U.S. patent application number 09/386940 was filed with the patent office on 2002-01-31 for optical fiber amplifier with oscillating pump energy.
Invention is credited to WAARTS, ROBERT, ZANONI, RAYMOND.
Application Number | 20020012163 09/386940 |
Document ID | / |
Family ID | 25517028 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020012163 |
Kind Code |
A1 |
ZANONI, RAYMOND ; et
al. |
January 31, 2002 |
OPTICAL FIBER AMPLIFIER WITH OSCILLATING PUMP ENERGY
Abstract
An optical fiber amplifier has an amplification stage that uses
an optical fiber pumped with pump energy of a first wavelength that
oscillates through the gain medium. In one embodiment, the pumping
is essentially a cavity resonator that is coupled to either end of
the optical fiber such that oscillating pump energy is directed
into one end of the fiber and out the other, as it reflects back
and forth between the ends of the cavity. Highly reflective
gratings are used to maintain the oscillation of the pump energy,
and a pump energy source, such as pumped doped optical fiber, is
coupled to at least one of the gratings. In another embodiment, the
pump source comprises multiple reflectors that are employed at each
end of the fiber, and independent pump sources each having a
slightly different wavelength within the absorption spectrum of the
amplifier are coupled together, such that two pump wavelengths are
simultaneously oscillated through the gain medium. In another
embodiment of the invention, the reflective gratings are integrated
directly into a portion of the pathway through which the signal to
be amplified passes. This embodiment uses a pump source that causes
amplification of the pump energy in the gain medium which, in turn,
provides amplification of the optical signal. A two-pass embodiment
is also shown in which the optical signal enters and exits from the
same optical side of the amplifier fiber. An optical circulator may
be used to provide the necessary unidirectional porting of the
input and output signals.
Inventors: |
ZANONI, RAYMOND; (FREMONT,
CA) ; WAARTS, ROBERT; (FREMONT, CA) |
Correspondence
Address: |
KUDIRKA & JOBSE, LLP
ONE STATE STREET
SUITE 1510
BOSTON
MA
02109
US
|
Family ID: |
25517028 |
Appl. No.: |
09/386940 |
Filed: |
August 31, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09386940 |
Aug 31, 1999 |
|
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|
08970493 |
Nov 14, 1997 |
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5991070 |
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Current U.S.
Class: |
359/341.3 |
Current CPC
Class: |
H01S 3/094003 20130101;
H01S 3/094096 20130101; H01S 3/094015 20130101; H01S 3/094011
20130101 |
Class at
Publication: |
359/341.3 |
International
Class: |
H01S 003/00 |
Claims
What is claimed is:
1. An optical amplifier system for amplifying an optical signal at
a signal wavelength, comprising: at least one first pump source to
provide first pump light at a first wavelength; a first optical
fiber having a first active material for generating second pump
light at a second wavelength and including a lasing resonator
between spatially disposed reflectors forming a second pump laser
source, the second pump source optically coupled to receive the
first pump light from the first pump source, the first optical
fiber absorptive of the first pump light and providing gain to the
second pump light; and a second optical fiber having a second
active material forming a fiber amplifier at the signal wavelength,
the second optical fiber optically coupled within the lasing
resonator of the second pump laser source to launch the second pump
light into the second optical fiber, the second optical fiber
absorptive of the second pump light and providing gain to the
signal wavelength.
2. The optical amplifier system of claim 1 further comprising a
first pump source at each end of the second pump laser source.
3. The optical amplifier system of claim 1 wherein the second
optical fiber comprises a double clad fiber having a core doped
with a rare earth material through which the signal wavelength to
be amplified propagates, and an inner cladding surrounding the core
for receiving the second pump light via the second pump laser
source.
4. The optical fiber amplifier of claim 1 wherein the reflectors
comprise fiber Bragg gratings reflective of the second pump
light.
5. The optical fiber amplifier of claim 1 further comprising a
second lasing resonator in said second optical fiber so that the
fiber amplifier functions as a fiber laser.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of patent application
Ser. No. 08/970,493 filed Nov. 14, 1997.
FIELD OF THE INVENTION
[0002] This invention relates to the field of optical fiber
amplifiers and, more particularly, to means of applying pump energy
to an optical fiber amplifier.
