EP0929894A1 - Tete optique utilisant des elements micro-usines - Google Patents

Tete optique utilisant des elements micro-usines

Info

Publication number
EP0929894A1
EP0929894A1 EP97939651A EP97939651A EP0929894A1 EP 0929894 A1 EP0929894 A1 EP 0929894A1 EP 97939651 A EP97939651 A EP 97939651A EP 97939651 A EP97939651 A EP 97939651A EP 0929894 A1 EP0929894 A1 EP 0929894A1
Authority
EP
European Patent Office
Prior art keywords
optical
micro
mirror
machined
pair
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97939651A
Other languages
German (de)
English (en)
Inventor
Jeffrey P. Wilde
Joseph E. Davis
Jerry E. Hurst, Jr.
John F. Heanue
Kurt Petersen
Terry Mcdaniel
Joseph Drake
Jeff Drazan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Seagate Technology LLC
Original Assignee
Seagate Technology LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Seagate Technology LLC filed Critical Seagate Technology LLC
Publication of EP0929894A1 publication Critical patent/EP0929894A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
    • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
    • G02B26/085—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting means being moved or deformed by electromagnetic means
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
    • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
    • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
    • G02B26/0841—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting element being moved or deformed by electrostatic means
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
    • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
    • G02B26/0866—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting means being moved or deformed by thermal means
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4246—Bidirectionally operating package structures
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10532—Heads
    • G—PHYSICS
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    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/1055—Disposition or mounting of transducers relative to record carriers
    • G11B11/1058—Flying heads
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/122—Flying-type heads, e.g. analogous to Winchester type in magnetic recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/127—Lasers; Multiple laser arrays
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1362—Mirrors
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1384—Fibre optics
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
    • H02N1/00—Electrostatic generators or motors using a solid moving electrostatic charge carrier
    • H02N1/002—Electrostatic motors
    • H02N1/006—Electrostatic motors of the gap-closing type
    • H02N1/008—Laterally driven motors, e.g. of the comb-drive type
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2572—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to forms of polarisation-dependent distortion other than PMD
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/35—Optical coupling means having switching means
    • G02B6/351—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements
    • G02B6/3512—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being reflective, e.g. mirror
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/35—Optical coupling means having switching means
    • G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
    • G02B6/3544—2D constellations, i.e. with switching elements and switched beams located in a plane
    • G02B6/3548—1xN switch, i.e. one input and a selectable single output of N possible outputs
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/35—Optical coupling means having switching means
    • G02B6/3564—Mechanical details of the actuation mechanism associated with the moving element or mounting mechanism details
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10502—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing characterised by the transducing operation to be executed
    • G11B11/10515—Reproducing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10532—Heads
    • G11B11/10534—Heads for recording by magnetising, demagnetising or transfer of magnetisation, by radiation, e.g. for thermomagnetic recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10532—Heads
    • G11B11/10541—Heads for reproducing
    • G11B11/10543—Heads for reproducing using optical beam of radiation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/1055—Disposition or mounting of transducers relative to record carriers
    • G11B11/10552—Arrangements of transducers relative to each other, e.g. coupled heads, optical and magnetic head on the same base
    • G11B11/10554—Arrangements of transducers relative to each other, e.g. coupled heads, optical and magnetic head on the same base the transducers being disposed on the same side of the carrier
    • G—PHYSICS
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    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/1055—Disposition or mounting of transducers relative to record carriers
    • G11B11/10556—Disposition or mounting of transducers relative to record carriers with provision for moving or switching or masking the transducers in or out of their operative position
    • G11B11/10563—Access of indexed parts
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    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/085—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam into, or out of, its operative position or across tracks, otherwise than during the transducing operation, e.g. for adjustment or preliminary positioning or track change or selection
    • G11B7/08547—Arrangements for positioning the light beam only without moving the head, e.g. using static electro-optical elements
    • G11B7/08564—Arrangements for positioning the light beam only without moving the head, e.g. using static electro-optical elements using galvanomirrors
    • G—PHYSICS
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    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/085—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam into, or out of, its operative position or across tracks, otherwise than during the transducing operation, e.g. for adjustment or preliminary positioning or track change or selection
    • G11B7/0857—Arrangements for mechanically moving the whole head
    • G11B7/08576—Swinging-arm positioners
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    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/22—Apparatus or processes for the manufacture of optical heads, e.g. assembly

Definitions

  • the present invention relates generally to optical data storage systems. More particularly, the present invention relates to the use of micro-machined elements in optical data storage systems.
  • a magneto-optical storage system using a magneto-optical (MO) recording material deposited on a rotating disk, information may be recorded on the disk as spatial variatioas of 0 magnetic domains.
  • a magnetic domain pattern modulates an optical polarization, and a detection system converts a resulting signal from optical to electronic format.
  • a magneto-optical head assembly is located on a linear actuator that moves the head along a radial direction of the disk to position the optical head assembly over data tracks during recording and readout.
  • a magnetic coil is placed on a 5 separate assembly on the head assembly to create a magnetic field that has a magnetic component in a direction perpendicular to the disk surface.
  • a vertical magnetization of polarity, opposite to that of the surrounding magnetic material of the disk medium is recorded as a mark indicating zero or a one by first focusing a beam of laser light to form an optical spot on the disk.
  • the optical spot functionoas to heat the magneto-optical material to a temperature near or above a Curie point (a temperature at o which the magnetization may be readily altered with an applied magnetic field).
  • a current passing through the magnetic coil orients the spontaneous vertical magnetization either up or down. This orientation process occurs in the region of the optical spot where the temperature is suitably high.
  • the orientation of the magnetization mark is preserved after the laser beam is removed. The mark is erased or overwritten if it is locally reheated to the Curie point by the laser beam during a time the 5 magnetic coil creates a magnetic field in the opposite direction.
  • the Information is read back from a particular mark on the disk by taking advantage of the magnetic Kerr effect so as to detect a Kerr rotation of the optical polarization that Is imposed on a reflected beam by the magnetization at the mark of interest.
  • the magnitude of the Kerr rotation is determined by the material's properties (embodied in the Kerr coefficient).
  • the sense of the rotation 0 is measured by established differential detection schemes and, depending on the direction of the spontaneous magnetization at the mark of interest, is oriented clockwise or counter-clockwise.
  • a commercial magneto-optical storage device presently available provides access to only one side of a 130 mm double sided 2.6 ISO gigabyte magneto-optical disk, a 40 ms disk access time, and a data transfer rate of 4.6 MB/Sec.
  • Yamada discloses a low-profile flying optical head for o accessing an upper and lower surface of a plurality of optical disks.
  • the flying optical head disclosed by Yamada describes an actuating arm that has a static (fixed relative to the arm) mirror or prism mounted thereon, for delivering light to and receiving light from a phase-change optical disk.
  • the static optics described by Yamada provides access to both surfaces of a plurality of phase-change optical disks contained within a fixed volume
  • Yamada is limited by how small the optics can be 5 made. Consequently, the number of optical disks that can be manufactured to function within a given volume is also limited.
  • Another shortcoming relates to the use of static optics.
  • a method for moving a folding prism or mirror with a galvanometer actuator for fine tracking has been disclosed by C. Wang in US Patent 5,243,241.
  • the galvanometer consists of bulky wire coils and a rotatable magnet mounted on a linear actuator arm attached to a flying 5 magneto-optical head, but not mounted on the slider body itself. This design limits the tracking servo bandwidth and achievable track density due to its size and weight. Its complexity also increases the cost and difficulty of manufacture.
  • T e o improved optical head should preferably provide a high numerical aperture, a reduced head size and mass, and a high resonant frequency tracking servo device that provides a very fine track servo bandwidth. Additionally, the optical head should improve upon prior art access to disk surfaces, disk drive access times, data transfer rates, and ease of alignment and manufacture.
  • the present invention provides improvements over prior art optical disk drives.
  • the improvements allow an increase in the number of storage disks that can be placed within any given 5 volume.
  • the improvements enable the use of a high resonance frequency tracking servo device on a reduced profile head to provide improved access to storage media, improved disk drive access times, and improved data transfer rates.
  • the optical disk of the present invention utilizes Winchester magnetic disk technology.
  • a laser optics assembly couples an optical light source through a small micro-machined optical switch 0 to one or more rotary arms, each of which support an optical head for writing and reading data to the storage media. Lighting is delivered through an optical fiber to a respective optical head for the purpose of probing the storage media with a focused optical spot. The reflected light signal from the storage media then couples back through the optical head for processing.
  • the light transmitted from the optical fiber to the optical head is affected by a micro- 5 machined element.
  • the light is affected by a steerable micro-machined mirror.
