JP5013377B2 - Optical device - Google Patents

Description

  The present invention relates to an optical device, and more particularly to an optical device in which a nonlinear optical material and a silicon substrate are combined.

  Optical devices in which optical components are integrated on a silicon substrate, which is expected to be further increased in speed, size, and cost as the data transmission speed is increased, are being studied.

As such an optical device, a wavelength conversion technique using a silicon waveguide has been reported (for example, see Non-Patent Document 1). According to Non-Patent Document 1, wavelength conversion from a digital signal (1542 nm) to an analog modulation signal (1328 nm) by coherent anti-Stokes Raman Scattering (CARS) using a silicon waveguide is reported. Yes. However, the conversion efficiency is as extremely low as 1.37 × 10 ⁻⁵ and is not practical. Therefore, it is desirable to have a wavelength conversion element that can be integrated on a silicon substrate, or other elements that realize optical functions.
V. Raghunathan et al., Appl. Phys. Lett. , Vol. 85, pp. 34

  An object of the present invention is to provide an optical device integrated on a silicon substrate that realizes an optical function, and a manufacturing method thereof.

Invention 1, wavelength conversion, and an optical device having an optical adjustment structure for performing at least one of the optical modulation, and crystal substrate, and a crystal of a material different from that of the crystal substrate, the crystal substrate And the crystal body, the crystal substrate includes a waveguide, and the crystal body includes the light adjustment structure and a further waveguide optically coupled to the waveguide. The light adjusting structure is a domain-inverted structure.
Invention 2 is the optical device according to Invention 1, wherein the crystal substrate is a silicon substrate.
Invention 3 is the optical device according to any one of Inventions 1 to 2, wherein the crystal constituting the light adjusting structure is LiTaO ₃ , LiNbO ₃ , KTiOPO ₄ , KNbO ₃ , and LiNb _(1-x) Ta It is selected from the group consisting of _X O ₃ (0 ≦ x ≦ 1).
Invention 4 is the optical device according to any one of Inventions 1 to 3, wherein the waveguide is formed in the crystal substrate.
A fifth aspect of the present invention provides the optical device according to any one of the first to fourth aspects of the present invention, comprising: a light source that supplies light guided to the light adjusting structure to the waveguide; and an electronic circuit that controls the operation of the light source. It is characterized by having.
A sixth aspect of the present invention is the optical device according to any one of the first to fifth aspects, further comprising an electric field application structure that applies an electric field to the light adjustment structure to change a degree of the light modulation. .

  An optical device that transmits a signal by optical communication technology according to the present invention and exhibits a predetermined function has a single crystal thin film installed at a location corresponding to the optical signal system on the surface of the silicon substrate, and the single crystal thin film has a polarization inversion structure. It is characterized by having. Thereby, the optical function using the nonlinear optical constant of the single crystal thin film can be exhibited even on the silicon substrate.

  Furthermore, in the optical device according to the present invention, since the silicon substrate and the single crystal thin film are optically coupled via the waveguide, the existing silicon electronic device and the optical communication using the nonlinear optics by the single crystal thin film are used. It can be combined with high-speed transmission technology. As a result, it is possible to increase the speed and capacity of existing silicon electronic devices. In such an optical device, in addition to the single crystal thin film, other electronic components (for example, an electronic circuit, a light source, a lens, a filter, and the like) can be mounted on the same silicon substrate, thereby enabling miniaturization. In addition, when the optical device according to the present invention is used, intra-circuit wiring, inter-element wiring, and inter-board wiring are possible, so that data transmission can be speeded up.

  Embodiments of the present invention will be described below with reference to the drawings. In the figure, the same reference numerals are assigned to similar elements to avoid redundant description. Prior to the embodiment, the basic configuration of the present invention will be described. The inventor of the present application has devised to develop a silicon hybrid by optically coupling a single crystal thin film and a silicon substrate through a waveguide, and exhibiting optical functions in a silicon substrate to which a single crystal thin film is bonded. Achieved.

(Basic configuration)
FIG. 1 shows a schematic diagram of an optical device according to the present invention.

  In the optical device 100, a single crystal thin film (crystal body) 120 is integrated on a silicon substrate (crystal substrate) 100.

