JP4253606B2 - Light control element - Google Patents

Description

  The present invention relates to a light control element having a core and a clad forming an outer layer portion of the core.

Patent Document 1 discloses a configuration in which a semiconductor substrate on which a light emitting element can be configured is in contact with a low refractive index medium such as SiO ₂ .

JP 2000-232258 A

  By forming a photonic band gap, which is a forbidden band of light, by using a dielectric periodic structure of a wavelength called photonic crystal, or by utilizing a phenomenon peculiar to photonic crystal that exhibits a unique effect due to strong dispersibility. It is expected that the light control element different from the past and the size of the conventional light control element can be dramatically reduced. Many light control elements such as a polarization separation element using a photonic band gap, an optical waveguide capable of rapid bending with a defect introduced therein, and a low threshold laser have been studied.

  For complete light control, it is necessary to control light in the three-dimensional direction, but extremely advanced technology is required to stably manufacture a three-dimensional photonic crystal in a large area. Compared with a three-dimensional structure, a two-dimensional photonic crystal formed in a plane can be formed relatively easily by diverting semiconductor process technology. That is, it can be configured by a method in which a pattern is formed by lithography in a two-dimensional plane and the pattern is transferred by etching. The two-dimensional photonic crystal needs to realize light confinement in a direction perpendicular to the plane constituting the crystal, and in many cases, a slab structure is adopted. The slab structure is a structure in which a high refractive index medium having a submicron thickness is formed on a low refractive index medium. In photonic crystals, a large difference in refractive index is required in order to show the effect remarkably, and therefore a semiconductor having a refractive index of about 3 is often used.

As the semiconductor slab structure, a photonic crystal is formed on a GaAs-based or InP-based compound semiconductor or Si formed on the sacrificial layer, and the sacrificial layer is removed to expose the air bridge type two-dimensional photo. A typical structure is a nick crystal or a structure using a difference in refractive index between Si and SiO ₂ by an SOI substrate.

  However, the air bridge structure is fragile as a structure, and is not suitable for practical use. In addition, although the SOI substrate has a solid foundation, since it is Si, it can be used only for passive elements such as optical waveguide applications.

Thus, for example, Patent Document 1 discloses a configuration in which a semiconductor substrate on which a light emitting element can be configured is in contact with a low refractive index medium such as SiO ₂ . FIG. 16 is a schematic diagram of the configuration, and a GaAs substrate 115 having a semiconductor photonic crystal 113 having a periodic array hole 117 which is a photonic crystal array made of GaAs and a low refractive index dielectric layer 114 made of SiO _{2 on the} surface. Are in flat contact. As a result, the semiconductor light emitting device can be constituted by a photonic crystal, and the structure is stronger than the air bridge.

  However, when an optical waveguide with defects introduced in the photonic crystal array is formed, a low refractive index that is the foundation is required unless a waveguide band on the lower frequency side than the light line generated by the slab type is used. It is expected that light will leak into the medium. If the refractive index difference is large, the band shifts to the low frequency side, so a large area where light does not leak can be taken. That is, when a slab type two-dimensional photonic crystal array is used, it is necessary to use a semiconductor layer having a relatively high refractive index.

  On the other hand, as materials used for the light control element, many materials such as organic materials, electro-optic materials, and nonlinear optical materials are used in addition to semiconductors. For example, as a high-speed light control element, a directional coupler type light control element or a Mach-Zehnder type light control element made of lithium niobate is generally used and commercialized. There are also problems such as reducing applied voltage. If a photonic crystal array can be formed with such a material, it is thought that the device can be dramatically miniaturized and the voltage can be lowered.

  As described above, even with these materials, it is difficult to form a three-dimensional structure. Further, since many of these materials have a refractive index of about 2, even if a two-dimensional photonic crystal array is formed on a slab structure formed on a low refractive index medium, it can be used from the influence of the light line described above. The photonic band gap portion becomes extremely small, and it becomes difficult to use the unique effect as a photonic crystal.

  An object of the present invention is to provide a light control element in which a composite core is formed and the refractive index of the core is equivalently improved.

The present invention provides a light control element having a core and a clad forming an outer layer portion of the core, a first layer having an electro-optic material or a nonlinear optical material, and a second layer having a higher optical refractive index than the first layer. A circular core having a refractive index lower than a refractive index of the composite core, wherein the first layer and the second layer form a composite core to be the core. The light control element is characterized in that a photonic crystal array structure in which holes having a shape or a polygonal shape are periodically arranged is formed, and the photonic crystal array structure has a line defect structure.

