Patent Application
20070242352
Illustrated in
The polarizing device 10 can include a substrate 28, which may have its own optical function. The substrate 28, for example, could be a quarter wave-plate (as described in JP2005-195824A, which is incorporated by reference) in addition to being a substrate. The substrate 28 can be transparent to the electromagnetic waves of electromagnetic radiation (e.g., visible light) so that the electromagnetic waves of electromagnetic radiation (e.g., visible light) can be transmitted by, or pass through, the substrate. Thus, the substrate 28 can have an optical property of transmitting the electromagnetic waves of electromagnetic radiation (e.g., visible light). In one aspect, the substrate 28 can transmit the electromagnetic waves of electromagnetic radiation without otherwise altering it, such as, without changing the phase, angle, etc. The substrate 28 can include, or be formed by, a glass material or a polymeric material. It will be appreciated that other materials, such as quartz, etc. can be used. Suitable polymeric materials include, but are not limited to, polymethylmethacrylate (PMMA), polycarbonate (PC), polystyrene (PS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), diethylene glycol bis carbonate (CR-39), styrene/acrylonitrile copolymer (SAN), styrene/methacrylic acid copolymer (MS), alicyclic acrylic resin and alicyclic polyolefin resin.
In addition, the polarizing device 10 can include an array of a plurality of spaced-apart, elongated elements 32. The elements 32 can be both reflective to light and electrically conductive, and can be disposed on or supported by a surface of the substrate 28. The elements 32 can be formed from a conductive material. For example, the elements can include, but are not limited to metals, such as aluminum, chromium or silver, as well as various conducting polymers (provided the conducting polymers are reflective to light of the type the polarizing device is polarizing, e.g., visible light for use in visible displays). It will be appreciated that other structures, materials, or layers can be disposed between the elements 32 and the substrate 28, including for example, ribs, gaps, grooves, layers, films, etc. In addition, a region can be formed between the elements and the substrate with a low refractive index (or a refractive index lower than a refractive index of the substrate), and a controlled thickness. The low index region separating the elements from the substrate can shift the longest wavelength resonance point to a shorter wavelength, and can reduce the fraction of P polarized electromagnetic waves or light that is reflected from the polarizer. Spaces between adjacent elements 32 can be occupied by air, substrate material, or some other material.
The elements 32 are relatively long and thin. All or most of the elements 32 can have a length that is generally larger than the wavelength of the desired electromagnetic waves (e.g., electromagnetic waves of visible light). Thus, the elements 32 have a length of at least approximately 0.7 μm (micrometer or micron) for visible light applications. The typical length, however, may be much larger. The length of the elements 32 do not have to span the length of the substrate 28 as shown in
Having the elements 32 be comprised of two or more layers in this invention is advantageous in alleviating or overcoming refractive index mismatch(es) between or among layer(s). As one example, there is a refractive index mismatch when elements 32 are aluminum and layer 24 is chromium oxide. This mismatch can be substantially corrected by having the elements 32 be two layers—one of aluminum and one of chromium, such that the chromium layer of elements 32 is sandwiched between the aluminum layer of elements 32 and the chromium oxide layer 24 in the polarizing device 10.
In addition, the elements 32 are located in generally parallel arrangement with a spacing, pitch, or period P of the elements being smaller than the wavelength of the desired electromagnetic waves of electromagnetic radiation (e.g., visible light). Thus, the elements 32 have a pitch P of less than 0.4 μm (micrometer or micron) for visible light applications. In one aspect, the pitch P can be approximately one-half the wavelength of light, or approximately 0.15-0.2 μm for visible light applications where the shortest wavelength of the visible light is approximately 370 nm. In one embodiment, the pitch P is 0.15 μm. The elements 32 also can have a width w less than the period P, or less than 0.4 μm or 0.2 μm for visible light applications. In one aspect, the width can be less than 0.1-0.2 μm for visible light applications. It should be noted that arrays with longer periods (greater than approximately twice the wavelength of light or 1.4 μm) can operate as diffraction gratings, while arrays with shorter periods (less than approximately half the wavelength of light or 0.2 μm) operate as polarizers, while arrays with periods in a transition region (between approximately 0.2 and 1.4 μm) also act as diffraction gratings and are characterized by abrupt changes or anomalies referred to as resonances. Thus, it will be appreciated that the actual size of the elements 32 is quite small, and the array of elements 32 can actually appear as a continuous, reflective surface to the unaided eye. As shown in the figures, however, the array of elements 32 actually creates a very small structure, or nano-structure with a size or scale on the order of 10−8 meters.
