Herbert De Smet

Ghent University | UGhent · Centre for Microsystems Technology

To realize laser-driven high-luminance white light sources, many reflective configurations have been studied, often resulting in a challenging optical design. In this paper it is demonstrated that the efficacy of a transmissive configuration can be significantly enhanced by using a sapphire half-ball lens as out-coupling optic. This lens not only i...

There is an increasing interest in atomic layer deposition (ALD) on polymers for the development of membranes, electronics, (3D) nanostructures and specially for the development of hermetic packaging of the new generation of flexible implantable micro-devices. This evolution demands a better understanding of the ALD nucleation process on polymers,...

Objective The perform pre-clinical testing using optical design tools to simulate the optical quality of a smart artificial iris platform encapsulated in a scleral contact lens. These tools allow us to generate aniridia eye models and evaluate different metrics of visual quality and retinal illumination based on the aperture of the artificial iris...

Resumen Objetivo Realizar las pruebas pre-clínicas por medio de herramientas de diseño óptico para simular la calidad óptica de una plataforma inteligente de iris artificial encapsulada en una lente de contacto escleral. Estas herramientas nos permiten generar modelos de ojo de aniridia y evaluar distintas métricas de calidad visual y de iluminaci...

Nowadays, smart contact lenses (SCLs) display interesting features for healthcare monitoring; however, their comfort and practical usability strongly depend on the outermost material in contact with the eye. In this publication, the embedding of a custom‐made and thermoformed Near‐Field Communication based circuit in a conventional soft CL is prese...

jats:p>Emerging applications requiring light beam manipulation, such as high-efficiency sunlight concentrators for solar cells, switchable micro-lens arrays for autostereoscopic displays, tunable lenses for augmented reality goggles, auto-focusing spectacles, and smart contact lenses, mostly depend on one or more active optical components with the...

This paper presents the simulated performance assessment of an artificial iris embedded on a scleral contact lens using real data from an aniridia patient. The artificial iris is based on guest–host liquid crystal cells (GH-LCD) in order to actively modify the transmittance of the lens and effective pupil size. Experimental validation of the GH-LCD...

Biocompatible BPA-PPD polyimide is widely used in the packaging of implantable devices. Plasma activation can improve its interaction with the surrounding tissue upon implantation. The influence of He, air, N2 and Ar plasma activation on polyimide's surface hydrophilicity, roughness, topography, composition and cell-surface interaction was evaluate...

In a normally functioning eye, the iris controls the pupil diameter to regulate the amount of light reaching the retina. Various iris deficiencies exist, manifesting as defects in the iris or an absence of one which result in too much light reaching the retina. Some iris deficiencies, such as aniridia or leiomyoma, can be mitigated with fixed or ad...

Plasmas can be generated in a wide range of pressures from a few Pa up to atmospheric pressure. Generating plasmas at low and medium pressures has the advantage of larger plasma volumes, allowing the surface modification of bigger objects with complex surface geometries. The plasma chemistry under operating conditions is dominantly driven by radica...

An electrochemical smart contact lens (ESCL) capable of real-speed spatiotemporal electrochemical sensing across the surface of the eye is demonstrated. Four microelectrode arrays, each comprising 33 gold microdiscs of 30 μm diameter, and a distributed common gold counter electrode, are integrated into a soft smart contact lens platform based on po...

In recent years, there has been an increased interest in soft packaging for non-rigid medical implants. A promising technique to realize reliable soft packaging involves the inclusion of thin layers of atomic layer deposited (ALD) ceramics between biocompatible polymer layers. Crucial requirements are that those ALD layers are biocompatible and pin...

The design and technology of tunable liquid crystal based lenses is discussed. Specific attention is paid to lenses with small diameters and high f‐number and it is demonstrated that in that case a segmented Fresnel lens approach can be most favorable in terms of both ease of manufacturing and optical performance.

We demonstrate a real-speed spatiotemporal electrochemical map showing both time- and position-varying concentration of an analyte in contact with a flexible microelectrode array. A polymer-based device of 11 μm in thickness comprising patterned gold metallisation on a polyimide substrate was fabricated, with eight individually addressable working...

