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This paper deals with single-stranded DNA detection using Dirac point changes in a graphene-based FET device. The device utilized a shadow mask to minimize contamination of the graphene surface due to photoresist when depositing source/drain electrodes. Thereafter, micro-scale graphene channels were formed by dry etching. As single-stranded DNA was adsorbed on the graphene surface of the fabricated device, it showed an efficient Dirac voltage shift up to 10V.

The Fabry-Perot interference filter is effective at passing only specific wavelengths optically. A diffraction grating is attached to the multilayered interference filter to diffract only at a specific wavelength. This paper describes how the diffraction efficiency varies with wavelength in this structure for various number of layers of the interference filter.

The static and dynamic operating characteristics of blue laser diodes grown on wurtzite AlGaInN multiple quantum well structures were investigated using the rate equations with the three-level model. The device parameters were obtained from the optical gain properties of the MQW active region using the self-consistent numerical method for the multiband Hamiltonian for the strained wurtzite crystal. The performance of the LDs were analyzed by using the PSPICE equivalent circuit method and were compared with the 4th order Runge-Kutta method. The resulting equivalent circuit model for a blue laser diode was schematically presented, and its pseudorandom binary sequence (PRBS) modulation characteristics, including the pulse response and the frequency response, have been demonstrated by using a conventional PSPICE. Finally their Q factor was analyzed.

This is a historical description about how Korea was transformed from the fringe to the global forefront in mobile telecommunications. It was an audacious challenge to develop a commercial CDMA(Code Division Multiple Access) cellular system which is technically more advanced, but not field proven hence risky, than TDMA cellular system that was the main trend of the times and opted by established majors. ETRI with Samsung, LG, Hyundai and Maxon pursed a co-development path to the national project supported by the Ministry of Information and Communication, Korea, at that time, in along with the joint development with Qualcomm, the original proponent of CDMA. After the successful commercialization first in Korea, CDMA turned into the major trend of the times, and Korean manufacturers became innovative leaders in the world.

The epitaxial layer structures for blue InGaN light emitting diodes have been optimized for high brightness applications with the output power levels exceeding 1000 W/cm 2 by using a self-consistent finite element method. The light-current-voltage relationship has been directly estimated from the multiband Hamiltonian for wurtzite crystals. To analyze the efficiency droop at high injection levels, the major nonradiative recombination processes and carrier spillover have also been taken into account. The wall-plug efficiency at high injection levels up to several thousand A/cm 2 has been successfully evaluated for various epilayer structures facilitating optimization of the epitaxial structures for desired output power levels.

본 논문에서는 패브리 페롯 레이저 다이오드 (FP-LD : Fabry-Perot LD)에서 활성층 구조에 따른 주입 잠금 특성을 비교하였다 . 편광 및 무편광 다중양자우물 구조와 무편광 벌크 구조의 이득 스펙트럼 및 주입 캐리어 밀도에 따른 최대 이득 특성 을 TE, TM 편광에 대하여 계산하였다. 계산된 이득 파라미터를 시영역 대신호 모델에 적용하여 FP-LD의 주입 잠금 특성을 확인한 결과, 무편광 FP-LD가 편광 FP-LD 에 비하여 RIN(Relative Intensity Noise) 특성 면에서 약 3 dB 정도 우수하고, 2.5 Gbps 변조 시에 아이 특성이 훨씬 우수함을 알 수 있다.

The PSPICE equivalent circuit elements of a 1550 nm InGaAsP laser diode were derived by using multi-level rate equations. The device parameters were extracted by using a self-consistent numerical method for the optical gain properties of the MQW active regions. The resulting equivalent circuit model is also applied to an actual optical transmitter, and its PSPICE simulation results show good agreement with the measured results once the parasitic capacitance due to the packaging is taken into account.

PSPICE circuit parameters of the blue laser diodes grown on wurtzite AlGaInN multiple quantum well structures were extracted directly from the three level rate equations. The relevant optical gain parameters were separately calculated from the self-consistent multiband Hamiltonian. The resulting equivalent circuit model for a blue laser diode was schematically presented, and its modulation characteristics, including the pulse response and the frequency response, have been demonstrated by using a conventional PSPICE.

The lasing characteristics of three-guide coupled rectangular ring laser containing active and passive sections were investigated numerically and experimentally. The rectangular laser cavity consists of four low-loss total internal reflection mirrors and an output coupler made from three passive coupled waveguides. The laser having active section lengths of 350 µm and total cavity lengths of 780 µm was fabricated. The lasing threshold current in the clockwise circulating direction is approximately 35 mA, while that in the counterclockwise circulating direction is around 40 mA under continuous wave operation. The lasing characteristics are bidirectional operation of the single mode with a side mode suppression ratio better than 27 dB.

