Polarization-independent low-pass spatial filters based on one-dimensional photonic crystals containing negative-index materials

A new application of one-dimensional photonic crystals containing negative-index materials is proposed as low-pass spatial filters. Through optimizing the parameters of defect layer, a series of polarization-independent defect modes in the zero-average-index gap of the photonic crystals are obtained with the increase of the incident angle. Based on these defect modes, polarization-independent low-pass spatial filters are designed. The spatial-frequency bandwidth of the spatial filters can be adjusted by changing the period number of the defective photonic crystal structures. In addition, the effect of the losses of negative-index materials on the spatial filters is considered.     

Quantum electron plasma in one-dimensional metallic–dielectric photonic crystal

The interaction of the electromagnetic radiation with one-dimensional photonic crystal consisting of metal and transparent dielectric medium is studied numerically. Dielectric permeabilities of the electron plasma in the metal are considered both in the quantum Mermin and in the classical Drude–Lorentz approaches. It is shown that the reflection, transmission and absorption-frequency zones of electromagnetic radiation appear in the photonic crystal. In addition, the reflectance, transmittance and absorptance optical coefficients for such photonic crystal in the quantum approach differ from those coefficients in the Drude–Lorentz approach.     

Ultra-narrow bandwidth optical filters consisting of one-dimensional photonic crystals with anomalous dispersion materials

We present a new type of optical filter with an ultra-narrow bandwidth and a wide field-of-view （FOV）. This kind of optical filter consists of one-dimensional photonic crystal （PC） incorporating an anomalous-dispersion-material （ADM） with, for instance, an anomalous dispersion of 6P3/2←6S1/2 hyperfine structure transition of a caesium atom. The transmission spectra of optical filters are calculated by using the transfer-matrix method. The simulation results show that the designed optical filter has a bandwidth narrower than 0.33GHz and a wide FOV of ±30°as well. The response of transmission spectrum to an external magnetic field is also investigated.     

Design and parametric amplification analysis of dispersion-flat photonic crystal fibers

In recent years, a new type of broadband amplifier, fiber optical parametric amplifier (FOPA) has been investi- gated, which utilizes four-wave mixing (FWM) to amplify the signals and offers a broadband amplification at arbi- trary wavelengths[1]. Though simple single-pump FOPA could offer a gain bandwidth of more than 200 nm, the gain spectrum is not flat over the amplifier bandwidth but has a difference as high as 15 dB between the lowest and the highest values, which brings to the diffi…     

Spontaneous transition of one-dimensional plasma photonic crystal’s orientation in a dielectric barrier discharge

A novel one-dimensional plasma photonic crystal whose crystal orientation can change spontaneously is demonstrated using a dielectric barrier discharge with two liquid electrodes. The orientation of the plasma photonic crystal will vary from transverse to longitudinal or vary from longitudinal to transverse and then revert to longitudinal by self-adjustment, while the experimental conditions are kept fixed. The dispersion relation of these plasma photonic crystals are calculated, and the changes of the photonic band diagrams during the orientation transition are studied.     

Extending the zero-effective-phase photonic bandgap by one-dimensional ternary photonic crystals

A novel method to enlarge the zero-effective-phase bandgap has been presented in the one-dimensional photonic crystals by sandwiching the third material between the two single-negative materials to form a one-dimensional ternary periodic structure. The band-edges formula for the one-dimensional ternary photonic crystal is derived based on the effective-medium theory and the expressions of the upper and lower frequency limits for the ternary photonic crystals are obtained. Then two schemes to enlarge the zero-effective-phase bandgaps are put forward. Moreover, the angular- and polarization-dependences of the photonic bandgap are investigated. Finally, the role of the dispersion in the sandwiched layer on the bandgap extending has been discussed and two schemes are also presented to enlarge the zero-effective-phase photonic bandgap.     

