WO2023276053A1 - Optical device - Google Patents
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- WO2023276053A1 WO2023276053A1 PCT/JP2021/024783 JP2021024783W WO2023276053A1 WO 2023276053 A1 WO2023276053 A1 WO 2023276053A1 JP 2021024783 W JP2021024783 W JP 2021024783W WO 2023276053 A1 WO2023276053 A1 WO 2023276053A1
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- 230000003287 optical effect Effects 0.000 title claims abstract description 154
- 239000006185 dispersion Substances 0.000 claims abstract description 45
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
Definitions
- the present invention relates to an optical device having an optical waveguide.
- optical integrated device technology using micro optical waveguides has been remarkable.
- the integration of optical communication devices has progressed, and in addition to passive devices such as optical splitters and wavelength filters, there are also high-performance devices including active devices such as laser light sources, photodetectors, and modulators.
- active devices such as laser light sources, photodetectors, and modulators.
- a SiN optical waveguide is used in a micro-ring resonator and is designed to have wavelength dispersion control, especially anomalous dispersion, in order to utilize the nonlinear optical effect described above.
- desired dispersion characteristics can be obtained by appropriately designing the shape of the optical waveguide core as described in Non-Patent Document 1, or by providing a rib-type core structure with a multi-layer clad structure as described in Non-Patent Document 2.
- Structural dispersion was given so that Further, as described in Non-Patent Document 3, a double ring structure is used to adjust the propagation length to obtain appropriate mode coupling between even and odd modes, thereby realizing desired dispersion characteristics.
- Non-Patent Document 1 mentions that anomalous dispersion can be obtained by increasing the core height (thickness) to 0.75 ⁇ m or more.
- Such a core height is large compared to the 600 nm upper limit of the core height of single-mode SiN optical waveguides commonly provided by optical device foundries, for example, as mentioned in Non-Patent Document 4.
- FIG. 12 shows the chromatic dispersion of the SiN optical waveguide having a 600 ⁇ 1000 nm core shown in Non-Patent Document 4.
- D ⁇ 0 normal dispersion
- the core layer will be deposited thicker when forming the core layer by, for example, the CVD method.
- Non-Patent Document 2 as one approach to obtain desired dispersion characteristics other than increasing the core height, which has such problems, a rib-type SiN core is combined with a multi-cladding structure.
- this technology also has the problem that it is not a structure that can be easily manufactured and provided by an optical device foundry, and that a redesign that is optimized for such an optical waveguide structure is required to configure a passive device. rice field.
- Non-Patent Document 3 a technique of forming a double ring structure using a thin SiN core has been proposed.
- this technique requires proper mode coupling between even and odd modes by adjusting the propagation length, and has the problem of a narrow operating band.
- optical device foundries have good single-mode properties, low loss properties, ease of design and manufacture, and good integration with other optical elements (for example, laser light sources, photodetectors, and passive optical waveguide elements). There is a problem that there is no optical device with a low introduction barrier in the field.
- the present invention has been made to solve the above problems, and has a single-mode property, low loss property, ease of design and manufacture, good integration with other optical elements, and an optical device.
- the purpose is to provide an optical device with a low introduction barrier in the device foundry.
- An optical device includes a first core having a nonlinear optical effect formed on a lower clad layer, a second core formed on the lower clad layer, and a first core on the lower clad layer. and an upper clad layer formed covering the second core, the first core and the second core constitute an optical waveguide having a super mode, and the refractive index and cross section of each of the first core and the second core.
- the shape and the positional relationship between the first core and the second core in the cross section perpendicular to the waveguide direction are such that the supermode has the desired dispersion.
- an optical waveguide having a super mode is formed by the first core and the second core, and the refractive index, cross-sectional shape, and waveguide of each of the first core and the second core are Since the positional relationship between the first core and the second core in the cross section perpendicular to the direction is set to a state in which the super mode has the desired dispersion, single mode property, low loss, ease of design and manufacture, and other optical It is possible to provide an optical device with good integration with elements and a low introduction barrier in the optical device foundry.
- FIG. 1 is a cross-sectional view showing the configuration of an optical device according to Embodiment 1 of the present invention.
- FIG. 2 is a distribution diagram showing the electromagnetic field distribution of the light propagation mode in the first core 102 and the second core 103.
- FIG. 3 is a characteristic diagram showing chromatic dispersion (D 2 ) by the first core 102 and the second core 103.
- FIG. 4 is a characteristic diagram showing the relationship between the change in the gap between the first core 102 and the second core 103 and D2.
- FIG. 5 is a characteristic diagram showing the relationship between the core width of the second core 103 and D2.
- FIG. 6 is a characteristic diagram showing the optical confinement factor in the first core 102 when the core widths of the second core 103 shown in FIG. 5 are 400 nm, 300 nm, and 200 nm.
- FIG. 7 is a perspective view showing the configuration of an integrated optical device to which the optical device according to Embodiment 1 is applied.
- FIG. 8A is a distribution diagram showing light propagation modes in the output optical waveguide of the membrane laser 201 of the integrated optical device to which the optical device according to Embodiment 1 is applied.
- FIG. 8B is a distribution diagram showing light propagation modes at the tapered tip of the InP core 203a of the integrated optical device to which the optical device according to the first embodiment is applied.
- FIG. 8C is a distribution diagram showing light propagation modes in the SiN core 204a of the integrated optical device to which the optical device according to Embodiment 1 is applied.
- 8D is a distribution diagram showing light propagation modes in a nonlinear optical waveguide to which an integrated optical device to which the optical device according to Embodiment 1 is applied is connected.
- FIG. FIG. 9 is a cross-sectional view showing the configuration of an optical device according to Embodiment 2 of the present invention.
- FIG. 10A is a distribution diagram showing the electromagnetic field distribution of the light propagation mode of the second core 103 in the first core 102a and the second core 103.
- FIG. 10B is a distribution diagram showing the electromagnetic field distribution of the light propagation mode of the first core 102a in the first core 102a and the second core 103.
- FIG. 10C is a distribution diagram showing the electromagnetic field distribution of the light propagation mode of the first core 102a in the case of only the first core 102a.
- FIG. 11 is a characteristic diagram showing chromatic dispersion (D 2 ) by the first core 102a and the second core 103.
- FIG. 12 is a characteristic diagram showing chromatic dispersion of a SiN optical waveguide having a core with cross-sectional dimensions of 600 ⁇ 1000 nm.
- Embodiment 1 an optical device according to Embodiment 1 of the present invention will be described with reference to FIG.
- This optical device comprises a lower clad layer 101 , a first core 102 , a second core 103 and an upper clad layer 104 .
- First core 102 and second core 103 are formed on lower clad layer 101 .
- Upper clad layer 104 is formed on lower clad layer 101 to cover first core 102 and second core 103 .
- the first core 102 is arranged above the second core 103 when viewed from the lower clad layer 101 side.
- the first core 102 has a nonlinear optical effect.
- the first core 102 and the second core 103 constitute an optical waveguide having a super mode.
- the refractive index and cross-sectional shape of each of the first core 102 and the second core 103, and the positional relationship between the first core 102 and the second core 103 in the cross section perpendicular to the waveguide direction are such that the super mode has the desired dispersion. It is considered to be in a state of having For example, even if each of the optical waveguide by the first core 102 and the optical waveguide by the second core 103 has normal dispersion, the first core 102 and the second core are arranged such that the above-described super mode has anomalous dispersion.
- 103 are set in cross-sectional shape and positional relationship.
- the operating band can be designed with a high degree of freedom.
- the core height of the first core 102 is set to a height that matches another optical device that is optically connected to the optical waveguide by the first core 102 .
- the core height of the second core 103 is set to match other optical devices optically connected to the optical waveguide by the second core 103 . Therefore, it is easy to integrate these other optical devices with the optical device according to the first embodiment.
- the first core 102 can be made of SiN
- the second core 103 can be made of InP.
- the first core 102 can have a cross-sectional shape perpendicular to the waveguide direction with a width of 1000 nm and a core height of 600 nm.
- the second core 103 can have a cross-sectional shape perpendicular to the waveguide direction with a width of 300 nm and a core height of 350 nm.
- the distance (gap) between the first core 102 and the second core 103 in the thickness direction can be set to 300 nm.
- the distance (offset) between the center of the first core 102 and the center of the second core 103 in the planar direction of the lower clad layer 101 within the plane perpendicular to the waveguide direction can be set to 0 nm.
- FIG. 1 shows an example in which the center of the first core 102 and the center of the second core 103 are shifted and the offset is not zero.
