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Sonic/phononic crystals named acoustic/sonic band gap media are the elastic analogues of photonic crystals and have received renewed attention recently in many acoustic applications [...]

A new filter array and a demosaicking method for snapshot multispectral polarization imaging are proposed in this paper. The proposed filter array is a thin-film wavy multilayer structure regarded as a photonic crystal that can be fabricated using the autocloning method. The multispectral polarization filter array is developed by altering the wave structure of the photonic crystal at each pixel. In addition, we propose a demosaicking method for multispectral polarization images by considering snapshot imaging as a linear model. In the experiments, we evaluated the recovered spectrum error in some color charts and showed various demosaicked images such as multispectral polarization images, specific-band degree of linear polarization images, polarized RGB images, and non-polarized RGB images.

Omni-directional reflectors (ODRs) for deep blue LED were designed and fabricated using symmetric autocloning method. The symmetric stack multi-layers for the reflectors were designed by finite-difference time-domain simulation. The fabricating process of ODR is combined with the techniques of anodic aluminum oxide (AAO) process and autocloning method. The two-dimensional structure template of nano-channel array was grown using AAO with the period of 150 nm. Then the shaping layer was deposited on the AAO template by evaporation deposition. Besides, the ion etching was applied to modify the apex angle to the triangle shape at 100°. Finally, the sub/(0.5TiO2 SiO2 0.5TiO2)8 multi-layer stack was deposited on the shaping layer using autocloning method to achieve the ODR. The results show the reflective spectra of ODR at the incident angles of 0, 30, 45, and 60° had high values within the range 400–450 nm. Besides, the central wavelength shifting is not obvious which is very good for keeping the color of LED stable.

Based on the autocloning technique the photonic crystals were fabricated using E-beam gun evaporation with ion-assisted deposition (IAD) on the periodic corrugation patterns of substrates. In this research, the surface evolution function based on the unified process model was simulated to analyze the influence of the etching and redeposition effects of the different etching time. As the etching time was longer, the top roof angle was larger and the redeposition thickness was getting thicker. The difference of the top roof angle in the experiment and the simulated result are less than 4°. It shows the simulation method achieved very good agreement with the fabricated result for different etching times from 40 to 120 min. We found the surface angular was depended on the etching effect more than the redeposition effect.

The autocloning technique is an attractive deposition method for the making of photonic crystals. With it various photonic crystals can be produced simply by changing the substrate periodicity and the structure of the stacking materials. We report on a method for the fabrication of autocloned photonic crystals. This method has better step-coverage, a higher deposition rate and a larger deposition area than can be achieved by the more traditional sputtering method and the periodic surface corrugation is preserved even after ion-assisted deposition (IAD) of multilayer stacks using E-beam gun evaporation. The shaping process can be freely controlled by controlling the IAD power and the ion source etching time. Ion source etching is a physical etching process which does not require any chemical reaction or dangerous reactive gas. The process parameters are described in this paper. The refractive index can be adjusted by changing the deposition rate and the substrate temperature during the deposition process. The deposition rate is about 0.7–1 nm/s for SiO 2 which is almost ten times faster than that of the sputtering method. This makes this method good for the mass production of photonic crystals.

Ge/SiO2 multilayer type two-dimensional photonic crystals (PhCs) for short wave infrared (λ~2000 nm) application are demonstrated. The PhCs are fabricated by the autocloning method, which stacks multilayer on a glass substrate with initial line and space pattern by bias-sputtering. We verified their multi-channel wavelength filtering operation. Long wave pass or short wave pass filtering function is observed. Typical PhC dimensions are: Ge and SiO2 thickness is 220 nm, total number of layers is 16, horizontal lattice constant is approximately 500 nm. Transmission losses are the order of 30%, which mainly originates from the absorption of Ge layer. Extinction coefficient (κ) of the sputtered Ge was estimated to be less than 0.05 for the wavelength range between 1600 and 2400 nm.

Multichannel wavelength filters consisting of 2-D photonic crystal (PhC) for the near-infrared wavelength region (~800 nm) are demonstrated. The filter is a thin-film wavy multilayer structure and is fabricated by the autocloning method, which is based on a radio frequency bias sputtering process. Twelve long-pass-type filter regions are integrated on a common silica substrate. Sharp cutoff characteristics and almost equal channel spacing are experimentally verified. To precisely control the effective lattice constant of PhC, a modulated lattice structure on the substrate is utilized

Two novel wide-angle and broadband 2D photonic crystal polarization splitters (PCPS) which are the multilayer wavy films (MWF) structure and arrow-head like structure are designed based on the autocloning method. Plane wave expansion (PWE) method is used to calculate the band structure and explain the reason for the wide-angle and broadband polarization splitting effect. In order to verify the result derived from PWE method, finite-difference time-domain (FDTD) method is employed to test and measure the polarization effect for the MWF structure.

