Title: Device for coupling light into the fiber
Abstract: An optical source is provided to the side of a fiber. The fiber is a single mode fiber which has a core and a cladding. The Bragg grating is written into the core at a low angle. Light emitted from the optical source is index-match coupled into the cladding by using an index matched element. Then, light is coupled into the fiber core along its length.
Patent Number: 6,904,198 Issued on 06/07/2005 to Dykaar
| Inventors:
|
Dykaar; Douglas Raymond (465 Kingsford Place, Waterloo, CA)
|
| Appl. No.:
|
347488 |
| Filed:
|
January 21, 2003 |
| Current U.S. Class: |
385/31; 385/27; 385/124 |
| Intern'l Class: |
G20B 006/26 |
| Field of Search: |
385/12,24,27,31,37,50,123-128
372/6,96,102
|
References Cited [Referenced By]
U.S. Patent Documents
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| 4794615 | Dec., 1988 | Berger et al.
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| 4815079 | Mar., 1989 | Snitzer et al.
| |
| 4856017 | Aug., 1989 | Ungar.
| |
| 4914667 | Apr., 1990 | Blonder et al.
| |
| 5022038 | Jun., 1991 | Bradley.
| |
| 5022042 | Jun., 1991 | Bradley.
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| 5033812 | Jul., 1991 | Yoshida et al.
| |
| 5123070 | Jun., 1992 | Bradley.
| |
| 5140607 | Aug., 1992 | Paiva.
| |
| 5243676 | Sep., 1993 | Bierlein et al.
| |
| 5455838 | Oct., 1995 | Heritier et al.
| |
| 5590147 | Dec., 1996 | Hobbs et al.
| |
| 5594747 | Jan., 1997 | Ball.
| |
| 5619369 | Apr., 1997 | Yamamoto et al.
| |
| 5621749 | Apr., 1997 | Baney.
| |
| 5623508 | Apr., 1997 | Grubb et al.
| |
| 5647038 | Jul., 1997 | Minden et al.
| |
| 5663979 | Sep., 1997 | Marshall et al.
| |
| 5694248 | Dec., 1997 | Erdogan et al.
| |
| 5712715 | Jan., 1998 | Erdogan et al.
| |
| 5818630 | Oct., 1998 | Fermann et al.
| |
| 5838700 | Nov., 1998 | Dianov et al.
| |
| 5848204 | Dec., 1998 | Wanser.
| |
| 5999673 | Dec., 1999 | Valentin et al.
| |
| 6490388 | Dec., 2002 | Manzur.
| |
Other References
Weber et al. "Side-pumped fiber laser" Applied Physics B. Feb. 27, 1996.
Ma et al. "High-Performance Side-Polished Fibers and Applications as Liquid Crystal
Clad Fiber Polarizers". Journal of Lightwave Technology IEEE, vol. 15, No. 8, Aug. 1997.
|
Primary Examiner: Palmer; Phan T. H.
Attorney, Agent or Firm: Teitelbaum & MacLean, Teitelbaum; Neil, MacLean; Doug
Parent Case Text
The present application claims the benefit of U.S. Provisional Patent Application
Ser. No. 60/350,757 filed on Jan. 22, 2002, the contents of which are hereby incorporated
by reference.
Claims
1. A device for coupling light comprising: a single mode optical fiber having
a core and a cladding, said core including a low angle, tilted grating; and an
optical source, which is optically coupled to the fiber, for directing light through
the side surface of the fiber so as to couple the light into the core, wherein
the fiber is a curved fiber for focusing directly onto the optical source.
2. A device for coupling light comprising: a single mode optical fiber having
a core and a cladding, said core including a low angle, tilted grating; and an
optical source, which is optically coupled to the fiber, for directing light through
the side surface of the fiber so as to couple the light into the core, wherein
the fiber includes more than one fiber, each of which has a low-angle, tilted grating.
3. A device for coupling light comprising:
a fiber laser including;
a single mode optical fiber having a core and a cladding, said core including
a low angle, tilted grating; and an optical source, which is optically coupled
to the fiber, for directing light through the side surface of the fiber so as to
couple the light into the core, wherein the fiber laser has a loop configuration
and the fiber laser further comprises an isolator for unidirectional operation.
