Patent ID: 12210241

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.

Backlight technology for liquid crystal displays (LCDs) is progressively migrating toward high dynamic range (HDR) displays using mini and/or micro light-emitting diodes (LEDs) in an effort to match the performance of organic LED (OLED) displays in regard to color and contract performance. In addition, the industry is beginning to replace traditional white backlights with color-by-blue backlights, in which only LEDs which emit blue wavelengths of light are used in the backlight unit, and “down-conversion” sheets with narrow emitting phosphors and/or quantum dots are used to convert the blue-only light into white light. There are several advantages to a blue-only backlight, including simplified manufacturing, simplified architectures, lower system costs, etc. Finally, LCD panel manufacturers have demonstrated replacing the traditional, color-absorbing filters of an LCD with down-converting filters (i.e., deposition of the down-converting material directly into the panel, rather than a standalone sheet.) Moving the down-converting material into the LCD panel requires the development of an in-cell polarizer. This progression in LCD technology provides a number of opportunities for non-traditional solutions in LCD backlights, including optical film and backlight architectures optimized specifically for blue-only backlight units, as described herein.

According to some aspects of the present description, an optical stack for reflecting and transmitting light in a predetermined wavelength range is provided. In some embodiments, the predetermined wavelength range may extend at least from about 400 nm to about 600 nm, and may define a first wavelength range within the predetermined wavelength range, and a remaining wavelength range within the predetermined wavelength range. In some embodiments, the first wavelength range may extend from about 400 nm to about 480 nm, representing primarily blue wavelengths of light.

The optical stack may include stacked first and second optical films. In some embodiments, the first optical film may be a reflective polarizer. In some embodiments, the reflective polarizer may be optimized for wavelengths of light corresponding to the first wavelength range (e.g., human-visible blue light or a subset thereof). In some embodiments, for substantially normally incident light and for each wavelength in at least the first wavelength range, the first optical film may reflect at least 80% of light having a first polarization state, Px, and may transmit at least 80% of light having an orthogonal second polarization state, Py. In some embodiments, Pxmay represent light of a linear s-polarization type, and Pymay represent light of a linear p-polarization type. In other embodiments, Px may represent light of a linear p-polarization type, and Py may represent light of a linear s-polarization type. However, Pxand Pymay be any appropriate, different, orthogonal polarization types.

In some embodiments, the second optical film may be a collimating multilayer optical film. In some embodiments, the collimating multilayer optical film may be optimized for wavelengths of light corresponding to the first wavelength range (e.g., human-visible blue light or a subset thereof), and may substantially reflect wavelengths of light corresponding to the remaining wavelength range (e.g., human-visible red and green light, or subsets thereof). In some embodiments, for each of the first and second polarization states, and for each wavelength in the first wavelength range, the second optical film may have a maximum optical transmittance Tmaxfor light incident at a first incident angle (θ1), and an optical transmittance Tmax/2 for light incident at a second incident angle (θ2), where the second incident angle is greater than the first incident angle by less than about 50 degrees. For each wavelength in the remaining wavelength range, the second optical film may reflect at least 80% of light.

According to some aspects of the present description, a backlight for providing illumination to a display panel is provided. In some embodiments, the backlight may be configured to emit light substantially in a single primary color wavelength range of a visible spectrum (e.g., wavelengths corresponding to human-visible blue light). The emitted light may be substantially collimated and have a half angle divergence (a) of less than about 50 degrees. In some embodiments, the single primary color wavelength range may be a blue wavelength range. In some embodiments, the light emitted by the backlight may be substantially linearly polarized. For example, the light emitted by the backlight may be of a linear polarization type (e.g., s-pol light, or p-pol light) which may be selectively blocked or transmitted by an LCD module to create an image on a display. In some embodiments, the light emitted by the backlight may have a first emitted light portion having a first polarization state, Px, and a first intensity, and a second emitted light portion having an orthogonal second polarization state, Py, and a second intensity, such that a ratio of the second intensity to the first intensity is greater than about 10.