The single crystal thin film 120 is a nonlinear optical single crystal that can exhibit a nonlinear optical effect. Preferably, the single crystal thin film 120 is selected from the group consisting of LiTaO ₃ , LiNbO ₃ , KTiOPO ₄ , KNbO ₃ , and LiNb _(1-x) Ta _X O ₃ (0 ≦ x ≦ 1). These materials are available as nonlinear optical single crystals that can exhibit nonlinear optical effects. In particular, LiTaO ₃ and LiNbO ₃ are promising because they are materials having a large nonlinear optical constant. Note that LiTaO ₃ and LiNbO ₃ are both non-doped or doped with an element selected from the group consisting of Mg, Zn, In, and Sc, both congruent and substantially stoichiometric compositions. These dopants are preferable because they can reduce optical damage. LiTaO ₃ and LiNbO ₃ are intended to have a congruent composition in which Ti or protons are diffused and a substantially stoichiometric composition. LiTaO ₃ and LiNbO ₃ in which Ti or protons are diffused are preferable as the waveguide.

Further, in the present specification, the phrase “substantially stoichiometric composition” means that although the molar fraction of Li ₂ O / (Nb ₂ O ₅ + Li ₂ O) is not completely 0.50, Also has a composition close to the stoichiometric ratio (mol fraction of Li ₂ O / (Nb ₂ O ₅ + Li ₂ O) = 0.495 to 0.5), This means that the degradation is not a problem in normal device design. Similarly, in LiTaO ₃ , “having a stoichiometric composition” means that although the molar fraction of Li ₂ O / (Ta ₂ O ₅ + Li ₂ O) is not completely 0.50, Also has a composition close to the stoichiometric ratio (molar fraction of Li ₂ O / (Ta ₂ O ₅ + Li ₂ O) = 0.495 to 0.5), resulting in a decrease in device characteristics. Means that it does not become a problem in normal device design. In particular, the coercive electric field of LiTaO ₃ and LiNbO _{3 having} a substantially stoichiometric composition is smaller than that of LiTaO ₃ and LiNbO _{3 having} a congruent composition, which is preferable because a domain-inverted structure described later is easily formed. Among them, the absorption edge of LiTaO ₃ having a substantially stoichiometric composition is 256 nm and is transparent up to the ultraviolet region, which is advantageous for an optical device that oscillates light in the ultraviolet region.

  The single crystal thin film 120 includes a polarization inversion structure (light adjustment structure) 130 and a waveguide 140. Although FIG. 1 shows an example in which the single crystal thin film 120 has a periodic polarization inversion structure, the polarization inversion structure 130 is not limited to this. For example, a lens-like domain-inverted structure may be used. Moreover, the single crystal thin film 120 may have a Mach-Zehnder waveguide type shape, and one of the branch waveguides may have a polarization inversion structure in which polarization is inverted, or periodic polarization in which both branch waveguides are staggered. You may have an inversion structure. When the domain-inverted structure 130 is a periodic domain-inverted structure, the period is set so that the input light 160 input to the single crystal thin film 120 satisfies the quasi phase matching condition. Those skilled in the art can appropriately set such settings according to the wavelength of the input light 160, the material of the single crystal thin film 120, and the like.

  The waveguide 140 is tapered so that the light 170 guided through the domain-inverted structure 130 is guided into the silicon substrate 110. In FIG. 1, the tapered shape of the waveguide 140 has a constant thickness and a tapered width in the traveling direction of the light 170, but is not limited thereto. For example, the waveguide 140 may have a tapered shape, and the waveguide 140 may have a constant width and a small thickness in the traveling direction of the light 170 (not shown).

  Such a single crystal thin film 120 is, for example, several μm thick. This thickness is sufficient to allow the single crystal thin film 120 to guide light and to exhibit a nonlinear optical effect, and to form the above-described domain-inverted structure 130 easily.

The single crystal thin film 120 having such a thickness can be obtained by thin film growth by a physical vapor deposition method or a chemical vapor deposition method, but a high-quality single crystal thin film epitaxially grown on a silicon substrate is obtained. Therefore, it can be obtained by growing a single crystal by the Czochralski method or the like. From such a point of view, LiTaO ₃ and LiNbO _{3 that} have already established a single crystal growth technique (see, for example, registration 3551242) and can obtain a high-quality single crystal are preferable.

  The silicon substrate 110 is an arbitrary silicon substrate that is commercially available. The thickness of the silicon substrate 110 is, for example, 500 μm. A waveguide 150 optically coupled to the waveguide 140 is formed on the silicon substrate 110. A portion of the waveguide 150 that is optically coupled to the waveguide 140 is tapered.

