JPH10161164A - Nonlinear optical element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonlinear optical element which is low in loss, high in reliability and small in size and is small in driving energy and a process for producing the same. SOLUTION: At the time of forming an optical waveguide 11 by forming a core region 13 consisting of Ge-doped SiO2 glass having a high refractive index on a substrate 12 and enclosing this core region 13 with a clad region 14 having a low refractive index, an electric field of a high DC voltage is impressed from the outside so as to intersect with the core region 13 and simultaneously the core region 13 is irradiated with excitation light of a wavelength of <=550nm so as to intersect with the electric field and the core region 13, by which an optically anisotropic region is formed in the core region 13. The nonlinear optical element which is low in the loss, high in the reliability and small in the size and is small in the driving energy is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonlinear optical element and a method for manufacturing the same.

[0002]

_2. Description of the Related Art With the development of the fields of communication, measurement and information processing using light, highly functional and highly reliable SiO ₂ -Ge
There is a demand for the development of an optical element using O ₂ glass and an optical element having nonlinear characteristics such as an electro-optical effect and second harmonic generation. In particular, a waveguide-type optical element using a quartz-based material has received the most attention because it has the possibility of forming a complicated circuit on a flat substrate in addition to its low loss.

[0003] These waveguide type optical elements are made of Si having a low refractive index layer called a buffer layer (lower cladding layer).
In general, a light propagation region called a core having a relatively high refractive index is formed on a substrate or a quartz substrate, and this core portion is further covered with a clad layer having a low refractive index. Particularly, as the material composition of the core portion, a SiO ₂ —GeO ₂ composition glass that has been proven as a low-loss core material of an optical fiber is considered to be effective.

[0004] In general, inorganic glass such as silica glass is an optically isotropic substance, and inherently has nonlinear optical characteristics such as an electro-optical effect and second harmonic generation due to its inversion symmetry. Have been considered not.

[0005] However, it has recently been clarified that even in such an optically isotropic glass material, a second-order optical nonlinearity is induced by performing the poling treatment.

Here, the poling treatment means that a DC electric field is applied to a sample, that is, a glass material in a high temperature state, the electric field is kept applied for a certain period of time, heat is released, and the DC electric field is reduced after the optical waveguide is lowered to room temperature. This is the process of canceling. The nonlinear optical effect of such a glass material has been confirmed in various glasses such as tellurite glass and phosphate glass in addition to silica glass.

However, the mechanism of inducing the nonlinear optical effect by the polling process has not been elucidated in detail, and it is considered that there are some factors relating to the origin of the nonlinear optical effect. That is, it is considered that there are several different types of electric dipoles induced in the glass by the poling treatment depending on the structure, composition, poling treatment conditions, and the like of the glass as follows.

First, due to the drift of mobile proton ions (such as Na ⁺ ) as impurities, a cation-deficient region (space charge layer) is formed near the anode during the poling process, and this cation-deficient region forms an electric dipole. May result in orientation. In this case, only the surface layer of several tens μm on the anode side mainly serves as an optically anisotropic region.

On the other hand, electric dipoles generated by factors related to the presence of point defects, OH groups, non-crosslinking oxygen, etc., if these factors are present in the entire optical waveguide, the optical waveguide to which an electric field is applied by the poling process is used. Optical anisotropy is observed over the entire waveguide.

[0010] New attempts to incorporate anisotropic features in such optically isotropic glass materials have attracted increasing academic and practical interest. Especially Si
Silica glass containing O ₂ as a main component is a material that plays a central role in the current optoelectronics in terms of low loss and reliability, and manufacturing technologies for making optical fibers and planar optical waveguides have already been established. . In addition, silica glass has a particularly wide band gap, and is a material that can be greatly expected in the future as an element in the ultraviolet region and the far ultraviolet region even in fields other than the communication field.

[0011]

However, in order to realize a practical optical device such as an optical modulator, an optical switch, or a wavelength conversion device, the nonlinear optical effects in glass materials that have been reported to date have not yet been achieved. Weak. At the current level, for example, in order to perform an optical switching operation using the electro-optic effect, an element length (the length of the core region of the optical waveguide) is required to be several tens of cm, and a driving voltage for controlling the guided light is required. However, it is not realistic because several hundred volts are required. At least Li which has already been put to practical use as a nonlinear optical element
It is desired to realize a nonlinear optical effect comparable to a ferroelectric material such as NbO ₃ and to develop an optimum device.

An object of the present invention is to solve the above-mentioned problems and to provide a non-linear optical element having low loss, high reliability, small size and small driving energy, and a method of manufacturing the same.

