U.S. patent application number 09/426460 was filed with the patent office on 2002-01-31 for semiconductor-solid state laser optical waveguide pump.
Invention is credited to ZENTENO, LUIS A..
Application Number | 20020012378 09/426460 |
Document ID | / |
Family ID | 22360064 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020012378 |
Kind Code |
A1 |
ZENTENO, LUIS A. |
January 31, 2002 |
SEMICONDUCTOR-SOLID STATE LASER OPTICAL WAVEGUIDE PUMP
Abstract
The invention includes a solid state laser which outputs
wavelength emission .lambda..sub.ss, centered about 946 nm,
combined with a lasing waveguide which includes a Yb doped optical
waveguide such that when the .lambda..sub.ss output is inputted
into the lasing waveguide the lasing waveguide produces a
wavelength emission .lambda..sub.y centered about 980 nm. The
invention further includes the utilization of pump light with
optical waveguide amplifying devices.
Inventors: |
ZENTENO, LUIS A.; (PAINTED
POST, NY) |
Correspondence
Address: |
JULIANA AGON
CORNING INCORPORATED
SP TI 03
CORNING
NY
14831
|
Family ID: |
22360064 |
Appl. No.: |
09/426460 |
Filed: |
October 25, 1999 |
Current U.S.
Class: |
372/108 |
Current CPC
Class: |
H01S 3/094003 20130101;
H01S 3/094042 20130101; H01S 3/06716 20130101; H01S 3/1618
20130101; H01S 3/0675 20130101 |
Class at
Publication: |
372/108 |
International
Class: |
H01S 003/08 |
Claims
What is claimed is:
1. An optical waveguide device comprised of: a solid state laser
for outputting an emission .lambda..sub.ss centered about 946 nm, a
lasing waveguide, said lasing waveguide comprising a Yb doped
optical waveguide, said Yb doped optical waveguide having an input
end and an output end, said input end is optically coupled to said
solid state laser such that said emission .lambda..sub.ss outputted
from said solid state laser is inputted into said Yb doped optical
waveguide input end and an emission .lambda..sub.y centered about
980 nm is outputted from said Yb doped optical waveguide output
end.
2. An optical waveguide device as claimed in claim 1, wherein said
solid state laser comprises a neodymium doped solid state
laser.
2a. An optical waveguide device as claimed in claim 2, wherein said
neodymium doped solid state laser is pumped with a semiconductor
laser that emitts light having a wavelength X, wherein X is
selected from the group comprising the Nd absorption bands near 880
nm, 808 nm, 740 nm, and 690 nm..
3. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide comprises a Yb doped silica fiber.
4. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide comprises a Yb doped alumino-silicate
fiber.
5. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide comprises a single mode optical
waveguide fiber.
6. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide comprises an Er free Yb doped fiber.
7. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide comprises a silica fiber doped with 0.1
to 4 wt. % Yb and 0.1 to 10 wt. % Al.
8. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide comprises 60-99 wt. % SiO.sub.2.
9. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide comprises a silica fiber doped 0.2 to
2.5 wt. % Yb and about 0.2 to 8.3 wt. % Al.
10. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide comprises a single cladding optical
fiber.
11. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide comprises an optical fiber which
consists essentially of a single waveguiding cladding and a
waveguiding core.
12. An optical waveguide device as claimed in claim 1, further
comprising a filter, said filter for inhibiting light having a
.lambda..sub.x centered about 1030 nm from propagating in said Yb
doped optical waveguide.
13. An optical waveguide device as claimed in claim 12, wherein
said filter is a fiber grating positioned between said solid state
laser and said Yb doped optical waveguide input end.
14. An optical waveguide device as claimed in claim 1, wherein said
lasing waveguide comprises at least one fiber Bragg grating.
15. An optical waveguide device as claimed in claim 1, wherein said
lasing waveguide comprises a back reflector proximate said Yb doped
optical waveguide input end.
16. An optical waveguide device as claimed in claim 1, wherein said
lasing waveguide comprises a pump reflector proximate said Yb doped
optical waveguide output end.
17. An optical waveguide device as claimed in claim 1, wherein said
lasing waveguide comprises an output coupler proximate said Yb
doped optical waveguide output end.
18. An optical waveguide device as claimed in claim 1, wherein said
lasing waveguide produces a 980 nm single mode output of at least
0.5 W.
19. An optical waveguide device as claimed in claim 1, wherein said
lasing waveguide produces a 980 nm single mode output of at least
300 mW.
20. An optical waveguide device as claimed in claim 1, which has a
Yb laser slope efficiency of at least 80%.
21. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide output end is optically coupled to an Er
doped optical amplifier.
22. An optical waveguide device as claimed in claim 1 which has an
optical to optical conversion efficiency greater than 25%.
23. An optical waveguide device as claimed in claim 1 which has an
optical to optical conversion efficiency greater than 30%.
24. An optical waveguide device as claimed in claim 1 which has an
optical to optical conversion efficiency greater than 40%.
25. An optical waveguide device as claimed in claim 1 which has a
conversion efficiency greater than 50%.
26. An optical device as claimed in claim 1, wherein light in the
range of 780 to 880 nm is inputted into said solid state laser.
27. An optical waveguide device as claimed in claim 1, wherein said
Yb doped optical waveguide has a gain G.sub.980 at 980 nm and a
gain G.sub.1030 at 1030 nm, wherein G.sub.980>G.sub.1030.
28. An optical waveguide device as claimed in claim 27, said Yb
doped optical waveguide having a Yb weight percent concentration
CONC.sub.Yb, a pump absorption PA.sub.946 at 946 nm, and a length
L.sub.Yb, said lasing waveguide comprising an output coupler having
a reflectivity OCR, wherein G.sub.980 is dependent on CONC.sub.Yb
band PA.sub.946 and OCR and L.sub.Yb is optimized such that
G.sub.980>G.sub.1030.
29. An optical waveguide device as claimed in claim 28, wherein
CONC.sub.Yb is about 0.2 wt. %, OCR is about 5% at 980 nm, and
L.sub.Yb is about 60 cm.
30. A method of producing a 980 nm pump light, said method
comprising: providing a first laser for producing an emission
.lambda..sub.1, centered about 808 nm; inputting said produced
emission .lambda..sub.1, centered about 808 nm into a second laser
for producing an emission .lambda..sub.2 centered about 946 nm;
producing an emission .lambda..sub.2 centered about 946 nm;
inputting said produced emission .lambda..sub.2 centered about 946
nm into a third laser for producing an emission .lambda..sub.3
centered about 980 nm; producing an emission .lambda..sub.3
centered about 980 nm.
31. A method as claimed in claim 30, further comprising providing a
second semiconductor laser for producing said emission
.lambda..sub.1, centered about 808 nm.
