In this paper we will present two technological processes necessary to experimentally obtain diffractive optical elements (DOE) operating in reflection which generate optical beams presenting orbital angular momentum. This class of DOE, also known as spiral phase plates (SPP), are three-dimensional structures consisting in disks where the variation of their thickness is directly proportional with the azimuthal angle Φ. In this case a beam of light applied on the SPP surface acquires an angular orbital momentum (OAM) and a vortex – like configuration. The first technique is the 3D electron beam lithography (EBL). The materials utilized in this case are the positive electronresist PMMA 35 K which has a deposition thickness of 500 nm and the negative electronresist SU8. To obtain the three dimensional structure, the PMMA and SU-8 films were configured by different exposure doses such that after development process each exposure corresponds to a defined thickness of the electronresist. The calibration curve between exposure dose and the height of the structure was determined. The second technique investigated here is photolithography. In this case a photoresist layer was exposed through a mask presenting regions with various levels of transmittance in order to obtain different levels of heights.
This work presents a numerical analysis using the finite difference time domain (FDTD) method of the optical
properties (modal characteristics, dispersion, propagation length, and optical confinement) exhibited by a particular class of plasmonic waveguides named dielectric loaded surface plasmon (DLSP) devices. The DLSP systems investigated here consist in ridge like waveguides realized from PMMA with typical cross section areas of 100x100 nm configured on the top of a silver substrate. The FDTD simulations show that in the visible range an optimal compromise between a high degree of optical confinement and an adequate propagation length of around 10 μm can be achieved. This indicates that in this spectral range the proposed DLSP waveguides could possesses applications in various sensing and optical signal processing devices.
In this paper we present simulation of transmission / reflection spectra of polymeric rectangular and hexagonal
photonic crystals (PC) as well as the propagation of radiation in a hexagonal PC - based waveguide. The polymeric PC
are periodic structures consisting in square arrays of holes configured in suspended membranes of PMMA with different
diameters and pitch (100 nm diameter with 500 nm, respectively 800 nm pitch; 200 nm diameter with 500 nm pitch; 400
nm diameter with 700 nm pitch).
For fabrication, we propose the bi-layer EBL technique based on simultaneous patterning of a bottom
sacrificial layer (LOR 5A - Microchem Corporation) and a positive electron resist (PMMA of different molecular
weights). Characterization of nanostructures was performed using SEM imaging and AFM measurements .
In this paper we describe a traceable to the meter standard method to measure the height of an artifact used as a calibrator for observation instruments in nanotechnologies and nanosciences. The artifact is a grating specially manufactured so that its features (height, pitch, width, wall angles) are highly uniform across its area. A Linnik microscope designed for longitudinal (vertical) measurements using the principle of white light interferometry was used to determine the height of the grating. To insure the traceability of the measurements a laser source of known wavelength was used and the measurements obtained using white light were calibrated to it. The experimental data was statistically analyzed and the measurement precision was estimated to be in the range of nanometers. The data were compared with the results obtained using the TIC method with a Carl Zeiss microscope.
This paper reports fabrication methods of polymer-based micro/nano optical structures based on replica molding.
Various molds have been used: polymer, silicon, and SiO2-based. Different types of treatment and release agent were
investigated in order to achieve an optimum demolding. Diffractive optical elements, micro-lenses and antireflective
layers have been obtained in commercial or doped polymers with controlled refractive index. The quality of the
replication was investigated using optical microscopy, SEM, profilometry and functional tests. The micro-optical
components can be transferred onto silicon silicon chip with photodetectors, or photonic integrated circuits using
Theoretical and numerical studies regarding the possibility of using simple laterally coupled microring resonators as
refractometers are presented in this work. We have considered a core waveguide layer with its refractive index varying in the range 1.5...2 deposed on the silicon dioxide thermal grown layer. The waveguide width is set for achieving
single-mode condition at 1.55 &mgr;m radiation wavelength. The aim of this work is finding the optimum configurations for
microring resonators based refractive index sensors.
