Nonperturbative analysis of spontaneous emission in one dimensional special photonic crystals

The retarded spontaneous emission (SpE) process of a two-level atom embedded in realistic one dimensional photonic crystals (1DPC) is investigated with the quantum nonperturbative theory. The atomic transient decay is divided into two processes: the first comes from the natural decay to free space and the second is induced by the reflected field emitted from the atom itself. Due to the multi-reflection in the multi-layer structure, the correct delay time of the induced decay process is hard to calculate in the usual ways. However with the special but practical 1DPC provided, we give the analytic result of the atomic dynamic decay in 1DPC. Our result gives a clear picture to show the process which the atom feels the surrounding.     

The influence on atomic decay by inserting a LHM layer into an ordinary one dimensional multi-layer structure

Inserting left-handed material (LHM) layers into a one dimensional structure can influence the spontaneous emission (SpE) of a two-level atom. This has been investigated, starting from the simplest case of a three-layer system, where we find the reflected field (atom can “see”) passing through LHM layer is stronger than that through the corresponding normal layer. Indeed the induced decay is more strongly influenced by reflected field passing through LHM layer. Based on this and after further analysis of reflectivity, we find that, a quarter photonic crystal (PC) composed of alternately LHM and RHM can inhibit the atomic spontaneous emission more intensely compared to an ordinary PC.     

Coherent effects under suppressed spontaneous emission

An ensemble of resonance atoms is considered, which are doped into a medium with well developed polariton effect, when in the spectrum of polariton states there is a band gap. If an atom with a resonance frequency inside the polariton gap is placed into the medium, the atomic spontaneous emission is suppressed. However, a system of resonance atoms inside the polariton gap can radiate when their coherent interaction is sufficiently strong. Thus the suppression of spontaneous emission for a single atom can be overcome by a collective of atoms radiating coherently. Conditions when such collective effects can appear and their dynamics are analysed. Received 7 June 2000     

Study on composite photonic crystal patch antenna

The paper investigated a composite photonic crystal patch antenna by using the method of finite difference time domain (FDTD). The results show that there exists a wave resonance state at 2.635 GHz, where the real part of the permittivity and permeability are all negative; its refraction index is –1. The effect has largely enhanced the electromagnetic wave’s resonance intensity, and has improved the localized extent of electromagnetic energy obviously in such photonic crystal structure (PBG), resulting in a higher antenna gain, a lower return loss, and a better improvement of the antenna’s characteristics. Due to such the advantages, the use of patch antennas can be extended to such fields as mobile communication, satellite communication, aviation, etc.     

Phase control of group velocity in one-dimensional photonic crystal with a dispersive defect layer

Propagation of an electromagnetic pulse through one-dimensional photonic crystal doped with three-level ο-type atomic systems is discussed. It is found that in the presence of quantum interference and incoherent pump, the transmitted pulse becomes completely phase dependent. So, the group velocity of the transmitted pulse can be switched from subluminal to superluminal light propagation just by adjusting the relative phase of applied fields.     

Lateral shift dependence of spontaneous emission in a planar cavity with perfect conducting cladding

We consider the effect of lateral shift of the “beams" resulting from the atom emissions on spontaneous decay of an excited atom embedded in a planar cavity with perfect conducting cladding. It is found that the spontaneous decay could be enhanced or suppressed owing to the positive and negative lateral shift at the interfaces of the cavity mirror. Compared with the emission between two perfect conducting plates, the surface guided modes could exist and for very thin planar cavity, the density of surface guided modes may be obviously larger than those of the propagating guided modes.     

Analysis of photonic band gaps in a two-dimensional photonic crystal with centrifugal core-shell rods

The absolute photonic band gap (PBG) in two-dimensional (2D) photonic crystal with excentric core-shell rods is studied in this paper. The core rod shifts away from the core-shell rod center, and its position is decided by two new introduced parameters — the shift angle θ and the offset ρ. We use the FDTD algorithm to calculate the photonic bands of the photonic crystal, and analyze how the offset and shift angle affect the photonic bang gap of excentric core-shell photonic crystal for different core rod size. It has been shown that the variation of the photonic band gap is quite peculiar.     

