U.S. patent application number 10/146215 was filed with the patent office on 2003-01-09 for variable optical dispersion compensating module.
Invention is credited to Fuke, Nobutaka, Ishiguro, Jun, Nakamura, Shiro, Raijo, Hiroshi, Umeda, Atsushi.
Application Number | 20030007725 10/146215 |
Document ID | / |
Family ID | 26615192 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030007725 |
Kind Code |
A1 |
Fuke, Nobutaka ; et
al. |
January 9, 2003 |
Variable optical dispersion compensating module
Abstract
The present invention provides a variable optical dispersion
compensating module comprised of (a) an optical dispersion
compensating unit having an input optical switch, an optical
dispersion compensating fiber, connected to the optical switch,
having a predetermined optical dispersion amount, a bypass path for
bypassing the optical dispersion compensating fiber, and an output
optical switch connected to the optical dispersion compensating
fiber and the bypass path, (b) an optical dispersion compensating
circuit with at least one of the unit connected in series, and (c)
an optical attenuator provided, in the direction of an optical
path, after the input optical switch or before the output optical
switch of the optical dispersion compensating circuit.
Inventors: |
Fuke, Nobutaka; (Tokyo,
JP) ; Nakamura, Shiro; (Tokyo, JP) ; Ishiguro,
Jun; (Tokyo, JP) ; Raijo, Hiroshi; (Tokyo,
JP) ; Umeda, Atsushi; (Tokyo, JP) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
|
Family ID: |
26615192 |
Appl. No.: |
10/146215 |
Filed: |
May 15, 2002 |
Current U.S.
Class: |
385/27 ; 385/16;
385/39 |
Current CPC
Class: |
G02B 6/29395 20130101;
G02B 6/29394 20130101; G02B 6/3562 20130101; G02B 6/4457 20130101;
H04B 10/2525 20130101; G02B 6/3546 20130101; G02B 6/29376 20130101;
G02B 6/356 20130101 |
Class at
Publication: |
385/27 ; 385/39;
385/16 |
International
Class: |
G02B 006/26; G02B
006/35 |
Foreign Application Data
Date |
Code |
Application Number |
May 16, 2001 |
JP |
146591/2001 |
May 1, 2002 |
JP |
130112/2002 |
Claims
What is claimed is:
1. A variable optical dispersion compensating module comprising:
(a) an optical dispersion compensating unit having an input optical
switch, an optical dispersion compensating fiber, connected to said
optical switch, having a predetermined optical dispersion amount, a
bypass path for bypassing said optical dispersion compensating
fiber, and an output optical switch connected to said optical
dispersion compensating fiber and said bypass path; (b) an optical
dispersion compensating circuit with at least one of said unit
connected in series; and (c) an optical attenuator provided between
said input switch or said output switch of said optical dispersion
compensating circuit and an optical connector for input or
output.
2. The variable optical dispersion compensating module according to
claim 1, wherein a single optical switch is provided at a midpoint
in said bypass path, which operates as said input optical switch
and said output optical switch.
3. The variable optical dispersion compensating module according to
claim 1, wherein with respect to an optical dispersion amount of
said optical dispersion compensating fiber composing said at least
one of said optical dispersion compensating unit, when an optical
dispersion amount of one optical dispersion compensating fiber is
set at X, a negative optical dispersion amount of another optical
dispersion compensating fiber is set at 2.sup.N.times.X (N is an
integer ranging from 1 to j).
4. The variable optical dispersion compensating module according to
claim 2, wherein with respect to an optical dispersion amount of
said optical dispersion compensating fiber composing said at least
one of said optical dispersion compensating unit, when an optical
dispersion amount of a specific optical dispersion compensating
fiber is set at X, a negative optical dispersion amount of another
optical dispersion compensating fiber is set at 2.sup.N.times.X (N
is an integer ranging from 1 to j).
5. The variable optical dispersion compensating module according to
claim 1, further comprising: a control device that controls
switching of an optical path of each optical switch composing said
at least one of said optical dispersion compensating unit and an
attenuation of said optical attenuator so as to obtain a set
predetermined optical dispersion amount and a set predetermined
optical attenuation.
6. The variable optical dispersion compensating module according to
claim 2, further comprising: a control device that controls
switching of an optical path of each optical switch composing said
at least one of said optical dispersion compensating unit and an
attenuation of said optical attenuator so as to obtain a set
predetermined optical dispersion amount and a set predetermined
optical attenuation.