Optical beam deflectors based on the combination of cholesteric liquid crystals and polymer micro gratings are reported. Dual frequency cholesteric liquid crystal (DFCh-LC) is adopted to accelerate the switching from the homeotropic state back to the planar state. Polarization independent beam steering components are realized whose transmission ver...

In this paper, we have experimentally investigated polarization properties of the blue phase of a cholesteric liquid crystal in polycrystalline cells with different alignment layers. Experiments were carried out by various temperatures and wavelengths within the spectral range covering Bragg reflection. It was conclusively demonstrated that the cha...

A stretchable platform with spherical-shaped electronics based on thermo- plastic polyurethane (TPU) is introduced for soft smart contact lenses. The low glass transition temperature of TPU, its relatively low hardness, and its proven biocompatibility (i.e., protection of exterior body wounds) fulfill the essential requirements for eye wearable...

A spherically curved liquid crystal display based on a guest-host liquid crystal configuration is fabricated. An asymmetric display design is introduced: two flexible display substrates with varying surface area are used, allowing for compact integration of powering and driving electronics. A matrix of spacer structures composed of photosensitive a...

A polarization independent and fast electrically switchable beam steering device is presented, based on a surface relief grating combined with polymer stabilized blue phase liquid crystals. Switching on and off times are both less than 2 milliseconds. The prospects of further improvements are discussed.

We show an active artificial iris based on solely thin-film components, wherein several LCD elements are controlled a metal-oxide TFT and by powered by thin-film photovoltaics (TFPV). Key aspects for the driver are size and low power consumption. We demonstrate power consumption down to 25μW for the full iris.

We report on efficient optical beam-steering using a hot-embossed reflective blazed grating in combination with liquid crystal. A numerical simulation of the electrical switching characteristics of the liquid crystal is performed and the results are used in an FDTD optical simulator to analyze the beam deflection. The corresponding experiment on th...

In this contribution, a conformable 64×45 RGB light-emitting diode (LED) matrix is presented. A design concept of stretchable electronics is used: non-stretchable polymer islands host rigid LEDs and are interconnected by horseshoe shaped metallic conductors, which are able to deform together with an elastomeric substrate. Thin-film metallization is...

LC beam steering devices are realized using the combination of liquid crystal and polymer micro grating structures. The micro gratings are fabricated by combining two major techniques: laser ablation for a master mold and soft lithography for replicas with the desired optical materials. The LC components demonstrate effective beam deflections with...

In this work, we report two types of electrically tunable photonic devices with circularly symmetric polarization independent beam steering performance (beam condensing resp. beam broadening). The devices consist of circular micro grating structures combined with nematic liquid crystal (LC) layers with anti-parallel alignment. A single beam deflect...

An effective tunable optical beam deflection device based on a periodic gradient refractive index (GRIN) profile is reported, which is capable of achieving a 5° beam deflection with an angle resolution of 0.5°. The operation voltage is around 6 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub>...

Fast patterning of highly conductive polymers like PEDOT:PSS (poly (3,4-ethylene dioxythiophene): polystyrene sulfonate) with lasers can contribute to the development of industrial production of liquid crystal displays on polymer foils. In this article, the selective UV laser patterning of a PEDOT:PSS film on flexible polymer films is investigated....

In this article, we describe an electrically switchable light beam steering component, based on the combination of microprism structures and nematic liquid crystals, which effectively deflects both a laser beam and a collimated white light beam with a controllable steering range of 38.

In reflective liquid crystal devices that have an asymmetric electrode structure, an internal cell voltage is often present that interferes with the proper functioning of the device. Contrary to transmissive devices, this internal voltage cannot be attributed solely to ionic charges in the liquid crystal. On the basis of extensive measurements, an...

The issue of long term stability of polymer stabilized blue phase liquid crystals was investigated. It was found that for certain liquid crystals and commonly used chiral dopant combinations, polymer stabilized blue phase liquid crystals develop dendrite like structures. These features are highly scattering and are detrimental to the uniformity of...

In this article, we present how alignment layers affect blue phase liquid crystals and how we can use this effect to our advantage.

A technology is presented for the production of soft and rigid circuits with an arbitrary 2.5D fixed shape. The base of this technology is our proprietary technology for elastic circuits with a random shape, in which the elastic thermoset (mostly PDMS) polymer is now replaced by soft or rigid thermoplastic variants. An additional thermoforming step...

