The fabrication of three-dimensional photonic bandgap materials and the controlled incorporation of point, linear and planar defects into these crystals is a major challenge in materials research today. We show in this report that these purposes can be achieved by photoelectrochemical etching of lithographically prestructured silicon. Our advanced etching method allows the fabrication of three-dimensional photonic crystals with simple cubic symmetry. The performed calculations suggest complete bandgaps of 5% for the realized bulk structures. By lithographic prestructuring vertical line and planar defects can be induced, whereas horizontal planar defects can be created during the etching step. By combining both structuring techniques point defects can be fabricated.

The major challenge in todays photonic crystal fabrication is the experimental realization of perfect, disorder-free structures. Macroporous silicon etching is a versatile technique for the manufacturing of large-scale well-ordered porous materials and three-dimensional photonic crystals. We investigate the degree of local disorder by scanning electron microscopy and a subsequent image processing, as well as the homogeneity of our large area crystals by an optical two-dimensional mapping. The observed disorder is related to the applied fabrication parameters. The deduced dependencies help to avoid disorder and to optimize our structures.

A new kind of substrate called Silicon-On-Mirror has been fabricated for nanophotonics applications. It is composed of a monocrystalline silicon layer separated from the silicon substrate by a buried distributed Bragg reflector. Photoluminescence of silicon at 80 K is used to investigate two-dimensional (2D) photonic crystal hexagonal microcavities etched in the monocrystalline silicon layer. Two types of substrates are compared: silicon-on-insulator (SOI) substrates and the new substrates where the silicon layer is bonded on a buried distributed Bragg reflector (DBR). Quality factors of the in-plane resonant modes are analyzed both experimentally and theoretically when the substrate structure is changing. It is shown that the underlying DBR can enhance the in-plane quality factors by a factor 2.5 by reducing the losses. The out-of-plane light extraction efficiency of the cavities and of defectless photonic crystals are also discussed.

Since the pioneering works of Yablonovitch and John, the concept of photonic crystals has attracted great attention from both fundamental and practical points of view. Different types of approaches have been taken to realize the spatial periodic structures: nanolithography techniques developed to produce semiconductors, sedimentation of monodispersed nanoscale spheres, or holographic illumination of photosensitive materials. In our work, we employed two newly discovered fascinating phenomena: particle drag effect and particle pumping effect in a liquid crystal to build the ordered colloidal structures. Combining the moving nematic-isotropic transition line with a patterned electric field can be used to move particles from one place to another. This can be used to pack particles in a certain place in an ordered periodic structure. The speed of the interface and the magnitude of the applied electric field controls the size, density and/or dielectric property of the particle that can be moved and determines those that are left behind. This capability allows us to place “defects” at particular locations in the photonic crystals constructed. Although many challenges remain before this system can be used in practical optical components, this new technique provides an excellent means of producing complex photonic crystals tailored for specific optical affects and applications.

We review certain novel optical properties of two-dimensional dielectric photonic crystals (PCs) which exhibit negative refraction behavior. We investigate two mechanisms which utilize the band structure of the PC and lead to a negative effective index of refraction (n_eff < 0). The negative refraction phenomenon is demonstrated experimentally and by simulations when the incident beam couples to a photonic band with n_eff < 0. Further, the PC slab acts like a focusing lens to an omnidirectional source where the properties of focusing depends on the details of the band structure. In one case, by utilizing the TM polarized first band, an image of the source can be formed in the vicinity of the interface with subwavelength resolution. In another case, a TE polarized upper band is used which is able to focus the omnidirectional field far away from the interface with a resolution on par with the wavelength. In the latter case, we explicitly show the flat lens behavior of the structure. These examples indicate that PC based lenses can surpass limitations of conventional lenses and greatly enhance and extend optics applications.

In this paper we present self-collimation in three-dimensional (3D) photonic crystals (PhCs) consisting of a simple cubic structure. By exploiting the dispersive properties of photonic crystals, a cubic-like shape equi-frequency surface (EFS) is obtained. Such surfaces allow for structureless confinement of light. Due to the degeneracy of propagation modes in a 3D structure, self-collimation modes can be distinguished from other modes by launching a source with a particular polarization. To this end, we found that polarization dependence is a key issue in 3D self-collimation. The results hold promise for high-density PhCs devices due to the lack of structural interaction. Finally, a novel method for the fabrication of three-dimensional (3D) simple cubic photonic crystal structures using conventional planar silicon micromachining technology is presented. The method utilizes a single planar etch mask coupled with time multiplexed sidewall passivation and deep anisotropic reactive ion etching in combination with isotropic etch processes to create three-dimensional photonic crystal devices. Initial experimental results are presented.

