Polarization multiplexed fluorescence enhancer using a pixelated one-dimensional photonic band gap structure

Fluorescence enhancement using photonic crystals can produce a significant improvement in the signal-to-noise ratio for single molecule and low molecule-concentration fluorescence imaging in biological and biochemical studies. In this Letter, a pixelated one-dimensional photonic band gap structure was designed to enhance both transverse electric and transverse magnetic polarizations through a spatially multiplexed photonic crystal resonance. The average enhancement of 15.6 and 17.9 fold were experimentally verified for the transverse and longitudinal fields on the same substrate. This device may be used as an optical platform for molecular orientation determination.     

具有态守恒赝隙的光子晶体中两能级原子自发辐射的增强与抑制

论证了在赝带隙光子晶体中存在一个全频率域态总数守恒规则，在完全带隙光子晶体中还存在一个局域态总数守恒规则.态总数守恒规则指出，如果一个光子晶体的态密度在某些频率范围存在相对于等效介质态密度的谷，则一定由其他频率范围内相对于等效介质态密度的峰来补偿.使用符合态总数守恒规则的态密度模型，解释了态密度调制导致的自发辐射谱增强、抑制、变窄、红移、蓝移以及谱分裂等光子晶体中的量子光学现象.该理论比较适合研究在具有赝带隙的光子晶体中大量随机分布的发光原子或分子的自发辐射行为. 关键词： 光子晶体 自发辐射 态密度 光子赝带隙     

Photobleaching on Photonic Crystal Enhanced Fluorescence Surfaces

The effect of resonant fluorescent enhancement from a photonic crystal surface upon the fluorescent photobleaching rate of Cyanine-5 labeled protein has been investigated. We show that the enhanced excitation mechanism for photonic crystal enhanced fluorescence, in which the device surface resonantly couples light from an excitation laser, accelerates photobleaching in proportion to the coupling efficiency of the laser to the photonic crystal. We also show that the enhanced extraction mechanism, in which the photonic crystal directs emitted photons approximately normal to the surface, does not play a role in the rate of photobleaching. We show that the photobleaching rate of dye molecules on the photonic crystal surface is accelerated by 30x compared to an ordinary glass surface, but substantial signal gain is still evident, even after extended periods of continuous illumination at the resonant condition.     

Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host

Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.     

Line-scanning detection instrument for photonic crystal enhanced fluorescence

A laser line-scanning instrument was developed to optimize the near-field enhancement capability of a one-dimensional photonic crystal (PC) for excitation of surface-bound fluorophores. The excitation laser beam is shaped into an 8 μm × 1 mm line that is focused along the direction of the PC grating, while remaining collimated perpendicular to the grating. Such a beam configuration offers high excitation power density while simultaneously providing high resonant coupling efficiency from the laser to the PC surface. Using a panel of 21 immunofluorescence assays on the PC surface in a microarray format, the approach achieves an enhancement factor as high as 90-fold between on-resonance and off-resonance illumination. The instrument provides a capability for sensitive and inexpensive analysis of cancer biomarkers in clinical applications.     

Faraday rotation in a two-dimensional photonic crystal with a magneto-optic defect

We study the magneto-optic (MO) Faraday rotation in a two-dimensional square-lattice photonic crystal with a central MO defect layer in the optical wavelength range. We show that when a TM plane wave is incident upon a photonic crystal, an enhancement of Faraday rotation takes place in a region where a resonance peak appears in the photonic bandgap. In this region the mode conversion is high.     

Investigation of the Purcell effect in photonic crystal cavities with a 3D Finite Element Maxwell Solver

Photonic crystal cavities facilitate novel applications demanding the efficient emission of incoherent light. This unique property arises when combining a relatively high quality factor of the cavity modes with a tight spatial constriction of the modes. While spontaneous emission is desired in these applications the stimulated emission must be kept low. A measure for the spontaneous emission enhancement is the local density of optical states (LDOS). Due to the complicated three dimensional geometry of photonic crystal cavities the LDOS quantity has to be computed numerically. In this work, we present the computation of the LDOS by means of a 3D Finite Element (FE) Maxwell Solver. The solver applies a sophisticated symmetry handling to reduce the problem size and provides perfectly matched layers to simulate open boundaries. Different photonic crystal cavity designs have been investigated for their spontaneous emission enhancement by means of this FE solver. The simulation results have been compared to photoluminescence characterizations of fabricated cavities. The excellent agreement of simulations and characterizations results confirms the performance and the accuracy of the 3D FE Maxwell Solver.     

