Hugo Thienpont

Vrije Universiteit Brussel | VUB · Brussels Photonics Team (PHOT)

For many decades, the famous Aphrodite Sanctuary at Palaepaphos, Kouklia has been the area of various archaeological activities. Since 1973 the site has been investigated systematically by the Swiss-German Archaeological Mission, sponsored by the German Archaeological Institute and the University of Zürich, under the supervision of Franz Georg Maie...

Flexible and compact beam shaping optical systems are gaining more attention due to their use in a broad range of applications. A monolithic freeform beam shaper for slanted, top-hat illumination is designed and fabricated, demonstrating a super-compact, flexible configuration.

Recently, freeform optics has been widely used due to its unprecedented compactness and high performance, especially in the reflective designs for broad-wavelength imaging applications. Here, we present a generalized differentiable ray tracing approach suitable for most optical surfaces. The established automated freeform design framework simultane...

The limited penetration depth of visible light in biological tissues has encouraged researchers to develop novel implantable light-guiding devices. Optical fibers and waveguides that are made from biocompatible and biodegradable materials offer a straightforward but effective approach to overcome this issue. In the last decade, various optically tr...

Compact and broadband spectrometers are very useful in various application domains such as agriculture, food, health and security. In minimally-invasive image-guided procedures spectral tissue sensing helps for screening and diagnostic purposes aiming at discriminating between healthy and tumorous tissue at point-of-care locations and outpatient ce...

Dye-functionalized polymers have been extensively studied to understand polymer chain dynamics, intra or inter-molecular association and conformational changes as well as in practical applications such as signal amplification in diagnostic tests and light-harvesting antennas. In this work, the Förster resonance energy transfer (FRET) of dye-functio...

Various biopolymers including gelatin, have already been applied to serve a plethora of tissue engineering purposes. However, substantial concerns have arisen related to the safety and the reproducibility of these materials due to their animal origin and the risk associated with pathogen transmission as well as batch-to-batch variations. Therefore,...

Coupled-cavity VCSELs typically support two fundamental longitudinal modes. Their wavelengths as a function of the difference of the optical lengths of the two cavities display avoided wavelength crossing (or anticrosing). In this paper, we numerically solve the set of Maxwell equations for a coupled-cavity VCSEL. We show that when brought closer s...

When adequately mounted, fiber Bragg grating sensors can be effectively exploited in harsh environmental conditions. Examples include measuring vibration characteristics of nuclear fuel pins in liquid metal and detecting impact damage of aerospace composite materials.

Graphene is known to have a strong nonlinear‐optical refractive response, both in free‐space setups and in waveguide configurations. This image illustrates nonlinearity‐induced spectral broadening of laser pulses propagating in a graphene‐covered waveguide. The propagating field E interacting with the graphene excites free carriers N c which in tur...

Corneal blindness is the fourth leading cause of visual impairment. Of specific interest is blindness due to a dysfunctional corneal endothelium which can only be treated by transplanting healthy tissue from a deceased donor. Unfortunately, corneal supply does not meet the demand with only one donor for every 70 patients. Therefore, there is a huge...

Connections between standard single-mode fibers and waveguides in photonic integrated circuits tend to have relatively high coupling losses due to a difference in mode size and mode profile between both light guiding media. Edge coupling strategies involving specialty fibers are frequently used to obtain the best performance in terms of coupling ef...

Nonlinear‐optical refraction is typically described by means of perturbation theory near the material's equilibrium state. Graphene, however, can easily move far away from its equilibrium state upon optical pumping, yielding strong nonlinear responses that cannot be modeled as mere perturbations. So far, one is still lacking the required theoretica...

We present a Raman spectroscopy setup containing a conical beam shaper in combination with a freeform segmented reflector for surface enhanced Raman scattering (SERS) analysis. The freeform segmented reflector and the conical beam shaper are designed by numerical approaches and fabricated by means of ultra-precision diamond tooling. The segmented r...

Improved chemical- and bio-sensing with Surface Enhanced Raman Spectroscopy (SERS) requires nanostuctures that can be flexibly designed and fabricated with different physical and optical properties. Here, we present nano-pillar arrays ranging from 200 nm to 600 nm as SERS substrates for mycotoxin detection that are fabricated by means of two-photon...

Biocompatible optical waveguides receive increasing attention owing to their application potential in the biomedical field. Our focus is on the fabrication and characterization of a new step-index biodegradable polymer optical fiber (bioPOF) using two commercial polyesters: poly(D,L-lactic-co-glycolic acid) (PDLGA) and poly(D,L-lactic acid) (PDLLA)...

We present a freeform-segmented reflector-based microfluidic system for conventional Raman and Surface-Enhanced Raman Scattering (SERS) analysis. The segmented reflector is directly designed by a numerical approach. The polymer-based Raman system strongly suppresses the undesirable background because it enables confocal detection of Raman scatterin...

