JP2000314903A - Manufacture of light wavelength converting module and light wavelength converting module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily display respective performances of EOM(electro-optic modulation) and SHG (wavelength conversion) and to easily obtain high wavelength conversion efficiency. SOLUTION: Respective devices of an LD element 32 exiting a laser beam, an EOM element 34 having an electrode and an SHG element 36 being a second higher harmonic generator in which a periodic domain inversion structure is formed are separately manufactured. The EOM element 34 is directly coupled to the LD element 32, further the SHG element 36 is optically coupled by direct coupling to the coupled block after confirming to become a characteristic of the preliminarily measured desired EOM element 34, and whereby an integrated light wavelength converting module 30 having a desired function is obtained. The block of the LD element 32 and the EOM element 34 is coupled to the SHG element 36. The satisfactorily characteristic is obtained by individual elements and the yield as a whole is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical wavelength conversion module and an optical wavelength conversion module, and more particularly to a method for manufacturing an optical wavelength conversion module for converting the wavelength of a fundamental wave and an optical wavelength conversion module.

[0002]

2. Description of the Related Art A method of wavelength-converting a fundamental wave into a second harmonic using an optical wavelength conversion element provided with a region in which spontaneous polarization (domain) of a ferroelectric material having a nonlinear optical effect is periodically inverted. Has already been proposed by Bleombergen et al. (See Phys. Rev., vol. 127, No. 6, 1918 (1962)). In this method, the period ド メ イ ン of the domain inversion portion is represented by: c = 2π / {β (2ω) -2β (ω)} where β (2ω) is the propagation constant of the second harmonic β (ω) is the propagation constant of the fundamental wave By setting the coherent length Δc to be an integral multiple of the coherent length Δc, the fundamental wave and the second harmonic can be phase-matched (so-called quasi-phase matching). Attempts have also been made to form such a periodic domain inversion structure in an optical waveguide type optical wavelength conversion element that converts the wavelength of a fundamental wave guided by an optical waveguide made of a nonlinear optical material to achieve efficient phase matching. I have.

As one example, there is known an optical element in which a wavelength conversion element and an electro-optical modulator are monolithically integrated (see Japanese Patent Application Laid-Open No. 4-333835). In this technique, as shown in FIGS. 11 and 12, as an optical element 100, waveguides 102 and 104 are formed on a substrate, and an EOM (electro-optical modulator) 1 having electrodes 120 and 122 is provided.
14 and an SHG section (wavelength converter) 116 in which a periodic domain inversion structure is formed. The periodic domain inversion structure is formed at either the cross port 108 or the bar port 110. The light of wavelength λ passing through the port in which the periodic domain inversion structure is formed is converted into light of wavelength λ / 2 and output. In the examples of FIGS. 11 and 12, a periodic domain inversion structure is formed in the bar port 106 on the waveguide 102 side.

In the optical element 100, when light having a wavelength λ is input to the optical waveguide 102, the electrodes 120, 122
When no voltage is applied to the cross port 108, most of the input light transfers to the cross port 108, and no light is guided to the bar port 106. At this time, when a voltage is applied to the electrodes 120 and 122, the crossport 10 is changed according to the applied voltage.
8, the light amount is reduced and the light is output to the bar port 106. In this way, the light is modulated and the wavelength can be converted.

[0005] A technique using a Z-cut substrate is known in order to perform the wavelength conversion efficiently.
As the optical element, a Z-cut substrate such as LiNbO ₃ or LiTaO ₃ is used. As shown in FIGS. 13 and 14, in the voltage application method, when the periodic domain inversion is formed, the inversion region extends along the Z-axis.
When a cut substrate is used, a deep periodic domain inversion structure can be formed. Therefore, by forming the periodic domain inversion structure in the optical element 130 and forming the optical waveguide 132 in a region where the periodic domain inversion structure is formed, highly efficient wavelength conversion can be performed.

However, when a Z-cut substrate is used,
Although a domain inversion structure can be formed deeply, when a semiconductor laser is used as a light source, the incident optical system of the fundamental wave becomes complicated, and electric power is generated due to factors such as a pyroelectric effect and subtle fluctuations in the refractive index of the buffer layer. There has been a problem that a high extinction ratio cannot be obtained in the optical modulator.

An optical waveguide type optical wavelength conversion device having such a periodic domain inversion structure will be described. Optical waveguide type optical wavelength conversion elements having a periodic domain inversion structure are roughly classified into two types in terms of the direction of spontaneous polarization of a substrate. One type of optical wavelength conversion device is shown in FIG.
As shown in FIG. 2, the direction of spontaneous polarization of the substrate 2 indicated by an arrow P is perpendicular to one substrate surface 2a (the substrate surface along which the optical waveguide 1 extends), and As shown in FIG. 16, the optical wavelength conversion element has a spontaneous polarization direction of the substrate 2 parallel to the substrate surface 2a.

An optical wavelength conversion element of the type shown in FIG.
For example, it is disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 5-29207 and the like. Although the domain inversion portion can be formed sufficiently deep from the substrate surface, when used in combination with a semiconductor laser, the incident optical system of the fundamental wave is complicated. Become Specifically, in the configuration of FIG. 15, the beam pattern of the guided light
As shown by, the beam diameter in the direction parallel to the direction of the polarization vector indicated by the arrow R is small, and the beam diameter in the direction perpendicular to the direction is large. At this time, the direction of the polarization vector coincides with the direction of the spontaneous polarization of the substrate 2 (generally, in a ferroelectric material such as LiNbO ₃ , the direction of the spontaneous polarization is parallel to the Z axis), and the waveguide mode is the TM mode. Become. on the other hand,
The beam pattern of the laser beam 4 emitted from the semiconductor laser 3 has a large beam diameter in a direction parallel to the direction of the polarization vector indicated by an arrow Q and a small beam diameter in a direction perpendicular thereto, as shown in FIG. Becomes

In order to input the laser beam 4 emitted from the semiconductor laser 3 to the optical waveguide 1, if the respective polarization directions are adjusted, the beam shapes will be mismatched, and the laser beam 4 can be efficiently input to the optical waveguide 1. Can not. If so, the intensity of the second harmonic will be small.

In order to rotate the polarization direction of the laser beam 4 by 90 ° while keeping the beam pattern of the laser beam 4 unchanged, a λ /
A complicated fundamental wave incident optical system having two plates 7 is required.

On the other hand, in the case of the optical wavelength conversion element of the type shown in FIG. 16, the linear polarization direction of the laser beam 4 and the Z-axis direction of the substrate 2 are set without the λ / 2 plate 7. Since they coincide with each other, a complicated fundamental wave incident optical system is unnecessary, and the semiconductor laser 3 can be directly coupled to the end face of the optical waveguide 1. The waveguide mode at this time is the TE mode.

