This PDF file contains the front matter associated with SPIE Proceedings Volume 12012, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

High-resolution microfabrication techniques such as two-photon polymerization have been extensively developed in response to the increasing demand for non-spherical optical surfaces. However, these fabrication processes are limited to polymer materials. On the other hand, glass freeform optics fabrication relies on complex and expensive processes, with strong limits on accessible dimensions, particularly for micro-optics. We present here a flexible, time-efficient and potentially low-cost fabrication process for freeform optics fabricated in fused silica. The process starts from a three-dimensional (3D) CAD model of a freeform surface which is precisely printed into a block of fused silica using tightly focused ultrashort laser pulses, with the precision up to 1 µm. The exposed volumes of the glass part are then removed in a KOH etch to reveal the freeform surface, which is still topically rough. In a subsequent step, the sample is subjected to a smoothening process using thermal annealing, where the sample is placed in an oven at 1350°C for 1 hour, followed by a slow cooling at a rate of 0.5°K/min. The roughness of the sample is then reduced from µm to sub nm, and is thus of optical quality. The results demonstrate the possibility of a novel micro fabrication process for glass freeform optics.

Two-photon fabrication is expected to be a technique for fabricating biological tissues for regenerative medicine and drug discovery because of its capability of fabricating 3D structures on a subcellular scale. In this study, we conducted two-photon fabrication of biocompatible materials without photoinitiators. By using a visible-wavelength femtosecond pulsed laser as excitation light, two-photon polymerization is induced in deep UV absorbing moieties without the use of photo-initiators. We performed 3D micro/nanofabrication of a biocompatible hydrogel material. By using Raman spectral change, we investigated the photo-chemical process of the biocompatible upon the irradiation of visible pulsed laser light.

Here, the structures fabricated using direct laser writing and interference lithography techniques are demonstrated. By the tightly focused femtosecond laser beam in the thin gold film, various structures such as the gold bumps, needles, or cones can be fabricated. The shape of the gold structures depends on the used laser pulse energy. By the treatment of the thin films using nanosecond laser pulses, the direct synthesis of nanoparticles on the glass substrate can be realized. The laser processing of photopolymers enables the formation of structures suitable for micro-optics.

Helical structures exhibit novel optical and mechanical properties and are commonly used in different fields such as metamaterials and microfluidics. A few methods exist for fabricating helical microstructures, but none of them has the throughput or flexibility required for patterning large surface areas with tunable pitch. In this paper, we report a method for fabricating helical structures with high-throughput and adjustable form based on multiphoton polymerization (MPP) using single-exposure, three-dimensionally structured, self-accelerating, axially tunable light-fields. The light-fields are generated as a superposition of high-order Bessel modes and have a closed-form expression relating the design of the phase mask to the rotation rate of the beam. The method is used to fabricate helices with different pitches and handedness in the material SU-8. Beam splitting and galvo-scanning can be implemented in the system. The fabrication of helical matrices is demonstrated. Compared to point-by-point scanning, our method increases the fabrication speed by two orders of magnitude, paving the way for adopting MPP for mass production of functional devices in many industrial applications.

Liquid Crystal Elastomers (LCEs) are promising candidates for soft-matter-based actuators for MEMS devices. They are loosely crosslinked polymer networks that show high strain rates. The ordering of embedded liquid crystals defines their actuation profile, and these actuators can demonstrate complex actuating mechanisms such as radial contraction and helical bending. However, their applications are limited in MEMS technology because of limited fabrication processes compatible with the actuator's fabrication.

We present a new method to structure the LCE actuators with spatially structured light compatible with MEMS fabrication processes. Fabrication of 50-100 μm thick actuators is done with the standard glass-cell filling process via capillary forces. As material polymerization is light-initiated, material structuring is achieved by selective polymerization with UV light. Then, after developing the material, the polymerized LCE is bonded to a secondary substrate via a stamp-and-stick technique.

A digital micromirror based (DMD) based projection setup was built to project the computer-generated arbitrary patterns on the substrate. This setup allows spatial structuring of the light, thereby enabling the pixel-by-pixel selective polymerization of the LCE actuators. This so-called maskless photolithography of the material enables the patterning of LCE actuators without any printed mask, hence improving the fabrication of the LCE-based MEMS devices. This process ow is automated to easily scale up the fabrication process to the 100mm wafer level.