Adipose tissue engineering aims to provide solutions to patients who require tissue reconstruction following mastectomies or other soft tissue trauma. Mesenchymal stromal cells (MSCs) robustly differentiate into the adipogenic lineage and are attractive candidates for adipose tissue engineering. This work investigates whether pore size modulates ad...

We report on the first step-index biodegradable polymer optical fiber (bioPOF) fabricated using commercially available polyesters, with a core made from poly(D,L-lactic-co-glycolic acid) and a cladding made from poly(D,L-lactic acid). We prepared the preforms with a rod-in-tube technique and the fibers with a standard heat drawing process. We discu...

High cycle rates are important in commercial weaving machines to maximize productivity. Faster operation, however, can lead to higher tension on the yarns, which in turn increases the occurrence of yarn breakage and thus machine interruptions. Significant work has therefore been conducted to improve the many weaving machine components with the goal...

The nonlinear-optical refractive behavior of a wide range of materials is typically described by means of perturbation theory near equilibrium. Graphene, however, can easily move far away from its equilibrium state after optical pumping, yielding strong nonlinear responses that cannot be modeled as mere perturbations. So far, it has been challengin...

So far, illumination optics design for extended sources (like LEDs) has been mainly treated as perturbations of ideal point sources without any extent. Such approaches work well provided that this ideal case is approximately met. However, the demand for very compact luminaires equipped with modern high-brightness LEDs results in configurations wher...

Current soft tissue repair techniques for women with breast cancer remain associated with several drawbacks including surgical complications and a high resorption rate for lipofilling techniques. Hence, the need to develop improved adipose tissue reconstruction strategies. Additive manufacturing can be a promising tool towards the development of pa...

Vertical-cavity surface-emitting lasers with vertically integrated electro-absorption modulators (EAM-VCSELs) potentially can reach higher modulation bandwidths than directly current-modulated VCSELs. The aforementioned device modulation capabilities are, however, currently restricted by their electrical contact parasitics. It, thus, becomes critic...

Stem cells are characterized by their self-renewal capacity and their ability to differentiate into multiple cell types of the human body. Using directed differentiation strategies, stem cells can now be converted into hepatocyte-like cells (HLCs) and therefore, represent a unique cell source for toxicological applications in vitro. However, the ac...

Over the recent decades gelatin has proven to be very suitable as an extracellular matrix mimic for biofabrication and tissue engineering applications. However, gelatin is prone to dissolution at typical cell culture conditions and is therefore often chemically modified to introduce (photo-)crosslinkable functionalities. These modifications allow t...

Biodegradable polymers derived from renewable resources can be interesting materials for a plethora of applications and have therefore gained increased interest over the last decades. We herein report for the first time the synthesis of random copolymers based on lactic and mandelic acid via ring-opening-polymerisation of their corresponding 0-carb...

Gelatin is frequently used in various biomedical applications. However, gelatin is generally extracted from an animal source, which can result in issues with reproducibility as well as pathogen transmittance. Therefore, we have investigated the potential of a recombinant peptide based on collagen I (RCPhC1) for tissue engineering applications and m...

There exists a clear clinical need for adipose tissue reconstruction strategies to repair soft tissue defects which outperform the currently available approaches. In this respect, additive manufacturing has shown to be a promising alternative for the development of larger constructs able to support adipose tissue engineering. In the present work, a...

Optical fibre sensors are being investigated since many years as candidates of choice for supporting structural health monitoring (SHM) in aerospace applications. Fibre Bragg grating (FBG) sensors, more specifically, can provide for accurate strain measurements and therefore return useful data about the mechanical strain state of the structure to w...

We demonstrate a biodegradable and biocompatible unclad optical fiber made from poly(D,L-lactic acid) (PDLLA), which is a well-known and commercially available amorphous polyester. We first deal with the chemical and optical characterization of the bulk polymer material and we report on the influence of the processing on the molecular weight and th...

Optical fibre sensors are being investigated since many years as candidates of choice for supporting structural health monitoring (SHM) in aerospace applications. Fibre Bragg grating (FBG) sensors, more specifically, can provide for accurate strain measurements and therefore return useful data about the mechanical strain state of the structure to w...

We demonstrate that commercially available poly(D,L-lactic acid) (PDLLA) is a suitable material for the fabrication of biodegradable optical fibers with a standard heat drawing process. To do so we report on the chemical and optical characterization of the material. We address the influence of the polymer processing on the molecular weight and ther...

We present in this paper the vertical integration of an electro-absorption modulator (EAM) onto a vertical-cavity surface-emitting laser (VCSEL). We discuss the design, fabrication, and measured characteristics of the combined VCSEL and EAM. We previously demonstrated a standalone EAM with an optical bandwidth around 30 GHz. In this paper we presen...

We present the design of refractive beam shaping optics for transforming a circular Gaussian beam into a top hat beam for an additive manufacturing process. The designed components are prototyped in zinc sulfide using single-point diamond turning.

We present a method to associate wavefronts to a given intensity pattern. This “wavefront-tailoring” technique is at the core of a powerful wavefront-coupling design tool, particularly suited for freeform illumination optics with extended source.

