Symmetrically glass-clad photonic crystal nanocavities with ultrahigh quality factors

We design and fabricate ultra-high-quality (Q) photonic nanocavities in a symmetrically glass-clad silicon (Si) two-dimensional (2D) photonic crystal (PhC) structure. We theoretically investigate the dependence of the refractive index of the glass on the Q factors for asymmetric and symmetric structures. We show that the index-symmetric distribution of the glass is a critical factor to realize ultrahigh Q factors for glass-clad 2D PhC structures. We fabricate symmetrically glass-clad Si PhC nanocavities and achieve a record Q factor of 1×10(6), comparable with the highest Q factors of nanocavities in air-bridge structures.     

Design,fabrication and optical characterization of GaAs photonic crystal nanocavity lasers with InAs quantum dots gain wafer-bonded onto Si substrates

We designed and fabricated III–V compound semiconductor two-dimensional photonic crystal (PhC) thin film slabs with quantum dots (QDs) inside formed on Si substrates for highly integrated silicon photonic circuits with built-in nanolasers. Defect-shifted L3 type PhC nanocavities formed in GaAs thin films embedding 1.3 μm-emitting InAs QDs layer-transferred onto Si substrates were investigated. Quality factors <1000 for the PhC nanocavities on SiO₂ were enhanced up to ∼8000 by removing SiO₂ to form air-bridge structures, resulting in room temperature, continuous wave lasing.     

Reconfigurable photonic crystal circuits

We describe progress in the field of tuning, (re)configuration of Photonic crystal (PhC) based devices with a particular emphasis on our recent concepts and techniques that we have developed to tune and/or reconfigure the properties of photonic crystal nanocavities. We show how our hybrid approach based on photosensitive material and tapered silica fiber can tune the (Q, λ) properties of preexisting Photonic crystal cavities. We describe our alternative techniques to create ‘a posteriori’ spatially (re)configurable high‐Q cavities in a PhC platform. We show that optofluidics – the fusion of microfluidics with photonic devices – offers an unquestionable added value to the quest of a truly versatile, (re)configurable photonic crystal based photonic chip.     

Design of a novel sensor based on tapered photonic crystal with negative refraction structures

We report a novel design of an ultracompact sensor consisting of two-dimension photonic crystal with negative refraction coupled to a taper ended by multicavity structure. It is shown that this system exhibits promising properties in the area of sensing. The presence of nanocavities enables the detection of small amount of analytes. By controlling their radii, a large quality factor, Q is reached. It is demonstrated that the quality factor is a key parameter in determining the sensitivity to the analytes.     

Effect of Gaussian acoustic nanocavities in a narrow constriction on ballistic phonon transmission

We investigate the effect of Gaussian acoustic nanocavities in a narrow constriction on ballistic phonon transport through a semiconductor nanowire at low temperatures. When the transverse width of acoustic nanocavities takes a Gaussian function, it is found that the resonant peaks and band gaps in transmission spectra are obvious, indicating that the system has selective transmission and filters actions for ballistic phonons. The number and length of nanocavities have significant effects on the phonon transmission and thermal conductance. The results are compared with those in uniform width acoustic nanocavities. The Gaussian acoustic nanocavities are therefore a promising phononic device to manipulate ballistic phonons in nanophononics.     

Analysis of a diode-pumped Nd:YVO4 laser passively Q switched with GaAs

A diode-pumped Nd:YVO₄ laser passively Q switched with GaAs is studied theoretically and experimentally. We have demonstrated the influence of single-photon absorption, two-photon absorption and free-carrier absorption in GaAs on the Q-switched pulse characteristics. The pulse profile, pulse energy and pulse width of the Q switching with GaAs are simulated by using the conventional rate equations of the four-level laser system. The experimental results show reasonable agreement with the theoretical results on the whole.     

GaAs被动调Q兼输出耦合Nd∶YVO4激光特性研究

利用可饱和吸收半导体GaAs作为被动调Q元件和FP输出耦合镜,实现了半导体激光器(LD)抽运Nd:YVO4激光调Q运转,获得脉宽度为47ns,重复频率为1183kHz,平均功率为430mW,光束质量为M2=113的TEM00激光基横模输出,调Q抽运阈值为1700mW.并数值求解了含有GaAs被动调Q兼输出耦合的速率方程,分析了GaAs被动调Q机理以及脉宽宽度、重复频率、平均功率随抽运速率、腔长的变化关系,理论与实验结果相一致.为多功能综合型微型调Q固体激光器提供了简单有效的方法. 关键词： 被动调Q 输出耦合 GaAs     

Ballistic phonon transport through a Fibonacci array of acoustic nanocavities in a narrow constriction

We investigate the ballistic phonon transport through a Fibonacci array of acoustic nanocavities in a narrow constriction of a semiconductor nanowire at low temperatures. It is found that the transmission spectrum of such a system consists of quasiband gaps and narrow resonances caused by the coupling of phonon waves. Both phonon transmission and thermal conductance exhibit the similarity due to the Fibonacci sequence structure. The similarity is sensitive to the number n and parameters of nanocavities. The results are compared with those in a periodic acoustic nanocavities.     

