This PDF file contains the front matter associated with SPIE Proceedings Volume 8974, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

One photon diffusive photopolymers enable self-developing three dimensional (3D) refractive index patterning of up to cm thick solid volumes for the fabrication of micro-optics. However, one photon absorption in solid, thick materials does not yield complete control of the 3D refractive index distribution due to diffraction and the excessive development time for index features measuring 100’s of microns in diameter or larger. We present a fabrication method and photopolymer formulation that can efficiently create mm³ optical devices with programmable, gradient index of refraction with arbitrary feature size and shape. Index contrast of 0.1 is demonstrated, which is 20 times larger than commercial holographic photopolymers. Devices are fabricated by repetitive micro-fluidic layering of a self-developing photopolymer structured by projection lithography. The process has the unusual property that total fabrication time for a fixed thickness decreases as the number of layers is increased, reducing the fabrication time for high axial resolution micro-optics. We demonstrate the process by fabricating thick waveguide arrays and gradient index lenses.

We report on vortex-assisted femtosecond direct laser writing (DLW) in silver-containing phosphate glasses with complex light fields endowed with optical phase singularities. This allows us to engrave complex patterns showing sub-wavelength dimensions. The associated linear and nonlinear optical properties show remarkably correlated but distinct spatial distributions. The creation of a perennial buried electric field leads to an efficient electric- field induced second harmonic generation. The magnitude and distribution of such buried field is also considered to actively drive the pattern topology of the fluorescent silver clusters. Using DLW with phase and amplitude engineered beams, we demonstrate a promising approach to control both fluorescent and nonlinear responses below the diffraction limit.

Advanced micro- and nanofabrication processes are constantly evolving from academic R&D environment towards real production technology. Therefore, the availability of suitable polymers for optical applications plays a crucial role to satisfy not only application based requirements but also the compatibility to industrial production technologies. In this context, UV-curable hybrid polymers, i.e. inorganic-organic materials obtained by sol-gel chemistry, were recently implemented into mass production environment, e.g. for micro-lenses in mobile device applications. In this contribution, we report on the development of innovative hybrid polymers and their tailoring towards an easy and fast processing with reliable and reproducible performance output for industrial large-scale production. Based on a discussion on standard process parameters with respect to optimize the material’s performance, the technical demands of industrial manufacture to the hybrid polymers will be subsequently reviewed by giving selective examples. This will be complemented by a brief description of current R&D activities adapting hybrid polymers to future patterning technologies.

In this work, 3-D nanoscale line patterns were fabricated on SU-8 layers by Ga+ focused ion beam (FIB) lithography and used as Nanoimprint lithography (NIL) mold. Both V-shape side wall and opposing dose deficiency effect were observed and analyzed during the FIB milling process. Different beam currents were utilized to fabricate SU-8 pattern and it is found that the lower beam currents provide higher quality pattern with smooth edges and straight side walls. In addition, the impact of crosslink density of SU-8 material on the FIB milling efficiency was discussed. Both thermal and ultraviolet (UV) NIL were conducted using these line patterns to study the deformation of SU-8 mold and filling ratio of imprinting material. The experiments revealed that the imprint pressure and physic properties of imprinting material are the most critical factors in these NIL processes.

We utilized a hybrid lithography technique in the fabrication of a 45 degree micro mirror coupler to be used for a 3D optical circuit. The hybrid process combines traditional mask-based lithography techniques with mask-less methods. The result is a CMOS compatible process that can be used for fabrication of integrated micro-optics.

Chalcogenide glasses, namely the amorphous compounds containing sulfur, selenium, and/or tellurium, have emerged as a promising material candidate for mid-infrared integrated photonics given their wide optical transparency window, high linear and nonlinear indices, as well as their capacity for monolithic integration on a wide array of substrates. Exploiting these unique features of the material, we demonstrated high-index-contrast, waveguide-coupled As2Se3 chalcogenide glass resonators monolithically integrated on silicon with a high intrinsic quality factor of 2 × 10⁵ at 5.2 micron wavelength, and what we believe to be the first waveguide photonic crystal cavity operating in the mid-infrared.

