U.S. patent application number 11/711130 was filed with the patent office on 2011-02-17 for optical transceiver with gradual stop or start function.
Invention is credited to Hiroto Ishibashi, Hiromi Tanaka.
Application Number | 20110038641 11/711130 |
Document ID | / |
Family ID | 38555559 |
Filed Date | 2011-02-17 |
United States Patent
Application |
20110038641 |
Kind Code |
A1 |
Tanaka; Hiromi ; et
al. |
February 17, 2011 |
OPTICAL TRANSCEIVER WITH GRADUAL STOP OR START FUNCTION
Abstract
The present invention provides an optical transmitter applicable
to the WDM communication system. The optical transmitter includes a
light-emitting device, an APC circuit and a processing unit. The
processing unit, responding to a command TX_DISABL, which is sent
from the control unit that communicates with the host controller,
stops the optical output power of the transmitter by decreasing the
reference to a preset value in step wise. Moreover, the processing
unit, responding to a command ENABLE that is also sent from the
control unit, starts the optical output by increasing the reference
to another preset value in step wise.
Inventors: |
Tanaka; Hiromi;
(Yokohama-shi, JP) ; Ishibashi; Hiroto;
(Yokohama-shi, JP) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL
1130 CONNECTICUT AVENUE, N.W., SUITE 1130
WASHINGTON
DC
20036
US
|
Family ID: |
38555559 |
Appl. No.: |
11/711130 |
Filed: |
February 27, 2007 |
Current U.S.
Class: |
398/197 |
Current CPC
Class: |
H04B 10/564 20130101;
H04J 14/0221 20130101 |
Class at
Publication: |
398/197 |
International
Class: |
H04B 10/04 20060101
H04B010/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2006 |
JP |
2006-053054 |
Claims
1-3. (canceled)
4. An optical transmitter applied to a WDM system that transmits a
number of optical signals each having a signal wavelength different
from each other, the transmitter comprising: a semiconductor laser
diode for outputting the optical signal; an auto-power-control
circuit for adjusting a magnitude of the optical signal to a target
value; and a control unit having a reference table to hold a
plurality of references, the control unit being configured to
receive a command to stop the output of the optical signal when the
optical transmitter is in an operating mode or to start the output
of the optical signal when the optical transmitter is in a hold
mold, and to sequentially set, synchronizing with the reception of
the command, one of references read from the table in the
auto-power-control circuit as the target value, wherein the
magnitude of the optical signal output from the laser diode
gradually decreases step wise when the command is to stop the
output of the optical signal or gradually increases in step wise
when the command is to start the output of the optical signal.
5. The optical transmitter according to claim 4, wherein the
control unit further holds the number of optical signals
transmitted in the WDM system, and wherein the control unit is
further configured to determine, synchronizing with the reception
of the command and depending on the number of optical signals, a
number of steps to vary the magnitude of the optical signal.
6. A method for adjusting output power of an optical signal output
from an optical transceiver communicating with a host controller,
the optical transceiver including a semiconductor laser diode for
outputting the optical signal, an auto-power-control circuit to set
the power of the optical signal to a target value, and a control
unit providing a reference table that stores a plurality of
references, the method comprising steps of: (a) receiving a command
from the host controller, the command determining whether the
optical transceiver is in an operating mode or a holding mode; (b)
reading one of references stored in the reference table by the
control unit; (c) setting the one of the references that is read
from the reference table into the auto-power-control circuit as the
target value; (d) varying the output power of the optical signal
output from the laser diode to the target value by the
auto-power-control circuit; and (e) iterating steps from (b) to (d)
until the output power of the optical signal becomes a
predetermined value, wherein the output power of the optical signal
is gradually varied in step wise.
7. The method according to claim 6, wherein the optical transceiver
further includes a processing unit with a register and a
digital-to-analog converter, the processing unit controlling the
auto-power-control circuit, and the method further including; (b1)
after the step (b), transmitting the one of references to the
register in the processing unit by the control unit, and holding
the control unit by a predetermined period, and (b2) during the
holding of the control unit, converting the one of the references
set in the register into an analog form.
8. The method according to claim 7, wherein the predetermined
period for holding the control unit is a constant period for
respective steps (b).
9. The method according to claim 7, wherein the predetermined
period for holding the control unit is a variable period for
respective steps (b).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical transceiver
applied in an optical communication.