We present the design and fabrication of a segmented freeform reflector for confocal Raman and SERS spectroscopic analysis in a microfluidic-based system. Further, we simulate the confocal performance and assess the results by experiments.

Surface Plasmon Resonance devices have the promise to become the prevailing device technology for miniaturized point-of-care diagnosis. We have designed, fabricated and tested a disposable freeform SPR device outperforming traditional prism devices.

The physics of nonlinear-optical refraction in graphene has remained unclear for almost a decade now. We solve this issue through self-phase modulation experiments in graphene-covered waveguides, revealing the extra-ordinary free-carrier interactions that underpin the refraction process.

Over the recent decades gelatin has proven to be very suitable as an extracellular matrix mimic for bio-fabrication and tissue engineering applications. However, gelatin is prone to dissolution at typical cell culture conditions and is therefore often chemically modified to introduce (photo-)crosslinkable functionalities. These modifications allow...

The Fiber Bragg Gratings (FBGs) inside Photonic Crystal Fibers having high fiber birefringence, such as in PCF with butterfly shape microstructure, are characterized by two Bragg peaks. The spectral distance between these two peaks is not affected by a change of temperature or by a longitudinally applied strain, but this spectral separation evolves...

JPhys Photonics is a new open access journal from IOP Publishing reporting high-quality, significant, and original research at the forefront of photonics and optics. The journal will showcase the most exciting research advances and discoveries that constitute today's science and will shape tomorrow's technologies. With a particular focus on interdi...

We report on the design, fabrication and experimental demonstration of single-crystal diamond (SCD) waveguide devices with integrated grating couplers optimized for 850 nm, 635 nm, and 405 nm wavelengths, respectively. The devices are fabricated on SCD thin films using electron-beam lithography and reactive-ion etching technologies. To reduce the w...

Small misalignments between two standard telecom single-mode fibers in a physical contact connection can lead to large optical losses. It is known that by expanding the mode field diameter of the fiber, the misalignment tolerances can be relaxed. One of the approaches to obtain this beam expansion is to use tapers. We propose an air-clad taper stru...

Tunable vertical-cavity surface-emitting lasers (VCSEL) provide broad wavelength tuning range at very high modulation speed, but usually employ micro electromechanical systems, which are sensitive to vibrations. In this paper we propose a tunable 1550 nm VCSEL design with enclosed intra-cavity liquid-crystal (LC) cell. The laser is electrically pum...

Applying graphene in optical and photonic applications is anticipated to be a promising strategy to attain new technological functionalities. To maximize the exploitation of graphene’s extraordinary optical properties, precise control over its Fermi level will be of vital importance. Therefore, chemical doping is a viable approach to manipulate gra...

Graphene is considered a record-performance nonlinear-optical material on the basis of numerous experiments. The observed strong nonlinear response ascribed to the refractive part of graphene's electronic third-order susceptibility χ(3) cannot, however, be explained using the relatively modest χ(3) value theoretically predicted for the 2D material....

In vascular tissue engineering, great attention is paid to the immobilization of biomolecules onto synthetic grafts to increase bio‐ and hemocompatibility—two critical milestones in the field. The surface modification field of poly(ethylene terephthalate) (PET), a well‐known vascular‐graft material, is matured and oversaturated. Nevertheless, most...

In the present work, gelatin type B is modified with highly reactive norbornene functionalities (Gel‐NB) following a one‐pot synthesis approach to enable subsequent thiol–ene photo‐click crosslinking. The modification strategy displays close control over the amount of introduced functionalities. Additionally, Gel‐NB exhibits considerably improved p...

Fiber Bragg grating inscription with infrared femtosecond pulsed lasers in photonic crystal fiber is far from being trivial due to the presence of air holes in the cladding region and the non-linear nature of the absorption process inducing the required refractive index changes. We have studied this problem numerically and experimentally for a phas...

A transducer for assisting in measuring displacement or strain in an object of interest is described. It comprises a plate (1) having at least two end sections (5) for mounting the transducer to the object of interest. It furthermore comprises a flexible connection between the two end sections (5). The flexible connection comprises a plurality of r...

It is common belief that photonic crystals behave similarly to isotropic and transparent media only when their feature sizes are much smaller than the wavelength of light. Here, we counter that belief and we report on photonic crystals that are transparent for anomalously high normalized frequencies up to 0.9, where the crystal's feature sizes are...

Environmentally degradable polyesters offer an interesting perspective for a vast number of applications. However, current front-runners like poly(lactide), poly(glycolide) and poly(ε-caprolactone) are either semi-crystalline excluding applications for which optical transparency is desired, or exhibit low glass transition temperatures (Tg) resultin...

Electro-absorption modulators, either embedded in CMOS technology or integrated with a semiconductor laser, are of high interest for many applications such as optical communications, signal processing and 3D imaging. Recently, the integration of a surface-normal electro-absorption modulator into a vertical-cavity surface-emitting laser has been con...