32. A method as claimed in claim 31, wherein said first laser and
said second semiconductor laser are broad-area laser diodes and
producing an emission .lambda..sub.1, centered about 808 nm
comprises polarization multiplexing said first laser and said
second semiconductor laser.
33. A method as claimed in claim 30, wherein said second laser for
producing an emission .lambda..sub.2 centered about 946 nm is
comprised of a Nd:YAG laser.
34. A method as claimed in claim 30, wherein said third laser for
producing an emission .lambda..sub.3 centered about 980 nm is
comprised of a Yb doped fiber laser.
35. A method as claimed in claim 30 further comprising: inhibiting
the feedback of 1030 nm light into said third laser for producing
an emission .lambda..sub.3 centered about 980 nm.
36. A method as claimed in claim 30 further comprising: inputting
said produced emission .lambda..sub.3 centered about 980 nm into an
Er doped optical amplifier.
37. An optical amplifier device comprised of: a semiconductor laser
which produces an emission .lambda..sub.1, centered about a first
semiconductor wavelength; a first solid state laser which is
optically pumped by said semiconductor laser, said first solid
state laser produces an emission .lambda..sub.2 centered about a
first solid state wavelength, said first solid state wavelength in
the Yb absorption spectrum peak centered about 920 nm; a second
solid state laser which is optically pumped by said first solid
state laser, said second solid state laser produces an emission
.lambda..sub.3 centered about 980 nm; an optical amplifier for
amplifying an optical transmission signal, said optical amplifier
optically pumped by said second solid state laser.
38. An optical amplifier device as claimed in claim 37, wherein
said first solid state laser comprises a Nd:YAG laser.
39. An optical amplifier device as claimed in claim 37, wherein
said first solid state wavelength is in the range of 880-960
nm.
40. An optical amplifier device as claimed in claim 37, wherein
said second solid state laser is comprised of an optical
waveguide.
41. An optical amplifier device as claimed in claim 37, wherein
said second solid state laser is comprised of a Yb doped silica
optical waveguide fiber.
42. An optical amplifier device as claimed in claim 37, wherein
said second solid state laser is comprised of a fiber Bragg grating
back reflector and a fiber Bragg grating pump reflector.
43. An optical amplifier device as claimed in claim 37, wherein
said device is comprised of a filter for inhibiting light having a
wavelength proximate 1030 nm from entering said second solid state
laser.
44. A method of amplifying an optical transmission signal, said
method comprising: providing a first laser for producing
.lambda..sub.1 light; providing a second laser for producing
.lambda..sub.2 light; providing a third laser for producing
.lambda..sub.3 light; providing an optical amplifier which utilizes
.lambda..sub.3 light to amplify an optical signal; pumping said
second laser with .lambda..sub.1 light produced by said first
laser; pumping said third laser with .lambda..sub.2 light produced
by said second laser; and pumping said optical amplifier with
.lambda..sub.3 light.
45. A method as claimed in claim 44, wherein
.lambda..sub.3>.lambda..su- b.2>.lambda..sub.1.
46. A method as claimed in claim 44, wherein the optical
transmission signal has a wavelength .lambda..sub.t, with
.lambda..sub.t>.lambda..s- ub.3>.lambda..sub.2>80
.sub.1.
47. A method as claimed in claim 44, wherein .lambda..sub.1 light
is centered about 808 nm.
48. A method as claimed in claim 44, wherein .lambda..sub.2 light
is centered about 946 nm.
49. A method as claimed in claim 44, wherein .lambda..sub.3 light
is centered about 980 nm.
50. A method as claimed in claim 44 further comprising suppressing
light having a wavelength centered about 1030 nm.
51. A method of making a 980 nm pump for an optical amplifier
comprising: providing at least one semiconductor laser diode;
coupling said semiconductor laser diode into a solid state laser;
coupling said solid state laser into a Yb doped optical fiber
laser.
52. A method as claimed in claim 51, wherein providing at least one
semiconductor laser diode comprises providing at least two
semiconductor laser diodes.
53. The method as claimed in claim 52, wherein providing at least
two semiconductor laser diodes comprises providing two broad area
lasers, with each of said two broad area lasers outputting at least
2 W each at a wavelength centered about 808 nm.
54. The method as claimed in claim 51, wherein said Yb doped
optical fiber laser comprises a single clad single mode
alumino-silicate fiber.
55. An optical amplifier system comprising a single cladding
optical waveguide lasing fiber and a multimode pump source.
56. An optical amplifier system as claimed in claim 55, wherein
said lasing fiber is indirectly pumped by said multimode pump
source.
57. A method of making an optical amplifier pump, comprising the
steps of: providing a multimode pump source; providing a single
cladding optical waveguide lasing fiber; and indirectly pumping
said lasing fiber with said multimode pump source.
58. An method as claimed in claim 57, wherein said single cladding
optical waveguide lasing fiber is single mode.
59. A method of amplifying an optical signal .lambda..sub.t
comprising the steps of: providing a multimode light pump source
having a wavelength .lambda..sub.mm multimode brightness output;
converting said multimode brightness output into a single mode
output having a wavelength .lambda..sub.pump; inputting said single
mode output into an optical amplifier for amplifying an optical
signal .lambda..sub.t.
60. A method as claimed in claim 59, wherein
.lambda..sub.t>.lambda..su- b.pump>.lambda..sub.mm.
61. An optical amplifier pump for pumping an optical amplifier with
a pump wavelength .lambda..sub.pump, said pump including a
semiconductor laser which produces a wavelength .lambda..sub.semi;
said pump outputting at least 500 mW of light at
.lambda..sub.pump.
62. An optical amplifier pump as claimed in claim 61, wherein
.lambda..sub.semi.apprxeq..lambda..sub.pump.
63. An optical amplifier pump as claimed in claim 62, wherein
.lambda..sub.semi>.lambda..sub.pump.
64. An optical amplifier pump as claimed in claim 61, wherein
.lambda..sub.semi is in the range of 780 to 880 nm.
65. An optical amplifier pump as claimed in claim 61, wherein
.lambda..sub.semi is at a wavelength which excites neodymium
ions.
66. An optical amplifier pump as claimed in claim 61, wherein
.lambda..sub.pump is centered about 946 nm.
67. An optical amplifier pump as claimed in claim 61 wherein
.lambda..sub.pump is centered about 980 nm.
68. An optical amplifier pump comprising: a semiconductor laser
which produces a wavelength .lambda.hd t for pumping Nd ions; a
plurality of Nd ions, which when pumped by said wavelength
.lambda..sub.1, produces a wavelength .lambda..sub.2 for pumping Yb
ions; a plurality of Yb ions, which when pumped by said wavelength
.lambda..sub.2 produces a wavelength .lambda..sub.3 for pumping Er
ions.
