Kiyoshi Asakawa - Academia.edu (original) (raw)
Papers by Kiyoshi Asakawa
Conference on Lasers and Electro-Optics 2010, 2010
Abstract: We have succeeded all-optical Mach-Zehnder type switch by optical Kerr effect around 15... more Abstract: We have succeeded all-optical Mach-Zehnder type switch by optical Kerr effect around 1550nm in AlGaAs photonic crystal slab waveguide. We also studied nonlinear refractive index n'2 in this waveguide. © 2010 Optical Society of America OCIS codes: (130.5296) ...
Physical Review B, 2002
Coupling of defects in one-dimensional ͑1D͒ and two-dimensional ͑2D͒ photonic crystals ͑PC's͒ is ... more Coupling of defects in one-dimensional ͑1D͒ and two-dimensional ͑2D͒ photonic crystals ͑PC's͒ is analyzed theoretically and investigated numerically using the transfer-matrix method and the finite-difference timedomain technique. Basically, the coupling behavior of defects is reflected in the spectra of PC molecules formed by two identical PC atoms ͑single defects͒. In both 1D and 2D cases, PC atoms can be roughly classified into two types based on the spectral shape of the resulting PC molecules. One type of PC atom generates clear bonding and antibonding states in the spectra of PC molecules. In contrast, the other type of PC atom creates PC molecules whose spectra are nearly flat on top. It is shown that this kind of PC atom is crucial for the construction of coupled cavity waveguides with quasiflat impurity bands. More accurately, we use a quantity related to the valley depth in the spectra of PC molecules to describe the coupling behavior of PC atoms. The dependence of this quantity on the properties of individual PC atoms is investigated in detail. It is revealed that the coupling of PC atoms is governed by the linewidth ͑␦͒ and the frequency shift of the PC atoms ͑⌬͒ upon increasing the confinement. The factor (⌬/␦) 2 is confirmed by theoretical analysis and numerical calculation to be a universal criterion to characterize the coupling behavior of both 1D and 2D PC defects.
Optics Express, 2007
High transmission of slow-light in a photonic crystal (PC) waveguide (WG) using a hetero group-ve... more High transmission of slow-light in a photonic crystal (PC) waveguide (WG) using a hetero group-velocity (Ht-V g) PC-WG was proposed and experimentally investigated. The Ht-V g WG, which comprises a low-group-velocity (L-V g) PC-WG section between two identical highgroup-velocity (H-V g) PC-WGs, is designed to decrease the impedance mismatch of the L-V g PC-WG. The increase in transmittance of a propagating pulse was confirmed in the Ht-V g PC-WG even in the vicinity of the band-gap, whereas the homogeneous PC-WG showed a gradual decrease in transmittance with the pulse wavelength approaching the bandgap. The group index (n g) of the L-V g region in the Ht-V g PC-WG was measured by the cross-correlation method and attained a value above 20. On the other hand, the transmittance of the Ht-V g structure recovered approximately 16dB compared to the homogeneous L-V g WG having same n g , 17. This recovery is mainly dominated by the coupling improvement due to the Ht-V g structure, around 12dB. These results indicate the effectiveness of the Ht-V g structure to use slow light in a PC-WG, which leads to various applications in PC-based optical devices.
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
We demonstrated a novel two-dimensional photonic crystal (PC) based Symmetric Mach Zehnder type a... more We demonstrated a novel two-dimensional photonic crystal (PC) based Symmetric Mach Zehnder type all-optical switch (PC-SMZ) with InAs quantum dots (QDs) acting as a nonlinear phase-shift source. The 600- ?m-long PC-SMZ having integrated wavelength-selective PC-based directional couplers and other PC components exhibited a 15-ps-wide switching-window with 2-ps rise/fall time at a wavelength of 1.3 ?m. Nonlinear optical phase shift in the 500-?m-long straight PC waveguide was also achieved at sufficiently low optical-energy (e.g., ??phase shift at ~100-fJ control-pulse energy) due to the small saturation energy density of the QDs, which is enhanced in the PC waveguide, without using conventional measures such as SOAs with current-injected gain. The results pave the way to novel PC- and QD-based photonic integrated circuits including multiple PC-SMZs and other novel functional devices.
