Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-12-17
2004-08-24
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S075000
Reexamination Certificate
active
06782028
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser module, and an optical amplifier using the semiconductor laser module, and more particularly, to a semiconductor laser device provided with two stripes from which two laser beams are emitted, and an optical amplifier.
2. Discussion of the Background
With progress in optical communications based on a high-density wavelength division multiplexing transmission system over the recent years, a higher output is increasingly demanded to a pumping light source used for the optical amplifier.
Further, a greater expectation is recently given to a Raman amplifier as means for amplifying the beams having a much broader band than by an erbium-doped optical amplifier that has hitherto been used as the optical amplifier. The Raman amplification is defined as a method of amplifying the optical signals, which utilizes such a phenomenon that a gain occurs on the side of frequencies as low as about 13 THz from a pumping beam wavelength due to the stimulated Raman scattering occurred when the pumping beams enter an optical fiber, and, when signal beams having the wavelength band containing the gain described above are inputted to the optical fiber in the thus pumped (excited) state, these signal beams are amplified.
According to the Raman amplification, the signal beams are amplified in a state where a polarizing direction of the signal beams is coincident with a polarizing direction of the pumping beams, and it is therefore required that an influence caused by a deviation between polarizing planes of the signal beam and of the pumping beam be minimized. For attaining this, a degree of polarization (DOP) has hitherto been reduced by obviating the polarization of the pumping beam (depolarization).
As a method for simultaneously realizing a higher output and depolarization of a pumping light source, as disclosed in U.S. Pat. No. 5,589,684, a method in which a laser beam emitted from two semiconductor laser modules oscillating on the same wavelength is polarization-synthesized by a polarization synthesizing coupler is known.
FIG. 35
is an explanatory view in explaining a conventional semiconductor laser apparatus disclosed in U.S. Pat. No. 5,589,684.
As shown in
FIG. 35
, a conventional semiconductor laser apparatus comprises: a first semiconductor laser device
100
and a second semiconductor laser device
101
for emitting laser beams in the orthogonal direction with each other on the same wavelength; a first collimation lens
102
for collimating the laser beam emitted from the first semiconductor laser device
100
; a second collimation lens
103
for collimating the laser beam emitted from the second semiconductor laser device
101
; a polarization synthesizing coupler
104
for orthogonally polarization-synthesizing the laser beam collimated by the first collimation lens
102
and the second collimation lens
103
; a condenser lens
105
for condensing the laser beams polarization-synthesized by the polarization synthesizing coupler
104
; and an optical fiber
107
with a fiber Bragg grating (FBG)
106
for receiving the laser beams condensed by the condenser lens
105
and letting the beams travel to the outside.
According to a conventional semiconductor laser apparatus, since the laser beams emitted in the orthogonal direction with each other from the first semiconductor laser device
100
and the second semiconductor laser device
101
are polarization-synthesized by the polarization synthesizing coupler
104
, a laser beam whose degree of polarization is small can be emitted from the optical fiber
107
. Furthermore, since fiber Bragg grating
106
is formed in the optical fiber
107
, oscillation wavelengths of the semiconductor laser devices
100
and
101
are fixed in the same degree, a laser beam whose wavelength is fixed can be emitted from the optical fiber
107
.
Accordingly, the above-mentioned conventional semiconductor laser apparatus can be applied as a pumping light source of an optical amplifier which requires a high optical output, especially of a Raman amplifier, which requires a low polarization dependency and a wavelength stability.
A conventional semiconductor laser apparatus has the following problems.
(1) In the conventional semiconductor laser apparatus, two chip carriers with two semiconductor laser devices
100
and
101
attached thereto respectively need to be disposed on a base plate by soldering. At this time, since positioning need to be conducted so that laser beams emitted from the two semiconductor laser devices
100
and
101
be orthogonal with each other, it is difficult to conduct the positioning of the semiconductor laser devices and a time for positioning becomes longer. As a result, a time for manufacturing a semiconductor laser module is increased.
(2) Since the beams emitted from each of the semiconductor laser devices
100
and
101
are emitted in completely different directions from each other, there arises, for example, a warp of a package in which optical components are aligned and fixed under a state of a high temperature. Due to this, it is difficult to stabilize beam intensity and a degree of polarization of the beam emitted from the optical fiber.
(3) In the conventional semiconductor laser apparatus, since collimation lenses
102
and
103
for collimating the laser beams emitted from the semiconductor laser device
100
are used, a beam diameter and an image magnification are enlarged. Therefore, there is a problem in that a tolerance for the position and angle is strict.
(4) In order to cool the two semiconductor laser devices
100
and
101
positioned at a space, a large-sized Peltier module is required. As a result, there is a problem in that the electric power consumption of a semiconductor laser module is increased.
(5) In the conventional semiconductor laser apparatus, an optical fiber with the fiber Bragg grating
106
and the semiconductor laser devices
100
and
101
need to be optically coupled. Since the optical coupling is performed mechanically in a resonator, there is a fear that an oscillation characteristic of the laser beam is changed due to a mechanical vibration. Therefore, there is a problem in that it is impossible to provide a stable optical output in some cases.
(6) Wavelengths of the laser beams emitted from each of the semiconductor laser devices
100
and
101
are determined by a sole FBG and thus a degree of freedom for setting up the wavelengths of each of the stripes is not provided.
Furthermore, when this semiconductor laser device is regarded as a pumping light source used for the Raman amplification, there are the following problems.
(7) In the conventional semiconductor laser device, since the semiconductor laser devices
100
and
101
and the fiber Bragg grating
106
are widely spaced, relative intensity noise (RIN) is made loud due to resonance between the fiber Bragg grating
106
and an optical reflection surface. For example, since amplification occurs at an early stage in the Raman amplification, if a pumping beam intensity fluctuates, a Raman gain also fluctuates. Therefore, fluctuation of the Raman gain is outputted as fluctuation of an amplified signal intensity as it is and there is a problem in that a stable Raman amplification can not be conducted.
(8) As an optical amplification method, in addition to a back pumping method in which a pumping beam is supplied in the opposite direction of the traveling direction of the signal beam, there is a forward pumping method in which a pumping beam is supplied in the same direction of the traveling direction of the signal beam and a bidirectional pumping method in which pumping is conducted from both the directions. At present, the back pumping method is mainly used as the Raman amplifier. This is because in the forward pumping method in which a weak signal beam moves together with a strong pumping beam in the same direction, there is a problem in that the fluctuation of the pumping beam intensity largely influences on the fluctuation of t
Aikiyo Takeshi
Funabashi Masaki
Kimura Toshio
Konishi Mieko
Matsuura Hiroshi
Ip Paul
Nguyen Tuan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
The Furukawa Electric Co. Ltd.
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