Advances in photonic crystals with MEMS and with semiconductor quantum dots

We discuss photonic crystals (PCs) with a microelectromechanical system (MEMS) and semiconductor quantum dots (QDs) as novel classes of PC devices. Integration of MEMS structures into PC devices enables one to realize several kinds of functional devices, such as modulators, switches, and tunable filters for highly integrated photonic circuits. We describe the basic concept of MEMS-integrated PC devices and show numerical and experimental demonstrations of MEMS-integrated functional PC devices. On the other hand, QDs are promising candidates for active media in PC devices. Spontaneous emission control of QD emission in PC nanocavities is especially important for novel optoelectronic devices and quantum information devices. In PC nanocavities, the interaction between QD excitons and photons is enhanced dramatically. The control of spontaneous emission spectrum and the enhancement of the luminescence intensity of InAs QDs by PC nanocavities are demonstrated at telecommunication wavelengths. The Purcell effect for ensemble and single QDs in PC nanocavities are also discussed.     

On the temperature dependence of the electronic states and the mobility in AlGaAs/GaAs heterostructures

Experiment shows that in AlGaAs/GaAs heterostructures the sheet electron concentration remains almost constant up to a certain temperature, while it increases at higher temperatures. We attempt an interpretation of this temperature dependence, taking into account the fact that in the bulk, n-AlGaAs deep and shallow donors exist, which independently and by different mechanisms provide electrons to the different conduction band minima of the bulk n-AlGaAs, and contribute to the formation of the Q2DEG. We calculate the electronic states of this structure, the Q2DEG and the bulk concentrations, and the corresponding mobilities as a function of temperature. Our numerical results are in an excellent agreement with experimental data.PACS:     

Liquids on topologically nanopatterned surfaces

We report here surface x-ray scattering studies of the adsorption of simple hydrocarbon liquid films on nanostructured surfaces-silicon patterned by an array of nanocavities. Two different regimes, filling and growing, are observed for the wetting film evolution as a function of the chemical potential offset from the bulk liquid-vapor coexistence. The strong influence of geometrical effects is manifested by a dependence of liquid adsorption in the nanocavities that is stronger than the van der Waals behavior for flat surfaces. The observed dependence is, however, much weaker than predicted for the infinitely deep parabolic cavities, suggesting that the finite-size effects contribute significantly to the observed adsorption behavior.     

Enhanced efficiency of the second harmonic inhomogeneous component in an opaque cavity

In this Letter, we experimentally demonstrate the enhancement of the inhomogeneous second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612 nm, using 3 ps pump pulses having peak intensities of the order of 10 MW/cm(2). We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.     

Electronic states of self-organized InGaAs quantum dots on GaAs (3 1 1)B studied by conductive scanning probe microscope

We have used conductive scanning probe microscope (SPM) in high vacuum and operated at 173 K in order to investigate the electronic properties of self-organized InGaAs quantum dots (QDs) grown on GaAs (3 1 1)B and (0 0 1) substrates. Ordered InGaAs quantum dot arrays on GaAs (3 1 1)B surface were fabricated by atomic-H assisted molecular beam epitaxy (H-MBE), and Si SPM tips coated with Au which warrants electrical conductivity were used to measure simultaneously both the topographic and current images of QDs surface. From the current–voltage (I–V) curves, unique and different plateau features were observed for QDs formed on GaAs (3 1 1)B and (0 0 1) substrates. The results suggested that a high degree of symmetry of InGaAs QDs on (3 1 1)B was responsible for the observed degeneracy of electronic states and artificial atom-like states. We demonstrate that this conductive SPM technique becomes a powerful tool in studies of single electron charging of individual dots.     

Fast bistable all-optical switch and memory on a silicon photonic crystal on-chip

We demonstrate extremely low-power all-optical bistability by utilizing silicon photonic crystal nanocavities, based on the plasma effect of carriers generated by two-photon absorption. Owing to the high quality factor and the small volume of the nanocavities, the photon density inside the cavity becomes extremely high, which leads to a large reduction in operation power. Optical bistable operation in a single nanocavity permits optical read-write memory operation, which opens the possibility of an integrated optical logic circuit on a single chip, based on photonic crystals. The demonstrated bistable threshold power is 0.4 mW with a set pulse energy of 74 fJ, at a switching speed of <100 ps.     

