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This paper aims at understanding the capabilities and limitation of combining Nanocomposite Force myography sensors (FMG) and optical fiber sensors in standalone systems and their synergy influence on the classification of ambiguous hand gestures. A set of 10 highly similar hand signs from the fingerspelling of the American sign language is adopted in this study. Force myography (FMG) signals are collected from one healthy subject performing the selected set of gestures with 40 repetitions for each gesture. The K-Tournament Grasshopper Extreme Learner (KTGEL) classifier has been implemented to perform an automated feature selection and hand sign classification with an efficient network size and a high accuracy.

In many fields of research and high-value industry, the estimation of distances and displacements is crucial. Due to their extremely high spatial resolution and flexible application possibilities interferometers are cross-sectorally used in measurement practice. However, classical length measuring interferometers are subject to two residual restrictions. On the one hand, only displacements that are exactly aligned to the interferometer optical axis can be measured. On the other hand, deviating refractive indices in the measuring and reference arm due to different atmospheric conditions represent an accuracy-limiting disturbance. In this paper, a new interferometric concept for length measurement is presented. The concept is based on the range-resolved interferometry technology which enables the simultaneous readout and evaluation of two symmetrical interferometric signals which result from the superposition of two non-collimated spherical wavefronts. This allows a point-to-point measurement between two optical fiber ends and the separation of undesired changes of the optical path length outside the measurement cavity and within the measurement cavity.

A dual-fibre single-plane angle-sensing tape that utilizes optical Fibre Segment Interferometry and Range- Resolved Interferometry (RRI) for angle sensing is presented. The sensing tape facilitates the multiplexing of an array of angle sensors along its length and can be retrofitted into small robots and construction equipment. We demonstrate its application on three non-rotational joints of a small five-axis robot, describing the design, construction, measurement principle, and presenting measurement results. Preliminary data shows that the angles measured by the sensing tape exhibited agreement within a range of ±0.005˚ with the manufacturer-installed angle encoder of the robot.

This work describes the use of a compact fiber-interferometric sensor for velocity measurements for the Kibble balance method. Our fiber-interferometric sensor was compared within a Planck-balance setup with a commercial reference interferometer. Results show that the fiber-interferometric sensor is capable of high accuracy velocity measurement comparable with the reference interferometer. High performance and compactness of the sensor head allow it to be integrated into small-size systems, where the use of the conventional interferometer systems is limited or not possible.

The work presented demonstrates that key parameters in aerodynamic structural characterisation of pressure, strain, and structural dynamics, can be all measured via optical fibre sensors interrogated using the principles of range-resolved interferometry (RRI). When used to interrogate sensors simultaneously deployed on a high lift wind in a wind tunnel, the approach yielded resolutions of 31 μPa/ &worte; Hz and 1 nε/ &worte; Hz at a bandwidth of 1526 Hz for pressure and strain, respectively, demonstrating the accuracy and versatility of the RRI signal processing technique.

Due to the frequency stabilization of He-Ne-lasers directly to a frequency comb controlled by a GPS atomic clock disciplined oscillator and their direct coupling with a Nanopositioning and Nanomeasuring Machine, directly traceable measurements are demonstrated.

Since the turn of the millennium, the development and commercial availability of optical frequency combs has led to a steadily increase of worldwide installed frequency combs and a growing interest in using them for industrial-related metrology applications. Especially, GPS-referenced frequency combs often serve as a "self-calibrating" length standard for laser wavelength calibration in many national metrology institutes with uncertainties better than u = 1 × 10^-11. In this contribution, the application of a He-Ne laser source permanently disciplined to a GPS-referenced frequency comb for the interferometric measurements in a nanopositioning machine with a measuring volume of 200 mm × 200 mm × 25 mm (NPMM-200) is discussed. For this purpose, the frequency stability of the GPS-referenced comb is characterized by heterodyning with a diode laser referenced to an ultrastable cavity. Based on this comparison, an uncertainty of u = 9.2 × 10^-12 (τ = 8 s, k = 2) for the GPS-referenced comb has been obtained. By stabilizing a tunable He-Ne source to a single comb line, the long-term frequency stability of the comb is transferred onto our gas lasers increasing their long-term stability by three orders of magnitude. Second, short-term fluctuations-related length measurement errors were reduced to a value that falls below the nominal resolving capabilities of our interferometers (ΔL/L = 2.9 × 10^-11). Both measures make the influence of frequency distortions on the interferometric length measurement within the NPMM-200 negligible. Furthermore, this approach establishes a permanent link of interferometric length measurements to an atomic clock.

Range-resolved interferometry (RRI) allows the simultaneous demodulation of multiple interferometric signal sources and provides a tomographic view of all constituent interferometers that may be present in a setup. Through comparison with a reference distance of known length, absolute distance measurements can be performed. RRI is tailored to the use of laser frequency modulation through injection-current modulation of regular, monolithic laser diodes that are both cost-effective and highly coherent and therefore this approach promises broad applicability. In this paper, two methods for absolute distance measurement, one based on the direct evaluation of the signal peak positions and one based on the phase demodulation of an additional lock-in modulation signal, are experimentally demonstrated. Using an external verification displacement interferometer, both techniques are shown to achieve in-situ absolute distance measurements with systematic errors below over a 50 mm travel range. The aim of this paper is to establish the general suitability of RRI for absolute distance measurements and in-situ tomographic interferometer characterisation for precision engineering. In future, this approach could be used to diagnose interferometric setups for parasitic signal contributions, multiple reflections or to determine the dead path length for accurate environmental compensation, either for use during initial setup of, or for continuous operation alongside, a regular displacement measuring interferometer.

Displacement measuring interferometers, commonly employed for traceable measurements at the nanoscale, suffer from non-linearities in the measured displacement that limit the achievable measurement uncertainty for microscopic displacements. Two closely related novel non-linearity correction methodologies are presented here that allow for the correction of non-linearities in cases where the displacement covers much less than a full optical fringe. Both corrections have been shown, under ideal conditions, to be capable of reducing all residual non-linearity harmonics to below the 10 pm level.

Non-linearities in interferometric displacement measurements commonly affect both homodyne and heterodyne optical interferometers. Unwanted back reflections (ghost reflections) or polarisation leakage introduce non-linearity terms at harmonics of the illuminating wavelength that cannot be fully corrected for with standard non-linearity correction techniques. A two-wavelength interferometric approach, operating at 632.8 and 785 nm, is presented here that is capable of correcting such non-linearities. Non-linearities are separated from the difference between two displacement measurements made at differing wavelengths with a Fourier approach. Compared to a standard Heydemann ellipse fitting correction, the proposed approach reduces estimated residual non-linearities from 84 to 11 pm in the case of a linear displacement profile. In particular this approach is applicable to the correction of higher order non-linearities that are caused by multiple reflections, and that are therefore very sensitive to alignment conditions.