U.S. patent application number 09/773613 was filed with the patent office on 2001-08-09 for optical amplifying device.
Invention is credited to Fuse, Masaru, Shiozaki, Toru.
Application Number | 20010012146 09/773613 |
Document ID | / |
Family ID | 26584824 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012146 |
Kind Code |
A1 |
Shiozaki, Toru ; et
al. |
August 9, 2001 |
Optical amplifying device
Abstract
An optical brancher 110 branches an input optical signal into
two. An optical detector 120 converts one optical signal branched
by the optical brancher 110 into an electrical signal. A first
controller 122 generates a control electrical signal having a
waveform obtained by inverting the envelope of the electrical
signal. Based on the control electrical signal, an optical signal
generator 124 produces a dummy optical signal having a waveform
.lambda.d and an amplitude .alpha./2. The other signal branched by
the optical brancher 110 is delayed by a delay unit 112 for a
predetermined time, and then multiplexed by an optical multiplexer
114 with the dummy optical signal from the optical signal generator
124. An optical amplifier 116 amplifies a multiplexed optical
signal. An optical filter 118 separates an optical signal of a
wavelength .lambda.1 from the amplified optical signal. Thus,
optical signal amplification can be carried out without optical
surges.
Inventors: |
Shiozaki, Toru; (Kobe,
JP) ; Fuse, Masaru; (Toyonaka, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
26584824 |
Appl. No.: |
09/773613 |
Filed: |
February 2, 2001 |
Current U.S.
Class: |
359/337 |
Current CPC
Class: |
H04B 10/296
20130101 |
Class at
Publication: |
359/337 |
International
Class: |
H01S 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 3, 2000 |
JP |
2000-26806 |
Apr 20, 2000 |
JP |
2000-118987 |
Claims
What is claimed is:
1. An optical amplifying device for amplifying an input optical
signal, said device comprising: control electrical signal
generating means for generating a control electrical signal having
a waveform obtained by inverting an envelope of said input optical
signal; light-emitting means for outputting, based on said control
electrical signal, a dummy optical signal having a wavelength that
is different from a wavelength of said input optical signal;
multiplex means for multiplexing said input optical signal and said
dummy optical signal; amplifying means for amplifying a multiplexed
optical signal; and separating means for separating at least said
input optical signal from an optical signal after amplification by
said amplifying means.
2. The optical amplifying device according to claim 1, wherein said
dummy optical signal is one-half in amplitude of said input optical
signal.
3. The optical amplifying device according to claim 1, further
comprising: branching means for branching said input optical signal
into two; and light receiving means for converting one branched
optical signal into an electrical signal, wherein said control
electrical signal generating means generates said control
electrical signal based on said electrical signal from said light
receiving means, and said multiplex means multiplexes another
optical signal branched by said branching means and said dummy
optical signal.
4. The optical amplifying device according to claim 1, wherein said
control electrical signal generating means is provided with an
electrical signal before converted into said input optical signal
and generates said control electrical signal based on said provided
electrical signal.
5. The optical amplifying device according to claim 3, further
comprising delay means for delaying said other branched optical
signal for a predetermined time.
6. The optical amplifying device according to claim 4, further
comprising delay means for delaying, before input to said multiplex
means, said input optical signal for a predetermined time.
7. The optical amplifying device according to claim 1, wherein said
amplifying means is an optical fiber amplifier.
8. The optical amplifying device according to claim 1, wherein said
input optical signal is a burst optical signal.
9. An optical amplifying device for amplifying an input optical
signal, said device comprising: light-emitting means for
transmitting said input optical signal and emitting, based on said
optical signal transmitted by said light-emitting means, a dummy
optical signal having a waveform obtained by inverting a waveform
of said input optical signal and having a wavelength that is
different from a wavelength of said input optical signal; control
means for controlling the wavelength of said dummy optical signal
emitted from said light-emitting means; amplifying means for
amplifying said optical signal and said dummy optical signal
transmitted from said light-emitting means; and separating means
for separating said input optical signal from an optical signal
after amplification.
10. The optical amplifying device according to claim 9, wherein
said dummy optical signal is equal in amplitude to said input
optical signal.
11. The optical amplifying device according to claim 9, wherein
said control means controls the wavelength and an amplitude of said
dummy optical signal emitted from said light-emitting means.
12. The optical amplifying device according to claim 9, wherein
said separating means separates said input optical signal and said
dummy optical signal individually.
13. The optical amplifying device according to claim 12, wherein
said control means carries out feedback control of said
light-emitting means based on the dummy optical signal separated by
said separating means.
14. The optical amplifying device according to claim 12, wherein
said control means controls the wavelength and an amplitude of said
dummy optical signal emitted from said light-emitting means, and
carries out feedback control of said light-emitting means based on
the dummy optical signal separated by said separating means.
15. The optical amplifying device according to claim 9, wherein
said separating means collectively separates said input optical
signal and said dummy optical signal.
16. The optical amplifying device according to claim 15, wherein
said separating means is an optical router with an AWG (Arrayed
Wave Guide) structure.
17. The optical amplifying device according to claim 9, wherein
said light-emitting means is a distributed Bragg ref lector (DBR)
type semiconductor laser.
18. The optical amplifying device according to claim 9, wherein
said input optical signal is a burst optical signal.
