WO2018026854A1

WO2018026854A1 - Displays with spatial light modulators

Info

Publication number: WO2018026854A1
Application number: PCT/US2017/044964
Authority: WO
Inventors: Ivan Knez; Sajjad A. KHAN; Volodymyr Borshch; Chun-Yao Huang; Graham B. MYHRE; Young Cheol YANG
Original assignee: Apple Inc.
Priority date: 2016-08-04
Filing date: 2017-08-01
Publication date: 2018-02-08

Abstract

Electronic devices may include displays. In certain displays, such as in holographic displays, it may be desirable to control both the phase and amplitude of the emitted light. In order to modulate the phase and amplitude of emitted light, a spatial light modulator (SLM) may be used. The spatial light modulator (38) may modulate both the phase and amplitude of the emitted light by dividing each pixel into three or more sub-pixels, modulating individual beams of light for each sub-pixel, and combining the beams of light into a single beam of light that will ultimately be emitted from the pixel. The spatial light modulator (38) may include a patterned retarder (30) that modifies the phase of incoming light before the light reaches a liquid crystal layer (32). This may result in the liquid crystal layer having a reduced thickness, and the display operating with a fast refresh rate.

Description

Displays with Spatial Light Modulators

This application claims priority to U.S. provisional patent application No. 62/371,099, filed on August 4, 2016, which is hereby incorporated by reference herein its entirety.

Background

[0001] This relates generally to electronic devices, and, more particularly, to electronic devices with displays.

[0002] Electronic devices often include displays. For example, an electronic device may have an organic light-emitting diode display based on organic-light-emitting diode pixels or a liquid crystal display based on liquid crystal pixels. Conventional liquid crystal displays may have pixels that each modulate the amplitude of emitted light. However, in some cases it may be desirable to additionally control the phase of emitted light. Conventional displays may also suffer from slow refresh rates.

[0003] It would therefore be desirable to be able to provide improved displays for electronic devices.

Summary

[0004] A display may have an array of pixels. The display may be a liquid crystal display and may be a holographic display.

[0005] Each pixel in the display may receive a respective incoming beam of light, split the incoming beam of light into multiple beams of light, modulate the multiple beams of light, and combine the multiple beams of light into an emitted beam of light with a desired amplitude and phase. The display may be a reflective display or a transmissive display.

[0006] The display may include a light source that provides light for the display and a black matrix with openings over pixels in the display. Each pixel in the display may include at least three sub-pixels. Beam splitting layers within the display may split incoming beams of light into multiple beams of light such that each sub-pixel receives a respective beam of light. The beams of light for each sub-pixel may pass through a patterned retarder that delays the phase of the beam of light by a particular amount. The phase of the beams may then be further shifted by a liquid crystal layer. When the beams of light from each sub-pixel are combined into a single beam of light to be emitted, the single beam of light may have the desired amplitude and phase.

[0007] A display pixel may control the amplitude of emitted light using first and second pixel halves. The display pixel may include beam splitting layers that split an incoming beam of light into a first beam of light for the first pixel half and a second beam of light for the second pixel half. The beams of light may then pass through a patterned retarder and a liquid crystal layer. When the first and second beams of light are combined into a single beam of light to be emitted, the single beam of light may have the desired amplitude.

Brief Description of the Drawings

[0008] FIG. 1 is a schematic diagram of an illustrative electronic device having a display in accordance with an embodiment.

[0009] FIG. 2 is a schematic diagram of an illustrative reflective display that includes a patterned retarder and a spatial light modulator in accordance with an embodiment.

[0010] FIG. 3 is a schematic diagram of an illustrative transmissive display that includes a patterned retarder and a spatial light modulator in accordance with an embodiment.

[0011] FIG. 4A is a top view of various display layers in an illustrative display with a spatial light modulator in accordance with an embodiment.

[0012] FIGS. 4B and 4C are cross-sectional side views of various display layers in the illustrative display of FIG. 4A that includes a spatial light modulator in accordance with an embodiment.

[0013] FIG. 5 is a schematic diagram of an illustrative spatial light modulator with an amplitude modulator and a phase modulator formed separately from the amplitude modulator in accordance with an embodiment.

[0014] FIG. 6 is a schematic diagram of an illustrative spatial light modulator with a phase and amplitude modulator that uses a single liquid crystal layer in accordance with an embodiment.

[0015] FIG. 7 is a top view of an illustrative patterned retarder that is used to selectively delay the phase of incoming light beams to each sub-pixel in a pixel in accordance with an embodiment.

[0016] FIG. 8 is a graph representing light beams of four different sub-pixels as vectors in accordance with an embodiment.

[0017] FIGS. 9A and 9B are graphs showing how the vectors representing light beams for each sub-pixel may be added together to determine the attributes of the beam of light that will ultimately be emitted from the display pixel in accordance with an embodiment.

[0018] FIGS. 10A and 10B are top views of illustrative patterned retarders that are used to selectively delay the phase of incoming light beams to each sub-pixel in pixels with three sub-pixels in accordance with an embodiment.

[0019] FIG. 11 is a graph representing the light beam for each sub-pixel in a pixel with three sub-pixels as a vector in accordance with an embodiment. [0020] FIG. 12A is a top view of various display layers in an illustrative display that uses multiple sub-pixels to modulate the amplitude of emitted light in accordance with an embodiment.

[0021] FIG. 12B is a cross-sectional side view of various display layers in the illustrative display of FIG. 12A that uses multiple sub-pixels to modulate the amplitude of emitted light in accordance with an embodiment.

[0022] FIG. 13 is a circuit diagram of a pixel that may be used to modulate the amplitude of emitted light in accordance with an embodiment.

[0023] FIG. 14 is a graph representing light beams for two different sub-pixels as vectors in accordance with an embodiment.

