Photonic integrated adaptive delay lines for high-speed absolute distance measurement.

A novel optical technique for very high speed, high accuracy absolute distance measurement has been developed within the Loughborough University spoke of the EPSRC funded Future Metrology Hub. The technology has many potential industrial applications, particularly in the automotive and aerospace sectors, such as low-cost jig-less assembly, robot path planning, and dimensional quality control. Proof of concept experiments have been carried out, patent applications have been submitted ("Method and Apparatus for measuring Distance": Greek PA No: 20200100260, UK PA No: 2009723.4) and two papers published on the subject (JOSA A, 37, 11, 1874 (2020); OSA Continuum, accepted 1/12/2020). The initial demonstrator (size 1 m^2) was then miniaturized on a photonic integrated circuit (size < 1 cm^2) in collaboration with the silicon photonics group at Southampton Optoelectronics Research Centre. This would have significant benefits allowing highly portable metrology systems incorporating the invention to be embedded on the production line, as well as costing a tiny fraction of the current bulk optics system. This iCASE studentship will study the performance of the chip-scale demonstrator to test the commercial viability of future products based on this technology.

Novel research challenges
The first demonstrator achieved 100,000 measurements (of target range, displacement and velocity) per second, with a range resolution <100 nm, displacement resolution < 1nm, and velocity resolution of 12e^-6 m/s for ranges up to ~0.3 m. The chip-scale devices present new challenges to match and exceed that performance, including: thermal stabilization, electronic control of active switches on the chip, cross-talk, dispersion effects on the signal linearity and distance uncertainty and calibration of the frequency scan of the tuneable laser source and real-time signal processing.

Work plan
Year 1
1.1 Training on the theoretical aspects of the proposed technique and photonics devices; 1.2 Set up chip-scale system with a measurement range of a few cm to a retroreflector target; 1.3 Study and mitigate effects of waveguide losses and optical dispersion.

Year 2
2.1 Optical path calibration and effects of polarization instability; 2.2 Measure phase/temperature coupling between switches and its effect on measurement uncertainty (range, displacement, and velocity). Paper 1, month 24

Year 3
3.1 Implement real-time analysis of the interference signal to provide target range and axial velocity with a throughput of 100,000 coordinates per second; 3.2 Thermal stability and uncertainty study for different target ranges. Paper 2, month 36

Year 4
4.1 Case studies proposed and coordinated with Renishaw (e.g. machine tool spindle metrology, machine tool positioning); 4.2 Study commercial viability of future products that incorporate the technology; 4.3 Write Thesis. Paper 3, month 48.