69. An optical amplifier pump as claimed in claim 68, wherein
.lambda.=hd 1 is in the range of 780-880 nm, .lambda..sub.2 is in
the range of 900-960 nm, and .lambda..sub.3 is in the range of
970-980 nm.
70. An optical amplifier pump for pumping an optical amplifier
which amplifies optical signals in the range of 1560 to 1620 nm,
comprising: at least one broad area semiconductor laser; and a
neodymium doped solid state laser, said solid state laser pumped by
said semiconductor laser.
71. An optical amplifier comprising: a semiconductor laser; a solid
state laser, said solid state laser pumped by said semiconductor
laser; an Er doped optical amplifier fiber, said Er doped optical
amplifier fiber for amplifying signals in the range of 1560 to 1620
nm, said amplifier fiber pumped by said solid state laser.
72. An optical amplifier as claimed in claim 71, wherein said Er
doped optical amplifier fiber has a length in the range of 50 to
250 meters.
73. An optical amplifier as claimed in claim 71, wherein said Er
doped optical amplifier fiber has a length in the range of 100 to
200 meters.
74. An optical amplifier as claimed in claim 71, wherein said solid
state laser is comprised of neodymium.
75. An optical amplifier as claimed in claim 71, wherein said
semiconductor laser is a broad area semiconductor laser.
76. A method of amplifying a L-band optical signal comprising:
providing an Er doped optical fiber; pumping a neodymium solid
state laser with a broad area semiconductor laser; inputting said
solid state laser into said Er doped optical fiber; and amplifying
a L-band optical signal with said Er doped optical fiber.
77. A method as claimed in claim 76 wherein said Er doped optical
fiber has a length of at least 50 meters.
78. A method as claimed in claim 76 wherein said Er doped optical
fiber has a length of 100-200 meters.
79. A method as claimed in claim 76, wherein said Er doped optical
fiber is comprised of Al doped silica.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional patent
application Ser. No. 60/115,229, filed on Jan. 8, 1999, the content
of which is relied upon and incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to optical waveguide
devices, semiconductor lasers, solid state lasers, and particularly
to the utilization of lasers to pump optical waveguide
amplifiers.
[0003] Optical amplifiers and lasers are important components used
in optical fiber telecommunications systems. Optical signals
transmitted in optical fibers tend to weaken as they travel along
the optical fibers. Optical amplifiers provide an economic means of
amplifying such weakened optical signals while maintaining the
optical nature of the signal.
[0004] Erbium doped optical fiber amplifiers have become the
dominant means of amplifying optical signals in the 1550 nm optical
telecommunications window. Such erbium doped optical fiber
amplifiers are normally directly pumped with 980 nm and/or 1480 nm
semiconductor pump lasers. With such an amplifier-pump system,
electrical energy applied to the 980 nm (1480 nm) semiconductor
pump laser produces 980 nm (1480 nm) photons which are coupled
through an optical fiber pigtail into the erbium doped optical
fiber. The 980 nm and/or 1480 nm pump light excites/energizes the
erbium ions in the erbium doped optical fiber so that 1550 nm
optical telecommunications signals are amplified by the
excited/energized erbium ions. Such direct optical pumping of
optical amplifiers with semiconductor produced photons has become
the standard in the optical telecommunications industry because of
reliability and related use requirements, for example compact space
utilization. But, in addition to economic expense problems, such
direct semiconductor pump lasers pose problems in terms of already
reaching maximum optical output power limitations while the
development of optical amplifiers has continued to require higher
and higher pump power input requirements. It appears that the
commercially available maximum reliable output power of 980 nm
semiconductor laser pumps may plateau in the 300 mW output power
range while the input pump power requirements of optical amplifiers
continue to climb. Semiconductor laser research and development
continue to strive towards improving the structure and performance
of 980 nm semiconductor laser pumps in an effort to try to meet the
needs of optical amplifiers.
[0005] The optical amplifier industry needs a pump laser technology
that is able to meet its ever increasing optical power demands.
SUMMARY OF THE INVENTION
[0006] One aspect of the present invention is an optical waveguide
device which includes a solid state laser which outputs wavelength
emission .lambda..sub.ss centered about 946 nm, combined with a
lasing waveguide which includes a Yb doped optical waveguide such
that when the .lambda..sub.ss output is inputted into the lasing
waveguide the lasing waveguide produces a wavelength emission
.lambda..sub.y centered about 980 nm.
[0007] In another aspect, the present invention includes a method
of producing 980 nm optical amplifier pump wavelength light which
includes providing a first laser for producing an emission
.lambda..sub.1, inputting the produced emission .lambda..sub.1 into
a second laser for producing an emission .lambda..sub.2, producing
an emission .lambda..sub.2, inputting the produced emission
.lambda..sub.2 into a third laser for producing an emission
.lambda..sub.3 centered about the 980 nm optical amplifier pump
wavelength.
[0008] In a further aspect the invention includes an optical
amplifier device which includes at least one semiconductor laser
which produces an emission .lambda..sub.1, centered about 808 nm, a
first solid state laser which is optically pumped by the
semiconductor laser such that it produces an emission
.lambda..sub.2 centered about 946 nm, a second solid state laser
which is optically pumped by the first solid state laser such that
it produces an emission .lambda..sub.3 centered about 980 nm, and
an optical amplifier waveguide for amplifying an optical
transmission signal wherein the optical amplifier is optically
pumped by the second solid state laser.
[0009] The invention further includes a method of amplifying an
optical transmission signal which comprises the steps of: providing
a first laser for producing .lambda..sub.1 light, a second laser
for producing .lambda..sub.2 light, and a third laser for producing
.lambda..sub.3 light, and an optical amplifier which utilizes
.lambda..sub.3 light to amplify an optical signal; pumping the
second laser with .lambda..sub.1 light produced by the first laser;
pumping the third laser with .lambda..sub.2 light produced by the
second laser; and pumping the optical amplifier with .lambda..sub.3
light produced by the third laser.
[0010] Additionally, the invention includes a method of making a
980 nm pump for an optical amplifier, with the method including:
providing at least one semiconductor laser diode, coupling the
semiconductor laser diode into a Nd:YAG laser, and coupling the
Nd:YAG laser into a Yb doped optical waveguide fiber laser.
[0011] In a further aspect the invention includes an optical
amplifier system comprising a single cladding optical waveguide
lasing fiber and a multimode pump source.
[0012] The invention further comprises a method of making an
optical amplifier pump, which includes providing a multimode pump
source; providing a single cladding optical waveguide lasing fiber;
and indirectly pumping the lasing fiber with the multimode pump
source.
