Edge Of Photonic Band Gap Research Articles

Spectral characterization of a photonic bandgap fiber for sensing applications

We study the measurand-induced spectral shift of the photonic bandgap edge of a hollow-core photonic crystal fiber. The physical measurands considered are strain, temperature, curvature, and twist. A noticeable sensitivity to strain, temperature, and twist is observed, with a blueshift to increase strain and twist. An increase in temperature induces a redshift. On the other hand, curvature has no observable effect on the spectral position of the photonic bandgap edge.

Pneumatic photonic crystals

We theoretically study a 1D elastic photonic crystal containing air voids as an opto-pneumatic medium. This medium is sensitive to weak deviations of the external pressure and, owing to its elasticity, can vary its geometry depending on the external conditions. We show that the reflectivity can be drastically changed at a chosen working frequency near the photonic band-gap edge or the reflection window. The resonance properties of such pneumatic photonic crystals made of glass, silicon, and mica with directly excited eigenmodes in the infrared region of frequencies are analyzed. The ways to determine small changes in the pressure on the micro- and nanobar scale are discussed.

Enhancement of temperature measurement by using photonic bandgap effect

A novel temperature sensor by using photonic bandgap (PBG) effect is demonstrated. The solid core photonic bandgap fiber (PBGF) with infiltrated high refractive index solution is used for temperature measurement. It shows that the rising photonic bandgap edges of PBGF has a blue shifting of 120.54 nm when the ambient temperature was changing from 24 to about 64 °C. The sensitivity of the temperature measurement 3.01 nm/°C was achieved.

Bottom-Up Photonic Crystal Approach with Top-Down Defect and Heterostructure Fine-Tuning

We combine the most efficient (chemical) approach toward three-dimensional photonic crystals with the most convenient (physical) technique for creating non-close-packed crystalline structures. Self-assembly of colloidal particles in artificial opals is followed by a carefully tuned plasma etching treatment. By covering the resulting top layer of more open structure with original dense opal, embedded defect layers and heterostructures can be conveniently designed for advanced photonic band gap and band edge engineering.

A spectral route to determining chirality

We show how one-dimensional structured media can be used to measure chirality, via the spectral shift of the photonic band gap edges. Analytically, we show that a chiral contrast can, in some cases, be mapped unto an index contrast, thereby greatly simplifying the analysis of such structures. Using this mapping, we derive a first-order shift of the band gap edges with chirality. Potentially, this effect could be used for measuring enantiomeric excess.

Polarization bandpass filter based on one-dimensional photonic crystal heterostructures

A new kind of polarization bandpass filters (P-BPFs), which fulfill the functions of high reflectivity for one polarization and high transmittance in the passband for the other, are proposed. The P-BPFs consist of a stack of two one-dimensional (1D) photonic crystals (PCs) that are referred to as 1D PC heterostructures. The essential function of P-BPFs is realized by making the first transmitted peak near the photonic bandgap edges of one PC coincide with that of the other PC. Based on this method, three kinds of filters have been designed and discussed in detail: an isotropic 1D PC single-polarization bandpass filter (SP-BPF) at oblique incidence with a narrow passband for TM polarization and a broadened stop band for TE polarization, an anisotropic 1D PC SP-BPF at normal incidence with a narrow passband for TE polarization and a broadened stop band for TM polarization, and an anisotropic 1D PC double-polarization bandpass filter (DP-BPF) at oblique incidence with a spectral separated narrow passband for both polarizations, respectively. The filters can be fabricated by a lot of coating methods and integrated easily with other photonic components.

Giant enhancement of second harmonic generation in nonlinear photonic crystals with distributed Bragg reflector mirrors

We theoretically investigate second harmonic generation (SHG) in one-dimensional multilayer nonlinear photonic crystal (NPC) structures with distributed Bragg reflector (DBR) as mirrors. The NPC structures have periodic modulation on both the linear and second-order susceptibility. Three major physical mechanisms, quasi-phase matching (QPM) effect, slow light effect at photonic band gap edges, and cavity effect induced by DBR mirrors can be harnessed to enhance SHG. Selection of appropriate structural parameters can facilitate coexistence of these mechanisms to act collectively and constructively to create very high SHG conversion efficiency with an enhancement by up to seven orders of magnitude compared with the ordinary NPC where only QPM works.

Optical properties of chiral photonic crystals with linear profiles of modulation parameters

The oblique propagation of light through a layer of chiral photonic crystal (PC) with linear profiles of modulation parameters is considered. The problem is solved by the method of Ambartsumyan layer addition. The wavelength dependences of the amplitude characteristics have been studied at different angles of incidence in two cases, i.e., in a chiral PC with a linear profile of modulation period and a chiral PC with a linear profile of modulation depth. It is shown that the photonic band gap is broadened in both cases and that omnidirectional reflection occurs under certain conditions. The nonreciprocity features are investigated for these two cases and it is shown that a chiral PC with a linear profile of modulation period can operate as an ideal optical diode in a certain frequency range. The features of the effect of change in the modulation parameters on the photon density of states, group velocity, and group velocity dispersion are analyzed. It is shown that, when the modulation parameters change in space, the photon density of states at the photonic band gap edges significantly decreases. It is proposed to use PCs with a spatially changing modulation period can be used to compress (expand) light pulses.

