JPH0519310A - Optical modulation wavelength converting element - Google Patents

Abstract

PURPOSE:To perform the generation and modulation of a 2nd harmonic by the same element by forming a three-dimensional waveguide on a substrate and performing mode conversion by an electrode structure which produces a periodic electric field in a light guide direction. CONSTITUTION:When a comb line electrode 3A of the electrode structure 3 is applied with a voltage while a comb line electrode 3B is grounded, the periodic electric field is produced in a waveguide in the light propagation direction of the three-dimensional waveguide 2. The period LAMBDA2 of intervals of the comb line electrodes producing the electric field is set to LAMBDA2=lambda/(Nte-Ntm), where Nte and Ntm are the transmission refractive indexes of modes TE and TM. Here, lambda is the wavelength of basic wave laser light. When the electric field is made to operate in a direction Y while the basic wave laser light is guided to the three-dimensional waveguide 2, the main axial rotation of a refractive index elliptic body in the waveguide is caused, a nondiagonal component is generated in a specific dielectric tensor to cause coupling between both modes, and mode conversion is performed, thereby compensating the mismatching between the phases of both the modes with the electric field period of the electrode structure 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light modulation wavelength conversion element.

[0002]

2. Description of the Related Art An SHG element known as a wavelength conversion element is an optical element that utilizes a nonlinear optical effect to generate a second harmonic wave of a wavelength: λ / 2 from a laser beam of a wavelength: λ. When such a second harmonic is used, the recording density of information in an optical information recording medium such as an optical disk can be dramatically increased. Therefore, active development has been made in recent years, and a three-dimensional waveguide type is used. Various products are known (for example, JP-A-63-44781).

In order to record or process information by using the second harmonic, it is necessary to modulate the second harmonic itself.
It would be extremely convenient if the generation and modulation of harmonics could be performed by the same element, but such an element has not been realized in the past.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a completely novel optical modulation wavelength conversion element capable of performing the generation of the second harmonic and its modulation in the same element.

[0005]

An optical modulation wavelength conversion element according to a first aspect of the present invention is constructed by "integrating a harmonic generation means and an optical modulation means on the same substrate". The "harmonic generating means" has a three-dimensional waveguide that guides the fundamental laser light, and generates the second harmonic from the fundamental laser light. The "light modulator" modulates the second harmonic by performing mode conversion between TE-TM modes on the fundamental wave laser light guided in the three-dimensional waveguide. This optical modulation means sets the wavelength of the fundamental laser light to λ, and TE in the three-dimensional waveguide.
And TM mode equivalent refractive indices are Nte and Ntm, respectively.
Then, "an electrode structure having a period of an electrode interval of Λ ₂ (= λ / {Nte-Ntm}) so as to generate a periodic electric field in the waveguide direction in the three-dimensional waveguide".

When the second harmonic is generated, the fundamental wave and the second harmonic
Although it is necessary to perform phase matching with the higher harmonic wave, this phase matching can be performed using a dedicated phase matching means or can be performed by selecting a substrate.

That is, according to the second aspect of the present invention, the propagation constant of the guided mode light with respect to the fundamental laser light in the three-dimensional waveguide is β (ω), and the propagation constant of the guided mode light with respect to the second harmonic wave. Is β (2ω), the period Λ
₁ (= 2 (2m-1) π / {β (2ω) -2β (ω)}; m: natural number), the polarization inversion region formed in the waveguide is used as the phase matching means, and the harmonic generation means is used. Can be part of.

In addition, “a LiNbO ₃ c plate on which a three-dimensional waveguide is formed by diffusion is selected as a substrate, the light propagation direction is aligned with the y direction, and the z direction orthogonal to this is aligned with the c axis direction. X-direction polarization with electric field direction parallel to x-axis, second
Using the z-direction polarized wave whose electric field direction is parallel to the z-axis for the harmonics, the wavelength of the fundamental wave is set to 1 μm or more. "
it is possible to perform phase matching by birefringence of bO ₃ (claim 7).

When the periodic domain-inverted region is used as the phase matching means as in the second aspect of the invention, L is used as the substrate.
It can be used -c plate or c plate LiNbO ₃ of iTaO _3. Three-dimensional waveguides are formed on these substrates by diffusion. The substrate of LiNbO ₃ was MgO-doped Li.
Includes NbO ₃ substrate.

When a -Ta plate of LiTaO ₃ is used, the propagation direction of light is defined as the y direction, and the z direction orthogonal thereto is aligned with the -c axis direction. As a fundamental wave, "the electric field direction is parallel to the z axis. z-direction polarization ", the second harmonic is" electric field direction is z
It is possible to use "z-direction polarization parallel to the axis" (Claim 3), and when the light propagation direction is aligned with the y direction and the z direction orthogonal thereto is aligned with the -c axis direction, the "electric field" is generated as the fundamental wave. It is possible to use "x-direction polarized wave whose direction is parallel to the x-axis" and "z-directional polarized wave whose electric field direction is parallel to the z-axis" as the second harmonic (claim 4).

When a c-plate of LiNbO ₃ is used, when the light propagation direction is the y direction and the z direction orthogonal to this is aligned with the c axis direction, the electric field direction as the fundamental wave is polarized in the z direction parallel to the z axis. A z-direction polarized wave whose electric field direction is parallel to the z-axis can be used as the wave and the second harmonic (claim 5), the light propagation direction is the y-direction, and the z-direction orthogonal thereto is the c-axis direction. When combined, the electric field direction of the fundamental wave is parallel to the x-axis.
Directional polarization, z as the electric field direction as the second harmonic is parallel to the z-axis
Directionally polarized waves can also be used (claim 6).

