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.     

Photon confinement in photonic crystal nanocavities

The quest for enhanced light‐matter interactions has enabled a tremendous increase in the performance of photonic‐crystal nanoresonators in the past decade. State‐of‐the‐art nanocavities now offer mode lifetime in the nanosecond range with confinement volumes of a few hundredths of a cubic micrometer. These results are certainly a consequence of the rapid development of fabrication techniques and modeling tools at micro‐ and nanometric scales. For future applications and developments, it is necessary to deeply understand the intrinsic physical quantities that govern the photon confinement in these cavities. We present a review of the different physical mechanisms at work in the photon confinement of almost all modern PhC cavity constructs. The approach relies on a Fabry‐Perot picture and emphasizes three intrinsic quantities, the mirror reflectance, the mirror penetration depth and the defect‐mode group velocity, which are often hidden by global analysis relying on an a posteriori analysis of the calculated cavity mode. The discussion also includes nanoresonator constructs, such as the important micropillar cavity, for which some subtle scattering mechanisms significantly alter the Fabry‐Perot picture.     

二维GaAs 基光子晶体微腔的制作与光谱特性分析

研究了以InAs量子点为有源区的二维GaAs基光子晶体微腔的设计与制作,测试并分析了室温下微腔的光谱特性.观察到了波长约为1137 nm,谱线半高宽度约为1 nm的尖锐低阶谐振模式发光峰.我们比较了不同刻蚀条件下光子晶体微腔的发光谱线,结果表明空气孔洞截面的垂直度是影响光子晶体微腔发光特性的重要因素之一.通过调节干法刻蚀工艺,改变空气孔半径与晶格常数的比率,可以在较大范围内调节谐振模式发光峰位置,达到谐振模式与量子点发光峰调谐的目的.     

Wide-field-of-view narrow-band spectral filters based on photonic crystal nanocavities

We describe a novel approach to implementing wide-field-of-view narrow-band spectral filters, using an array of resonant nanocavities consisting of periodic defects in a two-dimensional three-material photonic-crystal nanostructure. We analyze the transmissivity of this type of filter for a range of wavelengths and in-plane incidence angles as a function of the defect's refractive index, the number of layers in the photonic-crystal reflectors, and the period of the defects and find that this structure diminishes the angular sensitivity of the resonance condition relative to that of a standard multilayer filter.     

Charge controlled self-assembled quantum dots coupled to photonic crystal nanocavities

The system of charge controlled self-assembled quantum dots coupled to high-Q photonic crystal cavity modes is studied. The quantum dots are embedded in a p-i-n diode structure. Different designs of photonic crystal cavities are used, namely H1 and L3 and the Purcell effect is demonstrated. Furthermore, the fine tuning of the H1 cavity design is studied in order to achieve far field emission profiles that result in higher collection efficiency. An increase in the overall signal from the quantum dot when it is coupled to a cavity is observed, due to the Purcell effect and the improved collection efficiency. This together with the deterministic charging of the quantum dot that is demonstrated, can be used for a single electron spin measurement.     

Polarization properties of dipolelike defect modes in photonic crystal nanocavities

Far-field measurements of the in-plane polarization properties of spontaneous emission from optical nanocavities formed in two-dimensional photonic crystal slab waveguides are presented. A strong polarization signature, even subthreshold, is found for a pair of highly localized dipolelike resonant modes. This polarization signature is used to study the effects of symmetry lowering within the cavity.     

Single layer silicon photonic crystal slab

We present here the fabrication and characterization of single layer silicon photonic crystal mirror on a silicon-on-insulator wafer. By a combination of electron beam lithography, fast atom beam etching with deep reactive ion etching, silicon photonic crystal slabs are achieved on 260 nm freestanding silicon membrane and sandwiched with air on the top and bottom. Their high refractive index contrasts enable photonic crystal slabs function as dielectric mirrors for externally incident light. The optical performances of fabricated photonic crystal slabs can be tuned by varying the width of separation grooves or the air-hole size, which represents a significant advantage of offering various approaches for optical response control.     