  According to the present invention, the first layer using the electro-optic material or the nonlinear optical material and the second layer having a higher refractive index are combined to form a composite core. It is possible to provide a light control element capable of making the rate larger than that of the first layer.

  A plurality of examples of the best mode for carrying out the present invention will be described.

  FIG. 1 is a configuration diagram schematically showing a light control element 1 of the present embodiment. The light control element 1 has a core, and a clad such as an air layer forms an outer layer portion of the core. Reference numeral 11 denotes a thin film layer formed from an electro-optic material or a nonlinear optical material (first layer). An electro-optic material is a material whose optical properties such as refractive index change when electricity is applied, and a nonlinear optical material is a material having a large optical nonlinear constant. The thin film layer 12 (second layer) has a refractive index higher than that of the thin film layer 11, and the thin film layer 11 and the thin film layer 12 are arranged close to each other in plane or in contact with each other to form the composite core 13. is doing. The composite core 13 serves as the aforementioned core of the light control element 1. The equivalent refractive index of the composite core 13 is an intermediate refractive index between the thin film layer 11 and the thin film layer 12.

Here, the meaning of “equivalent” when the equivalent refractive index is described. That is, when light propagates through a medium that does not form a transmission path, the speed of light is affected by the refractive index (n) in the medium, and propagates at c ₀ / n (c ₀ : speed of light in vacuum). . However, when a transmission path by total reflection is formed, a standing wave is formed in a direction perpendicular to the traveling direction (a mode is formed), and light propagates under the influence of the refractive indexes of the core and the cladding. The refractive index felt by the standing wave is expressed as “equivalent refractive index”.

In general, the equivalent refractive index takes a value between the refractive indexes of the core and the cladding. In other words, the light propagating through the transmission line formed of the core and the clad can be considered as being replaced with the light propagating through the medium having the equivalent refractive index (n _eq ), and the speed of the light is c ₀ / It can be expressed as propagating with n _eq .

  When light is described sensuously as light rays, when there are two angles that can form a mode within the angle where total reflection is allowed, light is incident at a larger angle compared to light incident at a smaller angle. As a result, the number of reflections at the interface increases. That is, the light will propagate slowly in the transmission path.

  Expressing this in a wavelike manner, a slow light speed corresponds to an increase in the refractive index perceived by the light mode in the transmission path, which means that the perceived refractive index varies depending on the mode.

  The same can be considered when the composite core 13 is used as in the present embodiment. For example, if there are 13 composite cores formed with a refractive index of low / high / low, light propagates slower as compared with the case where the composite core is not used, as shown in FIG. That is, it is considered that the refractive index felt by the light propagating through the transmission line propagates as if it is “equivalently” increased.

  In a transmission line with a large equivalent refractive index, light is strongly confined (this is a wave nature, so it cannot be explained by light rays, and there is a jump in logic in that respect), and will be described later. The improvement in performance can be expected when a photonic crystal is constructed.

  When the meaning of the equivalent refractive index is such, the composite core 13 is disposed on a substrate having a refractive index lower than the equivalent refractive index of the composite core 13 or is sandwiched between substrates having a low refractive index. By being disposed (the substrate is not shown in FIG. 1), an optical waveguide is formed using air or a low-refractive index substrate as a clad, and the total inside of the composite core 13 is reflected in a direction perpendicular to the layer thickness direction. Light propagates along.

  Since the equivalent refractive index of the composite core 13 is higher than the refractive index of the thin film layer 11, the light propagating through the composite core 13 is higher than the refractive index received by the light propagating through the thin film layer 11 made of an electro-optic material. Propagate while receiving refractive index.

  By adopting such a configuration, a material having a low refractive index as the core 13 can be combined with a material having a high refractive index to increase the equivalent refractive index, and light confinement can be increased.

  Then, by controlling the layer thickness of the thin film layer 11 and the thin film layer 12, the equivalent refractive index of the composite core 13 can be controlled between the refractive indexes of the thin film layer 11 and the thin film layer 12.

  The above-mentioned electro-optical material is a material whose optical properties such as refractive index change when an electric field is applied, inorganic crystals such as lithium niobate, titanium niobate and KTP, ceramics such as PZT and PZLT, azo dyes Organic molecules or organic crystals such as stilbenzene dyes and dusts, and semiconductor crystals having a quantum well structure can be used.