In some embodiments, the backlight ofFIG.1may be configured to emit substantially linearly polarized blue light, such that light emitted by the backlight in a blue wavelength range (e.g., extending from about 425 nm to about 475 nm) and having a first polarization state, Px, has a maximum intensity T1 along a normal direction substantially normal to the backlight and a half angle divergence (α1) of less than about 45 degrees, and such that light emitted by the backlight in the blue wavelength range having an orthogonal second polarization state, Py, and propagating within a first angular range making angles from about zero to about 70 degrees with respect to the normal direction, has a maximum optical transmittance T2, and for light for each of the first and second polarization states and propagating within the first angular range, the light has a maximum optical transmittance T3, for a green wavelength range extending from about 525 nm to about 575 nm, and T4, for a red wavelength range extending from about 625 nm to about 675 nm, wherein each of T1/T2, T1/T3 and T1/T4 is greater than about 5.FIGS.5-7provide additional information related to optical transmittance values of an optical stack, and will be discussed in more detail elsewhere herein.

Turning now to the figures,FIG.1provides a cross-sectional view of a display and backlight assembly, in accordance with an embodiment described herein. A display400includes a display panel300disposed on backlight200, and configured to received light emitted by backlight200. Backlight200provides illumination to display panel300and includes an optical stack100, an optical reflector70, and at least one light source90. The optical reflector70is disposed adjacent optical stack100and an optical cavity80is defined between optical reflector70and optical stack100. The optical reflector70is configured to reflect at least 80% of light for each of the first and second polarization states and for each wavelength in a predetermined wavelength range. In some embodiments, the predetermined wavelength range may extend at least from about 400 nm to about 600 nm. In some embodiments, the predetermined wavelength range may define a first wavelength range within the predetermined wavelength range, and a remaining wavelength range within the predetermined wavelength range. In some embodiments, the first wavelength range may extend from about 400 nm to about 480 nm, representing primarily blue wavelengths of light. In some embodiments, optical reflector70may be optimized for the first wavelength range (e.g., may substantially reflect wavelengths in the first wavelength range, and may substantially transmit or absorb wavelengths in the remaining wavelength range.) In some embodiments, light source90may be configured to emit light in the first wavelength range into optical cavity80.

In some embodiments, optical stack100is configured for reflecting and transmitting light in a predetermined wavelength range, the predetermined wavelength range defining a first wavelength range and a remaining wavelength range. In some embodiments, optical stack100comprises a first optical film40and a second optical film50. In some embodiments, first optical film40may be a reflective polarizer. In some embodiments, second optical film50may be a collimating multilayer optical film. In some embodiments, the second optical film50may be disposed between the first optical film40and the optical reflector70.

In some embodiments, the first optical film40may be a hybrid reflective/absorbing polarizer. This may allow the elimination of an absorbing polarizer in the LCD panel in some embodiments, or increase the backlight polarization contrast ratio.

In some embodiments, optical stack100may include a bonding layer60disposed between, and bonding to each other, the first optical film40and the second optical film50. In some embodiments, optical stack100may include an optical diffuser110stacked with the first optical film40and the second optical film50. In some embodiments, the optical diffuser110may be disposed between first optical film40and the second optical film50. In some embodiments, the bonding layer60disposed between first optical film40and the second optical film50may also be the optical diffuser110.

In some embodiments, the optical diffuser110may be configured to diffused light more in the first wavelength range and less in the remaining wavelength range. In some embodiments, optical diffuser110may be a low-haze, low-clarity diffuser, such that light120exiting from optical stack100may still be at least partially collimated. For example, emitted light120may have a half angle divergence, a, of less than about 50 degrees from a line perpendicular to the surface of diffuser110. In some embodiments, a bonding layer may be disposed between the optical stack100and the display panel300. In some embodiments, the bonding layer may be an optically clear adhesive.

In some embodiments, backlight200may include at least one light source90which emits light in the first wavelength range. In some embodiments, the backlight200may not include any light source90which emits light in the remaining wavelength range into optical cavity80. In some embodiments, at least one light source90amay be disposed within an interior81of optical cavity80between the optical stack100and the optical reflector70. In some embodiments, as least one light source90b/90c may be disposed outside, and proximate a lateral side82/83of optical cavity80.