Theoretical study of enhancement and suppression of the fluorescent spectra of dye molecules in a photonic crystal with a pseudogap

We have investigated the analytical forms of the photonic density of states (DOS) in a photonic crystal in the interested frequency regime according to the rule of state conservation in a photonic crystal with pseudogaps, which states that, if a valley of the DOS appears in some range of frequencies, it must be compensated for by increasing over some other ranges. By using a model DOS with a state-conservative photonic pseudogap, we have also investigated the enhancement and suppression of spontaneous emission of two-level atoms with different frequency positions and widths of emission spectra in a state-conservative electromagnetic reservoir; and the DOS-induced suppression, enhancement, narrowing and redshifting or blueshifting of spontaneous emission spectra are naturally obtained.     

纳米集成光路中的光源、光波导和光增强

使用近场光学显微术(scanning near-field optical microscopy, SNOM)研究了ZnO亚微米线端面出射性质，不同空间形貌Ⅱ-Ⅵ族半导体荧光器件光波导特性，二维光子晶体、准晶光子晶体对LED的出射增强作用以及表面等离激元(surface plasmon polariton, SPP)与半导体纳米荧光器件的相互作用，对纳米集成光路中的光源、光波导、光增强三个重要问题做了实验和理论上的分析.研究发现半导体微纳米线端面出射光束的质量与样品的直径有密切关系.通过合理地设计其直径和     

纳米集成光路中的光源、光波导和光增强

使用近场光学显微术(scanning near-field optical microscopy, SNOM)研究了ZnO亚微米线端面出射性质,不同空间形貌Ⅱ-Ⅵ族半导体荧光器件光波导特性,二维光子晶体、准晶光子晶体对LED的出射增强作用以及表面等离激元(surface plasmon polariton, SPP)与半导体纳米荧光器件的相互作用,对纳米集成光路中的光源、光波导、光增强三个重要问题做了实验和理论上的分析.研究发现半导体微纳米线端面出射光束的质量与样品的直径有密切关系.通过合理地设计其直径和 关键词： 纳米集成光路 扫描近场光学显微术 光波导 光增强     

Experimental realization of highly efficient broadband coupling of single quantum dots to a photonic crystal waveguide

We present time-resolved spontaneous emission measurements of single quantum dots embedded in photonic crystal waveguides. Quantum dots that couple to a photonic crystal waveguide are found to decay up to 27 times faster than uncoupled quantum dots. From these measurements beta-factors of up to 0.89 are derived, and an unprecedented large bandwidth of 20 nm is demonstrated. This shows the promising potential of photonic crystal waveguides for efficient single-photon sources. The scaled frequency range over which the enhancement is observed is in excellent agreement with recent theoretical proposals taking into account that the light-matter coupling is strongly enhanced due to the significant slow-down of light in the photonic crystal waveguides.     

Optimization of two-photon absorption enhancement in one-dimensional photonic crystals with defect states

One-dimensional photonic crystals with a defect layer of CdS were fabricated. The observed enhancement of two-photon absorption (TPA) in the CdS layer can be attributed to the intensified optical field confined within the defect layer of the photonic crystal. The results show that the enhancement of TPA coefficient depends basically on the number of periods of the photonic crystal and the defect mode position in the photonic band gap. The observation agrees qualitatively with the expectations of a computation by matrix transfer formulation.     

Spontaneous emission from a microwave-driven four-level atom in an anisotropic photonic crystal

The spontaneous emission from a microwave-driven four-level atom embedded in an anisotropic photonic crystal is studied. Due to the modified density of state(DOS) in the anisotropic photonic band gap(PBG) and the coherent control induced by the coupling fields, spontaneous emission can be significantly enhanced when the position of the spontaneous emission peak gets close to the band gap edge. As a result of the closed-loop interaction between the fields and the atom,the spontaneous emission depends on the dynamically induced Autler–Townes splitting and its position relative to the PBG.Interesting phenomena, such as spectral-line suppression, enhancement and narrowing, and fluorescence quenching, appear in the spontaneous emission spectra, which are modulated by amplitudes and phases of the coherently driven fields and the effect of PBG. This theoretical study can provide us with more efficient methods to manipulate the atomic spontaneous emission.     

