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Focus, Seek, and Dither Algorithms for Liquid Crystal Lens

IP.com Disclosure Number: IPCOM000126801D
Original Publication Date: 2005-Aug-02
Included in the Prior Art Database: 2005-Aug-02
Document File: 5 page(s) / 242K

Publishing Venue

IBM

Abstract

This article desires to provide control algorithms, in the areas of focus, seek, and dither, for liquid crystal lenses for optical disk drives, including Blu-Ray, HD-DVD, DVD, CD, and holography.

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Focus, Seek, and Dither Algorithms for Liquid Crystal Lens

Figure 1 shows liquid crystal lens assembly 11, which comprises a front liquid crystal (LC) lens 13 which is proximal relative to optical media 95, a rear LC lens 15 which is distal relative to optical media 95, and a transparent spacer plate 17 separating lenses 13 and 15. A laser light source 19 (indicated schematically by the arrow) is projected into rear lens 15 from right to left, in the direction of the +X axis, through spacer 17, and then through front lens 13. Light source 19 is independently focused by each lens 13, 15 into a conical beam 23, 25, respectively, and focused to a common point 21 to the left of front lens 13. The thickness of spacer plate 17 is selected to be one-half of one wavelength of the light emitted by light source 19. Light source 19 is preferably a blue-laser light source with a wavelength of 405 nm which is the wavelength being considered for both High Definition Digital Versatile Disk (HD-DVD) and Blu-Ray. However, other wavelengths could be used, such as red laser light at 650 nm which is used in today's Digital Versatile Disk (DVD).

FIGs 1, 3, and 4 show a portion of an optical disk 95. Optical disk 95 rotates about the X-axis, and the Z-axis defines the radial direction along the optical disk. If optical disk 95 is either writable or re-writable, optical disk 95 may have grooves 97 and lands 98. Each groove 97 has sidewalls 96. Data is on data layer 99. Data layer 99 may comprise stamped pits for Read-Only-Memory (ROM). If data layer 99 is stamped pits, then grooves 97 and lands 98 are probably absent. Alternately, data layer 99 may comprise magneto-optical media, phase-change media, or holographic media for the storage of data which can be rewritten. Also, data layer 99 may comprise phase-change, dye, or holographic media which is write-once, read-many (WORM).

Lenses 13, 15 are identical in construction and are illustrated in detail in FIG. 2. For simplicity, only lens 13 is discussed in FIG. 2, even though the following description applies equally to lens 15. Lens 13 consists of a pair of parallel, glass plates, 31, 33, and a plurality of thin, rectangular, insulative, polymer films 35 sandwiched perpendicular to glass plates 31 and 33. In the embodiment shown, plates 31, 33 are 1 mm squares. The inner surfaces of plates 31, 33 are spaced apart by 70 microns which is also the width of films 35. Each film 35 has a length of 1 mm and a thickness of 2 microns. Glass substrates 41, 43 are located at the upper and lower ends, respectively, of lens 13 with films 35 sandwiched therebetween. Films 35 and substrates 41, 42 are parallel to one another, and perpendicular to plates 31,
33. Films 35 and substrates 41, 43 are evenly spaced apart from one another by fifty microns. Thus, in FIGs 1-4, there are seven films 35 which define six layers between substrates 41, 43. In general, the number of layers is one less than the number of films 35. Pre...