In some embodiments, the optical stack100may have a thickness, H1, and the optical cavity may have a height, H2, defined as a distance between optical stack100and optical reflector70, such that the ratio H2/(H1+H2) is greater than about 0.65.

In some embodiments, display400includes a display panel300disposed on backlight200and configured to receive light120emitted by backlight200. In some embodiments, display panel300may include an in-cell polarizer layer135. In some embodiments, a light-converting layer137may be disposed adjacent to in-cell polarizer layer135. In some embodiments, the light-converting layer137may convert at least a portion of light having a first wavelength and received from the backlight to light having a different second wavelength. For example, in some embodiments, the light-converting layer137may convert at least about 80%, or at least about 85%, or at least about 90%, or at least about 95% of light having a first wavelength and received from the backlight to light having a different second wavelength. In some embodiments, light-converting layer137may convert a first portion of the received light (e.g., light of a blue wavelength) to light having a second wavelength (e.g., light of a red wavelength) different from the first wavelength, and converting a second portion of the received light (e.g., light of a blue wavelength) to light having a third wavelength (e.g., light of a green wavelength) different from the first and second wavelengths.

For example, in some embodiments, light-converting layer137may be patterned into smaller sections (i.e., light-converting elements)137R,137G, and137B, representing individual red, green, and blue pixels in display panel300, respectively. In some embodiments, incoming light120entering display panel300will include wavelengths of light substantially in the first wavelength range (e.g., a blue-wavelength range). When a blue wavelength enters an element137R, the blue wavelength is absorbed by the element137R and emitted as (i.e., converted to) a red wavelength. When a blue wavelength enters an element137G, the blue wavelength is absorbed by the element137G and emitted as (i.e., converted to) a green wavelength. In some embodiments, light-converting element137R may contain or include a light-converting phosphor. In some embodiments, the light-converting phosphor in137R may be a red phosphor. In some embodiments, light-converting elements137R may contain or include light-converting quantum dots. In some embodiments, the light-converting quantum dots in137R may include red quantum dots for converting blue light to red light. In some embodiments, light-converting element137G may contain or include a light-converting phosphor. In some embodiments, the light-converting phosphor in137G may be a green phosphor. In some embodiments, light-converting elements137G may contain or include light-converting quantum dots. In some embodiments, the light-converting quantum dots in137G may include green quantum dots for converting blue light to green light. In some embodiments, one or more of the light-converting elements137may include a mixture of quantum dots for converting blue light to white light.

In some embodiments, light-converting elements137B may be clear (e.g., may not contain light-converting phosphors or quantum dots) as incoming light120may already substantially consist of wavelengths of light in the first wavelength range (i.e., may already be blue wavelengths). In some embodiments, light-converting elements137B may be combined with a localized diffuser layer, so that blue light emitted from elements137B is as diffuse as light emitted from elements137R and137G. As light passing through elements137R and137G is absorbed and re-emitted in a different wavelength, the light emitted by elements137R and137G already exhibits a level of diffusion (i.e., the light absorbed and re-emitted by the phosphors and/or quantum dots is broadcast in a diffuse pattern).

FIG.2is a diagram illustrating various wavelength ranges applicable to the display400ofFIG.1, in accordance with an embodiment of the present description. In some embodiments, the optical stack100(FIG.1) is configured to reflect and/or transmit light in predetermined wavelength range10. In some embodiments, predetermined wavelength range10may extend from about 400 nm to about 600 nm. In some embodiments, predetermined wavelength range10may define a first wavelength range20, and a remaining wavelength range30. In some embodiments, as shown in the top portion ofFIG.2, remaining wavelength range30may be discontinuous, and may include the wavelengths of light from predetermined wavelength range10which are outside of first wavelength range20.