In addition, the size and configuration of the array of elements 32 is designed to interact with the electromagnetic waves of electromagnetic radiation (e.g., visible light to generally transmit electromagnetic waves of one polarization, and generally reflect electromagnetic waves of another polarization. As stated above, a beam 12 can be incident on the polarizer device 10. The polarizer device 10 can divide the beam 12 into a reflected component 40, and a non-diffracted, transmitted component 44. Using the normal definitions for S and P polarization, the electromagnetic wave or light with S polarization has the polarization vector orthogonal to the plane of incidence, and thus parallel to the conductive elements. Conversely, the electromagnetic wave or light with P polarization has the polarization vector parallel to the plane of incidence and thus orthogonal to the conductive elements.
In general, the polarizer device 10 can reflect waves of electromagnetic radiation (e.g. visible light) with their electric field vectors parallel to the elements 32 (or the S polarization), and transmit waves of electromagnetic radiation (e.g., visible light) with their electric field vectors perpendicular to the elements (or the P polarization). Ideally, the polarizer device can function as a perfect mirror for one polarization of electromagnetic radiation, such as the S polarized light, and can be perfectly transparent for the other polarization, such as the P polarized light. In practice, however, even the most reflective metals used as mirrors absorb some fraction of the incident light and reflect only 90% to 95%, and neither typical polymeric materials nor plain glass transmits 100% of the incident light due to surface reflections.
A key aspect of the present invention is that there is a layer 24 (having an outer surface 25) comprised of material having low reflectivity present on the elements 32 that imparts low reflectivity characteristics to the polarizer device with respect to incident electromagnetic radiation as shown in
There are two principal ways to achieve low reflection on the surface of a highly reflective metal that are useful in obtaining the layer 24 according to the invention. One is by using a light absorbing material on the surface and the other is using interferometric means. Light absorbing materials (e.g., black paint or carbon black) can be employed using processes (e.g., evaporation or sputtering) that leave one or more sides of the WGP elements 32 uncoated with these materials or using a coating/patterning/etching process to selectively apply these materials to desired surfaces of the WGP elements 32. The second way is interferimetrically. In this way, again the process to apply can be the same as described above except that the material is specifically suited for evaporative deposition and can be applied in any WGP fabrication technique. These materials are generally transparent to visible wavelengths. What is important is that the thickness and refractive index must be paired (not matched) with the reflective metal to form the light absorbing function. In this case, it is important to remember that, although metals are highly reflective, they are also perfect absorbers. The thickness and index will eliminate reflection in the same way that an antireflective (AR) coating works, which entails destructive interference in a back direction or at an interface where reflection is not desired.
The thickness of the layer 24 can be in the range from about 300 angstroms to about 700 angstroms. In one embodiment, the thickness of the layer 24 is the range from about 500 angstroms to about 600 angstroms using chromium oxide (having refractive index n of 2.25) as the layer 24 material for application in WGPs for visible displays operating with 500-600 nm visible light. If the thickness is less than about 300 angstroms, the layer is too thin to afford suitably low reflectivity characteristics at its surface. If the thickness is greater than about 700 angstroms, the layer is too thick such that it imparts deleterious optical characteristics to the polarizer. In one embodiment, the layer 24 is comprised of a monlayer of material that is characterized to be of low reflectivity and to be non-birefringent.
For certain materials having suitable properties, layer 24 can be a continuous layer across the surface of the substrate. For example, when layer 24 is chromium oxide (Cr2O3), this layer can be continuous for most display applications since chromium oxide is approximately 90% transmissive to visible light at ¼ wave optical thickness. An example of a material where layer 24 cannot be continuous is black paint, which would essentially absorb most or all light.