[0024] FIG. 15 is a graph showing how the vectors representing light beams for two different sub-pixels may be added together to determine the amplitude of the beam of light that will ultimately be emitted from the display pixel in accordance with an embodiment.

Detailed Description

[0025] Electronic devices may include displays. In certain displays, it may be desirable to control both the phase and amplitude of the light emitted from the display (i.e., in a holographic display). In order to modulate the phase and amplitude of emitted light, a spatial light modulator (SLM) may be used. The spatial light modulator may be capable of modulating both the phase and amplitude of the emitted light by dividing each pixel into three or more sub-pixels, modulating individual beams of light for each sub-pixel, and combining the beams of light into a single beam of light that will ultimately be emitted from the pixel. Dividing each pixel into three or more sub-pixels may enable spatial light modulation while having fast refresh rates in the display. The spatial light modulator may include a patterned retarder that modifies the phase of incoming light before the light reaches a liquid crystal layer. This may result in the liquid crystal layer having a reduced thickness, and the display operating with a fast refresh rate.

[0026] An illustrative electronic device of the type that may be provided with a display is shown in FIG. 1. Electronic device 10 may be a computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user's head, or other wearable or miniature device, a display, a computer display that contains an embedded computer, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, or other electronic equipment.

[0027] As shown in FIG. 1, electronic device 10 may have control circuitry 16. Control circuitry 16 may include storage and processing circuitry for supporting the operation of device 10. The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-readonly memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access memory), etc. Processing circuitry in control circuitry 16 may be used to control the operation of device 10. The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc.

[0028] Input-output circuitry in device 10 such as input-output devices 12 may be used to allow data to be supplied to device 10 and to allow data to be provided from device 10 to external devices. Input-output devices 12 may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device 10 by supplying commands through input-output devices 12 and may receive status information and other output from device 10 using the output resources of input-output devices 12.

[0029] Input-output devices 12 may include one or more displays such as display 14.

Display 14 may be a touch screen display that includes a touch sensor for gathering touch input from a user or display 14 may be insensitive to touch. A touch sensor for display 14 may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. A touch sensor for display 14 may be formed from electrodes formed on a common display substrate with the pixels of display 14 or may be formed from a separate touch sensor panel that overlaps the pixels of display 14. If desired, display 14 may be insensitive to touch (i.e., the touch sensor may be omitted). Display 14 in electronic device 10 may be a head-up display that can be viewed without requiring users to look away from a typical viewpoint. The head-up display may be incorporated into an automobile, for example. Display 14 may also be a head-mounted display that is incorporated into a device that is worn on a user's head. If desired, display 14 may also be a holographic display used to display holograms.

[0030] Control circuitry 16 may be used to run software on device 10 such as operating system code and applications. During operation of device 10, the software running on control circuitry 16 may display images on display 14.

[0031] FIG. 2 shows an illustrative reflective display that may use a patterned retarder to help modulate the phase and amplitude of the light emitted from the display. As shown in FIG. 2, display 14 may include a light source 20 that emits light 22 for display 14. The light may pass through various layers to ultimately reach reflective backplate 34. The reflective backplate may reflect incoming light such that light is emitted towards viewer 36 of the display. Light source 20 may be any desired light source. For example, light source 20 may include lasers used to emit light for display 14. Lasers of different colors may be used in light source 20 if desired (i.e., red, blue, and green lasers). Alternatively, light-emitting diodes or organic light-emitting diodes may be included in light source 20. Light emitting diodes of different colors may be used if desired. Light from a light guide plate may also be used to provide light for the display. If desired, quantum dot structures may be incorporated into light source 20 to convert light into different colors. For example, light source 20 may include a blue light source. The display may also include red and green quantum dots to convert some of the blue light from the blue light source to narrowband red and green light. In some embodiments, ambient light may be used to illuminate display 14 in addition to or instead of light from light source 20.

[0032] Light 22 from light source 20 may be reflected towards various display layers such as layers 26, 28, 30, 32, and 34 by a reflective layer 24. If desired, other arrangements for providing light 22 to the display layers may be used. Light from reflective layer 24 may pass through black matrix 26. Black matrix 26 may be formed by an opaque layer that does not pass through light. The black matrix 26 may therefore be used to define openings for pixels in display 14. Black matrix 26 may be formed from any desired opaque material. The amount of display area taken up by the black matrix compared to the openings in the black matrix that allow light to pass through may sometimes be referred to as fill factor. In some cases where the amplitude and phase of emitted light needs to be precisely controlled, decreasing fill factor in a display may be necessary to reduce cross-talk and enable high precision control of emitted light.

[0033] As previously discussed, beams of light 22 from light source 20 may pass through openings in black matrix 26. It may be desirable for the beams of light to be split before reaching other layers in the display. Beam splitting and combining layers 28 may help split an incoming beam of light into multiple beams of light. After the multiple beams reflect off of the reflective backplate, the multiple beams may be combined back into a single beam of emitted light by the beam splitting and combining layers 28. Beam splitting and combining layers 28 may include any desired number of layers of any desired types. For example, beam splitting and combining layers 28 may include one or more savart plates, half-wave plates, quarter-wave plates, other types of waveplates (sometimes referred to as retarders), linear polarizers, and other types of polarizers. One or more of the layers in the beam splitting and combining layers may be patterned to only selectively cover portions of the underlying pixels.

