University of Southampton’s ORC (Optoelectronics Research Centre) use Aerotech ABL9000 series stage and A3200 motion controller for ground breaking research projects
One of the many varied and interesting research projects at the University of Southampton’s ORC (Optoelectronics Research Centre) involves direct UV laser writing of integrated optical circuits on specialised glass substrates and on its own patented ‘flat’ optical cable. With application potential from telecom network components through to lab-on-a-chip (LOC) biological and chemical sensors, the photonic circuits are produced with the help of nanometre level precision positioning systems and motion controls from Aerotech.
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 Ltd. The basis principle involves passing a sample material over a sensing window and the wavelength of the light reflected from the Bragg grating confirms that its refractive index is within a certain band. With a typical sensitivity of one part in a million, these devices are proving an excellent solution for a wide range of commercial bio/chemical detection applications from sugar concentrations in foods, to toxin, virus and bacteria discovery for pharmaceuticals, and petro-chemical quality control processing.
When a similar UV writing process is directly applied to the special flat optical cable which is manufactured at the ORC, the potential for these types of sensors may be produced without the need to connect high loss pigtail connections between optical fibre and optical material substrates – and may be applied for multiple sensor solutions over extremely long distances for applications that could include biological and chemical monitoring in supply pipes and rivers. The work in this area is at an early stage but the potential outcome using such techniques may also lead to the ‘holy grail’ of producing complete active switching circuits for optical computing.
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 basics of the direct writing process involves modifying the core layer material by manipulating the substrate under the focussed UV laser, so clearly the precision and dynamic performance of the positioning system is fundamental and an intrinsic ‘enabling technology’ for the success of the process.
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 overall positioning system flatness, derived from pitch, roll, yaw and Abbe errors from both X and Y axes, must maintain sub-micron 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 PSO or Position Synchronised Output.