[0013] Additionally the invention includes the method of amplifying
an optical signal .lambda..sub.t, by providing a multimode light
pump source having a wavelength .lambda..sub.mm multimode
brightness output; converting the multimode brightness output into
a single mode output having a wavelength .lambda..sub.pump; and
inputting the single mode output into an optical amplifier for
amplifying an optical signal .lambda..sub.t.
[0014] In a further aspect the invention includes an optical
amplifier pump for pumping an optical amplifier with a pump
wavelength .lambda..sub.pump where the pump includes a
semiconductor laser which produces a wavelength .lambda..sub.semi
and the pump outputs at least 500 mW of light at
.lambda..sub.pump.
[0015] Additionally the invention includes an optical amplifier
pump comprising: a semiconductor laser which produces a wavelength
.lambda..sub.1 for pumping Nd ions; a plurality of Nd ions, which
when pumped by the wavelength .lambda..sub.1, produces a wavelength
.lambda..sub.2 for pumping Yb ions; and a plurality of Yb ions,
which when pumped by the wavelength .lambda..sub.2 produces a
wavelength .lambda..sub.3 for pumping Er ions.
[0016] In a further aspect the invention includes an optical
amplifier pump for pumping an optical amplifier which amplifies
optical signals in the range of 1560 to 1620 nm (L-band), which has
at least one broad area semiconductor laser; and a neodymium doped
solid state laser, with solid state laser pumped by the
semiconductor laser.
[0017] Additionally the invention includes an optical amplifier
that comprises a semiconductor laser; a solid state laser, the
solid state laser pumped by the semiconductor laser; and an Er
doped optical amplifier fiber, with the Er doped optical amplifier
fiber for amplifying signals in the range of 1560 to 1620 nm and
pumped by the solid state laser.
[0018] In a further aspect the invention includes a method of
amplifying a L-band optical signal by providing an Er doped optical
fiber, pumping a neodymium solid state laser with a broad area
semiconductor laser, inputting said solid state laser directly into
the Er doped optical fiber, and amplifying a L-band optical signal
with the Er doped optical fiber.
[0019] Additional features and advantages of the invention will be
set forth in the detailed description which follows, and in part
will be readily apparent to those skilled in the art from that
description or recognized by practicing the invention as described
herein, including the detailed description which follows, the
claims, as well as the appended drawings.
[0020] It is to be understood that both the foregoing general
description and the following detailed description are merely
exemplary of the invention, and are intended to provide an overview
or framework for understanding the nature and character of the
invention as it is claimed. The accompanying drawings are included
to provide a further understanding of the invention, and are
incorporated in and constitute a part of this specification. The
drawings illustrate various embodiments of the invention, and
together with the description serve to explain the principles and
operation of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic representation in accordance with the
present invention.
[0022] FIG. 2 is schematic representation in accordance with the
present invention.
[0023] FIG. 3 is schematic representation in accordance with the
present invention.
[0024] FIG. 4 is a graph of output power (milliwatts) at 980 nm
versus input power (milliwatts) at 946 nm.
[0025] FIG. 5 is an output spectrum plot of light from a Yb fiber
laser.
[0026] FIG. 6 is an output spectrum plot of light, which shows
three output spectrums from Yb fiber lasers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. An exemplary embodiment
of the present invention is shown in FIG. 1. The laser system of
the invention is designated generally throughout by reference
numeral 20.
[0028] In accordance with the invention, the present invention for
an optical waveguide device 18 includes a solid state laser 22.
Solid state laser 22 outputs a wavelength emission .lambda..sub.ss
centered about 946 nm. Solid state laser 22 provides a reliable
source for producing a high powered laser light output centered
about 946 nm. Preferably solid state laser 22 is a neodymium doped
solid state laser.
[0029] Solid state laser 22 is preferably a neodymium doped solid
state laser, such as the Nd:YAG solid state laser shown in FIGS. 2,
that is pumped by two semiconductor laser diodes 32. Preferred
semiconductor lasers for pumping the neodymium doped soild state
laser are semiconductor lasers that emitt light having a wavelength
X with X selected from the Nd absorption bands near 880 nm (from
about 860 to about 900 nm), 808 nm (from about 780 to about 830
nm), 740 nm (from about 720 to about 760 nm), and 690 nm (from
about 670 to about 710 nm). These Nd absorption wavelength bands
are for the Nd solid state YAG host, and with other soild state
hosts for Nd the wavelengths and widths of these Nd absorption
bands may vary. Preferably laser diodes 32 are broad area lasers
with each producing about 2 watts of multimode light (2 W MM) at
808 nm. With optical element lenses 34 and a polarization combiner
36, the output of broad area laser diodes 32 is inputted into
Nd:YAG solid state laser 22. Nd:YAG solid state laser 22 is
comprised of a 946 nm laser cavity 38 which includes Nd:YAG crystal
40 and glass substrate spherical surface laser element 42. Nd:YAG
crystal 40 includes a 946 nm high reflectivity (about 99%) coating
44 and an anti-reflection coating 48 that prevents reflections (946
nm and 1060 nm) other than at 808 nm, coating 48 may include a 808
nm high reflector to provide beneficial reflection of 808 nm light.
Spherical surface laser element 42 includes a coating 50 that
provides for high reflectivity (about 95%) at 946 nm and high
transmission at 1060 nm. Solid state laser 22 preferably produces
at least about 1 watt of single mode light at 946 nm. Preferably
light in the range of 780 to 880 nm is inputted into solid state
laser 22, most preferably 800 to 880 nm. In addition to this
external cavity solid state Nd doped crystal embodiment of solid
state laser 22, solid state laser 22 may comprise a tapered Nd
doped waveguide laser device or a Nd doped double clad optical
waveguide fiber laser device.
[0030] As shown in FIG. 1, optical waveguide device 18 includes a
lasing waveguide 24 that is comprised of a Yb doped optical
waveguide 26. Yb doped optical waveguide 26 has an input end 28 and
an output end 30. Input end 28 is optically coupled to solid state
laser 22 such that the emission .lambda..sub.ss outputted from
solid state laser 22 is inputted into the lasing Yb doped optical
waveguide and an emission .lambda..sub.y centered about 980 nm is
outputted from lasing waveguide output end 30.
[0031] Yb doped optical waveguide 26 is preferably a silica optical
waveguide fiber that is doped with Yb. It is further preferred that
the silica optical fiber is an alumino-silicate fiber such as a
silica optical fiber doped with Al and Yb. In a most preferred
embodiment the Yb doped optical waveguide is Er free, in that the
waveguide does not contain erbium so that the Yb ions are the
excitable ions in the waveguide. Preferably the Er free Yb doped
waveguide is a silica waveguide fiber.
