A review is given on the recent progress in 3D all-metallic photonic-crystals in the near- and mid-infrared wavelengths. Results of optical spectroscopy of the sample will be described. Unique light emission characteristics at a narrow band from the photonic-crystal will also be presented. This new class of 3D all-metallic photonic-crystal is promising for thermal photo-voltaic power generatin and for lighting application.

The recent development of photopumped 1.5 - 1.65 μm GaInAsP microdisk, microgear and photonic crystal lasers is re-viewed. For the former two lasers, room temperature cw lasing characteristics are presented. Their small cavity volume and high Q factor simply reduced the threshold pump power to a record low value of 10 microwatt order, and provided a large sponta-neous emission factor of over 0.1 potentially with the Purcell effect. In the microdisk, nonlasing resonant modes with differ-ent order and different phase often appear. Rate equation analysis indicated that such modes with a high Q affect the laser performance. The microgear having a rotational periodic structure is unique because it not only suppresses such modes, but also increases the Q factor by the minute control of electromagnetic fields so that the radiation field is minimized. The latter advantage will allow a further reduction in cavity size from the smallest limit of the microdisk. A couple of microdisks lased even in a form of a coupled cavity, which can be treated as a photonic molecule. The photonic crystal cavity is also unique because it is easy to construct various types of cavities by the composite of line and point defects inside the uniform photonic crystal slab. The pulsed lasing was obtained in some of them, while we found a large thermal resistance that dis-turbed the cw lasing. We also found through the rate equation analysis that carriers are effectively confined in the microdisk by the strain relaxation effect in compressively-strained quantum wells. However, the result also suggested that the carrier confinement is rather degraded by this effect, so a structural optimization is necessary in the photonic crystal laser.

We have fabricated planar photonic crystal nanocavity lasers, based on our new high-quality factor design that incorporates fractional edge dislocations in triangular lattice photonic crystal cavities. Lasers with InGaAsP quantum well active material emitting at 1550nm were optically pumped with 10ns pulses, and lase at room temperature at threshold pumping powers below 220 microWatt. We have attributed this to the small mode volume and the high Q factors inherent to our device design. We have performed detailed numerical analysis of our structures, and have found an excellent agreement between theoretical predictions and experimental results. The optical field of the lasing mode in our nano-laser is localized in the air-hole region and therefore the laser can be used to investigate interaction between light and matter introduced in the cavity and nanospectroscopy.

Quantum dot photonic crystal lasers are demonstrated at room temperature by optical pulse pumping. Coupled cavities were designed based on square lattice PC slabs. Optimized two-dimensional photonic crystal cavities were defined in 200nm slabs with five-stacked InAS QDs layers. The two- and four-coupled cavities showed as incident pump power threshold as 120μW and 370μW, respectively, both from QD ground state emission range. Both clear threshold in pump power-output resonance power and resonance line width narrowing were observed from our membrane samples. The measured wavelengths matched very well with wavelengths predicted by 3D-Finite Difference Time Domain modelling.

We present a method for fabricating 3D photonic crystal structures by means of interference pattern of laser beams. Four laser beams are introduced into a glass cell filled with a liquid photopolymerizable resin. The resin is polymerized according to the interference patter of four laser beams formed in the resin, so that a square lattice of solid polymer rod-array is formed. Four beams are introduced into the cell again from another face, which is perpendicular to the previous entrance face, to form another rod-array inside the previous one, thereby producing a 3D photonic crysatl structure. The shape of the formed lattice is so-called "wood-pile" which has diamond-like lattice symmetry. The lattice constant of the photonic crystal can be tuned by selecting incident angles of laser beams and can be minimized to about a half of the laser wavelength. After irradiation of laser light, the non-solidified resin is washed out of the polymer structure by ethanol. The proposed method does not require complicated multiple processes compared with the layer-by-layer fabrication method, and thick photonic crystals are immediately produced with high precision.

We propose a novel method for creating photonic crystals with designed defects. The method exploits a newly discovered property of some photoresists, which under ultraviolet (UV) illumination exhibit positive contrast whereas at the same time they behave as negative resists under electron beam exposure. In the process, substrate is spin-coated with the resist and then soft-baked to remove solvent. In order to define a defect, the sample is exposed with electron beam using a Raith50 e-beam lithography system. Subsequently, large area containing the e-beam patterned defect is exposed with a regular pattern of photonic crystal structure using ultraviolet illumination. Upon chemical developing, large photonic crystal region with local patterned defects is created in resist. This patterned resist acts as a template for etching high index material. We detail the fabrication process and present the resulting structures.