[0003] 2. Related Prior Art
[0004] The United States patent application published as US
2002/0149821A has disclosed an optical transceiver with the SFP
(Small Form factor Pluggable) configuration, where the transceiver
terminates or starts the operation for outputting an optical signal
in response to a state, the high level or the low level, of the
TX_DISABLE signal sent from the host controller. A multi source
agreement provided from the SFF committee has disclosed the
specification of the SFP transceiver.
[0005] When an optical transceiver is applied in the WDM
(Wavelength Division Multiplexing) system, a plurality of optical
signals each transmitted from individual optical transceiver is
multiplexed by an optical multiplexer to transmit on an optical
transmission line. Thus multiplexed signal is amplified by optical
amplifiers arranged on the transmission line. The optical
amplifier, which includes an optical excitation source, adjusts the
power of the excitation source, by monitoring the power of the
input and output of the optical signals, so as to keep the optical
gain thereof.
[0006] Each transceiver in the WDM system outputs the optical
signal, which is directly or indirectly modulated by the electrical
signal input therein. This state, namely, a state outputting a
modulated optical signal, is called as the ON state. On the other
hand, the optical transceiver is sometimes compelled to stop the
modulation independent of the input electrical signal by a command
sent from the host system, or to keep the optical output power
constant at a preset level smaller than the low level in the ON
state, which is called as the OFF state. The transition from the ON
state to the OFF state is often called as the DISABLE of the
optical output, while, the transition from the OFF state to the ON
state is sometimes called as the ENABLE of the optical output.
[0007] In the WDM system, the input level of the optical amplifier
depends on the states of the optical transceivers that send optical
signals in the optical transmission line. As explained, the optical
amplifier operates to keep the optical gain thereof constant; the
time constant to keep the optical gain is slower than the time
constant to change the state of the optical transceiver, namely, a
time from the ON state to the OFF state or from the OFF state to
the ON state. Accordingly, the gain of the optical amplifier
becomes excessive or insufficient during the transition period of
the optical gain, which disarranges the optical level of each
optical signal. In the WDM system with a long reach, the optical
signal transmitted in the optical transmission line is amplified by
a plurality of the optical amplifiers until the signal reaches the
end station, which accumulates the variation of the optical levels
of each signal.
SUMMARY OF THE INVENTION
[0008] One aspect of the present invention relates to an optical
transceiver that solves above subject appeared in the WDM system.
The optical transceiver according to the present invention that
communicates with a host controller comprises a semiconductor laser
diode, an auto-power-controller circuit and a control unit. The
laser diode outputs an optical signal. The auto-power-control
circuit adjusts output power of the optical signal to a target
value. The control unit that provides a reference table to store a
plurality of references is configured to receive a command from the
host controller, and to sequentially set, synchronizing with the
command, one of references read from the table, in the
auto-power-control circuit as the target value. In the present
invention, the output power of the optical signal from the laser
diode gradually varies in step wise.
[0009] Another aspect of the present invention relates to a method
for adjusting output power of an optical signal output from the
optical transceiver. The process comprises steps of; (a) receiving
a command from the host controller, where the command determines
whether the optical transceiver is in an operating mode or a
holding mode, (b) reading one of references stored in the reference
table by the control unit, (c) setting one of the references that
is read from the reference table into the auto-power-control
circuit as the target value, (d) varying the output power of the
optical signal output from the laser diode to the target value by
the auto-power-control circuit, and (e) iterating steps from (b) to
(d) until the output power of the optical signal becomes a
predetermined value. According to the present method, the output
power of the optical signal is gradually varied in step wise.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is a schematic diagram showing the WDM system with
the long reach configuration;
[0011] FIG. 2 is a block diagram of the optical transceiver
according to the present invention;
[0012] FIG. 3 is a flow chart executed at the DISABLE of the
optical signal;
[0013] FIG. 4 is a time chart of the DISABLE operation of the
optical transceiver;
[0014] FIG. 5 is a schematic diagram showing a look-up table
storing control parameters;
[0015] FIG. 6 is a flow chart executed at the ENABLE of the optical
signal;
[0016] FIG. 7 is a time chart of the ENABLE operation of the
optical transceiver;
[0017] FIG. 8 is a time chart of the DISABLE operation of a
conventional transceiver; and
[0018] FIG. 9 is a time chart of the ENABLE operation of a
conventional transceiver.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0019] Next, preferred embodiments of the present invention will be
described as referring to accompanying drawings. In the
description, the same numerals or symbols will refer to the same
elements without overlapping explanations.