BACKGROUND OF THE INVENTION
[0003] As is known in the art, an optical amplifier is a device
that increases the amplitude of an input optical signal fed
thereto. If the optical signal at the input to such an amplifier is
monochromatic, the output will also be monochromatic, with the same
frequency. A conventional fiber amplifier comprises a gain medium,
such as a single mode glass fiber having a core doped with a rare
earth material, connected to a WDM coupler which provides low
insertion loss at both the input signal and pump wavelengths. The
input signal is provided, via the coupler, to the medium.
Excitation occurs through optical pumping from the pumping source.
Pump energy that is within the absorption band of the rare earth
dopant is combined with the optical input signal within the
coupler, and applied to the medium. The pump energy is absorbed by
the gain medium, and the input signal is amplified by stimulated
emission from the gain medium.
[0004] Such amplifiers are typically used in a variety of
applications including, but not limited to, amplification of weak
optical pulses such as those that have traveled through a long
length of optical fiber in communication systems. Optical
amplification can take place in a variety of materials including
those materials, such as silica, from which optical fibers are
formed. Thus, a signal propagating on a silica-based optical fiber
can be introduced to a silica-based optical fiber amplifier, and
amplified by coupling pump energy into the amplifier gain
medium.
[0005] Fiber amplifiers are generally constructed by adding
impurities to (i.e. "doping") an optical fiber. For a silica-based
fiber, such dopants include the elements erbium and ytterbium. For
example, one type of fiber amplifier referred to as an erbium (Er)
amplifier typically includes a silica fiber having a single-mode
core doped with erbium ions (conventionally denoted as Er.sup.3+).
It is well known that an erbium optical fiber amplifier operating
in its standard so-called three level mode is capable, when pumped
at a wavelength of 980 nanometers (nm), of amplifying optical
signals having a wavelength of approximately 1550 nanometers (nm).
Likewise, an amplifier having a silica-based fiber "co-doped" with
erbium and ytterbium shows excellent amplification of a 1550 nm
optical signal when pumped with a wavelength of approximately 1060
nm. Since 1550 nm is the lowest loss wavelength of conventional
single-mode glass fibers, these amplifiers are well-suited for
inclusion in fiber systems that propagate optical signals in the
wavelength vicinity of 1550 nm.
[0006] It has been an ongoing pursuit in the field of optical fiber
amplifiers to increase the power output of the amplifiers.
Traditionally, pump energy is applied to the gain medium by
coupling into the doped fiber either in the same propagation
direction as the signal to be amplified (referred to as
"co-pumping"), or by coupling it into the doped fiber in the
opposite direction as the signal to be amplified (referred to as
"counter-pumping). Each of these pumping methods has its own
advantages, but also its own limitations. It is an object of this
invention to go beyond these traditional pumping methods to provide
a high power optical amplifier by providing a new means of pumping
a doped optical fiber.
SUMMARY OF THE INVENTION
[0007] In accordance with the present invention, an optical fiber
amplifier is provided in which a doped optical fiber gain medium is
pumped by pump energy that is oscillated through a substantial
portion of the gain medium. That is, a resonant cavity for the pump
energy is formed that includes the amplifier fiber, such that the
pump energy is reflected back and forth through the gain medium.
The output coupling for the resonant cavity is absorption by the
doped fiber, which results in amplification of the optical signal
by stimulated emission as it passes through the fiber.
[0008] The optical pumping apparatus used to generate the
oscillating pump energy may take a number of different forms. In
general, reflectors that reflect optical energy at the pump
wavelength are coupled to either side of the optical fiber, and
reflect the pump energy back and forth through the gain medium. In
one embodiment, each reflector is located in its own optical
pathway separate from the optical fiber, a first of these pathways
being coupled to a first side of the optical fiber while the second
is coupled to the second side of the fiber. The coupling is
preferably by wavelength selective couplers, such as WDMs, so that
only the pump energy is diverted from the signal path and directed
to the reflectors. In one variation of this embodiment, each
reflector is coupled to a pump energy generator, preferably in the
form of a pumped optical fiber, so that pump energy is generated on
either side of the optical fiber. In another variation, the pump
energy is generated at only one side, while the other side has only
a reflector. In either case, the pump energy is oscillated in the
pathway between the reflectors, providing the desired oscillation
of pump energy through the fiber gain medium.