Photonic crystal based devices received attention in recent years. Based on the superprism effect in photonic crystals, beam steering devices can be made with properties sensitively dependent on the wavelength and incident angle of light. One stumbling block for designing superprism-based demultiplexers is that current numerical methods have difficulties in simulating a practical superprism device with commonly available computational facilities. Examining the superprism effect in a more general perspective, we previously developed a rigorous theory to solve the photonic crystal refraction problem for any surface orientation and any lattice type. This paper will compare our theory with other methods with regard to computational workload to demonstrate the advantages of our theory. Excellent agreement of numerical results with the transfer matrix method is also demonstrated. Heuristic discussions on the beam width variation and energy conservation are presented. A technique for direct computation of the dispersion surface is compared with the methods that combine a photonic band solver with certain interpolation or 1D-searching techniques.

In this paper we demonstrate ultra-low loss transmission across a photonic crystal super-prism device consisting of 600 lattice periods etched into a slab waveguide at wavelengths both above and below the primary band-gap. By modifying the refractive index of the holes we have reduced overall insertion loss to 4.5 dB across the entire visible region of the spectrum, greatly enhancing transmission and extinction in higher order stop-bands. In addition we show that the remaining loss is predominantly due to impedance mismatch at the boundary between patterned/unpatterned slab waveguide regions and so is no longer proportional to the length of the photonic crystal or the number of lattice periods. This is an important step forward for the realization of functional photonic crystal time delay elements, dispersion compensators and super-prism spectrometer devices. Experimental loss measurements compare extremely well with Finite difference time domain simulations which were used to investigate the effect of etch depth on scattering loss. We find that partial penetration into the underlying buffer region causes massive scattering loss to substrate modes due to loss of waveguiding in the holes.

We demonstrate the fabrication, characterization and simulation of visible wavelength superprism devices in photonic crystal waveguides. We studied the super refraction dependence on lattice symmetry orientation and for propagation angles close to the main symmetry orientation. A variety of rectangular lattices devices with various pitches and hole diameters as well as number of rows have been fabricated. We used our previously developed automated broadband spectral and angular measurement to map the chromatic refractivity. We found the refraction angles and sign to be dependent on the lattice orientation and bandgap. As the lattice was rotated away from the main symmetry direction the magnitude of the angular dispersion increased indicating enhanced super-refractive properties away from symmetry direction. We found the chromatic refraction to be up to 1°/nm close to the band edge of the principal bandgaps, 10x more than equivalent gratings, and 100x more than equivalent prisms [[^xiv]]. Dispersion curve obtained from plane wave simulation allowed us to model the Bloch mode propagation directions in the periodic structure. We found these simple models to be in excellent agreement with the experimental results, allowing us to design a range of effective superprism devices.

In this paper, we study the linear and nonlinear responses of 1-D photonic bandgap (PBG) structures. We show that, the nonlinear interaction can be greatly enhanced by the use of Kerr defect modes in a 1D dielectric photonic crystal structure, such as low-intensity bistability and multistability, and by optimizing the design of the layer sequence. 1-D PBG structure can also be promising candidate as low-intensity nonlinear phase shifter. Nonlinear z-scan measurements of a 3-cavity thin-film PBG sample show that the nonlinearity is enhanced over the native material by a factor over 30, while maintaining a bandwidth greater than 1T Hz, which is great for all-optical switching.

We report a dramatic increase in the photoluminescence (PL) emitted from InGaN/GaN quantum wells (QW), obtained by covering these sample surface with thin metallic films. Remarkable enhancements of PL peak intensities were obtained from In_0.3Ga_0.7N QWs with 50 nm thick silver and aluminum coating with 10 nm GaN spacer. These PL enhancements can be attributed to strong interaction between QWs and surface plasmons (SPs). No such enhancements were obtained from samples coated with gold, as its well-known plasmon resonance occurs only at longer wavelengths. We also showed that QW-SP coupling increase the internal quantum efficiencies by measuring the temperature dependence of PL intensities. QW-SP coupling is a very promising method for developing the super bright light emitting diodes (LEDs). Moreover, we found that the metal nano-structure is very important facto to decide the light extraction. A possible mechanism of QW-SP coupling and emission enhancement has been developed, and high-speed and efficient light emission is predicted for optically as well as electrically pumped light emitters.

It is known that free-space focusing of light from sub-wavelength apertures, the so-called beaming effect of light, can be achieved through the excitation of radiative surface modes and their subsequent constructive interference in space surrounding the apertures. This effect, studied extensively in metallic thin films, has recently been shown to exist in photonic-crystal structures. In this paper, we present a comprehensive study of the beaming effect and light directional emission achieved through simple geometric and material engineering of the surface and near-surface structures in two types of photonic-crystal waveguides, classified as increased- and decreased-index structures. We analyze different methods to enhance the directional emission and calculate the resulting efficiencies, highlighting the influence of reflections and matching conditions at the waveguide terminations.