[0013]

In order to solve the above-mentioned problems, it is necessary to find the optimum conditions from all viewpoints such as the composition of the glass material, the manufacturing method, the poling method, and the structure of the optical element. .

In view of the above, the present invention has focused on Ge-doped SiO ₂ glass. As described above, this material has many excellent characteristics such as low loss, high reliability, and processability for element formation, and has already been put into practical use as a passive element for communication. If a nonlinear optical effect can be induced with high efficiency by using such a material, it can be applied to more optical functional elements. Moreover, considering the mechanism of the nonlinear optical effect due to the poling process, it was found that the Ge-doped SiO ₂ glass can obtain a larger nonlinear optical effect than other glass materials.

That is, in order to achieve the above object, a method of manufacturing a nonlinear optical element according to the present invention comprises forming a core region made of Ge-doped SiO ₂ glass having a high refractive index on a substrate and forming the core region into a low refractive index. In a method of manufacturing a nonlinear optical element in which an optical waveguide is formed by being surrounded by a cladding region, an electric field of DC high voltage is applied from outside so as to intersect with the optical waveguide, and at the same time, excitation of a wavelength of 550 nm or less so as to intersect with the electric field and the optical waveguide. By irradiating light, an optically anisotropic region is formed in the core region.

According to the method of manufacturing a nonlinear optical element of the present invention, an optical waveguide is formed by forming a core region made of Ge-doped SiO ₂ glass having a high refractive index on a substrate and surrounding the core region with a clad region having a low refractive index. In the method of manufacturing a nonlinear optical element to be formed, a DC high voltage electric field is applied from the outside so as to intersect with the optical waveguide, and at the same time, the wavelength 55
An optically anisotropic region is formed in the core region by propagating excitation light of 0 nm or less.

In addition to the above structure, the method for manufacturing a nonlinear optical element according to the present invention applies a DC high-voltage electric field in a direction crossing the optical waveguide and simultaneously irradiates or propagates the core region. The polarization direction of the electric field of the excitation light is
It is preferable that the direction is substantially parallel to the direction of the DC high voltage electric field.

In addition to the above-described structure, the method for manufacturing a nonlinear optical element according to the present invention is characterized in that the core region is locally heated to a high temperature, and an external DC high-voltage electric field is applied in the high-temperature state and, at the same time, the core region is irradiated with excitation light. Alternatively, the optical waveguide is propagated in the core region, heat is released after a lapse of a certain time, and after the temperature of the optical waveguide is lowered to room temperature, the electric field of the DC high voltage is released and the irradiation of the excitation light is stopped, thereby causing an optical abnormality in the core region. Preferably, an isotropic region is formed.

In addition to the above structure, the method of manufacturing a nonlinear optical element according to the present invention is characterized in that the core region is irradiated simultaneously with the application of an electric field of a high DC voltage to the optical waveguide or the excitation light having a wavelength of 550 nm or less propagates in the core region. The light is Hg lamp light, Ar laser, ArF excimer laser, KrF excimer laser,
Ar laser or dye laser second harmonic or N
d ³⁺ : preferably one of the fourth harmonics of the YLF laser.

In addition to the above configuration, in the method of manufacturing a nonlinear optical element according to the present invention, it is preferable that an electrode closer to the core region among electrodes for applying a high DC voltage is used as an anode.

In addition to the above configuration, in the method of manufacturing a nonlinear optical element of the present invention, the core region is preferably formed by a high frequency sputtering method.

In addition to the above-described structure, the method of manufacturing a nonlinear optical element according to the present invention is characterized in that the substrate on which the optical waveguide is formed is maintained in a high-temperature hydrogen atmosphere or a high-pressure hydrogen atmosphere for a certain period of time, or at least a part of the optical waveguide is oxyhydrogen burner. After the heat treatment, it is preferable to apply an external electric field of DC high voltage and simultaneously irradiate the core region inside the optical waveguide with the excitation light or propagate the excitation light into the core region.

In addition to the above configuration, in the method of manufacturing a nonlinear optical element according to the present invention, it is preferable to use aluminum or a transparent conductor as a material of the electrode for applying a high voltage.

In addition to the above structure, the method for manufacturing a nonlinear optical element according to the present invention is characterized in that at least one of the electrodes for applying a high voltage is made a transparent electrode, and at the same time as a high DC voltage is applied, the transparent electrode passes through the transparent electrode and crosses the optical waveguide. It is preferable to irradiate the excitation light from the direction in which the light is emitted.