[0032] Preferably the Yb doped silica fiber is comprised of 60 to
99 wt. % SiO.sub.2. Preferably Yb doped waveguide 26 is a silica
fiber which includes 0.1 to 4 wt. % Yb and 0.1 to 10 wt. % Al, and
most preferably a waveguide with 0.2 to 2.5 wt. % Yb and 0.2 to 9
wt. % Al, with a further preferred Al wt. % of 0.2 to 8.3wt. % Al.
In a preferred embodiment the Yb doped silica fiber composition
further comprises Ge (germanium).
[0033] It is preferred that lasing waveguide 24 and Yb doped
optical waveguide 26 are comprised of single mode optical waveguide
fiber with such single mode optical waveguide fiber the guiding of
light by the waveguide is restrained to a single mode.
Additionally, Yb doped optical waveguide 26 is preferably a single
cladding optical fiber, in that the optical fiber has a single clad
as compared to a double clad optical fiber or other multi-clad
fibers. Preferably Yb doped waveguide 26 consists essentially of a
single waveguide cladding and a waveguiding core so that the
optical waveguide fiber only has a single waveguide cladding
surrounding a waveguide core with appropriate optical fiber
protective coatings.
[0034] As shown in FIG. 1, optical waveguide device 18 includes a
filter 52. Filter 52 is a filter for inhibiting light having a
wavelength .lambda..sub.x centered about 1030 nm from propagating
in Yb doped optical waveguide 26. Light removal filter 52 removes
1030 nm light so that light produced in the Yb doped waveguide 26
is biased towards the production of 980 nm light. Preferably filter
52 is positioned outside of the 980 nm resonant cavity and most
preferably is a fiber grating positioned between solid state laser
22 and Yb doped optical waveguide input end 28. As depicted in FIG.
1, fiber filter 52 is preferably a long period fiber grating that
removes unwanted 1030 nm light that may be produced by solid state
laser 22. Filter 52 removes and prevents detrimental light having a
wavelength centered about 1030 nm from degrading the performance of
lasing waveguide 24 and ensures that the beneficial 946 nm
excitation light is utilized by Yb ions to produce 980 nm light and
to suppress the production of 1030 nm light by Yb ions in Yb doped
waveguide 26. In addition to a long period grating, filter 52 can
comprise a filter such as a dielectric thin film filter which also
removes the unwanted 1030 nm light that is produced by excited Yb
ions.
[0035] As shown in FIG. 1, lasing waveguide 24 preferably includes
at least one fiber Bragg grating. Fiber Bragg gratings provide a
beneficial means of reflecting light in an optical fiber waveguide
format. Lasing waveguide 24 includes a back reflector 54 proximate
Yb doped optical waveguide input end 28. Back reflector 54 is
centered about 980 nm and is highly reflective so as to benefit the
output of 980 nm light from the lasing waveguide. Lasing waveguide
24 includes a pump reflector 56 proximate Yb doped optical
waveguide output end 30. Pump reflector 56 is centered about 946 nm
and is highly reflective so that 946 nm pump light that reaches the
end of the Yb doped waveguide is contained in the Yb doped
waveguide so that it can pump Yb ions into the proper excited
state. Lasing waveguide 24 includes an output coupler 58 proximate
Yb doped optical waveguide output end 30. Output coupler 58 is
centered about 980 nm and is less reflective than back reflector 54
so as to benefit the output of 980 nm light from the lasing
waveguide. Output coupler 58 and back reflector 54 are fiber Bragg
gratings that provide reflectivity of light to benefit the lasing
operation. Pump reflector 56 is also a fiber Bragg grating that
provides beneficial reflections. These fiber Bragg gratings can be
made in separate optical waveguide fibers which are spliced
together with Yb doped optical waveguide fiber 26 to form lasing
waveguide 24 or could be one unitary, integral, and complete single
optical fiber or spliced variations thereof.
[0036] Yb doped optical waveguide 26 has a gain G.sub.980 at 980 nm
and a gain G.sub.1030 at 1030 nm with G.sub.980>G.sub.1030.
Output coupler 58 of lasing waveguide 24 has a reflectivity OCR,
and Yb doped waveguide 26 has a Yb weight percent concentration
CONC.sub.Yb, a pump absorption PA.sub.946 at 946 nm (percent of 946
nm pump power absorbed by the Yb ions) which depends on the 946 nm
pump power and the removal of 1030 nm light by 1030 nm light
removal filter 52, and a length L.sub.Yb, wherein gain G.sub.980 is
dependent on CONC.sub.yb, PA.sub.946 and OCR and the waveguide
length L.sub.yb is optimized such that G.sub.980>G.sub.1030 with
G.sub.980 depending on CONC.sub.Yb, OCR, PA.sub.946 and L.sub.Yb.
For a given CONC.sub.Yb, PA.sub.946 and OCR, the length L.sub.Yb is
set at an optical length so that G.sub.980>G.sub.1030 and
beneficial production of 980 nm light is obtained. In practicing
the invention it has been found that for a CONC.sub.Yb of about 0.2
wt. % Yb , a PA.sub.946 greater than 90% (with the long period
fiber grating filter removing 1030 nm light), and an OCR
reflectivity of about 5% at 980 nm, that the optimized optical
fiber length is at about 60 cm. For a given inputted pump power the
length is adjusted to insure G.sub.980>G.sub.1030. If light
removal long period fiber grating filter 52 is not utilized to
remove 1030 nm light and bias the production of 980 nm light by 946
nm pump light, then PA.sub.946 needs to be kept below 60% so that
G.sub.980>G.sub.1030 and to maintain the production of 980 nm
which results in wasting 946 nm pump power.
[0037] Optical waveguide device 18 of the invention provides at
least 300 milliwatts (mW) of 980 nm output which is readily usable
for pumping an optical amplifier and meets the high pump power
demands of optical amplifiers. Preferably lasing waveguide 24
produces a 980 nm single mode output of at least 0.5 W (a half of a
watt). Yd doped optical waveguide output end 30 is optically
coupled to an Er doped optical amplifier 60 as depicted in FIG. 1.
As such, the invention comprises an optical amplifier pump that
produces at least 500 milliwatts of 980 nm pump power and includes
a semiconductor laser. Preferably the waveguide device of the
invention has a Yb laser slope efficiency of at least 80%. With
such, the inventive device provides an optical to optical
conversion efficiency greater than 25% (1 W out at 980 nm, 4 W in
at 808 nm), preferably greater than 30%, more preferably greater
than 40%, and most preferably greater than 50%.
[0038] The invention further includes a method of producing a 980
nm pump light. This method of producing a 980 nm pump light
includes the steps of providing a first laser for producing an
emission .lambda..sub.1 centered about 808 nm; inputting the
emission .lambda..sub.1 into a second laser for producing an
emission .lambda..sub.2 centered about 946 nm; producing emission
.lambda..sub.2, centered about 946 nm; inputting the produced
emission .lambda..sub.2 into a third laser for producing an
emission .lambda..sub.3 centered about 980 nm; and then producing
emission .lambda..sub.3 centered about 980 nm.
