JPH05204008A - Wavelength conversion element - Google Patents

Abstract

PURPOSE:To enable the efficient emission of short wavelength light and the simultaneous execution of light modulation. CONSTITUTION:Two pieces of waveguides 2, 3 consisting of a nonlinear optical medium are formed to intersect each other on a substrate 1. Electrodes 5 which can impress the potential difference for changing the optical path of the basic wave guided in the waveguides are provided in the intersected part. A polarization inversion layer 6 for forming the short wavelength light in accordance with the basic wave guided in the waveguide 3 is formed on one piece of the waveguide 3. The basic wave BM guided in the waveguide 2 is changed in the optical path like A or B according to the potential difference of the electrodes 5 upon arrival at the intersected part. The short wavelength light is emitted when the optical path changes to B and therefore, the short wavelength light is thereby modulated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength conversion element for converting a wavelength of a light beam into a shorter wavelength one using a non-linear optical medium.

[0002]

2. Description of the Related Art Conventionally, a second harmonic generation (SHG) element has been known as a wavelength conversion element for converting the wavelength of light from a laser light source into a shorter wavelength one using a non-linear optical medium. For example, Japanese Patent Application Laid-Open No. 63-44781 discloses a thin film waveguide type SHG element.

FIG. 8 is a block diagram of a thin film waveguide type SHG element of this type. In this SHG element, for example, LiNb is used.
_On a substrate 101 made of a nonlinear optical crystal material of O ₃ , Ti
Is diffused to form a waveguide 102, and a diffraction grating 103 is formed on the upper surface of the waveguide 102 at a predetermined pitch. In the SHG element having such a configuration, when the light BM having the wavelength λ from the laser light source is incident from one side of the waveguide 102 and guided as the fundamental wave in the waveguide 102,
Based on this fundamental wave, it is possible to generate the second harmonic (SH light) of this half wavelength (λ / 2) and emit it from the other side of the waveguide 102. At this time, the diffraction grating 103 provided on the upper surface of the waveguide 102 has a function of canceling the difference between the refractive index of the fundamental wave and the refractive index of the SH light in the waveguide 102. It is possible to match the phases of the fundamental wave and the SH light to improve the conversion efficiency of the SH light. For this purpose, it is necessary to set the pitch of the diffraction grating 103 to be the same as the wavelength of the fundamental wave guided in the waveguide 102 and satisfy the black condition.

[0004]

By the way, since the wavelength conversion element such as the SHG element can emit short wavelength light,
It is suitable for increasing the capacity of optical discs, etc., and therefore is required to be applied to optical disc devices and laser printers. However, when wavelength conversion elements are applied to optical disc devices, etc., the optical disc devices are downsized. That there is no problem and that short wavelength light can be modulated, that is, ON / OFF
What you can do is essential. Miniaturization of optical disk devices and the like is high when a semiconductor laser suitable for miniaturization is used as the laser light source of the wavelength conversion element instead of the gas laser, and when a semiconductor laser having a lower output than the gas laser is used as the laser light source. This can be achieved to some extent by configuring the wavelength conversion element as a waveguide type as described above, which can expect conversion efficiency.

However, conventionally, it is difficult to modulate and output short-wavelength light, and therefore, it is suitable for an optical disk device or the like which can efficiently emit short-wavelength light and at the same time perform optical modulation. It has been extremely difficult to realize a wavelength conversion element. That is, when modulating the short wavelength light, for example, when the semiconductor laser itself is attempted to be modulated, the wavelength of the fundamental wave is not stable, and in this case, the short wavelength light may not be efficiently emitted.

An object of the present invention is to provide a wavelength conversion element suitable for an optical disk device or the like which can efficiently emit short wavelength light and can also perform optical modulation.

[0007]

In order to achieve the above object, the present invention provides a plurality of waveguides made of a non-linear optical medium intersecting a substrate, and the waveguides are waveguided at the intersections. Is provided with a potential difference applying means capable of applying a potential difference for changing the optical path of the fundamental wave, and at least one of the plurality of waveguides has a fundamental wave guided through the waveguide. It is characterized in that a short-wavelength light generation section that generates short-wavelength light or a short-wavelength light extinction section that extinguishes the generated short-wavelength light is provided.

The plurality of waveguides are made of LiTaO.
It is characterized by being formed of ₃ non-linear optical media.