[0020] The embodiment explained below is related to an optical
transceiver that operates as not only the optical transmitter but
also the optical receiver. FIG. 1 is a schematic diagram showing
the WDM system with the long reach that applies optical
transceivers, 10 and 20, of the present embodiment. The WDM system
100 performs the full-duplex optical communication between
transceivers, 10 and 20.
[0021] The WDM system 100 configures N-channels, where N is greater
than two (2), and each channel is attributed with a wavelength
selected from .lamda..sub.1.about..lamda..sub.N different from each
other. Depending on the number of channels, the WDM system 100
provides N count of optical transceivers 10 in one station and also
N count of optical transceivers 20 in another station. These
transceivers, 10 and 20, may configure the same architecture, and
will be referred by 10.sub.1, 10.sub.2, . . . 10.sub.N for the
optical transceiver 10, while, by 20.sub.1, 20.sub.2, . . .
20.sub.N for the transceivers 20 in the counter station. One of the
transceiver 10.sub.m optically communicates with the counter
transceiver 20.sub.m by an optical signal with the wavelength
.lamda..sub.m, where m is an integer grater than or equal to 1 and
smaller than or equal to N.
[0022] FIG. 2 is a block diagram of the optical transceiver 10.
Here, another optical transceiver 20 may configure the same
architecture with that of the optical transceiver 10. Accordingly,
explanations below may be applicable to the other optical
transceiver 20 in the counter station.
[0023] The optical transceiver 10 is a type of the SFP (Small Form
factor Pluggable) transceiver and may be applicable to the DWDM
(Dense Wavelength Division Multiplexing) communication system. The
transceiver 10 provides a transmitter optical subassembly (TOSA) 22
that transmits an optical signal 41, a receiver optical subassembly
(ROSA) 24 that receives another optical signal 42, a processing
unit 26 to control the operation of the TOSA 22 and ROSA 24, and a
control unit 28 to control the processing unit 26.
[0024] The TOSA 22 installs a semiconductor laser diode (LD) 21
that emits the optical signal 41. The processing unit 26 integrates
an LD driver 30 that sends an electrical driving signal
corresponding to the optical signal 41 to the LD 21 to drive the
LD. The processing unit 26 also includes an auto-power control
(APC) circuit 32 to adjust a magnitude and an extinction ratio of
the optical signal. That is, the APC circuit 32 keeps it constant
for the average magnitude and the extinction ratio of the optical
signal 41 output from the LD 21.
[0025] The LD 21 is mounted on a thermo-electric cooler (TEC) in
the TOSA 22, which is not illustrated in FIG. 2. A TEC controller
23 controls a temperature of the LD 21 by adjusting the temperature
of the TEC. The control unit 28 controls the TEC controller 23.
[0026] The ROSA 24 includes an avalanche photodiode (APD) to
receive the optical signal 42. An APD controller 25 supplies a bias
voltage whose level is controlled by the control unit 28 to the APD
to convert the optical signal 42 into an electric signal with a
preset conversion gain. The electrical signal converted by the APD
is amplified by a pre-amplifier installed within the ROSA 24 and
thus amplified electrical signal is sent to the post amplifier 34.
The post amplifier 34 further amplifies the electrical signal and
outputs the amplified signal to the outside of the optical
transceiver 10.
[0027] The processing unit 26 intervenes between the controller
unit 28 that is a digital circuit and analog circuits such as the
LD driver 30, the APC circuit 32 and the post amplifier 34. The
processing unit 26 installs a register 38 that temporally stores a
target parameter to be set in the APC circuit 32 and a
digital-to-analog converter to convert the preset parameter in a
digital form into a corresponding analog signal so as to be used in
the APC circuit 32. The control unit 28 can overwrite the target
parameter in the register 38. The APC circuit 32 operates so as to
set the output power of the optical signal 41 equal to the target
parameter in the register 38.
[0028] The optical transceiver 10 is configured to couple with the
host controller 50. The host controller 50, by communicating with
the control unit 28 in the transceiver 10, monitors and controls
the optical transceiver 10. A command TX_DISABLE, which is sent
from the host controller 50 to the control unit 28, instructs the
transceiver 10 to change the operation thereof from the operating
mode to the hold mode, or from the hold mode to the operating
mode.
