Nonlinear optics enabled transparent display

A display includes a plurality of elongated waveguides positioned adjacent to each other and extending along a first direction, a plurality of elongated upper electrodes positioned adjacent to each other on a first side of the waveguides and extending along the first direction, and a plurality of elongated lower electrodes positioned adjacent to each other on a second side of the waveguides opposite the first side and extending along a second direction transverse to the first direction. At least one of the waveguides comprises nonlinear materials having a third order susceptibility.

TECHNICAL FIELD

The present specification generally relates to an apparatus for displaying visual information and, more specifically, to two-dimensional transparent displays utilizing nonlinear optics.

BACKGROUND

Passive matrix displays are a common type of two-dimensional display. A passive matrix liquid crystal display (LCD) comprises a liquid crystal material positioned between a grid of conductors. One side of the liquid crystal material has a series of conductors arranged in rows and the other side of the liquid crystal material has a series of conductors arranged in columns. Each point where a conductor row and a conductor column cross represents a pixel.

To illuminate a particular pixel, a charge is applied to one particular conductor row while one particular conductor column is grounded. This creates a potential difference between the conductors at the point where the activated row and the activated column intersect, thus causing the liquid crystal to emit light at that pixel.

However, given the materials necessary for creating a passive matrix LCD display, it is difficult for those materials and the resulting display to be transparent. Accordingly, a need exists for alternative systems for creating a transparent display.

SUMMARY

In one embodiment, a display includes a plurality of elongated waveguides positioned adjacent to each other and extending along a first direction, a plurality of elongated upper electrodes positioned adjacent to each other on a first side of the waveguides and extending along the first direction, and a plurality of elongated lower electrodes positioned adjacent to each other on a second side of the waveguides opposite the first side and extending along a second direction transverse to the first direction. At least one of the waveguides comprises nonlinear materials having a third order susceptibility.

In another embodiment, an apparatus includes a plurality of fiber elongated waveguides positioned adjacent to each other and extending in a first direction and a plurality of transparent, flexible electrode pairs extending in a second direction parallel to the first direction and interwoven between the waveguides. Each electrode pair comprises two adjacent electrodes. For each waveguide, one electrode of each electrode pair is positioned on a first side of the waveguide and the other electrode of the electrode pair is positioned on a second side of the waveguide opposite the first side. At least one of the waveguides comprises nonlinear materials having a third order susceptibility.

In another embodiment, a method comprises injecting light into a waveguide of a display to produce a color pixel and applying a potential difference across a pair of electrodes positioned on either side of the waveguide. The display comprises a plurality of elongated waveguides positioned adjacent to each other and extending along a first direction, a plurality of elongated upper electrodes positioned adjacent to each other on a first side of the waveguides and extending along the first direction, and a plurality of elongated lower electrodes positioned adjacent to each other on a second side of the waveguides opposite the first side and extending along a second direction perpendicular to the first direction. At least one of the waveguides comprises nonlinear materials having a third order susceptibility.

DETAILED DESCRIPTION

FIG. 1generally depicts one embodiment of a transparent display. The transparent display ofFIG. 1comprises a passive display matrix comprising a plurality of optical waveguides made of nonlinear materials surrounded on either side by a plurality of transparent electrodes. The electrodes on one side of the waveguides are arranged parallel to the waveguides and the electrodes on the other side of the waveguides are arranged perpendicular to the waveguides. Each point on a waveguide where an electrode on one side of the waveguide crosses an electrode on the other side of the waveguide represents a pixel.

To operate the display, laser light is passed through the waveguides at particular wavelengths. To illuminate a particular pixel, a voltage is applied to one electrode on one side of the waveguides and to one electrode on the other side of the waveguides, thereby creating a potential difference across the waveguide at the point where the two electrodes cross each other. This potential difference across the waveguide interacts with the nonlinear optical waveguide as described herein to cause light to be emitted from the display at the selected pixel.

The example displays disclosed herein utilize a passive matrix display, which may be easily accessed using conventional display systems. The passive matrix allows for control of emission from the display at selected pixels while allowing laser light to continuously pass through the display. The disclosed display also minimizes reflections between stacked materials leading to a more transparent system.

