Second harmonic wave-generating element

Details Second harmonic wave-generating element Second harmonic wave-generating element

1999-05-07

2001-03-20

Phan, James (Department: 2872)

Optical: systems and elements

Optical frequency converter

Harmonic generator

C359S332000, C252S584000

Reexamination Certificate

active

06204957

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a second harmonic wave-generating (SHG) element preferably usable for a device such as a blue laser source.
2. Related Art Statement
An element to generate a blue laser is suggested which is made by forming an optical waveguide having periodically polarization-inversed structure and in which an infrared semiconductor laser is introduced into the optical waveguide (U.S. Pat. No. 4,740,265, JP-A-5-289131, and JP-A-5-173213). For example, JP-A-6-51359 discloses a SHG element in which a polarization-inversed layer, an optical waveguide, a dielectric film, and a reflective grating layer are formed and a thickness of the dielectric film is defined into a given value.
Although these techniques require high-precisely controlling of domains, it is very hard to do so. An allowable temperature for the phase-matching must be controlled within a precision range of ±0.5° C. Moreover light damage of the optical waveguide may be recognized at 3 mw and over of a light energy. Considering these phenomena, it is pointed out that these techniques have a problem as a practical device.
On the other hand, NGK Insulators, Ltd. suggested in JP-A-8-339002 a SHG element having little light damage without a quasi-phase-matching or controlling domains at a high-precision. In this literature, a single crystal substrate is made of lithium potassium niobate or Ta-substituted lithium potassium niobate by micro pull-down method, and an optical waveguide made of a material of the same kind as of that of the substrate is formed on the substrate.
The SHG element was an epoch-making element because the element could make light damage remarkably small in the optical waveguide for converting a wavelength, and thereby an outlook for providing an element for a practical use can be obtained. However, for wide use as a blue laser source, it is required that a generation efficiency of a second harmonic wave be further increased.
SUMMARY OF THE INVENTION
It is an object of the present invention to further develop a generation efficiency of a second harmonic wave. It is also an object to make light damage much smaller.
This invention relates to a second harmonic wave-generating element for generating a second harmonic wave from a fundamental wave, comprising an optical waveguide layer made of first epitaxial material having a fundamental composition of K
3
Li
2−X
(Nb
1−Y
Ta
Y
)
5+X
O
15+Z
, an underclad part made of second epitaxial material having a fundamental composition of K
3
Li
2−X+A
(Nb
1−Y−B
Ta
Y+B
)
5+X−A
O
15+Z
, an overclad part made of third epitaxial material having a fundamental composition of K
3
Li
2−X+C
(Nb
1−Y−D
Ta
Y+D
)
5+X−C
O
15+Z
and formed on and contacting the optical waveguide layer, wherein X=0.006 to 0.5, Y=0.00 to 0.05, A=0.006 to 0.12, B=0.005 to 0.5, C=0.006 to 0.12, D=0.005 to 0.5, X−A≧0, X−C≧0, |A−C|≦0.006, and |B−D|≦0.005).
This invention will be still more described with reference to FIG.
1
.
According to the investigation of the inventors, in a structure in which a single-layered three-dimensional optical waveguide is formed on a single-crystal substrate, an integrated value of an overlapped portion of a fundamental mode between a fundamental wave and a second harmonic wave, is small, whereby a high converting efficiency can not be obtained. In the case that a film made of another material such as a dielectric material (SiO
2
, Ta
2
O
5
) is formed on the three-dimensional optical waveguide, the above integrated value of the overlapped portion could little improved, because the refractive index of the dielectric film is quite different from that of the three-dimensional optical waveguide.
In this invention, the inventors conceived the structure as schematically shown in
FIG. 1
in which an optical waveguide layer
2
A is sandwiched between an underclad part
1
and an overclad part
4
A and controlling, as above mentioned, each of the fundamental compositions of the optical waveguide layer, the underclad part, and the overclad part. Consequently, they found that in a wavelength range of a light capable of generating a blue laser, particularly preferably a range in which the wavelength of a light to be phase-matched, is 780 nm to 940 nm, the optical waveguide becomes a single mode (fundamental mode)-optical waveguide and the mode-overlapping integration between the fundamental wave and the second harmonic wave become large, whereby the generation efficiency of the second harmonic wave become conspicuously large.
The second harmonic wave-generating element according to the present invention can generate a laser of a range of 390 nm to 470 nm, for example. Thus, it can be widely used as a device for optical disk memory, a medicine uses, an optochemical uses, various optical measurements, etc. by using such a laser having a short wavelength.


REFERENCES:
patent: 4740265 (1988-04-01), Bierlein et al.
patent: 5737117 (1998-04-01), Imaeda et al.

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