Highly collimated emission from a left-handed photonic crystal with a quasi-cavity

We study the collimated emission characteristics from a dipole source inside a negative-effective-refractive-index photonic crystal with a quasi-cavity constructed by a concave photonic crystal reflector. The emissions along the ±X and −Y directions are forbidden by the quasi-cavity, so that most emissions propagate along the +Y direction. Simulation results show that a narrow collimated beam is achieved due to the near-zero negative effective refractive index. Moreover, the half-power beam width of such a collimated beam can be reduced to 3.48° by optimizing the size of the source area. Such a compact structure would have potential applications in micro-optical devices.     

Manipulating light flow with one-dimensional photonic crystals of an electromagnetically induced transparency medium

The band structures and equifrequency contours of one-dimensional photonic crystals (PCs), which consist of an electromagnetically induced transparency (EIT) medium and a common dielectric medium, can be dramatically changed by tuning the coupling field intensity (or coupling Rabi frequency, CRF) of the EIT medium. It is found that for a probe light at a fixed frequency, either positive or negative refraction in the EIT PC can be realized with a proper CRF. The behavior of a Gaussian beam (probe light) obliquely incident on such an EIT PC slab is simulated numerically. The probe light beam transmitted from the slab can be shifted transversely in a large range, and negative refraction enhances this effect. The present scenario can be applied in some areas such as quantum optical and photonic device designs.     

Observation of enhanced beaming from photonic crystal waveguides

We report on the experimental observation of the beaming effect in photonic crystals using experimentally mapped spatial field distributions of energy emitted from a subwavelength photonic crystal waveguide into free-space, rendering with crisp clarity the diffractionless beaming of energy. Our experimental data agree well with our numerical studies of the beaming enhancement in photonic crystals with modulated surfaces. Without loss of generality, we study the beaming effect in a photonic crystal scaled to microwave frequencies and demonstrate the technological capacity to deliver long-range wavelength-scaled beaming of energy.     

Single laser exposure fabrication of diamond-like 3-dimensional photonic crystal microstructures using circularly polarized light

Phase tunable multi-level diffractive optical elements define an attractive approach for single laser exposure fabrication of 3-dimensional photonic crystal microstructures. The significant advantage of these multi-level diffractive optical elements over two-level diffractive optical elements is the flexibility of fabricating a wide range of 3-dimensional periodic structures by manipulating the relative phase of different diffracted beams. Here, phase tuning was applied to demonstrate fabrication of a hybrid 3-dimensional structure intermediate between previously reported diamond-like Woodpile-type structure of tetragonal symmetry and structure having body-centered-tetragonal lattice symmetry. Circularly polarized light was applied for the first time to balance the diffraction order efficiencies and improve the structural uniformity. Design guidelines are presented for generating diamond-like photonic crystal template that possesses complete photonic bandgap when inverted with high refractive index materials.     

Modulation of photonic band structures with dielectric anisotropy

By the multiple scattering method and the extended Mie theory, we have calculated the photonic band structure of the photonic crystals consisting of the dielectric spheres with uniaxial/biaxial anisotropy. The results demonstrate that for fcc lattice structure there exist two partial photonic band gaps which does not appear in the isotropic case. Among them, the lower one, lying between the second and the third bands, exists in one third of the first Brillouin zone, while the upper one, opening between the fourth and fifth bands, can appear simultaneously in the rest two thirds of the first Brillouin zone. The effects of anisotropy on the band structures are studied as well, which suggests the biaxial anisotropy are much more flexible than the uniaxial anisotropy in modulating the band structures.     

Demonstration of a new transport regime of photon in two-dimensional photonic crystal

A new transport regime of photon in two-dimensional photonic crystal near the Dirac point has been demonstrated by exact numerical simulation. In this regime, the conductance of photon is inversely proportional to the thickness of sample, which can be described by Dirac equation very well. Both of bulk and surface disorders always reduce the transmission, which is in contrast to the previous theoretical prediction that they increase the conductance of electron at the Dirac point of graphene. However, regular tuning of interface structures can cause the improvement of photon conductance. Furthermore, large conductance fluctuations of photon have also been observed, which is similar to the case of electron in graphene.     

