Optical waveguides – With splice – Fusion splicing
Reexamination Certificate
2001-03-08
2003-09-02
Kim, Robert H. (Department: 2882)
Optical waveguides
With splice
Fusion splicing
C385S095000, C385S098000, C385S134000, C385S140000, C065S501000
Reexamination Certificate
active
06612754
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is base upon European Application Serial Number 00400815,7 filed on Mar. 23, 2000, from which the benefit of priority is hereby claimed, and the full content which is incorporated herein by reference as though fully set forth.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an apparatus for localized heating of optical fibers, and more particularly to an apparatus and method for splicing optical fibers. The present invention also relates to an apparatus for controlling the intensity of a laser beam.
2. Technical Background
Manufacturers and assemblers of optical networks, systems, and components often must splice two optical fibers together. This is typically accomplished by aligning and fusing the ends of the fibers.
FIG. 1
shows an electric splicer commonly used to splice the ends
14
a
and
14
b
of two fibers
12
a
and
12
b
together. Support members
20
a
and
20
b
support fibers
12
a
and
12
b
such that the fibers are aligned and the two ends abut one another. Fibers
12
a
and
12
b
extend from support members
20
a
and
20
b
in a cantilevered fashion with the ends of the fibers positioned equidistant from the support members by a distance a. A pair of electrodes
16
a
and
16
b
are provided on opposite sides of the splicing area
15
with their tips
18
a
and
18
b,
respectively, aligned along an axis that extends through the center of the splicing region
15
. Then, by creating an electric arc between electrode tips
18
a
and
18
b
, the electric arc heats the ends
14
a
and
14
b
of the fibers above the melting point of the fibers to fuse the ends of the fibers together.
In the arrangement shown in
FIG. 1
, the cantilever distance a must be at least 3 mm to prevent the electric arc produced by the electrodes
16
a
and
16
b
from straying and reaching one of support members
20
a
or
20
b.
A cantilever distance a of 3 mm causes problems since this distance is about 24 times the diameter of the typical fiber (125 &mgr;m ). This relatively large cantilever distance allows ends
14
a
and
14
b
to sag, which makes it very difficult to properly align the two ends
14
a
and
14
b.
Also contributing to alignment problems is the intrinsic curl that most fibers exhibit. This intrinsic curl is typically about 4 meters in radius. Also, when the fiber ends are pushed together, the fibers are more likely to flex with the larger cantilever distance and thereby cause misalignment. On average, such transverse misalignment of the fiber ends results in a 1 dB loss in the signals propagating through the spliced area.
Another difficulty in utilizing an electric splicer is in the control and maintenance of the electric arc in a small space with a predetermined and constant intensity. The localization and intensity of the electric arc at the splicing area is affected by numerous parameters including air pressure, hygrometry dependence of the electric arc, erosion of the electrode point, and dust and fiber particles on the electrodes.
Because of the above-noted problems experienced when utilizing an electric splicer, there exists a need for a fiber splicing apparatus that allows accurate and consistent splicing.
While CO
2
lasers have been utilized previously to heat portions of fibers to produce diffraction gratings and the like, the manner by which such CO
2
lasers were controlled is not sufficient to control a CO
2
laser to splice together the ends of two fibers. Specifically, when splicing optical fibers, the intensity of the laser beam is preferably maintained at a constant level to provide the appropriate energy density in splicing area
115
. In the past, the intensity of CO
2
lasers has been controlled by monitoring the intensity level of the beam and by varying the duty cycle of the electrical power signal used to power the CO
2
laser. More specifically, a portion of the laser beam is split and provided to a thermo-pile detector that produces a voltage level corresponding to the intensity of the impinging laser beam. The voltage level generated by the detector is compared against a reference and used to regulate the duty cycle using pulse width modulation to thereby vary the voltage applied to an internal RF amplifier stage that controls the RF drive applied to the laser electrodes. Although CO
2
lasers are generally quite stable after an initial heating period, the intensity control system described above tends to destabilize the laser output by repeatedly undercompensating and then overcompensating the laser.
A CO
2
laser controlled using the above control system exhibits a random behavior in the range of ±2 percent of the total laser power. Knowing that the energy quantity is given by: &Dgr;Q=P&Dgr;t=mC
P
&Dgr;T, where P is the energy on the fiber, &Dgr;t is the pulse duration, m is the fiber weight, C
p
is the heat capacity which is 1200 J/kg/°C. and &Dgr;T is the temperature difference. Thus,
Δ
T
=
P
Δ
t
mC
p
.
Therefore, a ±2 percent variation in power P induces a ±2 percent variation in temperature at the splicing area. The temperature during the splice is about 1800° C. which is the melting temperature of the fiber. Thus, a ±2 percent variation in temperature leads to ±36° C. of temperature variation. Such a variation causes unacceptable inconsistencies during the fiber-splicing process.
SUMMARY OF THE INVENTION
Accordingly, it is an aspect of the present invention to solve the above problems by providing a splicing apparatus that allows the reduction of the cantilever distance of the fibers. It is another aspect of the present invention to provide a splicing apparatus having a stable splicing temperature thereby providing consistent spliced fiber characteristics. Another aspect of the invention is to provide a splicing apparatus that does not suffer from the problems associated with cleaning of electrodes.
To achieve these and other aspects and advantages, the splicing apparatus of the present invention comprises a support for supporting the two optical fibers such that the ends thereof are aligned and in physical contact. The splicing apparatus further includes a laser for projecting a laser beam onto the ends of the optical fibers to heat and thereby fuse together the ends of the fibers.
According to another embodiment, an apparatus is provided for heating a region of one or more optical fibers. The apparatus comprises a laser for producing a laser beam, and an optical modulator positioned to receive and selectively modulate the intensity of the laser beam to project a modulated laser beam along a first optical path that is directed to the ends of the optical fiber(s) to be heated. The apparatus further includes a control loop to monitor the intensity of the modulated laser beam and control the optical modulator to thereby regulate the intensity of the modulated laser in response to the monitored intensity level.
Additional features and advantages of the invention will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing the invention as described in the following description together with reference to the claims and appended drawings.
It is to be understood that the foregoing description is exemplary of the invention only and is intended to provide an overview for the understanding of the nature and character of the invention as it is defined by the claims. The accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute part of this specification. The drawings illustrate various features and embodiments of the invention which, together with their description serve to explain the principals and operation of the invention.
REFERENCES:
patent: 4727237 (1988-02-01), Schantz
patent: 4739287 (1988-04-01), Staupendahl et al.
patent: 4788514 (1988-11-01), Fox
patent:
Dahmani Brahim
Paris Bertrand
Ramel Romain
Caley Michael H.
Corning Incorporated
Kim Robert H.
Price Heneveld Cooper DeWitt & Litton
Suggs James
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