Characteristics of local photonic state density in an infinite two-dimensional photonic crystal

The local density of photonic states （LDPS） of an infinite two-dimensional （2D） photonic crystal （PC） composed of rotated square-pillars in a 2D square lattice is calculated in terms of the plane-wave expansion method in a combination with the point group theory. The calculation results show that the LDPS strongly depends on the spatial positions. The variations of the LDPS as functions of the radial coordinate and frequency exhibit “mountain chain” structures with sharp peaks. The LDPS with large value spans a finite area and falls abruptly down to small value at the position corresponding to the interfaces between two different refractive index materials. The larger/lower LDPS occurs inward the lower/larger dielectric-constant medium. This feature can be well interpreted by the continuity of electricdisplacement vector at the interface. In the frequency range of the pseudo-PBG （photonic band gap）, the LDPS keeps very low value over the whole Wiger-Seitz cell. It indicates that the spontaneous emission in 2D PCs cannot be prohibited completely, but it can be inhibited intensively when the resonate frequency falls into the pseudo-PBG.     

Coupling of two defect modes in photonic crystal fibers

The coupling characteristics of two defect modes in photonic crystal fibers are investigated theoretically by the finite-difference time-domain (FDTD) method. The transmission spectrum and eigenmodes of optical wave are found to be very sensitive to the geometrical and physical parameters of the structure, as well as to the relative position of the two defects.     

Holographically recorded reverse-mode transmission gratings in polymer-dispersed liquid crystal cells

We have synthesized one-dimensionally structured and switchable reverse-mode transmission gratings in polymer-dispersed liquid crystalline materials by holographic exposure technique using the 540 nm wavelength from a solid-state laser. These structures offer the potential for electrically switchable diffractive optical elements, whose functionality can be switched on by applied electric fields. We present results for the diffraction efficiency (η) as functions of curing-time, intensity of the writing-beams, polarizations of the writing, as well as probe beams, and frequency of the electric field. For exposure times much shorter than the time needed for complete-cure of the grating structure, η increases upon application of the electric field; for an electric field of 14 MV/m @1.1 kHz, we observe $\frac{\Delta\eta}{\eta}\sim 1100\%$ with switching time constant of ～15 ms.     

Laser physical vapor deposition of nanocrystalline dots using nanopore filters

Nanocrystalline dots of n-type Bi₂Te_2.7Se_0.3 thermoelectric compound and of silicon were deposited by laser physical vapor deposition using polycarbonate or alumina nanopore filters as templates. The films were characterized by scanning electron microscopy and transmission electron microscopy. Using a pore size of 0.2 μm in the nanopore filters, a uniform distribution of crystallites with size 3 to 4 nm and separated from each other was observed by high-resolution transmission electron microscopy. The dots were all single crystals, as seen by the resolved crystal lattice planes. The compositions of the crystallites, of both the thermoelectric compound and silicon, were analyzed by energy dispersive X-ray analysis. The composition of the thermoelectric compound nanocrystals differed significantly from that of the bulk target, likely due to vapor pressure differences of the constituent elements. The results are promising for synthesis of nanocrystalline dots with controlled size but compositional control is a different task that is not carried out. The observations illustrate that nonstoichiometry is a result of difference in the vapor pressure of different elements in the compound. The method of synthesis is found to be suitable for deposition of quantum dots below certain size determined by the size of the pores in the porous filter.     

Nonlinear refractive index of multicomponent glasses designed for fabrication of photonic crystal fibers

The second order nonlinear refractive index n ₂ of various multicomponent glasses was measured at the wavelength of 1240 nm close to the 1.3-μm fiber transmission window. With the refractive index covering the range from 1.45 to 2.3, a comparatively broad range of n ₂ with values from 1.1×10^?20 m²/W for boro-silicate based glass NC21 to 4.3×10^?19 m²/W for lead–bismuth-gallate based glass PBG08 was measured using the Z-scan method. Considering the broad infrared transmission range of multicomponent glasses, these materials pose a great potential for future applications as photonic crystal fiber sources of infrared supercontinuum.     

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.     