7. The variable optical dispersion compensating module according to
claim 3, further comprising: a control device that controls
switching of an optical path of each optical switch composing said
at least one of said optical dispersion compensating unit and an
attenuation of said optical attenuator so as to obtain a set
predetermined optical dispersion amount and a set predetermined
optical attenuation.
8. The variable optical dispersion compensating module according to
claim 4, further comprising: a control device that controls
switching of an optical path of each optical switch composing said
at least one of said optical dispersion compensating unit and an
attenuation of said optical attenuator so as to obtain a set
predetermined optical dispersion amount and a set predetermined
optical attenuation.
9. The variable optical dispersion compensating module according to
claim 1, wherein said optical dispersion compensating fiber
composing said optical dispersion compensating unit is an optical
fiber which is set for a predetermined dispersion amount and is
wounded around a bobbin having a barrel portion on whose opposite
ends are provided flange portions, one of which is provided with an
insertion portion through which said optical fiber is passed.
10. The variable optical dispersion compensating module according
to claim 1, wherein said optical dispersion compensating fiber
composing said optical dispersion compensating unit is an optical
fiber which is set for a predetermined dispersion amount and is
wounded around a bobbin having a barrel portion on whose opposite
ends are provided flange portions, said barrel portion having a
plurality of support poles and a plurality of expanding/shrinking
axes to enable a diameter of said barrel portion to be expanded or
shrunk.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a variable optical
dispersion compensating module used in an optical communication
field, and more particularly, to a variable optical dispersion
compensating module used in a WDM (Wavelength Division
Multiplexing) communication system.
DESCRIPTION OF THE RELATED ART
[0002] In a long-distance transmission using an optical fiber,
since wavelength dispersion occurs due to the optical fiber, it is
required to compensate the wavelength dispersion. In particular,
when a signal band system already installed with single mode fiber
(hereinafter referred to as "SM fiber") is applied to a WDM
communication system the compensation of the wavelength dispersion
becomes important, since the wavelength dispersion due to the
optical fiber is increased.
[0003] As a means for compensating the wavelength dispersion due to
the optical fiber, an optical dispersion compensating module is
installed which has an optical dispersion compensating fiber
(hereinafter referred to as "DC fiber") with negative wavelength
dispersion characteristics that is inverse to wavelength dispersion
characteristics of the SM fiber composing a main part of a
transmission path. The module cancels the wavelength dispersion
occurring in the SM fiber using the wavelength dispersion of the DC
fiber.
[0004] However, the dispersion amount to be compensated using such
an optical dispersion compensating module differs for each optical
path (transmission path), and is not determined until a final stage
of construction of the optical fiber. Therefore, a customer is
prevented from reducing the construction time, and a manufacturer
is required to delivery the module in a short time, thereby to
carry heavy burdens. Accordingly, a variable optical dispersion
compensating module has been required which enables optical
dispersion compensating amount to be adjusted variable.
[0005] Japanese Laid-Open Patent Publication No. 11-252010(1999)
discloses an example of a conventional wavelength dispersion
compensating apparatus. In the example, dispersion selecting units
are coupled in series which are capable of selecting specific
dispersion amount such as normal dispersion, abnormal dispersion
and zero dispersion with different optical dispersion compensating
amount, and an optical amplifier is inserted in between the units.
Each of the dispersion selecting units is provided with, at least,
an input switch, an output switch, a dispersion equalizing fiber,
and an optical attenuator.
[0006] Therefore, since it becomes necessary to construct the
entire module while adjusting an optical attenuation, a dedicated
facility is required and processes are made complicated, resulting
in a problem that production cost is increased.
[0007] Further, for example, when the DC fiber of the optical
dispersion compensating module needs to be exchanged, a variation
occurs in a loss caused by new fusion splicing between the fiber
and an optical switch even in the case where a loss of the new DC
fiber is the same as that of the previous DC fiber, as well as the
case where a loss of the new DC fiber is different from that of the
previous DC fiber. Therefore, the need arises of installing again a
fixed optical attenuator with a re-adjusted optical attenuation.
Accordingly, there is another problem that the cost is increased
due to exchange of DC fiber.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a variable
optical dispersion compensating module to be produced by its
simplified production processes and reduced production cost.
