y-axis, and the second polarization state is approximately along the x-axis.

[0043] refer to Figure 3 , Figure 4 and Figure 6 For the approximately normal incident light 202 and the first polarization state, the reflecting polarizer 102 includes any one of transmission bands 502, 506, and 510. Transmission bands 502, 506, and 510 correspond to the transmission spectra 522, 524, and 526 of the approximately normal incident light 202 and the first polarization state, respectively. The transmission spectrum 420 of the approximately normal incident light 202 and the second polarization state... Figure 5 (As shown) can correspond to each of the transmission spectra 522, 524, and 526 of the first polarization state.

[0044] Transmission band 502 has a cutoff wavelength 504. Transmission band 506 has a cutoff wavelength 508. Transmission band 510 has a cutoff wavelength 512. The minimum wavelength 406 is less than each of the cutoff wavelengths 504, 508, and 512 of the corresponding transmission bands 502, 506, and 510. In other words, the cutoff wavelengths 504, 508, and 512 of the corresponding transmission bands 502, 506, and 510 are greater than the minimum wavelength 406 of the blue FWHM410 of the display panel 108. Figure 6In the exemplary embodiments, the maximum wavelength 407 is less than each of the cutoff wavelengths 508 and 512 of the corresponding transmission bands 506 and 510. In other words, the cutoff wavelengths 508 and 512 of the transmission bands 506 and 510 are greater than the maximum wavelength 407 of the blue FWHM 410 of the display panel 108. However, the cutoff wavelength 504 of the transmission band 502 is less than the maximum wavelength 407 of the blue FWHM 410 of the display panel 108. Therefore, the cutoff wavelength 504 of the transmission band 502 is greater than the minimum wavelength 406 and less than the maximum wavelength 407. In some embodiments, the cutoff wavelength 504 of the transmission band 502 of the reflective polarizer 102 is about 450 nm. In some embodiments, the cutoff wavelength 504 of the transmission band 502 of the reflective polarizer 102 is greater than about 425 nm and less than about 475 nm. In some other embodiments, the cutoff wavelength 504 of the transmission band 502 of the reflective polarizer 102 is greater than about 470 nm. In some embodiments, the cutoff wavelength 508 of the transmission band 506 of the reflective polarizer 102 is about 525 nm. In some embodiments, the cutoff wavelength 508 of the transmission band 506 of the reflective polarizer 102 is greater than about 500 nm and less than about 550 nm. In some embodiments, the cutoff wavelength 512 of the transmission band 510 of the reflective polarizer 102 is about 475 nm. In some other embodiments, the cutoff wavelength 512 of the transmission band 510 of the reflective polarizer 102 is greater than about 450 nm and less than about 500 nm.

[0045] For a first polarization state, the reflective polarizer 102 reflects at least about 60% of the incident light 202 with a first wavelength W1 less than each of the cutoff wavelengths 504, 508, and 512, and transmits at least about 50% of the incident light 202 with a second wavelength W2 greater than each of the cutoff wavelengths 504, 508, and 512. In some other embodiments, for the first polarization state, the reflective polarizer 102 reflects at least about 70%, at least about 80%, at least about 90%, at least about 95%, or at least about 99% of the incident light 202 with a first wavelength W1 less than each of the cutoff wavelengths 504, 508, and 512. In some embodiments, for the first polarization state, the reflective polarizer 102 transmits at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90% of the incident light 202 with a second wavelength W2 greater than each of the cutoff wavelengths 504, 508, and 512. The first wavelength W1 is located in the blue wavelength range. Therefore, for the first polarization state, the reflective polarizer 102 reflects a portion of the wavelengths within the blue wavelength range.

[0046] For the generally normal incident light 202 and the second polarization state, the reflecting polarizer 102 transmits at least 70% of the incident light 202 of at least the first wavelength and at least each of the second wavelengths W1 and W2. In some other embodiments, for the second polarization state, the reflecting polarizer 102 transmits at least about 80%, at least about 85%, or at least about 90% of the incident light 202 of at least the first wavelength and at least each of the second wavelengths W1 and W2.

