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Publications (63)
Colonoscopy and endoscopic ultrasound play pivotal roles in the assessment of rectal diseases, especially rectal cancer and inflammatory bowel diseases. Optical coherence tomography (OCT) offers a superior depth resolution, which is a critical factor for individualizing the therapeutic concept and evaluating the therapy response. We developed two d...
Circumferential scanning in endoscopic imaging is crucial across various disciplines, and optical coherence tomography (OCT) is often the preferred choice due to its high-speed, high-resolution, and micron-scale imaging capabilities. Moreover, real-time and high-speed 3D endoscopy is a pivotal technology for medical screening and precise surgical g...
The realization of optical interconnects between multimode (MM) optical fibers and waveguides based on a self-writing process in photopolymer media represents an efficient approach for fast and easy-to-implement connection of light-guiding elements. When light propagates through photopolymer media, it modulates the material properties of the media...
Spectral domain optical coherence tomography (SD-OCT) is a highly versatile method which allows for three dimensional optical imaging in scattering media. A number of recent publications demonstrated the technique to benefit from structured illumination and beam shaping approaches, e.g. to enhance the signal-to-noise ratio or the penetration depth...
We propose a compact setup for wavefront manipulation in spectral domain optical coherence tomography (OCT). The system can easily be implemented into existing free-space OCT setups through modification of the source path only. We demonstrate complex-valued OCT signal acquisition based on phase shifting combined with iterative optical wavefront sha...
Optical transmission paths consisting of waveguides, light sources and detectors form basic components in a large variety of applications ranging from photonic sensors to short distance communication. We demonstrate the design and fabrication of a polymer transmission path which incorporates standard semiconductor light sources. In this work, we es...
Advances in illumination technology in the automotive industry are heading toward the use of coherent sources for adaptable and high-resolution head lamps as well as interior and rear-end lights. We present a cost-effective method to fabricate and design laser-based lighting systems for the rear end in automobiles and other vehicles. The design rel...
A diffusion-based material model is implemented and linked to the Crank–Nicholson beam propagation method to carry out numerical investigations on self-written bent waveguide couplers on a polymer basis. Such couplers are established in a photopolymer mixture when two opposing Gaussian laser beams with an offset or gap along their propagation axes...
Straight and bent self-written waveguides (SWWs) are formed within a photomonomer mixture by means of a
self-trapping effect when a single laser beam or two laser beams with tilt are propagated inside. These SWWs
can be used as optical interconnects in integrated photonic circuits if two laser beams are launched in opposite
directions into the phot...
A new multimodal system for rapid, noninvasive in vivo skin cancer screening is presented, combining optical coherence tomography (OCT) and optoacoustic (OA) modalities to provide precise tumor depth determination with a Raman spectroscopic modality capable of detecting the lesion type and, thus, providing diagnostic capability. Both optoacoustic a...
We demonstrate the implementation of wavefront shaping in Optical Coherence Tomography (OCT). This combination opens up new ways for OCT signal enhancement as well as for non-invasive focusing of light inside scattering media.
Confocal microscopy is one of the dominating measurement techniques in surface metrology, with an enhanced lateral resolution compared to alternative optical methods. However, the axial resolution in confocal microscopy is strongly dependent on the accuracy of signal evaluation algorithms, which are limited by random noise. Here, we discuss the inf...
Optical interconnects are key components for integrated optics to link photonic integrated circuits (PICs) or to connect external elements such as light sources and detectors. However, misalignment of the optical elements contained and its compensation is a remaining challenge for integrated optical devices. We present a novel method to establish r...
In this work different fibre optic sensors for the structural health monitoring of civil engineering structures are reported. A fibre optic crack sensor and two different fibre optic moisture sensors have been designed to detect the moisture ingress in concrete based building structures. Moreover, the degeneration of the mechanical properties of op...
We present a process to fabricate fully polymer based integrated optical devices which is based on maskless lithography and hot embossing. Using the maskless lithographic setup, we are able to create a hot embossing stamp in a flexible and fast manner. We demonstrate that our process is capable of creating linear optical waveguides, Y-splitters and...
For sensing applications in structural health monitoring, process technology or life sciences polymer micro-optical sensors are highly promising as they offer several advantages in comparison to other sensor types. In this work, a fabrication process of low-cost planar polymer optical waveguides based on hot embossing and doctor blading is presente...
