Patent Description:
A light tunnel comprises a tube with reflective inner surface. In an optical design in which a light tunnel connects a light source with downstream optical components, the light tunnel serves as an optical integrator rod to homogenize the light. For example, in a projection display device, a projector lamp may be focused onto the input aperture of a light tunnel, and the light exiting the output aperture of the light tunnel is thereby made more uniform over the area of the output aperture. A light tunnel is largely etendue-preserving - accordingly, the divergence characteristics of the light output at the exit aperture can be designed by way of a suitable taper in the light tunnel. A light tunnel can provide additional or other benefits, such as providing an enclosed optical pathway for connecting a hot incandescent lamp with heat-sensitive downstream optics. A light tunnel can also be used to shape the light - for example, in a projector system for a pixelated display device a light tunnel with rectangular cross-section provides a rectangular light source at the output aperture that can be designed to match a rectangular Digital Micromirror Device (DMD), pixelated LCD display device, or the like.

Light tunnels rely upon strong interaction between the light and the reflective inside surfaces of the light tunnel to provide an optical integrator (light mixing) effect. In geometric light ray modeling this amounts to multiple reflections (on average) of light rays passing through the light tunnel. Consequently, for high optical efficiency the inside surfaces of the light tunnel should have very high reflectivity. If there are (on average) N reflections and the surfaces have reflectivity r then the output is rN and losses are (<NUM>-rN). For example, if r=<NUM>% and there are on average N=<NUM> reflections, the optical loss is (<NUM>-<NUM><NUM>)=<NUM>% loss. If reflectivity is increased to r=<NUM>% this decreases to <NUM>% loss, and at r=<NUM>% the loss is down to <NUM>%. In one approach for manufacturing a light tunnel with rectangular cross-section having high optical efficiency, four glass plates with high reflectivity coatings are arranged end-to-end with each plate at <NUM>° orientation to the adjacent plate, and with the high-reflectivity coatings forming the inside surfaces of the light tunnel. A mandrill may be used to temporarily hold the four glass plates while their adjacent ends are glued or otherwise secured.

Some improvements are disclosed herein. <CIT> discloses a method of fabricating a light tunnel comprising a first element having a first reflective flat surface, a second element having a second reflective flat surface, and two flat spacer plates each having a reflective sidewall. Especially, this document discloses an internally-mirrored tube of constant cross-section, for use as a beam-shaper-uniformizer in an optical lithography tool, requires precision assembly, closely approaching total internal reflection, to be able to accept at the entry end a beam of laser light of specified numerical aperture, having an arbitrary cross-section and a nonuniform intensity profile, and deliver at the exit a beam having the same numerical aperture, the desired cross-sectional shape, and a substantially uniform intensity profile across the illuminated area. Imperfections at the edges of the component slabs would interfere with operation. <CIT> discloses a projection system and a light tunnel applied in the projection system. The light tunnel comprises a first reflector, a second reflector, a third reflector, a fourth reflector, a light entrance, and a light exit. A distance between the third and fourth reflectors gradually changes from the light entrance to the light exit. The distance between the third and fourth reflectors at the light entrance and the light exit is less than length of each of the first and second reflectors.

The invention is set out in the appended set of claims and relates to a method of fabricating a light tunnel.

In some illustrative and non-claimed aspects disclosed herein, an optical device is disclosed, which comprises a first element having a first reflective flat surface, a second element having a second reflective flat surface, and two flat spacer plates each having a reflective sidewall. The two flat spacer plates are arranged in a single plane with the reflective sidewalls of the two flat spacer plates facing each other with a gap between the two facing reflective sidewalls. The first reflective flat surface is arranged parallel with the single plane containing the two flat spacer plates and in contact with two flat spacer plates. The second reflective flat surface is arranged parallel with the single plane containing the two flat spacer plates and in contact with two flat spacer plates. The first reflective flat surface and the second reflective flat surface are arranged on opposite sides of the single plane.

In some illustrative aspects disclosed herein, an optical device comprises a first element having a first reflective flat surface, a second element having a second reflective flat surface facing the first reflective flat surface, and two flat spacer plates of thickness H arranged along a single plane with facing reflective spacer plate sidewalls. The two flat spacer plates are disposed between the facing first and second reflective flat surfaces and space apart the facing first and second reflective flat surfaces apart by the thickness H.

In some illustrative aspects disclosed herein, an optical device comprises two flat plates each having a reflective flat surface, and two flat spacer plates of thickness H each having a reflective sidewall. The two flat plates and the two flat spacer plates are arranged as a stack of plates with the reflective flat surfaces of the two flat plates facing each other and the two flat spacer plates arranged along a single plane and disposed between the two flat plates with the reflective sidewalls facing each other and with a gap between the two reflective sidewalls of the two flat spacer plates. The facing reflective flat surfaces of the two flat plates and the facing reflective sidewalls of the two flat spacer plates define a light tunnel passage with dimension H in the direction transverse to the single plane.

