High numerical aperture optical focusing device having a conical incident facet and a parabolic reflector for use in data storage systems

• US 6,377,535 B1
• Filed: 10/26/1998
• Issued: 04/23/2002
• Est. Priority Date: 07/06/1998
• Status: Expired due to Term

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: Read-Rite Corporation (Western Digital Corporation)
• Inventors: He, Chuan, Chen, Hong, Cheng, Charles C., Miceli, Joseph J. Jr., Wang, Yugang, Carlson, Carl J.
• Primary Examiner(s): Hudspeth, David
• Assistant Examiner(s): CHU, KIM KWOK
• Application Number:
  US09/179,279
• Time in Patent Office: 1,275 Days
• Field of Search: 369/13, 369/44.14, 369/44.23, 369/112, 369/119, 369/109, 369/103, 369/118, 359/575, 359/565, 359/571
• US Class Current: 369/112.09
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G02B 5/1885 Arranged as a periodic array
• CPC Class Codes: G11B 11/10532 Heads
• CPC Class Codes: G11B 11/10543 using optical beam of radiation
• CPC Class Codes: G11B 11/10554 the transducers being disposed on the same side of the carrier flying heads G11B11/1058
• CPC Class Codes: G11B 11/1058 Flying heads
• CPC Class Codes: G11B 2007/13722 Fresnel lenses
• CPC Class Codes: G11B 7/122 Flying-type heads, e.g. analogous to Winchester type in magnetic recording
• CPC Class Codes: G11B 7/1353 Diffractive elements, e.g. holograms or gratings diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44
• CPC Class Codes: G11B 7/1372 Lenses
• CPC Class Codes: G11B 7/1374 Objective lenses optical objectives per se G02B9/00
• CPC Class Codes: G11B 7/22 Apparatus or processes for the manufacture of optical heads, e.g. assembly

Abstract

An optical focusing device for focusing an incident optical beam onto a focal plane, as a focal spot. The optical focusing device includes an incident central refractive facet upon which an optical beam impinges, and a high-index glass body through which the incident optical beam passes toward a bottom reflective surface. The bottom reflective surface reflects the optical beam through the body, toward a peripheral reflector. The peripheral reflector focuses the optical beam toward a focal plane on which the focal spot is formed. The focal plane is defined within a pedestal that forms part of the optical focusing device, and that extends from the bottom reflective surface. The central facet is conically shaped for refracting the incident optical beam away from the pedestal, onto the bottom reflective surface. The peripheral reflector surrounds the central facet and can have various appropriate shapes, such as an aspherical shape or a tilted parabolic shape, which compensates for the conical factor and aberrations introduced by the central facet. The top surface includes the central facet and the peripheral facet, and can be made substantially flat using diffractive optical elements or Fresnel optics.

Claims

1. An optical data storage system comprising:

an optical focusing device for focusing an incident optical beam to a focal spot, comprising;

a top surface comprised of a peripheral reflector and a central facet upon which the optical beam impinges;

a body through which the incident optical beam passes;

a bottom reflective surface for reflecting the optical beam through said body toward said peripheral reflector;

a pedestal extending from said bottom reflective surface for defining a focal plane on which the focal spot is formed;

said peripheral reflector focusing the optical beam reflected from the bottom reflective surface to the focal spot; and

said central facet being generally conically shaped;

wherein the beam is any of;

a collimated, convergent, or divergent beam;

wherein said central facet refracts the incident optical beam away from said pedestal, onto said bottom reflective surface;

wherein said central facet is optically refractive; and

wherein the incident optical beam is refracted by said central facet as a generally collimated beam with a donut shaped cross-section.

2. An optical data storage system according to claim 1, wherein said peripheral reflector has a curved shape.

3. An optical data storage system according to claim 1, wherein said peripheral reflector is generally flat.

4. An optical data storage system according to claim 1, wherein said peripheral reflector is generally aspherically shaped.

5. An optical data storage system according to claim 1, wherein said peripheral reflector has a generally parabolic shape.

6. An optical data storage system according to claim 1, wherein said peripheral reflector has any of:

a generally tilted hyperbolic, titled tilted parabolic, or tilted elliptical shape.

7. An optical data storage system according to claim 1, wherein said central facet is any of:

positively or negatively lensed.