[0029] When the optical transceiver 10 is in the operating mode,
the LD 21 outputs the optical signal 41 which is directly or
indirectly modulated by the electrical signal input to the LD
driver 30. On the other hand, when the optical transceiver 10 is in
the hold mode, the LD 21 stops to output the optical signal
independent of the electrical signal by turning off the LD 21 or
decreases the optical output therefrom to a level below the LOW
level in the operating mode. In the explanation below, the
transition from the operating mode to the hold mode will be called
as the DISABLE, while the transition from the hold mode to the
operating mode will be called as the ENABLE. When the command
TX_DISABLE is asserted, which corresponds to the hold mode, the
optical signal 41 from the LD 21 is stopped, while, the LD 21
outputs the optical signal 41 when the command TX_DISABLE is
negated.
[0030] The control unit 28 passes the command TX_DISABLE sent from
the host controller 50 to the processing unit 26. The processing
unit 26, responding to the command TX_DISABLE, stops or starts the
LD 21 to output optical signal 41.
[0031] Referring to FIG. 1 again, respective outputs of the TOSA 22
of transceivers, 10.sub.1 to 10.sub.N in one station are merged by
the optical multiplexer 12, while, the output of the de-multiplexer
14 is divided to respective ROSA 24 in transceivers, 10.sub.1 to
10.sub.N. The output of another de-multiplexer 16 is divided into
respective ROSAs 24 in transceivers, 20.sub.1 to 20.sub.N, while,
the output from the TOSAs 22 in transceivers, 20.sub.1 to 20.sub.N,
are merged in the optical multiplexer 18. Between the optical
multiplexer 12 and the optical de-multiplexer 16 are provided with
the optical transmission line 17, while, between another pair of
the multiplexer 14 and the de-multiplexer 18 are provided with
another optical transmission line 19. The respective transmission
lines, 17 and 18, interpose a plurality of optical amplifiers
15.
[0032] The optical multiplexer 12 multiplexes optical signals,
S.sub.1 to S.sub.N, with wavelengths from
.lamda..sub.1.about..lamda..sub.N, they are output from optical
transceivers, 10.sub.1 to 10.sub.N to generate one wavelength
multiplexed optical signal. This WDM signal transmits on the
optical transmission line 17 as amplified by optical amplifiers 15.
The optical de-multiplexer 16, receiving the amplified WDM signal,
divides respective optical signals, S.sub.1 to S.sub.N. The ROSA 24
in each optical transceiver 20 receives one of the de-multiplexed
signals, S.sub.1 to S.sub.N.
[0033] Similarly, the optical multiplexer 18 multiplexes optical
signals, S.sub.1 to S.sub.N, with wavelengths different from each
other each output from the optical transceivers, 20.sub.1 to
20.sub.N, and the optical transmission line 19 carries this WDM
signal as amplified by the plurality of optical amplifiers 15. The
optical de-multiplexer 14, receiving this WDM signal,
de-multiplexes it into a plurality of optical signals, S.sub.i to
S.sub.N with wavelengths different from each other. Further, thus
de-multiplexed optical signals, S.sub.1 to S.sub.N, are received by
respective ROSAs of the optical transceivers, 10.sub.1 to
10.sub.N.
[0034] Next will explain a protocol of to stop the optical signal
41 in the optical transceivers, 10 and 20, which is called as the
DISABLE operation. FIG. 3 is a flow chart showing the protocol of
the DISABLE operation carried out by the control unit 28. The
leading edge of the command TX_DISABLE from the LOW level, which
corresponds to the operating mode, to the HIGH level, which
corresponds to the hold mode, triggers the process shown in FIG. 3
as an interruption process for the primary process.
[0035] FIG. 4 is a time chart showing the DISABLE operation of the
optical signal. Synchronizing with the command TX_DISABLE that
rises from the LOW level, which corresponds to the operating mode,
to the HIGH level corresponding to the hold mode, the optical
output power of the signal 41 gradually decreases in step wise from
the target value V.sub.H in the operating mode to the minimum value
V.sub.L in the hold mode.
[0036] FIG. 5 schematically shows a reference table 44 referred by
the control unit during the process shown in FIG. 3. The reference
table 44 stores a series of preset references, APC_REG[0],
APC_REG[1], . . . and APC_REG[N]. The reference APC_REG[0]
corresponds to the target value V.sub.H of the optical output power
in the operating mode, that is, while, the reference APC_REG[N]
corresponds to the minimum value V.sub.L, which is the value when
the transceiver 10 is in the hold mode. Other references set the
optical output power of the signal 41 to a value between the target
value V.sub.H and the minimum value V.sub.L. The larger the numeral
in the parenthesis, the closer the optical output power
corresponding to the minimum value V.sub.L.
