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

Hydrogen contamination in Ge-doped SiO[sub 2] thin films prepared by helicon activated reactive evaporation

Germanium-doped silicon oxidethin films were deposited at low temperature by using an improved helicon plasma assisted reactive evaporation technique. The origins of hydrogen contamination in the film were investigated, and were found to be H incorporation during deposition and postdeposition water absorption. The H incorporation during deposition was avoided by using an effective method to eliminate the residual hydrogen present in the depositionsystem. The microstructure, chemical bonds, chemical etch rate, and optical index of the films were studied as a function of the deposition conditions. Granular microstructures were observed in low-density films, and were found to be the cause of postdeposition water absorption. The granular microstructure was eliminated and the film was densified by increasing the helicon plasma power and substrate bias during deposition. A high-density film was shown to have no postdeposition water absorption and no OH detected by using a Fourier-transform infrared spectrometer

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

Structure and physical properties of GexAsySe1−x−y glasses with the same mean coordination number of 2.5

We have prepared and analyzed five different compositions of GexAsySe1−x−yglasses that have the same mean coordination number (MCN) of 2.5 in order to understand whether MCN or chemical composition has the dominant effect on the physical properties of the glass. Density measurements showed a maximum for the chemically stoichiometric Ge12.5As25Se62.5 sample and suggested that some rearrangement of the atoms was occurring as one atom substituted for another. The measurements of Tg, however, showed that the glasses had almost same glass transition temperature and suggested that the glassnetwork connectivity did not change much with composition. Although Raman scattering and x-ray photoelectron spectra of the glasses indicate that the percentage of the different structural units changes with the composition, there was no evidence of the existence of structural units that could change the overall connectivity of the glassnetwork. Therefore, we concluded that glasses with same MCN but different composition have similar glassnetwork connectivity, and that chemical composition has only a secondary effect on the physical properties of the glasses.This research was partly supported by the Australian Research Council through its Centres of Excellence and Discovery DP110102753 programs

Identifying the best chalcogenide glass compositions for the application in mid-infrared waveguides

We prepared numbers of GeAsSe glasses and investigated their thermal stability and optical properties in order to search the best glasses with relatively high glass transition temperature Tg, strong structural stability, low optical loss and high optical nonlinearity. Through our systematical measurements, we concluded that the glasses with a mean coordination number around 2.45-2.5 are the best for the applications in photonics with Tg of 450K, low optical loss of 0.2dB/cm, high optical nonlinearity 7.5×10-14cm2/W and less photosensitivity. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Local tuning of photonic crystal cavities using chalcogenide glasses

We demonstrate a method to locally change the refractive index in planar optical devices by photodarkening of a thin chalcogenide glass layer deposited on top of the device. The method is used to tune the resonance of GaAs-based photonic crystal cavities by up to 3 nm at 940 nm, with only 5% deterioration in cavity quality factor. The method has broad applications for postproduction tuning of photonic devices.Financial support was provided by ONR Young Investigator Award, the MURI Center for photonic quantum information systems ARO/DTO Program No. DAAD19-03-1- 0199, and NSF Grant No. CCF-0507295. Work was performed in part at the Stanford Nanofabrication Facility of NNIN supported by the National Science Foundation under Grant No. ECS-9731293. CUDOS is an Australian Research Council Centre of Excellence

Broadband wavelength conversion at 40Gb/s using long serpentine As2S3 planar waveguides

We demonstrate broadband wavelength conversion of a 40 Gb/s return-to-zero signal by cross-phase modulation in a newly developed chalcogenide glass waveguide based photonic chip. These new serpentine As2S3 waveguides offer a nonlinear coefficient ≈1700 W-1km-1 with 5× lower propagation loss over a length of 22.5 cm which ensures the full propagation length contributes towards the nonlinear process. This reduces the peak operating power thereby allowing a ×4 increase in the data rate compared with previous results. Spectral measurements show the device operates over a span of 40 nm while system measurements show just over 1 dB of power penalty at a bit-error rate of 10-9. This is primarily due to the compact planar waveguide design which minimizes the effect of groupvelocity dispersion

Highly-nonlinear chalcogenide glass devices for high-speed signal processing and characterization

We review the latest advances in dispersion-shifted Chalcogenide waveguides enabling highly nonlinear and low dispersion planar rib circuits of centimetre length. Its performance advantages for more broadband and higher speed nonlinear signal processing are shown

Long, low loss etched As2S3 chalcogenide waveguides for all-optical signal regeneration

We report on the fabrication and optical properties of etched highly nonlinear As2S3 chalcogenide planar rib waveguides with lengths up to 22.5 cm and optical losses as low as 0.05 dB/cm at 1550 nm - the lowest ever reported. We demonstrate strong spectral broadening of 1.2 ps pulses, in good agreement with simulations, and find that the ratio of nonlinearity and dispersion linearizes the pulse chirp, reducing the spectral oscillations caused by self-phase modulation alone. When combined with a spectrally offset band-pass filter, this gives rise to a nonlinear transfer function suitable for all-optical regeneration of high data rate signals

Terahertz bandwidth RF spectrum analysis of femtosecond pulses using a chalcogenide chip

We report the first demonstration of the use of an RF spectrum analyser with multi-terahertz bandwidth to measure the properties of femtosecond optical pulses. A low distortion and broad measurement bandwidth of 2.78 THz (nearly two orders of magnitude greater than conventional opto-electronic analyzers) was achieved by using a 6 cm long As2S3 chalcogenide waveguide designed for high Kerr nonlinearity and near zero dispersion. Measurements of pulses as short as 260 fs produced from a soliton-effect compressor reveal features not evident from the pulse’s optical spectrum. We also applied an inverse Fourier transform numerically to the captured data to re-construct a time-domain waveform that resembled pulse measurement obtained from intensity autocorrelation