WO2012104839A1

WO2012104839A1 - Polarizing beam splitter

Info

Publication number: WO2012104839A1
Application number: PCT/IL2012/000056
Authority: WO
Inventors: Yitzhak Weissman
Original assignee: Advisol Ltd.
Priority date: 2011-02-02
Filing date: 2012-02-02
Publication date: 2012-08-09

Abstract

A polarizing beam splitter having a first grate of parallel wires disposed on a first planar surface of an optically transparent substrate; and a second grate of parallel wires disposed on a second planar surface of an optically transparent substrate, the first planar surface and the second planar surface intersecting each other, defining an intersection line which co-exists in both the first and the second planar surfaces, wherein a first angle is defined between any one of the wires of the first grate and the intersection line, and a second angle, adjacent to the first angle, is defined between any one of the wires of the second grate and the intersection line, such that the sum of the first angle and the second angle is 90 or 270 degrees.

Description

POLARIZING BEAM SPLITTER

CROSS REFERENCE TO RELATED APPLICATIONS

[001] This application claims the benefit of U.S. Serial No. 61/438658, filed on February 2, 2011, incorporated in its entirety herein by reference. BACKGROUND OF THE INVENTION

[002] This invention relates to light polarization, and in particular, relates to a polarizing beam splitter having orthogonally disposed wire-grids.

[003] There are many types of polarizing beam splitters in which a non-polarized light beam is split into sigma (s) and pi (p) polarization components.

[004] The shortcoming of such splitters is that the output directions of the polarization components are asymmetrical in relation to each other and this complicates their use in applications requiring prefect symmetry between both polarization components.

[005] This asymmetry issue has been addressed with a four-element, x-prism beam- splitter in which each of four triangular elements has a first leg coated with a dielectric material and a second leg coated with a material acting as a half-wave plate. When all four triangular elements are held together so as to form a cube, the resulting polarizing, beam splitter is capable of outputting symmetrical polarization components; but, only for a narrow range of wavelengths and limited acceptance angles, thereby precluding their use in applications requiring good performance over the entire visible spectrum or requiring large range of acceptance angles.

[006] Therefore, there is a need for a polarizing beam splitter capable of outputting polarization components symmetrical to each other, functional throughout the entire spectrum of interest, and capable of handling large ranges of acceptance angles. SUMMARY OF THE INVENTION

[007] According to the teachings of the present invention there is provided a polarizing beam splitter including: a first grate of parallel wires disposed on a first planar surface of an optically transparent substrate; and a second grate of parallel wires disposed on a second planar surface of an optically transparent substrate, the first planar surface and the second planar surface intersecting each other, defining an intersection line which co-exists in both the first and the second planar surfaces, wherein a first angle is defined between any one of the wires of the first grate and the intersection line, and a second angle, adjacent to the first angle, is defined between any one of the wires of the second grate and the intersection line, such that sum of the first angle and the second angle is 90 or 270 degrees.

[008] According to a further feature of the present invention, the first angle or the second angle is substantially 90 degrees.

[009] According to a further feature of the present invention, the first planar surface and the second planar surface define a substantial right angle between them.

[0010] According to a further feature of the present invention, there is also provided at least two optically transparent prisms held in abutment with the substrate, the two prisms being disposed opposite each other.

[001 1] According to a further feature of the present invention, the optically transparent substrate comprises at least one prism.

[0012] According to a further feature of the present invention, the wires of the first grate and the second grate comprise conductive wires.

[0013] According to a further feature of the present invention, the conductive wires are made of metal selected from the group of metals that consists of aluminum and gold,

[0014] There is also provided according to the teachings of the present invention, a method for splitting light including: directing light into a polarizing beam splitter having: [0015] a first grate of parallel wires disposed on a first planar surface of an optically transparent substrate and a second grate of parallel wires disposed on a second planar surface of an optically transparent substrate, the first planar surface and the second planar surface intersecting each other, defining an intersection line which co-exists in both the first and the second planar surfaces, wherein a first angle is defined between any one of the wires of the first grate and the intersection line, and a second angle, adjacent to the first angle, is defined between any one of the wires of the second grate and the intersection line, such that the first angle and the second angle is 90 or 270 degrees; reflecting a first polarization component of the light from the first grate; and reflecting a second polarization component of the light from the second grate.

