JPH0523412B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical wavelength conversion device using a semiconductor laser to realize a short wavelength compact laser light source, and the field of application is optical memory, optical display, etc. This is the field of optical information processing.

Structure of conventional example and its problems LiNbO ₃ single crystal subjected to ion exchange treatment using benzoic acid etc. takes advantage of the fact that the extraordinary refractive index increases by 0.12 to 0.13 due to Li ⁺ −H ⁺ substitution.
An optical waveguide can be formed. Therefore, in order to confine the light, aluminum or other material is used as a mask, and a mask with a width of 1 to 5 μm and a thickness of 0.3 to 3 μm is used.
Dimensional optical waveguides have been formed, and research on optical modulation devices and optical wavelength conversion devices is underway.

Figure 1 is a block diagram of a conventional example of an optical wavelength conversion device manufactured by such a method (Japanese Patent Application No. 139889/1989), in which a light guide is formed on the surface of a LiNbO ₃ substrate 1 by an ion exchange method. A semiconductor laser beam 3 (wavelength λ ₁ =0.84 μm) is coupled to the end face of the wave path 2, and a second harmonic wave 4 (hereinafter abbreviated as SH wave) is generated inside the LiNbO ₃ substrate 1.
This is an optical wavelength converter that emits wavelength λ ₂ =0.42 μm).

However, this method has the following problems.

(i) In the ion exchange treatment, chemical damage (due to crystal lattice defects) occurs in the Y-axis direction of LiNbO ₃ , and the side surfaces of the three-dimensional optical waveguide are disturbed, resulting in large scattering and transmission loss of 2 to 3 dB/
It is as large as cm.

(ii) Therefore, the conversion efficiency of the SH wave generated is small in proportion to the square of the input optical power.

OBJECT OF THE INVENTION An object of the present invention is to provide a highly efficient wavelength conversion device by reducing transmission loss in an optical waveguide.

Structure of the Invention In the conventional ion exchange method, which proceeds simultaneously in the thickness direction and the lateral direction through a mask, chemical damage tends to occur in either direction, making it difficult to reduce loss. Therefore, the present invention uses an ion exchange method to confine light in the thickness direction, and a loaded optical waveguide structure (also called an optical strip guide) to confine light in the lateral direction, thereby avoiding chemical damage and reducing loss. It is characterized by the fact that it has achieved the following.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows a first embodiment of the present invention,
The surface of the LiNbO ₃ substrate 1 is treated in benzoic acid at 240° C. for 13 minutes to form a thin film-like refractive index increasing portion 5, and SiO ₂ is deposited on the upper surface by electron beam evaporation to a width of 2.0 μm and a thickness of 0.5 μm. A loading section 6 was formed. Since the light is mainly confined and propagated in the thin film-like refractive index increasing part 7 below the loading part 6, the incident light of the semiconductor laser beam 3 propagates with low loss, and highly efficient wavelength conversion can be performed. .

The transmission loss according to the present invention is 0.5 to 1 dB/cm, much smaller than conventional methods, and the optical wavelength conversion efficiency is 30 to 50%.
It was improved compared to before. The principle of optical wavelength conversion in this example is based on the maximum nonlinear optical constant d ₃₃ of LiNbO ₃
is used to achieve phase matching between the fundamental wave guided mode and the harmonic substrate radiation mode, and the SH wave 4 is radiated into the LiNbO ₃ substrate.

FIG. 3 is a side view of a second embodiment according to the present invention, in which ion exchange is performed as deep as 2 to 5 μm as the optical input section 8 in order to improve the coupling efficiency with the fundamental wave, and the optical wavelength conversion section 9 (Thickness is 0.4-0.6μm)
The light from the semiconductor laser 10 is coupled in a smooth tapered manner, and the wavelength of the light from the semiconductor laser 10 is converted with high efficiency.

Effects of the Invention The ion exchange method can form an optical waveguide with a large refractive index change and optical damage resistance, and is effective for optical wavelength conversion elements, but the disadvantage is that three-dimensional waveguides have large transmission losses. It was hot. The present invention eliminates this disadvantage, and it goes without saying that it is effective not only for the optical wavelength conversion device described here but also for devices such as optical modulators that use the ion exchange method.

As an optical wavelength conversion device, although the optimal waveguide size differs from the fundamental wavelength, the combination of the ion exchange method and the loaded optical waveguide structure of the present invention is effective for any wavelength, especially when the fundamental wavelength is 0.8~
This is effective in terms of scattering loss when using a 0.9 μm semiconductor laser.

The conditions for ion exchange are: in benzoic acid;
The treatment may be carried out at 160 to 250°C for 5 to 20 minutes depending on the purpose. In addition to benzoic acid, lithium benzoic acid and the like can also be used.

In addition to SiO ₂ , Al ₂ O ₃ ,
A high frequency sputtered film of Ta ₂ O ₃ can also be used.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective configuration diagram of a conventional optical wavelength conversion device, FIG. 2 is a schematic perspective configuration diagram of an optical wavelength conversion device according to a first embodiment of the present invention, and FIG. 3 is a schematic perspective configuration diagram of an optical wavelength conversion device according to a first embodiment of the present invention. FIG. 1 is a schematic cross-sectional view of an optical wavelength conversion device. DESCRIPTION OF SYMBOLS 1... LiNbO ₃ crystal substrate, 3... Semiconductor laser light (fundamental wave), 4... SH wave, 5... Thin film-like refractive index increasing part formed by ion exchange method, 6... Loading part, 7... ... Portion where light is confined, 8 ... Light incidence section, 9 ... Optical wavelength conversion section, 10 ... Semiconductor laser.

Claims (1)

[Scope of Claims] 1. A semiconductor laser that emits a fundamental wave; a LiNbO ₃ single crystal substrate; a thin film-like refractive index increasing portion formed by ion-exchanging one entire principal surface of the LiNbO ₃ single crystal substrate; a striped loading section formed on the increasing section, the fundamental wave emitted from the semiconductor laser is made incident on the end face of the increasing section directly below the loading section, and the fundamental wave is directed into the loading section in the thickness direction of the substrate. The harmonics that are confined by the increasing part and laterally confined by the loading part and radiated into the substrate are taken out. An optical wavelength conversion device characterized in that it uses a phase matching method to match the effective refractive indices of modes. 2. The optical wavelength conversion device according to claim 1, wherein the thickness of the end portion of the thin film-like refractive index increasing portion through which the fundamental wave is incident is increased.