[0039] The step of providing a first laser for producing
.lambda..sub.1 and inputting .lambda..sub.1 includes providing a
semiconductor laser 32 and coupling semiconductor laser 32 into
solid state laser 22. The method preferably includes providing a
second semiconductor laser 32 for producing the emission
.lambda..sub.1 centered about 808 nm, and polarization multiplexing
or wavelength multiplexing the first laser 32 and the second
semiconductor laser 32. Preferably first laser 32 and second
semiconductor laser 32 are broad-area laser diodes which produce a
multimode emission .lambda..sub.1.
[0040] Preferably the second laser which provides emission
.lambda..sub.2 centered about 946 nm is a solid state laser 22,
most preferably a Nd doped laser, such as a Nd:YAG laser which
comprises a Yd doped solid state lasing waveguide laser, such as a
Yb doped laser fiber 26.
[0041] Preferably the method of producing a 980 nm pump light
includes the step of inhibiting the feedback of 1030 nm light into
third laser 24, such as by filtering with filter 52. As shown in
FIG. 1, the method further includes inputting the produced emission
.lambda..sub.3 centered about 980 nm into Er doped optical
amplifier 60.
[0042] In a further aspect the invention includes an optical
amplifier device 18 which includes a semiconductor 32 which
produces an emission .lambda..sub.1 centered about a first
semiconductor wavelength and a first solid state laser 22 which is
optically pumped by semiconductor laser 32. First solid state laser
22 produces an emission .lambda..sub.2 centered about a first solid
state wavelength in the Yb absorption spectrum peak that is
centered about 920 mm. The device further includes a second solid
state laser 24 that is optically pumped by first solid state laser
22. Second solid state laser 24 produces an emission .lambda..sub.3
centered about 980 nm and optical amplifier 60 for amplifying an
optical transmission signal is optically pumped by second solid
state laser 24. Preferably the first solid state laser 22 is a Nd
doped laser and the first solid state wavelength is in the range of
880 to 960 nm. Preferably second solid state laser 24 is comprised
of an optical waveguide which includes a Yb doped silica optical
waveguide fiber 26. Additionally, second solid state laser 24
preferably includes a fiber Bragg grating back reflector 54 and a
fiber Bragg grating pump reflector 56. In a most preferred
embodiment of the invention the device includes filter 52 for
inhibiting light having a wavelength proximate 1030 nm from
entering second solid state laser 24.
[0043] The invention further includes a method of amplifying an
optical transmission signal, which includes: providing a third
laser for producing .lambda..sub.3 light; providing an optical
amplifier which utilizes .lambda..sub.3 light to amplify an optical
signal; pumping the second laser with .lambda..sub.1 light produced
by the first laser, pumping the third laser with .lambda..sub.2
light produced by the second laser, and pumping the optical
amplifier with the .lambda..sub.3 light. Preferably with the method
.lambda..sub.3>.lambda..sub.2>.lambda..s- ub.1, and most
preferably the method includes amplifying an optical transmission
signal which has a wavelength .lambda..sub.t such that
.lambda..sub.t>.lambda..sub.3>.lambda..sub.2>.lambda..sub.1.
In preferred methods: .lambda..sub.1 light is centered about 808
nm; .lambda..sub.2 light is centered about 946 nm; and
.lambda..sub.3 light is centered about 980 nm. The method also
further includes suppressing light having a wavelength centered
about 1030 nm, such as with a filter 52.
[0044] The invention further comprises a method of making a 980 nm
pump for an optical amplifier which includes the steps of providing
at least one semiconductor laser diode, coupling at least one
semiconductor laser diode into a solid state laser, and coupling
the solid state laser into a Yb doped optical fiber laser.
Preferably the step of providing at least one semiconductor laser
diode 32 comprises providing at least two semiconductor laser
diodes 32, most preferably providing two broad area semiconductor
lasers with each of the semiconductor lasers outputting at least 2
W (two watts) each at a wavelength centered about 808 nm and
coupling into a solid state laser includes combining the
polarization of the two semiconductor lasers. Preferably the solid
state laser 22 comprises a Nd doped solid state laser. Preferably
Yb doped optical waveguide fiber laser 24 comprises a single clad
single mode alumino-silicate Yb doped fiber 26.
[0045] In an additional aspect, the invention includes an optical
amplifier system that comprises a single cladding optical waveguide
lasing fiber and a multimode pump source. As shown in FIG. 1, the
optical amplifier system of the invention comprises single cladding
optical waveguide lasing fiber 126 and multimode pump source 132.
Preferably single cladding optical waveguide lasing fiber 126
comprises a single mode Yb doped optical 26 and multimode pump
source 132 is comprised of a first and second broad area
semiconductor laser 32. Most preferably the single cladding optical
waveguide lasing fiber is indirectly pumped by said multimode pump
source. Additionally, the invention includes a method of making an
optical amplifier pump which comprises providing a multimode pump
source 132, providing a single cladding optical waveguide lasing
fiber 126 and indirectly pumping the lasing fiber 126 with
multimode pump source 132.
[0046] In a further aspect the invention comprises a method of
amplifying an optical signal .lambda..sub.t by providing a
multimode light pump source having a wavelength .lambda..sub.mm
multimode brightness output; converting the multimode brightness
output into a single mode output having a wavelength
.lambda..sub.pump; and inputting the single mode output into an
optical amplifier for amplifying an optical signal .lambda..sub.t.
Preferably .lambda..sub.t>.lambda..sub.pump>.lambda-
..sub.mm.
[0047] Additionally, the invention includes an optical amplifier
pump for pumping an optical amplifier with a pump wavelength
.lambda..sub.pump, with the pump including a semiconductor laser
which produces a wavelength .lambda..sub.semi and the pump
outputting at least 500 mW of light at .lambda..sub.pump.
Preferably .lambda..sub.semi is not equal to .lambda..sub.pump
(.lambda..sub.semi.noteq..lambda..sub.pump) and most preferably
.lambda..sub.semi is less than .lambda..sub.pump
(.lambda..sub.semi>.lambda..sub.pump). Preferably
.lambda..sub.semi is in the range of 780 to 880 nm, and most
preferably .lambda..sub.semi is at a wavelength which excites
neodymium ions. In a preferred embodiment .lambda..sub.pump is
centered about 946 nm. In a further preferred embodiment
.lambda..sub.pump is centered about 980 nm.