- the lower clad layer 101 and the upper clad layer 104 can be made of silicon oxide.
- the lower clad layer 101 can be made of silicon oxide formed by thermally oxidizing the surface of a silicon substrate.
- the upper cladding layer 104 can be composed of a SiO 2 film deposited by a known CVD method.
- FIG. 2 shows the electromagnetic field distribution of the light propagation mode in the first core 102 and the second core 103 calculated under the conditions described above.
- FIG. 2A shows the lowest order TE mode, and it can be seen that light is strongly confined within the second core 103 .
- (b) of FIG. 2 is a high-order TE mode, in which light is strongly confined in the first core 102, and at the same time, the second core 103 also has an electromagnetic field distribution, resulting in a super mode. I know there is.
- the light confinement factor to the first core 102 is 73%.
- FIG. 3(a) shows second-order chromatic dispersion (D 2 ) in the lowest-order TE mode. It is a normal dispersion optical waveguide having a negative value of D 2 over the entire wavelength range of 1500 nm to 1600 nm, and is poorly used as a nonlinear optical waveguide as it is.
- D 2 of the single SiN optical waveguide shown in FIG. 12 is shown in FIG. 3(c).
- FIG. 3B shows the chromatic dispersion of the high-order TE mode described above. It can be seen that D 2 can be anomalous dispersion having a positive value in the entire wavelength range of 1500 nm to 1600 nm.
- FIG . 4 shows the relationship between the change in gap and D2. As shown in FIG. 4, the gap can realize anomalous dispersion in a wide range of 200 nm to 500 nm, and a large manufacturing margin can be obtained.
- FIG. 5 shows the relationship between the core width of the second core 103 and D2. Note that the gap described above is set to 500 nm. As shown in FIG. 5, when the core width of the second core 103 is 400 nm, normal dispersion is obtained. On the other hand, when the core width of the second core 103 is 300 nm and 200 nm, anomalous dispersion is obtained.
- FIG. 6 shows the optical confinement coefficient in the first core 102 when the core widths of the second core 103 shown in FIG. 5 are 400 nm, 300 nm, and 200 nm.
- the confinement factor in the first core 102 is about 73% (wavelength 1550 nm).
- the confinement factor in the first core 102 decreases to about 67% (wavelength 1550 nm). In this way, the design may be made by comprehensively considering the dispersion and the optical confinement factor.
- the wavelength band of 1500 nm to 1600 nm has been described, but in a wider wavelength range, suitable materials with low loss as optical waveguide materials are combined, and the first core 102 and the second core 102 of the optical device according to Embodiment 1 are combined. It is clear that designing the structural parameters for core 103 provides the desired dispersion characteristics.
- the configuration of the optical device according to Embodiment 1 described with reference to FIG. 1 is an example, and can be changed as appropriate in consideration of, for example, manufacturability.
- the upper clad layer 104 made of silicon oxide may be formed up to the bottom surface of the first core 102 , and the first core 102 may not be covered with the upper clad layer 104 .
- it can be applied to an optical sensor that optically detects the presence or absence of some substance above the first core 102, which is particularly important industrially.
- This integrated optical device is a combination of the semiconductor laser light source and the optical device according to the first embodiment.
- reference numeral 201 is a membrane laser described in Non-Patent Document 4, which is fabricated on a SiO 2 /Si substrate 202 .
- InP cores 203a, 203b, and 203c correspond to the second cores.
- the InP core 203a serves as an output optical waveguide core of the membrane laser 201, which is also made of an InP-based material.
- a SiN core 204a is placed over the InP cores 203a and 203b, and a SiN core 204b is placed over the InP core 203c.
- the SiN cores 204a and 204b correspond to the first core.
- the light propagation mode has an electromagnetic field within the InP core 203a as shown in FIG. 8A.
- the width of the InP core 203a is gradually narrowed in a tapered shape, and the mode is adiabatically converted while the output light from the membrane laser 201 propagates.
- This is a light propagation mode in which an electromagnetic field mainly exists in the SiN core 204a.
- the taper tip 205 is butt-coupled with a SiN optical waveguide as used in Patent Document 3, in which the InP core 203a does not exist, and beyond that, a SiN core having a light propagation mode as shown in FIG. 8C 204a for optical wiring.
- the InP core 203b is tapered again at the connection point, and then adiabatically mode-converted to the light propagation mode of the nonlinear optical waveguide shown in FIG. 8D. be done.
- the mode shown in FIG. 8D is the nonlinear optical waveguide of the optical device according to Embodiment 1 described using FIG.
- a ring resonator 206 is fabricated by the SiN core 204a, the ring-shaped InP core 203c, the InP core 203b, and the ring-shaped SiN core 204b, which constitute the nonlinear optical waveguide.
- the ring resonator 206 is a nonlinear optical waveguide device that takes advantage of the increased light intensity within the resonator.
- the mode is adiabatically converted again through the taper of the InP core 203b, and is connected to the SiN optical waveguide of the output destination.
- the SiN optical waveguide may be a general-purpose optical waveguide as disclosed in Non-Patent Document 3, and not only optical wiring but also various passive devices can be integrated.
- a wavelength filter for cutting pump light from the membrane laser 201, a low-loss fiber coupling device, a spatial light radiation device, etc. can be integrated.
- the InP cores 203a, 203b, and 203c are made to have the same thickness in the output optical waveguide portion of the membrane laser 201 and in the nonlinear optical waveguide portion by a manufacturing method as shown in Non-Patent Document 5. They can be easily formed in the same layer.
- the SiN cores 204a and 204b are made to have a layer thickness that becomes the designed gap by depositing SiO 2 by CVD method and performing CMP polishing after producing the InP core described above. They may be formed in the same layer by such a manufacturing method.
- membrane lasers Although only membrane lasers are described here, other membrane devices such as phase shifters for generating solitons in nonlinear microcavities and heater structures for wavelength tuning of ring cavities are integrated as membrane devices. It is also possible to
- This optical device comprises a lower clad layer 101 , a first core 102 a , a second core 103 and an upper clad layer 104 .
- First core 102 a and second core 103 are formed on lower clad layer 101 .
- Upper clad layer 104 is formed on lower clad layer 101 to cover first core 102 a and second core 103 .
- the second core 103 is arranged above the first core 102a.
- the first core 102a has a nonlinear optical effect. Also, the first core 102a and the second core 103 constitute an optical waveguide having a super mode. In this example, the first core 102a is rib-shaped.
- the refractive index, the cross-sectional shape, and the positional relationship between the first core 102a and the second core 103 in the cross section perpendicular to the waveguide direction of each of the first core 102a and the second core 103 are , the supermode is assumed to have the desired dispersion.
- the first core 102a and the second core may 103 are set in cross-sectional shape and positional relationship.
- the core height of the first core 102a is set to a height that matches another optical device that is optically connected to the optical waveguide by the first core 102a.
- the core height of the second core 103 is set to match other optical devices optically connected to the optical waveguide by the second core 103 . Therefore, it is easy to integrate these other optical devices with the optical device according to the second embodiment.
- the first core 102a can be made of, for example, LiNbO 3 and the second core 103 can be made of InP.
- the first core 102a can have a slab thickness of 100 nm, a width of 1000 nm in a cross-sectional shape perpendicular to the waveguide direction, and a total height including the slab of 200 nm.
- the second core 103 can have a cross-sectional shape perpendicular to the waveguide direction with a width of 300 nm and a core height of 350 nm.
- the distance (gap) between the first core 102a and the second core 103 in the thickness direction can be set to 300 nm.
- the distance (offset) between the center of the first core 102a and the center of the second core 103 in the planar direction of the lower clad layer 101 within the plane perpendicular to the waveguide direction can be set to 0 nm.
- FIG. 9 shows an example in which the center of the first core 102a and the center of the second core 103 are deviated, and the offset is not zero.
- FIGS. 10A, 10B, and 10C The electromagnetic field distributions of the light propagation modes calculated under the above conditions are shown in FIGS. 10A, 10B, and 10C.
- FIG. 10A shows the lowest order TE mode, and it can be seen that light is strongly confined within the second core 103 .
- FIG. 10B shows a higher-order TE mode, in which light is strongly confined in the first core 102a and, at the same time, the second core 103 also has an electromagnetic field distribution. .
- the light confinement factor to the first core 102a in the mode of FIG. 10B is 43%.
- FIG. 10C also shows the electromagnetic field distribution of the lowest-order TE mode when only the first core 102a exists.
- FIG. 10 shows the electromagnetic field distribution of the light propagation mode calculated for such an optical waveguide structure.