Further, the short-wavelength light generation section is characterized by being constituted by a phase matching section for matching the phases of the fundamental wave and the short-wavelength light generated based on the fundamental wave.

The plurality of waveguides are made of LiNbO.
The _third non-linear optical medium, or MgO is characterized in that it is formed by a non-linear optical medium of LiNbO ₃ doped.

Further, the phase matching section is characterized by being formed as a polarization inversion structure having a predetermined period, or by being formed by the birefringence of a nonlinear optical medium.

A proton exchange optical waveguide is used for the plurality of waveguides.

[0013]

When the fundamental wave or the short wavelength light guided through at least one of the plurality of waveguides reaches the intersection, it changes the optical path according to the potential difference. For example, when the potential difference is a predetermined potential, it shifts to another waveguide intersecting this waveguide, and when the potential difference is "0", it does not shift and goes straight through the original waveguide. Therefore, when the fundamental wave is guided to the intersection,
If the short wavelength light generating section is formed on the light emitting side of the original waveguide or another waveguide, the short wavelength light can be modulated by changing the potential difference. That is, for example, when a short-wavelength light generation section is formed on the light emitting side of another waveguide, when the potential difference is a predetermined value, the fundamental wave is transferred to another waveguide, and the short-wavelength light formed in it Short wavelength light can be emitted from the generator, and when the potential difference is “0”, the fundamental wave does not move, so short wavelength light is not emitted. Therefore, it is possible to control the ON / OFF control of the emission of the short wavelength light from the element by changing the potential difference.

If the short-wavelength light is efficiently generated when the fundamental wave reaches the intersection, the short-wavelength light extinction portion is formed in at least one waveguide. In this case, the short-wavelength light propagating through at least one waveguide moves to another waveguide when the potential difference at the intersection is a predetermined value, and does not move when the potential difference is “0”, and Propagate through the waveguide. Therefore, if a short-wavelength light extinction portion is formed on the light emitting side of the original waveguide or another waveguide, the short-wavelength light generation portion can be shortened by changing the potential difference, which is the principle opposite to the case of forming the short-wavelength light generation portion. Wavelength light can be modulated.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a first embodiment of a wavelength conversion element according to the present invention. In the wavelength conversion element of FIG. 1, LiTaO
Two waveguides 2 and 3 having a refractive index higher than that of the substrate 1 are formed on the substrate 1 made of the nonlinear optical material ₃ (single crystal having a -C plate orientation) so as to cross each other. Planar electrodes 5 (5a, 5b) are arranged at the intersections. The planar electrode 5 is provided to reduce the refractive index in proportion to the electric field generated in the substrate 1 by the Pockels effect when a positive voltage is applied to the planar electrode 5 and form a boundary surface of total reflection directly under the electrode. ing. When LiTaO ₃ of -C plate as shown in FIG. 1 is used as the substrate 1 or LiNbO ₃ of C plate as described later is used, as shown in more detail in FIG. In order to utilize the component, one electrode 5a of the planar electrode 5 is arranged on the waveguide with its edge aligned with the center of the waveguide intersection, and a predetermined voltage is applied to the other electrode 5a.
For b, it is placed outside the waveguide and held at ground potential.

Here, the condition for causing total reflection at the intersection of the waveguides 2 and 3 is as follows according to Snell's law.

[0017]

Cos θ> (n _i −Δn _i ) / n _i Δn ₀ = n ₀ ³ r ₁₃ E / 2, Δn _e = n _e ³ r ₃₃ E / 2

In Equation 1, n _i is the refractive index of the medium, E is the electric field generated in the substrate, and r ₁₃ and r ₃₃ are Pockels constants. For example, in the LiTaO ₃ substrate, r ₁₃ is 7.
0/10 ⁶ (μm / V), r ₃₃ is 30.3 / 10 ⁶ (μm /
/ V). Therefore, when no voltage is applied to the electrodes 5 on the intersections of the waveguides 2 and 3, that is, 5a, for example, the fundamental wave BM propagating in the waveguide 2 is totally reflected at the intersections as indicated by arrow A. Without going straight, it goes straight on the waveguide 2,
In the state where a predetermined voltage V is applied to the electrode 5a, the fundamental wave BM guided in the waveguide 2 is totally reflected at the intersection as shown by the arrow B and moves to the waveguide 3, and then from the waveguide 2 Waveguide 3
The optical path is switched to. At this time, the smaller the crossing angle θ between the waveguides 2 and 3 and the planar electrode 5, the smaller the applied voltage V required to switch the optical path according to the equation (1).

