Patent Application
20070273970
Referring now to
Advantageously, each of the polarizing assemblies includes a polarization selective optical element (“PS element”) that reflects radiation having one polarization state while transmitting radiation having the orthogonal polarization state. For example, a preferred PS element is the ProFlux™ polarizer manufactured by Moxtek, Inc., which includes a thin layer of aluminum ribs formed onto a glass substrate. An alternative is provided by using a thin film material, such as the Dual Brightness Enhancement Film (“DBEF”) made by 3M®. Such material can be designed to efficiently reflect electromagnetic radiation in a broad band of wavelengths, for example visible light, that has a particular plane, or linear, polarization while transmitting light of an orthogonal polarization. For example, a PS element can be designed to reflect p-polarized visible light while transmitting s-polarized light. The PS element does not alter either the polarization of the transmitted light or the polarization of the reflected light.
In the present embodiment, the polarizing assembly 101 includes a PS optical element 102 juxtaposed with a quarter-wave plate 103. Likewise, the polarizing assembly 107 includes a PS optical element 109 juxtaposed with a quarter-wave plate 108. The quarter-wave plates permit appropriate transformations between linear polarization and circular polarization, while the PS elements reflect linearly polarized light having one polarization state and transmits linearly polarized light having the orthogonal polarization state.
In this embodiment, the total width w1 of the collimating apparatus 100 is approximately 20 mm, with the image source 111 located at a distance d1 approximately 10 mm behind the device.
Image source 111 typically transmits linearly polarized light, and therefore may include polarizer sheets 117 for that purpose, such as Q-12 polarizing optical film made by Nitto Denko Corp., or UHC-125U transmissive polarizer made by Polatechno Co., Ltd. Thus, an image comprised of p-linear polarized light is transmitted into the collimating apparatus 100.
The operation of the collimating apparatus will be explained with reference to two image rays 150, 160. Image ray 150 is representative of a point of light emanating from the center of the image source and directed toward the center of the collimating apparatus. Image ray 160 is representative of a point of light emanating from near the top of the image source and therefore directed at a sharper angle toward the top portion of the collimating apparatus.
Image ray 150 is transmitted by the image source 111 through polarizers 117 toward the collimating apparatus 100 as linear polarized light. The p-linear polarized light passes through the PS element 109 (s-polarized light is reflected), and quarter-wave plate 108 operates to transform the ray into right-handed circularly polarized (“RCP”) light. Upon hitting the partially reflective coating 115, some of the light is reflected back toward polarizing assembly 107 while the rest of the light is passed through the combiner element 105. The reflected light reverses sense to become left-handed circularly polarized (“LCP”) light, but upon passing through the quarter-wave plate 108, the LCP light is transformed back to a linear polarization state, and the PS element 109 thus now reflects the s-linear component back through the quarter-wave plate 108, where it regains its character as LCP light. As before, the surface coating 115 continues to reflect a portion and pass a portion of the light rays. The radiation that passes through the combiner element then hits the polarizing assembly 101. By passing through quarter-wave plate 103, the ray is transformed from a circular polarization to a linear polarization, and then upon hitting the PS element 102, s-linear polarized light is passed through the device.
A second image ray 160 is not transmitted along the viewing axis like ray 150, but is transmitted at some angle to the viewing axis. However, the same basic functional operation ensues. The ray 160 transmitted by the image source 111 through polarizers 117 consists of linear polarized light. The p-linear component passes through PS element 109, and quarter-wave plate 108 operates to transform the ray into RCP light. Upon hitting the partially reflective coating 115, some of the light is reflected back toward polarizing assembly 107 while the rest of the light is passed through the combiner element 105, but with some angle of refraction. The reflected light reverses sense to become LCP light, but upon passing back through the quarter-wave plate 108, the LCP light is transformed back to a linear polarization state, and the PS element 109 reflects the s-linear component back through the quarter-wave plate 108, where it regains its character as LCP light. The surface coating 115 continues to reflect a portion and pass a portion of the light rays. The radiation that passes (refracts) through the combiner element then hits the polarizing assembly 101. By passing through quarter-wave plate 103, the ray is transformed from a circular polarization to a linear polarization, and upon hitting the PS element 102, s-linear polarized light is passed through the device.
Although the described embodiment creates left-handed then right-handed circularly polarized light inside the collimating device, other orientations could be used. For example, the orientation could be reversed such that the light rays inside the collimating device are initially right-handed then left-handed circularly polarized light.
Advantageously, the field of view using the inventive collimating apparatus is larger by at least 10-20% than that of similar devices.
The preferred collimating apparatus 100 has the capability for broad-band imaging, thus enabling it to be used as a compact, multi-color (i.e., multi-wavelength) collimating system. The primary limitation to this broad-band capability (other than for the output of the source) is that imposed by the wavelength dependence of the reflective coating, and to address this issue, a broad-band reflective coating is preferably used. Such coatings are well known by those of skill in the art and therefore will not be described in detail in this specification.
In general, those skilled in the art to which this invention pertains will recognize that many changes in construction and widely differing embodiments will suggest themselves without departing from the spirit and essential characteristics of the invention. For example, the curvature of the combiner lens 105 may be varied in order to impart different optical powers to the system. Further, depending upon the desired application, the spacing between components may be adjusted. Further still, the reflective coating need not be a 50/50 dielectric coating, but could have other characteristics, including a different dielectric ratio, and the reflectivity could also be provided through the use of a partial metal mirror rather than a dielectric coating. More significantly, the image source may transmit other types of polarized light than described herein, and the system can be modified accordingly so that the PS element will reflect the particular polarization of light that is passed through the quarter-wave plate.
Accordingly, the disclosures and descriptions herein are intended to be illustrative only, and not limiting. The scope of the invention is set forth in the claims.
