Holographic lithography is well-adapted to the production of three-dimensional photonic crystals for applications in the technologically important optical regime. We illustrate the flexibility of this approach by considering the design and fabrication of photonic crystals with symmetries that favour the formation of a complete photonic band gap. One of them, a structure with diamond symmetry, is calculated to have a complete gap at a refractive index contrast equal to the lowest yet reported.

We present a method for fabricating three-dimensional photonic crystal structures by interference lithography, capable of generating face-centered cubic lattices with lattice periods that can be controllably varied over a wide range. The method consists of three separate exposures of a layer of photoresist by interfering laser beams, where each exposure generates a two-dimensional interference pattern, specifically a tilted set of parallel rods. When properly oriented, superimposing these three rod arrays within a common volume of resist material yields an fcc lattice. The lattice period is controlled by the spacing of the rod arrays, which can be tuned independently of the laser wavelength by varying the relative orientations of the interfering beams. We have developed a method for generating the necessary laser beams that is highly repeatable and requires zero alignment, using an array of diffraction gratings patterned on a single mask plate and a rotating beam blocker to select which subset of the grating array is to be used for any given exposure. This paper contains a description of the method and our fabrication setup, and presents the samples that have been fabricated using this method.

An approach is introduced to accurately explore methods of fabricating photonic crystals formed by holographic lithography. Analytical background is given for synthesizing the exposure beam configuration to form the desired lattice. This is combined with a comprehensive model that can predict lattice distortions due to physics of the photolithography process. Simulations are compared to experimental results and to results obtained by conventional intensity threshold methods.

We have developed a new approach for the fabrication of three-dimensional photonic crystals based on multi-layer photolithography. This method, which uses commercially available photoresist, allows parallel fabrication of three-dimensional photonic crystals, and possesses the flexibility to create a variety of different lattice arrangements and the freedom of arbitrary defect introduction. We describe in this work how this method is derived from mature two-dimensional photolithography and demonstrate it with the fabrication of multi-layer woodpile structures with and without defects as well as other unique three-dimensional microstructures.

Modern optoelectronic devices require micro and nano-structures to be etched into a wide range of substrate materials. The ability to plasma etch a wide range of semiconductor and glass materials is required to produce devices that provide technical solutions to challenging optical designs for optoelectronic applications. This paper addresses the etching practices developed primarily for microoptical devices including lenses and gratings. The materials considered are compound semiconductors in the III-V materials group as well as high index of refraction optical glasses. Many of the materials investigated were evaluated for optical data storage applications for future generation devices.

We present an efficient method for the fabrication of three-dimensional photonic crystals in GaAs-based materials. The method exploits the dependence of the oxidation rate of AlGaAs on the aluminum content in the alloy. As a result, a wide range of oxidation profiles is possible. The oxidation profiles are determined by the Al concentration profiles in a GaAs/AlGaAs stack grown by molecular beam epitaxy, and the resulting three-dimensional structure depends on the initial two-dimensional pattern defined by standard lithography. We detail the process and present preliminary results showing the viability of the method to realize three-dimensional photonic crystals of various geometries.

Arsenic based chalcogenide glasses present several advantages for nano-structured optical devices in the infrared. First they possess a good transparency in this optical window, second their amorphous nature is ideal for coating based applications or for hybrid integration, third their photo-structural transformation properties give the possibility of creating high-resolution patterns on films and finally their high index make them particularly suitable for the fabrication of photonic crystal devices. We have demonstrated the fabrication of two-dimensional and three-dimensional (wood-pile) photonic crystal structures for typically 500 nm period structures using interferometric lithography to create the periodic pattern. We show here different techniques in order to obtain specific patterns on the chalcogenide glass using a combination of illumination, etching and redeposition techniques. Moreover, in order to create very steep contrast, we have used the fact that silver ions can freely propagate in the glass under light action, providing a very effective contrast between illuminated and non-illuminated regions. 130 nm patterns with a 500 nm periodicity have been obtained using silver doping of chalcogenide glasses. We will finally show different examples of pattern sculpturing using different illumination and film preparation conditions.