The nonlinear optical element of the present invention comprises an optical waveguide formed of a core region made of Ge-doped SiO ₂ glass having a high refractive index formed on a substrate and a cladding region having a low refractive index surrounding the core region. In the nonlinear optical element provided, the high voltage application electrode used to form the optically anisotropic region in the core region is used as it is or partly for controlling light propagating through the core region of the optical waveguide. It is used as a drive electrode.

The nonlinear optical element according to the present invention comprises at least one pair of drive elements in a nonlinear optical element having a core region made of Ge-doped SiO ₂ glass having a high refractive index and a cladding region having a low refractive index surrounding the core region. The electrodes are formed on the same surface, and a DC high voltage electric field is externally applied by a driving electrode in a direction intersecting the optical waveguide to control the propagation of the guided light.

A nonlinear optical element according to the present invention includes a core region made of Ge-doped SiO ₂ glass having a high refractive index and a cladding region having a low refractive index surrounding the core region. The cross-sectional shape of the peripheral cladding region has a trapezoidal shape with inclined side surfaces, at least a pair of drive electrodes are formed on the inclined side surfaces, and the drive electrodes apply an external electric field in a direction intersecting the optical waveguide. This is to control the propagation of guided light by applying.

The nonlinear optical element of the present invention is a nonlinear optical element comprising a core region made of Ge-doped SiO ₂ glass having a high refractive index and a cladding region having a low refractive index surrounding the core region. A low-resistance semiconductor layer or metal electrode is formed in the portion, and a transparent electrode or metal electrode is formed in the upper portion of the core region, and an external electric field for controlling propagation of guided light is applied to the optical waveguide in the thickness direction. It is something to do.

According to the present invention, an optically anisotropic region having a large nonlinear optical coefficient can be realized in a glass waveguide. The mechanism is presumed as follows.

As described above, a nonlinear optical effect is induced in various glass materials by performing poling.
The factors are mobile proton ions, point defects, OH groups,
It is thought that the formation of different types of electric dipoles such as non-bridging oxygen is involved.

The nonlinear optical effect in the SiO ₂ —GeO ₂ glass of the present invention is mainly due to S
This utilizes oxygen deficiency defects in iO ₂ -GeO ₂ glass.

The SiO ₂ glass doped with GeO ₂ is
Two types of NOV (neutral oxygen deficiency) with absorption in the 5eV band
And GLPC (lone electron pair of Ge). Among them, NOV is a defect having a structure represented by the following chemical formula 1. When ultraviolet light such as an excimer laser or blue-green light such as an Ar laser is irradiated, a photochemical reaction represented by the following chemical formula 2 proceeds, and GeE A paramagnetic center called an 'center' and an electric dipole are simultaneously generated.

[0033]

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[0034]

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Regarding the formation of the GeE 'center, not only the aforementioned structural change due to NOV, but also the electron trapping center (GE
C), a part of which undergoes a structural change to a GeE ′ center, or a G with a structure of = Ge:
It is considered that there is also a process in which a GeE ′ center is generated by a reaction between LPC and hydrogen molecule H ₂ via a structural change to NOV. GeE 'center is 6.3 eV
The band has an absorption peak, and the refractive index increases as the absorption band changes. The phenomenon that this GeE 'center is generated is now widely used for writing a grating in an optical fiber or the like by photo-induced light.

The present invention focuses on the generation of an electric dipole generated at the same time, rather than the existence of a GeE 'center, and utilizes it.

However, in the process of generating the GeE 'center, the GeE' center and the electric dipole are generated in pairs, so that the resulting nonlinear optical effect is G
It will be proportional to the density of the eE 'center.

The present invention utilizes the mechanism of electric dipole generation as described above to induce the nonlinear optical effect most efficiently. The points of interest for that purpose are described below.

First, it is necessary to increase the absolute amount of the oxygen deficiency defect itself of NOV or GLPC. Next, GeE '
The structural change to the center must be promoted to increase the efficiency of generating electric dipoles. It is important to induce the optical anisotropy by the regular electric dipole orientation by the strong external electric field simultaneously with the generation of the electric dipole.

The present invention has been proposed from such a viewpoint.

