JPH05289134A - Manufacture of non-linear optical device - Google Patents

Abstract

PURPOSE:To obtain a non-linear optical device which has high efficiency and superior output characteristics efficiently in manufacturing and with high yield by forming periodic domain structure in a ferroelectric substance. CONSTITUTION:Periodic domain structure adapted to a wavelength of a fundamental wave light source 5 is formed in a state in which the light source 5 is optically coupled to a ferroelectric substance 1 having a light waveguide path. Therefore, since period domain structure having an optimum period can be formed independently of dispersion of oscillation wavelength of the light source 5 for instance a semiconductor laser, a nonlinear optical device which has high conversion efficiency and superior output characteristics for instance short wavelength light source can be constituted. And after the light waveguide path 2 is formed, periodic domain structure is formed, but the light waveguide path 2 previously formed can be formed so as not to be affected any by adopting a method in which reversal of domain can be performed at a low temperature in forming this periodic domain structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-linear optical device, for example, a method for manufacturing an optical second harmonic generating element (hereinafter referred to as SHG element).

[0002]

2. Description of the Related Art An SHG element is one which introduces a fundamental wave having a frequency ω and generates light of a second harmonic having a frequency of 2ω.

Therefore, by combining this SHG element with a semiconductor laser, for example, near infrared light can be used as a short-wavelength light source of green light, and a feasible wavelength range of single-wavelength light obtained by the semiconductor laser can be obtained. Therefore, the range of use of the laser can be expanded and the use of the laser in each technical field can be optimized. For example, by shortening the wavelength of the laser light, it is possible to improve the recording density and the resolution in optical recording / reproducing and magneto-optical recording / reproducing using the laser light.

In this SHG element, the optical waveguide type SHG element for confining light in the optical waveguide is a bulk type SHG element.
Higher efficiency can be achieved as compared with the HG element. Furthermore, SH
In a G element, for example, an optical waveguide type SHG element, a domain-inverted structure, in which the polarization is periodically inverted in the optical waveguide direction, is provided, and a high output can be achieved by selecting the phase period corresponding to the wavelength of the fundamental wave. It is known to come off.

Further, in a Cherenkov radiation type SHG element having an optical waveguide, when the fundamental wave is introduced into the optical waveguide, the radiation direction of the second harmonic wave is in the substrate direction, so that it is arranged practically. I have problems,
Also in this Cherenkov radiation type SHG, a Cerenkov radiation type SHG is proposed in which the Cherenkov radiation angle is reduced by providing a domain inversion structure in which the polarization is periodically inverted in the optical waveguide, and the output beam spot shape is adjusted. (JP-A-2-9362)
(See No. 4).

As described above, the optical waveguide type SHG element having the periodic domain structure can improve the optical output characteristics, and the wavelength of the fundamental wave to be introduced is selected by selecting the inversion period of the periodic domain structure. However, once the polarization domain inversion period is set, the margin with respect to the wavelength of the fundamental wave is small and only 1 nm exists at most.

On the other hand, when a semiconductor laser is used as the fundamental wave light source, the oscillation wavelength varies from laser to laser due to variations in the thickness of the active layer forming the oscillation resonator of the semiconductor laser. The variation of the oscillation wavelength is several nm.

Therefore, for example, a semiconductor laser and an SHG
In the case where elements are combined and these are optically coupled and integrated to be used as a short wavelength light source, etc., the characteristics of the semiconductor laser and the SHG element are accurately measured, and a good combination is selected from the results. However, there is a problem in that such an operation is complicated, production efficiency is low, and it is difficult to obtain a short-wavelength light source excellent in output characteristics with a sufficient light output with a good yield.

[0009]

DISCLOSURE OF THE INVENTION The present invention is directed to the above-mentioned nonlinear optical device, in particular, as shown in FIG. 5, for example, a ferroelectric material 1 is provided with an optical waveguide 2, and a periodic structure is provided as shown by alternate arrows. In a method of manufacturing a non-linear optical device in which the domain structure 11, that is, the periodically poled structure is provided and the fundamental wave light source LD is optically coupled to the optical waveguide 2, it is possible to manufacture such a device having excellent output characteristics with a high yield. It can be so.