The second harmonic can be generated by Cherenkov radiation by forming the three-dimensional waveguide on the c-plate of LiNbO ₃ by "proton exchange" (claim 8).

In the optical modulation wavelength conversion device according to any one of claims 1 to 8, "the second harmonic is obtained by performing mode conversion between TE-TM modes on the fundamental laser light guided in the three-dimensional waveguide. The wave modulation is performed ", but another modulation method is used in the optical modulation wavelength conversion element according to claim 9 or below.

That is, the optical modulation wavelength conversion element of claim 9 is
The harmonic generation means and the pair of electrodes are integrated on the same substrate. The “harmonic generating means” has a Y-shaped three-dimensional waveguide that branches into two on the emission side and guides the fundamental laser light,
The second harmonic is generated from the fundamental wave laser light. The “pair of electrodes” changes the phase of the guided light before the branch point of the three-dimensional waveguide to select the branch waveguide. Therefore, the optical modulation is performed "by selecting a branched three-dimensional waveguide (branch waveguide)". Also in the optical modulation wavelength conversion element of claim 9, the substrate is made of a non-linear medium, and the harmonic generating means is "3.
When the propagation constant of the guided mode light with respect to the fundamental laser light is β (ω) and the propagation constant of the guided mode light with respect to the second harmonic is β (2ω) in the two-dimensional waveguide, the period in the waveguide direction is: Λ (= 2 (2m-1) π / {β (2ω) -2β
(ω)}; m: natural number) as a domain-inverted region can be defined as a “refractive index changing region formed in the three-dimensional waveguide” (claim 10). In this case, the harmonic generating means itself has the function of phase matching.

Further, in this case, the "harmonic generating means by the refractive index changing region" may be formed in an intermediate portion from the incident side of the fundamental wave laser light to the branch point of the waveguide, but it is three-dimensionally guided. It may be formed on one branching waveguide that is branched into two branches of the waveguide (claim 11).

In the device of claims 9 and 10, a LiTaO ₃ -c plate having a three-dimensional waveguide formed by diffusion is used as the substrate of the non-linear medium, and the light propagation direction is set to the y direction, and is orthogonal to this. The z-direction is adjusted to the −c-axis direction, and “Z-direction polarized wave whose electric field direction is parallel to the z-axis or x-direction polarized wave whose electric field direction is parallel to the x-axis” is used as the fundamental wave, and “ A z-polarized wave whose electric field direction is parallel to the z-axis may be used (claim 12), and a LiNbO ₃ c plate having a three-dimensional waveguide formed by diffusion is used as a nonlinear medium to propagate light. The direction is defined as the y direction, and the z direction orthogonal thereto is aligned with the c axis direction, and the fundamental wave is defined as "z direction polarized wave whose electric field direction is parallel to the z axis or x whose electric field direction is parallel to the x axis.
The “directional polarization” and the “z-direction polarization in which the electric field direction is parallel to the z axis” may be used as the second harmonic (claim 13).

Further, as the substrate of the optical modulation wavelength conversion element of claim 9, LiN having a three-dimensional waveguide formed by diffusion is used.
The c-plate of bO ₃ is used, the propagation direction of light is set to the y direction, and the fundamental wave is “polarization in the x direction whose electric field direction is parallel to the x axis”.
“Z-polarized light whose electric field direction is parallel to the z-axis” can be used as a harmonic, and the birefringence of the substrate can be used for phase matching (claim 14). In this case, a metal cladding can be formed on the branch waveguide that does not emit the modulated second harmonic (claim 15).

Further, as the substrate of the optical modulation wavelength conversion element of claim 9, a plate of LiNbO ₃ crystal or LiTaO ₃ crystal in which a three-dimensional waveguide is formed by proton exchange is used,
The second harmonic can be generated by Cherenkov radiation (claim 16).

[0019]

According to the optical modulation wavelength conversion element of claims 1 to 8,
The electrode structure of the light modulation means causes an electric field to act in the light propagation direction of the waveguide to cause rotation of the principal axis of the index ellipsoid, and TE
-Initiate TM mode coupling. The second harmonic is modulated by utilizing the mode conversion associated with this mode coupling.

In the optical modulation wavelength conversion device according to the ninth aspect, the second harmonic is generated in the three-dimensional waveguide, and the modulation is performed by selecting the branch waveguide.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete embodiment will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 indicates a substrate made of a LiTaO ₃ single crystal. This substrate 1 is a -c plate. Reference numeral 2 indicates a three-dimensional waveguide formed on the substrate 1, reference numeral 3 indicates an electrode structure forming a light modulating means, and reference numeral 4 indicates a domain inversion region. When the x, y, and z directions are set as shown, the −c axis of the substrate 1 is parallel to the z direction, and the y direction corresponds to the light propagation direction of the three-dimensional waveguide 2.

In this embodiment, the three-dimensional waveguide 2 is formed by diffusing Ti on the surface of the substrate at a temperature of about 1000 ° C. and making the refractive index higher than that of the substrate 1. As the diffusing material, Cu or the like can be used in addition to Ti. The three-dimensional waveguide 2 is preferably a single mode waveguide.

The polarization inversion region 4 is a region in which the polarization is periodically inverted in the propagation direction of the guided light, that is, the y direction. To form this domain-inverted region, for example, the following may be performed.