19. An optical transmission system for amplifying and transmitting
an input optical signal, said system comprising: light-emitting
means for transmitting said input optical signal, and emitting,
based on said transmitted input optical signal, a dummy optical
signal having a waveform obtained by inverting a waveform of said
input optical signal and having a wavelength that is different from
a wavelength of said input optical signal; control means for
controlling the waveform of said dummy optical signal emitted by
said light-emitting means; first amplifying means for amplifying an
optical signal from said light-emitting means; first separating
means for collectively separating said input optical signal and
said dummy optical signal from an optical signal after
amplification by said first amplifying means; second amplifying
means for amplifying an optical signal composed of said input
optical signal and said dummy optical signal collectively separated
by said first separating means; and second separating means for
separating at least said input optical signal from an optical
signal after amplification by said second amplifying means.
20. An optical amplifying method for amplifying an input optical
signal, said method comprising the steps of: generating a control
electrical signal having a waveform obtained by inverting an
envelope of said input optical signal; outputting, based on said
control electrical signal, a dummy optical signal having a
wavelength that is different from a wavelength of said input
optical signal; multiplexing said input optical signal and said
dummy optical signal; amplifying a multiplexed optical signal; and
separating at least said input optical signal from an optical
signal after amplification.
21. An optical amplifying method for amplifying an input optical
signal, said method comprising the steps of: transmitting said
input optical signal, and emitting, based on said transmitted input
optical signal, a dummy optical signal having a waveform obtained
by inverting a waveform of said input optical signal and having a
wavelength that is different from a wavelength of said input
optical signal; collectively amplifying said transmitted input
optical signal and said emitted dummy optical signal; and
separating said input optical signal from an optical signal after
amplification.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to optical amplifying devices
for amplifying an input optical signal and, more specifically, to
an optical amplifying device suitable for use in amplifying a burst
optical signal.
[0003] 2. Description of the Background Art
[0004] As well known, when intermittently-inputted optical signals
(hereinafter referred to as burst optical signals) are amplified
through a general optical fiber amplifier, for example, waveform
degradation, called optical surges, occurs in the optical signals.
Optical surges are now briefly described with reference to the
accompanying drawings.
[0005] Optical surges are caused by transient response of optical
amplifiers. How much the input optical signal is degraded in
waveform depends on the characteristics of the optical amplifier,
such as a relaxation time constant. Waveform degradation also
depends on the input optical signal itself. As the input light
varies in power, the waveform becomes degraded.
[0006] FIG. 18a shows the waveform of an optical signal when the
amount of data traffic is small and data is intermittently
transmitted, such as a case where data packets are spaced long. If
such burst optical signal as shown in FIG. 18a is provided to an
optical amplifier, temporary periods during which no data is
provided at all are observed, which are hereinafter referred to as
no-data period. If an optical signal is provided after a long
no-data period, input light optical power varies. Therefore, as
shown in FIG. 18b, the optical signal after amplification is
instantaneously increased in level (optical surges), thereby
causing degradation in waveform.
[0007] Such waveform degradation in a transmission system makes it
difficult for a receiving side to always optimally identify data.
Thus, optical surges have to be suppressed. From this viewpoint,
one optical amplifying device capable of carrying out optical
amplification while suppressing optical surges is disclosed in
Japanese Patent Laid-Open Publication No. 11-135862 (1999-135862).
This conventional optical amplifying device (hereinafter referred
to as conventional device) is described below with reference to the
drawings.
[0008] As shown in FIG. 19, a conventional device 9000 is provided
with an input optical signal of a wavelength .lambda.1 as shown in
FIG. 20a. The provided optical signal is branched into two by an
optical brancher 910. One branched optical signal goes through an
optical receiver 920, an inverting amplifier 940, and a light
source 924, thereby being converted into an optical signal of a
wavelength .lambda.d with its logic level inverted, as shown in
FIG. 20b. Then, the converted optical signal is multiplexed with
the other optical signal branched by the optical brancher 910. The
optical signal after such multiplexing is constant in optical
power, as shown in FIG. 20c.
[0009] The optical signal after multiplexing is amplified by an
optical fiber amplifier 916. At this time, optical surges do not
occur since the input light is constant in optical power. The
amplified optical signal is provided to an optical filter 918,
wherein the optical signal of the wavelength .lambda.1 is passed
through.
[0010] As such, according to the conventional device 9000, the
input optical signal is superposed with a dummy optical signal
differed in wavelength. Thus, the input light provided to the
amplifier 916 can become temporarily constant in optical power. In
this way, optical amplification can be carried while optical surges
are suppressed.
[0011] As stated above, in the conventional device, the input
optical signal is superposed with the dummy optical signal, and
then provided to the amplifier. Therefore, the optical signal
provided to the amplifier becomes larger in optical power on
average than the input optical signal. In general, amplification
gain of the amplifier varies according to the average optical power
of the optical signal provided to the amplifier. The larger the
optical power of the input light is, the less the amplification
gain is. Therefore, in the conventional device, the amplification
gain of the amplifier is disadvantageouly reduced.
[0012] Moreover, the conventional device has to accurately detect
data provided at a higher bit rate such as 10 gigabits/second for
logic level inversion. Accordingly, the electrical load on the
conventional device is increased. This increase leads to a
degradation in device's performance and an increase in cost.
[0013] Also, a large number of components are required for the
conventional device. Thus, the conventional device is complex in
structure.
SUMMARY OF THE INVENTION
[0014] Therefore, one object of the present invention is to provide
an optical amplifying device capable of carrying out optical
amplification while suppressing optical surges and also preventing
reduction in amplification gain of an amplifier. A further object
of the present invention is to provide an optical amplifying device
capable of carrying out optical amplification while suppressing
optical surges without requiring a large-load electrical process. A
still further object of the present invention is to provide an
optical amplifying device capable of carrying out optical
amplification while suppressing optical surges in a simple
structure.