Feasibility studies and statistical analyses generated using specially tailored software tools of 2D photonic bandgap waveguides containing structural deviations are presented. Waveguide structures comprising two wide angle bends within a photonic bandgap structure were used in this analysis. The results demonstrate that small variations in the location and size of ordered media create significant changes in the photonic bandgap properties of the material. Deviations with a statistical mean of 20 nm in locaiton and size of this particular model designed for 1.55 μm wavelength are enough to cause the waveguide transmission to reduce by up to 90%.

Abrupt discontinuity in the broad band density of states in a photonic crystal near PBG and low group velocity can have practical impact in many exiting applications of photonic crystals, for example, optical transistor, tunable filters, chromatic dispersion compensators and pulse compression. However it is difficult to excite EM modes in the photonic crystal at frequency close to its PBG by external beam because of tremendous group index mismatch. To solve this problem we propose an idea of a transition interface with a smooth group index profile. Firstly, the idea has been investigated in general using a multi-layer stack as a “toy” model. Then, general trends have been verified for 2D photonic crystals with infinite thickness and slab photonic crystals with one-dimensional periodicity. It has been shown that if there is no interface, reflection/back-diffraction from the photonic crystal at the frequency in the transmission window near its edge is close to 100%. However in case of transition interfaces the transmission increases and abrupt edge of the broad band transmission spectrum takes place. The thicker transition interface - the more abrupt transmission spectrum. It has been shown that not only thickness, but also the group velocity profile in the transition interface is essential.

A new approach for the analytical calculation of band structures in one-dimensional periodic media, such as photonic crystals and superlattices, is reported based on the recently reported differential transfer matrix method (DTMM). The media analyzed in this paper can have arbitrary profile of refractive index. A closed form dispersion equation is obtained and simplified under different assumptions. Several numerical cases are discussed.

The spectral and dispersive behavior of anisotropic layered structures forming a one dimensional "polarization dependent" photonic band gap are discussed. The finite dimension of the structure has been taken into account. Interesting field localization properties are found when the optical axis of layesr are not aligned each with the other one, i.e. principal axis of layers are rotated one with respect to the other. The field localization behavior has been also discussed through a suitable definition of density of modes for the anisotorpic layered structure.

In this paper, the band structure for 1-D photonic crystal structure, which is composed of two different dielectric layers in a one-dimensional pattern, obtained by transfer matrix method, is reported. It has been observed that the bandgap depends on the contrast of dielectric constant and thickness of dielectric layers. Further, it is found that the enhanced bandgap can be obtained by changing the dielectric contrast and thickness of the layers. Primary & Secondary bandgaps are also estimated and the bandgaps have been engineered with reference to their dependence on spacing between layers and dielectric contrasts. Further, we also report the band gap calculation of three different dielectric layers stacked in 1-D periodic structure. Such structure might find its application in the design & development of asymmetric planar photonic crystals

We theoretically calculate the resonance fluorescence spectrum from a two-level atom which is embedded in a photonic bandgap crystal and is resonantly driven by a classical pump light. Non-Markovian noises caused by the non-uniform distribution of photon density states near the photonic bandgap are taken into account by a new approach which linearizes the optical Bloch equations by using the Liouville operator expansion. These linearized equations can be solved directly in the Fourier domain to obtain the correlation functions of the atomic operators and then the fluorescence spectrum from the atom. We find that if the atomic energy level is far from the bandgap, fluorescence spectra with Mollow triplets are observed. When the atomic energy level is near the bandgap, the relative magnitude and the number of the fluorescence peaks are found to be varied according to the wavelength offset.