In some embodiments, and as shown in the bottom portions ofFIG.2, a first wavelength range20′ may include a blue-wavelength range, and the remaining wavelength range30′ may include a green-wavelength range30aand a red-wavelength range30b. Various elements of display400(FIG.1) may be optimized for first wavelength range20′ (e.g., may be optimized to function best with blue wavelengths of light, such as the blue wavelengths emitted by light sources of the embodiment shown inFIG.1.)

FIG.3is a diagram illustrating optical transmittance patterns for light incident on the second optical film50ofFIG.1, in accordance with an embodiment of the present description. In some embodiments, the second optical film50may be a collimating multilayer optical film. In some embodiments, for each of the first and second polarization states, and for each wavelength in the first wavelength range, the second optical film50has a maximum optical transmittance Tmaxfor light120aincident at a first incident angle (θ1), and an optical transmittance Tmax/2 for light120bincident at a second incident angle (θ2) greater than the first incident angle by less than about 50 degrees. In some embodiments, θ1 may be about zero degrees, θ2 may be less than about 45 degrees, and T max may be greater than about 70%.FIG.8shows a plot of optical transmission values versus angle of incidence for an example embodiment of the second optical film50. Additional discussion ofFIG.8is presented elsewhere within this specification.

In some embodiments, the first and second optical films may each be constructed from a plurality of layers of polymeric materials.FIGS.4A and4Billustrate embodiments of the first and second optical films, respectively.FIG.4Ashows an embodiment of the first optical film40, including a plurality of alternating first polymeric layers41and second polymeric layers42. In some embodiments, the combined alternating first41and second42polymeric layers may number between 100 and 700. In some embodiments, each first41and second42polymeric layer may have an average thickness less than about 500 nm, or less than about 400 nm, or less than about 300 nm, or less than about 200 nm, or less than about 100 nm.

In some embodiments, for each pair of adjacent first41and second42polymeric layers: in planes of the first41and second42polymeric layers, the first41and second42polymeric layers may have respective indices of refraction, n1x and n2x, along the first polarization state, my and n2y along the second polarization state, and n1z and n2z along a z-axis orthogonal to the first and second polarization states, such that for at least one wavelength in the predetermined wavelength range: n1x is greater than each of my and n1z by at least 0.2, a difference between my and n1z is less than about 0.05, a maximum difference between n2x, n2y and n2z is less than about 0.01, and a difference between n1x and n2x is greater than about 0.2.

In some embodiments, the first optical film40may include a top skin layer43and a bottom skin layer44disposed on opposite top and bottom sides of the plurality of alternating first41and second42polymeric layers, respectively. In some embodiments, each skin layer43/44may have a thickness greater than about 5 microns. In some embodiments, the plurality of alternating first41and second42polymeric layers may be divided into a first plurality45of alternating first41and second42polymeric layers and a second plurality46of alternating first41and second42polymeric layers, where the first plurality45and the second plurality46are separated from each other by a spacer layer47having a thickness greater than about 1 micron.

FIG.4Bshows an embodiment of the second optical film50, including a plurality of alternating first polymeric layers51and second polymeric layers52. In some embodiments, the combined alternating first51and second52polymeric layers may number between 100 and 700. In some embodiments, each first51and second52polymeric layer may have an average thickness less than about 500 nm.

In some embodiments, for each pair of adjacent first51and second52polymeric layers: in planes of the first51and second52polymeric layers, the first51and second52polymeric layers may have respective indices of refraction, n1x and n2x, along the first polarization state, n1y and n2y along the second polarization state, and n1z and n2z along a z-axis orthogonal to the first and second polarization states, such that for at least one wavelength in the predetermined wavelength range: each of n1x and my is greater than n1z by at least 0.1, a difference between n1x and n1x is less than about 0.05, a maximum difference between n2x, n2y and n2z is less than about 0.01, and a difference between n1x and n2x is greater than about 0.2.