[0015] The present invention has the following features to achieve
the objects above.
[0016] A first aspect of the present invention is directed to an
optical amplifying device for amplifying an input optical signal,
the device comprising:
[0017] a control electrical signal generator for generating a
control electrical signal having a waveform obtained by inverting
an envelope of the input optical signal;
[0018] a light-emitter for outputting, based on the control
electrical signal, a dummy optical signal having a wavelength that
is different from a wavelength of the input optical signal;
[0019] a multiplexer for multiplexing the input optical signal and
the dummy optical signal;
[0020] an amplifier for amplifying a multiplexed optical signal;
and
[0021] a separator for separating at least the input optical signal
from an optical signal after amplification by the amplifier.
[0022] As described above, in the first aspect, the input optical
signal is multiplexed with the dummy optical signal having a
waveform obtained by inverting the envelope of the input optical
signal. Thus, optical amplification can be carried out without
waveform degradation.
[0023] A second aspect of the present invention is directed to an
optical amplifying device for amplifying an input optical signal,
the device comprising:
[0024] a light-emitter for transmitting the input optical signal,
and emitting, based on the optical signal transmitted by the
light-emitter, a dummy optical signal having a waveform obtained by
inverting a waveform of the input optical signal and having a
wavelength that is different from a wavelength of the input optical
signal;
[0025] a controller for controlling the wavelength of the dummy
optical signal emitted from the light-emitter;
[0026] an amplifier for amplifying the optical signal and the dummy
optical signal from the light-emitter; and
[0027] a separator for separating the input optical signal from an
optical signal after amplification.
[0028] As described above, in the second aspect, by being
transmitted through the light-emitter, the optical signal is
multiplexed with the dummy optical signal having the waveform
obtained by inverting the waveform of the input optical signal.
Thus, optical amplification can be carried out in a more simplified
structure without optical surges.
[0029] These and other objects, features, aspects and advantages of
the present invention will become more apparent from the following
detailed description of the present invention when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a block diagram showing the structure of an
optical amplifying device 1000 according to a first embodiment of
the present invention;
[0031] FIGS. 2a to 2d are diagrams showing waveforms of optical
signals in the optical amplifying device 1000;
[0032] FIGS. 3a and 3b are diagrams in assistance of explaining the
operation of an optical filter 118;
[0033] FIG. 4 is a block diagram showing the structure of a system
using an optical amplifying device 1500, which is one modification
of the optical amplifying device 1000;
[0034] FIG. 5 is a block diagram showing the structure of an
optical amplifying device 2000 according to a second embodiment of
the present invention;
[0035] FIGS. 6a to 6d are diagrams showing waveforms of optical
signals in the optical amplifying device 2000;
[0036] FIG. 7 is a block diagram showing the structure of an
optical amplifying device 3000 according to a third embodiment of
the present invention;
[0037] FIGS. 8a to 8d are diagrams showing waveforms of optical
signals in the optical amplifying device 3000;
[0038] FIG. 9 is a block diagram showing the structure of an
optical amplifying device 4000 according to a fourth embodiment of
the present invention;
[0039] FIGS. 10a and 10b are diagrams showing waveforms of optical
signals in the optical amplifying device 4000;
[0040] FIG. 11 is a block diagram showing the structure of an
optical amplifying device 5000 according to a fifth embodiment of
the present invention;
[0041] FIGS. 12a to 12c are diagrams showing waveforms of optical
signals in the optical amplifying device 5000;
[0042] FIGS. 13a and 13b are diagrams in assistance of explaining
the operation of a first optical router 536;
[0043] FIG. 14 is a block diagram showing the structure of an
optical transmission system using the optical amplifying device
5000;
[0044] FIG. 15 is a block diagram showing the structure of an
optical amplifying device 6000 according to a sixth embodiment of
the present invention;
[0045] FIG. 16 is a block diagram showing the structure of an
optical transmission system according to a seventh embodiment of
the present invention;
[0046] FIGS. 17a and 17b are diagrams in assistance of explaining
the operation of a second optical router 736;
[0047] FIGS. 18a and 18b are diagrams in assistance of explaining
optical surges that occur when a burst optical signal is
amplified;
[0048] FIG. 19 is a block diagram showing the structure of a
conventional optical amplifying device 9000; and
[0049] FIGS. 20a to 20c are diagrams showing waveforms of optical
signals in the conventional optical amplifying device 9000.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] The embodiments of the present invention are described below
with reference to the drawings.
[0051] (First Embodiment)
[0052] FIG. 1 is a block diagram showing the structure of an
optical amplifying device according to a first embodiment of the
present invention. An optical amplifying device 1000 includes an
optical brancher 110, a delay unit 112, an optical multiplexer 114,
an optical amplifier 116, an optical filter 118, an optical
detector 120, a first controller 122, and an optical signal
generator 124. With reference to FIGS. 1, 2a to 2d, 3a, and 3b, the
operation of the optical amplifying device according to the present
embodiment is now described.
[0053] The optical amplifying device 1000 is provided with an input
optical signal having a waveform .lambda.1 and an amplitude
.alpha.. This optical signal carries burst-like binary digital
data. FIG. 2a shows the waveform of this optical signal. In FIG.
2a, A period during which binary digital data is carried on the
optical signal is referred to as a data period, while a period
during which no binary digital data is carried thereon is referred
to as a no-data period. A dotted line indicates an envelope of the
optical signal.