We study various types of two-dimensional photonic crystal (PhC) waveguides (WG) on silicon-on-insulator (SOI) substrates for future photonic integrated circuit (PIC) applications. One of our goals is to realize a low-loss single-mode PhC WG. Off-plane diffractive leakage above the cladding layer light line is a serious problem in SOI-based PhC-WGs. We overcame this problem in width-varied line defect waveguides whose core-widths are changed by sliding PhC domains or deforming holes beside the waveguides. Narrow-core WGs have a wide transmission band below the cladding layer light line, and wide-core WGs can greatly suppress the diffractive leakage even above the cladding layer light line, and both types have a very low propagation loss. Another goal is to achieve a highly efficient coupling between SOI-based PhC WGs and single-mode fibers (SMFs). Normally, the loss of such a coupling system is very large, i.e. over 20 dB, because of the quite different mode profiles of the WGs and SMFs, and this loss is an obstacle to the development of PhC-based devices. Our system achieves a very small mode-profile-conversion loss of about 3-4 dB/connection from 1500 to 1600 nm wavelength.

We introduce a general design procedure of creating a linear defect in any photonic crystal slabs that functioned as a waveguide. This involves embedding a dielectric block waveguide into a photonic crysatl slab such that the group velocity dispersion relation is phase matched with the bandgap of the crystal. A specific scheme of integration is required to remove any edge states within the guiding bandwidth. Such methodology allows a systematic tuning of waveguide properties such that it can be non-dispersive, and possesses wide bandwidth that contains only a single mode band. As a support of our argument, we demonstrate a particualr waveguide design that is single mode with essentially no group velocity dispersion, and possesses a bandwidth of 13% of the center band frequency.

We have proposed a width-varied photonic crystal (PhC: triangular air-hole lattice) waveguide to overcome the disadvantage of SOI (Silicon on Insulator)-type PhC waveguides, which have no useful propagation mode in the photonic band gap (PBG), and accomplished propagation with a very low loss of 6dB/mm. However, this waveguide can only be made straight because its effective core width is varied by shifting PhC domains. That is, the width is not commensurate with the whole PhC lattice. To solve this problem, we designed a commensurate width-varied PhC waveguide that can be bent. The effective core width is varied by deforming the shape of the holes on either side of a single line defect so that the holes become elongated and tapered toward the center of the core. As a result of the hole deformation, in SOI-type PhC waveguides, the condition for single-mode propagation is satisfied in the PBG below the cladding layer light line. We fabricated this waveguide using SOI substrates and measured the TE-polarized transmission spectrums. The measured spectrums have a 25-50 nm transmission band in the PBG (1280-1580 nm), and they agree well with 3D-FDTD calculations. These results show that the deformed holes are effective.

A method for controlling the dispersion and thus group velocity of guided modes in photonic crystal (PC) waveguides using bi- and quasi-periodic lattices is presented. Rectangular lattice photonic crystals are proposed as possible candidates for implementing such control. However, these structures, and generally all bi-periodic lattices, develop undesirable characteristics as the perfect square lattice is perturbed. Thus, quasi-periodic photonic crystals, which have been shown to be promising in selective mode engineering, were examined next. A possible scheme for engineering of a single mode PC waveguide with guiding through the entire bandgap is presented.

Starting from an intuitive picture of photons bouncing back and forth within a slab of a uniform medium surrounded by photonic crystal (PC) layers, we develop a coupled mode formalism for the analysis of a PC waveguide. The modal solution in the core is given by counter-propagating waves while the cladding field is derived from a modified coupled mode formalism. This coupled mode approach is used to analyze the dispersion and loss of the PC waveguide. Although coupled mode theory is usually applied to structures with a small index contrast perturbation, we find that our coupled mode formalism with an empirical coupling constant can be used to model a large index contrast PC waveguide. A single constant is used to analyze the dispersion and the loss of a two dimensional PC waveguide, a GaAs substrate with air holes. Our results are corroborated with a two dimensional finite-difference time-domain (FDTD) simulation and we find good quantitative agreement between the coupled mode theory and the FDTD analysis.

We have proposed the hybrid integration of photonic crystals (PhCs) and conventional index-guided waveguides (CWGs) as a potentially attractive method of realizing compact waveguide elements for large-scale planar lightwave circuits (PLCs). In this paper we briefly review the properties of PhC/CWG 90° bends in low index, low index contrast waveguides and then extend them to waveguides with high index and low index contrast. We find that diffraction from the boundary of the PhC region limits the optical efficiency of the bend. To overcome this we use a rigorous design tool based on a micro-genetic algorithm (microGA) and a finite difference time domain (FDTD) method to optimize the boundary layer to suppress the unwanted diffraction. We find that this approach yields an improvement in the bend efficiency for light at 1.55 micron from 80% to 95%.