[0009] When the pump energy is coupled into the optical fiber using
wavelength selective couplers, another variation of the invention
involves using a plurality of pump wavelengths, each of which is
within the absorption band of the doped optical fiber. In such an
embodiment, a plurality of reflectors may be used in each of the
two pump energy pathways located, respectively, to either side of
the optical fiber. The different pump wavelengths are preferably
close in wavelength, and each set of reflectors (i.e. each group of
reflectors located to one optical side of the doped fiber) may be
coupled together using narrowband wavelength selective couplers,
such as narrowband WDMs. Furthermore, some or all of the reflectors
may be coupled to pump sources that generate optical energy at the
desired pump wavelengths.
[0010] In each of the above embodiments, the optical fiber may be
doped with erbium/ytterbium (Er/Yb), which provides amplification
of a 1550 nm optical signal when the fiber is pumped at a
wavelength of 1064 nm. The highly reflective gratings of the fiber
may then be selective to reflect the 1064 nm wavelength, and the
pump sources may themselves be optical fibers doped, preferably
with ytterbium (Yb), and pumped with optical energy at a wavelength
of, for example, 915 nm.
[0011] In another embodiment of the invention, the reflectors for
providing oscillation of the pump energy through the gain medium
are integrated into a portion of the signal pathway, and may be
integrated into the amplifier fiber itself. These reflectors,
preferably highly reflective Bragg gratings, are wavelength
specific, and do not significantly interfere with the optical
signal to be amplified. That is, the reflectors maintain
oscillation of optical energy at the pumping wavelength through the
gain medium, while the optical signal passes through them and
through the doped optical fiber. To cause generation of energy at
the pump wavelength, a pump source is coupled into the gain medium
and causes amplification of optical energy at the pump wavelength
within the gain medium. Thus, the output of the pump source is
absorbed by the doped optical fiber, and amplifies the pump energy
that oscillates between the two reflectors. The oscillating pump
energy, in turn, is absorbed by the gain medium and amplifies the
optical signal passing through the fiber. In such an embodiment, a
ytterbium-doped fiber may be used. The signal wavelength could then
be 1090 nm, the pump energy wavelength 1064 nm, and the pump source
wavelength 915 nm.
[0012] In one variation of the embodiment having reflectors
integrated into the signal pathway, the amplifier is a two-pass
amplifier. A signal reflector is provided at one end of the doped
fiber that reflects optical energy at the wavelength of the optical
signal. The optical signal is then coupled through an input port
into the other end of the fiber. The optical signal is amplified as
it passes through the fiber, which is pumped by oscillating pump
energy. Upon reaching the end of the fiber, the optical signal
encounters the signal reflector, and is directed back through the
optical fiber, where it is further amplified. At the end of the
fiber where it initially entered, the amplified optical signal is
coupled out through an output port.
[0013] The foregoing embodiment may be accomplished by using an
optical circulator, which allows unidirectional coupling of an
optical signal from one port of the circulator to another. If the
optical signal is input to a first port of the circulator, the
amplifier may be located in a branch coupled to a second port,
which receives the optical signal from the first port. The
amplified optical signal, after passing twice through the gain
medium, returns to the second port of the circulator, where it is
coupled to a third port. In one version of this embodiment, the
third port is simply a system output port. However, a second
amplifier, identical to that connected to the second port, may be
located in a branch coupled to the third port, and a fourth port of
the circulator could then serve as the system output port.
Additional amplifier branches can also be added in a similar manner
up to the maximum port capacity of the circulator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic view of a fiber amplifier according to
a first embodiment of the present invention that couples pump
sources into either side of a gain medium to oscillate pump energy
across the gain medium.
[0015] FIG. 2 is a schematic view of a fiber amplifier according to
a second embodiment of the present invention that couples a pump
source into a first side of a gain medium, and reflects pump energy
into an opposite side of the gain medium using a periodic grating
that is highly reflective at the pump wavelength.
[0016] FIG. 3 is a schematic view of an alternative embodiment of
the invention which is similar to the embodiment of FIG. 2, but
which uses a plurality of coupled pump sources directed into each
side of the amplifier gain medium.
[0017] FIG. 4 is a schematic view of another alternative embodiment
of the invention in which gratings that reflect the pump signal are
integrated directly into the path of the signal to be
amplified.