8. An optical data storage system according to claim 1, wherein a diffractive microstructure provides a phase distribution function Φ

(r) of said central facet is defined by the following equation;

$\mathrm{\Phi <br><br>}<br><br>\left(r\right)=-\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>r;<br><br>\mathrm{and}$

wherein a phase distribution function Φ

(r) of said peripheral reflector is defined by the following equation;

$\mathrm{ <br><br>}<br><br>\mathrm{\Phi <br><br>}<br><br>\left(r\right)=\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\left(a_1<br><br>r+a_2<br><br>r^2+a_3<br><br>r^3+a_4<br><br>r^4\right),<br><br>\mathrm{where}<br><br>\text{\hspace{1em}<br><br>}<br><br>r=<br><br>\sqrt{x^2+y^2}<br><br>;<br><br>$

where r is the radius of the curvature;

x and y represent the coordinates system and λ

is the wavelength of the optical beam;

a₁ is approximately 0.848330;

a₂ is approximately 7.440246;

a₃ is approximately −

15.700477; and

a₄ is approximately 14.359795.

9. An optical data storage system according to claim 1, wherein a surface of said peripheral reflector is defined by a tilted parabola expressed by the following equation $Z=-\mathrm{ctg}$

 



 



θ

·

ρ

+2

f·

cos

 



θ

sin2

θ

-2

fsin2

θ



1-Sin

 



θ

f·

ρ

,

where θ

is the rotation angle of the parabola curve;

f is a focus length of the parabola; and

ρ

is the radius along a coordinate axis Z.

10. An optical data storage system according to claim 1, wherein said bottom reflective surface is reflective;

and

wherein the beam refracted by said central facet is reflected by said bottom reflective surface as a collimated beam onto said peripheral reflector.

11. An optical data storage system according to claim 1, wherein the beam reflected by said bottom reflective surface impinges upon said peripheral reflector;

and

wherein said peripheral reflector is any of;

reflective;

reflective and refractive;

or reflective and diffractive.

12. An optical data storage system according to claim 1, wherein said central facet defines an apex;

and

wherein the focal spot is co-aligned with said apex along a central axis.

13. An optical data storage system according to claim 1, wherein said peripheral reflector compensates for conical factors introduced by said central facet.

14. An optical data storage system according to claim 1, wherein a surface of said peripheral reflector is substantially aspherically shaped, the function of which is approximated by the following equation:

$Z=\frac{\mathrm{CV}·<br><br>r^2}{1+\sqrt{1-{\mathrm{CV}}^2<br><br>\left(\mathrm{CC}+1\right)<br><br>r^2}}+a_4<br><br>r^4+a_6<br><br>r^6+a_8<br><br>r^8+a_{10}<br><br>r^{10},$

where Z is the function of the aspherical surface;

CV is the curvature of the surface, such that (CV=1/r), where r is the radius of the curvature and is defined as follows;

r=(x²+y²)^½

, where x and y represent the coordinates system;

CC is the conic constant of the optical focusing device; and

a₄, a₆, a₈, and a₁₀ are polynomial parameters.

15. An optical data storage system according to claim 1, wherein said central facet is coated with an anti-reflective (AR) coating.

16. An optical data storage system according to claim 1, wherein said surface of said peripheral reflector is optimized for minimal focal spot size by means of an iterative process.

17. An optical data storage system according to claim 16, wherein said iterative process includes a plurality of iterations using pre-defined polynomial coefficients in the following equation:

$Z<br><br>\left(r\right)=-h+\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>a_i<br><br>r^i$

where Z is the function defining the curvature of said peripheral reflector;

r is the radius of curvature of said peripheral reflector.

18. An optical data storage system according to claim 17, wherein said iterative process includes using a Sequential Quadratic Program (SQP).

19. An optical data storage system comprising:

an optical focusing device for focusing an incident optical beam to a focal spot, comprising;

a top surface comprised of a peripheral reflector and a central facet upon which the optical beam impinges;

a body through which the incident optical beam passes;

a bottom reflective surface for reflecting the optical beam through said body toward said peripheral reflector;

a pedestal extending from said bottom reflective surface for defining a focal plane on which the focal spot is formed;

said peripheral reflector focusing the optical beam reflected from the bottom reflective surface to the focal spot; and

said central facet being generally conically shaped;

wherein said top surface includes a peripheral reflector that is generally flat and that has a patterned grating profile; and

wherein said patterned grating profile includes a non-periodic distribution of gratings.

20. An optical data storage system according to claim 19, wherein said peripheral reflector has any one or more of:

a generally curved shape;

a generally flat shape;

a generally aspherical shape;

a generally parabolic shape;

a generally hyperbolic shape, a generally tilted parabolic shape;

or a generally elliptical shape.

21. An optical data storage system according to claim 19, wherein said central facet is any of:

positively or negatively lensed.

22. An optical data storage system according to claim 19, wherein said bottom reflective surface is reflective;

and

wherein the beam refracted by said central facet is reflected by said bottom reflective surface as a collimated beam onto said peripheral reflector.