In this work we report the fabrication of polymer micro-photonic gratings for use in liquid-crystal based actively tunable electro-optic components. The gratings are produced by moving the sample surface sideways across a perpendicularly impinging KrF excimer laser beam (λ = 248 nm), which is shaped by specially designed triangular and trapezoidal...

In this work, the reverse replication of circular micro grating structures on glass substrates is implemented using an ultra-violet curable resin and a polydimethylsiloxane (PDMS) mold which has the same structure as the original circular grating master. Two different techniques (“double PDMS replication” and “polymer- PDMS replication”) are employ...

In this paper, we present an electrically controllable microoptical component for light beam steering and light intensity distribution built on the combination of nematic liquid crystal (LC) and polymer microprisms. Polymer microprism arrays are fabricated using soft embossing with elastic polydimethylsiloxane molds and ultraviolet curable resins....

In the present work, the effect of alignment layers on blue phase liquid crystals was investigated. It was found that homogeneous alignment layers have profound selective influence on blue phase II (BPII). In the absence of alignment layers, BPII domains were randomly oriented and showed weak Bragg reflection in the UV, whereas with assistance of a...

A method of operating by pulse width modulation a micromirror device is disclosed. In one aspect, the method includes providing a micromirror device having a micromirror element electrostatically deflectable around a rotation axis between a first and second position. The micromirror element is controllable by applying voltage signals to a first and...

In this article we report the fabrication of large arrays of micro-optical gratings using soft embossing with elastic Polydimethylsiloxane (PDMS) molds and ultra-violet (UV) curable resins. Three different kinds of resins are used to replicate the master gratings in a process akin to a roll to roll process. The optical surface profiling measurement...

Well-being applications demand unobtrusive treatment methods in order to reach user acceptance. In the field of light therapy this needs to be carefully addressed because, in most cases, light treatment system size has to be significant with respect to human body scale. At the same time we observe the push to make wearable devices that deliver the...

Analog driven LCOS panels can exhibit flicker due to Vcom offset rooted in both electro-chemical reactions at the interfaces and ionic impurities in the liquid crystal. A possible solution is offered where a combined alignment layer and suitable barrier layer is obtained in a single step using oblique evaporation.

Characterization of Blue Phase liquid crystals (BPLC) at different temperatures is an interesting but time consuming research activity. We present a quick and efficient one step method to record the Polarization optical micrograph (POM) depicting texture of BPLC at various temperatures simultaneously and also support our case with COMSOL simulation...

An artificial iris utilizing a spherically shaped liquid crystal cell filled with a guest–host mixture is presented. By patterning the cell in concentric circles, the opening and closing of an iris can be mimicked. A practical implementation of the artificial iris is described and remaining problems are listed.

Recent progress in microsystems integration technology such as ultra-thin chip packaging, stretchable interconnections, thin-film batteries and organic photovoltaics makes it feasible to incorpo-rate various electronic components and transducers in extremely confined spaces and inside flexible or conformable objects. Can this ultimately lead to a g...

A contact lens embeddable display using electro-optic modulation was designed and fabricated. Using a guest–host liquid crystal configuration, a spherically deformed liquid crystal cell was fabricated comprising poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT : PSS) as a conductive layer and obliquely evaporated SiO2 as an alignment...

Direct view displays are nowadays common in vehicle displays of various nature to convey information. They are mostly LCD-based and benefit from the maturity and reliability of this well-developed technology. However, they also have some drawbacks that prevent them from being completely adapted to the wishes of human-machine interface designers. Pr...

A new liquid crystal based technology is presented that can be embedded in a contact lens. Although the long term goal is an augmented reality application, its use as an artificial iris is explored. The potential impact and future work is discussed.

Disparity estimation is a highly complex and time consuming process in multiview video encoders. Since multiple views taken from a two-dimensional camera array need to be coded at every time instance, the complexity of the encoder plays an important role besides its rate-distortion performance. In previous papers we have introduced a new frame type...