[0018] FIG. 5 is an embodiment similar to that of FIG. 4 that uses
an optical circulator to direct a signal to be amplified into and
out of one or more arms of the circulator, each of which contains
an oscillating pump signal in a gain medium.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Depicted in FIG. 1 is a fiber amplifier having an optical
pumping arrangement that uses two pump sources 30, 32 together to
provide oscillation of the pump signal. In the preferred
embodiment, an optical signal entering the amplifier via input port
10 has a wavelength .lambda..sub.S in the wavelength range of 1550
nm, and is therefore in the peak transmission range of conventional
silica-based optical fiber. From port 10, the input signal is
directed to wavelength division multiplexer (WDM) 24, by which it
is coupled into doped optical fiber 26. The signal is amplified in
the fiber 26, and is coupled out of the fiber gain medium by WDM 28
and directed to output port 34, where the amplified signal may be
used in any desired application.
[0020] The optical fiber 26 is doped with a rare earth element, and
is the heart of the fiber amplifier. In the preferred embodiment,
the fiber is doped with erbium/ytterbium (Er/Yb) to create the
desired gain medium. Given an Er/Yb doping, the optical fiber 26
may then be pumped with optical pump energy in the wavelength range
of 1064 nm by the combination of pump sources 30 and 32, which are
coupled into the fiber 26 via 1064/1550 WDMs 24 and 28,
respectively. Pumping at this wavelength results in absorption of
the pump energy by the doped fiber, and a corresponding
amplification of the optical signal within the amplifier gain
medium by stimulated emission at the signal wavelength. As
discussed below, the arrangement of pump sources 30, 32 as shown
provides pump energy that oscillates back and forth through the
amplifier gain medium.
[0021] In the preferred embodiment, each of the pump sources 30, 32
is of identical construction. Pump source 30 consists of
double-clad optical fiber 36, laser diode 40 and highly reflective
Bragg grating 42. Pump source 32 consists of double-clad optical
fiber 38, laser diode 44 and highly reflective Bragg grating 46.
Each of the Bragg gratings 42, 46 is highly reflective to the
pumping wavelength of 1064 nm. The fibers 36, 38 are each doped
with ytterbium and each has optical energy input to it by its
respective laser diode source 40, 44 at a wavelength in a high
absorption wavelength range for a Yb-doped fiber. This results in a
population inversion in each of the pump fibers 36, 38 which, in
the resonant cavity arrangement of the two pump sources, results in
the development of pump signal energy at the desired 1064 nm
wavelength that oscillates between the gratings 42, 46. For
example, generating pump energy at a wavelength of 915 nm with
diodes 40, 44 and injecting it into the double-clad fibers is
sufficient to cause the stimulated emission of optical radiation at
1064 nm. The gratings 42, 46 then reflect the 1064 nm pump energy
back and forth between them, and through the optical fiber 26.
[0022] By establishing the pump energy reflection path through the
optical fiber 26 itself, the pump energy at 1064 nm, necessary to
continuously amplify the 1550 nm optical signal, can be replenished
without the risk of destabilization that would exist if the outputs
of two individual lasers were directed toward each other. For
example, the direction of 1064 nm fiber lasers toward each other
has been shown to destabilize both lasers, and cause both to lase
at 1106 nm. In this embodiment, the two gratings 42, 46 combine to
form the two ends between which the pump energy is reflected. The
output coupler of the cavity is the absorption of pump energy by
the fiber amplifier. Thus, by having the two sources 30, 32 act in
concert, the risk of destabilization is removed.
[0023] In order to maximize the efficiency of the amplifier, the
relationship between the absorption by the amplifier and the
pumping by the sources 30, 32 may be exploited. The optimum output
transmission for a laser cavity is given by:
T.sub.opt=-L.sub.i+%(g.sub.oL.sub.i)
[0024] where T.sub.opt is the optimum output transmission, L.sub.i
is the internal cavity losses, and g.sub.o is the unsaturated gain
of the laser cavity. Since the fiber amplifier can be considered to
be the output coupler for the resonant cavity formed by the pump
sources 30, 32, and since the transmission through the fiber
amplifier is T=e.sup.-.alpha.R (where R is the length of the fiber
amplifier), the optimum length for optical fiber 26 is:
R.sub.opt=(-1/.alpha.)log[-L.sub.i+%(g.sub.oL.sub.i)].