That is, in the present invention, the polarization reversal according to the method previously proposed by the present applicant, for example, the method disclosed in Japanese Patent Application Laid-Open No. 2-187735 or the Japanese Patent Application No. 3-107392 related to the present application. According to the control method, that is, the method of forming the domain inversion structure, a low temperature, for example, 150 ° C.
Based on the proposal of a method of forming a periodic domain structure with less than, by combining with this method, the fundamental wave light source is optically coupled, that is, in the final structure, high efficiency and output characteristics (EN) An excellent nonlinear optical device can be obtained with high manufacturing efficiency and high yield.

[0011]

That is, in the present invention, first, an optical waveguide is formed on a single-domain ferroelectric material,
After optically coupling the fundamental wave light source to this optical waveguide,
A procedure for forming a periodic domain structure in a ferroelectric substance is adopted.

Further, according to the present invention, an optical waveguide is formed in a ferroelectric material having a single domain, a fundamental wave light source is optically coupled to this optical waveguide, and then the fundamental wave of the optical waveguide is in this coupled state. The wavelength of the light from the fundamental wave light source, which is derived from the end opposite to the coupling part of the light source, is measured, and based on this, a periodic domain structure is formed that has the effect of performing phase matching with the wavelength of the fundamental wave. To do. Further, in the present invention, an optical waveguide is formed in a ferroelectric material having a domain structure, a fundamental wave light source is optically coupled to this optical waveguide, and then the fundamental wave light source of the optical waveguide is coupled in this coupled state. The wavelength of the light from the fundamental wave light source derived from the end opposite to the section is measured, and then at least one of which sandwiches the ferroelectric substance is a cycle in which the phase is matched to the measured fundamental wave wavelength. An electrode of 1 kV / mm to 100 kV / mm is provided between the first and second electrodes having a pattern corresponding to the pattern of the domain structure,
The periodic domain structure is formed in the ferroelectric by applying at a temperature not higher than C, preferably at a temperature lower than 150C.

[0013]

As described above, according to the method of the present invention, by using a method capable of forming a periodic domain structure at a low temperature and deeply forming a periodic domain structure, an optical waveguide is formed before the formation of the periodic domain structure. By doing so, a fundamental wave light source such as a semiconductor laser used as a light source is coupled to the optical waveguide, and then the period of the domain structure based on the fundamental wave wavelength measured in this state is determined. Since the domain inversion structure having the periodic structure that can be determined and the phase matching is formed, the linear optical device such as the SHG element having a high conversion efficiency with respect to the fundamental wave light source can be obtained with a high yield, and the purpose thereof can be ensured. In the case where a non-linear optical device is obtained, and the good ones are measured by measuring both the semiconductor laser and the SHG element one by one as before. Greatly improved production efficiency is tomb.

Then, the above-mentioned polarization inversion (domain inversion)
According to the control method, the shape of the domain inversion region could be formed with good controllability and without causing crystal deterioration.

This is probably because of the following reasons. That is, in general, in a ferroelectric material such as LN (LiNbO ₃ ) single crystal whose crystal is destroyed when a high voltage is applied, polarization reversal occurs even if a voltage that does not cause crystal destruction is applied. It is said that in the past, in order to cause polarization reversal by applying a relatively low voltage that does not cause crystal breakdown, that is, in order to lower the coercive electric field,
Relatively low voltage at high temperature, eg several V / mm
A polarization inversion was formed by applying a voltage of about several hundreds V / mm.

However, it was found that the crystal breakdown actually depends on the shape of the electrode to which a voltage is applied, the electrode width, and the like. That is, such crystal destruction is due to the piezoelectric effect, and the stress generated near the electrodes can be dispersed by properly selecting the electrode width and the like according to the symmetric ferroelectric material. The polarization inversion of the ferroelectric material can be performed without causing mechanical breakdown, that is, crystal breakdown.

