Patent Application
20100079872
Embodiments relate generally to the field of projection display systems and methods, and more particularly, to a double-refractive collimator.
Projection displays are used for a wide variety of applications, such as producing the pictures viewed on television screens. A typical projection display system includes a number of components, including a display screen, a light source, and an optical path between them. To create the pictures, one or more light sources are provided to emit light when it is needed. The light they produce is then manipulated by a series of optical devices in order to create the visual image. The visual image created along the optical path is then displayed on the display screen, the television screen for example, or another visual display. In most cases, the goal is to produce the best picture possible. The key to producing a desirable visual display, of course, is the configuration of the various optical devices along the optical path. The selection, operation, and configuration of these devices also contribute to unseen characteristics of the system, such as cost, size, and efficient use of system resources.
Several types of projection displays have recently been developed. These new display systems are now becoming much more common, serving as a replacement for the widely-used CRT (cathode ray tube) display, which produces a visual image by producing and directing a stream of electrons at a treated display surface. The stream could only be directed to one point at any given time, but can be systematically swept across the display with such speed as to create the visual impression of a single image. This technology is fairly well-developed, but has reached the point where perceptible increases in quality are difficult to achieve. A CRT also takes up a relatively-large amount of space because the components used for generating the electron stream must be placed at a certain distance from the display screen. Many recently-developed projection display systems, in contrast, feature a much slimmer profile. In addition, projection display systems often produce much cleaner visual images. The combination of these advantages has made such systems immensely popular.
One such projection-display system is a spatial light modulator (SLM) commercially available from Texas Instruments of Dallas, Tex. under the trademark DLP® (or Digital Light Processing®). DLP® projection-display systems utilize a digital micromirror device (DMD) in their optical path. The DMD typically includes an array of thousands of tiny mirrors that are used to manipulate colored light originating at an internal light source. Lenses and other components in the optical path adjust the light for use by the SLM, or convey the image it generates to a display plane. The colored light is reflected by the SLM and projected onto a display plane for viewing according to an input image. Projection lenses may be used to magnify and/or focus the image on the display plane.
It should be noted that the light source may be any type of light source, including a light-emitting diode (LED), a lamp, a laser, or the like. Some light sources, particularly LEDs, emit light that exhibit Lambertian characteristics. As illustrated in
These attempts, however, typically require a series of lenses that must be in strict alignment relative to each other as well as the LED light source and the SLM. Due to the alignment issues, the lens system can be extremely difficult and expensive to produce.
Accordingly, there is a need for a system and method to collimate light that is easy and efficient to produce.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by embodiments of the present invention that provide a system and a method for a collimator suitable for use in, for example, a display system.
In accordance with an embodiment, an image projection system is provided. The image projection system includes a light source, a spatial light modulator, and a collimator positioned between the light source and the spatial light modulator along the light path. The collimator includes a first lens and a second lens in direct contact with each other. The first lens may be a hemispherical or hyperhemispherical ball lens. In an embodiment in which a hemispherical ball lens is used, the second lens may be in direct contact with the entire hemispherical surface, and the second lens may include a converging lens such as a Fresnel lens.
In accordance with another embodiment, a collimator is provided. The collimator includes a first lens having a first surface and a second surface and a second lens having a third surface and a fourth surface. At least a portion of the third surface of the second lens is in direct contact with the second surface of the first lens. The first lens may be hemispherical or hyperhemispherical.
In accordance with another embodiment, a method of providing a projection system is provided. The projection system includes providing a light source and positioning a collimator along the light path of the light source. The collimator includes a first lens and a second lens having a positive power and in direct contact with each other.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
a-5c illustrate another double-refractive collimator in accordance with another embodiment.
The making and using of the embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
Embodiments will be described in a specific context, namely, a spatial light modulator (SLM) based projection display system. Embodiments may also be applied, however, to projection display systems, in general, and specifically to other microdisplay-based projection display systems, such as those utilizing transmissive or reflective liquid crystal displays, liquid crystal on silicon, ferroelectric liquid-crystal-on-silicon, deformable micromirrors, and so forth. It should also be appreciated that embodiments described herein are illustrated with reference to specific sizes and materials. One of ordinary skill in the art will realize that the embodiments herein may be adjusted to account for variations in the dimensions, the wavelengths of the relevant light, the materials, and/or the like.