  In FIG. 1, the horizontal size of the silicon substrate 110 and the single crystal thin film 120 is shown as the same size, but it is not limited to this. The optical device 100 according to the present invention may be integrated with other elements (for example, a light source, an electronic circuit, a lens, a filter, an electrode, etc.) in addition to the single crystal thin film 120 on the silicon substrate 110.

  Next, an example of the operation of such an optical device will be described.

  In the optical device 100 of FIG. 1, the single crystal thin film 120 having the periodically poled structure 130 is disposed on the silicon substrate 110 as described above, and thereby wavelength conversion can be achieved.

  The input light 160 is input to the single crystal thin film 120 of the optical device 100. As the input light 160 is guided through the single crystal thin film 120, it satisfies the quasi-phase matching condition by the periodically poled structure 130 formed in the single crystal thin film 120, and the output light 170 has a wavelength different from the wavelength of the input light 160. Is converted to The converted output light 170 is guided through the waveguide 140, then travels to the waveguide 150, travels through the silicon substrate 110, and exits from the optical device 100. The tapered overlapping portions of the waveguide 140 and the waveguide 150 are optically coupled, and light loss is reduced when the output light 170 is emitted from the waveguide 140. As a result, the low-loss optical device 100 is provided as a whole. Wavelength conversion using the periodically poled structure 130 of the single crystal thin film 120 is arbitrary such as sum frequency, difference frequency, second harmonic, parametric oscillation, and the like.

  FIG. 2 shows a schematic diagram of another optical device according to the invention.

  The optical device 200 of FIG. 2 is the same except that the waveguide 210 is different from the waveguide 140 of the optical device 100 of FIG. The waveguide 210 of the optical device 200 is composed of segments. Each segment tapers toward a region that is optically coupled to the waveguide 150. Such a segmented waveguide 210 also functions to guide the light 170 guided through the domain-inverted structure 130 into the silicon substrate 110, similarly to the waveguide 140 of FIG.

  FIG. 3 shows a schematic diagram of yet another optical device according to the invention.

  The optical device 300 of FIG. 3 is the same except that the waveguide 310 is different from the waveguide 140 of the optical device 100 of FIG. The waveguide 310 of the optical device 300 is composed of a photonic crystal. Such a photonic crystal waveguide 310 also functions to guide the light 170 guided through the domain-inverted structure 130 into the silicon substrate 110, similarly to the waveguide 140 of FIG.

  Next, a manufacturing process of such an optical device 100, 200, 300 will be described. In the optical devices 100, 200, and 300 of the present invention, the waveguide 150 is formed on the silicon substrate 110 (FIG. 1) or the silicon substrate 110 on which the waveguide 150 is formed is used.

  FIG. 4 is a flowchart showing a manufacturing process of the optical devices 100, 200 and 300 according to the present invention.

Step S410: A resist corresponding to the domain-inverted structure is patterned on the single crystal thin film 120 (FIG. 1) bonded to the silicon substrate 110 (FIG. 1) on which the waveguide 150 is formed. The single crystal thin film 120 is bonded to the silicon substrate 110 so that the polarization plane is the surface. For example, when the single crystal thin film 120 is LiNbO ₃ , the single crystal thin film 120 is bonded to the silicon substrate 110 such that the Z plane (more specifically, the + Z plane) is the surface.

  The resist is a photoresist. A resist corresponding to the domain-inverted structure is formed by photolithography and patterned. When the domain-inverted structure is a periodic domain-inverted structure, a periodic resist pattern is obtained.

  Step S420: A first electrode is provided on the single crystal thin film 120 on which the resist is patterned, and a second electrode is provided on the silicon substrate 110 facing the single crystal thin film 120. The application of such an electrode is performed by a physical vapor deposition method such as sputtering. The electrode is, for example, Cr.

  Step S430: An electric field is applied between the first electrode and the second electrode. Thereby, only the region of the single crystal thin film 120 where the resist is not formed undergoes polarization inversion.

  Step S440: A predetermined region of the single crystal thin film 120 is etched. Such etching is performed by dry etching. The predetermined region is, for example, a region other than a region where light is to be guided on the silicon substrate. Thereby, the waveguides 140, 210, and 310 are formed.