Further, in the example of FIG. 1, the phase matching section 6 for efficiently converting the fundamental wave guided through the waveguide 3 into light having a shorter wavelength than this, for example, SH light is provided on the waveguide 3. Is provided. The phase matching section 6 is composed of, for example, a polarization inversion layer formed by heat treatment after proton exchange, and a period of a nonlinear constant with respect to the fundamental wave and SH light generated based on this by the polarization inversion layer 6. Change. The frequencies of the fundamental wave and SH light in the waveguide 3 are ω and 2ω, respectively, and the propagation constants of the fundamental wave and SH light in the waveguide 3 are β.
Assuming that (ω) and β (2ω), in order to match the phases of the fundamental wave and the SH light, the period Λ of polarization inversion needs to satisfy the relationship of the following equation.

[0020]

[Formula 2] β (2ω) −2β (ω) = 2π · (2m−1) / Λ (m: natural number)

In the waveguide 3, the equivalent refractive index for the fundamental wave is N (ω) and the equivalent refractive index for SH light is N (2ω).
Then, the equivalent refractive index N and the propagation constant β are β = 2πN /
Since there is a relation of λ, the above equation 2 can be further replaced by the following equation.

[0022]

Λ = (2m−1) λ / 2 {N (2ω) −N (ω)} (m: natural number)

If there is a domain-inverted structure with a period Λ that satisfies the relation of the above expression 3, SH light can be efficiently obtained. Therefore, in the domain-inverted layer 6, polarization domains are created at the pitch of this period Λ. Is good.

For example, if the fundamental wave has a wavelength λ of 0.83 μm and the electric field direction thereof is the _Exoo mode in the x-axis direction ( _normal light), then the waveguide 3 of this fundamental wave is used.
The wavelength dispersion of the equivalent refractive index in (LiTaO ₃ ) is 2.
It becomes 1538. Further, 0.415μ generated by the nonlinear constant d ₃₁ of the nonlinear optical crystal material based on this fundamental wave
Waveguide 3 for E- _zoo mode SH light of wavelength m (λ / 2)
The wavelength dispersion of the equivalent refractive index at is 2.814.
Therefore, the period Λ of the refractive index change in this case is about 3.3 μm according to the equation 3, and in this case, if the polarization domain of the polarization inversion layer 6 is created at a pitch of about 3.3 μm, the The phase of the wave and the SH light can be matched.

Further, for example, the fundamental wave has a wavelength λ of 0.83 μm, and its electric field direction is E in the z-axis direction.
_{When using a zoo} mode light (extraordinary light), the wavelength dispersion of the equivalent refractive index of the fundamental wave waveguide (LiTaO ₃ ) is 2.1578. Further, 0.4 generated by the nonlinear constant d ₃₃ of the nonlinear optical crystal material based on this fundamental wave
The chromatic dispersion of the equivalent refractive index in the waveguide of the E _zoo mode SH light having a wavelength (λ / 2) of 15 μm is 2.2814. Therefore, the period Λ of the polarization inversion in this case is about 3.4 μm according to the equation 3, and in this case, if the polarization domain of the polarization inversion layer 6 is created at a pitch of about 3.4 μm, the fundamental wave in the polarization inversion layer 6 is generated. And SH light can be matched in phase.

Further, for example, the fundamental wave has a wavelength λ of 1.2 μm, and its electric field direction is E in the x-axis direction.
_{When the xoo} mode one (ordinary light) is used, the wavelength dispersion of the equivalent refractive index of the fundamental wave waveguide (LiTaO ₃ ) is 2.1305. In addition, 0.6 μ generated by the nonlinear constant d ₃₁ of the nonlinear optical crystal material based on this fundamental wave
The wavelength dispersion of the equivalent refractive index in the waveguide of the E _zoo mode SH light of the wavelength m (λ / 2) is 2.1878. Therefore, the period Λ of the polarization reversal in this case is about 1 according to Equation 3.
It becomes 0.5 μm, and in this case, if the polarization domain of the polarization inversion layer 6 is formed at a pitch of about 10.5 μm, the phase of the fundamental wave and the SH light can be matched in the polarization inversion layer 6.