The heterostructured photonic crystal waveguide fabricated by the autocloning technology allows fabrication jointly with other functional devices. Hence, this approach is useful for elemental components for the next-generation high-function planar optical circuits. When this waveguide is used for interconnection of optical circuits, its propagation loss should be as small as possible. In this investigation, Ta2O5/SiO2 is selected as the construction material. Further, by using a waveguide configuration minimizing the scattering loss, substantial loss reduction was achieved. It is especially effective to use a simple flat multilayered film structure. A loss reduction up to a propagation loss of 0.1 dB/mm was realized. The present waveguide has a small coupling loss of 0.43 dB with an existing optical fiber (a high-Δ fiber with a mode field diameter of 2.7 µm) and hence is easily adapted to the optical communication system. The heterostructured photonic crystal waveguide is thus extremely practical. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(11): 10–20, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20195

We propose a novel static parallel-processing ellipsometer consisting of arrays of photonic crystal polarizers and quarter-wave plates (QWP) having different orientations of the optical axes. On the basis of the autocloning technique, each array is monolithically integrated on a substrate in a single deposition process. The pattern of light transmitted through the two photonic crystals, a number of pairs of QWP, and polarizer with different axes is detected by an array of photodiodes, and the polarization is analyzed instantaneously from the image. No mechanical rotation or electrooptic modulation is necessary. Preliminary experiments of the ellipsometer are performed for the first time, and the principle of operation is confirmed. This type of ellipsometer is simple, compact, and robust, and therefore, will open up new applications for industrial use.

We report a strategy for the industrialization of photonic-crystal-based optical devices, starting with a review of the requirements for passive photonic crystal components. Although they have remarkable properties, such components are difficult to couple to/from optical fibers and have a relatively large propagation loss. We present an approach for meeting the requirements by using heterostructured photonic crystals fabricated by the autocloning technology. A low-loss, simple structured waveguide and sophisticated functional blocks (such as a resonator) can be integrated by a simple process. We first prepare a substrate patterned and corrugated by electron beam lithography and dry etching. Ta2O5/SiO2 multilayers are repeatedly deposited on the substrate, and no other process is needed to complete the chip. After dicing and polishing, the waveguide can be butt-jointed with an optical fiber, and the loss is estimated as 0.1 dB/mm. A resonator with Q = 11,700 is also demonstrated. Recent progress and the future outlooks for the technology are also discussed.

We developed a dry-etching process to form holes with diameters of 5–50 m mi n 7-mm thick a-SiySiO three-dimensional 2 (3D) photonic crystal layers fabricated on InP substrates by the autocloning method. We also demonstrated wet-etching processes to remove damaged surfaces of exposed InP substrates and selectively grew In Ga AsyIn Ga Al As multiple quantum 0.62 0.38 0.45 0.31 0.24 well by molecular beam epitaxy in a region surrounded by a-SiySiO 3D photonic crystals. Polarization dependence was observed 2 in a spontaneous emission transmitted at 75 mm in a lateral direction in the photonic crystal layer. 2002 Elsevier Science B.V. All rights reserved.

We investigate the characteristics of in-plane light propagation in 2-D photonic crystals fabricated by the autocloning method, by which multiple layers are stacked while preserving periodic surface corrugation. A numerical analysis shows that Ta/sub 2/O/sub 5//SiO/sub 2/ autocloned photonic crystals are applicable to waveguides and lenses since a sufficient amount of change of the effective refractive index is obtained by adjusting the aspect ratio of the unit structure. It is also shown that the crystals have a wide bandgap applicable to Bragg reflectors and resonators. Experimental results reveal that in-plane propagation losses for the two directions are less than 1.4 dB/mm at /spl lambda/=1.55 /spl mu/m, showing the crystals are useful for low loss in-plane devices.

This paper discusses how to enhance the ability to tailor material structures within a unit cell of photonic crystals fabricated by the autocloning method which is based on stacking corrugated multilayers of constant thickness by a bias-sputtering process. We developed a new process by introducing reactive ion etching into autocloning, and thus created a novel structure having multilayers whose thicknesses are modulated, and the new structure has bandgaps in the directions parallel to the substrate. The new process allows photonic bands of autocloned photonic crystals to be designed with greater controlability, which should facilitate the application of autocloning, such as for in-plane optical circuits.