The miniband structure of a quantum dot lattice based on GaN/AlN nanowire arrays has been investigated using the finite element method and Floquet theorem. The quantum dot modes and the quantum wire modes in the nanowire arrays were graphically verified. The optimum geometries of GaN/AlN quantum wire arrays were investigated by using a correlation between the width of nanowires and the separation of the minibandgap which is to be larger than the thermal energy at room temperature.

The relative intensity noise (RIN) characteristics in 405 nm blue laser diodes grown on wurtzite AlGaInN multiple quantum well structures were investigated using the rate equations with the quantum Langevin noise model. The device parameters were extracted from the optical gain properties of the MQW active region using the self-consistent numerical method developed for calculating the multiband Hamiltonian in the strained wurtzite crystal. These methods have been applied to laser diodes for various conditions including the external feedback and the high frequency current injection.

A new scheme to fabricate quantum dot arrays using the edge-defined nanowires is proposed. The three-dimensional quantum size effect due to the nanowire crossing was analyzed by using the finite-difference method taking into account the periodic nature of the superlattices. The quantum dot modes were graphically verified, and the miniband gap between quantum dot and quantum wire modes was quantitatively analyzed.

The switching characteristics of an electroabsorption modulator fabricated on a waveguide-coupled micro-ring-cavity resonator were investigated. The ring cavity resonator consists of ridge waveguide regions, total internal reflector mirrors, and a coupling region. The coupling region is implemented with a multimode interferometer (MMI) waveguide to enhance the coupling coefficient. The total internal reflection mirrors were fabricated by self-aligned RIBE process resulting in minimal insertion losses of around 0.7 dB/mirror. The gain medium was a 1.55 μm InGaAsP MQW ridge waveguide, and the passive waveguide was a re-grown 1.4 μm InGaAsP ridge structure. The sharp variation of the optical transmission through the micro-ring-cavity resonator near the resonance wavelength was utilized to realize efficient semiconductor optical modulators with a high extinction ratio. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The high frequency modulation effects on the relative intensity noise (RIN) characteristics of 405 nm InAlGaN laser diodes have been investigated taking into account the strain and thermal effects on the laser diode itself as well as external optical feedback effects. The simulation results indicate that the critical external optical feedback for –125 dB/Hz RIN is around 0.1%, a typical order found in practical DVD operating environments.By optimizing the injection current levels and its frequency, one can reduce the RIN with 0.1∼1% external feedback effect by more than 15 dB/Hz. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate the properties of a multimode-interference (MMI) coupled ring cavity resonator with total-internal-reflection (TIR) mirrors and a semiconductor optical amplifier (SOA) in an InGaAsP material system. The TIR mirrors were fabricated by the self-aligned process with a loss of about 1.4 dB per mirror. The resulting free spectral range (FSR) was approximately 0.8 nin (97 GHz) near 1569 rim. The on-off ratio and the full width at half maximum (FWHM) were 8 dB and 0.152 nm, respectively, corresponding to a finesse of 5.2 and a Q factor of 10,322. Hence, such resonators can be directly integrated with other devices making possible the fabrication of compact and highly functional photonic integrated circuits.

Graphene is a promising material for its exceptional electrical and mechanical properties. Starting with the initial demonstration of isolating a single graphene sheet from graphite, much progress has been made in realizing graphene based devices for diverse applications. Here, we introduce an experiment in which the electrical properties of graphene are modified by coating different-sequence single-stranded deoxyribonucleic acid (ssDNA) molecules. We fabricated a graphene-field effect transistor (FET) by transferring CVD graphene on copper foil onto a Si/SiO2 wafer. A passivation layer opened up windows on the surface of the graphene to enable interaction with liquid buffers. ssDNA molecules with different base sequences were coated onto the active graphene channels. We observed a variation in the Dirac voltage of the ssDNA-coated graphene FETs according to the ssDNA base sequences. Electrical control of the graphene FET is obtained via gating effect of the deposited ssDNAs. We conduct a systematic study of this ssDNAinduced gating effect with different base sequences, concentrations, and lengths of molecules, leading to extraction of characteristic parameters of the graphene FET accordingly.

The external feedback effect on the relative intensity noise (RIN) characteristics of blue InAlGaN laser diode has been analyzed taking into account the spontaneous emission noise and the injection current for the high frequency modulation. A Langevin diffusion model was exploited to characterize its relative intensity noise. The simulation parameters were quantitatively evaluated from the optical gain properties of the InAlGaN multiple quantum well active regions by using the multiband Hamiltonian for the strained wurtzite crystals. The extracted parameters were then applied to the rate equations taking into account the external feedback and the high frequency modulation current. The RIN characteristics were investigated to optimize the low frequency laser diode noise characteristics.

