U.S. patent application number 14/727175 was filed with the patent office on 2015-09-17 for optical device.
This patent application is currently assigned to Fujitsu Limited. The applicant listed for this patent is FUJITSU LIMITED. Invention is credited to Miki ONAKA.
Application Number | 20150263477 14/727175 |
Document ID | / |
Family ID | 50933932 |
Filed Date | 2015-09-17 |
United States Patent
Application |
20150263477 |
Kind Code |
A1 |
ONAKA; Miki |
September 17, 2015 |
OPTICAL DEVICE
Abstract
An optical device includes a first fiber; a liquid crystal
member configured to have liquid crystal pixels that reflect light
output from the first fiber; a second fiber configured to have a
core to which a first order light ray in the light reflected by the
liquid crystal member is optically connected; a light receiving
circuit configured to receive higher order light rays in the light
reflected by the liquid crystal member; and a control circuit
configured to control based on a light receiving result of the
light receiving circuit, efficiency of optical connection of the
first order light ray to the core of the second fiber, by varying
an angle of the light reflected by the liquid crystal member.
Inventors: |
ONAKA; Miki; (Kawasaki,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU LIMITED |
Kawasaki-shi |
|
JP |
|
|
Assignee: |
Fujitsu Limited
Kawasaki
JP
|
Family ID: |
50933932 |
Appl. No.: |
14/727175 |
Filed: |
June 1, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2012/082430 |
Dec 13, 2012 |
|
|
|
14727175 |
|
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Current U.S.
Class: |
372/6 |
Current CPC
Class: |
G02F 1/13439 20130101;
G02F 2203/48 20130101; G02F 2203/02 20130101; G02F 1/1337 20130101;
H01S 3/136 20130101; H01S 3/06754 20130101; H01S 3/1305 20130101;
H01S 3/1608 20130101; G02F 2203/58 20130101; H04Q 2213/1301
20130101; H01S 3/09415 20130101; G02F 1/136277 20130101; G02B
6/02042 20130101; G02B 6/3806 20130101; G02F 2001/136281 20130101;
H01S 3/094069 20130101; G02F 1/13318 20130101; H01S 3/0941
20130101; H04Q 11/0005 20130101; G02B 6/2817 20130101; G02B 6/3556
20130101; H01S 3/06737 20130101 |
International
Class: |
H01S 3/067 20060101
H01S003/067; H01S 3/0941 20060101 H01S003/0941; H01S 3/16 20060101
H01S003/16; H01S 3/136 20060101 H01S003/136; G02F 1/1343 20060101
G02F001/1343; G02F 1/1337 20060101 G02F001/1337; H01S 3/13 20060101
H01S003/13; H01S 3/094 20060101 H01S003/094; G02F 1/1362 20060101
G02F001/1362 |
Claims
1. An optical device comprising: a first fiber; a liquid crystal
member configured to have liquid crystal pixels that reflect light
output from the first fiber; a second fiber configured to have a
core to which a first order light ray in the light reflected by the
liquid crystal member is optically connected; a light receiving
circuit configured to receive higher order light rays in the light
reflected by the liquid crystal member; and a control circuit
configured to control based on a light receiving result of the
light receiving circuit, efficiency of optical connection of the
first order light ray to the core of the second fiber, by varying
an angle of the light reflected by the liquid crystal member.
2. The optical device according to claim 1, wherein the control
circuit varies the angle of the light reflected by the liquid
crystal member, by varying a refractive index difference among a
plurality of liquid crystal pixels among the liquid crystals and to
which the light output from the first fiber is incident.
3. The optical device according to claim 1, further comprising a
slit configured to reduce a light receiving diameter for the higher
order light rays at the light receiving circuit.
4. The optical device according to claim 1, wherein the first fiber
is a multicore fiber configured to have a plurality of cores, the
liquid crystal member reflects light rays output from the plurality
of cores of the first fiber, the second fiber is a multicore fiber
configured to have a plurality of cores to which first order light
rays in the light rays reflected by the liquid crystal member are
optically connected, the light receiving circuit receives higher
order light rays in the light rays reflected by the liquid crystal
member, the control circuit respectively controls based on a light
receiving result obtained for the higher order light rays by the
light receiving circuit, efficiency of optical connection of the
first order light rays to the plurality of cores of the second
fiber, by varying an angle of the light rays reflected by the
liquid crystal member.
5. The optical device according to claim 1, wherein the first fiber
is an amplifying medium in which erbium is added to a core and pump
light is injected into cladding.
6. The optical device according to claim 1, further comprising a
separator configured to separate the light output from the first
fiber into differing polarized wave components and output the
polarized wave components to be incident on respectively differing
positions of the liquid crystal member; and a coupler configured to
couple first order light rays of the polarized wave components
reflected by the liquid crystal member and input the coupled first
order light rays into the second fiber.
7. The optical device according to claim 6, further comprising a
coupler configured to couple higher order light rays of the
polarized wave components reflected by the liquid crystal member
and to output the coupled higher order light rays to be incident on
the light receiving circuit.
8. The optical device according to claim 1, further comprising: a
diffraction grating disposed at a core of the first fiber and,
configured to reflect light of a specific wavelength in light
propagated by the core and to output the light of the specific
wavelength to a destination outside the first fiber; and a second
light receiving circuit configured to receive light output from the
first fiber by the diffraction grating, wherein the control circuit
controls based on a light receiving result of the second light
receiving circuit, the efficiency of the optical connection of the
first order light ray to the core of the second fiber.
9. The optical device according to claim 8, wherein the diffraction
grating and the second light receiving circuit are disposed near at
least any one among an input end and an output end of the first
fiber.
10. The optical device according to claim 1, wherein the control
circuit controls based on correspondence information of a light
receiving result of the light receiving circuit and power of light
output from the second fiber, the efficiency of the optical
connection of the first order light ray to the core of the second
fiber.
11. The optical device according to claim 1, wherein the first
fiber outputs wavelength multiplexed light.
12. The optical device according to claim 1, further comprising a
filter disposed between the liquid crystal member and any one among
the first fiber and the second fiber, and configured to have a loss
wavelength property equivalent to a gain wavelength property in the
first fiber.
13. An optical device comprising: a first fiber; a liquid crystal
member configured to have liquid crystal pixels that transmit light
output from the first fiber; a second fiber configured to have a
core to which a first order light ray in the light output by the
liquid crystal member is optically connected; a light receiving
circuit configured to receive higher order light rays in the light
output by the liquid crystal member; and a control circuit
configured to control based on a light receiving result of the
light receiving circuit, efficiency of optical connection of the
first order light ray to the core of the second fiber, by varying
an angle of the light output by the liquid crystal member.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of
International Application PCT/JP2012/082430, filed on Dec. 13, 2012
and designating the U.S., the entire contents of which are
incorporated herein by reference.
FIELD
[0002] The embodiment discussed herein is related to an optical
device.
BACKGROUND
[0003] Conventionally, when light is amplified, not only is
amplification performed simply, but attenuation is also adjusted
for each optical signal to control gain and output, for example.
For such adjustment, for example, an optics element (brancher) such
as a branch coupler that extracts a portion of an optical signal is
used. Further, an attenuator that can adjust the optical
attenuation of the light of the optical signal is used. For an
example of such a technique, refer to Japanese Laid-Open Patent
Publication No. 2006-49405.
[0004] Nonetheless, with the conventional techniques above, a
problem arises in that to measure the power of output light, a
portion of the output light has to be removed and attenuation
cannot be efficiently controlled. In cases where the fiber is a
multicore fiber, portions of the light are removed (extracted) from
plural adjacent locations and thus, the degree of freedom of the
extraction diminishes, making the above problem more
remarkable.
[0005] To solve the problem above related to the conventional
techniques, one object of the present invention is to provide an
optical device capable of efficiently controlling attenuation.