In some illustrative aspects disclosed herein, a method is disclosed of fabricating a light tunnel. Two flat surfaces are coated with a reflective coating to define two reflective flat surfaces. At least one sidewall of each of two flat spacer plates is coated with a reflective coating to define spacer plates each having a reflective sidewall. The two flat surfaces and the two spacer plates are secured together with the two flat surfaces facing each other and the two flat spacer plates disposed in a single plane between the two facing flat surfaces, and with the reflective sidewalls facing each other. In this way, a light tunnel passage is defined by the two facing flat surfaces and the two facing reflective sidewalls.

The rectangular light tunnel manufacturing approach of arranging four glass plates to form a rectangle with high-reflectivity surfaces of the glass plates arranged facing inward to form the inside surfaces of the light tunnel is effective for typical light tunnel sizes, e.g. with aperture area of approximately one square centimeter to a few square centimeters or larger. However, it has been found that manufacturing smaller light tunnels with cross-sectional areas on the order of sub-millimeter squared to a few square millimeters by this method is difficult, due to tediousness in handling, positioning, and assembling the constituent glass plates. Embodiments disclosed herein provide improved manufacturability with improved handling, easier component positioning and assembly. Embodiments disclosed herein are also scalable for high throughput manufacturing. Still further, embodiments disclosed herein are readily employed for tapered light tunnels.

With reference to <FIG>, an end view of a light tunnel <NUM> is shown. <FIG> illustrates Section S-S indicated in <FIG>. The light tunnel <NUM> includes a first element <NUM> and a second element <NUM>. The first element <NUM> has a first reflective flat surface <NUM>, and the second element <NUM> has a second reflective flat surface <NUM>. In a suitable embodiment, the two elements <NUM>, <NUM> are flat plates, e.g. flat glass plates. The light tunnel <NUM> further includes two flat spacer plates <NUM>, <NUM>. The flat spacer plate <NUM> has a reflective sidewall <NUM>, and the flat spacer plate <NUM> has a reflective sidewall <NUM>. In a suitable embodiment, the two flat spacer plates <NUM>, <NUM> are flat glass plates.

The reflective surfaces <NUM>, <NUM> and the reflective sidewalls <NUM>, <NUM> preferably have high reflectivity, e.g. reflectivity r ≥ <NUM>%, and more preferably r ≥ <NUM>%, and still more preferably r ≥ <NUM>%. For example, each of the reflective surfaces <NUM>, <NUM> and reflective sidewalls <NUM>, <NUM> may comprise a reflective multi-layer optical interference filter coating designed using conventional interference filter design methods to provide the desired high reflectivity for a design-basis spectral wavelength or wavelength band. By way of non-limiting illustration, the reflective surfaces <NUM>, <NUM> and sidewalls <NUM>, <NUM> may have interference filter coatings made up of alternating layers of silicon (a-Si:H) and a lower refractive index dielectric such as SiO2, silicon oxynitride (SiOxl\ly), tantalum pentoxide (Ta205), niobium pentoxide (Nb205), or titanium dioxide (Ti02). Instead of an interference filter, the reflective surfaces <NUM>, <NUM> and reflective sidewalls <NUM>, <NUM> may comprise a reflective metal such as silver (Ag, up to r=<NUM>% depending on wavelength), aluminum (Al, up to r=<NUM>% depending on wavelength), or so forth, optionally with still higher reflectivity provided by surface passivation or other surface treatm ent/overl ayer(s). In some embodiments, the reflective coatings of the reflective surfaces <NUM>, <NUM> and reflective sidewalls <NUM>, <NUM> have reflectivity of at least <NUM> over the wavelength range <NUM>-<NUM> nanometers inclusive. More generally, the reflective surfaces <NUM>, <NUM> and reflective sidewalls <NUM>, <NUM> preferably have reflectivity of <NUM> or higher (i.e. <NUM>% or higher) for a design wavelength or wavelength band, and more preferably have reflectivity of <NUM> or higher (i.e. <NUM>% or higher) for the design wavelength or wavelength band.

As best seen in <FIG>, in the light tunnel <NUM> the two flat spacer plates <NUM>, <NUM> are arranged along a single plane (e.g., the plane of indicated Section S-S) with the reflective sidewalls <NUM>, <NUM> of the two flat spacer plates <NUM>, <NUM> facing each other with a gap W (indicated in Section S-S shown in <FIG>) between the two facing reflective sidewalls <NUM>, <NUM>. This gap W defines the width W of the light tunnel <NUM>. It should be noted that the drawings are diagrammatic - typically, the reflective coatings applied to form the reflective surfaces <NUM>, <NUM> and the reflective sidewalls <NUM>, <NUM> are assumed to have negligible thickness, e.g. on the order of a micrometer or so. If the coating thicknesses are not negligible, then the position of each of reflective surface <NUM>, <NUM> and of each reflective sidewall <NUM>, <NUM> is defined as top exposed reflective surface of reflective coating.