However, in the optical wavelength conversion element of the type shown in FIG. 16, the domain inversion section 8 cannot be formed sufficiently deep from the substrate surface 2a. More specifically, in FIG. 17, D indicates an electrode for forming the domain inversion portion 8. The direction in which the domain inversion portions 8 are arranged and the thickness direction of the substrate 2 are the X-axis direction of the substrate and the Y direction, respectively.
In the axial direction. Considering the actual wavelength of the fundamental wave to be wavelength-converted, the period of the domain inverting unit 8 shown by a in FIG.
m. If this is set to 5 μm for convenience, in order to obtain the maximum wavelength conversion efficiency, the width of the domain inversion unit 8 and the width of the non-inversion unit must be set to 1: 1 in order to obtain the maximum wavelength conversion efficiency. The middle b dimension) is 2.5 μm. When the electrode D is formed by the current general process, it is difficult to make the electrode line width shown in FIG.
If c = 0.5 μm, the domain inversion section 8
When the domain inversion portion 8 is grown by d = 1 μm in the direction of the arrangement, the width of the domain inversion portion 8 becomes 2.5 μm.

The growth rate of the domain-inverted region is high in the direction along the direction of spontaneous polarization of the substrate 2 and is low in the direction perpendicular to the direction of spontaneous polarization (ie, in the X-axis direction and the Y-axis direction). , The growth rates in the X-axis direction and the Y-axis direction of the domain inversion region are the same. Therefore,
If the width of the domain inversion portion 8 is 2.5 μm as described above, the depth (dimension in the Y-axis direction) is about 1 μm.

For the reasons described above, in the conventional optical wavelength conversion element of this type, the depth of the domain inversion portion is only about 1 μm, which is shallower than the field distribution of the guided light. The spatial conversion with the field distribution of the guided light was small and the wavelength conversion efficiency was low.

In order to solve this problem, as shown in FIGS. 18 and 19, periodic domain inversion is performed by forming an inversion region at an angle inclined at a predetermined angle along the Z axis. A technique using a substrate inclined in a direction is known (see Japanese Patent Application Laid-Open No. 10-161165). According to this technique, both high-efficiency wavelength conversion in the wavelength conversion unit and a high extinction ratio in the EOM unit are possible.

[0016]

However, in the conventional device described above, since the EOM portion and the SHG portion are formed (integrated) on the same substrate, the EOM portion and the SHG portion are not formed.
The performance of both HG sections must be simultaneously good and sufficient. That is, when the performance of either the EOM section or the SHG section is insufficient, the performance of the entire device becomes insufficient.

In view of the above facts, the present invention provides a method of manufacturing an optical wavelength conversion module that can sufficiently exhibit the performance of each of an EOM section and an SHG section and can easily obtain high wavelength conversion efficiency. The purpose is to obtain an optical wavelength conversion module.

[0018]

In order to achieve the above object, a method of manufacturing an optical wavelength conversion module according to the present invention is to provide a method for manufacturing an optical wavelength conversion module, comprising: transmitting at least an incident light to a substrate for optical modulation using a ferroelectric crystal having a nonlinear optical effect; One optical waveguide is formed, and an electrode for applying a voltage to the optical waveguide is formed on the substrate surface, and the light is incident on a substrate for wavelength conversion by a ferroelectric crystal having a nonlinear optical effect. An optical wavelength converting means for forming at least one optical waveguide for propagating light, and forming a domain inversion portion in which the direction of spontaneous polarization of the substrate is inverted and the optical waveguide is periodically formed in the waveguide direction; Are independently formed. Then, the electro-optic modulation unit and the optical wavelength conversion unit are joined so that at least one waveguide of the electro-optic modulation unit and at least one waveguide of the optical wavelength conversion unit can propagate guided light. .

A light beam is propagated through the optical waveguide of the electro-optic modulation means. By injecting a current (applying a voltage) to the electrodes, the propagated light beam is modulated by an electro-optic effect involving a change in refractive index. Is done. In the present invention, the electro-optic modulation means can be independently manufactured. Therefore, only the efficiency of the electro-optic modulator can be considered, and a high-performance electro-optic modulator can be manufactured alone.

In the optical waveguide of the optical wavelength conversion means, a domain inversion portion in which the direction of spontaneous polarization of the substrate is inverted and which is periodic in the waveguide direction is formed. Thereby, the wavelength of the fundamental wave guided in the direction in which the domain inversion portions are arranged in the optical waveguide can be converted. In the present invention, the light wavelength conversion means can be independently manufactured. Therefore, a high-performance optical wavelength converter can be manufactured alone by considering only the efficiency of the optical wavelength converter.

Then, at least one of the electro-optic modulation means is provided.
The electro-optic modulator and the optical wavelength converter are joined so that the two waveguides and at least one waveguide of the optical wavelength converter can propagate the guided light. For example, one waveguide having a high modulation efficiency of the light beam modulated by the electro-optic modulation unit and one waveguide having a high conversion efficiency of the light beam whose wavelength is converted by the optical wavelength conversion unit are joined. This makes it possible to manufacture an optical wavelength conversion module in which the efficiency of each of the electro-optic modulator and the optical wavelength converter is maximized.

It is necessary to make a light beam incident on the optical waveguide of the electro-optic modulation means. In this case, this can be achieved by further providing a semiconductor laser for emitting the light beam. Therefore, when manufacturing an optical wavelength conversion module,
The semiconductor laser may be joined so that the light beam enters the optical waveguide of the electro-optic modulation means. In this connection, the electro-optic modulation means and the semiconductor laser can be directly bonded, or can be bonded via an optical fiber. In this way, the light beam emitted from the semiconductor laser is modulated by the electro-optic modulator, and the wavelength can be converted by the light wavelength converter using the modulated light beam as a fundamental wave.

The following optical wavelength conversion module can be obtained by the above-described method of manufacturing the optical wavelength conversion module of the present invention. Specifically, the optical wavelength conversion module includes a substrate for optical modulation made of a ferroelectric crystal having a nonlinear optical effect, at least one optical waveguide formed on the substrate and transmitting incident light, An electrode formed on the surface of the substrate to apply a voltage to the substrate, an electro-optic modulator, a substrate for wavelength conversion by a ferroelectric crystal having a nonlinear optical effect, and at least a substrate formed on the surface of the substrate. The optical wavelength conversion means having one optical waveguide and a domain inversion portion in which the direction of the spontaneous polarization of the substrate is inverted in the optical waveguide and formed periodically in the waveguide direction is joined to each other. I have.

In the light wavelength conversion module, a directional optical coupler can be formed using a plurality of waveguides as the electro-optic modulation means. A current is injected (voltage applied) to the electrodes by forming a directional optical coupler
By doing so, it is possible to control the amount by which the propagated light beam transfers to any one of the plurality of waveguides due to the electro-optic effect accompanied by the change in the refractive index. By turning on / off the control of the amount, the switch can function as a switch.

The configuration of the directional optical coupler is not limited. In the optical wavelength conversion module, the electro-optic modulation means includes a Mach-Zehnder type modulator or switch, a TE-TM mode conversion type modulator, or the like. It may be configured to function as a container or a switch.

In the light wavelength conversion module, the light waveguide of the light wavelength conversion means may be formed so as to extend along the surface of the substrate and have a polarization component parallel to the substrate. By doing so, the light beam propagating through the light wavelength conversion means becomes a polarization component parallel to the substrate, and only the TE mode light beam can be efficiently propagated. Therefore, the electro-optic modulation means is changed to TE
-When configured to function as a modulator or switch of the TM mode conversion type, it is possible to more efficiently control the guided light propagating.