4. A device for coupling light comprising: a single mode optical fiber having
a core and a cladding, said core including a low angle, tilted grating; and an
optical source, which is optically coupled to the fiber, for directing light through
the side surface of the fiber so as to couple the light into the core, wherein
the fiber further includes a grating for forming a downstream output coupler.
5. The device as claimed in claim 4, wherein the fiber further includes a section
where rare-earth is inside a cavity, the section being located between the grating
and the downstream grating.
6. The device as claimed in claim 5, wherein the gratings reflect light at a
specific pump wavelength.
7. The device as claimed in claim 4, wherein the downstream output coupler is
chirped or multiple-discrete to couple multiple wavelengths.
8. The device as claimed in claim 4, wherein the fiber has a gain medium.
9. The device as claimed in claim 4, wherein the fiber further includes a filter
for defining multiple wavelengths as desired wavelengths and spacing.
10. The device as claimed in claim 4, wherein the fiber further includes a filter
for outputting a constant amplitude signal as a function of wavelength.
11. A device for coupling light comprising an optical fiber having a core and
a cladding, wherein the fiber includes a grating; and,
an optical source, which is optically coupled to the fiber, for directing light
through a surface of the fiber so as to couple the light into the core, wherein
the fiber includes a first reflector, and wherein a laser cavity is formed between
the optical source and the first reflector, and wherein the grating is disposed
within the laser cavity.
12. A device for coupling light as defined in claim 11, wherein the grating is
a low angle tilted grating, and wherein the grating directs light between the optical
source and the reflector.
13. A device for coupling light as defined in claim 12, wherein the optical source
is a laser diode having a facet which forms a second reflector of the laser cavity.
Description
FIELD OF THE INVENTION
This invention relates to an optical fiber technology, and more particularly,
to a device for coupling light into an optical fiber.
BACKGROUND OF THE INVENTION
Existing techniques for coupling light into an optical fiber introduces
the light into the end of the fiber. This limits the area available for coupling
light to what amounts to a point. The diameter of the point is typically less than
10 microns for single-mode fiber. Even in the case of cladding-pumped fibers, the
diameter of the cladding is still only on the order of several hundred microns.
In addition, some form of coupling optic is required to couple the laser emission
into the fiber. This optic can be in the form of a discrete lens, or the lens may
be formed onto the end of the fiber.
FIGS. 1(A) and (B) show end views for existing fiber configurations.
A fiber shown in FIG. 1(A) includes a core 2 and a cladding 4.
A fiber shown in FIG. 1(B) includes a core 6, a secondary core (cladding)
8 and a cladding 10.
The index of the core 2 shown in FIG. 1(A) can be stepped with
respect to the gladding or graded. However, the light that is coupled into a propagating
mode in the fiber must satisfy the total internal reflection criteria of Snell's
law. This limits the area over which light can be coupled to the approximate size
of the core. Enlarging the core beyond this limit results in multi-mode propagation.
In FIG. 1(B), the larger secondary core 8 is provided for propagating
multimode pump light. The small diameter single-mode central core 6 is doped
with atomic gain species, such as erbium. The pump light excites the gain species
as it passes back and forth across the central core 6, converting light
at the pump wavelength to light at gain species emission wavelength.
Both approaches place significant restrictions on the allowable optics and power
levels that can be used. Typically, the damage threshold of the fiber-end surface
limits the power that can be couple into the fiber.
The larger size of the multi-mode core allows a relatively larger diode pump
array to be end-coupled onto the fiber. However, the pump laser is still limited
to the area of the fiber cladding, which is typically less than 500 μm in diameter.
Fiber gratings have been available for several years. Conventionally, Side
Tape Gratings (STG) and Long Period Gratings (LPG) have been used to couple light
out of a fiber. For the STG, the angle at which the radiated light is coupled out
of the fiber is:
##EQU1##
where,
n
clad≡Cladding Index;
n
eff(λ)≡Effective index at wavelength, λ;
θ(λ)≡Wavelength dependent angle
subtended by light radiated out of the core;
θ
g≡Grating period;
Δ
g≡Tilt of the grating with
respect to the propagation direction; and
N≡Order of the grating.
