导光板注塑成型技术的研究

导光板注塑成型技术是一种通过光学网点转移的方法成型导光板的技术,即将融熔树脂注入带光学网点的模具型腔,经过保压、冷却后脱模得到导光板,注塑成型得到的导光板具有模具型腔(stamper部分)所赋予的光学网点,这些网点的凹凸性和模具型腔网点的凹凸性互补。介绍了该技术的基本原理,通过工艺试验优化了相关工艺参数,证明了该技术用于导光板生产具有较高的精度和效率。     

Generation and Concentration of Terahertz Radiation in a Microcavity with an Open Quantum Dot

A scheme to generate terahertz radiation by an array of quantum dots localized at the center of a semiconducting heterostructure is developed. Electrons are injected into the active part due to the source and drain Fermi energy difference induced by a dc electric field. The structure is placed inside a microcavity stimulating the electronic transition in the quantum dots accompanied by the emission of a photon to the cavity mode. This process is optimized using the filters formed by the quantum wells, which facilitate the electron density concentration in a quantum dot. The electromagnetic field radiated by the cavity in the waveguide can be used for a local effect on the charge qubits. The parameters of such a source depend on the working characteristics of the quantum dots and cavity.     

Quantum operations on charge qubits with the electrostatic control in semiconductor cavities

We consider one- and two-qubit operations on charge qubits that represent double quantum dots with one electron in each of them. The dots are formed inside a high-Q semiconductor cavity (disk, toroidal, or spherical) in the antinodes of one of its optical eigenmodes; the frequencies of the transitions between the ground (logic) and excited (auxiliary) states of the discrete electron spectrum in quantum dots are close to the frequency of this mode. The precise tuning of the transition frequency is performed by applying an electric potential on the qubit control gate. Within the model of qubits coherently interacting with a cavity quantum field, a few methods for controlling their states are developed. In particular, we propose different variants for implementing two-qubit CNOT and CZ gates and generating qubit entangled states. By the example of a micro-disk cavity, we calculate the operating characteristics that ensure a high rate of quantum gate implementation.     

Power conversion efficiency of quantum dot laser diodes

The power conversion efficiency of laser diodes with an array of quantum dots in the active region is analyzed. A model is proposed which allows analytical determination of the optimal cavity length corresponding to the highest conversion efficiency for a given output power. A comparison is made with experimental data for high-power lasers based on submonolayer quantum dots emitting at 0.94 μm. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 5, 2000, pp. 628–632. Original Russian Text Copyright ? 2000 by Zhukov, Kovsh, Mikhrin, Maleev, Odnoblyudov, Ustinov, Shernyakov, Kondrat’eva, Livshits, Tarasov, Ledentsov, Kop’ev, Alferov, Bimberg.     

Implementation of a Two-Qubit C-NOT Quantum Gate in a System of Two Double Quantum Dots,a Microcavity,and a Laser

We study the possibility of implementing a two-qubit controlled-NOT gate operation in a structure consisting of two semiconductor double quantum dots placed in a high-Q optical microcavity and governed by a resonant laser field. The effect of relaxation processes on the dynamics of the two-electron system is discussed. The dissipation rates allowing quantum error correction algorithms to be used are determined. The existing additional excitation channel (laser pulse) is shown to weaken the effect of the nonideality of the cavity on the evolution of the states. Optimal electron coupling coefficients in the quantum dots with control fields are fitted, in which the controlled qubit is switched with the highest probability and the gate implementation takes several hundreds of picoseconds.     

Role of thermal ejection of carriers in the burning of spatial holes in quantum dot lasers

The role of thermal carrier ejection from quantum dots and free carrier diffusion in the burning of spatial holes in semiconductor quantum dot lasers is analyzed. The balance of the spatially inhomogeneous population inversion in the longitudinal direction of the cavity is shown to be controlled by thermal ejection from quantum dots. Because of this circumstance, hole burning in quantum dot lasers can show up more strongly and the threshold for multimode lasing can be lower than in semiconductor lasers with three-dimensional active regions or quantum-well lasers. The threshold for multimode lasing is determined as a function of the dispersion in the quantum dot size, cavity length, and temperature for structures that have been optimized to minimize the threshold current density of the fundamental mode. Fiz. Tekh. Poluprovodn. 33, 1076–1079 (September 1999)     