In the optical wavelength conversion module, at least one of the substrates has an angle θ between the surface and the spontaneous polarization of the ferroelectric crystal within a predetermined angle range (0 ° <θ <20).
°) can be used.

In this case, it is preferable that the angle θ exceeds 0.2 °.

Further, in the optical wavelength conversion module, the optical waveguide is formed by proton exchange and annealing, and the angle θ can be manufactured so as to exceed 0.5 °.

In the optical wavelength conversion module of the present invention,
The direction of the spontaneous polarization of the substrate is a predetermined angle θ with respect to the surface of the substrate in a plane perpendicular to the waveguide direction of the fundamental wave.
Can be formed. This angle θ is
Preferably, the angle θ is set to exceed 0.2 °, and when the optical waveguide is formed by proton exchange and annealing, the angle θ is preferably set to exceed 0.5 °.

As described above, by forming the substrate at a predetermined angle θ with respect to the substrate surface, the direction of spontaneous polarization of the substrate, that is, the Z-axis direction is not perpendicular to the substrate surface. be caused to enter the optical waveguide at the laser beam state that linearly polarized light direction is parallel to the substrate surface, the nonlinear optical constant d ₃₃ becomes possible to use has been wavelength conversion.

In the optical waveguide formed by proton exchange and subsequent annealing, the light beam
It is known that the waveguide in the single mode occurs when the angle φ between the Z axis and the substrate surface is 0 ° <φ <20 °. Therefore, when the optical waveguide is formed by proton exchange and annealing, the angle θ is set to θ <2.
When the angle is set in the range of 0 °, the wavelength conversion is efficiently performed.

On the other hand, when a domain inversion structure having an optimum duty ratio for obtaining the maximum wavelength conversion efficiency (that is, the width ratio between the domain inversion portion and the non-inversion portion is 1: 1) is formed, the angle θ becomes It was found that if it was within several degrees, it would be approximately 50 μm. In general, the field distribution of the guided mode can be reduced to about 1.2 μm when it is made the narrowest. Therefore, if θ = 0.2 °, the depth of the domain inversion portion is 1.2.
μm, and the domain inversion portion has substantially the same size as the field distribution of the guided mode in the depth direction. Therefore,
If 0.2 ° <θ, the domain inversion portion overlaps with the field distribution of the waveguide mode and becomes excessive, so that the wavelength conversion is efficiently performed.

The light wavelength conversion module further includes a semiconductor laser for emitting a light beam, and the semiconductor laser is applied to the electro-optic modulation means so that the light beam is incident on the optical waveguide of the electro-optic modulation means. Further, they can be directly bonded or bonded via an optical fiber.

Therefore, by the optical wavelength conversion module,
The light beam emitted from the semiconductor laser is modulated by the electro-optic modulator, and the wavelength can be converted by the light wavelength converter using the modulated light beam as a fundamental wave.

When the electro-optic modulator and the semiconductor laser are coupled via an optical fiber, the core diameter of the optical fiber is gradually changed along the light propagation direction, or the shape of the optical fiber core is changed. Or gradually along the direction of propagation. By doing this,
It is possible to provide a light beam whose size matches the entrance pupils of both the electro-optic modulation means and the semiconductor laser.

Also, the shape of the core of the optical fiber can be elliptical. By doing so, the degree of conformity of the optical fiber with the shape of the waveguide can be increased.

Further, in the optical wavelength conversion module, the semiconductor laser whose oscillation wavelength can be adjusted can be used.

That is, the semiconductor laser is a distributed Bragg DBR having a mechanism for adjusting the oscillation wavelength of a light beam.
(Distributed Bragg Reflector) and distributed feedback DFB
(Distributed feedback) semiconductor lasers can be used. As described above, by employing a structure capable of adjusting the oscillation wavelength of the light beam, the oscillation wavelength of the semiconductor laser can be easily adjusted to the phase matching wavelength of the optical wavelength conversion element. This makes it possible to adjust the wavelength so that the efficiency of the light wavelength conversion unit is maximized, and to maximize the output light amount.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. [First Embodiment] FIG. 1 shows a perspective view of an optical wavelength conversion module according to the present embodiment.

As shown in FIG. 1A, an optical wavelength conversion module 30 according to the present embodiment has an electro-optic modulator (hereinafter, referred to as an EOM element) 34 having electrodes and a periodic domain inversion structure. Each device of the formed optical wavelength converter (hereinafter, referred to as SHG element) 36 as the second harmonic generator is individually manufactured. Thereafter, as shown in FIG. 1B, a semiconductor laser (hereinafter, referred to as an LD element) 32,
By directly connecting the EOM element 34 and the SHG element 36,
By performing optical coupling, an integrated optical wavelength conversion module 30 having a desired function is obtained.

The LD element 32 is for emitting a laser beam as a light beam, and an LD element having a wavelength tuning mechanism may be used. As an LD device having a wavelength tuning mechanism, a distributed Bragg DBR (Distributed Br
agg Reflector). As another example,
A distributed feedback DFB (distributed feedback) can be used. In this case, the oscillation wavelength of the LD element can be tuned and the phase matching wavelength of the SHG element
Locking can be performed so that the oscillation wavelengths of the elements match.

The EOM element 34 modulates the guided light propagating through the waveguide, and in the present embodiment, modulates the guided light with a directional optical coupler. For example, the details are also described in JP-A-10-161165 and the like,
By applying a voltage to the electrodes adjacent to the two optical waveguides having the electro-optic effect, switching between the two waveguides is performed, or by applying an intermediate voltage, the light is guided to an intermediate level of light intensity. Modulates wave light.

The EOM element 34 is disclosed in Japanese Unexamined Patent Publication No. 7-146.
A proton exchange annealing waveguide and an electrode are manufactured by a self-alignment method according to the technology described in Japanese Patent No. 457, and the electrode is plated by a technology described in Japanese Patent Application Laid-Open No. 10-133237 to reduce the electric resistance and modulate. It is preferable to increase the production speed. In the present embodiment, the substrate of the EOM element 34 is an off-cut substrate MgO-doped LiNbO ₃ .

The SHG element 36 emits a second harmonic laser beam using the wavelength of the incident laser beam as a fundamental wave. The SHG element 36 is made of, for example, LiNbO ₃ doped with 5 mol% of MgO (hereinafter, MgO—
It has an optical waveguide formed by, for example, proton exchange on a crystal substrate of LN) and a periodic domain inversion section (details will be described later). The periodic domain inversion unit is SHG
Element (second harmonic generator), MgO-L
It has a periodic domain inversion structure in which domain inversion portions where the spontaneous polarization (domain) of the N substrate is inverted are repeated at a predetermined cycle.

In this embodiment, the SHG element 36 is made of an off-cut substrate (the details of which will be described later) whose polarization plane is slightly inclined with respect to the horizontal. This off-cut substrate can be manufactured by the method disclosed in Japanese Patent Application Laid-Open No. 9-218431.

In the LD element 32, the substrates are directly coupled to each other at one end face of the optical waveguide of the EOM element 34. Further, the other end face portion of the optical waveguide of the EOM element 34 is directly coupled to the substrate at the end face portion of the optical waveguide 42 of the SHG element 36.

In the present embodiment, the EOM element 34
And an input / output end of the SHG element 36 have an anti-reflection coat (AR
Coat). Thereby, loss due to reflection at the end face can be suppressed.

