Direct UV laser writing achieved with nanopositioning equipment

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Aerotech has revealed that researchers at the University of Southampton's Optoelectronics Research Centre (ORC) have made use of a ABL9000 positioning system in order to achieve direct UV laser writing of integrated optical circuits on specialised glass substrates.

The types of optical components that are typically written into the substrates include curved or straight waveguides and splitters that channel light around the circuit; and Bragg gratings which can be used to measure the refractive index of fluids or other materials. These refractive index sensors are now built into complete optical microchip solutions for bio/chemical sensing by the ORC spin out company Stratophase.

As opposed to more traditional photolithography mask processing methods for these types of devices, the direct write approach benefits from single-step integration and is consequently much faster and very adaptable for rapid prototyping/short production runs at reasonable costs. The high power UV laser is directed through an interferometer to produce an intense dual beam interference pattern at the target area. During the writing process, its focal length is held constant and the positioning system must maintain sub-micron flatness tolerances. Furthermore, the writing process needs to be continuous as the core materials are adversely affected by heating, so the control of the UV lasers’ power and firing pattern is completely synchronised with the on-the-fly compound translation of the X and Y axes. This synchronisation is another key factor for the process and is carried out within the Aerotech controller by an advanced software feature called position synchronised output (PSO)

The positioning system used at the ORC is an Aerotech ABL9000 series air bearing stage complete with the A3200 Digital Automation Platform motion control system with FireWire networked Ndrive linear stage amplifiers. With a 300mm x 300mm travel range, this brushless linear servomotor driven, ultra-high precision stage features a balanced air-on-air preload system for maximum stiffness and glass scale encoder feedback with an encoder resolution of just one nanometre.

The complete system was supplied to the ORC on a customised granite base with an additional fixed bridge arrangement that provides a stable platform for the ORC supplied interferometer optical system. The scope of supply also included direct drive rotary and vertical lift stages with comparable resolution and precision that are used together for pre-alignment of the substrate. Full cable management was included in the design which greatly assisted commissioning at the ORC.

The performance of the ABL9000 series has now been enhanced with Aerotech’s PlanarHD air bearing stage, featuring larger air bearing surfaces for improved load capacity and higher dynamic characteristics. A brief performance specification includes 2m/sec scan velocity and peak acceleration to 5g, with a positioning resolution of up to 0.25nm, repeatability to 50nm and accuracy to +/- 300nm.