We review our recent progress in the fabrication and understanding of ultra-low mode volume, high Q-factor microcavities for quantum dot based cavity QED experiments. The cavities are realized by the controlled incorporation of defects into 2D photonic crystals that consist of a triangular lattice of air holes within an active Air-GaAs-Air slab waveguide containing InGaAs self-assembled quantum dots. Two specific cavity designs are studied: the L3-cavity consisting of three missing holes along a line and the Y1-cavity consisting of a single missing hole with strongly reduced symmetry. Very good quantitative agreement is obtained between the results of spatially resolved optical spectroscopy and 3D calculations of the photonic bandstructure and cavity mode structure. For both cavity designs, cavity Q-factors up to ~8000 are measured for specific designs with ultra-low mode volumes _Vmode< (λ/n)³. The relative contribution of cavity losses due to out of plane coupling to the free space continuum, in-plane losses through the photonic crystal and via scattering due to disorder and fabrication imperfections are probed for both cavity designs. We demonstrate that in-plane loss can be almost completely inhibited by tuning the localized cavity modes deeper into the photonic bandgap and the potential to fine tune the out-of plane losses via subtle modifications of the cavity design parameters. This procedure is shown to result in up to ~3x improvements of the cavity Q-factor. The Y1-design is shown to be particularly suitable for QD based cavity QED experiments, due to its very low mode volume, high Q-factors achievable (~7000) and flexibility for enhancement through careful modification of the cavity design.

We present our design and fabrication of a semiconductor based photonic bandgap (PBG) nano-membrane device with MEMS features. This device could be used as a basic building block for a reconfigurable optoelectronic integrated circuit that can be reprogrammed for different functionalities. We combine a PBG platform with a MEMS feature to build such a reconfigurable device. The device has a top PBG membrane layer structure composed of hexagon holes in a triangular lattice. Below that, a separate suspended bridge layer can insert a line of posts into the photonic crystal holes to create a defect line. This MEMS feature can generate/cancel a section of the waveguide in the PBG platform, or it can change the dispersion of the waveguide. Therefore, the same structure can be used as different types of devices such as switches, modulators, time delay lines, etc. This device is fabricated on GaAs/Al_x1GaAs/Al_x2GaAs/GaAs-substrate epi-layers grown by MBE. We have developed the fabrication technique for such a device using e-beam lithography, inductively coupled plasma (ICP) reactive ion etching, and multiple steps of regular photolithography and selective wet chemical etching. The fabricated PBG membranes are 60 nm to 300 nm thick, with a thin wall between the holes of ~120 nm. A line of mushroom shaped MEMS posts are inserted into the ~1 μm PBG holes. We are fine tuning each of these processing steps toward the fabrication of a workable device.

In this work, we have experimentally and theoretically studied the emission of radiation from a monopole source embedded in a two and three dimensional photonic crystal. We have demonstrated the enhancement of radiation at the band edges and at the cavity modes including coupled cavity modes. We have shown that the emission of radiation from a source depends on the group velocities of the modes and on the electric field intensities of the modes at the source location. Moreover, we have studied the angular distribution of power emitted from a radiation source embedded inside a photonic crystal. Our results show that it is possible to obtain highly directive radiation sources operating at the band edge of the photonic crystal.

A novel photonic band-gap (PBG) based nano-sensor is proposed for biomolecule gas/chemical agents, and various industrial gas detections. The proposed sensor is based on the plannar waveguide formed by utilizing the PBG. Sensor structure is optimized for a fixed wavelength of light and fixed recpetor. Biomolecule gas adsorbed/interact with the receptor, cause changes in refractive index, which thereby reduces the output optical power. Type of gas and its density in the air can be known from the changes in output optical power, compared with no-gas (reference) adsorption. The proposed sensor can able to detect the fixed gas in several tens of parts-per-billion. We will present detailed simulation and the results of this proposed sensor for various biomolecule gas/chemical agents and also industrial gases. In addition to biomolecule gas/chemical agents detection, the proposed nano-sensor is also expected to be useful for various applications for example in clinical diagnostic system to measure the specific cell or DNA.

We present examples of two-dimensional photonic crystal band structures which defy the conventional wisdom that a photonic crystal provides optimal confinement for frequencies at the middle of the photonic band gap. This is due to the presence of an ultra-flat photonic band that leads to enhanced confinement in an adjacent band gap at frequencies near the band gap edge and far from midgap.