With reference now to
The SLM 205 may be coupled to a controller 230, which may be responsible for loading image data into the SLM 205, controlling the operation of the SLM 205, controlling the light produced by the light source 210, and so forth. A memory 235, which may be coupled to the SLM 205 and the controller 230, may be used to store the image data, as well as configuration data, color correction data, and so forth.
It should be noted that the light source 210 may be any type of light source, including a light-emitting diode (LED), a lamp, a laser, or the like. Embodiments such as those described herein, however, may be more beneficial when using light sources that exhibit Lambertian characteristics, such as a LED.
The light source 210 may also include a plurality of light sources. For example, a plurality of LEDs may be used. In this embodiment, one or more LEDs emitting different colors, such as a red-light emitting LED, a blue-light emitting LED, and a green-light emitting LED, are used. In some applications, it may be desirable to utilize multiple LEDs (or other light sources) for each color to increase the brightness of the resulting image on the display plane 215.
It should be noted that the embodiments discussed above are provided for illustrative purposes only, and that other configurations may be used. For example, other light sources, lens systems, mirrors, and the like may be used. Furthermore the number of each individual component may vary. For example, the number and colors included in the light source may vary, the number and size of the DMD may vary, and the like. As another example, a display system may include scanning elements, such as a rotating reflective element or a rotating refractive element, to scan one or more light sources across the surface of the SLM.
Referring now to
As illustrated in
The first lens 410 is preferably a (nearly or) hemispherical ball lens having a first surface 410a and a second surface 410b. The second surface 410b of the first lens 410 comprises an outer spherical surface of a hemispherical ball lens and the first surface 410a of the first lens 410 is a concave spherical surface formed into the otherwise planar surface of the hemisphere. The first lens 410 may be molded from a flint glass or plastic, such as SF66 having a refractive index of about 1.93 or OHARA LAH79 having a refractive index of about 2.0. Other materials may be used; however, it is preferred that the material used for the first lens have a refractive index of at least 1.7.
It is preferred that the first lens 410 be in an aplanetic configuration in that there is little or no spherical aberration or coma. Accordingly, the first lens 410 is preferably configured such that the center of the radial curvature of the first surface 410a and the second surface 410b of the first lens 410 are along the optical axis. In this configuration, the first surface 410a and the second surface 410b of the first lens 410 are rotationally symmetric about the optical axis. The center of the radial curvature for the first surface 410a is preferably along a line drawn from the leftmost portions of the first lens 410, e.g., the first lens 410 is hemispherical.
The second lens 412 has a first surface 412a that shares a common interface with the second surface 410b of the first lens 410 and a second surface 412b having a shape that acts to further converge the light, such as a Fresnel lens, an aspherical surface, a convex lens, or the like. By sharing a common surface, the first lens 410 and the second lens 412 may be assembled easily with little or no misalignment between the lenses. In an embodiment, the second lens 412 is formed of a crown glass or plastic, such as polymethyl methacrylate (PMMA) having a refractive index of about 1.5 or polycarbonate having a refractive index of about 1.59. Other materials may be used; however, it is preferred that the material used for the second lens 412 have a refractive index of about 1.5, and more preferably has a refractive index less than the refractive index of the first lens 410. If desired, the first lens 410 and the second lens 412 may be coupled together using an optical adhesive.
Preferably, the first lens 410 and the second lens 412 both have a positive power such that both the first lens 410 and the second lens 412 act to converge the light emitted from the light source 210. In this manner, divergent light emitted from a light source such as an LED is converged and collimated. This allows an easier propagation of the light to the downstream optics and provides an easier way to conserve the etendue and makes a more efficient system with an optimum (or higher) luminance. Furthermore, the first lens 410 preferably has a higher refractive index (most preferably greater than about 1.7) than the refractive index of the second lens (most preferably between about 1.4 and 1.7) for the relevant light wavelengths.