While these types of gratings are described as exemplary types of fiber gratings,
the function they serve may be generated using other types of induced index change
within the fiber to cause coupling of incident light along the length of the fiber
to the core of the fiber. An example of such a structure is a regular pattern of
notches along the length of the fiber, which, like a grating have a period as described
in the above equation.
The approach described above has been used previously as a way to filter or reject
unwanted light or to couple light out of a fiber to a power monitoring device.
It is, therefore, desirable to provide a new optical device that can couple light
into an optical fiber to achieve higher coupled power.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a novel optical device that obviates
or mitigates at least one of the disadvantages of existing systems.
In accordance with an aspect of the present invention, there is provided a device
including a single mode optical fiber having a core and a cladding. The core has
a low angle, tilted grating. The device further includes an optical source, which
is optically coupled to the fiber, for directing light through the side surface
of the fiber so as to couple the light into the core.
Other aspects and features of the present invention will be readily apparent
to those skilled in the art from a review of the following detailed description
of preferred embodiments in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further understood from the following description with
reference to the drawings in which:
FIG. 1(A) is a schematic cross-sectional end view of a conventional fiber configuration;
FIG. 1(B) is a schematic cross-sectional end view of another conventional
fiber configuration;
FIG. 2 is a schematic perspective view of a device for coupling light into a
fiber in accordance with an embodiment of the present invention;
FIG. 3 is a schematic diagram showing one example of close-coupled arrangement
of the optical source shown in FIG. 2;
FIG. 4 is a schematic diagram showing a curved-fiber 22 of FIG. 2;
FIG. 5 is a schematic diagram showing one example of the device shown in FIG. 2;
FIG. 6 is a schematic diagram showing the device of FIG. 5 with a filter;
FIG. 7(A) is a graph showing one example of the feature of the filter
shown in FIG. 6;
FIG. 7(B) is a graph showing anther example of the feature of the filter
shown in FIG. 6;
FIG. 8(A) is a schematic diagram showing an amplifier application based
on the device of FIG. 6;
FIG. 8(B) is a graph showing one example of the feature of the amplifier
shown in FIG. 8(A);
FIG. 9 is a schematic diagram showing a further example of the device shown
in FIG. 2;
FIG. 10 is a schematic diagram showing a first example of the electrode pattern
of the laser diode shown in FIG. 2;
FIG. 11(A) is a schematic diagram showing a second example of the electrode
pattern of the laser diode shown in FIG. 2;
FIG. 11(B) is a schematic diagram showing a third example of the electrode
pattern of the laser diode shown in FIG. 2;
FIG. 12 is a schematic diagram showing the device of FIG. 2 with a fiber-bundle;
FIG. 13 is a schematic end-view diagram showing symmetrical configuration for
the device of FIG. 2;
FIG. 14 is a schematic diagram showing loop configuration for the device of
FIG. 2;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2 shows a schematic perspective view of a device for coupling light into
an optical fiber
22 in accordance with an embodiment of the present invention.
The optical fiber
22 is a single-mode fiber and has a core and a cladding.
The device shown in FIG. 2 includes a laser diode
20 of length "l", which
is close coupled at an angle "θ" to a fiber grating formed within the core
of the fiber
22. A mirror
24 or an alternative reflective optic may
be provided to allow light, which is not coupled into the fiber, to be reflected
back onto the grating. In the event the grating has sufficiently high reflectivity,
the external mirror becomes unnecessary. The device of FIG. 2 may be a fiber laser.
"l" is the length of the laser stripe. "θ" is the angle at which the light
is emitted, and is eventually matched to the fiber grating tilt angle. The laser
emission angle may be different from the fiber tilt angle.
FIG. 3 shows one example of close-coupled arrangement of the optical source
20 of FIG.