  Through the above steps S410 to S440, the optical devices 100, 200, and 300 are formed. As described above, the present inventor arranges a single crystal thin film, which is a different material from a silicon substrate, on a silicon substrate by bonding, and optically couples them to express an optical function. succeeded in. Usually, in a semiconductor technology using a silicon substrate, it is necessary to select a different material and an arrangement method thereof so as to match the lattice constant of the silicon substrate. Therefore, the combination of the silicon substrate and the single crystal thin film in the present invention, Bonding is a very new idea, and its effect was confirmed for the first time by experiments.

  In the optical devices 100, 200, and 300, the waveguides 140, 210, and 310 have been described as part of the single crystal thin film 120. The waveguides 140, 210, and 310 may be made of a material different from that of the single crystal thin film 120. Is preferred.

  Further, in the optical devices 100, 200, and 300, an example in which the input light 160 is guided through the single crystal thin film 120, is wavelength-converted to the output light 170, and is guided from the waveguides 140, 210, and 310 to the waveguide 150. Although shown, it is not limited to this. For example, the optical device 100, so that the input light is guided from the waveguide 150 to the waveguides 140, 210, and 310, then travels to the single crystal thin film 120, and then is converted into an output light. 200, 300 may be used.

  Such selection can be determined by the wavelength of light guided through the waveguide 150. This is because light having a wavelength of less than 1.1 μm is absorbed by the silicon substrate. For example, when converting to light having a wavelength of 1.1 μm or more in the polarization inversion structure 130, the configuration of the optical device 100 (200, 300) can be adopted, and light having a wavelength of 1.1 μm or more is polarized. When the inversion structure 130 is converted into light having a wavelength of less than 1.1 μm, a configuration in which the above-described input light is guided from the waveguide 150 to the waveguide 140 (210, 310) can be employed.

  Further, in the devices 100, 200, and 300, the optical coupling portion between the single crystal thin film 120 and the silicon substrate 110 has been described as one, but the light guided in the silicon substrate 110 is guided to the single crystal thin film 120. Additional optical binding sites may be provided for the wave.

  Next, a further application example based on the optical device 100 of FIG. 1 will be described.

(Embodiment 1)
FIG. 5 is a schematic diagram of another optical device 500 according to the present invention.

  The optical device 500 is a device that realizes wavelength conversion for optical communication using the difference frequency (for example, wavelength conversion from C band to L band). The optical device 500 includes a silicon substrate 110, a single crystal thin film 120, a waveguide 140, a waveguide 150, a light source unit 510, a waveguide 520, and an electronic circuit 530.

The silicon substrate 110, the single crystal thin film 120 bonded thereto, and the optically coupled waveguide 140 and waveguide 150 are the same as those of the optical device 100 described with reference to FIG. In FIG. 5, the single crystal thin film 120 is Mg-doped LiNbO ₃ and has a periodically poled structure having a period of 16 to 17 μm. The length in the longitudinal direction (waveguide length) of the single crystal thin film 120 is 12 mm, the length in the short direction is 10 μm, and the thickness of the single crystal thin film 120 is 4 μm. Note that the specification of the single crystal thin film 120 is not limited thereto.

  The light source unit 510 further includes a first light source 540 and a second light source 550. The first light source 540 is a semiconductor laser that emits light having a wavelength of 1.55 μm band corresponding to C-band light. The second light source 550 is a semiconductor laser that emits light having a wavelength of 0.78 μm as pump light. An existing semiconductor laser is applied to the first light source 540 and the second light source 550.

  The waveguide 520 is optically coupled to the light source unit 510 and the single crystal thin film 120, and guides light from the light source unit 510 to the single crystal thin film 120. Such a waveguide 520 may be made of the same material as the single crystal thin film 120 or may be different, but the same material is preferable because the manufacturing process can be simplified.

  The electronic circuit 530 controls the operation of the light source unit 510. For example, the electronic circuit 530 controls the emission timing of the laser light from the first light source 540 and the second light source 550 of the light source unit 510. Thereby, the on / off timing of the C-band light and the L-band light finally emitted from the optical device 500 is controlled.

  Next, the operation of such an optical device 500 will be described.

  The electronic circuit 530 controls the emission timing of the laser light from the first light source 540 and the second light source 550 of the light source unit 510 at a predetermined timing. When the electronic circuit 530 drives both the first light source 540 and the second light source 550, the first light source 540 and the second light source 550 emit C-band light and pump light, respectively. The C-band light and the pump light are guided through the waveguide 520 and are incident on the single crystal thin film 120. As the C-band light and the pump light are guided through the periodically poled structure of the single crystal thin film 120, the L-band light (1.58 μm) that satisfies the quasi-phase matching condition and corresponds to the difference frequency between the C-band light and the pump light. Is converted to The converted L-band light is guided through the waveguide 140 and the waveguide 150 and travels into the silicon substrate 110. Thereby, since input / output to / from the Si circuit is possible, an existing circuit (for example, a light receiving element) can be used as appropriate.