[0037] As shown in FIG. 3, the control unit 28 reads the preset
reference APC_REG[0] from the reference table 44 and transfers this
reference APC_REG[0] to the processing unit 26, at step S302. A
serial interface, such as the I.sup.2C bus, may perform this
transfer. The control unit 28 holds by a predetermined period after
the transfer at step S304. During the holding period of the control
unit 28, the processing unit 26 overwrites the register 38 with the
received reference, and transmits this reference converted into an
analog from by the digital-to-analog converter 40 to the APC
circuit 32. Finally, the APC circuit 32 adjusts the optical output
power of the signal 41 corresponding to the reference
APC_REG[0].
[0038] Subsequently, the control unit 28 re-reads the reference
APC_REG[1] from the reference table 44 and transfer thus read
reference to the processing unit 26 at step s306. The control unit
28 holds itself again by the preset period at step S308. During the
holding of the control unit 28, the processing unit 26 overwrites
the register 38 by thus transferred reference APC_REG[1] to
decrease the optical output power of the signal 41 to a value
corresponding to the reference APC_REG[1].
[0039] Thus, preset references with smaller value are sequentially
read from the reference table 44 with a constant period, and the
register 38 is sequentially overwritten by thus read references.
The control unit 28, after setting the final reference APC_REG[N]
to the processing unit 26 at step S310, changes the command
TX_DISABLE to be sent to the processing unit 26 from the operating
mode to the hold mode at step S312. The processing unit 26, after
setting the optical output power of the signal 41 to be the minimum
value V.sub.L that corresponds to the reference APC_REG[N] and
responding to the asserting of the command TX_DISABLE, stops to
supply the driving current from the LD-Driver 30 to the LD 21.
[0040] Subsequently, the control unit 28 resumes the primary
routine as enabling the interrupt of the command TX_DISABLE at step
S314. Thus, by sequentially revising the register 38 with
references stored in the reference table 44, the optical output
power of the signal 41 may be gradually decreased in step wise.
[0041] In the present embodiment, the optical output power of the
signal 41 may change in step wise at the start of the operation.
FIG. 6 is a flow chart showing a protocol when the control unit 28
resumes the operation of the transceiver, 10 or 20. This process is
executed as the interruption process synchronizing with the
negating of the command TX_DISABLE, namely, the falling edge
thereof and the command is sent from the host controller 50 to the
control unit 28.
[0042] FIG. 7 is a time chart showing the operation of the
transceiver, 10 or 20, at the start of the operation. Synchronizing
with the command TX_DISABLE from the holding mode to the operating
mode, that is, triggering by the command TX_DISABLE from the HIGH
level to the LOW level, the optical output power of the signal 41
gradually increases in step wise from the minimum value V.sub.L,
the level of the holding mode, to the target value V.sub.H in the
operating mode.
[0043] As shown in FIG. 6, the control unit 28 passes the command
TX_DISABLE to the processing unit 26. The command TX_DISABLE
changes from the DISABLE (HIGH level) to the ENABLE (LOW level) at
step S602. The processing unit 26, responding to the negating of
the command TX_DISABLE, starts to supply the driving current to the
LD 21.
[0044] Subsequently, the control unit 28 reads the reference,
APC_REG[N], from the reference table 44 and transfers this
reference to the processing unit 26 at step S604. A serial
interface such as the I.sup.2C interface may perform this transfer.
The control unit 28, after the transfer of the reference, holds
itself by a predetermined period at step S606. During the holding
of the control unit 28, the processing unit 26 overwrites the
register 38 with the transferred reference, APC_REG[N]. This
reference, converted to an analog form by the digital-to-analog
converter 40, is sent to the APC circuit 32. Thus, the optical
output power of the signal 41 may be set to the minimum value
V.sub.L that corresponds to the reference APC_REG[N].
[0045] Next, the control unit 28 reads the next reference
APC_REG[N-1] from the reference table 44, transfers thus read
reference to the processing unit 26 at step S608, and enters the
holding mode for a moment. During the holding mode of the control
unit 28, the processing unit overwrites the register 38 with the
reference APC_REG[N-1]. Thus, the optical output power of the
signal 41 increases to a value corresponding to the reference
APC_REG[N-1].