- FIG. 10A shows the lowest order TE mode, and it can be seen that light is strongly confined within the second core 103 .
- FIG. 10B shows a higher-order TE mode, in which light is strongly confined in the first core 102a, and at the same time, the second core 103 is also in a super mode in which an electromagnetic field distribution exists. I understand.
- the light confinement factor to the LiNbO 3 core in the mode of FIG. 10B is 43%.
- 10-3 also shows the electromagnetic field distribution of the lowest-order TE mode when only the LiNbO 3 core exists.
- FIG. 11(a) shows D 2 of the lowest-order TE mode (FIG. 10A). It is a normal dispersion optical waveguide having a negative value of D 2 over the entire wavelength range of 1500 nm to 1600 nm, and is poorly used as a nonlinear optical waveguide as it is.
- FIG. 11(c) shows D 2 of the lowest-order TE mode in the case of only the first core 102a shown in FIG. 10C.
- the normal dispersion optical waveguide has a negative value of D 2 over the entire wavelength range of 1500 nm to 1600 nm, and is poorly used as a nonlinear optical waveguide.
- the chromatic dispersion of the high-order TE mode shown in FIG. 10B can be anomalous dispersion in which D 2 has a positive value over the entire wavelength range of 1500 nm to 1600 nm, as shown in FIG. 11(b).
- the ability to obtain anomalous dispersion even in the first core 102a having a small core thickness is particularly effective in reducing propagation loss, and is particularly effective in increasing the Q value of an optical resonator.
- the smaller the core height the smaller the effect of scattering loss caused by rough processing of the core side walls.
- the wavelength band of 1500 nm to 1600 nm has been described, but in a wider wavelength range, suitable materials with low loss as optical waveguide materials are combined, and the first core 102a and the second core 102a of the optical device according to the second embodiment are combined. It is clear that designing the structural parameters for core 103 provides the desired dispersion characteristics. Moreover, it is clear that not only D 2 and the optical confinement coefficient but also higher-order dispersion, polarization mode dispersion, etc. can be appropriately controlled.
- the configuration of the optical device according to Embodiment 2 described with reference to FIG. 9 is an example, and can be changed as appropriate in consideration of, for example, manufacturability.
- the upper clad layer 104 made of silicon oxide may extend to the bottom surface of the second core 103 , and the second core 103 may not be covered with the upper clad layer 104 . With such a structure, it can be applied to an optical sensor that optically detects the presence or absence of some substance above the second core 103, which is particularly important industrially.
- LiNbO 3 forming the first core 102a is widely used as a material having ⁇ (2) nonlinearity in addition to ⁇ (3) nonlinearity. Therefore, according to the optical device according to the second embodiment, in addition to the ⁇ (3) nonlinear process that is generally used in SiN and the like, it is possible to utilize the ⁇ (3) nonlinear process, which is an excellent effect. is obtained.
- the nonlinear optical device realized by the existing LiNbO 3 optical waveguide does not have an integrated excitation light source, but the use of the optical device according to the second embodiment makes it possible to integrate the excitation light source. effect is obtained. For example, when configuring an integrated comb light source with a semiconductor laser light source as described with reference to FIG. 7, it can be similarly realized by appropriately adjusting the arrangement of the first core and the second core.
- an optical waveguide having a super mode is formed by the first core and the second core, and the refractive index, cross-sectional shape, and waveguide of each of the first core and the second core are determined.
- the positional relationship between the first core and the second core in the cross section perpendicular to the wave direction is set to a state in which the supermode has a desired dispersion. It is possible to provide an optical device that is highly integrated with an optical element and has a low introduction barrier in an optical device foundry.
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Abstract
A first core (102) of this optical device constitutes an optical waveguide having a nonlinear optical effect and having a super mode by the first core (102) and a second core (103), and the respective refractive indexes and cross-sectional shapes of the first core (102) and the second core (103), and the positional relationship between the first core (102) and the second core (103) in a cross section perpendicular to a waveguide direction are in a state in which the super mode has desired dispersion.
Description
本発明は、光導波路を備える光デバイスに関する。
The present invention relates to an optical device having an optical waveguide.
近年、微小光導波路を用いた光集積デバイス技術の進展が目覚ましい。例えば、いわゆるシリコンフォトニクスと呼ばれる技術領域において、光通信デバイスの集積化が進展し、光スプリッタや波長フィルタのようなパッシブデバイスに加えて、レーザ光源、フォトディテクタ、変調器といったアクティブデバイスも含めた高機能な光集積デバイスが実用化されている。
In recent years, the progress of optical integrated device technology using micro optical waveguides has been remarkable. For example, in the so-called silicon photonics technology area, the integration of optical communication devices has progressed, and in addition to passive devices such as optical splitters and wavelength filters, there are also high-performance devices including active devices such as laser light sources, photodetectors, and modulators. optical integrated devices have been put into practical use.
さらに、光集積回路を構成する微小光導波路の強い光閉じ込めを活かし、非線形光学効果を積極的に活用することで、例えば周波数コム光源、スーパーコンティニュウム光源、波長変換素子、位相感応増幅素子、量子もつれ光子対源などの高機能素子が実現でき、現在商用化されている光通信応用に加えて、光集積デバイスのさらなる適用領域拡大が期待されている。
Furthermore, by taking advantage of the strong optical confinement of the micro-optical waveguides that make up optical integrated circuits and actively utilizing nonlinear optical effects, for example, frequency comb light sources, supercontinuum light sources, wavelength conversion elements, phase-sensitive amplifier elements, High-performance devices such as quantum entangled photon pair sources can be realized, and further expansion of the application area of optical integrated devices is expected in addition to the currently commercialized optical communication applications.
特に近年、シリコンフォトニクスデバイスとの集積性を考慮し、非線形光導波路としてSiNからなる光導波路を用いたデバイスが広く提案されている。例えば周波数コム光源を実現するために、SiN光導波路が微小リング共振器に用いられ、上述の非線形光学効果を活用するために波長分散制御、特に異常分散を有するように設計されておいる。例えば、非特許文献1にあるように光導波路コアの形を適切に設計したり、非特許文献2にあるようにリブ型コア構造に多層クラッド構造としたりすることで、所望の分散特性が得られるように構造分散を付与していた。また、非特許文献3にあるように、2重リング構造とすることで、伝搬長を調整して偶奇モード間の適切なモード結合を得ることで、所望の分散特性を実現していた。
Especially in recent years, devices using optical waveguides made of SiN as nonlinear optical waveguides have been widely proposed in consideration of integration with silicon photonics devices. For example, in order to realize a frequency comb light source, a SiN optical waveguide is used in a micro-ring resonator and is designed to have wavelength dispersion control, especially anomalous dispersion, in order to utilize the nonlinear optical effect described above. For example, desired dispersion characteristics can be obtained by appropriately designing the shape of the optical waveguide core as described in Non-Patent Document 1, or by providing a rib-type core structure with a multi-layer clad structure as described in Non-Patent Document 2. Structural dispersion was given so that Further, as described in Non-Patent Document 3, a double ring structure is used to adjust the propagation length to obtain appropriate mode coupling between even and odd modes, thereby realizing desired dispersion characteristics.
しかしながら、従来技術には以下のような課題があった。
However, the conventional technology had the following problems.
例えば、非特許文献1では、コア高さ(厚さ)を0.75μm以上に大きくすることで異常分散を得られると言及している。このようなコア高さは、例えば、非特許文献4で言及されているような、光デバイスファンダリが一般的に提供するシングルモードSiN光導波路のコア高さの上限600nmに比べて大きい。参考までに、非特許文献4に示された600×1000nmコアを有するSiN光導波路の波長分散を図12に示す。波長1500mm~1600nmで正常分散(D<0)であることがわかる。
For example, Non-Patent Document 1 mentions that anomalous dispersion can be obtained by increasing the core height (thickness) to 0.75 μm or more. Such a core height is large compared to the 600 nm upper limit of the core height of single-mode SiN optical waveguides commonly provided by optical device foundries, for example, as mentioned in Non-Patent Document 4. For reference, FIG. 12 shows the chromatic dispersion of the SiN optical waveguide having a 600×1000 nm core shown in Non-Patent Document 4. In FIG. It can be seen that normal dispersion (D<0) is obtained at wavelengths of 1500 nm to 1600 nm.