[0016] According to a further feature of the present invention, the first polarization component is substantially "p" polarized light.

[0017] According to a further feature of the present invention, the first polarization component is substantially "s" polarized light.

[0018] According to a further feature of the present invention, either the first angle or the second angle is 90 degrees.

[0019] According to a further feature of the present invention, the first planar surface and the second planar surface define a substantial right angle between them.

[0020] According to a further feature of the present invention, there is also provided at least two optically transparent prisms held in abutment with the substrate, the two prisms being disposed opposite each other.

[0021] According to a further feature of the present invention, the optically transparent substrate comprises at least one prism. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to its organization, method of operation, components, features, advantages, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[0023] FIG. 1 is a perspective, top view of a polarizing beam splitter depicting "p" polarizing wire grid disposed on a first planar surface and a "s" polarizing wire grid disposed on a second planar surface intersecting the first surface;

[0024] FIG. 2 is a perspective, top view of a polarizing beam splitter analogous to that of Figure 1 except that the wires grates are oriented in a non-parallel manner to a planar intersection line;

[0025] FIG. 3 is a schematic side view of the polarizing beam splitter depicted in Figure 2 views from the right side as noted;

[0026] FIG. 4 is a schematic, cross-sectional top view of the polarizing beam splitter of Fig. 1 depicting splitting of polarization components of an incident beam;

[0027] FIGS. 5 and 6 are cross-sectional, top-views of the polarizing beam splitter of Fig. 1 with four and two optically transparent triangular-support-prisms, respectively; and

[0028] FIG. 7 is a schematic, cross-sectional side-view of a polarizing beam splitter in which the polarizing grids are disposed directly on the prism surfaces.

[0029] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate same, corresponding or analogous elements. DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0030] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced even without these specific details. Well-known methods, procedures, and components have not been described in detail to avoid obscuring the description of the present invention.

[0031] The present invention is directed to splitting incoming light into "s" and "p" polarization components. In some embodiments the polarization components are oriented in a symmetrical or a parallel orientation to each other regardless of their propagation direction.

[0032] The following definitions will be used through this document.

[0033] "Wire-grid" refers to a grate of fine, parallel conductive wires, equally separated from each other at distance considerably less than the wavelength of the illumination to be polarized. The wire width should be a small fraction of this distance and various cross-sectional shapes of a single wire are included within the scope of the present invention. The wire-grid, i.e. grates, may be deposited on an optically transparent substrate like glass or quartz, for example, or other materials exhibiting optical transparency. For the purposes of this document the terms "grid wires" and "grate wires" are used interchangeably. It should be appreciated that wire-grids fully or partially embedded in a substrate are also included within the scope of the present invention. Alternatively, the wire-grids may be held by a frame instead of a substrate are also included within the scope of the present invention.

[0034] The wires of the grid are typically constructed from aluminum or gold; however, it should be appreciated that any metallic material having sufficient conductivity is included within the scope of this invention [0035] "P-polarization" component refers to the polarization component which is substantially parallel to the plane of incidence and an "s-polarization" refers to the polarization component which is perpendicular to the plane of incidence.

[0036] The advantages of embodiments of the present invention include output polarization components oriented symmetrically with respect to the incoming beam, thereby facilitating three- dimensional stereo applications where perfect symmetry between the two channels is a necessity. Furthermore, embodiments of the present invention are operative throughout the visible spectrum and are capable of accepting a wide range of incident angles, thereby adding versatility.

[0037] Examples of relevant applications include three-dimensional cinema, optically efficient polarization of DLP projectors, handheld projector systems, head-up displays, optical systems, and helmet mounted visor displays.