Direct-write electron-beam lithography has proven to be a powerful technique for fabricating a variety of micro and nano-optical devices. Binary E-beam lithography is the workhorse technique for fabricating optical devices that require complicated precision nano-scale features. We describe a bi-layer resist system and virtual-mark height measurement for improving the reliability of fabricating binary patterns. Analog E-beam lithography is a newer technique that has found significant application in the fabrication of diffractive optical elements. We describe our techniques for fabricating analog surface-relief profiles in E-beam resist, including a technique for overcoming the problem of resist heating. We also describe a multiple field size exposure scheme for suppression of diffraction orders produced field-stitch errors in blazed diffraction gratings on non-flat substrates.

Trihedral corner cube arrays are efficient retro-reflectors. They are integral parts in numerous imaging and sensing applications. However, the fabrication of these trihedral arrays can prove to be both difficult and cost prohibitive. Using a phase-only mask, we have fabricated an array of analog reflectors which can then be tiled using a photolithographic stepper. The elements are designed using a fixed period and varying fill factor to create the analog slope of each side wall. The overall depth of the array can be controlled by both the exposure and etching processes to ultimately create the desired effect. After etching, a single coating of metal finishes the process, and the elements can then be diced out and integrated into each specific application. The etched arrays may alternatively be used as a mold to create high volumes of the desired element. The design and fabrication parameters for trihedral corner cube arrays will be discussed in detail. The advantages and limitations will then be discussed.

Interference in the Fresnel regime of periodic structures creates a wide variety of intricate diffraction patterns. The diffraction patterns from both amplitude and phase gratings can bear a strong resemblance to the grating itself, or have much more complex structures. In this paper, we discuss a general approach for using interference patterns from amplitude gratings for lithographic fabrication of optical microstructures. We address the generation of the interference patterns from the standpoint of Talbot self-imaging. This approach enables the realization of complex optical structures with a single exposure in an appropriate fractional Talbot plane. Design approaches are discussed, and both theoretical and experimental results are presented.

We report bubble scattering effects on photoresist when a 193nm immersion interferometric lithographic system is employed. According to Mie theory and FDTD simulation, the scattering effect of a bubble becomes significant and may cause defects on a resist pattern when its diameter is greater than 60nm. Some preliminary experimental results are also included.

Optical waveguide propagation loss due to sidewall roughness, material impurity and inhomogeneity has been the focus of many studies in fabricating planar lightwave circuits (PLC's) In this work, experiments were carried out to identify the best fabrication process for reducing propagation loss in single mode waveguides comprised of silicon nitride core and silicon dioxide cladding material. Sidewall roughness measurements were taken during the fabrication of waveguide devices for various processing conditions. Several fabrication techniques were explored to reduce the sidewall roughness and absorption in the waveguides. Improvements in waveguide quality were established by direct measurement of waveguide propagation loss. The lowest linear waveguide loss measured in these buried channel waveguides was 0.1 dB/cm at a wavelength of 1550 nm. This low propagation loss along with the large refractive index contrast between silicon nitride and silicon dioxide enables high density integration of photonic devices and small PLC's for a variety of applications in photonic sensing and communications.

This paper addresses guided-mode resonance elements with binary profiles and their spectral and physical properties. It is shown that these subwavelength periodic waveguide films yield rich spectra that are critically influenced by the shape of the grating profile. The symmetry of the profile controls the resonance spectral density. Symmetric profiles generate a single resonance on either side of the second stopband whereas two resonances arise, one on each side of the band, for asymmetric structures. The profile's Fourier harmonic content, along with the absolute value of the grating modulation strength, affects the resonance linewidths and their relative locations. Computed Brillouin diagrams illustrate key properties of the resonant leaky-mode spectra in relation to modulation strength and profile symmetry at the second stopband. Associated mode plots elucidate the spatial distribution of the leaky-mode field amplitude at resonance and show that at higher modulation, the shape appears as a complex mixture of modes. The results presented include wavelength and angular spectra for several example devices including narrowband transmission filter, wideband reflectors and transmission elements for TE and TM polarization, and a wideband polarizer. Effects of fabrication errors are considered for the polarizing device and an example of a fabricated narrow-band reflector is provided. These results demonstrate new dimensions in optical device design and may provide complementary capability with the field of thin-film optics.