[0046] Thus, references each showing greater optical output power,
are sequentially read from the reference table 44 by the
predetermined period, and the register 38 is sequentially
overwritten by such references. The control unit 28, after
transferring the last reference ACP_REG[0] to the processing unit
26 at step S612, resumes the primary routine as enabling the
interruption of the command TX_DISABLE at step S614, while, the
processing unit 26 sets the optical output power of the signal 41
to be the target value V.sub.H corresponding to the reference
APC_REG[0]. Thus, by sequentially setting the register 38 with the
references stored in the reference table 44, the optical output
power of the signal 44 may gradually increase in step wise.
[0047] Next will compare the embodiment of the present invention
with a conventional configuration. FIG. 8 is a time chart to stop
the optical output power of the signal by the conventional process.
Synchronizing with the assertion of the command TX_DISABLE, the
optical output power of the signal 41 reduces from the value
V.sub.H to the other value V.sub.L in a short period. FIG. 9 is a
time chart to enable the optical output power of the signal 41.
Synchronizing with the negating of the TX_DISABLE, the optical
output power of the signal 41 increases from the minimum value
V.sub.L to the target value V.sub.H in a short period.
[0048] When the conventional optical transmitter that functions
shown in FIGS. 8 and 9, various problems such as that described
below may occur. That is, when an optical output from one optical
transceiver in the WDM system stops or starts, the input level of
the optical amplifier provided in the system such as shown in FIG.
1 increases or decreases by an optical power corresponding to the
optical signal of the channel that stops or starts its optical
signal. The amplifier adjusts the gain thereof by adjusting the
strength of the exciting source so as to keep the optical output
power from the amplifier to be a preset level.
[0049] However, the time constant to adjust strength of the
exciting source is greater than a time to stop or start the
operation of the transceiver for the target channel, which is
generally between 1 .mu.sec to 10 msec. Accordingly, the gain of
the optical amplifier becomes an underestimate or overestimate
state until the adjustment of the exciting source becomes stable,
which greatly affects the optical power of rest channels. For
instance, when the gain of the amplifier becomes the overestimate
state, an excess noise may occur in the optical signal or an
optical input power may exceed the rated value of the optical
transceiver in the receiver side. On the other hand, the
underestimate gain of the amplifier may result in the increase of
the error rate due to the lack of the optical power. In particular
in the long-distance WDM system, the fault above mentioned may be
distinguishable because the plurality of the optical amplifiers
interposed in the transmission line iteratively amplifies the
optical signal. Thus, the fault in single amplifier may be
accumulated.
[0050] On the other hand in the embodiment of the present
invention, the magnitude of the optical signal increases or
decreases in step wise in a longer period than that of the
conventional configuration. Accordingly, the optical amplifier 15
in the adjustment of the gain thereof may be configured to follow
the change of the input optical level, and to keep the magnitude of
the optical signals in respective channels. Thus, the optical
transceiver, 10 or 20, of the present invention may be applicable
for the WDM communication system. In particular, the optical
transceiver of the present embodiment may be distinguishably
applicable to the long distance WDM system.
[0051] The embodiment of the present invention may start or stop
the operating mode further rapidly by providing additional function
described below. That is, the optical transceivers, 10 and 20, of
the present embodiment may preserve the number of signal channels L
in the memory. The optical transceiver, receiving a command to stop
or start the optical output, reads out the number of signal
channels L from the memory and determines the number of steps to
vary the optical output power from the transceiver in step
wise.
[0052] In a case that the number of signal channels L is large, the
stop or the start of the optical output in one channel slightly
affects the other signal channels. For instance, in the case that
the optical amplifier receives 64 optical signals and one signal of
them is stopped, the change of the optical power input to the
optical amplifier is only 0.07 dB. On the other hand, the signal
channels L is small, the stop or the start of the operation of one
channel, which means that the number L increases or decrease by
one, may cause a greater effect to the system.
[0053] The memory within the optical transceiver may store
parameters as a look-up-table how the optical amplifier decides the
steps to change the optical output power depending on the signal
channels. Generally, the number of steps increases as the period to
vary the optical output power becomes smaller. Thus, to decide the
number of steps to vary the optical output power may accelerate the
DISABLE or the ENABLE of the optical output power without
unnecessarily increasing the number of steps.
[0054] The present invention is thus described as referring to
favorable embodiment. However, the present invention is not
restricted to those shown in the embodiments, and various
modifications may be considered within the scope of the listed
claims. For example, although the embodiments concentrate on the
optical transceiver, the optical transmitter according to the
present invention is unnecessary to provide a function of the
optical receiver. Moreover, the embodiment describes that the
control unit 28 overwrites the register 38 with a constant period,
this period is unnecessary to be constant.
* * * * *