Light propagation through the sharp 45° bend coupled cavity waveguide is analyzed theoretically and numerically. We design the waveguide device based on two-dimensional photonic crystal with square lattice. The degenerate defect state is used as a guided mode of the device. In order to control the light propagation through the corner a splitting of the degenerate defect state is used.

Nanophotonics including photonic crystals promises to have a revolutionary impact on the landscape of photonics technology. Photonic crystal line defect waveguides show high group velocity dispersion and slow photon effect near transmission band edge. By using photonic crystal waveguides to build true time delay based phased array antenna or other optical signal processing systems, the length of the tunable true time delay lines can be dramatically reduced inversely proportional to group velocity dispersion in dispersion enhanced system architecture or reduced inversely proportional to group index in slow photon enhanced system architecture. The group index of the fabricated silicon photonic crystal line defect waveguide is experimentally demonstrated as high as 40 at optical wavelength around 1569 nm. The group velocity dispersion of the fabricated silicon photonic crystal line defect waveguide is as high as 50 ps/nm∙mm at wavelength around 1569 nm, which is more than 10⁷ times the dispersion of the standard telecom fiber (D = 3 ps/nm∙km). Due to the integration nature of photonic crystals, system-on-chip integration of the true time delay modules can be easily achieved.

We review the progress made on the fabrication and applications of hollow-core photonic crystal fibres. The mechanism of the light guidance in these fibers is described along with their dispersion properties. We review the HC-PCF fabrication, the different results achieved in the fields of laser-induced particle guidance, low-threshold stimulated Raman scattering in hydrogen (vibrational and rotational) and in laser frequency metrology. Finally, we show the different new prospects opened up by these fibres.

Supercontinuum generation in photonic crystal fibers with two zero dispersion wavelengths (ZDWs) is investigated numerically. The role of the second ZDW is examined for 5 fiber designs where the higher ZDW differs while the lower ZDW is almost the same for all fibers. We find that tapering can arrest pump depletion, thereby improving the flatness and bandwidth of the supercontinuum. Pumping with low-power picosecond pulses is also investigated; we find that the low peak power leads to a broad four-wave mixing gain bandwidth, resulting in a supercontinuum that is extremely flat over almost 500 nm.

Annular Photonic structures, which occur on bulk and fibers, are Bragg structures that share both Bragg resonances and waveguiding. They are related to Photonic crystals because of their large enough refraction difference indexes (n₂ - n₁) that makes unavoidable to consider in full the reflected wave, well beyond the approximations required for analytical gap solitons. Effectively, their confining capabilities are or primary importance, however, the potential of those structures are substantial and deserves to be further explored. Waveguiding occurs where the structure is homogenous, and may be handled on well known methods. Nonlinear propagation has been observed on solid core Bragg fibers and the soliton distribution on a nonlinear circular and annular region have been described. Linear Photonic annular structures, such as resonators, have been studied by A. Yariv as well as on omniguide fibers. The propagation along the direction where the material is inhomogenous, and that correspond to the beam profile, is a complex task and it is the objective of this paper.

We characterize coupling between two identical collinear hollow core Bragg fibers, assuming TE₀₁ launching condition. Using multipole method and finite element method we investigate dependence of the beat length between supermodes of the coupled fibers and supermode radiation losses as a function of the inter-fiber separation, fiber core radius and index of the cladding. We established that coupling is maximal when fibers are touching each other decreasing dramatically during the first tens of nanometers of separation. However, residual coupling with the strength proportional to the fiber radiation loss is very long range decreasing as an inverse square root of the inter-fiber separation, and exhibiting periodic variation with inter-fiber separation. Finally, coupling between the TE₀₁ modes is considered in a view of designing a directional coupler. We find that for fibers with large enough core radii one can identify broad frequency ranges where inter-modal coupling strength exceeds super-mode radiation losses by an order of magnitude, thus opening a possibility of building a directional coupler. We attribute such unusually strong inter-mode coupling both to the resonant effects in the inter-mirror cavity as well as a proximity interaction between the leaky modes localized in the mirror.

Photonic crystal fibers confine light within a periodic array of elements. We used multiple extrusions of silver halide (AgCl_xBr_1-x) crystalline materials to fabricate photonic crystal fibers, which are transparent in the middle infrared (mid-IR) in the spectral range 2-20 μm. The cores of these fibers consisted of pure silver bromide (AgBr) of refractive index n=2.16, and the cladding area included concentric rings of tens of fiberoptic elements made of pure silver chloride (AgCl), of a lower refractive index n=1.98. Simulations on photonic crystal structures showed that all the fabricated fibers guide a small number of modes. Furthermore, adding rings to such a structure should lower the number of bound modes in the core. We measured the attenuation and the output power distribution of these fibers and carried out spectroscopic measurements in the mid-IR. Good correlation was found between the experimental and the theoretical results. These findings will pave the way for the fabrication of single-mode fibers in the mid-IR range.