That is, after diffusing a diffusing substance in a portion to be a three-dimensional waveguide, an electric field is applied in the c direction at a temperature near the Curie point to perform poling to align the polarization directions. Then, after masking portions of the three-dimensional waveguide 2 other than the part indicated by the broken line in FIG. 1 with Ti, proton exchange was performed in a benzoic acid solution at a temperature of about 250 ° C., and LiTaO ₃
At a temperature immediately below the Curie point (Tc to 600 ° C.), the domain inversion layer 4a is formed on the unmasked portion. In this way, the polarization inversion regions 4 in which the polarization directions are alternately inverted in the y direction are formed. The formation of the polarization inversion layer 4a is reported in Proceedings 27-P-10 distributed at the Japan Society of Applied Physics in 1989.

In some cases, after forming the domain inversion region by the above method, metal ions are ion-diffused, or proton exchange is performed at a temperature of about 250 ° C., and then annealing is performed at 380 ° C. By 3
It is also possible to form a dimensional waveguide. Rb, Cs, Ag
In the case of forming a three-dimensional waveguide by diffusion of a metal capable of diffusing at a temperature in the vicinity of 300 to 400 ° C., it is necessary to adopt this method.

As a substrate of the nonlinear medium, KTiOP is used.
When using the O ₄ z-plate, RbNO ₃ / Ba (N
By using a molten salt of O ₃ ) ₂ as the ion source, a three-dimensional waveguide similar to the above can be formed by ion exchange.

The thickness of the polarization inversion layer can be adjusted by changing the temperature rising rate. The width L of the polarization inversion layer 4a does not necessarily have to match the width of the three-dimensional waveguide 2.

The electrode structure 3 comprises a pair of comb-shaped electrodes 3A and 3B.
Are combined in a finger-like manner, and are formed as follows. That is, a buffer layer of a silicon oxide film is formed by plasma CVD on the surface of the substrate on the side where the three-dimensional waveguide 2 is formed, and NiCr-Au is vapor-deposited thereon as an adhesive. Then, the thick film resist is patterned into the illustrated electrode shape, Au is grown by electroplating using the formed pattern as a guide, and then the resist is removed by a resist remover. Finally, the portions other than the Au plating are removed by etching. In addition, it is also possible to use Al, Ni or the like to form by a lift-off method, photolithography, electric field plating or the like.

The period Λ ₁ in the periodic change of the refractive index of the domain-inverted region 4 is β (ω) which is the propagation constant of the fundamental laser light guided in the three-dimensional waveguide 2, and the propagation constant of the second harmonic wave. Is set to β (2ω), Λ ₁ = 2 (2m−1) π / {β (2ω) -2β (ω)}; m: set to a size given by a natural number.

In the electrode structure 3, when the comb-teeth electrode 3B is grounded and a voltage is applied to the comb-teeth electrode 3A, a periodic electric field is formed in the waveguide in the light propagation direction of the three-dimensional waveguide 2. However, the period Λ ₂ of the spacing between the comb-shaped electrodes that gives such an electric field is a magnitude given by Λ ₂ = λ / | Nte-Ntm |, where the transmission refractive indices of the TE and TM modes are Nte and Ntm. Is set to λ is the wavelength of the fundamental laser light.

As is well known, when an electric field is applied in the y direction while the fundamental wave laser light is guided in the three-dimensional waveguide 2, rotation of the principal axis of the index ellipsoid in the waveguide occurs,
The off-diagonal component is generated in the dielectric tensor and TE mode and TM
Mode coupling occurs and mode conversion is performed. At that time, the phase mismatch between the modes is compensated by the electric field period of the period Λ ₂ by the electrode structure 3.

The generated phase mismatch between the second harmonic and the fundamental laser light is compensated by the refractive index changing region 4 in which the refractive index alternately changes with the period Λ ₁ .

In the embodiment of FIG. 1, the substrate 1 is a LiTaO ₃ -c plate as described above.

Assuming that a semiconductor laser having a wavelength of 0.83 μm is used as a light source, the wavelength dispersion of the equivalent refractive index in the three-dimensional waveguide 2 is such that, in the fundamental wave having a wavelength of 0.83 μm, the electric field direction corresponding to ordinary light is in the x direction. 2.1538 when using the Ex ₀₀ mode, where the electric field direction corresponding to extraordinary light is z
2.157 when using Ez ₀₀ mode, which is oriented in the direction
8, the second harmonic having a wavelength of 0.415 μm is 2.2414 when the Ex ₀₀ mode corresponding to ordinary light is used, and 2.2814 when the Ez ₀₀ mode corresponding to extraordinary light is used.

Assuming a semiconductor laser light source having a wavelength of 1.2 μm, the wavelength dispersion of the equivalent refractive index is 1.2
The fundamental wave of μm is 2.1305 when the Ex ₀₀ mode corresponding to ordinary light is used, 2.1341 when the Ez ₀₀ mode corresponding to extraordinary light is used, and becomes ordinary light at the second harmonic of wavelength 0.6 μm. 2.183 when using the equivalent Ex ₀₀ mode
4, 2.1 when using Ez ₀₀ mode corresponding to extraordinary light
878.

Therefore, the equivalent refractive index for the fundamental wave is N
(ω), and the equivalent refractive index for the second harmonic is N (2ω), the propagation constant β = 2πN / λ, and thus the above relation, Λ ₁ = 2 (2m−1) λ / {β (2ω ) -2β (ω)};
m: Natural number is Λ ₁ = (2m−1) λ / [2 · {N (2ω) −N
(ω)}], and if Λ ₁ that satisfies this relationship is set to the period of the polarization inversion in the polarization inversion region, phase matching can be performed well and a stable second harmonic can be obtained.