Dramatic reductions in the size of waveguide bends for materials with low core/clad refractive index contrast can be achieved with single air interface bends (SAIBs) based on total internal reflection. However, high optical efficiency for such bends requires vertical interfaces with low surface roughness. In this presentation we report the development of a highly anisotropic etch for perfluorocyclobutane (PFCB) waveguide structures. We examine the use of inductively coupled plasma reactive ion etching (ICP RIE) based on both oxygen/helium and carbon dioxide/helium etch chemistries to achieve the desired interface quality for high efficiency waveguide bends.

Bragg gratings have been used relatively extensively in recent years due to their highly dispersive and wavelength selective nature. Typically used as a reflective structure, the gratings reflect specific wavelengths at specific locations along the structure based on the grating periodicity to spatially shape an incident pulse of light according to its spectral components. Usually the purpose is to either compress or stretch the pulse. Unfortunately, fabrication tolerances severely limit the amount of chirp per unit of waveguide length that can be placed on a Bragg grating. For some applications, a few nanometers of chirp over a meter or more of waveguide would be ideal, yet placement accuracy of individual features is usually far less than is needed for such a task. We propose an alternative fabrication method which would provide a long grating with substantially increased placement accuracy. Instead of fashioning the grating in the typical linear manner, a waveguide is fabricated in a spiral shape. This has been done for delay lines and amplifier structures in the past. However, we propose to incorporate a radial grating underneath it. This provides us an additional degree of freedom, since the period of the grating changes very linearly with its radius, and a waveguide can be accurately positioned on top of it so as to gradually spiral inwards (or outwards) and change radius (and, hence, grating period) very slowly along its length. We present fabrication results, optical comparisons between similar linear and spiral structures, and preliminary theoretical modeling of the structures.

We present a unique method for real-time polarization measurement by use of a discrete space-variant subwavelength grating. The formation of the grating is done by discrete orientation of the local subwavelength grooves. The complete polarization analysis of the incident beam is determined by spatial Fourier transform of the near-field intensity distribution transmitted through the discrete subwavelength dielectric grating followed by a subwavelength metal polarizer. We discuss a theoretical analysis based on Stokes-Muller formalism and experimentally demonstrate our approach with polarization measurements of infrared radiation at a wavelength of 10.6um. Moreover, a new far-field polarimetry approach is presented along with preliminary experimental results.

The spatial-frequency filtering of high power laser beams with a high divergence requires pinholes with small hole diameters, small thicknesses and a high laser damage threshold. Conventional pinholes, based on absorption or reflec-tion are difficult to realize under these conditions. We present a new method for the filtering of laser beams by using dielectric pinholes, which do not absorb or reflect but rather deflect the high spatial-frequency parts of the beam. Ad-vantages of this new kind of pinholes are a significantly increased resistance to high laser energies, which is comparable to the damage threshold of the bulk form of the dielectric material, and a simplified handling because of the permanent visibility of the beam. To demonstrate the principle, we fabricated diffractive pinholes in fused silica by use of electron beam lithography with subsequent reactive ion beam etching. Finally some measurements of the filtering effect are presented.

Nanofibers made from organic molecules such as para-hexaphenyl allow guiding of electromagnetic waves. Since they possess nanometric widths and heights but macroscopic lengths they represent the smallest possible optical waveguides. Recently, gain enhancement has been observed, pointing to possible applications as nanolasers. Owing to their self assembly growth mode on mica substrates the nanofibers posses well-defined morphology. In order to implement these aggregates into new optical devices or to enhance feedback and thus build up a resonator structure a defined cutting of the end faces is necessary. This article presents results from the first experimental studies in this direction. Irradiation with UV laser pulses of 193 nm at a fluence of 100 mJ/cm² removes the fibers completely without damaging the substrate. In addition, the fibers can be cut in any orientation relative to their long axes. The quality of the ablation process in terms of readsorbed debris and steepness of cutting is investigated by atomic force and scanning electron as well as fluorescence microscopy.