We briefly review recent progress in the fabrication and characterization of air-core photonic band-gap fibers. These are silica fibers with an hexagonal array of air holes in the cladding, and a larger air hole creating the core. Improved structural uniformity transverse to the fiber axis and down the fiber axis has yielded fibers with better transmission characteristics. We have measured a minimum loss of 13 dB/km at 1500 nm for a 100 m length of our fiber. This is a marked improvement over previous loss measurements for air-core fibers of any kind. A comparison of observed spectra and calculated gap modes suggests that coupling between surface modes and core modes may be an important contributor to the remaining loss. We present a detailed analysis of the expected losses associated with mode crossings between the fundamental core mode and surface modes, showing that Lorentzian-shaped loss peaks are predicted.

The imaginary-distance beam propagation method is successfully employed to investigate the effective index of the fundamental mode in the air-filled silica index-guiding photonic crystal fibers (PCFs). A PCF characterized by a hexagonal distribution of air holes with a central defect is taken as example. The convergence behaviro of the modal index versus the air hole radius is investigated. It is demonstrated that the converging speed is proportional to the air hole radius. The modal birefringence in the HE state is numerically investigated and demonstrated to strongly depend on the precision of the numerical mesh.

Although previous direct measurements of the microstructure-fiber continuum have all showed a smooth and stable spectrum, our cross-correlation frequency-resolved optical gating (XFROG) full-intensity-and-phase characterization of the continuum pulse, utilizing sum-frequency-generation with a pre-characterized reference pulse and the angle-dithered-crystal technique, indicates that fine-scale spectral structure exists on a single-shot basis, contrary to previous observations. In particular, deep and fine oscillations are found in the retrieved spectrum, and the retrieved trace contains a "measles" pattern, whereas the measured trace and the independently-measured spectrum are rather smooth. The discrepancy is shown to be the result of unstable single-shot spectral structure. Although the XFROG measurement is not able to directly measure the single-shot fine structure in the trace, the redundancy of information in FROG traces enables the retrieval algorithm to correctly recognize the existence of the spectral fine structure, and restore the structure in the retrieved trace and spectrum. Numerical simulations have supported our hypothesis, and we directly observed the fine spectral structure in single-shot measurements of the continuum spectrum and the structure was seen to be highly unstable, the continuum spectrum appearing smooth only when many shots are averaged. Despite the structure and instability in the continuum spectrum, coherence experiments also reveal that the spectral phase is rather stable, being able to produce well-defined spectral fringes across the entire continuum bandwidth.

It is reported that the spectral loss of a photonic crystal fiber having a large hole-to-hole distance (~10 micron) is sensitive to micro- and macrobending on the fiber. For the macrobending experiment, the fiber was simply wound round a circular structure of known radius, which was reduced up to a few centimeters. As the bending radius was decreased, the transmission loss was increased. In terms of wavelength, the spectral loss was rather flat, which looked suitable for a wide-band fiber attenuator. For the microbending case, a series of regularly spaced silica rods was attached on a slide glass and pressed against the fiber by loading a series of metal plates of known mass on the glass. With this scheme, it was possible to induce periodic microbending on the photonic crystal fiber. The silica rods had the same diameter of a few hundred microns and spaced by about 500 micron. The bending loss was increased by adding the weight. The photonic crystal fiber having a large hole-to-hole distance was found to be highly sensitive to both microbending and macrobending when compared to the conventional single-mode fiber. In this paper, we will discuss the microbending effect on the photonic crystal fiber with various experimental conditions, such as the periodicity and the length of the microbend-inducing region.

We demonstrate optical bistability in a class of non-linear photonic crystal devices, through the use of detailed numerical experiments, and analytical theory. Our devices are shorter than the wavelength of light in length, they can operate with only a few mW of power, and can be faster than 1ps.