The TE mode waveguide type EOM element 3
4. If the SHG element 36 and the LD element 32 having the wavelength tuning mechanism are directly coupled, each element becomes the same TE mode waveguide, and the optical adjustment and fixing becomes easy. Further, a structure in which the LD is wavelength locked and the wavelength can be tuned (for example, a distributed Bragg DBR:
buted Bragg Reflector, distributed feedback DBR: distribute
With ed feedback), the oscillation wavelength can be adjusted to the phase matching wavelength of the SHG element 36. Therefore, the LD element can be adjusted so that the SHG efficiency is maximized, and the output light amount can be maximized.

Next, a method for individually manufacturing the optical wavelength conversion module having the above configuration will be described.

First, a method for manufacturing the LD element 32 alone will be described.

As shown in FIG. 2, the LD element 32 is formed, for example, by using a MOCVD crystal apparatus, on a GaAs substrate 40, on a ladder layer (not shown), an active layer 42 for emitting laser light, and a ladder layer (not shown). Omitted), cap layer 44,
The electrodes 46 and 48 are sequentially laminated and formed. The LD element 32 of the present embodiment has a wavelength tuning mechanism. The electrode 46 functions as a current injection unit 47 for laser emission, and the electrode 48 functions as a wavelength tuning unit 49 for adjusting the oscillation wavelength. Configured to work. The oscillation wavelength is locked to the wavelength tuning unit 49,
The grating 50 for tuning is the active layer 4
2 is formed in the vicinity. A current I _laser for laser oscillation is injected into the electrode 46 for laser emission. Thereby, the LD element 32 oscillates. A current _Itune equal to or less than laser oscillation is injected into the wavelength tuning electrode 48. Thus, the Bragg wavelength at the grating 42 can be changed by changing only the refractive index of the element. In addition, as the LD element 32, a three-electrode type that further includes a phase control electrode capable of tuning the wavelength more continuously can be used.

Next, the EOM element 34 and the SHG element 36
A method for manufacturing the device will be described. EOM element 34 and SHG element
36 is, for example, LiN doped with 5 mol% of MgO.
bO _Three(Hereinafter referred to as MgO-LN) on a crystal substrate
For example, having an optical waveguide formed by proton exchange
You. Also, as details of the method of manufacturing the EOM element 34 alone,
Are described in Japanese Patent Application Laid-Open No.
Using the technology described in Japanese Patent Application Laid-Open No. Hei 10-133237.
Can be.

The EOM element 34 according to the present embodiment is, for example, an off-cut substrate of LiNbO ₃ crystal (details will be described later).
Forming a directional optical coupler on the surface of a substrate made of
The channel optical waveguides are provided in the Y direction, and electrodes are formed on the right and left sides of portions of these channel optical waveguides that extend in close proximity to each other and in parallel. The electrodes are connected to a driving circuit and used to apply a predetermined voltage to each channel optical waveguide.

An example of a method for manufacturing the EOM element 34 will be described with reference to FIGS. FIG. 3 shows the EOM element 34.
FIG. 4 shows the transition of the planar shape of the substrate. 3 (1) to FIG.
(8) respectively show the vertical sectional shapes of the portions along the line AA in FIG.

First, after a resist pattern 20 having the shape of the channel optical waveguide 11 is formed on the substrate 10 by a known lithography method (see FIGS. 3A and 4A), a Ta film 21 is formed by sputtering. , An Au film 22 and a Ta film 23 are formed in this order (see FIG. 3B). Next, the substrate 10 is immersed in acetone, ultrasonically cleaned, and lift-off removed (see FIGS. 3 (3) and 4 (2)). next,
The substrate 10 is immersed in pyrophosphoric acid heated to 150 ° C. to 200 ° C. for a predetermined time, thereby proton-exposing the exposed portion of the substrate 10 to form the channel optical waveguide 11 on the surface portion of the substrate 10 (FIG. 3 (4)).

Next, as shown in FIG.
After a heat treatment at 340 ° C. to 400 ° C. for a predetermined time, the Ta film 23 on the surface is removed by etching with hydrofluoric nitric acid (1: 2), and then this wiring is formed to form a wiring connecting the central electrode and the pad electrode. A resist pattern having an opening is formed by a lithography method. Then, Au / Cr is vacuum-deposited with low resistance heating, and the resist pattern is lifted off to form a connection wiring 25 made of Au / Cr as shown in FIG.

Next, as shown in FIG. 3 (6), a negative photoresist 26 is applied on the substrate,
13, 14 and pad electrode 16 (see (6) in FIG. 4)
A photomask having a shape conforming to the peripheral shape of the substrate is arranged and exposed from the front side of the substrate to expose a portion of the photoresist 26 that is not hidden by the photomask. After that, the Ta film 21
Then, exposure is performed from the back side of the substrate by using the Au film 22 as a mask to expose the photoresist 26 immediately above the channel optical waveguide 11 (the portion of the connection wiring 25 is not exposed). Next, when development is performed, the photoresist 26 is removed.
A resist pattern including only the exposed portions is formed (see FIG. 4 (4)).

Next, as shown in FIG. 3 (7), after Au 27 is plated to a thickness of, for example, 1 to 4 μm by electrolytic plating using the pattern of the photoresist 26 as a mask, as shown in FIG. 3 (8). Next, the pattern of the photoresist 26 is removed by a plasma asher or a resist stripper (see (5) of FIG. 4), and the Au film 22 shown in FIG.
And the Ta film 21 is removed by etching. By the above processing, the Ta film 21, the Au film 22, and the thick A
The electrodes 12, 13, 14 and the pad electrode 16 made of the u27 laminate are formed (see FIG. 4 (6)). The connection wiring 25 is also plated with Au 27 and becomes thick.

The electrodes 12, 1 formed as described above
3, 14 and the pad electrode 16 are made of the Ta film 21 and A
Since the Au film 22 is formed by plating a thick Au 27 on the u film 22, the resistance is low. Therefore, it is possible to apply a voltage to the channel optical waveguide 11 at a high frequency of, for example, several hundred MHz or more. Driving is realized.

In this embodiment, the Ta film 21 and the Au film 22 are processed into a predetermined shape after the Au 27 is plated. However, the Au 27 is plated after the Ta film 21 and the Au film 22 are processed into a predetermined shape. It is also possible.

Next, a method of manufacturing the SHG element 36 alone will be described.

In the SHG element 36 of this embodiment, an optical waveguide extending along the surface of a ferroelectric crystal substrate having a non-linear optical effect is formed, and the direction of spontaneous polarization of the substrate is reversed in the optical waveguide. The domain inversion portion is periodically formed, and in the optical waveguide, a wavelength of a fundamental wave guided in a direction in which the domain inversion portions are arranged is converted, and in a plane perpendicular to the waveguide direction of the fundamental wave. The direction of the spontaneous polarization of the substrate is an angle θ with respect to the one surface of the substrate.
(0 ° <θ <20 °).