  • Track following and seeks to adjacent tracks are performed by rotating a central mirror portion of the steerable micro-machined mirror about an axis of rotation.
  • a reflected light from the steerable micro-machined mirror is directed through an embedded micro-objective lens such as a GRIN (Graded Index) lens or a molded leas.
  • GRIN Gramded Index
  • a focused optical spot is scanned back and forth in a o direction that is approximately parallel lo the radial direction of the storage media.
  • track following and seeks to adjacent tracks may be performed with more than one storage media at a time by operating a set of steerable micro-machined mirrors independently from each other.
  • the steerable micro-machined mirror includes a flexure layer having a structure defining an 5 opening.
  • a central mirror portion is disposed in the opening.
  • the central mirror portion includes a parallelogrammatic reflective structure that includes a pair of first opposed sides and a pair of second opposed sides, with the pair of flexure layer hinges being integrally bound to the pair of the first opposed sides and to the flexure layer.
  • at -east one tether member may be integrally bound to the second opposing sides of the central mirror portion and to the flexure o layer.
  • the at least one tether member includes a structure defining at least one tether channel. The tether functions for limiting a range of movement of the mirror and for preventing the mirror from contacting an actuation electrode.
  • the steerable micro-machined mirror includes: a substrate, at least one actuation electrode supported by the substrate, and at least one plate member supported by the at least one actuation electrode.
  • the actuation electrode may include a first electrode surface, and a second electrode surface that is generally parallel to the first electrode surface and at a different elevation than the first electrode surface.
  • the steerable micro-machined mirror is attached to a flying magneto-optical head.
  • the flying magneto-optical head is preferably one of a set of magneto-optical heads for use in a magneto-optical system.
  • FIGURE 1 is an exploded view of a prior art silicon torsion mirror structure
  • FIGURE 2 is a perspective view of a steerable micro-machined mirror
  • 5 FIGURE 3 is a perspective view of a steerable micro-machined mirror including a pair of tether members
  • FIGURE 4 is a top plan of the steerable micro-machined mirror of FIGURE 3;
  • FIGURE 7 is a top view of a magneto-optical data storage and retrieval system
  • FIGURE 8 is a diagram showing one embodiment of the laser-optics assembly of the 5 magneto-optical data storage system of FIGURE 7 ;
  • Figure 9 is a diagram showing a representative optical path that includes the use of a DFB laser source
  • FIGURES 10-a-d are respective diagrams showing a top view, a side view, a front view and a side view, of a magneto-optical head; o FIGURE 11 is a diagram showing the representative optical path of Figure 9 in further detail;
  • FIGURE 12 is a diagram showing a steerable micro-machined mirror assembly that includes a reflective type quarter-wave plate
  • FIGURE 13 illustrates the thickness and composition of the quarter- wave plate of 5 Figure 12;
  • FIGURE 14 is a perspective view of an embodiment of the flying magneto-optical head shown in FIGURES 10-a-c;
  • FIGURE 15 is a second perspective view of an embodiment of the flying magneto-optical head shown in FIGURES 10-a-c; o FIGURE 16 illustrates an embodiment of the fiber optic switch;
  • FIGURES 17-a-b illustrate the fiber optic switch of FIGURE 16 in further detail;
  • FIGURE 18 illustrates a stage of fabrication of the fiber optic switch of FIGURE 16;
  • FIGURE 19 illustrates a stage of fabrication of the optical switch of FIGURE 16;
  • FIGURE 20 illustrates a stage of fabrication of the optical switch of FIGURE 16;
  • FIGURES 21a-b are cross-sectional diagrams showing a magneto-optical data storage and retrieval system as part of a magneto-optical disk drive;
  • FIGURE 22 is a graph depicting actuation voltage as a function of angular deflection for 5 three embodiments of a steerable micro-machined mirror;
  • FIGURE 23 is a graph of a frequency response for an embodiment of a steerable micro- machined mirror
  • FIGURE 26 is a graph depicting the frequency respoase for two embodiments of a steerable micro-machined mirror
  • FIGURE 27 is a graph depicting the phase response for two embodiments of a steerable 5 micro-machined mirror
  • FIGURE 28 is a graph depicting actuation voltage as a function of an angular deflection for two embodiments of a steerable micro-machined mirror
  • FIGURE 29 is a graph depicting actuation voltage as a function of an angular deflection for two embodiments of a steerable micro-machined mirror
  • o FIGURE 30 is a graph depicting actuation voltage as a function of an angular deflection for two embodiments of a steerable micro-machined mirror
  • FIGURE 31 is a graph depicting actuation voltage as a function of angular deflection for an embodiment of a steerable micro-machined mirror.
  • FIG. 1 a prior art steerable micro-machined torsional mirror assembly, generally illustrated as 20.
  • the mirror assembly 20 includes a substrate 22 that comprises a peripheral rim 22a defining a recessed well 23.
  • a pair of spaced apart and electrically isolated actuation electrodes 24 are disposed within the well 23.
  • a support ridge, generally illustrated as 26, is mounted on the substrate 22 and is disposed in o the well 23 and is surrounded by the rim 22a.
  • the ridge 26 is disposed between the pair of electrodes 24.
  • a silicon nitride flexure layer 30 functions as an upper mirror support member and is supported by the support ridge 26 and surrounding frame 26a in a spaced relationship with respect to the pair of electrodes 24.
  • the mirror support member 30 defines a pair of slotted apertures, generally illustrated as 32 a,b.
  • the apertures 32 a,b are configured to define a portion of the flexure 5 layer 30 as a planar mirror, generally illustrated as 36, and are suspended by a pair of axially aligned torsion hinge members (ie., flexure layer hinges) 38 which mechanically interconnect or couple one pair of respective opposite edges of the mirror 36 to the mirror support member 30.
  • the mirror 36 is configured symmetrically about the axially aligned hinges 38 to present symmetrically opposed halves 36 a, 36 b extending distally from the axially aligned hinges 38.
  • the actuation electrodes 24 are positioned such that a portion of each is aligned facing generally opposite to a respective half of the mirror 36.
  • the actuation electrodes 24 are connected to an external power source.
  • the actuation electrodes 24 receive current from the external power source to become oppositely charged in accordance with an applied actuation voltage.
  • the actuation voltage is arranged to cause the mirror 36 to rotate about the axially aligned hinges 38 at 5 an angle theta (• ) by electrostatic image charges induced by the oppositely charged electrodes 24.
  • FIG 2 there is seen a preferred embodiment of a micro-machined mirror assembly 400 of the present invention.
  • the steerable micro-machined mirror assembly 400 includes a .silicon substrate 401 that has a recess 406 formed therein.
  • a spaced apart pair of planar drive (actuation) electrodes broadly and generally illustrated as 402 and 403 are disposed along the o bottom of the recess 406.
  • a ridge 398 separates the drive electrodes 402 and 403.
  • a planar silicon plate 407 is bonded to respective portions of the electrodes 402, 403.
  • a planar flexure layer 408 made from a material such as silicon dioxide or silicon nitride is bonded to the outward face of the plate 407. Flexure layer 408 is formed to comprise opposed annular portioas 408a and 408b.
  • An outward facing reflective central mirror portion 420 is defined in a portion of the top flexure layer 408 and a respective portion of the inner silicon plate layer 407 by spaced apart opposing C-shaped aperture slots 409-a, 409-b formed there through.
  • the reflective central mirror portion 420 is configured to provide integral opposed halves 420a and 420b.
  • the opposing halves 420a and 420b are symmetrically disposed about and distally extending from an axis formed by a pair of axially aligned, opposed flexure layer hinges 410.
  • the flexure layer hinges 410 are integrally formed from the flexure layer 408 and provide torsional restoring torque to the reflective central mirror portion 420.
  • the reflective central mirror portion 420 may be metalized with gold or a similar substance to increase the optical reflectivity and to improve electrostatic actuation of the reflective central mirror portion 420.
  • the steerable micro-machined mirror assembly 400 operates over a bandwidth of approximately 50 to 200 KHz with an application to electrodes 402 and 403 of an actuation voltage of approximately 90 to 200 volts.
  • the reflective central mirror portion 420 is a generally parallelogrammatic structure that includes: a linear dimension, a and b, that is 5 approximately 300 microns or less; and a thickness, tm2, that is approximately 3 microns or less.
  • the gap spacing between the bottom of the reflective central mirror portion 420 and the drive electrodes 402 and 403, gm, is approximately 10 microns or less.
  • an outside thickness of the steerable micro-machined mirror assembly 400, tml is approximately 2(X) microas or less.
  • the reflective central mirror portion 420 achieves a o preferable physical angular rotation of at least +2 degrees about a longitudinal axis defined by hinges 410.
