Patent Grant
6989938
In traditional optical systems having reflecting and refracting surfaces, it is common to assume that the light passing through the system is limited to paraxial rays, specifically, rays that are near the optical axis and are sustained within small angles. However, practical optical systems rarely are limited to paraxial rays, and thus, the actual images assumed by gaussian optics often depart from the “perfect” image. This departure from the “perfect” image results in the introduction of distortion into the optical system, called aberrations. These aberrations are most problematic in small focal ratio optical systems where the angle from the optical axis is larger.
In a monochromatic optical system with only spherical surfaces, there are five (5) basic ray and wave aberrations, namely, spherical aberrations, coma, astigmatism, curvature of field, and distortion. Optical systems for use with multi-chromatic light have an additional source of distortion, namely, chromatic aberration.
Because the distortion introduced by aberrations into an optical system significantly degrades the quality of the images on the image plane of such system, there are significant advantages to the reduction of those aberrations. Various techniques are often used to minimize the aberrations. For example, in order to minimize spherical aberrations or coma, a lens may be “bent” to have different radii of curvature on opposite sides while maintaining a constant focal length, such as is contemplated by using the Coddington shape factor. Also, a pair of lenses, where one glass lens has a positive focal length, and the other made from a different glass has a negative focal length, are used together to correct spherical aberrator. One example of this technique is the “doublet” lens in which the two lenses have the same radius of curvature on the facing sides, and are cemented together.
Despite the available techniques to minimize the various aberrations, it is often difficult to simultaneously minimize all aberrations. In fact, corrections to an optical system to minimize one type of aberration may result in the increase in one of the other aberrations. Typically, one may decrease coma, at the expense of increasing spherical aberrations. Moreover, because it is often necessary to measure the aberrations only after an optical system is constructed due to additional aberrations from manufacturing or assembly tolerances, the creation of an optical system with minimal aberration typically requires several reconstructions before a suitable system is developed.
In complex optical systems, in addition to traditional aberration correction, it is often advantageous to create an optical element which generates a unique wavefront phase profile. Typically, these unique optical elements have been created by sophisticated grinding and polishing of traditional lenses. However, this method of manufacturing a unique optical element requires a significant amount of time and expertise, and results in a high cost of manufacturing the optical element.
Consequently, a need exists for the creation of an optical element which can generate a unique wavefront phase profile, and that can simultaneously minimize the chosen aberrations within an optical system.
The wavefront aberrator of the present invention includes a pair of transparent windows, or plates, separated by a layer of a monomers and polymerization initiators, such as epoxy. This epoxy exhibits a variable index of refraction as a function of the extent of its curing. Curing of the epoxy may be made by exposure to light, such as ultraviolet light. The exposure to light may be varied across the surface of the epoxy to create a particular and unique wavefront retardation profile such that when an ideal plane wave passes through the wavefront aberrator, a predetermined change of the wavefront profile can be affected by the wavefront aberrator device. Conversely, if a distorted wavefront is known, such as by measuring the wavefront with a Hartmann/Shack sensor, a correction of such aberrated or distorted wavefront aberration may be achieved by first producing a complementary wavefront aberrator device such that passing the abnormal wavefront through the wavefront aberrator device, a plane wave emerges.
One method of creating the wavefront aberrator of the present invention includes the exposure of the epoxy to an array of light emitting diodes (LEDs). These LEDs may be selectively illuminated such that different portions of the epoxy are exposed to different levels of illumination. This variance in illumination results in the creation of a wavefront aberrator having a varying index of refraction across its surface, and may include the formation of multiple sub-regions, where the index of refraction of the cured epoxy in a sub-region has a constant index of refraction, with the index of refraction varying between adjacent sub-regions.
An alternative method of creating the wavefront aberrator of the present invention includes the exposure of the epoxy to an array of LEDs through a demagnifier lens. In this manner, the LEDs may create a curing pattern which is then focussed onto the surface of the epoxy to create a similar, yet smaller, version of the curing pattern to provide for reduced-sized wavefront aberrators.