[0048] In a further aspect the invention includes an optical
amplifier pump with a semiconductor laser which produces a
wavelength .lambda..sub.1 for pumping Nd ions, a plurality of Nd
ions which when pumped by the wavelength .lambda..sub.1 produces a
wavelength .lambda..sub.2 for pumping Yb ions, and a plurality of
Yb ions which when pumped by the wavelength .lambda..sub.2 produces
a wavelength .lambda..sub.3 for pumping Er ions. Preferably
.lambda..sub.1 is in the range of 780 to 880 nm, .lambda..sub.2 is
in the range of 900-960 nm, and .lambda..sub.3 is in the range of
970-980 nm.
[0049] In addition, the invention includes an optical amplifier
pump for pumping an optical amplifier which amplifies optical
signals in the L-band range of 1560 to 1620 nm which comprises at
least one broad area semiconductor laser and a neodymium doped
solid state laser with the neodymium doped solid state laser pumped
by the semiconductor laser. As shown in FIG. 3, optical amplifier
pump 120 comprises using the first part 110 of laser system 20 of
FIG. 1 to directly pump L-band optical amplifier 160 with the 946
nm output from Nd doped solid state laser 22. Broad area
semiconductor lasers 32 pump solid state laser 22 which inputs the
946 nm light directly into L-Band optical amplifier 160 without
utilizing the Yb doped optical fiber. Pump 120 effectively pumps an
L-band optical amplifier such as a long length of Er doped Al doped
silica amplifier fiber.
[0050] The application of the invention to directly pump a L-band
optical amplifier includes an optical amplifier 160 which has a
semiconductor 32, a solid state laser 22 which is pumped by
semiconductor laser 32, and an Er doped optical amplifier fiber 260
for amplifying signals in the range of 1560 to 1620 nm with the
amplifier fiber pumped by solid state laser 22. Preferably Er doped
optical amplifier fiber 260 is a long length of fiber having a
length in the range of 50 to 250 meters, and more preferably 100 to
200 meters. Preferably solid state laser 22 is comprised of
neodymium, such as a neodymium doped solid state laser. Preferably
semiconductor lasers 32 are broad area multimode semiconductor
lasers. The neodymium doped solid state laser may comprise a Nd
doped crystal, a Nd doped double clad waveguide, or a Nd doped
tapered waveguide. A Nd doped crystal is the preferred solid state
laser, with Nd:YAG most preferred.
[0051] The invention includes a method of amplifying a L-band
optical signal which includes the steps of providing an Er doped
optical fiber, pumping a neodymium solid state laser with a broad
area semiconductor laser, inputting the solid state laser directly
into the Er doped optical fiber, and amplifying a L-band optical
signal with the Er doped optical fiber. In a preferred method the
provided Er doped fiber has a length of at least 100 meters, and
most preferably has a length from 100 to 200 meters. Most
preferably the Er doped optical fiber is an Al doped silica
fiber.
EXAMPLES
[0052] The invention will be further clarified by the following
examples which are intended to be exemplary of the invention.
Example 1-2
[0053] As shown in FIG. 1-2, a single-mode Yb:SiO.sub.2 fiber laser
pumped by a diode-pumped 1.1 W Nd:YAG laser at 946 nm in accordance
with the invention provided >650 mW output power at 980 nm and
>80% slope efficiency. Such high output power at 980 nm was
achieved by pumping at 946 nm using a TEM .sub.0,0
laser-diode-pumped Nd:YAG. Although the Yb absorption cross section
has a minimum near this wavelength, there was still enough
absorption to provide the 980 nm output. This inventive pumping
scheme obtained 0.65 W of single-mode output from a CS980 brand
optical fiber (Corning Incorporated; Corning, N.Y.) output fiber,
and is scaleable to much higher output powers and has been found to
be useful for pumping Er-doped amplifiers. In this high output
power operation of the invention the 1030 nm transition was
suppressed.
[0054] In practicing the invention as shown in FIG. 1 and described
herein, the invention involves the quasi-four-level transition of
Nd:YAG at 946 nm to directly pump Yb:SiO.sub.2 which lases at 980
nm and directly pumps Er. Such production of 980 nm pump light has
provided certain advantages such as compatibility with existing
amplifier component technology and pre-amp stage pumping without
significant NF degradation as observed with Yb:Er co-doped
fibers.
[0055] As shown in FIG. 1-2, the TEM.sub.0,0 pump laser consisted
of a Nd:YAG solid state crystal pumped by a pair of
polarization-multiplexed 2 W multimode, broadened-waveguide,
broad-area semiconductor laser diodes at 808 nm with emitting
aperture of 100.times.1 .mu.m.sup.2. The solid state laser crystal
had a 1 dB absorption length of 3 mm, and dimensions
3.times.3.times.8 mm. The plano-concave resonator had a length of 7
mm (optical length is 1 cm). The radius of curvature was about 10
cm and the thermal lens at 4 W pump power was about 15 cm. Thermal
lensing caused the resonator spot size to decrease with increasing
pump power, and therefore beam divergence increased with pump
power. This was verified experimentally, with measured TEM.sub.0,0
beam divergence in the range 3.4-6 mrad, depending on output power.
A schematic of the Nd:YAG laser is shown in FIG. 2. The threshold
and slope efficiency of this laser was 1 W of input pump power and
50%, respectively. It had a FWHM of 0.30 nm centered at 945.8 nm.
The Nd:YAG solid state crystal laser utilized in the invention was
obtained from InnoLight GmbH (Hannover, Germany) and the broad-area
semiconductor laser diodes were Polaroid POL-5100BW series brand
laser diodes (Polaroid Corporation; Norwood, Mass.). The laser
diodes were collimated in the fast axis by a .mu.-lens element with
100 .mu.m diameter. This reduced the fast axis NA from 0.6 to about
0.03. An image of the glens aperture was made by a spherical lens
element which had a focal length of 1.8 cm. The beams from each
laser diode were spatially overlapped in the polarization
multiplexer and magnified .times.1.5 by a lens element, which had a
focal length of 2.7 cm. The focused pump spot radius (1/e.sup.2)
was approximately 80.+-.10 .mu.m. The measured laser beam spot
radius at 100 mW output power was 80-100 .mu.m, corroborating good
pump-signal overlap necessary for efficient quasi-four-level
operation.
[0056] With a double-pass pump absorption using appropriate
coatings in the Nd:YAG laser resonator, about 1.7 W at 946 nm can
be achieved with the same 2.times.2 W laser diode pumps. With 85%
coupling of this 1.7 W output into the fiber and an 80% Yb laser
slope efficiency, greater than 1.2 W @980 nm should be
obtained.