  • the reflective central mirror portion 420 may be driven torsionally without any excessive transverse motion and should maintain an optical flatness of lambda/ 10 during static and/or upon dynamic operation.
  • the maximum stress upon electrostatic deflection should be below the expected yield stress of the material used to construct the reflective central mirror portion 420.
  • the 5 aforementioned characteristics and dimensions of the steerable micro-machined mirror assembly 400 are meant to be exemplary in nature and should be limited by the scope of the ensuing claims only.
  • the steerable micro-machined mirror assembly 400 may be fabricated by etching the recess 406 into the silicon substrate wafer 401.
  • the silicon plate 407 may be oxide bonded to achieve electrical isolation from the electrodes 402, 403 and may be o subsequently thinned and polished to a desired thickness.
  • the flexure layer 408 may be deposited and patterned to define the periphery of the reflective central mirror portion 420 and the width of the hinge 410.
  • An iso tropic etch may be used to form the aperture slots 409-a, b around reflective central mirror portion 420 and beneath the flexure hinges 410, while leaving the silicon plate 407 under the reflective central mirror portion 420 to provide rigid support.
  • the etch step may be used to provide access to electrodes 402 and 403 so that the bonding pads 404 and 405 may be formed by a deposition of metal to electrically and mechanically connect to the respective electrodes 402, 403.
  • the steerable micro-machined mirror assembly 400 has been described can be fabricated using 5 bulk micro-machining techniques or surface micro-machining techniques, for example, surface micro-machining techniques as disclosed in "Design techniques for surface micro-machining MEMS processes," J. Comtois et aL, 1991 SPIE Proceeding Series Volume 2639, pp. 211-222.
  • exemplary analyses show that as the angular deflection of the reflective central mirror portion 420 increases, the reflective central mirror portion o 420 may experience instability as electrostatic torque forces overwhelm a restoring torque provided by the torsional hinges.
  • Use of the relatively wide gap of the prior art with a desired +2 degrees of deflection of the reflective central mirror portion 420 of the present invention may require a relatively large actuation voltage to be applied to the electrodes 402 and 403.
  • use of a relatively wide gap between the reflective central mirror portion 420 and the electrodes 402 and 403 5 may result in a relatively non-linear relationship between the angular deflection of the reflective central mirror portion 420 and an applied voltage to the electrodes 402 and 403.
  • the steerable micro-machined mirror assembly 400 is described in the following discussion to include modifications that change the operating characteristics of the steerable micro-machined mirror assembly 400 including: a reduced gap width, improved linearity, decreased actuation voltage o required for full scale angular deflection, and an increase in the range of angular deflection that can be achieved before the aforementioned instability occurs.
  • the steerable micro-machined mirror assembly 400 may include at least one tether member 50 for further coupling the reflective central mirror portion 420 to the flexure layer 408. More specifically, the at least one tether member 50 respectively 5 couples a respective at least one of the opposed annular portions 408a and 408b of the flexure layer
  • Each tether member 50 may be a parallelogrammatic structure 52 having at least one, preferably a pair of transverse channels 54. As shown in Figure 3, distal edges of opposed halves 420a and 420b each have a pair of spaced apart tethers 52 secured thereto, separated by gap 53. o
  • the grooves or channels 54 may be plasma etched using a planar etch to define isotropically etched contours within a selected surface area of flexure layer 408. An etch stop may be diffused into the convoluted surface so that the etched contours follow the etch-stop layer.
  • the flexure layer 408 portion that includes the tether member 50 may be patterned and etched from the surface opposed to that of channels 54, with the etch stop layers producing the desired corrugated cross-section. With conventional plasma etching techniques, etched groove depths may be produced from a fraction of a micrometer to about 50 micrometer. If boron etch stops are used, the available tether member 50 thickness may range from about 0.5 micrometer to about 10 micrometer. A similar range is available 5 with diffused electrochemical etch stops, although the maximum thickness can be increased above 20 micrometer with sufficiently long diffusions.
  • the tether members 50 permit torsional motion of the reflective central mirror portion 420 about axially aligned flexure layer hinges 410, but limit transverse motion; that is, the tether member 50 limits movement of the distal edges of reflective central mirror portion 420 towards sides 408a o and 408b of the flexure layer 408.
  • the tether member 50 also provides a torsional restoring force
  • the tether member 50 also limits the reflective central mirror portion 420 from contacting the actuation electrodes 402 and 403 in a high drive situation, along with preventing contact deformation and warping of the reflective central mirror portion 420. 5 The tether member 50 further prevents the reflective central mirror portion 420 from deflecting beyond a critical angle which would otherwise result in spontaneous deflection to one of the actuator electrodes 402 or 403.
  • Rotation or torsional movement of the reflective central mirror portion 420 causes the tether members 50 to deflect downwards (z-direction) while remaining attached to the sides 420a and 0 420b of the reflective central mirror portion 420.
  • tether members 50 preferably stretch somewhat to accommodate the increased distance from the sides 420a and 420b of the reflective central mirror portion 420 to the sides 408a and 408b of the flexure layer 408.
  • the amount of force required to deflect the beam in the 5 z-direction is approximately linearly proportional to the amount of deflection realized. For larger deflections, this relationship may be non-linear, with larger incremental amounts of force required to obtain incremental deflections.
  • the non-linearity of the tether member 50 may be tailored to meet the non-linearity in electrostatic torque caused by large angular rotations of the reflective central mirror portion 420.
  • the range of stability of the reflective central mirror portion 420 o with respect to its angular deflection may be increased and a wider range of angular deflection may be realized by deterring effects of the electrostatic non-linearity for larger angular deflections.
  • the restoring torque available from the torsional hinges 410 alone may be insufficient at times to counteract the torque exerted by the electrostatic field at some critical rotation angle.
  • the tether members 50 serve to provide additional restoring torque to combine with the hinge restoring torque, thus offsetting the electrostatic torque. Therefore, the point of iastability can be changed to occur at larger deflection angles.
  • the resonant frequency of the reflective central mirror portion 420 is preferably increased due to the additional effective torsional spring constant created 5 by the tether members 50. Hence, the resonant frequency is somewhat further decoupled from the actuation voltage.
  • the non-linearity of the tether members 50 dominates at roughly the same angular deflection that causes the electrostatic force to dominate.
  • the tether 50 stretches significantly; o therefore, the non-linearity in the deflection of the beam deflection becomes apparent for rather small reflective central mirror portion 420 angles.
  • the use of traasverse channels 54 serves to extend the linear range of the tether member 50 by allowing for the stretching to be largely accommodated by the bend in the corrugation.
  • Onset of effective non-linearity in the tether member 50 is a function of the length (c) of the tether member 50, its width (d), its thickness (t), the depth (e), the width (f) and 5 the number of corrugations.
  • the tether member 50 further •allows design flexibility in determining the onset of non-linearity.
  • the tether thickness (t) is made smaller than the thickness of the reflective central mirror portion 420 so that the non-linear force from the tether member 50 does not cause excessive warping of the reflective central mirror portion 420.
  • Actuation electrodes 402 and 403 may also include electrode surfaces 402b and 403b respectively parallel to electrodes surfaces 402a and 403a that are respectively at a different gap spacing; that is, electrode surfaces 402a and 403a are at a smaller gap spacing than electrode surfaces 402b and 403b.
  • Figure 5 indicates two gap separations, additional benefit could be gained by fabricating a larger number of such steps in the electrodes 402 and 403.
  • actuation electrodes 402 and 403 are each shown with two electrode surfaces (i.e., 402a and 402b and 403a and 403b), the spirit and scope of the present invention may include actuation electrodes 402 and 403 that comprise three or more electrode 5 surfaces.
  • This modification acting separately from the tether members 50 may serve to decouple the actuation voltage performance from the steerable micro-machined mirror assembly 400 resonant frequency, in that, the resonance of the steerable micro-machined mirror assembly 400 is unchanged. It is to be understood that a plurality of electrode steps may be used alone or in combination with the tether members 50 described above.
  • a magneto-optical (MO) data storage and retrieval system 100 includes a set of Winchester-type flying heads 106 that are adapted for use with a set of double-sided first surface MO disks 107 (one flying head for each MO disk
  • the .set of flying heads 106 (hereinafter referred to as flying MO heads) are coupled to a rotary actuator magnet and coil assembly 120 by a respective suspension 130 and actuator arm 105 so as to be positioned over the surfaces of the set of MO disks 107.
  • flying MO heads are coupled to a rotary actuator magnet and coil assembly 120 by a respective suspension 130 and actuator arm 105 so as to be positioned over the surfaces of the set of MO disks 107.
