Fiber mini-bend light guide

Details Fiber mini-bend light guide Fiber mini-bend light guide

1999-09-23

2001-11-06

Epps, Georgia (Department: 2873)

Optical waveguides

With optical coupler

Input/output coupler

C385S096000, C385S099000, C385S080000

Reexamination Certificate

active

06314219

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is related generally to the field of losses introduced in an optical light guide resulting from the need to abruptly change the directional orientation of the path of the optical light guide and, more particularly, to a highly advantageous miniature bend arrangement and associated method employing a particular configuration of fiber optic light guide members which avoids the introduction of significant bend losses.
Attention is immediately directed to
FIG. 1
which is a representation of FIG. 6 of U.S. Pat. No. 5,138,676 issued to Stowe et al and hereinafter referred to as the '676 patent. Optical fibers used, for example, in communications systems are known to produce losses with respect to light signals traveling on the fibers with the introduction of a sufficiently sharp bend. At the same time, it is often desirable to introduce such sharp bends for purposes such as, for instance, device miniaturization. In this regard, a typical optical fiber may be bent at a diameter of approximately 50 mm before introducing appreciable bend losses. One approach in attempting to resolve this problem is described in the '676 patent, as illustrated by FIG.
1
. The latter shows a structure, generally indicated by the reference numeral
5
, configured for introducing a sharp bend in a light path. Structure
5
includes a jacket
10
surrounding an optical fiber
32
which is, in turn, mounted in a right angle grooved supporting structure
34
. The fiber enters the structure at reference number
36
and exits at
38
with its core
39
shown. Fiber
32
includes a reduced diameter section
18
which is bent at approximately a 90° angle. The diameter of the reduced diameter section is approximately 15 microns as compared to a normal diameter of approximately 125 microns. A polished end face
40
is included at one end which may be positioned adjacent to another device or fiber. A cladding
42
surrounds core
39
of the fiber. It is noted that a 180 degree bend using this reduced diameter section technique is disclosed in an article by David W. Stowe and Frederick J. Gillham entitled “Miniature Fiber Bends Offer Flexibility in Component and Circuit Design.”
Having generally described structure
5
of
FIG. 1
, it should be appreciated that one underlying feature of the structure resides in substantially reducing the diameter of section
18
of fiber
32
in a way which removes the cladding. Initially, this fiber is surrounded by jacket
10
and is configured with cladding
42
. To remove the cladding, the jacket is removed, as illustrated, and reduced diameter section
18
is produced, for example, in an etching process in combination with drawing. The cladding is removed at least to an extent that the interface between the reduced diameter section and the surrounding air is relied on to produce internal reflection of light traveling around the bend and through the reduced diameter section. Upon such removal of the cladding, the numerical aperture of the fiber itself in this region is submitted to be so low as to not serve as a useful light guide without further provisions. That is, the numerical aperture in the reduced diameter region is now determined based upon the difference between the index of refraction of the fiber as a whole and the index of refraction of the surrounding medium, in this instance, air. Typically, this numerical aperture is quite high, resulting in low bend losses for light traveling through reduced diameter section
18
. While structure
5
generally serves its intended purpose, several disadvantages have been discovered, as will be described immediately hereinafter.
Still referring to
FIG. 1
, it is important to note that reduced diameter section
18
must be exposed to air (or some other suitable medium) along its entire length. Hence, the requirement for supporting structure
34
. That is, reduced diameter section
18
must not contact anything but air to avoid adversely affecting the index of refraction produced through the cooperation of the air and the reduced diameter section. This requirement is submitted to be disadvantageous in and by itself. Moreover, the significance of achieving a sharp bend in the fiber is considered to be overshadowed by the disadvantageous requirement of supporting structure
34
. The latter limits the usefulness of structure
5
particularly with regard to producing miniaturized devices, since such a housing must accompany the bent fiber. In future device generations this limitation is considered as being unacceptable. Moreover, it is submitted that structure
5
is complex and, as such, factory production environments are mandated using precision fixtures resulting in a relatively expensive final product.
The present invention provides a highly advantageous and heretofore unseen mini-bend arrangement and associated method which eliminates the foregoing disadvantages and which provides still further advantages.
SUMMARY OF THE INVENTION
As will be described in more detail hereinafter, there is disclosed herein a mini-bend optical arrangement and an associated method. This arrangement, like the prior art structure illustrated in
FIG. 1
, is designed to change the directional orientation of a light path. However, the arrangement of the present invention includes a first and a second fiber optic member defining first and second light paths, respectively, which first and second fiber optic members include a numerical aperture and which introduce substantial bend losses upon being bent at less than a predetermined bend radius. The first and second fiber optic members are arranged along the first and second paths preferably bent by less than the predetermined bend radius. A bent fiber optic member including a numerical aperture that is greater than the numerical aperture of the first and second fiber optic members interconnects the first and second fiber optic members so as to define a continuous light path including the first and second light paths with the bent fiber optic member defining a curved path therebetween such that the bent fiber optic member has a bend radius which is less than the predetermined bend radius but which avoids introducing substantial bend losses.
In one aspect of the invention, the mini-bend arrangement is useful in highly advantageous miniaturized device configurations. As a first example, a miniaturized add/drop module is described. Other examples include miniaturized tree couplers, EDFA modules and WDM modules.


REFERENCES:
patent: 4669817 (1987-06-01), Mori
patent: 5138676 (1992-08-01), Stowe et al.
patent: 5233677 (1993-08-01), Winslow
patent: 5452393 (1995-09-01), Stowe et al.
patent: 5495541 (1996-02-01), Murray et al.
Frederick J Gillham et al, Miniature Fiber Optic Loop for Compact Optical Sensors, Nov. 1998, SPIE Conference on Fiber Optic and Laser Sensors and Applications, SPIE vol. 3541.
James E Hefferon, Calculating Bend and Twist Stress in Optical Fibers, 1986, Components for Fiber Optic Applications, SPIE vol. 722.
David W Stowe and Frederick J Gillham, Miniature Fiber Bends Offer Flexibility in Component and Circuit Design, Lightwave Special Reports (no date available).
David W Stowe, Frederick J Gillham, and Thomas R Ouellette, Compact Components Using Miniature-bend Technology, Jul. 1998, Fiberoptic News.

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