The absolute amount of oxygen deficiency defects varies greatly depending not only on the Ge concentration but also on the glass production method. GeO ₂
Ge-doped SiO ₂ glass films formed by high-frequency sputtering using SiO ₂ as a target contain more oxygen deficiency defects than methods formed by electron beam evaporation or melting glass fine particles. Do you get it. In addition, high energy density is achieved by irradiating excitation light having a wavelength of 550 nm or less from the vicinity of the Ge-doped SiO ₂ glass film or by propagating in a core region having a waveguide structure, thereby increasing the generation efficiency of electric dipoles. Can be. Further, as described above, since the GeE ′ center and the electric dipole are also generated by the reaction between GLPC and H ₂ , the step of holding the optical waveguide in a high-temperature or high-pressure hydrogen atmosphere for a certain time in order to promote this reaction. Alternatively, through a step of burning at least a part of the optical waveguide with an oxyhydrogen burner, a DC high voltage electric field may be applied, and at the same time, the core region may be irradiated with excitation light or may be propagated in the core region.

In order to enhance the regular orientation of the electric dipole, in the present invention, the direction of the electric field of the DC high voltage applied to the optical waveguide and the electric field of the excitation light irradiated to the core region or propagating in the core region. Were made substantially parallel in polarization direction. At the same time as applying a DC high voltage electric field and irradiating the excitation light, the substrate is kept at a high temperature, thereby promoting the orientation of the electric dipole.

[0043]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a conceptual view showing an embodiment of a method for manufacturing a nonlinear optical element according to the present invention.

The optical waveguide 11 as a nonlinear optical element has:
Ge doped SiO formed on a quartz substrate 12
_It comprises a core region 13 made of _two glasses, and a cladding region 14 having a lower refractive index than the core region 13 and surrounding the core region 13.

The core region 13 is made of SiO containing GeO _2.
The core film formed on the quartz substrate 12 by the high frequency sputtering method using O ₂ as a target is subjected to patterning of the waveguide by the photolithography method, and CHF ₃
It is formed in a rectangular cross section by a reactive ion etching method using a gas.

The cladding region 14, after the core region 13 is formed by flame hydrolysis deposition, the whole on a quartz substrate 12 in the SiO ₂ by flame hydrolysis P (phosphorus) and B (boron)
Are deposited and sintered together with the quartz substrate 12 at a high temperature of 1300 ° C. to make the fine particles vitrified.

[0048] The addition of P in the SiO ₂ higher refractive index of SiO ₂ is, SiO ₂ on the contrary the addition of B to SiO ₂
Has a low refractive index. By adjusting the amounts of P and B, the refractive index of the cladding region 14 becomes substantially equal to the refractive index of the quartz substrate 12. In the present embodiment, core region 13
Was set to about 5 × 5 μm, and the relative refractive index difference between the core region 13 and the cladding region 14 was set to 0.8%.

The cladding region 1 thus formed
A pair of electrodes 15 and 16 were formed on both sides of the surface of No. 4 so as to sandwich the core region 13.

When these two electrodes 15 and 16 are connected to a DC high voltage power supply 17, an electric field is generated in a direction transverse to the core region 13 of the optical waveguide 11. An optically anisotropic region is formed in the core region 13 of the optical waveguide 11 by irradiating the excitation light in the direction of arrow A in a direction (from above in the figure) crossing the core region 13 and the electric field simultaneously with the generation of the electric field. Is done.

The excitation light is linearly condensed by a cylindrical lens (not shown) and is irradiated over the core region 13 in the longitudinal direction. Even if a circular beam obtained by condensing the excitation light by a lens is irradiated while scanning in the longitudinal direction of the core region 13, an optically anisotropic region having a specific length is formed inside the core region 13. Is done. In the present embodiment, the intensity of the electric field applied to the core region 13 by the electrodes 15 and 16 is about 10 ⁶ to 10 ⁷ V / cm.

The excitation light applied to the core region 13 simultaneously with the application of the DC high voltage includes 100 to 200 mJ, 10 pp
s KrF excimer laser was used, and the irradiation time was 20 to 30 minutes. Note that the excitation light is not limited to this, and Hg lamp light having a wavelength of 550 nm or less, Ar laser,
A similar nonlinear optical effect can be obtained by the second harmonic of an ArF excimer laser, an Ar laser, a dye laser or the fourth harmonic of an Nd ³⁺ : YLF laser.

Here, in the case of low-energy Hg lamp excitation, the oxygen deficiency defect NOV becomes G due to the one-photon absorption process.
It is considered that the structure changes to eE ′, and in the case of Ar laser excitation, a similar structure change is performed by a two-photon absorption process. In the case of irradiation with high-energy-density ultraviolet excitation light such as an excimer laser, a two-step reaction in which the defect-free structure changes to GEC by the two-photon absorption process and a part of the structure changes to the GeE 'center also contributes. it seems to do.

