Interferometric surface measurement using phone technology

Louise Davis

Epigem has announced that its quality control of transparent electronic film had taken a significant step forward, thanks to Loughborough University’s pioneering research on surface measurement based on inexpensive fibre-optics and mobile phone cameras.

As a partner in the project, Synthetic aperture interferometry: High-resolution optical measurement over an exceptionally large field of view, the Redcar-based company challenged the University to develop instrumentation to inspect and measure precision embossed thin film and microfluidic devices. 

Loughborough’s solution is an array of cameras and sources that produces a sequence of digital holographic images that can be combined to synthesise the output of an interference microscope but with 10,000 times the field of view.

In order to meet this challenge, the University has developed methods to micro-machine the tip of optical fibres and has exploited additive manufacturing (3D printing) to produce miniature, digital holographic cameras. 

Each camera is connected to a Raspberry Pi single board computer to pre-process the images before the data is combined to give a map of surface height. 

Using this technology, Loughborough researchers have now demonstrated surface height measurements with a precision of 10 nanometres, a lateral resolution of 1.7 micrometres and a field of view of almost 50 x 50m.  

The next step is to produce an array of 225 cameras, which could achieve similar measurement precision with a lateral resolution of 0.85 micrometres and a field of view of 100 x 100 m.  

Tim Ryan, Epigem’s Managing Director, said: “This is a fantastic achievement, going in a very short time from idea, to design, converting to hardware through to development. It has huge potential for quality control of electronic films and our microelectrode enabled products. Working with Loughborough University, state-of-the-art micro fabrication techniques have been deployed throughout the project. Interferometry can tell us a lot about the roughness of a surface. As Epigem expands its measurement for the life sciences capability, we are now asking ourselves where else the technology can be applied in relation to serious disease diagnosis”

Jeremy Coupland, Professor of Applied Optics and Associate Dean (Research) at the Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University said: “We have made a huge step forward here using inexpensive over-the-counter technology to build what is essentially a gigantic interference microscope and are now looking to exploit this technology in real-world applications. You could say that we are developing cutting-edge metrology with a few mobile phones and Christmas tree lights!”

This project is a partnership between Loughborough University, Taylor Hobson, the National Physical Laboratory (NPL), The Manufacturing Technology Centre (MTC) and Epigem, and is funded by the EPSRC (EP/M020940/1). Work related to Epigem’s applications is carried out by Jorge Garcia – a PhD student sponsored by Epigem and NPL.