We have fabricated and measured electrooptic modulator using coupled stack InAs/InGaAs quantum dots. The height of the quantum dot is 16 nm and quantum dots are stacked including an InGaAs capping layer. The peak wavelength of photoluminescence is 1260 nm at room temperature and 1158 nm at 12 K. The operation characteristics of the quantum dots show high modulation efficiency of electrooptic modulator at 1550 nm compared to that of existing III-V bulk and MQW type semiconductor. The measured switching voltage () is 540 and 600 mV, for TE mode and TM mode, respectively. From the results, the modulation efficiency can be determined as 333.3 and for TE and TM modes. The results reported here may lead to the design and fabrication of a novel electrooptic modulator with low switching voltage and high efficiency.

The miniband and minigap structures of the lateral superlattice quantum wires in grid-inserted quantum well are analyzed by using a self-consistent finite-element method with a periodic boundary condition. Conduction band diagram and the mobile charge concentration as well as the energy dispersion relation are self-consistently analyzed. It is shown that even a few monolayers of AlAs at the center of the GaAs quantum well can create a minigap greater than 10 meV resulting in anisotropic carrier transport.

Single-mode P–p–n–N InGaAsP/InP ridge waveguide phase modulators have been fabricated and investigated at 1.55 µm. The ridge waveguide structure has been designed using a finite element method, grown by metal-organic-chemical-vapor-deposition (MOCVD), and fabricated by chemical wet etching. Their phase modulation characteristics were measured by using the Fabry–Perot resonance method with a tunable laser. The measured phase modulation efficiency for a 2-mm-long device was determined to be as high as 34 deg/Vmm for the TE mode. This value corresponds to the highest experimental electrooptic modulation efficiency reported thus far for InGaAsP/InP DH-type phase modulators at the said wavelength region.

The effects of strain distribution in quantum wire arrays have been analyzed using a finite-element method including both the hydrostatic and shear strain components. Their effects on the optical properties of the quantum wire arrays are assessed for various types of stress profiles by calculating the optical gain and the polarization dependence. The results show unique polarization dependency, which can be exploited either for the single polarization or the polarization-independent operation in quantum wire photonic devices.

A numerical approach for the analysis of quantum wire structures has been presented using a finite-element method which includes the strain analysis and the band analysis of the Luttinger-Kohn Hamiltonian with the deformation potential. A systematic implementation of the multiband Hamiltonian in the finite-element scheme is outlined and the corresponding variational functional is derived for arbitrarily shaped strained quantum wire arrays. This method is then applied to calculate the band structures of strained quantum wire arrays.

The anisotropic transport properties of quantum dot arrays fabricated by the nanoimprinted multilayer quantum wires have been investigated. The vertical transport characteristics are estimated by the carrier capture time from the electron reservoir to the low dimensional structures, which turned out to be longer than the spontaneous emission lifetime. The lateral transport characteristics are modeled after the quantum conductance between quantum dot arrays which are readily available from the miniband structures. The resulting lateral transport revealed that lateral quantum conductance can be minimized when the Fermi level is kept at the center of the miniband gap when the gap is larger than 4kT.

Rectangular microring resonators containing active and passive sections are fabricated and characterized with various multimode-interference (MMI) lengths. The optimum MMI length and width turn out to be 110 and 9 µm, respectively. The material platform and fabrication process used are the same used for other active and passive devices except for a deep etch step. Hence such resonators are easily integrated with other active and passive devices. A free spectral range of approximately 244 GHz is observed with an on–off ratio of 13 dB.

Novel rectangular ring lasers containing active and passive sections are fabricated and characterized. The rectangular laser cavity is formed using four low-loss total internal reflection (TIR) mirrors and an output coupler made out of passive three coupled waveguides. The fabrication process is exactly the same as for other active and passive devices except for one deep etch step for TIR mirror fabrication. Two different lasers having active section lengths of 250 and 350 mum and total cavity lengths of 580 and 780 mum are fabricated. For both devices, lasing thresholds of 38mA are obtained at room temperature and under continuous-wave operation. Lasing is predominantly single-mode with a sidemode suppression ratio better than 20 dB. The power loss of a single TIR mirror is also determined to be about 0.5 dB. Such low-loss TIR mirrors enabled lasers with very small footprints