Further, in the method of the present invention, the counter electrode is arranged in the polarization direction of the single-domain ferroelectric substance 1 and a voltage is applied between the both electrodes. By reducing the electric field component generated in the direction perpendicular to the direction of spontaneous polarization and reducing the stress generated by the piezoelectric effect, it is possible to suppress crystal strain and crystal breakage.

[0018]

Embodiments of the method of manufacturing a nonlinear optical device according to the present invention will be described in detail. For example, as shown in the schematic cross-sectional view of FIG. 1, first, an optical waveguide 2 is formed in a ferroelectric material 1 having a single domain.

This ferroelectric substance 1 is, for example, a 100 μm thick ferroelectric substance 1 which is optically polished to a precise plane, for example K.
TiOPO ₄ (KTP), LiNbO ₃ (LN), Li
It is made of a single crystal of a nonlinear optical material such as TaO ₃ .

Then, the ferroelectric body 1 is divided into, for example, a single domain in the thickness direction.

This division into single domains is performed, for example, by raising the temperature directly below the Curie temperature to, for example, about 1200.degree.
Specifically, for example, by applying an external DC voltage over the entire surface of the LN in the c-axis direction, the entire area can be divided into single domains in the c-axis direction.

An optical waveguide 2 is formed on the ferroelectric body 1.

For example, an optical waveguide 2 is formed on the surface on the positive side of the spontaneous polarization of the ferroelectric 1 made of an LN single crystal substrate having a thickness of 100 μm.

The optical waveguide 2 can be formed, for example, on the one main surface 1S side of the ferroelectric body 1 by using the well-known ion exchange, that is, the proton exchange method or the like. In this case, both end surfaces 2 of the optical waveguide 2
Each of a and 2b is optically polished into a flat surface with high precision.

The principal surface 1 on the negative side of the spontaneous polarization of the ferroelectric substance 1
An Al electrode 3 having a thickness of 400 nm, for example, is directly applied to b by vapor deposition, sputtering or the like.

Then, the ferroelectric body 1 having the optical waveguide 2 and the fundamental wave light source such as a semiconductor laser are mechanically and optically coupled. That is, the semiconductor laser and the ferroelectric body 1 are mechanically integrated in a state where the emission end of the semiconductor laser is closely opposed to the incident end of the optical waveguide 2, for example, one end face 2a.

This integration is carried out, for example, as shown in FIG.
On the heat sink 6 made of, for example, Cu, to which the semiconductor laser chip 5 is attached by the L-shaped jig 4, the ferroelectric 1 is arranged so that the emitting end of the light of the semiconductor laser closely faces the incident end face 2a of the optical waveguide 2. It is mechanically and optically bonded by a transparent adhesive 7 such as polycarbonate.

In this way, the semiconductor laser is efficiently optically coupled to the optical waveguide 2 of the ferroelectric substance 1.

A clad layer of silicon nitride, silicon oxide, alumina, tantalum oxide or the like is provided on the optical waveguide 2 of the ferroelectric substance 1 as needed.

In this state, the wavelength of the fundamental wave emitted from the other end surface 2b of the optical waveguide 2 on the ferroelectric 1 is measured. Then, the period of the periodic domain structure of the optical waveguide is determined according to the measured wavelength.

Next, the periodic domain structure 11 shown in FIG. 5 is formed in the ferroelectric 1 with the determined period.

In this case, an electrode substrate 12 having an electrode pattern corresponding to a periodic domain structure having a period determined corresponding to the wavelength of the fundamental wave light source finally obtained, that is, measured, is prepared. As shown in FIG. 4, the electrode substrate 12 is covered with an electrode layer such as Al having a thickness of 200 nm by vapor deposition sputtering or the like on an insulating substrate 13 such as a quartz substrate which is optically polished into a flat surface with high precision. Then, the patterned electrode 14 having a predetermined periodic structure capable of phase matching of the measured fundamental wave described above is patterned by a lithography technique into a parallel pattern of, for example, a comb shape or a lattice shape.