[0034] In order to control the phase and amplitude of the light emitted from display 14, display 14 may include patterned retarder 30. Patterned retarder 30 may shift the phase of the incoming light before it reaches liquid crystal layer 32. Each pixel may have three or more sub-pixels, and the patterned retarder may shift the phase of incoming light by a different amount for each respective sub-pixel. For example, in a pixel with three sub-pixels, the patterned retarder may shift the phase of light in a first sub-pixel by 0, may shift the phase of light in a second sub-pixel by 2π/3, and may shift the phase of light in a third sub-pixel by 4π/3. In a pixel with four sub-pixels, the patterned retarder may shift the phase of light in a first sub-pixel by 0, may shift the phase of light in a second sub-pixel by π/2, may shift the phase of light in a third sub-pixel by π, and may shift the phase of light in a fourth sub-pixel by 3π/2.

[0035] After passing through patterned retarder 30, incoming light may pass through liquid crystal layer 32. Liquid crystal layer 32 may further delay the phase of the light. In embodiments where patterned retarder 30 is not included in the display and each pixel is not divided into sub-pixels, liquid crystal layer 32 may need to have a thickness necessary to delay the phase of incoming light between 0 and π (which becomes 2π after the reflection) to enable light to be emitted with any desired phase between 0 and 2π. By including patterned retarder 30 and dividing each pixel into sub-pixels, the liquid crystal layer 32 may only be required to delay the phase of incoming light between 0 and π/4 or π/3 (i.e., less than π) to be capable of emitting light with any desired phase between 0 and 2π. This may allow the liquid crystal layer to operate faster, increasing the refresh rate of the display.

[0036] Liquid crystal 32 may be formed on a reflective backplate 34. Reflective backplate 34 may be used to reflect the incoming light back through layers 26, 28, 30, and 32.

Reflective backplate 34 may be reflective such that any incoming light is reflected and emitted from display 14. Reflective backplate 34 may also include components for addressing liquid crystal 32 (i.e., thin-film transistors, electrodes, etc.). Patterned retarder 30, liquid crystal 32, and reflective backplate 34 may sometimes be collectively referred to as a spatial light modulator (i.e., spatial light modulator 38). In some embodiments, reflective backplate 34 may be formed from silicon and the display may alternately be referred to as a liquid crystal on silicon display.

[0037] A display that controls the amplitude and phase of emitted light may be used to display holograms. Accordingly, although not explicitly shown in FIG. 2 display 14 may include other layers such as a field lens or a beam steering layer. The beam steering layer may be a diffraction grating or any other desired layer. The field lens may change the displayed image to a desired size for viewing by viewer 36. Additionally, display 14 may include a color filter layer with color filters to ensure that the emitted light has the desired color. In some embodiments, a uniform color light may be used (i.e., white) as light source 20. Each pixel may then have a specific color filter to ensure that the white light is converted to the desired color for that pixel. Alternatively, in some embodiments each pixel may receive light from a specifically colored light source (i.e. red, blue, or green). Each pixel may alternately receive red, green, and blue light in what is sometimes referred to as a sequential color display scheme. In these cases, a color filter layer may not be necessary.

[0038] FIG. 2 shows an illustrative reflective display with a spatial light modulator.

However, this example is merely illustrative. If desired, a transmissive display may include a spatial light modulator, as shown in FIG. 3. The transmissive display in FIG. 3 has similar components as the reflective display in FIG. 2. Light source 20 may be used to provide light for the display. Light source 20 may include one or more lasers, light-emitting diodes, light- guide plates, or any other desired components. Light 22 from light source 20 may be split into multiple beams by beam splitting layers 28-1. Beam splitting layers 28-1 may include one or more savart plates, half-wave plates, quarter-wave plates, other types of waveplates, linear polarizers, or other types of polarizers. After the light from light source 20 has been split and polarized by beam splitting layers 28-1, the light may be modulated by spatial light modulator 38. First, the light may pass through patterned retarder 30. Then the light may pass through liquid crystal 32 which is controlled by thin-film transistor layer 40. After passing through the spatial light modulator, the beams of light may be combined by beam combining layers 28-2. Beam combining layers 28-2 may include one or more savart plates, half-wave plates, quarter-wave plates, other types of waveplates, linear polarizers, or other types of polarizers. Finally, the light may pass through black matrix 26 to reach viewer 36. If desired, a black matrix layer may be provided between light source 20 and beam splitting layers 28-1.

[0039] Using the reflective display shown in FIG. 2 effectively doubles the thickness of liquid crystal layer 32 compared to the transmissive display shown in FIG. 3. The light passes through liquid crystal layer 32 twice in the reflective display (i.e., once before being reflected and once after being reflected). This means that liquid crystal layers in reflective displays only need to be half the thickness of liquid crystal layers in transmissive displays to achieve the same effect. This may reduce the thickness and increase the refresh rate of the display.

[0040] FIGS. 4A-4C show various views of display layers in display 14. FIG. 4A is a cross-sectional top view of various display layers, while FIGS. 4B and 4C are different cross- sectional side views of display layers in display 14. Display layers for a single pixel 42 are shown in FIGS. 4A-4C. As shown in FIG. 4A, pixel 42 may include four sub-pixels (42-1, 42-2, 42-3, and 42-4). Black matrix 26 may cover three of the four sub-pixels in each pixel, leaving an opening for incoming light 22 to pass through one sub-pixel (i.e., sub-pixel 42-4) in each pixel. The incoming light that passes through black matrix 26 may be linearly polarized at 45°. After passing through the black matrix, it may be desirable to split the incoming beam of light into multiple beams of light so that each sub-pixel receives a uniform light beam. Accordingly, after passing through black matrix 26 the incoming beam of light may pass through beam splitting and combining layers 28.

[0041] The first beam splitting layer may be savart plate 46. Savart plate 46 may split the incoming light beam into two separate light beams with orthogonal polarization, as shown in FIG. 4A. The light may then pass through a passive half-wave plate at 22.5° which converts each light beam into light linearly polarized at 45°. Half-wave plate 48 and savart plate 46 may be formed from any desired materials (i.e., quartz, mica, calcite, etc.). After passing through half-wave plate 48, the incoming light may reach another savart plate 50. Savart plate 50 may split the two incoming beams into four beams with orthogonal polarizations. Savart plate 50 may be orthogonal to savart plate 46, meaning that one savart plate splits incoming light along a first axis and the second savart plate splits the incoming light on a second axis that is perpendicular to the first axis.

