Note: Descriptions are shown in the official language in which they were submitted.
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OPTICAL FIBER DEVICES USING COMPONENT INSERTION
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to fiber optic devices. More
s particularly, the invention relates to a method of
manufacturing fiber , optic devices that uses functional
components inserted in the optical path.
2. Description of the Prior Art
Several in-line optical fiber devices use the
to insertion of optical components between two optical fibers
for performing various functions as spectral filtering,
spatial filtering, beam splitting, sensing, isolating or
polarizing. Most devices use lenses to collimate a light
beam exiting an input optical fiber and to collect the light
15 beam to an output optical fiber after propagation across the
optical component or components. Precise alignment and high
mechanical stability of the optical fiber cores and lenses
are required to obtain a collimated beam.
The use of collimating lenses may not be necessary
2o when using very thin optical component which reduces the
optical path length between the two fibers. Alignment of the
fiber cores requires high precision and high mechanical
stability in order to optimize light collection at the
output optical fiber and to minimize insertion loss and
z5 insertion loss variation. The high mechanical requirements
are difficult to achieve in severe environmental conditions.
The prior art has not completely fulfilled
requirements of insertion loss, alignment and mechanical
stability for optical fiber devices using in-line insertion
30 of optical components. There is thus a need for a method of
manufacturing of optical fiber devices that overcomes at
least some of the above-mentioned drawbacks.
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SUMMARY OF~THE INVENTION
It is an object of the present invention to
provide an optical fiber device that overcomes at least some
of the above-mentioned drawbacks.
s It is also an object of the present invention to
provide a method for manufacturing optical fiber devices
that overcomes at least some of the above-mentioned
drawbacks.
Therefore, in accordance with the present
to invention, there is provided an optical fiber device
comprising: an optical fiber for guiding light to be
propagated in the optical fiber, said optical fiber having a
peripheral surface, a fiber core and a fiber clad; a cavity
in said optical fiber, said cavity penetrating said optical
15 fiber through said peripheral surface and said fiber clad in
direction of said fiber core; and a solid component secured
inside said cavity and associated with said core so as to
create a functional effect on said light to be propagated in
said optical fiber.
2o In accordance with the present invention, there is
also provided a method for manufacturing an optical fiber
device comprising: machining a cavity in an optical fiber;
providing a solid component to be inserted in said optical
fiber; positioning said component inside said cavity; and
2s securing said component in said cavity.
The present invention provides an optical fiber
device that takes advantage of the fiber structure to
construct mechanically stable devices with components
inserted in the optical path. An optical component is
3o inserted in a cavity transversally machined across an
optical fiber. The component is secured in the cavity and
functionally interrelates with light propagated in the
optical fiber. The invention also provides a method for
manufacturing an optical fiber device with a component
35 insertion into an optical fiber by machining a cavity in an
optical fiber, providing a solid component to be inserted in
the optical fiber, positioning the component inside the
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cavity, and securing the component in the cavity. The
component is preferably provided as a glass ribbon and the
component is preferably secured in the cavity using laser
fusion.
BRIEF DESCRIPTION OF DRAWINGS
Further features and advantages of the present
invention will become apparent from the following detailed
description, taken in combination with the appended
drawings, in which:
to Fig. 1 is a perspective view of an optical fiber
device according to an embodiment of the present invention;
Fig. 2 is a flowchart illustrating a method of
manufacturing an optical fiber device according to another
embodiment of the present invention;
i5 Fig. 3 is a cross-section view of an optical fiber
with a cavity and a ribbon positioned in the cavity,
according to an embodiment of the method of Fig. 2;
Fig. 4 is a flowchart illustrating steps involved
in providing a component to be inserted in an optical fiber;
20 Fig. 5 is a cross-section view of the optical
fiber device of Fig. l, wherein the optical fiber is
inserted in a capillary;
Fig. 6A is a top plan view of a fiber-integrated
laser using the optical fiber device configuration of
25 Fig. l, wherein mirrors are adjoined to a cavity and pump is
guided in the optical fiber;
Fig. 6B is a front elevation view of a fiber-
integrated laser using the optical fiber device
configuration of Fig. 1, wherein mirrors are distant to a
3o cavity and pump is provided from an opening of the cavity;
and
Fig. 7 is a front elevation view of a 45-degree
mirror device using the optical fiber device configuration
of Fig. 1.