Computed axial lithography (CAL) is an emerging volumetric additive manufacturing technology which presents unique opportunities in layerless ultra-rapid fabrication. However, the required process control places particular demands on computing and delivering the appropriate 3D distribution of optical energy, as well as monitoring the solidifying structure within the photo-resin. For example, continued reaction after tomographic exposure is not currently accounted for and could lead to higher degree-of-conversion than designed and consequent feature dilations. Color Schlieren Tomography (CST) is developed as an in-situ metrology tool to monitor volumetrically the internal refractive index and the forming geometry. Major improvements of CST in real-time computation and processing of 3D reconstruction have enabled event-driven patterning control such as auto-termination. With this technique, we monitored the polymerization process in real-time during and after termination of the exposure period signaled by an index-volume termination criterion. Monitoring of continued polymerization after termination (dark polymerization) shows that the refractive index change can rise to 10 times higher than its value at termination. The time-resolved 3D reconstruction data provided by CST can be used for chemical kinetics modeling and development of compensation schemes.

On a Silicon Photonics integrated circuit, information is carried by the light that propagates within silicon waveguides. The waveguide’s geometry determines the functionality. The curvilinearity of Silicon Photonics designs would raise challenges for the manufacturability. However, so far Silicon Photonics design dimensions are considered relaxed by the industry. Also, the type of shapes that are drawn would generally use rather simple geometry objects. This allows the usage of conventional techniques in the different phases of the manufacturability. Recently has emerged a type of Silicon Photonics design, referred to as “inverse design”. This new technique produces designs that are very exotic and quite unpredictable. It shows complex geometries which critical dimensions require innovative Resolution Enhancement Techniques at the different stages of the Optical Proximity Correction flow. The success of these “inverse designs” relies on a very accurate pattern fidelity. This presentation will demonstrate a flow going from modelling, to OPC and metrology and verification of the manufactured wafer data. This flow permits to tackle the challenges brought newly to the Silicon Photonics environment.

One of the challenges in integrated photonics is to build optical coupler for seamless coupling the light from fiber to nano-size waveguides or devices on semiconductor or photonics based chips. Here we present a design and technique based on polymer-made 3D structure of nano/mico size for suspended Silicon Nitride nanobeam, a 3D coupler which has in-port for single mode fiber. We show a scattering-free design of the optical interface with some compromises due to resolution limited 3D printer tool with the fiber plug into interface feature. Finite-difference time-domain (FDTD) simulations are performed to optimize the tapering regions. With this optimization upto 95% waveguide to coupler and 62% coupler to waveguide transmission is obtained for large bandwidth(∼ 100nm) at 600 nm. Conical-shaped single mode fiber is fabricated using wet etching technique and plugged into 3D coupler to obtain a compact fiber-to-chip optical device.

Generally, optical multilayer coatings are formed on the optical surface for the purpose of anti-reflection. However, these coatings have problems of environmental resistance such that cracks or peelings.

Lately, a technique for realizing an anti-reflection function by forming a sub-wavelength scale structure on the optical surface has been widely studied [1] [2] [3] [4] [5] [6]. Such a structure is called ARS, Anti-Reflective Structure. ARS has excellent environmental resistance compared to multilayer coatings and has the advantage of low dependence on the incidence angle in terms of optical characteristics.

We have studied a method for fabricating ARS using RIE, Reactive Ion Etching. We found that ARS with fine optical properties is formed on the surface of the glass lens by adjusting plasma condition at each etching process. In this report, we will introduce examples of applications to quartz glass. The first case is ARS for the visible light, which achieved a transmittance of 99% or higher. The other is ARS for the deep ultraviolet light. In addition, these ARS have characteristic of water repellency which is useful for optical components.

Silicon has been commonly used in the microelectromechanical systems (MEMS) community for the past sixty years, and anisotropic wet etching with tetramethylammonium hydroxide (TMAH) has been central to these fabrication efforts. It has been shown anisotropic wet etching of silicon is an ideal method to rapidly fabricate components with huge production volume, and low cost. Although TMAH has been commonly used to create integrated circuits, the technology hasn’t been fully explored for optical applications. Four types of light concentrating arrays were fabricated with this technology in this work: (i) micropyramids with 54.7˚ sidewall angle, (ii) microcones with 45˚ sidewall angle, (iii) inverted square pyramids with 54.7˚ sidewall angle, and (iv) inverted triangular pyramids with different sidewall angles. The 54.7˚ sidewall angle arrays have smooth sidewalls due to etching with TMAH, which reduces scattering loss. The 3-D microphotonic structures were created through a comparable fabrication protocol, but require different photoresists, mask alignments, and if the surfactant Triton X-100 was utilized during the etch. The fabricated structures can be either heterogeneously integrated with front-illuminated focal plane arrays (FPAs) created in material systems with high quantum efficiency, or be monolithically integrated with metal/silicide Schottky barrier photodetectors for operation in short-wave infrared (SWIR) or mid-wave infrared (MWIR) regimes. The light concentrating capability of the proposed structures was tested by finite-difference time-domain modeling. Experimentally, the formation of photonic nanojets at the tips of micropyramids was demonstrated using illumination by a 2.96 μm wavelength Er:YAG laser.