Further, in order to enhance the orientation of the electric dipole during the irradiation of the excitation light, the polarization direction of the electric field of the excitation light is made substantially parallel to the electric field lines of the DC high-voltage electric field. Further, during the poling process, that is, during the excitation light irradiation performed simultaneously with the application of the high DC voltage (20 to 30 minutes), the optical material induced in the core region 13 also by maintaining the entire quartz substrate 12 at about 300 ° C. There is a tendency that the thermal anisotropy is enhanced, and holding at a high temperature during the poling treatment is also effective.

In order to enhance the efficiency of the electric dipole generation process, high-temperature or high-pressure hydrogen is used as a pretreatment for the step of generating a DC high-voltage electric field and simultaneously irradiating the core region 13 in the optical waveguide 11 with excitation light. The effect of enhancing the optical anisotropy can be observed even after the step of holding the optical waveguide 11 together with the quartz substrate 12 in the atmosphere for a certain period of time or the step of burning at least a part of the optical waveguide 11 with an oxyhydrogen burner. This is considered to be because the process of generating a GeE ′ center by the reaction between GLPC and hydrogen molecules is promoted as described above.

In this embodiment, the core region 13 is formed by the high-frequency sputtering method using GeO ₂ as a target as described above. The Ge-doped SiO ₂ layer for forming the core region 13 may be formed not only by the sputtering method as in the present embodiment but also by an electron beam evaporation method or a flame deposition method. However, the core region 13
Since the amount of the defects in the inside greatly depends on the method of forming the core layer, as a result of examination, it was found that the high frequency sputtering method employed in the present embodiment was the most effective.

In the embodiment shown in FIG. 1, a KrF excimer laser having a high energy density is used as the excitation light.
Although the laser light is mainly applied to the core region, a part of the laser light is also applied to the electrodes 15 and 16, so that the electrodes 15 and 16 may be thermally damaged. To prevent this thermal damage, aluminum was used as the material of the electrode. The reflectivity of a metal in the wavelength band of an excimer laser is, for example, about 32.9% when using gold as a material, whereas it is as high as about 92.4% when using aluminum as a material. Of the materials, aluminum is least likely to cause thermal damage due to absorption. As a material for the electrodes 15 and 16, besides preventing thermal damage by reflection like aluminum, a transparent electrode material such as ITO (indium-tin-oxide) may be used to form the electrodes 15, 16 by irradiation with excitation light. 16 is effective to prevent damage.

The electrodes 15 and 16 shown in FIG. 1 are electrodes for applying a high voltage used for forming an optically anisotropic region in the core region 13. If an appropriate control power supply is replaced, the optical waveguide 1
It can be used as a drive electrode for controlling the guided light propagating through one core region 13 at high speed.

FIG. 2 is a conceptual diagram showing another embodiment of the method for manufacturing a nonlinear optical element of the present invention.

The difference from the embodiment shown in FIG. 1 is that the shape of the cladding region 22 has a trapezoidal cross-sectional shape, and electrodes 23 and 24 are formed on both slopes of the cladding region 22. The purpose is to further improve the efficiency of inducing the nonlinear optical effect or the efficiency of applying a driving voltage for controlling the guided light.

The optical waveguide 21 is the same as the optical waveguide 1 shown in FIG.
As in the first embodiment, the core region 13 is made of a Ge-doped SiO ₂ glass having a high refractive index, and a cladding region 22 having a low refractive index surrounding the core region 13. The cross-sectional shape of the peripheral cladding region 22 surrounding the core region 13 has a trapezoidal shape with an inclined side surface, and electrodes 23 and 24 for applying a high voltage for inducing a nonlinear optical effect are formed on the inclined side surface. Have been.

The method of irradiating the excitation light at the time of the poling process is to apply a high DC voltage between the electrodes 23 and 24 and irradiate the excitation light in the direction of arrow B at the same time as in the case shown in FIG. Peripheral cladding region 2 surrounding core region 13
In order to make the cross-sectional shape of 2 into a trapezoidal shape whose side surface is inclined, a flat clad layer is formed by the flame deposition method as in the embodiment shown in FIG. However, it can be formed by using, for example, reactive ion etching or the like. The inclination angle of the side surface of the cladding region 22 surrounding the core region 13 varies depending on the side etching of the mask, but is determined by the material of the mask or etching conditions. The cladding region 22 having a trapezoidal cross-sectional shape can be formed by, for example, a bias sputtering method in addition to the flame deposition method and the etching process suitable for flattening. The bias sputtering has a smaller planarizing effect than the flame deposition method, and the shape as shown in FIG. 2 can be directly formed only by depositing SiO ₂ on the core. The structure as shown in the figure not only increases the efficiency of inducing the nonlinear optical effect during the poling process, but also uses the electrodes 23 and 24 for applying a high voltage as drive electrodes for directly controlling the guided light. The guided light can be controlled with a smaller voltage.