Excitonic dynamics of a quantum dot coupled to a laser-driven semiconductor microcavity

Within the density matrix formalism, we report on the quantum control of the excitonic coherences in quantum dots coupled to a single mode field resonant semiconductor cavity. We use an external classical laser field to drive the dynamical response of the excitonic states. Dissipation mechanisms associated with the cavity field and the excitonic states are explicitly included in the model. Our numerical simulations of the excitonic dynamics are in good agreement with recent experimental reports. Furthermore, we compute and show how to tailor such a dynamics in the presence of the laser field by means of controlling the detuning between the laser and the cavity field frequencies. The results are analyzed with a view to implementing quantum control of local qubit operations.     

Possibility of room temperature intra-band lasing in quantum dot structures placed in high-photon density cavities

We study the possibility of room temperature intraband lasing in quantum dots placed in high-photon density cavities. In general, if intra-band population inversion is to created in a quantum well by carrier injection at the barrier energy, it is necessary that the electron intra-band energy relaxation times are long. Additionally the bandedge electron-hole recombination times should be short. The use of sub-two-dimensional structures (quantum dots) allows us to increase the intra-band energy relaxation time from about a picosecond for bulk or quasi-two-dimensional systems to several hundred picoseconds at room temperatures. Also, by placing these structures in a high coherent photon density optical cavity, it is possible to decrease the bandedge electron-hole recombination times through stimulated emission. Our studies show that strong population inversion is possible at room temperature in such systems. Gain versus injection curves are also calculated.     

High-power 1.5 µm InAs-InGaAs quantum dot lasers on GaAs substrates

Light-current, spectral, and temperature characteristics of long-wavelength (1.46–1.5 μm) lasers grown on GaAs substrates, with an active area based on InAs-InGaAs quantum dots, are studied. To reach the required lasing wavelength, quantum dots were grown on top of a metamorphic InGaAs buffer layer with an In content of about 20%. The maximum output power in pulsed mode was 7 W at room temperature. The differential efficiency of the laser, which had a 1.5-mm-long cavity, was 50%. The temperature dependence of the threshold current is described by a characteristic temperature of 61 K in the temperature range 10–73°C. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 6, 2004, pp. 763–766. Original Russian Text Copyright ? 2004 by Maksimov, Shernyakov, Kryzhanovskaya, Gladyshev, Musikhin, Ledentsov, Zhukov, Vasil’ev, Kovsh, Mikhrin, Semenova, Maleev, Nikitina, Ustinov, Alferov.     

腔耦合量子点系统的非常规几何量子计算

提出了在量子点与腔相互作用系统中，利用双拉曼过程来实现非常规几何量子逻辑门方案。在本方案中，所有的演化本身与腔场态无关，因而对热场是不敏感的。在总位相中既包含有几何位相,又包含有动力学位相,但它的确仅依赖于量子态演化的整体几何特征。通过调节耦合常数和失谐量来选择我们所要的量子控制门，在实际的操作中不需要考虑消除动力学相位问题因而易于操作，且避免因消除动力学相位引入的误差。     

Characteristics of pH sensors fabricated by using protein-mediated CdSe/ZnS quantum dots

The pH sensors using protein-mediated CdSe/ZnS quantum dots in an electrolyte-insulator-semiconductor (EIS) structure have been investigated. The hydrophobic cylindrical cavity of the chaperonin (GroEL) protein template was used to trap CdSe/ZnS quantum dots on hydrophobically treated SiO₂ surface. The CdSe/ZnS quantum dot with a small diameter of 3.98 nm is observed by atomic force microscope. A fair pH response with a sensitivity of 39 mV/pH and a linearity of 99.48% are obtained by using CdSe/ZnS quantum dot based EIS sensor, while those values are found to be 53 mV/pH and 99.95% for bare SiO₂ based EIS pH sensors. The pH response and linearity of CdSe/ZnS based quantum dot sensors are inferior (slightly) as compared to the bare SiO₂ sensors owing to the initial negative charges of CdSe quantum dots membrane, which has been explained by energy band diagrams. It is expected that this kind of quantum dot membrane can be useful in future bio-molecule detections.     