[0057] The Yb doped fiber laser consisted of a length of Yb-doped
fiber with 2 gratings fusion spliced on each side of it as
illustrated in FIG. 1. In the input side, pump power was coupled
through a X10 aspheric lens element (Newfocus brand lens #5726)
into Flexcore 1060 brand optical fiber (Corning Incorporated;
Corning, N.Y.) containing a 1030 nm long-period grating (LPG) which
was spliced to CS980 brand optical fiber (Corning Incorporated;
Corning, N.Y.) containing a Bragg grating back reflector. In the
output side, Flexcore 1060 brand optical fiber (Corning
Incorporated) containing a Bragg grating pump reflector was spliced
to CS980 brand optical fiber (Corning Incorporated) containing a
Bragg grating output coupler.
[0058] It was found that efficient pump absorption and exclusive
three-level laser operation pull the required Yb fiber length in
opposite directions; it was found that 946 nm pump absorption
should be at most 4-5 dB at threshold, in order to avoid
quasi-four-level oscillation in a fiber laser with 14 dB round-trip
loss. Since low pump absorption was unacceptable, a spectral filter
was used to increase pump absorption. The Yb-doped alumino-silicate
fiber with length of 50 cm allowed .apprxeq.85% absorption of pump
power just below laser threshold; however, besides three-level
oscillation between the .sup.2F.sub.5/2.fwdarw..sup.2F.sub.7/- 2
manifolds at 978 nm, unwanted quasi-four-level lasing at 1030 nm
and at 1012 nm between two other pairs of strong Stark levels of
the same manifolds was simultaneously observed. This was eliminated
by the LPG which had a 13 dB notch at 1027 nm; this grating had a
loss of 0.15 dB at 946 nm and 1.2 dB at 1012 nm.
[0059] The back reflector was a 0.5 nm FWHM FBG centered at 979.8
nm with peak reflectivity >99%. The pump reflector was a 0.6 nm
FWHM FBG centered at 945.8 nm with peak reflectivity of >99%;
this grating allowed .apprxeq.97% pump absorption in a double-pass;
for the given fiber length, by taking the pump reflector out about
15% of pump power leaks from the fiber end; it was found that the
pump reflector grating also helped to suppress unwanted oscillation
at 1012 nm. The output coupler had a 0.5 nm FWHM centered at 979.9
nm with peak reflectivity of 5%; this grating maintained
narrow-line oscillation at high pump powers. Without the output
coupler, the fiber lased between its cleaved facets at high pump
power. The Yb:SiO.sub.2 fiber was 0.2 wt. % Yb and 0.2 wt. Al,
NA=0.22, cut-off wavelength of 870 nm and peak absorption of 1.77
dB/cm at 980 nm with background loss of 8 dB/km.
[0060] The laser power measured from a cleaved facet of the output
CS980 fiber end is shown in FIG. 4 vs. input pump power (measured
before the Newfocus brand .times.10 aspheric lens element); black
dots 401 represent result points and solid line 402 is a linear
interpolation of these results. Threshold was approximately 41 mW
of input pump power and the slope efficiency was 59% with respect
to input pump power. Measured losses were as follows: 1.0 dB fiber
coupling loss (which corresponds to a coupling efficiency of 88%
taking into account the lens 97% transmission and 7% Fresnel
reflection from fiber facets), 0.25 dB splicing loss (for a total
of 4 splices) and 0.15 dB LPG insertion loss, for a total of about
1.4 dB. After correcting for these losses, the laser slope
efficiency is 81% and laser threshold is 30 mW, both with respect
to absorbed pump power. The spectrum at 655 mW output power is
shown in FIG. 5; it has a FWHM of 0.15 nm centered at 979.8 nm.
[0061] A second alumino-silicate Yb-doped fiber was utilized in the
invention, having 2.5 wt. % Yb and 8.3 wt. % Al, NA=0.26, cut-off
wavelength of 940 nm and peak absorption of 9.75 dB/cm at 980 nm
with background loss of 20 dB/km. A 9.5 cm length of this Yb-doped
fiber allowed about 85% pump absorption, with measured threshold
and slope efficiency of approximately 60 mW and 60%, with respect
to absorbed pump power.
[0062] These alumino-silicate Yb-doped fibers were prepared by the
method by MCVD (modified chemical vapor deposition) process. The
results for measured slope efficiency and power threshold are
summarized in Table 1. In each case, the Yb fiber length was
optimized for lasing at 980 nm with 90% pump absorption, and splice
losses were reduced to a minimum. These measurements were obtained
with input LPG and back reflector in place, but no gratings in the
output end in that the output reflector was the cleaved Yb fiber
facet
1TABLE 1 Length for 90% pump Pump power Composition absorp-
threshold Slope Fiber (oxide wt. %) tion (cm) (mW) efficiency
Reference 0.06Yb 50 12 0.67 First 0.2Yb/0.2Al 60 28 0.79 Example
Second 2.5Yb/8.3Al/0.5Ge 10 56 0.57 Example
[0063] All of these fiber lasers contained two splices: one
Flexcore to CS980 splice which consistently had a measured loss of
<0.1 dB, and one CS980 to Yb fiber with estimated loss <0.2.
The numbers for slope efficiency and threshold were obtained by
linear fit to measured input/output points and corrected for pump
leakage, pump coupling and Flexcore-CS980 splice loss; they were
not corrected for the less reproducible CS980-Yb fiber splice loss;
thus, slope efficiency with respect to absorbed pump power may be
up to 5% higher in these alumino-silicates.
[0064] FIG. 6 shows typical spectra observed without the output
gratings (pump reflector and output coupler) for 300 mW of output
power. Curve 601 shows how the spectrum breaks with only the LPG
and back reflector FBG in place; about 92% of the laser power
output is within the FBG bandwidth; weak spurious feedback causes
the remaining 8% to be emitted near the peak of the
2F.sub.5/2.fwdarw..sup.2F.sub.7/2 transition at 978 nm. For
comparison, the free-running spectrum (curve 602) and the spectrum
obtained with the FBG replaced by a chirped FBG (curve 603) are
also shown; the former has a FWHM of 3.3 nm centered at 978.0 nm,
while the latter has a FWHM of 3.2 nm centered at 979.0 nm. The
chirped FBG had reflectivity >98% over 25 nm centered at 980.0
nm. Thus the use of proper gratings provided bandwidth control.
Example 3
[0065] The Nd doped solid state laser system was utilized to
directly pump an Er doped L-Band optical amplifier to provide
optical amplification in the 1560 to 1620 range. As shown in FIG.
3, the Nd:YAG solid state laser output of about 1 watt at 946 nm
was directly coupled into a L-Band optical amplifier so that
approximately 29 dBm of 946 nm light was inputted into a 200 meter
length of Er doped optical amplifier fiber. The Er doped optical
amplifier fiber was a silica fiber doped with Er and Al. This
provided about 22 dBm of amplified output power at 1585 nm with 8.9
dBm of input power at 1585 nm. Er propagation loss of about 20
dBm/km were estimated and the Er absorption at 940 nm was measured
to be about 0.2 dB/m.
[0066] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit and scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *