GRIN fiber lenses

• US 20020146202A1
• Filed: 06/29/2001
• Published: 10/10/2002
• Est. Priority Date: 02/17/2001
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Schnitzer, Mark J., Reed, William Alfred
• Granted Patent: US 6,542,665 B2
• Time in Patent Office: Days
• US Class Current: 385/34
• CPC Class Codes: A61B 5/0084 for introduction into the body, e.g. by catheters A61B5/1459 takes precedence
• CPC Class Codes: C03B 2201/12 doped with fluorine C03B2201/14 takes precedence
• CPC Class Codes: C03B 2201/28 doped with phosphorus
• CPC Class Codes: C03B 2201/31 doped with germanium
• CPC Class Codes: C03B 2201/32 doped with aluminium C03B2201/36 takes precedence
• CPC Class Codes: C03B 2203/26 Parabolic or graded index [GRIN] core profile
• CPC Class Codes: C03B 37/01861 Means for changing or stabilising the diameter or form of tubes or rods
• CPC Class Codes: G02B 6/14 Mode converters
• CPC Class Codes: G02B 6/262 Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements
• CPC Class Codes: G02B 6/264 with optical elements between opposed fibre ends which perform a function other than beam splitting having lens focusing means G02B6/32; utilising prism or grating G02B6/34
• CPC Class Codes: G02B 6/32 having lens focusing means positioned between opposed fibre ends with lens being an integral part of the single fibre end G02B6/262
• CPC Class Codes: G02B 6/3512 the optical element being reflective, e.g. mirror
• CPC Class Codes: G02B 6/3548 1xN switch, i.e. one input and a selectable single output of N possible outputs
• CPC Class Codes: G02B 6/3552 1x1 switch, e.g. on/off switch
• CPC Class Codes: G02B 6/3556 NxM switch, i.e. regular arrays of switches elements of matrix type constellation
• CPC Class Codes: G02B 6/3582 Housing means or package or arranging details of the switching elements, e.g. for thermal isolation
• CPC Class Codes: G02B 6/3594 Characterised by additional functional means, e.g. means for variably attenuating or branching or means for switching differently polarized beams

Abstract

A GRIN fiber lens has a silica-glass core whose refractive index has a radial profile. The profile has a radial second derivative whose average magnitude in the core is less than about 1.7×10⁻⁶ microns⁻² times the value of the refractive index on the axis of the GRIN fiber lens.

Claims

1. An apparatus, comprising:

a GRIN fiber lens having a silica-glass core whose refractive index has a radial profile, the profile has a radial second derivative whose average magnitude in the core is less than about 1.7×

10<sup>−

6</sup> microns<sup>−

2</sup> times the value of the refractive index on the axis of the GRIN fiber lens.

2. The apparatus of claim 1, wherein the average magnitude of the radial second derivative is less than about 0.9×

10<sup>−

6</sup> microns<sup>−

2</sup> times the value of the refractive index on the axis of the GRIN fiber lens..

3. The apparatus of claim 1, wherein the fiber lens further comprises a cladding surrounding the core, a ratio of an outer diameter of the core to an outer diameter of the cladding being at least as large as 85/125.

4. The apparatus of claim 1, wherein the lens does not have a silica-glass cladding.

5. The apparatus of claim 1, wherein the lens has an free end surface whose normal vector is cleaved by at least 0.5°

with respect to an optical axis of the lens.

6. The apparatus of claim 1, wherein the lens includes first and second GRIN lens elements, the first and second GRIN lens elements being serially coupled and having different optical powers.

7. The apparatus of claim 1, further comprising:

an optical fiber having a non-GRIN core and a cladding; and

wherein the fiber lens is attached to one end of the optical fiber.

