ANU Laser Centre Facilities
The CUDOS team in the Laser Physics Centre (LPC) at the Australian National University fabricates planar optical waveguides and photonic crystal structures from chalcogenide glasses in support of the CUDOS program. The resulting structures are supplied to other researchers within CUDOS, involved in device development and testing, particularly those at the University of Sydney. LPC’s offices and laboratories occupying some 1500m2 of space are located in the John Carver, Cockroft and Huxley buildings in the Research School of Physical Sciences and Engineering at ANU.
The main laboratories supporting the CUDOS program comprise a glass chemistry laboratory; the laser deposition laboratory used for thin film production; a lithography laboratory dedicated to patterning sub-micron patterning of optical waveguide structures; the plasma etching laboratory; and the ion mill facility located in the ANU’s electron microscopy unit.
A new 50m2 glass chemistry laboratory is dedicated to the production of bulk chalcogenide glasses with novel compositions. The laboratory contains a dry nitrogen glove box for mixing the raw materials before sealing into evacuated ampoules and rocking and annealing furnaces for glass melting and post processing. Glass boules from this laboratory are cut and polished before assessment for suitability for device fabrication. Glass characterization involves techniques such as spectrophotometry; photo-thermal deflection spectroscopy; differential scanning calorimetry; Raman spectroscopy; refractive index measurements; determination of optical nonlinearity via four wave mixing and Z-scan measurements across the visible and IR; and compositional analysis such as Energy Dispersive X-ray Analysis (EDX).
Glass samples are turned into thin films deposited onto various substrates using LPC’s ultra-fast pulsed laser deposition (UFPLD) facility. In 2005 a new custom deposition chamber was commissioned designed for pulsed laser deposition of micron thick films with high uniformity over 100mm diameter wafers. Film uniformity better that ±0.25% over the wafer is achieved.
The films produced by UFPLD can be assessed using a similar range of diagnostic tools as applied to the bulk glass. Additionally, refractive index and thickness is mapped using an SCI Filmtek 4000. Films can be post processed in a range of vacuum annealing ovens prior to patterning to create optical waveguides. The photolithography laboratory uses an SVG-800 dual track coating and development system in conjunction with a Karl Suss MA6 exposure tool to transfer waveguide patterns into photoresist masks with sub-micron resolution. Pattern transfer into the glass is then accomplished using an Oxford Instruments RIE-100 ICP plasma etching tool. The resulting structures undergo characterization for linear and nonlinear optical properties using a range of waveguide testing facilities.
The production of photonic crystal membranes requires dimensional control at the nanoscale not possible using the facilities in the photolithography laboratory. As a result the CUDOS team has developed a unique capability for directly patterning structures into free standing chalcogenide glass membranes using the ANU’s Orsay Physics focussed ion beam mill (FIB). Extensive hardware and software development in particular allowing “on-the-fly” correction of any mechanical drift at the few nanometer level that inevitably occurs in the FIB over hour-long milling times sets the machine aside from other FIB facilities elsewhere.