SUMMARY
[0006] According to an aspect of an embodiment, an optical device
includes a first fiber; a liquid crystal member configured to have
liquid crystal pixels that reflect light output from the first
fiber; a second fiber configured to have a core to which a first
order light ray in the light reflected by the liquid crystal member
is optically connected; a light receiving circuit configured to
receive higher order light rays in the light reflected by the
liquid crystal member; and a control circuit configured to control
based on a light receiving result of the light receiving circuit,
efficiency of optical connection of the first order light ray to
the core of the second fiber, by varying an angle of the light
reflected by the liquid crystal member.
[0007] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0008] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the invention.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a diagram depicting a first configuration example
of an optical attenuating apparatus according to an embodiment;
[0010] FIG. 2 is a diagram depicting a second configuration example
of the optical attenuating apparatus according to the
embodiment;
[0011] FIG. 3 is a diagram depicting a third configuration example
of the optical attenuating apparatus according to the
embodiment;
[0012] FIG. 4 is a diagram depicting a fourth configuration example
the optical attenuating apparatus according to the embodiment;
[0013] FIG. 5 is a diagram depicting and example of a first
fiber;
[0014] FIG. 6 is a diagram depicting an example of a second
fiber;
[0015] FIG. 7 is a diagram depicting an example of a light incident
surface of a liquid crystal member;
[0016] FIG. 8 is a diagram depicting an example of configuration of
the liquid crystal member;
[0017] FIG. 9 is a diagram depicting an example of transmittance of
each position on an incident surface of the liquid crystal
member;
[0018] FIG. 10 is a diagram depicting an example of reflection of
light at the liquid crystal member;
[0019] FIG. 11 is a diagram depicting an example of a polarization
separating plate;
[0020] FIG. 12 is a diagram depicting an example of a polarization
combining plate;
[0021] FIG. 13 is a diagram depicting an example of separation and
combination of polarized wave components;
[0022] FIG. 14 is a diagram depicting an example of incidence of
polarized wave components on the incident surface of the liquid
crystal member;
[0023] FIG. 15 is a diagram depicting an example of a relation of
power and angle of the light rays output from the liquid crystal
member;
[0024] FIG. 16 is a diagram depicting an example of control of the
transmittance of each position on the incident surface of the
liquid crystal member;
[0025] FIG. 17 is a diagram depicting an example of an incident
surface of a light receiving unit;
[0026] FIG. 18 is a diagram depicting an example of a light
receiving surface of a light receiving element;
[0027] FIG. 19 is a diagram depicting another example of the light
receiving surface of the light receiving element;
[0028] FIG. 20 is a diagram depicting an example of the first fiber
used as an amplifying medium;
[0029] FIG. 21 is a diagram depicting an example of a configuration
for measuring optical power in the first fiber;
[0030] FIG. 22 is a diagram depicting another example of the
configuration for measuring the optical power in the first
fiber;
[0031] FIG. 23 is a diagram depicting an example of a configuration
of an optical amplifying apparatus to which the optical attenuating
apparatus is applied;
[0032] FIG. 24 is a diagram depicting an example of configuration
of a control circuit;
[0033] FIG. 25 is a diagram depicting an example of a relation of
main signal light power and monitored values of higher order light
rays;
[0034] FIG. 26 is a diagram depicting a fifth configuration example
of the optical attenuating apparatus according to the embodiment;
and
[0035] FIG. 27 is a diagram depicting an example of bandwidth for
monitoring optical power in the first fiber.
DESCRIPTION OF EMBODIMENTS
[0036] An embodiment of an optical device according to the present
invention will be described in detail with reference to the
accompanying drawings.
[0037] FIG. 1 is a diagram depicting a first configuration example
of an optical attenuating apparatus according to an embodiment. As
depicted in FIG. 1, an optical attenuating apparatus 10 according
to the embodiment, for example, is an optical device that includes
a first fiber 11, a microlens 12, a liquid crystal member 13, a
microlens 14, a second fiber 15, a light receiving unit 16, and a
control circuit 17.
[0038] The first fiber 11, for example, is a multicore fiber having
plural cores and capable of transmitting plural light rays
simultaneously. The first fiber 11 outputs to the microlens 12, the
light rays transmitted by the cores.
[0039] The microlens 12 transmits the light rays output from the
cores of the first fiber 11, and outputs the light rays to the
liquid crystal member 13. For example, the microlens 12 is a
collimating lens group that collimates the respective light rays
output from the cores of the first fiber 11 and outputs the
collimated light to the liquid crystal member 13.
[0040] In the liquid crystal member 13, pixels are formed whose
refractive index varies according to the voltage applied. For
example, the liquid crystal member 13 is realized by forming the
pixels on a signal chip. The liquid crystal member 13 depicted in
FIG. 1 is a reflective liquid crystal cell that reflects the light
rays output from the microlens 12. For example, the liquid crystal
member 13 can be realized by a drive IC liquid crystal element such
as LCOS.
[0041] For example, the technology of non-patent literature (Yasuki
Sakurai, Masahiro Kawasugi, Yuji Hotta, MD. Saad Khan, Hisashi
Oguri, Katsuyoshi Takeuchi, Sachiko Michihata, and Noboru Uehara,
"LCOS-Based 4.times.4 Wavelength Cross-Connect Switch For Flexible
Channel Management in ROADMs", June 2011) can be applied as the
liquid crystal member 13.
[0042] The reflected light of the liquid crystal member 13 includes
first order light rays and higher order light rays (second order
light ray, third order light ray, . . . ). According to Fourier
optics image formation, the reflection angle of higher order light
rays is greater than that of first order light rays and therefore,
first order light rays and higher order light rays are output in
relatively different directions. First order light rays in the
light reflected by the liquid crystal member 13 are output to the
microlens 14. Further, higher order light rays in the light
reflected by the liquid crystal member 13 are output to the light
receiving unit 16. The voltages applied to the pixels of the liquid
crystal member 13 are controlled by the control circuit 17. Control
of the liquid crystal member 13 by the control circuit 17 will be
described hereinafter.
[0043] The microlens 14 transmits the light rays (first order light
rays) output from the liquid crystal member 13 and outputs the
light rays to the second fiber 15. For example, the microlens 14 is
a collecting lens group that collects the respective light rays
output from the liquid crystal member 13 and inputs the collected
light into the cores of the second fiber 15.
[0044] The second fiber 15, for example, is a multicore fiber
having plural cores and capable of transmitting plural light rays
simultaneously. The light rays output from the microlens 14 are
optically connected to the cores of the second fiber 15, which
outputs the light rays. Thus, the light rays input through the
cores of the first fiber 11 can be output by the respective cores
of the second fiber 15. Further, the power of the light rays output
from the second fiber 15 varies according to the efficiency of the
optical connection of the light rays from the microlens 14 to the
cores of the second fiber 15.
[0045] The light receiving unit 16 receives the light rays (higher
order light rays) output from the liquid crystal member 13. For
example, the light receiving unit 16 is optical receiving devices
respectively corresponding to the light rays output from the cores
the first fiber 11 and reflected by the liquid crystal member 13.
The light receiving unit 16 outputs to the control circuit 17,
signals that correspond to the power of the received light
rays.
[0046] The control circuit 17 controls the voltage applied to the
pixels of the liquid crystal member 13, based on the signals output
from the light receiving unit 16, and thereby controls the
reflection angle of the light rays at the liquid crystal member 13.
For example, the control circuit 17 controls the voltage applied to
the pixels of the liquid crystal member 13 such that for each light
ray incident on the liquid crystal member 13 from the microlens 12,
the equiphase plane of the light beam becomes a given value.