Experimental investigation of thermo-optic effects in SiC and Si photonic crystal nanocavities

We experimentally investigate and compare the thermo-optic effects of silicon carbide (SiC) and silicon (Si) photonic crystal nanocavities on their resonant wavelengths over a temperature range of 25?°C to nearly 200?°C by using a laser source with a wavelength close to the telecommunication wavelength range of 1550?nm. The measured results clearly show that the shift in the resonant wavelength of the SiC cavity is significantly (by a factor of 3) less than that of the Si cavity for the same ambient temperature changes. In addition, the measured results provide direct estimates of the thermo-optic coefficients (dn/dT) for thin SiC and Si as 3.87×10(-5)/°C and 1.60×10(-4)/°C, respectively, for this temperature range.     

Designs of photonic crystal nanocavities for stimulated Raman scattering in diamond

Diamond is a good candidate for producing Raman laser due to its high first-order Raman gain coefficient. Since its Raman shift (~1,332.5 cm^?1) is large compared to other solid-state materials, it is possible to produce a Raman frequency converter using diamond crystals. Photonic crystals can be employed for confining photons within periodic structures, the scale of which is on the order of the incident wavelength, making it convenient for integrating all-optical circuits. Combining the merits of both diamond and photonic crystals, we present two designs of photonic crystal nanocavities (in hexagonal and square lattice structures) which can produce stimulated Raman lasing with low-threshold power. After optimizing the photonic bandgaps, triple resonant modes with high Q and small modal volume are realized in each design by tuning the radii of dot defects in the nanocavities. Numerical simulations show that for such designs, the threshold power for generating Raman lasers in the range of a few hundred nano-Watts can be achieved.     

Enhanced single-photon emission from quantum dots in photonic crystal waveguides and nanocavities

A theoretical formalism is presented to investigate enhanced radiative decay of excited dipoles in photonic crystal waveguides and nanocavities with a view to achieving efficient single-photon emission from embedded quantum dots. Surprisingly, large enhancement effects are achievable in both waveguides and nanocavities, and enhanced emission in the waveguide is shown to scale proportionally (inversely) with the photon group index (velocity). Further, a way to include radiative coupling of the quantum dot is shown, and the importance of its inclusion is subsequently demonstrated.     

Ultrahigh-quality photonic crystal cavity in GaAs

Membrane-based photonic crystal GaAs cavities with a double-heterostructure design were investigated. They show the highest quality factors for GaAs photonic crystal cavities to date, exhibiting quality factors higher than 10(5). The resonances of these cavities were fine-tuned in steps smaller than 2 nm by digital etching.     

Photonic crystal nanocavities in GaAs/AlGaAs with oxidised bottom cladding

We present a solution to the difficult task of removing an oxide-based hard mask from a photonic crystal fabricated in the GaAs/AlGaAs system. We use a polymer backfill technique to seal the AlGaAs layer, thereby making it inaccessible to the wet-etch solution. This allows us to use a GaAs active layer for the photonic crystal placed on an oxidised AlGaAs layer which provides mechanical and thermal support. Using this technique, we fabricated GaAs-based photonic crystal cavities and measured respectable quality factors (Q ≈ 2200) despite the intrinsic asymmetry of the system. The technique presents a viable method for producing electrically injected photonic crystal cavities for operation on a mechanically stable and thermally conducting buffer layer.     

Design and fabrication of bismith-silicate photonic crystal fiber

The process of design and fabrication of bismuth-silicate photonic crystal fiber (Bi-PCF) is reported. The Bi-PCF was fabricated by stack and draw method. This is the first trial of the fabrication of photonic crystal fiber made of bismuth-based glass with stack and draw method. The Bi-PCF structure was designed to reduce group-velocity-dispersion (GVD) in a plausible process. Thermal properties of the glass are investigated to establish the fabrication process. The applying pressure and pumping in fiber preform preparation were effectively utilized to control the air-hole diameter and arrangement. The fabricated Bi-PCF shows the well reduced GVD as the numerical calculation predicted. Fusion splicing between Bi-PCF and SMF-28 was also demonstrated.     