[0047] Figure 7 A half-wave delayer 104 is shown. Figure 8 This is a graph 600 showing the delay versus wavelength of a half-wave delayer 104 according to one embodiment of the present disclosure. Graph 600 includes delay curves 602 depicting the delay of the half-wave delayer 104 at various wavelengths.

[0048] refer to Figure 7 and Figure 8 For the approximately normal incident light 204, the half-wave delayer 104 has a first delay R1 of less than about 250 nm at a first wavelength W1 and a second delay R2 at a second wavelength W2. In some embodiments, the second delay R2 is greater than about 200 nm. In some embodiments, the second delay R2 is less than the first delay R1. In other words, the second delay R2 is less than about 250 nm.

[0049] In addition, such as Figure 8 As shown, the half-wave delay 104 has a minimum blue delay Rb at the corresponding blue wavelength Wb, a minimum green delay Rg at the corresponding green wavelength Wg, and a minimum red delay Rr at the corresponding red wavelength Wr. The minimum blue delay Rb, minimum green delay Rg, and minimum red delay Rr are all within 20% of each other. In some other embodiments, the minimum blue delay Rb, minimum green delay Rg, and minimum red delay Rr are all within 15% of each other. Figure 8 As shown, the minimum blue delay Rb, minimum green delay Rg, and minimum red delay Rr are all less than 250 nm. In some embodiments, the second delay R2 is less than the minimum blue delay Rb and minimum green delay Rg. In some embodiments, the second delay R2 is greater than the minimum red delay Rr. In some embodiments, the first delay R1 is greater than the minimum blue delay Rb, minimum green delay Rg, and minimum red delay Rr. It is clear from graph 600 that the delay of the half-wave delayer 104 does not change significantly with the wavelength of the incident light 204. Therefore, the half-wave delayer 104 is a non-achromatic half-wave delayer.

[0050] refer to Figure 8The half-wave curve 604 represents the variation of the delay of an ideal half-wave retarder with wavelength. In other words, the delay at each point on the half-wave curve 604 is half the corresponding wavelength (i.e., delay = wavelength / 2). The half-wave curve 604 intersects the delay curve 602 of the half-wave retarder 104 only at one point C. Therefore, the half-wave retarder 104 has an ideal half-wave delay only at a wavelength Wc corresponding to point C. The wavelength Wc can be approximately 450 nm. Otherwise, the delay curve 602 deviates from the half-wave curve 604 at all other wavelengths. Furthermore, the delay curve 602 generally decreases with increasing wavelength, while the half-wave curve 604 increases with increasing wavelength. The half-wave curve 604 has a first half-wave delay H1 at a first wavelength W1 (i.e., H1 = W1 / 2). Furthermore, the half-wave curve 604 has a second half-wave delay H2 at a second wavelength W2 (i.e., H2 = W2 / 2).

[0051] Figure 9 This is a graph 700 showing the delay deviation of the half-wave delayer 104 against wavelength. Graph 700 includes a delay deviation curve 702 depicting the delay deviation of the half-wave delayer 104 at various wavelengths.

[0052] refer to Figure 8 and Figure 9 Delay deviation curve 702 shows the deviation between the delay curve 602 and the half-wave curve 604 of the half-wave delay 104. The deviation D1 between the first delay R1 and the first half-wave delay H1 corresponding to the first wavelength W1 is smaller than the deviation D2 between the second delay R2 and the second half-wave delay H2 corresponding to the second wavelength W2. The first half-wave delay H1 corresponding to the first wavelength W1 can be considered as the ideal delay of the half-wave delay 104 at the first wavelength W1. Similarly, the second half-wave delay H2 corresponding to the second wavelength W2 can be considered as the ideal delay of the half-wave delay 104 at the second wavelength W2. It can be clearly seen from curve 700 that for the wavelength range of approximately 400 nm to approximately 500 nm, the deviation of the delay of the half-wave delay 104 from the half-wave curve 604 is lower than the deviation for wavelengths greater than 500 nm (e.g., in the red wavelength range). The wavelength range of approximately 400 nm to approximately 500 nm can correspond to the blue wavelength range. Therefore, the half-wave delay 104 can be optimized for the blue wavelength range. In other words, compared to other wavelengths, the half-wave delayer 104 performs closer to an ideal half-wave delayer in the wavelength range of about 400 nm to about 500 nm.