Numerical analysis of multicore photonic crystal fibers

A Galerkin's method-based numerical procedure is extended to obtain the modal field distribution of multicore photonic crystal fibers for the first time to our knowledge, which can reveal how the air hole size influences the mode coupling and how the coupling strength varies with wavelength. These results will be helpful in the future design of multicore photonic crystal fibers with proper guidance properties.     

Broadband-cascaded four-wave mixing in a photonic crystal fiber around 1 μm

To our knowledge, efficient generation of broadband four-wave mixing cascades centered at 1 μm and spanning 600 nm is experimentally demonstrated for the first time. This frequency comb is generated from a two-tone seed with a maximum peak power of 25 W in a low-dispersion photonic crystal fiber. It consists of up to 44 new idler waves generated symmetrically around the seed.     

Design and analysis of all-optical 4–2 binary encoder based on photonic crystal

In this paper we theoretically propose combining optical waveguides with nonlinear photonic crystal based ring resonators for realizing an all optical 4–2 encoder. Nonlinear resonant rings are constructed from GaAs as the material used for dielectric rods. By application of optical beam to input ports of the structure the on/off states are realized and the resulting truth table confirms functionality of proposed device. The switching threshold and time delay of the device are about 1 kW/µm² and 1 ps, respectively. The normalized power at the output ports for all the ports in ON states is the same and equal to 60%.     

Highly confined and continuous single-mode operation of self-align photonic crystal oxide VCSEL

In this letter, we report on single-mode operation of originally multi-mode oxide VCSEL by using etched photonic crystal air holes and unique trench structure. The device fabrication utilized conventional photolithography; with simplified lithography step of self-aligning the photonic crystal and trench structures to the laser aperture for efficient and vigorous device processing. The fabricated photonic crystal VCSEL with trench device exhibits a single-mode output power of 0.7 mW, threshold current of 3.5 mA, slope efficiency of 0.10 W/A, and continuous single-mode output spectra at wide operating current range. The results are compared with conventional multi-mode oxide VCSEL of similar device geometry. In addition, theoretical analysis is presented for developing further understanding of the photonic crystal VCSEL.     

Fabrication of fiber-embedded multi-core photonic crystal fibers

A novel fabrication method of multi-core photonic crystal fibers is proposed on the basis of a fiber- embedded technique.A taper tower is used to modify the structures of the fiber preform,and four steps of fiber fabrication and different structures of fiber samples are given.The mode structures and beating characteristics of a photonic crystal fiber sample with two successive cores are investigated in detail with the help of a supercontinuum light source,a charge-coupled device(CCD)camera,and an optical spectrum analyzer.The test results show a clear beating phenomenon between two orthotropic polarization modes with a 2.8-nm peak interval in wavelength.     

Measurement of glycerol concentration in B–H–G solution using 3D photonic crystal structure

A novel technique is used to measure the concentration of glycerol in blood-hemoglobin-glycerol (B–H–G) solution using 3D photonic crystal structure is presented in this paper. Glycerol concentration is estimated accurately by measuring the intensities of transmitted light. Here, reflection as well as absorption losses is considered to measure the transmitted intensity of light having wavelength 540 nm. The principle of measurement is based on the linear variation of photonic band gap with respect to glycerol concentration. Simulations for photonic band gap are made using plane wave expansion (PWE) method. An experimental set up is theoretically designed to measure the concentration of glycerol at different hemoglobin concentration.     

Probe spectrum of a four-level atom in a double-band photonic crystal

In this paper, the probe absorption spectrum of an atom in a double-band photonic crystal have been studied. In the modes, we assume that one of the two atomic transitions in a Λ-type atomic system is interacting with free vacuum modes, and another transition is interacting with free vacuum modes, isotropic photonic band gap (PBG) modes and anisotropic PBG modes, separately. The effects of the fine structure of the atomic lower levels on the probe absorption spectrum are investigated in detail in the three cases. The most interesting thing is that the two (four) transparencies at one (two) probe absorption peak(s), caused by the fine structure of the lower levels of an atom, are predicted in the case of isotropic PBG modes.