We report characterization and modeling of serpentine superlattice nanowire-array lasers. These samples were grown by molecular beam epitaxy on (100) n/sup +/-GaAs vicinal substrates. In-plane ridge-waveguide lasers with ridge stripes either parallel or perpendicular to the nanowire arrays have been characterized at low temperatures. The measured net gain spectra at 1.4 K showed strong optical gain anisotropy such that the TM mode gain became greater than the TE mode gain when the optical cavity was placed along the nanowire direction. This provides strong evidence that the lateral quantum confinement in the serpentine superlattice is stronger than the vertical quantum confinement. Optical gain spectra in the serpentine superlattice are calculated with consideration of coupling between wires and homogeneous line broadening. A good fit to the measured polarization-dependent gain spectra is achieved when the lateral Al segregation and the homogeneous line broadening are chosen to be 8% and 7 meV, respectively. This small but finite Al segregation in the serpentine superlattice provides lateral quantum confinement for holes, which results in significant anisotropy in the relation between net gain and injection current density,. >

The valence subband dispersion of quantum-wire arrays grown on vicinal substrates in GaAs-Al/sub x/Ga/sub 1-x/As material system is calculated using a finite-element method with periodic boundary conditions. The variational functional for the Luttinger-Kohn Hamiltonian is derived using the integration by parts with proper boundary conditions. The validity of this method is confirmed by calculating subband structure of quantum wells and rectangular quantum wires. Along with the electronic band structure, a detailed study of gain in the quantum-wire arrays with rectangular and serpentine shapes is presented, including the effect of coupling between wires and polarization dependence of the momentum matrix element. Finally, these results are compared to those of quantum wells. >

The nonlinear gain suppression coefficients of GaN-based MQW LDs at high output power have been extracted from the measured optical spectra by using a self-consistent multiband Hamiltonian equations along with the density matrix formulation taking into account the strain effects and piezoelectric effects.

The optical gain properties of the quantum dot arrays fabricated by the edge-defined nanowires have been investigated to quantitatively assess the modulation bandwidth for various minibandgap of the quantum dot arrays on GaN wurtzite substrate.

The optical characteristics of GaN-based MQW LDs such as the linear and nonlinear optical gain have been investigated by a self-consistent analysis of the multiband Hamiltonian taking into account the strain effects and piezoelectric effects in the wurtzite crystal. The nonlinear optical gain properties at high power density have also been investigated experimentally and the gain suppression coefficients were extracted by comparing measured spectra with the calculation results from the density matrix formulation.

We have modeled the lateral quantum confinement in a GaAs quantum well due to partial strain release on the side walls of an InGaAs stressor located on the top of the well. We used the finite element method to solve both the continuum elasticity equation and the Luttinger four‐band Hamiltonian with strain. This model was used to systematically study the wire width dependence of lateral band edge modulation, subband splitting, and relative transition strength in the strain‐induced quantum well wire structures.

The relative intensity noise (RIN) characteristics in blue laser diodes on wurtzite AlGaInN MQW structures were investigated using the rate equations with the quantum Langevin noise model. The device parameters were extracted from the band structures of the MQW active region by using the self-consistent multiband Hamiltonian for the strained wurtzite crystal structure.

The quantum noises in typical Blu‐ray laser diodes have been modeled after the quantum Langevin formalism into three level rate equations. The required material parameters have also been extracted by using the multiband Hamiltonian for strained wurtzite crystals. The results reveal the existence of an optimum current modulation level to minimize the relative intensity noise.

The RIN characteristics in AlGaInN LDs were investigated using the rate equations with the quantum Langevin noise model. The device parameters were extracted by using the self-consistent multiband Hamiltonian for the strained wurtzite crystal.

Novel triangular ring resonators combining extremely small multimode-interference (MMI) coupler, low loss total internal reflection (TIR) mirrors, and semiconductor optical amplifiers are reported for the first time. The MMI length of 90 microm is among the shortest reported. The incidence angle of the TIR mirror inside the resonator is 22 degrees. A free-spectral range of approximately 2 nm is observed near 1550 nm along with an on-off ratio of 17 dB. The triangular resonators with a sharp angle are very attractive components due to their promise of compact size and high levels of integration. Therefore, large numbers of resonators can be integrated on a chip to increase functionality in future optical wavelength division multiplexing system.

We report a single-mode P-P-p-i-n-N-N GaAs/AlGaAs W waveguide phase modulator with a high phase modulation efficiency and a low propagation loss. The phase modulator with a W-shaped refractive-index profile utilizes a novel epilayer structure to reduce the propagation loss associated with doped layers and to obtain a phase modulation efficiency larger than those of P-i-N double heterostructure modulators. The phase shift and propagation loss were measured with a Fabry-Perot resonance method at 1.31-mum wavelength. A phase modulation efficiency as high as 34.6 degrees /V mm was measured for TE polarized light. Also propagation losses of less than 0.6 dB/cm were achieved. As a result, the W waveguide phase modulator that exhibits a high phase modulation efficiency and a low propagation loss have been experimentally realized for the first time as far as we know.