The wavelength of the fundamental laser light is 0.83 μm, and the fundamental wave is the Ex ₀₀ mode corresponding to ordinary light.
When the Ez ₀₀ mode corresponding to extraordinary light is used as a harmonic, in the case of the equivalent refractive index, the period Λ ₁
Is about 3.1 μm. In this case, the nonlinear constant d ₃₁ will be used.

Further the Ez ₀₀ mode corresponding to the abnormal light as a fundamental wave in the wavelength 0.83 .mu.m, when using the Ez ₀₀ mode corresponding to the abnormal light as a second harmonic of the equivalent refractive index case, the refractive index The change period Λ ₁ is about 3.2 μm. In this case, the non-linear constant d ₃₃ will be used.

When the wavelength of the fundamental wave laser light is 1.2 μm and the Ex ₀₀ mode corresponding to the ordinary light is used as the fundamental wave and the Ez ₀₀ mode corresponding to the extraordinary light is used as the second harmonic,
In the case of the above equivalent refractive index, the period Λ ₁ of the refractive index change is about 1
It becomes 0.5 μm. In this case, the nonlinear constant d ₃₁ will be used.

When the Ez ₀₀ mode corresponding to extraordinary light is used as the fundamental wave and the Ez ₀₀ mode corresponding to extraordinary light is used as the second harmonic at the wavelength of 1.2 μm, the refractive index changes in the case of the above equivalent refractive index. The period Λ _{1 of} is about 11.2 μm.
In this case, the non-linear constant d ₃₃ will be used.

Refractive indexes of ordinary light and extraordinary light in the three-dimensional waveguide 2 are No and Ne, respectively, and | Nte-Ntm | ≈ (No-N
e), the period Λ ₂ in the electrode structure 3 has a wavelength of 0.
It becomes about 195 μm for 78 μm and about 333 μm for a wavelength of 1.2 μm. With such a size, the electrode structure 3 can be easily formed.

[0043] Using Ex ₀₀ mode corresponding to the ordinary light as a fundamental wave, a second corresponds to the abnormal light as a harmonic to form a domain-inverted regions 4 as used Ez ₀₀ mode, while inputting light of Ex ₀₀ mode When a periodic electric field is applied by the electrode structure 3, the Ex ₀₀ mode is converted to the Ez ₀₀ mode and the second harmonic is not generated, but if the electric field is not applied, the second harmonic is generated.

Further, the refractive index changing region 4 is formed so that the E _{X 00} mode corresponding to the ordinary light is used as the fundamental wave and the Ez ₀₀ mode corresponding to the extraordinary light is used as the second harmonic, and the Ez ₀₀ mode light is input. Meanwhile, when a periodic electric field is applied by the electrode structure 3, the Ex ₀₀ mode is converted to the Ez ₀₀ mode and the second harmonic is generated, but the second harmonic is not generated unless the electric field is applied.

Therefore, in any case, the second harmonic can be modulated by turning on and off the voltage applied to the comb-shaped electrode 3A.

FIG. 2 shows a modification of the embodiment shown in FIG. In order to avoid complication, the same symbols as those in FIG. The difference from the embodiment of FIG. 1 lies in the configuration of the electrode structure. That is, in this embodiment, the electrode structure is provided along the three-dimensional waveguide 2,
Comb-tooth-shaped electrode 3C such that the period of the comb-toothed portion is Λ _2.
And a rectangular electrode 3D provided so as to face the electrode 3C via the three-dimensional waveguide 2. Even with such an electrode structure, the same operation as in the embodiment of FIG. 1 can be performed.

FIG. 3 shows another embodiment. Also in this figure, the same symbols as those in FIG. Substrate 1 in this example
A is a LiNbO ₃ c plate, and the z axis is set according to the c axis, and the x and y directions are determined as shown in the figure.

In this case, assuming that a semiconductor laser having a wavelength of 0.83 μm is used as the light source, the wavelength dispersion of the equivalent refractive index in the three-dimensional waveguide 2 uses the Ex ₀₀ mode corresponding to ordinary light for the fundamental wave having a wavelength of 0.83 μm. 2.2 if
2. 2.1 in case of using Ez ₀₀ mode corresponding to extraordinary light
7. For the second harmonic having a wavelength of 0.415 μm, it is 2.39 when the Ex ₀₀ mode corresponding to ordinary light is used, and 2.28 when the Ez ₀₀ mode corresponding to extraordinary light is used.

[0049] The Ex ₀₀ mode of the fundamental wavelength laser light is 0.83 .mu.m, corresponding to the ordinary light as a fundamental wave, second
When the Ez ₀₀ mode corresponding to extraordinary light is used as a harmonic, in the case of the equivalent refractive index, the period Λ ₁
Is about 3.1 μm. Ez ₀₀ mode, which corresponds to extraordinary light as the fundamental wave, corresponds to extraordinary light as the second harmonic
When the Ez ₀₀ mode is used, the refractive index change period Λ ₁ is about 3.2 μm. The period Λ ₂ in the electrode structure 3 is about 16.6 μm for a wavelength of 0.83 μm. With such a size, the electrode structure 3 can be easily formed.