In the embodiment shown in FIGS. 1 and 2, a DC high-voltage electric field is applied, and at the same time, the excitation light is
Although the case where the irradiation is performed from the direction (upper direction in the drawing) intersecting the core region 13 of 1 (21) has been described, the excitation light may be propagated into the core region 13 without being limited to this.

Although an excimer laser is used as the excitation light, the present invention is not limited to this, and an Ar laser having a wavelength of about 488 nm may be incident on the waveguide. In the method of irradiating the excitation light in a direction intersecting with the waveguide as shown in FIG. 1 or 2, the efficiency of inducing the nonlinear optical effect is smaller in the Ar laser than in the excimer laser having higher light energy.

However, if the pumping light propagates in the core region 13 of the optical waveguide 11 (21), its light energy density reaches several MW / cm ² , so that the two-photon absorption process causes a high efficiency of optical difference. An isotropic region can be induced. However, also in this case, it is better to make the polarization direction of the electric field of the excitation light propagating in the core region 13 of the optical waveguide 11 (21) parallel to the direction of the electric field of the DC high voltage, and to induce the nonlinear optical effect more efficiently. Can be increased.

FIG. 3 is a conceptual diagram showing another embodiment of the method for manufacturing a nonlinear optical element of the present invention.

The difference from the embodiment shown in FIG. 1 is that a DC high voltage is applied in the thickness direction of the quartz substrate 12 and the core region 13 is irradiated with excitation light in a direction crossing the DC high voltage electric field. It is a point.

Electrodes 33 and 34 are formed on the upper and lower portions of the quartz substrate 12 of the optical waveguide 32 comprising the quartz substrate 12, the core region 13 and the cladding region 31, and are formed in the thickness direction of the quartz substrate 12 (vertical direction in the figure). Simultaneously with the application of the DC high voltage, the excitation light is applied to the core region 13 in a direction intersecting the longitudinal direction of the core region 13 (the direction of arrow C in the figure). With such a structure, it is easy to form an electrode on the optical waveguide 32. In general, it is known that when poling is performed by applying a high DC voltage between two electrodes, an optically anisotropic region is more easily formed on the anode side. Therefore, in the embodiment shown in FIG. 3, the electrode 33 immediately above the core region 13 is set to be on the anode side. The direction of the electric field of the applied excitation light is set to be parallel to the direction of the lines of electric force of the applied DC high-voltage electric field in the same manner as described above. Aluminum is used as a material of the electrodes 33 and 34.

In the case of this optical waveguide 32, it is impossible to irradiate the excitation light from above the core region 13 as in the embodiment shown in FIG. Therefore, the excitation light is irradiated from the side surface of the core region 13 as shown in FIG.
If the distance L between the side surface 2 and the core region 13 is long, the beam diameter may expand before the excitation light reaches the core region from the side surface, and irradiation with high energy density may not be possible.

Therefore, the optical waveguide is cut into an elongated shape so that the core region 13 is sufficiently irradiated with the excitation light even when irradiated from the side. However, depending on the circuit configuration, efficient irradiation from the side may be difficult. In such a case, the electrode 3
By using a transparent electrode such as ITO as 3, 34, the excitation light can be efficiently transmitted from above the core region 13 through the transparent electrode.

Instead of irradiating the excitation light from the side surface of the core region 13, the excitation light may be directly incident on the core region 13 and propagated in the longitudinal direction.

Although a quartz substrate is used as the substrate, the present invention is not limited to this, and a low-resistance semiconductor substrate may be used. When a low-resistance semiconductor substrate is used, electrodes may be formed on the front and back of the optical waveguide, and a DC high-voltage electric field may be applied in the thickness direction. In this case, the semiconductor substrate functions as a cathode because of its low resistance, and it is not necessary to provide the electrode 34 as shown in FIG. 3 on the back surface of the substrate.