この場合、非線形光導波路を集積するにあたり、光集積デバイス上の他のSiN光導波路を非線形光導波路と同じレイヤで形成しようとすると、非線形光導波路に合わせたコア高さが必要となる。スプリッタや波長フィルタといった他のパッシブデバイスは、非線形光導波路に合わせるための設計が必要となり、大きな問題であった。
In this case, when integrating a nonlinear optical waveguide, if another SiN optical waveguide on the optical integrated device is formed in the same layer as the nonlinear optical waveguide, a core height that matches the nonlinear optical waveguide is required. Other passive devices, such as splitters and wavelength filters, have been a big problem as they have to be designed for nonlinear optical waveguides.
また、コア高さが大きくなること自体が、様々な問題を有していた。例えば、高いコアを形成するためには、より深いエッチング加工をすることになるため、コア側面が荒れた状態となりやすい。コア側面が荒れると、この荒れの影響を光散乱として受けやすく、伝搬損失が増大するという大きな問題があった。
In addition, increasing the core height itself had various problems. For example, in order to form a high core, a deeper etching process is required, so the core side surface tends to be roughened. If the side surface of the core becomes rough, there is a serious problem that the roughening tends to scatter light and increase the propagation loss.
また例えば、コア高さが大きくなると、例えばCVD法などによりコア層を形成するときに、より厚く堆積することになり、ウェハ内部応力の増大への対応などが製造上大きな問題であった。
Also, for example, if the core height increases, the core layer will be deposited thicker when forming the core layer by, for example, the CVD method.
さらに、こうした非線形光導波路と、一般的なパッシブデバイスを同一レイヤながら異なるコア高さを有するものとするためには、部分的にコア高さを小さくするプロセスが必要となり、製造プロセスを冗長化させることが、大きな問題であった。
Furthermore, in order to make such a nonlinear optical waveguide and a general passive device have different core heights in the same layer, a process to partially reduce the core height is required, making the manufacturing process redundant. That was the big problem.
このような問題を有するコア高さを大きくする以外に、所望の分散特性を得る1つのアプローチとして、非特許文献2では、リブ型SiNコアに多重クラッド構造を組み合わせている。しかし、この技術も、光デバイスファンダリで容易に作製・提供できる構造ではなく、またパッシブデバイスを構成するには、このような光導波路構造に最適化された再設計が必要となるという問題があった。
In Non-Patent Document 2, as one approach to obtain desired dispersion characteristics other than increasing the core height, which has such problems, a rib-type SiN core is combined with a multi-cladding structure. However, this technology also has the problem that it is not a structure that can be easily manufactured and provided by an optical device foundry, and that a redesign that is optimized for such an optical waveguide structure is required to configure a passive device. rice field.
また、もう1つのアプローチとして、非特許文献3にあるように、薄いSiNコアを用いて2重リング構造とする技術が提案されていた。しかし、上述の通り、この技術では、伝搬長を調整して偶奇モード間の適切なモード結合を得る必要があり、動作帯域が狭いという問題があった。
In addition, as another approach, as described in Non-Patent Document 3, a technique of forming a double ring structure using a thin SiN core has been proposed. However, as described above, this technique requires proper mode coupling between even and odd modes by adjusting the propagation length, and has the problem of a narrow operating band.
上述したように、従来、シングルモード性、低損失性、設計・製造の容易さ、他の光学素子(例えばレーザ光源、フォトディテクタ、パッシブ光導波路素子)との集積性が良好で、かつ光デバイスファンダリでの導入障壁が低い光デバイスがないという問題があった。
As described above, conventional optical device foundries have good single-mode properties, low loss properties, ease of design and manufacture, and good integration with other optical elements (for example, laser light sources, photodetectors, and passive optical waveguide elements). There is a problem that there is no optical device with a low introduction barrier in the field.
本発明は、以上のような問題点を解消するためになされたものであり、シングルモード性、低損失性、設計・製造の容易さ、他の光学素子との集積性が良好で、かつ光デバイスファンダリでの導入障壁が低い光デバイスの提供を目的とする。
The present invention has been made to solve the above problems, and has a single-mode property, low loss property, ease of design and manufacture, good integration with other optical elements, and an optical device. The purpose is to provide an optical device with a low introduction barrier in the device foundry.
本発明に係る光デバイスは、下部クラッド層の上に形成された非線形光学効果を有する第1コアと、下部クラッド層の上に形成され、第2コアと、下部クラッド層の上で第1コアおよび第2コアを覆って形成された上部クラッド層とを備え、第1コアと第2コアとによりスーパーモードを有する光導波路を構成し、第1コアおよび第2コアの各々の屈折率、断面形状、および導波方向に垂直な断面における第1コアと第2コアとの位置関係は、スーパーモードが所望の分散を有する状態とされている。
An optical device according to the present invention includes a first core having a nonlinear optical effect formed on a lower clad layer, a second core formed on the lower clad layer, and a first core on the lower clad layer. and an upper clad layer formed covering the second core, the first core and the second core constitute an optical waveguide having a super mode, and the refractive index and cross section of each of the first core and the second core The shape and the positional relationship between the first core and the second core in the cross section perpendicular to the waveguide direction are such that the supermode has the desired dispersion.
以上説明したように、本発明によれば、第1コアと第2コアとによりスーパーモードを有する光導波路を構成し、第1コアおよび第2コアの各々の屈折率、断面形状、および導波方向に垂直な断面における第1コアと第2コアとの位置関係を、スーパーモードが所望の分散を有する状態とするので、シングルモード性、低損失性、設計・製造の容易さ、他の光学素子との集積性が良好で、かつ光デバイスファンダリでの導入障壁が低い光デバイスが提供できる。
As described above, according to the present invention, an optical waveguide having a super mode is formed by the first core and the second core, and the refractive index, cross-sectional shape, and waveguide of each of the first core and the second core are Since the positional relationship between the first core and the second core in the cross section perpendicular to the direction is set to a state in which the super mode has the desired dispersion, single mode property, low loss, ease of design and manufacture, and other optical It is possible to provide an optical device with good integration with elements and a low introduction barrier in the optical device foundry.
以下、本発明の実施の形態に係る光デバイスについて説明する。
An optical device according to an embodiment of the present invention will be described below.
[実施の形態1]
はじめに、本発明の実施の形態1に係る光デバイスについて、図1を参照して説明する。この光デバイスは、下部クラッド層101、第1コア102、第2コア103、上部クラッド層104を備える。第1コア102、第2コア103は、下部クラッド層101の上に形成されている。また、上部クラッド層104は、下部クラッド層101の上で第1コア102および第2コア103を覆って形成されている。この例では、下部クラッド層101の側から見て、第2コア103より上側に第1コア102が配置されている。 [Embodiment 1]
First, an optical device according to Embodiment 1 of the present invention will be described with reference to FIG. This optical device comprises a lowerclad layer 101 , a first core 102 , a second core 103 and an upper clad layer 104 . First core 102 and second core 103 are formed on lower clad layer 101 . Upper clad layer 104 is formed on lower clad layer 101 to cover first core 102 and second core 103 . In this example, the first core 102 is arranged above the second core 103 when viewed from the lower clad layer 101 side.
はじめに、本発明の実施の形態1に係る光デバイスについて、図1を参照して説明する。この光デバイスは、下部クラッド層101、第1コア102、第2コア103、上部クラッド層104を備える。第1コア102、第2コア103は、下部クラッド層101の上に形成されている。また、上部クラッド層104は、下部クラッド層101の上で第1コア102および第2コア103を覆って形成されている。この例では、下部クラッド層101の側から見て、第2コア103より上側に第1コア102が配置されている。 [Embodiment 1]
First, an optical device according to Embodiment 1 of the present invention will be described with reference to FIG. This optical device comprises a lower
ここで、まず、第1コア102は、非線形光学効果を有している。また、第1コア102と第2コア103とによりスーパーモードを有する光導波路を構成している。さらに、第1コア102および第2コア103の各々の屈折率、断面形状、および導波方向に垂直な断面における第1コア102と第2コア103との位置関係が、スーパーモードが所望の分散を有する状態とされている。例えば、第1コア102による光導波路、および第2コア103による光導波路の各々が正常分散を有していても、上述したスーパーモードが異常分散を有するように、第1コア102および第2コア103それぞれの断面形状および位置関係が設定されている。
Here, first, the first core 102 has a nonlinear optical effect. Also, the first core 102 and the second core 103 constitute an optical waveguide having a super mode. Furthermore, the refractive index and cross-sectional shape of each of the first core 102 and the second core 103, and the positional relationship between the first core 102 and the second core 103 in the cross section perpendicular to the waveguide direction are such that the super mode has the desired dispersion. It is considered to be in a state of having For example, even if each of the optical waveguide by the first core 102 and the optical waveguide by the second core 103 has normal dispersion, the first core 102 and the second core are arranged such that the above-described super mode has anomalous dispersion. 103 are set in cross-sectional shape and positional relationship.