Plasmonic Enhancement of Single-Molecule Fluorescence Near a Silver Nanoparticle

In this short paper, we reported the enhanced fluorescence from a single fluorophore bound to a 50nm silver nanoparticle. We found that on average the Cy5 molecules bound to metal nanoparticles are approximately 15-fold brighter than that of free dyes, and that single molecule lifetimes are shorter as compared to free fluorophores. The increased emission rate is primarily the result of local plasmon enhancement. These results demonstrate that the use of fluorophore-metal interactions can increase the brightness and photostability of fluorophores for single molecule detection.     

Enhanced stimulated Raman scattering in slow-light photonic crystal waveguides

We investigate for the first time, to our knowledge, the enhancement of the stimulated Raman scattering in slow-light silicon-on-insulator (SOI) photonic crystal line defect waveguides. By applying the Bloch-Floquet formalism to the guided modes in a planar photonic crystal, we develop a formalism that relates the intensity of the downshifted Stokes signal to the pump intensity and the modal group velocities. The formalism is then applied to two prospective schemes for enhanced stimulated Raman generation in slow-light photonic crystal waveguides. The results demonstrate a maximum factor of 104(66,000) enhancement with respect to SOI channel waveguides.     

用一维光子带隙结构增强硫化镉双光子吸收研究

用真空镀膜方法制备了含有单个CdS缺陷层的具有不同周期和结构参量的TiO2／SiO2一维光子晶体。用抽运一探测技术研究了CdS缺陷层的双光子吸收（TPA）现象。实验结果表明：一维光子晶体中CdS缺陷层的双光子吸收显著增强。不同周期和结构参量的一维光子晶体中CdS缺陷层的双光子吸收系数不同。双光子吸收的增强来源于由光局域化导致的缺陷层的电场强度的增加。缺陷层电场强度与一维光子晶体的结构有关,如周期,光子带隙的位置与宽度及缺陷模式等因素都会影响缺陷层电场强度。采用四分之一波长的高低折射率介质层和与入射波长匹配的缺陷模可以得到最大的缺陷层电场强度。     

Creation of tunable absolute bandgaps in a two-dimensional anisotropic photonic crystal modulated by a nematic liquid crystal

Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the tunable absolute bandgap in a two-dimensional anisotropic photonic crystal structures modulated by a nematic liquid crystal. The PC structure composed of an anisotropic-dielectric cylinder in the liquid crystal medium is studied by solving Maxwell's equations using the plane wave expansion method. The photonic band structures are found to exhibit absolute bandgaps for the square and triangular lattices. Numerical simulations show that the absolute bandgaps can be continuously tuned in the square and triangular lattices consisting of anisotropic-dielectric cylinders by infiltrating nematic liquid crystals. Such a mechanism of bandgap adjustment should open up a new application for designing components in photonic integrated circuits.     

Thermal radiation from photonic crystals: a direct calculation

A classical simulation of equilibrium thermal emissivity from dispersive, lossy photonic crystals is presented. Normal emission results consistent with those assuming Kirchoff's law are obtained; i.e., a photonic crystal does not emit more than what a blackbody does. Significant enhancement, however, can be achieved over the radiation intensity from a uniform slab, indicating the potential usefulness of photonic crystals in incandescent lighting and thermal photovoltaic applications.     

Enhancement of the SHG efficiency in a doubly resonant 2D-photonic crystal microcavity

In this paper we discuss the conditions to obtain the enhancement of second harmonic generation in a two-dimensional circular photonic crystal AlGaAs cavity. The photonic crystal circular cavity offers the possibility of having high-Q resonance modes with respect to those obtained with other types of photonic crystal lattices. The crystallographic cut of the AlGaAs provides a strong nonlinear coupling between a transverse-magnetic (TM) polarized resonant mode at the fundamental wavelength and a transverse-electric (TE) polarized resonant mode at second harmonic wavelength. The double resonance condition leads to a strong improvement of the second harmonic generation process. A preliminary linear analysis has been performed by using the finite-difference time-domain method, which includes the dispersive response of the material, modeled using the well-known one-pole pair Lorentzian function.     

Beam focusing upon the reflection from crystals and multilayer periodic structures with variable period

The experimental spectral dependence of the intensity of the second harmonic (SH) generated in microcavities based on porous silicon photonic crystal demonstrates resonant intensity enhancement (by a factor of ～2×10²) in the vicinity of the cavity mode and at the edges of the photonic band gap. The enhancement is due to the combined effect of pump radiation localization inside the microcavity, multiple SH interference in the photonic crystal, and two-photon resonance of the porous silicon quadratic susceptibility at the SH frequency.