Optical: systems and elements – Optical frequency converter – Dielectric optical waveguide type
Reexamination Certificate
2000-03-23
2003-02-11
Lee, John D. (Department: 2874)
Optical: systems and elements
Optical frequency converter
Dielectric optical waveguide type
C385S122000, C385S129000, C385S130000, C385S141000
Reexamination Certificate
active
06519077
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical waveguide used with a coherent light in the field of optical information processing or optical measurement, a light wavelength conversion device using the same, a short wavelength light generation apparatus using the same, an optical information processing apparatus using the same, and a method for producing the same. The present invention further relates to a coherent light generation apparatus and an optical system using the same.
2. Description of the Related Art
An optical waveguide has been used as an optical wave controlling means in a wide variety of technical fields, including optical communications, optical information processing, optical measurement, and the like. Particularly, the application of an optical waveguide to an optical wavelength conversion device has been actively studied. Such an optical wavelength conversion device can convert the wavelength of a semiconductor laser device to realize a small-size short wavelength light source.
A conventional optical wavelength conversion device
600
will now be described with reference to
FIGS. 24A and 24B
.
FIG. 24A
is a perspective view illustrating an exemplary structure of the conventional optical wavelength conversion device
600
.
FIG. 24B
is a schematic diagram illustrating the conversion of a fundamental wave P
1
to a higher harmonic wave P
2
through the optical wavelength conversion device
600
of FIG.
24
A.
A conventional optical wavelength conversion device as the optical wavelength conversion device
600
of
FIG. 24A
is disclosed in, for example, Japanese Laid-Open Publication No. 5-273624. In the conventional optical wavelength conversion device
600
, a nonlinear deterioration layer is provided in the vicinity of the surface of the optical waveguide so as to achieve an increased efficiency and stabilization of the operation of the optical wavelength conversion device. Referring to
FIG. 24A
, the optical wavelength conversion device
600
includes an LiTaO
3
substrate
601
, an optical waveguide
602
, a polarization inverted region
603
, and a nonlinear deterioration layer
605
.
The TM00 mode fundamental wave P
1
enters the optical waveguide
602
of the optical wavelength conversion device
600
illustrated in FIG.
24
. Then, the TM00 mode fundamental wave P
1
is converted into a TM10 mode higher harmonic wave P
2
as it propagates through the optical waveguide
602
along which a plurality of the polarization inverted regions
603
are provided periodically. Typically, the nonlinear deterioration layer
605
has a thickness of about 0.45 &mgr;m, and the optical waveguide
602
has a thickness of 1.8 &mgr;m.
As illustrated in
FIG. 24B
, the TM10 mode higher harmonic wave P
2
has two peak outputs of about the same amplitude, on the +E side and on the −E side, respectively. The efficiency of the wavelength conversion operation is increased by increasing the overlap between the TM10 mode higher harmonic wave P
2
and the TM00 mode fundamental wave P
1
each having an intensity distribution as illustrated in FIG.
24
B. Moreover, by choosing TM10 mode for the mode of the higher harmonic wave P
2
obtained by the wavelength conversion, it is possible to distribute the power density. Thus, it is possible to suppress optical damages even when the higher harmonic wave output is high.
Another conventional optical wavelength conversion device is disclosed in, for example, Japanese Laid-Open Publication No. 4-254834, in which a high refractive index layer having a higher refractive index than that of the optical waveguide is provided on the optical waveguide.
FIG. 25A
is a perspective view illustrating such a conventional optical wavelength conversion device
640
with a high refractive index layer.
FIG. 25B
is a schematic diagram illustrating the confinement of the fundamental wave P
1
incident on the optical wavelength conversion device of FIG.
25
A.
The fundamental wave P
1
enters an end surface
645
of a proton exchange optical waveguide
642
provided on an LiNbO
3
substrate
641
of the optical wavelength conversion device
640
as illustrated in FIG.
25
A. Then, the fundamental wave P
1
is converted into the higher harmonic wave P
2
as it propagates through the optical waveguide
642
along which a plurality of the polarization inverted regions
644
are provided periodically. The higher harmonic wave P
2
is output through another end surface
646
of the optical waveguide
642
.
The device illustrated in
FIG. 25A
further includes a TiO
2
high refractive index layer
643
on the surface of the optical waveguide
642
. The refractive index of TiO
2
used in the high refractive index layer
643
is greater than that of the proton exchange optical waveguide
642
. When such layer
643
having a high refractive index is provided on the optical waveguide
642
, the confinement of the fundamental wave P
1
into the optical waveguide
642
(strictly speaking, the polarization inverted regions
644
therein), as illustrated in
FIG. 25B
, thereby increasing the efficiency of the wavelength conversion operation of the optical wavelength conversion device
640
.
Still another conventional structure for an optical waveguide of an optical wavelength conversion device is disclosed in, for example, Japanese Laid-Open Publication No. 1-238631. Japanese Laid-Open Publication No. 1-238631 discloses an optical wavelength conversion device which employs a ridge-shaped optical waveguide structure in order to increase the light confinement into the optical waveguide.
It has also been suggested in the prior art to provide on the optical waveguide a high refractive index cladding layer having a refractive index higher than that of the optical waveguide, so as to match the phase of the fundamental mode wave propagating through the optical waveguide with that of the higher mode wave, thereby increasing the overlap between the guided optical waves, and thus realizing an efficient wavelength conversion.
Japanese Laid-Open Publication No. 9-281536 discloses another conventional wavelength conversion technique, in which a proton exchange optical waveguide is provided through a proton exchange process and an annealing process, and a second proton exchange region is further provided, so as to convert a fundamental wave propagating through the optical waveguide into a second harmonic wave having a higher guide mode.
The problems associated with the above-described conventional optical wavelength conversion devices will now be described.
The conventional optical wavelength conversion device
600
illustrated in
FIG. 24A
, the nonlinear deterioration layer
605
is provided in the vicinity of the surface of the optical waveguide
602
, as described above, so as to match the phase of the TM00 mode fundamental wave P
1
and that of the TM10 mode higher harmonic wave P
2
, thereby increasing the efficiency of the wavelength conversion operation and improving the resistance against optical damages. With this conventional structure, the emitted TM10 mode higher harmonic wave P
2
has an intensity distribution with two peaks on the +E side and the −E side, respectively. Therefore, the focusing characteristics may be low.
With this conventional structure, the output higher harmonic wave P
2
has two peaks having about the same amplitude, so as to distribute the power density of the higher harmonic wave P
2
among the higher mode peaks. In order to focus the higher harmonic wave output having such an intensity distribution, it is necessary to provide a special optical system. Such an optical system is complicated and difficult to downsize. Moreover, in order to focus the beam to the diffraction limit, it is necessary to shape the beam significantly, thereby reducing the efficiency of the output light to 50% or less.
Moreover, the nonlinear deterioration layer
605
does not act to increase the confinement of the fundamental wave P
1
. Therefore, it is not possible to increase the power density
Kitaoka Yasuo
Mizuuchi Kiminori
Yamamoto Kazuhisa
Yokoyama Toshifumi
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