  In addition, although the optical device 500 showed the example of difference frequency generation, it is not limited to this. The optical device 500 may be used for sum frequency generation, second harmonic generation, etc. by changing the period of the periodically poled structure. For example, in the case of second harmonic generation, in the optical device 500, the light source unit 510 may be a single light source.

(Embodiment 2)
FIG. 6 is a schematic diagram of yet another optical device 600 according to the present invention.

  The optical device 600 is a device that realizes a Mach-Zehnder waveguide type optical modulator. The optical device 600 includes a silicon substrate 110, a single crystal thin film 120, waveguides 140 and 150, an electronic circuit 530, and a pair of electrodes 610 and 620. The waveguide 140 and the waveguide 150 are optically coupled as described with reference to FIG.

The single crystal thin film 120 bonded to the silicon substrate 110 has a Mach-Zehnder waveguide type shape and includes branched waveguides 630 and 640. The branch waveguide 630 has a polarization inversion structure. For example, the single crystal thin film 120 is LiNbO ₃ . The directions of spontaneous polarization of the branching waveguides 630 and 640 are opposite to each other.

  The pair of electrodes 610 and 620 are arranged so that electric fields of the same magnitude are applied to the branch waveguides 630 and 640 of the single crystal thin film 120 in the same direction. The pair of electrodes 610 and 620 is, for example, Ti or Au.

  The electronic circuit 530 supplies power to the pair of electrodes 610 and 620 and controls application of an electric field to each of the branched waveguides 630 and 640 of the single crystal thin film 120. The pair of electrodes 610 and 620 and the electronic circuit 530 are collectively referred to as an electric field application structure.

  Next, the operation of such an optical device 600 will be described.

  Input light 650 is input to the optical device 600. The input light 650 is guided through the single crystal thin film 120 and is divided into two equal parts by the branching waveguides 630 and 640 to become the input light 660 and 670.

  The electronic circuit 530 sends a digital signal of “10010” to the pair of electrodes 610 and 620, for example, and controls to apply an electric field to each of the branching waveguides 630 and 640. Based on the digital signal, an electric field of “V1 → V0 → V0 → V1 → V0” is applied to the branch waveguides 630 and 640. Here, V1 is a state where an electric field is applied, and V0 is a state where no electric field is applied.

  When the electric field V1 is applied to the branching waveguides 630 and 640, the branching waveguides 630 and 640 have spontaneous polarizations in opposite directions, so that the refractive index change induced in the branching waveguides 630 and 640 has an opposite sign. . As a result, the phase of the input light 660 guided through the branching waveguide 630 is shifted by −π / 2, and the phase of the input light 670 guided through the branching waveguide 640 is shifted by + π / 2. The sum of the phase differences of the input lights 660 and 670 divided into two equal parts is π.

  The input lights 660 and 670 that are divided into two equal parts and shifted in phase by π / 2 are merged at the point where the branching waveguides 630 and 640 are coupled. Here, when the lights are merged, the input lights 660 and 670 cancel each other and become an output 0 because of the phase difference π.

  On the other hand, when the electric field V0 is applied to the branch waveguides 630 and 640 (when no electric field is applied), there is no phase difference between the input lights 660 and 670 that are guided through the branch waveguides 630 and 640, respectively. Accordingly, the input lights 660 and 670 divided into two equal parts are merged at the point where the branching waveguides 630 and 640 are coupled, and the output becomes the output 1 and the output light 680 is output. The output light 680 travels through the optically coupled waveguide 140 and waveguide 150, travels through the silicon substrate 110, and enables input and output to the Si circuit.

  Thus, the optical device 600 generates a pulse of “01101” light. According to the optical device 600, since the branch waveguide 630 which is a part of the single crystal thin film 120 has a domain-inverted structure, the same modulation action can be obtained by applying the same electric field to both the branch waveguides 630 and 640. Therefore, the drive voltage can be halved. In addition, since a pair of electrodes for applying an electric field is sufficient, the manufacturing process can be simplified.