スーパーモードの分散設計は、2次元断面モード計算で可能であり、伝搬方向のモード結合を考慮した非特許文献4のような複雑な設計を必要としない。このため、実施の形態1に係る光デバイスによれば、動作帯域の設計自由度が高いものとなる。
Super mode dispersion design is possible by two-dimensional cross-sectional mode calculation, and does not require a complicated design like Non-Patent Document 4, which considers mode coupling in the propagation direction. Therefore, according to the optical device according to the first embodiment, the operating band can be designed with a high degree of freedom.
また、第1コア102のコア高さは、第1コア102による光導波路に光学的に接続される他の光デバイスと整合する高さとされている。同様に、第2コア103のコア高さは、第2コア103による光導波路に光学的に接続される他の光デバイスと整合する高さとされている。このため、これらの他の光デバイスと、実施の形態1に係る光デバイスとは、集積することが容易である。
Also, the core height of the first core 102 is set to a height that matches another optical device that is optically connected to the optical waveguide by the first core 102 . Similarly, the core height of the second core 103 is set to match other optical devices optically connected to the optical waveguide by the second core 103 . Therefore, it is easy to integrate these other optical devices with the optical device according to the first embodiment.
第1コア102は、例えば、SiNから構成し、第2コア103は、InPから構成することができる。第1コア102は、導波方向に垂直な断面の形状を、幅1000nm、コア高さ600nmとすることができる。第2コア103は、導波方向に垂直な断面の形状を、幅300nm、コア高さ350nmとすることができる。また、厚さ方向の第1コア102と第2コア103との間隔(ギャップ)は、300nmとすることができる。また、導波方向に垂直な平面内の下部クラッド層101の平面方向における、第1コア102の中心と第2コア103の中心との間の間隔(オフセット)は、0nmとすることができる。なお、図1には、上述した第1コア102の中心と第2コア103の中心とがずれて、オフセットが0ではない例を示している。
For example, the first core 102 can be made of SiN, and the second core 103 can be made of InP. The first core 102 can have a cross-sectional shape perpendicular to the waveguide direction with a width of 1000 nm and a core height of 600 nm. The second core 103 can have a cross-sectional shape perpendicular to the waveguide direction with a width of 300 nm and a core height of 350 nm. Also, the distance (gap) between the first core 102 and the second core 103 in the thickness direction can be set to 300 nm. Also, the distance (offset) between the center of the first core 102 and the center of the second core 103 in the planar direction of the lower clad layer 101 within the plane perpendicular to the waveguide direction can be set to 0 nm. Note that FIG. 1 shows an example in which the center of the first core 102 and the center of the second core 103 are shifted and the offset is not zero.
また、下部クラッド層101および上部クラッド層104は、酸化シリコンから構成することができる。例えば、シリコン基板の表面を熱酸化して形成した酸化シリコンにより下部クラッド層101を構成することができる。また、公知のCVD法によって堆積したSiO2の膜により、上部クラッド層104を構成することができる。
Also, the lower clad layer 101 and the upper clad layer 104 can be made of silicon oxide. For example, the lower clad layer 101 can be made of silicon oxide formed by thermally oxidizing the surface of a silicon substrate. Also, the upper cladding layer 104 can be composed of a SiO 2 film deposited by a known CVD method.
上述した各条件において計算した、第1コア102、第2コア103における光の伝搬モードの電磁界分布を図2に示す。図2の(a)は、最低次TEモードであり、第2コア103内に強く光が閉じ込められていることが分かる。一方、図2の(b)は、高次TEモードであり、第1コア102に強く光が閉じ込められているのと同時に、第2コア103にも電磁界分布が存在するスーパーモードとなっていることが分かる。なお、図2の(b)に示すモードにおいて第1コア102への光閉じ込め係数は73%である。
FIG. 2 shows the electromagnetic field distribution of the light propagation mode in the first core 102 and the second core 103 calculated under the conditions described above. FIG. 2A shows the lowest order TE mode, and it can be seen that light is strongly confined within the second core 103 . On the other hand, (b) of FIG. 2 is a high-order TE mode, in which light is strongly confined in the first core 102, and at the same time, the second core 103 also has an electromagnetic field distribution, resulting in a super mode. I know there is. In the mode shown in FIG. 2(b), the light confinement factor to the first core 102 is 73%.
図3の(a)に、最低次TEモードにおける2次の波長分散(D2)を示す。波長1500nm~1600nm全域でD2が負の値を有する正常分散光導波路となっており、このままでは非線形光導波路としての用途に乏しい。また参考までに、図12に示したSiN光導波路単体でのD2を、図3の(c)に示す。次に、前述した高次TEモードの波長分散を図3の(b)に示す。波長1500nm~1600nm全域でD2が正の値を有する異常分散とできることが分かる。
FIG. 3(a) shows second-order chromatic dispersion (D 2 ) in the lowest-order TE mode. It is a normal dispersion optical waveguide having a negative value of D 2 over the entire wavelength range of 1500 nm to 1600 nm, and is poorly used as a nonlinear optical waveguide as it is. For reference, D 2 of the single SiN optical waveguide shown in FIG. 12 is shown in FIG. 3(c). Next, FIG. 3B shows the chromatic dispersion of the high-order TE mode described above. It can be seen that D 2 can be anomalous dispersion having a positive value in the entire wavelength range of 1500 nm to 1600 nm.
さらに、ギャップの変化とD2との関係について図4に示す。図4に示すように、ギャップは、200nm~500nmの広い範囲で異常分散が実現でき、大きな製造マージンが得られることがわかる。
Further, FIG . 4 shows the relationship between the change in gap and D2. As shown in FIG. 4, the gap can realize anomalous dispersion in a wide range of 200 nm to 500 nm, and a large manufacturing margin can be obtained.
次に、第2コア103のコア幅とD2との関係について図5に示す。なお、上述したギャップは、500nmとしている。図5に示すように、第2コア103のコア幅を400nmとすると、正常分散となる。これに対し、第2コア103のコア幅を300nm,200nmとすると、異常分散が得られることがわかる。
Next, FIG. 5 shows the relationship between the core width of the second core 103 and D2. Note that the gap described above is set to 500 nm. As shown in FIG. 5, when the core width of the second core 103 is 400 nm, normal dispersion is obtained. On the other hand, when the core width of the second core 103 is 300 nm and 200 nm, anomalous dispersion is obtained.
第1コア102内の光閉じ込めを増大させ、より効率的に非線形光学効果を発現させるためには、上記の断面構造を設計する際に、分散だけではなく第1コア102への光閉じ込め係数がなるべく大きくなるように設計する。
In order to increase the optical confinement in the first core 102 and more efficiently develop the nonlinear optical effect, when designing the above cross-sectional structure, not only the dispersion but also the optical confinement coefficient to the first core 102 should be considered. Designed to be as large as possible.
図6に、図5に示した第2コア103のコア幅400nm、300nm、200nmの各々の場合における第1コア102内の光閉じ込め係数を示す。異常分散が得られる第2コア103のコア幅300nmの場合、第1コア102内への閉じ込め係数は73%程度(波長1550nm)が得られる。一方、同じく異常分散が得られる第2コア103のコア幅200nmの場合、第1コア102内への閉じ込め係数は67%程度(波長1550nm)まで低下する。このように、分散および光閉じ込め係数を統合的に考慮して設計すればよい。
FIG. 6 shows the optical confinement coefficient in the first core 102 when the core widths of the second core 103 shown in FIG. 5 are 400 nm, 300 nm, and 200 nm. When the core width of the second core 103 is 300 nm, which provides anomalous dispersion, the confinement factor in the first core 102 is about 73% (wavelength 1550 nm). On the other hand, in the case of the second core 103 having a core width of 200 nm, which also provides anomalous dispersion, the confinement factor in the first core 102 decreases to about 67% (wavelength 1550 nm). In this way, the design may be made by comprehensively considering the dispersion and the optical confinement factor.
上述では、1500nm~1600nmの波長帯に関して示したが、より広範な波長範囲で、光導波路材料として損失が少ない適切な材料を組み合わせ、実施の形態1に係る光デバイスの第1コア102および第2コア103に関する構造パラメータを設計することで、所望の分散特性が得られることは明らかである。
In the above description, the wavelength band of 1500 nm to 1600 nm has been described, but in a wider wavelength range, suitable materials with low loss as optical waveguide materials are combined, and the first core 102 and the second core 102 of the optical device according to Embodiment 1 are combined. It is clear that designing the structural parameters for core 103 provides the desired dispersion characteristics.