[0009] A basic concept of the present invention is a variable
optical dispersion compensating module provided with following
members:
[0010] (a) an optical dispersion compensating unit comprising an
input optical switch, an optical dispersion compensating fiber
being connected to the optical switch and having a predetermined
optical dispersion amount, a bypass for bypassing the optical
dispersion compensating fiber, and an output optical switch
connected to the optical dispersion compensating fiber and the
bypass path;
[0011] (b) an optical dispersion compensating circuit with at least
one of the unit connected in series; and
[0012] (c) an optical attenuator provided between the input optical
switch or the output optical switch of the optical dispersion
compensating circuit and an optical connector for input and
output.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic diagram showing a variable optical
dispersion compensating module according to a first embodiment of
the present invention;
[0014] FIG. 2 is a schematic diagram showing a variable optical
dispersion compensating module according to a second embodiment of
the present invention;
[0015] FIG. 3 is a schematic diagram showing a variable optical
dispersion compensating module according to a third embodiment of
the present invention;
[0016] FIG. 4 is a schematic diagram showing a variable optical
dispersion compensating module according to a fourth embodiment of
the present invention;
[0017] FIG. 5A is a perspective view of an example of a bobbin
around which an optical dispersion fiber is wounded according to
the present invention;
[0018] FIG. 5B is a plan view of a flange portion of the bobbin
shown in FIG. 5A;
[0019] FIG. 6 is a plan view of a flange portion showing another
example of the bobbin;
[0020] FIG. 7 is a plan view of a flange portion showing another
example of the bobbin;
[0021] FIG. 8 is a plan view of a flange portion showing another
example of the bobbin;
[0022] FIG. 9 is a plan view of a flange portion showing another
example of the bobbin; and
[0023] FIG. 10 is a plan view of a flange portion showing another
example of the bobbin.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Embodiments of the present invention will be described
below.
[0025] A basic embodiment is a variable optical dispersion
compensating module provided with following members:
[0026] (a) an optical dispersion compensating unit comprising an
input optical switch, an optical dispersion compensating fiber
being connected to the optical switch and having a predetermined
optical dispersion amount, a bypass for bypassing the optical
dispersion compensating fiber, and an output optical switch
connected to the optical dispersion compensating fiber and the
bypass path;
[0027] (b) an optical dispersion compensating circuit with at least
one of the unit connected in series; and
[0028] (c) an optical attenuator provided between the input optical
switch or the output optical switch of the optical dispersion
compensating circuit and an optical connector for input and
output.
[0029] Another embodiment is a variable optical dispersion
compensating module with a single optical switch installed at a
midpoint in the bypass path where the single optical switch
operates as the input optical switch and the output optical
switch.
[0030] Another embodiment is a variable optical dispersion
compensating module in which with respect to an optical dispersion
amount of the optical dispersion compensating fiber composing the
at least one of the optical dispersion compensating unit, when an
optical dispersion amount of a negative optical dispersion
compensating fiber is set at X (negative numeral), an optical
dispersion amount of another optical dispersion compensating fiber
is set at 2.sup.N.times.X (N is an integer ranging from 1 to
j).
[0031] Further, the variable optical dispersion compensating module
is provided with a control device that controls switching of an
optical path of each optical switch composing the at least one of
the optical dispersion compensating unit and an attenuation of the
optical attenuator so as to obtain a set predetermined optical
dispersion amount and optical attenuation.
[0032] Furthermore, in the variable optical dispersion compensating
module, the optical dispersion fiber composing the optical
dispersion compensating unit is an optical fiber which is set for a
predetermined dispersion amount and is wounded around a bobbin
having a barrel portion on whose opposite ends are provided flange
portions one of which is provided with an insertion portion through
which the optical fiber is passed.
[0033] Moreover, in the variable optical dispersion compensating
module, the optical dispersion fiber composing the optical
dispersion compensating unit is an optical fiber which is set for a
predetermined dispersion amount and is wounded around a bobbin
having a barrel portion on whose opposite ends are provided flange
portions and which is comprised of a plurality of support poles and
a plurality of expanding/shrinking axes to enable a diameter of the
barrel portion to be expanded and shrunk.
[0034] A first embodiment of the present invention will be
described below with reference to FIG. 1. FIG. 1 is a schematic
diagram showing a variable optical dispersion compensating module
according to the first embodiment of the present invention.