  The above-mentioned nonlinear optical material is an optical material having a strongly nonlinear dielectric response function with respect to light radiation, and is a material used for optical harmonic generation, optical mixing, optical parametric oscillation, etc. using nonlinear polarization. It is.

The aforementioned nonlinear optical material has a large second-order nonlinear constant, preferably a second-order nonlinear constant of 0.01 pm / V or more, more preferably a material having a second-order nonlinear constant of 1 pm / V or more. is there. Alternatively, the above-described nonlinear material has a large third-order nonlinear constant, preferably a third-order nonlinear constant of 0.01 × 10 ⁻²² m ² / V ² , and more preferably a third-order nonlinear constant of 1 It is a material which is × 10 ⁻²² m ² / V ² .

The foregoing materials, the inorganic optical _{material, ADP (NH4H2PO4), KDP (} KH 2 PO 4), DKDP (KD 2 PO 4), RDP (RbH 2 PO 4), RDA (RbH 2 AsO 4), LN, LT, KN, KT, BNN, SBN, LI, BBO, LBO, BSO, GaAs, GaP, InP, ZnTe, ZnSe, ZnS, ZnO, CdTe, CdS, CdSe, Te, Se, Ag ₃ AsS ₃ , Ag ₃ SbS _{3, AgGaS 2, AgGaSe 2,} ZnGeP 2, GdGeAs 2, Bi 12 SiO 20, Bi 12 GeO 20, Bi 12 TiO 20, KTiOAsO 4, KTiOPO 4, BaTiO 3, SrTiO 3, KTaO 3, KTa 0.65 Nb 0 _{.35 O 3, Cd 2 Nb 2} O 7, L BGeO _5, PZT as ceramics, PLZT, Ga, In, Al , As, P, N, Sb, Zn, III-V Group Se, semiconductor quantum well structure is a Group II-VI semiconductor mixed crystal, as the organic optical materials , Azo dyes, stilbenzene dyes, dust, polydiacetylene, low molecular weight second-order nonlinear optical materials such as mNA, MNA, MAP, POM, DAN, DIVA, NPP, COANP, MNBA, MMONS, MBANP, TC-28, DNBB , DMNP, MNA, MNP, MMNA, PCNB, ECNB, IPMPU, ECPMDA, p-NMDA, MNPMDA, 4NpNa, high molecular second-order nonlinear optical materials, host guest materials, polymer side complex or main complex with NLO group There are modified and chemically bonded materials, cross-linked materials, and host guest materials As materials, host polymers (LCP, PMMA, POE, Poly (Vp-co-St), PVP, PRO, PCL, PBSSe, PBDG) and guest dyes (DANS, DANS ₃₃ , DR1, DCV, TCV, p-NMDA, p-NA, p-DMNP, CPABMCA, MNA), a modified type material in which NLO group is chemically bonded to the side complex or main complex of the polymer, NLO polymer as Poly (St-DR1), Poly (St-DASP) ), Poly (St-NPP), Poly (MMA-HNS), Poly (MMA-co-MMA-DCV), Poly (St-co-MAAB), Poly (St-co-MABA), Poly (St-co -MA-CM), Poly (MMA-co-MMA-DR1), Poly (organ pho-sphazene-ANS), PPNA, Poly (VA-co-Vat-NA), Poly (VAc-co-Vat-NA), Poly (ST-NA), Poly (MMA-NA), Poly (MMA-co -MMA-2R), Poly (MMS-co-MMA-3R), P6CS / MMA, polyallylamine, pNA-EG, PMMA / MNA, pNA-PVA, Poly (VDCN-co-VAc), MSMA, cross-linked material (Bis-A, NPDA), (Bis-A, ANT), (NNDN, NAN), (DGE + PS (O), NPP), (PVCN, CNNB- R), LB film materials include DCAMP, FA6, PO86, AODA, TMSC, Poly (HE -Co-A-ASB), PtBM, and high-molecular third-order nonlinear optical materials such as polydiacetylene (PTS, TCDU, DCHDFMP, BTFP, mBCMU), polyacetylene derivatives, polyphenylacetylene derivatives, polyarylene vinylenes (PPV, PTV) , MO-PPV, PFV), polythiophene, annulene, phthalocyanine, fullerene, and the like.