The ferroelectric crystal group suitably used in the present invention
As a plate, LiNb which is not doped_XTa
_1-XO_Three(0 ≦ x ≦ 1) or Li doped with MgO
NbO_Three Substrates include, but are not limited to
No, LiNb doped with Zn_XTa_1-XO_ThreeBase
Plate, LiNb doped with Sc, MgO_XTa_1-X
O_ThreeSubstrate, KTiOPO_Four, KNbO_ThreeOther materials such as
It is also possible to use a substrate made of a material. Mg above
O-doped LiNbO_ThreeThe substrate is resistant to light damage
And non-doped LiNb_XTa_1-XO_ThreeThan substrate
preferable. In the present embodiment, the SHG element 36
The substrate is an off-cut substrate MgO-doped LiNbO_ThreeFor
Have been.

In the SHG element 36 having such a configuration, the direction of spontaneous polarization of the substrate 2, that is, the Z-axis direction is not perpendicular to the substrate surface 2a as shown in FIG.
For example be caused to enter the optical waveguide 1 in a state where a laser beam emitted from the LD element 32 and EOM element 34 that linearly polarized light the direction (arrow Q direction) is parallel to the substrate surface 2a, the nonlinear optical constant d ₃₃ is utilized Wavelength conversion becomes possible.
In this case, the direction of the electric field vector of the laser beam 4 is parallel to the substrate surface 2a, and the laser beam 4 guides the optical waveguide 1 in the TE mode. The effective nonlinear optical constant at that time is d ₃₃ cos θ.

As described above, the laser beam 4 is applied to the optical waveguide 1 with its linear polarization direction being parallel to the substrate surface 2a.
In this case, a λ / 2 plate or the like for rotating the direction of linearly polarized light is not required, and the fundamental wave incident optical system becomes simple, and the LD element 32 can be directly coupled to the end face of the optical waveguide 1. Becomes When the laser beam 4 is made to enter the optical waveguide 1 in this manner, the laser beam 4
Input efficiency to the optical waveguide 1 is also increased.

When the direction of spontaneous polarization of the substrate 2, that is, the Z-axis direction is at an angle θ with respect to the substrate surface 2 a, the depth d of the domain inversion section 8 is basically d as shown in FIG. = L · tan θ, but considering the spread of the domain inversion region of 1 μm, d = L · tan θ + 1 μm (1) Here, the value of L is a means for applying an electric field for domain inversion (in FIG. 6, as an example, the comb-shaped electrode E
u and the plate electrode Ed) are not directly determined by the size of the electrode, but tend to increase as the value of θ increases. When the domain inversion unit 8 is formed with θ = 0 °, L becomes minimum, and in the example of FIG.
Since the domain inversion portion 8 is formed at 90 °, L becomes maximum (that is, domain inversion occurs in the entire area facing the electric field application electrode).

Therefore, by setting the angle θ to be somewhat large, the depth d of the domain inversion portion 8 can be made sufficiently large. If the domain inversion section 8 can be made sufficiently deep in this way, the overlap integral between the domain inversion section 8 and the guided light increases, and high wavelength conversion efficiency can be obtained.

It is considered that the light beam is guided in the TE single mode in the proton exchange optical waveguide when the angle φ between the Z axis and the substrate surface is 0 ° <φ <70 °. (For example, Journal of Optical Commu
nications 5 (1984) 1.pp. 16-19). In the present invention, since the angle φ is the angle θ, when the optical waveguide is formed by proton exchange, if the angle θ is set in the range of θ <70 °, the wavelength conversion is efficiently performed. Become like

In the optical waveguide formed by proton exchange and subsequent annealing, the light beam
It is known that the waveguide in the single mode occurs when the angle φ between the Z axis and the substrate surface is 0 ° <φ <20 °. Therefore, when the optical waveguide is formed by proton exchange and annealing, the angle θ is set to θ <2.
When the angle is set in the range of 0 °, the wavelength conversion is efficiently performed.

On the other hand, when a domain inversion structure having an optimum duty ratio for obtaining the maximum wavelength conversion efficiency (that is, the width ratio between the domain inversion portion and the non-inversion portion is 1: 1) is formed, FIG. It was found that the indicated L dimension was approximately 50 μm if θ was within several degrees. In general, the field distribution of the guided mode can be reduced to about 1.2 μm when it is made the narrowest. Therefore, from the above equation (1), θ =
If the angle is set to 0.2 °, the depth d of the domain inversion portion is 1.2 μm, and the domain inversion portion has substantially the same size as the field distribution of the guided mode in the depth direction. Therefore, 0.2
If the angle θ <θ, the domain inversion portion overlaps with the field distribution of the waveguide mode, and the wavelength inversion is efficiently performed.

Although the field distribution of the guided mode can be at least about 1.2 μm as described above, the larger the field distribution, the more stable the external light can be incident on the optical waveguide. . In practice, if the field distribution of the guided mode is larger than 1.4 μm, external light is stably incident on the optical waveguide. From the above equation (1), if θ = 0.5 °, the depth d of the domain inversion portion is 1.4 μm, so that 0.5
If θ <θ, the fundamental wave is stably incident on the optical waveguide, and the domain inversion portion overlaps with the field distribution of the waveguide mode, so that the wavelength conversion is efficiently performed.

Therefore, the SHG element 36 of the present embodiment
Is formed on the surface of the LiNbO ₃ substrate by proton exchange and annealing, so that a waveguide is formed near the substrate surface, and the laser beam propagating through the waveguide also guides near the surface.

Next, the LD element 32 and the EOM element 34
And the optical adjustment at the time of coupling with the SHG element 36 will be described. First, the LD element 32 and the EOM element 34 are coupled while being adjusted or adjusted so that the optical coupling efficiency is maximized. Next, the block in which the LD element 32 and the EOM element 34 are coupled and the SHG element 36 are adjusted and coupled so as to maximize the optical coupling efficiency. The LD element 32 is a TE mode waveguide, and the EOM element 34 and the SHG element 36 can be coupled without any problem because they have a TE mode waveguide structure.

As described above, the block of the LD element 32 and the EOM element 34 is a block of the desired EOM element 34 measured in advance.
After confirming that the characteristics described above are obtained, it is coupled to the SHG element 36. As described above, since sufficient characteristics can be obtained in individual elements, the combination of these can lead to improvement in performance as a whole, and can suppress production of an optical wavelength conversion module with insufficient performance. In addition, since each element can be individually manufactured, a defective portion (defective element) can be easily specified, and trouble during assembly can be reduced.

The present inventor manufactured the module. As a result, in the case of an integrated device in which the EOM element and the SHG element were manufactured on the same substrate, the pass rate was 25%. As a result of analyzing the breakdown, the pass rate of each performance was 50
%, But it was found to be lower because of composite production. That is, when modules are manufactured on the same substrate, the product of the respective yields becomes the yield. For example, conventional:
0.5 × 0.5 = 0.25. However, in the present embodiment, since it is possible to manufacture each element individually, even if the value is 0.5 for each element, the yield does not decrease to 0.25.

Therefore, in the present embodiment, it is possible to assemble components each having a pass rate of 50%, which are individually manufactured, so that the pass rate is about 50% as a whole, and the yield is increased twice. It became.