[0042] After passing through savart plate 50, the four beams of incoming light may pass through a patterned half-wave plate at 45°. Patterned half-wave plate 52 may have portions that alter the polarization of the incoming beams and portions that allow incoming beams to pass through without alteration. After passing through patterned half-wave plate 52, the four beams of incoming light should all have the same polarization. A linear polarizer 54 may be included after half-wave plate 52 to ensure that all of the light that is passed to spatial light modulator 38 has the same polarization. The uniform polarization of each beam of light may enable spatial light modulator 38 to effectively modulate the phase and amplitude of each light beam. Savart plate 50, half-wave plate 52, and linear polarizer 54 may be formed from any desired material (i.e., quartz, mica, calcite, etc.).

[0043] In FIGS. 4A-4C, an illustrative arrangement for beam splitting and combining layers 28 is shown. In particular, an arrangement with two savart plates, two half-wave plates, and one linear polarizer is shown. However, this example is merely illustrative. Any desired arrangement of layers may be used to split the incoming beam of light into multiple beams of light with uniform polarization. For example, if pixel 42 had only three sub-pixels (instead of four as pictured in FIGS. 4A-4C), an alternate arrangement may be used.

[0044] Spatial light modulator 38 may receive the incoming beams of light with uniform polarization and output light that has a precisely controlled amplitude and phase. There are multiple ways to implement a spatial light modulator in a display. As shown in FIG. 5, the spatial light modulator may include an amplitude modulator and a phase modulator that is formed separately from the amplitude modulator. The phase modulator and amplitude modulator may each have respective liquid crystal layers. Alternatively, as shown in FIG. 6, a single phase and amplitude modulator may form spatial light modulator 38. In this type of arrangement, a single layer of liquid crystal can be used to modify the phase and amplitude of light. The light may be split and later combined such that the combination of the individually altered beams has the desired phase and amplitude. The spatial light modulator in FIG. 4 is of the type shown in FIG. 6, where a single liquid crystal layer is used. As shown in FIG. 4, spatial light modulator 38 may include liquid crystal layer 32 and backplate 34. Each sub- pixel in spatial light modulator 38 may modify the phase of an incoming light beam. In this arrangement, sub-pixel 42-4 may be used to adjust the phase of the incoming light between 0 and π/2, sub-pixel 42-2 may be used to adjust the phase of the incoming light between π/2 and π, sub-pixel 42-1 may be used to adjust the phase of the incoming light between π and 3π/2, and sub-pixel 42-3 may be used to adjust the phase of the incoming light between 3π/2 and 2π. When the light is then combined by beam splitting and combining layers 28, the resulting emitted beam will have the desired amplitude and phase.

[0045] In order to maximize the refresh rate of the display and minimize the thickness of the display, a passive patterned retarder 30 may be provided above liquid crystal layer 32 and backplate 34. Patterned retarder 30 may have different sections above each sub-pixel in pixel

42. For example, patterned retarder portion 30-1 may be positioned over sub-pixel 42-1 and shift the phase of an incoming beam by π, patterned retarder portion 30-2 may be positioned over sub-pixel 42-2 and shift the phase of an incoming beam by π/2, patterned retarder portion 30-3 may be positioned over sub-pixel 42-3 and shift the phase of an incoming beam by 3π/2, and patterned retarder portion 30-4 may be positioned over sub-pixel 42-4 and may not shift the phase of an incoming beam. Patterned retarder portion 30-4 may have a first thickness, patterned retarder portion 30-2 may have a second thickness that is greater than the first thickness, patterned retarder portion 30-1 may have a third thickness that is greater than the second thickness, and patterned retarder portion 30-3 may have a fourth thickness that is greater than the third thickness. Because the incoming beams to liquid crystal layer 32 have a known phase delay, the liquid crystal layer may only need to be capable of a phase shift between 0 and π/4 (which effectively becomes 0 - π/2 after the reflection occurs). This minimizes the thickness of the display and decreases the electrically controlled birefringence response time in the liquid crystal, which allows for a faster refresh rate for the display. Additionally, some of the increase in refresh rate of the display can be sacrificed for reduction of power consumption in the display if desired.

[0046] FIG. 7 shows a top view of illustrative patterned retarder 30 with portions 30-1, 30- 2, 30-3, and 30-4. As shown, portions 30-1, 30-2, 30-3, and 30-4 may shift the phase of an incoming beam by π, π/2, 3π/2, and 0, respectively. Thus, even though the liquid crystal is only capable of a phase shift between 0 and π/4, sub-pixel 42-1 is capable of a phase shift between π and 3π/2, sub-pixel 42-2 is capable of a phase shift between π/2 and π, sub-pixel 42-3 is capable of a phase shift between 3π/2 and 2π, and sub-pixel 42-4 is capable of a phase shift between 0 and π/2. The pixel as a whole, therefore, is capable of a phase shift between 0 and 2π.

