Miltiadis Vasileiadis

Potential of InGaAs/GaAs Quantum Dots for Applications in Vertical Cavity Semiconductor Optical Amplifiers

The use of InGaAs/GaAs quantum dots (QDs) in vertical cavity semiconductor optical amplifiers (VCSOAs) is proposed and analyzed. The results underline the distinctive differences between practical designs for QD vertical cavity semiconductor lasers and QD-VCSOAs. By means of a QD rate-equation scheme that accounts for both homogeneous and inhomogeneous broadening and the VCSOA cavity characteristics, the effects of material properties are identified. The design routes outlined here ensure the suitability of QD-VCSOAs for high-speed applications (>100 Gb/s) that rely on the fast carrier dynamics.

Diffractive optic sensor for remote-point detection of ammonia

Remote-point photonic sensors are fabricated and evaluated. They are based on nanocomposite thin films comprising NiCl(2) nanocrystals embedded in sol-gel silica matrix and are patterned using direct UV laser microetching techniques to form surface relief structures, which exhibit environment sensitive optical diffraction effects. A strong response to ammonia is detected via the alteration of diffraction efficiency of its orders upon exposure to the analyte. Detection of ammonia in the 2 ppm level with a typical response time of about 30 s in the ambient, 50% RH 20 degrees C, room environment is demonstrated.

Nanocomposite hybrid photonic media for remote point sensors

The use of lossless optical media exhibiting reversible optical interactions upon exposure to physical and chemical agents allows for the implementation of remote point photonic sensors. Hybrid nanocomposite media represent a new class of sensor materials. They are produced by flexible chemical synthesis methods and can potentially be tailored by design to implement specific functionalities. These materials combined with externally manipulated optical interfaces lead to an emerging class of diffractive photonic devices offering unique sensing potential and advantageous operational features at low cost. The first case studies on ammonia and methanol detection are discussed.

ArF excimer laser microprocessing of polymer optical fibers for photonic sensor applications

A study of polymer optical fiber microstructuring by use of deep ultraviolet excimer laser radiation at 193 nm wavelength is performed. The ablation characteristics of the fiber cladding and core materials are analyzed comparatively. The laser irradiation effects are dynamically studied by on-line monitoring of the laser ablation induced waveguiding losses, the latter being correlated with the spatial structuring parameters. The fiber surface is modified to incorporate cavities, which are subsequently employed as sensitive material receptors for the development of customized photonic sensors. The sensing capability of the microstructured plastic optical fibers is demonstrated by ammonia and humidity detection.

Micro-fabrication by laser radiation forces: a direct route to reversible free-standing three-dimensional structures.

The origins and first demonstration of structurally stable solids formed by use of radiation forces are presented. By experimentally proving that radiation forces can indeed produce stable solid material forms, a novel method enabling two- and three-dimensional (2d and 3d) microfabrication is introduced: An optical, non-contact single-step physical operation, reversible with respect to materials nature, based on the sole use of radiation forces. The present innovation is elucidated by the formation of polyisoprene and polybutadiene micro-solids, as well as plasmonic and fluorescent hybrids, respectively comprising Au nanoparticles and CdS quantum dots, together with novel concepts of polymeric fiber-drawing by radiation forces.

Multilayer metal/metal-oxide diffractive structure for photonic temperature sensing

We designed and fabricated multilayer metal/metal-oxide surface relief diffractive grating structures by growing alternating Pt and SnO(x) layers. Optical interrogation at 633 nm reveals the temperature dependence of their reflection and transmission diffractive effects. This function is explored here in the context of a remote, spatially localized, photonic temperature sensing operation, achieving sensitivity of 10% per °C for the zeroth-order in the transmission mode. The experimental demonstration is found to be in good agreement with the results of rigorous coupled wave analysis of the composite metal/metal-oxide element.

Optimized design of remote point diffractive optical sensors

We present an optimization study of surface relief grating based sensors for use in optical remote point sensing. Our study includes the effects of geometrical characteristics of the photonic structure on the efficiencies of the first and second diffraction orders and the exhibited sensor responsivities of these orders. Our predictions are verified experimentally with measurements of surface relief gratings patterned by direct laser ablation on SiO2 sol–gel nanocomposite material with embedded NiCl2 nanocrystals developed for ammonia sensing.

Multianalytes Gas Sensors by Soft Lithography Induced Gratings with Sol-Gel and Copolymers Nanocomposites

In this work, the study and development of photonic sensors using as sensitive material new nanostructured inorganic/organic hybrid optical materials and polymers is presented. Particularly, the development of some diffractive optical sensors based on inorganic salts (NiCl2, CuCl2) dissolved in sol-gel matrices, or by utilizing a novel amphiphilic diblock copolymer material, namely, poly(styrene sulfonate-b-tert-butylstyrene) (SPS-b-PtBS)is discussed. Soft lithography techniques were employed for the fabrication of the diffraction gratings followed by proper tailoring of the sensing materials to optimize sensors’ response. The gas sensors were successfully tested in the detection of ammonia and aromatic hydrocarbons (benzene, toluene) achieving a relative low detectable analyte concentration (down to 30 ppm). The obtained results confirm the efficient and low cost implementation of point gas sensors for a variety of analytes. By further optimization of the fabrication technique for the diffraction gratings and by employing also customizable sensitive materials, this sensing approach could attract a lot of interest in various applications.

Direct ArF excimer laser microfabrication methods for polymer photonics

Direct laser ablative microfabrication methods are exploited in the development of polymer photonic structures. A dedicated experimental microfabrication facility using ArF excimer laser radiation at λ = 193 nm has been developed. It operates, in conjunction with soft-lithography, chemical post-processing and laser deposition methods, aiming to high quality materials processing. The flexibility of the alternative techniques developed here is demonstrated through the fabrication of exemplar photonic structures, including surface relief holograms, planar optical waveguide and polymer fiber structures. The versatility of the technique is verified by patterning geometrically complex and non-planar surfaces, towards a complete suite of alternative and flexible tools for fabricating polymer photonics.

Effect of 193 and 157 nm laser light illumination on the surface properties of TMOS-NiCl2 sol-gel derived material

Sol?gel tetramethoxyorthosilicate (TMOS) derived composite thin films comprising embedded NiCl2 nanoparticles, were illuminated and processed by 193 and 157?nm excimer laser radiation. The effect of different laser fluences of 193?nm and the number of 157?nm pulses on the material surface was studied. Atomic force microscopy imaging was used to evaluate the effects of the irradiation. It was found that surface morphology was modified in a controllable way, with physical and chemical properties strongly depending on the illumination conditions. Ablative ultraviolet laser surface processing is a generic single-step approach that can be applied successfully in composite materials. Applications involve micro/nanostructure formation for use in hybrid photonic and optoelectronic devices and other applications.