  • the set of MO disks 107 are rotated by a spindle motor 195 so as to generate aerodynamic lift forces between the set of flying MO heads 106 and so as to maintain the set of flying MO heads
  • System 100 further includes: a laser-optics assembly 101, an optical switch 104, and a set of single-mode PM optical fibers 102.
  • Each of the set of single-mode PM optical fibers 102 may be respectively coupled through a respective one of the set of actuator arms 105 and set of suspensions 130 to a respective one of the set of flying MO heads 106.
  • the steerable micro-machined mirror assembly 400 is used with the set of flying MO
  • FIG. 8 is a diagram showing one embodiment of the laser-optics assembly of the magneto-optical data storage and retrieval system of Figure 7.
  • the laser-optics assembly 101 is shown to include a linearly polarized diode laser source 231 operating in a visible or near ultraviolet frequency region and emitting an optical power sufficient for reading and writing using the set of MO disks 107.
  • the laser diode source may be a RF modulated laser source.
  • the linearly polarized laser source 231 may be a DFB laser source.
  • the linearly polarized laser source 231 operates within a range 635-685 nm; however, a laser source of other frequencies could also be used.
  • the laser-optics assembly 101 further includes: a collimating optics 234, a low wavelength dispersion leaky beam splitter 232, and a coupling lens 233.
  • the laser-optics assembly 101 directs (from the linearly polarized laser source 231) a linearly polarized outgoing laser beam 191 (shown in Figure 7) to the optical switch 104.
  • Laser-optics assembly 101 further includes: a l ⁇ wave plate 238, a mirror 235, and a polarizing beam splitter 232.
  • a linearly polarized reflected laser beam 192 (shown in Figure 7) is directed by the optical switch 104 to the coupling lens 233, and is routed by the leaky beam splitter 232 to a differential detector comprising: the l ⁇ wave plate 238, the mirror 235, and the polarizing beam splitter 239.
  • the laser-optics assembly functions as above, but further includes an optical isolator 297 between the laser source 231 and the collimating lens 234.
  • this type of differential detection scheme measures the optical power in two orthogonal polarization components of the reflected laser beam 192, with a differential signal being a sensitive measure of polarization rotation induced by the Kerr effect at the surface of one of the set of MO disks 107.
  • the differential signal is processed by the differential amplifier 237 and is output as signal 294.
  • the present invention is not meant to be limited to the aforementioned arrangement of optical elements and sources of light, as other techniques for directing the outgoing laser beam 191 and for detecting the reflected laser beam 192 are well known in the art.
  • Figure 9 is a diagram showing a representative optical path that includes the use of a DFB laser source.
  • a representative optical path is shown in Figure 9 to include: the optical switch 104, one of the set of single-mode PM optical fibers 102, and one of the set of flying MO heads 106.
  • the optical switch 104 provides sufficient degrees of selectivity for directing the outgoing laser beam 191 (with reference to laser source 231) towards a respective proximal end of a respective single-mode PM optical fiber 102.
  • the outgoing laser beam 191 is further directed by the single-mode PM optical fiber 102 to exit a respective distal end so as to pass through the flying MO head 106 onto a surface recording layer 349 of a respective MO disk 107.
  • the outgoing laser beam 191 is provided by a linearly polarized laser source 231 that is a DFB laser source.
  • a distributed feedback (DFB) diode laser source unlike an RF-modulated Fabry-Perot diode laser, produces a very narrowband single-frequency output due to the use of a wavelength selective grating element inside the laser cavity.
  • the light exiting the optical fiber has a polarization state that depends on the relative orientation between the fiber axes and the incident polarization, and moreover, the output polarization state is very stable in time as long as external perturbations which alter the fiber birefringence are negligible. This behavior is in contrast to that observed with a RF-modulated Fabry-Perot diode laser source that is characterized by high-frequency fluctuations in its spectral output.
  • MO disk 107 MO disk 107.
  • the outgoing laser beam 191 is selectively routed by the optical switch 104 to the MO disk 107 so as to lower a coercivity of the surface recording layer 349 by heating a selected spot of interest 340 to at least the Curie point of the MO recording layer 349.
  • the optical intensity of outgoing laser beam 191 is held constant, while a time varying vertical bias magnetic field is used to define a pattern of "up” or “down” magnetic domains perpendicular to the MO disk 107. This technique is known as magnetic field modulation (MFM).
  • MFM magnetic field modulation
  • outgoing laser beam 191 may be modulated in synchronization with the time varying vertical bias magnetic field at the spot of interest 340 in order to better control domain wall locations and reduce domain edge jitter.
  • the outgoing laser beam 191 (at a lower intensity compared to writing) is selectively routed to the MO disk 107 such that at any given spot of interest 340, the Kerr effect cau.ses (upon reflection of the outgoing laser beam 191 from the surface layer 349) a reflected laser beam 192 to have a rotated polarization of either clockwise or counter clockwise sense 363 that depends on the magnetic domain polarity at the spot of interest 340.
  • the aforementioned optical path is bi-directional in nature. Accordingly, the reflected laser beam 192 is received through the flying MO head 106 and enters the distal end of the single-mode PM optical fiber 102. The reflected laser beam 192 propagates along the single- mode PM optical fiber 102 to exit at its proximal end and is selectively routed by the optical switch 104 for transmission to laser-optics assembly 101 for subsequent conversion to the signal 294.
  • Figures 10-a-d are diagrams showing a magneto-optical head in a top view, a side view, a front view, and a side view, respectively.
  • the set of flying MO heads may be illustrated with reference to a single representative flying MO head 106.
  • a single representative flying MO head 106 is shown in Figures 10-a-c to be positioned respectively above or below a surface recording layer 349 of one of the set of spinning MO disks 107.
  • the flying MO head 106 includes: a slider body 444, an air bearing surface 447, a transmissive quarter-wave plate 493, the steerable micro-machined mirror assembly 400, an objective optics 446, and a magnetic coil 460.
  • the magnetic coil 460 is a micro multi-turn coil positioned near the air-bearing surface 447 so as to generate a magnetic field that is: approximately 300 Oersteds of either polarity, reversible in a time of about 4ns, and approximately perpendicular to the plane of the spinning MO disk 107.
  • the magnetic coil 460 should not interfere with the outgoing and reflected laser beams 191 and 192 during passage through the flying MO head 106 to the spinning MO disk 107, or vice versa.
  • the slider body 444 dimensions may be characterized to include those of industry standard
  • the slider body 444 may include a height of approximately 889 um and a planar footprint area that corresponds to that of a nano slider (2032 um x 1600 um).
  • the quarter-wave plate 493 includes a square dimension of approximately 250um, a thickness of approximately 89um, and a phase retardation of about 90 degrees (+/- 3 degrees) at a wavelength of interest.
  • Single- mode PM optical fiber 102 is preferably coupled to the flying MO head 106 and is held along an axis of the slider body 444 by a v- groove 443 or other suitably dimensioned channel.
  • the single-mode PM optical fiber 102 is positioned within the v- groove 443 to preferably direct the outgoing laser beam 191 as an optimally focused optical spot 448.
  • the single-mode PM optical fiber 102 may be subsequently secured in place by using an ultraviolet curing epoxy or a similar adhesive. Use of the PM optical fiber 102 within a V- groove permits accurate alignment and delivery of the outgoing laser beam 191 to the small area of the reflective central mirror portion 420.
  • the steerable micro-machined mirror assembly 400, the quarter-wave plate 493, and objective optics 446 are preferably compact and low mass so as to fit within a physical volume defined by approximating the rectangular outer dimensions of the slider body 444 and yet sufficiently large to direct a full cross section of the outgoing and reflected laser beams 191 and 192 so that minimal power is lost and significant distortion and aberrations in the outgoing and reflected laser beams 191 and 192 arc not introduced.
  • the reflective central mirror portion 420 of the steerable micro-machined mirror assembly 400 is aligned in the representative optical path so as to direct the outgoing laser beam 191 through the objective optics 446 and quarter-wave plate 493 so as to direct the reflected laser beam 192 from the MO disk 107 back to the laser optics assembly 101 of Figure 8.
  • the objective optics 446 may be a icrolens with a numerical aperture (NA) of approximately .67. In an exemplary embodiment at a wavelength of 650 nm, the micro-lens focuses the optical spot 448 with a full width at half-maximum intensity (FWHM) of approximately .54um.
  • the micro- lens may be a GRIN (Graded Index) lens 446, of simple and compact cylindrical shape.
  • a cylindrical shape permits the lens 446 to be easily inserted into a simple cylindrical lens receiving aperture provided in the slider body 444.
  • the GRIN lens 446 may be polished to assume a plano- convex shape, with the convex surface being a simple spherical shape.