As shown in
In addition, the layer 24 advantageously is chemically bonded to, or reacts with, the elements 32, or to a natural oxide layer 48 on the elements, so that the layer covers some exposed surfaces of the elements (the exposed surfaces being those not contacting the substrate). It is believed that the chemical bond of the layer 24 to the elements 32 permits the layer to be relatively thin, and contributes to the layer's ability to resist corrosion. Again, the chemical bond formed only with the elements 32 is believed to be another reason why the layer 24 does not affect the optical properties of the polarizer device 10 for the embodiments illustrated in
In one embodiment of a polarizing device (e.g., wire grid polarizer) according to the invention, elements 32 are made to contain a layer 24 of low reflectivity material opposite the substrate side of the elements 32 and then all three exposed sides (3 sides not including the substrate side) are coated with a secondary coating to protect the elements 32 against corrosion and other adverse effects. Suitable secondary coatings include, but are not limited to, a polymer coating (e.g, polyethylene terephthalate) or a coating of pressure-sensitive adhesive (PSA).
The polarizing devices (e.g., wire-grid polarizers) of this invention are useful in transmissive displays and afford both high contrast and brightness for the displays in comparison to prior art displays when operated at comparable power levels. The wire-grid polarizers (WGPs) of this invention act as recycling polarizers in that they both polarize light that is incident upon them and recycle light back toward the light guide that is of the wrong polarity to be transmitted through the WGPs. Consequently, the transmissive displays of this invention can utilize and contain a single WGP that replaces one or the other or both of a conventional recycling polarizer (e.g., dual brightness enhancement film from 3M) and the rear polarizer of a conventional LCD display.
In yet another embodiment of a display according to the invention, a polarizing element (e.g., wire-grid polarizer) is assembled directly on a side of a light guide that will be the front side in a transmissive display. In this embodiment, there is no substrate layer(s). This polarizing elements can serve to function both as a recycling polarizer and a rear polarizer and does not have a substrate layer. Hence it can have two fewer layers in relation to a conventional transmissive display that has both a recycling polarizer and a rear polarizer.
In one embodiment, a transmissive display of the invention is one having a polarizer device (e.g., wire grid polarizer) in direct contact with a liquid crystal display cell, which contact serves to protect the elements of the polarizer device from corrosion. As one specific case of this embodiment, the polarizer device can be laminated to the LCD cell to afford the transmissive display.
In a related embodiment, a polarizer device (e.g., wire grid polarizer) is placed inside of a liquid crystal display cell.
This sample was made by spin-coating a mixture of one-third Microposit® Type P Thinner (Rohm and Haas Electronic Materials, LLC, Marlborough, Mass.) and two-third Microposit® S1805 Positive Photoresist (Rohm and Haas Electronic Materials, LLC, Marlborough, Mass.) onto a 152 mm×100 mm×2 mm thick piece of soda-lime glass for 30 seconds at 3500 RPM. The plate was then dried on a hotplate at 100° C. for 15 minutes. The plate was placed into a Lloyd's mirror set-up at 56° incident. The plate was exposed using the 364.8 nm line from a Coherent Argon Sabre Laser (Coherent, Inc., Santa Clara, Calif.) for 30 seconds to form an interference sinusoidal interference pattern with a period of 220 nm peak to peak. The sample was then developed in a mixture of 4 parts deionized water and one part Microposit® 351 Developer (Rohm and Haas Electronic Materials, LLC, Marlborough, Mass.) for 20 seconds, rinsed with deionized water for 10 seconds, and dried with forced air. The developed plate was then exposed to 254 nm UV light (UVP, Upland, Calif.) for one hour and placed in a 110° C. oven overnight. The plate was placed into a Denton e-gun Evaporator (Denton Vacuum, Moorestown, N.J.) on a hanger making a 56° angle with the source whereby 800 angstroms of chromium followed by 500 angstroms of chromium oxide were deposited onto the exposed edge of the sinusoidal pattern. The sample was measured for transmission, reflection, and color with a HunterLab UltraScan XE (HunterLab, Reston, Va.). The sample was then measured in transmission parallel and crossed with an identical sample made at the same time with the same process conditions. The data was then used to calculate polarization efficiency and extinction ratio for the WGP on glass that was produced. The results are detailed in Table 1. As shown in Table, this WGP on glass exhibited high polarization efficiency and low back reflection characteristics. As the results in Table 1 indicate, back reflection (both total and specular) for the inventive sample of Example 1 is comparable with that for an incumbent dichroic polarizer (i.e., the Nitto polarizer) and much better than the back reflection for a prior art wire grid polarizer (Moxtek) or for DBEF (dual brightness enhancement film from 3M).
