Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-03-16
2001-12-25
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C359S204200, C359S344000, C385S129000
Reexamination Certificate
active
06333943
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical element such as an optical wavelength conversion element, a laser light source and a laser device suitable for use in the field of optical information processing or optical measuring control where coherent light is used, and also relates to a method for producing an optical element.
BACKGROUND ART
Referring to
FIG. 1
, a conventional laser light source using an optical wavelength conversion element will be described. The laser light source is basically composed of a semiconductor laser
20
, a solid state laser crystal
21
and an optical wavelength conversion element
25
made of KNbO
3
, which is a non-linear optical crystal.
As shown in
FIG. 1
, pumped light P
1
a
emitted from the semiconductor laser
20
, which oscillates at 807 nm, is collected by a lens
30
so as to excite YAG as a solid state laser crystal
21
. A total reflection mirror
22
is formed on an incident surface of the solid state laser crystal
21
. The total reflection mirror reflects 99% of light having a wavelength of 947 nm but transmits light in the 800 nm wavelength band. Although the pumped light P
1
a
is thus efficiently introduced into the solid state laser crystal
21
, the light with a wavelength of 947 nm, which is generated by the solid state laser crystal
21
, is reflected to the optical wavelength conversion element
25
side without being emitted to the semiconductor laser
20
side. Moreover, a mirror
23
, which reflects 99% of light having a wavelength of 947 nm but transmits light in the 400 nm wavelength band, is provided on the output side of the optical wavelength conversion element
25
. These mirrors
22
and
23
form a resonator (cavity) for light having a wavelength of 947 nm, capable of generating oscillation at 947 nm as a fundamental wave P
1
.
The optical wavelength conversion element
25
is inserted in the cavity defined by the mirrors
22
and
23
, whereby a harmonic wave P
2
is generated. The power of the fundamental wave P
1
within the cavity reaches to 1 W or higher. Therefore, the conversion from the fundamental wave P
1
to the harmonic wave P
2
is increased, whereby a harmonic wave having a high power can be obtained. A harmonic wave of 1 mW can be obtained by using a semiconductor laser having an output of 500 mW.
Next, referring to
FIG. 2
, a conventional optical wavelength conversion element having an optical waveguide will be described. The illustrated optical wavelength conversion element, when a fundamental wave having a wavelength of 840 nm is incident thereupon, generates a secondary harmonic wave (wavelength: 420 nm) corresponding to the fundamental wave. Such an optical wavelength conversion element is disclosed in K. Mizuuchi, K. Yamamoto and T. Taniuchi, Applied Physics Letters, Vol 58, p. 2732, June 1991.
As shown in
FIG. 2
, in this optical wavelength conversion element, an optical waveguide
2
is formed in an LiTaO
3
substrate
1
, with layers whose polarization is inverted (domain inverted layers)
3
being periodically arranged along the optical waveguide
2
. Portions of the LiTaO
3
substrate
1
where the domain inverted layer
3
is not formed will serve as a domain non-inverted layer
4
.
When the fundamental wave P
1
is incident upon one end (an incident surface
10
) of the optical waveguide
2
, the harmonic wave P
2
is created in the optical wavelength conversion element and is output from the other end of the optical waveguide
2
. At this point, light propagating through the optical waveguide
2
is influenced by a periodic structure formed by the domain inverted layers
3
and the domain non-inverted layer
4
, whereby propagation constant mismatching between the generated harmonic wave P
2
and the fundamental wave P
1
is compensated by the periodic structure of the domain inverted layers
3
and the domain non-inverted layer
4
. As a result, the optical wavelength conversion element is able to output the harmonic wave P
2
with a high efficiency.
Such an optical wavelength conversion element includes, as a basic component, the optical waveguide
2
produced by a proton exchange method.
Hereinafter, referring to
FIG. 3
, a method for producing such an optical wavelength conversion element will be described.
First, at step S
10
in
FIG. 3
, a domain inverted layer formation step is performed.
More particularly, a Ta film is first deposited so as to cover the principal surface of the LiTaO
3
substrate
1
, after which ordinary photolithography and dry etching techniques are used to pattern the Ta film into a striped pattern, thereby forming the Ta mask.
Next, a proton exchange process is performed at 260° C. for 20 minutes for the LiTaO
3
substrate
1
whose principal surface is covered by the Ta mask. Thus, 0.5 &mgr;m thick proton exchange layers are formed in portions of the LiTaO
3
substrate
1
which are not covered by the Ta mask. Then, the Ta mask is removed by etching for 2 minutes using a mixture containing HF:HNF
3
at 1:1.
Next, a domain inverted layer is formed within each of the proton exchange layers by performing a heat treatment at 550° C. for 1 minute. In the heat treatment, the temperature rise rate is 50° C./sec and the cooling rate is 10° C./sec. In portions of the LiTaO
3
substrate
1
where the proton exchange has been performed, the amount of Li is reduced as compared to that in other portions thereof where the proton exchange has not been performed. Therefore, the Curie temperature of the proton exchange layer decreases, whereby the domain inverted layer can be formed partially in the proton exchange layer at a temperature of 550° C. This heat treatment allows for formation of the proton exchange layer having a pattern upon which the pattern of the Ta mask is reflected.
Next, at step
2
in
FIG. 3
, an optical waveguide formation step is performed.
More particularly, step
2
is generally divided into step S
21
, step S
22
and step S
23
. The mask pattern is formed at step S
21
; the proton exchange process is performed at step S
22
; and high-temperature annealing is performed at step S
23
.
These steps will be described below.
At step S
21
, the Ta mask used for forming the optical waveguide is formed. The Ta mask is obtained by forming slit-shaped openings (width: 4 &mgr;m, length: 12 mm) in a Ta film. At step S
22
, a high refractive index layer (thickness: 0.5 &mgr;m) linearly extending in one direction is formed in the LiTaO
3
substrate
1
by performing a proton exchange process at 260° C. for 16 minutes for the LiTaO
3
substrate
1
which is covered by the Ta mask. The high refractive index layer will eventually function as an optical waveguide. However, the non-linearity of the portions where the proton exchange has been performed (the high refractive index layers), as thus formed, is deteriorated. In order to restore the non-linearity, annealing is performed at 420° C. for 1 minute at step S
22
after removing the Ta mask. This annealing expands the high refractive index layer in the vertical direction and in the lateral direction, thereby diffusing Li into the high refractive index layers. By reducing the proton exchange concentration in the high refractive index layers in this way, it is possible to restore the non-linearity. As a result, the refractive index of the regions located directly under the slits of the Ta mask (the high refractive index layers) is increased by about 0.03 from the refractive index in other regions, whereby the high refractive index layers function as an optical waveguide.
Next, a protective film formation step (step S
30
), an end face polishing step (step S
40
), and an AR coating step (step S
50
) are performed, thereby completing an optical wavelength conversion element.
By setting the arrangement pitch of the domain inverted layers periodically arranged along the waveguide to 10.8 &mgr;m, it is possible to form a third-order pseudo phase-matched structure.
With the above-described optical wavelength conversion element, when the length of the optical waveguide
2
is set to 9 mm, the har
Kato Makoto
Kitaoka Yasuo
Mizuuchi Kiminori
Yamamoto Kazuhisa
Arroyo Teresa M.
Inzirillo Gioacchino
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
LandOfFree
Optical device, laser beam source, laser apparatus and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical device, laser beam source, laser apparatus and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical device, laser beam source, laser apparatus and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2577553