When a low-resistance Si substrate is used as the substrate, it is preferable to form an SiO ₂ film as a buffer layer (lower cladding layer) on the Si substrate by thermal oxidation or sputtering. The core region 13 is formed on the buffer layer, and the other structure is the same as that of FIG. The thickness of the buffer layer is preferably about 20 μm so that the absorption of the guided light by the Si substrate can be ignored. The excitation light is applied from the side surface of the core region as in FIG. Alternatively, if a transparent electrode is used as the electrode on the upper side of the core region, the excitation light can be irradiated from above the core. Since the quartz substrate is used in the embodiment shown in FIG. 3, the distance between the electrode 33 and the electrode 34 is large. Therefore, to apply a large electric field in the core region 13, a very high DC voltage must be applied between the electrodes 33 and 34. On the other hand, if a low-resistance semiconductor substrate is used as the cathode, the distance between the upper electrode of the core region 13 and the cathode (low-resistance substrate) is close to several tens of μm. A large electric field can be applied to the core region 13. Using a low-resistance semiconductor substrate as a substrate, and using this low-resistance semiconductor substrate as a cathode,
It is advantageous not only at the time of the poling process for inducing an optically anisotropic region in the core region 13 but also at the time of controlling the guided light, because it operates at a low driving voltage.

FIG. 4 is a conceptual diagram showing an example of the nonlinear optical element of the present invention.
1 shows an hender-type optical modulator 41.

In the optical modulator 41, a core region 43 is formed on a quartz substrate 42, and a cladding region 44 is formed so as to surround the core region 43. Y branches 45 and 46 are formed on the input side and the output side of the guided light, respectively. Arrow D
The guided light incident in the direction is divided into two equal parts by the Y branch 45 on the input side, and propagates through two waveguide arms 47 and 48 having the same length.

Two electrodes 49 and 50 are formed on both sides of one waveguide arm 47 on the cladding region 44 with the waveguide arm 47 interposed therebetween, and are connected to an AC power supply 51. The guided light propagating in the waveguide arm 47 undergoes a phase change due to the electric field of the AC voltage. This waveguide light is multiplexed and interferes with the reference waveguide light propagating through the other waveguide arm 48 at the output side Y branch 46, so that the output intensity changes according to the phase difference between the two waveguide lights, and Emitted in the E direction.

Here, the polarization of the guided light incident on the optical modulator 41 is set to be parallel to the direction of the AC electric field. The electrodes 49 and 50 for causing a phase change are provided on both electrodes 4.
The electrode used at the time of the poling process for inducing an optically anisotropic region in the core of the waveguide arm 47 sandwiched between 9, 50 can be used as it is. During the polling process, a DC high voltage power supply (not shown) is connected between the electrodes 49 and 50, and a high voltage of several hundreds to several KV is applied. On the other hand, to control the propagation of the guided light and operate as a modulator, it is sufficient to connect an AC power supply of several volts.

As described above, according to the present invention, a very large optically anisotropic region can be efficiently induced in Ge-doped SiO ₂ glass, which has conventionally only realized a weak nonlinear optical effect. This makes it possible to integrate various functions such as light switching, modulation, and wavelength conversion utilizing the non-linear optical effects such as the electro-optical effect and the second harmonic generation in the quartz-based planar optical circuit. As a result, a functional optical device with low loss, high reliability, small size, and small driving energy can be realized.

[0079]

In summary, according to the present invention, the following excellent effects are exhibited.

By applying a DC high voltage electric field from the outside so as to cross the optical waveguide and simultaneously irradiating excitation light having a wavelength of 550 nm or less so as to cross the electric field and the optical waveguide, the core region of the optical waveguide is optically irradiated. It is possible to provide a small-sized nonlinear optical element having low anisotropy, high reliability, high reliability and low driving energy, and a method of manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing one embodiment of a method for manufacturing a nonlinear optical element of the present invention.

FIG. 2 is a conceptual diagram showing another embodiment of the method for manufacturing a nonlinear optical element of the present invention.

FIG. 3 is a conceptual diagram showing another embodiment of the method for manufacturing a nonlinear optical element of the present invention.

FIG. 4 is a conceptual diagram illustrating an example of the nonlinear optical element of the present invention.

[Explanation of symbols]

 Reference Signs List 11 optical waveguide 12 substrate (quartz substrate) 13 core region 14 clad region 15, 16 electrode 17 DC high voltage power supply

Claims (14)