Referring now toFIG. 1, one embodiment of a transparent, two-dimensional display100is illustrated. The display100generally comprises a plurality of elongated waveguides102, a plurality of elongated first electrodes104positioned on one side of the waveguides102, and a plurality of elongated second electrodes106positioned on the other side of the waveguides102.

The display100comprises a plurality of waveguides102arranged adjacent to each other. The waveguides102extend along the length of the display100(e.g., the y-direction in the orientation ofFIG. 1). When light is injected into a waveguide102, the light travels along the length of the waveguide102. The waveguides102are positioned adjacent to each other along the width of the display100(e.g., the x-direction in the orientation ofFIG. 1). In the example ofFIG. 1, six waveguides102are shown for purposes of illustration. However, it should be understood that the display100may comprise any number of waveguides102. In some examples, the number of waveguides102is equal to the number of columns of pixels in the display100. The waveguides102have sufficient width such that light may be injected into the waveguides102.

The waveguides102comprise nonlinear materials having a high third-order susceptibility, such as polymers or χ(3) ceramics. The χ(3) waveguides102induce a second order harmonic signal when a voltage is applied as described herein. Example materials that produce induced second order harmonic signals include, but are not limited to, alumina oxide, silicon nitride, hafnium oxide, other ceramic oxides, and other polymers such as (poly(9,9-di-n-dodecylfuluorenyl-2,7-diyl) PFO film. The crystal orientation of such films should be such that the largest change in the effective second order susceptibility tensor is in the direction of light propagation, thereby maximizing phase matching.

If the waveguides102were to comprise nonlinear materials that have a high second-order susceptibility, then light injected into such a waveguide would generate a χ(2) second-harmonic signal without the ability to control which pixels emit a signal. Instead, by using centrosymmetric materials with a high third-order susceptibility and no second-order susceptibility, when light is injected into the waveguides102without applying a voltage to any of the electrodes104,106, no nonlinear interactions would occur and no induced light signals would be emitted. This allows individual pixels to be controlled by applying voltages to particular electrodes104,106as described herein, which is desirable for a functioning display.

The waveguides102are transparent to visible light. In some embodiments, the waveguides102comprise a transparent polymer or crystalline thin film that has a third order nonlinear optical tensor. The larger the optical tensor, the stronger the performance of the generated nonlinear optical signal. As used herein, the term transparent means total transmittance of greater than 75%.

During operation, light is injected into one or more of the waveguides102. Referring toFIG. 2A, in some embodiments, a plurality of light sources200are used to inject light into the waveguides102. In the example ofFIG. 2A, the number of light sources is equal to the number of waveguides102.

The light sources200inject light into the waveguides102that is coherent and phase matched to the nonlinear materials of the waveguides102along the length of the waveguides102. Light at different wavelengths may be injected into the waveguides102to produce different colors from the display100, as explained in further detail below. In some examples, the light sources200comprise one or more lasers. In some embodiments, the light sources200comprise one or more optical fibers attached to the waveguides102. An individual light source200may be a pulsed laser, a continuous wave laser, or any other type of laser capable of injecting the appropriate light signal into the waveguides102. In some embodiments, the light source200may comprise another type of light source capable of producing coherent light at appropriate wavelengths.

Referring toFIG. 2B, in some embodiments, a single light source (e.g., a laser) is used to inject light into each of the waveguides102. In the example ofFIG. 2B, a single light source202emits light to an array of mirrors204. A light processing unit (not shown) may be used to adjust the mirrors204such that light is only injected to selected waveguides102. The array of mirrors204direct light from the light source202into the selected one or more waveguides102.

Referring to the non-limiting example ofFIG. 3, each waveguide102may comprise three adjacent sections300,302,304. The three sections300,302,304each comprise different nonlinear materials such that they have different nonlinear properties. Specifically, the sections300,302,304each have different a different third-order susceptibility tensor such that each section corresponds to a different color (e.g., red, green, and blue). This allows for the display100to be a color display. The wavelength of light injected into the waveguides102may be adjusted to change the color of light emitted by a pixel, as explained in further detail below.