[0035] As shown in FIG. 1, the variable optical dispersion
compensating module according to this embodiment is composed of
five optical dispersion compensating units in which five DC fibers
10a to 10e with different optical dispersion compensating amount
are connected in series using six optical switches 12a to 12f.
Optical dispersion compensating amount of the five DC fibers 10a to
10e is respectively, for example, -160 ps/nm, -80 ps/nm, -40 ps/nm,
-20 ps/nm, and -10 ps/nm. As a general rule, with respect to DC
fibers, when a negative optical dispersion amount of a specific
optical dispersion compensating fiber is set at X (hereinafter X is
a negative numeral), an optical dispersion amount of another
optical dispersion compensating fibers are set at 2.sup.N.times.X
(N is an integer ranging from 1 to j).
[0036] Each of input/output fibers 14 of the six optical switches
12a to 12f is an optical fiber with the same structure as that of
the DC fibers 10a to 10e.
[0037] With respect to a first unit, the input/output fiber 14
extending from an input of the optical switch 12a is connected to
an input connector 16a. Among two input/output fibers 14 extending
from an output of the optical switch 12a, one is connected to one
end of the DC fiber 10a through a fusion splice 18. The other one
is connected to the input/output fiber 14 extending from an input
of the optical switch 12b through the fusion splice 18. The other
end of the DC fiber 10a is connected to the input/output fiber 14
extending from an input of the optical switch 12b through the
fusion splice 18.
[0038] Also with respect to a second unit, among two input/output
fibers 14 extending from an output of the optical switch 12b, one
is connected to one end of the DC fiber 10b through the fusion
splice 18. The other one is connected to the input/output fiber 14
extending from an input of the optical switch 12c through the
fusion splice 18. The other end of the DC fiber 10b is connected to
the input/output fiber 14 extending from an input of the optical
switch 12c through the fusion splice 18.
[0039] The third to fifth units have the same structure as that of
the above two units. Further, the input/output fiber 14 extending
from an output of the optical switch 12f of the fifth unit is
connected to an output connector 16b.
[0040] This embodiment features a single variable optical
attenuator 20 that adjusts a loss of the entire variable optical
dispersion compensating module installed in a portion of the
input/output fiber 14 connecting the optical switch 12f of the
fifth unit and the output connector 16b.
[0041] As an optical switch, various optical switches such as a
mirror type switch may be used, as long as the switch is capable of
being set for transferring input light to an optical dispersion
compensating fiber or an adjacent optical switch, for example,
12b.
[0042] The operation of the variable optical dispersion
compensating module in FIG. 1 will be described below.
[0043] Corresponding to a required optical dispersion compensating
amount, one or more switches are arbitrarily selected from the
optical switches 12a to 12f of the variable optical dispersion
compensating module for operation, and thereby the optical path is
switched so that transmission light is passed through a desired DC
fiber(s) selected from the DC fibers 10a to 10e as shown in FIG. 1
with respective optical dispersion compensating amount of, for
example, -160 ps/nm, -80 ps/nm, -40 ps/nm, -20 ps/nm, and -10
ps/nm, while bypassing the other DC fibers. Thus, the optical
dispersion compensating amount is adjusted in a range from 0 ps/nm
to -310 ps/nm on a 10 ps/nm basis.
[0044] Then, for example, since an output intensity to the optical
connector 16b is generally too high when only the fiber 10e with a
small optical dispersion compensating amount is used, the variable
optical attenuator 20 adjusts the output intensity to control so
that an optical loss of the entire variable optical dispersion
compensating module remains constant always whenever the
transmission light passes through any route of the optical
path.
[0045] In other words, for example, when transmission light passes
through all the DC fibers 10a to 10e as a route of the optical
path, an optical intensity loss of the route is assumed to be A and
an attenuation of the variable optical attenuator 20 is 0 (zero).
In the case where the transmission light is passed through another
route having a bypass path(s), the entire loss is decreased from A
by an amount corresponding to a loss of the bypassed optical
dispersion compensating fiber. Therefore, the variable optical
attenuator 20 provides an attenuation corresponding to a loss in
accordance with the bypass loss. Thus, the loss of the entire
variable optical dispersion compensating module is always held
constantly.