It should be appreciated that an outer surface 412c of the second lens 412 may be any shape, provided that the convergence of the light is not interrupted. In this manner, the outer surfaces 412c may be shaped to provide an easy, secure, and accurate alignment with the light source 210. For example, the light source 210 may be mounted to a frame, which is shaped to receive the second lens 412. This allows the first lens 410 and the second lens 412 to be assembled as one piece and attached to the frame, wherein the frame helps maintained proper alignment with the light source 210.
The cavity 418 may comprise air, a light transmissive liquid, gel, or other non-solid material, or the like. Optionally, a transmissive window 416 may be included, and may be used to seal the liquid, gel, or other material in the cavity 418, if used. Alternatively, the cavity 418 may be filled with a curable liquid resin or adhesive. In this embodiment, the cavity is initially filled with a liquid such as Norland Optical Adhesive 81 (NOA81) and then cured or hardened by exposure to UV light, short wavelength radiation or the like. If used, the material filling the cavity 418 preferably has a refractive index of about 1.4 to about 1.6. The transmissive window 416 is preferably a rigid element having highly transmissive properties, such as BK7 having a refractive index of about 1.45 to about 1.55. At the same time, the doublet can advantageously replace the window and still seal the emitting source.
Details of an example of the construction of double-refractive collimator such as that illustrated in
In this embodiment, the surface of the Fresnel lens comprises an aspherical surface as defined by the following polynomial expansion:
where k is the “conic coefficient” for the surface, and where c is the curvature (1/radius) of the base sphere (from which the asphere deviates) at the vertex, and the coefficients αi are the aspheric coefficients defining the shape of the asphere. The aspheric coefficients according to an embodiment are provided below in Table 2.
One of ordinary skill in the art will appreciate the materials and dimensions used for the first lens 410 and the second lens 412, as well as the window 416 and/or the material contained in the cavity 418, may be adjusted to obtain the desired results. Additionally, it should be appreciated that the materials and dimensions are dependent upon, among other things, the light source 210.
As an example, the thickness of the second lens 412, i.e., the distance between the common interface between the first lens 410 and the second lens 412 and the second surface 412b of the second lens 412 along the optical axis may be varied depending upon the type of material and the characteristics of converging lens used along the second surface 412b, as the amount of convergence desired for the optical system, e.g., the SLM 205 and the focus lenses 312.
a-5c illustrate a dual-channel collimator that may also act as the collimator 310 (see
The first lens 510 is preferably a hyperhemispherical ball lens, although a hemispherical ball lens may also be used, having a first surface 510a and a second surface 510b. The first surface 510a of the first lens 510 is a concave spherical surface formed into an opposing surface from the second surface 510b. The first lens 510 may be molded from a flint glass or plastic, such as SF66 having a refractive index of about 1.92 or OHARA LAH79 having a refractive index of about 2.0. Other materials may be used; however, it is preferred that the material used for the first lens 510 have a refractive index of at least 1.7.
Similar to the embodiment discussed above with reference to
The second lens 512 has an inner portion 512a and an outer portion 512b, wherein the inner portion 512a comprises a lens having a first set of characteristics and the outer portion 512b comprises an aspherical lens ring around the circumference of the inner portion 512a. The effect of the inner portion 512a and the outer portion 512b is to provide two different paths for the light: one path for light relatively close to the optical axis; and another path for light farther from the optical axis. In an embodiment the inner portion 512a and the outer portion 512b of the second lens 512 are configured such that the inner portion 512a creates a first channel for light between about 0 degrees to about 40 degrees relative to the optical axis and the outer portion 512b creates a second channel for light between about 40 degrees to about 80 degrees relative to the optical axis.
As illustrated in
In this preferred embodiment, an inner surface 512b1 and an outer surface 512b2 of the outer portion 512b has an aspherical shape. It should be noted that the inner surface 512b1 of the outer portion 512b of the second lens 512 does not share a common interface with the outer surface 510b of the first lens 510. Rather, these two surfaces are separated by a material, preferably air, though other materials may be used.
Details of an example of the construction of double refractive lens system such as that illustrated in
One of ordinary skill in the art will appreciate the materials and dimensions used for the first lens 510 and the second lens 512, as well as the encapsulant 514, may be adjusted to obtain the desired results. Additionally, it should be appreciated that the materials and dimensions are dependent upon, among other things, the light source 210.
Although the embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