[0047] As a result, the reflection angle of first order light rays
and higher order light rays at the liquid crystal member 13 also
vary. Consequently, the efficiency of the optical connection of the
first order light rays to the cores of the second fiber 15 varies,
enabling the attenuation of the light output from the second fiber
15 to be varied. Further, the reflection angle of the first order
light rays together with the reflection angle of the higher order
light rays also vary and therefore, the efficiency of the optical
connection of the higher order light rays at the light receiving
unit 16 varies. The optical connection efficiency of the first
order light rays at the second fiber 15 and the optical connection
efficiency of the higher order light rays at the light receiving
unit 16 have a constant relation, thereby enabling the power of the
light output from the second fiber 15 to be monitored based on
signals obtained by the light receiving unit 16.
[0048] In this manner, the optical attenuating apparatus 10
reflects the light rays from the first fiber 11 by the liquid
crystal member 13 to vary the efficiency of the optical connection
to the second fiber 15, enabling the power of the light rays to be
individually controlled. Further, by receiving the higher order
light rays output from the liquid crystal member 13, the output
power can also be monitored.
[0049] For example, in a configuration employing a micro electro
mechanical systems (MEMS) mirror, individual control of the output
angle of neighboring light rays output from the cores of a
multicore fiber is difficult. In contrast, in the optical
attenuating apparatus 10, for example, by employing the liquid
crystal member 13 that can be realized by a single chip through
micro-scale liquid crystal technology, the output angle of the
neighboring light rays output from the cores of the first fiber 11
can be individually controlled.
[0050] Further, for example, this configuration is simple to
implement compared to a configuration in which light rays
transmitted by a multicore fiber are branched to plural single core
fibers and the power thereof is controlled by respective
attenuators.
[0051] Further, since the higher order light rays output from the
liquid crystal member 13 are monitored, the effect thereof on the
light rays output from the second fiber 15 is suppressed, enabling
the power of each light ray output from the second fiber 15 to be
monitored. Further, since a configuration to remove a portion of
the light rays output from the second fiber 15 need not be
provided, reductions in the size of the apparatus can be
facilitated.
[0052] In this manner, the optical attenuating apparatus 10 enables
optical attenuation to be controlled efficiently.
[0053] FIG. 2 is a diagram depicting a second configuration example
of the optical attenuating apparatus according to the embodiment.
In FIG. 2, portions identical to those depicted in FIG. 1 are given
the same reference numerals used in FIG. 1 and description thereof
is omitted hereinafter. As depicted in FIG. 2, the optical
attenuating apparatus 10 may further include a polarization
separating plate 21 and polarization combining plates 22 and 23, in
addition to the configuration depicted in FIG. 1.
[0054] The polarization separating plate 21 (separator) separates
the light output from the first fiber 11 and incident on the liquid
crystal member 13, into respectively different polarized wave
components. More specifically, the polarization separating plate 21
separates the light rays output from the microlens 12 into
polarized wave components that are orthogonal to each other and
outputs the polarized wave components to the liquid crystal member
13. As a result, the light rays output from the cores of the first
fiber 11 can be separated respectively into polarized wave
components, incident on the liquid crystal member 13.
[0055] The polarization combining plate 22 (first combiner)
combines the first order light rays of the polarized wave
components that are reflected by the liquid crystal member 13 and
input to the second fiber 15. More specifically, concerning the
first order light rays reflected by the liquid crystal member 13 as
separated polarized wave components, the polarization combining
plate 22 combines the polarized wave components and outputs the
combined polarized wave components to the microlens 14.
[0056] The polarization combining plate 23 (second combiner)
combines the higher order light rays of the polarized wave
components that are reflected by the liquid crystal member 13 and
incident on the light receiving unit 16. More specifically,
concerning the higher order light rays reflected by the liquid
crystal member 13 as separated polarized wave components, the
polarization combining plate 23 combines the polarized wave
components and outputs the combined polarized wave components to
the light receiving unit 16. A configuration that omits the
polarization combining plate 23 is also possible.
[0057] Thus, input light can be separated into orthogonal polarized
wave components and the polarized wave components can be incident
on the liquid crystal member 13, at different positions thereof. As
a result, the liquid crystal member 13 has polarized wave
dependency caused by molecular structure anisotropy and even if the
polarization state of the light input to the optical attenuating
apparatus 10 varies, the polarization state of the light incident
on each position of the liquid crystal member 13 does not vary.
Thus, variation of loss at the liquid crystal member 13 caused by
polarized wave dependency can be suppressed.
[0058] FIG. 3 is a diagram depicting a third configuration example
of the optical attenuating apparatus according to the embodiment.
In FIG. 3, portions identical to those depicted in FIGS. 1 and 2
are given the same reference numerals used in FIGS. 1 and 2, and
description thereof is omitted. As depicted in FIG. 3, the optical
attenuating apparatus 10 according to the embodiment may further
include at least any one among an isolator 31, an optical filter
32, and a prism 33, in addition to the configuration depicted in
FIG. 1 or FIG. 2.
[0059] The isolator 31 transmits to the second fiber 15, the light
rays output from the liquid crystal member 13, and blocks light
output from the second fiber 15 side. As a result, light returning
from the second fiber 15 side to the first fiber 11 side can be
suppressed. The position at which the isolator 31 is provided is
not limited to being between the liquid crystal member 13 and the
second fiber 15, and for example, may be provided between the first
fiber 11 and the liquid crystal member 13.
[0060] The optical filter 32 transmits the light rays output from
the liquid crystal member 13 and outputs the light rays to the
second fiber 15. Further, the optical filter 32 has a loss
wavelength property that equalizes the gain of the transmitted
light rays. For example, when the first fiber 11 is used as an
amplifying medium, the gain wavelength property of the first fiber
11 can be equalized by providing the optical filter 32.
[0061] The optical filter 32, for example, can be realized by
dielectric multilayers that can be implemented on a single chip and
that equalize the gain of the transmitted light rays. The position
at which the optical filter 32 is provided is not limited to being
between the liquid crystal member 13 and the second fiber 15, and
for example, may be provided between the first fiber 11 and the
liquid crystal member 13.
[0062] For example, when multicore batch pumping by high pumping
optical power, such as double cladding pumping, using multimode
pumping is used in the first fiber 11, in the first fiber 11, each
of the cores operates according to the saturation state, without
transmission condition dependency (inverse distribution of rare
earth ions is ideally 1). Thus, even if the condition of the input
signal varies for each core, the gain of the cores at the first
fiber 11 is constant and the gain wavelength property is also
constant. Therefore, batch gain equalization by the optical filter
32 having a given loss wavelength property can be performed even
without performing gain equalization with respect to each core.
[0063] The prism 33 transmits the light rays output from the liquid
crystal member 13 and outputs the light rays to the second fiber
15. Further, the prism 33 has a property that compensates the
wavelength characteristics of the transmitted light waves. As a
result, for example, the light input to the cores of the first
fiber 11 is wavelength multiplexed light and even if wavelength
characteristics are induced by the refractive index of the liquid
crystal member 13, wavelength characteristics of the light rays
output from the second fiber 15 can be compensated.
[0064] FIG. 4 is a diagram depicting a fourth configuration example
the optical attenuating apparatus according to the embodiment. In
FIG. 4, portions identical to those depicted in FIGS. 1 to 3 are
given the same reference numerals used in FIGS. 1 to 3 and
description thereof is omitted. As depicted in FIG. 4, the liquid
crystal member 13 may be a transmissive liquid crystal member.
[0065] More specifically, the liquid crystal member 13 depicted in
FIG. 4 is a transmissive liquid crystal cell that transmits the
light rays output from the microlens 12. Accordingly, by
controlling the voltage applied to the pixels of the liquid crystal
member 13 by the control circuit 17, the output angle of the light
rays output from the liquid crystal member 13 can be
controlled.