This sample was made by spin-coating a mixture of one-third Microposit® Type P Thinner (Rohm and Haas Electronic Materials, LLC, Marlborough, Mass.) and two-third Microposit® S1805 Positive Photoresist (Rohm and Haas Electronic Materials, LLC, Marlborough, Mass.) onto a piece of 200 gauge Melinex® 455 polyethylene terephthalate (PET, DuPont Teijin Films, Hopewell, Va.) taped on all four sides down to a 152 mm×100 mm×2 mm thick piece of soda-lime glass for 30 seconds at 3500 RPM. The plate was then dried on a hotplate at 100° C. for 15 minutes. The plate was placed into a Lloyd's mirror set-up at 56° incident. The plate was exposed using the 364.8 nm line from a Coherent Argon Sabre Laser (Coherent, Inc., Santa Clara, Calif.) for 30 seconds to form an interference sinusoidal interference pattern with a period of 220 nm peak to peak. The sample was then developed in a mixture of 4 parts deionized water and one part Microposit® 351 Developer (Rohm and Haas Electronic Materials, LLC, Marlborough, Mass.) for 20 seconds, rinsed with deionized water for 10 seconds, and dried with forced air. The developed plate was then exposed to 254 nm UV light (UVP, Upland, Calif.) for one hour and placed in a 110° C. oven overnight. The plate was placed into a Denton e-gun Evaporator (Denton Vacuum, Moorestown, N.J.) on a hanger making a 56° angle with the source whereby 800 angstroms of chromium followed by 500 angstroms of chromium oxide were deposited onto the exposed edge of the sinusoidal pattern. The sample was removed from the glass and measured for transmission, reflection, and color with a HunterLab UltraScan XE (HunterLab, Reston, Va.) with light incident on the Melinex® side of the sample. The sample was then measured in transmission parallel and crossed with an identical sample made at the same time with the same process conditions but held with the pattern sides to one another. The data was then used to calculate polarization efficiency and extinction ratio for the WGP on PET that was produced. The results are detailed in Table 1. As shown in Table 1, this WGP on PET exhibited high polarization efficiency and low back reflection characteristics. As the results in Table 1 indicate, back reflection (both total and specular) for the inventive sample of Example 2 is comparable with that for an incumbent dichroic polarizer (i.e., the Nitto polarizer) and much better than the back reflection for a prior art wire grid polarizer (Moxtek) or for DBEF (dual brightness enhancement film from 3M).
The columns in Table 1 are labeled for the above-described patent examples as well as
3M's DBEF purchased from 3M (St. Paul, Minn.), a commercial Moxtek wire-grid polarizer purchased from Edmund Scientific (Barrington, N.J.), and a Nitto NPF polarizer purchased from Nitto Denko (Shatin, N.T., Hong Kong).
Tvis(single) is a total transmission measurement across the visible spectrum of a single polarizer and is reported as a percentage of incident. Tvis(parallel) is a total transmission measurement across the visible spectrum of two like polarizers whose polarization axes are parallel and is reported as a percentage of incident on the first. Tvis(crossed) is a total transmission measurement across the visible spectrum of two like polarizers whose polarization axes are orthogonal (90°) and is reported as a percentage of incident on the first.
The efficiency ratio is the square root of ([Tvis(parallel)−Tvis(crossed)]/[Tvis(parallel)+Tvis(crossed)]) and reported as percentage. The extension ratio is the ratio of Tvis(single) to Tvis(crossed) and rounded to the nearest whole number.
CIE 1976 L a* b* is a three-dimensional color space defining lightness (L), a blue to yellow hue (a*), and a red to green hue. The value of lightness, L, ranges from 0 to 100 with a value of 100 defining white and a value of 0 defining black. The hues tending yellow to blue, a*, are on a scale of −100 to +100 with saturated yellow having a value of +100 and saturated blue having a value of −100 for the a* value. The hues tending red to green, b*, are on a scale of −100 to +100 with saturated red having a value of +100 and saturated green having a value of −100 for the b* value.
Back reflection is a measurement of reflected visible light from the front surface of the sample. The total back reflection is the percentage of incident light reflected from the front surface into any direction. The specular reflection is the percentage of incident light reflected from the front surface reflected in the specular direction which is the direction of equal but negative angular direction as the incident light, θ(specular)=−θ(incident).
| Number | Date | Country | |
|---|---|---|---|
| 60791816 | Apr 2006 | US |