上述では、D2や光閉じ込め係数の制御に関して述べたが、実施の形態1に係る光デバイスにおいて、第1コア102,第2コア103の各々の材料や寸法パラメータを適宜設計することで、例えば高次分散、偏波モード分散なども適宜制御可能なことは明らかである。またさらに、光伝搬(導波)方向において、第1コア102,第2コア103の構造を周期的に変化させることで、伝搬光の疑似位相整合等の条件を満たすようにし、あるいは光伝搬方向において非特許文献3に示されている設計論に基づき、必要となるモード結合条件を得ることが可能となる。
In the above description, the control of D 2 and the optical confinement factor has been described. It is clear that higher-order dispersion, polarization mode dispersion, etc. can also be appropriately controlled. Further, by periodically changing the structures of the first core 102 and the second core 103 in the light propagation (guiding) direction, conditions such as quasi-phase matching of propagating light can be satisfied, or the light propagation direction can be satisfied. Based on the design theory shown in Non-Patent Document 3, it is possible to obtain the necessary mode coupling conditions.
ところで、図1を用いて説明した実施の形態1に係る光デバイスの構成は、一例であり、例えば、製造性などを考慮し、適宜変更することができる。例えば、酸化シリコンから構成した上部クラッド層104は、第1コア102の底面まで形成され、第1コア102は、上部クラッド層104には覆われていない構成とすることができる。このような構成とすることで、例えば、第1コア102の上部における、何らかの物質の存在の有無を、光学的に検知する光センサに応用することができ、産業上、特に重要となる。
By the way, the configuration of the optical device according to Embodiment 1 described with reference to FIG. 1 is an example, and can be changed as appropriate in consideration of, for example, manufacturability. For example, the upper clad layer 104 made of silicon oxide may be formed up to the bottom surface of the first core 102 , and the first core 102 may not be covered with the upper clad layer 104 . With such a configuration, for example, it can be applied to an optical sensor that optically detects the presence or absence of some substance above the first core 102, which is particularly important industrially.
次に、実施の形態1に係る光デバイスを集積光デバイスに適用した例について、図7を参照して説明する。この集積光デバイスは、半導体レーザ光源に実施の形態1に係る光デバイスを組み合わせたものである。
Next, an example in which the optical device according to Embodiment 1 is applied to an integrated optical device will be described with reference to FIG. This integrated optical device is a combination of the semiconductor laser light source and the optical device according to the first embodiment.
図7において、符号201は非特許文献4で述べられているメンブレンレーザであり、符号202のSiO2/Si基板上に作製される。符号203a,203b,203cはInPコアであり、第2コアに相当する。InPコア203aは、同じくInP系材料で作製されたメンブレンレーザ201の出力光導波路コアとなる。InPコア203a,203bの上部には、SiNコア204aが設置され、InPコア203cの上部には、SiNコア204bが設置されている。SiNコア204a,204bは、第1コアに相当する。
In FIG. 7, reference numeral 201 is a membrane laser described in Non-Patent Document 4, which is fabricated on a SiO 2 /Si substrate 202 . InP cores 203a, 203b, and 203c correspond to the second cores. The InP core 203a serves as an output optical waveguide core of the membrane laser 201, which is also made of an InP-based material. A SiN core 204a is placed over the InP cores 203a and 203b, and a SiN core 204b is placed over the InP core 203c. The SiN cores 204a and 204b correspond to the first core.
メンブレンレーザ201の出力光導波路では、光の伝搬モードは、図8Aに示すようにInPコア203a内に電磁界が存在している。InPコア203aは漸次テーパ状に幅が狭められており、メンブレンレーザ201からの出力光が伝搬する過程で断熱的にモード変換され、InPコア203aのテーパ先端部205では、図8Bに示すようにSiNコア204aに主に電磁界が存在する光の伝搬モードとなる。テーパ先端部205では、InPコア203aが存在しない特許文献3で用いられるようなSiN光導波路とバットカップリングされており、その先には、図8Cに示すような光の伝搬モードを有するSiNコア204aによる光導波路に接続され、光配線される。
In the output optical waveguide of the membrane laser 201, the light propagation mode has an electromagnetic field within the InP core 203a as shown in FIG. 8A. The width of the InP core 203a is gradually narrowed in a tapered shape, and the mode is adiabatically converted while the output light from the membrane laser 201 propagates. This is a light propagation mode in which an electromagnetic field mainly exists in the SiN core 204a. The taper tip 205 is butt-coupled with a SiN optical waveguide as used in Patent Document 3, in which the InP core 203a does not exist, and beyond that, a SiN core having a light propagation mode as shown in FIG. 8C 204a for optical wiring.
次に、本発明に係る非線形光デバイスと接続するため、接続箇所において再びInPコア203bがテーパ状に配置され、その後、図8Dに示す非線形光導波路の光の伝搬モードへと断熱的にモード変換される。図8Dに示すモードは、図1を用いて説明した実施の形態1に係る光デバイスの非線形光導波路となっている。
Next, in order to connect with the nonlinear optical device according to the present invention, the InP core 203b is tapered again at the connection point, and then adiabatically mode-converted to the light propagation mode of the nonlinear optical waveguide shown in FIG. 8D. be done. The mode shown in FIG. 8D is the nonlinear optical waveguide of the optical device according to Embodiment 1 described using FIG.
非線形光導波路を構成しているSiNコア204a、リング状のInPコア203c、InPコア203b、リング状のSiNコア204bにより、リング共振器206が作製されている。リング共振器206は、共振器内の光強度増大を活用する非線形光導波路デバイスとなっている。
A ring resonator 206 is fabricated by the SiN core 204a, the ring-shaped InP core 203c, the InP core 203b, and the ring-shaped SiN core 204b, which constitute the nonlinear optical waveguide. The ring resonator 206 is a nonlinear optical waveguide device that takes advantage of the increased light intensity within the resonator.
この後、再びInPコア203bのテーパを介して断熱的にモード変換し、出力先のSiN光導波路に接続されている。ここでSiN光導波路は、非特許文献3に示されているような汎用的な光導波路でよく、光配線のみならず、様々なパッシブデバイスが集積可能となる。例えば、メンブレンレーザ201からのポンプ光をカットするための波長フィルタ、低損失ファイバ結合デバイス、空間光放射デバイスなどを集積することができる。
After that, the mode is adiabatically converted again through the taper of the InP core 203b, and is connected to the SiN optical waveguide of the output destination. Here, the SiN optical waveguide may be a general-purpose optical waveguide as disclosed in Non-Patent Document 3, and not only optical wiring but also various passive devices can be integrated. For example, a wavelength filter for cutting pump light from the membrane laser 201, a low-loss fiber coupling device, a spatial light radiation device, etc. can be integrated.
ここで、InPコア203a,203b,203cは、メンブレンレーザ201の出力光導波路の部分と、と非線形光導波路の部分とで同じ厚さとすることで、非特許文献5に示されるような作製方法によって容易に同一層に形成可能である。またSiNコア204a,204bは、上述したInPコアを作製した後、CVD法によってSiO2を堆積しCMP研磨を行うことで設計したギャップとなる層厚とし、さらにその後、非特許文献5に示されるような作製方法によって、同一の層に形成すれば良い。
Here, the InP cores 203a, 203b, and 203c are made to have the same thickness in the output optical waveguide portion of the membrane laser 201 and in the nonlinear optical waveguide portion by a manufacturing method as shown in Non-Patent Document 5. They can be easily formed in the same layer. In addition, the SiN cores 204a and 204b are made to have a layer thickness that becomes the designed gap by depositing SiO 2 by CVD method and performing CMP polishing after producing the InP core described above. They may be formed in the same layer by such a manufacturing method.
図7に示した集積光デバイスによって、例えばメンブレンレーザ201の発振波長をリング共振器206の共振波長をまたいで短波長側から長波長側へとスイープすることで、SiNコア204a,204b内でのχ(3)非線形過程を経て、出力SiN光導波路から周波数コム光が得られる。すなわち、励起レーザと非線形マイクロ共振器が集積された集積コム光源が実現できる。
With the integrated optical device shown in FIG. 7, for example, by sweeping the oscillation wavelength of the membrane laser 201 from the short wavelength side to the long wavelength side across the resonance wavelength of the ring resonator 206, the inside of the SiN cores 204a and 204b Through the χ (3) nonlinear process, frequency comb light is obtained from the output SiN optical waveguide. That is, an integrated comb light source in which a pump laser and a nonlinear microresonator are integrated can be realized.