In this paper we show that using optical photolithography it’s possible to obtain submicron features for periodic structures using the Talbot effect. To use the Talbot effect without the need of an absolute distance measurement between the mask and the wafer we integrate over several exposures for varying wafer mask distances. Here we discuss the salient features of ‘integrated Talbot lithography’. Particularly, we show that to obtain good contrasts an excellent control of the illumination light is essential; for this we use the MO Exposure Optics (MOEO) developed by SUSS MicroOptics (SMO). Finally we show that 1μm and 0.55μm diameter holes can be made using this technique.

The fabrication of complex nano-optical structures for plasmonics, photonic-crystals, or meta-materials on application relevant areas by electron-beam lithography requires a highly parallel writing strategy. In case of periodic pattern as they are found in most of the mentioned optical elements this can be achieved by a so called character projection writing principle where complex exposure pattern are coded in a stencil mask and exposed with a single shot. Resulting shotcount and writing time reductions compared to standard Variable-Shaped-Beam exposures can be in the order of 100...10000. The limitation in flexibility by using hard-coded exposure shapes can be overcome by implementing the character projection principle with a highly precise motorized aperture stage capable of carrying several 1000 different apertures. Examples of nano-optical elements fabricated with the new character projection principle are presented.

Hybrid photolithography and focused ion beam (FIB) patterning of coupled photonic cavities is reported. This technique is used for rapid prototyping of nanophotonic devices, where previously mass-produced devices by conventional lithography steps, such as photolithography, projection lithography or nano/micro-imprinting can be customized by a versatile approach on a focused ion beam microscope. This requires accurate positioning of the FIB pattern relative to the pre-patterned devices and minimal drift during the writing phase. Various fabrication parameters that mimic process variability can be studied and the obtained experimental results compared with numerical simulations of the fabricated devices. This allows the calibration of the simulation models for more accurate design to manufacturing predictability. As a proof of concept, the experimental optimization of the localized modes in a photonic molecule formed by placing two one-dimensional photonic crystal cavities on a nanowire coupler is reported. The effects of different photonic crystal geometry, material removal depth and rate, sidewall profile and roughness, patterning drift on the performance of the photonic molecule resonator are investigated. These fabricated photonic molecule devices can be used as refractive index sensors with measured sensitivities on the order of 400 nm/RIU with a sensing volume as low as 18 femtoliters. The dimensions of the fabricated devices and the understanding of their optical behavior on environmental influence open the door for near-field optical spectroscopy of single bacterial specimens.

The structures in advanced complementary metal-oxide-semiconductor (CMOS) integrated circuit technology are in the range of deep-submicron. It allows designing and integrating nano-photonic structures for the visible to near infrared region on a chip. In this work, we designed and fabricated an image sensor with on-pixel metal wire grid polarizers by using a 65-nm standard CMOS technology. It is known that the extinction ratio of a metal wire grid polarizer is increased with decrease in the grid pitch. With the metal wire layers of the 65-nm technology, the grid pitch sufficiently smaller than the wavelengths of visible light can be realized. The extinction ratio of approximately 20 dB has been successfully achieved at a wavelength of 750 nm. In the CMOS technologies, it is usual to include multiple metal layers. This feature is also useful to increase the extinction ratio of polarizers. We designed dual layer polarizers. Each layer partially reflects incident light. Thus, the layers form a cavity and its transmission spectrum depends on the layer position. The extinction ratio of 19.2 dB at 780 nm was achieved with the grid pitch greater than the single layer polarizer. The high extinction ratio is obtained only red to near infrared region because the fine metal layers of deepsubmicron standard CMOS process is usually composed of Cu. Thus, it should be applied for measurement or observation where wide spectrum is not required such as optical rotation measurement of optically active materials or electro-optic imaging of RF/THz wave.