Since the SHG element 36 has a higher SHG generation efficiency as the incident light power density is higher, the conditions of the proton exchange annealing waveguide are such that the waveguide light is confined well and the beam profile is shallow. The higher the SHG efficiency is obtained. For example, MgO-doped LiNb
The O ₃ substrate was subjected to proton exchange at 160 ° C. for 64 minutes, and then the annealing temperature was increased to 370 ° C. for 60 minutes and 350 ° C.
Compared with the 60 ° C. annealing time of 60 minutes, the guided light profile is 3 ° C. since the protons do not diffuse at 350 ° C.
3.7 μm, smaller than 4 μm at 70 ° C., SH
High G efficiency.

However, if the confinement of the guided light is good, the bleeding to the outside of the waveguide is small, so that the coupling does not occur unless the distance between the waveguides of the EOM element is small. As a result, the width of the electrode of the EOM element to be manufactured between the waveguides is 3
At 50 ° C., a line width of 1.8 μm is required and 370 °
C is smaller than 2.8 μm, and it becomes difficult to manufacture an electrode. So far, it has been manufactured under the condition of 370 ° C. where it can be manufactured, and a decrease in SHG efficiency has been unavoidable.

In the present embodiment, the EOM element 34
The module was manufactured at 0 ° C., and the SHG element 36 was manufactured at 350 ° C., and thereafter, the module was manufactured by direct coupling, so that a high SHG output could be obtained. Note that 350
The loss due to the difference in the beam diameter of the guided light between ° C and 370 ° C was very small, and the coupling efficiency of direct coupling was 99.7%. At this time, the coupling efficiency between the LD element 32 and the EOM element 34 was 50 to 60%, which was equivalent to the conventional efficiency.
Note that the reason why the efficiency is lower than the coupling between the EOM element 34 and the SHG element 36 is that the waveguide of the EOM element 34
It is considered that the difference in beam diameter from the D element 32 is large.

[Second Embodiment] In this embodiment, since the configuration is the same as that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description is omitted. In the above embodiment,
Although the off-cut substrate MgO-doped LiNbO ₃ is used for the substrates of the EOM element 34 and the SHG element 36, the present invention is not limited to this. In the present embodiment, an X-cut substrate, for example, an X-cut MgO drive LiNbO ₃ is used as the substrate of the EOM element 34.

That is, the conventional EOM element 34 and SH
Since the G element 36 had to be manufactured on the same substrate,
It was adjusted to the SHG element 36. In the present embodiment, E
Since the OM element 34 and the SHG element 36 can be separately manufactured, they are not limited to the same substrate.

The present inventor has stated that the substrate of the EOM element 34 includes:
It has been found that the same characteristics can be obtained with either the X-cut substrate or the off-cut substrate. As described above, the off-cut substrate is the substrate orientation that is employed to increase the SHG efficiency. Therefore, the EOM element 34 may be an inexpensive X-cut that is sold for general use.
In the present embodiment, when the combination of the X-cut EOM element 34 and the SHG element 36 of the off-cut substrate is combined, the same characteristics as those of the related art can be obtained.

Therefore, considering the above embodiment, E
The combination of the OM element 34 and the SHG element 36 depends on the performance and the price, depending on the performance and the price.
A combination of the M element 34 and the SHG element 36 of the off-cut substrate can be selected.

[Third Embodiment] In this embodiment, since the configuration is the same as that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description is omitted. In the above embodiment,
A proton exchange annealing waveguide is used for the waveguide of the SHG element 36. This is because the proton exchange annealed waveguide has excellent optical damage characteristics. The photo-damage property is a property that does not have resistance to short wavelength light, particularly visible light, and is not preferable for devices. The Ti diffused waveguide is a waveguide that is largely affected by the optical damage, and cannot be generally used for the SHG element 36 that generates visible light. Ti
When a diffusion waveguide is used, strong optical power cannot be converted due to an optical damage phenomenon, which is impractical.

However, the Ti diffused waveguide can guide both a TE mode having a horizontal polarization mode and a TM mode having a vertical polarization mode on the substrate. On the other hand, the proton exchange annealing waveguide can guide only light in one of the TE mode and the TM mode.

Further, the Ti diffusion waveguide is superior in the DC drift characteristic of the EOM characteristic to the proton exchange annealing waveguide. The DC drift characteristic is a phenomenon in which the characteristic of the EOM element 34 with respect to the input voltage is unstable and drifts.
This is an undesirable characteristic on the device. The cause of the DC drift is considered to be due to proton ions in the waveguide among several causes.

Therefore, the proton exchange annealing waveguide having proton as a main component has a very large drift. For this reason, in order to make this operate normally, a measure for eliminating DC drift is indispensable. One example of the drift countermeasure is disclosed in Japanese Patent Application Laid-Open No. Hei 7-294860.
There is a technology described in the issue.

This embodiment makes effective use of the characteristics of the Ti diffusion waveguide. That is, since the LD element 32 for SHG excitation has an infrared light having a fundamental wavelength of 950 nm, even if a Ti diffusion waveguide is used, the influence of optical damage is small. Therefore, the waveguide of the EOM element 34 forms a Ti diffusion waveguide having a good DC drift characteristic, and the waveguide of the SHG element 36 forms a proton exchange annealing waveguide to increase the SHG efficiency. That is, the Ti diffusion waveguide is used only for the EOM element 34,
The HG element 36 uses a proton exchange annealing waveguide that is resistant to optical damage. By doing so, the EO
It is possible to obtain an optical wavelength conversion module in which the characteristics of the M element 34 with respect to the input voltage are stable and the influence of optical damage is suppressed. With this configuration, a short-wavelength light source that has little DC drift and is resistant to optical damage can be manufactured.

When waveguides of such different fabrication processes are fabricated on the same substrate, for example, Ti diffusion is about 1000
° C high temperature treatment, proton exchange is about 200 ° C
Because of the low-temperature treatment described above, restrictions on the fabrication are increased.
Therefore, it is necessary to develop a process for fabricating the EOM element 32 and the SHG element 36 without deteriorating the characteristics of both. In this embodiment, since the fabrication is possible individually, the conventional process is used. It can be easily manufactured.

Therefore, according to the present embodiment, as the combination of the EOM element 34 and the SHG element 36, the EOM element 34 of the Ti diffusion X cut substrate and the SHG element 36 of the proton exchange annealing off cut substrate are added.

[Fourth Embodiment] In this embodiment, the TE
The present invention is applied to an optical wavelength conversion module including an EOM element having a TM mode conversion function. In the present embodiment, since the configuration is the same as that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted. Since the EOM element using Ti diffusion can propagate light in both the TE mode and the TM mode, it can be used as a TE-TM mode conversion type switch that was impossible with a proton exchange annealing waveguide. Therefore, in the optical wavelength conversion module of the present embodiment, the TE-TM mode conversion type switch 60 is used as the EOM element 34.

As shown in FIGS. 7A and 7B, the book
TE-TM in optical wavelength conversion module of embodiment
The mode conversion type switch 60 is composed of Ti diffusion X cut LiN
bO _ThreeA Ti diffusion waveguide 64 is formed on a substrate 62 and
And comb-shaped electrodes 66 and 68 are formed on the surface thereof.
You. A supply circuit 70 is connected to the comb-shaped electrode 66.
The comb-shaped electrode 68 is grounded.

The Ti diffusion TE-TM mode conversion type switch 60 takes the light propagation direction in the Z-axis direction, and when a voltage is applied by the supply circuit 70, the polarization of the incident light is changed as shown in FIG. In the case of the TE mode, the mode is converted to the TM mode, and as shown in FIG.
In the case of the M mode, the device converts the mode to the TE mode.

