Photonic Band Edge Research Articles

Enhancement of photocurrent in ultrathin active-layer photodetecting devices with photonic crystals

We demonstrate an enhancement of the photoelectric-conversion efficiency of an ultrathin (50 nm) silicon active-layer photodetecting device using a two-dimensional photonic crystal positioned nearby to boost the optical absorption. We show both experimentally and with simulations that the incident-light absorption within the active layer is enhanced by optical-resonance effects at the photonic band edge. We also find that a photonic crystal with deeper holes can lead to an even larger absorption enhancement due to better quality (Q)-factor matching between the photonic band-edge modes and the intrinsic material absorption. The experimentally observed photocurrent of the fabricated photonic-crystal sample is increased by a factor of ∼20 at the photonic band-edge wavelength relative to that of a control sample without the photonic crystal which is attributed to the improved Q matching.

Semiclassical analysis of two-level collective population inversion using photonic crystals in three-dimensional systems

I theoretically demonstrate the population inversion of collective two-level atoms using photonic crystals in three-dimensional (3D) systems by self-consistent solution of the semiclassical Maxwell-Bloch equations. In the semiclassical theory, while electrons are quantized to ground and excited states, electromagnetic fields are treated classically. For control of spontaneous emission and steady-state population inversion of two-level atoms driven by an external laser which is generally considered impossible, large contrasts of electromagnetic local densities of states (EM LDOS’s) are necessary. When a large number of two-level atoms are coherently excited (Dicke model), the above properties can be recaptured by the Maxwell-Bloch equations based on the first-principle calculation. In this paper, I focus on the realistic 1D PC’s with finite structures perpendicular to periodic directions in 3D systems. In such structures, there appear pseudo photonic band gaps (PBG’s) in which light leaks into air regions, unlike complete PBG’s. Nevertheless, these pseudo PBG’s provide large contrasts of EM LDOS’s in the vicinity of the upper photonic band edges. I show that the realistic 1D PC’s in 3D systems enable the control of spontaneous emission and population inversion of collective two-level atoms driven by an external laser. This finding facilitates experimental fabrication and realization.

Broadband optical absorptions in inversed woodpile metallic photonic crystals

Here we demonstrate enhanced optical absorptions within three-dimensional inversed woodpile metallic photonic crystals fabricated via the combination of the direct laser writing method and the electrodeposition method. These metallic microstructures operating in the optical wavelengths are found to possess multiple enhanced absorption peaks over a broad spectral range. We characterize the optical properties with detailed numerical simulations and show that the broadband enhanced absorptions originate from the excitation of robust localized plasmon resonances and enhanced interactions at the photonic band edge within the metallic photonic crystals.

Efficient light amplification in low gain materials due to a photonic band edge effect

One of the possibilities of increasing optical gain of a light emitting source is by embedding it into a photonic crystal (PhC). If the properties of the PhC are tuned so that the emission wavelength of the light source with gain falls close to the photonic band edge of the PhC, then due to low group velocity of the light modes near the band edge caused by many multiple reflections of light on the photonic structure, the stimulated emission can be significantly enhanced. Here, we perform simulation of the photonic band edge effect on the light intensity of spectrally broad source interacting with a diamond PhC with low optical gain. We show that even for the case of low gain, up to 10-fold increase of light intensity output can be obtained for the two-dimensional PhC consisting of only 19 periodic layers of infinitely high diamond rods ordered into a square lattice. Moreover, considering the experimentally feasible structure composed of diamond rods of finite height - PhC slab - we show that the gain enhancement, even if reduced compared to the ideal case of infinite rods, still remains relatively high. For this particular structure, we show that up to 3.5-fold enhancement of light intensity can be achieved.

Optical contrastivity and sensitivity of multicomponent ordered structures

We discuss the definition of an intrinsic optical contrastivity for a complicated structure as a relative total gap taken over a chosen range of frequencies. An optical material contrast sensitivity to the variation of parameters is analyzed for a wide area. The contrastivity and sensitivity parametric maps are calculated for 1D combs with various fillings. The existence of highly sensitive areas on the parametric maps to contrast deviations is shown for different materials. It is shown that for the found parameters the photonic band edge shifts are of the order of 0.3–0.5eV/bar for glass, silicon and microporous silicon matrices.

Slow-light enhanced optical forces between longitudinally shifted photonic-crystal nanowire waveguides

We reveal that slow-light enhanced optical forces between side-coupled photonic-crystal nanowire waveguides can be flexibly controlled by introducing a relative longitudinal shift. We predict that close to the photonic band edge, where the group velocity is reduced, the transverse force can be tuned from repulsive to attractive, and the force is suppressed for a particular shift value. Additionally the shift leads to symmetry breaking that can facilitate longitudinal forces acting on the waveguides, in contrast to unshifted structures where such forces vanish.