The adoption of spectral imaging by industry has so far been limited due to the lack of high speed, low cost and compact spectral cameras. Moreover most state-of-the-art spectral cameras utilize some form of spatial or spectral scanning during acquisition, making them ill-suited for analyzing dynamic scenes containing movement. This paper introduces a novel snapshot multispectral imager concept based on optical filters monolithically integrated on top of a standard CMOS image sensor. It overcomes the problems mentioned for scanning applications by snapshot acquisition, where an entire multispectral data cube is sensed at one discrete point in time. This is enabled by depositing interference filters per pixel directly on a CMOS image sensor, extending the traditional Bayer color imaging concept to multi- or hyperspectral imaging without a need for dedicated fore-optics. The monolithic deposition leads to a high degree of design flexibility. This enables systems ranging from application-specific, high spatial resolution cameras with 1 to 4 spectral filters, to hyperspectral snapshot cameras at medium spatial resolutions and filters laid out in cells of 4x4 to 6x6 or more. Through the use of monolithically integrated optical filters it further retains the qualities of compactness, low cost and high acquisition speed, differentiating it from other snapshot spectral cameras.

We report realisation of structural colour in dielectrics using direct laser write technique. 3D porous dielectric structures with woodpile photonic crystal architecture were fabricated by femtosecond direct laser write lithography in photoresist and characterised structurally and optically. The fabricated samples were found to exhibit resonant high-reflectance bands at visible wavelengths depending on the lattice parameters, and correspondingly, led to coloration of the structure without light absorption or emission. Structural colour was found to originate from slow-light spectral regions occurring in some higher photonic bands at visible wavelengths. Visible coloration in samples with relatively large lattice period, a > 1μm can be achieved due to this peculiarity, which helps alleviate the requirement for high resolution of the fabrication, shortened the fabrication time. In the future, similar structures may be useful for preparation of photonic crystal-based environmental and imaging sensors.

Arsenic trisulfide (As₂S₃) is a transparent material from ~620 nm to 11 μm with direct applications in sensors, photonic waveguides, and acousto-optics. As₂S₃ may be thermally deposited to form glassy films of molecular chalcogenide (ChG) clusters. It has been shown that linear and multi-photon exposure can be used to photo-pattern thermally deposited As₂S₃. Photo-exposure cross-links the film into a network solid. Treating the photo-patterned material with a polarsolvent removes the unexposed material leaving behind a structure that is a negative-tone replica of the photo-pattern. In this work, nano-structure arrays were photo-patterned in As₂S₃ films by multi-photon direct laser writing (DLW) and the resulting structure, morphology, and chemical composition were characterized and correlated with the conditions of the thermal deposition, patterned irradiation, and etch processing. Raman spectroscopy was used to characterize the chemical structure of the unexposed and photo-exposed material, and near infrared ellipsometry was used to measure the refractive index. Physical characterization including structure size and surface adhesion of nano-scale features is related to the processing conditions.

Ultrashort pulsed lasers are used to fabricate 3D structures in single crystal CVD diamond. The interaction of the laser with diamond lattice leads to a permanent structural modification, which is highly localized at the focus. Severe spherical aberrations compromise fabrication precision below the diamond surface. We implement adaptive aberration compensation to ensure optimum fabrication performance. The nature of the structural modification is analysed for both surface and subsurface laser fabrications.