[0047] The phase and amplitude of light may be represented as a vector on the complex plane, where the amplitude of the light is the magnitude of the vector, and the phase of the light is the angle of the vector. The light from each sub-pixel in pixel 42 is represented graphically in FIG. 8. Vector 62 represents light from sub-pixel 42-4, vector 64 represents light from sub-pixel 42-2, vector 66 represents light from sub-pixel 42-1, and vector 68 represents light from sub-pixel 42-3. The magnitude of vectors 62, 64, 66, and 68 may be the same. The liquid crystal layer may be capable of adjusting the direction of the vector (by shifting the phase of the light). The liquid crystal for sub-pixel 42-4, for example, receives light with a given magnitude and a known phase of 0. The liquid crystal may shift the phase anywhere from 0- π/2, as shown by vector 62. The liquid crystal for sub-pixel 42-2 receives light with the given magnitude and a known phase of π/2. The liquid crystal may further shift the phase anywhere from π/2 to π, as shown by vector 64. The liquid crystal for sub-pixel 42- 1 receives light with the given magnitude and a known phase of π. The liquid crystal may further shift the phase anywhere from π to 3π/2, as shown by vector 66. The liquid crystal for sub-pixel 42-3 receives light with the given magnitude and a known phase of 3π/2. The liquid crystal may further shift the phase anywhere from 3π/2 to 2π, as shown by vector 68.

[0048] As discussed in connection with FIGS. 2 and 3, after the amplitude and phase of light for each sub-pixel is controlled, the beams from each sub-pixel may be combined into a beam that will be emitted. When the light from each sub-pixel is combined, the properties of each individual beam are combined. This can be represented by vector addition, as shown in FIGS. 9 A and 9B. FIG. 9 A shows vectors 62, 64, 66, and 68 representing light emitted from sub-pixels 42-4, 42-2, 42-1, and 42-4, respectively. As shown in FIG. 9 A, each vector may have the same magnitude (meaning the light from each sub-pixel has the same amplitude) and a unique angle relative to 0 (corresponding to the phase of the light from the sub-pixel).

When vectors 62, 64, 66, and 68 are added together, a new vector 70 is the result, as shown in FIG. 9B. Vector 70 has a magnitude and angle associated with the amplitude and phase of the light emitted from the pixel after the beams from the sub-pixels are combined. This demonstrates how by controlling the phase of the light emitted from each sub-pixel, the phase and amplitude of the combined beam light from the pixel can be controlled.

[0049] The concept described above where a pixel has four sub-pixels that independently control the phase of light is merely illustrative. A pixel may include three sub-pixels, five sub-pixels, or more than five sub-pixels that control the phase of light in a spatial light modulator. Illustrative arrangements for a patterned retarder 30 for a pixel with three sub- pixels are shown in FIGS. 10A and 10B. As shown, a patterned retarder 30 for a pixel with three sub-pixels may have retarder portions 30-1, 30-2, and 30-3. For example, patterned retarder portion 30-1 may not shift the phase of an incoming beam, patterned retarder portion 30-2 may shift the phase of an incoming beam by 2π/3, and patterned retarder portion 30-3 may shift the phase of an incoming beam by 4π/3. Because the incoming beams to liquid crystal layer 32 have a known phase delay, the liquid crystal layer may only need to be capable of a phase shift between 0 and π/3 (which means the liquid crystal layer is capable of a phase shift of 0 - 2π/3 after the reflection occurs). This increases the refresh rate and minimizes the thickness of the display. As shown in FIG. 10A, the patterned retarder sections (and corresponding sub-pixels) may have hexagonal shapes. Alternatively, as shown in FIG. 10B, the patterned retarder sections may have rectangular shapes. These examples are merely illustrative, and each pixel in the display may have any desired number of sub- pixels with any desired shape.

[0050] The light from each sub-pixel in a pixel with three sub-pixels is represented graphically in FIG. 11. Vector 72 represents light from the sub-pixel associated with patterned retarder portion 30-1 from FIGS. 10A and 10B, vector 74 represents light from the sub-pixel associated with patterned retarder portion 30-2 from FIGS. 10A and 10B, and vector 76 represents light from the sub-pixel associated with patterned retarder portion 30-3 from FIGS. 10A and 10B. The magnitude of vectors 72, 74, and 76 may be the same. The liquid crystal layer may be capable of adjusting the direction of the vector (by shifting the phase of the light). The liquid crystal for the sub-pixel associated with retarder portion 30-1, for example, receives light with a given magnitude and a known phase of 0. The liquid crystal may shift the phase anywhere from 0- 2π/3, as shown by vector 72. The liquid crystal for the sub-pixel associated with retarder portion 30-2 receives light with the given magnitude and a known phase of 2π/3. The liquid crystal may further shift the phase anywhere from 2π/3 to 4π/3, as shown by vector 74. The liquid crystal for the sub-pixel associated with retarder portion 30-3 receives light with the given magnitude and a known phase of 4π/3. The liquid crystal may further shift the phase anywhere from 4π/3 to 2π, as shown by vector 76.

[0051] In the aforementioned embodiments, a spatial light modulator uses a patterned retarder over sub-pixels to maximize the refresh rate of the display while controlling the amplitude and phase of emitted light. This is accomplished by having input beams of a constant amplitude to multiple sub-pixels. The beams may be phase shifted by the patterned retarder and the liquid crystal layer. The phase of each beam is determined such that when the beams are combined before emission the resulting beam will have a desired amplitude and phase. The concept of modifying the phase of light from three or more sub-pixels to control the light ultimately emitted from the pixel can also be used to modify the amplitude of light emitted from a pixel with two sub-pixels.

[0052] FIGS. 12A and 12B show various views of display layers in display 14 that are used to control the amplitude of emitted light. FIG. 12A is a cross-sectional top view of various display layers, while FIG. 12B is a cross-sectional side views of display layers in display 14. Display layers for a single pixel 42 are shown in FIGS. 12A and 12B. As shown in FIG.12A, pixel 42 may include two sub-pixels (42-1 and 42-2). Sub-pixels 42-1 and 42-2 may sometimes be referred to as pixel halves 42-1 and 42-2. Black matrix 80 may cover one of the two sub-pixels in each pixel, leaving an opening for incoming light 22 to pass through the black matrix. The incoming light that passes through black matrix 80 may be linearly polarized at 45°. After passing through the black matrix, it may be desirable to split the incoming beam of light into multiple beams of light so that each sub-pixel receives a uniform light beam. Accordingly, after passing through black matrix 80 the incoming beam of light may pass through beam splitting and combining layers 82.