In this work we investigated the nonlinear optical properits of a one-dimensional, tranparent metallo-dielectric photonic band gap structure. Specifically, we consider multilayer samples having a nonlinear material as a component. We chose ZnO due to its transparency in the visible region and to its well known optical nonlinearity. By means of dual ion beam sputtering technique we realized a four period sample where the single period consists of ZnO and Ag layers. Sample structure was opportunely designed in order to achieve high nonlinear optical response. A Q-switched frequency doubled Nd:YAG laser has been used in order to investigate the transmissive properties of the sample under high light intensities. A transmission decrease of approximately 50% was found for a maximum incident light intensity of 2 GW/cm².

We have calculated the photonic band structure of a 2D photonic crystal whose empty cylinders are infiltrated by a liquid crystal; a D.C. electric field is applied in the direction parallel to the cylinders. The local dielectric constant within the cylinders is obtained by minimizing the free energy, which has elastic and electrostatic contributions. We have assumed strong anchoring of the molecules of the nematic liquid crystal at the cylinder boundaries and have averaged over the cross-sectional area of the cylinder. The resulting dielectric tensor is diagonal and depends on the applied field. Moreover, it has the same symmetry as a uniaxial material, so that the optical response of the H-modes and E-modes is given by different dielectric constants (“ordinary” and “extraordinary”). The photonic band structures exhibit a notable dependence on the applied field with shifts up to 6% of the bands. For the E-modes, with a careful choice of the filling fraction it is possible to design a complete photonic gap for a certain range of electric fields, and close the gap for other values of the field. Such behaviour could be applied to optical tuning, switching, and polarizing of light.

Photonic crystals are three dimensional periodic structures having the property of reflecting the electromagnetic (EM) waves in all dimensions, for a certain range of frequencies. Defects or cavities around the same geometry can also be built by means of adding or removing material. The electrical fields in such cavities are usually enhanced, and by placing active devices in such cavities, one can make the device benefit from the wavelength selectivity and the large enhancement of the resonant EM field within the cavity. By using coupled periodic defects, we have experimentally observed a new type of waveguiding in a photonic crystal. A complete transmission was achieved throughout the entire waveguiding band. The transmission, phase, and delay time characteristics of the various coupled-cavity structures were measured and calculated. We observed the eigenmode splitting, waveguiding through the coupled cavities, splitting and switching of electromagnetic waves in waveguide ports, and Mach-Zender interferometer effect in such structures. The corresponding field patterns and the transmission spectra were obtained from the finite-difference-time-domain (FDTD) simulations. We developed a theory based on the classical wave analog of the tight-binding (TB) approximation in solid state physics. Experimental results are in good agreement with the FDTD simulations and predictions of the TB approximation.

We analyze the abnormal refraction and propagation when a light beam of finite and practical width enters a photonic crystal from a uniform medium. The beam propagation in the photonic crystal is very complex, and in many cases, is beyond the realm of refraction (even with a renormalized refractive index given by photonic band calculation). Generally, light propagation is restricted to a triangular region (or a fan), although the light may not fill the whole triangle, nor is the light intensity uniform in the triangle. It is found beam divergence does not have a definite connection with the fan shape of the region of light propagation, in contrast to dynamic X-ray theory. A new origin of the fan shape is suggested. Also simulations indicate that at microscale, a narrow light beam may zigzag in a photonic crystal with sufficiently high index contrast. An application of this phenomenon is to make a wide angle bend for waveguides. The designed bending structure has low loss and matches the mode size of a typical single-mode waveguide for fiber-optic communications. Our simulations are based on two-dimensional photonic crystals.

By adding a point defect to a photonic crystal structure, a microcavity can be made to trap electromagnetic energy with wavelength inside the photonic bandgap (PBG). This property together with other unique properties of photonic crystals enables us to control the propagation and spectrum of transmitted wave inside the photonic crystal waveguiding structures and to design and implement microscale optical filters. In this paper we focus on the design of notch filters in photonic crystal waveguides based on the coupling of waveguide and cavity. We discuss about the properties of a single cavity and its necessary modifications to achieve efficient coupling between cavity and waveguide and eventually obtain desired notch filters at the frequency range of interest. We also discuss the coupling of multi-cavities to a waveguide and the possibility of attaining filters with better performances is presented, and the spectrum and lineshapes of the resulting filters are characterized.