[0046] The conventional technique requires the provision of at
least the same number of fixed optical attenuators as the number of
DC fibers, where the attenuators have respective optical
attenuation predetermined for each unit connected in series as one
or a plurality of stages. However, according to the variable
optical dispersion compensating module according to this
embodiment, a single variable attenuator 20 is installed for the
entire variable optical dispersion compensating module. Then, the
operation of the single variable optical attenuator 20 enables a
loss of the entire variable optical dispersion compensating module
to be held always at a constant value, and it is thereby possible
to greatly decrease the number of optical attenuators to be
installed.
[0047] Further, in installing the variable optical attenuator 20,
since it is not necessary to construct the module using the
attenuator while adjusting the optical attenuation unlike in
installing the conventional fixed optical attenuates, a dedicated
facility or the like is not needed and the process is simplified
and resulting in reduced production cost.
[0048] Furthermore, when the need arises of exchanging DC fibers of
the variable optical dispersion compensating module, it is not
necessary to install again an optical attenuator with a newly
adjusted optical attenuation unlike the conventional technique.
Therefore, it is possible to reduce the cost for exchanging DC
fibers.
[0049] In addition, in the above first embodiment, the insertion
direction (the direction of light) of the variable optical
dispersion compensating module in the transmission path is not
limited to the direction, as shown in FIG. 1, in which transmission
light is incident on the input connector 16a and output from the
output connector 16b, and a direction may be possible in which
transmission light is incident from the output connector 16b and is
output from the input connector 16a.
[0050] Moreover, an install portion of the variable optical
attenuator 20 is not limited to a portion of the input/output fiber
14 connecting the optical switch 12f of the fifth unit and the
output connector 16b. For example, the attenuator 20 may be
installed between the input/output fiber 14 connecting the optical
switch 12a of the first unit and the input connector 16a.
[0051] A second embodiment of the present invention will be
described below with reference to FIG. 2.
[0052] FIG. 2 is a schematic diagram showing a variable optical
dispersion compensating module according to the second embodiment
of the present invention. In addition, the same structural elements
as those of the variable optical dispersion compensating module of
the first embodiment shown in FIG. 1 are assigned the same
reference numerals as in FIG. 1 to omit the descriptions.
[0053] As shown in FIG. 2, the variable optical dispersion
compensating module according to this embodiment basically has the
same configuration as that of the variable optical dispersion
compensating module of the first embodiment as shown in FIG. 1. In
other words, five DC fibers 10a to 10e with different optical
dispersion compensating amount are connected in series using six
optical switches 12a to 12f, while the single variable optical
attenuator 20 that adjusts a loss of the entire variable optical
dispersion compensating module is installed between the
input/output fiber 14 connecting the optical switch 12f and output
connector 16b.
[0054] In addition, it is a feature of this embodiment that a
control device 22 is installed which is connected to each of the
six optical switches 12a to 12f and variable optical attenuator 20,
calculates a loss of the entire variable optical dispersion
compensating module corresponding to switching of each of the
optical switches 12a to 12f, and using a calculated result,
automatically adjusts the optical attenuation of the variable
optical attenuator 20. The control device is connected to each
optical switch between the optical switch 12a at the input and the
optical switch 12f at the output, and the device measures a
dispersion amount of input and output light of each optical switch,
selects one or more optical switches as appropriate from among the
switches 12a to 12f using a preset dispersion amount as a
reference, and thereby automatically controls a dispersion
amount.
[0055] Further, it is possible to install an optical amplifier at a
midpoint in the circuit when the optical intensity attenuates, and
it is thereby possible to amplify the optical intensity to an
intensity preset by the control device.
[0056] The operation of the variable optical dispersion
compensating module as shown in FIG. 2 will be described below.
[0057] As in the first embodiment, corresponding to a required
optical dispersion compensating amount, the optical switches 12a to
12f of the variable optical dispersion compensating module is
selectively operated, thereby the optical path is switched so that
transmission light is passed through a desired DC fiber(s) among
the DC fibers 10a to 10e while bypassing the other DC fibers, and
thus the optical dispersion compensating amount is adjusted. At
this point, whichever route of the optical path transmission light
is passed through, the control device 22 calculates a loss of the
entire variable optical dispersion compensating module
corresponding to the switching of each of the optical switches 12a
to 12f, and based on the calculated result, automatically adjusts
the optical attenuation of the variable optical attenuator 20.