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It will be noted that throughout the appended
drawings, like features are identified by like reference
numerals.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
s A method for manufacturing an optical fiber device
with a component insertion in an optical fiber is described
herein. A cavity is made in the optical fiber, for instance,
by laser micromachining. The cavity enters the optical fiber
by its peripheral surface and typically crosses the fiber
to core. In an embodiment, the cavity preferably goes
throughout the optical fiber. A solid functional component
is provided and positioned in the cavity and across the
fiber core. The component is secured and sealed in the
cavity using glass fusion. The inserted component is
15 typically a solid component (e. g., optical component) that
will have a functional effect on light propagated in the
optical fiber. The component may be a spectral filter, a
spatial filter, a coupler, a sensor using spectroscopy, a
sensor using fluorescence, a sensor by polarization or any
20 other functional solid component including crystals,
filters, mirrors, indicators, piezoelectric components,
polarizers, etc. The component insertion in an optical fiber
also offers the possibility of creating numerous
applications by combining various functional components in
z5 the same optical fiber.
Referring to the drawings, Fig. 1 illustrates an
optical fiber device 10 created by an insertion of a solid
functional component 16 in an optical fiber 12 through a
cavity 14. In the embodiment of Fig. 1, the cavity 14 is
3o transversally defined in the optical fiber 12 from the
peripheral surface 24 of the fiber clad 22 and across the
fiber core 20. The component is positioned in the cavity to
intersect the fiber core 20 and is secured in place. Light
18 injected and guided in the optical fiber 12 propagates
35 through the component and is coupled forwardly within the
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optical fiber 12. The component modifies light 18 to create
a functional effect like those cited above.
In an embodiment, the cavity 14 is a transverse
hole going throughout the optical fiber 12. The cavity 14
could also stop in the optical fiber 12 so that there would
be only one opened end 26. Additionally, the cavity 14 is
drilled transversally in the optical fiber and crosses the
fiber core with a 90-degree angle. The cavity may also cross
the core at a different angle depending on the function to
to be performed. The angle typically ranges from about 30
degrees to 150 degrees.
Fig. 2 illustrates a method for manufacturing an
optical fiber device by an insertion of a component in an
optical fiber. The method 50 comprises step 52 of machining
a cavity (e.g., transversally) in an optical fiber. The
cavity preferably intersects the fiber core. Thereafter, in
step 54, a solid component to be inserted into the optical
fiber is provided. In step 56, the component is positioned
inside the cavity. In step 58, the component is secured to
2o the cavity.
According to one embodiment, the cavity is drilled
in a fused silica optical fiber using laser drilling. The
optical fiber is typically a multi-mode optical fiber with a
clad diameter of 125 Vim. The laser is preferably a carbon
dioxide (C02) laser, and the following parameters can be
used to machine the cavity. A 200 W laser beam is focalized
on the optical fiber. The modulation frequency is of 25 kHz
with a duty cycle of 0.5. A cavity going throughout the
fiber and with a diameter of 15 ~m is obtained after about
3o ten laser pulses. Multiple repetitions of these steps with a
10 ~m translation perpendicular to the laser beam between
each repetition allow obtaining cavities with different
shapes. The cavity obtained by drilling fused silica optical
fiber has smooth surfaces compared to ones obtained by
drilling in other kinds of glass or with other lasers. Micro
cracks have been known to appear on the surface when the
melted material solidifies. As will be discussed later, a
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cavity with smooth surfaces will give rise to a less brittle
optical device after fusion of a component in the cavity.
Alternatively, the laser used for micro-machining
could also have been a femtosecond laser or an excimer
s laser. A femtosecond laser gives increased accuracy and
resolution in the micro-machined patterns but the process
can be longer than it is in the case of a COZ laser. It has
been observed that optical fibers drilled using excimer
lasers and femtosecond lasers are more brittle than the ones
to processed using COZ lasers, which is an advantage of the
last one. C02 lasers are widely used in the industry for
their reliability, compactness, relative low cost and low
maintenance requirements.
The same process could be applied to any other
15 kind of fused silica fibers instead of the mufti-mode fiber.
For specific applications of the optical device, one could
find it advantageous to use a single-mode fiber, a multi
clad fiber, a larger fiber or a doped fiber.
In the above-described embodiment, laser drilling
2o has been used for machining a cavity in an optical fiber. In
the manufacturing of an optical device with insertion of a
component, other machining techniques could replace the
laser drilling.