We have predicted that reversed and anomalous non-relativisitic Doppler shifts can be observed under some circumstances when light reflects from a shock wave front propagating through a photonic crystal. This theoretical prediction is generalizable and applies to wave-like excitations in a variety of periodic media. The first experimental observation of a non-relativistic reversed Doppler effect has recently been made by Seddon and Bearpark in a creative experiment involving the propagation of an electromagnetic shock through a periodic electrical transmission line. We show how our theory quantitatively describes this experiment and how the theory is fundamentally different from the theoretical description proposed by Seddon and Bearpark.

We have theoretically investigated wave propagation in nonreciprocal photonic crystals (PC), which break simultaneously space-inversion and time-reversal symmetries. We identify a remarkable set of properties that are consequences of simply imposing the two symmetry constraints (independent of material choices, dimensionality, etc.). The model material system that we have investigated is a 1D periodic, lossless dielectric helical medium with magnetooptic activity for which we obtained both analytic and numerical solutions of the dispersion relations. We show that nonreciprocal PC display indirect photonic band gaps (band edges are not aligned in k-space, by analogy with the electronic case) even in the 1D case. Furthermore, we find that these PC support backward wave eigenmodes (opposite group and phase velocities). By analyzing the isofrequency contour diagrams, we show that it is also possible to obtain negative refraction at the interface between air and the photonic crystal, that nonlinearities of the photonic bands allow for superprism effects which differ from the known case by being unidirectional (i.e. not present if the light path is reversed), and that the propagation direction of light waves inside the nonreciprocal PC can be laterally deflected by perpendicular magnetic fields.

The effect of a long-range, slowly varying, modulation of the refractive index of a photonic crystal is investigated. It is shown that the Bloch modes are modified by essentially being modulated by an envelope function which adapts to the long-range dielectric function perturbation. This envelope function obeys a simple linear Schroedinger equation of classical (non-quantum) origin. Close to a band extremum, at a gap edge, the envelope functions can be interpreted as wave functions of relativistic particles possessing a finite rest mass. These effective energy carriers come as two species, referred to as “effective photons” (for positive band curvatures) or “photonic holes” (for negative band curvatures). The energy transfer through the chirped structure can be viewed as resulting from the migration of these particles under forces implied by the long-range dielectric function modulation.

The reflection phenomena of a light beam incident upon the interfaces between the crystal and a uniform dielectric are explored in this paper. We show that neither the phase velocity nor the group velocity directions of the reflected beam satisfy Snell’s law and we prove that a generalized wave-vector conservation relation still applies even when the interface is not aligned with special crystal directions. Moreover, the system exhibits remarkable and unusual reflection effects. In particular, total internal reflection is absent except at discrete angular values. The direction of reflection beam can also be pinned along special crystal directions, independent of the orientation of the interface. And finally, at glancing incidences, strong backward reflection may occur. These effects may be important for creating integrated photonic circuits, and for on-chip image transfer.

The study of nonlinear photonics crystals is quite complex and cumbersome, because of their inherent architectural complexity and, in addition, because of the nonlinearity that couples propagating and counterpropagating waves. However, they are quite attractive because of their potential capabilities, and that has lead to use different approximated methods. In a one dimensional stack, it has been successfully demonstrated that they show switching, bistability and chirping as nonlinear characteristics. Band gap solitons are a well established feature of the coupled wave equations. We have extended a method that have previously shown its success for a stack with a Kerr nonlinearity, to a much more complex structure such as an omniguide fiber, as part of our suggestion that such method could be applied to numerical or analytical methods as long as the linear solution were available. Such a restriction, hinder our ability of getting analytical solution beyond their enabling approximations, however, it is completely adequate for the purpose of to develop devices. A comparative numerical analysis of a one dimensional photonic crystal and an omniguide fiber, made of a dielectric and stratified linear and nonlinear media, has been carried out. They were considered as multilayer arrangements with a finite numbers of periods: linear-linear, nonlinear-linear and nonlinear- nonlinear in order to study and isolate those features. Finally, a comparison of multilayer systems with variations in the diffraction indexes profiles is presented.