SiO2/air three-dimensional (3D) periodic structures were fabricated by removing Si layers partially from Si/SiO2 3D photonic crystals (PhCs) formed by using autocloning. CdS/SiO2 3D periodic structures were formed by introducing CdS into the SiO2/air structures by the TEA method and photoluminescence (PL) was observed from the introduced CdS. TiO2/air/CdS two-dimensional (2D) PhCs were also fabricated by introducing CdS into the voids of TiO2/air 2D periodic structures, in which SiO2 layers were partially etched out from TiO2/SiO2 2D PhCs fabricated by using autocloning. PL radiating normal to the surface was measured and large polarization dependence was observed.

We fabricate photonic crystals for the visible range by the ‘autocloning’ technique, in which multilayers are stacked by an appropriate combination of sputter deposition and sputter etching. TiO2/SiO2 and Ta2O5/SiO2 are chosen as materials since they are transparent in the range and give a high contrast of refractive indices. The fabrication technique has flexibility regarding materials and size and is very reliable and reproducible even if the pitch is less than 0.2 μm. We also study the application of photonic crystals to birefringent elements such as waveplates and polarization selective gratings and experimentally verify that they are useful for optical pick-up systems.

We have proposed a method for fabricating photonic crystals, which is named autocloning. It is based on sputtering deposition and sputter etching. When we stack multilayer with the autocloning method on a substrate patterned periodically, we can preserve corrugated surface shape whose symmetry and periodicity reflect those of the substrate pattern. Consequently, we can realize the multi-dimensional structures automatically. Almost all the processes are carried out in a vacuum chamber without alignment process, accordingly the autocloning is simple, reliable, and suitable for mass-production. In this paper, we report the mechanisms of the autocloning and its applications to optical devices. Particularly, we describe the polarization splitters and the channel waveguides utilizing lattice modulation of the photonic crystals.

We propose a method to experimentally determine the full photonic band structure of photonic crystals by monitoring the beam propagation, and we demonstrate the experimental results of the band-structure measurement in the near-infrared regime for ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ three-dimensional hexagonal photonic crystals fabricated by autocloning bias-sputtering process.

3D photonic crystals can produce a number of fascinating optical devices utilizing the band gap, the dispersive passband, and unisotropic band structure. We previously proposed a process for fabricating a 3D periodic nanostructure which can behave as photonic crystals. The key technique in the process is the deposition of a multilayer by bias sputtering replicating periodically a corrugated layer pattern, which is named the autocloning effect. This paper reviews our recent works on 3D photonic crystals: the mechanism of the autocloning effect, propagation analysis in the 3D photonic crystal by an FDTD method, and applications such as plane-normal waveguides or wavelength-selective filters. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(9): 43–52, 1999

Extraordinary angle-sensitive light propagation, which we call a superprism phenomenon, was demonstrated at optical wavelength in photonic crystals with three-dimensional-periodic structure fabricated on Si substrate. The propagation beam was swung from $\ensuremath{-}90\ifmmode^\circ\else\textdegree\fi{}$ to $+90\ifmmode^\circ\else\textdegree\fi{}$ with a slight change in the incident angle within $\ifmmode\pm\else\textpm\fi{}12\ifmmode^\circ\else\textdegree\fi{}.$ This effect together with wavelength sensitivity is at least two orders of magnitude stronger than that of the conventional prism. The incident-angle dependence including negative refraction and multiple beam branching was interpreted from highly anisotropic dispersion surfaces derived by photonic band calculation. These phenomena will be available to fabricate microscale light circuits on Si with LSI-compatible lithography techniques.

We successfully fabricated channel waveguides utilizing photonic crystal (PhC) dispersion having a very low loss of /spl sim/0.1 dB/mm by the autocloning method. We achieved the loss reduction by improving the fabrication condition and adjusting the core width. The result of propagation loss can be regarded as a "milestone," and it enables us to realize practical PhC circuits that contain functional components such as chromatic dispersion equalizers and high Q wavelength filters.

We report on the fabrication of multichannel photonic crystal (PC) wavelength filters and their evaluation at wavelength division multiplexing (WDM) wavelengths. The devices utilize three-dimensional (3D) PCs consisting of Ta2O5/SiO2 multilayer thin films fabricated by the autocloning method. The 3D PCs serve as Bragg mirrors in the devices and finite-difference time-domain (FDTD) simulations of these mirrors revealed that their Bragg wavelength shifted by +19.8 nm as the in-plane lattice constant of the crystal increased from 400 nm to 800 nm. We fabricated these filters with a Ta2O5 cavity and obtained a wavelength shift of +24.0 nm.