[0053] As mentioned above Figure 3 , Figure 5 and Figure 6Specifically, for the approximately normal incident light 202 and the first polarization state, the reflecting polarizer 102 reflects at least about 60% of the incident light 202 at least a first wavelength W1 less than each of the cutoff wavelengths 408, 504, 508, 512 of the corresponding transmission bands 404, 502, 506, 510, and transmits at least about 50% of the incident light 202 at least a second wavelength W2 greater than each of the cutoff wavelengths 408, 504, 508, 512 of the corresponding transmission bands 404, 502, 506, 510. For the approximately normal incident light 204, the half-wave delayer 104 has a first delay R1 of less than about 250 nm at the first wavelength W1 and a second delay R2 at the second wavelength W2. The second delay R2 is less than the first delay R1. Furthermore, the deviation D1 between the first delay R1 and the first half-wave delay H1 corresponding to the first wavelength W1 is less than the deviation D2 between the second delay R2 and the second half-wave delay H2 corresponding to the second wavelength W2.

[0054] Such optimization of the half-wave delayer 104 in wavelengths smaller than the cutoff wavelengths 408, 504, 508, 512 of the corresponding transmission bands 404, 502, 506, 510 can reduce Figure 1 and Figure 2 Color shift during operation of the optical stack 100 is reduced. Specifically, a half-wave delayer 104 optimized in the blue wavelength range is used, wherein the reflective polarizer 102 has cutoff wavelengths 408, 504, 508, 512 of corresponding transmission bands 404, 502, 506, 510 in or near the blue wavelength range, which reduces color shift. Therefore, the combination of reflective polarizer 102 and half-wave delayer 104 exhibits improved performance in reducing color shift. Furthermore, half-wave delayers optimized in this manner are easier and cheaper to manufacture than conventional achromatic half-wave delayers with multiple layers. It can be noted that any of the possible transmission bands 404, 502, 506, 510 of reflective polarizer 102 can be selected based on desired application properties, such as the delay characteristics of half-wave delayer 104, the emission characteristics of display panel 108, etc.

[0055] Figure 10 An absorption polarizer 106 is shown. Figure 11 This is a graph 800 showing the percentage of transmission of the absorbing polarizer 106 against wavelength. Graph 800 includes a transmission curve 802, which depicts the percentage of transmission of the absorbing polarizer 106 at various wavelengths. (Reference) Figure 10 and Figure 11For approximately normal incident light 206 and a first polarization state, the absorbing polarizer 106 has a first transmittance T1 at a first wavelength W1 and a larger second transmittance T2 at a second wavelength W2. In some embodiments, for the first polarization state, the first transmittance T1 of the absorbing polarizer 106 is at least about 60%. In some embodiments, for the first polarization state, the first transmittance T1 of the absorbing polarizer 106 may be at least about 70%. In some embodiments, for the first polarization state, the second transmittance T2 of the absorbing polarizer 106 is at least about 65%. In some other embodiments, for the first polarization state, the second transmittance T2 of the absorbing polarizer 106 may be at least about 75%, at least about 80%, at least about 85%, or at least about 90%. In some embodiments, for approximately normal incident light 206 and the second polarization state, the absorbing polarizer 106 may absorb at least 70% of the incident light 206 in the visible wavelength range.

[0056] Therefore, compared to other wavelengths, the absorbing polarizer 106 can transmit less light in the blue wavelength range. When the absorbing polarizer 106 is... Figure 1 and Figure 2 The combination of the reflective polarizer 102 and the half-wave delayer 104 in the optical stack 100 can further reduce color shift.

[0057] Unless otherwise stated, all figures used in the specification and claims to indicate feature dimensions, quantities, and physical properties should be understood to be modified by the term "about". Therefore, unless stated to the contrary, the numerical parameters listed in the foregoing specification and appended claims are approximations and can vary according to the desired properties sought by those skilled in the art using the teachings disclosed herein.