[0054] The optical brancher 110 branches the received optical
signal into two. The optical detector 120 converts one optical
signal outputted from the optical brancher 110 into an electrical
signal. The first controller 122 generates a control electrical
signal having a waveform obtained by inverting the envelope of the
electrical signal. Based on this control electrical signal, the
optical signal generator 124 produces a dummy optical signal having
a waveform .lambda.d and an amplitude .alpha./2. FIG. 2b shows the
waveform of the dummy optical signal.
[0055] On the other hand, the other optical signal outputted from
the optical brancher 110 is delayed by the delay unit 112 for a
predetermined time, and then forwarded to the optical multiplexer
114. Here, the predetermined time is a time required for the one
optical signal outputted from the optical brancher 110 to go
through the optical detector 120, the first controller 122, and
then the optical signal generator 124 to become the dummy optical
signal. The optical multiplexer 114 multiplexes the optical signal
from the delay unit 112 and the dummy optical signal from the
optical signal generator 124 together, and then produces a
multiplexed optical signal. FIG. 2c shows the waveform of the
multiplexed optical signal.
[0056] The optical amplifier 116 amplifies the multiplexed optical
signal. At this time, as shown in FIG. 2c, the multiplexed optical
signal is always at .alpha./2 in level during the no-data periods
during which transmission data does not exist, and also at
.alpha./2 in average during the data periods during which
transmission data exists. Therefore, the optical signal provided to
the optical amplifier 116 is approximately constant in optical
power, and is not degraded in waveform when amplified.
[0057] The optical filter 118 has such a transmittance
characteristic as shown in FIG. 3a to separate the optical signal
of the wavelength .lambda.1 from the amplified optical signal
having a spectrum as shown in FIG. 3b. FIG. 2d shows the waveform
of the passed optical signal.
[0058] As described above, in the first embodiment, the optical
signal having the wavelength .lambda.1 and the amplitude a to be
amplified is multiplexed with the dummy optical signal having the
wavelength .lambda.d (.noteq..lambda.1) and the amplitude .alpha./2
obtained by inverting the envelope of the input optical signal.
Thus, optical amplification can be carried out without waveform
degradation. Furthermore, the average optical power of the optical
signal provided to the optical amplifier 116 is cut in half,
compared with that in the conventional device as shown in FIG. 19.
Therefore, higher amplification gain can be achieved. Still
further, the control electrical signal outputted from the first
controller 122 is generated based on the envelope of the input
optical signal. Thus, the present optical amplifying device is less
electrically loaded than the conventional device shown in FIG.
19.
[0059] In the present embodiment, the dummy optical signal is
one-half in amplitude of the input optical signal, but is not
necessarily restricted to the above. For making the optical power
to the optical amplifier 116 more constant, however, one-half the
amplitude of the input optical signal is preferable, as in the
present embodiment.
[0060] Furthermore, in the present embodiment, the input optical
signal is a burst optical signal. Alternatively, an arbitrary
optical signal can be amplified.
[0061] Still further, in the present embodiment, the input optical
signal has a single wavelength, that is, only the wavelength
.lambda.1. Similarly, if optical signals with different wavelengths
.lambda.1 to .lambda.n are provided in a time-division manner, for
example, these optical signals can be amplified without degradation
in waveform. In this case, however, the wavelength .lambda.d of the
dummy optical signal has to be different from any of the
wavelengths .lambda.1 to .lambda.n.
[0062] Still further, in the present embodiment, the optical filter
118 is used for the purpose of separating the optical signal of the
wavelength .lambda.1 from the amplified optical signal.
Alternatively, an optical router may be used to achieve the same
purpose.
[0063] In the present embodiment, the input optical signal is
converted by the optical detector 120 into an electrical signal,
and the control electrical signal is generated by the first
controller 122 based on this electrical signal. Alternatively, for
example, the control electrical signal may be generated based on an
electrical signal to be carried on the input optical signal. Such
modification example of the present embodiment is briefly described
with reference to FIG. 4. In FIG. 4, components identical in
structure to those in FIG. 1 are provided with the same reference
numerals.
[0064] In FIG. 4, a data unit 10 produces an electrical signal
carrying burst-like binary digital data. This electrical signal is
converted by an optical signal generator 20 into an optical signal
having a wavelength .lambda.1. The optical signal is provided to an
optical amplifying device 1500 as the input optical signal.
[0065] The electrical signal from the data unit 10 is also provided
to the first controller 122 in the optical amplifying device 1500.
As in the optical amplifying device 1000 shown in FIG. 1, the first
controller 122 provides the optical signal generator 124 with a
control electrical signal having a waveform obtained by inverting
the waveform of the electrical signal.
[0066] The optical signal generator 124 generates a dummy optical
signal based on the control electrical signal. The optical
multiplexer 124 multiplexes the input optical signal coming through
the delay unit 112 and the dummy optical signal together.
Thereafter, the operation of the optical amplifying device 1500 is
the same as that of the optical amplifying device 1000 shown in
FIG. 1, and therefore not described herein. As such, in the optical
amplifying device 1500 according to this modification example, the
same effects can be achieved as those in the optical amplifying
device 1000 shown in FIG. 1.