[0066] In this manner, the liquid crystal member 13 may be a
reflective liquid crystal member (for example, refer to FIGS. 1 to
3), or may be a transmissive liquid crystal member (for example,
refer to FIG. 4).
[0067] FIG. 5 is a diagram depicting and example of the first
fiber. FIG. 5 depicts an optical output surface of the first fiber
11. As depicted in FIG. 5, the first fiber 11 has first cladding
11a and second cladding 11b. In the first cladding 11a, cores 51 to
57 are formed. The cores 51 to 57 are exposed at the output surface
of the first fiber 11. Further, for example, the cores 51 to 57 are
doped with a rare earth element. In this case, the first fiber 11
is a multicore Erbium doped fiber (EDF) having plural cores doped
with the rare earth element.
[0068] The light rays transmitted by the cores 51 to 57 may be
signal light of a single wavelength or may be wavelength
multiplexed light. The first fiber 11 outputs to the microlens 12
(for example, refer to FIGS. 1 to 4), the light rays transmitted by
the cores 51 to 57.
[0069] FIG. 6 is a diagram depicting an example of the second
fiber. FIG. 6 depicts an optical input surface of the second fiber
15. As depicted in FIG. 6, the second fiber 15 has first cladding
15a and second cladding 15b. In the first cladding 15a, cores 61 to
67 are formed. The cores 61 to 67 are exposed at the input surface
of the second fiber 15. The light rays (first order light rays)
that are output from the cores 51 to 57 (for example, refer to FIG.
5) of the first fiber 11 and reflected at the liquid crystal member
13 are optically connected to the cores 61 to 67. The second fiber
15 outputs the light rays optically connected to the cores 61 to
67.
[0070] In FIG. 6, although a case has been described where the
second fiber 15 has a double cladding structure, for example, if
the second fiber 15 is not used as an amplifying medium, the second
fiber 15 may have a single cladding structure. In other words, the
second fiber 15 may be structured as a fiber that omits the first
cladding 15a and only has the second cladding 15b.
[0071] FIG. 7 is a diagram depicting an example of the light
incident surface of the liquid crystal member. As depicted in FIG.
7, liquid crystal pixels 70 are formed in the light incident
surface of the liquid crystal member 13. Incident light rays 71 to
77 represent the light rays output from the cores 51 to 57 of the
first fiber 11 (for example, refer to FIG. 5). The liquid crystal
pixels 70 are formed such that the incident light rays 71 to 77 are
respectively incident across plural pixels.
[0072] For example, the reflection angle of the incident light ray
71 can be adjusted by controlling the refractive index gradient
(refractive index difference) of the liquid crystal pixels 70a to
which the incident light ray 71 is incident among the liquid
crystal pixels 70. Similarly, the reflection angles of the incident
light rays 72 to 77 can be adjusted by controlling the refractive
index gradient of the pixels to which the incident light rays 72 to
77 are respectively incident among the liquid crystal pixels
70.
[0073] For example, on the incident surface of the liquid crystal
member 13, a refractive index gradient of the liquid crystal pixels
70a is provided in one direction only and in another direction on
the incident surface of the liquid crystal member 13, the
refractive index of the liquid crystal pixels 70a is constant. As a
result, the reflection angle can be controlled without dispersion
of the light incident on the liquid crystal member 13.
[0074] FIG. 8 is a diagram depicting an example of configuration of
the liquid crystal member. As depicted in FIG. 8, the liquid
crystal member 13 has a silicon substrate 81, an active matrix
circuit 82, aluminum electrodes 83a to 83e, an orientation layer
84, a liquid crystal molecule layer 85, an orientation layer 86, a
transparent electrode 87, and a transparent substrate 88. In the
incident surface of the liquid crystal member 13, each portion
formed by the aluminum electrodes 83a to 83e is respectively one
pixel.
[0075] The active matrix circuit 82 applies voltage to the aluminum
electrodes 83a to 83e, respectively. The control circuit 17 (for
example, refer to FIGS. 1 to 4) controls the voltages applied to
the aluminum electrodes 83a to 83e via the active matrix circuit
82. As a result, the direction of the liquid crystal molecules in
the liquid crystal molecule layer 85 changes and the refractive
index of the liquid crystal member 13 to which incident light 80 is
incident changes.
[0076] FIG. 9 is a diagram depicting an example of the
transmittance of each position on the incident surface of the
liquid crystal member. In FIG. 9, the horizontal axis represents
positions on the incident surface of the liquid crystal member 13
and the vertical axis represents the refractive index of the liquid
crystal member 13. An area 91 along the horizontal axis represents
an area at which one light ray (for example, the incident light ray
71 depicted in FIG. 7) is incident on the surface of the liquid
crystal member 13.
[0077] As depicted in FIG. 9, by providing a gradient of the
voltages applied to the cells included in the area 91 and a
gradient of the refractive indices (refractive index difference) of
the cells included in the area 91, the reflection angle of the
light from the liquid crystal member 13 can be set to an angle
different from the angle at which the light is incident on the
liquid crystal member 13. Further, by controlling the refractive
index gradient (refractive index difference) of the cells included
in the area 91, the reflection angle of the light incident on the
area 91 can be controlled.
[0078] FIG. 10 is a diagram depicting an example of the reflection
of light at the liquid crystal member. Incident light rays 101 to
103 depicted in FIG. 10 are light rays incident on the liquid
crystal member 13. Reflected light rays 101a to 103a are higher
order light rays in the reflected incident light rays 101 to 103.
Reflected light rays 101b to 103b are first order light rays in the
reflected incident light rays 101 to 103. By controlling the
voltages applied to the pixels of the liquid crystal member 13, the
reflection angles of the incident light rays 101 to 103 incident on
the liquid crystal member 13 can be independently controlled, as
depicted in FIG. 10.
[0079] FIG. 11 is a diagram depicting an example of the
polarization separating plate. In FIG. 11, a case will be described
where light of random polarization is incident on the polarization
separating plate 21. An incident light ray 111 represents light (of
one core) incident on the polarization separating plate 21. Output
light rays 112, 113 represent the light rays output from the
polarization separating plate 21. A polarization direction 111a
indicates the polarization direction of the incident light ray 111.
As indicated by the polarization direction 111a, the incident light
ray 111 is light of random polarization.
[0080] A polarization direction 112a indicates the polarization
direction of the output light ray 112. As indicated by the
polarization direction 112a, the output light ray 112 is linearly
polarized in a vertical direction. A polarization direction 113a
indicates the polarization direction of the output light ray 113.
As indicated by the polarization direction 113a, the output light
ray 113 is linearly polarized in a horizontal direction.
[0081] As depicted in FIG. 11, the polarization separating plate 21
separates and outputs the incident light ray 111 as the output
light rays 112 and 113 whose polarization directions are
orthogonal. Although description has been given in a case where
light of random polarization is incident on the polarization
separating plate 21, the polarization direction of the light
incident on the polarization separating plate 21 is not limited to
being random. For example, when light linearly polarized in a
vertical direction is incident on the polarization separating plate
21, only the output light ray 112 is output, without output of the
output light ray 113.
[0082] FIG. 12 is a diagram depicting an example of the
polarization combining plate. In FIG. 12, incident light rays 121
and 122 represent the light rays (of one core) incident on the
polarization combining plate 22. For example, the incident light
rays 121 and 122 are the reflected light rays of the output light
rays 112 and 113 that are depicted in FIG. 11 and reflected by the
liquid crystal member 13. Output light 123 represents light output
from the polarization combining plate 22.
[0083] A polarization direction 121a indicates the polarization
direction of the incident light ray 121. As indicated by the
polarization direction 121a, the incident light ray 121 is linearly
polarized in a vertical direction. A polarization direction 122a
indicates the polarization direction of the incident light ray 122.
