Low loss high index contrast nanoimprinted polysiloxane waveguides

Nanoimprint lithography is gaining rapid acceptance in fields as diverse as microelectronics and microfluidics due to its simplicity high resolution and low cost. These properties are critically important for the fabrication of photonic devices, where cost is often the major inhibiting deployment factor for high volume applications. We report here on the use of nanoimprint technology to fabricate low loss broadband high index contrast waveguides in a Polysiloxane polymer system for the first time

Thermal annealing of arsenic tri-sulphide thin film and its influence on device performance

Arsenic tri-sulphide (As₂S₃)thin filmwaveguides have been used successfully as nonlinear optical devices for all-optical signal processors. For such devices, low propagation loss is vital if high performance is to be obtained. In this study, thermal annealing was employed not only to stabilize the physical properties of the films, but also to reduce the sources of light attenuation in the as-deposited material. Here we investigated heat-induced changes to the microstructure and optical properties of As₂S₃thin films and, based on this information, determined the best annealing conditions. The refractive index of the films rises with annealing due to thermal densification and increased heteropolar bond density. The growth of surface roughness and thermal stress in the film, however, limits the annealing temperature to ∼130 °C. We fabricated and analyzed waveguides produced from as-deposited and annealedfilms and found that the propagation loss of the guides dropped by ∼0.2 dB/cm as a result of appropriate annealing.Rayleigh scattering and absorption from defects associated with phase separation, homopolar bonds, voids, and dangling bonds in the as-deposited film are shown to contribute to the higher light attenuation in unannealed films.This research was supported by the Australian Research Council through its Centre of Excellence program

Stoichiometric Low Loss Tellurium Oxide Thin Films for Photonic Applications

Stoichiometric low loss Tellurium Oxide, TeO2, films have been produced by reactive RF sputtering. TeO2 films with propagation loss below 0.1dB/cm at 1550nm have been achieved in as deposited films

Improved method for hot embossing As 2 S 3 waveguides employing a thermally stable chalcogenide coating

We demonstrate the fabrication of As2S3 rib waveguides using hot embossing. Because of the high temperature required, a thin (50nm) Ge11.5As24Se64.5 was thermally evaporated on top of an 870nm As2S3 layer to protect against surface degradation during embossing. The waveguides propagation loss was 0.52dB/cm for the TE and 0.41dB/cm for the TM polarizations at 1550nm for a waveguide cross-section dimension of 3.8 × 1μm. The nonlinearity of a 2.2μm wide waveguide was shown to be 13500W-1km-1 using four-wave mixing demonstrating that these embossed waveguides were capable of being used for all-optical processing

Polarization-independent chalcogenide glass nanowires with anomalous dispersion for all-optical processing

We demonstrate the design and fabrication of square Ge11.5As24Se64.5 (Ge11) nonlinear nanowires fully embedded in a silica cladding for polarization independent (P-I) nonlinear processing. We observed similar performance for FWM using both TE and TM modes confirming that a near P-I operation was obtained. In addition we find that the supercontinuum spectrum that can be generated in the nanowires using 1ps pulse pulses with around 30W peak power was independent of polarization

The Impact of Thermal- and Photo-annealing of Chalcogenide Films for Optical Waveguides

We applied thermal- and band-edge light annealing on an as-deposited As2S3 film to mitigate its phase separation and, thus to improve the propagation losses of fabricated optical waveguides. Studies of the film micro structure revealed a difference between atomic bonds and linked phases among the as-deposited, thermally-annealed, and optically-annealed films. We fabricated rib-type waveguides with 4 micron width from 0.85 μm thick films, and measured the insertion losses. Around 0.4 and 0.2 dB/cm propagation losses were obtained in the waveguides produced from as-deposited and annealed films, respectively. The waveguides produced from photo-annealed film showed almost the same propagation losses to those from thermally-annealed material. Our results, however, indicate optical-annealing provides some advantages over thermal annealing for waveguide fabrication, such as the absence of film cracking which observed at high temperature processing

Nanoscale phase separation in ultrafast pulsed laser deposited arsenic trisulfide (As₂S₃) films and its effect on plasma etching

We have observed nanoscale phase separation in amorphous arsenic trisulfide (As₂S₃)films produced by ultrafast pulsed laser deposition and its effect on the surface morphology of the film after plasma etching. When the film was etched in CF₄–O₂plasma, a grainy structure was observed on the surface. From Raman and x-ray photoelectron spectroscopies, we concluded that the grainy structure of the etchedsurfaces comes from the differential chemical attack between different phases in the film.This research was supported by the Australian Research Council through its Centres of Excellence and Federation Fellow Programs

Annealing induced phase transformations in amorphous As2S3 films

Amorphous arsenic sulphide (As2S3) films prepared by ultrafast pulsed laser deposition have been vacuum annealed at a range of different temperatures. Measurements of the glass transition temperature indicate that a crystallization process initiates at annealing temperatures around 170 °C. In combination with Raman scattering analysis, we conclude that phase separation is intrinsic for our as-deposited films. During annealing two sorts of phase transformation are identified: one between different amorphous polymorphs, and another from the amorphous to a crystalline state. We point out a correlation between these two types of transformation and two characteristic time scales identified from measurements of the relaxation of the refractive index, and explain the Arrhenius and non-Arrhenius behaviors leading to the observed temporal characteristic

Properties of GexAsySe1-x-y glasses for all-optical signal processing

We present a systematic study of GexAsySe1-x-y bulk chalcogenide glasses to determine the best composition for fabricating alloptical devices. The dependence of physical parameters such as the bandgap, glass transition temperature and third order optical nonlinearity (n2) on composition has been studied and a relation between the bond-structure and elevated linear loss levels in high Germanium glasses has been identified. It is found that glasses with 11<x<13 % are most suitable for all-optical devices

High index contrast polysiloxane waveguides fabricated by dry etching

The authors demonstrate the production of low loss enhanced index contrast waveguides by reactive ion etching of IPG™ polysiloxane thin films. The use of a silica mask and CHF₃∕O₂etch gas led to large etch selectivity between the silica and IPG™ of >20 and etch rates of >100nm∕min. This work indicates that compact optical circuits could be successfully fabricated for telecommunication applications using polysiloxane films.The support of the Australian Research Council through its Linkage grant and Federation Fellow programs is gratefully acknowledged as well as the financial support of RPO Inc