Glass manufacturing – Processes – Sol-gel or liquid phase route utilized
Reexamination Certificate
1997-07-29
2002-09-10
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
Sol-gel or liquid phase route utilized
C065S395000, C359S599000, C359S707000, C423S338000
Reexamination Certificate
active
06446467
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to holographic Light Shaping Diffusers® (LSDs)® and, more particularly relates to an LSD formed from a monolithic glass material and to a method of forming a monolithic glass LSD.
2. Background of the Invention
Holographic Light Shaping Diffusers® (LSDs)®, sometimes known as light shaping homogenizers or simply diffusers, are a type of diffuser used in a variety of illuminating, imaging, and light projecting applications. An LSD is a transparent or translucent structure having an entrance surface, an exit surface, and light shaping structures formed on its entrance surface and/or in its interior. These light shaping structures, sometimes collectively known as speckle (particularly when they are present within the volume of the structure as opposed to only on its surface), are random, disordered, and non-planar microsculpted structures that act as miniature lenses which produce non-discontinuous and smoothly varying changes in the refractive index of the LSD medium. They often are akin in appearance to sponges distributed randomly through the product. These light shaping structures refract light passing through the LSD so that the beam of light emitted from the LSD's exit surface exhibits a precisely controlled energy distribution along horizontal and vertical axes. LSDs can be used to shape a light beam so that over 90% (and up to 95%-98%) of the light beam entering the LSD is directed towards and into contact with a target located downstream of the LSD. An LSD can be made to collect incoming light and either 1) distribute it over a circular area from a fraction of a degree to over 100° or 2) send it into an almost unlimited range of elliptical angles. For example, a 0.2°×50° LSD will produce a line when illuminated by an LED or laser and a 35°×90° LSD will form a narrow field, high resolution rear projection screen when illuminated by the same light source.
Rather than exploiting a property of monochromatic laser light known as coherence that requires that the finished holographic element be used only at the laser's wavelength, an LSD operates perfectly in white light. LSDs therefore exhibit a high degree of versatility because they may be employed with light from almost any source, including LEDs, daylight, a tungsten halogen lamp, or an arc lamp.
Two types of LSDs are currently available, namely a “volume LSD” and a “surface LSD”. A surface LSD is a surface relief holographic element characterized by the incorporation of light shaping structures (or a computer generated approximation of them) on its surface. A volume LSD is a volumetric holographic element characterized by the incorporation of light shaping structures (or a computer generated approximation of them) within its body and possibly also on its surface. Volume LSDs and surface LSDs are interchangeable in most applications. There are some limited applications, however, in which only volume LSDs can be used, such as applications in which the LSD is submerged in a liquid.
Both volume and surface LSDs typically are produced using a “sub-master” that is itself an LSD which contains the holographic surface structures forming the light shaping structures. In the case of a volume LSD, the light shaping structures are recorded in the product structure using standard holographic recording techniques (one or two beam) or a process akin to a printing process. In the case of a surface LSD, the surface structures are embossed or formed in some other way directly onto the surface of the product structure. LSD production using a light shaping structure-bearing master or sub-master is disclosed in U.S. Pat. No. 5,365,354 to Jannson et al. (the '354 patent), U.S. Pat. No. 5,609,939 to Petersen et al. (the '939 patent), and U.S. Pat. No. 5,534,386 to Petersen et al. (the '386 patent). The '354 patent, the '386 patent, and the '939 patent hereby are incorporated by reference for their disclosure of the production of an LSD.
LSDs heretofore were formed solely from plastics such as acrylic or polycarbonate plastics because only these materials were sufficiently deformable (under conditions suitable for interaction with a sub-master) to accept the light shaping structures. Limitations resulting from the physical properties of these plastics restrict the applicable range of LSD operation.
For instance, the plastics from which LSDs are formed typically have a glass transition temperature of below about 150° C. and often below about 100° C. Conventional plastic LSDs therefore cannot be used in applications in which the LSD may be subjected to sufficient heat to raise the temperature of the LSD to above this glass transition temperature. This heat may be received directly from a light source such as an arc lamp or may be absorbed in the form of UV or infrared radiation. Plastic LSDs therefore generally cannot be used in heat lamps, liquid crystal display projectors, projector lamps, track lighting, or other light sources that generate significant heat near the location of the LSD. Plastic LSDs also are not widely usable with light sources operating in the ultraviolet range or infrared range which emit radiation that is absorbed by the plastic.
Conventional plastic LSDs also are not useable with many UV light sources for the additional reason that the plastic material is a poor transmitter of UV radiation. The typical plastic LSD transmits only about 75% of incoming light of a 365 nm wavelength. Transmission efficiency drops to below about 50% when the incoming light has a wavelength of 350 nm, rendering conventional plastic LSDs ill-suited for use with light sources of less than about 400 nm and effectively useless for light sources of less than about 350 nm. This is a serious limitation of conventional plastic LSDs because many widely-used light sources operate in the UV range, including a mercury laser (365 nm), a triple band laser (355 nm), and a number of excimer lasers (approximately 270 nm).
Another limitation of plastic LSDs is that they cannot be subject to a hot coating operation. It is often desirable to coat a diffuser with a layer of an anti-reflective (AR) coating in order to raise the efficiency of the diffuser. Many coatings, including many AR coatings, can be applied only at temperatures above the glass transition temperature of plastics commonly used in LSDs. Conventional LSDs are not usable with these coatings.
Yet another problem associated with a conventional plastic LSD is that it is difficult or impossible to form a high quality three-dimensional lens on its exit surface. It is desirable in a variety of diffuser applications to place a lens on the exit surface of the diffuser. Conventional plastic LSDs cannot be ground, polished, or molded into high quality lenses. High quality lenses can be produced on the exit surface of an LSD only by laminating or otherwise attaching a Fresnel lens on it. (As is well known in the art, a Fresnel lens is one having a planar or two-dimensional surface that in use creates an effect that is designed to approximate the effect of a three-dimensional curved lens.) Mounting a separate Fresnel lens onto the exit surface of a diffuser is substantially more difficult and expensive than simply grinding or otherwise forming a conventional curved lens on the exit surface and may produce a lower quality lens.
Many of the above-identified disadvantages of a plastic LSD could be avoided if the LSD were to be formed from glass rather than a plastic. However, light shaping structures cannot be embossed on or otherwise recorded in a conventional glass structure during its production process because the high temperatures accompanying formation of conventional glass (on the order of 1,800° C.) would destroy the master or sub-master bearing the light shaping structures.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore a principle object of the invention to provide an LSD that has a wider operating range in terms of temperature and/or wavelength than currently available plas
Lieberman Robert A.
Mendoza Edgar A.
Mintzer David
Nilles & Nilles S.C.
Physical Optics Corporation
Vincent Sean
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