Further, for example, the fundamental wave has a wavelength λ of 1.2 μm, and its electric field direction is E in the z-axis direction.
_{If a zoo} mode light (extraordinary light) is used, the wavelength dispersion of the equivalent refractive index of the fundamental wave waveguide (LiTaO ₃ ) is 2.1341. Further, based on this fundamental wave, 0.6 generated by the nonlinear constant d ₃₃ of the nonlinear optical crystal material
The wavelength dispersion of the equivalent refractive index in the waveguide of the SH light of the E _zoo mode having the wavelength (λ / 2) of μm is 2.1878.
Therefore, the period Λ of the refractive index change in this case is about 11.2 μm according to the equation 3, and in this case, if the polarization domain of the polarization inversion layer 6 is created at a pitch of about 11.2 μm, the The phase of the wave and the SH light can be matched.

The wavelength conversion element as shown in FIG. 1 can be manufactured by the following method. That is, for example, T is formed on the surface of the substrate 1 made of a nonlinear optical material such as LiTaO _3.
Waveguides 2 and 3 are formed by diffusing i, Cu and the like at a temperature of about 1000.degree. The waveguides 2 and 3 are preferably made in a single mode. After that, an electric field is applied at a temperature near the Curie point in the C-axis direction of the cut chip, and poling is performed to align the polarization directions. further,
After masking the area other than the shaded area (see FIG. 1) on the upper surface of the substrate 1,
At a temperature of about 250 ° C. and proton exchange in benzoic acid solution, which Curie point of LiTaO ₃ (Tc~6
By performing heat treatment at a temperature just below (00 ° C.), the phase matching portion, that is, the polarization inversion layer 6 can be formed in the portion not masked. The thickness of the domain inversion layer 6 can be adjusted by changing the temperature rising rate, and the length of the domain inversion layer 6 in the width direction of the waveguide 3 does not always match the width of the waveguide 3. May be. That is, the polarization inversion layer 6 may be formed not only on the waveguide 3 but also in the y direction of the upper surface of the substrate.

The planar electrode 5 (5a, 5b) is
It can be formed by electrolytic plating on the buffer layer of the silicon oxide film formed by plasma CVD. That is, NiCr- as an adhesive layer on the buffer layer.
After vapor deposition of Au, a thick film resist is patterned, Au is grown by electrolytic plating using the pattern as a guide, and then the resist is removed, and the portions other than the Au-plated portion are removed by etching. , 5
b) can be created.

For the waveguides 2 and 3, in addition to the above-described method of making, instead of Ti, CU, etc., Rb, C
It is possible to use a metal such as s or Ag that can diffuse at around 300 to 400 ° C. At this time, first, the polarization inversion layer 6 is formed by the same procedure as described above, and thereafter, the metal ions are ion-diffused or the waveguides 2 and 3 are formed by proton exchange with benzoic acid, pyrophosphoric acid or the like. Can be formed. Further, Au or Ni can be used instead of Au as the material of the electrodes 5 (5a, 5b). In this case, the electrodes 5 (5a, 5b) are formed by lift-off method, photolithography, electrolytic plating method, or the like. To be done.

Next, the operation of the wavelength conversion element having the structure shown in FIG. 1 will be described. When light from a laser light source is incident on the waveguide 2 and the fundamental wave BM is guided to the waveguide 2,
This fundamental wave propagates through the waveguide 2 to the position of the planar electrode 5, that is, to the intersection. Now, when no voltage is applied to the electrode 5a, the fundamental wave propagating through the waveguide 2 is not reflected at the crossing portion, and the same waveguide 2 as shown by arrow A is shown.
And goes out from the waveguide 2, and the transfer of the fundamental wave from the waveguide 2 to the waveguide 3 does not occur. At this time, the SH in the waveguide 2 is based on the fundamental wave propagating in the waveguide 2.
Although light is also generated, since the fundamental wave and the SH light are not phase-matched in the waveguide 2, the conversion efficiency into the SH light is extremely poor. Therefore, substantially only the fundamental wave is emitted from the waveguide 2. It is emitted and SH light is not emitted. Further, since there is no transfer of the fundamental wave to the waveguide 3, no SH light is emitted from the waveguide 3 either.