In an embodiment, the component to be inserted in
2s the optical fiber is provided as a glass ribbon. The glass
ribbon is typically manufactured using a method similar to
optical fiber manufacturing method. For instance, ribbons
with rectangular shapes and dimensions of about 20 to 300 ~m
are manufactured using optical fiber drawing technique. A
3o functional element is fixed to the ribbon and the ribbon is
inserted in the cavity like a thread in a needle eye. Fig. 3
illustrates a ribbon 70 positioned in the cavity 14. The
ribbon 16 to be inserted in the optical fiber has a specific
shape and dimensions in order to fit into and to preferably
35 fill the cross section of the cavity 14. According to an
embodiment, a fused silica ribbon 70 with dimensions of
33 ~m by 100 ~.m is used. A functional element 72 is
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installed on the ribbon using, for instance, thin film
deposition, gravity deposition or dip-coating. The solid
functional element 72 could also be inserted in a cavity
machined in the ribbon. Providing the solid functional
element 72 on or in a ribbon provides a mechanical support
to align the element 72 in the optical fiber 12.
Fig. 4 illustrates the main steps involved in
providing 54 the component to be inserted in the optical
fiber when the component is provided as a ribbon. In the
to first step 80 a fused silica optical fiber drawing preform
is provided. The preform has a diameter of several
millimeters. The second step 82 is to machine the preform to
obtain a rectangular shaped preform. In the third step 84,
the rectangular preform is drawn as an optical fiber would
be. Temperature and drawing speed parameters are previously
adjusted. The last step 86 is to install a functional
element on or in the ribbon.
The functional element to be installed on the
ribbon may be a material with physical properties that
2o varies with temperature or other environmental conditions, a
dielectric material for obtaining semitransparent mirrors, a
spatially distributed opaque material for partially blocking
light propagated in the optical fiber or any other element
that accomplishes a useful operation. In an embodiment,
2s installation of the functional element on the ribbon is made
by thin film deposition in vacuum. A thicker functional
element could be obtained by gravity deposition or by
dip-coating.
The above described method for providing the
3o component as a ribbon is meant to be exemplary only. The
component could be provided as single-piece component or
multiple integrated elements machined or otherwise
fabricated to fit in the cavity. It is only required that
the component fits in the cross section of the cavity while
35 the component may be fully enclosed in the cavity or may
exceed the fiber diameter.
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In an embodiment, the component to be positioned
inside the cavity is a ribbon. The ribbon is positioned in
the cavity by threading the ribbon in the cavity like in a
needle eye. Insertion and positioning of the component in
s the cavity is made using micromanipulators and cameras for
visual feedback. The process may be automated using
computer-controlled micromanipulators and imaging software
feedback. Optical feedback may also be used for alignment by
propagating an optical signal in the optical fiber to the
io component and reading the output signal that provides a
feedback signal for optimizing the alignment of the
component.
The component to be positioned in the cavity could
be a single-piece component as opposed to a ribbon. A
i5 single-piece component could be positioned in the cavity
using micromanipulators and visual feedback. The component
may be dropped in the cavity if the cavity has one closed
end, i.e. the cavity does not go throughout the fiber.
According to an embodiment, the component is
2o secured in the optical fiber using laser glass fusion.
Fig. 5 shows an optical fiber device after securing with
glass fusion. The component 16 is secured and sealed in the
optical fiber 12. The optical fiber 12 locally surrounding
the component 16 and the component itself are melted using
2s laser heating. The component 16 and the optical fiber 12 are
therefore fused together to create an integrated
hermetically sealed a11-optical fiber device 10 with
suitable mechanical stability and strength.
The component is secured in the optical fiber
3o using COz laser glass fusion and the following parameters
can be used to fuse the component to the optical fiber. A
laser beam is focalized on the optical fiber at the position
of the ribbon. As an example, a 50 W laser beam operated at
a frequency of 25 kHz and a duty factor of 0.1 can be used.
35 The ribbon preferably fills the cross-section of the cavity
and preferably exceeds the fiber diameter so that the fused
material completely fills the cavity, leaving no empty spots
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in the optical device. The fused material rounds in shape
because of surface tensions and the very sharp surfaces are
rounded by the process. Ribbon exceeding the fiber diameter
easily separates by melting it with the same laser.
s For fused device to show suitable strength
properties the fusion conditions need to be appropriately
tuned and the cavity surfaces to be clean and smooth. Smooth
surfaces are obtained by machining using COZ lasers.