A robust scheme is proposed to adiabatically couple the light into and out of propagation modes of photonic crystal structures out of photonic bandgap. It is shown that group index plays the main role in reflection from layers with slight variations. This principle is used to design smoothly varying structures to adiabatically match the incident region to the transmission region. The smooth variation is obtained by modifying the size of holes and the aspect ratio of the unit cells in the buffer layers. It is shown that this method is insensitive to incident angle and wavelength and is therefore appropriate as general-purpose input and output buffer stages for dispersion-based applications of photonic crystal such as superprism-based demultiplexing, diffraction-free propagation, diffraction compensation, and dispersion compensation.

Effects of increase in absorption of electromagnetic radiation, enhancement of photoconductivity and surface wave formation in 2D photonic macroporous silicon were investigated. Dependence of photoconductivity on a corner of the falling of the electromagnetic radiation, prevalence of absorption over reflection of light, as well as enhancement of the photoconductivity in comparison with the monocrystalline silicon testify to formation of surface waves (surface polaritons) in illuminated macroporous silicon structures. For wavelengths less than optical period of macropores there is an essential reduction in transmittance of electromagnetic radiation to (2-3)•10^-2 (in comparison with the homogeneous material) and the polaritonic band formation. Conformity of spectra of photoconductivity of macroporous silicon to spectra of intrinsic photoconductivity of monocrystal silicon testifies the enrichment of a macropore surface by photocarriers and formation of a surface electromagnetic wave of plasmon type. Elecrtroreflectance spectroscopy of macroporous silicon surface showed an intrinsic electric field near 10⁶ V/cm due to positive charge built in oxide layer on the walls of the macropores. Thus, electronic gas is quantified in a surface layer of the macroporous silicon structure. Polariton frequencies in long-wave part of the macroporous silicon optical transmittance are commensurable with experimental values of the surface plasmon frequency in the two dimensional electronic gas on Si-SiO₂ boundary.

Periodicity implies the creation of discretely diffracted beams while various departures from periodicity lead to broadened scattering angles. This effect is investigated for disturbed lattices exhibiting randomly varying periods. In the Born approximation, the diffused reflection is shown to be related to a pair correlation function constructed from the distribution of the film scattering power. The technique is first applied to a natural photonic crystal found on the ventral side of the wings of the butterfly Cyanophrys remus, where scanning electron microscopy reveals the formation of polycrystalline photonic structures. Second, the disorder in the distribution of the cross-ribs on the scales another butterfly, Lycaena virgaureae, is investigated. The irregular arrangement of scatterers found in chitin structure of this insect produces light reflection in the long-wavelength part of the visible range, with a quite unusual broad directionality. The use of the pair correlation function allows to propose estimates of the diffusive spreading in these very different systems.

Two different original theoretical approach for the analysis of vapour sensors based on a porous silicon optical microcavity are presented. The devices under analysis are based on a cavity with a high porosity layer of optical thickness λ_B/2, where λ_B is the Bragg resonant wavelength. This is enclosed between two distributed Bragg reflectors with seven periods made of alternate low and high porosity layers. When such a porous silicon microcavity is exposed to chemical vapours, a marked red-shift of its resonant peak, ascribed to capillary condensation of vapour in the pores, is observed. According to the first approach, the features of porous silicon microcavities are analyzed looking at the correspondent band structure. In particular, the microcavity structure is viewed as a 1-D photonic crystal with a defect of optical thickness λ_B/2 giving rise to a narrow resonant transmittance peak at λ_B in a wide transmittivity stop-band. We then compare the derivation of the band structure with an original approach based on the dynamical diffraction theory, the same widely used in x-ray diffraction. Using this approach we get an analytical expression of the reflectivity, giving the position but also the shape of the resonant peak.

We present a novel approach for the accurate and efficient modeling of photonic crystal-based integrated optical circuits. Within this approach, the electromagnetic field is expanded into an orthogonal basis of highly localized Wannier functions, which reduces Maxwell's equations to low-rank eigenvalue problems (for defect mode and waveguide dispersion calculations) or to sparse systems of linear equations (for transmission/reflection calculations through/from functional elements). We illustrate the construction of Wannier functions as well as the subsequent determination of defect modes, waveguide dispersion relations, and the characterization of functional elements for realistic two-dimensional photonic crystal structures consisting of square and triangular lattices of air pores in a high-index matrix. Moreover, on the basis of our Wannier function calculations we suggest a novel type of broad-band integrated photonic crystal circuits based on the infiltration of low-index materials such as liquid crystals or polymers into individual pores of these systems. We illustrate this concept through the design of several functional elements such as bends, beam splitters, and waveguide crossings.