Photonics: Design, Technology, and Packaging, 2004
ABSTRACT
Optics Express, 2004
We have observed laser action from optically-pumped InAsquantum-dots embedded in a line-defect wa... more We have observed laser action from optically-pumped InAsquantum-dots embedded in a line-defect waveguide in an air-bridge type GaAs-photonic-crystal slab (an array of air-holes). The lasing is found to occur without any optical cavity such as a set of Fabry-Perot mirrors. Comparison of the observed transmittance spectrum with the calculated band dispersion of the W3 defect-mode enables us to specify the lasing wavelength as that at the band edge. From this fact it follows that distributed feedback mechanism at the band edge with a vanishingly small groupvelocity should be responsible for the present lasing. Usefulness of this kind of compact laser in a future ultrafast planar photonic integrated circuit is discussed.
Optics Express, 2012
Transmission phase control is experimentally demonstrated using stacked metal-dielectric hole arr... more Transmission phase control is experimentally demonstrated using stacked metal-dielectric hole arrays with a two-dimensional geometric design. The transmission phase varies drastically with small frequency shifts due to structural resonances. Laterally propagating surface plasmon polaritons excited by the periodic hole array roughly determine the resonance frequency, whereas localized resonances in each hole determine the dispersion. The transmission phase at various frequencies is directly evaluated using interferometric microscopy, and the formation of an inclined wavefront is demonstrated using a beam steering element in which the hole shapes gradually change in-plane from square to circular.
Optics Express, 2006
Topology optimization has been used to design intersections in two-dimensional photonic crystal s... more Topology optimization has been used to design intersections in two-dimensional photonic crystal slab waveguides. We have experimentally confirmed that the optimized intersection displays high-transmittance with low-crosstalk for the straightforward beam-propagation line.
Optics Communications, 2002
ABSTRACT
Journal of the Optical Society of America B, 2003
Using numerical simulations, we systematically investigated the transmission properties of couple... more Using numerical simulations, we systematically investigated the transmission properties of coupled-cavity waveguides (CCWs) formed in two-dimensional photonic-crystal dielectric slabs with a triangular array of air holes. We place emphasis on achieving a quasi-flat impurity band in such CCWs, which is important for the perfect transmission of ultrashort optical pulses. We show that the quasi-flat impurity band can be obtained by controlling the ratio of the air-hole radius to the lattice constant in the triangular lattice. As an example, we demonstrate the perfect transmission of a 500-fs-wide optical pulse through a CCW with a quasi-flat impurity band, indicating the possibility of application to high-speed all-optical communication systems with a maximum bit rate of approximately terabits per second.
Materials Science and Engineering: B, 2002
In situ site-control techniques for self-organized InAs quantum dots (QDs) have been developed us... more In situ site-control techniques for self-organized InAs quantum dots (QDs) have been developed using an electron beam (EB) and a scanning tunneling microscope (STM) probe combined with molecular beam epitaxy. In the in situ EB-assisted process, InAs dots are preferentially formed in shallow, sub-μm-size GaAs holes with the InAs supply. We find that the specific slope of a hole acts
Journal of Nonlinear Optical Physics & Materials, 2011
In order to develop an ultra fast all-optical switch, we have studied optical Kerr effect and two... more In order to develop an ultra fast all-optical switch, we have studied optical Kerr effect and two photon absorption in photonic crystal line defect waveguides. Based on these results, we have succeeded in all-optical Mach-Zehnder interferometer switching.
Journal of Lightwave Technology, 2005
AbstractThe authors fabricated GaAs-based width-reduced photonic-crystal (PC) slab line-defect w... more AbstractThe authors fabricated GaAs-based width-reduced photonic-crystal (PC) slab line-defect waveguides with asymmetric cladding, characterized optically by broadband transmission spec-tral results. These waveguides were vertically sandwiched between air and oxide ...