  • the desired thickness and radius of curvature of the GRIN lens 446 is a function of a number of factors including: the magnitude of the refractive index gradient, the wavelength of light, the numerical aperture of the PM optical fiber 102, and the desired focused optical spot 448 size.
  • the GRIN lens 446 height is approximately 350 um
  • the radius of curvature is approximately 200 um
  • the lens diameter may be approximately 250 um.
  • the optimum focus occurs on the planar side of the GRIN lens 446 and preferably comprises a depth of focus that is approximately 25 micro-inches. Because flying height of the air bearing surface 447 is preferably maintained at a value to be approximately 15 micro-inches, a focusing servo is not necessarily required.
  • the present invention may include a linearly adjustable optical element 495 (shown in Figure 10b and lOd).
  • the linearly adjustable optical element may be positioned in the optical path between the single-mode PM optical fiber 102 and the reflective central mirror portion 420 so as to optically alter the outgoing laser beam 191 as the beam exits the single-mode PM optical fiber 102.
  • the optical spot 448 may be focused to include exemplary focal positions 486, 487, and 488; multi-layer MO disks could therefore be used.
  • Linear motion of the optical element 495 along the representative optical path may be effectuated by coupling a moving means 433 to the slider body 444 and to a mount containing the optical element 495 by using, for example, a micro-machined actuator, micro-motor, or piezoelectric transducer capable of linear motion.
  • a single dynamic focusing lens with electrically controlled focus may be used in place of linearly adjustable optical element 495, obviating the need for a moving means.
  • Such a lens may, for example, comprise a holographic lens element in combination with a liquid crystal or electro-optic PLZT coating.
  • a micro-machined actuator may also be used to position the single-mode PM optical fiber 102 in a lateral, vertical, or longitudinal direction, thus, providing a means of movement and alignment of the single-mode PM optical fiber 102 relative to other optical elements on the slider body 444.
  • a number of micro-actuator designs are referenced in "Silicon-Micro-actuators: Activation Mechanisms And Scaling Problems," W. Benecke, 1991 International Conference on Solid-State Sensors and Actuators, pp. 46-50, and the papers referenced therein.
  • the single-mode PM optical fiber 102 functions as an aperture of a confocal optical system that has a large depth resolution along its optical axis and an improved transverse resolution.
  • the improved transverse resolution improves the detection of smaller magnetic domain orientations as well as detection of magnetic domain edges as compared to a non- confocal system.
  • the large depth resolution minimizes cross-talk between closely spaced surface recording levels when using multi-level storage media.
  • Another advantage that arises from the confocal nature of the present invention is that stray light reflected from the objective optics 446 is filtered.
  • fine tracking and short 5 seeks to nearby tracks are performed by rotating the reflective central mirror portion 420 of the steerable micro-machined mirror assembly 400 about a rotation axis so that the propagation angle of the outgoing laser beam 191 is changed before transmission to the objective optics 446.
  • the reflective central mirror portion 420 is rotated by applying a differential voltage to the drive electrodes 402 and 403.
  • the differential voltage on the electrodes 402 and 403 creates an l o electrostatic force that rotates the reflective central mirror portion 420 about the hinges 410 and enables the focused optical spot 448 to be moved in the radial direction 450 on the MO media 107.
  • the central mirror portion 420 rotates approximately +/- 2 degrees, which is equivalent to approximately +/- 4 tracks at the surface of the MO disk 107.
  • a movement of +/- 4 tracks is disclosed, depending on the desired
  • the track following signals used to follow a particular track of the MO disk 107 may be derived using combined coarse and fine tracking servo techniques that are well known in the art.
  • a sampled sector servo format may be used to define tracks.
  • the servo format may include either embossed pits stamped into the MO disk 107 or magnetic domain orientations
  • a set of steerable micro-machined mirror assemblies 400 may be used to operate independently and thus permit track following and seeks so as to read and/or write information using more than one MO disk surface at any given time.
  • Independent track following and seeks using a set of concurrently operating steerable micro-machined assemblies 400 preferably requires a set of separate respective read channel and fine track electronics and mirror driving electronics. Because the aforementioned embodiment would also preferably require use of separate laser-optics assemblies 101, an optical switch 104 for switching between each of the separate optical paths may not necessarily be required.
  • Figure 11 is a diagram showing a representative optical path that includes the use of a RF modulated laser source.
  • the set of optical paths of the present invention may be illustrated with reference to a single representative optical path, which is shown in Figure 11 to include: the reflective substrate 420, the quarter- wave plate 493, the objective optics 446, and the single-mode PM optical fiber 102.
  • the single-mode PM optical fiber 102 comprises a first segment 598 coupled to a second segment 599, each segment comprising a fast axis (Px) and slow axis (Py).
  • the fast axis of the first segment 598 is preferably aligned with the slow axis of the second segment 599.
  • the outgoing laser beam 191 has an Ox component and an Oy component and is preferably linearly polarized at an angle of approximately 45 degrees relative to the Px and Py axes of the first segment 598, and the quarter-wave plate 493 comprises a fast axis 489 which is preferably aligned in the optical path at an angle of 45 degrees relative to the Px and Py axes of the second segment 599.
  • the quarter-wave plate 493 comprises a square dimension of about 250um, a thickness of about 89um, and a phase retardation of about 90 degrees (+/- 3 degrees) at a wavelength of interest.
  • first and second segments 598 and 599 may be subject to external and/or internal stresses resulting from: mechanical motion, temperature, and pressure; and that, these stresses may affect optical properties of the first and second segments 598 and 599, for example, their birefringent properties. Accordingly, as the Ox and Oy polarization components propagate through the first and second segments 598 and 599, the Oy component acquires a shift in phase of ⁇ relative to the Ox component. The polarization components Ox and Oy exit the distal end of the second segment 599 and are reflected by the reflective substrate 420 so as to be incident with the surface of the quarter- wave plate 493.
  • the Ox and Oy components are preferably reflected equally (within 3% of each other) from a gold surface of the reflective substrate 420.
  • the Ox component is converted to a left-hand circular polarization
  • the Oy component is converted to a right-hand circular polarization
  • the two circular polarizations sum to preferably be an outgoing linear polarization having a polarization angle that depends on the phase shift ⁇ .
  • the outgoing linear polarization is reflected from the MO disk 107 and is rotated by the Kerr effect so as to return with a net phase shift between the circular polarization components equal to ⁇ + ⁇ -, where ⁇ is a phase shift 5 introduced by the Kerr effect.
  • the reflection from the MO disk 107 reverses the sense of each circular polarization (ie., left-hand becomes right-hand and vice-versa), such that, upon a second pass through the quarter-wave plate 493, the right-hand component is converted to a linear polarization component Tx, and the left-hand component is converted to a linear polarization component Ty.
  • the Tx and Ty polarization components of the reflected laser l o beam 192 are preferably rotated 90 degrees with respect to the Ox and Oy polarization components of the outgoing laser beam 191, and the Tx component exhibits a phase shift of ⁇ + ⁇ relative to the Ty component.
  • the Ty component acquires an additional phase shift of ⁇ with respect to the Tx component.
  • the Ty polarization component of the reflected laser beam 192 is phase shifted relative to the Tx polarization component, preferably by only the Kerr phase ⁇ .
  • the linear polarization is detected and converted so as to represent the information stored at the spot of interest 340 as the output signal 294.
  • the quarter- wave plate 493 also minimizes phase shifts introduced by the optical properties of the reflective surface of the reflective substrate 420. Additionally, although the quarter-wave plate 493 is disclosed to be positioned in the optical path after the reflective substrate 420, in an alternative embodiment, the quarter-wave plate 493 may be positioned between the objective optics 446 and the MO disk 107.
  • a laser source 231 that comprises a RF modulated laser diode may reduce the effects of optical feedback of the reflected laser beam 192 to the laser diode.
  • RF modulated diodes do not operate at a single wavelength, but rather, as a source of laser light having mullet-mode spectral characteristics (typically with a lOnm bandwidth) and that for each ⁇ , the corresponding phase shift may be minimized by specifying the quarter-wave plate 493 to operate over the bandwidth of the laser source 231.
  • the Ox and Oy components of the outgoing laser beam 191 are not 5 optimally aligned at 45 degrees relative to the Px and Py axes of the first segment 598, and/or the quarter-wave plate 493 is not exactly quarter-wave, and/or other optical components in the optical path are not aligned, the phase shift ⁇ and, thus, the RF noise components it generates in the output signal 294 may exhibit a dependence on the wavelength fluctuations of the laser source 231. Accordingly, because in practice the optical components of system 100 may be o aligned to only a limited degree of precision, the wavelength fluctuations of the RF-modulated laser source 231 may function to degrade the signal-to-noise ratio of the output signal 294.