[0058] While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that various alternative and / or equivalent embodiments may be used in place of the illustrated and described embodiments without departing from the scope of this disclosure. This application is intended to cover any modifications or variations of the specific embodiments discussed herein. Therefore, this disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. An optical stack, comprising: A reflective polarizer, the reflective polarizer comprising a transmission axis and a reflection axis that are orthogonal to each other; Absorption polarizer; and A half-wave delayer, wherein the half-wave delayer is a non-achromatic half-wave delayer and is disposed between the reflecting polarizer and the absorbing polarizer, such that for approximately normal incident light: For a first polarization state, the reflective polarizer includes a transmission band having a cutoff wavelength, wherein the reflective polarizer reflects at least 60% of incident light of at least a first wavelength less than the cutoff wavelength and transmits at least 50% of incident light of at least a second wavelength greater than the cutoff wavelength; For an orthogonal second polarization state, the reflective polarizer transmits at least 70% of the incident light of each of the at least first wavelength and the at least second wavelength; The half-wave delay has a first delay of less than 250 nanometers (nm) at the first wavelength and a second delay at the second wavelength, wherein the deviation of the first delay from the first half-wave delay corresponding to the first wavelength is less than the deviation of the second delay from the second half-wave delay corresponding to the second wavelength; and For the first polarization state, the absorbing polarizer has a first transmittance at the first wavelength and a larger second transmittance at the second wavelength.

2. The optical stack of claim 1 further includes a display panel disposed below the reflective polarizer opposite to the half-wave delayer, the display panel being configured to emit display light comprising a blue emission spectrum having a full width at half maximum (FWHM) of blue light defined between a minimum wavelength and a maximum wavelength, wherein the minimum wavelength is less than the cutoff wavelength of the transmission band of the reflective polarizer.

3. The optical stack according to claim 2, wherein the cutoff wavelength of the transmission band of the reflective polarizer is less than the maximum wavelength of the blue FWHM.

4. The optical stack according to claim 2, wherein the cutoff wavelength of the transmission band of the reflective polarizer is greater than the maximum wavelength of the blue FWHM.

5. The optical stack according to claim 1, wherein the cutoff wavelength of the transmission band of the reflective polarizer is less than 550 nm and greater than 450 nm.

6. The optical stack of claim 1, wherein the reflective polarizer comprises a plurality of alternating first polymer layers and second polymer layers totaling at least 40, each of the first polymer layers and the second polymer layers having an average thickness of less than 350 nm.

7. The optical stack of claim 1, wherein the second retardation is greater than 200 nm, and wherein the first transmittance of the absorbing polarizer is at least 60%.

8. An optical stack, comprising: The display panel is configured to emit display light including a blue emission spectrum having a full width at half maximum (FWHM) of blue light defined between a minimum wavelength and a maximum wavelength. A reflective polarizer configured to receive and reflect a portion of the display light from the display panel as reflected polarized light, the reflective polarizer including a transmission axis and a reflection axis that are orthogonal to each other; Absorption polarizer; A half-wave delayer, wherein the half-wave delayer is a non-achromatic half-wave delayer and is disposed between the reflective polarizer and the absorptive polarizer, such that for approximately normal incident light; For a first polarization state, the reflective polarizer includes a transmission band having a cutoff wavelength greater than the minimum wavelength of the blue emission spectrum of the display panel, wherein the reflective polarizer reflects at least 60% of incident light of at least a first wavelength less than the cutoff wavelength and transmits at least 50% of incident light of at least a second wavelength greater than the cutoff wavelength; For an orthogonal second polarization state, the reflective polarizer transmits at least 70% of the incident light of each of the at least first wavelength and the at least second wavelength; The half-wave delay has a first delay of less than 250 nm at the first wavelength and a second delay at the second wavelength, wherein the deviation of the first delay from the first half-wave delay corresponding to the first wavelength is less than the deviation of the second delay from the second half-wave delay corresponding to the second wavelength; and For the first polarization state, the absorbing polarizer has a first transmittance at the first wavelength and a larger second transmittance at the second wavelength.

9. The optical stack of claim 8, wherein the minimum wavelength is greater than 430 nm and the maximum wavelength is less than 480 nm, and wherein the cutoff wavelength of the transmission band of the reflective polarizer is less than the maximum wavelength of the blue FWHM.

10. The optical stack of claim 8, wherein the cutoff wavelength of the transmission band of the reflective polarizer is greater than the maximum wavelength of the blue FWHM.

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