[0050] Instead as the material of the substrate 1A in LiNbO ₃ crystal, the same as the embodiment can be obtained even by using a LiNbO ₃ crystal doped with MgO. When a LiNbO ₃ crystal or a MgO-doped LiNbO ₃ crystal is used as the substrate 1A, the fundamental wave Ex corresponding to ordinary light is used.
_{When the 00} mode and the Ez ₀₀ mode corresponding to the extraordinary light are used for the second harmonic, if the wavelength of the fundamental wave is 1 μm or more, phase matching can be performed by utilizing the birefringence of the substrate, which is a nonlinear medium. Therefore, in such a case, the refractive index change region 4 for achieving the phase matching between the fundamental wave and the second harmonic can be omitted. FIG. 4 shows an example of such a case.

The embodiment of FIG. 4 is the same as the embodiment of FIG. 3 except that there is no refractive index changing region. In the embodiment of FIGS. 3 and 4, when the Ex ₀₀ mode is used as the input light, when a voltage is applied to the electrode 3A, the Ex ₀₀ mode is converted to the Ez ₀₀ mode.
Although no harmonic is generated, a second harmonic is generated when no voltage is applied to the electrode 3A.

It is known that a stable second harmonic can be generated by Cherenkov radiation when a three-dimensional waveguide is formed on the LiNbO ₃ substrate 1A by proton exchange (Applied Physics: Vol. 56, No. 12, 1637). (4
9) page 1987). Also in this case, the refractive index changing region for phase matching is unnecessary.

Therefore, when the three-dimensional waveguide 2 is formed by proton exchange in the configuration of FIG. 4, the second harmonic wave by Cherenkov radiation can be modulated by turning on / off the voltage application to the electrode 3A.

In the practice of this invention, the substrate is L
iTaO ₃ or LiNbO ₃ can be preferably used,
Since the LiTaO ₃ substrate has a larger optical damage threshold than the LiNbO ₃ substrate, the photorefractive effect is small.

The above is the description of the embodiments relating to the light modulation wavelength conversion elements of the first to eighth aspects. Hereinafter, with reference to FIG. 5 to FIG. 11, an embodiment of the optical modulation wavelength conversion element according to claim 9 or below will be described. In order to avoid complication, the reference numerals of FIG. 1 to FIG. 4 are used in each of the drawings starting from FIG.

In FIG. 5, reference numeral 1 designates a substrate using a LiTaO ₃ -c plate as in the embodiment of FIG. Reference numeral 20 indicates a three-dimensional waveguide. Three-dimensional waveguide 20
Is Y-shaped, and the light exit side is branched into two to form branch waveguides 20A and 20B. Of course, the three-dimensional waveguide 2
0 is preferably a "single mode waveguide". Reference numeral 4A indicates a region in which the polarization is inverted at the period of Λ.

In the domain-inverted region 4A, the period of domain-inversion: Λ is the propagation constant of the guided mode light for the fundamental laser light in the three-dimensional waveguide β (ω), and the guided mode for the second harmonic. When the propagation constant of light is β (2ω), m is a natural number and is given by Λ = 2 (2m−1) π / {β (2ω) −2β (ω)}.

Reference numeral 30 indicates a pair of electrodes. The pair of electrodes is composed of electrodes 30A and 30B, and changes the phase of the guided light before the branch point of the three-dimensional waveguide 20 to select the branch waveguides 20A and 20B. Is provided along the three-dimensional waveguide 20 from the front side of
Each of the electrodes 30A, 30B has a branch waveguide 20A,
It covers a part of 20B.

The three-dimensional waveguide 20 is formed by the same method as the three-dimensional waveguide 2 in the embodiment of FIG. 1, and the polarization inversion region 4A and the electrode pair 30 are the polarization inversion regions 4 and 4 in the embodiment of FIG. It is formed by the same method as the electrode structure 3.

Substrate 1 using the LiTaO ₃ -c plate
In place of LiNbO ₃ crystal or MgO-doped Li
It goes without saying that a three-dimensional waveguide, a domain-inverted region, and a pair of electrodes can be formed using the NbO ₃ crystal, the KTiOPO ₄ substrate, etc. by the method described in connection with the embodiment of FIG.

In the embodiment of FIG. 5, the electrode 30 as shown
When B is grounded and the voltage applied to the electrode 30A is V ₀ , when the voltage V ₀ is 0, the effective refractive index distribution for the guided light is uniform in the waveguide, and the Ez ₀₀ mode field distribution is It becomes centrally symmetric. When the voltage V ₀ is not 0, a high-refractive-index region of the three-dimensional waveguide 20 is generated above the electrode 30A, and the guided light is confined in the high-refractive-index region to be guided to the branch waveguide 20A. It is drawn in and is emitted from the branch waveguide 20A.

Therefore, as shown in FIG. 5, polarized laser light whose electric field is directed in the Z direction is used as the fundamental wave in the three-dimensional waveguide 20.
When the light is guided in the y direction, the phase-matched second harmonic is generated in the domain-inverted region 4A and guided toward the branch point of the three-dimensional waveguide 20. In this state, when the modulation signal is applied to the electrode 30A as the voltage signal V ₀ , the second harmonic wave modulated in accordance with the above is obtained.
Will be obtained from A. Of course, if the electrode 30A is grounded and a modulation voltage signal is applied to the electrode 30B, the modulated second harmonic wave is emitted from the branch waveguide 20B.

If the branch angles of the two branch waveguides 20A and 20B in the three-dimensional waveguide 20 are set to about 1 degree or less, the scattering loss at the branch point can be suppressed to 1 dB or less,
Generation of higher modes can be suppressed. LiTaO ₃ substrate 1
In this embodiment using the same method, the photorefractive effect is smaller than that of the LiNbO ₃ substrate, as in the case of the embodiment of FIG.