[0025] Shown in FIG. 2 is an alternative embodiment of the present
invention. Unlike the embodiment of FIG. 1, which uses two pumped
optical sources 30, 32 as the ends of the pump energy pathway, in
FIG. 2, one of these sources is replaced with a periodic grating
that is highly reflective at the pump energy wavelength. For
example, grating 42 may be used to replace pump source 30. As in
FIG. 1, the input signal enters port 10, is coupled into the gain
medium of doped optical fiber 26 via WDM 24, and is coupled out of
the gain medium via WDM 28 and directed toward output port 34.
However, while the embodiment of FIG. 1 uses two individual pump
sources 30, 32, the FIG. 2 embodiment uses only one. The high
reflectivity of grating 42 at the desired wavelength of the pump
energy (e.g., 1064 nm) allows it to function as one end of an
oscillation path, while pump source 32 acts as the other end. The
pump energy developed in the fiber 38 at 1064 nm is thus reflected
back and forth between grating 46 and grating 42, passing through
amplifier fiber 26 in the process and providing the desired pumping
to the amplifier.
[0026] Shown in FIG. 3 is another alternative embodiment of the
present invention in which a plurality of fiber laser sources is
used for each of the pump sources 30, 32. In the preferred version
of this embodiment, each of the fiber lasers is similar to those
used in the FIG. 1 embodiment, consisting of a double-clad fiber
with a highly reflective Bragg grating and a laser diode pump.
However, the fiber lasers for a given pump source 30, 32 each have
different wavelengths, close to each other, in the range of 1064
nm. In pump source 30, double-clad fiber 68 is Yb-doped, and has a
laser diode 70 as a source which provides pump energy in the range
of, e.g., 915 nm. The grating 72 is selected to be highly
reflective at a first wavelength in the 1064 nm range, such as 1060
nm. The double-clad fiber 74 and diode 76 can be identical to the
fiber 68 and diode 70, respectively, except that Bragg grating 78
is highly reflective at a wavelength close to, but different from,
the wavelength of grating 72. For example, grating 78 may be
selected to be highly reflective at a wavelength of 1070 nm. The
two different wavelengths (e.g. 1060 nm and 1070 nm) of pump source
30 are both in the wavelength absorption range of the Er/Yb doped
amplifier fiber 26, and are therefore both adequate pump
wavelengths for pumping the amplifier. These wavelengths are
coupled together into the fiber 26 after being combined using
narrowband WDM coupler 80, a 1060/1070 WDM.
[0027] In the preferred version of this embodiment, the
construction of pump source 32 is identical to that of pump source
30. Yb-doped, double-clad optical fiber 82 is pumped by diode 84 at
a wavelength of, e.g., 915 nm, and is stabilized by highly
reflective grating 86 to an output wavelength of 1060 nm. Yb-doped,
double-clad optical fiber 88 is pumped by diode 90 at a wavelength
of, e.g., 915 nm, and is stabilized by highly reflective grating 92
to an output wavelength of 1070 nm. The 1060 nm and 1070 nm
wavelengths of the two fiber lasers are combined by narrowband WDM
94, which is coupled to the opposite end of the amplifier fiber
26.
[0028] In the embodiment of FIG. 3, two overlapping oscillation
paths are established, one for pump energy at 1060 nm and one for
pump energy at 1070 nm. WDMs 80 and 94 allow these pump energies to
be coupled for propagation through the optical fiber 26 of the
amplifier, and segregated at the different fibers of each pump
source 30, 32. It will be understood by those skilled in the art
that, while the embodiment of FIG. 5 shows two fiber lasers per
pump source, more than two fiber lasers per pump source could also
be used. This would require the coupling of the additional pump
energy wavelengths into the fiber amplifier using additional WDMs,
but would function according to the same principles as the
construction shown in FIG. 3.
[0029] Shown in FIG. 4 is another alternative embodiment of the
invention, in which the oscillating pump energy used to pump a
fiber amplifier is achieved by integrating two pump gratings
directly into a fiber pathway through which the input optical
signal passes. This pathway may or may not be part of the doped
region of the amplifier fiber, but the embodiment removes the need
for coupling the pump signals into the doped fiber, as is done
using WDMs in the foregoing embodiments. As shown, one of the pump
reflection gratings 42, 46 is positioned to either side of doped
amplifier fiber 26. The gratings are highly reflective at the
desired pumping wavelength, e.g. 1064 nm. Certain amplifier fibers
(e.g., a double-clad, Yb-doped fiber), can serve as the gain medium
for generating both the pump energy at 1064 nm, as well as for a
desired signal wavelength .lambda..sub.S such as 1090 nm.