A review of the principal issues related to the fabrication of long-ranging surface plasmon metal waveguides (MWG's) and associated passive and active elements is presented. A discussion of the fabrication requirements for MWG devices is given, followed by examples of various challenges encountered in their fabrication along with associated solutions. The examples cover devices made in a range of materials, including glass, lithium niobate, and PLZT ferroelectrics. Finally, a view on future fabrication strategies is given.

High resolution, conformable phase masks provide a means to fabricate, in an experimentally simple manner, classes of three dimensional (3D) nanostructures that are technologically important but difficult to generate in other ways. This proposed approach can answer the greatest challenge of photonic system; a simple and reliable fabrication method of periodic and aperiodic structure. Those unique advantages of proximity field nanopatterning originated from direct conformal contact and a further application to multi-photon process, and a representative waveguiding structure are investigated. The patterning capability in a broad range of wavelengths (from UV to near-IR) and unusual structures place this method as a key technique for photonic system.

Multi-photon three-dimensional micro-/nano-fabrication (3DM) is a powerful technique for creating complex 3D micro-scale structures of the type needed for micro-electromechanical systems (MEMS), micro-optics, and microfluidics. In 3DM high peak-power laser pulses are tightly focused into a medium which undergoes a physical or chemical change following multi-photon excitation at the focal point. Complex structures are generated by serial 3D-patterned exposure within the material volume. To further the application of 3DM to micro-component engineering, we are developing a fully automated and integrated 3DM system capable of creating complex cross-linked polymer structures based on patterns designed in a CAD environment. The system consists of four major components: (1) a femtosecond laser and opto-mechanical system; (2) 3-axis micro-positioner; (3) a computer-controlled fabrication interface; and (4) software for fabrication-path planning. The path-planning software generates a 3DM command sequence based on an object-design input file created using standard commercial CAD software. The 3DM system can be used for start-to-finish design and fabrication of waveguides, 3D photonic crystals, and other complex micro-structures. These results demonstrate a technological path for implementing 3DM as a tool for micro- and nano-optical component manufacture.

A novel laser micro-machining technique to produce high density micro-structures called Synchronized Image Scanning (SIS) was introduced a couple of years ago. Over this period of time, the technique was refined in a major effort to meet the needs of various industries. There is an increasing demand for micro-structuring of large and super large area optical films, e.g. for Rear Projection TV, anti counterfeit packaging material and 3D displays. Especially in the display industry, where the screens are ever increasing in size, established micro-structuring methods like e-beam milling, diamond turning or the reflow technique struggle to keep up with the development. This paper explains how it is possible to direct laser etch hundreds of millions of lenses into a 2 m x 1.5 m substrate. It looks at the advances made in SIS in recent years regarding seam reduction, overall accuracy and precision when structuring super large area optical films, and it presents the tools and subsystems needed to generate the features in those films. Furthermore, the potential of this exciting laser micro-machining technique for rapid prototyping for all sorts of optical and non-optical structures is mapped out.

Bending loss is the biggest drawback to hollow waveguides used for light delivery applications such as laser ablation. One way to overcome this limitation without changing the fiber design or fabrication is to engineer the input light to excite specific modes with better optical properties. Our first order calculations of the transmission and bending losses inside the cylindrical hollow waveguides showed that the TE₀₁ mode suffers the least amount of losses. To selectively excite this mode, it is desired to design an optical component that converts incident linearly polarized light into a rotating wave similar to the TE₀₁ mode. This work focuses on the design and fabrication of a subwavelength structure that converts the input polarization into that of the TE₀₁ mode.

This paper describes the fabrication of very high-sag (up to 42 μm) microlenses by direct laser writing and their integration onto a simple microoptical bench processed by conventional microfabrication technologies pertaining to MOEMS. At the heart of such a work is INO's laser writer. It is based on a He-Cd laser operating at 442 nm whose intensity can be modulated up to 1024 levels, and on a 40 nm accuracy X-Y translation stage. Laser writing into thick photoresist layers introduces however particular problems in terms of the roughness achievable. Simulations show that the writing beam diameter, the line-to-line spacing and the translation stage accuracy contribute to some unavoidable residual roughness. By applying optimized laser writing parameters, arrays of 1 x 5 aspherical microlenses were fabricated in a thick positive photoresist, along with alignment marks concurrently generated for on-chip alignment purposes. The microlenses were successfully integrated with a microoptical bench by first generating a UV-transparent mold from the photoresist laser written master. The microlenses imprinted in the mold were then replicated in a layer of hybrid glass material cast on the microoptical bench by UV-embossing with a modified MA6 mask aligner. The uniformity of focal lengths was approximately 3% as determined from best fits of profilometric traces. The replication with alignment of this array in a hybrid glass material was demonstrated on a 12 mm x 12 mm microoptical bench chip. An alignment accuracy of less than 5 μm was obtained. The replication error was less than about 4%. The measured surface roughness was 50-60 nm RMS, in good agreement with simulation results.

