GRIN fiber lenses

Details GRIN fiber lenses GRIN fiber lenses

2001-06-29

2003-04-01

Lee, John D. (Department: 2874)

Optical waveguides

With optical coupler

Input/output coupler

C385S124000, C359S652000, C359S654000

Reexamination Certificate

active

06542665

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to optical devices and graded refractive index lenses.
2. Discussion of the Related Art
A graded refractive index (GRIN) lens has a refractive index whose value varies with radial distance from the axis of the lens. The non-trivial variation in refractive index causes light refraction and gives the GRIN lens focussing capabilities that are similar to those of an ordinary lens. Therefore, many optical devices.employ GRIN or ordinary lenses interchangeably.
Many optical devices use lenses to focus, collimate, or expand light beams.
FIG. 1
shows a fiber device
10
in which a GRIN fiber lens
11
is fused to a terminal end
12
of an optical fiber
13
. The GRIN fiber lens
11
expands and collimates the light beam emitted by the optical fiber
13
. The GRIN fiber lens
11
improves the optical coupling between optical fiber
13
and fiber device
15
as compared to the coupling that would otherwise exist between the fiber
13
and device
15
due to diffraction. The GRIN fiber lens
11
reduces diffraction losses when the optical fiber
13
is optically coupled to another optical fiber.
Since the diameter of a light beam varies along the axis of a GRIN lens, the beam diameter variations provide a measure of the lens' length. The length over which the variations in the beam diameter make two complete cycles is known as the pitch of the lens. Typically, lengths of GRIN lens are referred to in multiples of the pitch length, e.g., ½ pitch or ¼ pitch.
BRIEF SUMMARY OF THE INVENTION
Some optical devices embodying principles of the inventions include a GRIN fiber lens in which the refractive index has a new radial profile. When attached to an end of an optical fiber, the new GRIN fiber lens increases the Rayleigh range of the emitted beam above that of a light beam emitted by a similar fiber attached to a conventional GRIN lens. The increased Rayleigh range improves beam collimation so that the fiber may couple to other optical devices over larger distance ranges.
In various embodiments, a GRIN fiber lens has a silica-glass core whose refractive index has a radially graded profile. On the axis of the GRIN fiber lens, the profile has a radial second derivative whose magnitude 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. Henceforth, microns are written as &mgr;m.


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