A heterostructured photonic-crystal functional chip consisting of a resonator and waveguides is fabricated by a simple "autocloning" process. First, we prepare a substrate with different corrugation patterns by electron beam lithography and dry etching, and Ta/sub 2/O/sub 5/-SiO/sub 2/ multilayers are successively formed upon the substrate. An in-line resonator is fabricated and characterized by fiber-in-fiber-out measurement, and a resonance peak with Q=270 is demonstrated. The future outlook for the technology is also discussed.

The process of fabricating photonic crystals comprised of alternately stacked high- and low-index dielectric materials on periodic substrates to form zigzag films is called the autocloning technique. In this study, we have fabricated TiO2/SiO2 two-dimensional polarization filters by using electron beam gun evaporation with ion-beam-assisted deposition. The shape of the zigzag structure is preserved, and the total thickness is 8 μm. The symmetric structural design can be utilized as an antireflection coating applied to reduce ripples and achieve a 200 nm working wavelength range.

Si/SiO2 multilayers having zigzag layer interfaces are fabricated on a patterned substrate using Autocloning method. The multilayer was designed as multichannel edge filters. Shift of the cut-off wavelengths by 190nm in NIR was experimentally demonstrated.

We propose a three-dimensional photonic crystal structure having a wide full photonic band gap in the optical regime, which can be fabricated by an alternating-layer deposition and etching (drilling) process. This fabrication process is much simpler than that previously reported. The combination of current lithographic technology and autocloning bias-sputtering deposition is a promising way of realizing these photonic crystals.

We demonstrate a self-healing effect of unwanted defects in the autocloning process: autocloning is a previously proposed technique to fabricate multidimensional periodic nanostructures by stacking up corrugated multilayers. With the self-healing effect, aperiodic perturbations in the initial periodic shape of the structure immediately disappear and the surface shape becomes periodic in a few cycles of stacking. If the perturbations exist in photonic crystal, they cause light-scattering loss and also make the boundaries between photonic bands and band gaps unclear. In other words, they make the attenuation of light at the frequency in photonic band gaps weak. Consequently, to attain uniformity of the shape automatically with this effect is very important in the fabrication process for practical photonic crystal devices. In this letter, we verify this phenomenon experimentally, and discuss the mechanism by comparison with process simulation.

A novel design of photonic-crystal polarization filter was demonstrated with dual-band and wide working wavelength range. The structure of the filter is a 2-dimensional wavy structure of multilayer thin films consisted with a number of alternate high and low refractive indices transparent dielectric layers deposited sequentially on a periodic structured substrate. The fabrication of the photonic-crystal polarization filter is based on an autocloning method which integrated the techniques of lithography and thin film deposition. Different from the traditional polarizing beam splitters, the photonic-crystal polarization filter is a flat type of polarizer with normal incident angle. The transmission and reflectance spectra were analyzed using finite-difference time-domain method (FDTD). From the analysis result, we found the photonic bandgap was happened at transverse electric (TE) mode and the passband at transverse magnetic (TM) mode. So, the photonic crystal polarization filter can separate TE mode and TM mode effectively as the field is incident normally. We design the working wavelength range of the photonic-crystal polarization filter at both visible and near infrared regions, and have wide polarization separated band at normal incident. Finally, the bandwidth is about 100 nm in visible region and 300 nm at near infrared region. The extension ratio is about 20 both in visible region and near infrared region.

We previously demonstrated a process for fabricating three-dimensional (3D) periodic nanostructures composed of corrugated a-Si/SiO2 multilayers, which behave as 3D photonic crystals. In this process, bias sputtering is a key technique by which the pattern is self-forming. This letter clarifies the mechanism of the self-shaping effect of bias sputtering by comparing deposition simulation and experiments. The mechanism is decomposed into three main effects: diffuse incidence of neutral particles of film material, sputter etching by normally incident rare-gas ions, and subsequent redeposition of sputtered film material. Specifically, redeposition has a self-adjusting effect on the depth of holes or valleys, and is the key of formation of stable patterns.

Using patterned photonic crystals fabricated by autocloning, novel functional elements, devices, and systems are realized. Applications of axisymmetric polarization, photoelasticity imaging, and spectroscopic imaging are introduced.

The triangle shape of two dimensional photonic crystals were fabricated based on autocloning technique, and preserved the periodic surface corrugation after the deposition of multilayer stacks using an E-beam gun evaporation with ion-assisted deposition (IAD). Drude model has been applied to analyze the effective refractive indices of the structural single-layer and multilayer autocloning films with triangle shape in the visible range which divided into several periodic parts. The advantage of using the model of effective refractive index is the optical properties of structural multilayer films can be analyzed easily. The effective refractive indices have been calculated based on this model, and simulated the reflectance and transmittance of the different incident angles. The influences of the structure period on the reflectance and transmittance were also analyzed.