Macroporous titania (TiO₂) monoliths have been prepared by the sol-gel method including phase separation, and the light-scattering properties have been investigated by means of coherent backscattering. Macroporous TiO₂ gels are obtained in the systems containing aqueous titania colloid and poly(ethylene oxide)(PEO). Threedimensionally interconnected macroporous structure is formed when the transient structure of phase separation is fixed as the permanent morphology by the sol-gel transition. The domain size of macroporous TiO₂ gels can be controlled reproducibly by adjusting the concentration of PEO. During the heat treatment above 1000 °C, the TiO₂ skeleton is sintered into fully dense body and the crystalline structure is transformed from anatase to rutile, while maintaining macroporous morphology. We show that the rutile-type TiO₂ -based macroporous monoliths are strongly scattering media for visible light.

A poly-silicon piston micro-mirror array, which has been enhanced with a multilayer coating to exhibit special reflective properties at Cu K_α emission line of 1.54 Å is presented. The micro-mirror array is fabricated using the MEMSCAP PolyMUMPs process and packaged in a ceramic package. The packaged array is coated using atomic layer deposition with an Al₂O₃/W multilayer. The first Al₂O₃ layer is thicker than for a normal bilayer pair and prevents the mirror coating from creating an electrical short. This device was tested before and after coating. The snap-down voltage was reduced by half, but qualitatively the mechanical motion remained similar. The fabrication process presented for the Cu K_α wavelength at 1.54 Å can be easily adapted to other optical MEMS and for other wavelengths.

We describe an approach to use the thin layer of SU-8 submicron pattern produced by holographic lithography as dry etching mask in chemically assisted ion beam etching (CAIBE) system. The effect of chlorine gas flow on etched sidewall was investigated; by matching the lateral etch and deposition rate, etching selectivity of about 7:1 has been achieved with vertical and smooth sidewall and damage-free upper portion of the etched structure. As an application, a half wavelength retardation plate for 1.55 mm wavelength was designed, fabricated and characterized.

Sm²⁺-doped Al₂O₃-SiO₂ glasses with three-dimensionally interconnected macroporous morphology have been prepared via the alkoxy-derived sol-gel process containing poly (ethylene oxide) and SmCl₃·6H₂O. The macroporous morphology is obtained by concurrently inducing the phase separation and sol-gel transition. Using a visible laser with the wavelength of 488 nm, the valence state of Sm²⁺ has been manipulated spatially. When the photoionization of Sm²⁺ is combined with multiple light scattering in the porous glasses, holes are burned in wave-vector domain. The hole profile can be controlled by adjusting the macroporous morphology.

In many applications, where the period of a grating structure is less than the wavelength of the incident light, the grating structure will function more like a medium of uniform index of refraction than as a normal grating. The effective medium index being equivalent to the volume mean index of the grating structure. The equalivent refractive index will depend on its structure or material. When the structure is given orientation, anisotropy called constitutive birefringence will be generated. A refractive index profile can be also be provided on material surface. Making use of these properties of sub-wavelength structure, we have successfully established methods to design, fabricate, prototype, and evaluate elements which perform polarization separation. The polarization separation elements consist of two-layers, plastic material (low refractive-index layer) and vacuum evaporation material (high refractive-index layer). The grating structure has a very small depth. Polarization separation elements both for single wavelength and two wavelengths can be designed. These elements can be designed for any fixed incident angle to the substrate, They can replace glass polarization separation elements and half mirror elements currently used for DVD/CD. It is also one of advantages that they can be mass produced with low cost.