Most of these materials have a refractive index of about 2.5 even if the refractive index is high, and there are few materials having a refractive index exceeding 3 such as a semiconductor. Therefore, this material is made into a thin film on a low refractive index medium such as SiO _2. Even if it is formed, a large difference in refractive index cannot be obtained.

  The light control element 1 that needs to increase the equivalent refractive index difference can be realized by the structure of the composite core 13 formed of such a material and a material having a high refractive index.

  As a result, it is possible to utilize the optical characteristics of the electro-optic material and the nonlinear optical material while maintaining a high refractive index difference.

  As the optical characteristics of the electro-optic material and the nonlinear optical material, for example, it is possible to use a phenomenon such as a property of refractive index modulation by applying an electric field or light irradiation or a wavelength conversion using the nonlinear characteristics.

  Although it is possible to cause refractive index modulation or the like by a semiconductor having a quantum well structure, there are many aspects that are equivalent to or slightly inferior to a light control element using an electro-optic material in terms of light modulation characteristics. Therefore, an optical element using the electro-optic effect or the nonlinear optical effect can be configured according to the present embodiment by increasing the difference in refractive index equivalently.

  Next, another embodiment will be described.

  3A and 3B are configuration diagrams schematically showing the light control element 1 of the present embodiment, in which FIG. 3A is a longitudinal sectional view, and FIG. 3B is a plan view. The same members and the like as those in the embodiment of FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  3 also includes a thin film layer 11 formed of an electro-optic material or a nonlinear optical material, and a thin film layer 12 having a refractive index higher than that of the thin film layer 11, and the thin film layer 12 is planar with the thin film layer 11. The composite core 13 is formed by close contact or planar contact. By forming the composite core 13 on a substrate having a refractive index lower than the equivalent refractive index of the composite core 13 or forming an arrangement sandwiched between substrates having a low refractive index (the substrate will be described later). An optical waveguide is formed using air or a low refractive index substrate as a clad, and light propagates along the substrate in a direction perpendicular to the layer thickness direction by total reflection in the composite core.

  The light control element 1 in FIG. 3 differs from that in FIG. 1 in that a two-dimensional photonic crystal array structure is formed in the composite core 13. The photonic crystal in this example is configured by a triangular arrangement of circular holes 21 that penetrate in the layer thickness direction of the composite core 13.

  The photonic crystal array structure can have a photonic band gap which is a light forbidden body by adjusting the periodic structure. The characteristics of the photonic crystal are determined by the difference in dielectric constant between the substrate and the formed structure (here, air holes), its arrangement, the wavelength of light and the size of the structure, the distance between the structures, etc. . Therefore, if any of these is changed, the characteristics of the photonic crystal can be changed.

  As the photonic crystal arrangement structure, in addition to the circular holes 21, a structure in which a dielectric pillar is used and the periphery is a low refractive index medium may be used. Moreover, the dielectric periodic structure does not need to have a circular hole shape, and may be configured as a polygonal hole.

  Further, as shown in FIG. 4, by eliminating the arrangement of the photonic crystal arrangement structure in a part of the photonic crystal arrangement structure (reference numeral 22), an optical waveguide can be formed by providing a line defect structure. .

  In such a two-dimensional photonic crystal, light is confined by total reflection in the layer thickness direction, and the photonic crystal is formed in a portion where the layer is formed. Since the layer thickness direction confines light by total reflection, the light confinement may not be possible depending on the wave number of propagating light. Light confinement due to total reflection becomes impossible when the wave number changes greatly in a portion where light is confined or when a mode having a large wave number distribution is excited. This phenomenon is greatly influenced by the refractive index of the material of the upper and lower clad parts, and the difference in refractive index between this part and the core part determines whether or not the optical confinement due to total reflection becomes invalid. In the photonic band diagram, if there is a photonic band structure in the lower part than the straight line determined by the refractive index of the cladding part called the light line, the optical confinement in that part will not be invalidated, The two-dimensional photonic crystal works effectively.

  In other words, in order to use the effect of the photonic crystal, it is necessary to open the photonic band gap widely and to be present on the lower frequency side than the light line. In the photonic crystal arrangement, a refractive index difference is necessary to widen the photonic band gap. Furthermore, in order to open the photonic band gap below the above-mentioned light line, it is necessary to move the band gap itself to the low frequency side.