[0053] The first beam splitting layer may be savart plate 84. Savart plate 84 may split the incoming light beam into two separate light beams with orthogonal polarization, as shown in FIG. 12B. The light may then pass through a patterned half-wave plate at 45°. Patterned half-wave plate 86 may have portions that alter the polarization of the incoming beams and portions that allow incoming beams to pass through without alteration. After passing through patterned half-wave plate 86, the two beams of incoming light should have the same polarization. Half-wave plate 86 and savart plate 84 may be formed from any desired materials (i.e., quartz, mica, calcite, etc.).

[0054] As shown in FIG. 12B, after passing through the beam splitting and combining layers 82, the light may pass through patterned retarder 88 and reach liquid crystal layer 92 and reflective backplate 94. Each sub-pixel may modify the phase of an incoming light beam. For example, sub-pixel 42-1 may be used to adjust the phase of the incoming light between 0 and π/2, and sub-pixel 42-2 may be used to adjust the phase of the incoming light between π/2 and π. When the light is then combined by beam splitting and combining layers 82, the resulting emitted beam will have the desired amplitude.

[0055] Passive patterned retarder 88 may be provided above liquid crystal layer 92 and reflective backplate 94 in order to maximize the refresh rate of the display and minimize the thickness of the display. Patterned retarder 88 may have a portion above pixel half 42-2 that shifts the phase of an incoming beam by π/2. Patterned retarder 88 may not shift the phase of light in pixel half 42-1. Because the incoming beams to liquid crystal layer 92 have a known phase delay, the liquid crystal layer may only need to be capable of a phase shift between 0 and π/4 (which effectively becomes 0 - π/2 after the reflection occurs). This minimizes the thickness of the display and decreases the electrically controlled birefringence response time in the liquid crystal, which allows for a faster refresh rate for the display. Additionally, some of the increase in refresh rate of the display can be sacrificed for reduction of power consumption in the display if desired.

[0056] A linear polarizer 90 may be included above liquid crystal layer 92 to ensure that the light that is passed to liquid crystal layer 92 has the same polarization. The uniform polarization of each beam of light may enable the display to effectively modulate the amplitude of each light beam.

[0057] In FIGS. 12A and 12B, an illustrative arrangement for beam splitting and combining layers 82 is shown. In particular, an arrangement with one savart plate and one half-wave plate is shown. However, this example is merely illustrative. Any desired arrangement of layers may be used to split the incoming beam of light into two beams of light with uniform polarization.

[0058] As shown in FIG. 13, both sub-pixels 42-1 and 42-2 from FIG. 12 may be driven from the same pixel circuit. The pixel circuit may include column lines 102, row line 104, and any other desired circuitry (i.e., transistors, inverters, Xor gates, etc.). The pixel circuit may receive clock signals (CLK) that help determine when a bias voltage is applied to respective pixel electrodes. The pixel may also include a liquid crystal layer LC (i.e. liquid crystal layer 92) that is interposed between pixel electrodes and a common electrode (COM). Sub-pixel 42-1 may be biased from the output node Q to a target bias voltage Vo while sub- pixel 42-2 may be biased from the conjugate node Q^cto a bias voltage VDD - Vo.

Consequently, when sub-pixel 42-1 has a given phase φ, sub-pixel 42-2 will have a complementary phase π - φ. The resulting combined beam from the two sub-pixels will have a phase of π/2 and an amplitude that can be precisely controlled. This concept is shown graphically in FIG. 14.

[0059] The phase and amplitude of light may be represented as a vector on the complex plane, where the amplitude of the light is the magnitude of the vector, and the phase of the light is the angle of the vector. The light from sub-pixels 42-1 and 42-2 as shown in FIGS.

12 and 13 is represented graphically in FIG. 14. Vector 112 represents light from sub-pixel

42-1, while vector 114 represents light from sub -pixel 42-2. The magnitude of vectors 112 and 114 may be the same. The liquid crystal layer may be capable of adjusting the direction of each vector (by shifting the phase of the light). The liquid crystal for sub-pixel 42-1, for example, receives light with a given magnitude and a known phase of 0. The liquid crystal may shift the phase anywhere from 0- π/2, as shown by vector 112. The liquid crystal for sub-pixel 42-2 receives light with the given magnitude and a known phase of π/2. The pixel circuit may be arranged (as described in connection with FIG. 13) such that sub-pixel 42-2 shifts the phase of the incoming light from π to π/2 as shown by vector 114.

[0060] FIG. 15 further shows how sub-pixels 42-1 and 42-2 from FIGS. 12 and 13 may be used to adjust the amplitude of emitted light. As shown, the light from sub-pixel 42-1 is represented by vector 112. The light from sub-pixel 42-2 is represented by complementary vector 114. The resulting light from the combination of beams from sub-pixels 42-1 and 42-2 is represented by vector 116. The resulting light will always have a phase of π/2, and the amplitude of the resulting light will be determined by the phase shift of sub-pixels 42-1 and 42-2.

[0061] In accordance with an embodiment, a display with a plurality of pixels is provided that includes a light source, where each pixel in the plurality of pixels is configured to receive an incoming beam of light from the light source, and each pixel includes at least three sub- pixels, beam splitting layers configured to split the incoming beam of light from the light source into multiple beams of light, each sub-pixel of the at least three sub-pixels receives a respective beam of light of the multiple beams of light, and each beam of light has an amplitude and a phase, a patterned retarder that delays the phase of the beam of light for each sub-pixel and a liquid crystal layer that receives each beam of light after each beam of light passes through the patterned retarder, the multiple beams of light are combined into an emitted beam of light after each beam of light passes through the liquid crystal layer.