Furthermore, in the light tunnel <NUM> the first reflective flat surface <NUM> is arranged parallel with the single plane containing the two flat spacer plates <NUM>, <NUM> (i.e., parallel with the section plane of section S-S shown in <FIG>). Furthermore, the two reflective flat surfaces <NUM>, <NUM> are arranged facing each other on opposite sides of the single plane (i.e. illustrative section plane S-S) and in contact with two flat spacer plates <NUM>, <NUM>. With this arrangement, the light tunnel <NUM> has a rectangular cross-section with the already-mentioned width W and with a height H equal to the thickness of the two flat spacer plates <NUM>, <NUM> (which are assumed to have the same thickness within design tolerances). In general, there is no requirement for height H and width W to be equal, although these dimensions could be equal if appropriate for the specific light tunnel design. The light tunnel <NUM> has a rectangular passage <NUM> of dimensions HxW defined by (<NUM>) the two facing reflective surfaces <NUM>, <NUM> of the respective first and second elements <NUM>, <NUM> having thickness H and (<NUM>) the two facing reflective sidewalls <NUM>, <NUM> of the two flat spacer plates <NUM>, <NUM> spaced apart by the gap W. It should be noted that the illustrative sidewalls <NUM>, <NUM> are straight and orthogonal to the reflective surfaces <NUM>, <NUM>.

It is noted that in the Section S-S view of <FIG>, the two flat spacer plates <NUM>, <NUM> are drawn as being opaque, so that the underlying reflective surface <NUM> of the first element <NUM> is not visible except in the gap W between the reflective surfaces <NUM>, <NUM> of the two flat spacer plates <NUM>, <NUM>. It will be appreciated that if the two flat spacer plates <NUM>, <NUM> are made of a transparent material such as glass, then the sectional view of Section S-S would actually have the reflective surface <NUM> visible through the transparent flat spacer plates <NUM>, <NUM>. However, since the two facing reflective surfaces <NUM>, <NUM> and the two facing reflective sidewalls <NUM>, <NUM> together form a continuous perimeter of the rectangular passage <NUM> of dimensions HXW, the transparency or opacity of the flat spacer plates <NUM>, <NUM>, or for that matter the transparency or opacity of the elements <NUM>, <NUM>, does not impact the optical properties of the rectangular passage <NUM> which is the optical light tunnel.

With reference now to <FIG>, a manufacturing process for manufacturing the light tunnel <NUM> of <FIG> is described. The first and second elements <NUM>, <NUM> are manufactured in this illustrative example from glass plates <NUM> (e.g., glass microscope slides, by way of non-limiting illustrative example) by coating two flat surfaces of the glass plates <NUM> with a reflective coating to define two reflective flat surfaces <NUM>, <NUM>. In some embodiments, this may be done by coating a single surface of a larger glass plate that is then cut (i.e. diced) to form the individual glass plates <NUM>, <NUM> with reflective coatings <NUM>, <NUM>. It will be appreciated that scalability is readily achieved as a large industrial-scale coating machine can coat many such elements in a single batch process.

In parallel, the two flat spacer plates <NUM>, <NUM> are formed, optionally as individual parts of a large batch process. As diagrammatically shown in <FIG>, two constituent glass plates <NUM> each of thickness H are assembled, with other fungible glass plates <NUM>, to form a plates stack <NUM>. In this stack, all sidewalls on one side of the stack <NUM> are parallel and facing the same direction - thus, all these sidewalls can be coated in a single batch coating process to produce a coated stack <NUM> with coated sidewalls. Moreover, smaller thickness H for the glass plates <NUM> enables more such plates to be assembled in the stack <NUM>, so that scalability actually increases with decreasing thickness H (and hence with decreasing dimension H of the resulting light tunnel passage <NUM>). The individual plates of the coated stack <NUM> are then disassembled and any two constituent coated plates of the stack <NUM> of fungible plates are chosen as the two flat spacer plates <NUM>, <NUM> with respective coated sidewalls <NUM>, <NUM>.

Finally, as indicated in <FIG>, the four constituent pieces <NUM>, <NUM>, <NUM>, <NUM> are secured together with the two flat surfaces <NUM>, <NUM> facing each other and the two flat spacer plates <NUM>, <NUM> disposed in a single plane between the two facing flat surfaces <NUM>, <NUM> and with the reflective sidewalls <NUM>, <NUM> facing each other whereby the light tunnel passage <NUM> is defined by the two facing flat surfaces <NUM>, <NUM> and the two facing reflective sidewalls <NUM>, <NUM>.