8. An apparatus, comprising:

a first optical fiber;

a first GRIN fiber lens attached to the first optical fiber;

a second optical fiber;

a second GRIN fiber lens attached to the second optical fiber; and

an optical device capable of directing a portion of a light beam emitted from a free end of the first GRIN fiber lens to the second GRIN fiber lens; and

wherein the GRIN fiber lenses have silica-glass cores and refractive indexes with radial profiles, the profiles having radial second derivatives with average magnitudes in cores of less than about 1.7×

10<sup>−

6</sup> microns<sup>−

2</sup> times the refractive index on the axes of the respective GRIN fiber lenses.

9. The apparatus of claim 8, wherein the optical device is one of a reflector, a polarization splitter, an optical isolator, and a polarization rotator.

10. The apparatus of claim 8, further comprising:

a micro-electro-mechanical controller physically coupled to the optical device.

11. The apparatus of claim 8, further comprising:

a third optical fiber;

a third GRIN fiber lens attached to the third optical fiber; and

wherein the optical device is capable of directing a portion of a light beam emitted from the free end of the first GRIN fiber lens to the third GRIN fiber lens.

12. The apparatus of claim 8, wherein the bulk optical device is capable of intercepting a light beam emitted by of the first GRIN lens at a point within a Rayleigh range of the beam'"'"'s waist.

14. The method of claim 13, further comprising:

attaching a portion of the GRIN fiber to another optical fiber, the attaching including one of fusing ends of the fibers together and gluing ends of the fibers together.

15. The method of claim 13, further comprising:

cleaving the attached GRIN fiber to form a GRIN fiber lens.

16. The method of claim 13, wherein providing a preform comprises:

forming a tube of silica-glass having a tubular core and a tubular cladding located adjacent and external to the tubular core, the core have a dopant density with a radially graded profile;

partially collapsing the tube by applying heat thereto, the partially collapsed tube having a central channel; and

passing a glass etchant through the central canal to remove an internal layer of silica glass.

18. The method of claim 17, further comprising:

drawing a GRIN fiber from the preform.

19. The method of claim 18, wherein the drawing produces a GRIN fiber whose core has a refractive index with a profile having a radial second derivative whose average magnitude is less than about 1.7×

10<sup>−

6</sup> microns<sup>−

2</sup> times the value of the refractive index on the axis of the GRIN fiber lens.

20. The method of claim 18, wherein the drawing produces a GRIN fiber whose core has a refractive index with a profile whose radial second derivative has an average magnitude that is less than about 0.9×

10<sup>−

6</sup> microns<sup>−

2</sup> times the value of the refractive index on the axis of the GRIN fiber lens.

21. The method of claim 17, wherein the forming further comprises:

depositing a portion of the core on an inside surface of the tubular cladding, the depositing including introducing a mixture of a precursor for dopant deposition and a precursor for silica-glass deposition inside the tubular cladding, the depositing including varying the percentage of the precursor for dopant in the mixture with time.

22. The method of claim 21, further comprising:

removing at least an outer layer of the tubular cladding tube from the preform.

23. The method of claim 18, further comprising:

fusing a portion of the GRIN fiber to another optical fiber.

24. The method of claim 23, further comprising:

cleaving the fused GRIN fiber to form a GRIN fiber lens with a length of at least 2 millimeters.

25. The method of claim 23, further comprising:

cleaving the fused GRIN fiber to form a GRIN fiber lens with an end face whose normal is not parallel to the axis of the GRIN fiber lens.

13. A method for fabricating a GRIN fiber, comprising:

providing a doped silica-glass preform having an axial core and a tubular cladding surrounding and adjacent the core, the core having a graded index of refraction, the cladding having a lower refractive index than the core;

etching the preform to remove an outer layer of the tubular cladding; and

drawing the GRIN fiber from the etched preform.

17. A method for fabricating a GRIN fiber, comprising:

forming a tube of silica-glass having a tubular core and a concentric tubular cladding adjacent and external to the tubular core, the core having a dopant density with a radially graded profile;

partially collapsing the tube by applying heat thereto, the partially collapsed tube having a central channel;

passing a glass etchant through the central canal to remove an internal layer of silica glass; and

then, collapsing the etched tube to a rod-like preform.