As indicated by the polarization direction 122a, the incident light
ray 122 is linearly polarized in a horizontal direction. A
polarization direction 123a indicates the polarization direction of
the incident light ray 123. As indicated by the polarization
direction 123a, the output light 123 is randomly polarized.
[0084] In this manner, the polarization combining plate 22 combines
the incident light rays 121 and 122, whose polarization directions
are orthogonal, and outputs the output light 123. Although the
polarization combining plate 22 has been described, the same is
true for the polarization combining plate 23 (for example, refer to
FIGS. 2 to 4).
[0085] FIG. 13 is a diagram depicting an example of separation and
combination of polarized wave components. In FIG. 13, although a
case where the liquid crystal member 13 is transmissive (for
example, refer to FIG. 4) will be described, the same is true for a
case where the liquid crystal member 13 is reflective (for example,
refer to FIGS. 1 to 3). As depicted in FIG. 13, the polarization
separating plate 21 separates incident light into a P component and
an S component having orthogonal polarization directions, and
outputs the respective components to the liquid crystal member 13.
The liquid crystal member 13 transmits the P component and the S
component, which are respectively incident thereon at different
positions, and outputs the components in variable directions. The
polarization combining plate 22 combines and outputs the P
component and the S component output from the liquid crystal member
13.
[0086] FIG. 14 is a diagram depicting an example of incidence of
polarized wave components on the incident surface of the liquid
crystal member. In FIG. 14, among the liquid crystal pixels 70 of
the liquid crystal member 13, the liquid crystal pixels 70a on
which the incident light ray 71 is incident is depicted. An
incident light ray 71P represents the P component in the incident
light ray 71. An incident light ray 71S represents the S component
in the incident light ray 71. As depicted in FIG. 14, polarization
separation by the polarization separating plate 21 enables the
incident light ray 71 to be incident on respectively differing
positions of the liquid crystal pixels 70a, as the incident light
ray 71P and the incident light ray 71S.
[0087] As a result, even if the polarization state of the light
input to the optical attenuating apparatus 10 varies, the
polarization state of the light rays incident on various positions
of the liquid crystal member 13 does not vary, enabling variation
of loss caused by polarized wave dependency to be suppressed.
[0088] If the refractive index of the liquid crystal pixels 70 has
polarized wave dependency, for example, the refractive indices of
the liquid crystal pixels on which the incident light ray 71P is
incident and of the liquid crystal pixels on which the incident
light ray 71S is incident among the liquid crystal pixels 70a may
be independently controlled. Thus, if the refractive index of the
liquid crystal pixels 70 has polarized wave dependency, even if the
polarization state of the light input to the optical attenuating
apparatus 10 varies, variation of loss caused by polarized wave
dependency can be suppressed.
[0089] Further, if the refractive index of the liquid crystal
pixels 70 has polarized wave dependency, the direction in which the
refractive index gradient of the liquid crystal pixels 70a is
provided may differ for the liquid crystal pixels on which the
incident light ray 71P is incident and the liquid crystal pixels on
which the incident light ray 71S is incident.
[0090] FIG. 15 is a diagram depicting an example of the
relationship of power and the angle of the light rays output from
the liquid crystal member. In FIG. 15, the horizontal axis
represents the angle of the light rays output from the liquid
crystal member 13 and the vertical axis represents the power
(optical power) of the light rays output from the liquid crystal
member 1.
[0091] A first order light ray 151 is a first order light ray among
the light rays output from the liquid crystal member 13. A second
order light ray 152 is a second order light ray among the light
rays output from the liquid crystal member 13. A power ratio 153 is
power ratio of the first order light ray 151 and the second order
light ray 152 (higher order light ray).
[0092] FIG. 16 is a diagram depicting an example of control of the
transmittance of each position on the incident surface of the
liquid crystal member. In FIG. 16, the horizontal axis represents
positions on the incident surface of the liquid crystal member 13;
and the vertical axis represents the refractive index of the liquid
crystal member 13. An area 160 represents an area on the incident
surface of the liquid crystal member 13, and on which one light ray
(for example, the incident light ray 71 depicted in FIG. 7) is
incident.
[0093] Refractive indices 161, 162, . . . are the respective
refractive indices of neighboring first, second, . . . pixels in
the area 160. As depicted in FIG. 16, the refractive indices of the
neighboring first, second, . . . pixels do not all have to differ
and it suffices for a refractive index gradient (refractive index
difference) to be provided in the area 160. In the example depicted
in FIG. 16, the voltage applied to the pixels in the area 160 is
controlled to such that for every four pixels, the refractive index
difference increases by .DELTA.N.
[0094] A power ratio 153 of the first order light ray 151 and the
second order light ray 152 (higher order light ray) depicted in
FIG. 15 can be adjusted by the refractive index difference
.DELTA.N. For example, the power ratio 153 of the first order light
ray 151 and the second order light ray 152 (higher order light
rays) can be properly adjusted by controlling the refractive index
difference .DELTA.N corresponding to the sensitivity of the light
receiving unit 16.
[0095] FIG. 17 is a diagram depicting an example of the incident
surface of the light receiving unit. Light receiving elements 171
to 177, for example, are provided on the light receiving surface of
the light receiving unit 16. High order reflected light rays of the
incident light rays 71 to 77 depicted in FIG. 7, for example, are
incident on the light receiving elements 171 to 177. The light
receiving elements 171 to 177 output to the control circuit 17,
signals corresponding to the power of the light rays respectively
incident on the light receiving elements 171 to 177.
[0096] FIG. 18 is a diagram depicting an example of the light
receiving surface of the light receiving element. In FIG. 18,
although the light receiving surface of the light receiving element
171 is described, the same is true for the light receiving elements
172 to 177. As depicted in FIG. 18, a slit 181 that blocks light
may be provided in the light receiving surface of the light
receiving element 171. A light receiving unit 171a is a portion of
the light receiving surface of the light receiving element 171
exposed from the slit 181.
[0097] A light receiving diameter 183 of the light receiving
element 171 is larger than the beam diameter of the incident higher
order light rays, and the slit 181 is provided such that with
respect to the light receiving diameter 183, only the light
receiving unit 171a of the light receiving element 171 receives
light. A light receiving diameter 182 of the light receiving unit
171a, for example, can be about the size of the beam diameter of
the incident higher order light rays.
[0098] In this manner, the mutual relation between the second fiber
15 optical connection efficiency of the first order light rays
output from the liquid crystal member 13 and the light receiving
unit 16 optical connection efficiency of the higher order light
rays output from the liquid crystal member 13 is enhanced by
providing a blocking unit that reduces the light receiving diameter
of the higher order light rays at the light receiving element 171.
As a result, the output power from the second fiber 15 can be
monitored more accurately based on the signal output from the light
receiving unit 16.
[0099] FIG. 19 is a diagram depicting another example of the light
receiving surface of the light receiving element. In FIG. 19,
portions identical to those depicted in FIG. 18 are given the same
reference numerals used in FIG. 18 and description thereof is
omitted hereinafter. For example, in a case of a configuration in
which the polarization combining plate 23 is omitted from the
configurations depicted in FIGS. 2 to 4, light that has been
separated into the P component and the S component is incident on
the light receiving element 171. Therefore, the slit 181 may be
shaped such that the separated incident P and S components are
received by the light receiving unit 171a as depicted in FIG.
19.
[0100] FIG. 20 is a diagram depicting an example of the first fiber
used as an amplifying medium. In FIG. 20, portions identical to
those depicted in FIG. 5 are given the same reference numerals used
in FIG. 5 and description thereof is omitted hereinafter. In FIG.
20, the reference numerals of the cores 51 to 57 are omitted.
[0101] As depicted in FIG. 20, a multimode pumping source 201 may
be provided at the input end of the first fiber 11. The multimode
pumping source 201 generates multimode pump light that is injected
into the first cladding 11a of the first fiber 11 in a
co-propagating direction. As a result, in the first cladding 11a,
the pump light is propagated by multimode in the same direction as
signal light and the signal light propagated by the cores 51 to 57
can be amplified.