Japanese Journal of Applied Physics, 2004
We designed and fabricated ultra-small photonic-crystal (PC)-waveguide (WG)-based components of s... more We designed and fabricated ultra-small photonic-crystal (PC)-waveguide (WG)-based components of straight-WGs, 60°-bends and Y-splitters, utilizing single-line-defect in the air-bridge type GaAs PC, and revealed their optical properties in detail by observing a transmittance (T) spectrum over a broad wavelength-region from 850 to 1600 nm. For this purpose, we developed a halogen-lamp-based spectrometer for an ultra-thin slab-sample, which has turned out very useful. We also calculated the corresponding T-spectrum by using three-dimensional finite-difference-time-domain method. In all cases where comparison is possible, the observed spectrum agrees essentially with the calculated one. Owing to these broad spectra, we have unambiguously identified the high-T region due to single guided-mode in the respective components. Comparisons of the spectrum between different samples or components, such as the straight-WGs with much different lengths, or the straight-WG and the sharp bend have al...
IEICE Transactions on Electronics, 2012
We developed advanced techniques for the growth of selfassembled quantum dots (QDs) for fabricati... more We developed advanced techniques for the growth of selfassembled quantum dots (QDs) for fabricating a broadband light source that can be applied to optical coherence tomography (OCT). Four QD ensembles and strain reducing layers (SRLs) were grown in selective areas on a wafer by the use of a 90 • rotational metal mask. The SRL thickness was varied to achieve appropriate shifts in the peak wavelength of the QD emission spectrum of up to 120 nm. The four-color QD ensembles were expected to have a broad bandwidth of more than 160 nm due to the combination of excited state emissions when introduced in a current-induced broadband light source such as a superluminescent diode (SLD). Furthermore, a desired shape of the SLD spectrum can be obtained by controlling the injection current applied to each QD ensemble. The broadband and spectrum shape controlled light source is promising for high-resolution and low-noise OCT systems.
IEICE Transactions on Electronics, 2012
This paper reviews our recent activities on nanophotonics based on a photonic crystal (PC)/quantu... more This paper reviews our recent activities on nanophotonics based on a photonic crystal (PC)/quantum dot (QD)-combined structure for an all-optical device and a metal/semiconductor composite structure using surface plasmon (SP) and negative refractive index material (NIM). The former structure contributes to an ultrafast signal processing component by virtue of new PC design and QD selective-area-growth technologies, while the latter provides a new RGB color filter with a high precision and optical beam-steering device with a wide steering angle.
Electronics and Communications in Japan (Part II: Electronics), 2007
ABSTRACT
Applied Surface Science, 2008
ABSTRACT We have demonstrated the selective area growth of stacked self-assembled InAs quantum do... more ABSTRACT We have demonstrated the selective area growth of stacked self-assembled InAs quantum dot (QD) arrays in the desired regions on a substrate and confirmed the photoluminescence (PL) emission exhibited by them at room temperature. These InAs QDs are fabricated by the use of a specially designed atomic force microscope cantilever referred to as the Nano-Jet Probe (NJP). By using the NJP, two-dimensional arrays with ordered In nano-dots are fabricated in the desired square regions on a GaAs substrate and directly converted into InAs QD arrays through the subsequent annealing by the irradiation of As flux. By using the converted QD arrays as strain templates, self-organized InAs QDs are stacked. These stacked QDs exhibit the PL emission peak at a wavelength of 1.02μm.
Applied Physics Letters, 2003
ABSTRACT
Applied Physics Letters, 2005
We report on the design, fabrication, and optical characterization of a GaAs two-dimensional phot... more We report on the design, fabrication, and optical characterization of a GaAs two-dimensional photonic-crystal-based symmetric Mach-Zehnder interferometer (PC-SMZ) aimed at all-optical switches in planar photonic integrated systems. The directional couplers that constitute ...