In such a state, when the voltage applied to the electrode 5a is increased, a reflecting surface is formed at the intersection of the two waveguides 2 and 3 by the Pockels effect, and the waveguide 2 to the waveguide 3 is formed. When the voltage of the fundamental wave is changed to a predetermined voltage V and the total reflection surface is formed at the intersection, the fundamental wave propagated to the intersection on the waveguide 2 is By the way, as shown by an arrow B, all the light is moved to the waveguide 3. The fundamental wave transferred to the waveguide 3 propagates in the waveguide 3 and substantially generates SH light at the phase matching portion, that is, the polarization inversion layer 6. That is, at the polarization inversion layer 6, the phases of the fundamental wave and SH light generated based on the same are matched, and the fundamental wave can be efficiently converted into SH light. As a result, SH light is emitted from the waveguide 3.

As described above, in the example of FIG. 1, by changing the voltage V to the electrode 5a, the transfer of the fundamental wave from the waveguide 2 to the waveguide 3 is controlled, and the SH light is substantially modulated. You can That is, by turning on / off the voltage V, it becomes possible to turn on / off the emission of SH light.

More specifically, the waveguide and the planar electrode 5
The crossing angle θ with is 1/100 radian, and the wavelength λ is, for example, 0.83 μm, and the fundamental wave of the E _xoo mode is guided to the waveguide 2, and the SH light of the E _zoo mode is emitted from the waveguide 3. At times, the electric field strength required for total reflection of the fundamental wave at the intersection is 3.0 V / μm or more. Further, when the wavelength λ is, for example, 0.83 μm and the E _zoo mode fundamental wave is guided to the waveguide 2 and the E _zoo mode SH light is to be emitted from the waveguide 3, the fundamental wave at the crossing portion is changed. The electric field strength required for total reflection is 0.7 V / μm or more. In addition, the fundamental wave of the _Exoo mode with a wavelength of, for example, 1.2 μm is _applied to the waveguide 2
The electric field strength required for total reflection is 3.
1 V / μm or more and E at wavelength of 1.2 μm
When guiding the _zoo mode fundamental wave to the waveguide 2,
The electric field strength required for total reflection is 0.72 V / μm or more.

3 to 4 are views showing modifications of the wavelength conversion element shown in FIG. In addition, in FIG. 3 to FIG.
The same parts as those in FIG. 1 are designated by the same reference numerals.

In the wavelength conversion element shown in FIG. 3, a phase matching section 11 similar to the phase matching section 6 formed in the wavelength conversion element of FIG. 1 is formed in the waveguide 2. Also in this case,
Similar to the example of FIG. 1, by changing the voltage to the electrode 5a, the transfer of the fundamental wave from the waveguide 2 to the waveguide 3 can be controlled and the SH light can be substantially modulated. Three
Contrary to the wavelength conversion element of FIG. 1, the wavelength conversion element of No. 2 does not emit SH light when the voltage is the predetermined voltage V, but can emit the SH light from the waveguide 2 when the voltage is “0”. it can. That is, the emission of SH light can be turned OFF / ON by turning the voltage ON / OFF.

Further, in the wavelength conversion element shown in FIG. 4, the phase matching portion, that is, the polarization inversion layer 20 is provided on the light incident side with respect to the intersecting portion. In this case, SH light can be efficiently generated at the polarization inversion layer 20 before the fundamental wave reaches the crossing portion in the waveguide 2, and the path of the SH light itself can be controlled by the voltage of the electrode 5a. , SH light can always be emitted from one of the waveguides 2 and 3. That is, when the voltage is “0”, the SH light can be emitted from the waveguide 2, and when the voltage is equal to or higher than the predetermined value V, the SH light can be emitted from the waveguide 3. In addition,
When the crossing angle θ is 1/100 radian and the fundamental wave has a wavelength of 0.83 μm, the electric field strength required for total reflection is 0.63 V / μm or more, and the fundamental wave has a wavelength of 1. When the thickness is 2 μm, the electric field strength required for total reflection is 0.68 V / μm or more.

