Abstract

To achieve very high data rates (>109 bits/s) in optical data storage systems it is necessary to employ a large number of laser beams for parallel read–write–erase operations. Bringing all these beams to diffraction-limited focus with a high-numerical-aperture objective lens (while maintaining focus and tracking) requires techniques that are fundamentally different from those that are currently practiced in the field of optical data storage. We present two possible solutions to the problem of designing an objective lens for such systems, one involving an array of high-quality lenslets and the other based on a single, high-numerical-aperture annular-field-of-view conventional lens. Both approaches have advantages and disadvantages, on which we elaborate in the course of our discussions.

© 1999 Optical Society of America

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References

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  1. M. Mansuripur, The Physical Principles of Magneto-optical Recording (Cambridge U. Press, Cambridge, UK, 1995).
    [CrossRef]
  2. M. A. Fitch, “Molded optics: mating precision and mass production,” Photon. Spectra 25, 83–87 (1991).
  3. Examples of these emerging technologies include vertical cavity laser diode arrays, large arrays of miniature spatial light modulators, integrated optical waveguide–modulator–detector arrays, smart-pixel detector arrays, micromechanical actuators, and miniature beam scanners.
  4. F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
    [CrossRef]
  5. Each focused spot covers an area roughly equal to p2. Covering N tracks would require an area of Np2, which is approximately 1/N of the area of the circle.
  6. A. Offner, “New concepts in projection mask aligners,” Opt. Eng. 14, 130–132 (1975).
    [CrossRef]
  7. J. Braat, “Quality of microlithographic projection lenses,” in Optical Microlithography for Integrated Circuit Fabrication and Inspection, H. L. Stover, S. Wittekoek, eds., Proc. SPIE811, 22–30 (1987).
    [CrossRef]

1992

F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
[CrossRef]

1991

M. A. Fitch, “Molded optics: mating precision and mass production,” Photon. Spectra 25, 83–87 (1991).

1975

A. Offner, “New concepts in projection mask aligners,” Opt. Eng. 14, 130–132 (1975).
[CrossRef]

Braat, J.

J. Braat, “Quality of microlithographic projection lenses,” in Optical Microlithography for Integrated Circuit Fabrication and Inspection, H. L. Stover, S. Wittekoek, eds., Proc. SPIE811, 22–30 (1987).
[CrossRef]

Cloonan, T. J.

F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
[CrossRef]

Feldblum, A. Y.

F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
[CrossRef]

Fitch, M. A.

M. A. Fitch, “Molded optics: mating precision and mass production,” Photon. Spectra 25, 83–87 (1991).

Hinton, H. S.

F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
[CrossRef]

Mansuripur, M.

M. Mansuripur, The Physical Principles of Magneto-optical Recording (Cambridge U. Press, Cambridge, UK, 1995).
[CrossRef]

McCormick, F. B.

F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
[CrossRef]

Mersereau, K. O.

F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
[CrossRef]

Offner, A.

A. Offner, “New concepts in projection mask aligners,” Opt. Eng. 14, 130–132 (1975).
[CrossRef]

Sasian, J. M.

F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
[CrossRef]

Tooley, F. A. P.

F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
[CrossRef]

Opt. Eng.

A. Offner, “New concepts in projection mask aligners,” Opt. Eng. 14, 130–132 (1975).
[CrossRef]

Opt. Quantum Electron.

F. B. McCormick, F. A. P. Tooley, T. J. Cloonan, J. M. Sasian, H. S. Hinton, K. O. Mersereau, A. Y. Feldblum, “Optical interconnections using microlens arrays,” Opt. Quantum Electron. 24, 465–477 (1992).
[CrossRef]

Photon. Spectra

M. A. Fitch, “Molded optics: mating precision and mass production,” Photon. Spectra 25, 83–87 (1991).

Other

Examples of these emerging technologies include vertical cavity laser diode arrays, large arrays of miniature spatial light modulators, integrated optical waveguide–modulator–detector arrays, smart-pixel detector arrays, micromechanical actuators, and miniature beam scanners.

Each focused spot covers an area roughly equal to p2. Covering N tracks would require an area of Np2, which is approximately 1/N of the area of the circle.

J. Braat, “Quality of microlithographic projection lenses,” in Optical Microlithography for Integrated Circuit Fabrication and Inspection, H. L. Stover, S. Wittekoek, eds., Proc. SPIE811, 22–30 (1987).
[CrossRef]

M. Mansuripur, The Physical Principles of Magneto-optical Recording (Cambridge U. Press, Cambridge, UK, 1995).
[CrossRef]

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Figures (7)

Fig. 1
Fig. 1

Schematic diagram showing an array of lenslets focusing a large number of laser beams onto a moving storage medium. Each lens covers n tracks within its field of view, and the number of beams assigned to each lenslet may be less than or equal to n. Each focused spot may be used to address more than one track, provided that some form of scanning in the cross-track direction is implemented.

Fig. 2
Fig. 2

Simple, biaspherical objective lens designed for use as an element of a lenslet array. This lens has a diameter of 1 mm, a NA of 0.5, a working distance of 300 µm, and a flat field of view of better than ±50 µm. The infinite-conjugate lens is telecentric and, at the design wavelength of = 670 nm, its rms wave-front error at the edge of the field is less than 0.01λ (Strehl ratio ≥0.98). This lens, found by a lens design computer program, may or may not be manufacturable with the present-day glass molding technology, but it demonstrates that the numbers used in the example given in the text are realistic.

Fig. 3
Fig. 3

Microlens system layout showing a single write channel. Shown are a collimating microlens that collimates light from a VCSEL, a thick plate representing a beam splitter to permit write–read operations, a thin plate representing a beam-angular modulator, and a focusing microlens.

Fig. 4
Fig. 4

Schematic diagram showing the annular field of view of a single, large lens covering many tracks of a moving storage medium. Inasmuch as for each track there are two different points of access within the annulus, the system designer is free to choose either point for placing the corresponding focused spot on the storage surface. We have, somewhat arbitrarily, divided the tracks into groups of n and placed the focused spots in alternating groups on these tracks, but any other arrangement would be acceptable as well. If the number of available beams happens to be less than the total number of tracks covered within the lens’s field of view, then each beam must be used to address more than one track, thus requiring some form of cross-track scanning.

Fig. 5
Fig. 5

Schematic diagram of a typical lens used in microlithography. This lens with a NA of 0.5 is made of several different glasses that have flat or spherical surfaces. The lens is diffraction limited over a flat field of view of ∼10-mm diameter and is telecentric in the image space.

Fig. 6
Fig. 6

Eight-element lens with a 10.8-mm-diameter annular field of view, designed for optical data storage applications. The criteria used in this design are listed in Table 2.

Fig. 7
Fig. 7

Nine-element lens with a 10.8-mm-diameter annular field of view, designed for optical data storage application. The criteria used in this design are listed in Table 2.

Tables (4)

Tables Icon

Table 1 rms Wave Front/Strehl Ratio as a Function of Wavelength

Tables Icon

Table 2 Requirements for a Lens Intended for Optical Data Storage Applications

Tables Icon

Table 3 Wave-Front Distortion for the Annular-Field Lens Shown in Fig. 6

Tables Icon

Table 4 Wave-Front Distortion for the Annular-Field Lens Shown in Fig. 7

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