A reliable, fast, and non‐invasive determination of melanoma thickness in vivo is highly desirable for clinical dermatology as it may facilitate the identification of surgical melanoma margins, determine if a sentinel node biopsy should be performed or not, and reduce the number of surgical interventions for patients. In this work, optical coherenc...
For various applications such as optical communication, sensor technology and optical interconnects, micro-optical polymer devices show great promise. Especially, straight and bent optical waveguides as well as beam splitters represent the building blocks of these devices. In this work, we introduce a novel combination of simple fabrication techniq...
We present a simple and efficient Monte Carlo model to predict the scattering coefficients and the influence of multiple photon scattering with increasing concentration of scattering centers from optical coherence tomography (OCT) data. While the model reliably estimates optical sample parameters for a broad range of concentrations, it does not req...
In the past years, several examples of waveguides or gratings manufactured by laser radiation in various glasses or transparent polymers have been demonstrated. As these devices rely on a modification of the refractive index in the vicinity of the focal point of a writing laser, phase retrieval methods are well suited to determine the induced phase...
In the above paper [1], in paragraph III, for a displacement of 6 over a reference length of 100 , the corresponding strain was mistakenly reported with 60 . The correct value is 60 .
While automatic hot embossing systems are available for large- and small-scale productions of polymeric devices, one of the process challenges remains to be the manufacturing of precise, durable, and yet inexpensive hot embossing stamps. The use of metallic stamps manufactured by electroplating a photoresist pattern or by precision milling and thei...
To produce diffractive or holographic structures in a photolithographic process, an optical projection system enabling structure resolution in the submicrometer range is highly desirable. To ensure that the optical focus of such a system lies on the substrate surface during the whole lithographic fabrication process, an autofocus system able to foc...
We demonstrate the manufacturing of embedded multimode optical waveguides through linking of polymethylmethacrylate (PMMA) foils and cyclic olefin polymer (COP) filaments based on a lamination process. Since the two polymeric materials cannot be fused together through interdiffusion of polymer chains, we utilize a reactive lamination agent based on...
Melanoma skin cancer has one of the highest mortality rates of all types of cancer if not detected at an early stage. The survival rate is highly dependent on its penetration depth, which is commonly determined by histopathology. In this work, we aim at combining optical coherence tomography and optoacoustic as a non-invasive all-optical method to...
Micro-optical sensors based on optical waveguides are widely used to measure temperature, force and strain but also to detect biological and chemical substances such as explosives or toxins. While optical micro-sensors based on silicon technology require complex and expensive process technologies, a new generation of sensors based completely on pol...
We present our recent results on the fabrication of photonic devices such as single-mode and few-mode waveguides, Ycouplers as well as integrated interferometric sensor devices. The devices were created by means of a fabrication method based on maskless lithography, which allows for fabricating embedded integrated polymer elements on a scale of sev...
We demonstrate an epoxy acrylate based system on which various micro-optical applications can be realized. With this innovative and flexible material concept, it is possible to adjust viscosity (3 mPa s < η < 46 Pa s) as required for different microstructuring processes e.g. inkjet printing, spin coating, and stereolithography and simultaneously pr...
Optical displacement sensors made entirely from plastic materials offer various advantages such as biocompatibility and high flexibility compared to their commonly used electrical and glass-based counterparts. In addition, various low-cost and large-scale fabrication techniques can potentially be utilized for their fabrication. In this work we pres...
We present a novel one-step calibration methodology for geometrical distortion correction for optical coherence tomography (OCT). A calibration standard especially designed for OCT is introduced, which consists of an array of inverse pyramidal structures. The use of multiple landmarks situated on four different height levels on the pyramids allow p...
We describe a novel technique for determination of the refractive index of hard biological tissue as well as nonopaque technical samples based on optical coherence tomography (OCT). Our method relies on an inverse refractive-index correction (I-RIC), which matches a measured feature geometry distorted due to refractive-index boundaries to its real...
Novel concepts for planar optical deformation measurement promise broad application potential in fields such as structural health monitoring, process control or life sciences, among others. In this paper we present a new approach to optical displacement and tilt sensing in thin polymer foils. We report on the design, simulation, realization, and ch...