Yet another alternative method of creating the wavefront aberrator of the present invention includes the creation of a curing pattern by the transmission of light through a liquid crystal display (LCD). A non-coherent light source may be positioned adjacent to a diffuser to create a diffused light source. This diffused light may then be transmitted through a LCD containing a curing pattern, and onto a wavefront aberrator. As the epoxy is exposed, the curing pattern on the LCD creates the desired refractive index profile. New patterns may be generated by changing the pattern on the LCD.
A sensor may be placed beneath the wavefront aberrator to monitor the transmitted image of the curing pattern. The output of this sensor may be used to actively modulate the transmission of light through the LCD to create a wavefront aberrator having a desired refractive index profile, and to provide for an active monitor and control of the curing of each sub-region of the wavefront aberrator.
Another alternative method of creating the wavefront aberrator of the present invention includes the creation of a curing pattern by the selective illumination of portions of the epoxy using a point light source, such as a laser. This selective illumination may be accomplished by rastering a portion of the surface of the epoxy, varying the speed and/or intensity of the light source to vary the curing of the epoxy. Alternatively, the light source could trace particular curing patterns directly onto the wavefront aberrator at various speeds and/or intensities of light, such as by raster or vector scanning the curing pattern onto the aberrator. Also, a positive or negative, or “contact print,” containing a particular wavefront retardation design may be positioned adjacent the wavefront aberrator and exposed to a diffused or collimated light to create the desired refractive index profile.
Referring initially to
The shape of aberrator 100 is shown in
Referring to
Epoxy 104 is, in a preferred embodiment, a light-curable resin comprised of monomers and polymerization initiators. The refractive index of the resin changes as the resin is cured, and it varies between locations within the resin layer depending on the extent of curing of the epoxy. The extent of curing is determined by the percentage of cross-linking between the monomers within the epoxy. Suitable resins include VLE-4101 UV-Visible Light Cure Epoxy, available from Star Technology, Inc., or Optical Adhesive #63, U.V. Curing, available from Norland Products, Inc. Typically, these resins are curable by exposure to UV or visible light radiation in the range of 300 to 550 nanometers (300–550 nm). Generally, the present invention applies to any type of epoxy that exhibits an index of refraction change upon curing and the corresponding curing light source may have wavelengths ranging between 300 nm and 3000 nm.
It is to be appreciated that many other suitable resins exist which exhibit a similar change in its index of refraction upon exposure to light. Other monomers that polymerize into long-chain molecules using photo-initiators may be used in the present invention. For example, a suitable monomer may be chosen from the family of epoxides, urethanes, thiol-enes, acrylates, cellulose esters, or mercapto-esters, and a broad class of epoxies. Also, for example, a suitable photo-initiator may be chosen from alpha cleavage photoinitiators such as the benzoin ethers, benzil ketals, acetophenones, or phosphine oxides, or hydrogen abstraction photoinitiators such as the benzophenones, thioxanthones, camphorquinones, or bisimidazole, or cationic photoinitiators such as the aryldiazonium salts, arylsulfonium and aryliodonium salts, or ferrocenium salts. Alternatively, other photoinitiators such as the phenylphosphonium benzophene salts, aryl tert-butyl peresters, titanocene, or NMM may be used.
In the present invention, a light source containing a particular wavelength irradiates the monomer layer which activates the photo-initiator and begins the curing process within the epoxy. The curing process results in a corresponding change of the index of refraction within the resin. However, it is also to be appreciated that terminating the exposure to the particular wavelength of light ceases the curing of the epoxy, and ceasing the change of the index of refraction exhibited by the epoxy. In this manner, a aberrator 100 of the present invention may be formed by exposing certain portions of the resin 104 to a light source which varies with time and position, resulting in an aberrator having a varied index of refraction across its surface.
From
It is to be appreciated that the incorporation of three (3) different levels of refractive index in
Referring now to
In a preferred embodiment, upper transparent cover 106 and lower transparent cover 104 are formed from a rigid transparent material, such as glass or plastic. While glass provides a stable platform for the formation of the refractive index profile, such rigidity is not necessary. In fact, covers 102 and 106 may be made from a flexible material, such as a transparent polymer. A suitable transparent polymer may include, but not be limited to, mylar film, polycarbonate film, or acetate film. Use of such materials results in a flexible aberrator having a distinct refractive index profile.