Conference on Lasers and Electro-Optics 2010, 2010
Abstract: We have succeeded all-optical Mach-Zehnder type switch by optical Kerr effect around 15... more Abstract: We have succeeded all-optical Mach-Zehnder type switch by optical Kerr effect around 1550nm in AlGaAs photonic crystal slab waveguide. We also studied nonlinear refractive index n'2 in this waveguide. © 2010 Optical Society of America OCIS codes: (130.5296) ...
Physical Review B, 2002
Coupling of defects in one-dimensional ͑1D͒ and two-dimensional ͑2D͒ photonic crystals ͑PC's͒ is ... more Coupling of defects in one-dimensional ͑1D͒ and two-dimensional ͑2D͒ photonic crystals ͑PC's͒ is analyzed theoretically and investigated numerically using the transfer-matrix method and the finite-difference timedomain technique. Basically, the coupling behavior of defects is reflected in the spectra of PC molecules formed by two identical PC atoms ͑single defects͒. In both 1D and 2D cases, PC atoms can be roughly classified into two types based on the spectral shape of the resulting PC molecules. One type of PC atom generates clear bonding and antibonding states in the spectra of PC molecules. In contrast, the other type of PC atom creates PC molecules whose spectra are nearly flat on top. It is shown that this kind of PC atom is crucial for the construction of coupled cavity waveguides with quasiflat impurity bands. More accurately, we use a quantity related to the valley depth in the spectra of PC molecules to describe the coupling behavior of PC atoms. The dependence of this quantity on the properties of individual PC atoms is investigated in detail. It is revealed that the coupling of PC atoms is governed by the linewidth ͑␦͒ and the frequency shift of the PC atoms ͑⌬͒ upon increasing the confinement. The factor (⌬/␦) 2 is confirmed by theoretical analysis and numerical calculation to be a universal criterion to characterize the coupling behavior of both 1D and 2D PC defects.
Optics Express, 2007
High transmission of slow-light in a photonic crystal (PC) waveguide (WG) using a hetero group-ve... more High transmission of slow-light in a photonic crystal (PC) waveguide (WG) using a hetero group-velocity (Ht-V g) PC-WG was proposed and experimentally investigated. The Ht-V g WG, which comprises a low-group-velocity (L-V g) PC-WG section between two identical highgroup-velocity (H-V g) PC-WGs, is designed to decrease the impedance mismatch of the L-V g PC-WG. The increase in transmittance of a propagating pulse was confirmed in the Ht-V g PC-WG even in the vicinity of the band-gap, whereas the homogeneous PC-WG showed a gradual decrease in transmittance with the pulse wavelength approaching the bandgap. The group index (n g) of the L-V g region in the Ht-V g PC-WG was measured by the cross-correlation method and attained a value above 20. On the other hand, the transmittance of the Ht-V g structure recovered approximately 16dB compared to the homogeneous L-V g WG having same n g , 17. This recovery is mainly dominated by the coupling improvement due to the Ht-V g structure, around 12dB. These results indicate the effectiveness of the Ht-V g structure to use slow light in a PC-WG, which leads to various applications in PC-based optical devices.
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
We demonstrated a novel two-dimensional photonic crystal (PC) based Symmetric Mach Zehnder type a... more We demonstrated a novel two-dimensional photonic crystal (PC) based Symmetric Mach Zehnder type all-optical switch (PC-SMZ) with InAs quantum dots (QDs) acting as a nonlinear phase-shift source. The 600- ?m-long PC-SMZ having integrated wavelength-selective PC-based directional couplers and other PC components exhibited a 15-ps-wide switching-window with 2-ps rise/fall time at a wavelength of 1.3 ?m. Nonlinear optical phase shift in the 500-?m-long straight PC waveguide was also achieved at sufficiently low optical-energy (e.g., ??phase shift at ~100-fJ control-pulse energy) due to the small saturation energy density of the QDs, which is enhanced in the PC waveguide, without using conventional measures such as SOAs with current-injected gain. The results pave the way to novel PC- and QD-based photonic integrated circuits including multiple PC-SMZs and other novel functional devices.