[0067] (Second embodiment)
[0068] FIG. 5 is a block diagram showing the structure of an
optical amplifying device according to a second embodiment of the
present invention. An optical amplifying device 2000 includes the
optical brancher 110, the delay unit 112, the optical multiplexer
114, the optical amplifier 116, the optical filter 118, a logic
level determination unit 226, a second controller 228, and the
optical signal generator 124. Note that, in FIG. 5, components
identical in structure to those in FIG. 1 are provided with the
same reference numerals. With reference to FIGS. 5 and 6a to 6d,
the operation of the optical amplifying device according to the
second embodiment is described below.
[0069] The optical amplifying device 2000 is provided with an input
optical signal having a waveform .lambda.1 and an amplitude
.alpha.. This optical signal carries burst-like binary digital
data. FIG. 6a shows the waveform of this optical signal. In FIG.
6a, a period during which binary digital data is carried on the
optical signal is referred to as a data period, while a period
during which no binary digital data is carried thereon is referred
to as a no-data period.
[0070] The optical brancher 110 branches the received optical
signal into two. The logic level determination unit 226 determines
the level of the binary digital data carried on one optical signal
outputted from the optical brancher 110. The second controller 228
generates a control electrical signal based on a determination made
by the logic level determination unit 226. This control electrical
signal becomes .alpha./2 in level from 0, for example, when the
logic level determination unit 226 determines that the value of the
digital data continuously indicates 0 for more than a predetermined
time A1, and returns to "0" when the value of the digital data
becomes 1. The time A1 is predetermined based on physical
characteristics of the optical amplifier 116, such as a relaxation
time constant, and other factors. Based on this control electrical
signal, the optical signal generator 124 produces a dummy optical
signal having the wavelength .lambda.d and the amplitude .alpha./2.
FIG. 6b shows the waveform of this dummy optical signal.
[0071] On the other hand, the other optical signal outputted from
the optical brancher 110 is delayed by the delay unit 112 for a
predetermined time, and then forwarded to the optical multiplexer
114 Here, the predetermined time is a time required for the one
optical signal outputted from the optical brancher 110 to go
through the logic level determination unit 226, the second
controller 228, and then the optical signal generator 124 to become
the dummy optical signal. The optical multiplexer 114 multiplexes
the optical signal from the delay unit 112 and the dummy optical
signal from the optical signal generator 124 together, and then
produces a multiplexed optical signal. FIG. 6c shows the waveform
of the multiplexed optical signal.
[0072] The effects of optical surges that occur when the input
optical signal is changed in level from 0 to a become larger as the
period at the level 0 before the change is longer. Therefore, if
the no-data period continues for more than the predetermined time
A1, the input optical signal is multiplexed with the dummy optical
signal so that the no-data period of the multiplexed optical signal
provided to the optical amplifier 116 does not continue for more
than the time Al. Thus, the effects of optical surges at
amplification can be suppressed within a permissible range.
[0073] The optical amplifier 116 amplifies the multiplexed optical
signal. At this time, as shown in FIG. 6c, a period during which
the multiplexed optical signal is at the "0" level is, at most, the
time A1.
[0074] After amplification, similarly to the first embodiment, the
optical filter 118 separates the optical signal having the
wavelength .lambda.1 from the amplified optical signal. FIG. 6d
shows the waveform of the separated optical signal.
[0075] As described above, according to the second embodiment, the
no-data period of the multiplexed optical signal provided to the
optical amplifier 116 is controlled so as to become, at most, the
time A1. Thus, the effects of optical surges at amplification can
be suppressed within a permissible range. Moreover, the average
optical power of the optical signal provided to the optical
amplifier 116 is smaller than that in the conventional device shown
in FIG. 19. Thus, more amplification gain can be obtained.
[0076] (Third Embodiment)
[0077] FIG. 7 is a block diagram showing the structure of an
optical amplifying device according to a third embodiment of the
present invention. An optical amplifying device 3000 includes the
optical brancher 110, the delay unit 112, the optical multiplexer
114, the optical amplifier 116, the optical filter 118, the logic
level determination unit 226, a third controller 330, and the
optical signal generator 124. Note that, in FIG. 7, components
identical in structure to those shown in FIG. 5 are provided with
the same reference numerals. With reference to FIGS. 7 and 8a to
8d, the operation of the optical amplifying device according to the
third embodiment is described below.
[0078] The optical amplifying device 3000 is provided with an input
optical signal having a waveform .lambda.1 and an amplitude
.alpha.. This optical signal carries burst-like binary digital
data. FIG. 8a shows the waveform of this optical signal.
[0079] The optical brancher 110 branches the received optical
signal in two. The logic level determination unit 226 determines
the level of the binary digital data carried on one optical signal
outputted from the optical brancher 110. The third controller 330
generates a control electrical signal based on a determination made
by the logic level determination unit 226. The generated control
electrical signal has pulses with the amplitude a and a width A2,
for example. Every time when the logic level determination unit 226
determines that the value of the data continuously indicates "0"
for more than the predetermined time A1, the pulse is outputted.
The time A1 is predetermined based on a relaxation time constant of
the optical amplifier 116 and other factors. Based on this control
electrical signal, the optical signal generator 124 produces a
dummy optical signal having the wavelength .lambda.d. FIG. 8b shows
the waveform of this dummy optical signal.
[0080] On the other hand, the other optical signal outputted from
the optical brancher 110 is delayed by the delay unit 112 for a
predetermined time, and then forwarded to the optical multiplexer
114. Here, the predetermined time is a time required for the one
optical signal outputted from the optical brancher 110 to go
through the logic level determination unit 226, the third
controller 330, and then the optical signal generator 124 to become
the dummy optical signal. The optical multiplexer 114 multiplexes
the optical signal from the delay unit 112 and the dummy optical
signal from the optical signal generator 124 together, and then
produces a multiplexed optical signal. FIG. 8c shows the waveform
of the multiplexed optical signal.
