BRIEF DESCRIPTION OF THE DRAWINGS
The nature of this invention is to convert electromagnetic radiation into a selected polarization state. This invention provides significant advantages for many applications requiring polarized electromagnetic radiation. The present invention can be clearly understood from the following descriptions of the preferred embodiments in conjunction with the accompanying drawings, wherein
FIG. 1 is the preferred embodiment showing the arrangement of the single high index of refraction, birefringent substrate with a reflective layer on the second surface of the birefringent substrate;
FIG. 2 is an addition to the preferred embodiment, wherein the birefringent section of the optic is a optical coating applied to a substrate that acts as a reflector to radiation internal to the interface between the coating and the substrate, and the substrate acts to become the major structural member of the optic;
FIG. 3 shows an alternate design to the preferred embodiment wherein the substrate which acts as the supporting structure, and includes birefringent capability, has an additional optical layer of high index amorphous or isotropic optical characteristics over the birefringent optical layer, the second surface of the birefringent layer also acting as a mirror surface with a mirror coating;
FIG. 4 shows an alternate design wherein the birefringent coating or layer is applied to both sides of a substrate whose surfaces acts as a mirror on both sides, and the substrate acts as the main supporting medium;
FIG. 5 is an arrangement of multiple substrates arranged in a manner to form an array of radiation input apertures, a polarization conversion and channeling section between two substrates, and an array of radiation exit apertures;
FIG. 6 is an alternate configuration wherein the mirror substrates with birefringent coating or layers on both sides are shown as flat plates arranged in a simple parallel structure, as an array of radiation input apertures that channel and convert the incoming unpolarized electromagnetic radiation and exit at an array of radiation output apertures;
FIG. 7 is an alternate design wherein the mirrored substrates formed in parallel flat plates are arranged in a manner at the exit apertures to exit the radiation in a single direction, with the overall outside dimensions of the optic in the form of a wedge;
FIG. 8 is an alternate design wherein the layers formed in parallel flat mirrored plates are arranged in a staggered fashion at the input and output apertures to exit the radiation in a single direction as well as maintain a uniform thickness for the overall optic assembly.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 Detailed Description
FIG. 1 shows a side view of the preferred embodiment, 10, in its most simple form. The substrate, 30, has two surfaces 31 and 32. The surface 31 is the input surface. Incident radiation, 101, is shown impinging on surface 31, with one linear polarization, 102, preferentially reflected, with orthogonal polarization, 103, preferentially refracted. The refracted radiation, 103, transverses the birefringent substrate, 30, impinges onto surface 32, which is treated to be reflective. Accordingly electromagnetic radiation 103 reflects from surface 32 and impinges onto surface 31, wherein the electromagnetic radiation 103 is both partially refracted to exit the substrate, and reflected to retransverse the substrate 30, repeating the cycle. The maximum conversion efficiency for a single or small number of interactive surfaces occurs where the electromagnetic radiation 101 is preferentially set at Brewster's angle with respect to surface 31, causing the reflected electromagnetic radiation 102 to be totally plane polarized, and the first electromagnetic radiation 103 to be plane polarized of the opposite polarization. High conversion efficiency is also obtained by angles less than Brewster's angle between surfaces 31 and 101, when multiple reflection refraction interactions are selected. By action of the birefringent crystal, electromagnetic radiation 103 polarization is modified to have both polarizations, and upon exiting the substrate adds to the plane polarization of the first electromagnetic radiation 101. Thus upon one interaction, the reflected electromagnetic radiations 102 may be up to 75% plane polarized for a narrow bandwidth.
Other angles with respect to Brewster's angle between electromagnetic radiation path 101 and substrate surface 31 also perform polarization conversion; however, more interactions are necessary to achieve conversion.
Multiple optics of the single optic as shown in FIG. 1 act to convert potentially 50% of the unconverted polarization at each interaction with the substrate, adding to the total converted polarization.
In order to preserve collimation, surfaces 31 and 32 are constructed parallel. However, a construction that is not parallel has the effect to separate the two beams, and has the effect of acting as a beam splitter to separate the two orthogonal polarizations at two different angles, which is a variation of the design.
FIG. 2 Detailed Description
FIG. 2 shows a cross section of a variation of the preferred embodiment. A substrate 40 which may be a metal or a glass substrate material is shown with a layer of birefringent material 30 formed on the surface of substrate 40. The thickness of formed material 30 is shown exaggerated in necessary thickness in order to show the electromagnetic radiation paths. The incoming radiation 101 is shown with one polarization preferentially reflected, 102, and orthogonal radiation preferentially refracted, 103. The surface 41, formed by the contact of 30 and 40 is formed to be highly reflective. The layer 30 is selected to be highly birefringent with a high index of refraction and transparency in the desired wavelengths. Rutile and anatase are good selections for the visible because of the high index of refraction and high transparency to the visible. ZnS is a good selection for the IR. The impinging electromagnetic radiation 101, interacts with surface 31 by both reflecting of one preferred polarization as electromagnetic radiation 102, and refracting as electromagnetic radiation 103, of orthogonal polarization. If the angle between surface 31 and electromagnetic radiation 101 is set to Brewster's angle, the refracted electromagnetic radiation 103 and reflected electromagnetic radiation 102 are of totally opposite polarizations. However, Brewster's angle is dependent on wavelength; therefore, only works well in a very narrow bandwidth. The electromagnetic radiation transversing the coating 30, is acted upon by the birefringent crystal to undergo a polarization change, thus partially changing to the desired polarization. Electromagnetic radiation 103 upon interacting with surface 31 is both refracted and reflected, with the refracted electromagnetic radiation being partially polarized to the desired polarization. In an array designed for multiple reflection, conversion cycles the cycle is repeated, increasing the polarization conversion to a limit, mostly determined by the index of refraction of the high index first surface. Angles less than the critical angle yield the highest conversion for multiple interactions.