2. In FIG. 3, the laser (source) elements are perpendicular
to the back surface to form (optionally coated) high reflectors at the rear of
the optical source (
20), and are curved at the output (possibly coated)
to match the angle required by the tilted grating. The source can arranged to emit
at near Brewster's angle for minimum loss. If the system is properly designed,
no other optics would be required.
Light is coupled into the fiber
22 along its length, thus increasing
the power so as to be effectively coupled into the fiber
22. This also simplifies
the mechanical requirements on the coupling optics, as light can be distributed
linearly along the length of the fiber, as opposed to being focused onto what amounts
to a point on the cross-section of the fiber core. In addition, the distributed
nature of the coupling tends to spatially average the noise present in the pump
laser (i.e. laser diode
20), which is coupled into the fiber
22 from
the pump laser
20.
Light is coupled into the fiber
22 using the grating formed within the
fiber
22. The coupling is easy to implement in practice since the alignment
is oriented along the length of the fiber
22, as opposed to the end (i.e.
along a line versus a point).
In the fiber
22, a low-angle, tilted Bragg grating is used. Preferably,
the grating is a Bragg grating written into the fiber
22 at less than about
20 degree with respect to the length of the fiber
22. The grating of the
fiber
22 may be written to achieve high reflectivity, e.g. 100% reflectivity.
The low-angle tilted-grating of the fiber
22 maximizes the coupling of light
from the core to the cladding, or vice-versa.
Bragg gratings are formed in fibers using optical interference to create a
region where intensity variations in the light interact with the glass of the fiber
to change the index in regions of higher intensity. The interference is created
by directly interfering two laser beams at an angle, or by using plus and minus
diffraction orders from a phase mask. In all cases a range of factors determines
the spatial extent of the interference region including optical element quality,
mechanical stability, optical coherence length, etc. In order to obtain the tilt
in the desired grating, the fiber is tilted in the interference region. As the
fiber is tilted, the length of the fiber inside the interference region will be
reduced. For a given grating writing arrangement, therefore, the maximum strength
of grating will be obtained if the angle of the grating is kept small (e.g. less
than 20 degree). The longer the physical extent of the grating, the larger the
number of alternating regions high and low relative index in the grating region
and the higher the effective coupling to the core.
The angled gratings are described in Kashyap R. "Fiber Bragg Gratings" Academic
Press, NY, 1999, Chapter 3, Section 3.1.4, pp 69-71; "Novel and improved methods
of writing Bragg gratings with phase masks," Othonos, A.; Xavier Lee, IEEE Photonics
Technology Letters, (7) 10, October 1995, 1183-1185; and "Chirped fibre gratings
produced by tilting the fibre," Chandonnet, A.; Lauzon, J.; Painchaud, Y., Electronics
Letters, (31) 3, 2 Feb. 1995, 171-172.
The level of coupling achievable in conventional Bragg-gratings is in the few
percent range. In the embodiment of the present invention, the grating is implemented
in the fiber
22 so as to form the output coupler of a laser cavity, such
that the strength of the grating is now of an appropriate value. That increases
the coupling of light. In the simplest configuration, the laser diode
20
(or diode array), with a gain stripe angled relative the cleave plane, is close
coupled to the grating shown in FIG.
2. This is in contrast to an end-coupled
arrangement, wherein the axis of the light is preferably transverse to the cleaved
end of the fiber.
Light is index-match coupled into the cladding of the fiber
22. Index
matched coupling occurs when the coupling medium has essentially the same index
as the cladding. In this way, light is brought from outside the fiber
22
directly to the core-cladding interface at the appropriate angle so as to couple
the grating within the core. By minimizing the mechanical operations that the fiber
22 is subject to, risk of failure due to breakage is minimized.
The external configuration of the coupling optic allows light to direct from
the optical gain medium to the grating such that the optical field pattern is optimally
mapped onto the grating. There are many ways in which this can be achieved using
standard combinations of optics, including lenses and gradient-index glass, as
well as tailoring of the grating within the fiber to match a particular configuration.
The tailoring can take the form of a chirp in the profile, or patterning of discrete
sections to match discrete gain regions in a multiple stripe diode-gain element
for example.