[0081] The effects of optical surges that occur when the input
optical signal is changed in level from 0 to a become larger as the
period at the level 0 before the change is longer. Therefore, if
the no-data period continues for more than the predetermined time
A1, the input optical signal is multiplexed with the dummy optical
signal so that the no-data period of the multiplexed optical signal
provided to the optical amplifier 116 does not continue for more
than the time A1. Thus, the effects of optical surges at
amplification can be suppressed within a permissible range.
[0082] The optical amplifier 116 amplifies the multiplexed optical
signal. At this time, as shown in FIG. 8c, a period during which
the multiplexed optical signal is at the "0" level is, at most, the
time A1.
[0083] After amplification, similarly to the first embodiment, the
optical filter 118 separates the optical signal of the wavelength
.lambda.1 from the amplified optical signal. FIG. 8d shows the
waveform of the separated optical signal.
[0084] In the present embodiment, the pulse width A2 is fixed, but
may be variable if, for example, the pulses of the dummy optical
signal overlap with the data period of the input optical signal. In
such case, pulses are changed to be shorter in width for preventing
the overlapping.
[0085] As described above, according to the third embodiment, the
no data period of the multiplexed optical signal provided to the
optical amplifier 116 is controlled so as to become the time A1 at
most. Thus, the effects of optical surges at amplification can be
suppressed within a permissible range. Moreover, the average
optical power of the optical signal provided to the optical
amplifier 116 is significantly smaller than that in the
conventional device shown in FIG. 19. Thus, more amplification gain
can be obtained.
[0086] Note that, in the second and third embodiments, the input
optical signal is a burst optical signal. Alternatively, similarly
to the case in the first embodiment, an arbitrary optical signal
can be amplified.
[0087] Furthermore, in the second and third embodiments, the input
optical signal has a single wavelength, that is, only the
wavelength .lambda.1. Similarly, if optical signals with different
wavelengths .lambda.1 to .lambda.n are provided in a time-division
manner, for example, these optical signals can be amplified without
degradation in waveform. In this case, however, the wavelength
.lambda.d of the dummy optical signal has to be different from any
of the wavelengths .lambda.1 to .lambda.n.
[0088] Still further, in the second and third embodiments, the
optical filter 118 is used for the purpose of separating the
optical signal of the wavelength .lambda.1 from the amplified
optical signal. Alternatively, an optical router may be used to
achieve the same purpose.
[0089] Still further, in the second and third embodiments, based on
the determination made by the logic level determination unit 226,
the second and third controller 228 and 330 generate the control
electrical signal. Alternatively, for example, the control
electrical signal may be generated based on an electrical signal to
be carried on the input optical signal.
[0090] (Fourth Embodiment)
[0091] FIG. 9 is a block diagram showing the structure of an
optical amplifying device according to a fourth embodiment of the
present invention. An optical amplifying device 4000 includes a
semiconductor laser 432, a controller 434, the optical amplifier
116, and the optical filter 118. Note that, in FIG. 9, components
identical in structure to those shown in FIG. 1 are provided with
the same reference numerals. With reference to FIGS. 9, 10a, and
10b, the operation of the optical amplifying device according to
the present embodiment is now described.
[0092] The optical amplifying device 4000 is provided with an input
optical signal having a waveform .lambda.1. This optical signal
carries burst-like binary digital data. FIG. 10a shows the waveform
of this optical signal.
[0093] The semiconductor laser 432 is controlled by the controller
434 so as to produce an optical signal having a wavelength
.lambda.d and identical in amplitude of the received optical signal
having the wavelength .lambda.1. The semiconductor laser 432 is
implemented as a distributed Bragg reflector (DBR) type
semiconductor laser, for example. Such semiconductor laser has
characteristics of, when an optical signal having a wavelength
different from that of the semiconductor laser is externally
provided thereto, suppressing oscillation thereof and transmitting
this externally-provided optical signal.
[0094] In other words, while the input light with wavelength
.lambda.1 to the semiconductor laser 432 is 0 in optical power,
that is, while the optical power is 0 during both of the data and
no-data periods shown in FIG. 10a, the semiconductor laser 423
produces an optical signal of predetermined power having a
wavelength .lambda.d under the control of the controller 434. On
the other hand, while the input light to the semiconductor laser
432 is not 0 in optical power, the semiconductor laser 432 is
suppressed in oscillation in response to the optical power.
Therefore, the waveform of the optical signal having the wavelength
.lambda.d outputted from the semiconductor laser 432 becomes the
inverted one of the input light, as shown in FIG. 10b. This optical
signal of the wavelength .lambda.d corresponds to the dummy optical
signal in the above-described conventional device and optical
amplifying device according to the first embodiment.
[0095] From the semiconductor laser 432, the light of the
wavelength .lambda.1 transmitted therethrough and the above-stated
dummy optical signal of the wavelength .lambda.d are both
outputted. As stated above, the light and the dummy optical signal
are inverted in waveform to each other. Therefore, the light
outputted from the semiconductor laser 432 is constant in optical
power.
[0096] The light outputted from the semiconductor laser 432 is
amplified by the optical amplifier 116. At this time, the light
provided to the optical amplifier 116 is approximately constant in
optical power, and therefore optical surges do not occur. After
amplification, the optical filter 118 passes the optical signal of
the wavelength .lambda.1.