1.3-μm CW lasing characteristics of self-assembled InGaAs-GaAsquantum dots

This paper presents the lasing properties and their temperature dependence for 1.3-μm semiconductor lasers involving self-assembled InGaAs-GaAs quantum dots as the active region. High-density 1.3-μm emission dots were successfully grown by the combination of low-rate growth and InGaAs-layer overgrowth using molecular beam epitaxy. 1.3-μm ground-level CW lasing occurring at a low threshold current of 5.4 mA at 25°C with a realistic cavity length of 300 μm and high-reflectivity coatings on both facets. The internal loss of the lasers was evaluated to be about 1.2 cm^-1 from the inclination of the plots between the external quantum efficiency and the cavity length. The ground-level modal gain per dot layer was evaluated to be 1.0 cm^-1, which closely agreed with the calculation taking into account the dot density, inhomogeneous broadening, and homogeneous broadening. The characteristic temperature of threshold currents T₀ was found to depend on cavity length and the number of dot layers in the active region of the lasers. A T₀ of 82 K was obtained near room temperature, and spontaneous emission intensity as a function of injection current indicated that the nonradiative channel degraded the temperature characteristics. A low-temperature study suggested that an infinite T₀ with a low threshold current (~1 mA) is available if the nonradiative recombination process is eliminated. The investigation in this paper asserted that the improvement in surface density and radiative efficiency of quantum dots is a key to the evolution of 1.3-μm quantum-dot lasers     

On the physics of semiconductor quantum dots for applications in lasers and quantum optics

The progression of carrier confinement from quantum wells to quantum dots has received considerable interests because of the potential to improve the semiconductor laser performance at the underlying physics level and to explore quantum optical phenomena in semiconductors. Associated with the transition from quantum wells to quantum dots is a switch from a solid-state-like quasi-continuous density of states to an atom-like system with discrete states. As discussed in this paper, the transition changes the role of the carrier interaction processes that directly influence optical properties. Our goals in this review are two-fold. One is to identify and describe the physics that allows new applications and determines intrinsic limitations for applications in light emitters. We will analyze the use of quantum dots in conventional laser devices and in microcavity emitters, where cavity quantum electrodynamics can alter spontaneous emission and generate nonclassical light for applications in quantum information technologies. A second goal is to promote a new connection between physics and technology. This paper demonstrates how a first-principles theory may be applied to guide important technological decisions by predicting the performances of various active materials under a broad set of experimental conditions.     

Optically pumped intersublevel MidInfrared lasers based on InAs-GaAs quantum dots

We propose an optically pumped laser based on intersublevel transitions in InAs-GaAs pyramidal self-assembled quantum dots. A theoretical rate equations model of the laser is given in order to predict the dependence of the gain on pumping flux and temperature. The energy levels and wave functions were calculated using the 8-band k/spl middot/p method where the symmetry of the pyramid was exploited to reduce the computational complexity. Carrier dynamics in the laser were modeled by taking both electron-longitudinal optical phonon and electron-longitudinal acoustic phonon interactions into account. The proposed laser emits at 14.6 /spl mu/m with a gain of g/spl ap/ 570 cm/sup -1/ at the pumping flux /spl Phi/=10/sup 24/ cm/sup -2/ s/sup -1/ and a temperature of T=77 K. By varying the size of the investigated dots, laser emission in the spectral range 13-21 /spl mu/m is predicted. In comparison to optically pumped lasers based on quantum wells, an advantage of the proposed type of laser is a lower pumping flux, due to the longer carrier lifetime in quantum dots, and also that both surface and edge emission are possible. The appropriate waveguide and cavity designs are presented, and by comparing the calculated values of the gain with the estimated losses, lasing is predicted even at room temperature for all the quantum dots investigated.     

微腔调制常温Ge量子点光致发光特性

报道了微腔对Ge量子点常温光致发光的调制特性. 生长在SOI硅片上的Ge量子点的常温光致发光呈多峰分布，随波长增加，峰与峰之间的间隔增加. 这种多峰结构与SOI硅片所形成的微腔有关，只有满足特定波长的光致发光才能透出腔体并被探测器搜集. 模拟结果与实验结果吻合得很好，变功率实验也进一步证实了该结论.     