Polymer-based holographic and diffractive optical elements have gained increasing interest due to their potential to be used in a broad range of applications, such as illumination technology, micro-optics, and holography. We present a production process to fabricate polymer-based diffractive optical elements and holograms. The process is based on m...
Polymer based diffractive optical elements have gained increasing interest due to their potential to be used in various applications such as illumination technology, micro optics and holography. We present a novel production process to fabricate polymer based diffractive optical elements and holograms. The process is based on maskless lithography,...
Low-loss optical-coupling structures are highly relevant for applications in fields as diverse as information and communication technologies, integrated circuits, or flexible and highly-functional polymer sensor networks. For this suitable and reliable production methods are crucial. Self-written waveguides are an interesting solution. In this work...
Optical aberrations of microscope lenses are known as a source of systematic errors in confocal surface metrology, which has become one of the most popular methods to measure the surface topography of microstructures. We demonstrate that these errors are not constant over the entire field of view but also depend on the local slope angle of the micr...
Die Optische Kohärenztomographie (OCT) ist ein etabliertes volumetrisches Bildgebungsverfahren, das insbesondere in der Ophthalmologie und Dermatologie angewandt wird. Die vorliegende Arbeit stellt eine neuartige Methode zur Kalibrierung von OCT Systemen vor, die auf Messungen einer selbst angefertigten 3D Referenzstruktur und anschließender landma...
The generation of diffractive optical elements often requires time and cost consuming production techniques such as photolithography. Especially in research and development, small series of diffractive microstructures are needed and flexible and cost effective fabrication techniques are desirable to enable the fabrication of versatile optical eleme...
Micro-optical sensors integrated into polymer foils hold great promise for a wide range of applications. One major challenge to date is the reliable, large-scale and cost-effective manufacturing of the required waveguide structures. Several techniques are currently investigated in the field, hot-embossing being particularly promising. In this work,...
Hot embossing techniques enable the use of inexpensive polymers, e.g. as functional materials in optical devices or structural materials in fluidic systems. While automatic hot embossing systems are available for large and small-scale productions, the main challenge remains to be the manufacturing of precise, inexpensive and durable hot embossing s...
form only given. Optical techniques are utilized in robot aided surgery as navigation tools to guide surgical instruments. The advantages are a reduction of severe damage during surgery and of post-surgical trauma. A common approach is to place spherical markers inside the operating field, which can be detected by a 3D imaging device, in order to d...
Holograms are industrially used as decorative design elements to increase the value of products. As they are hard to copy, holograms are also used for brand protection and product identification. The state-of-the-art is to emboss holograms in the surface of polymeric foils and to apply them to products by adhesive bonding. Examples are holograms on...
This article presents a one step geometric calibration for an optical
coherence tomography (OCT) which forms part of a medical navigation
system. The 3D landmark-based geometric calibration with a self-produced
3D reference structure is based on the identification of a parameterized
grey-box OCT model. We show in experimental results by comparing c...
Zusammenfassung
Virtual measurement systems can be used for the estimation of measurement uncertainties during the construction and provide knowledge concerning the working principle of the measurement system. Furthermore it is possible to integrate the virtual system into an assistance tool to calculate intelligent measurement strategies with diff...
Rotating machinery parts, e. g. roller bearings or turbine engines, are present in many industrial applications. Within this paper, a metrology system for determining the out-of-plane and in-plane deformation and vibration of rotating objects is presented. The system consists of an optomechanical image derotator, which is combined with a high speed...
Most rotating machinery parts like roller bearings or jet engine components are subjected to high static and dynamic loads during operation. These excitations cause in-plane and out-of-plane deformation and vibration of the machinery parts, which can lead to minor operation performance, higher wear rates and finally the destruction of these compone...
Es wird ein einfaches physikalisches Modell zur Erklärung von Artefakten bei der To-pographiebestimmung an steilen Kanten mit einem Weißlichtinterferometer aufge-stellt. Anhand des Modells werden die physikalischen Parameter identifiziert, die die Artefaktentstehung beeinflussen. Unter Berücksichtigung dieser Parameter wird der Entwurf und die Real...
Electronic Speckle Pattern Interferometry with a light source of short coherence length allows depth-resolved deformation analysis below the surface of light-scattering objects (Low Coherence Speckle Interferometry - LCSI). Interference is tuned to a thin layer - called the coherence layer - by appropriate adjustment of the length of the reference...