[0097] As described above, in the fourth embodiment, the optical
signal of the wavelength .lambda.1 to be amplified is provided to
the semiconductor laser 432 oscillating with the wavelength
.lambda.d that is different from the wavelength .lambda.1. Thus, an
optical signal constant in optical power and composed of the input
optical signal superposed with the dummy signal is produced.
Therefore, the optical amplifying device capable of carrying out
optical amplification without degradation in waveform can be
achieved in a more simplified structure, compared with the
above-described conventional device and the optical amplification
device according to the first embodiment.
[0098] In the present embodiment, the input optical signal is a
burst optical signal. Alternatively, an arbitrary optical signal
can be amplified.
[0099] Furthermore, in the present embodiment, the input optical
signal has a single wavelength, that is, only the wavelength
.lambda.1. Similarly, if optical signals with different wavelengths
.lambda.1 to .lambda.n are provided in a time-division manner, for
example, these optical signals can be amplified without degradation
in waveform. In this case, however, the wavelength .lambda.d of the
dummy optical signal has to be different from any of the
wavelengths .lambda.1 to .lambda.n.
[0100] Still further, in the present embodiment, the optical filter
118 is used for the purpose of separating the optical signal of the
wavelength .lambda.1 from the amplified optical signal.
Alternatively, an optical router may be used to achieve the same
purpose. If the optical router is used, the dummy optical signal
may be used for data transmission or feedback control. Described
below are modification examples according to the present
embodiment, as fifth and sixth embodiments.
[0101] (Fifth Embodiment)
[0102] FIG. 11 is a block diagram showing the structure of an
optical amplifying device according to the fifth embodiment of the
present invention. An optical amplification device 5000 includes
the semiconductor laser 432, the controller 434, the optical
amplifier 116, and a first optical router 536. Note that, in FIG.
11, components identical in structure to those in FIG. 9 are
provided with the same reference numerals. With reference to FIGS.
11 and 12a to 12c, the operation of the optical amplifying device
according to the present embodiment is now described. Note that the
fifth embodiment is different from the fourth only in that the
first optical router 536 is provided instead of the optical filter
118. Therefore, the other components are not described in detail
herein.
[0103] The optical amplifying device 5000 is provided with an input
optical signal having a waveform .lambda.1. FIG. 12a shows the
waveform of this optical signal. Similarly to the fourth
embodiment, the optical signal transmitted through the
semiconductor that oscillates with a wavelength .lambda.d is
multiplexed with a dummy optical signal of the wavelength
.lambda.d, and then amplified by the optical amplifier 116.
[0104] The amplified optical signal is provided to the first
optical filter 536. The first optical filter 536 has first and
second output ports each having transmittance characteristics as
shown in FIG. 13a. Out of the amplified optical signal having a
spectrum shown in FIG. 13b, the first optical router 536 outputs
the optical signal of the wavelength .lambda.1 from the first
output port and the dummy optical signal of the wavelength
.lambda.d from the second output port. FIG. 12b shows the waveform
of the optical signal outputted from the first output port, while
FIG. 12c shows that of the optical signal outputted from the second
output port.
[0105] As evident from FIGS. 12b and 12c, the optical signals
outputted from the first and second output ports are inverted in
waveform, but these signals carry the same information. Therefore,
by transmitting both of the optical signals, the information
identical to that carried on the input optical signal can be
transmitted.
[0106] As such, in the fifth embodiment, not only the optical
signal of the wavelength .lambda.1 to be amplified but also the
dummy optical signal of the wavelength .lambda.d is used for data
transmission. Thus, the generated optical signals can be utilized
more effectively.
[0107] In the present embodiment, the input optical signal is a
burst optical signal. Alternatively, an arbitrary optical signal
can be amplified.
[0108] Furthermore, in the present embodiment, the input optical
signal has a single wavelength, that is, only the wavelength
.lambda.1. Similarly, if optical signals with different wavelengths
.lambda.1 to .lambda.n are provided in a time-division manner, for
example, these optical signals can be amplified without degradation
in waveform. In this case, however, the wavelength .lambda.d of the
dummy optical signal has to be different from any of the
wavelengths .lambda.1 to .lambda.n.
[0109] In the present embodiment, the first optical router 536 has
two output ports. Alternatively, the first optical router 536 may
have three or more output ports for outputting lights of the
wavelengths .lambda.1 to .lambda.n and .lambda.d.
[0110] Here, consider a case where the optical amplifying device
5000 according to the present embodiment is used to construct a
system as shown in FIG. 14. If a distance L1 between the optical
amplifying device 5000 and a first optical receiver 30 is different
from a distance L2 between the optical amplifying device 5000 and a
second optical receiver 32, optical signals of wavelengths
.lambda.1 and .lambda.d both outputted from the optical amplifying
device 5000 are disadvantageously differed in transmission
characteristic (S/N ratio), even though they are identical in
amplitude.
[0111] To get around the above problem, if the distance L1 is
longer than the distance L2, the controller 434 controls the dummy
optical signal of the wavelength .lambda.d outputted from the
semiconductor laser 432 to be smaller in amplitude than the optical
signal of the wavelength .lambda.1 to be amplified. Thus, the same
transmission characteristics can be observed in these optical
signals and, by extension, in the system as a whole.