Detailed theoretical investigation of bending properties in solid-core photonic bandgap fibers

In this paper, detailed properties of bent solid-core photonic bandgap fibers (SC-PBGFs) are investigated. We propose an approximate equivalent straight waveguide (ESW) formulation for photonic bandgap (PBG) edges, which is convenient to see qualitatively which radiation (centripetal or centrifugal radiation) mainly occurs and the impact of bend losses for an operating wavelength. In particular, we show that cladding modes induced by bending cause several complete or incomplete leaky mode couplings with the core mode and the resultant loss peaks. Moreover, we show that the field distributions of the cladding modes are characterized by three distinct types for blue-edge, mid-gap, and red-edge wavelengths in the PBG, which is explained by considering the cladding Bloch states or resonant conditions without bending. Next, we investigate the structural dependence of the bend losses. In particular, we demonstrate the bend-loss dependence on the number of the cladding rings. Finally, by investigating the impacts of the order of PBG and the core structure on the bend losses, we discuss a tight-bending structure.

Polarized micro-cavity organic light-emitting devices

We present the results of a study of light emissions from a polarized micro-cavity Organic Light-Emitting Device (OLED), which consisted of a flexible, anisotropic one-dimensional (1-D) photonic crystal (PC) film substrate. It is shown that luminous Electroluminescent (EL) emissions from the polarized micro-cavity OLED were produced at relatively low operating voltages. It was also found that the peak wavelengths of the emitted EL light corresponded to the two split eigen modes of the high-energy band edges of the anisotropic PC film, with a strong dependence on the polarization state of the emitting light. For polarization along the ordinary axis of the anisotropic PC film, the optical split micro-cavity modes occurred at the longer high-energy photonic band gap (PBG) edge, while for polarization along the extraordinary axis, the split micro-cavity modes occurred at the shorter high-energy PBG edge, with narrow bandwidths. We demonstrated that the polarization and emission mode of the micro-cavity OLED may be selected by choosing the appropriate optical axis of the anisotropic 1-D PC film.

Energy Squeeze of Ultrashort Light Pulse by Kerr Nonlinear Photonic Crystals

Self-phase modulation can efficiently shape the spectrum of an optical pulse propagating along an optical material with Kerr nonlinearity. In this work we show that a one-dimensional Kerr nonlinear photonic crystal can impose anomalous spectrum modulation to a high-power ultrashort light pulse. The spectrum component at the photonic band gap edge can be one order of magnitude enhanced in addition to the ordinary spectrum broadening due to self-phase modulation. The enhancement is strictly pinned at the band gap edge by changing the sample length, the intensity or central wavelength of the incident pulse. The phenomenon is attributed to band gap induced enhancement of light-matter interaction.

Characteristic investigation of high quality three-dimensional photonic crystals fabricated by self-assembly: theory analysis, simulation and measurement

The recently reported pressure controlled isothermal heating vertical deposition (PCIHVD) method is improved and a sealed suction setup, filled with silica gel spheres, is used to provide an optimal growing condition with better stability and reproducibility for fabricating photonic crystals (PCs). The optimal pressure condition (p = 45 mmHg) is determined. High quality PCs are fabricated with this improved method from polystyrene spheres. The characteristics of these PCs are analyzed theoretically, simulatively and experimentally. The results demonstrate the good quality of these PCs. The deep photonic band gap (≥85%) and steep photonic band edge (>8% nm−1) of the samples display the strong localization potentials of photons, which provide a basis for studying advanced optical elements such as ultra-fast all-optical switches.

Directional radiation pattern of luminescent photonic crystals at frequencies near the second photonic stop band

The possibility of the directional enhancement of luminescence at frequencies near the edge of the second photonic bandgap of opal-type photonic crystals has been demonstrated both theoretically and experimentally. The directional patterns of radiation have been simulated by calculating the angular dependences of the density of optical states. The calculation results are compared to the experimental data obtained for the thin-film opals with terbium-containing complexes. Good agreement is achieved after the strong smoothing of the calculated curves; this smoothing is necessary because of the imperfection of the structure of actual samples.

Chemosorption-related shift of a photonic bandgap in photoconductive ZnO inverse opal

A change of up to 40% of the relative transmission at the photonic bandgap edge has been observed in photoconductive inverted ZnO opals under ultraviolet laser irradiation. This effect has been related to the irradiation-stimulated change of the refraction index of the photonic crystal. The desorption (chemosorption) of oxygen molecules on the surface of the ZnO backbone leading to destruction (formation) of a depletion layer at the ZnO surface has been suggested as the mechanism responsible for the slow variation of polarizability of the inverted ZnO opal.