In some embodiments, a cladding layer306is positioned on either side of each of the waveguide102. In these embodiments, the cladding layer306has a refractive index that is lower than the refractive index of the nonlinear materials of the waveguides102such that light injected within a waveguide102remains within the waveguide102. In some examples, the cladding layer306comprises silica.

Referring back toFIG. 1, the display100comprises two sets of electrodes104,106positioned on either side of the waveguides102. An upper set of electrodes104are positioned above the waveguides102in the orientation ofFIG. 1and a lower set of electrodes106are positioned below the waveguides102in the orientation ofFIG. 1. The upper electrodes104extend parallel to the waveguides102(e.g., along the y-direction in the orientation ofFIG. 1) and the lower electrodes106extend perpendicular to the waveguides102(e.g., along the x-direction in the orientation ofFIG. 1). In other embodiments, the upper electrodes104may extend perpendicular to the waveguides102and the lower electrodes106may extend parallel to the waveguides102.

In the example ofFIG. 1, six upper electrodes104and six lower electrodes106are shown for purposes of illustration. However, it should be understood that the display100may comprise any number of upper and lower electrodes104,106. The number of upper electrodes104multiplied by the number of lower electrodes106corresponds to the number of pixels in the display100.

The upper electrodes104are positioned adjacent to each other along the width of the display100(along the x-direction in the orientation ofFIG. 1) and the lower electrodes106are positioned adjacent to each other along the length of the display100(along the y-direction in the orientation ofFIG. 1). The electrodes104,106are transparent to electromagnetic radiation in the visible spectrum such that a viewer can see through the electrodes104,106. In some embodiments, the electrodes104,106are comprised of indium tin oxide. In other embodiments, the electrodes104,106are comprised of conductive electronic polymeric films.

The upper electrodes104and the lower electrodes106form a grid pattern with the upper electrodes104corresponding to pixel rows and the lower electrodes106corresponding to columns of pixels. Each location where an upper electrode104crosses a lower electrode106corresponds to a single pixel. Thus, to turn on a particular pixel and emit light from that pixel, a voltage is applied to the appropriate upper electrode104and lower electrode106such that a potential difference is created across the waveguide102at the location of a selected pixel.

In some embodiments, the upper electrodes104and/or the lower electrodes106have a corrugated surface to induce scattering and guide light emissions from the display100, as explained in further detail below. In some embodiments, the corrugated surface of the electrodes104,106is a grating structure.

In operation, a pixel of the display100is turned on by injecting light into the appropriate waveguide102and simultaneously applying a voltage to the appropriate upper electrode104and lower electrode106to create a potential difference across the waveguide102at the appropriate pixel location. In some examples, light is continuously injected into and passed through each of the waveguides102. In other examples, light is only injected into a particular waveguide102when a pixel along that waveguide is to be turned on.

Referring toFIG. 4, light is injected into a waveguide102such that the light travels through the waveguide102along its length (e.g., in the y-direction in the orientation ofFIG. 4). In some embodiments, a mirror400is positioned at the end of the waveguide102opposite from the light source200such that light that is injected into the waveguide102reflects back through the waveguide102after is passes through the waveguide102.

When a voltage is applied to a selected upper electrode104and a selected lower electrode106, the potential difference between the upper electrode104and the lower electrode106creates a static electric field at the selected pixel location of the waveguide102. This static electric field interacts with the χ(3) nonlinear materials of the waveguide102to induce a χ(2) nonlinear response through a process known as electric-field induced second harmonic generation (EFISH). This induced χ(2) response causes the emission of light at double the frequency of the injected light. Specifically, as a static electric field is applied to the waveguide102, the normal component of the third order susceptibility tensor of the waveguide102is multiplied by the static field, as shown in the equation below. In thin film structures, a large electric field may be applied across the material with only a modest driving voltage.
I2ωα[[χ3EDC+χ2]Eω2]2

This induced frequency doubled light emission initially propagates in the same direction as the injected light. The induced light is coupled out of the waveguide102via the corrugated structure of the electrodes104,106in conjunction with the effective refractive index of the induced light. The corrugated structure of the electrodes104,106may be configured such that the induced light is emitted out of the display100in a direction transverse to the direction of travel of the injected light (e.g., orthogonal in the z-direction in the orientation ofFIG. 4). Thus, a viewer of the display100would see the selected pixel illuminate.