With continuing reference to <FIG>, in a modified embodiment shown as a parenthetical, the stack <NUM> is coated on two opposite sides to produce the coated stack <NUM>. The advantage of this approach is that handling is improved, and the possibility of assembly error is reduced.

The light tunnel passage <NUM> has a rectangular cross section of dimensions H×W with constant dimension H in the direction transverse to the single plane (i.e., the section plane of Section S-S in illustrative <FIG>) and constant dimension W in the direction parallel with the single plane. With the two facing sidewalls <NUM>, <NUM> mutually parallel, the dimensions H and W are constant along the entire length of the light tunnel. The dimension H is determined by the thickness of the two spacer plates <NUM>, <NUM> (neglecting any thickness of glue or other adhesive that may optionally be applied to bond the surfaces <NUM>, <NUM> to the spacer plates <NUM>, <NUM>; in some embodiments, no adhesive is used and instead the assembly is clamped together). This dimension H can be made as small as the practical thickness of the stock glass plate or plates from which the plates <NUM> are cut or obtained. For example, in some contemplated embodiments H is four millimeters or smaller, although larger values for H are also contemplated. Similarly, the gap W between the facing reflective sidewalls <NUM>, <NUM> can be made almost arbitrarily small. For example, a mandrill (or spacer) can be inserted during the assembly to provide a defined gap W, which is then removed after the assembly. The gap W may, therefore, in some embodiments be four millimeters or smaller as well, although again larger values for the gap W are contemplated. In some embodiments, the dimensions of the aperture H×W are contemplated to define a submillimeter aperture, i.e. H and/or W may be less than one millimeter.

With reference to <FIG> and <FIG>, a variant embodiment is shown by way of an exploded sectional view along Section S-S (<FIG>) and the assembled section sectional view along Section S-S (<FIG>). In this embodiment, the two rectangular spacer plates <NUM>, <NUM> are replaced by wedge-shaped spacer plates <NUM>, <NUM>, so that the two flat spacer plates <NUM>, <NUM> are arranged along the single plane (e.g. of Section S-S) with facing reflective sidewalls <NUM>, <NUM> arranged at an angle to each other. (Alternatively, the rectangular plates <NUM>, <NUM> could be used with the plates tilted relative to one another to define the angle, variant not shown). In this way, as best seen in <FIG>, a tapered light tunnel passage is defined between the facing first and second reflective flat surfaces (identical with the embodiment of <FIG>). The facing reflective sidewalls <NUM>, <NUM> are arranged at an angle to each other. The tapered light tunnel passage has the constant dimension H in the direction transverse to the single plane, which is defined by the thickness of the flat spacer plates <NUM>, <NUM> identically to the embodiment of <FIG>. However, in the embodiment of <FIG> and <FIG> the constant dimension W of the embodiment of <FIG> (resulting from the facing sidewalls <NUM>, <NUM> being parallel to each other) is replaced by a non-constant dimension that varies linearly along the length of the light tunnel passage due to the angle of the facing reflective sidewalls <NUM>, <NUM>. Not part of the invention, even more generally, a non-linear tapering could be achieved by having facing reflective sidewalls of parabolic or other curvature, e.g. cut using a diamond saw or other precision glass-cutting machine.

Claim 1:
A method of fabricating a light tunnel (<NUM>), the method comprising:
coating two flat surfaces with a reflective coating to define two reflective flat surfaces (<NUM>, <NUM>);
assembling two plates (<NUM>) to form a plates stack (<NUM>), wherein all sidewalls on one side of the plates stack are parallel and facing the same direction;
coating all sidewalls on one side of the plates stack (<NUM>) in a single batch coating process to produce a coated stack (<NUM>) with coated sidewalls,
disassembling the two plates (<NUM>) of the coated stack (<NUM>) into two flat spacer plates (<NUM>, <NUM>) with respective coated reflective sidewalls (<NUM>, <NUM>); and
securing the two reflective flat surfaces (<NUM>,<NUM>) and the two flat spacer plates (<NUM>, <NUM>) together with the two reflective flat surfaces (<NUM>,<NUM>) facing each other and the two flat spacer plates (<NUM>,<NUM>) disposed along a single plane between the two facing reflective flat surfaces (<NUM>,<NUM>) and with the reflective sidewalls (<NUM>, <NUM>) facing each other and orthogonal to the two reflective flat surfaces (<NUM>, <NUM>), the two flat spacer plates (<NUM>,<NUM>) being arranged with a gap between the two facing reflective sidewalls (<NUM>,<NUM>), the two flat spacer plates (<NUM>,<NUM>) spacing apart the two facing reflective flat surfaces (<NUM>,<NUM>), whereby a light tunnel passage (<NUM>) is defined by the two reflective facing flat surfaces (<NUM>, <NUM>) and the two facing reflective sidewalls (<NUM>, <NUM>).