  FIG. 5 shows the result of computer simulation using the plane wave expansion method. Assuming a two-dimensional photonic crystal arrangement, calculation was performed assuming that a circular hole 21 having a refractive index of 1 is provided in a substrate having a refractive index of 3 and a refractive index of 2. Calculated for TE polarization. A band diagram corresponding to the refractive index 3 is shown in FIG. 5A, and a band diagram corresponding to the refractive index 2 is shown in FIG. 5B. For any wave number on the horizontal axis, the portion where no normalized frequency exists is the photonic band gap. It can be seen that when the refractive index is 3, the photonic band gap itself moves to the lower frequency side and the gap itself is larger than the refractive index 2. Therefore, the large difference in the refractive index in the portion where the photonic crystal array is formed has a great influence on the characteristics of the light control element by the photonic crystal and the design tolerance, and the refractive index difference is increased. I understand that it is necessary.

  Specifically, the configuration of the two-dimensional photonic crystal arrangement structure can be realized as follows. For example, a circular hole 21 having a half wavelength of light can be formed in the composite core 13 by lithography and etching using a semiconductor process. Lithography can be performed by patterning a resist by electron beam exposure, short wavelength photolithography, or the like. In addition, the resist pattern can be transferred by using a dry etching technique.

  More specifically, when Si is used for a thin film layer having a high refractive index, a microscopic hole having a size of 1 μm or less is patterned in a resist by photolithography or electron beam exposure, and the resist is etched with a Freon-based etching gas. A photonic crystal array can be formed by dry etching using a resist as a mask. In this case, since the thin film layer is extremely thin with a thickness of 1 μm or less, an etching process that provides a high aspect ratio is not necessary and can be easily formed.

  If lithium niobate (LN) is used as the electro-optic material, the surface of the Z-axis cut crystal substrate is dry-etched against a CF gas using a metal mask. Thereby, micropores having a depth of 1 μm or less can be formed. A combination with silicon is more preferable because a common gas can be used, but the aforementioned fine holes can be formed even if etching is performed by changing the gas.

  If electrodes are provided in the upper and lower portions near the micropores of the LN or the micropores in advance, strong electrolysis can be applied to the microspace, which is more effective. Further, an electric drive element is provided on the silicon, and the electrode on the LN and the electric drive element on the silicon are electrically connected by electrophoresis to produce a light control element integrated with the electric drive element using the composite substrate. be able to.

  Instead of lithium niobate, titanium niobate, KTP, SBN (Sr: strontium, Ba: barium, Nb: composite oxide of niobium), barium titanate and other inorganic crystals, high refractive index organic materials, or PZT, For inorganic ceramics such as PZLT and barium titanate, fine holes may be similarly produced by dry etching. Further, instead of the silicon substrate, an LN substrate, an MgO-doped LN substrate, a GaAs substrate, or another substrate may be used. Further, a waveguide by proton diffusion or titanium diffusion may be provided in a part of the photonic crystal of LN, or a ridge type or buried type waveguide by dicing or dry etching may be produced.

  Further, the thin film of LN or PZT or the photonic crystal structure thin film is not limited to the use of crystals, and may be prepared by a precursor using a sol-gel method and dry etching of the precursor. Furthermore, liquid crystal may be filled in fine holes formed by dry etching on silicon. At this time, it is also effective to use a liquid crystal photonic crystal produced by applying a transverse electric field with the liquid crystal orientation perpendicular to the substrate. Furthermore, instead of a simple substrate, a liquid crystal may be partially filled in a substrate having an electro-optic effect such as an LN substrate, so that the electro-optic effect is generated in a composite manner.

  Another embodiment will be described.

  FIG. 6 is a longitudinal sectional view schematically showing the light control element 1 of the present embodiment. The same reference numerals are used for the same members as those in the embodiment of FIGS.

  In FIG. 6, two layers of a thin film layer 11 made of an electro-optic material or a non-linear optical material and a thin film layer 12 having a higher refractive index than the thin film layer 11 are arranged close to each other in plan or in contact with each other to form a composite core. 13, the composite core 13 is arranged in contact with the substrate 31, and the substrate 31 is configured with a refractive index lower than that of the thin film layer 11. When forming the composite core 13 on the substrate 31, the thin film layer 11 and the thin film layer 12 may be sequentially formed as shown in FIG. 6, or the thin film layer 12 and the thin film layer 11 may be formed in this order as shown in FIG. You may form sequentially.

As a specific configuration of the substrate 31, a substrate using SiO ₂ or glass, or a substrate in which a SiO ₂ or organic material layer having a thickness of 1 μm or more is formed on Si can be used.