  • the present invention identifies that by rotating the fast axis of the first segment 598 orthogonally to the fast axis of the second segment 599, the RF phase noise created by wavelength fluctuations of the laser source 231 may be canceled in a common mode manner.
  • the first and second segments 598 and 599 may comprise commercially available single-mode PM optical fiber selected to operate at the frequency of interest.
  • the first segment 598 is coupled to the second segment 599 using fusion splicing techniques that are well known in the art, and the fast axis of the first segment 598 is aligned with the slow axis of the second segment 599, preferably to within an angle of less than .5 degree.
  • first and the o second segments 598 and 599 are preferably selected from the same optical fiber manufacturing batch and are preferably of equal length to a precision of less than 1mm.
  • the phase shift encountered by a linearly polarized light propagating with a wavelength ⁇ through each of the first and second segments 598 and 599 is proportional to 2 ⁇ blJ ⁇ (where b is the birefringence of the PM optical fiber and L is the PM optical fiber 5 length). Therefore, fluctuations in the wavelength ⁇ yield corresponding fluctuations in the phase shift.
  • the present invention identifies that the net birefringence introduced in the optical path by the two segments will be approximately zero and, thus, the o phase shift ⁇ will be approximately zero and independent of wavelength.
  • the nonzero net birefringence will be proportional to the difference between the lengths of the first and the second segments 598 and 599, hence, as compared to the prior art, the RF phase noise in the output signal 294 will be reduced.
  • the signal-to-noise ratio of the output signal 294 is reduced approximately 40dB.
  • Figure 12 is a diagram showing the representative optical path of Figure 11 in a second embodiment.
  • a multi-layer stack 646 of alternating layers of ZnS (high refractive index) and SiO 2 (low refractive index) materials is deposited on a reflective substrate 420.
  • Figure 13 illustrates the thickness of the various layers for an exemplary embodiment having a total of 12 layers.
  • a thick layer of gold is deposited as a first layer on the reflective substrate 420 to improve reflectivity at low incidence angles.
  • the thickness of the layers is controlled during deposition on the reflective substrate 420 so that mean reflectance from the reflective substrate 420 is preferably greater than 95% and so that, reflected components of a linearly polarized light source incident on the multi-layer stack 646 (within an incidence angle of 45 degrees +/- 10 degrees) acquire a phase retardation of 90 degrees (+/- 1 degree).
  • the exemplary embodiment is not meant to be 5 limiting, as other operating wavelengths and different numbers of layers, each with a different thickness, could be deposited on the reflective substrate 420.
  • the multi-layer stack 646 functions as a quarter-wave plate.
  • the effective fast axis 689 of the quarter- wave plate is preferably aligned in the optical path at an angle of 45 degrees relative to the Px and Py axes of the second segment 599. Accordingly, in the second embodiment, the o multi- layers 646 function to reduce birefringence induced phase shifts between the Tx and Ty components of the outgoing laser beam 192. Because the materials used for the design are preferably not birefringent, neither phase retardation nor reflectance depends on the azimuth of the incidence.
  • the quarter wave-plate multi- layer stack 646 of 5 second embodiment effectuates low mass and low-profile optical paths having fast seek and data transfer rates, and increased data storage capacity per unit volume. While the present invention has been described with reference to one type of polarization altering element (i.e., a quarter-wave plate), those skilled in the art will recognize that with suitable changes in the detection optics of laser optics assembly 101, other types of polarization altering elements o could be used on the flying MO head 106, for example, a faraday rotator.
  • the magneto-optical data storage and retrieval system 100 of Figure 10 provides the ability to rapidly move a focused beam of laser light across the MO disk 107 by incorporating the steerable micro-machined mirror assembly 400 with a flying magneto-optical head 106.
  • a mirror support 453 may be provided for attachment of the steerable micro-machined mirror assembly 400.
  • the mirror support 453 includes raised electrode pads 451 and 452 that provide an electrical contact point for application of a differential voltage to the set of corresponding pads 404 and 405 5 (refer to Fig. 2) located on the steerable micro-machined mirror assembly 400.
  • mirror support 453 further includes access holes 461 and 462 so as to provide a clear optical path from the single-mode PM o optical fiber 102 to the reflective central mirror portion 420 (not visible), and subsequently, to the surface of the MO disk 107.
  • the mirror support 453 provides the steerable micro-machined mirror assembly 400 a support surface oriented at a 45 degree angle relative to the optical path from the optical fiber 102.
  • mirror support 453 may be attached to the slider body 444 and manufactured using any number of techniques, for example, by micro- 5 machining the slider body 444 and the mirror support 453 separately, then adhesively bonding the two pieces together.
  • a 45 degree support angle for the steerable micro-machined mirror assembly 400 may be provided by using other techniques, for example, by leaning the mirror assembly 400 against a suitably dimensioned slider having suitably dimensioned steps 493 and 494.
  • the slider body may be manufactured to provide a 45 degree beveled edge along which the steerable micro-machined mirror assembly 400 may be positioned.
  • the steerable micro-machined mirror assembly 400, the slider body 444, and the V-groove 454 for holding the PM optical fiber 102 may be micro-machined as a flying MO head that comprises one integral piece.
  • An integral micro-machined flying MO head can reduce the amount of pre and post 5 manufacturing alignment necessary for accurate focusing of the optical spot 448 (shown in Figure
  • the slider body 444 may also be micro-machined to include the aforementioned micro-machined actuator as an integral element.
  • the fiber-optic switch 104 is of a small size so as to require only a small o volume within the magneto-optical system 100.
  • the optical switch preferably provides a fast switching speed between a set of optical paths that include the set of single-mode PM optical fibers 102 and the laser-optics assembly 101.
  • the optical switch 104 comprises: an upper silicon substrate 350; a linear micro-machined micro-motor 321; a micro- machined mirror 314; and generally parallel and spaced apart transverse flexure members 323 and 324.
  • Adjacent spaced apart ends of flexure members 323 and 324 are connected to a movable output of the micro-motor 321 and a fixed location on substrate 350, respectively.
  • the opposing adjacent ends of flexure members 323 and 324 are connected to adjacent spaced apart locations on the micro-mirror 314 to provide pivot axes oriented generally vertically with respect to a top surface of the substrate 350.
  • the flexure 324 provides a transversely fixed reference mechanical fulcrum relative to the transversely movable flexure 323.
  • a set of output optical fibers 102 are disposed such that their respective optical axes are angularly displaced parallel to the substrate 350 and directed generally in a radial direction toward the mirror 321.
  • a free space outgoing laser beam 191 from the laser-optics assembly 101 is directed toward an aperture formed in the substrate 350.
  • the outgoing laser beam 191 is directed towards a reflective face of the mirror 314 through the aperture and through a GRIN lens 329 aligned thereto.
  • the GRIN lens 329 is preferably disposed into an etched groove in the substrate 350. After emerging from the GRIN lens 329, the laser beam 191 is reflected by the micro-mirror 314.
  • a suitable electric potential is applied to the micro-motor 321 such that the outgoing laser beam 191 is reflected from the micro-mirror 314 and directed to a selected one of the set of optical fibers 102.
  • the micro-motor 321 imparts motion (indicated by the double headed transverse arrow 322) to the flexure 323 relative to flexure 324 by rotatably displacing the micro-mirror 314 about its pivot axis.
  • the micro-mirror 314 is provided thereby with an angular motion degree of freedom indicated by double headed arrow 370 parallel to the plane of the substrate 350.
  • the angular position of the micro-mirror 314 is determined by the electric potential applied to the micro-motor 321, and the outgoing laser beam 191 is focused by the GRIN lens 329 to one of a set of points several microns from the reflective face of the mirror 314.
  • the points correspond to the proximal ends of each of the single-mode PM optical fibers 102.
  • the rotational range of motion of the mirror 314 is preferably sufficient to direct the outgoing laser beam to any one of the PM optical fibers 102.
  • the aforementioned in-plane rotation 370 provides one degree of deflection and alignment, another degree of o deflection and alignment is provided by an out-of-plane motion of the micro-mirror 314, as is discussed with reference to Figures 17a-b below.
  • the optical switch 104 is shown to further include: a support portion 412, a patterned first insulator oxide layer "hinge" portion 416, a conductor layer pattern 425, a patterned second insulator oxide layer portion 418, and a reflective surface 415.
  • the reflective surface 415 is deposited on the face of the micro-mirror 314 as a metal such as gold.
  • Respective opposing edges of the micro-mirror 314 are connected to corresponding edges of the support portion 412 by the respective insulator portions 416 at one edge and insulator portion 418 at the other edge.
  • Both of the insulator portions 416 and 418 provide dual function to electrically isolate the micro-mirror 314 from the support portion 412 and to provide structural support between the mirror 314 and the support portion 412.