[Claims] 1. Ge-doped Si having a high refractive index on a substrate
In a method for manufacturing a nonlinear optical element in which an optical waveguide is formed by forming a core region made of O ₂ glass and surrounding the core region with a clad region having a low refractive index, a high DC voltage is applied from outside so as to intersect the optical waveguide. A method for manufacturing a nonlinear optical element, characterized in that an optically anisotropic region is formed in a core region by irradiating excitation light having a wavelength of 550 nm or less so as to intersect the electric field and the optical waveguide at the same time as applying the electric field. 2. A Ge-doped Si having a high refractive index on a substrate.
In a method for manufacturing a nonlinear optical element in which an optical waveguide is formed by forming a core region made of O ₂ glass and surrounding the core region with a clad region having a low refractive index, a high DC voltage is applied from outside so as to intersect the optical waveguide. And forming an optically anisotropic region in the core region by applying an electric field of (1) and exciting light having a wavelength of 550 nm or less in the optical waveguide at the same time. 3. A DC high-voltage electric field is applied in a direction crossing the optical waveguide, and at the same time, the direction of polarization of the electric field of the excitation light irradiated to the core region or propagating in the core region is changed to the DC high voltage. 3. The method for manufacturing a nonlinear optical element according to claim 1, wherein the non-linear optical element is substantially parallel to a direction of the electric field. 4. A method in which the core region is locally heated to a high temperature, and at the same time, an external electric field of DC high voltage is applied in a high temperature state, and at the same time, the core region is irradiated with excitation light or propagated in the core region, and after a predetermined time elapses. The optically anisotropic region is formed in the core region by releasing heat and releasing the electric field of direct current high voltage and stopping irradiation of the excitation light after the temperature of the optical waveguide is lowered to room temperature. A method for manufacturing a nonlinear optical element. 5. An excitation light having a wavelength of 550 nm or less, which is applied to the core region simultaneously with the application of an electric field of a DC high voltage to the optical waveguide or propagates in the core region, is Hg lamp light.
The nonlinear optical element according to claim 1, wherein the nonlinear optical element is one of a second harmonic of an Ar laser, an ArF excimer laser, a KrF excimer laser, an Ar laser, a dye laser, and a fourth harmonic of a Nd ³⁺ : YLF laser. Production method. 6. The method for manufacturing a nonlinear optical element according to claim 1, wherein an electrode closer to the core region among electrodes for applying a high DC voltage is used as an anode. 7. The method according to claim 1, wherein the core region is formed by a high frequency sputtering method. 8. An external electric field of DC high voltage after holding the substrate on which the optical waveguide is formed in a high-temperature hydrogen atmosphere or a high-pressure hydrogen atmosphere for a certain time or burning at least a part of the optical waveguide by an oxyhydrogen burner. The method for manufacturing a nonlinear optical element according to claim 1, wherein the excitation light is applied to the core region inside the optical waveguide or the excitation light is propagated in the core region at the same time as applying. 9. The method for manufacturing a nonlinear optical element according to claim 1, wherein aluminum or a transparent conductor is used as a material of the high voltage application electrode. 10. The method according to claim 1, wherein at least one of the high voltage application electrodes is a transparent electrode, and the excitation light is applied from a direction crossing the optical waveguide through the transparent electrode simultaneously with the application of a DC high voltage. 3. The method for manufacturing a nonlinear optical element according to item 1. 11. A high refractive index Ge formed on a substrate.
In order to form an optically anisotropic region in the core region in a nonlinear optical element having an optical waveguide including a core region made of doped SiO ₂ glass and a cladding region having a low refractive index surrounding the core region. A non-linear optical element characterized in that the high-voltage application electrode used in (1) or (2) is used as it is or partially as a drive electrode for controlling light propagating in the core region of the optical waveguide. 12. A nonlinear optical element having a core region made of Ge-doped SiO ₂ glass having a high refractive index and a cladding region having a low refractive index surrounding the core region, wherein at least a pair of drive electrodes are on the same plane. Is formed in,
A non-linear optical element, wherein the drive electrode controls the propagation of guided light by applying an electric field of DC high voltage from the outside in a direction crossing the optical waveguide. 13. A nonlinear optical element including a core region made of Ge-doped SiO ₂ glass having a high refractive index and a clad region having a low refractive index surrounding the core region, wherein a peripheral clad region surrounding the core region is provided. Has a trapezoidal shape in which the side surface is inclined, at least a pair of drive electrodes are formed on the inclined side surface, and the drive electrode applies an external electric field in a direction crossing the optical waveguide. A nonlinear optical element wherein propagation of guided light is controlled. 14. A nonlinear optical element including a core region made of Ge-doped SiO ₂ glass having a high refractive index and a clad region having a low refractive index surrounding the core region, wherein a low portion is formed below the core region. A resistive semiconductor layer or a metal electrode is formed, and a transparent electrode or a metal electrode is formed above the core region, so that an external electric field for controlling propagation of guided light is applied to the optical waveguide in a thickness direction. A nonlinear optical element characterized by the above-mentioned.