Simultaneous near field imaging of electric and magnetic field in photonic crystal nanocavities

The insertion of a metal-coated tip on the surface of a photonic crystal microcavity is used for simultaneous near field imaging of electric and magnetic fields in photonic crystal nanocavities, via the radiative emission of embedded semiconductor quantum dots (QD). The photoluminescence intensity map directly gives the electric field distribution, to which the electric dipole of the QD is coupled. The magnetic field generates, via Faraday's law, a circular current in the apex of the metallized probe that can be schematized as a ring. The resulting magnetic perturbation of the photonic modes induces a blue shift, which can be used to map the magnetic field, within a single near-field scan.     

Deformable two-dimensional photonic crystal slab for cavity optomechanics

We have designed photonic crystal suspended membranes with optimized optical and mechanical properties for cavity optomechanics. Such resonators sustain vibration modes in the megahertz range with quality factors of a few thousand. Thanks to a two-dimensional square lattice of holes, their reflectivity at normal incidence at 1064?nm reaches values as high as 95%. These two features, combined with the very low mass of the membrane, open the way to the use of such periodic structures as deformable end mirrors in Fabry-Perot cavities for the investigation of cavity optomechanical effects.     

Coherent thermal antenna using a photonic crystal slab

We show that a photonic crystal film can emit coherent thermal radiation. We demonstrate the key role of leaky waves existing at the air-photonic crystal interface. The frequency and direction of emission depend on the lattice parameters. This paves the way towards the design of coherent infrared antennas.     

部分空气桥式硅膜二维光子晶体

描述在Si基底上制备带隙在近红外波段部分空气桥式二维光子晶体（PC）.选用HF酸溶液作为腐蚀液，利用聚焦离子束刻蚀技术直接刻蚀出具有三角形空气洞结构的二维PC，并测出了二维PC完整的第一带隙透过谱的带隙范围为123—155μm.实验测得的透过谱与理论计算的空气桥式二维PC的计算结果一致.类TM0模的存在减小了带隙的宽度.由于部分SiO2支撑桥式平板，二维PC易于按所需尺寸进行制备.同时，通过改变平板下的支撑材料，可以制出有源的PC，利用这种机理可以把光从支撑材料中引出. 关键词： 二维光子晶体 带隙 平板波导     

Simulation and fabrication study of porous silicon photonic crystal

The present work reports design and fabrication of porous silicon based one-dimensional (1D) photonic crystal. Distributed Bragg reflector (DBR) is a 1D photonic crystal composed of multilayer stack of high and low refractive index layers. Design of porous silicon DBR is a complex one and requires appropriate control in optical parameters of its constituent layers. In order to design DBR, two porous silicon single layer samples were fabricated using current density of 10 and 50 mA/cm². Optical characterization of single layer samples showed series of interference fringes. Reflective interferometric Fourier transform spectroscopy (RIFTS) method was employed to determine optical constants of porous silicon single layers. DBR simulation was carried out based on transfer matrix method. DBR was then fabricated using optical parameters obtained from RIFTS method. Reflection bandwidth of prepared DBR was found to be 216 nm, which is comparable to the simulated value of 203 nm.     

Application of fast Pade approximation in simulating photonic crystal nanocavities by FDTD technology

The exact calculation of mode quality factor Q is a key problem in the design of high-Q photonic crystal nanocavity. On the basis of further investigation on conventional Pade approximation, FDM and DFT, Pade approximation with Baker’s algorithm is enhanced through introducing multiple frequency search and parabola interpolation. Though Pade approximation is a nonlinear signal processing method and only short time sequence is needed, we find the different length of sequence requirements for 2D and 3D FDTD, which is very important to obtain convergent and accurate results. By using the modified Pade approximation method and 3D FDTD, the 2D slab photonic crystal nanocavity is analyzed and high-Q multimode can be solved quickly instead of large range high-resolution scanning. Monitor position has also been investigated. These results are very helpful to the design of photonic crystal nanocavity devices.