Andrew John Henning

Focus variation microscopy is a non-contact technique for surface topography measurement, which utilizes the limited depth of focus of a microscope to allow the topography of a surface to be determined after it has been scanned through the focal plane. Recently, approaches using a chromatic dependence of the focal plane location, realized using multiple glass elements in a custom objective, have been developed that remove the need to physically scan elements. Here, we demonstrate how a metalens can be used to simultaneously deliver the focusing and wavelength-dependent focal shift required with only a single lightweight element, opening up the path to the development of ultra-compact lightweight focus variation instrumentation.

Metasurfaces allow the manipulation of light without the size and weight of traditional optical elements, and offer a path to the type of ultra-compact optical systems needed if optical sensors are to be integrated within manufacturing chains without disrupting them. Here we look at the use of a spatially interleaved metasurface as a method to extend the spectral range over which high-resolution measurements can be obtained with an off-axis metasurface lens. Such a spectrometer exploits chromatic abberation to separate out different wavelengths of light, however the abberation will lead to a degredation in the resolution. By spatially interleaving two such devices the measurement range over which the abberation is minimised can be extended, leading to a more useful device.

In order to calculate the electromagnetic fields that are produced after light passes through a metasurface, simulation methods such as the Finite-Difference Time-Domain method are often employed. While these provide a good approximation to the fields, the level of detail at which the volume of space that the light is propagating in needs to be modelled and the time for which simulations need to run, mean that as the area of the metasurface is increased these simulations rapidly become unwieldy. In this paper we show how the result of a FDTD simulation of a unit cell can be used to generate a good approximation of the vectorial field that large area metasurfaces will generate, but using a fraction of the computational resources. This approach can provide an intermediate design step, allowing potentially interesting designs to be rapidly identified or discarded.

The development of ultra-compact lightweight optical instrumentation that can be used on-machine and to carry out in-process measurements is vital in realizing improved manufacturing processes, increasing the quality of parts being made while saving time and energy by reducing scrappage rates. Only incremental progress is being made in developing suitable instrumentation based on conventional components such as traditional refractive elements as fundamental limits in terms of size and weight are already reached. Here we demonstrate a chromatic confocal sensor that utilizes the natural chromatic aberration found with a basic hyperbolic metalens to realize an ultra-compact and simple probe. Further, we demonstrate how this can be combined with a compact specklemeter as the detection element, thus realizing the whole sensing system in a compact manner. Even with the proof-of-principle instrument in its preliminary and unoptimised state we achieve the successful recovery of the location of a scatterer as it is scanned over a 227 μm range, with a standard deviation of error in the position of 1.37 μm. Sensors of this form can be deployed in areas where traditional instrumentation would typically impede the manufacturing processes, increasing the number of processes that can have metrology applied directly and providing real-time feedback to improve manufacturing outcomes.

Smart, automated processes in manufacturing require highly integrated sensors. We present our development of ultra-compact confocal and chromatic confocal sensors suited for integration into manufacturing platforms, including how functionality can be improved through meta-atom selection.

With increasing digitalisation of engineering and the development of smart manufacturing, precision metrology is gradually moving away from the laboratory into real-world environments and production platforms. Interferometry and focus detection are the most popular optical techniques for these types of application due to their non-destructive measurement, high resolution, and fast response. In this article, we discuss their basic principles, limitations and challenges, and new opportunities. Motivated by the rapid development of artificial materials, the application of metasurfaces to drive a new era for future miniaturisation of optical systems becomes suddenly viable. The article discusses advances in modern miniaturisation of optical techniques; and introduces an approach for evolving to a future using metasurface optics. Optical principles and feasibility studies are included in the discussion.

Several optical instruments have been presented over recent years that use a tilted diffraction grating in the reference arm, describing its effect as introducing a continuous optical delay in the direction of the grating dispersion. Having examined these types of system carefully, we believe this description does not fully capture the manner by which the signal is formed in these instruments, and present here a simple model that clearly demonstrates the essential elements behind the way such systems operate. This analysis not only illustrates the reason for signals of the form seen being generated, but also shows how great care needs to be taken with systems such as these in the interpretation of the results.

Interferometric instruments with dispersion introduced in the reference arm have previously been created, as the controlled dispersion can be used to generate a signal that contains a clearly identifiable point, the location of which relates to the position of the scattering surface in the measurement arm. In the following, we illustrate that the linear approximations that have been used previously can lead to significant errors, and that second-order terms need to be included in order to correct this. These corrections are vital if these instruments are to be used for metrological applications.

The analysis of signals created by a variety of instruments involves calculating the phase of a sinusoidal type signal. One widely used method to extract this information is through the use of Fourier transforms, but it is known that significant errors can arise when a low number of cycles of a sinusoid are present in the signal. In the following, we examine the case where the fringe pattern of interest only contains a few cycles of a sinusoid, looking at the adjustments that need to be made to the previous method in order to allow it to be used successfully, the causes of errors that arise, and the accuracy that can be expected to be obtained.