Referring to
In operation, once a desired refractive index profile is determined, computer 136 determines a particular pattern to be illuminated in the LED array panel 132 thereby generating a curing pattern which is directed through diffuser element 140 onto a aberrator 100. By selectively illuminating particular LEDs 135 and 137, for example, within the LED array panel 132, the epoxy (not shown this Figure) is selectively cured. This selective curing creates a pre-determined, particular refractive index profile corresponding to the time of exposure of the epoxy as well as the intensity of the exposure. This selective curing results in an aberrator with areas having different indices of refraction. Thus, by varying the intensity and period of illumination of LEDs 135 and 137, for example, the aberrator may be formed to exhibit the desired refractive index profile.
Referring now to
In a preferred embodiment, light source 172 of system 170 is a constant fluence light having a constant intensity across the illuminated surface of the light. For example, light source 172 may contain an array of LEDs, or any other suitable source of illumination. The optical transmissive properties of the LCD can be controlled by applying a variable electrical voltage to an array of electrodes on an LCD device. This provides for the spatial and temporal variation of the intensity of light transmitted through the LCD device to selectively cure the resin 104 in the aberrator 100.
As an addition to system 170, a detector 185 may be placed beneath aberrator 100 to detect the transmitted image 186 through aberrator 100. A feedback interface 188 may connect sensor 185 to computer 189, which may in turn control LCD panel 176. In this manner, a refractive index profile may be determined in the computer 189, implemented in the LCD 176, and verified in sensor 185, thereby ensuring the appropriate wavefront profile was created in aberrator 100. Sensor 185 may include a intensity imager, such as a CCD or a wavefront sensor, such as a Shack-Hartmann sensor.
Although panel 176 is discussed above as a LCD panel, an alternative embodiment could incorporate a photographic negative or positive that may be used to form the refractive index profile 184 in aberrator 100. In this manner, light source 172 would present a constant source of illumination, and the photographic negative or positive containing the refractive index profile 182 would control the spatial and intensity level of illumination reaching aberrator 100 to create the proper refractive index profile 184.
Referring now to
Alternatively, a spot 200 may be formed and moved across aberrator 100 in paths 202, 204 and 206. Yet another alternative method of forming refractive index profile 212 includes the formation of spot 210 in the center of aberrator 100, and movement of the spot along an outwardly spiraling path 212. Also, a particular refractive index profile 212 may be traced, or circumscribed in a predetermined area, by laser beam 193 directly forming the boundaries between the areas 214, 215, and 216, for example. In an alternative embodiment, laser beam 193 may remain stationary and the aberrator device 100 may be moved relative to the laser beam 193 such that the spot 210 moves across the surface of the aberrator. Specifically, aberrator 100 may be moved in directions 220 and/or 222 to move the spot 210 across the surface of the aberrator.
An alternative embodiment of the wavefront aberrator of the present invention is shown in
The present invention may be used to correct aberrations in virtually any optical system. For instance, the present invention may be particularly useful to correct inherent static aberrations in optical imaging systems, such as telescopes, binoculars, or microscopes. The present invention may also be particularly useful by incorporating aberration corrections into eyepieces of optical systems such as telescopes, binoculars, or microscopes.
The aberrator of the present invention may also be used to correct static aberrations in laser beams or associated optics for use in laser ranging, detection, scanning, communication, or tracking instruments. This listing of uses for the present invention is merely exemplary, and is not intended to limit the scope of the invention whatsoever.
While there have been shown what are presently considered to be preferred embodiments of the present invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope and spirit of the invention.
This application is a divisional of U.S. application Ser. No. 09/875,447, filed Jun. 4, 2001, now U.S. Pat. No. 6,813,082, which claims priority to U.S. Provisional Patent Application No. 60/253,418, filed Nov. 27, 2000.
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| Number | Date | Country | |
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| Parent | 09875447 | Jun 2001 | US |
| Child | 10946373 | US |