FIG. 3 Detailed Description
FIG. 3 shows a cross section of a variation of the preferred embodiment with the addition of a optical coating 20. The incoming radiation 101 is shown with one polarization preferentially reflected, 102, and orthogonal radiation preferentially refracted, 103. The coating 20 is of high index of refraction, and of amorphous or isotropic nature. The coating allows selection of materials of higher index of refraction and or materials that are amorphous than available for substrate 30, such as amorphous diamond. The coating 20 is selected to be preferably amorphous in order to eliminate polarization changes during reflection of electromagnetic radiation 101. The refracted electromagnetic radiation 103 is shown without reflection at the surface between 20 and 30, surface 31; however if an index of refraction difference exists between coating 20 and substrate 30, some reflection is expected at surface 31. A good material selection for visible application for 20 is an optical coating of amorphous diamond. The thickness of 20 is determined by maximizing the index of refraction, and the material as well as the method of deposition. The selection of 20 to be amorphous allows the optical axis of 30 not to be an issue caused by polarization shifts during reflection.
Selection of amorphous diamond for 20 allows the layer 20 to act as the main substrate structure.
Surface 32 is shown as a mirrored surface to reflect electromagnetic radiation 103.
FIG. 4 Detailed Description
FIG. 4 shows a cross section of a preferred embodiment, 10 with additional options added to the design. A substrate 40, manufactured of a thin metal or other material is selected to have similar coefficient of thermal expansion characteristics as the optical birefringent coating, 30. The substrate, 40, is polished or coated to be a mirror on both sides shown as reflective surfaces, 41. Surface 41 may be designed to be a highly reflective dielectric mirror or a metallic polished surface to be highly reflective. The birefringent layer, 30, is shown exaggerated in thickness in order to show the interaction of electromagnetic radiation 103. The incoming radiation 101 is shown with one polarization preferentially reflected, 102, and orthogonal radiation, 103, preferentially refracted. Radiation 103 reflects off of surface 41, back to surface 31, partially reflecting, and adding to the preferred polarization, with the preferentially orthogonal polarization partially reflecting from surface 31 and repeating the cycle.
Layer 30, is maintained as thin as possible in order to minimize the walk of 103 along the optic substrate, and minimize absorption effects of layer 30. Not shown on the other side of substrate 41, is a similar electromagnetic radiation tracing.
FIG. 5 Detailed Description
FIG. 5 shows an arrangement of the optical substrates 10, also referred to as elements. The elements, 10, are arranged in a manner to form an array of entrance apertures. The electromagnetic radiations 101, is shown for one aperture in the input aperture array. The electromagnetic radiation reflects multiple times between elements 10, arranged in layers, causing the polarization conversion. The electromagnetic radiation reflecting and refracting from the surface supported by elements 10, is shown as electromagnetic radiations 103. The refraction component being converted is not shown. At a single exit aperture in the exit aperture array, is shown exiting electromagnetic radiations 102. The form of the entrance aperture array is determined by the spacing of elements, 10. The elements 10, are positioned in a manner to channel the electromagnetic radiations at desired angle of intersection between the elements, 10. This angle is a function of the refractive index layer mounted on the element 10 substrate. The elements 10 are formed at the exit apertures to colliminate the exiting radiation 102. A desired divergence can also be formed by elements 10 at the exit aperture array. The construction shown in FIG. 5 allows multiple interactions in a narrow volume, and allows efficiency as to the number of elements 10 required to serve a larger entrance and exit aperture. The elements 10, are not shown with spacers, but as an option, micro beads of low index of refraction will maintain the elements 10, at a known, constant spacing.
The spacing between the elements 10, may be a gas, such as air, a liquid or a solid. The preferential selection is a gas such as air because it avoids the necessity for AR coatings at the entrance and exit apertures.
A low index of refraction material may also be utilized to form elements 10 spacing. Such a design has inherent manufacturing challenges and is more complex accordingly.
FIG. 6 Detailed Description
FIG. 6 is a geometric variation to the placement of substrates elements, 10. A pancake layer of substrates 10 are constructed with spacers, now shown. The spacers can be shims preferably placed at the ends or in a areas inside the active area of the optic. Micro beads placed in the active area form a spacer to maintain know distance between elements 10. The micro beads are preferably made from material with an index of refraction approaching one. The spacing between the layers 10, may be a gas, such as air, a liquid or a solid. The preferential selection is air because it avoids the necessity for anti reflective coatings at the entrance and exit apertures.
The exit radiation 102 is shown diverged by the nature of the geometry and reflections between the layers 10.
The electromagnetic radiation 103 is shown channeled between elements 10, while the polarization conversion occurs with each interaction at the surface of the layers 10.
FIG. 7 Detailed Description
FIG. 7 is a variation of the parallel construction of elements 10, wherein the elements 10 are staggered at the exit aperture to cause the channeled electromagnetic radiation 103 to exit the optic as electromagnetic radiation 102 in a non diverged manner. The optic acts as a mirror, reflecting the incoming electromagnetic radiation 101 to exit the optic as electromagnetic radiation 102 as a mirror would reflect the electromagnetic radiation.
The optic's exterior dimensions forms a slight wedge because of the staggered layers 10.
FIG. 8 Detailed Description
FIG. 8 is a variation of the parallel construction of elements 10, wherein the elements 10 are staggered at the entrance and exit apertures in order to construct an optic that conforms to a uniform thickness. Shown are the electromagnetic radiation tracing for the entering electromagnetic radiations 101, the channeled electromagnetic radiations 103, and the exiting electromagnetic radiations 102.
Patent Application
20070236793