Surfaces may also be subsequently smoothed using COZ laser
to in cases were another laser is used for machining.
For specific applications, it may be desirable
that the component be completely enclosed in fused silica.
As an example, if the inserted component is not a glass
component and does not fuse with the optical fiber,
15 enclosing of the component may be desired to properly secure
and seal the component in the optical fiber. As shown in
Fig. 5, the optical fiber 12 including the component 16 may
be inserted in a fused silica capillary 90, with the
capillary 90 being fused to the optical fiber 12 using, for
2o instance, laser fusion as described previously.
For specific applications using temperature
sensitive components as, for instance, crystals, it may be
useful to use glass powder with low melting temperature in
the fusion process. The powder is selected as a function of
25 its coefficient of thermal expansion, of its melting
temperature, of its spectral transmission and of its
miscibility. In this case, powders from Schott is used but
SEM-COM powders could be used as well. The powder is
inserted in the cavity and around the functional component.
3o As an example, fusion is performed using a C02 laser with a
200 ~m diameter focused laser beam. The laser power is
100 W, the operation frequency is 25 kHz and the duty factor
is 0.05.
Electrical arc fusion could be used as an
35 alternative to laser fusion for securing the component in
the optical fiber. Laser fusion is more localized and offers
a well suited control of the fusion process.
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The above description has been limited to single
component insertion but it is contemplated that multiple
components or mufti-layer components can be inserted in a
single cavity. As an example, multiple layers could be
s deposited on one ribbon that would be inserted in the
optical fiber. Multiple components can be stacked and
inserted simultaneously into a single cavity. Additionally,
numerous configurations of devices can be created by
combining various functional components in the same optical
to fiber.
Optical fiber devices with component insertion in
an optical fiber offer the opportunity for various potential
applications by taking advantage of the fiber structure to
construct mechanically stable devices. Some of them will be
is described in the following paragraphs.
Fig. 6A depicts a fiber-integrated laser 120.
Dichroic mirrors 124 are integrated on each side of a laser-
drilled cavity 122 and are adjoined to the cavity 122.
Lacing medium is inserted in the cavity 122. In this case,
zo the lasing medium is a crystal, but it could also be a
liquid. A laser pump 128 is provided by the optical fiber 12
and a laser emission 130 is collected using the optical
fiber 12.
In the configuration of Fig. 6B, a mirror 124 is
25 integrated on each side of a cavity 122 and is distant to
the cavity 122. A laser pump 128 is provided by the opening
126 of the cavity and a laser emission is collected using
the optical fiber 12.
Dye micro lasers can be manufactured using a
3o similar configuration. A liquid containing the dye and
circulating across the cavity could be excited by the
openings of the cavity. Highly reflective mirrors would be
required as the gain is low due to small amplification
length.
35 Complex devices such as the fiber-integrated laser
120 can be manufactured using various processes. One is to
secure a mirror 124 on each side of a large cavity 122 using
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local laser fusion. Alternatively, a ribbon including a
mirror on each of its sides and filling a first cavity is
positioned and secured inside this first cavity. The ribbon
is subsequently drilled out to create a central cavity 122
s for introducing the lacing medium.
The method of manufacturing an optical fiber
device by component insertion involves various degrees of
insertion. Fig. 7 illustrates a 45-degree mirror device 160
for laser pump injection. A dichroic mirror 162 is inserted
to and secured using laser fusion in a 45-degree cavity in the
optical fiber 12. The 45-degree mirror device 160 can be
used in a fiber laser for injecting laser pump 162 from the
side of the optical fiber. In fiber lasers, pump efficiency
decreases rapidly along the laser length. It is considered
15 to inject pump at different positions along the laser fiber.
Polarization sensors are useful for smoke and
other particles detection. An optical fiber device is used
for diffusion measurement. Two crossed polarizers are
inserted in an optical fiber, one on each side of a channel.
2o A gas to be analyzed passes though the channel while light
is provided at one end of the optical fiber. Diffusion is
measured by measuring light intensity at the other end of
the fiber.
One skilled in the art would understand that the
z5 method of manufacturing optical fiber devices by an
insertion of a component in an optical fiber could be used
for manufacturing a device using a plastic optical fiber.
With some adjustments to the process parameters, plastic
optical fibers could be machined using laser and a component
3o could be secured in the fiber using thermal fusion.
The embodiments of the invention described above
are intended to be exemplary only. The scope of the
invention is therefore intended to be limited solely by the
scope of the appended claims.