To improve light absorption, previously various antireflection material layers were created on solar wafer surface including multilayer dielectric film, nanoparticle sludges, microtextures, noble metal plasmonic nanoparticles and 3D silicon nanostructure arrays. All of these approaches involve nanoscale prepatterning, surface-area-sensitive assembly processes or extreme fabrication conditions; therefore, they are often limited by the associated high cost and low yield as well as the consequent industry incompatibility. In comparison, our nanomanufacturing, an unique synchronized and simultaneous top-down and bottom-up nanofabrication approach called simultaneous plasma enhanced reactive ion synthesis and etching (SPERISE), offers a better antireflection solution along with the potential to increase p-n junction surface area. High density and high aspect ratio anechoic nanocone arrays are repeatedly and reliably created on the entire surface of single and poly crystalline silicon wafers as well as amorphous silicon thin films within 5 minutes under room temperature. The nanocone surface had lower than 5% reflection over the entire solar spectrum and a desirable omnidirectional absorption property. Using the nanotextured solar wafer, a 156mm × 156mm 18.1%-efficient black silicon solar cell was fabricated, which was an 18.3% enhancement over the cell fabricated by standard industrial processes. This process also reduces silicon loss during the texturing step and enables tighter process control by creating more uniform surface structures. Considering all the above advantages, the demonstrated nanomanufacturing process can be readily translated into current industrial silicon solar cell fabrication lines to replace the costly and ineffective wet chemical texturing and antireflective coatings.

A growing number of commercial products such as displays, solar panels, light emitting diodes (LEDs and OLEDs), automotive and architectural glass are driving demand for glass with high performance surfaces that offer anti-reflective, self-cleaning, and other advanced functions. State-of-the-art coatings do not meet the desired performance characteristics or cannot be applied over large areas in a cost-effective manner. “Rolling Mask Lithography” (RML™) enables highresolution lithographic nano-patterning over large-areas at low-cost and high-throughput. RML is a photolithographic process performed using ultraviolet (UV) illumination transmitted through a soft cylindrical mask as it rolls across a substrate. Subsequent transfer of photoresist patterns into the substrate is achieved using an etching process, which creates a nanostructured surface. The current generation exposure tool is capable of patterning one-meter long substrates with a width of 300 mm. High-throughput and low-cost are achieved using continuous exposure of the resist by the cylindrical photomask. Here, we report on significant improvements in the application of RML™ to fabricate anti-reflective surfaces. Briefly, an optical surface can be made antireflective by “texturing” it with a nano-scale pattern to reduce the discontinuity in the index of refraction between the air and the bulk optical material. An array of cones, similar to the structure of a moth’s eye, performs this way. Substrates are patterned using RML™ and etched to produce an array of cones with an aspect ratio of 3:1, which decreases the reflectivity below 0.1%.

We fabricated large-area stacked complementary plasmonic crystals (SC PlCs) by employing ultra-violet (UV) nanoimprint lithography (NIL). The SC PlCs was made on silicon on insulator (SOI) substrates, consisting of three layers: the top layer contacting air was perforated Au film, the bottom layer contacting buried oxide (BOX) layer included Au disk array corresponding to the holes in the top layer, and the middle layer was Si photonic crystal slab. The SC PlCs have prominent resonances in the optical wavelengths. It is shown that the fabricated PlCs were precisely made in structure and well uniform in the optical properties. We have examined photoluminescence (PL) enhancement of dye molecules on the SC PlC substrates in the visible range and found large enhancement up to 100-fold in comparison with the dye molecules on non-processed Si wafers.

Glassy carbon is used nowadays for a variety of applications because of its mechanical strength, thermal stability and non-sticking adhesion properties. One application is glass molding that allows to realize high resolution diffractive optical elements on large areas and at affordable price appropriate for mass production. We study glassy carbon microstructuring for future precision compression molding of low and high glass-transition temperature. For applications in optics the uniformity, surface roughness, edge definition and lateral resolution are very important parameters for a stamp and the final product. We study different methods of microstructuring of glassy carbon by etching and milling. Reactive ion etching with different protection layers such as photoresists, aluminium and titanium hard masks have been performed and will be compare with Ion beam etching. We comment on the quality of the structure definition and give process details as well as drawbacks for the different methods. In our fabrications we were able to realize optically flat diffractive structures with slope angles of 80° at typical feature sizes of 5 micron and 700 nm depth qualified for high precision glass molding.

