Design criteria and optical characteristics of one-dimensional photonic crystals based on periodically grooved silicon

Photonic bandgap (PBG) regions have been calculated for periodically grooved Si structures, acting as a one-dimensional photonic crystal. The wavelength range of the PBG as a function of the ratio (DSi/A) is presented, where DSi is the width of the Si walls and A is the grooved silicon lattice constant. The influence of the parameter DSi, the refractive index of the space between the Si walls and the number of structure periods, m, on the forming of PBG regions is discussed. A good correlation between the calculated and the experimentally observed PBG regions is obtained.     

Self‐Assembly Approaches to Three‐Dimensional Photonic Crystals

A brief review of the historical development of photonic bandgap (PBG) materials is provided and the fabrication methods employed are discussed with emphasis on self‐assembly processes. The factors influencing the generation of a complete bandgap, from both an experimental and a calculational standpoint are then presented and discussed. The Figure shows a diamond‐like 3D periodic structure.     

Sensor properties of hollow-core photonic crystal fibers

A new class of hollow-core photonic crystal fibers (PCFs) with various modifications of spatial lattices is considered. The influence of the PCF structure geometry on the photonic band gap (PBG) in the visible spectral range is demonstrated. A relationship between a change in the PCF core refractive index due to filling of the hollow core with various liquids and the PBG position is established. PCFs show new possibilities for use as biological and chemical sensors.     

Spontaneous and Induced Atomic Decay in Photonic Band Structures

Abstract

We present a comprehensive quantum electrodynamical analysis of the interaction between a continuum with photonic band gaps (PBGs) or frequency cut-off and an excited two-level atom, which can be either ‘bare’ or ‘dressed’ by coupling to a near-resonant field mode. A diversity of novel features in the atom and field dynamics is shown to arise from the non-Markovian character of radiative decay into such a continuum of modes. Firstly the excited atom is shown to evolve, by spontaneous decay, into a superposition of non-decaying single-photon dressed states, each having an energy in a different PBG, and a decaying component. This superposition is determined by the atomic resonance shift, induced by the spontaneously emitted photon, into or out of a PBG. The main novel feature exhibited by the decaying excited-state component is the occurrence of beats between the shifted atomic resonance frequency and the PBG cut-off frequencies, corresponding to a non-Lorentzian emission spectrum. Secondly the induced decay of a resonantly driven atom into such a continuum exhibits a cascade of transitions down the ladder of dressed states, which are labelled by decreasing photon numbers of the driving mode. Remarkably, this cascade is terminated at the dressed-state doublet, from which all subsequent transitions to lower doublets are forbidden because they fall within the PBG. This doublet then becomes an attractor state for the populations of higher-lying doublets. As a result, the photon-number distribution of the driving mode becomes strongly sub-Poissonian.     

Nitride compounds as photonic crystals in the optical region

Usin the transfer matrix method we have studied the optical properties related to the photonic band gap (PBG) concept of the III-nitride family particularly InN and AlN. We have shown that these materials present, for a particular lattice constant and for the same structure, PBGs in all near infrared, optical and ultaviolet regions. In order to give optimal conditions for experiments, the number and the width of these PBGs are studied in more detail. The case of the absorption which occurs for the higher lattice parameter is discussed. This novel class of material opens up many potential applications. For example, PBG crystals can be used to inhibit spontaneous emission in photonic devices, leading to more efficient light emitters such as single-mode-light emitting diodes.     

Optical resonance near the edge of a photonic band gap (PBG): turning the effects of a PBG on/off using a resonant driving field

We studied the effects of a coherent monochromatic resonant laser field driving the transition of a two-level atom embedded in a photonic band gap (PBG) material on the emission dynamics of the atom. When the transition frequency of the atom lies outside a PBG and sufficiently far from the band edge that the emission dynamics of the atom is not normally affected by the gap, the dynamic stark splitting of the upper level of the atom into two dressed states by a sufficiently strong resonant driving field can bring the lower dressed state close enough to the band edge or even inside the gap so as to be affected by the gap, providing a switchable means of extending the novel effects of atom–photon interaction near the edge of a PBG for atomic transitions outside the gap and far from the band edge. The net effect is as if a sufficiently strong resonant field driving a transition of an atom embedded in a PBG actively shifts the PBG close enough to the transition so that the gap affects the emission dynamics associated with the transition.     

Phase retrieval from a single near-field diffraction pattern with a large Fresnel number

A new method of phase retrieval from a single near-field diffraction image with a large Fresnel number is presented and discussed. This method requires only the oversampled diffraction pattern without any other information such as the object envelope. Moreover, we show that the combination with a fast computational method is possible when the linear oversampling ratio is an integer. Numerical simulations are also presented, showing that the method works well with noisy data.     

Spurious suppression of a microstrip filter using three types of rectangular PBG loops

A novel microstrip bandpass filter with three types of rectangular, photonic bandgap (PBG) loops on a middle layer was designed and demonstrated using a full-wave electromagnetic (EM) simulator, with the predicted results verified by experiment. This investigation presents the configurations of conventional parallel-coupled 2 GHz filters with arid without a PBG. The middle-layer of PBG loops adds an extra stopband-rejection mode to filter stop-band; and it provides attenuation in excess of 25 dB at the second, third, and fourth harmonics, thus demonstrating that superior stopband characteristics at high frequency can be obtained using the proposed PBG loops in microwave filters.     

