Optical waveguides – Optical imaging tunnel
Reexamination Certificate
2002-03-19
2004-08-03
Healy, Brian (Department: 2874)
Optical waveguides
Optical imaging tunnel
C385S146000, C385S901000, C362S257000, C362S297000, C362S298000, C362S317000, C362S346000, C362S559000, C362S560000
Reexamination Certificate
active
06771870
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to components and the method of manufacturing of hollow reflective tubes, and specifically relates to reflective tubes used as integrators and/or angle converters for illumination systems.
BACKGROUND OF THE INVENTION
Some optical illumination systems benefit from the use of a spatial and/or an angular beam reformatting element to reformat the spatially dependent and/or the angular dependent intensity distribution of a light beam. For example, U.S. Pat. No. 5,625,738 to Magarill describes the use of a straight or symmetrically tapered, hollow, light transmitting tunnel with a rectangular input and output cross sectional shape as an optical element to increase the spatially dependent illumination uniformity of a light valve in a projection display system. European Pat. No. 00734183/EO B1, to Chiu et al. notes that “typical illumination schemes usually produce non-uniform illumination on the light valves resulting in poor intensity uniformity . . . ” and teaches a light tunnel comprised of four mirrors assembled to form a hollow rectangular tunnel. U.S. Pat. No. 5,842,767 Rizkin et al. describes another use of a symmetrically tapered hollow cone as an angle converter element to increase the coupling efficiency of an elliptical reflector lamp to a large, round fiber optic bundle input area. While these and other patents describe the use of hollow reflective tubes as integrators and/or angle converters, they don't describe, in general, a preferred manufacturing method.
The present invention is related to U.S. Pat. No. 6,356,700 of one of the authors of this invention (Strobl) which utilizes, among other things, asymmetrically stretched, hollow anamorphic reflective tubes as integrators and/or angle converter elements to increase the delivery efficiency of an etendue efficient Minimal Light Engine (lamp reflector module) having an asymmetric angular dependent energy distribution in its exit beam that is optically coupled to a light valve or fiber optic light guide. With the emerging large volume market for light valve containing projection display systems for the home entertainment market, there is a need to be able to produce a wide variety of differently shaped, highly reflective rectangular tubes in high volume and at low cost, for use as integrators and angle converters.
When hollow rectangular tubes are manufactured for light beam integrator and/or angle converter applications, the usual prior art method is (1) to manufacture a large sheet of mirror-surfaced material (reflective material), and then (2) to cut or break the reflective material into four suitably sized rectangular sub-components, (3) to assemble these sub-components into a rectangular shaped tube and (4) to glue the four assembled sub-components together to form a permanent and rigid reflective rectangular tube. When a focused light beam is transmitted through such a device, repeated multiple light reflections cause an integration (beam homogenization) of the spatially dependent light intensity distribution. When the four sub-components are assembled in a non-parallel manner, for example as 1-dimensional or as a 2-dimensional rectangular taper, the angular dependent intensity distribution of the incoming focused beam gets modified. In this case, the reflective tube has, beside a spatial beam intensity integration function, also an angle converter function.
The process of cutting or breaking the reflective sheets into the respective rectangular sub-components and their subsequent assembly into a rectangular tube leads to small edge defects (chips) and/or small areas of separation or cracks between the coating and the substrate. In time, these fault areas can lead to a degradation of significant usable area of the reflective coating surface, resulting in parallel in a significant reduction in transmission performance. The transmission efficiency of such a manufactured reflective tube is further reduced by the size of the total area of the gaps and edge imperfections in the four corners between the four assembled neighboring sub-components. This transmission defect is caused by the above-described traditional sub-component manufacturing process. Additionally, this prior art manufacturing process allows economically viable high volume production of rectangular tubes only with a dimensional tolerance of about 100 &mgr;m. While this is only a small dimensional uncertainty, it can lead to significant effective transmission losses for very small rectangular integrators. This is in particular important because the overall shortest dimension of a typical integrator for projection display application is already in the range of 4-5 millimeters. The OEM projection display market anticipates that in the near future, when smaller and lower cost light valves become commercially viable for rear projection display systems, the integrator dimensions will shrink proportionally, thus leading to even higher effective transmission losses.
In addition, inside a projection display light engine, the temperature of such hollow reflective tubes is often elevated. Higher efficiency projection illumination technologies are coming to the market in the coming years. These technologies increase the energy density inside such reflective hollow tubes even further. Since there is always some absorption loss even with the best reflective coatings, this increased energy density loading causes a higher head load on the reflective hollow tube components and materials. This increased head load, if not properly managed can lead to a new long term product defect, where the glue holding the four sub-assemblies together becomes mechanically unstable with time, and the performance of the respective projection device is compromised.
Thus, in order to make mass producible, low cost and high performance, small hollow reflective rectangular tubes possible, a new manufacturing method is needed, that, while still suitable for large-scale production, does not suffer from at least some of the above outlined deficiencies.
Traditionally a thin film Ag (silver) over-coating produces the highest substrate reflectivity enhancement in the visible spectral range over a broad range of incident angles. However, the reflectivity of Ag in the visible spectral range has a poor environmentally dependent performance. This is (1) mainly due to its softness, which can lead easily to coating damage during handling, (2) due to its low temperature stability limit (Ag re-crystallization effects cause a surface roughness increase and reflectivity loss above 100 deg C.), and (3) due to the fact that it corrodes readily if it is exposed to air without protection (sulfur binds with Ag and reduces its reflectivity dramatically), i.e. it's reflectivity in the blue spectral region drops quickly. For these reasons, it is desirable to overcoat Ag with at least one barrier layer. Such a barrier layer must be cohesive to avoid pits, where corrosion of the Ag could begin, and must be hard, to prevent physical damage to the Ag.
U.S. Patent No. 6,128,126, to Hohenegger et al. (Hohenegger I) teaches that while various metal oxide coatings may be used for their hardness and resistance to environmental contaminants, the oxide layer can “cause a degradation of the silver”. Hohenegger I mentions various methods to overcome this, such as first covering the Ag layer with further metallic layers to form a barrier between the Ag and the oxide. However, Hohenegger I teaches away from the use of metal oxides and in particular from TiO
2
layers stating “The solutions attempted in the prior art described above, which suggest packing the Ag containing layer with a metal or a hypostoichiometric oxide layer, fail since as a rule these do not meet the optical specification in any case, at least not with very high reflection values in the visible spectral range at 0-45 deg incident angles.” U.S. Pat. Nos. 5,751,474 and 5,548,440 to Hohenegger et al. (Hohenegger II and III) while utilizing Ag for the mirror and silicon dioxide and titanium in the barri
Gasteiger Paul
Strobl Karlheinz
eele Laboratories
Healy Brian
Lillie James J.
Lillie Law LLC
Petkovsek Daniel
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