  An optical waveguide is formed using the low refractive index portion of the substrate 31 and air as a cladding. As a method of forming the optical waveguide, a structure sandwiched between low refractive index layers or an air bridge structure in which the composite core 13 is exposed to air may be used.

  By forming the above-described photonic crystal array structure in the composite core 13, a slab type two-dimensional photonic crystal can be formed.

  Since the composite core 13 has an equivalent refractive index larger than the refractive index of the thin film layer 11, light is strongly confined in the composite core 13, so that the low power resulting from the influence of the light line by the low refractive index medium as described above. Light leakage toward the refractive index medium is eliminated or reduced.

This structure can be realized as follows. For example, an SOI (Silicon on insulator) substrate having an Si thin film with a thickness equal to or less than a wavelength formed on SiO ₂ having a refractive index of 1.45, which is used in an electronic circuit, is electrically connected to an uppermost Si layer of about 100 nm Bond thin films of optical material. The electro-optic material thin film is formed by, for example, heating the substrate in which cations such as protons and helium ions are implanted into the substrate of the electro-optic material such as lithium niobate by an ion implantation apparatus. It can be formed by separating the material thin film layer. The thickness of the thin film layer can be adjusted to several hundred nm by adjusting the ion implantation energy. By utilizing this, the electro-optic material substrate is bonded to the SOI substrate, and the substrate is heated so that the electro-optic material is separated at the ion-implanted portion, and the electro-optic material thin film is formed on the Si layer. A layer is formed. This thin film layer is a thin film layer of 500 nm or less. Then, the surface of the electro-optic material thin film layer and the low refractive index medium layer are joined, the silicon layer of the SOI substrate is removed by polishing and wet etching, and the SiO ₂ layer is removed by wet etching. For the bonding, it is possible to use room temperature bonding, plasma activation bonding, wafer fusion technique, or the like that is bonded in vacuum. Thereafter, the structure can be realized by forming a two-dimensional photonic crystal array by lithography and etching. The last SiO ₂ layer does not need to be removed, and if not removed, it becomes a protective layer 71 described later. The bonding can be realized by a method such as heating bonding or room temperature bonding using an ultrahigh vacuum apparatus. As the low refractive index medium, SiO ₂ or glass can be used. If, for example, lithium niobate is used as the electro-optic material, layer separation due to thermal expansion is unlikely to occur in the thermal separation of the thin film after bonding by bonding with a SiO ₂ layer having almost the same thermal expansion coefficient. .

  Another embodiment will be described.

  FIG. 8 is a longitudinal sectional view schematically showing the light control element 1 of the present embodiment. The same reference numerals are used for the same members as those in the embodiment of FIGS.

  In FIG. 8, the light control element 1 has a structure in which the composite core 13 is laminated by sandwiching a thin film layer 12 having a higher refractive index between a thin film layer 11 made of an electro-optic material.

  With such a structure, the refractive index distribution in the composite core 13 has a symmetrical shape from the center of the core, so that more stable operation as an optical waveguide can be expected.

  The optical power is concentrated in the high refractive index thin film layer. However, if the high refractive index layer is an extremely thin layer of about 100 nm, the optical mode propagating in the core propagates while spreading to the electro optical thin film layer. Alternatively, the propagating light can receive the characteristics of the nonlinear optical material.

  Further, as shown in FIG. 9, the composite core 13 may have a structure in which the thin film layer 11 is sandwiched between the thin film layers 12 and laminated.

  With such a structure, the refractive index distribution in the composite core 13 has a symmetrical shape from the center of the core, so that more stable operation as an optical waveguide can be expected.

  Compared with the structure of FIG. 8, in the structure of FIG. 9, since the thin film layer 11 of the electro-optic material is present in the portion where the optical power is concentrated, the propagating light has sufficient characteristics of the electro-optic material or the nonlinear optical material Can receive.

  Another embodiment will be described.

  FIG. 9 is a longitudinal sectional view schematically showing the light control element 1 of the present embodiment. The same reference numerals are used for the same members as those in the embodiment of FIGS.

  The light control element 1 of FIG. 9 includes a thin film layer 11 formed of an electro-optic material or a nonlinear optical material and thin film layers 12 and 41 having a higher refractive index than the thin film layer 11 to form a composite core 13. Yes. The refractive index of the thin film layer 41 (third layer) is higher than the refractive index of the thin film layer 12. Then, the thin film layers 41, 11, and 12 are arranged in close proximity or in plane contact with a substrate 31 having a refractive index lower than that of the thin film layer 11 in this order.