AB initio calculation of the atomic and electronic structure for Sb adsorbed on GaAs(110)

We report results obtained by a systematic study of Sb adsorption on the relaxed GaAs(110) surface, using density-functional theory within the local-density approximation (LDA) and norm-conserving, fully separable, ab-initio pseudopotentials. The GaAs(110) surface is simulated by a slab geometry wherein the atomic structure of the Sb atoms at the preferred adsorption positions and the uppermost substrate layer is optimized by minimizing the total energy, in contrast to previously reported theoretical approaches obtaining the surface bandstructure for given geometrical equilibrium structures. Sb coverages of Q=1/2 and Θ=1 are considered. We give a detailed analysis of the total-energy surface of the Sb/GaAs(110) system and identify stable and metastable adsorption sites. The resulting equilibrium geometries are discussed: We interpret these results in terms of the Sb-Sb interaction within the chains parallel to the [1¯11] direction and of possible structural instabilities in such chains. The atomic positions are compared with results of LEED analysis, stating an overall agreement except the buckling of the chain atoms. The resulting electronic properties (surface bandstructure, photothreshold, Schottky barrier) are discussed within the context of experimental data available from STM, photoemission spectroscopy, etc.     

NMR and AFM investigations of nanocavities on the double rare-earth fluoride crystal surface

Nanocavities with a size of less than 30 nm on the crystal surface of superfine LiYF₄ powders and single crystals of the Van Vleck paramagnet LiTmF₄ were detected by nuclear magnetic resonance (NMR) cryoporometry and atomic-force microscopy (AFM) and liquid³He NMR cryoporometry. NMR investigations show that the nanocavities are evidently present on the surface of the LiYF₄ powder particles. The distribution of nanocavities has two maxima corresponding to the specific porous sizes of 3–5 and 10–15 nm. AFM investigations detect the presence of the nanocavities with sizes in the range 50–300 nm on the surface of powder particles and single crystals. The cases of powder microparticles and of a single crystal differ in the value of the parameter “surface roughness”, which is 14.5 and 11 nm, respectively. The mechanism of creation of nanocavities is proposed and verified by additional investigations with CaF₂ powders.     

GaAs被动调Q Nd:YAG激光器激光特性的研究

报道了用半导体材料 Ga As实现氙灯抽运 Nd:YAG激光器的被动调 Q运转 ,测量了激光器的阈值、脉冲宽度和输出能量。从 Ga As的能级结构出发 ,理论上研究了 Ga As材料的饱和吸收原理 ,建立了调 Q激光器速率方程并给出了数值解 ,对理论结果与实验结果进行了比较和讨论。     

Analysis and applications of nanocavity structures used as tunable filters and sensors

This paper reports on a novel design for a tunable filter and plasmonic sensor based on the metal–insulator–metal waveguide with a nanocavity resonator. Simulation results show that as a one-channel filter, the resonance wavelengths show a linear red-shift with an increase in nanocavity length with a slope of 1742 nm/μm and a nonlinear blue-shift with an increase in nanocavity width, respectively. A two-channel filter can be realized using two nanocavities and the arrangement of the two nanocavities with respect to the waveguide and the value of the distance between the nanocavities has only a marginal effect on the filter notch wavelength. Finally, both in-slit and out-slit refractive index plasmonic sensors are investigated with a sensitivity of 710 nm/RIU and 250 nm/RIU, respectively.     

Magnetoelectric Effect in Gallium Arsenide–Nickel–Tin–Nickel Multilayer Structures

Experimental data have been presented for the magnetoelectric effect in nickel–tin–nickel multilayer structures grown on a GaAs substrate by cathodic electrodeposition. The method of fabricating these structures has been described, and the frequency dependence of the effect has been demonstrated. It has been shown that tin used as an intermediate layer reduces mechanical stresses due to the phase mismatch at the Ni–GaAs interface and, thus, makes it possible to grow good structures with a 70-μm-thick Ni layer. The grown structures offer good adhesion between layers and a high Q factor.     

Coherent NMR Stark spectroscopy

We demonstrate phase-coherent Stark effects from a radiofrequency E field at twice the NMR frequency (2ω(0)) of (69)Ga in GaAs. The 2ω(0) phase (?(E)) selects component responses from the nuclear quadrupole Hamiltonian (H(Q)). This is possible by synchronizing few-μs 2ω(0) pulses with an NMR line-narrowing sequence, which averages the Stark interaction to dominate spectra on a background with 10(3)× enhanced resolution. Spectra vs ?(E) reveal relative sizes of tensorial factors in H(Q). Comparative modeling and numerical simulations evaluate spectral features unexplained by average Hamiltonian theory, and suggest improvements for quantitative calibration of individual response components. Application of this approach to bulk samples is of value to define Stark responses that may later be used to interrogate the internal electrostatics of structured samples.