Poly (vinyl alcohol) [PVA] is a photo-induced cross-linking polymer, water-soluble,
biocompatible, used in holography, nonlinear optics, as tissue engineering scaffolds and as polymer
matrices for enzymes immobilization. PVA has been investigated for use as binder polymer in optical
waveguides for sensor applications. The Y-shaped waveguides is composed of a buffer layer (lower
refractive index) - SiO2, a core layer (higher refractive index) - PVA doped for the refractive index and
sensibility increasing and a cladding layer (lower refractive index) - an other polymer. The light
propagation in doped PVA waveguides represents the sensing element of the sensor. The preliminary
results suggest that doped PVA polymers are promising for optical (bio)chemical sensors; the processes
used to make them, represent environmentally friendly technology.
Air pollution monitoring needs real-time measurement systems for low pollutant concentration levels. The authors
have designed and manufactured an experimental integrated chemo-optical sensor on silicon containing a sol-gel
layer, a silicon nitride waveguide and a silicon photodiode. This sensor was included in a measurement system, which
has its own microcontroller for data acquisition and an autonomous power supply. The measured data are calculated
and managed when the microcontroller is serially connected to the computer, dedicated software being performed. In
this way, the "classical" laboratory equipment for air pollution measurements can be replaced by an autonomous real-time measurement system.
Microring resonators will be one of the most important components of the next generation of optical communications. In this work, we have analyzed from theoretical perspective a new proposed microring resonator structure based on the wafer-bonding technique which implies the vertical coupling between the passive bus waveguide and the active ring resonator. We have investigated the possibility to obtain the monomode operation of the active ring waveguide for certain ring radius values by the selective attenuations of the higher order modes and the obtaining of the desired coupling efficiency by varying the technological parameters like the layers thickness, etching depth, bus waveguide width and the offset (misalignment between the ring and the bus waveguide). Depending on the fabrication method, the misalignment between the ring resonator and the bus waveguide may vary within a significant range. Therefore, we considered a much wider bus waveguide in the coupling region in order to minimise the effects of misalignment.
In this paper we present the design and the experiments performed to obtain a micromechanical voltage tunable Fabry-Perot interferometer integrated with a p-n photodiode on a silicon substrate. It can be used as a voltage tunable filter for the input radiation or as a voltage controlled attenuator to regulate the light from a monochromatic source. Different solution have been analyzed and experimented. The top mirror of the Fabry-Perot cavity is a doped poly-Si or Au/SiO2 movable membrane, electrostatically actuated, obtained using Si micromachining. A complex design process was performed: optical, electomechanical and technological. All these phases were performed interactively. Different materials were considered in order to perform an optimum design. Experimental micromachined interferometers were obtained using two techniques: (1) surface micromachining, and (2) anisotropic etching of (111)-oriented Si wafers, combined with an isotropic pre-etching step. These processes were optimized and matched to the photodiode fabrication process. Monolithic integrated interferometers coupled to p-n photodiodes were obtained.
This paper presents the experiments we have performed to obtain freestanding SiO2 and c-Si based microphotonic components by anisotropic wet etching of silicon (111) wafers. The process is simpler than surface micromachining. It requires only one grown or deposited layer and one mask for SiO2 structure, or two masks for c-Si structures. Moreover, the technique provides plan-parallel microstructure with very flat (111) surfaces, useful for photonic components like micromirrors and waveguides. Movable SiO2 and silicon-based micromirrors and waveguides with very smooth surfaces were obtained by anisotropic etching in a KOH solution combined with plasma etching. The possible applications of SiO2 and silicon based freestanding structures include devices for optical communications and bio- or chemo-optical sensors.
This paper presents the experiments we have performed to obtain microphotonic components using a new technique: the anisotropic wet etching of Si <111>-oriented wafers. The anisotropic etching was combined with an isotropic pre-etch step, followed or not by sidewall passivation. The influence of the mask orientation and layout on the shape and size of the etched cavity was studied and then the masks and the technological process for fabrication of S3N4/SiO2 and c-Si freestanding structures were established. Movable Si3N4 micromirrors, SiO2 or c-Si waveguides were obtained using a low-cost technological process. These components can be further integrated with optoelectronic devices on a silicon substrate.