Efficient transmission in cascaded photonic crystal waveguides via a strong coupling effect

A design of cascaded photonic crystal waveguide is proposed in this paper inspired by the work of Tang et al. [D. Tang, L. Chen, W. Ding, Appl. Phys. Lett. 89 (2006) 131120]. In contrast to a conventional waveguide source, a plane wave source is applied in the current design. We show that an efficient guide mode in the photonic band gap can be achieved. The same idea also works for a slight variation by defects introduction in the photonic crystal. Finally, the strong coupling effect present in the cascaded waveguides is demonstrated by an analogy with photonic quantum wells.     

Applications of the expanded basis method to study the behavior of light in a two-dimensional photonic crystal slab

We apply the expanded basis method (EBM) to investigate the behavior of light in a two-dimensional photonic crystal (PC) slab. This method is based on expanded completeness bases, including both the propagation and evanescence modes. We calculate the reflected and transmitted coefficients and the corresponding field distributions in the case of multiple mode transportation. We also show the related phases which exhibit oscillations with the frequency of the incident light.     

Effects of the upper level coupling field on lasing without inversion in a V-type system

Driven by one upper level coupling field, a three-level V-type atomic system with a pair of upper levels is studied. With one strong coupling field and one weak probe field, it is found that, due to the effects of the upper level coupling field, the quantum coherence between the two upper levels can be induced, and the absorption of the probing field is very sensitive to the relative phase of the probe, the pumping and the upper level coupling fields. With proper parameters, lasing without inversion (LWI) can be realized.     

Experiment study of tunneling phenomenon occurring in the photonic heterostructure containing single-negative metamaterials

In this paper, the tunneling phenomenon occurring in the photonic heterostructure consisting of single-negative (SNG) metamaterials is experimentally studied. First, the SNG metamaterials are fabricated using coplanar waveguide with lumped-element series capacitors and shunt inductors loading. Then, the tunneling phenomenon occurring in the photonic heterostructure containing SNG media is experimentally demonstrated. Moreover, the insensitivity of the tunneling frequency to the breakdown of periodicity of phonotic crystals was also illustrated.     

Transport and photoinduced properties in highly Sr-deficient manganite films

We used the method of finite-difference time domain (FDTD) to study the characteristics of the patch antenna based on a novel periodic structure, and the theory of photonic crystal structure (also photonic band gap [PBG]) structure was introduced. The results obtained show that the surface waves propagating along the substrate surface can be suppressed by the periodic structure due to the influence of its forbidden band, and the energy of the electromagnetic waves is concentrated mainly in the substrate. As a result, the patch antenna based on the periodic structure has a wider bandwidth in comparison with the conventional patch antennae; and a higher gain is reached, so the patch antenna’s performance is improved. Due to such the advantages, the application of patch antennae can be extended in such fields as mobile communication, satellite communication, aviation, etc.     

The directional emission sensitivity of photonic crystal waveguides to air hole removal

To obtain highly directional light output from photonic crystal waveguides (PCWs), the emission characteristics of the narrow-width waveguide structures are investigated by tailoring the geometry of the exit sides. The local structural deformations in the form of air hole removal from the triangular-lattice photonic crystal (PC) show the effectiveness of the previously proposed approach that was implemented by us for another type of PC. The spatial broadening of the beam is greatly suppressed. With the modified waveguide exits, highly directional emissions with small side lobes are achieved. The frequency dependency of the directional emissions is evaluated. We show that the divergence angles of the beams depend linearly on the wavelength for a regular type of PCW but the modified PCW exits have local minima with respect to wavelength in terms of the divergence angle. The present work may prove to be helpful in the design of couplers and edge-emitting lasers and in the implementation of free-space optical communications.     

Resonant modes and inter-well coupling in photonic quantum well with negative index materials

The transfer matrix method was used to study the resonant modes in photonic quantum well by stacking different photonic crystals consisting of positive index materials and negative index materials. The eigenfrequency equation for the resonant modes is derived. It is found that these resonant modes are omnidirectional, and the number of resonant modes is equal to the period number of photonic quantum wells. Moreover, the resonant modes become N-fold splitting in the N photonic quantum wells. The splitting intervals increase with the deceasing of photonic barrier thickness due to the coupling among the wells.