Photonics: Design, Technology, and Packaging, 2004
ABSTRACT
Optics Express, 2004
We have observed laser action from optically-pumped InAsquantum-dots embedded in a line-defect wa... more We have observed laser action from optically-pumped InAsquantum-dots embedded in a line-defect waveguide in an air-bridge type GaAs-photonic-crystal slab (an array of air-holes). The lasing is found to occur without any optical cavity such as a set of Fabry-Perot mirrors. Comparison of the observed transmittance spectrum with the calculated band dispersion of the W3 defect-mode enables us to specify the lasing wavelength as that at the band edge. From this fact it follows that distributed feedback mechanism at the band edge with a vanishingly small groupvelocity should be responsible for the present lasing. Usefulness of this kind of compact laser in a future ultrafast planar photonic integrated circuit is discussed.
Optics Express, 2012
Transmission phase control is experimentally demonstrated using stacked metal-dielectric hole arr... more Transmission phase control is experimentally demonstrated using stacked metal-dielectric hole arrays with a two-dimensional geometric design. The transmission phase varies drastically with small frequency shifts due to structural resonances. Laterally propagating surface plasmon polaritons excited by the periodic hole array roughly determine the resonance frequency, whereas localized resonances in each hole determine the dispersion. The transmission phase at various frequencies is directly evaluated using interferometric microscopy, and the formation of an inclined wavefront is demonstrated using a beam steering element in which the hole shapes gradually change in-plane from square to circular.
Optics Express, 2006
Topology optimization has been used to design intersections in two-dimensional photonic crystal s... more Topology optimization has been used to design intersections in two-dimensional photonic crystal slab waveguides. We have experimentally confirmed that the optimized intersection displays high-transmittance with low-crosstalk for the straightforward beam-propagation line.
Optics Communications, 2002
ABSTRACT
Journal of the Optical Society of America B, 2003
Using numerical simulations, we systematically investigated the transmission properties of couple... more Using numerical simulations, we systematically investigated the transmission properties of coupled-cavity waveguides (CCWs) formed in two-dimensional photonic-crystal dielectric slabs with a triangular array of air holes. We place emphasis on achieving a quasi-flat impurity band in such CCWs, which is important for the perfect transmission of ultrashort optical pulses. We show that the quasi-flat impurity band can be obtained by controlling the ratio of the air-hole radius to the lattice constant in the triangular lattice. As an example, we demonstrate the perfect transmission of a 500-fs-wide optical pulse through a CCW with a quasi-flat impurity band, indicating the possibility of application to high-speed all-optical communication systems with a maximum bit rate of approximately terabits per second.
Materials Science and Engineering: B, 2002
In situ site-control techniques for self-organized InAs quantum dots (QDs) have been developed us... more In situ site-control techniques for self-organized InAs quantum dots (QDs) have been developed using an electron beam (EB) and a scanning tunneling microscope (STM) probe combined with molecular beam epitaxy. In the in situ EB-assisted process, InAs dots are preferentially formed in shallow, sub-μm-size GaAs holes with the InAs supply. We find that the specific slope of a hole acts
Journal of Nonlinear Optical Physics & Materials, 2011
In order to develop an ultra fast all-optical switch, we have studied optical Kerr effect and two... more In order to develop an ultra fast all-optical switch, we have studied optical Kerr effect and two photon absorption in photonic crystal line defect waveguides. Based on these results, we have succeeded in all-optical Mach-Zehnder interferometer switching.
Journal of Lightwave Technology, 2005
AbstractThe authors fabricated GaAs-based width-reduced photonic-crystal (PC) slab line-defect w... more AbstractThe authors fabricated GaAs-based width-reduced photonic-crystal (PC) slab line-defect waveguides with asymmetric cladding, characterized optically by broadband transmission spec-tral results. These waveguides were vertically sandwiched between air and oxide ...