ここではメンブレンレーザのみを記載したが、他のメンブレンデバイス、例えば非線形マイクロ共振器内でソリトンを生成するための位相シフタや、リング共振器の波長チューニングをするためのヒータ構造などをメンブレンデバイスとして集積することも可能である。
Although only membrane lasers are described here, other membrane devices such as phase shifters for generating solitons in nonlinear microcavities and heater structures for wavelength tuning of ring cavities are integrated as membrane devices. It is also possible to
[実施の形態2]
次に、本発明の実施の形態2に係る光デバイスについて、図9を参照して説明する。この光デバイスは、下部クラッド層101、第1コア102a、第2コア103、上部クラッド層104を備える。第1コア102a、第2コア103は、下部クラッド層101の上に形成されている。また、上部クラッド層104は、下部クラッド層101の上で第1コア102aおよび第2コア103を覆って形成されている。この例では、下部クラッド層101の側から見て、第1コア102aより上側に第2コア103が配置されている。 [Embodiment 2]
Next, an optical device according to Embodiment 2 of the present invention will be described with reference to FIG. This optical device comprises a lowerclad layer 101 , a first core 102 a , a second core 103 and an upper clad layer 104 . First core 102 a and second core 103 are formed on lower clad layer 101 . Upper clad layer 104 is formed on lower clad layer 101 to cover first core 102 a and second core 103 . In this example, when viewed from the lower clad layer 101 side, the second core 103 is arranged above the first core 102a.
次に、本発明の実施の形態2に係る光デバイスについて、図9を参照して説明する。この光デバイスは、下部クラッド層101、第1コア102a、第2コア103、上部クラッド層104を備える。第1コア102a、第2コア103は、下部クラッド層101の上に形成されている。また、上部クラッド層104は、下部クラッド層101の上で第1コア102aおよび第2コア103を覆って形成されている。この例では、下部クラッド層101の側から見て、第1コア102aより上側に第2コア103が配置されている。 [Embodiment 2]
Next, an optical device according to Embodiment 2 of the present invention will be described with reference to FIG. This optical device comprises a lower
実施の形態2において、第1コア102aは、非線形光学効果を有している。また、第1コア102aと第2コア103とによりスーパーモードを有する光導波路を構成している。この例において、第1コア102aは、リブ型とされている。
In Embodiment 2, the first core 102a has a nonlinear optical effect. Also, the first core 102a and the second core 103 constitute an optical waveguide having a super mode. In this example, the first core 102a is rib-shaped.
また、実施の形態2においても、第1コア102aおよび第2コア103の各々の屈折率、断面形状、および導波方向に垂直な断面における第1コア102aと第2コア103との位置関係が、スーパーモードが所望の分散を有する状態とされている。例えば、第1コア102aによる光導波路、および第2コア103による光導波路の各々が正常分散を有していても、上述したスーパーモードが異常分散を有するように、第1コア102aおよび第2コア103それぞれの断面形状および位置関係が設定されている。
Also in the second embodiment, the refractive index, the cross-sectional shape, and the positional relationship between the first core 102a and the second core 103 in the cross section perpendicular to the waveguide direction of each of the first core 102a and the second core 103 are , the supermode is assumed to have the desired dispersion. For example, even if each of the optical waveguide by the first core 102a and the optical waveguide by the second core 103 has normal dispersion, the first core 102a and the second core may 103 are set in cross-sectional shape and positional relationship.
また、第1コア102aのコア高さは、第1コア102aによる光導波路に光学的に接続される他の光デバイスと整合する高さとされている。同様に、第2コア103のコア高さは、第2コア103による光導波路に光学的に接続される他の光デバイスと整合する高さとされている。このため、これらの他の光デバイスと、実施の形態2に係る光デバイスとは、集積することが容易である。
Also, the core height of the first core 102a is set to a height that matches another optical device that is optically connected to the optical waveguide by the first core 102a. Similarly, the core height of the second core 103 is set to match other optical devices optically connected to the optical waveguide by the second core 103 . Therefore, it is easy to integrate these other optical devices with the optical device according to the second embodiment.
第1コア102aは、例えば、LiNbO3から構成し、第2コア103は、InPから構成することができる。第1コア102aは、スラブ厚100nmとし、また、導波方向に垂直な断面の形状について、幅1000nmとし、スラブを含めた全高さを200nmとすることができる。第2コア103は、導波方向に垂直な断面の形状を、幅300nm、コア高さ350nmとすることができる。
The first core 102a can be made of, for example, LiNbO 3 and the second core 103 can be made of InP. The first core 102a can have a slab thickness of 100 nm, a width of 1000 nm in a cross-sectional shape perpendicular to the waveguide direction, and a total height including the slab of 200 nm. The second core 103 can have a cross-sectional shape perpendicular to the waveguide direction with a width of 300 nm and a core height of 350 nm.
また、厚さ方向の第1コア102aと第2コア103との間隔(ギャップ)は、300nmとすることができる。また、導波方向に垂直な平面内の下部クラッド層101の平面方向における、第1コア102aの中心と第2コア103の中心との間の間隔(オフセット)は、0nmとすることができる。なお、図9には、上述した第1コア102aの中心と第2コア103の中心とがずれて、オフセットが0ではない例を示している。
Also, the distance (gap) between the first core 102a and the second core 103 in the thickness direction can be set to 300 nm. Also, the distance (offset) between the center of the first core 102a and the center of the second core 103 in the planar direction of the lower clad layer 101 within the plane perpendicular to the waveguide direction can be set to 0 nm. Note that FIG. 9 shows an example in which the center of the first core 102a and the center of the second core 103 are deviated, and the offset is not zero.
上述した各条件において計算した、光の伝搬モードの電磁界分布を図10A、図10B、図10Cに示す。図10Aは、最低次TEモードであり、第2コア103内に強く光が閉じ込められていることが分かる。一方、図10Bには高次TEモードを示し、第1コア102aに強く光が閉じ込められているのと同時に、第2コア103にも電磁界分布が存在するスーパーモードとなっていることが分かる。なお、図10Bのモードにおいて第1コア102aへの光閉じ込め係数は43%である。また参考までに第1コア102aのみが存在する場合の最低次TEモードも電磁界分布を図10Cに示す。
The electromagnetic field distributions of the light propagation modes calculated under the above conditions are shown in FIGS. 10A, 10B, and 10C. FIG. 10A shows the lowest order TE mode, and it can be seen that light is strongly confined within the second core 103 . On the other hand, FIG. 10B shows a higher-order TE mode, in which light is strongly confined in the first core 102a and, at the same time, the second core 103 also has an electromagnetic field distribution. . Note that the light confinement factor to the first core 102a in the mode of FIG. 10B is 43%. For reference, FIG. 10C also shows the electromagnetic field distribution of the lowest-order TE mode when only the first core 102a exists.
このような光導波路構造に対して計算した、光の伝搬モードの電磁界分布を図10に示す。図10Aには、最低次TEモードを示し、第2コア103内に強く光が閉じ込められていることが分かる。一方、図10Bには、高次TEモードを示し、第1コア102aに強く光が閉じ込められているのと同時に、第2コア103にも電磁界分布が存在するスーパーモードとなっていることが分かる。
Fig. 10 shows the electromagnetic field distribution of the light propagation mode calculated for such an optical waveguide structure. FIG. 10A shows the lowest order TE mode, and it can be seen that light is strongly confined within the second core 103 . On the other hand, FIG. 10B shows a higher-order TE mode, in which light is strongly confined in the first core 102a, and at the same time, the second core 103 is also in a super mode in which an electromagnetic field distribution exists. I understand.
なお、図10BのモードにおいてLiNbO3コアへの光閉じ込め係数は43%である。また参考までにLiNbO3コアのみが存在する場合の最低次TEモードも電磁界分布を10-3に示す。
Note that the light confinement factor to the LiNbO 3 core in the mode of FIG. 10B is 43%. For reference, 10-3 also shows the electromagnetic field distribution of the lowest-order TE mode when only the LiNbO 3 core exists.
図11の(a)に最低次TEモード(図10A)が有するD2を示す。波長1500nm~1600nm全域でD2が負の値を有する正常分散光導波路となっており、このままでは非線形光導波路としての用途に乏しい。また、図11の(c)に、図10Cに示した第1コア102aのみの場合の最低次TEモードが有するD2を示す。図11の(a)と同様に、波長1500nm~1600nm全域でD2が負の値を有する正常分散光導波路となっており、このままでは非線形光導波路としての用途に乏しい。
FIG. 11(a) shows D 2 of the lowest-order TE mode (FIG. 10A). It is a normal dispersion optical waveguide having a negative value of D 2 over the entire wavelength range of 1500 nm to 1600 nm, and is poorly used as a nonlinear optical waveguide as it is. FIG. 11(c) shows D 2 of the lowest-order TE mode in the case of only the first core 102a shown in FIG. 10C. As in FIG. 11(a), the normal dispersion optical waveguide has a negative value of D 2 over the entire wavelength range of 1500 nm to 1600 nm, and is poorly used as a nonlinear optical waveguide.
