Medical micromotors have the potential to lead to a paradigm shift in future biomedicine, as they may perform active drug delivery, microsurgery, tissue engineering, or assisted fertilization in a minimally invasive manner. However, the translation to clinical treatment is challenging, as many applications of single or few micromotors require real-time tracking and control at high spatiotemporal resolution in deep tissue. Although optical techniques are a popular choice for this task, absorption and strong light scattering lead to a pronounced decrease of the signal-to-noise ratio with increasing penetration depth. Here, a highly reflective micromotor is introduced which reflects more than tenfold the light intensity of simple gold particles and can be precisely navigated by external magnetic fields. A customized optical IR imaging setup and an image correlation technique are implemented to track single micromotors in real-time and label-free underneath phantom and ex vivo mouse skull tissues. As a potential application, the micromotors speed is recorded when moving through different viscous fluids to determine the viscosity of diverse physiological fluids toward remote cardiovascular disease diagnosis. Moreover, the micromotors are loaded with a model drug to demonstrate their cargotransport capability. The proposed reflective micromotor is suitable as theranostic tool for sub-skin or organ-on-a-chip applications.

Multimode fibers (MMF) are promising candidates to increase the data rate while reducing the space required for optical fiber networks. However, their use is hampered by mode mixing and other effects, leading to speckled output patterns. This can be overcome by measuring the transmission matrix (TM) of a multimode fiber. In this contribution, a mode-selective excitation of complex amplitudes is performed with only one phase-only spatial light modulator. The light field propagating through the fiber is measured holographically and is analyzed by a rapid decomposition method. This technique requires a small amount of measurements N, which corresponds to the degree of freedom of the fiber. The TM determines the amplitude and phase relationships of the modes, which allows us to understand the mode scrambling processes in the MMF and can be used for mode division multiplexing.

Inverse precoding algorithms in multimode fiber based communication networks are used to exploit mode dependent losses on the physical layer. This provides an asymmetry between legitimate (Bob) and unlegitimate (Eve) receiver of messages resulting in a significant SNR advantage for Bob. In combination with dynamic mode channel changes, Eve has no chance to reconstruct a sent message even in a worst case scenario in which she is almighty. This is the first time, Physical Layer Security in a fiber optical network is investigated on the basis of measured transmission matrices. These results show that messages can be sent securely with conventional communication techniques. Translating the task of securing data from software to hardware represents the potential of a scientific paradigm shift. The introduced technique is a step towards the development of cyber physical systems.

Background: Optical distortions can significantly deteriorate the measurement accuracy in particle image velocimetry systems. Such distortions can occur at fluctuating phase boundaries during flow measurement and result from the accompanied refractive index changes. The usage of a wavefront sensor can be hindered by disturbing light reflexes or scattering. Methods: A combination of sharpness metric image evaluation and iterative optimization is demonstrated. The sharpness metric is used as an indicator for wavefront aberrations in order to correct low-order Zernike modes that influence the image quality of particle image velocimetry. Results: In this work we outline a sharpness metric based aberration correction with a deformable mirror, applied for the first time to particle image velocimetry. The proposed method allows for the reduction of systematic measurement uncertainties in particle image velocimetry. Conclusion: Our approach offers a new way to reduce static or slowly changing wavefront distortions in a fluid flow measurement setup in which a wavefront sensor is not applicable.

Laser optical techniques are widely used for flow measurements as they offer a high spatial and velocity resolution. However, undisturbed optical access to the measurement volume is desired. In order to measure through a fluctuating phase boundary, we present the use of adaptive optics. In an experiment, we prove that the Fresnel reflex of a phase boundary can be used as a proper guide star for adaptive velocity measurements with a single optical access. Interferometric flow measurements through a fluctuating phase boundary have been accomplished by a Mach-Zehnder interferometer.