Japanese Journal of Applied Physics, 2004
We designed and fabricated ultra-small photonic-crystal (PC)-waveguide (WG)-based components of s... more We designed and fabricated ultra-small photonic-crystal (PC)-waveguide (WG)-based components of straight-WGs, 60°-bends and Y-splitters, utilizing single-line-defect in the air-bridge type GaAs PC, and revealed their optical properties in detail by observing a transmittance (T) spectrum over a broad wavelength-region from 850 to 1600 nm. For this purpose, we developed a halogen-lamp-based spectrometer for an ultra-thin slab-sample, which has turned out very useful. We also calculated the corresponding T-spectrum by using three-dimensional finite-difference-time-domain method. In all cases where comparison is possible, the observed spectrum agrees essentially with the calculated one. Owing to these broad spectra, we have unambiguously identified the high-T region due to single guided-mode in the respective components. Comparisons of the spectrum between different samples or components, such as the straight-WGs with much different lengths, or the straight-WG and the sharp bend have al...
IEICE Transactions on Electronics, 2012
We developed advanced techniques for the growth of selfassembled quantum dots (QDs) for fabricati... more We developed advanced techniques for the growth of selfassembled quantum dots (QDs) for fabricating a broadband light source that can be applied to optical coherence tomography (OCT). Four QD ensembles and strain reducing layers (SRLs) were grown in selective areas on a wafer by the use of a 90 • rotational metal mask. The SRL thickness was varied to achieve appropriate shifts in the peak wavelength of the QD emission spectrum of up to 120 nm. The four-color QD ensembles were expected to have a broad bandwidth of more than 160 nm due to the combination of excited state emissions when introduced in a current-induced broadband light source such as a superluminescent diode (SLD). Furthermore, a desired shape of the SLD spectrum can be obtained by controlling the injection current applied to each QD ensemble. The broadband and spectrum shape controlled light source is promising for high-resolution and low-noise OCT systems.
IEICE Transactions on Electronics, 2012
This paper reviews our recent activities on nanophotonics based on a photonic crystal (PC)/quantu... more This paper reviews our recent activities on nanophotonics based on a photonic crystal (PC)/quantum dot (QD)-combined structure for an all-optical device and a metal/semiconductor composite structure using surface plasmon (SP) and negative refractive index material (NIM). The former structure contributes to an ultrafast signal processing component by virtue of new PC design and QD selective-area-growth technologies, while the latter provides a new RGB color filter with a high precision and optical beam-steering device with a wide steering angle.
Electronics and Communications in Japan (Part II: Electronics), 2007
ABSTRACT
Applied Surface Science, 2008
ABSTRACT We have demonstrated the selective area growth of stacked self-assembled InAs quantum do... more ABSTRACT We have demonstrated the selective area growth of stacked self-assembled InAs quantum dot (QD) arrays in the desired regions on a substrate and confirmed the photoluminescence (PL) emission exhibited by them at room temperature. These InAs QDs are fabricated by the use of a specially designed atomic force microscope cantilever referred to as the Nano-Jet Probe (NJP). By using the NJP, two-dimensional arrays with ordered In nano-dots are fabricated in the desired square regions on a GaAs substrate and directly converted into InAs QD arrays through the subsequent annealing by the irradiation of As flux. By using the converted QD arrays as strain templates, self-organized InAs QDs are stacked. These stacked QDs exhibit the PL emission peak at a wavelength of 1.02μm.
Applied Physics Letters, 2003
ABSTRACT
Applied Physics Letters, 2005
We report on the design, fabrication, and optical characterization of a GaAs two-dimensional phot... more We report on the design, fabrication, and optical characterization of a GaAs two-dimensional photonic-crystal-based symmetric Mach-Zehnder interferometer (PC-SMZ) aimed at all-optical switches in planar photonic integrated systems. The directional couplers that constitute ...