一方、図10Bに示した高次TEモードの波長分散は、図11の(b)に示すように、波長1500nm~1600nm全域でD2が正の値を有する異常分散とできることが分かる。
On the other hand, it can be seen that the chromatic dispersion of the high-order TE mode shown in FIG. 10B can be anomalous dispersion in which D 2 has a positive value over the entire wavelength range of 1500 nm to 1600 nm, as shown in FIG. 11(b).
上述したように、コア厚が薄い第1コア102aにおいても異常分散が得られることは、特に伝搬損失提言において優れた効果を有し、光共振器の高Q値化等に特に有効である。例えば、LiNbO3などの加工しにくい材料においては、コア高さを小さくできるほどコア側壁の加工荒れに起因する散乱損失の影響を小さくできるため、薄いコアとできることは優れた効果を有する。
As described above, the ability to obtain anomalous dispersion even in the first core 102a having a small core thickness is particularly effective in reducing propagation loss, and is particularly effective in increasing the Q value of an optical resonator. For example, in the case of materials such as LiNbO 3 that are difficult to process, the smaller the core height, the smaller the effect of scattering loss caused by rough processing of the core side walls.
上述では、1500nm~1600nmの波長帯に関して示したが、より広範な波長範囲で、光導波路材料として損失が少ない適切な材料を組み合わせ、実施の形態2に係る光デバイスの第1コア102aおよび第2コア103に関する構造パラメータを設計することで、所望の分散特性が得られることは明らかである。また、D2や光閉じ込め係数のみならず、例えば高次分散、偏波モード分散等も適宜制御可能なことは明らかである。また、さらに光伝搬方向において、第1コア102aおよび第2コア103の構造を周期的に変化させることで、伝搬光の疑似位相整合等の条件を満たすようにし、あるいは光伝搬方向において非特許文献2に示されている設計論に基づき必要となるモード結合条件を得ることも可能である。
In the above description, the wavelength band of 1500 nm to 1600 nm has been described, but in a wider wavelength range, suitable materials with low loss as optical waveguide materials are combined, and the first core 102a and the second core 102a of the optical device according to the second embodiment are combined. It is clear that designing the structural parameters for core 103 provides the desired dispersion characteristics. Moreover, it is clear that not only D 2 and the optical confinement coefficient but also higher-order dispersion, polarization mode dispersion, etc. can be appropriately controlled. In addition, by periodically changing the structure of the first core 102a and the second core 103 in the light propagation direction, conditions such as quasi-phase matching of propagating light can be met, or in the light propagation direction It is also possible to obtain the required mode-coupling conditions based on the design theory presented in 2.
図9を用いて説明した実施の形態2に係る光デバイスの構成は、一例であり、例えば、製造性などを考慮し、適宜変更することができる。例えば、酸化シリコンから構成した上部クラッド層104は第2コア103の底面まで存在し、第2コア103は、上部クラッド層104には覆われていない構成とすることができる。このような構造とすることで、第2コア103の上部における、何らかの物質の存在の有無を、光学的に検知する光センサに応用することができ、産業上、特に重要となる。
The configuration of the optical device according to Embodiment 2 described with reference to FIG. 9 is an example, and can be changed as appropriate in consideration of, for example, manufacturability. For example, the upper clad layer 104 made of silicon oxide may extend to the bottom surface of the second core 103 , and the second core 103 may not be covered with the upper clad layer 104 . With such a structure, it can be applied to an optical sensor that optically detects the presence or absence of some substance above the second core 103, which is particularly important industrially.
ところで、第1コア102aを構成するLiNbO3は、χ(3)非線形性に加えてχ(2)非線形性も有する材料として広く用いられている。このため、実施の形態2に係る光デバイスによれば、SiNなどで一般的に活用されるχ(3)非線形過程に加えて、χ(3)非線形過程も活用できるようになるという優れた効果が得られる。また、既存のLiNbO3光導波路で実現されている非線形光デバイスは、励起光源が集積されていなかったが、実施の形態2に係る光デバイスを用いることで、励起光源も集積可能になるという優れた効果が得られる。例えば、図7を用いて説明したような、半導体レーザ光源との集積コム光源を構成するにあたっても、第1コアと第2コアの配置を適宜調整することで同様に実現可能である。
By the way, LiNbO 3 forming the first core 102a is widely used as a material having χ (2) nonlinearity in addition to χ (3) nonlinearity. Therefore, according to the optical device according to the second embodiment, in addition to the χ (3) nonlinear process that is generally used in SiN and the like, it is possible to utilize the χ (3) nonlinear process, which is an excellent effect. is obtained. In addition, the nonlinear optical device realized by the existing LiNbO 3 optical waveguide does not have an integrated excitation light source, but the use of the optical device according to the second embodiment makes it possible to integrate the excitation light source. effect is obtained. For example, when configuring an integrated comb light source with a semiconductor laser light source as described with reference to FIG. 7, it can be similarly realized by appropriately adjusting the arrangement of the first core and the second core.
以上に説明したように、本発明によれば、第1コアと第2コアとによりスーパーモードを有する光導波路を構成し、第1コアおよび第2コアの各々の屈折率、断面形状、および導波方向に垂直な断面における第1コアと第2コアとの位置関係を、スーパーモードが所望の分散を有する状態とするので、シングルモード性、低損失性、設計・製造の容易さ、他の光学素子との集積性が良好で、かつ光デバイスファンダリでの導入障壁が低い光デバイスが提供できるようになる。
As described above, according to the present invention, an optical waveguide having a super mode is formed by the first core and the second core, and the refractive index, cross-sectional shape, and waveguide of each of the first core and the second core are determined. The positional relationship between the first core and the second core in the cross section perpendicular to the wave direction is set to a state in which the supermode has a desired dispersion. It is possible to provide an optical device that is highly integrated with an optical element and has a low introduction barrier in an optical device foundry.
なお、本発明は以上に説明した実施の形態に限定されるものではなく、本発明の技術的思想内で、当分野において通常の知識を有する者により、多くの変形および組み合わせが実施可能であることは明白である。
It should be noted that the present invention is not limited to the embodiments described above, and many modifications and combinations can be implemented by those skilled in the art within the technical concept of the present invention. It is clear.
101…下部クラッド層、102…第1コア、103…第2コア、104…上部クラッド層。
101...lower clad layer, 102...first core, 103...second core, 104...upper clad layer.
Claims (3)
- 下部クラッド層の上に形成された非線形光学効果を有する第1コアと、
前記下部クラッド層の上に形成され、第2コアと、
前記下部クラッド層の上で前記第1コアおよび前記第2コアを覆って形成された上部クラッド層と
を備え、
前記第1コアと前記第2コアとによりスーパーモードを有する光導波路を構成し、
前記第1コアおよび前記第2コアの各々の屈折率、断面形状、および導波方向に垂直な断面における前記第1コアと前記第2コアとの位置関係は、前記スーパーモードが所望の分散を有する状態とされている
ことを特徴とする光デバイス。 a first core having a nonlinear optical effect formed on the lower clad layer;
a second core formed on the lower clad layer;
an upper clad layer formed over the lower clad layer and covering the first core and the second core;
An optical waveguide having a super mode is configured by the first core and the second core,
The refractive index of each of the first core and the second core, the cross-sectional shape, and the positional relationship between the first core and the second core in the cross section perpendicular to the waveguide direction are such that the super mode has desired dispersion. An optical device characterized by being in a state of having. - 請求項1記載の光デバイスにおいて、
前記第1コアのコア高さは、前記第1コアによる光導波路に光学的に接続される他の光デバイスと整合する高さとされていることを特徴とする光デバイス。 The optical device of claim 1, wherein
An optical device, wherein the core height of the first core is matched with another optical device optically connected to the optical waveguide by the first core. - 請求項1または2記載の光デバイスにおいて、
前記第2コアのコア高さは、前記第2コアによる光導波路に光学的に接続される他の光デバイスと整合する高さとされていることを特徴とする光デバイス。 3. The optical device according to claim 1, wherein
The optical device according to claim 1, wherein the core height of the second core is matched with another optical device optically connected to the optical waveguide by the second core.
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