In the first embodiment described above, Li
Since TaO ₃ is used and LiTaO ₃ generally has a high optical damage threshold, the degree of optical damage is small. Therefore, even if LiTaO ₃ is used for the substrate 1 for a long period of time, the performance of the device deteriorates to a considerable extent. You don't have to. Also, LiT
Since the Curie point Tc of aO ₃ is as low as 600 ° C,
The wavelength conversion element can be made at a relatively low temperature.

[0039] In contrast, the LiNbO ₃ or LiNbO ₃ of MgO-doped, is often used as a conventional non-linear optical crystal, the optical damage threshold is lower than the LiTaO _3, susceptible to photodamage, These Curie Point Tc
Is as high as about 1100 ° C, so L
It requires higher temperature treatment than iTaO ₃ . However, it is of course possible to produce a wavelength conversion element having the same function as the wavelength conversion element of the first embodiment by using LiNbO ₃ or MgO-doped LiNbO ₃ as the substrate.

FIG. 5 is a constitutional view of a second embodiment of the wavelength conversion element according to the present invention. In this second embodiment, Li is used.
A non-linear optical material of NbO ₃ or MgO-doped LiNbO ₃ (single crystal having a C plate orientation) is used as the substrate 21. The wavelength conversion element of FIG. 5 has a structure corresponding to that of FIG. 1, and two waveguides 22 and 23 are provided on the substrate 21.
Are formed so as to intersect with each other, a planar electrode 25 (25a, 25b) is provided at the intersection, and a polarization inversion layer 26 as a phase matching portion is formed on the waveguide 23.

The pitch of the polarization domain of the polarization inversion layer 26 is created with the period Λ determined by the equation 3 as in the case of the polarization inversion layer 6. However, in this case, the substrate 1 is not LiTaO ₃ but LiNbO ₃ or MgO.
Since doped LiNbO ₃ is used, the period Λ is shown in FIG.
Is different from the case.

That is, for example, the fundamental wave is 0.83 μm
When the E _xoo mode (ordinary _ray ) of which the electric field direction is the x-axis direction is used, the wavelength dispersion of the equivalent refractive index of the fundamental wave waveguide (LiNbO ₃ ) is 2.22. Becomes Further, 0.415 generated by the nonlinear constant d ₃₁ of the nonlinear optical crystal material based on this fundamental wave
The wavelength dispersion of the equivalent refractive index in the waveguide of the SH light of the E _zoo mode having the wavelength (λ / 2) of μm is 2.22. Therefore, the period Λ of the polarization inversion in this case is approximately 7 μ according to the equation 3.
m, and in this case, the polarization inversion layer 2 has a pitch of about 7 μm.
If the polarization domain 6 is created, the phase of the fundamental wave and the SH light can be matched in the polarization inversion layer 26.

Further, for example, the fundamental wave has a wavelength λ of 0.83 μm, and its electric field direction is E in the z-axis direction.
_{When a zoo} mode light (extraordinary light) is used, the wavelength dispersion of the equivalent refractive index of the fundamental wave waveguide (LiNbO ₃ ) is 2.17. Further, 0.415 μm generated by the nonlinear constant d ₃₁ of the nonlinear optical material based on this fundamental wave
The wavelength dispersion of the equivalent refractive index in the waveguide of the SH light of the E _zoo mode having the wavelength (λ / 2) is 2.28. Therefore,
The period Λ of the change in the refractive index in this case is about 3.8 according to Equation 3.
μm, and in this case, if the polarization domain of the polarization inversion layer 26 is created at a pitch of about 3.8 μm, the polarization inversion layer 26
In, it is possible to match the phases of the fundamental wave and the SH light.

The wavelength conversion element having the structure as shown in FIG. 5 also operates in the same manner as the wavelength conversion element of FIG. 1 and changes the voltage applied to the electrode 25a to shift the fundamental wave from the waveguide 22 to the waveguide 23. Can be controlled to substantially modulate the SH light. In this case, the Pockels constant is such that r ₁₃ is 8.6.
^{/ 10 6 (μm / V)} , r 33 is 30.8 / 10 ⁶ (μm /
V). Therefore, when the crossing angle θ between the waveguide and the planar electrode 25 is set to 1/100 radian and a fundamental wave having a wavelength of 0.83 μm and an _Exoo mode is used, the electric field strength required for total reflection is 2.3 V / When the fundamental wave has a wavelength of 0.83 μm and an E _zoo mode, the electric field strength required for total reflection is 0.68 μm.
V / μm or more.