Thus, the loss of the entire variable optical dispersion
compensating module is automatically controlled to be always
constant. In other words, the operation of the variable optical
attenuator 20 in the variable optical dispersion compensating
module in the first embodiment is automatically controlled, and the
loss of the entire variable optical dispersion compensating module
is always held at a constant value automatically.
[0058] According to the variable optical dispersion compensating
module according to the second embodiment provided with the control
device 22 that thus adjusts an optical attenuation automatically,
in addition to the same effect as in the first embodiment, it is
possible to automatically control the operation of the variable
optical attenuator 20 and to automatically hold a loss of the
entire optical dispersion compensating module always at a constant
value.
[0059] A third embodiment of the present invention will be now
described below with reference to FIG. 3.
[0060] FIG. 3 is a schematic diagram showing a variable optical
dispersion compensating module according to the third embodiment of
the present invention. In addition, the same structural elements as
those of the variable optical dispersion compensating module shown
in FIG. 1 in the first embodiment are assigned the same reference
numerals as in FIG. 1 to omit the descriptions.
[0061] As shown in FIG. 3, the variable optical dispersion
compensating module according to this embodiment is composed of
five units in which five kinds of DC fibers 10a to 10e with
different optical dispersion compensating amount are connected in
series using five optical switches 24a to 24f.
[0062] In a first unit, among two input/output fibers 14 extending
from an input of the optical switch 24a, one is connected to the
input connector 16a. The other one is connected to one end of the
DC fiber 10a through the fusion splice 18. Further, among two
input/output fibers 14 extending from an output of the optical
switch 24a, one is connected to the other end of the DC fiber 10a,
and the other one is connected to the input/output fiber 14
extending from an input of the optical switch 24b through the
fusion splice 18.
[0063] The second to fifth units have the same structure as that of
the first unit. Further, among the input/output fibers 14 extending
from an output of the optical switch 24e of the fifth unit, one is
connected to the output connector 16b.
[0064] Also in the variable optical dispersion compensating module
according to this embodiment, it is a feature that a single
variable optical attenuator 20 that adjusts a loss of the entire
variable optical dispersion compensating module is provided in a
portion of the input/output fiber 14 connecting the optical switch
24e of the fifth unit and the output connector 16b. A difference
from the example in FIG. 1 is that the number of optical switches
is less than that in FIG. 1 by one, which is preferable in
operation and production cost. In other words, this embodiment is
the variable optical dispersion compensating module in which a
single optical switch operating as both an input optical switch and
output optical switch is provided at a midpoint in the bypass path
in the example shown in FIG. 1.
[0065] In addition, since the operation of the variable optical
dispersion compensating module in FIG. 3 is basically the same as
in the variable optical dispersion compensating module in FIG. 1 in
the first embodiment, description thereof is omitted.
[0066] According to the variable optical dispersion compensating
module according to this embodiment, as in the first embodiment
previously mentioned, since a single variable optical attenuator 20
is installed in the entire variable optical dispersion compensating
module, it is possible to always hold a loss of the entire variable
optical dispersion compensating module at a constant value. As a
result, it is possible to exhibit the same effect as in the
variable optical dispersion compensating module according to the
first embodiment.
[0067] A fourth embodiment of the present invention will be
described below with reference to FIG. 4.
[0068] FIG. 4 is a schematic diagram showing a variable optical
dispersion compensating module according to the fourth embodiment
of the present invention. In addition, the same structural elements
as those of the variable optical dispersion compensating module
shown in FIG. 3 in the third embodiment are assigned the same
reference numerals as in FIG. 3 to omit the descriptions.
[0069] As shown in FIG. 4, the variable optical dispersion
compensating module according to this embodiment basically has the
same configuration as that of the variable optical dispersion
compensating module in FIG. 3 in the third embodiment. In other
words, five DC fibers 10a to 10e with different optical dispersion
compensating amount are connected in series using five optical
switches 24a to 24e, while the single variable attenuator 20 that
adjusts a loss of the entire variable optical dispersion
compensating module is installed in a portion of the input/output
fiber 14 connecting the optical switch 24e and output connector
16b.
[0070] In addition, in this embodiment, as the variable optical
dispersion compensating module in FIG. 2 in the second embodiment
previously mentioned provided with the control device 22, it is a
feature that a control device 26 is installed which is connected to
each of the five optical switches 24a to 24e and variable optical
attenuator 20, calculates a loss of the entire variable optical
dispersion compensating module corresponding to switching of each
of the optical switches 24a to 24e, and using a calculated result,
automatically adjusts the optical attenuation of the variable
optical attenuator 20.