The finite-difference time-domain (FDTD) approach is now widely used to simulate the expected performance of photonic crystal, plasmonic, and other nanophotonic devices. Unfortunately, given the computational demands of full 3-D simulations, researchers can seldom bring this modeling tool to bear on more than a few isolated design points. Thus 3-D FDTD -- as it stands now -- is merely a verification rather than a design optimization tool. Over the long term, continuing improvements in available computing power can be expected to bring structures of current interest within general reach. In the meantime, however, many researchers appear to be exploring alternative modeling techniques, trading off flexibility of approach in return for more rapid turnaround on the devices of specific interest to them. In contrast, we are trying to improve the efficiency of 3-D FDTD by reducing its computational expense without sacrificing accuracy. We believe that these two approaches are completely complementary because even with vast amounts of computational power, any real-world system will still require a modular approach to modeling, spanning from the nanometer to the millimeter scale or beyond.

We present a new method for sensitivity analysis of photonic crystal devices and nanophotonic devices in general. The algorithm is based on the finite-difference frequency-domain method and uses the adjoint variable method and perturbation theory techniques. We show that our method is highly efficient and accurate and can be applied to the calculation of the sensitivity of transmission parameters of resonant nanophotonic devices.

There has been significant interest in the non-orthogonal modes in resonator systems in the context of the excess noise factor in laser cavities. Conventional non-orthogonal modes are created by the gain of the laser cavity during a round trip since gain makes the propagation of light non-unitary. Here, we theoretically demonstrate that these non-orthogonal modes can also be generated in passive photonic crystal systems. We further show that it can have a broader implication in optical resonator systems. In particular, we probe the characteristics of non-orthogonal modes in a resonator system by looking at the transport properties.

A series of microcavities in 2D hexagonal lattice photonic crystal slabs (PCS’s) are studied. A combination of FDTD techniques and Pade approximation with Baker's algorithm is used to accurately determine the resonant frequencies and quality factors of the cavity modes simultaneously. Q factor larger than 10⁶ is obtained for a one missing hole cavity. Another cavity with smaller and simpler design keeps Q factor larger than 10⁵. Microcavities in silicon-on-insulator-type (SOI-type) PCS’s are also studied. Simulations show that Q factors of cavities in SOI-type PCS’s are much smaller than those in the membrane PCS’s. Deep etching of air holes is still required to obtain relatively high Q cavities in SOI-type PCS’s.

We have developed a design method for a photonic crystal directional coupler switch (PCDCSw) with a short switching length and wide bandwidth. Usually, the relationship between the switching length and bandwidth has a trade-off. To overcome this trade-off relation, we invented the suitable dispersion curve of eigenmodes of the PCDCSw. To actually obtain this dispersion curve, we examine the electromagnetic field of an ordinary PCDC at each wavenumber, and modify the even-mode mainly by enlarging the radius of the airs-holes and by shifting the position of the air-holes closer to the waveguides in the photonic crystals. We confirm using numerical simulation that the switching length of the new designed structure is only 4% of that for the ordinary PCDC.

A novel method for producing photonic crystals with high orders of rotational symmetry using an inverse Fourier transform (IFT) method is presented. The IFT of an n-sided polygon is taken and the position of the peaks are computed in order to obtain a set of discrete points in real space where the scattering centres are to be located. We show, by simulating the diffraction pattern, that although these points appear disordered, they possess long range order, which also confirms that the arrangement of points has n-fold rotational symmetry. The structures thus possess an arbitrary number of rotational symmetries, whilst retaining the sharp diffraction patterns characteristic of known crystal lattices which exhibit wide band gaps. We present simulation results using the finite difference time domain method (FDTDM) for large non repeating patterns of scatterers produced by this method. We also present results where around 50 points have been generated in a square unit cell and tiled to produce a lattice. These, were simulated using both the finite element method (FEM) and the FDTDM, which agree well. Our results demonstrate that the method is capable of producing crystal structures with wide band gaps where the scattering centres are either non-repeating with no fundamental unit cell, or consist of a (large) number of points in a unit cell, which may then be tiled to form a lattice.

By formulating Maxwell's equations in perturbation matched curvilinear coordinates, we have derived the rigorous perturbation theory (PT) and coupled mode theory (CMT) expansions that are applicable in the case of generic non-uniform dielectric profile perturbations in high index-contrast waveguides, including photonic band gap fibers, 2D and 3D waveguides. PT is particularly useful in the optimization stage of a component design process where fast evaluation of an optimized property with changing controlling variables is crucial. We demonstrate our method by studying radiation scattering due to common geometric variations in planar 2D photonic crystals waveguides. We conclude the paper by statistical analysis of experimental images of 2D planar PCs to characterize common imperfections in such structures.