Dispersionless tunneling of slow light in antisymmetric photonic crystal couplers

We suggest a novel and general approach to the design of photonic-crystal directional couplers operating in the slow-light regime. We predict, based on a general symmetry analysis, that robust tunneling of slow-light pulses is possible between antisymmetrically coupled photonic crystal waveguides. We demonstrate, through Bloch mode frequency-domain and finite-difference time-domain (FDTD) simulations that, for all pulses with strongly reduced group velocities at the photonic band-gap edge, complete switching occurs at a fixed coupling length of just a few unit cells of the photonic crystal.

Quantum Information Processing in Photonic Crystals

We have studied the quantum information processing phenomenon in photonic crystals doped with four-level nanoparticles. This phenomenon occurs due to the switching mechanism in the system. We consider that one of the transition energies of nanoparticles is coupled near resonantly with a photonic band gap edge. The dipole-dipole interaction between the nanoparticles has also been included. It is found that the system switches between the transparent and nontransparent states due to the dipole-dipole interaction and the band edge coupling. This is an interesting finding and can be used to produce logical photon switches in the quantum information processing.

Photonic crystals based on chiral liquid crystal

AbstractLiquid crystals including chiral molecule have a self‐organized helical structure with nano‐scaled periodicity, which can be regarded as a one‐dimensional (1D) photonic crystal. We have so far investigated lasing characteristics at an edge of the 1D photonic band gap (PBG) of dye‐doped chiral liquid crystals such as cholesteric liquid crystal (CLC) and ferroelectric liquid crystal (FLC). A band‐edge excitation effect on the CLC lasing has been experimentally demonstrated by matching the excitation laser wavelength to the higher energy‐edge of the PBG of a dye‐doped CLC. The wavelength tuning of the laser action upon changing electric field strength has been achieved in FLC. We have proposed the defect modes characteristic to the helicoidal structure of the chiral liquid crystal and demonstrated the lasing from the chiral defect modes. A twist defect mode in a transmission spectrum of the composite film consisting of two photopolymerized CLC layers has been experimentally demonstrated. A new type of defect mode in a chiral liquid crystal on the basis of the local deformation of the 1D periodic helical structure has also been proposed, and the possibility of the wavelength tuning has been demonstrated in this system. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photonic bandgap fiber for refractive index measurement

Abstract The use of photonic bandgap fibers for refractive index measurement has been demonstrated. The demonstrated PBGF has a wavelength shift of 280 nm in the falling photonic bandgap edge when the ambient refractive indices change from 1.333 to 1.39, which agrees well with the analytical prediction. A sensitivity of 2 × 10 −6 RIU is possible to be achieved assuming the demodulation system can resolve 0.01 nm wavelength shift.

Second harmonic generation in one-dimensional nonlinear photonic crystals solved by the transfer matrix method

The transfer matrix method has been widely used to calculate the scattering of electromagnetic waves. In this paper, we develop the conventional transfer matrix method to analyze the problem of second harmonic generation in a one-dimensional multilayer nonlinear optical structure. In the designed nonlinear photonic crystal structure, the linear and nonlinear optical parameters are both periodically modulated. We have taken into account the multiple reflection and interference effects of both the linear and nonlinear optical waves during the construction of the transfer matrix for each composite layer. Application of this method to multilayer nonlinear photonic crystal structures with different refractive indices indicates that the proposed method is an exact approach and can simulate the generation of the second harmonic field precisely. In an optimum structure, the second harmonic generation efficiency can be several orders of magnitude larger than in a conventional quasi-phase-matched nonlinear structure with the same sample length. The reason is that, due to the presence of photonic band gap edges, the density of states of the electromagnetic fields is large, the group velocity is small, and the local field is enhanced. All three factors contribute to significant enhancement of the nonlinear optical interactions.

Tunable one‐dimensional photonic crystal structures based on grooved Si infiltrated with liquid crystal E7

AbstractTuning of a photonic band gap in a composite one‐dimensional photonic crystal structure infiltrated with nematic liquid crystal E7 has been evaluated by simulations. It has been found that a sufficient shift of the short wavelength edge, λ edge of a main photonic band gap can be obtained in structures with a pronounced initial alignment of the liquid crystal director in the grooves of a single crystalline Si matrix. The largest effect is predicted for the reorientation of liquid crystal molecules from planar homogeneous alignment along the grooves to homeotropic alignment with respect to the Si walls due to an electro‐optical effect. The shift in photonic band gap due to thermal tuning, resulting from the transition of liquid crystal from the mesophase to the isotropic phase, is less than for electric tuning. Thermo‐tuning has been demonstrated experimentally. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)