[0071] In addition, since the operation of the variable optical
dispersion compensating module in FIG. 4 is basically the same as
in the variable optical dispersion compensating module shown in
FIG. 2 in the second embodiment, description thereof is
omitted.
[0072] According to the variable optical dispersion compensating
module according to this embodiment, the control device 26 is
installed which automatically adjusts the optical attenuation of
the variable optical attenuator 20 corresponding to switching of
each of the optical switches 24a to 24e, whereby it is possible to
automatically control the operation of the variable optical
attenuator 20 and to always hold a loss of the entire optical
dispersion compensating module at a constant value. As a result, it
is possible to exhibit the same effect as in the variable optical
dispersion compensating module according to the second
embodiment.
[0073] In the above-mentioned first to fourth embodiments, the
module is composed of five optical dispersion compensating units in
which five kinds of DC fibers 10a to 10e with different optical
dispersion compensating amount are connected in series using six
optical switches or five optical switches. Then, while the case is
described that there are fourteen or fifteen fusion splices 18 for
the DC fibers 10a to 10e composed of optical fibers with the same
structure and input/output fibers 14 of the optical switches 12a to
12f or optical switches 24a to 24e, the number of DC fibers, the
number of optical switches and the number of fusion splices are not
limited to the above case.
[0074] Moreover, the optical dispersion compensating amount of each
of the DC fibers is not limited to the value as described above,
and further is not limited to whether the optical dispersion
compensating amount is different from one another, whether the
optical dispersion compensating amount is negative values, or the
like.
[0075] As is apparent from the above description, the variable
optical dispersion compensating modules according to the present
invention enable the greatly decreased number of optical
attenuators to be installed and eliminate the need of constructing
the module using one or a plurality of fixed optical attenuators
with fixed optical attenuation while adjusting the optical
attenuation. As a result, corresponding to the forgoing, a
dedicated facility or the like is not needed and the process is
simplified, whereby it is possible to reduce the production
cost.
[0076] Further, since the module is provided with the control
device that automatically adjusts an optical attenuation of the
variable optical attenuator corresponding to switching of each of
the optical switches, it is made possible to automatically control
the operation of the variable optical attenuator and to always hold
a loss of the entire optical dispersion compensating module at a
constant value. As a result, it is possible to operate the variable
optical dispersion compensating module momentarily without
requiring manual operation.
[0077] A bobbin around which the DC fiber is wound will be
described below.
[0078] With reference to FIGS. 5A to 10, examples of the bobbin
around which the optical dispersion compensating fibers are wound
in the present invention will be described below. In addition, the
examples are explained with the same members as in FIG. 1 assigned
the same reference numerals as in FIG. 1.
[0079] DC fibers 10a to 10e with respective predetermined lengths
are wound around, for example, an aluminum bobbin 30 as shown FIG.
5A, FIG. 5B and FIGS. 6 to 10 so as to obtain respective
predetermined optical dispersion compensating amount, and the
aluminum bobbin 30 is fixed to a housing using screws or the like
to be accommodated therein.
[0080] FIG. 5A shows a perspective view of a bobbin with a fiber
insertion hole provided in one of flange portions of the bobbin,
and FIG. 5B shows a plan view of the flange portion.
[0081] The bobbin 30 shown in FIG. 5A has a fiber insertion hole 31
formed in a flange portion 30a that is one of flange portions on
opposite ends of a barrel portion 33. The insertion hole 31 is
formed in the direction from the center of the bobbin 30 to
outside. This structure makes it possible that the wound DC fiber
optically couples with a part disposed outside the bobbin 30, for
example, an optical switch, from any direction in the
circumference. In other words, the DC fiber is capable of coupling
with an optical switch with an arbitrary length. Further, a fiber
guide groove 30b is formed on a surface of the flange portion 30a
in the direction from the insertion hole 31 to outside. Since a
thickness of the flange portion 30a is about 1.5 mm, a depth of the
groove 30b may be about 1.0 mm. The groove is to avoid an external
stress applied to the DC fiber in stacking bobbins 30 to place.