In the embodiment of FIG. 5 using a LiTaO ₃ -c plate as the substrate, considering the one having an oscillation wavelength of 0.83 μm as the light source of the fundamental laser light, the wavelength of the equivalent refractive index in the three-dimensional waveguide 20 is considered. In the dispersion, the fundamental wave of the above wavelength has an Ex direction in which the electric field direction corresponding to ordinary light is in the x-axis direction.
2.1538 in the ₀₀ mode, and 2.157 in the Ez ₀₀ mode in which the electric field direction corresponding to the abnormal light is the z direction.
8, the second harmonic having a wavelength of 0.415 μm is 2.2414 in the case of using the Ex ₀₀ mode corresponding to ordinary light, and 2.2814 in the Ez ₀₀ mode corresponding to extraordinary light.

Considering a light source of the fundamental wave laser light having an oscillation wavelength of 1.2 μm, the chromatic dispersion of the equivalent refractive index in the three-dimensional waveguide 20 is, in the fundamental wave, in the case of Ex ₀₀ mode corresponding to ordinary light. 2.1305 in the Ez ₀₀ mode, which is equivalent to extraordinary light, and 2.1341 in the wavelength of 0.6 μm.
The second harmonic of the above is 2.1834 when the Ex ₀₀ mode corresponding to the ordinary light is used, and 2.1878 when the Ez ₀₀ mode corresponding to the extraordinary light is used.

Letting N (ω) be the equivalent refractive index with respect to the fundamental wave and N (2ω) be the equivalent refractive index with respect to the second harmonic in the three-dimensional waveguide 20, then between the propagation constant β and the equivalent refractive index N. Has the relation: β = 2πN / λ with λ as the wavelength, the above equation: Λ = 2 (2m−1) π / {β (2
ω) −2β (ω)}, the polarization inversion period Λ in the refractive index distribution region 4A is Λ = (2m−1) λ / [2 {N
(2ω) −N (ω)}] makes it possible to efficiently generate the second harmonic.

[0067] The wavelength of the fundamental wave and 0.83 .mu.m, Ex ₀₀ mode to the fundamental wave, in the case of using the Ez ₀₀ mode to the second harmonic,
The period Λ is 3.1 μm, and the nonlinear constant d ₃₁ is used. The Ez ₀₀ mode corresponding to the mode of the fundamental wave of the wavelength 0.83μm abnormal light, the use of Ez ₀₀ mode corresponding to extraordinary light to the second harmonic, lambda becomes 3.2 .mu.m. In this case, the non-linear constant d ₃₃ will be used.

The wavelength of the fundamental wave is 1.2 μm,
When the Ex ₀₀ mode and the Ez ₀₀ mode are used for the second harmonic, the period Λ becomes 10.5 μm, and the nonlinear constant d ₃₁ is used. The Ez ₀₀ mode corresponding to the mode of the fundamental wave of the wavelength 1.2μm to extraordinary light, the use of Ez ₀₀ mode corresponding to extraordinary light to the second harmonic, lambda is 11.2μ
m. In this case, the non-linear constant d ₃₃ will be used.

In the embodiment of FIG. 5, the polarization inversion region 4A using the Ez ₀₀ mode, which corresponds to extraordinary light for both the fundamental wave and the second harmonic, is formed, and laser light of the Ez ₀₀ mode is made to enter as a fundamental wave, and the electrode When a positive voltage is applied to 30A, the second harmonic wave is emitted from the branch waveguide 20A. When the polarity of the applied voltage is reversed, the second harmonic wave is emitted from the branch waveguide 20B. In addition, Ex _00, which is equivalent to ordinary light, is the fundamental wave mode.
When the Ez ₀₀ mode corresponding to the extraordinary light is used for the mode and the second harmonic, when the positive voltage V ₀ is applied to the electrode 30A, the second harmonic is emitted from the branch waveguide 20A and the polarity of the applied voltage V ₀ is changed. Conversely, the second harmonic is emitted from the branch waveguide 2
It starts from 0B.

E corresponding to extraordinary light as the mode of the fundamental wave
When the z ₀₀ mode is used, as in the embodiment shown in FIG. 6, the refractive index distribution region 4B for generating the second harmonic is formed in the branch waveguide 20.
B (or branch waveguide 20A), the applied voltage V
The second harmonic wave modulated according to ₀ can be obtained from the branch waveguide 20B.

In the embodiment shown in FIG. 7, the substrate 1A is a LiNbO ₃ c plate as in the embodiment shown in FIG. 3, the z axis is set according to the c axis, and the x and y directions are as shown in the figure. Establish. In this case, assuming that the light source has a wavelength of 0.83 μm, the chromatic dispersion of the equivalent refractive index in the three-dimensional waveguide 20 is the same when the Ex ₀₀ mode corresponding to ordinary light is used for the fundamental wave having a wavelength of 0.83 μm. 2.22, 2.17 when using Ez ₀₀ mode corresponding to extraordinary light, wavelength 0.415
The second harmonic of μm is 2.39 when the Ex ₀₀ mode corresponding to ordinary light is used and 2.28 when the Ez ₀₀ mode corresponding to extraordinary light is used.