Recent developments in the design and fabrication of visible photonic band gap waveguide devices

In this paper, we present the design, fabrication and initial optical testing of dielectric waveguide devices which incorporate photonic crystals with photonic band gaps (PBG) in the visible region of the spectrum. In the design of our devices we use a full three-dimensional plane wave analysis to solve the photonic band structure simultaneously with the dielectric waveguide boundary conditions for a fixed lattice and waveguide geometry. This takes into account the finite thickness of the waveguide core, and the evanescent wave in the dielectric cladding layers. Furthermore, we explain how the effective Bloch mode index can be extracted from the results. This enables us to tackle important problems associated with mode coupling between the input waveguide and guided Bloch modes within the porous PBG region, such as Fresnel reflections at the interface and up-scattering from the holes. Finally, we present the recent fabrication of quasi-periodic photonic crystals and PBG waveguide bends.     

Spurious suppression of a microstrip bandpass filter using three types of rectangular PBG loops.

A novel microstrip bandpass filter with three types of rectangular, photonic bandgap (PBG) loops on a middle layer was designed and demonstrated using a full-wave electromagnetic (EM) simulator, with the predicted results verified by experiment. This investigation presents the configurations of conventional parallel-coupled 2 GHz filters with and without a PBG. The middle-layer of PBG loops adds an extra stopband-rejection mode to filter stopband; and it provides attenuation in excess of 25 dB at the second, third, and fourth harmonics, thus demonstrating that superior stopband characteristics at high frequency can be obtained using the proposed PBG loops in microwave filters.     

Calculation and correction of subaperture tilt aberration modes in synthesis imaging

We extend the redundant spacings calibration method for finding piston coefficients affecting the elements of a dilute aperture array so that tilt phase coefficients can also be calculated and corrected without the need for assumptions about the object. The tilt coefficient retrieval method is successfully demonstrated in simulation, and the specifics of correction by image sharpness are discussed, showing that in dilute aperture systems this method does not necessarily produce a unique image.     

Space-variant Characteristics in Multiple Object Recognition with a Coherent Optical Processor

Abstract

When the input plane of a Van der Lugt correlator contains a composite object, the output plane will in general contain several correlation peaks. When these correlation peaks overlap, the total intensity will be given by the coherent addition of the amplitudes of the individual peaks. It is shown in this paper that the total intensity depends on the phase difference between the correlation signals. The phase differences are dependent both on the displacement of the input object and any aberration in the correlator. A theoretical analysis of the system is given, showing that the interference between the correlation signals causes the total correlation intensity to change with object displacement in an oscillatory fashion rather than in a monotonic way. Some experimental verification of the theoretical predictions is also presented.     

Spectroscopic properties of Nd 3 + and Pr 3 + in gallate glasses with low phonon energies

Absorption and fluorescence spectra of Nd3 +were measured in potassium tantalum gallate, lead bismuth gallate (PBG), fluorozirconate (ZBLAN), and Ge-Ga-S glasses. A Judd -Ofelt analysis was performed to determine the spontaneous emission probability and stimulated emission cross section of the4 F3/2 ?4 I11/2 transition of Nd3 +. Raman spectra were studied to clarify the maximum phonon energies of the glasses. The fluorescence of the1 G4?3 H5 transition of Pr3 + in a dehydrated PBG glass was observed for the first time to our knowledge. The PBG glass has a higher quantum efficiency than that of ZBLAN glass based on the Judd -Ofelt analysis.     

Bottom-up photonic crystal cavities formed by patterned III-V nanopillars

We report on the formation and optical properties of bottom-up photonic crystal (PC) cavities formed by III-V nanopillars (NPs) via catalyst-free selective-area metal-organic chemical vapor deposition on masked GaAs substrates. This method of NP synthesis allows for precise lithographic control of NP position and diameter enabling simultaneous formation of both the photonic band gap (PBG) region and active gain region. The PBG and cavity resonance are determined by independently tuning the NP radius r, pitch a, and height h in the respective masked areas. Near-infrared emission at 970 nm is achieved from axial GaAs/InGaAs heterostructures with in situ passivation by laterally grown InGaP shells. To achieve out-of-plane optical confinement, the PC cavities are embedded in polydimethylsiloxane (PDMS) and removed from the growth substrate. Spatially and spectrally resolved 77 K photoluminescence demonstrates a strong influence of the PBG resonance on device emission. Resonant peaks are observed in the emission spectra of PC cavities embedded in PDMS.     