[0102] A multimode pumping source 202 may be provided at the output
end of the first fiber 11. The multimode pumping source 202
generates multimode pump light that is injected into the first
cladding 11a of the first fiber 11 in a counter propagating
direction. As a result, in the first cladding 11a, the pump light
is propagated by multimode in the opposite direction of the signal
light and the signal light propagated by the cores 51 to 57 can be
amplified.
[0103] The multimode pumping sources 201 and 202 may be, for
example, laser diodes (LD) that generate pump light of a wavelength
of 0.98 [.mu.m]. Further, like the first fiber 11, the second fiber
15 may also be configured to receive injection of pump light as an
EDF. As a result, the first fiber 11 and the second fiber 15 can be
used respectively as Erbium doped fiber amplifiers (EDFA), enabling
a configuration in which a variable optical attenuator (VOA) is
provided between the two EDFAs.
[0104] In FIG. 20, although a configuration of bidirectional
pumping is described, configuration may be for co-propagating or
counter propagating alone. In other words, the configuration may
omit any one among the multimode pumping sources 201 and 202.
[0105] FIG. 21 is a diagram depicting an example of a configuration
for measuring optical power in the first fiber. As depicted in FIG.
21, for example, diffraction gratings 211 to 217 may be
respectively provided near the input ends of the cores 51 to 57 of
the first fiber 11.
[0106] The diffraction gratings 211 to 217, for example, can be
formed by exposing the cores 51 to 57 to ultraviolet rays to
cyclically vary the refractive index along the longitudinal
direction of the cores 51 to 57. By forming the diffraction
gratings 211 to 217 such that the surface of the diffraction
gratings 211 to 217 are oblique to the travelling direction of the
signal light, light of a specific wavelength included in the signal
light can be reflected and output at a given angle to a destination
outside the core.
[0107] For example, the diffraction grating 211 branches light of a
specific wavelength in the signal light propagated by the core 51
and outputs the branched light from a surface thereof on the first
fiber 11 side. Similarly, the diffraction gratings 212 to 217
respectively branch light of a specific wavelength in the signal
light propagated by the cores 52 to 57 and output the branched
light from the surface thereof on the first fiber 11 side.
[0108] A light receiving unit 210 is provided at a position that
receives the light reflected by the diffraction gratings 211 to 217
and output to destination outside the first fiber. The light
receiving unit 210 receives light rays output from the incident
light ray 111 and outputs signals that correspond to the power of
the received light rays. As a result, the power of the light rays
near the input end of the first fiber 11 can be monitored.
[0109] The light receiving unit 210, for example, has plural light
receiving elements that receive the light rays that are reflected
by the diffraction gratings 211 to 217 and output to a destination
outside the first fiber 11.
[0110] Alternatively, the light receiving unit 210 may have one
light receiving element that collectively receives the light rays
reflected by the diffraction gratings 211 to 217 and outputs the
light rays to a destination outside the first fiber 11. In this
case, for example, the light rays propagated by the cores 51 to 57
are intensity modulated by respectively different low frequencies
f1 to f7 and configuration may be such that the signal obtained by
the one light receiving element of the light receiving unit 210 is
subject to digital conversion and fast Fourier transform (FFT)
conversion and the power of the low frequency components (f1 to f7)
included in the light rays propagated by the cores 51 to 57 is
detected. Thus, even if the light receiving unit 210 is configured
to have only one light receiving element, the power of the light
rays of the cores, near the input end of the first fiber 11 can be
monitored.
[0111] The digital conversion, for example, can be performed by an
analog/digital converter (ADC). The FFT conversion, for example,
can be performed by a field programmable gate array (FPGA) or a
central processing unit (CPU).
[0112] Further, the configuration may further include a circuit
that with respect to the signal obtained by the one light receiving
element of the light receiving unit 210, performs synchronous
detection by the low frequencies f1 to f7, to achieve a
configuration that detects the power of the low frequency
components (f1 to f7) included in the light rays propagated by the
cores 51 to 57. As a result, even when the light receiving unit 210
is configured to have only one light receiving element, the power
of the light of the cores can be monitored near the input end of
the first fiber 11.
[0113] The wavelengths of the light rays reflected by the
diffraction gratings 211 to 217 and output to a destination outside
the first fiber 11 can be adjusted by the interval of the
diffraction gratings 211 to 217. Further, the wavelengths of the
light rays reflected by the diffraction gratings 211 to 217 and
output to a destination outside the first fiber 11 may be
wavelengths of a bandwidth that is resistant to gain variations
even when transmission conditions change such as a change in the
wavelength count of the wavelength multiplexed light. As a result,
gain can be stabilized to perform monitoring even when transmission
conditions change such as a change in the wavelength count of the
wavelength multiplexed light.
[0114] Further, the light rays reflected by the diffraction
gratings 211 to 217 and output to a destination outside the first
fiber 11 may be amplified spontaneous emission (ASE) components
included in the wavelength multiplexed light propagated by the
cores 51 to 57. As a result, deterioration of the transmission
quality of a main signal included in the wavelength multiplexed
light propagated by the cores 51 to 57 can be suppressed.
[0115] The light rays reflected by the diffraction gratings 211 to
217 and output to a destination outside of the first fiber 11 may
be a main signal included in the wavelength multiplexed light
propagated by the cores 51 to 57. In this case, for example, the
main signals reflected by the diffraction gratings 211 to 217 and
output to a destination outside the first fiber 11 may be light of
a narrow bandwidth (e.g., about 0.1 [nm]) (for example, refer to
FIG. 27). As a result, deterioration of the transmission quality of
the main signals included in the wavelength multiplexed light
propagated by the cores 51 to 57 can be suppressed.
[0116] Although a configuration that includes the light receiving
unit 210 and the diffraction gratings 211 to 217 near the input end
of the first fiber 11 has been described, the configuration may
include the light receiving unit 210 and the diffraction gratings
211 to 217 near the output end of the first fiber 11. As a result,
the power of the light rays of the cores can be monitored near the
output end of the first fiber 11. Further, the configuration may
include the light receiving unit 210 and the diffraction gratings
211 to 217 near the input end and the output end of the first fiber
11. As a result, the power of the light rays of the cores can be
monitored near the input end and the output end of the first fiber
11, enabling the gain of the light rays in the first fiber 11 to be
monitored.
[0117] Thus, at the cores 51 to 57 of the first fiber 11, the
diffraction gratings 211 to 217 may be provided that reflect light
of a specific wavelength of the light propagated by the cores 51 to
57 and output the light to a destination outside the first fiber
11. Furthermore, by providing the light receiving unit 210 that
receives the light output to a destination outside the first fiber
11 by the diffraction gratings 211 to 217, the power of the light
propagated by the cores of the first fiber 11 can be monitored. For
example, in a configuration that uses a conventional fused
branch/coupler to branch light, branching of the light of the cores
51 to 57, which are adjacent to one another, is difficult. However,
use of the diffraction gratings 211 to 217 enables the power of the
light propagated by the cores of the first fiber 11 to be
monitored.
[0118] For example, the light receiving unit 210 outputs to the
control circuit 17, a signal that corresponds to the power of the
received light. As a result, the control circuit 17 can control the
liquid crystal member 13, based on both the power of the light
propagated by the first fiber 11 and the power of the light output
from the second fiber 15.
[0119] FIG. 22 is a diagram depicting another example of the
configuration for measuring the optical power in the first fiber.
In FIG. 22, portions identical to those depicted in FIG. 21 are
given the same reference numerals used in FIG. 22 and description
thereof is omitted hereinafter. As depicted in FIG. 22, the
diffraction gratings 211 to 217 may be provided at respectively
different positions along the optical transmission direction of the
first fiber 11.