The micro lens array illumination device has an advantage on transmittance, but it also has the problem of the generation of diffraction pattern. Well-known method for reducing diffraction is adding randomness to array structure (random structure), but there are many choices to do it. In this study we examined the randomness with a scope that is realizable by diamond machining yet with good productivity. As the result, we have found that the diffraction pattern can be reduced sufficiently by adding randomness of some 10% of its lattice constant to spatial configuration of periodic lattice of micro lens array. In addition, we have also examined controlling the illuminance distribution, by taking advantage of high form accuracy which is special features of diamond machining.

In this paper, we demonstrate an ultra-thin, low-loss optical metamaterial filter with high transmission and near constant group delay across a broad pass-band from 3.0 to 3.5μ m. Deep-subwavelength air hole inclusions positioned at the corners of a conventional metallodiectric fishnet were used engineer the dispersive properties of the structure to have an impedance match to free space over the pass-band. The optical properties of the metamaterial filter were verified by experimentally fabricating and characterizing the optimized free-standing nano-notched fishnet. The measured experimental results agreed well with the simulated response, showing a high transmission band over the targeted wavelength band.

Here we present single exposure holographic fabrication of embedded defects in photonic crystal structures in a negative photoresist using a spatial light modulator (SLM). A phase pattern is engineered to form a desired interference pattern and displayed on a phase-only SLM. The resulting first order beams at the Fourier plane are used to recreate the interference pattern. Negative and positive defects are added to the photonic crystal in the following ways. A void-type defect is produced in two dimensional photonic crystal structures by replacing the phase of the engineered phase pattern with a constant value at the points where the defect is desired. And a positive bump defect can be made by allowing the zeroth order beam to interfere with the first order beams. Through these methods, it is possible to fabricate arbitrary shaped defect structures in photonic crystals through a single exposure process, thus improving cost effectiveness and simplifying the fabrication process of integrated photonics.

An optomechanical dual cantilever device has been fabricated with applications as a displacement sensor and variable attenuator. A novel fabrication approach using a precision dicing saw has benefits for fabrication time, cost and energy consumption. The displacement sensor sensitivity is 0.8 dB/micron and a suppression ratio of 25 dB is obtained when the device is used as an attenuator.

Gratings with binary and blazed profiles and periods in the low micron and sub-micron range define a class of microstructures with a huge application potential. We present a mask based photolithographic fabrication method for these demanding grating geometries. It combines the advantages of electron beam lithography and holographic exposure, which are superior homogeneity, high resolution and pattern flexibility on one hand, and a fast, large aerial exposure with the option for smooth profiles on the other hand. This is accomplished by the use of an electron beam written phase mask which contains a very homogeneous pattern of diffractive features and is used for a full-field exposure in a proximity mask aligner. The key for the beneficial use of the technology is the proper design of the phase mask surface profile which can have a binary or multilevel geometry. Since the patterns to be exposed are periodic, this is also the case for the phase mask which allows calculating their physical light transmission with exact methods like rigorous coupled wave analysis. An optimization algorithm has been developed which can find mask geometries that synthesize a desired complex aerial image in the proximity distance of choice. Aerial images offering e.g. high resolution features, phase shifts, and tilted propagation directions can be realized that way. This technology has been successfully used to fabricate e.g. binary gratings of very high quality with a period of 800 nm as well as blazed gratings with a period of 3 μm.

We investigate substrate overetch effect on resonance properties of sub-wavelength titanium oxide (TiO₂) Guided Mode Resonance Filters (TiO₂-GMRFs). The TiO₂-GMRF is designed and fabricated to possess a non-polarizing behavior, which is strongly dependent on substrate (fused silica) overetch depth. For non-polarizing gratings at resonance, TE- and TM-modes have the same propagation constants. However, an overetch substrate effect results in splitting of the degenerate modes, which is studied theoretically and experimentally. The TiO₂-SiO₂ GMRFs are designed by Fourier Modal method (FMM) based on the rigorous calculation of electromagnetic diffraction theory at a designed wavelength of 850 nm. The TiO₂-SiO₂ gratings are fabricated by Atomic Layer Deposition (ALD), Electron Beam Lithography (EBL), and Reactive Ion Etching (RIE), and they are subsequently characterized structurally by Scanning Electron Microscopy (SEM) and optically by a spectroscopic ellipsometer. Several grating samples are fabricated by gradually increasing the overetch depth into fused silica and measuring the extent of TE- and TM-mode-splitting. A close agreement between the calculated and experimentally measured resonance wavelength spectral shift is found to describe the mode splitting of non-polarizing gratings.