Experimental verification of enhanced electromagnetic field intensities at the photonic stop band edge of 3D polystyrene photonic crystals using Z-Scan technique

Enhancement of nonlinear absorption of polystyrene (PS) was investigated using 3D PS photonic crystals (PCs) with Z-scan technique. The Z-scan experiment was carried out at 532nm in the picosecond (ps) regime. The transmittance of the PC was found to get modified because of the nonlinear absorption of PS particularly when 532nm is near the photonic stop band (PSB) edge of PC. Calculations show that the field gets enhanced by 1.4 times the input field intensity within the crystal when the 532nm wavelength falls at the PSB edge while keeping the crystal at an angle of 35°.

Model calculations for enhanced fluorescence in photonic crystal phosphor

We propose a novel photonic structure, based on the photonic crystal (PC) effect, which simulations show results in an improved fluorescence efficiency from embedded phosphor. To be specific, the phosphor pumping efficiency can be significantly improved by tuning the pump photon energy to a photonic band-edge (PBE) of the PC phosphor. We have confirmed this theoretically by calculating optical properties of one-dimensional PC phosphor structures using the transfer-matrix method and plane-wave expansion method. For a particular model structure based on a quantum dot phosphor, the fluorescence enhancement factor was estimated to be as high as 6.9 for a monochromatic pump source and 2.2 for a broad bandwidth (20 nm) pump source.

Optical properties of three-dimensional woodpile photonic crystals composed of circular cylinders with planar defect structures

The optical properties of three-dimensional woodpile photonic crystals (PhCs) composed of circular cylinder rods with a planar defect structure at the central layer are theoretically investigated using the parallel finite-difference time-domain method and plane-wave expansion method. Three types of planar defects are introduced into the PhC by alternating respectively the dielectric constant, cylinder diameter, and misalignment of the rods at the defect layer. The transmission spectrum and band diagram of each planar defect structure are systematically studied. The resonance and transmission properties of the defect structures can be characterized by two distinct resonant modes, the defect mode and the band-edge resonant mode, which have been identified by detailed spectrum analysis, calculated mode profiles and field patterns. It is shown that, by modifying the rod diameter or the dielectric constant of materials at the defect layer, the resonant modes can be varied and controlled. Also, by applying dislocation to a layer of dielectric rods, the photonic band edges can be shifted.

Pressure and temperature controlled self-assembly of high-quality colloidal crystal films on optical fibers

High-quality annular colloidal multilayer films coated on an optical fiber were fabricated from aqueous solutions by the modified vertical deposition method with controllable pressure and temperature. The resulting cylindrical annulus was characterized by the scanning electron microscopy (SEM), and the SEM images illustrated the [111]-like plane of face-centered-cubic (fcc) structures parallel to the surface of the optical fiber. Transmission spectra demonstrated deep photonic band gap (PBG) of up to 76% and steep photonic band edge (PBE) of up to 5.2%/nm, as well as the excellent cylindrical symmetry was affirmed with off-axis incidence light. With the angles of out-of-plane incidence increasing from 0 to 60°, the peak positions and transmittance decreased gradually which agreed well with the Bragg formula.

Nanobeam photonic bandedge lasers

We demonstrate one-dimensional nanobeam photonic bandedge lasers with InGaAsP quantum wells at room temperature from the lowest dielectric band of photonic crystal nanobeam waveguides. The incident optical power at threshold is 0.6 mW (effectively ~18 μW). To confirm the lasing from the dielectric bandedge, the polarization and the photoluminescent spectra are taken from nanobeams of varying lattice constants. The observed shift of the lasing wavelength agrees well with the computational prediction.

Localized photonic band edge modes and orbital angular momenta of light in a golden-angle spiral

We present a numerical study on photonic bandgap and band edge modes in the golden-angle spiral array of air cylinders in dielectric media. Despite the lack of long-range translational and rotational order, there is a large PBG for the TE polarized light. Due to spatial inhomogeneity in the air hole spacing, the band edge modes are spatially localized by Bragg scattering from the parastichies in the spiral structure. They have discrete angular momenta that originate from different families of the parastichies whose numbers correspond to the Fibonacci numbers. The unique structural characteristics of the golden-angle spiral lead to distinctive features of the band edge modes that are absent in both photonic crystals and quasicrystals.

Advanced Materials for Sustainable Energy and a Greener Environment

Advanced Materials for Sustainable Energy and a Greener Environment

Continuation Finite Element Simulation of Second Harmonic Generation in Photonic Crystals

AbstractA computational study on the enhancement of the second harmonic generation (SHG) in one-dimensional (1D) photonic crystals is presented. The mathematical model is derived from a nonlinear system of Maxwell’s equations, which partly overcomes the shortcoming of some existing models based on the undepleted pump approximation. We designed an iterative scheme coupled with the finite element method which can be applied to simulate the SHG in one dimensional nonlinear photonic band gap structures in our previous work. For the case that the nonlinearity is strong which is desirable to enhance the conversion efficiency, a continuation method is introduced to ensure the convergence of the iterative procedure. The convergence of our method is fast. Numerical experiments also indicate the conversion efficiency of SHG can be significantly enhanced when the frequencies of the fundamental and the second harmonic wave are tuned at the photonic band edges. The maximum total conversion efficiency available reaches more than 50% in all the cases studied.