In some embodiments, the corrugated structure is on the external side of the electrodes104,106(i.e., the side of the electrodes104,106facing away from the waveguides102). This ensures that the corrugated structure of the electrodes104,106are not to close to the surface of the waveguides102, which may induce scattering loss from deferred light from the light source200. In some embodiments, a diffractive optical element may be used in addition to or instead of a corrugated structure for the electrodes104,106to cause the induced light to be emitted orthogonal to the direction of travel of the injected light signal.

To operate a color display100, the color of the emitted light may be selected by choosing an input light signal of an appropriate wavelength such that the interaction of the input light and the nonlinear materials produces an induced light signal at the desired wavelength. Because the nonlinear materials of the waveguide102produce a frequency doubled signal, the input light should have half the frequency (or twice the wavelength) of the desired output signal. In order to turn on more than one pixel at a time with different colors, the light from the light source200may be modulated such as with, for example, a digital light processing unit or an array of mirrors such as array204.

For example, in some embodiments, the three output colors are blue, with a wavelength between 450-495 nm, green, with a wavelength between 495-570 nm, and red, with a wavelength between 620-750 nm. Thus, the injected light from the light source200in this example would have a wavelength between 900-990 nm for a pixel to turn blue, between 990-1140 nm for a pixel to turn green, and between 1240-1500 nm for a pixel to turn red. The light from the light source200can modulate between these three wavelengths over time to change the pixel color such that the display100can operate with full color. Each section300,302,304of the waveguides102should comprise different nonlinear materials such that the input wavelengths are optimized (e.g., phase-matched) to the third order susceptibility of each section300,302,304of the waveguides102. In addition, multiple colors can be injected at the same time to create colors that are combinations of red, green, and/or blue. Alternatively, the display100may operate with a single color by always injecting the same color light into the waveguides102.

In the example ofFIG. 2B, the single light source202supplies light to each of the waveguides102through the mirrors204, which may be controlled by a light processing unit. As discussed above, the light processing unit may adjust the mirrors204such that light from the light source202is directed into one or more selected waveguides102at any given time. Thus, in the example ofFIG. 2B, it is not possible to input light at different wavelengths into one or more waveguides102at exactly the same time. Therefore, in order for the display100in the example ofFIG. 2Bto display an image at a particular time comprising more than one color, the wavelength of the light from the light source202may be modulated at a rate that is faster than the refresh rate of the human eye (e.g., 60 Hz).

For example, to display an image having a blue pixel in column4, row8of the display100and a red pixel in column4, row16of the display100, the light source202may output light having a wavelength to trigger a blue pixel (e.g., a wavelength between 900-990 nm) at a first time t1. Also at time t1, the light processing unit may adjust the array of mirrors204such that the light from the light source202is transmitted through the waveguide102at column4and a voltage may be applied across the electrodes104,106at row8. This will cause the display100to emit a blue pixel at column4, row8at a time t1.

Then, at a subsequent time t2, which may be after time t1by an amount less than the refresh rate of the human eye, the light source202may output light having a wavelength to trigger a red pixel (e.g., a wavelength between 1240-1500 nm). Also at time t2, the light processing unit may adjust the array of mirrors204(or maintain their position in this example) such that the light from the light source202is transmitted through the waveguide102at column4and a voltage may be applied across the electrodes104,106at row16. This will cause the display100to emit a red pixel at column4, row16at a time t2. Because the difference between the times t1and t2is within the refresh rate of the human eye, when the display100is viewed, it will appear to the viewer that the blue pixel at column4, row8and the red pixel at column4, row16are illuminated at the same time.

Because each section300,302,304of the waveguides102is phase-matched only to one input wavelength, when light having a particular wavelength is injected into a waveguide102, only the section to which it is phase-matched to that wavelength will induce a nonlinear signal. Thus, only one color at a time will be output by the display100at each pixel. Furthermore, because the input light from the light source200for each of the three sections300,302,304of the waveguides102is infrared light, as discussed above, this light is not visible to viewers of the display100should it leak out of the waveguides102. Only the frequency doubled induced light having wavelengths in the visible range of the electromagnetic spectrum will be visible to viewers. In some embodiments, one or more dichroic filters may be positioned on the surface of the waveguides102to reflect the injected infrared light.