Then, as shown in FIG. 3, the pattern electrode 14 of the electrode substrate 12 is used as the main surface 1S of the ferroelectric substance 1.
They are superposed so as to be in close contact with the side, and in this state, for example, a pulse voltage of the DC power supply 15 is applied between the electrodes 3 and 14.

In this case, 300 ° C. or lower, preferably 150
At a temperature of less than ℃, the electrode 3 side deposited on the surface of the ferroelectric body 1 on the negative side of the spontaneous polarization has a negative potential, and the electrode 14 on the surface of the positive side of the spontaneous polarization has a positive potential of 1 kV. / Mm ~
DC voltage of 100 kV / mm or pulse width of one or more, for example, 1 μsec to several minutes, for example, 100 μsec
By applying 10 to 100 pulses having a pulse width of, the periodic domain structure 11 shown in FIG. 5, that is, the domain inversion structure is formed.

In this way, a nonlinear optical element such as SHG in which the optical waveguide 2 and the periodic domain structure 11 are formed is formed on the ferroelectric body 1, and a semiconductor laser as a fundamental wave light source is integrated on the end face 2a of the optical waveguide 2. Thus, the objective non-linear optical device can be obtained. In the figure, d indicates the spontaneous polarization direction.

[0036]

As described above, according to the method of the present invention, in the state where the fundamental wave light source is optically coupled to the ferroelectric substance 1 having the optical waveguide, the periodic domain structure adapted to the wavelength of this light source is formed. Therefore, since the periodic domain structure 11 having the most suitable period can be formed regardless of the variation in the oscillation wavelength of the light source, for example, the semiconductor laser, a nonlinear optical device having a high conversion efficiency and excellent output characteristics, such as a short wavelength light source, is provided. Can be configured.

The optical waveguide 2 is formed and then the periodic domain structure is formed. The periodic domain structure is first formed by adopting the above-mentioned method capable of domain inversion at low temperature. The optical waveguide 2 can be made to have no influence on its characteristics.

[Brief description of drawings]

FIG. 1 is a perspective view of an example of a ferroelectric having an optical waveguide used in an example of a nonlinear optical device according to the present invention.

FIG. 2 is an explanatory diagram of an example of a method for manufacturing a nonlinear optical device according to the present invention.

FIG. 3 is an explanatory diagram of an example of the manufacturing method of the present invention.

FIG. 4 is a perspective view of an example of an electrode substrate used in the method of the present invention.

FIG. 5 is a schematic cross-sectional view of a periodic domain structure.

[Explanation of symbols]

 1 Ferroelectric 2 Optical Waveguide 3 Electrode 5 Semiconductor Laser Chip 12 Electrode Substrate 14 Patterned Electrode

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shuichi Matsumoto 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Inventor Yuji Koga 6-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Koichiro Kijima 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (3)

[Claims] 1. A method of producing an optical waveguide in a single-domain ferroelectric material, optically coupling a fundamental wave light source to the optical waveguide, and then forming a periodic domain structure in the ferroelectric material. And a method for manufacturing a nonlinear optical device. 2. An optical waveguide is produced in a single-domain ferroelectric material, a fundamental wave light source is optically coupled to the optical waveguide, and then, in this coupled state, the fundamental wave light source of the optical waveguide is coupled. A non-linear optical device characterized in that it measures the wavelength of light from the fundamental wave light source to be led out from the end opposite to the section, and forms a periodic domain structure that is phase-matched to the wavelength of this fundamental wave. Manufacturing method. 3. An optical waveguide is formed in a single-domain ferroelectric material, a fundamental wave light source is optically coupled to the optical waveguide, and then, in this coupled state, coupling of the fundamental wave light source of the optical waveguide is performed. The wavelength of the light from the fundamental wave light source that is derived from the end opposite to the section is measured, and then at least one of which sandwiches the ferroelectric substance is phase-matched to the measured fundamental wave wavelength. An electric field of 1 kV / mm to 100 kV / mm is applied between the first and second electrodes, which have a pattern corresponding to the pattern of the periodic domain structure, at a temperature of 300 ° C. or lower to the ferroelectric substance. A method for manufacturing a non-linear optical structure, which comprises forming a periodic domain structure.