An active spherically conformed liquid crystal cell is presented comprising PEDOT:PSS as a transparent conductive layer and obliquely evaporated SiO2 as an alignment layer. To tackle compatibility issues with the SU8 processing needed for the spacers, an additional buffer layer was included in the fabrication process. The electro-optic response is...

A new design of a spherically molded liquid crystal cell intended for embedding in a contact lens is proposed. Wrinkle formation in these cells was investigated and a correlation was found between the total thickness of the cell and its smoothness. Smooth cells with minimal thickness were obtained by using an asymmetric configuration with a thin la...

An efficient disparity estimation algorithm for multi-view video sequences, recorded by a two-dimensional camera array in which the cameras are spaced equidistantly, is presented. Because of the strong geometrical relationship among views, the disparity vectors of a certain view can for most blocks be derived from the disparity vectors of other vie...

Disparity estimation is a highly complex and time consuming process in multi-view video encoders. Since multiple views taken from a 2D camerea array need to be coded at every time instance, the complexity of the encoder plays an important role besides its rate-distortion performance. In previous papers we have introduced a new frame type called D f...

A projection optical system for hypothetic near eye displays that can be built into a contact lens or glasses is considered. The system parameters are evaluated. Aspects of practical usage of the displays and possible embodiments of the optical system are discussed.

Future airplanes could be fitted with several short-throw wide-angle LED projectors to create a seamless tiled cockpit interactive air-navigation display.

As the number of views comprised in multi-view videos increases, some challenging problems emerge. Besides the bandwidth problems caused by the huge data flow, the calculation power needed by the multi-view encoder is an even higher burden than that of a single view encoder. In this paper, a complexity efficient way to encode a single-time instant...

Microdisplays of the liquid crystals on silicon (LCOS) type have gone through a rapid evolution during the last decade. We present an overview of how vertically aligned nematic (VAN) LCOS have evolved from an attractive, but notoriously difficult and even infamous technology, to the mainstream microdisplay technology that it is today. At the same t...

The seven papers in this special issue address a selection of some of the issues concerning the liquid crystal on silicon technology, from fabrication and design to some of the applications.

The possibility of creating an 2D X-ray sensor array on the base of a-SiN:H thin films without switching elements and an X-ray conversion layer is presented in this report. The behavior of a-SiN:H Thin-Film Diode under X-ray irradiation its limitations, and ways of increasing longterm stability and sensitivity of the sensor are discussed.

Amorphous silicon thin film diodes (TFD), which are used for digital radiography are discussed. X-ray sensitivity of the sensor and overall performance of the sensor arrays are also presented. The results shows that the amorphous silicon TFD in a avalanche multiplication modes which can be used as a x-ray sensing device.

A characterization of the flicker-inducing DC offset in asymmetric (LCOS) LC cells is performed making use of barrier layers to differentiate between electro-chemical reactions and ionic impurities. This characterization is used to understand the internal behavior of LCOS cells and to improve their functioning.

Recently we presented a SiGe MEMS technology compatible with underlying CMOS. In this technology micromirrors were demonstrated employing a novel electromechanical PWM driving method. We now report optimized driving waveforms that implement the driving scheme using only CMOS compatible voltages.

We present two concepts to create multiview 3-D displays with high spatial and angular resolution at a reasonable system cost. We investigate a rear projection approach using only one projector with a digital micromirror device as a light modulator. The first concept is based on time sequentially illuminating the entire light modulator from differe...

In this work we present a prototype multiview projection display that combines high-spatial and high-angular resolution with low complexity, compact form factor and potentially low-cost design. The system consists of a single projector and an image steering projection screen. It is based on beam steering using decentered microlens arrays in the pro...

A novel six-electrode SiGe micromirror pixel enabling analog pulse-width modulation (PWM) in display applications is presented. Instead of utilizing bitplanes, arbitrary duty cycles can be realized, resulting in an analog gray-level distribution. This eliminates the posterization (contouring) effect that is typical for digital micromirrors. Moreove...

In imec's 200mm fab a dedicated poly-SiGe above-IC MEMS (Micro Electro-Mechanical Systems) platform has been set up to integrate MEMS and its readout and driving electronics on one chip. In the Flemish project Gemini the possibilities of this platform have been further explored together with the project partners. Three different demonstrators were...