As shown in FIG. 8, the Ti diffusion TE-T
The M-mode conversion type switch 60 is used as the EOM element 34.
By combining with the LD element 32 and the SHG element 36, an optical wavelength conversion module is manufactured. Here, the LD element 32 is
It oscillates an E-mode laser beam. Also,
The SHG element 36 has a proton exchange annealing waveguide.

Here, the proton exchange annealing waveguide using the X-cut, Y-cut or off-cut LiNbO ₃ substrate guides only the TE mode. That is, since the proton exchange waveguide has a refractive index increase only in the Z-axis direction, it guides only the TE mode having a polarization component only in the Z-axis direction. Therefore, in the SHG element 36, T
The TM mode in which the polarization direction is orthogonal to the E mode cannot be guided, and is a leaky mode radiated into the substrate.

The TE mode light oscillated by the LD element 32 is waveguide-coupled to the EOM element 34 which is the TE-TM mode conversion type switch 60 of the Ti diffusion Z-axis propagation X-cut LiNbO ₃ waveguide substrate. Therefore, when the voltage by the supply circuit 70 is ON, the TE oscillated by the LD element 32
The mode light has its polarization direction rotated by 90 degrees, and is propagated to the SHG element 36 as TM mode light. In the SHG element 36, the incident TM mode light cannot be guided and becomes a leaky mode, and no SHG light is generated. On the other hand, when the voltage by the supply circuit 70 is OFF, the light in the TE mode oscillated by the LD element 32 is propagated to the SHG element 36. In the SHG element 36, since the proton exchange annealing waveguide is in a waveguide mode, SHG light is generated using the incident TE mode light as a fundamental wave.

As described above, in this embodiment, since the Ti diffusion Z-axis propagating X-cut LiNbO ₃ waveguide substrate can be used as the EOM element 34, the TE-TM, which was impossible with the proton exchange annealing waveguide, was not possible. It can be used as a mode conversion type switch.

[Fifth Embodiment] In this embodiment, the LD
The present invention is applied to an optical wavelength conversion module that modulates a laser beam oscillated from an element 32. In the present embodiment, since the configuration is the same as that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted.

Since the LD element 32 is a device that oscillates a laser by injecting a current, the internal temperature of the LD element 32 rises due to the influence, and the luminous efficiency decreases, and as a result, the light output decreases. This phenomenon is called droop and is observed in all LD elements.

Therefore, the LD element 32 is simply turned on / off.
This droop phenomenon becomes an obstacle when applied to a system for precisely controlling the amount of light instead of the FF control, for example, to an application to a photographic material or the like. For this reason, conventionally, bulk type A
The modulation was performed using an OM (acoustic optical element) so that the light output did not decrease. However, when AOM is used,
There is a problem that the optical system becomes large.

Therefore, in the present embodiment, the EOM element 3
In step 4, control is performed to correct this droop.

As shown in FIG. 9A, the electrodes 12, 14
Is grounded, and the droop correction circuit 72 is connected to the electrode 13. The droop correction circuit 72 stores a table in which a supply voltage with respect to the internal temperature is determined in advance so that the light output becomes stable in order to suppress a decrease in luminous efficiency due to an increase in the internal temperature of the LD element 32. A supply voltage is determined with reference to a table, or an optical output is detected (not shown), and the supply voltage is determined according to the optical output fluctuation. Thus, a stable light output can be obtained without being affected by the droop phenomenon.

Also, as in this embodiment, by using a waveguide type EOM element, the LD element 32 and the EO
Since it can be directly coupled to the M element 34, the size of the optical system can be reduced as compared with the case where the AOM is used. further,
Since the EOM element 34 can be easily driven at a high frequency, high-speed modulation can be performed.

Further, since the LD element 32 and the EOM element 34 can be separately manufactured and directly connected, the EOM elements 34 can be connected in multiple stages as shown in FIG. 9B.
In this case, an optical wavelength conversion module with a high extinction ratio can be obtained. As a technique for configuring the EOM element 34 in multiple stages, a method described in JP-A-11-44896 may be used.

When the LD element 32 is driven at a high frequency, the optical signal has almost no high frequency components, so that noise of low frequency components is eliminated, and the problem caused by the noise is eliminated. Further, when the LD element 32 is for exciting the SHG element 36, the AC drive or the pulse drive is performed because the SHG efficiency is proportional to the square of the fundamental wave power even if the average power of the LD element 32 is the same. A higher SHG output can be obtained. The high frequency in this case may be any frequency higher than the modulation frequency used.

Further, when the LD element 32 is for exciting the SHG element 36, when the oscillation wavelength of the LD element 32 is from 930 nm to 1100 nm, the wavelength of the SHG element 36 is changed from 465 nm to 550 nm, which is half of the wavelength, and the emission color is blue. Color output from to green. Since the LD element 32 in this wavelength band does not exist at present, its utility value is high. As described above, the LD element in this wavelength band is formed on the substrate GaAs by using a gad, a guide layer, and an active layer In.
It can be formed by growing GaAs or InGaNAs, a guide layer, and a gladd layer in this order. The guide layer is designed so as to have a higher refractive index than the gladd layer, and functions as a waveguide. The active layer InGaAs or InGaNAs has a band gap of 91%.
It is possible to oscillate a wavelength of 0 nm to 1100 nm.

In order to select the oscillation wavelength of the LD element 32, it is preferable to use a wavelength selection element. This wavelength selection element includes a multilayer bandpass filter, a diffraction grating,
Fiber grating, etalon, and
A Rio filter disclosed in Japanese Patent Publication No. 254001 can be used.

[Sixth Embodiment] In the above embodiment,
Although the LD element 32 and the EOM element 34 are directly coupled, the present invention is not limited to this. In the present embodiment, the LD element 32 and the EOM element 34 are optically coupled using an optical element such as an optical fiber.
This embodiment has the same configuration as the above embodiment,
The same portions are denoted by the same reference numerals, and detailed description is omitted.

As shown in FIG. 10, the LD element 32 and EO
Optical coupling is performed by directly coupling the M element 34 to both ends of the optical fiber 74. Here, the beam shape of the laser beam emitted from the LD element 32 is, for example, vertical direction × horizontal direction = 1 μm × 3 μm, and the EOM element 34
The shape of the incident part of the waveguide is different, for example, 3 μm × 6 μm. Therefore, by gradually changing the diameter and shape of the core of the optical fiber 74 from the LD element 32 toward the entrance of the waveguide of the EOM element 34, the LD
The coupling efficiency between the element 32 and the EOM element 34 can be improved. Further, the cross-sectional shape of the optical fiber 74 is not limited to a circle, but may be an elliptical shape so as to include at least the beam shape of the laser beam emitted from the LD element 32 and the incident portion of the waveguide of the EOM element 34. There may be.

Note that, without providing a grating in the LD element 32 described in the above embodiment, the optical fiber 7
By providing a grating in the optical element 4, the wavelength of the LD element 32 can be locked.

As described above, according to each of the embodiments, since each element can be manufactured independently, the yield can be improved. That is, conventionally, the product of the respective yields was the yield on the same substrate, but since the elements manufactured independently can be combined, the yield does not decrease.

