Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-09-20
2001-03-20
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S245000, C359S246000
Reexamination Certificate
active
06204950
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical-fiber-amplifier measuring apparatus for measuring various characteristics of an optical fiber amplifier.
2. Description of the Related Art
FIG. 4
is a block diagram illustrating the configuration of a conventional apparatus for measuring an optical fiber amplifier in accordance with a probe method.
In
FIG. 4
, reference numerals
50
and
52
denote light sources. A light source whose wavelength is variable is generally used as the light source
52
. Meanwhile, a light source whose wavelength is fixed is generally used as the light source
50
.
The output light from the light source
50
and the output light from the light source
52
are multiplexed by a photocoupler
54
, and the multiplexed light is supplied to an acoustooptic modulator
56
.
In addition to the output light from the photocoupler
54
, a modulating signal, e.g., a low-frequency acoustic signal, is also inputted to the acoustooptic modulator
56
, but the illustration of an apparatus for outputting the acoustic signal and a detailed description thereof will be omitted herein.
The acoustooptic modulator
56
effects intensity modulation with respect to an optical signal which is inputted. The optical signal which is outputted after being subjected to predetermined intensity modulation by the acoustooptic modulator
56
is converted to two demultiplexed light beams with an optical power ratio of, for instance, 1:1 by a photocoupler
58
.
One of the demultiplexed light beams is inputted to an optical fiber amplifier to be measured (hereafter referred to as the subject optical fiber amplifier)
60
so as to be amplified with a predetermined gain.
The other demultiplexed light beam branched by the photocoupler
58
is inputted to one input terminal
63
a
of an optical switch
62
, while the optical signal outputted from the subject optical fiber amplifier
60
is inputted to the other input terminal
63
b
of the optical switch
62
.
The optical switch
62
selects either one of the optical signal inputted from the input terminal
63
a
and the optical signal inputted from the input terminal
63
b
, and outputs the same from an output terminal
63
c
. Under control by an unillustrated controller, the optical switch
62
selects either one of the optical signal inputted from the input terminal
63
a
and the optical signal inputted from the input terminal
63
b
, and outputs the same from the output terminal
63
c.
The optical signal outputted from the output terminal
63
c
of the optical switch
62
is inputted to an acoustooptic modulator
64
where the optical signal is subjected to predetermined intensity modulation and is outputted.
It should be noted that, in the same way as the above-described acoustooptic modulator
56
, in addition to the optical signal outputted from the optical switch
62
, a modulating signal, e.g., a low-frequency acoustic signal, is also inputted to the acoustooptic modulator
64
, but the illustration of an apparatus for outputting the acoustic signal and a detailed description thereof will be omitted herein.
Reference numeral
66
denotes an optical spectrum analyzer, which is used for measuring the optical power at the aforementioned portions. Further, numeral
68
denotes a reference optical power meter for calibrating the optical spectrum analyzer
66
.
Next, a description will be given of a method for measuring various characteristics of the optical fiber amplifier by the optical-fiber-amplifier measuring apparatus shown in FIG.
4
.
It should be noted that a description will be given here of a method of the various characteristics of the optical fiber amplifier in a case where light is outputted from light source
52
alone, so as to simplify the description.
The method for measuring various characteristics of the optical fiber amplifier by the configuration shown in
FIG. 4
is called a “pulse method”.
In the pulse method, signal optical power P
in
inputted to the subject optical fiber amplifier
60
, signal optical power P
out
after amplification by the subject optical fiber amplifier
60
, and power (power of an amplified spontaneous emission) P
ase
of spontaneously emitted light (ASE light) outputted from the subject optical fiber amplifier
60
are first measured by the optical spectrum analyzer
66
, respectively.
After completion of the measurement, a gain G and a noise figure NF of the subject optical fiber amplifier
60
are calculated on the basis of the signal optical power P
in
, the signal optical power P
out
, and the power P
ase
of the amplified spontaneous emission. The following Formulae (1) and (2) are used as formulae of this calculation:
G
=(
P
out
−P
ase
)/
P
in
(1)
NF
=(
P
ase
/h·&ggr;·G·&Dgr;&ggr;
)+(1
/G
) (2)
It should be noted that, in Formula (2) above, h represents a Planck's constant, &ggr; represents an optical frequency of the optical signal, and &Dgr;&ggr; represents a measurement resolution of the optical spectrum analyzer
66
.
FIGS.
5
(a)-
5
(b) are diagrams illustrating the phase relationship between the modulated signal from the acoustooptic modulator
56
and the modulated signal from the acoustooptic modulator
64
at the time of measurement of the aforementioned signal optical power P
in
and P
out
.
When measuring the signal optical power P
in
and P
out
, the output light from the light source
52
is amplified by the subject optical fiber amplifier
60
, and the power of each of the optical signals before the optical signal is inputted to the subject optical fiber amplifier
60
and after it is inputted thereto is measured. For this reason, the acoustooptic modulator
56
and the acoustooptic modulator
64
in terms of their phase relationship need to be set in the same phase.
Meanwhile, FIGS.
6
(a)-
6
(b) are diagrams illustrating the phase relationship between the modulated signal from the acoustooptic modulator
56
and the modulated signal from the acoustooptic modulator
64
at the time of measurement of the power P
ase
of the amplified spontaneous emission.
The power P
ase
of the amplified spontaneous emission is the power of a spontaneously emitted light component (continuous light) outputted by the subject optical fiber amplifier
60
.
Accordingly, to measure the power P
ase
of the amplified spontaneous emission, the subject optical fiber amplifier
60
needs to be set in a state in which an optical signal is not inputted to the subject optical fiber amplifier
60
. For this purpose, it suffices if the phase relationship between the modulated signal from the acoustooptic modulator
56
and the modulated signal from the acoustooptic modulator
64
is set such that their phases assume opposite phases, as shown in FIGS.
6
(a)-
6
(b), and it suffices if the power at a time when the optical signal is not being supplied to the subject optical fiber amplifier
60
is measured.
In addition, it is also necessary to effect evaluation by assuming a case where the wavelengths of the light are inputted to the subject optical fiber amplifier
60
after being multiplexed.
In this case, wavelength-division-multiplexing (WDM) signal light, in which wavelengths of light such as those shown in
FIG. 7
are multiplexed, is inputted as the light source
50
. Then, a light source whose wavelength is variable is used as the light source
52
.
FIG. 7
is a diagram illustrating an example of the configuration of light sources for generating WDM signal light.
The example shown in
FIG. 7
illustrates light sources for generating WDM signal light having four kinds of different central wavelengths.
In
FIG. 7
, reference
80
a
to
80
d
denote light sources for outputting optical signals with mutually different wavelengths &lgr;
1
-&lgr;
4
, Reference numerals
82
a
to
82
d
denote optical attenuators for attenuating the inputted light with predetermined attenuation indices.
The optical signals outputted from the light sources
80
a
to
80
d
are respectively inputted to their correspo
Ando Electric Co. Ltd.
Dang Hung Xuan
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
LandOfFree
Optical-fiber-amplifier measuring apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical-fiber-amplifier measuring apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical-fiber-amplifier measuring apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2460028