Advertisement feature Cover story

Centre) involves direct UV laser writing of integrated optical circuits on spe- cialised 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 refrac- tive index sensors are built into optical microchip solutions for bio/chemical sensing by the ORC spin out company Stratophase. The principle involves passing a sample material over a sensing window and the wavelength of the light reflected from the Bragg grating con- firms that its refractive index is within a certain band. With a typical sensitivity of one part in a million, these devices are proving a solution for 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 solu- tions over extremely long distances for applications that could include biolog- ical and chemical monitoring in supply pipes and rivers. The work in this area is at an early stage but the potential outcome using such tech- niques may also lead to the ‘holy grail’ of producing complete active switching circuits for optical computing. The direct write approach benefits

from single-step integration and is con- sequently much faster and very adapt- able for rapid prototyping/short production runs at reasonable costs. The basics of the direct writing process involves modifying the core layer mater- ial by manipulating the substrate under

8

Enabling positioning technology

O

Aerotech is providing enabling positioning technology for a nanometre precision direct-write laser application

ne of the many varied and inter- esting research projects at the University of Southampton’s ORC (Optoelectronics Research

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 flat- ness, 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 synchronised with the on-the-fly compound translation of the X and Y axes. This synchronisation is carried out in the Aerotech controller by an advanced software feature called PSO or Position Synchronised Output. PSO triggers the UV laser in real time

during continuous motion, processing high speed encoder feedback in con- junction with XY position array infor- mation for the feature being written. Not only is each feature held to nanometre level tolerances in all planes, but the accuracy and repeatability from feature to feature and the distance between them is realised with high precision. 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 bal- anced air-on-air preload system for max- imum stiffness and glass scale encoder feedback with an encoder resolution of just one nanometre. The H-bridge design maintains both axes and their respective encoders at the same level which co-locates the centrelines of mass, force and feedback – ensuring that errors are minimised for best perfor- mance straightness and flatness. With dual linear motor driven Y axes and active yaw con- trol, the ABL9000 is able to produce perfectly parallel scans, straight lines and interpolated curves over its entire working surface. Each axis is also factory calibrated by Aerotech against a laser interferome- ter with the error map

information added to the controller. In operation this ensures optimum translation stage accuracy. The combination of Aerotech’s BLM

series brushless linear servomotors and HLe series linear servo amplifiers provide the smoothness and stability required for nanometre resolution posi- tioning whilst ensuring the required high bandwidth, zero crossover distor- tion and ultra-quiet EMC characteristics which are essential for this application. Aerotech’s A3200 Digital Automation

Platform provides fully deterministic PC based motion control with advanced diagnostics, set-up and tuning features that ensure perfect results. As well as the PSO feature mentioned earlier, the A3200 includes trajectory generation with multi-block look ahead to min- imise geometry errors in tight profiles by regulating the speed and/or the position on each axis. The ORC use G-code programming for their particular appli- cation but the A3200 is also equipped for programming in Aerotech’s own AeroBASICTM or in C, C++, and Visual Basic. For complete application integra- tion the optional Ncontrol SDK software development kit may be used with Windows based ActiveX components, C++, VB and .NET class libraries. There are also a number of advanced software and hardware features available to opti- mise throughput performance and fur- ther improve overall machine operation. The complete system was supplied

One of the research projects at the University of Southampton’s ORC involves direct UV laser writing of integrated optical circuits on specialised glass substrates and on its own patented ‘flat’ optical cable

to the ORC on a customised granite base with an additional fixed bridge arrange- ment that provides a stable platform for the ORC supplied interferometer opti- cal 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 sub- strate. Full cable management was included in the design which greatly assisted commissioning at the ORC. The excellent performance of the

ABL9000 series has now been enhanced with Aerotech’s PlanarHD air bearing stage. The new stage is aimed at high throughput scanning and ultra-high precision step-and-settle applications found in semiconductor processing and other emerging MEMS/Nano technologies. The design features larger air bearing surfaces for improved load carrying and higher dynamic characteristics. A brief perfor- mance specification includes 2m/sec scan velocity and peak acceleration to 5g – with a positioning resolution of up to 0.25 nanometres, repeatability to 50 nanometres and accuracy to +/- 300 nanometres.

Aerotech T: 0118 940 9400

Enter 207

www.aerotech.co.uk http://www.orc.soton.ac.uk/

MARCH 2010 Design Solutions Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60