  • Insulator portion 418 is patterned in combination with the conductor 425 and is shown in a cross-section in Figure 17-b to form a transversely extending rectangular annular frame comprised of integrally formed parallel lateral segments 418-a,b and 425-a,b.
  • the segments 418-a,b and 425-a,b are formed in contact with the respective adjacent edges of mirror 314 and support portion 412.
  • Insulator portion 418 and conductor 425 form segments 418-d,e and 425-d,e extending laterally beyond the lateral extent of micro-mirror 314 and support portion 5 412 and provide resihent support for motion of the respective adjacent edge of micro-mirror 314 toward and away from the corresponding edge of support portion 412.
  • the insulator portion 418 that extends over the micro-mirror 314 and under conductor 425, comprises a feed through hole there through (not shown) which permits conductor 425 to make a first electrical connection with the micro-mirror 314.
  • a second electrical connection to 0 support portion 412 is made via flexure 324.
  • Micro-mirror 314 and planar support 425 may, therefore, be electrically charged by application of a electric potential between conductor 425 and flexure 324.
  • a suitable electric charge results in the formation of an electrostatic force between the micro-mirror 314 and the support portion 412.
  • the electrostatic force causes the micro-mirror 314 to tilt in a direction shown as rotation 480, away or towards the support 5 portion 412 and along an axis established by the insulator "hinge" portion 416.
  • the C-shaped bi-planar segments 418-d,e, 425-d,e are preferably resihent so as to provide a centering and restoring force to counteract the electrostatic force between micro- mirror 314 and support portion 412.
  • the restoring force limits the angular displacement 480.
  • the resulting o rotation 480 of the micro-mirror 314 may be used to re-direct a laser beam impinging on the reflective surface 415 by several degrees relative to a normal to the plane of support portion 412.
  • the rotation of micro-mirror 314 about the axis of hinge portion 416 enables the reflected laser beam 191 to be directed out-of-the plane of the substrate 350 in a direction generally orthogonal to the rotation 370, thereby providing two degrees of adjustment to direct the outgoing laser beam 191 to a core of a desired PM optical fiber 102.
  • the optical switch 104 may also function to direct the reflected laser beam 192 back to the laser- optics assembly 101.
  • Course and/or fine alignment signals representative of misalignment of outgoing laser beam 191 to the PM optical fiber 102 may be applied to move the micro-motor 321 and the micro-mirror 314 relative to the support portion so as to maintain fine alignment of the outgoing laser beam 191 to the core of the PM optical fibers 102.
  • course alignment signals may be obtained by using a look-up table of pre- calibrated values, while the fine alignment signals may be obtained by measuring an amplitude of the reflected laser beam 192.
  • the alignment signals may be applied as a closed loop feedback signal so as to maintain fine alignment.
  • a optical switch 104 is shown during various stages of fabrication.
  • silicon bonding and Deep Reactive Ion Etching (DRIE) techniques are used to manufacture the microstructures comprising optical switch 104.
  • the DRIE processing techniques enable high aspect ratio grooves, channels and other features to be reactively ion etched into silicon substrate 350.
  • the DRIE process is used to fabricate the optical fiber alignment structures, as well as optical deflection and guiding mechanisms.
  • the DRIE process may be controlled to produce etched sidewalls that are smooth and substantially perpendicular to the substrate surface.
  • the optical switch 104 includes micro-motor 321 , flexures 323 and 324, mirror 314, support portion 412, conductor 425, insulator portions 416 and 418, and silicon substrate 350.
  • the optical switch 104 further includes a lower silicon substrate 551.
  • a shallow etched gap 552 is provided at a top surface of the lower silicon substrate 551.
  • the gap 552 subsequently functions to provide a void for movement of the flexures 323 and 324, the micro-mirror 314, and the support portion 412.
  • biplanar oxide layer 418 and overlaying metal layer 425 are formed on an outward surface of substrate 350.
  • An oxide layer 416 is formed on an opposing inward face of the substrate 350.
  • Oxide layer 553 is formed on a facing surface of substrate 551.
  • Layer 553 is formed on a facing top surface of the bottom substrate 551 to subsequently provide a fusion bonding interface 555 between the two substrates 350 and 551.
  • Oxide layer 416 is patterned to subsequently provide the oxide hinge axis shown in Figure 17a.
  • facing surfaces of .substrate 350 and substrate 551 are joined at fusion interface 555.
  • a subsequent masking and DRIE step removes silicon from substrate 350 to form void regions 554, 556, 558 and 560 (shown as partially completed in Figure 19) which define micro-mirror 314, support portion 412, and spaced apart planar flexures 324 and 323 (overlaying in this view).
  • the oxide layer 553 at interface 555 functions to stop the DRIE etch step at the surface of substrate 551, creating an accurate depth for alignment of optical fibers to the other microstructures of the optical switch 104.
  • patterned insulator and metal regions are provided on the top or outward facing surface of the upper substrate wafer 350.
  • the sihcon underneath these insulator and metal regions is preferably etched in a wet or plasma isotropic etch step to form the insulator 418 and conductor 425 portions.
  • Slight adjustment to the DRIE parameters may be used to incorporate a small degree of lateral underetching to remove silicon underneath the narrow extended insulator and conductor regions (shown as flexible extensions 418-d,e and 425-d,e in Figure 17a) while leaving the silicon generally intact underneath those portions of the oxide layer 418 that form the micro-mirror 314, the support portion 412, and flexures 323 and 324.
  • fiber optic alignment guides may be DRIE etched into the substrate 350.
  • the PM optical fiber 102 is positioned within a lithographically defined and etched guide 562 and preferably aligned to the other micro-mechanical structures of optical switch 104.
  • Figure 20 shows the PM optical fiber 102 located within a particular DRIE etched alignment guide
  • the direction of etching chosen for fiber optic alignment guides may be selected to provide any number of geometrical relationships between the incoming laser beam 191 and the PM optical fibers 102 relative to the location of the micro-mirror 31 .
  • Micro- motor 321 may also be manufactured with a process that combines the sihcon fusion bonding and DRIE techniques used by the present invention or with a number of other techniques well known in the art, for example, sacrificial etching of thin-film polysilicon layers.
  • linear micro-motor 321 functions to adjust the focal point of an incoming beam of light that is in the plane of the substrate 350, and a tilting mechanism adjusts the focal point out of the plane of the substrate.
  • a tilting mechanism adjusts the focal point out of the plane of the substrate.
  • optical fibers that are not PM optical fibers use of an PM optical fiber rather than a free space optical path between the laser- optics assembly 102 and the optical switch 104, sources of light other than laser sources, different input and output fiber formats, greater or fewer than six optical fibers; different flexure, insulator, and metal line designs to effectively position the mirror in other planes relative to the plane of the substrate; different types of micro-motor technologies, including: electrostatic, electromagnetic, or thermal technologies; and various combinations of DRIE and conventional anisotropic etching to align the fibers and to create the mirror surfaces and micromotor designs.
  • Figure 21a is a diagram showing a magneto-optical data storage and retrieval system as part of a magneto-optical disk drive.
  • the magneto-optical system 100 may comprise a compact high-speed and high-capacity MO disk drive 800 that includes an industry standard 5.25 inch half-height form factor (1.625 inch), at least six double-sided MO disks 107, and at least twelve flying MO heads 106. As discussed above, the flying MO heads
  • 106 may be manufactured to include optical and magnetic elements that provide a very small mass and low profile high NA optical system so as to enable utilization of multiple MSR MO disks 107 at a very close spacing within the MO disk drive 800 and; therefore, to comprise a higher areal and volumetric and storage capacity than is permitted in an equivalent volume of the prior art.
  • a spacing between each of the at least six MO disks may be manufactured to include optical and magnetic elements that provide a very small mass and low profile high NA optical system so as to enable utilization of multiple MSR MO disks 107 at a very close spacing within the MO disk drive 800 and; therefore, to comprise a higher areal and volumetric and storage capacity than is permitted in an equivalent volume of the prior art.
  • 107 can be reduced to at least .182 inches.
  • the half-height form factor MO disk drive 800 may include a removable MO disk cartridge portion 810 and two fixed internal MO disks 107.
  • the removable MO disk cartridge portion 810 By providing the removable MO disk cartridge portion 810, the fixed internal and removable combination permits external information to be efficiently delivered to the MO disk drive 800 for subsequent transfer to the internal MO disks 107. The copied information may, subsequently, be recorded back onto the removable MO disk cartridge portion 810 for distribution to other computer systems.
  • the removable MO disk cartridge portion 810 may be provided in an alternative embodiment shown in Figure 21b.