In the second embodiment, the substrate is made of Li.
Since the C plate of NbO ₃ is used, the applied voltage for causing total reflection is a negative voltage, unlike the first embodiment. Further, also in the second embodiment, the wavelength conversion element of FIG. 5 can be modified into the structure of the first embodiment as shown in FIGS.

FIG. 6 is a block diagram of the third embodiment of the wavelength conversion element according to the present invention. In FIG. 6, the same parts as those in FIG. 5 are designated by the same reference numerals. In the third embodiment, as in the second embodiment, LiNbO ₃ or MgO is used.
Two waveguides 2 on a substrate 21 of doped LiNbO ₃
2 and 23 are formed to intersect with each other, and an electrode 25 is formed at the intersection.
Although (25a, 25b) is provided, the waveguide 22,
The domain-inverted layer is not formed on 23. That is, in this configuration, it is premised that an E _xoo wave having a wavelength λ of about 1 μm or more is used as a fundamental wave, and an _EXoo mode wave having a wavelength of λ of about 1 μm or more is used as the SH light. When using the E _zoo mode, L
Since the phase matching can be achieved by using the birefringence of iNbO _3, the SH light is not generated in either of the waveguides 22 and 23 without the need for a polarization inversion layer that gives a periodic change in the equivalent refractive index of the guided light. It can be generated efficiently. However, in this case, even if the voltage applied to the electrode 25a is changed, the SH light is always emitted from either one of the waveguides 22 and 23. The metal layer 27 is clad on the surface of the part
Is formed. As the metal layer 27, Al can be used, and a Nb ₂ O ₅ sputtered film can be used instead of Al.

In such a configuration, when a fundamental wave having a wavelength of about 1 μm or more and an _Exoo mode is incident on the waveguide 22, SH light is efficiently generated in the waveguide 22,
This SH light reaches the intersection. Here, when the voltage applied to the electrode 25a is the predetermined voltage V, the SH light reaching the intersection moves to the waveguide 23 and is emitted from the waveguide 23. On the other hand, when the voltage applied to the electrode 25a is "0", the SH light reaching the intersection does not move to the waveguide 23 but further propagates in the waveguide 22, but at this time, the cladding metal layer is clad. The waveguide 22 is absorbed by 27
SH light is not emitted from. As a result, the voltage V O
The emission of SH light can be turned ON / OFF by N / OFF.

FIG. 7 is a block diagram of the fourth embodiment of the wavelength conversion element according to the present invention. In this fourth embodiment, LiN
bO _3, a substrate 3 made of a nonlinear optical material such as LiTaO ₃
Proton-exchanged waveguides 32 and 33 are formed to intersect with each other on the electrode 1, and electrodes 35 (35a and 35b) are provided at the intersections.
Is provided, and a part of the surface of the waveguide 32 is
A cladding metal layer 37 is formed.

In such a configuration, since proton exchange optical waveguides are used for the waveguides 32 and 33, Cherenkov radiation is utilized in the waveguides 32 and 33 even if a polarization inversion layer is not separately provided. SH light can be generated. Also in this case, since the clad metal layer 37 is formed on the waveguide 32, SH light that is about to be emitted from the waveguide 32 is absorbed by this metal layer 37, and the SH is turned on / off by turning the voltage V ON / OFF. Turn on / off light emission
It can be turned off.

As described above, in each of the above-described embodiments, the function of generating short-wavelength light and the function of modulating this short-wavelength light can be realized compactly on the same substrate with a simple structure. The miniaturization of the element can be maintained. Moreover, since short-wavelength light can be easily modulated, it is possible to provide a wavelength conversion element suitable for an optical disc device.

Although the number of waveguides is two in each of the above-described embodiments, more complicated optical modulation control can be performed by using more waveguides.
In each of the above embodiments, the waveguides 2, 22, 32
When light is incident on the substrate, the front side of the intersection of the waveguides 3, 23 and 33 does not have to be formed to the end face of the substrate. Further, the waveguides can be crossed so that the center of the substrate has a structure symmetrical with respect to the y-axis.