Photonic and omnidirectional band gap engineering in stack of exponential graded index material and negative index material

We have investigated the photonic band gaps (PBG) and omnidirectional band gaps in one-dimensional photonic crystals made up of alternate layer of exponential graded index material and negative index material. We have considered the influence of material properties, geometrical parameters and material composition on the PBG and omnidirectional band gap. Results show that the parameters of exponential graded index material and negative index material can change the photonic and omnidirectional band structures remarkably. Number and bandwidth of PBG increases with increasing the negative index material layer thicknesses while thicknesses of graded index layer only have an effect on the bandwidth of PBGs. The bandwidth of PBG also depends on grading profile parameter of exponential graded index layers and bandwidth can be tuned with increase the value of grading profile parameter. This work can facilitate the design of filters and reflectors, and provide the basic understanding of the influence of graded index materials and metamaterials on the PBG properties.     

Quantum information processing in localized modes of light within a photonic band-gap material

Abstract

The single photon occupation of a localized field mode within an engineered network of defects in a photonic band-gap (PBG) material is proposed as a unit of quantum information (qubit). Qubit operations are mediated by optically-excited atoms interacting with these localized states of light as the atoms traverse the connected void network of the PBG structure. We describe conditions under which this system can have independent qubits with controllable interactions and very low decoherence, as required for quantum computation.     

Coherent population trapping in photonic and dispersive band-gap materials

A theory of coherent population trapping (CPT) has been developed in photonic band-gap (PBG) and dispersive polaritonic band-gap (DPBG) materials when doped with an ensemble of five-level atoms. These materials have gaps in their photon energy spectra leading to unusual optical properties. The atoms are prepared as coherent superpositions of the two lower states and interact with a reservoir and two photon fields. The transition between the two lower states of an atom is dipole forbidden. The Schrödinger equation and the Laplace transform method are used to calculate the expressions for the number densities of the atomic states. Numerical simulations are performed for both PBG and DPBG materials with the phase factor between the coherent states chosen such that the number density of the upper state becomes zero when the photon fields have the same intensity. It is found that when the resonance energies lie away from the band edges and within the lower band, the CPT effect is observed in both materials when the fields have identical intensities. Similar results are also found when the resonance energies lie away from the band edges and within the upper band. When one of the resonance energies lies near the lower band edge, the number density vanishes at all intensities of the fields for both materials. This is an effect of the band structure of the materials and is not due to the CPT effect. A similar result is seen when one of the resonance energies lies near the upper band edge of a PBG material. However, for a DPBG material, the number density does not become zero when one of the resonance energies lies near the upper band edge, except due to the CPT effect brought on by the identical intensities of the photon fields. This is a very interesting phenomenon.     

Uncovering the Circular Polarization Potential of Chiral Photonic Cellulose Films for Photonic Applications

Circularly polarized light (CPL) is central to photonic technologies. A key challenge lies in developing a general route for generation of CPL with tailored chiroptical activity using low‐cost raw materials suitable for scale‐up. This study presents that cellulose films with photonic bandgaps (PBG) and left‐handed helical sense have an intrinsic ability for circular polarization leading to PBG‐based CPL with extraordinary | g | values, well‐defiend handedness, and tailorable wavelength by the PBG change. Using such cellulose films, incident light ranging from near‐UV to near‐IR can be transformed to passive L‐CPL and R‐CPL with viewing‐side‐dependent handedness and | g | values up to 0.87, and spontaneous emission transformed to R‐CPL emission with | g | values up to 0.68. Unprecedented evidence is presented with theoretical underpinning that the PBG effect can stimulate the R‐CPL emission. The potential of cellulose‐based CPL films for polarization‐based encryption is illustrated. The evaporation‐induced self‐assembly coupled with nanoscale mesogens of cellulose nanocrystals opens new venues for technological advances and enables a versatile strategy for rational design and scalable manufacturing of organic and inorganic CPL films for photonic applications.     

声波在声子带隙材料中的传输

研究了声波在二维声子带隙材料中的传输特性,把声子带隙材料作为一个散射体进行处理。在远场近似下（kr〉〉1）,计算了声波在有限范围内声子带隙材料中的传输系数,得到了与带结构符合很好的计算结果。     

The optical responses of one-dimensional photonic crystals based on the transparent Ag‐anodic aluminum oxide composites with super low-refractive index

The super low refractive index of less than 1 is obtained through adjusting the deposition time of nano-metal Ag in Ag-anodic aluminum oxide (Ag-AAO) composite films. It is very interesting that the Ag-AAO composite films with super low refractive index are still transparent. Based on the results, the Ag-AAO composite films and titanium dioxide (TiO₂) films were used to assemble 1D TiO₂/Ag-AAO photonic crystal (PC) structure and its optical responses were simulated in the 500-2500 nm range by using the finite difference time domain method. It is found that the increase of Ag-AAO layer thickness makes the photonic band gap (PBG) become broad greatly, but has few effects on the blue edge of the PBG, which is different from the effect of TiO₂ layers. It is more important that a broad omnidirectional PBG can be easily obtained from the simple 1D TiO₂/Ag-AAO photonic crystal structure through the modulation of both the TiO₂ and Ag-AAO layer thicknesses. Furthermore, the absorption of 1D TiO₂/Ag-AAO PC structure at the PBG edges is very strong due to the photon localization in Ag-AAO layer. The different roles of Ag-AAO layer in the above mentioned 1D PC structure are mainly attributed to the different transmission process of optical pulse in Ag-AAO layer.