Optical waveguides – Having nonlinear property
Reexamination Certificate
2001-06-20
2004-09-28
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
Having nonlinear property
C385S123000
Reexamination Certificate
active
06798960
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to various optical devices exemplarily used for optical communications and, more specifically, an optical device such as a dispersion compensator for polarized waves and wavelengths of an optical fiber, an optical isolator, an optical modulator, and a photonic sensor used for detecting voltage or electric current flowing through a power transmission line or a power distribution line.
2. Description of the Background Art
Conventional various optical devices are first described below.
FIG. 31
is a schematic diagram illustrating the structure of an optical isolator, which is one example of the conventional optical devices. The optical isolator includes a first and second lenses
1003
and
1004
for coupling a first optical fiber
1001
and a second optical fiber
1002
to each other through an optical system. Placed between these lenses are a polarizer
1005
, a Faraday device
1006
, and an analyzer
1007
. Note that, in
FIG. 31
, outer lines of a light beam going through the optical system is represented as straight lines. Furthermore, there exists a magnetic field
1008
in the optical isolator enough to rotate the plane of polarization. Also, the polarizer
1005
and the analyzer
1007
form an angle of 45 degrees. The Faraday device
1006
is exemplarily implemented by a garnet crystal.
Described next is the principle of the optical isolator. In the optical isolator shown in
FIG. 31
, unpolarized light emitted from the first optical fiber
1001
is coupled through the first lens
1003
to the polarizer
1005
, and therein converted into linearly polarized light. Then, the linearly polarized light goes to the Faraday device
1006
that rotates a plane of polarization thereof by 45 degrees. The linearly polarized light with its plane of polarization rotated is coupled by the analyzer
1007
having the above stated angle to the second optical fiber
1002
through the second lens
1004
.
On the other hand, return light from the second optical fiber
1002
is coupled through the second lens
1004
to the analyzer
1007
for conversion into linearly polarized light. Then, the linearly polarized light goes to the Faraday device
1006
that rotates a plane of polarization thereof by 45 degrees. In the analyzer
1005
, however, the plane of polarization of the linearly polarized light is perpendicular to the polarizing direction of the polarizer
1005
. Therefore, no return light can be coupled to the first optical fiber
1001
through the first lens
1003
. As such, the conventional optical isolator requires two lenses for coupling optical fibers.
Described next is a conventional dispersion compensator. In the conventional dispersion compensator, an optical system is placed between optical fibers. Thus, for coupling therebetween the optical system, at least two lenses are required.
Described next is a conventional optical modulator. The optical modulator functionally includes, for example, a polarizer, a &lgr;/4 plate, a Pockels device, and an analyzer. Linearly polarized light obtained by the polarizer becomes circularly polarized light by the &lgr;/4 plate, and then becomes elliptically polarized light depending on the electric field applied to the Pockels device. In the analyzer, this elliptic polarization causes changes in the amount of light. Thus, optical modulation can be achieved depending on the applied electric field. Such conventional optical modulator also requires at least two lenses for coupling the optical system between optical fibers.
The structure of the conventional optical modulator is described in more detail. For example, as shown in
FIG. 32
, a Mach-Zehnder type modulator
2012
used as the optical modulator is formed on a substrate
2001
made of LiNbO
3
crystal, for example. In this Mach-Zehnder type modulator
2012
, a waveguide unit
2002
includes a waveguide supplied at its incidence side with unpolarized light (TM light+TE light)
2005
, and waveguides each polarizing and separating the unpolarized light into two polarized lights (TM light and TE light) for emission, and a waveguide coupling these lights for emission. Among these waveguides, the waveguides for polarization and separation are provided with electrodes
2003
to one of which a predetermined electric field is applied by a signal source
2004
. Output light
2010
is coupled to an optical fiber
2006
through a lens
1009
. The optical fiber
2006
is composed of a core
2007
through which light is transmitted, and a clad
2008
.
As stated above, the conventional optical device such as the optical modulator requires expensive waveguides and at least one lens for optically coupling the waveguides and the optical fibers. Moreover, such coupling requires enormous amount of time and effort.
Described next is a conventional optical sensor.
FIG. 33
is a schematic front perspective view of one conventional optical voltage sensor. This optical voltage sensor includes a sensor part, a light-emitting part, a light-receiving part, and signal processing circuits in light-emitting and light-receiving sides (not shown). The sensor part is composed of a polarizer
241
, a 1/4 waveplate (also called “&lgr;/4 plate”)
242
, an electro-optic crystal
243
, and an analyzer
244
, all arranged on the same optical axis in such order from a light incidence side as mentioned above. The light-emitting part includes an E/O circuit including a light-emitting device typified by LED (Light Emitting Diode) as a light source, and an incidence side optical system composed of an optical fiber
246
a
, a ferrule
248
a
, a GRIN lens
247
a
, and a holder
245
a
, all of these arranged on the same optical axis and attached together on each optical axis plane with an adhesive. The light-emitting part includes an output side optical system composed of an optical fiber
246
b
, a ferrule
248
b
, a GRIN lens
247
b
, and a holder
245
b
, all of these arranged on the same optical axis and attached together on each optical axis plane with an adhesive, and an O/E circuit including a device for converting an optical signal emitted from the output side optical system into an electrical signal.
In the sensor part of the above optical voltage sensor, the polarizer
241
, the &lgr;/4 plate
242
, the electro-optic crystal
243
, and the analyzer
244
all arranged on the same optical axis are attached together on each optical axis plane with an adhesive. Here, the optical axis plane is a plane perpendicular to the optical axis. Each of these optical components has two such planes: an plane of incidence and a plane of emittance. On the electro-optic crystal
243
, a pair of electrodes
235
is evaporated, and electrically connected to a pair of electrode terminals
249
by lead wires. Between the electrode terminals
249
, voltage to be measured by this optical voltage sensor is applied.
The signal processing circuits in the light-emitting and light-receiving sides are respectively connected through the light-emitting part and the light-receiving part to the sensor part. In the sensor part, the polarizer
241
is fixed, with an adhesive, at its plane of incidence to the optical axis plane of the GRIN lens
247
a
in the light-emitting part. The analyzer
244
is fixed, with an adhesive, at its plane of emittance to the optical axis plane of the GRIN lens
247
b
. The adhesively fixed sensor part, incidence side optical system in the light-emitting part, and output side optical system in the light-receiving part are mechanically fixed to a case (not shown). As the adhesive for the optical components in the above optical voltage sensor, epoxy resin or urethane resin is used.
In the above optical voltage sensor, used as the electro-optic crystal
243
is Bi
12
SiO
20
(BSO), KH
2
PO
4
(KDP), or a natural birefringent material such as LiNbO
3
and LiTaO
3
, for example.
With reference to
FIG. 34
, the operational principle of the optical voltage sensor is described next. When an LED whose center wavelength is 0.85 &mgr;m is exemplary used
Rahll Jerry T
Ullah Akm Enayet
Wenderoth , Lind & Ponack, L.L.P.
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