  With such a structure, three types of materials can be used for the thin film constituting the composite core 13, and the equivalent refractive index of the composite core 13 can also be larger than that of the thin film layer 11.

  If three types of materials can be used for the composite core 13 in this way, a semiconductor light emitting material such as GaAs or InP can be used. In addition, a material having a large electro-optic effect or nonlinear effect can be used as the core of the optical waveguide at the same time. At this time, the refractive index of the composite core 13 can be improved by using a medium having a high refractive index such as Si.

  Further, in the arrangement of the thin film layer as shown in FIG. 10, since the optical power of the guided light is concentrated because the electro-optic material exists in the center of the composite core 13, it depends on characteristics such as the electro-optic effect. The impact can be increased.

  Also, with this arrangement, since the thin film layer 12 is the outermost surface, it is possible to irradiate the thin film layer 12 with light and the like, which is also effective when the thin film layer 12 is a semiconductor light emitting material.

  Moreover, you may comprise as follows. That is, as shown in FIG. 11, unlike the example of FIG. 10, the thin film layers 12, 11, 41 are arranged on the substrate 31 in the order of the thin film layers 12, 11, 41 in a close proximity. .

  With the arrangement of the thin film layer as shown in FIG. 11, since the electro-optic material is present at the center of the composite core 13, the optical power of the guided light is concentrated. Can be bigger. Also, with this arrangement, the optical power distribution to the thin film layer 12 becomes larger than that in FIG. 7, so that it is also effective when the thin film layer 12 is a semiconductor light emitting material.

  Furthermore, you may comprise as follows. That is, as shown in FIG. 12, unlike the example of FIG. 10 and FIG. 11, the thin film layers 12, 41, and 11 are arranged in close proximity to each other or in plane contact with the substrate 31. Configure.

  With the arrangement of the thin film layer as shown in FIG. 12, since the thin film layer 41 having the highest refractive index exists in the center of the composite core 13, the mode shape of the guided light can be kept simple, Stable guided light propagation is possible.

  In addition, by making the thin film layer 41 sufficiently thin, it is possible to propagate light while distributing the optical power to the thin film layer 12, so that it is possible to cause changes in optical characteristics such as an electro-optic effect.

  Another embodiment will be described.

  FIG. 13A is a longitudinal sectional view schematically showing the light control element 1 of the present embodiment. The same members and the like as those in the embodiment of FIG. 9 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the configuration of FIG. 13, a thin film layer 11 made of an electro-optic material as a composite core is sandwiched between refractive index changing layers 51 (fourth layer) formed of a multilayer film whose refractive index gradually changes, and the composite core 13 is This is the structure to be formed. For the refractive index changing layer 14, a dielectric multilayer film, a semiconductor multilayer film, an organic film, or the like can be used.

In FIG. 13, the refractive index gradually increases toward the center of the core, and the refractive index distribution is such that the equivalent refractive index as the composite core 13 is larger than that of the thin film layer 11.
With this structure, the optical power is stably distributed in the composite core.

  In each of the above-described embodiments, the buffer layer 61 that prevents direct bonding between the thin film layers 11, 12, 41, and 51 is sandwiched between the thin film layers 11, 12, 41, and 51 that form the composite core. It may be.

For example, the composite core 13 is formed by forming a film of SiO ₂ or the like on a different material substrate to a thickness of 100 nm or less by sputtering and bonding the formed parts to each other. In this case, by setting the film thickness to 50 nm or less, the composite core can be formed without reducing the transmission refractive index even when a low refractive index material is used for the buffer layer.

  In each of the above-described embodiments, a protective layer 71 that protects the composite core 13 may be provided on the upper side of the composite core 13, that is, on the surface opposite to the side provided on the substrate 31 of the composite core 13. . The material of the protective layer 71 is preferably a material having the same refractive index as that of the substrate 31 on which the composite core 13 is disposed. More preferably, the material itself is the same as that of the substrate 31.

  The photonic crystal arrangement structure may be a structure formed including the clad layer including the protective layer 71. Rather, with such a structure, the equivalent refractive index of the clad portion also decreases at the same time. The impact can be mitigated.