There are many examples of the coupling optics for coupling light out of fibers,
such as Wagener, J. L., Strasser, T. A., Pedrazzini J. R., DeMarco J. and Giovani
D. J. "Fiber Grating Optical Spectrum Analyzer Tap", ECOC-97, Sep. 22-25, 1997,
Conference Publication No. 448, IEE, pp 65-68. Many of the coupling geometries,
which are conventionally used between fibers and detectors, are applicable to the
device in accordance with the embodiment of the present invention.
The grating of the fiber
22, the laser diode source
20 and the
coupling optics are at sufficiently separated in wavelength so that the individual
units do not interfere in multiple wavelength configurations. Coupling may be desirable,
however, and can be designed for within the gain medium.
In FIG. 2, the laser diode
20 is shown as an optical source. However,
the
source may be an array of laser diodes. The laser diode
20 may have single
or multi-element. The laser diode
20 may be optically coupled of close-coupled
to the grating (FIG.
3). The optical source (
20) may be any type
of a self-contained laser source, an extended cavity, or an extended cavity including
the fiber and downstream fiber-grating output-coupler (FIG.
5). Multiple
sources may be used to provide redundancy. Preferably, laser diode bars are used
for their reliability. The laser diode source
20 may generate single or
multi wavelengths. The laser diode
20 may output Continuous Wave (CW) or pulsed.
The fiber
22 may be a shaped fiber, e.g. either shaped cladding or core
(such as "D" cladding or oval core profile). The shaped fiber reduces the possible
extent of the grating within the cladding.
The fiber
22 may be a curved fiber as illustrated in FIG.
4. The
curved fiber
22 of FIG. 4 has a tilted grating, which is curved so as to
focus directly onto the optical source. For adjusting the focus, some lenses may
be used.
FIG. 5 shows one example of the device shown in FIG.
2. In FIG. 5, the
fiber
22 includes a grating
54 and a grating
56. The arrow
illustrated in FIG. 5 shows a light flow (downstream) direction. The beam light
from the laser diode source
20 is emitted to the grating
54. Leakage
in the backward direction can be used to illuminate a power monitor (not shown).
The fiber
22 has a core of index n1 and a cladding of index n
2(n
1>n
2:n
2
may be stepped or graded-index). The fiber
22 may be doped or modified (e.g.
hydrogen loaded) to facilitate grating production or doped or modified in other
ways. The fiber
22 may be doped with gain material, such as Erbium, Ytterbium
to form a laser amplifier. The fiber
22 may include a semiconductor gain
medium to form a semiconductor laser.
The grating
54 is a side-tapped low angle high-reflectivity grating which
is written in the core of the fiber
22.
The grating
56 serves as an output coupler and defines cavity if a laser
diode is used in extended configuration. The grating
56 may also be tilted
to couple light out the side in high power applications. The grating
56
may be chirped or multiple-discrete to generate multiple wavelengths.
An index matched coupling optic
50 with index n
3 is provided to
the fiber
22 such that light is index-match coupled into the cladding at
the area of the grating
54. The index matched coupling optic
50 may
be lens, mirror or prism, singly or in combination. The index matched coupling
optic
50 is coupled to the fiber, using index matched material, such as
glues, gels, oil, bonded or built up by deposition (partially or in total).
The index n
3 of the coupling optic
50 is equal or greater than
the index n
1 of the core. The index n
3 may be equal to the index
n
2 of the cladding.
The index matched coupling optic
50 may be placed, glued or held up to
the polished flat spot of the. For example, the part of the cladding is removed
by polishing it and is replaced with the index-matched material. The coupling optic
50 then optically couples the source light to the fiber through the index-matched material.
This allows cladding material that may have the grating written into it to be
removed. The source may be coupled to the fiber
22 or free space coupled.
A focusing optic
52 may be provided to the source
20. The focusing
optic
52 collects the output of the laser diode source
20, and focuses
it into the side-tapped low-angle high-reflective grating
54. The focusing
optic
52 may be integrated into the index matched coupling optic
50.
