Optical: systems and elements – Diffraction – From grating
Reexamination Certificate
2001-09-27
2004-11-30
Dunn, Drew (Department: 2872)
Optical: systems and elements
Diffraction
From grating
C359S565000, C359S569000, C359S015000, C359S016000
Reexamination Certificate
active
06825980
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to diffractive optical element (DOE) based optical systems of ultra-compact design capable of modifying the inherent elliptical, divergent, eccentric and astigmatic characteristics of laser beams produced from laser diode sources, such as visible laser diodes (VLDs).
2. Brief Description of the Prior Art
Laser diodes or visible laser diodes (VLD) are often used as light sources in many scientific_and engineering applications. While laser diodes offer significant advantages over other laser sources, e.g. gas lasers, in terms of efficiency, size, and cost, they nevertheless suffer from several undesirable optical characteristics, namely: high beam divergence, elliptical beam profile, and astigmatism. In order to use laser diodes in many communication, data-storage, scanning, and imaging applications, these inherent deficiencies in laser diodes must be corrected.
While complex refractive-optics type systems (employing anamorphic lenses and the like) have been developed for the purpose of correcting for laser diode characteristics, such systems are generally bulky and expensive, and thus ill-suited for use in numerous applications.
U.S. Pat. Nos. 5,247,162 and B1 4,816,660 disclose the use of a lens and aperture-stop to shape the laser beam produced from a VLD for use in laser scanners. While this technique all provides an inexpensive way of shaping the cross-section of a VLD laser beam, it does so at the expense of a substantial loss in beam power. Moreover, this “pinhole” technique is incapable of correcting for astigmatism in laser beams produced by VLDs.
In recent years, alternative approaches to VLD beam shaping and correction have been developed. Such alternative techniques include, for example, the use of: integrated-optics lenses; computer-generated hologram (CGH) gratings; micro-Fresnel lenses; waveguide optics; and holographic optical elements (HOEs).
The use of HOEs for beam collimation, shaping/profiling and astigmatism-correction has received great attention, as such devices can be made inexpensively and small in size to be used in CD-ROM players, consumer-products and analytical instruments employing VLDs and the like. Examples of prior art laser diode beam-correction techniques employing HOEs are disclosed in the following journal articles: “Efficient Beam-Correcting Holographic Collimator For Laser Diodes” by A. Aharoni, et al., published in Vol. 17, No. 18, OPTICS LETTERS, Sep. 15, 1992, at pages 1310-1312; “Beam-Correcting Holographic Doublet For Focusing Multimode Laser Diodes” by A. Aharoni, et al., published in Vol. 18, No. 3, OPTICS LETTERS, Feb. 1, 1993, at pages 179-181; and “Design of An Optical Pickup Using Double Holographic Lenses” by Hiroyasu Yoshikawa, et al., published in SPIE, Vol. 2652, 1996, at pages 334-340.
While the above-cited prior art publications disclose dual-HOE optics systems for beam-collimation, beam-shaping and astigmatism correction, such prior art design methods do not enable the design and construction of laser beams having any degree of astigmatism, focal-distance, spot-size, focused-spot aspect-ratio, and zero dispersion. These are critical requirements in many laser scanning bar code reading applications.
Prior art HOE-based systems do not address the fact that commercial VLDs suffer from beam eccentricity (i.e. poor beam pointing characteristics). Consequently, it has not been possible to successfully carry out many design objectives by virtue of the fact that assumptions made during system design are not satisfied during design realization.
Accordingly, there is a great need in the art for an improved method of designing and constructing optical systems for modifying the elliptical, divergent, eccentric and astigmatic characteristics of laser beams inherently produced from commercial-grade laser diodes, while avoiding the shortcomings and drawbacks of prior art systems, devices, and methodologies.
OBJECTS AND SUMMARY OF THE PRESENT INVENTION
Thus, it is a primary object of the present invention to provide an improved method of designing optical systems for modifying the inherent elliptical, divergent, eccentric and astigmatic characteristics of a laser diodes, while avoiding the shortcomings and drawbacks of prior art systems, devices, and methodologies.
Another object of the present invention is to provide a novel laser beam modification system employing a plurality of diffractive optical elements (DOEs) for modifying the size and IU shape of a laser beam produced from a commercial-grade laser diode, such as a VLD, over an extended range which has hitherto been impossible to achieve using conventional techniques, while avoiding the introduction of dispersion in the output laser beam which is commonly associated with prior art HOE doublets and the like.
Another object of the present invention is to provide such a DOE-based laser beam modifying system, wherein the inherent astigmatism characteristics associated with a VLD are eliminated or minimized.
Another object of the present invention is to provide a DOE-based laser beam modifying system, wherein beam dispersion is minimized, or normal dispersion or reverse dispersion characteristics are provided for any given beam compression or expansion ratio, by selecting the proper angle between the two DOEs of the system.
Another object of the present invention is to provide a DOE-based laser beam modifying system, wherein beam dispersion is minimized for the system acting alone, or fine-tuned to compensate for the dispersion of other elements preceding it or following the system.
Another object of the present invention is to provide a laser beam modifying system capable of producing a laser beam having a desired spot-size over a specified depth of field, achieved by focusing the laser beam with a lens (or variable DOE of a selected type), and then reshaping the laser beam using a pair of DOEs.
Another object of the present invention is to provide a laser beam producing system employing a set of beam-modifying DOEs which produce zero dispersion while simultaneously providing any desired aspect-ratio for the beam leaving (exiting) the second DOE.
Another object of the present invention it to provide a HOE-based laser beam modifying system adapted for use in a broad range of applications employing VLDs, which includes, but is not limited to, laser scanning applications.
Another object of the present invention it to provide a CGH-based laser beam modifying system adapted for use in a broad range of applications employing VLDs, which includes, but is not limited to, laser scanning applications.
Another object of the present invention is to provide an ultra-compact DOE-based device capable of collimating or focusing laser beams produced from astigmatic VLDs while minimizing dispersion beam dispersion and correcting for beam ellipticity.
A further object of the present invention is to provide an ultra-compact optics module for modifying the aspect-ratio of laser beams produced by VLDs, while eliminating beam astigmatism introduced by virtue of the inherent astigmatic difference in the VLD, and minimizing dispersion in the output laser beam created by wavelength-dependent variations in the spectral output of the VLD, such as superluminescence, multi-mode lasing, and laser mode hopping.
Another object of the present invention is to provide a novel optical-bench module which enables easy mounting and alignment of selected components of the laser beam producing systems of the present invention so that the inherently elliptical beam produced from commercial VLDs is simply aligned on the optical axis of the system.
Another object of the present invention is to provide a novel DOE-based laser beam producing device, wherein refractive optics (L
1
) having an axially symmetric surface profile characteristics are disposed between the laser diode source (VLD) and the diffractive optics (e.g. DOEs D
1
and D
2
), to enable the use the DOEs to modify (e.g. correct or eliminate) astigmatism in the output laser bea
Amundsen Thomas C.
Carullo Thomas
Dickson LeRoy
Good Timothy A.
Groot John
Assaf Fayez
Dunn Drew
Metrologic Instruments Inc.
Perkowski Esq. P.C. Thomas J.
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