Melt transcription molding is one of novel processes suitable for manufacturing large-area thin film with microstructures. We designed the mold which enables to transfer structures on both surfaces for the melt transcription molding machine and examined about relations of temperature and pressure on the accuracy of dimension and optical strain. To keep the high accuracy of relative position between both surfaces, the mold can avoid strain caused by the thermal expansion of metal and is optimized by three-dimension unsteady heat conduction analysis. As a result, distribution of pressure mainly affects stress and distribution density, influences shrinkage and accuracy of position. The decenter between both surfaces was several micrometers. This makes it possible to mass-produce the large-area optical elements which is formed the micro and nano structures on both surfaces with extremely low birefringence at high productivity.

In this work, we present a method of holographically fabricating photonic structures in photosensitive polymer using a phase pattern displayed on a spatial light modulator (SLM) as a digitally programmable phase mask. The phase pattern can be programmed in hexagonal and square symmetries. By changing the gray level of the pixelated units in the displayed phase pattern, we can achieve a digital control of the phases of one or more of the interfering beams, thus changing the interference pattern. By using the phase pattern on the SLM as a tunable phase mask, different photonic crystal templates can be fabricated.

A U-shaped optical fiber inline microchannel was fabricated by femtosecond laser irradiation and subsequent selective chemical wet etching. A high quality micro-cavity embedded inside the channel was obtained to construct a Fabry-Perot interferometer (FPI). A fringe visibility of 20 dB in spectrum domain was achieved. High temperature survivability of this micro device was also demonstrated. The proposed assembly-free optical fiber inline interferometer is attractive for sensing applications in high-temperature harsh environments.

The holographic lithography - ion beam etching is adopted to fabricate the nanoimprint template with periodic structures. The accurate control of the high aspect ratio of the profile is achieved by the optimization of the holographic lithography and the choice of the appropriate parameters of ion beam etching. There are two major challenging steps of this method: 1) the holographic exposure and development in the fabrication of the photoresist mask and 2) the ion beam etching to transfer the photoresist mask to the fused silica. The experiment indicates that titled rotation of the ion beam etching combined with reactive ion beam etching can achieve the accurate control of the high aspect ratio structure. Two types of nanoimprint template have been fabricated: the period of 250nm and the groove depth of 380nm; the period of 600nm and groove depth of 1400nm, respectively.

A compact Michelson interferometer (MI) in a single-mode fiber (SMF) is successfully formed by CO₂ laser irradiation to measure refractive index (RI) values. The fiber inline MI mainly consists of two parts: one is the waist region in fiber formed by CO₂ laser irradiation and the other one is the fiber tip end facet with pure gold sputter coating. Based on the MI theory, the interference signal is generate between the core mode and the cladding mode excited by the core mode at the waist region. Reflective spectra at two different interference lengths of 5mm and 15mm are given and the calculated lengths based on theory are well verified. After the measurements of matching liquids with seven different refractive indices, the RI sensitivity of the MI sample is tested of -197.3±19.1nm/RIU (refractive index unit), which suggests well potential application in RI sensing.

Photonic crystals are nanofabricated structures that enhance light as it is passed through the constructed design. These structures are normally fabricated out of silicon but have shown to be an improvement if fabricated from a more cost effective material. Photonic crystals have uses within biosensing as they may be used to analyze DNA and other analytes. Microfluidic channels are used to transport different analytes and other samples from one end to another. Microfluidics are used in biosensing as a means of transport and are typically fabricated from biocompatible polymers. Integrated together, the photonic crystals and microfluidic channels would be able to achieve better sensing capabilities and cost effective methods for large scale production. Results will be shown from the co-molding.