[0062] In accordance with another embodiment, the at least three sub-pixels includes first, second, third, and fourth sub-pixels configured to receive respective first, second, third, and fourth beams of light, and the patterned retarder has a first portion over the first sub-pixel, a second portion over the second sub-pixel, a third portion over the third sub-pixel, and a fourth portion over the fourth sub-pixel.

[0063] In accordance with another embodiment, the first beam of light has a first phase, the second beam of light has a second phase, the third beam of light has a third phase, the fourth beam of light has a fourth phase, the first portion of the patterned retarder does not delay the first phase, the second portion of the patterned retarder delays the second phase by π/2, the third portion of the patterned retarder delays the third phase by π, and the fourth portion of the patterned retarder delays the fourth phase by 3π/2.

[0064] In accordance with another embodiment, the liquid crystal layer is configured to further delay the first, second, third, and fourth phases by an amount between 0 and π/2.

[0065] In accordance with another embodiment, the at least three sub-pixels includes first, second, and third sub-pixels configured to receive respective first, second, and third beams of light, and the patterned retarder has a first portion over the first sub-pixel, a second portion over the second sub-pixel, and a third portion over the third sub-pixel.

[0066] In accordance with another embodiment, the first beam of light has a first phase, the second beam of light has a second phase, the third beam of light has a third phase, the first portion of the patterned retarder does not delay the first phase, the second portion of the patterned retarder delays the second phase by 2π/3, and the third portion of the patterned retarder delays the third phase by 4π/3.

[0067] In accordance with another embodiment, the liquid crystal layer is configured to further delay the first, second, and third phases by an amount between 0 and 2π/3.

[0068] In accordance with another embodiment, the first portion of the patterned retarder has a first thickness, the second portion of the patterned retarder has a second thickness that is greater than the first thickness, and the third portion of the patterned retarder has a third thickness that is greater than the second thickness.

[0069] In accordance with another embodiment, the beam splitting layers include a first savart plate, a second savart plate, a first half-wave plate interposed between the first and second savart plates, and a second half-wave plate.

[0070] In accordance with another embodiment, the display includes a linear polarizer.

[0071] In accordance with another embodiment, the first savart plate is orthogonal to the second savart plate.

[0072] In accordance with another embodiment, the liquid crystal layer is configured to delay the phase of the beam of light for each sub-pixel between 0 and π/2, and the emitted beam of light has a phase between 0 and 2π.

[0073] In accordance with another embodiment, the liquid crystal layer is configured to delay the phase of the beam of light for each sub-pixel between 0 and 2π/3, and the emitted beam of light has a phase between 0 and 2π.

[0074] In accordance with another embodiment, the display is a holographic display.

[0075] In accordance with an embodiment, a reflective display is provided that includes a plurality of pixels, each pixel is configured to receive a respective incoming beam of light, split the incoming beam of light into multiple beams of light, modulate the multiple beams of light, and combine the multiple beams of light into an emitted beam of light, the reflective display includes a plurality of pixels, each pixel has at least three sub-pixels, a black matrix layer that covers the plurality of pixels, the black matrix layer has a plurality of openings that are each aligned with one sub-pixel of the at least three sub-pixels of each pixel, a light source, the plurality of pixels receive the incoming beams of light from the light source through the plurality of openings in the black matrix layer, beam splitting and combining layers configured to split each incoming beam of light into the multiple beams of light, where each sub-pixel of the at least three sub-pixels receives a respective beam of light of the multiple beams of light, and a spatial light modulator configured to modulate each beam of light, the beam splitting and combining layers are configured to combine the modulated beams of light into the emitted beam of light that is emitted from the pixel.

[0076] In accordance with another embodiment, the spatial light modulator includes a liquid crystal layer and a reflective backplate.

[0077] In accordance with another embodiment, the modulated beams of light each have a respective amplitude and phase, the amplitude of each modulated beam of light is the same, each modulated beam of light has a different phase, and the emitted beam of light that is emitted from the pixel has a phase between 0 and 2π.

[0078] In accordance with an embodiment, a display pixel is provided that includes first and second pixel halves, a black matrix layer with an opening over the first pixel half, the black matrix layer is configured to allow an incoming beam of light to pass through the opening, beam splitting layers configured to split the incoming beam of light into first and second beams of light, the first beam of light is received by the first pixel half and the second beam of light is received by the second pixel half, the first beam of light has a first phase, and the second beam of light has a second phase, a liquid crystal layer with a first half that corresponds to the first pixel half and a second half that corresponds to the second pixel half; and a patterned retarder positioned between the beam splitting layers and the liquid crystal layer, where the patterned retarder has a first portion over the first half of the liquid crystal layer that does not shift the first phase, the patterned retarder has a second portion over the second half of the liquid crystal layer that shifts the second phase by π/2, and the first and second beams of light are combined into a single beam of light that is emitted by the display pixel after passing through the patterned retarder and the liquid crystal layer.

[0079] In accordance with another embodiment, first and second halves of the liquid crystal layer are driven from a single pixel circuit.

[0080] In accordance with another embodiment, as the first beam of light is delayed from 0 to π/2 by the first pixel half, the second beam of light is delayed from π to π/2.

[0081] The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Claims

Claims What is Claimed is:

1. A display with a plurality of pixels comprising:

a light source, wherein each pixel in the plurality of pixels is configured to receive an incoming beam of light from the light source, and wherein each pixel comprises at least three sub-pixels;

beam splitting layers configured to split the incoming beam of light from the light source into multiple beams of light, wherein each sub-pixel of the at least three sub-pixels receives a respective beam of light of the multiple beams of light, and wherein each beam of light has an amplitude and a phase;

a patterned retarder that delays the phase of the beam of light for each sub-pixel; and

a liquid crystal layer that receives each beam of light after each beam of light passes through the patterned retarder, wherein the multiple beams of light are combined into an emitted beam of light after each beam of light passes through the liquid crystal layer.