In FIG. 5, the device includes one source
20 for the fiber
22.
However,
the device may include more than one source for the fiber
22.
As illustrated in FIG. 6, the fiber
22 may includes a filter
58.
The filter
58 may be an intra cavity filter or an extra-cavity filter. The
filter
58 is a band pass filter. The filter
58 causes the signal
to be discrete or channelized independent of the laser source
20. The filter
has channel dependent amplitudes to match external amplifiers. Channel width on
the filer
22 is changed with the filter
58 as shown in FIG.
7(A).
The filter
58 may be an interleaver, which is a passive device having a
feature shown in FIG.
7(A), that defines multiple wavelengths at desired
wavelengths and spacing. For example, with many laser diode stripes defined, the
filter is used to control the width of the individual channels. By changing the
filter, channels widths can be easily changed.
The filter
58 may be a gain flattening filter as shown in FIG.
7(B).
The gain-flattening filter is used to control amplitude so that external amplifier
produces a flat amplitude in response to wavelength.
The device shown in FIG. 5 is applicable to an optical fiber amplifier. FIG.
8(A) shows an amplifier application based on the device of FIG.
6.
The fiber
22 of FIG.
8(A) includes a rare-earth doped section
60
(an intra cavity element) where the rare-earth is inside the cavity region of the
fiber
22. The section.
60 is located between the gratings
54
and
56. As illustrated in FIG.
8(B), the grating
56 reflects
light at the pump wavelength. Signal input to the fiber
22 passes through
the section
60. The pump wavelength may be visible, infra-red or ultra-violet.
The gratings
54 and
56 are as close to 100% reflectivity as available.
The doped intra cavity element with the gratings
54 and
56 provides
higher pomp power for the amplifier.
FIG. 9 shows a further example of the device shown in FIG.
2. In FIG.
8, a coupler/optics
80 is provided between a lower reflectivity tilted grating
54A and the optical source
20 (e.g. diode laser/array), and further
a coupler/optics
82 is provided between the grating
54A and another
optical source
84. The grating
54A is a low reflector. The optical
source
84 may be a reflector or a second diode laser/array to provide light
into the grating
54. The optical source
84 may be attached to the
fiber
22 in the similar geometry and manner as the optical source
20.
The fiber
22 of FIG. 8 further includes a standard fiber Bragg-grating
86
that acts as a mirror.
In the arrangement of FIG. 9, some light goes through the grating. The source
on the opposite side is therefore part of the cavity defined by the two laser arrays
20 and
84. The tilted grating
54A acts as a bidirectional
output coupler. The grating mirror
86 acts as a high reflector and reflects
light back so that the output is unidirectional. The same arrangement may be used
in a ring configuration, without the grating mirror
86.
FIG. 10 shows one example of the electrode pattern of the laser diode
20
shown in FIG.
2. In FIG. 10, an emission is illustrated by the numeral
90
and a electrode pattern is illustrated by the numeral
92. As shown in FIG.
10, the laser diode
20 may be fabricated or modified to emit light at an
angle "θ" relative to the cleave plane. Although stray light will be reflected
off the back surface
94 of the laser facet, an anti-reflection (AR) coating
may be used to minimize this effect. Although the output facet is preferably at
Brewster's angle to minimize reflections, an AR coating may be used to passivate
the surface
94.
FIGS.
11(A) and
11(B) show further examples of the laser diode
20 shown in FIG.
2. As shown in FIGS.
11(A) and
11(B),
the electrode
92 may be applied in a "V" or "W" pattern to produce laser
emission in two different directions. The emission is then coupled to the fiber
22 as described above.
The single fiber
22 may be replaced by multiple fibers in a bundle
100
shown in FIG.
12. FIG. 12 shows a further example of the device shown in
FIG.
2. The device shown in FIG. 12 includes the diode bar
20, the
bundle
100, a reflector
102 and a heat sink
104. The coupling
optic may be provided. It is noted that in case, multiple bars (e.g. stacked diode
bars) may be used, since in this case the diode is not being imaged onto the grating,
but supplying light to a laser cavity, in which light is coupled out through the
individual fibers.