[0112] (Sixth Embodiment) FIG. 15 is a block diagram showing the
structure of an optical amplifying device according to the sixth
embodiment of the present invention. An optical amplifying device
6000 includes the semiconductor laser 432, the controller 434, the
optical amplifier 116, and the first optical router 536. Note that,
in FIG. 15, components identical in structure to those shown in
FIG. 11 are provided with the same reference numerals. With
reference to FIG. 15, the operation of the optical amplifying
device according to the present embodiment is now described. The
optical amplifying device according to the sixth embodiment is
different from that according to the fifth only in that the optical
signal of the wavelength .lambda.d outputted from the first optical
router 536 is used not for transmission but for control of the
output light from the semiconductor laser 432. Therefore, the other
components are not described in detail herein.
[0113] The optical signal of the wavelength .lambda.d outputted
from the first optical router 536 in a manner similar to that in
the fifth embodiment is provided to the controller 434. The
controller 434 monitors this optical signal to control the
semiconductor laser 432 so that the oscillation wavelength thereof
becomes the wavelength .lambda.d and that the dummy optical signal
from the semiconductor laser 432 becomes equal in amplitude to the
optical signal of the wavelength .lambda.1 to be amplified.
[0114] In general, semiconductor lasers are feedback-controlled
based on an output light therefrom. However, in the present
embodiment, the output light from the semiconductor laser 432
includes the light of the wavelength .lambda.1 and the dummy
optical signal of the wavelength .lambda.d, and therefore cannot be
referred to for feedback control. For this reason, in the present
embodiment, the first optical router 536 separates the controller
434 with the optical signal of the wavelength .lambda.d from the
amplified optical signal for feedback control.
[0115] As described above, according to the present embodiment, the
optical signal of the wavelength .lambda.d outputted from the first
optical router 536 is monitored. Thus, in addition to the effects
similar to those in the fourth embodiment, the optical amplifying
device according to the fifth embodiment has such an effect as that
the output light from the semiconductor laser 432 can be controlled
more accurately.
[0116] With reference to FIGS. 16, 17a, and 17b, described is a
system in which an optical signal is amplified by an optical
amplifying device and then again amplified for long-distance
transmission
[0117] (Seventh Embodiment)
[0118] FIG. 16 is a block diagram showing the structure of an
optical transmission system according to a seventh embodiment of
the present invention. The optical transmission system includes an
optical amplifying device 7000, second optical amplifiers 40a and
40b, and optical filters 50a and 50b. The optical amplifying device
7000 includes semiconductor lasers 732a and 732b, controllers 734a
and 734b, an optical multiplexer 738, the first optical amplifier
116, and a second optical router 736. Note that the first optical
amplifier 116 shown in FIG. 16 is identical in structure to the
optical amplifier 116 shown in FIG. 11. The operation of the
present optical transmission system is now described below.
[0119] The optical amplifying device 7000 is provided with two
optical signals having different wavelengths, one with a wavelength
.lambda.1 and the other with a wavelength .lambda.2. The optical
signal of the wavelength .lambda.1 is provided to the semiconductor
laser 732a, which is controlled by the controller 734a, and then
multiplexed with a dummy optical signal of a wavelength .lambda.d1.
On the other hand, the optical signal of the wavelength .lambda.2
is provided to the semiconductor laser 732b, which is controlled by
the controller 734b, and then multiplexed with a dummy optical
signal of a wavelength of .lambda.d2.
[0120] Output lights from the semiconductor lasers 732a and 732b
are multiplexed each other by the optical multiplexer 738, and then
amplified by the first optical amplifier 116. At this time, the
output lights from the semiconductor lasers 732a and 732b are
constant in optical power and, accordingly, an output light from
the optical multiplexer 738 is also constant in optical power.
Therefore, optical surges at optical amplification do not occur in
the first optical amplifier 116.
[0121] The amplified optical signal is provided to the second
optical router 736. The second optical router 736 has first and
second output ports, and is structured as an AWG (Arrayed Wave
Guide) having cyclic transmittance characteristics as shown in FIG.
17a. Of the input optical signal having a spectrum shown in FIG.
17b, the second optical router 736 outputs, from the first output
port, the optical signal of the wavelength .lambda.1 to be
amplified and the dummy optical signal of the wavelength .lambda.d1
and, from the second output port, the optical signal of the
wavelength .lambda.2 to be amplified and the dummy optical signal
of the wavelength .lambda.d2.
[0122] The optical signal outputted from the first output port is
again amplified by the second optical amplifier 40a in the course
of transmission through an optical fiber. The optical signal
inputted to the second optical amplifier 40a is constant in optical
power, like the output light from the semiconductor laser 732a.
Therefore, optical surges at optical amplification do not occur in
the second optical amplifier 40a. The amplified optical signal is
provided to the optical filter 50a that passes the optical signal
of the wavelength .lambda.1.
[0123] Similarly, the optical signal outputted from the second
output port is again amplified by the second optical amplifier 40b,
and then provided to the optical filter 50b that passes the optical
signal of the wavelength .lambda.2.
[0124] As described above, according to the present embodiment,
when the amplified optical signal is transmitted through a router,
the input optical signal and the dummy optical signal are both
outputted from the same port for transmission. Therefore, optical
surges do not occur when the optical signal from the router is
again amplified by another optical amplifier. Thus, amplification
can be carried out twice or more without further requiring such
device as the optical amplifying device 4000 shown in FIG. 9 for
suppressing optical surges. Consequently, the system can be
simplified in structure.
[0125] While the invention has been described in detail, the
foregoing description is in all aspects illustrative and not
restrictive. It is understood that numerous other modifications and
variations can be devised without departing from the scope of the
invention.
* * * * *