Controllable preparation of the ordered pore arrays anodic alumina with high-quality photonic band gaps

High-quality photonic crystals (PCs) based on the ordered pore arrays anodic alumina are fabricated by the anodic oxidation method using the newly-designed periodic oxidation voltage wave. The obtained PCs own uniform narrow photonic band gaps (PBGs), steep photonic band edges, zero transmittances inside of the PBGs and high transmittances outside of the PBGs. Importantly, the high-quality PBGs of the anodic alumina PCs are tunable and controllable in the range from 350 nm to 1330 nm by modifying the anodizing voltage waveform. The benefit of newly-designed periodic oxidation voltage wave is to improve the optical properties of anodic alumina PCs.

Zero-effective-phase bandgaps in photonic multilayers: analytic expressions for band-edge frequencies and broadband omnidirectional reflection

The analytic expressions for frequency locations of the zero-effective-phase photonic band edge of the photonic multilayers containing single-negative materials are derived based on the effective medium theory. By adopting the derived band-edge formula, the properties, especially the thickness- and angular-dependence of the zero-effective-phase photonic bandgap are investigated in detail. The obtained results are consistent with the predictions in the transfer-matrix method. Moreover, the potential application of the band-edge formula in extending zero-effective-phase photonic bandgaps is proposed, which is verified in the photonic heterostructure realized by using composite right-/left-handed transmission line.

Plasmon-resonance-induced enhancement of the reflection band in a one-dimensional metal nanocomposite photonic crystal

We report the realization of a one-dimensional photonic crystal consisting of alternating layers of metal nanocomposite and polymer layers. The structure shows a large change in the width of the reflection band due to the interplay between the plasmon resonance of the metal nanoparticle and the Bloch modes of the photonic crystal. The width of the reflection band is found to increase by 200% when the photonic band edge approaches the plasmon resonance of the silver nanoparticles.

Tunable Light Emission from GaN-Based Photonic Crystal with Ultraviolet AlN/AlGaN Distributed Bragg Reflector

In this paper, the characteristics of GaN-based two-dimensional (2D) photonic crystal bandedge coupling operation with an ultraviolet AlN/AlGaN distributed Bragg reflector (DBR) have been investigated and analyzed. The 25-pair AlN/Al0.2GaN0.8 DBR shows a high reflectivity of 85% at 375 nm with the stop-band width of 15 nm. A strong light emission was observed from GaN photonic crystals within high reflectivity region of DBR. The emission wavelength can be also manipulated by varying the radius to lattice constant ratio. The photonic crystal bandedge mode was also characterized with three-dimensional plane-wave expansion (PWE) and finite-difference time-domain (FDTD) simulation.

LASER CONTROL OF OPTICAL PROPERTIES OF TWO-LEVEL ATOMS EMBEDDED IN A PHOTONIC CRYSTAL

A method of laser control of absorption and dispersion of two-level quantum system (atoms, ions, quantum dots) embedded into photonic band gap (PBG) material via variation of intensity and frequency of an external laser field is proposed. It is shown that in order to provide an effective control, the frequency of atomic transition should be located at the photonic band edge near the bottom of the PBG. The method is based on the laser induced Mollow splitting of the atomic energy levels and strong dependence of the decay rates of the so-called dressed states on the frequency of the Mollow splitting due to photonic band edge. This enables us to control absorption and dispersion of a signal laser field, which is near-resonant to the quantum transition of dopant.

Coherent control of a three-level atom in a photonic crystal

We demonstrate coherent control of the population and polarization of a two-level subsystem consisting of the two upper levels of a three-level atom in the V-configuration placed inside the structured reservoir of a photonic crystal. One of the excited state transition frequencies is located deep within the photonic band gap and the other transition is near the photonic band edge. Using the method of generalized-Laplace transforms, we study the population and polarization of the two-level subsystem of the three-level atom in the Born approximation without making the Markov approximation. The generalized-Laplace transform technique allows us to solve the Langevin equation for the operators and the correlation function of operators rather than the Schrodinger equations of motion. Coherent control of the population and the polarization dynamics of the two-level subsystem is demonstrated in the structured electromagnetic density of states of a photonic crystal. We demonstrate the tunability of the fractionalized steady-state population and the residual coherence in the photon–atom bound state by varying the Rabi frequency and the phase of the driving laser field.