  FIG. 6 illustrates an example in which the direction of spontaneous polarization of the branching waveguides 630 and 640 is reversed, but the present invention is not limited to this. For example, a periodic polarization inversion structure may be formed in each of the branched waveguides 630 and 640 and arranged so that they are staggered (that is, a checkered pattern). Thereby, in combination with the quasi phase matching technique, an optical modulator capable of operating efficiently in a high frequency region can be realized.

  Since the wavelength conversion function (Embodiment 1) and the light modulation function (Embodiment 2) can be expressed on the silicon substrate 110, the optical device 500 and the optical device 600 are formed on the single silicon substrate 110, You may combine. In this case, the electronic circuit 530 may be controlled to apply an electric field to each of the branching waveguides 630 and 640 in addition to the timing of emission of the laser light from the light source unit 510.

  As described above, the optical devices 100, 200, 300, 500, and 600 according to the present invention exhibit an optical function (that is, a nonlinear optical effect) using a polarization inversion structure on a silicon substrate. Further, in the optical devices 100, 200, 300, 500, and 600, since the silicon substrate and the single crystal thin film are optically coupled via the waveguide, the optical communication utilizing the above optical function for the silicon electronic device. High-speed transmission technology. Such optical devices 100, 200, 300, 500, and 600 are suitable for inter-circuit wiring, inter-element wiring, and inter-board wiring, and enable miniaturization and cost reduction.

  Next, the method of the present invention will be described using specific examples, but it should be understood that the present invention is not limited to the examples.

An optical device was manufactured using a 0.5 mm-thick silicon substrate (3 inches in diameter) on which Li-NbO ₃ doped with Z-cut Mg (hereinafter simply referred to as LN) was bonded as a single crystal thin film. The thickness of LN was 4 μm.

  A resist (photoresist) corresponding to the periodically poled structure was patterned on the + N surface of LN by photolithography (step S410 in FIG. 4). The period of the periodically poled structure was three types, each having a period of 16.6 μm, 16.8 μm, and 17.0 μm. Cr was deposited as a first electrode on the LN patterned with the photoresist, and Cr was deposited as a second electrode on the silicon substrate on the surface facing the photoresist by sputtering (step S420 in FIG. 4). The film thickness of Cr was 1000 mm. Next, the silicon substrate was cut into a 15 mm long piece in the longitudinal direction to obtain a chip shape.

  An electric field was applied between the first electrode and the second electrode to form a periodically poled structure (step S430 in FIG. 4). The application condition of the electric field was 30 pulses at a pulse voltage of 43.6 kV / mm at a temperature of 120 ° C.

Next, dry etching was performed using electron cyclotron resonance reactive ion beam etching so as to obtain a waveguide length of 11.9 mm having a width of 3.5 to 12.0 μm and a digging depth of 3 μm (step of FIG. 4). S440). The etching gas was Ar and C ₂ F ₆ mixed gas. As a result, optical devices in which ridge-type waveguides having various waveguide widths were integrated were obtained.

  The surface of the obtained optical device was observed using a differential interference microscope. From the observation results, the polarization inversion ratio (inversion width / inversion period) of the periodically poled structure was determined. The observation results and the polarization inversion ratio are shown in FIGS.

  FIG. 7 is a diagram showing the surface morphology and polarization inversion ratio of the optical device.

  FIG. 7A shows a surface form of the optical device. Regions 710, 720, and 730 are periodically poled structures with periods of 16.6 μm, 16.8 μm, and 17.0 μm, respectively. From the polarization reversal ratio in FIG. 7B, it was confirmed that a uniform periodic polarization reversal structure having a polarization reversal ratio of approximately 0.5 was obtained over the entire waveguide length (longitudinal direction).

  FIG. 8 is another view of the surface morphology of the optical device.

  FIG. 8 is an enlarged view of a part of the region 710 in FIG. As shown by the shading, it was confirmed that the periodically poled structure was formed uniformly.

  Next, the expression of the optical function (nonlinear optical effect) of the obtained optical device was examined.

  FIG. 9 is a schematic diagram of an experimental system.

  The experimental system 900 includes a light source 910, a polarization controller 920, collimator lenses 930 and 950, a condenser lens 940, and a detector 950. As the light source 910, a 1.55 μm band wavelength tunable laser or a 0.78 μm titanium sapphire laser was used. The numerical aperture NA of the collimator lenses 930 and 950 was 0.52. The numerical aperture NA of the condenser lens 940 was 0.40. In the drawing, an optical device 970 indicates an optical device manufactured in this example. Using such an experimental system 900, the fundamental wavelength dependence of the conversion efficiency and the insertion loss of the waveguide were examined. Each result is shown in FIG. 10 and FIG.