We fabricated and characterized photonic crystal (PhC) microcavities containing InAs quantum dots (QDs) grown on (100) GaAs substrates. QD emission coupled with a PhC cavity mode at a wavelength of 1.55 μm was observed at room temperature. The cavity quality factor Q and its ratio to the mode volume V, Q/V, reach up to 2700 and 3400 x (n/λ)³, respectively. To our knowledge, these are the highest values for microcavities containing QDs emitting at wavelengths around 1.5 μm. The large enhancement of emission intensity at the cavity resonances was clearly observed. The enhancement factor is ~10-100, which depends on cavity modes and pump power density.

A new type of photonic crystal (PC) based coupled-cavity waveguide (CCW), called an asymmetrical-defect coupled-cavity waveguide (AD-CCW), is presented. AD-CCWs produce single mode output with significantly narrower linewidths than conventional symmetrical-defect CCWs. We describe two different AD-CCW designs in two PC material systems: an alternating defect AD-CCW based on a silicon PC, and an incrementing defect AD-CCW based on an InGaAsP PC. The structures are simulated using three-dimensional (3D) finite-difference time-domain (FDTD) calculations. A comparison of AD-CCWs and conventional CCWs is presented based on the simulation results.

We use coupled optical and electronic simulations to investigate design tradeoffs in electrically pumped photonic crystal light emitting diodes. A finite-difference frequency-domain electromagnetic solver is used to calculate the spontaneous emission enhancement factor and the extraction efficiency as a function of frequency and of position of the emitting source. The calculated enhancement factor is fed into an electronic simulator, which solves the coupled continuity equations for electrons and holes and Poisson's equation. We simulate a two-dimensional structure consisting of a photonic-crystal slab with a single-defect cavity, and investigate different pumping configurations for such a cavity.

In this paper, we present the growth and optical characterization of the preliminary stages of amorphous silicon square spiral growth on pre-patterned and unpatterned sections of silicon substrates. The periodicity of the seeding was set to 1 μm using electron beam lithography, and a seed enhancement layer was deposited on top of the seeds, followed by a quarter-turn square spiral on top of that. It was found that the optical constants in the wavelength region of 1000 nm to 1700 nm for the film materials were higher for the patterned sections of the film as compared with the unpatterned sections of the film.

In this paper, we demonstrate the design and fabrication of a planar lens based on the dispersion property of a photonic crystal. When a photonic crystal is illuminated with a low frequency within its dispersion diagram it behaves very similar to an isotropic material, whose resultant index is kept a constant, and is determined by the ratio of high index material and low index material. To validate our design, we performed the experiment in millimeter regime, where the photonic crystal lens was fabricated using a CNC micro-milling machine, and a millimeter wave imaging system was built based on a vector network analyzer. For the lens, we have observed its ability to collimate an incident point source both in the amplitude and phase.

The photonic band gap of self-assembled thin film could be controlled precisely in this study using the seeded growth of spherical SiO₂ nanoparticles. The monodispersed SiO₂ nanoparticles were fabricated using the Stober process. The nanoparticle with the narrowest particle size distribution was used as the nucleation seed. The particle size could be controlled to between 50 nm and 1000 nm using the Stober process and seeded growth methods. When the seed content exceeded 0.1 wt% in solution, no new particles were observed and narrow size distribution was thus obtained. A self-assembled thin film was prepared on a glass substrate by evaporation with capillary extraction. A linear relationship was observed between the average particle size and the photonic band gap according to the transmittance and reflectance measurements. The variation of photonic band gap was well matched with the theoretical consideration of Bragg's diffraction law.

In this work we present the fabrication of tellurite glass photonic crystal fiber doped with a very large erbium concentration. Tellurite glasses are important hosts for rare earth ions due to its very high solubility, which allows up to 10,000 ppm Er³⁺ concentrations. The photonic crystal optical fibers and tellurite glasses can be, therefore, combined in an efficient way to produce doped fibers for large bandwidth optical amplifiers. The preform was made of a 10 mm external diameter tellurite tube filled with an array of non-periodic tellurite capillaries and an erbium-doped telluride rod that constitute the fiber core. The preform was drawn in a Heathway Drawing Tower, producing fibers with diameters between 120 - 140 μm. We show optical microscope photography of the fiber’s transverse section. The ASE spectra obtained with a spectra analyzer show a red shift as the length of the optical fiber increases.

We developed a procedure for the fabrication of functional micro-structured optical fibers (MOFs) through a selective filling technique. In this method, we selectively infiltrate the conventional silica MOF with a UV curable polymer and construct a mold for the fabrication of the functional MOF. Subsequently, we can build the functional MOF by introducing novel materials such as nonlinear optical polymers, nano-structures, and water-based solutions. Such functional MOFs can find wide applications in areas that include nonlinear optics, spectroscopy, chemical and biological sensing.