[0120] For example, using an excimer laser to shoot at the cores 51
to 57 respectively enables the diffraction gratings 211 to 217 to
be provided at arbitrary positions, respectively. Alternatively,
the diffraction gratings 211 to 217 may be formed such that the
surfaces thereof are respectively at different angles.
[0121] As a result, the light rays reflected by the diffraction
gratings 211 to 217 can be brought in proximity of each other,
facilitating a reduction in the size of the light receiving unit
210. Alternatively, the light rays reflected by the diffraction
gratings 211 to 217 can be distanced from one another.
Consequently, in a configuration where the light receiving unit 210
receives light rays by plural light receiving elements, the light
rays can be distanced from one another corresponding to the
interval at which the light receiving elements can be disposed.
[0122] Thus, by respectively adjusting the angles and the positions
of the diffraction gratings 211 to 217 in the light propagation
direction of the first fiber 11, optical paths of monitored light
rays output from the first fiber 11 can be adjusted.
[0123] FIG. 23 is a diagram depicting an example of a configuration
of an optical amplifying apparatus to which the optical attenuating
apparatus is applied. In FIG. 23, portions identical to those
depicted in FIGS. 4, 20, and 21 are given the same reference
numerals used in FIGS. 4, 20, and 21, and description thereof is
omitted hereinafter.
[0124] As depicted in FIG. 23, an optical amplifying apparatus 230
includes an input fiber 231, a lens 232, an isolator 233, a lens
234, the first fiber 11, the multimode pumping source 201, light
receiving units 210a and 210b, the microlens 12, the polarization
separating plate 21, the liquid crystal member 13, the polarization
combining plate 22, the isolator 31, the optical filter 32 (Fil),
the microlens 14, the second fiber 15, the polarization combining
plate 23, the light receiving unit 16, and the control circuit
17.
[0125] The input fiber 231, for example, is a multicore fiber
having plural cores and is capable of transmitting plural light
rays simultaneously. The input fiber 231 outputs to the lens 232,
light rays transmitted by the cores. The lens 232 outputs to the
isolator 233, the light rays output from the input fiber 231.
[0126] The isolator 233 transmits to the lens 234, the light rays
output from the input fiber 231, and blocks light output from the
lens 234 side. The lens 234 outputs to the first fiber 11, the
light rays output from the isolator 233.
[0127] The multimode pumping source 201 is provided near the input
end of the first fiber 11, which is used as an amplifying medium
(for example, refer to FIG. 20). Further, near the input end of the
first fiber 11, a diffraction grating (for example, refer to FIGS.
21 and 22) is provided and the light receiving unit 210a is
provided at a position that receives the light output from the
first fiber 11 by the diffraction grating. Near the output end of
the first fiber 11, a diffraction grating (for example, refer to
FIGS. 21 and 22) is provided and the light receiving unit 210b is
provided at a position that receives the light output from the
first fiber 11 by diffraction grating.
[0128] The light receiving units 210a and 210b, for example, are
respectively configured identically to the light receiving unit 210
depicted in FIGS. 21 and 22. The light receiving units 210a and
210b respectively output to the control circuit 17, a signal that
indicates the power of the received light. Thus, in the control
circuit 17, the input power to the first fiber 11 and the output
power can be monitored.
[0129] The microlens 12, the polarization separating plate 21, the
liquid crystal member 13, the polarization combining plate 22, the
isolator 31, the optical filter 32, the microlens 14, the second
fiber 15, the polarization combining plate 23, the light receiving
unit 16, and the control circuit 17, for example, are identical to
the configuration depicted in the FIG. 4. Nonetheless, the
configuration of the optical amplifying apparatus 230 is not
limited hereto and, for example, can adopt the optical attenuating
apparatus 10 that includes the liquid crystal member 13, which is a
reflective type, depicted in FIGS. 1 to 3.
[0130] Further, in FIG. 23, although a configuration has been
described in which the optical attenuating apparatus 10 is applied
downstream from the amplifying medium using the first fiber 11, the
optical attenuating apparatus 10 can be applied upstream from or at
an intermediate stage of the amplifying medium using the first
fiber 11.
[0131] The optical amplifying apparatus 230 enables the light rays
input from the input fiber 231 to be collectively amplified at the
first fiber 11 and enables the attenuation of the light rays to be
individually controlled by the liquid crystal member 13. Further,
the higher order reflected light rays from the liquid crystal
member 13 are received by the light receiving unit 16, whereby, for
example, compared to a configuration that removes a portion of the
light rays output from the second fiber 15, drops in the power of
the light rays output from the second fiber 15 can be suppressed.
Therefore, for example, the power of the pump light generated by
the multimode pumping source 201 can be reduced, facilitating
reduced power consumption.
[0132] Further, configuration may be such that the multimode
pumping source 201 is controlled by the control circuit 17. For
example, in a case where the control circuit 17 senses from an
input monitoring result of the light receiving unit 210a, that
input light has not been input, the output of the pump light by the
multimode pumping source 201 may be suspended.
[0133] FIG. 24 is a diagram depicting an example of configuration
of the control circuit. As depicted in FIG. 24, the control circuit
17 includes a higher-order light ray power monitor 241, an optical
power calculating unit 242, a wavelength count monitor 243, an
input power monitor 244, an output power monitor 245, a gain
monitor 246, a liquid crystal control unit 247, and a
correspondence information storage unit 248.
[0134] The higher-order light ray power monitor 241 monitors based
on the signals output from the light receiving unit 16, the power
of the higher order light rays of the light rays corresponding to
the cores and output from the liquid crystal member 13. The
higher-order light ray power monitor 241 notifies the optical power
calculating unit 242 of the power of the higher order light rays of
the light rays that correspond to the monitored cores.
[0135] The optical power calculating unit 242 respectively
calculates based on the power notified by the higher-order light
ray power monitor 241, the power of the light rays output from the
second fiber 15. The optical power calculating unit 242 outputs the
calculated power of the light rays to the liquid crystal control
unit 247.
[0136] For example, the correspondence information storage unit 248
stores correspondence information of the power of the higher order
light rays monitored by the higher-order light ray power monitor
241 and the power of the light output from the second fiber 15. For
example, the correspondence information can be created in advance
by measuring the power of the higher order light rays monitored by
the higher-order light ray power monitor 241 and the power of the
light output from the second fiber 15 while varying the voltage
applied to the liquid crystal member 13.
[0137] The correspondence information, for example, is a function
by which the power of the light output from the second fiber 15 can
be calculated from the power of the higher order light rays
monitored by the higher-order light ray power monitor 241.
Alternatively, the correspondence information may be a table that
indicates combinations of the power of the higher order light rays
monitored by the higher-order light ray power monitor 241 and the
power of the light output from the second fiber 15. The optical
power calculating unit 242 respectively derives the power of the
light rays output from the second fiber 15, based on the power of
the higher order light rays of the light rays that correspond to
the cores, the power of the higher order light rays being notified
by the higher-order light ray power monitor 241 based on the
correspondence information stored in the correspondence information
storage unit 248.
[0138] The wavelength count monitor 243 monitors the wavelength
count (multiplexed wavelength count) of the wavelengths included in
the signal light input to each core of the first fiber 11. For
example, the optical power calculating unit 242 monitors the
wavelength count based on a supervisory (SV) signal received from
an optical communications apparatus upstream. The wavelength count
monitor 243 notifies the liquid crystal control unit 247 of the
monitored wavelength count.
[0139] The input power monitor 244 monitors for each core of the
first fiber 11 and based on the signals output from the light
receiving unit 210a depicted in FIG. 23, the power (input power) of
the signal light input to the first fiber 11. The input power
monitor 244 notifies the gain monitor 246 of the monitored input
power. The output power monitor 245 monitors for each core of the
first fiber 11 and based on the signals output from the light
receiving unit 210b depicted in FIG. 23, the power (output power)
of the signal light output from the first fiber 11. The output
power monitor 245 notifies the gain monitor 246 of the monitored
output power.