[0030] In the embodiment of FIG. 4, initial pumping of the fiber 26
is provided by optical source 41, which may be a laser diode with
an output wavelength of 915 nm. This pumping energy is coupled into
the gain medium via 915/1090 WDM 27. Absorption of the energy at
915 nm results in the development of oscillating pump energy
between gratings 42 and 46 at the 1064 nm wavelength. That is, an
oscillation path for the 1064 nm pump energy is maintained between
the two gratings 42, 46. This further pumps the fiber gain medium,
and allows the input optical signal, at the 1090 nm wavelength, to
be amplified by stimulated emission as it passes through the
amplifier fiber. The amplifier optical signal is thereafter
directed to output port 34 via WDM 27.
[0031] FIG. 5 depicts a variation of the embodiment shown in FIG.
4. As in FIG. 4, gratings 42, 46 are integrated into a signal
pathway to either side of a fiber amplifier 26, doped with, e.g.,
ytterbium. The gratings 42, 46 are highly reflective at a desired
pumping wavelength, such as 1064 nm, and define the desired
oscillation path for the pump energy. In the FIG. 5 embodiment, the
amplifier and gratings 42, 46 are arranged as a first branch of an
optical circulator 35. An optical circulator is a commercially
available optical coupler that allows unidirectional one-to-one
optical coupling between a set of optical ports. That is, optical
energy input to one of the circulator ports is directed to only one
other port, and may only be coupled between those two ports in one
propagation direction.
[0032] Also in the signal path with the fiber amplifier is signal
grating 47, which is highly reflective at the wavelength of the
desired optical signal (e.g., 1090 nm) and is positioned to the
side of the amplifier fiber 26 and gratings 42, 46 away from
circulator 35. A pump energy source 41 is coupled into the optical
fiber amplifier. This source may be a laser diode having an output
wavelength of, e.g., 915 nm. The output wavelength of the pump
source 41 is absorbed by the doped fiber 26, and results in the
development of an oscillating pump signal between gratings 42 and
46 at the 1064 nm wavelength. The 1064 nm wavelength signal, in
turn, further pumps the amplifier fiber, allowing it to provide
amplification to a 1090 nm signal passing through it by stimulated
emission.
[0033] In FIG. 5, the signal to be amplified is directed from input
port 10 to a first port 43 of the circulator 35. This results in
the signal being output at a second port 45 of the circulator,
where it is directed into the pumped amplifier arrangement 51. The
optical signal is amplified as it passes through the fiber 26, and
is thereafter directed to grating 47. Grating 47, being highly
reflected at the signal wavelength, redirects the amplified signal
back through amplifier fiber 26, where it is further amplified.
When the amplified signal returns to circulator port 45, it is
directed to circulator port 49.
[0034] FIG. 5 shows a second amplifier stage 51 in the branch
connected to circulator port 49. The second amplifier stage 51 may
be identical to that located in the branch connected to port 45,
and provides additional amplification of the optical signal in the
same manner. After the signal passes through the amplification
stage 51 of the second branch, it returns to circulator port 49,
from which it is directed to port 53, and thereafter to signal
output port 34. While two amplifier stages 51 are shown in FIG. 5,
those skilled in the art will recognize that the number of stages
used is optional. For example, port 49 of the circulator could as
easily lead to signal output port 34, if only one stage of
amplification was desired. Likewise, a circulator with more than
four ports could be used, and additional amplification stages 51
beyond the two shown in FIG. 5 could be used.
[0035] In the embodiments of the present invention, pump energy is
oscillated through the gain medium comprising a fiber amplifier.
The pump energy is thereby directed into both ends of the fiber
amplifier without the destabilization risk associated with
directing two independent pump energy sources toward each other.
Oscillation of the pump energy through the gain medium also
provides recycling of the pump energy (as compared with simply
passing the pump energy once or twice through the gain medium), and
therefore helps to improve the overall power conversion of the
amplifier.
[0036] While the invention has been shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that various changes in form and detail
may be made therein without departing from the spirit and scope of
the invention as defined by the appended claims. For example, the
pumping arrangements of the invention may be applied to amplifiers
having different doping configurations and desired pump
wavelengths.
* * * * *