Optical waveguides – Polarization without modulation
Reexamination Certificate
1999-01-25
2001-09-25
Lee, John D. (Department: 2874)
Optical waveguides
Polarization without modulation
C385S033000
Reexamination Certificate
active
06295393
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a polarized light synthesizing apparatus, a polarized light splitting apparatus and a pump light outputting apparatus suitable for use in an optical amplifier for amplifying signal light in an optical communication system.
(2) Description of the Invention
There have been developed optical amplifiers each of which can amplify an optical signal without converting the optical signal into an electric signal in these years with development of an optical communication system. Among them, an optical fiber amplifier using an optical fiber which is doped with an rare-earth element such as erbium (Er) or the like (EDF: Erbium-Doped Fiber) has features such as high gain, low noise and the like, playing an important role in an optical communication system.
Meanwhile, there have been employed WDM (Wavelength Division Multiplexing) optical communication system, TDM (Time Division Multiplexing) optical communication system and the like, as systems for transmitting and communicating signal light of a plurality of channels over one optical fiber simultaneously.
An optical fiber amplifier (hereinafter, called an optical amplifier) used in the WDM optical communication system amplifies input signal waves (signal light) of a plurality of channels such as 4, 8, 16, 32 or 64 waves to output light of high power. Therefore, the optical amplifier requires a high power pumping light source since a pumping power required to amplify the waves is increased as signal light to be amplified is increased.
In order to obtain a high power output of the pumping source, it is necessary to consider employment of techniques for a high power pumping laser, bi-directional pumping, polarization synthesis of pump light, wavelength synthesis of pump light, and the like.
However, in order to realize the technique such as, in particular, polarization synthesis, wavelength synthesis or the like, an optical circuit device adaptable thereto becomes necessary. If devices for respective functions are configured, problem such as an increase in size of the apparatus, an increase of loss caused by insertion of the optical device and the like will arise. It is therefore desirable to integrate the function of polarization synthesis and the function of wavelength synthesis of pump light to configure an optical circuit device (pump light outputting apparatus), thereby suppressing an increase in size of the apparatus or an increase of insertion loss.
FIG. 11
is a plan view schematically showing a structure of a known pump light outputting apparatus. The pump light outputting apparatus shown in
FIG. 11
multiplexes pump light obtained by polarization-synthesizing and wavelength-synthesizing four kinds of light and signal light amplified by an EDF. In the pump light outputting apparatus, there are integrated and realized not only the function of polarization-synthesizing pump light and the function of wavelength-synthesizing the same but also a function of synthesizing signal light to be amplified and outputting the same.
The pump light outputting apparatus shown in
FIG. 11
has a first polarized light synthesizing unit
51
, a second polarized light synthesizing unit
52
, wavelength-division multiplexing films (WDMs)
504
and
505
, an isolator
506
, signal light collimators
510
e
and
520
and a casing
501
.
The first polarized light synthesizing unit
51
has polarized light synthesizing collimators
510
a
and
510
b
, a high reflection mirror (HR)
502
and a polarization beam splitter (PBS)
503
.
The polarized light synthesizing collimator
510
a
is configured with a polarization maintaining optical fiber
511
a
and a collimator lens
512
a
secured thereto. Similarly, the polarized light synthesizing collimator
510
b
is configured with a polarization maintaining optical fiber
511
b
and a collimator lens
512
b
secured thereto.
These polarized light synthesizing collimators
510
a
and
510
b
are secured on an outer periphery of the casing
501
. On the other hand, the collimator lenses
512
a
and
512
b
are secured inside the casing
501
. Pump light inputted from the polarization maintaining optical fibers
511
a
and
511
b
is emitted toward the inside of the casing through the collimator lenses
512
a
and
512
b.
The polarization maintaining optical fibers
511
a
and
511
b
are configured with birefringent optical fibers, each of which can transmit light at a wavelength of, for example, about 1.46 &mgr;m from a pumping source not shown as linearly polarized light (light whose electric field vector always points toward a constant direction) while maintaining a plane of polarization. The linearly polarized light that the polarization maintaining optical fibers
511
a
and
51
b
can propagate has electric field vectors pointing different directions. For example, the polarization maintaining optical fiber
511
a
propagates S wave, whereas the polarization maintaining optical fiber
511
b
propagate P wave.
The HR
502
totally reflects incident light, which is secured such as to emit pump light of S wave at a wavelength of 1.46 &mgr;m inputted from the polarized light synthesizing collimator
510
a
toward the PBS
503
.
The PBS
503
has a property that a transmittance thereof is varied according to a plane of polarization (direction of vibration) of incident light, which totally transmits light of P wave (at a wavelength of 1.46 &mgr;m) emitted from the polarized light synthesizing collimator
510
b
, while totally reflecting light of S wave (at a wavelength of 1.46 &mgr;m) emitted from the polarized light synthesizing collimator
510
a
through the collimator lens
512
a
. The PBS
503
is such secured as to multiplex (polarization-synthesize) the pump light of S wave from the above polarized light synthesizing collimator
510
a
and the pump light of P wave from the polarized light synthesizing collimator
510
b
into light of the same optical axis, and emits the light to the WDM
504
.
The second polarized light synthesizing unit
52
has a polarized light synthesizing collimators
510
c
and
510
d
, a HR
507
and a PBS
508
, similarly to the first polarized light synthesizing unit
51
. The polarized light collimators
510
c
and
510
d
are secured to the outer periphery of the casing
501
. On the other hand, the collimator lenses
512
c
and
512
d
are secured inside the casing
501
. Pump light inputted from the polarization maintaining optical fibers
511
c
and
511
d
is emitted to the inside of the casing
501
through the collimator lenses
512
c
and
512
d.
The polarization maintaining optical fibers
511
c
and
511
d
are configured with birefringent optical fibers, each of which can transmit light at a wavelength of about 1.48 &mgr;m, for example, from a pumping light source not shown as linearly polarized light while maintaining a plane of polarization. The linearly polarized light that the polarization maintaining optical fibers
511
c
and
511
d
can propagate has electric field vectors pointing different directions. For example, the polarization maintaining optical fiber
511
c
propagates S wave, whereas the polarization maintaining optical fiber
511
d
propagates P wave.
The HR
507
totally reflects incident light, similarly to the HR
502
, which is secured so as to emit the pump light of S wave at a wavelength of 1.48 &mgr;m inputted from the polarized light collimator
510
c
toward the PBS
508
.
The PBS
508
has a property that a transmittance thereof is varied according to a plane of polarization (direction of vibration) of incident light, similarly to the PBS
503
. The PBS
508
totally transmits light of P wave (at a wavelength of 1.48 &mgr;m) from the polarized light synthesizing collimator
510
d
, while totally reflecting light of S wave (at a wavelength of 1.48 &mgr;m) from the polarized light synthesizing collimator
510
c.
The PBS
508
is secured so as to multiplex (polarization-synthesize) the pump light of S wave from the above polarized light synthesizing collima
Fujistsu Limited
Lee John D.
Song Sarah N
Staas & Halsey , LLP
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