[0038] Turning now to the figures, Figure 1 illustrate a non-limiting example of a wire-grid, polarizing beam splitter generally labeled 1, according to an embodiment of the present invention. Beam splitter 1 includes wire-grids also generally labeled 2 and 3. Wire-grids 2 are grates of equally spaced, parallel grid wires 2a, and similarly, wire-grids 3 are grates of equally spaced, parallel grid wires 3a. As shown, grid wires 2a are mounted on a first, optically- transparent substrate surface 2c and, similarly, grid wires 3a are mounted on a second optically- transparent substrate surface 3c. Substrate surfaces 2c and 3c may be implemented as a single structure having an "X" shaped cross-section, as shown or alternatively, surfaces 2c and 3c may be implemented as surfaces of separate substrates held in abutment by way of a holding arrangement (not shown) or by way of an adhesive. As shown, surfaces 2c and 3c are planar surfaces intersecting so as to form a common intersection line 40 shared by both planar surfaces 2c and 3c. In some embodiments grid wires 2a are oriented parallel to intersection line 40 whereas grid wires 3a are oriented perpendicularly to intersection line 40. As depicted, wire grids 3a are "p" reflective and grate wires 2a are "s" reflective as will be further discussed. It should be appreciated that embodiments in which the orientation of the "p" reflective and the "s" reflective polarization components is reversed from that depicted are enclosed within the scope of the present invention.

[0039] Figure 2 depicts an alternative embodiment in which neither grate wires 3a or 2a are perpendicular with planar intersection line 40. However, the relative orthogonal orientation of grate wires 2a and 3a depicted in Figure 1 is preserved as most clearly shown in Figure 3.

[0040] Figure 3 is a right, side-view of the polarizing beam splitter of Figure 2 in which neither grate wires 3a or 2a are perpendicular with planar intersection line 40. Grate wires 3a form angle a with planar intersection line 40 measured from intersection line 40 towards grate wires 3a and similarly, grate wires 2a form angle β with planar intersection line 40 also measured from intersection line 40 towards grate wires 2a. The geometric condition for proper function of the polarizing beam splitter is fulfilled when the sum of angle a and angle β equals 90° or the sum of their supplementary angles equals 270°. It should be appreciated that consistency in the direction of measuring angles a and β is crucial in establishing compliancy with thi s geometrical condition. Both angles must be measured in the same direction, either from planar intersection line 40 as noted above, or from grate wires 3a or 2a towards planar intersection line 40.

[0041] FIG. 4 is a top, cross-sectional view of the polarizing beam splitter of Figure 1 depicting the orientation of polarization components split from incident beam 8 by way of wire-grid 2 mounted on optically transparent substrate 2c and wire-grid 3 mounted on optically transparent substrate 3c. Substrate surfaces 2c and 3c may be implemented as a single structure having an "X" shaped cross-section, in which an orthogonal angle is formed between the planar surfaces 3c and 2c in some embodiments and non-perpendicular angles in other embodiments. Alternatively, surfaces 2c and 3c may be implemented as surfaces of separate substrates held in abutment by way of a holding arrangement (not shown) or by way of an adhesive.

[0042] In operation, a beam of light 8 is directed at wire-grid, polarizing beam splitter 1 as shown. As previously noted, wire-grid 2 functions as a first component reflecting polarizer (or an s-component reflecting polarizer for the embodiment of Figure 1). Wire-grid 3, having grid wires 3a orthogonally oriented to grid wires 2a of wire-grid 2, functions as a second component reflecting polarizer (or p-component reflecting polarizer for the embodiment of Figure 1) As beam 8 strikes wire-grid 2, some beam components are reflected while others traverse depending on the alignment of these components with grate wires 2a. Beam polarization components parallel to grid wires 2a, are reflected as first polarization component 5. Beam polarization components orthogonal to grid wires 2a traverse wire-grid 2 and upon incidence with wire-grid 3, having grid wires 3a orthogonally disposed to grid wires 2a, is reflected as second-polarization component 6. Analogously, when beam 8 strikes wire-grid 3, beam polarization components parallel to grid wires 3a, are reflected as first-component polarization 6 and beam polarization components non-parallel to grid wires 3a traverse wire-grid 3 and upon incidence with second- polarizer, wire-grid 2, is now reflected as second-polarization component 5.