The fabrication process of c-Si waveguides based on the anisotropic etching of Si<111> oriented wafers is described. To obtain c-Si waveguides, the anisotropic etching was combined with an isotropic pre-etch step to a depth equal to the thickness of the final c-Si freestanding structure, followed by side-wall passivation. In addition, a second pre-etching step was performed to establish the depth of the air gap that acts as the bottom cladding of the waveguide. Freestanding c-Si waveguides with very smooth surfaces were obtained by anisotropic etching in a KOH solution. By using a Si3N4/SiO2 mask layer, double waveguides were obtained. The possible applications of c-Si based free standing structures include devices for optical communications and evanescent-wave bio- or chemical sensors.
The development of MEMS microsystems can be increased by integration of optically active parts. Micromachining techniques allow the fabrication of monolithically integrated Fabry-Perot microcavities, avoiding hybrid assembly technique, which is a combination of etching and wafer bonding. These microcavities can be used as sensors, as modulators or as tunable optical filters. We investigated different mirror materials: silicon nitride and polysilicon and different sacrificial layers: polysilicon and phosphorus doped silicon dioxide (PSG), using LPCVD and CVD techniques. Different arrays and shapes for the top mirror, which is movable, were analyzed in order to establish a structural material with low tensile stress. The optical constants were determined by spectrophotometric methods. Experimental data and simulations were compared.
We realized different types of optoelectronic integrated circuits by integrating on the same silicon chip: photo detectors, linear or logic electronic circuits, waveguides, coupling elements. This paper present the design, modeling and experimental realization of these components, underlining the original approaches and results. Special structures of photo detectors were designed, in order to allow optical coupling with waveguides and monolithic integration with electronic and photonic circuits. Original models for these photo detectors were developed. The electronic circuits we realized, unlike those reported in literature, can operate at very low input currents. Also new materials and processes were studied and experimented in order to improve the component performance. Specific technologies for optoelectronic circuits, compatible with either CMOS or bipolar processes, were established by analyzing the relationships between the technological parameters and circuit characteristics. Also the matching with waveguides and micro mechanical structures technologies was analyzed and experimented, as the aim of our research activity was to realize different types of micro-electro- mechanical systems for sensor applications.
The paper presents the integration ont he same chip of: Mach-Zehnder interferometers and Y junctions based on SiON waveguides, 3D movable micromechanical structures, optical couplers and photodetectors for optical read-out. The SiON low loss optical waveguides were fabricated by LPCVD processes, compatible with CMOS technology. The diaphragms, used for pressure sensing, obtained by p+ etch stop techniques, were placed under the sensing arm of the interferometer. The cantilevers, used in micromechanical resonators were manufactured by front side micromachining. The optical waveguides were coupled with different types of photodetectors, for optical read-out. Also experiments for hybrid integration of an emitting device have been performed. We used an AlGaAs emitting diode, with high edge emission, mounted in a silicon groove, on the same wafer with the sensor. The lateral emitted light is coupled in the waveguide. One of the main problems that had to be solved will be the matching of all the involved technologies. The result of our research is the demonstration of the compatibility between the technological process involved and the possibility of integration on the same silicon substrate of different components: waveguides, photodiodes, emitting devices, 3D movable microstructures in order to realize intelligent microsensors.
Integrated optics on silicon gives the opportunity to obtain microsystems for optical communications or sensor applications on one silicon chip. In all types of applications it is necessary to connect the waveguides to the photodetectors to transform the optical signal in an electrical signal. We have designed an opto-FET with a special structure that allow the optical coupling to a waveguide. A 3-D model was developed for the system: opto-FET-coupler-waveguide. The model takes into account two effects of the incident illumination: the variation of channel conductivity due to the carrier generation; the variation of channel depth due to the photovoltaic effect across the channel-gate junction. Also we studied the channel depth variation along the channel length (due to the potential variation) and along the channel width (due to the exponential decrease of optical power). The most important conclusion of the model is: in case of leaky-wave coupling of the opto-FET to a waveguide, the dependence of the photocurrent on optical power is practically linear, while in the case of uniform illumination it is logarithmic. The model was verified on a circuit integrated on silicon.