[0072] The Ex ₀₀ mode of the fundamental wavelength laser light is 0.83 .mu.m, corresponding to the ordinary light as a fundamental wave, second
When the above Ez ₀₀ mode corresponding to extraordinary light is used as a harmonic, the period Λ of polarization inversion in the refractive index change region is about 10 μm.
m, when Ez ₀₀ mode corresponding to extraordinary light is used as the fundamental wave, and Ez ₀₀ mode corresponding to extraordinary light is used as the second harmonic, Λ is about 3.8 μm.

Similar to the embodiment of FIG. 6, in the embodiment of FIG. 7 as well, as shown in FIG. 8, the refractive index changing region 4B as the second harmonic generation means is provided in the branch waveguide 20A (or 20B). May be.

[0074] Instead as the material of the substrate 1A in LiNbO ₃ crystal, the same as the embodiment can be obtained even by using a LiNbO ₃ crystal doped with MgO. As described in connection with the embodiment of FIG. 4, LiNbO ₃ crystal or M
When a LiNbO ₃ crystal doped with gO is used as the substrate 1A, if the Ex ₀₀ mode corresponding to the ordinary light is used as the fundamental wave and the Ez ₀₀ mode corresponding to the extraordinary light is used for the second harmonic, Ex
_When the fundamental wave of ₀₀ mode is made incident, it becomes Ez ₀₀ as extraordinary light.
Since the second harmonic of the mode is generated, the refractive index changing region as the second harmonic generating means is unnecessary, and if the wavelength of the fundamental wave is 1 μm or more, the birefringence of the substrate, which is a nonlinear medium, is used. Phase matching can be performed. Figure 9
An example of such a case is shown.

In the case of the embodiment shown in FIG. 9, when the Ex ₀₀ mode is used as the input light, the second harmonic becomes the Ez ₀₀ mode. Therefore, when the voltage V ₀ is applied to the electrode 30A, the generated second harmonic is generated. The light is emitted from the branch waveguide 20A. If the polarity of the applied voltage V ₀ is reversed, the second harmonic wave is emitted from the branch waveguide 20B. In this case, the extinction ratio can be effectively improved by providing the metal cladding 5 on the surface of the branch waveguide on which the second harmonic wave is not emitted.

Further, as shown in FIG. 10, LiTAO ₃
When a three-dimensional waveguide is formed by proton exchange on the crystalline substrate 1 or the LiNbO ₃ crystalline substrate 1A, stable second harmonics can be generated by Cherenkov radiation.
The second harmonic generated by Cherenkov radiation can be modulated and taken out from the branch waveguide 20A or 20B by turning on / off the voltage application to the electrode 30A without the refractive index changing region as the second harmonic generating means.

In each of the embodiments shown in FIGS. 5 to 10, the branched state of the three-dimensional waveguide 20 is symmetrical with respect to the incident direction of the fundamental wave, but as shown in FIG.
Even if the branched state is asymmetric with respect to the waveguide direction before branching, the same effect as that of the embodiments of FIGS. 5 to 10 can be obtained.

[0078]

As described above, according to the present invention, it is possible to provide a completely novel optical modulation wavelength conversion element which has not been available in the past. Since this element is configured as described above, the generation of the second harmonic and its modulation can be performed by the same element.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention.

FIG. 2 is a diagram for explaining another embodiment.

FIG. 3 is a diagram for explaining another embodiment.

FIG. 4 is a diagram for explaining still another embodiment.

FIG. 5 is a diagram for explaining still another embodiment.

FIG. 6 is a diagram for explaining still another embodiment.

FIG. 7 is a diagram for explaining still another embodiment.

FIG. 8 is a diagram for explaining still another embodiment.

FIG. 9 is a diagram for explaining still another embodiment.

FIG. 10 is a diagram for explaining still another embodiment.

FIG. 11 is a diagram showing only a characteristic part of still another embodiment.

[Explanation of symbols]

1,1A substrate 2,20 Three-dimensional waveguide 3 electrode structure 4,4A polarization inversion region 20A, 20B branch waveguide 30 pairs of electrodes

Claims (16)

