Optical communications – Remote control
Reexamination Certificate
2002-02-07
2003-11-11
Negash, Kinfe-Michael (Department: 2633)
Optical communications
Remote control
C398S085000, C398S079000, C359S308000
Reexamination Certificate
active
06647211
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a remote control device of an acousto-optic tunable filter used in the wavelength division multiplexed transmission system, an optical transmission system containing an equalizer using the acousto-optic tunable filter, and an optical transmission system containing a optical add/drop multiplexer using the acousto-optic tunable filter.
2. Description of the Related Art
The acousto-optic tunable filter (hereunder, referred to as “AOTF”) has been used for a device to build a wavelength division multiplexed transmission system. A gain equalizer, power equalizer, optical add-drop multiplexer (hereunder referred to as “OADM”) which utilize the transmittance characteristic of the AOTF have been proposed as devices to build a wavelength division multiplexed transmission system (hereunder, “wavelength division multiplexed” is abbreviated by “WDM”).
The AOTF is a device in which the acousto-optical effect is applied; and there have been proposed several constructions of the AOTF, however the basic principle of operation is the same.
Let us take an AOTF
30
′ shown in
FIG. 25
as an example of the construction.
As shown in
FIG. 25
, the AOTF
30
′ is constructed to comprise two input ports (PI)
01
,
02
and two output ports (PO)
01
′,
02
′, a transducer
30
′-
1
placed on a flat substrate, an absorber
30
′-
2
, a highly concentrated Ti diffusion region
30
′-
3
, and an optical waveguide
30
′-
4
and the like.
In the construction shown in
FIG. 25
, giving an RF (radio frequency) signal to the transducer
30
′-
1
through a control port
30
′-
7
excites the transducer
30
′-
1
to generate a surface acoustic wave (hereunder, “surface acoustic wave” is simply referred to as “SAW”). This SAW propagates through the SAW cladding layer to be absorbed by the SAW absorber
30
′-
2
.
On the other hand, a light signal comes in through the optical input port (PI)
01
to be polarized by a PBS (polarized beam splitter)
30
′-
5
and split into two optical waveguides. The SAW and the light signal are superposed to interfere with each other, and only a light signal of a part of wavelength is polarized selectively.
The light signal of the wavelength polarized is polarized and separated by a PBS
30
′-
6
on the output. The light signal split by the PBS
30
′-
6
goes out from the optical output port (PO)
02
′, and the rest goes out from the optical output port (PO)
01
′. The wavelength of the light signal polarized is in one-to-one correspondence with the frequency of the RF signal, namely, the SAW frequency, under a constant temperature. That is, varying the frequency of the RF signal makes it possible to select a wavelength of a light signal going out through the output ports (PO)
01
′,
02
′.
Utilizing this property, if an RF signal of a specific frequency is inputted through the control port
30
′-
7
where a WDM signal containing light signals having different wavelengths to each other comes in through the input port (PI)
01
, the AOTF
30
′ will output a light signal of a desired wavelength through the output port (PO)
02
. Serving the outputted light signal as a split light signal of the OADM, the AOTF
30
′ can be used as an OADM.
Concretely, when using the AOTF
30
′ as an OADM, for example, the input port (PI)
01
is used as the main input port, the input port (PI)
02
as the input port for adding a light signal, the output port (PO)
01
′ as the main output port (PO), and the output port (PO)
02
′ as the output port for splitting a light signal.
Inputting an RF signal through the control port will simultaneously adds/splits a light signal of the wavelength corresponding to the frequency of the inputted RF signal. And, to simultaneously input a plurality of RF signals having different frequencies will select the light signals of a plurality of wavelengths corresponding to these RF signals. That is, the AOTF
30
′ is very effective as an OADM filter that is able to simultaneously select light signals of plural and arbitrary wavelengths.
And, the AOTF
30
′ is also effective as an optical power equalizer or an optical gain equalizer. When the AOTF
30
′ is used as the foregoing application, either one of the two output ports (PO)
01
′,
02
′ is only needed to be used.
Further, the AOTF
30
′ will achieve a variable optical filter that is able to freely vary the transmittance characteristic (transmitted quantity/stopped quantity) of a light signal by varying the power of an inputted RF signal.
In comparison to an optical filter of the fixed wavelength type, the AOTF
30
′ is flexible in the choice of wavelengths, and the transmittance characteristic can be made variable as mentioned above.
Accordingly, a WDM transmission system
100
′ using the AOTF
30
′ can be made up, as shown in FIG.
26
. In the WDM transmission system
100
′ shown here, the AOTF
30
′ is placed on the transmission line through which a WDM light signal propagates between an optical main signal transmitter
11
and an optical main signal receiver
21
. And, a device
30
′A containing the AOTF
30
′ is comprised of an RF signal source
31
′ and a control/drive circuit
32
′. The device
30
′A containing the AOTF
30
′ can be used as an optical equalizing device, an OADM, or the like.
In the device
30
′A containing the AOTF
30
′ having such a construction, the AOTF
30
′ operates on the basis of the RF signal outputted by the RF signal source
31
′ that is equipped in the same place as the AOTF
30
′.
However, if the RF signal source
31
′ is installed in the same place as the AOTF
30
′ so as to output a desired RF signal to the AOTF
30
′ which is used for an optical equalizing device or the like, it will enlarge the scale of the device; and if the AOTF
30
′ is used in the transmission line in such a condition, it will increase the power consumption, which is a problem.
Further, if a plurality of the devices
30
′A using the AOTFs
30
′ are installed in the transmission line, the scale of the devices and the power consumption are further increased, and the maintenance of these devices require more manpower, which is also a problem.
Further, to install the RF signal source
31
′ and the control/drive circuit
32
′ in the same place as the AOTF
30
′ will invite a possibility of disturbances in the electronic circuit of the control/drive circuit
32
′ to cause crosstalks, which is another problem.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing problems, and an object of the present invention is to provide a remote control device of an AOTF, whereby an RF signal source for controlling the AOTF can be installed separately from the AOTF and a device containing the AOTF can be controlled from a remote place, and a WDM transmission system that contains such a device.
In order to accomplish the foregoing object, the remote control device of the acousto-optic tunable filter according to the invention is characterized by comprising: an acousto-optic tunable filter interpolated in an optical transmission line, capable of controlling an output state of an input light signal by being supplied with a surface acoustic wave control signal through a control port; a surface acoustic wave control signal source to generate the surface acoustic wave control signal, which is provided at a remote place from the acousto-optic tunable filter; and a control unit that receives an information of the surface acoustic wave control signal from the surface acoustic wave control signal source through remote transmission means, and supplies the surface acoustic wave control signal to the control port of the acousto-optic tunable filter.
Therefore, according to the remote contr
Chikama Terumi
Terahara Takafumi
LandOfFree
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