Patterned 3D photonic crystals are fabricated by autocloning, a unique process for film deposition. A number of novel devices/systems are realized. Applications to polarization imaging, fiber optic SOP monitor, biophotonics, and pickup for multilayer DVD are reviewed.

Self-assembly of microspheres prepared from air-liquid interface to construct two-dimension structural substrate and the thin-film autocloning technologies using E-beam gun evaporation with IAD superimposed on the periodic corrugation pattern were combined to fabricate three-dimension PhCs.

The outcoupling efficiency of organic light-emitting diodes was improved using a photonic crystal fabricated by autocloning, which has potential advantages for mass production. By using layer thicknesses optimized by optical simulations, the experimental external quantum efficiency of a device with the photonic crystal and a hemispherical lens was 43.4%, which is 2.13 times that of a device on a flat substrate without the lens. Comparisons with the simulated distributions of the light modes in the devices show that the photonic crystal reduces the light loss from the waveguide and evanescent modes. The emission pattern was independent of substrate rotation.

Autocloning technique is an attractive deposition method to make photonic crystals since it can produce various photonic crystals by changing the substrate periodicity and the structure of the stacking materials. We report a novel method to fabricate autocloned photonic crystals. This method has better step-coverage, higher deposition rate and large deposition area than the sputtering method. We successfully preserved the periodic surface corrugation after the deposition of multilayer stacks by using an E-beam gun evaporation with ion-assisted deposition (IAD). Freedoms of the shaping process can be controlled by the power of IAD and the time of the ion source etching. The ion source etching is a physical etching process without any chemical reaction and dangerously reactive gas. The process parameters were described in this paper. During the deposition process, the refractive index can be adjusted by changing the deposition rate and the substrate temperature. The deposition rate was about 0.7∼1 nm/s for SiO 2 which is almost ten times faster than the sputtering method. So this method is good for the mass production of photonic crystals.

A series of three-dimensional photonic crystals are fabricated. The existence of photonic bandgap is demonstrated in the near-infrared wavelength range and bandgap position shows red-shift with increasing feature size of photonic crystals.

In this paper, we investigated autocloning Ta/sub 2/O/sub 5//SiO/sub 2/ deposition using ECR sputtering, with the goal being a substantial reduction in optical loss.

Autocloning technology based on RF sputtering and sputter-etching (RF bias sputtering) is an unique method of fabricating photonic crystal composed of multilayer film, in which each layer has a wavy shape with sub-micrometer periodicity. Autocloning of Si-SiO/sub 2/ multilayer film is now being researched for optical devices in telecommunications. In practical applications, optical loss reduction is strongly required and improvement of the fabrication process becomes important. We constructed a new deposition apparatus equipped with two kinds of two sputtering sources (planar magnetron (PM) type and ECR type) for the fabrication of photonic crystal of three-dimensional periodic structure. We investigated deposition characteristics of Si and SiO/sub 2/ on wavy-shape substrate, and attained the following autocloning results by proper combination of PM and ECR sputtering.

We have fabricated three-dimensional (3D) periodic structures consisting of stacked a-Si/SiO/sub 2/ layers directly on two-dimensional (2D) sub-micron-patterned [100]-InP substrates by using autocloning technology. The initial 2D pattern has been reflected in the 3D periodic structures whose height has been amplified. We have measured the transmission and reflection spectra of the 3D periodic structures, and have observed the photonic band gaps in the wavelength region of around 1400 to 2200 nm. We have also observed strong polarization dependency for the samples with the triangular lattice and weak dependency for those of the square case.

We describe the fabrication and evaluation of a low-loss, high-delta optical waveguide consisting of heterostructured photonic crystals. The waveguide is composed of a multilayer stack of Ta2O5/SiO2 and is prepared by use of the autocloning technique. Light is guided in the waveguide by the difference in the effective refractive indices of the constituent photonic crystals. By improving the design of the core region so that is has a flat multilayer structure, we achieve delta = 3.09% for the in-plane direction and net propagation loss of 0.56 dB/mm at lambda = 1.6 microm. Experiments also suggest that the bending loss of the waveguide can be reduced to less than 0.1 dB if the curvature radius is larger than 700 microm.

We report a fiber butt-jointable Ta/sub 2/O/sub 5//SiO/sub 2/ photonic crystal waveguide with a record low-loss (0.56 dB/mm). The waveguide has a heterostructure and is fabricated by the autocloning technology. Details are described.