Theis Faber Quist Iversen

Optical touch screen based on waveguide sensing

We disclose a simple, optical touch screen technique based on a planar injection molded polymer waveguide, a single laser, and a small linear detector array. The solution significantly reduces the complexity and cost as compared to existing optical touch technologies. Force detection of a touching finger is also demonstrated.

Dynamical properties of speckled speckles

We consider the dynamical properties of speckles observed through a second static diffuser arising from a linear or angularly displaced first diffuser. Analytical expressions are obtained for general situations where both the space between the displaced and the static diffuser and the space between the static diffuser and the plane of observation consist of an optical system that can be characterized by a complex-valued ABCD-matrix (e.g. simple and complex imaging systems, free space propagation in both the near- and far-field, and Fourier transform systems). The use of the complex ABCD-method means that diffraction due to inherent apertures is included. One of the diffusers is assumed to give rise to fully developed speckle, i.e. the scattered phase is assumed to be delta-correlated, whereas the second and dynamic diffuser has a finite lateral scale. The illumination of the displaced diffuser is assumed to be Gaussian but the derived expressions are not restricted to a plane incident beam. The results are applicable for speckle-based systems for determining mechanical displacements, especially for long-range systems, and for analyzing systems for measuring biological activity beyond a diffuse layer, e.g. blood flow measurements through human skin.

Speckle-based three-dimensional velocity measurement using spatial filtering velocimetry

We present an optical method for measuring the real-time three-dimensional (3D) translational velocity of a diffusely scattering rigid object observed through an imaging system. The method is based on a combination of the motion of random speckle patterns and regular fringe patterns. The speckle pattern is formed in the observation plane of the imaging system due to reflection from an area of the object illuminated by a coherent light source. The speckle pattern translates in response to in-plane translation of the object, and the presence of an angular offset reference wave coinciding with the speckle pattern in the observation plane gives rise to interference, resulting in a fringe pattern that translates in response to the out-of-plane translation of the object. Numerical calculations are performed to evaluate the dynamic properties of the intensity distribution and the response of realistic spatial filters designed to measure the three components of the objects translational velocity. Furthermore, experimental data are presented that demonstrate full 3D velocity measurement.

Impact of primary aberrations on coherent lidar performance

In this work we investigate the performance of a monostatic coherent lidar system in which the transmit beam is under the influence of primary phase aberrations: spherical aberration (SA) and astigmatism. The experimental investigation is realized by probing the spatial weighting function of the lidar system using different optical transceiver configurations. A rotating belt is used as a hard target. Our study shows that the lidar weighting function suffers from both spatial broadening and shift in peak position in the presence of aberration. It is to our knowledge the first experimental demonstration of these tendencies. Furthermore, our numerical and experimental results show good agreement. We also demonstrate how the truncation of the transmit beam affects the system performance. It is both experimentally and numerically proven that aberration effects have profound impact on the antenna effciency, the optimum truncation of the transmit beam and the spatial sensitivity of a CW coherent lidar system. Under strong degree of aberration, the spatial confinement is significantly degraded. However for SA, the degradation of the spatial confinement can be reduced by tuning the truncation of the transmit beam, which results from the novel finding in this work, namely, that the optimum truncation ratio depends on the degree of SA.

Speckle and fringe dynamics in imaging- speckle-pattern interferometry for spatial-filtering velocimetry

This paper analyzes the dynamics of laser speckles and fringes, formed in an imaging-speckle-pattern interferometer with the purpose of sensing linear three-dimensional motion and out-of-plane components of rotation in real time, using optical spatial-filtering-velocimetry techniques. The ensemble-average definition of the cross-correlation function is applied to the intensity distributions, obtained in the observation plane at two positions of the object. The theoretical analysis provides a description for the dynamics of both the speckles and the fringes. The analysis reveals that both the magnitude and direction of all three linear displacement components of the object movement can be determined. Simultaneously, out-of-plane rotation of the object including the corresponding directions can be determined from the spatial gradient of the in-plane fringe motion throughout the observation plane. The theory is confirmed by experimental measurements.

Investigation of an optical method for determining the average radius of curvature of micro-optical lenticular lens arrays

Micro-optical elements are of great importance in areas of optoelectronics and information processing. Establishing fast, reliable methods for characterization and quality control of these elements is important in order to maintain the optical performance in a high volume production process. We investigate an optical technique, applied to a polymer-based, injection moulded, lenticular array, but the method is also applicable for the tooling for these elements. The cylindrical lenses have feature sizes of 1–15 µm. The method is based on observation of the intensity distribution, which can be obtained in the far field of surface reflections resulting from a plane wave incident on the lenticular array. The intensity distribution of the diffraction orders is highly correlated with the shape of the illuminated lenslets. This is exploited to attain information about possible defects and shape variations that have arisen in the moulding process. The experimental results are compared with a model, based on the Fraunhofer approximation to the Huygens–Fresnel principle. Furthermore, the optical elements under investigation are probed using a scanning probe microscope. Hence, access to accurate topological data of the elements is attained and used to confirm the validity of the proposed optical technique.

Opportunities for optics within high-tech of tomorrow

The use of miniaturized optical sensors as input devices based on speckle phenomena will be discussed alongside with some considerations on the path to industrial implementation.

Analysis of laser speckle patterns from fingertips

The trend in human-machine interface technology is heading towards optical solutions for tracking and movement detection. Especially, interactive touch screens and pads, in which the movement of the users fingertips is detected and tracked, are of great commercial interest. The applications range from mobile phones to laptops and PDA´s. However, the dynamics of scattered light from live tissue must be taken into account when designing optical sensor systems for tracking e.g. fingertips in touch-applications. Especially, when using coherent light sources, the statistics of the speckle-pattern originating from the scattering structure is of critical importance for the sensor performance and has to be understood in details. We investigate theoretically and experimentally the characteristics of the dynamics of backscattered speckle pattern generated by a human fingertip and address the effects of an intermediate optically flat interface, between the fingertip and the illuminating light source.