[Claims] 1. A harmonic wave generating means for generating a second harmonic wave from the fundamental wave laser light, which has a three-dimensional waveguide for guiding the fundamental wave laser light, and is guided to the three-dimensional waveguide. The fundamental wave laser light is integrated with the light modulating means for performing the second harmonic modulation by performing mode conversion between TE-TM modes on the same substrate, and the fundamental wave laser light has a wavelength of λ. When the equivalent refractive indexes of the TE and TM modes in the three-dimensional waveguide are Nte and Ntm, respectively, the optical modulation means generates a periodic electric field in the waveguide direction in the three-dimensional waveguide. An optical modulation wavelength conversion device having an electrode structure having a period of electrode spacing of Λ ₂ (= λ / {Nte-Ntm}). 2. The harmonic generation means according to claim 1, wherein the propagation constant of the guided mode light with respect to the fundamental wave laser light is β (ω) in the three-dimensional waveguide, and the guided mode light with respect to the second harmonic wave is When the propagation constant is β (2ω), the period Λ ₁ (= 2 (2m-1) π / {β (2ω) -2β in the waveguiding direction.
(ω)}; m: a natural number) An optical modulation wavelength conversion element having a polarization inversion region as a phase matching means. 3. The LiTa according to claim 2, wherein the substrate has a three-dimensional waveguide formed by diffusion.
It is a -c plate of O ₃ , and the light propagation direction is the y direction, and the z direction orthogonal to this is the -direction.
An optical modulation characterized by using a z-direction polarization whose electric field direction is parallel to the z-axis as a fundamental wave and a z-direction polarization whose electric field direction is parallel to the z-axis as a second harmonic when aligned with the c-axis direction. Wavelength conversion element. 4. The LiTa according to claim 2, wherein the substrate has a three-dimensional waveguide formed by diffusion.
It is a -c plate of O ₃ , and the light propagation direction is the y direction, and the z direction orthogonal to this is the -direction.
An optical modulation characterized by using an x-direction polarization whose electric field direction is parallel to the x-axis as a fundamental wave and a z-direction polarization whose electric field direction is parallel to the z-axis as a second harmonic when aligned with the c-axis direction. Wavelength conversion element. 5. The LiNb according to claim 2, wherein the substrate has a three-dimensional waveguide formed by diffusion.
It is a c-plate of O ₃ , the light propagation direction is the y-direction, and the z-direction orthogonal to this is the c-direction.
An optical modulation wavelength characterized by using a z-direction polarization whose electric field direction is parallel to the z-axis as a fundamental wave and a z-direction polarization whose electric field direction is parallel to the z-axis as a second harmonic when aligned in the axial direction. Conversion element. 6. The LiNb according to claim 2, wherein the substrate has a three-dimensional waveguide formed by diffusion.
It is a c-plate of O ₃ , the light propagation direction is the y-direction, and the z-direction orthogonal to this is the c-direction.
An optical modulation wavelength characterized by using an x-direction polarization whose electric field direction is parallel to the x-axis as a fundamental wave and a z-direction polarization whose electric field direction is parallel to the z-axis as a second harmonic when aligned in the axial direction. Conversion element. 7. The LiNb according to claim 1, wherein the substrate has a three-dimensional waveguide formed by diffusion.
It is a c-plate of O ₃ , the light propagation direction is the y-direction, and the z-direction orthogonal to this is the c-direction.
When aligned in the axial direction, an x-direction polarized wave whose electric field direction is parallel to the x-axis is used as a fundamental wave, and a z-direction polarized wave whose electric field direction is parallel to the z-axis is used as a second harmonic, and the phase is changed by birefringence of LiNbO ₃ An optical modulation wavelength conversion element characterized by performing matching. 8. The optical modulation according to claim 1, wherein the substrate is a LiNbO ₃ c plate in which a three-dimensional waveguide is formed by proton exchange, and the second harmonic is generated by Cherenkov radiation. Wavelength conversion element. 9. A harmonic wave generating means for generating a second harmonic wave from the fundamental wave laser light, which has a Y-shaped three-dimensional waveguide for branching the bifurcated emission side to guide the fundamental wave laser light. The optical modulation wavelength conversion, characterized in that a pair of electrodes for selecting a branching waveguide by changing the phase of the guided light before the branching point of the three-dimensional waveguide are integrated on the same substrate. element. 10. The substrate according to claim 9, wherein the substrate is a non-linear medium, and the harmonic generation means has a propagation constant of the guided mode light with respect to the fundamental wave laser light in the three-dimensional waveguide as β (ω), the second harmonic. When the propagation constant of the guided mode light with respect to the wave is β (2ω), the period Λ (= 2 (2m-1) π / {β (2ω) -2β in the waveguide direction.
(ω)}; m: natural number), which is a polarization inversion region formed in a three-dimensional waveguide. 11. An optical modulation wavelength conversion element according to claim 10, wherein the harmonic generation means by the polarization inversion region is formed in one of the two branched branches of the three-dimensional waveguide. . 12. The LiTa according to claim 10, wherein the substrate has a three-dimensional waveguide formed by diffusion.
It is a -c plate of O ₃ , and the light propagation direction is the y direction, and the z direction orthogonal to this is the -direction.
When aligned with the c-axis direction, a z-polarized wave whose electric field direction is parallel to the z-axis or x whose electric field direction is parallel to the x-axis is the fundamental wave.
An optical modulation wavelength conversion element characterized by using directional polarization and using z-direction polarization in which the electric field direction is parallel to the z-axis as the second harmonic. 13. The LiNb according to claim 10, wherein the substrate has a three-dimensional waveguide formed by diffusion.
It is a c-plate of O ₃ , the light propagation direction is the y-direction, and the z-direction orthogonal to this is the c-direction.
When aligned in the axial direction, a z-direction polarized wave whose electric field direction is parallel to the z-axis or an x-direction polarized wave whose electric field direction is parallel to the x-axis as a fundamental wave and a z-axis whose electric field direction is parallel to the z-axis as a second harmonic An optical modulation wavelength conversion element characterized by using directional polarization. 14. The LiNb according to claim 9, wherein the substrate has a three-dimensional waveguide formed by diffusion.
It is a c-plate of O ₃ , the light propagation direction is the x direction, and the electric field direction is y as the fundamental wave.
Y-direction polarization parallel to the axis, the electric field direction is z as the second harmonic
An optical modulation wavelength conversion element characterized by using z-direction polarization parallel to an axis and using the birefringence of a substrate for phase matching. 15. The metal cladding according to claim 14, wherein a metal cladding is formed on a surface of a waveguide of the three-dimensional waveguide which is branched into two or more and which does not output the modulated second harmonic. Characteristic light modulation wavelength conversion element. 16. The substrate according to claim 9, wherein the substrate is a plate of LiNbO ₃ crystal or LiTaO ₃ crystal in which a three-dimensional waveguide is formed by proton exchange,
An optical modulation wavelength conversion element, characterized in that the second harmonic is generated by Cherenkov radiation.