[0140] For each core of the first fiber 11, the gain monitor 246
monitors based on the input power notified by the input power
monitor 244 and the output power notified by the output power
monitor 245, the gain of the signal light at the first fiber 11.
The gain monitor 246 notifies the liquid crystal control unit 247
of the monitored gain.
[0141] The liquid crystal control unit 247 controls for each core
and based on the power notified by the optical power calculating
unit 242, the voltage applied to the pixels of the liquid crystal
member 13. As a result, for each core and based on monitoring
results of the power of the higher order light rays having a
correlation with the power of the signal light output from the
second fiber 15, constant output control can be performed in
controlling the power of the signal light output from the second
fiber 15.
[0142] For example, the liquid crystal control unit 247 controls
the voltage applied to the liquid crystal member 13 such that for
each core, the power notified by the optical power calculating unit
242 becomes a target value that corresponds to the wavelength count
notified by the wavelength count monitor 243. As a result, even if
the wavelength count of the signal light propagated by the cores
changes, the output power per single wavelength can be controlled
to be a given value.
[0143] Further, the liquid crystal control unit 247 controls for
each core and based in the gain notified by the gain monitor 246,
the voltage applied to the pixels of the liquid crystal member 13.
As a result, for each core and based on monitoring results of the
power of the higher order light rays linked to the power of the
signal light output from the second fiber 15, constant gain control
can be performed in controlling the gain of the signal light output
from the second fiber 15.
[0144] Further, the liquid crystal control unit 247 may perform a
combination of constant output control and constant gain control.
For example, pump light is excessively injected into the first
fiber 11 by double cladding pumping and inverse distribution of the
EDF is completely formed, maximally fixing gain. A state in which
gain is maximally fixed, for example, can be confirmed by the gain
monitor 246. Further, even if input conditions of the optical
amplifying apparatus 230 change, wavelength characteristics of gain
can be held constant while for each core, output can be controlled
to be a given value by controlling the liquid crystal member 13 by
the liquid crystal control unit 247 based on monitoring results
from the wavelength count monitor 243.
[0145] The control circuit 17, for example, can be implemented by a
computing circuit such as a FPGA and a digital signal processor
(DSP).
[0146] The input power monitored by the input power monitor 244
and/or the output power monitored by the output power monitor 245
can be used for startup (for example, ASE startup) of the optical
amplifying apparatus 230 and/or a monitoring alarm for the input
light.
[0147] Further, for example, a control unit that controls the
multimode pumping source 201 based on an input monitoring result of
the light receiving unit 210a may be provided in the control
circuit 17.
[0148] FIG. 25 is a diagram depicting an example of a relation of
main signal light power and monitored values of higher order light
rays. In FIG. 25, the horizontal axis represents the optical power
(main signal light power) [mW] of the signal light output from the
second fiber 15; and the vertical axis represents monitored values
(monitored values of higher order light rays) [mW] obtained by the
higher-order light ray power monitor 241.
[0149] Curves 251 to 25n respectively correspond to a first core, a
second core, . . . , n-th core and characterize the relation of the
optical power of the signal light output from the second fiber 15
and the monitored values obtained by the higher-order light ray
power monitor 241. The correspondence information stored in the
correspondence information storage unit 248 depicted in FIG. 24,
for example, is correspondence information representing the curves
251 to 25n.
[0150] By referring to the correspondence information that
represents the curves 251 to 25n, the optical power calculating
unit 242 can derive based on the monitored values obtained by the
higher-order light ray power monitor 241, the optical power of the
signal light output from the second fiber 1.
[0151] In the liquid crystal member 13, when the direction of the
first order light ray .theta. varies, the direction of the higher
order light rays can be thought to n.theta. vary. Therefore, as
indicated by the curves 251 to 25n, the optical power of the signal
light output from the second fiber 15 and the monitored value
obtained by the higher-order light ray power monitor 241 come to
have an exponential relation and not a proportional relation.
[0152] In contrast, the control circuit 17 stores and refers to the
correspondence information that is based on actual measured values
of the optical power of the signal light output from the second
fiber 15 and the monitored values (light receiving results of the
light receiving unit 16) obtained by the higher-order light ray
power monitor 241. As a result, the optical power of the signal
light output from the second fiber 15 can be accurately derived
based on the monitored values obtained by the higher-order light
ray power monitor 241.
[0153] FIG. 26 is a diagram depicting a fifth configuration example
of the optical attenuating apparatus according to the embodiment.
In FIG. 26, portions identical to those depicted in FIG. 1 are
given the same reference numerals used in FIG. 1 and description
thereof is omitted hereinafter. The first fiber 11 and the second
fiber 15 may be respectively a single core fiber.
[0154] In this case as well, the power of light rays can be
individually controlled by reflecting the light from the first
fiber 11 by the liquid crystal member 13 to vary the efficiency of
the optical connection to the second fiber 15. Monitoring of the
output power further becomes possible by optically receiving the
higher order light rays output from the liquid crystal member 13.
By monitoring the higher order light rays output from the liquid
crystal member 13, unfavorable effects on the light output from the
second fiber 15 can be suppressed and the power of the light output
form the second fiber 15 can be monitored. Further, since
configuration to remove a portion of the light output from the
second fiber 15 need not be provided, size reductions of the
apparatus can be facilitated.
[0155] Thus, the optical attenuating apparatus 10 can efficiently
control the attenuation of light even when the first fiber 11 and
the second fiber 15 are respectively a single core fiber. For
example, in the optical attenuating apparatus 10 depicted in FIGS.
2 to 4 and the optical amplifying apparatus 230 depicted in FIG. 23
as well, the multicore fibers may similarly be replaced with single
core fibers.
[0156] FIG. 27 is a diagram depicting an example of bandwidth for
monitoring optical power in the first fiber. In FIG. 27, the
horizontal axis represents the wavelength [nm] of the light; and
the vertical axis represents the power of the light (optical power)
[dBm]. Signal light rays Ps1 to Ps9 are main signals included in
the wavelength multiplexed light propagated in one core of the
first fiber 11. Further, the wavelength multiplexed light
propagated in the one core of the first fiber 11 includes an ASE
component 271.
[0157] For example, a component of the signal light ray Ps1 having
the shortest wavelength among the signal light rays Ps1 to Ps9 is
in a bandwidth 272 on the short wavelength side, and can be
reflected by the diffraction gratings 211 to 217 depicted in FIGS.
21 and 22 to be monitored by the light receiving unit 210.
Alternatively, a component of the signal light ray Ps9 having the
longest wavelength among the signal light rays Ps1 to Ps9 is in a
bandwidth 273, and may be reflected by the diffraction gratings 211
to 217 depicted in FIGS. 21 and 22 to be monitored by the light
receiving unit 210.
[0158] The bandwidths 272 and 273 are narrow bandwidths of about
0.1 [nm], for example. As a result, unfavorable effects on the
signal light rays Ps1 to Ps9 can be suppressed and the power of the
wavelength multiplexed light propagated in the one core of the
first fiber 11 can be monitored.
[0159] As described, the optical device enables attenuation to be
efficiently controlled.
[0160] All examples and conditional language provided herein are
intended for pedagogical purposes of aiding the reader in
understanding the invention and the concepts contributed by the
inventor to further the art, and are not to be construed as
limitations to such specifically recited examples and conditions,
nor does the organization of such examples in the specification
relate to a showing of the superiority and inferiority of the
invention. Although one or more embodiments of the present
invention have been described in detail, it should be understood
that the various changes, substitutions, and alterations could be
made hereto without departing from the spirit and scope of the
invention.
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