  • an MO disk o drive 800 may include: any number (including zero) of internal MO disks 107 and/or any number of MO disks 107 within any number of removable MO disk cartridge portions 1510.
  • the present invention does not necessarily require use of rotary actuator arms, for example, linear actuator arms may be used.
  • the low profile optical paths disclosed by the present invention may be used to convey information to and from a storage location without requiring objective optics (e.g., using a tapered optical fiber or an optical fiber with a lens formed on an end); and/or reflective substrates (e.g., using a curved optical fiber to convey information along surfaces of the magneto-optical head 106); and/or quarter-wave plates, as in a system that effectuates compensation of PM optical fibers using dynamic phase compensation.
  • Free space optical paths may also be used to deliver and receive laser light, for example, with a suitably aligned laser diode and detector mounted on the actuator arm or, alternatively, on the flying head itself.
  • Example 1 Referring again to Figure 2, there is shown a view of an embodiment of a steerable micro- machined mirror assembly 400. Relevant geometrical features are indicated in the drawings. As previously stated, the central mirror plate portion 420 is supported by suspension hinges 410 which may be of a different thickness than the reflective central mirror portion 420 itself. Spaced apart actuation electrodes 402 and 403 are shown below the reflective central mirror portion 420 and separated from the reflective central mirror portion 420 by a gap, g. For purposes of analysis, a square wave excitation at electrodes 402 and 403 is assumed (V a and Vt>) to rotate the reflective central mirror portion 420 around the y-axis by an angle, ⁇ .
  • the electrostatic force to actuate the torsional motion of the reflective central mirror portion 420 is balanced by the torsional restoring force provided by the suspension hinges 410.
  • the stiffness of the suspension hinges 410 is given by the following expressions from Roark's Formulas for Stress and Strain (6 Edition, published by McGraw Hill Text, p. 347):
  • ⁇ is the twist at the end of the hinge 410 (radians)
  • E and v are the Young's modulus and Poisson's ratio of the suspension material
  • 1 is the length of the suspension hinges 410
  • w is the hinge 410 width
  • U is the hinge 410 thickness.
  • the factor of two on the right hand side of equation ( 1 ) accounts for the presence of the two torsional hinges 410 at either end of the reflective central mirror portion 420.
  • the torque caused by the electrostatic attraction of the reflective central mirror portion 420 to the driving electrodes 402 and 403 may be expressed as follows:
  • dF(x) is the incremental attractive force acting on an infinitesimal element of width dx of the reflective central mirror portion 420
  • x is taken as the traasverse distance from the central axis of the l o reflective central mirror portion 420 to the position of the incremental element, and the integration is performed over half of the width of the reflective central mirror portion 420.
  • the incremental force dF(x) is a function of x because the angular deflection of the reflective central mirror portion 420 causes the separation between the electrode 402 (or 403) and the reflective central mirror portion 420 to vary linearly with position along the width of the reflective central mirror portion 420.
  • Equation (9) describes a function that peaks for a critical angle of the reflective central mirror portion 420 rotation.
  • the electrostatic force varies as the inverse of the square of the
  • equation (9) is not valid for deflection angles greater than the critical angle.
  • an actuator voltage slightly greater than the value needed to cause the spontaneous deflection to the electrode 402 or 403 is preferable.
  • the resonant frequency in hz (f) of the reflective central mirror portion 420 is defined as:
  • Equations (1-3) can be rearranged to show that k can be expressed as:
  • FIG. 22 shows the actuation voltage as a function of maximum deflection angle ⁇ vi (in radians, 2 degrees equals 0.035 radians) for the following two sets of geometrical parameters (dimensions are in microns, in both cases the reflective central mirror portion 420 and hinges 410 are preferably fabricated from silicon nitride which has a Young's modulus, E, of 385 Gpa and a Poisson's ratio, v, of 0.066). The calculated resonant frequency in both cases is 99 KHz.
  • the lowest of the three curves (V 2 ,i)in the graph of Figure 22 describes the situation for the case of a narrow (3 micron) initial gap between the electrodes 402 and 403 and the reflective central mirror portion 420.
  • the actuation voltage is small in this case (maximum voltage is 66.6 5 V)
  • the nonlinear affect of the electrostatic force causes instability at an angle of about 1.55 degrees (0.027 radians), the point wherein the voltage curve reaches a maximum.
  • the mirror's angle beyond 1.55 degrees cannot be predicted with accuracy, and in fact, due to the shallow slope of the curve beyond about 0.01 radians (0.6 degrees), control of the actuation voltage would require precise control to obtain a desired certainty of angular deflection.
  • the wider gap (7 microns) assumed for the middle of the three curves (V ⁇ , in the graph of Figure 22 keeps the maximum necessary deflection of 0.035 radians within the stable region of the deflection of the reflective central mirror portion 420.
  • the actuation voltage for 2 degrees deflection in this case is 215.7 V.
  • the voltage that causes instability in this case is roughly 237 V; therefore, relatively good control of the voltage would be required to keep clear of
  • Equations (13) (resonant frequency) and (15) (actuation voltage) are rearranged and reproduced below. The approximation described in the previous section is used so that the tradeoffs between voltage and resonant frequency are more clearly evident.
  • f ⁇ represents the damping in the torsional oscillations and all the other parameters have been previously defined.
  • An important damping mechanism is assumed to be due to a film of air (the squeeze film, not shown) between the reflective central mirror portion 420 and the electrodes 402, 403.
  • the squeeze film As the reflective central mirror portion 420 rotates, the pressure in the squeeze film is o increased above the electrode 402 or 403 where the reflective central mirror portion 420 tilts toward it. Conversely, the pressure is reduced at the opposite electrode as the mirror plate 402 tilts away from that electrode 402 or 403.
  • the pressure gradient developed by the squeeze film provides a moment that resists the motion of reflective central mirror portion 420.
  • ⁇ is the viscosity of air at room temperature (1.87e-5 Pa-sec).
  • the damping coefficient then can be defined as 0
  • Example 2 Use of the steerable micro -machined mirror assembly 400 at a desired actuation voltage of 100 V and with a bandwidth of 100 KHz requires a number of tradeoffs. Presented below
  • Non-linearity in the actuation voltage vs. angular deflection relationship for the steerable 5 micro-machined mirror assembly 400 is an important concern for the positional control of the reflective central mirror portion 420.
  • An effective way of dealing with this non-linearity is to increase the static gap between the electrodes 402 and 403 so as to stay clear of the point of electrostatic pull-in at the cost of requiring higher actuation voltage to get to the full +/- 2 degrees of angular deflection.
  • the actuation voltage vs. angular deflection relationships are shown for three different static gap widths (6, 8 and 10 microns).
  • the gap width is the entire electrode spacing, including the thickness of the reflective central mirror portion 420.
  • Two curves are plotted on each graph with the lower curve taking into account the presence of the higher dielectric constant provided by the (nitride) reflective central mirror portion 420 and the 5 upper curve neglecting this issue. Both curves are provided in order to indicate the approximate range expected for actuation voltages.
  • the x-axis is plotted in radians with 0.035 radians equal to 2 degrees.
  • the steerable micro-machined mirror assembly 400 preferably has a static gap on the order of 8-10 microns.
  • E and v are the Young's modulus and Poisson's ratio for the hinge material
  • eo is the permittivity of free space. Incorporating the two-step variable gap into this calculation involves a simple adjustment to the
  • Figure 31 shows voltage vs. angular deflection and the reduction in actuation that is provided by this design modification given the geometrical choices defined in the table below.
  • the point of instability has not changed, the maximum voltage for the variable gap case has been reduced from 169 volts to 125 volts.

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Abstract

Une tête optique utilise un élément micro-usiné conjointement avec une source de lumière et à une lentille pour l'écriture et la lecture de données sur un disque de stockage (107). L'élément micro-usiné peut comporter un miroir micro-usiné orientable (400) ou un micro-actionneur (433). Un rayon de lumière laser (191) est envoyé par la source de lumière (231) à la tête optique et une lumière réfléchie provenant du disque de stockage (107) est modifié par un mouvement de l'élément micro-usiné. Un point optique focalisé (448) est déplacé en va-et-vient dans un sens (450) sensiblement parallèle au sens radial du disque de stockage (107).
EP97939651A 1996-08-27 1997-08-27 Tete optique utilisant des elements micro-usines Withdrawn EP0929894A1 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US2580196P 1996-08-27 1996-08-27
US25801P 1996-08-27
US82342297A 1997-03-24 1997-03-24
US823422 1997-03-24
PCT/US1997/015215 WO1998009289A1 (fr) 1996-08-27 1997-08-27 Tete optique utilisant des elements micro-usines

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JP2001525972A (ja) 2001-12-11

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