2. The display defined in claim 1, wherein the at least three sub-pixels comprises first, second, third, and fourth sub-pixels configured to receive respective first, second, third, and fourth beams of light, and wherein the patterned retarder has a first portion over the first sub-pixel, a second portion over the second sub-pixel, a third portion over the third sub-pixel, and a fourth portion over the fourth sub-pixel.

3. The display defined in claim 2, wherein the first beam of light has a first phase, wherein the second beam of light has a second phase, wherein the third beam of light has a third phase, wherein the fourth beam of light has a fourth phase, wherein the first portion of the patterned retarder does not delay the first phase, wherein the second portion of the patterned retarder delays the second phase by π/2, wherein the third portion of the patterned retarder delays the third phase by π, and wherein the fourth portion of the patterned retarder delays the fourth phase by 3π/2.

4. The display defined in claim 3, wherein the liquid crystal layer is configured to further delay the first, second, third, and fourth phases by an amount between 0 and π/2.

5. The display defined in claim 1, wherein the at least three sub-pixels comprises first, second, and third sub-pixels configured to receive respective first, second, and third beams of light, and wherein the patterned retarder has a first portion over the first sub-pixel, a second portion over the second sub-pixel, and a third portion over the third sub- pixel.

6. The display defined in claim 5, wherein the first beam of light has a first phase, wherein the second beam of light has a second phase, wherein the third beam of light has a third phase, wherein the first portion of the patterned retarder does not delay the first phase, wherein the second portion of the patterned retarder delays the second phase by 2π/3, and wherein the third portion of the patterned retarder delays the third phase by 4π/3.

7. The display defined in claim 6, wherein the liquid crystal layer is configured to further delay the first, second, and third phases by an amount between 0 and 2π/3.

8. The display defined in claim 5, wherein the first portion of the patterned retarder has a first thickness, wherein the second portion of the patterned retarder has a second thickness that is greater than the first thickness, and wherein the third portion of the patterned retarder has a third thickness that is greater than the second thickness.

9. The display defined in claim 1, wherein the beam splitting layers comprise a first savart plate, a second savart plate, a first half-wave plate interposed between the first and second savart plates, and a second half-wave plate.

10. The display defined in claim 9, further comprising a linear polarizer.

11. The display defined in claim 9, wherein the first savart plate is orthogonal to the second savart plate.

12. The display defined in claim 1, wherein the liquid crystal layer is configured to delay the phase of the beam of light for each sub-pixel between 0 and π/2, and wherein the emitted beam of light has a phase between 0 and 2π.

13. The display defined in claim 1, wherein the liquid crystal layer is configured to delay the phase of the beam of light for each sub-pixel between 0 and 2π/3, and wherein the emitted beam of light has a phase between 0 and 2π.

14. The display defined in claim 1, wherein the display is a holographic display.

15. A reflective display comprising a plurality of pixels, wherein each pixel is configured to receive a respective incoming beam of light, split the incoming beam of light into multiple beams of light, modulate the multiple beams of light, and combine the multiple beams of light into an emitted beam of light, the reflective display comprising:

a plurality of pixels, wherein each pixel has at least three sub-pixels; a black matrix layer that covers the plurality of pixels, wherein the black matrix layer has a plurality of openings that are each aligned with one sub-pixel of the at least three sub-pixels of each pixel;

a light source, wherein the plurality of pixels receive the incoming beams of light from the light source through the plurality of openings in the black matrix layer;

beam splitting and combining layers configured to split each incoming beam of light into the multiple beams of light, wherein each sub-pixel of the at least three sub-pixels receives a respective beam of light of the multiple beams of light; and

a spatial light modulator configured to modulate each beam of light, wherein the beam splitting and combining layers are configured to combine the modulated beams of light into the emitted beam of light that is emitted from the pixel.

16. The reflective display defined in claim 15, wherein the spatial light modulator comprises a liquid crystal layer and a reflective backplate.

17. The reflective display defined in claim 16, wherein the modulated beams of light each have a respective amplitude and phase, wherein the amplitude of each modulated beam of light is the same, wherein each modulated beam of light has a different phase, and wherein the emitted beam of light that is emitted from the pixel has a phase between 0 and 2π.

18. A display pixel comprising:

first and second pixel halves;

a black matrix layer with an opening over the first pixel half, wherein the black matrix layer is configured to allow an incoming beam of light to pass through the opening;

beam splitting layers configured to split the incoming beam of light into first and second beams of light, wherein the first beam of light is received by the first pixel half and the second beam of light is received by the second pixel half, wherein the first beam of light has a first phase, and wherein the second beam of light has a second phase;

a liquid crystal layer with a first half that corresponds to the first pixel half and a second half that corresponds to the second pixel half; and

a patterned retarder positioned between the beam splitting layers and the liquid crystal layer, wherein the patterned retarder has a first portion over the first half of the liquid crystal layer that does not shift the first phase, wherein the patterned retarder has a second portion over the second half of the liquid crystal layer that shifts the second phase by π/2, and wherein the first and second beams of light are combined into a single beam of light that is emitted by the display pixel after passing through the patterned retarder and the liquid crystal layer.

19. The display pixel defined in claim 18, wherein first and second halves of the liquid crystal layer are driven from a single pixel circuit.

20. The display pixel defined in claim 19, wherein as the first beam of light is delayed from 0 to π/2 by the first pixel half, the second beam of light is delayed from π to π/2.