[0052]

As described above, according to the wavelength conversion element of the present invention, a potential difference can be applied to the intersection of a plurality of waveguides made of a non-linear optical medium, and a plurality of waveguides are applied. At least one of the waveguides has a short-wavelength light generation unit that efficiently generates short-wavelength light based on a fundamental wave that propagates in the waveguide or a short-wavelength light extinction unit that extinguishes the generated short-wavelength light. Is provided, it is possible to change the optical path of the fundamental wave or the short wavelength light by injecting light that becomes the fundamental wave into at least one of the plurality of waveguides and changing the potential difference at the intersection. As a result, the modulated short wavelength light can be efficiently emitted from this wavelength conversion element.

By forming the plurality of waveguides from the non-linear optical medium of LiTaO ₃ , it is possible to suppress the performance deterioration of the element due to long-term use and to fabricate the element at a relatively low temperature.

When the short-wavelength light generating section is composed of a phase matching section for matching the phases of the fundamental wave and the short-wavelength light generated based on the fundamental wave, the short-wavelength light is efficiently converted by the phase matching section. Can be generated well. Further, when the short-wavelength light extinguishing section is composed of a cladding metal layer that absorbs the short-wavelength light generated based on the fundamental wave, this can surely absorb and extinguish the short-wavelength light. it can.

In addition, a plurality of waveguides are formed by a non-linear optical medium of LiNbO ₃ or Li doped with MgO.
By using a nonlinear optical medium of NbO ₃ , phase matching can be achieved by using the birefringence of LiNbO _{3 in} the waveguide. In this case, short wavelength light generation is possible without separately providing a short wavelength light generation unit. Can be efficiently generated and modulated by providing a short wavelength light extinction portion.

When a proton exchange optical waveguide is used for the plurality of waveguides, short wavelength light can be generated by utilizing Cherenkov radiation. In this case, at least one of the plurality of waveguides is used. By providing the short-wavelength light extinction portion in the waveguide, the short-wavelength light can be modulated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of a wavelength conversion element according to the present invention.

FIG. 2 is a diagram for explaining a state when a voltage is applied to a planar electrode.

FIG. 3 is a diagram showing a modification of the wavelength conversion element shown in FIG.

FIG. 4 is a diagram showing a modification of the wavelength conversion element shown in FIG.

FIG. 5 is a configuration diagram of a second embodiment of the wavelength conversion element according to the present invention.

FIG. 6 is a configuration diagram of a third embodiment of the wavelength conversion element according to the present invention.

FIG. 7 is a configuration diagram of a fourth embodiment of the wavelength conversion element according to the present invention.

FIG. 8 is a configuration diagram of a conventional waveguide type SHG element.

[Explanation of symbols]

1,2,31 Substrate 2,3,22,23,32,33 Waveguide 5,25,35 Electrode 6,11,20,26 Phase matching part (polarization inversion layer) 27,37 Cladded metal layer

Claims (6)

[Claims] 1. A plurality of waveguides made of a non-linear optical medium are formed to intersect a substrate, and a potential difference for changing an optical path of a fundamental wave guided through the waveguides can be applied to the intersections. A potential difference applying means is provided, and at least one of the plurality of waveguides generates a short wavelength light based on a fundamental wave guided in the waveguide. A wavelength conversion element characterized in that a short-wavelength light extinction portion for extinguishing the short-wavelength light is provided. 2. The wavelength conversion element according to claim 1, wherein the plurality of waveguides are formed of a non-linear optical medium of LiTaO ₃ . 3. The short-wavelength light generation unit includes a phase matching unit that matches the phases of a fundamental wave and short-wavelength light generated based on the fundamental wave, and the short-wavelength light extinction unit generates based on the fundamental wave. The wavelength conversion element according to claim 1, wherein the wavelength conversion element is composed of a cladding metal layer that absorbs the short wavelength light. 4. The non-linear optical medium of LiNbO ₃ or MgO-doped L waveguides
The wavelength conversion element according to claim 1, which is formed of a non-linear optical medium of iNbO ₃ . 5. The wavelength conversion element according to claim 1, wherein the phase matching portion is formed as a polarization inversion structure having a predetermined period or is formed by the birefringence of a nonlinear optical medium. .. 6. A proton exchange optical waveguide is used for the plurality of waveguides, and in this case, at least one of the plurality of waveguides has a short wavelength light extinction portion. The wavelength conversion element according to claim 1, wherein the wavelength conversion element is provided.