Further, since each element can be manufactured independently, a module can be manufactured by mixing different types of substrates and different types of waveguides. For this reason, it is possible to combine different functions, and it is possible to increase the number of functions of the module. Further, it is possible to create a module having a function that has been impossible in the past.

Also, since each element can be manufactured independently, the best manufacturing process can be selected for each element. Further, the best process for fabricating only each element may be developed without considering the influence of other elements.

Further, after confirming the performance of each device, the device can be connected as a module, so that a defective portion can be specified for each device.

In the above embodiment, the substrate on which the optical waveguide is formed is made of LiNbO ₃ doped with MgO.
Not only the substrate but also other LiNbO ₃ substrates and undoped LiNbO ₃ , ZnO or Sc-doped LiNb
O ₃ substrate, may be LiTaO ₃ substrate, the MgO and ZnO utilizing doped LiTaO ₃ substrate.

In the above embodiment, the LD element 32
And the case where the EOM element 34 and the SHG element 36 are directly coupled to each other or via an optical fiber has been described. However, they may be coupled to each other via a SiO ₂ thin film between them.

[0118]

As described above, according to the present invention, each of the electro-optic modulation means and the light wavelength conversion means can be independently manufactured so as to exhibit high performance only in consideration of its own efficiency. By joining the electro-optic modulation means and the light wavelength conversion means, it is possible to produce an optical wavelength conversion module in which the efficiency of each of the electro-optic modulation means and the light wavelength conversion means is maximized.

Further, by further comprising a semiconductor laser for emitting a light beam, the light beam emitted from the semiconductor laser is modulated by the electro-optical modulator only by the light wavelength conversion module, and the modulated light beam is converted to the fundamental wave. There is an effect that the wavelength can be converted by the light wavelength converting means.

[Brief description of the drawings]

FIG. 1 is an image diagram showing a perspective shape of an optical wavelength conversion module according to a first embodiment of the present invention.

FIG. 2 is an image diagram showing a side shape and a front shape of the LD element according to the first embodiment of the present invention.

FIG. 3 is an explanatory view showing step by step a method of forming an electrode of an EOM element according to the first embodiment of the present invention.

FIG. 4 is a plan view showing a planar shape of the optical waveguide substrate in each step of FIG. 3;

FIG. 5 is a schematic perspective view showing a schematic shape of the SHG element according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram for explaining the polarization direction of the substrate of the SHG element according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram for explaining an EOM element having a TE-TM mode conversion function according to a fourth embodiment of the present invention.

FIG. 8 is an image diagram showing an optical wavelength conversion module according to a fourth embodiment of the present invention.

FIG. 9 is an image diagram showing an optical wavelength conversion module according to a fifth embodiment of the present invention.

FIG. 10 is an image diagram showing an optical wavelength conversion module according to a sixth embodiment of the present invention.

FIG. 11 is an image diagram showing a perspective shape of a conventional waveguide type light modulation element.

FIG. 12 is an image diagram showing a planar shape of a conventional waveguide type light modulation element.

FIG. 13 is an image diagram showing a perspective view of a waveguide type optical modulation element using a conventional Z-cut substrate.

FIG. 14 is an image diagram showing a side surface shape of a waveguide type optical modulation device using a conventional Z-cut substrate.

FIG. 15 is an image diagram showing an example of a light wavelength conversion element.

FIG. 16 is an image diagram showing another example of the light wavelength conversion element.

FIG. 17 is an explanatory diagram for describing a problem of the optical wavelength conversion element.

FIG. 18 is an image diagram showing a perspective shape of a conventional waveguide-type light modulation element using a substrate in which the Z axis is inclined in the thickness direction of the substrate.

FIG. 19 is an image diagram showing a side surface shape of a conventional waveguide-type light modulation device using a substrate whose Z-axis is inclined in the thickness direction of the substrate.

[Explanation of symbols]

 Reference Signs List 30 optical wavelength conversion module 32 LD element 34 EOM element 36 SHG element

Claims (10)

[Claims] 1. An optical modulator comprising a ferroelectric crystal having a non-linear optical effect and at least one light propagating to an optical modulation substrate.
An electro-optic modulation means in which an optical waveguide is formed and an electrode for applying a voltage to the optical waveguide is formed on the surface of the substrate; and light incident on a substrate for wavelength conversion by a ferroelectric crystal having a nonlinear optical effect. Optical wavelength conversion means, wherein at least one optical waveguide that propagates light is formed, and the direction of the spontaneous polarization of the substrate is inverted in the optical waveguide, and a domain inversion portion that is periodically formed in the waveguide direction is formed. And at least one waveguide of the electro-optic modulation means and at least one waveguide of the light wavelength conversion means.
A method of manufacturing an optical wavelength conversion module that joins the electro-optic modulation means and the optical wavelength conversion means so that two waveguides can propagate guided light. 2. A semiconductor laser for emitting a light beam, wherein the semiconductor laser is further directly bonded to the electro-optic modulation means or an optical fiber is connected to the electro-optic modulation means so that the light beam enters the optical waveguide of the electro-optic modulation means. The method for manufacturing an optical wavelength conversion module according to claim 1, wherein the optical wavelength conversion module is bonded through a step. 3. A substrate for optical modulation using a ferroelectric crystal having a nonlinear optical effect, at least one optical waveguide formed on the substrate and propagating incident light, and applying a voltage to the optical waveguide. An electrode formed on the surface of the substrate, an electro-optic modulation means, a substrate for wavelength conversion by a ferroelectric crystal having a non-linear optical effect, and at least one optical waveguide formed on the surface of the substrate; An optical wavelength conversion module, comprising: an optical wavelength conversion unit having a domain inversion portion in which the direction of spontaneous polarization of a substrate is inverted and periodically formed in the waveguide direction in the optical waveguide. 4. The optical wavelength conversion module according to claim 3, wherein said electro-optic modulation means includes a plurality of waveguides and constitutes a directional optical coupler. 5. An optical waveguide of the light wavelength conversion means, wherein the optical waveguide is formed so as to extend along the surface of the substrate and has a polarization component parallel to the substrate.
Or the optical wavelength conversion module according to 4. 6. A ferroelectric material wherein at least one of the substrates is cut such that an angle θ between a surface and spontaneous polarization of a ferroelectric crystal is within a predetermined angle range (0 ° <θ <20 °). The optical wavelength conversion module according to any one of claims 3 to 5, wherein the module is a crystal substrate. 7. The optical wavelength conversion module according to claim 6, wherein the angle θ exceeds 0.2 °. 8. The optical wavelength conversion module according to claim 6, wherein the optical waveguide is formed by proton exchange and annealing, and the angle θ exceeds 0.5 °. 9. A semiconductor laser for emitting a light beam, wherein the semiconductor laser is further directly bonded to the electro-optic modulation means or an optical fiber is connected to the electro-optic modulation means so that the light beam is incident on an optical waveguide of the electro-optic modulation means. The optical wavelength conversion module according to any one of claims 3 to 8, wherein the optical wavelength conversion module is joined via a cable. 10. The optical wavelength conversion module according to claim 3, wherein an oscillation wavelength of the semiconductor laser is adjustable.