  Further, in each of the above-described embodiments, it is not necessary to form a photonic crystal array structure (circular holes 21 or the like) on the entire composite core 13, and only a portion of the thin film layer that forms the composite core 13 is provided with photonics. A crystal arrangement may be formed and not formed in other thin film layers.

  As a result, it is possible to suppress a decrease in refractive index that occurs when the circular hole 21 or the pillar structure is formed.

The refractive index distribution is shown in FIG. As long as the minimum refractive index of the refractive index changing layer 51 is higher than the refractive index of the cladding 31, the refractive index of the thin film layer 11 may be larger, equal, or smaller than the maximum refractive index.
Even if the refractive index of the thin film layer 11 is low, if the maximum refractive index of the refractive index changing layer 51 is sufficiently large, the refractive index of the core as an equivalent refractive index becomes large, so that light can be confined more strongly.

It is sectional drawing of the composite core of the light control element of this Embodiment. It is explanatory drawing explaining the meaning of "equivalent" in the case of an equivalent refractive index. It is sectional drawing (a) and the top view (b) of the composite core which formed the circular hole which is a photonic crystal arrangement structure. It is a top view which shows the structural example which eliminated the arrangement | sequence of the photonic crystal arrangement structure linearly in a part of photonic crystal arrangement structure from the composite core. It is explanatory drawing which shows the computer simulation result using the plane wave expansion method. It is sectional drawing which shows the other structural example of a light control element. It is sectional drawing which shows the other structural example of a light control element. It is sectional drawing which shows the other structural example of a light control element. It is sectional drawing which shows the other structural example of a light control element. It is sectional drawing which shows the other structural example of a light control element. It is sectional drawing which shows the other structural example of a light control element. It is sectional drawing which shows the other structural example of a light control element. It is sectional drawing which shows the other structural example of a light control element. It is sectional drawing which shows the other structural example of a light control element. It is sectional drawing which shows the other structural example of a light control element. 10 is an explanatory diagram of a technique disclosed in Patent Literature 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light control element 11 1st layer 12 2nd layer 21 Photonic crystal arrangement structure (circular hole)
31 Substrate 41 Third layer 51 Fourth layer 61 Buffer layer 71 Protective layer

Claims (10)

In the light control element including the core and the clad forming the outer layer portion of the core,
A first layer comprising an electro-optic material or a non-linear optical material;
A second layer having a higher refractive index than the first layer;
With
The first layer and the second layer form a composite core to be the core,
The composite core is formed with a photonic crystal array structure in which circular holes or polygonal holes having a refractive index lower than the refractive index of the composite core are periodically arranged, and the photonic crystal array structure A light control element having a line defect structure therein.   2. The substrate according to claim 1, wherein the first layer and the second layer of the composite core are sequentially laminated on a substrate having a refractive index lower than that of the first layer. The light control element as described.   2. The substrate according to claim 1, wherein the second layer and the first layer of the composite core are sequentially laminated on a substrate having a refractive index lower than that of the first layer. The light control element as described.   2. The light control element according to claim 1, wherein the composite core is formed by sandwiching the second layer between the two first layers. 3.   2. The light control element according to claim 1, wherein the composite core is formed by sandwiching the first layer between the two second layers. 3. A third layer having a higher refractive index than the first and second layers forms the composite core together with the first layer and the second layer;
The third layer, the first layer, and the second layer are sequentially stacked on a substrate having a lower refractive index than the first layer.
The light control element according to claim 1. A third layer having a higher refractive index than the first and second layers forms the composite core together with the first layer and the second layer;
The second layer, the first layer, and the third layer are sequentially stacked on a substrate having a refractive index lower than that of the first layer.
The light control element according to claim 1. A third layer having a higher refractive index than the first and second layers forms the composite core together with the first layer and the second layer;
The second layer, the third layer, and the first layer are sequentially stacked on a substrate having a refractive index lower than that of the first layer.
The light control element according to claim 1.   The composite core is formed of a multilayer film in which the first layer is replaced with the second layer and the refractive index gradually decreases as the distance from the first layer increases, and at least a part of the multilayer film is the first layer. 6. The light control element according to claim 5, wherein the light control element is sandwiched between two fourth layers formed of a multilayer film having a refractive index higher than that of the first layer.   The protective layer which protects the said composite core is provided in the surface on the opposite side to the side provided in the said board | substrate of the said composite core, The any one of Claim 2, 3, 6, 7, 8 characterized by the above-mentioned. The light control element according to 1.

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