The lasing characteristics of three-guide coupled ring lasers using the self-aligned total internal reflection (TIR) mirrors were investigated numerically and experimentally. The rectangular laser cavity consists of four low loss TIR mirrors and an output coupler made out of passive three coupled waveguides. Two different lasers having active section lengths of 250 and 350 μm and total cavity lengths of 580 and 780 μm are fabricated. For both devices lasing thresholds of 38 mA is obtained at room temperature and under CW operation. Lasing is predominantly single mode with the side mode suppression ratio better than 20 dB.

A low-frequency finite-element method (FEM) developed to calculate the impedance of multi-strip-line electrodes on traveling-wave modulators is discussed. In this method, the divergence theorem is used to evaluate the electrode capacitance from the node potential values of discrete elements. This method is used to calculate the impedance of electrodes on anisotropic-inhomogeneous dielectric media. The effect of nonzero electrode thickness and a groove excavated at the electrode gap is analyzed. >

The strain effects on the optical gain properties of wurtzite InGaAIN multiple quantum well blue laser diode structures were investigated using the self-consistent method and the multiband Hamiltonian for the strained wurtzite crystal. 2% compressive strain gave up to 60% enhancement to the differential gain as well as 15 nm blue shift in the lasing wavelength.

We investigate the properties of a multimode-interference (MMI) coupled micro ring cavity resonator with total-internal-reflection (TIR) mirrors and a semiconductor optical amplifier (SOA). The TIR mirrors were fabricated by the self-aligned process with a loss of 0.7 dB per mirror. The length and width of an MMI are 142 mm and 10 mm, respectively. The resulting free spectral range (FSR) of the resonator was approximately 1.698 nm near 1571 nm and the extinction ratio was about 17 dB. These devices might be useful as optical switching and add-drop filters in a photonic integrated circuit or as small and fast resonator devices.

A modulation efficiency enhancement scheme for an InGaAsP waveguide-coupled micro-ring cavity resonator utilizing the self-aligned total internal reflector mirrors was proposed and investigated numerically and experimentally. Unlike the conventional electroabsorption modulators, the micro-ring cavity resonator was found to exhibit a singular modulation characteristics depending on the coupling coefficient between the micro-ring cavity and the input/output waveguide, which can be exploited to enhance the optical modulation efficiency as well as the extinction ratio.

We investigate the properties of novel ring cavity resonator based on InGaAsP material system using various multimode interference lengths. Optimum multimode interference length and on-off ratio are 110 mum and 13 dB, respectively.

The external feedback effect on the relative intensity noise characteristics of 405 nm InAlGaN laser diode has been analyzed taking into account the spontaneous emission noise and the high frequency modulation of the injection current. A Langevin diffusion model was exploited to characterize its relative intensity noise. The spontaneous emission noise components were quantitatively evaluated from the optical gain properties of the InAlGaN multiple quantum well active regions by using the multiband Hamiltonian for the strained wurtzite crystals. The extracted parameters were applied to the rate equations taking into account the external feedback and external current modulation effects. The simulation results were investigated to optimize the relative intensity noise characteristics.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper, the lasing characteristics of waveguide micro-ring cavity devices utilizing self-aligned total internal reflectors were analyzed by using a finite-difference time domain (FDTD) method and a transfer-matrix method (TMM). The simulation algorithm utilized a 2D FDTD combined with effective index method to analyze the total internal reflectors fabricated by the self-aligned SiN masks for RIE and re-growth. The whole micro-ring cavity performance was analyzed by using a TMM incorporating the device parameters extracted from the FDTD analysis. The simulation results were compared with the experimental results, which showed a good agreement.

Novel ring resonators combining very small multimode interference (MMI) couplers, low loss total internal reflection (TIR) mirrors, and a semiconductor optical amplifier in InGaAsP material system are reported for the first time. The MMI length of 113 /spl mu/m is among the shortest reported. Average TIR mirror loss is about 1.1 dB per mirror. The material platform and fabrication process used are the same used for other active and passive devices except for a deep etch step. Hence, such resonators are easily integrated with other active and passive devices. A free spectral range of approximately 2 nm is observed near 1568 nm along with an on-off ratio of 14 dB, a full-width at half-maximum of about 0.3 nm, a finesse of more than 6, and a Q-factor of more than 4900.