Theoretical calculation of lasing spectra of quantum-dot lasers:effect of homogeneous broadening of optical gain

A theoretical calculation is presented for the effect of homogeneous broadening of optical gain on lasing spectra of quantum-dot lasers. Based on a coupled set of rate equations considering both the size distribution of quantum dots and a series of longitudinal cavity modes, we show that dots with different energies start lasing independently due to their spatial localization when the gain spectrum is a delta-like function, and that the dot ensemble contributes to a narrow-line lasing collectively under large homogeneous broadening. The result explains quite excellently the experimental lasing spectra found in self-assembled InGaAs-GaAs quantum-dot lasers     

Quantum-Dot Sources for Single Photons and Entangled Photon Pairs

Quantum dots show excellent promise as triggered sources of both single and polarization entangled photons for quantum information applications. Our recent progress developing nonclassical light sources with single quantum dots is presented in this paper. Following radiative emission of an exciton confined in a quantum dot, there is a finite delay before re-excitation can occur; this results in an anti-bunching of the photons emitted providing a source of single photons. Excitation of a quantum dot with two electrons and two holes leads to the emission of a pair of photons; we show here that, provided the spin splitting of the intermediate exciton state in the decay is erased, the photon pair is emitted in an entangled polarization state. The fidelity of this entangled state is shown to exceed 70%. Using quantum dots to generate quantum light allows contacts for electrical injection to be integrated into a compact and robust device. A cavity may also be integrated into the semiconductor structure to enhance the photon collection efficiency and control the recombination dynamics. We detail a process to form a submicrometer current aperture within an electrical device, allowing individual quantum dots to be addressed electrically in devices.     

Room-temperature lasing in microring cavities with an InAs/InGaAs quantum-dot active region

Microring cavities (diameter D = 2.7–7 μm) with an active region based on InAs/InGaAs quantum dots are fabricated and their characteristics are studied by the microphotoluminescence method and near-field optical microscopy. A value of 22 000 is obtained for the Q factor of a microring cavity with the diameter D = 6 μm. Lasing up to room temperature is obtained in an optically pumped ring microlaser with a diameter of D = 2.7 μm.     

Quantum dot semiconductor lasers of the 1.3 μm wavelength range with high temperature stability of the lasing wavelength (0.2 nm/K)

Lasers that emit in the 1.3 μm wavelength range and include the active region based on InAs quantum dots were grown by the method of molecular-beam epitaxy and have been studied. The cavity includes a multilayer interference reflector, which brings about the fact that a large factor of optical confinement and low leakage losses are obtained only for the light propagating at some angle and, consequently, having a strictly definite wavelength. It is shown that, due to the use of such a waveguide structure, the temperature shift of the lasing wavelength is 0.2 nm/K, which is 2.5 times smaller than this shift in the lasers with quantum dots and with a conventional structure of the waveguide. The lasers with the stripe-contact width W = 10 μm exhibited the spatially single-mode emission, which verifies the advantages of the suggested nonconventional structure of the optical waveguide.

     

Characterization and analysis of two-dimensional GaAs-based photonic crystal nanocavities at room temperature

This paper describes the design and fabrication process of a two-dimensional GaAs-based photonic crystal nanocavity and analyzes the optical characterization of cavity modes at room temperature. Single InAs/InGaAs quantum dots (QDs) layer was embedded in a GaAs waveguide layer grown on an Al_0.7Ga_0.3As layer and GaAs substrate. The patterning of the structure and the membrane release were achieved by using electron-beam lithography, reaction ion etching, inductively coupled plasma etching and selective wet etching. The micro-luminescence spectrum is recorded from the fabricated nanocavities, and it is found that some high-order cavity modes are clearly observed besides the lowest-order resonant mode is exhibited in spite of much high rate of nonradiative recombination. The variance of resonant modes is also discussed as a function of r/a ratio and will be used in techniques aimed to improve the probability of achieving spectral coupling of a single QD to a cavity mode.