The bundle
100 includes a plurality of fibers
22A-
22G. The
fibers
22A-
22G may be interconnected. The fibers
22A-
22G
are similar to the fiber
22. The grating of each fiber
22A-
22G
is a tilted grating. Each grating may be chirped or multiple-discrete. The bundle
100 with coupling gratings may be assembled into a composite assembly.
The device shown in FIG. 12 may meet the same angle and tilt condition as those
of FIG. 2 to match the laser emission to the entrance angle of the gratings. The
bundle
100 may be made up of a single continuous fiber loop, thereby further
increasing efficiency.
The multiple wavelengths are now described in further detail. The approach described
above is especially applicable to multiple wavelengths. By using broadband semiconductor
gain media, for example, individual wavelengths can be selected by the design of
grating, simplifying the requirements placed on the design of the semiconductor.
In the case multiple wavelengths, the grating can be uniformly chirped or consist
of discrete sections of constant wavelength. The grating can be formed by one continuous
exposure, or made by multiple exposures using one or more masks. These types of
gratings are described in Kashyap (chapter 3, section 3.1.11 to section 3.1.15).
The configuration of the device shown in FIG. 2 is now described. The device
of FIG. 2 may have a symmetrical configuration as illustrated in FIG.
13.
In FIG. 13, laser diode bars
20A and
20B are symmetrically provided
to the fiber
22, through coupling optics
26 and
28, respectively.
The device of FIG. 2 may have a ring (loop) configuration. The ring configuration
is a well-known approach to laser design. The ring geometry is described in "High
Power Side Pumped Unidirectional Ring Yb-Doped Double-Clad Fiber Laser", Hideur
A. Chartier T. Sanchez S. Paper CThE50, European Conference on Lasers & Electro-Optics
(CLEO/Europe), 10-Sep., 2000, Nice, France, (0-7803-6319-1) p. 317; and U.S. Pat.
No. 5,623,508, "Article comprising a counter-pumped optical fiber Raman amplifier"
Grubb, et al. Apr. 22, 1997.
FIG. 14 shows one example of the ring configuration of the device of FIG.
2.
The ring of FIG. 14 achieves noise suppression, including isolators for unidirectional
operation or may be a symmetric construction. The device of FIG. 14 includes two
sided pump lasers
20C and an output coupler
30 for coupling light
in both directions for bi-directional operation. For bi-directional operation,
the lasers
20C include a first laser and a second laser or mirror. For unidirectional
operation, only one laser may be provided. The loop fiber shown in FIG. 14 may
include a polarization controller
32 and a Farady_isolator
34 for
unidirectional operation. The arrangement of FIG. 9 is also used in a ring, without
the grating mirror
86 of FIG.
9.
The present invention lends itself to this approach in either unidirectional
or bi-directional configuration. In the ring configuration, light propagates in
both directions. In this case, the grating couples light into and out of both sides
of the fiber with mirror symmetry. To account for this, a laser could be constructed
with symmetrically placed optical sources on either side of the fiber, or one of
the sources could be replaced by a mirror. Ring operation tends to average out noise.
The laser diode design is now described in further detail. For example, multiple
stripe sources may be fabricated with a high reflector at one end of the fiber
22, and an anti-reflection, or curved stripe at the far output end of the
fiber
22. The individual sources may operate as CW sources at the same,
or different wavelengths. In addition, the sources may be pulsed or modulated.
The sources may be close coupled to the fiber or coupled by optical elements.
The scaling is now described in detail. The approach in accordance with the embodiment
of the present invention enables scaling of high power lasers to be coupled into
a fiber. One or more large laser bars pumping multiple fibers (e.g. FIG. 12) is
one example of the scaling. Further, the scaling also refers to the relationship
among grating/laser/optics.
The device in accordance with the embodiment of the present invention may provide
signals to communication systems, or provide light for micro-machine, cancer treatment
(photodynamic therapy).
While particular embodiments of the present invention have been shown and described,
changes and modifications may be made to such embodiments without departing from
the true scope of the invention.
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