  FIG. 10 is a diagram illustrating the fundamental wavelength dependence of the conversion efficiency.

  In the experimental system 900, a tunable laser in the 1.55 μm band was used as the light source 910, and the fundamental wavelength was changed from 1.563 μm to 1.569 μm. A fundamental wave having each fundamental wavelength was input to an optical device 970 having a waveguide width of 12.0 μm and a polarization inversion period of 16.8 μm, a second harmonic was generated, and conversion efficiency was measured. From FIG. 10, the SHG normalized conversion efficiency at about 1565.9 nm was about 120% / W. This value corresponds to an SHG normalized conversion efficiency of 1200% / W at a waveguide length of 3 cm of a practical size, and was a sufficient value for practical use of a CL converter or the like.

  FIG. 11 is a diagram showing the insertion loss of the waveguide.

  In the experimental system 900, the light source 910 uses a 1.550 μm wavelength tunable laser and a 0.78 μm titanium sapphire laser, each having a waveguide insertion loss, a polarization inversion period of 16.8 μm, and various waveguide widths. It measured about the optical device.

  In the figure, the result of the 1.550 μm wavelength tunable laser is indicated by ▲, and the result of the 0.78 μm titanium sapphire laser is indicated by ◯. Low losses of 1.77 dB (@ 1.550 μm, waveguide width 12.0 μm) and 2.65 dB (@ 0.78 μm, waveguide width 11.0 μm) were obtained. These values were equal to or less than those of conventional devices, and were confirmed to be practical values.

  As described above, according to the present invention, an optical function can be expressed by using a single crystal thin film having a domain-inverted structure on a silicon substrate. Furthermore, since the silicon substrate and the single crystal thin film are optically coupled via the waveguide, the data transmission speed of the silicon electronic device can be increased, the device can be reduced in size, and the cost can be reduced. Since the optical function (nonlinear optical effect) according to the present invention can be mounted in addition to the function of the conventional optical device, a new device such as an all-optical switch can be constructed.

Schematic diagram of an optical device according to the present invention. Schematic diagram of another optical device according to the invention Schematic diagram of yet another optical device according to the present invention. Flowchart showing the manufacturing process of optical devices 100, 200, 300 according to the present invention Schematic diagram of another optical device 500 according to the present invention. Schematic diagram of yet another optical device 600 according to the present invention. Diagram showing surface morphology and polarization reversal ratio of optical device Another view of the surface morphology of the optical device Schematic diagram of the experimental system Diagram showing basic wavelength dependence of conversion efficiency Diagram showing insertion loss of waveguide

Explanation of symbols

100, 200, 300, 500, 600 Optical device 110 Silicon substrate 120 Single crystal thin film 130 Polarization inversion structure 140, 150, 210, 310, 520 Waveguide 160, 650, 660, 670 Input light 170, 680 Output light 510 Light source unit 530 Electronic circuit 540 First light source 550 Second light source 610, 620 Pair of electrodes 630, 640 Branched waveguide

Claims (6)

Wavelength conversion, and an optical device having an optical adjustment structure for performing at least one of the optical modulation,
A crystal substrate;
A crystal of a material different from that of the crystal substrate,
The crystal substrate and the crystal body are integrated,
The crystal substrate has a waveguide;
The crystal body includes the light adjusting structure and a further waveguide optically coupled to the waveguide;
The optical device is characterized in that the light adjusting structure is a polarization inversion structure.   2. The optical device according to claim 1, wherein the crystal substrate is a silicon substrate. 3. The optical device according to claim 1, wherein the crystal constituting the light adjustment structure is LiTaO ₃ , LiNbO ₃ , KTiOPO ₄ , KNbO ₃ , and LiNb _(1-x) Ta _X O _3. An optical device selected from the group consisting of (0 ≦ x ≦ 1).   4. The optical device according to claim 1, wherein the waveguide is formed in the crystal substrate. 5.   5. The optical device according to claim 1, further comprising: a light source that supplies light guided to the light adjusting structure to the waveguide; and an electronic circuit that controls an operation of the light source. Features optical device. 6. The optical device according to claim 1, further comprising an electric field application structure that applies an electric field to the light adjustment structure to change a degree of the light modulation.