[0043] Figures 5 and 6 illustrate the polarizing beam splitter having a substantially "X" shaped cross-section with alternative support arrangement for wire-grids 2a and 3a of Figures 1-4.

[0044] Specifically, Figure 5 depicts four right angle prisms 7 in which the orthogonal facets of prisms 7 are held in abutment with optically transparent substrates 2c and 3c by way of glue or a clamping arrangement and support the legs of the "X" structure formed by substrates 2c and 3c and the associated wire-grids, 2 and 3. The substantially parallel orientation between first and second polarization components is illustrated in Figure 4.

[0045] Figure 6 depicts a support structure similar to that of Figure 5 employing only two right angle prisms 7 disposed opposite to each other and secured as noted above.

[0046] Figure 7 depicts an embodiment of a polarizing beam splitter in which wire grids 2 and 3 are disposed directly onto respective orthogonal faces of an optically transparent substrate 7. Typically, it is easier to dispose wire-grids on flat substrates; however, situations in which the technological means allow, prisms are also suitable substrates. [0047] It should be noted that embodiments having wire-grids 2a and 3a bonded directly to different surfaces of any three dimensional object are included within the scope of the present invention.

[0048] Regarding manufacture, the above described wire-grid, polarizing beam splitter may be constructed using photolithography technology or other techniques known to those skilled in the art.

[0049] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

CLAIMS What is claimed is:

1. A polarizing beam splitter comprising: a first grate of parallel wires disposed on a first planar surface of an optically transparent substrate; and

a second grate of parallel wires disposed on a second planar surface of an optically transparent substrate, the first planar surface and the second planar surface intersecting each other, defining an intersection line which co-exists in both the first and the second planar surfaces,

wherein a first angle is defined between any one of the wires of the first grate and the intersection line, and a second angle, adjacent to the first angle, is defined between any one of the wires of the second grate and the intersection line, such that a sum of the first angle and the second angle is 90 or 270 degrees.

2. The polarizing beam splitter of claim 1 , wherein either the first angle or the second angle is 90 degrees.

3. The polarizing beam splitter of claim 1, wherein the first planar surface and the second planar surface define a substantial right angle between them.

4. The polarizing beam splitter of claim 1, further comprising at least two optically transparent prisms held in abutment with the substrate, the two prisms being disposed opposite each other.

5. The polarizing beam splitter of claim 1, wherein the optically transparent substrate comprises at least one prism.

6. The polarizing beam splitter of claim 1, wherein the wires of the first grate and the second grate comprise conductive wires.

7. The polarizing beam splitter of claim 6, wherein the conductive wires are made of metal selected from the group of metals that consists of aluminum and gold.

8. A method for splitting light comprising:

directing light into a polarizing beam splitter having:

a first grate of parallel wires disposed on a first planar surface of an optically transparent substrate and a second grate of parallel wires disposed on a second planar surface of an optically transparent substrate, the first planar surface and the second planar surface intersecting each other, defining an intersection line which co-exists in both the first and the second planar surfaces, wherein a first angle is defined between any one of the wires of the first grate and the intersection line, and a second angle, adjacent to the first angle, is defined between any one of the wires of the second grate and the intersection line, such that a sum of the first angle and the second angle is 90 or 270 degrees;

reflecting a first polarization component of the light from the first grate; and reflecting a second polarization component of the light from the second grate.

9. The method for polarizing light of claim 8, wherein the first polarization component is substantially "p" polarized light.

10. The method for polarizing light of claim 8, wherein the first polarization component is substantially "s" polarized light.

11. The polarizing beam splitter of claim 8, wherein either the first angle or the second angle is 90 degrees.

12. The polarizing beam splitter of claim 8, wherein the first planar surface and the second planar surface define a substantial right angle between them.

13. The polarizing beam splitter of claim 8, further comprising at least two optically transparent prisms held in abutment with the substrate, the two prisms being disposed opposite each other.

14. The polarizing beam splitter of claim 8, wherein the optically transparent substrate comprises at least one prism.