In some embodiments, the second optical film50may include a top skin layer53and a bottom skin layer54disposed on opposite top and bottom sides of the plurality of alternating first51and second52polymeric layers. In some embodiments, each skin layer53/54may have a thickness greater than about 5 microns. In some embodiments, the plurality of alternating first51and second52polymeric layers may be divided into a first plurality55of alternating first51and second52polymeric layers and a second plurality56of alternating first51and second52polymeric layers, where the first plurality55and the second plurality56are separated from each other by a spacer layer57having a thickness greater than about 1 micron.

FIGS.5,6, and7show the optical transmission percentage values for blue, green, and red wavelengths of light, respectively, at various angles of incidence of an embodiment of the optical stack of the present description.FIG.5illustrates the transmission of an example optical stack, such as the optical stack ofFIG.1, for blue wavelengths of light, and specifically for wavelengths extending from about 425 nm to about 475 nm.FIG.6illustrates the transmission of an example optical stack for green wavelengths of light, and specifically for wavelengths extending from about 525 nm to about 575 nm.FIG.8illustrates the transmission of an example optical stack for red wavelengths of light, and specifically for wavelengths extending from about 625 nm to about 675 nm.

Returning toFIG.5, it is shown that, in some embodiments of an optical stack, for each wavelength in a blue wavelength range extending from about 425 nm to about 475 nm, the optical stack may have a maximum optical transmittance, T1, for substantially zero incident angle, and an optical transmittance, T1/2, for light incident at less than about 45 degrees for light of the second polarization state, Py. For light of the first polarization state, Px, in some embodiments, the optical stack has a maximum optical transmittance T2 for incident angles from about zero to about 70 degrees, such that T1/T2 is greater than about 5. In some embodiments, the ratio of T1/T2 is greater than about 10.

Turning toFIGS.6and7, it is shown that, in some embodiments of an optical stack, for each wavelength in each of a green wavelength range extending from about 525 nm to about 575 nm (FIG.6) and a red wavelength range extending from about 625 nm to about 675 nm (FIG.7) and for each of the first and second polarization states, Pxand Py, the optical stack has a maximum optical transmittance (T3 for green wavelengths,FIG.6, T4 for red wavelengths,FIG.7) less than a value, TT, for incident angles from about zero degree to about 70 degrees, such that the ratio of maximum optical transmittance, T1, to TT may be greater than about 5. In some embodiments, the ratio of T1/TT may be greater than about 10.

As shown inFIG.1, optical stack100may comprise a first optical film40and a second optical film50. In some embodiments, the second optical film50may be a collimating multilayer optical film. Returning toFIG.5, in some embodiments, for each wavelength in a wavelength range extending from about 425 nm to about 475 nm (i.e., blue wavelength range), the second optical film50may have an optical transmittance greater than about 80% for substantially zero incident angle, and an optical transmittance less than about 50% for light incident at less than about 45 degrees. In some embodiments, for each wavelength in each of a green wavelength range (FIG.6), extending from about 525 nm to about 575 nm, and a red wavelength range (FIG.7), extending from about 625 nm to about 675 nm, the second optical film may reflect at least 90% of light for incident angles from about zero degree to about 70 degrees.

FIG.8shows a plot of optical transmission values versus angle of incidence for an example embodiment of the second optical film50. In some embodiments, for each of the first and second polarization states, Px and Py, and for each wavelength in the first wavelength range (e.g., blue wavelength range), the second optical film50has a maximum optical transmittance Tmax, for light at a first incident angle (e.g., about zero degrees) and an optical transmittance Tmax/2 at a second incident angle (e.g., about 45 degrees) greater than the first incident angle by less than about 50 degrees.

Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.9 and 1.1, and that the value could be 1.

Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially equal” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially equal” will mean about equal where about is as described above. If the use of “substantially parallel” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially parallel” will mean within 30 degrees of parallel. Directions or surfaces described as substantially parallel to one another may, in some embodiments, be within 20 degrees, or within 10 degrees of parallel, or may be parallel or nominally parallel. If the use of “substantially aligned” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially aligned” will mean aligned to within 20% of a width of the objects being aligned. Objects described as substantially aligned may, in some embodiments, be aligned to within 10% or to within 5% of a width of the objects being aligned.

All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. 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.