Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
2001-01-16
2003-03-18
Black, Thomas G. (Department: 3663)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S333000, C359S341100, C359S337100, C359S337110, C359S337130, C359S337200, C372S006000, C372S094000
Reexamination Certificate
active
06535331
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a wideband optical amplifier and a wideband variable wavelength optical source. More particularly, this invention relates to a wideband optical amplifier that can amplify optical signals with wavelengths ranging from 1.55 &mgr;m band (C-band: 1.53-1.565 &mgr;m) to 1.58 &mgr;m band (L-band: 1.565-1.60 &mgr;m) and a wideband variable wavelength optical source using such an optical amplifier.
BACKGROUND OF THE INVENTION
Optical communication systems and devices using optical fiber cables require wideband optical amplifiers and optical sources.
FIG. 1
shows an example of such a wideband optical amplifier in the conventional technology. This example is a wideband optical amplifier for amplifying optical signals ranging from C-band to L-band. The more details of which is shown in Japanese Patent Laid Open No. Hei 10-229238 and “Electron Letter, 33, pp 710, 1997, M. Yamada et. al.” This conventional example is briefly explained here with reference to FIG.
1
.
As shown in the block diagram of
FIG. 1
, the wideband optical amplifier is mainly comprised of a C-band optical amplifier
100
, an L-band optical amplifier
200
, an optical demultiplexer and an optical multiplexer. The wideband optical amplifier receives an input optical signal
10
s
and produces an output optical signal
62
s
by amplifying the input optical signal
10
s.
The C-band optical amplifier
100
includes a first optical isolator
11
, a first erbium doped optical fiber (EDF)
21
, a first pump light source
31
, a WDM (Wavelength Division Multiplexing) coupler
31
c
, and a second optical isolator
12
. The L-band optical amplifier
200
includes a third optical isolator
13
, a second pump light source
32
, a WDM coupler
32
c
, a second erbium doped optical fiber (EDF)
22
, a third pump light
33
, a WDM coupler
33
c
, and a fourth optical isolator
14
. In this example, the optical demultiplexer and optical multiplexer are a WDM coupler
61
and a WDM coupler
62
, respectively.
The input optical signal
10
s
provided to the WDM coupler (demultiplexer)
61
is divided into optical signals
10
s
1
, and
10
s
2
. The optical signal
10
s
, is supplied to the first optical isolator
11
in the C-band optical amplifier
100
and the optical signal
10
s
2
is supplied to the third optical isolator
13
in the L-band optical amplifier. Instead of the WDM coupler
61
, other type of optical demultiplexer or an optical switch may be used.
In the C-band optical amplifier, the first optical isolator
11
blocks the light moving in the opposite direction, i.e., backward scattering lights, and provides the input optical signal
11
s
to the first erbium doped optical fiber
21
. Thus, by the first optical isolator
11
, unwanted lights, such as pumping lights in a backward direction are blocked from travelling toward the input side.
The first erbium doped optical fiber
21
is used as an amplifying medium and has a fiber length optimized to amplify signals in the C-band. For instance, the first erbium doped optical fiber
21
has a fiber length of 20 m (meter) . The first erbium doped optical fiber
21
receives a pump light from the first pump light source
31
through the WDM coupler
31
c
. Based on a laser operation in the rare earth element (erbium) doped fiber, the first erbium doped optical fiber
21
amplifiers the input signal
11
s
by several ten dB, such as 20 dB or more, to produce an amplified optical signal
21
s
. The second optical isolator
12
receives the amplified optical signal and produces an optical signal
12
s
at its output. The second optical isolator
12
blocks lights propagating in the backward direction.
As noted above, the first pump light source
31
and the WDM coupler
31
c
provide the pump light to excite the first erbium doped optical fiber
21
. In this example, the pump light source
31
is placed at the back side of the first erbium doped optical fiber
21
so that the pump light travels in the backward direction (backward pumping).
In the L-band optical amplifier
200
, the third optical isolator
13
blocks the light moving in the opposite direction, i.e., backward scattering lights, and provides the input optical signal
14
s
to the second erbium doped optical fiber
22
through the WDM coupler
32
c
. By the third optical isolator
13
, unwanted lights, such as pumping lights in the backward direction are blocked from travelling toward the input side.
The L-band optical amplifier
200
works the same way as the C-band optical amplifier
100
. The second erbium doped optical fiber
22
is configured to have a fiber length most suitable for amplifying L-band optical signals. For example, the second erbium doped optical fiber
22
has a fiber length of 120 m (meter). As noted above, the second pump light source
32
is provided between the third optical isolator
13
and the second erbium doped optical fiber
22
. Further, the third pump light source
33
is provided between the fourth optical isolator
14
and the second erbium doped optical fiber
22
. Under this configuration, an L-band light signal can be amplified by several ten dB, for example, 20 dB or more.
As noted above, in order for the second erbium doped optical fiber
22
to amplify the L-band light signal, the length of the erbium doped optical fiber must be relatively long, for example, 120 m. Since the second erbium doped optical fiber
22
is long, it requires bidirectional pumping or high power pump lights to excite the optical fiber. In the example of
FIG. 1
, the pump light sources
32
and
33
are provided both the front side and back side of the second erbium doped optical fiber
22
(bidirectional pumping).
The WDM coupler (optical multiplexer)
62
is used for combining two input lights, from the C-band and L-band optical amplifiers, respectively, and producing a combined optical signal at its output. Namely, the WDM coupler
62
receives the C-band optical signal
12
s
from the C-band optical amplifier
100
and the L-band optical signal
13
s
from the L-band optical amplifier
200
and outputs a combined optical signal
62
s
. Instead of the WDM coupler
62
noted above, other type of optical multiplexer or an optical switch may be used.
As described in the foregoing with reference to
FIG. 1
, in the wideband optical amplifier ranging from the C-band to L-band, the optical signals passing through the optical isolators
11
and
13
, which limit the direction of the signals, are amplified by the erbium doped optical fibers
21
and
22
excited by the corresponding pump lights from the pump light sources
31
,
32
, and
33
. The amplified optical signals are output through the corresponding optical isolators
12
and
14
. In such an arrangement, it is known that the bandwidth or band of wavelengths of the optical amplifier can be controlled by varying the fiber length of the erbium doped optical fibers
21
and
22
and the intensity of the pump lights. For example, by increasing the fiber length of the erbium doped optical fibers, the wavelength of the signals to be amplified is increased.
As explained in the foregoing, in the conventional wideband optical amplifier of
FIG. 1
, for amplifying optical signals ranging from the C-band to L-band, several pump lights must be used. Further, the optical isolators are required at both the input side and the output side of each of the C-band and L-band amplifiers. Moreover, the optical demultiplexer and multiplexer are also necessary to divide and combine the light signals. Because the conventional optical amplifier requires many optical components, the amplifier involves a relatively large insertion loss as well as high cost. Moreover, the optical amplifier needs to have erbium doped optical fibers of considerable lengths. For example, as noted above, the optical amplifier includes both the first erbium doped optical fiber of 20 m for the C-band amplifier and the second erbium doped optical fiber of 120 m for the L-band amplifier.
SUMMARY OF THE INVENTION
It is, therefore, an object of the pr
Kanoh Eiji
Shiota Kazunori
Advantest Corp.
Black Thomas G.
Cunningham Stephen
Muramatsu & Associates
LandOfFree
Wideband optical amplifier and wideband variable wavelength... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wideband optical amplifier and wideband variable wavelength..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wideband optical amplifier and wideband variable wavelength... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3070531