Two-photon polymerization (2PP) is now an established technique for nanofabrication. Conventional fabrication
processes using laser 2PP commonly use a single point beam delivery system in order to write artifacts in the volume of
a resin. Complex shapes such as micro-models, woodpile photonic structures and spiral structures have been realized in
several material systems including, sol-gels, organically modified ceramics and resins. One area of current interest in
2PP micro fabrication is the introduction of more complex beam delivery systems, aimed at introducing a degree of
parallel processing to the writing method. In this paper we describe two alternative parallel processing approaches to beam delivery that demonstrate the use of
diffractive and refractive optics to shape the laser before focusing. Firstly a Fraunhofer diffractive optical element to
generate a linear array of 4 spots of equal intensity thus writing four structures simultaneously. Secondly an axicon lens
is used to form an annulus in the focal plane of the focusing element. This enables complete three dimensional annular
structure fabrication without the use of scanning stages.
For all experiments, a Ti:sapphire laser was used to initiate 2PP microfabrication. The materials system used was a
Zr/PMMA hybrid prepared by the sol-gel method on a glass substrate.
Two polymer technology platforms incorporating both polymer-based materials and UV-assisted and hot embossing fabrication processes have been developed for planar optical waveguiding applications. Firstly, a novel hybrid organic-inorganic (sol-gel) materials system with epoxy functionality has been developed for use in short-range optical interconnect applications. The sol-gel material can be easily formulated and deposited by spin or dip coating to form layers of up to 25μm in thickness. The resulting film can be selectively cross-linked using photo-lithography, as part of a UV-Thermal curing process. The basic refractive index of as-deposited layers can be adjusted between 1.48 and 1.515 by modifying the concentration of DPDMS present. The near-field image of transmitted radiation (633nm) demonstrated waveguiding and efficient light confinement within the UV-thermally produced core regions. Preliminary Telcordia reliability testing indicates that the hybrid material waveguides have good thermo-mechanical stability and meet the requirements for central office (CO) operation. This represents a significant improvement in thermal stability over previous inorganic-organic hybrid waveguide materials systems containing acrylate or methacrylate groups that are easily cured by thermal processes. Secondly, an imprint embossing process has been developed for fabrication of all polymer waveguiding components enabling simultaneous embossing of both waveguide and optical fibre alignment grooves. Optimised pairings of polymer materials for the substrate of the device, into which the waveguide grooves are imprinted, and the core, which provides the refractive index step necessary for guiding light through the device, have been identified and evaluated. Insertion loss measurements were performed at 850 and 1330nm using the cleave-back method and were found to be 0.4dB cm-1 and 0.7 dB cm-1 respectively. The measured waveguide loss from the optimised devices at 850nm after thermal reliability testing was 1.0dB/cm. These measurements indicate that polymer optical waveguides manufactured using this embossing process will satisfy several envisaged optical interconnect datacom applications.
For optical networks, the operating life of optoelectronic components is expected to be over 20 years. Network designers therefore require components, which have been reliability tested in accordance with assured protocols, such as Telcordia Generic Reliability Assurance Practices (BellCore). In this paper, we report on the development of a system for thermal reliability studies of optoelectronic devices. The system incorporates an environmental test chamber programmed to provide differing temperature environments in the range (-180° to 300° C) as well as constant bias current or voltage to the device udner test. Case studies for preliminary screenign and temperature cycling tests on a wide range of novel active and passive devices fabricated at NMRC for short-haul networks markets are assessed and reported using this system.
Excimer lamp deposited ultra-thin (< 250 angstrom) silicon dioxide and silicon oxynitride films were characterized using spectroscopic ellipsometry (SE) and Fourier transform infrared (FTIR) spectroscopy. SE analysis of the photo-deposited SiO2 films revealed no variation in the refractive index (n) of the films for deposition temperatures of 200 degree(s)C and 300 degree(s)C. Using a Bruggeman effective medium approximation (EMA), SE analysis was employed to determine both the silicon oxynitride layer thicknesses and compositions as a function of deposition temperatures and gas ratio, defined as (N2O/(N2O + NH3)). From this analysis the optical properties of the silicon oxynitride thin films were extracted. It was observed that the refractive index for the 200 degree(s)C and 300 degree(s)C series of samples decreased from n equals 1.81 to 1.46 and n equals 1.72 to 1.46 respectively as a function of increasing gas flow ratio. FTIR analysis revealed spectral features characteristic of Si-O, Si-N, Si-H and N-H bonding. The most significant feature in all recorded spectra was a mixed spectral absorption band ranging from 800 cm-1 to 1300 cm-1. Both the integrated band area and peak wavenumber of this absorption band was found to be sensitive to the degree of nitridation and layer thickness of the thin films. The N-H stretching bond density was calculated from the N-H peak at 3360 cm-1 using appropriate calibration factors. A slight decrease in the N-H bond density with increasing gas flow rate was observed. This variation in bond density was significantly less than that observed for PECVD silicon oxynitride films.