23. An optical data storage system according to claim 19, wherein the beam reflected by said bottom reflective surface impinges upon said peripheral reflector;

and

wherein said peripheral reflector is any of;

reflective;

reflective and refractive;

or reflective and diffractive.

24. An optical data storage system comprising:

an optical focusing device for focusing an incident optical beam to a focal spot, comprising;

a top surface comprised of a peripheral reflector and a central facet upon which the optical beam impinges;

a body through which the incident optical beam passes;

a bottom reflective surface for reflecting the optical beam through said body toward said peripheral reflector;

a pedestal extending from said bottom reflective surface for defining a focal plane on which the focal spot is formed;

said peripheral reflector focusing the optical beam reflected from the bottom reflective surface to the focal spot; and

said central facet being generally conically shaped;

wherein said central facet includes a holographic optical element.

25. An optical data storage system according to claim 24, wherein said peripheral reflector has any one or more of:

a generally curved shape;

a generally flat shape;

a generally aspherical shape;

a generally parabolic shape;

a generally hyperbolic shape, a generally tilted parabolic shape;

or a generally elliptical shape.

26. An optical data storage system according to claim 24, wherein said central facet is any of:

positively or negatively lensed.

27. An optical data storage system according to claim 24, wherein said bottom reflective surface is reflective;

and

wherein the beam refracted by said central facet is reflected by said bottom reflective surface as a collimated beam onto said peripheral reflector.

28. An optical data storage system according to claim 24, wherein the beam reflected by said bottom reflective surface impinges upon said peripheral reflector;

and

wherein said peripheral reflector is any of;

reflective;

reflective and refractive;

or reflective and diffractive.

29. An optical data storage system comprising:

an optical focusing device for focusing an incident optical beam to a focal spot, comprising;

a top surface comprised of a peripheral reflector and a central facet upon which the optical beam impinges;

a body through which the incident optical beam passes;

a bottom reflective surface for reflecting the optical beam through said body toward said peripheral reflector;

a pedestal extending from said bottom reflective surface for defining a focal plane on which the focal spot is formed;

said peripheral reflector focusing the optical beam reflected from the bottom reflective surface to the focal spot; and

said central facet being generally conically shaped;

wherein said top surface includes a generally flat central facet and a generally flat peripheral reflector;

wherein said peripheral reflector is formed of a pattern of stepped, diffractive micro-structures that are coated with a reflective layer; and

wherein said central facet is formed of a pattern of stepped, diffractive micro-structures.

30. An optical data storage system according to claim 29, wherein said central facet is any of:

positively or negatively lensed.

31. An optical data storage system according to claim 29, wherein said bottom reflective surface is reflective;

and

wherein the beam refracted by said central facet is reflected by said bottom reflective surface as a collimated beam onto said peripheral reflector.

32. An optical data storage system according to claim 29, wherein the beam reflected by said bottom reflective surface impinges upon said peripheral reflector;

and

wherein said peripheral reflector is any of;

reflective;

reflective and refractive;

or reflective and diffractive.

33. An optical data storage system according to claim 29, wherein said peripheral reflector has any one or more of:

a generally curved shape;

a generally flat shape;

a generally aspherical shape;

a generally parabolic shape;

a generally hyperbolic shape, a generally tilted parabolic shape;

or a generally elliptical shape.

34. An optical data storage system comprising:

an optical focusing device for focusing an incident optical beam to a focal spot, comprising;

a top surface comprised of a peripheral reflector and a central facet upon which the optical beam impinges;

a body through which the incident optical beam passes;

a bottom reflective surface for reflecting the optical beam through said body toward said peripheral reflector;

a pedestal extending from said bottom reflective surface for defining a focal plane on which the focal spot is formed;

said peripheral reflector focusing the optical beam reflected from the bottom reflective surface to the focal spot; and

said central facet being generally conically shaped;

wherein said bottom reflective surface includes any of a refractive or diffractive grating.

35. An optical data storage system according to claim 34, wherein said peripheral reflector has any one or more of:

a generally curved shape;

a generally flat shape;

a generally aspherical shape;

a generally parabolic shape;

a generally hyperbolic shape, a generally tilted parabolic shape;

or a generally elliptical shape.

36. An optical data storage system according to claim 34, wherein said central facet is any of:

positively or negatively lensed.

37. An optical data storage system according to claim 34, wherein said bottom reflective surface is reflective;

and

wherein the beam refracted by said central facet is reflected by said bottom reflective surface as a collimated beam onto said peripheral reflector.

38. An optical data storage system according to claim 34, wherein the beam reflected by said bottom reflective surface impinges upon said peripheral reflector;

and

wherein said peripheral reflector is any of;

reflective;

reflective and refractive;

or reflective and diffractive.