[0082] FIG. 6 shows another example of the bobbin with a different
form. The functional effect is the same as in the bobbin shown in
FIG. 5A.
[0083] FIGS. 7 and 8 show another examples of the bobbin, where the
insertion hole shown in FIG. 5A or FIG. 6 is not formed, and a
flange portion 32 that is one of the flange portions is in a form
of a cross to form an insertion portion 30c. The insertion portion
30c, i.e., gaps between the cross, exhibits the functions of the
insertion hole and fiber guide groove explained in FIG. 5A.
[0084] In the bobbins with structures as shown in FIGS. 5A to 8, it
is possible to wind several kinds of DC fibers with different
lengths around a single bobbin. The function will be described
using FIGS. 1 and 5A. The DC fiber 10a with a predetermined length
is wound around the bobbin 30, and a front end of the DC fiber 10a
is pulled out of the insertion hole 30 of the flange portion to be
connected to the optical switch 12b. A rear end of the DC fiber 10b
is connected to the optical switch 12b, and is wound around the
bobbin 30 by a predetermined length, and the front end of the DC
fiber 10b is pulled out of the insertion hole 31. DC fibers 10c,
10d and 10e are thus connected in this order.
[0085] In such a structure, it is possible to wind DC fibers with
five different lengths around a single bobbin 30. As a result,
while in general a single bobbin is used for DCF with a single kind
of length, DC fibers with four different lengths are further wound
around the single bobbin, resulting in cost reduction and
miniaturization. In addition, it is preferable to provide
connectors on the front and rear ends of each of the DC fibers to
facilitate the connection. Further, while in the above embodiment
DC fibers with five different lengths are wound around a single
bobbin, the present invention is not limited to the above case. DC
fibers with a few different lengths may be wound around a single
bobbin.
[0086] With reference to FIGS. 9 and 10, examples modified from
FIGS. 5A to 8 in the embodiments of the present invention will be
described below. In addition, the examples are explained with the
same members as in FIG. 1 assigned the same reference numerals as
in FIG. 1.
[0087] As shown in FIG. 9, the barrel portion 33 may be composed of
one or a plurality of support poles 34a and one or a plurality of
expanding/shrinking axes 34b. FIG. 9 shows a structure with four
expanding/shrinking axes 34b and four support poles 34a. In winding
DC fibers, it is necessary to wind the fibers so that the fibers
near barrel portion 33 are not stressed by the outer fibers. At
first, the diameter of the expanding/shrinking axes 34b is set at a
little larger than the diameter of the support pole 34a, and then
the fibers are wound around the axes. After winding, the diameter
of the expanding/shrinking axes 34b is lessened to the diameter of
the support pole 34a. The fiber inner circumference surface 35 is
supported by the expanding/shrinking axes 34b and support poles
34a, and the inner circumference surface of the wound fiber forms
almost a circular shape. At this point, in order to prevent a
partial stress from being applied to the fiber, it is preferable
that an outer surface of each of the support poles 34a forms a
curved surface. In addition, while FIG. 9 shows the structure
example with four expanding/shrinking axes 34b and four support
poles 34a, the present invention is not limited to the above
example, and is applicable to structures with three or more axes
and poles. In addition, a larger number prevents a stress from
being applied locally to the fiber to a more extent, and therefore
provides a preferable structure. Using a bobbin with such a
structure decreases a loss amount and improves wavelength
characteristics of a loss.
[0088] Further, as shown in FIG. 10, a tube 36 with a smooth
surface may be provided between the expanding/shrinking axes 34b
and support poles 34a, and the inner circumference surface of the
wound fiber. The tube 36 has a structure enabling its diameter to
be expanded and shrunk, and for example, is obtained by forming a
sheet-shaped material in the form of a tube. Accordingly, the
above-mentioned bobbin is provided with flange portions on opposite
ends of the barrel portion 33 composed of a plurality of support
poles and expanding/shrinking axes and thereby enables a diameter
thereof to be expanded or shrunk.
[0089] In the foregoing, the present invention is explained using
the embodiments, but is not limited to the embodiments, and
includes any combination of the embodiments as appropriate by those
skilled in the art. The present invention is different from the
conventional art, in particular, decreases the number of optical
attenuators, provides an optical dispersion compensating apparatus
that controls or compensates for an optical dispersion amount using
only a single attenuator that is the minimum number, and in this
respect, exhibits excellent effects.
* * * * *