Optical: systems and elements – Lens – Anamorphic
Reexamination Certificate
1998-11-23
2001-07-10
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Anamorphic
C359S670000, C264S001700
Reexamination Certificate
active
06259567
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microlens structure and fabrication method thereof. More particularly, the present invention relates to a microlens structures formed in high index materials using photolithography, gray scale masks, and reaction ion etching, the structures generally having two anamorphic surfaces on opposing ends of a single substrate, and fabrication methods thereof.
2. Discussion of Conventional Art
FIGS. 1A-1B
and
1
C-
1
D respectively illustrate a laser beam
1
output from an ideal laser beam diode (hereinafter, an ideal laser beam), and a laser beam
2
output from a laser diode. As shown in
FIGS. 1A-1B
, an ideal laser beam is a highly collimated, circular beam, with a gaussian intensity profile. By contrast, as shown in
FIGS. 1C-1D
, a laser beam generated by a laser diode is a non-collimated, elliptical aberrations. As such, the laser beam generated by a laser diode diverges by different amounts in orthogonal planes. To generate a laser beam having characteristics more closely resembling the characteristics of an ideal laser beam, the output of a laser diode must therefore be circularized (e.g., changed from its elliptical shape to a circular shape) and collimated. However, conventional systems for collimating and circularizing laser diode outputs experience at least three types of problems.
First, conventional systems require multiple separate elements. Specifically, conventional systems use a combination of two or more separate simple anamorphic elements such as prisms and cylindrical elements, combined with rotationally symmetric elements, to perform circularization and collimation of laser beams. For instance, as shown in
FIG. 2
, a conventional laser assembly includes a laser diode
21
followed by a three-part collimating lens
22
, a cylindrical lens
23
, and multiple anamorphic prisms
24
. Therefore, because conventional systems require several different anamorphic elements, they are expensive to manufacture and difficult to align.
Second, simple diffractive systems cannot provide the high optical powers required for collimating widely divergent laser beams, such as those generated by laser diodes. For instance, although diffractive optics are capable of achieving non-symmetric (anamorphic) beam shaping, their usefulness in correcting laser diodes is limited by fabrication constraints. Specifically, diffractive zone widths of less than approximately three (3) microns are required in order to collimate the wide divergence angles that are characteristic of laser beams generated by laser diodes. Yet, it is nearly impossible to fabricate diffractive optics with zone widths this small using conventional fabrication techniques including gray scale mask technology.
Third, simple refractive optics having anamorphic surface profiles suitable for collimating laser diode outputs are difficult to produce reliably. That is, although refractive optics typically achieve the optical powers required for collimation of a laser beam output, it is difficult to manufacture refractive optics with general anamorphic surfaces, i.e. different curvatures in orthogonal planes. One conventional method of manufacturing anamorphic refractive elements is to melt and stretch optical fibers. However, melting and stretching an optical fiber in this manner causes the design and fabrication process to become highly empirical and sensitive to numerous coupled process parameters (e.g., temperature and temperature distribution, fiber diameter, glass type, stress and strain, etc.). Another problem is that the resulting microlens is typically so small that alignment with the laser diode becomes very difficult.
Larger diameter refractive elements may be used to avoid alignment problems inherent in the melting and stretching process described above. Rather than melting and stretching, the surface of these elements may be shaped using conventional grinding and polishing techniques. However, when the conventional method of grinding and polishing is used to achieve a desired surface shape for the surface of refractive elements, the shape of those surfaces is limited to rotationally symmetric or simple cylindrical surface profiles. Arbitrary anamorphic surface profiles, such as saddle shapes, which are useful in collimating laser diode outputs, are therefore difficult to achieve with conventional grinding and polishing techniques.
New state-of-the-art diamond turning machines are capable of achieving bilaterally symmetric anamorphic profiles, but these are generally used for fabricating plastic molding tooling, not optical elements. Furthermore, diamond turning generates a fine periodic groove structure which must be removed with a post-polishing process to prevent scattering in the visible spectrum.
Moreover, conventional systems for collimating and circularizing laser diode outputs are problematic in at least three respects. First, conventional systems require multiple separate elements. Second, due to limitations and diffractive zone widths, conventional diffractive optics are not particularly well-suited for collimating laser diode outputs. Third, refractive optics having anamorphic surface profiles suitable for collimating laser diode outputs are difficult to reliably produce.
SUMMARY OF THE INVENTION
The present invention is directed towards a microlens structure and method of fabricating the same that substantially obviates one or more of the problems experienced due to the above and other limitations and disadvantages of the related art.
Accordingly, an object of the present invention is to reduce manufacturing costs and eliminate alignment problems associated with optics used to collimate and circularize a laser diode beam such as that output by a laser diode.
Another object of the present invention is to manufacture at least one of the opposing anamorphic surfaces of a microlens structure with a high index material.
Yet another object of the present invention is to manufacture an anamorphic surface of a microlens structure using a photolithographic process coupled with reactive ion etching or ion milling to eliminate manufacturing difficulties conventionally experienced.
Other and further objects, features and advantages of the present invention will be set forth in the description that follows, and in part will become apparent from the detailed description, or may be learned by practice of the invention.
To achieve these and other advantages, and in accordance with the purpose of the present invention as embodied and broadly described herein, the present invention includes a single microlens structure for circularizing and collimating incident light that includes a substrate having first and second opposing surfaces, a first anamorphic microlens positioned on one opposing surface and a second anamorphic microlens positioned on another of the opposing surfaces. The first microlens circularizes the light, while the second microlens collimates the light. The first and second surfaces are separated by a distance defined by the distance required for the first microlens to circularize incident light so that light passing through the first microlens is circularized at the second microlens. The first and second microlenses are preferably fabricated from a high index material such as GaP, TiO
2
, SrTiO
3
, Si, Ge, ZnSe, ZnS, InSb, InAs, YSZ, AlAs, BaTiO
3
, AlN, BN, CuGaS
2
, BiSiO
20
, Bi
12
GeO
20
, AgCl, AgBr, AgI, AgGaSe
2
, AgGaS
2
, Al
2
O
3
, LiTaO
3
, KnbO
3
, KRS-5 (TlI), KRS-6 (TlCl), and TlBr, and the incident light is preferably a laser beam. The single microlens structure may be a component in a device used to generate circularized and collimated light, such a device also including a laser diode for generating a laser beam that is circularized and collimated after passing through both of the anamorphic microlenses formed on opposing surfaces of the single microlens structure.
In addition, the present invention may include a method of circularizing and collimating incident light passing through a single microlens
Brown Daniel M.
Brown Jeremiah D.
Epps Georgia
Mems Optical Inc.
Thompson Tim
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