The intensity of light emitted by a particular pixel of the display100may be modulated by adjusting the voltage potential applied to either the upper electrode104or the lower electrode106for a particular pixel, thereby increasing or decreasing the potential difference across the waveguide. To emit light at particular colors from each pixel of the display100, a number of pixels may be illuminated within the period of the refresh rate of the human eye. Viewers will not notice changes that happen within this refresh rate period. Instead, viewers will witness all pixels illuminated within a single refresh rate of the eye as though they were all illuminated at the same instant.

FIG. 5shows another embodiment of a transparent display500. The display500comprises a plurality of polymer fiber optic waveguides502and a plurality of electrically conductive, flexible electrodes504,506arranged in pairs. Thus, the display500may be a flexible fabric display integrated into furniture, vehicle seats, clothing, or other fabrics. In the example ofFIG. 5, three waveguides502are shown along with two electrodes504and two electrodes506for illustrative purposes. However, it should be understood that the display500may comprise any number of waveguides and electrodes.

Referring toFIG. 5, the fiber optic waveguides502comprise polymer fiber optic nonlinear materials with a high third order susceptibility, similar to the waveguides102ofFIGS. 1-4. In some embodiments, the polymer fiber optical components of the waveguides502are rigid. In other embodiments, fiber optic cables may be created from flexible polymeric materials. During operation, correlated, phase-matched light is injected into one or more waveguides502in a similar manner as discussed above in connection with the display100. Each of the waveguides502may comprise three sections with each section optimized to a different input light wavelength, similar to the sections300,302,304of the waveguides102. Thus, the wavelength of light injected into the waveguides502determines the color emitted by the waveguides502.

The flexible electrodes504,506are interwoven around the waveguides502. That is, the electrodes504,506are positioned above one waveguide502and below the two adjacent waveguides502in an alternating weaving pattern. The electrodes504,506of each pair of electrodes are positioned adjacent to each other and are weaved around the waveguides502in a complimentary manner. That is, the electrode504of a pair of electrodes is positioned above a particular waveguide502while the electrode506of the electrode pair is positioned below the same waveguide502. The electrode504is then positioned below an adjacent waveguide502while the adjacent electrode506is positioned above that waveguide502. In this manner, the electrodes504,506create a grid of pixels for the display500.

In operation, light at an appropriate wavelength may be injected into one or more flexible waveguides502while a voltage is applied to appropriate electrodes504,506. This causes the display500to emit light of particular colors at selected pixel locations in a similar manner as discussed above in connection with the display100ofFIGS. 1-4.

FIG. 6Ashows another embodiment of a transparent display600. The display600is similar to the display100ofFIG. 1, except that instead of the plurality of waveguides102of display100, the display600ofFIG. 6Acomprises a single sheet of glass602that operates as a waveguide. In some embodiments, the waveguide602may comprise an automobile windshield. The display600may comprise transparent electrodes104,106overlaid on either side of the glass waveguide602in a similar manner as with the display100.

In the example ofFIG. 6A, the entire sheet of glass602has nonlinear properties. Light is injected and guided within the glass602. Because the display600comprises just a single waveguide602, light should remain parallel to the glass602in order to be phase-matched to the nonlinear materials of the waveguide602. In some embodiments, grooves604may be created in the glass602, as shown inFIG. 6B, wherein the grooves604have a different refractive index than the glass602. The refractive index of the grooves604can be chosen such that light injected within a groove604stays within that groove604by the process of total internal reflection. In this manner, each groove604acts as a channel or individual waveguide within the glass602, wherein the pixels of the display600comprise points along the grooves604where the electrodes104,106cross over each other.

The display600may operate in a similar manner as the display100where pixels are turned on by injecting light at particular wavelengths into particular grooves604of the glass602and creating a potential difference across the electrodes104,106at particular pixel locations to emit light from the pixels with certain colors. In this manner, the display600can be embedded within, for example, a window or windshield of a vehicle.

It is noted that the terms “substantially” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. It is noted that the terms “upper” and “lower” are utilized herein for convenience of illustration but these terms do not mean an intended direction.