We introduce a compound semiconductor based omnidirectional reflector. A four layer pair stack of GaAs/AlAs was grown epitaxially using molecular beam epitaxy, which was then converted to a GaAs/Al₂O₃ multilayer stack by selective oxidation of the AlAs layers. The resultant one-dimensional photonic crystal exhibited omnidirectional reflection properties in near infrared wavelength range below 1μm. Reflectance spectra measured at various incidence angles and polarizations were observed to be in good agreements with theoretically simulated results.

We have observed experimentally photonic band gap in dispersion curves of SPPs excited at a 1-D dielectric lattice structure on a flat metal surface. The observation result is compared with theoretical result by using of the well-known calculation method of diffraction, rigorous coupled wave analysis method.

In the present report we propose an innovative concept for effective diffractive wave guiding of optical (infrared, visible and X-rays) beams based on the effect of diffractive multifocal focusing of radiation (DMFR). The optical DMFR effect, predicted earlier by theory, on a bicomponent diffraction system, has recently been confirmed experimentally. The bicomponent diffraction system consists of two plane screens with circular apertures, which are located in the first open Fresnel zone of each other along optical axes. It was shown that the diffraction picture in the focal planes of such a system represents a bright narrow peak at the center for open odd Fresnel zones, whose intensity can exceed by six times the value of the intensity of the incident spherical wave. We propose to utilize the DMRF effect for multi-component system of pinholes, positioned along the optical axis, and design a new diffractive photonic-crystal-like fiber (wave-guide), in which space localization of an electromagnetic field is rigidly fixed for given values of the wavelength and the pinhole diameter. Thus, such a diffractive photonic crystal has an internal periodic macrostructure, but it differs from a traditional photonic crystal in that the forbidden zones are formed in a natural way as a result of the diffraction off the pinhole system.

Photonic crystal fibers (PCF) exhibit many challenges with respect to production. One property of such fibers that make them more complicated than standard fibers is their cladding structure that consists of air holes. These holes are typically arranged in a periodic pattern formation. We propose a novel monitoring method for non-destructive and non-invasive characterization of hole diameter and hole spacing of such photonic cladding structures. This method is applicable simultaneously to drawing a fiber but also as an off-line non-destructive characterisation method. By transversal illumination of a crystal fiber with a white light source, a colourful diffraction pattern can be observed. Hue, saturation and intensity (HSI) analysis of this diffraction pattern reveals information about 1) density of the number of cladding holes present, 2) air hole diameter, and 3) air hole spacing. This HSI based measurement method does not give absolute values for the fiber parameters but is very applicable as a differential measurement technique sensitive to even minor changes in the cladding structure, and may, therefore, potentially serve as a sensitive monitoring method during fabcication of PCFs. We will present comparative results for various types of photonic crystal fibers.

Fabry-Perot type resonances have been observed in the stop band of a metallodielectric photonic crystal at Ku band microwave frequencies. The metallodielectric photonic crystal has a face centered cubic Bravais lattice structure. The lattice constant is 15 mm. Metallic spheres with 6.35 mm diameter are placed at the lattice sites. In the transmission measurements, the metallodielectric photonic crystal displayed a directional bandgap with a lower band edge of 13.0 GHz, an upper band edge of 21.5 GHz, and a center frequency of 17.25 GHz, corresponding to a stop bandwidth center frequency ratio of 50%. The maximum rejection at the band center is 35 dB, corresponding to a 7 dB per unit cell rejection ratio. The Fabry-Perot type resonance has a quality factor of 200, with a maximum transmission peak of -5 dB.

The proposed one-dimensional photonic crystal waveguide structure can be optimized in three steps as outlined below. At first the imaginary part of the Bloch wavevector inside the 1D PC can be made maximum so that the evanescent light field decays most rapidly and thus the confinement factor of a guided mode becomes maximized when the waveguide is completed. This condition uniquely defines the thickness of two layers in 1D PC. Secondly, the omnidirectional mirror condition can be further enforced for the 1D PC to achieve complete inhibition of light escape in the vertical direction. This can be done by ensuring that for a given frequency the point, (ω, ωn0/c), on TM lightline falls in the forbidden bandgap. Lastly, the thickness of the centerguiding layer can be uniquely determined for given frequency and propagation constant, considering structural symmetry and phase matching condition between lights outgoing from and incoming to the guiding layer.