JEOS:RP - Journal of the European Optical Society Rapid publications
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All-optical modulation in a CMOS-compatible amorphous silicon-based device
Get PDFActive silicon photonic devices, which dynamically control the flow of light, have received significant attention for their use in on-chip optical networks. High-speed active silicon photonic modulators and switches rely on the plasma dispersion effect, where a change in carrier concentration causes a variation in the refractive index. The necessary electron and hole concentration change can be introduced either by optical pumping, or by direct electrical injection and depletion. We demonstrate a fast photoinduced absorption effect in low loss hydrogenated amorphous silicon (a-Si:H) waveguides deposited at a temperature as low as 190°C. Significant modulation (M% ~90%) occurs with a 1 mm-long device. We attribute the enhanced modulation to the significantly larger free-carrier absorption effect of a-Si:H. The complementary metal-oxide semiconductor (CMOS) compatible technology of a-Si:H could be considered as a promising candidate to enable an easy back-end integration with standard microelectronics processes
Wear recording at micro deep drawing tools with comparative digital holography
Get PDFWe present a method to record the wear on samples of micro deep drawing tools. The method is based on the basic idea of comparative holography and captures three dimensionally the surface of the tool in the initial state and compares it with used state after processing several parts. The comparison reveals scratches and other effects caused by wear. In an industrial environment the comparative method must compensate for linear and rotational displacement of the present tool with respect to the initial state. As a consequence to the single-step-measurement with sufficiently high illumination intensity the developed set-up can be made insusceptible against stray light and the method is capable of inline quality control during a production process in a micro deep drawing machine
Compact system design based on digital in-line holographic microscopy configuration
Get PDFWe present our study regarding a compact system design for cell counting and simultaneous 3D imaging, based on digital in-line holographic microscopy configuration. The system is built around the known experimental configuration which includes a pinhole but we also investigate the configuration with a monomode fiber as a light source. Considered samples consist of a very low concentration of cells in flow in a microchannel. The main challenge in our design is to obtain the digital hologram of one cell on a regular video camera sensor in proper resolution conditions, as opposed to the usual configurations where the aim is to visualize a large area. This fact is possible with shorter distances between pinhole and sample and with pinholes with diameters slightly larger than 1micron. These can now be realized by considering the microtechnological processes for microchannel and pinhole fabrication on the same substrate with high refractive index - to increase the numerical aperture of the system The geometrical parameters are established after the numerical analysis of the diffracted field from a single cell and of the entire system numerical aperture values
Scattering anisotropy measurements in dental tissues and biomaterials
Get PDFUnderstanding the behaviour of light propagation in biological materials is essential for biomedical engineering and applications, and even more so when dealing with incoming biomaterials. Many methods for determining optical parameters from biological media assume that scattered light is isotropically distributed over all angles. However, an angular dependence of light scattering may exist and affect the optical behaviour of biological media. The present work seeks to experimentally analyze the scattering anisotropy in different dental tissues (enamel and dentine) and their potential substitute biomaterials (hybrid dental-resin, nano-filled composite, and zirconia ceramic) and comparatively study them. Goniometric measurements were made for four wavelengths in the visible range, allowing a spectral characterization of the materials studied. Previously, for each material, measurements were made with two different sample thicknesses at the same wavelength, checking the behaviour of the angular scattering profile. The asymmetry of experimental phase functions was considered in the recovery of the scattering anisotropy factor. The results demonstrate that the thicker sample yielded a less forward-directed scattering profile than did the thinner sample. The biomaterials analysed show angular scattering comparable to those of the tissues that they may replace. Comparisons can be made by virtue of the low uncertainties found
Fiber optic sensors for precursory acoustic signals detection in rockfall events
Get PDFTwo fiber optic sensors (FOSs) for detection of precursory acoustic emissions in rockfall events are addressed and experimentally characterized. Both sensors are based on interferometric schemes, with the first one consisting of a fiber coil used as sensing element and the second one exploiting a micro-machined cantilever carved on the top of a ferrule. Preliminary comparisons with standard piezo-electric transducers shows the viability of such FOSs for acoustic emission monitoring in rock masses
Spatially encoded localized wavepackets for ultrafast optical data transfer
Get PDFArrays of highly localized wavepackets enable for an efficient multichannel processing of optical data because of their undistorted propagation in space and time domain. Reconfigurable arrangements of supercollimated and temporally nondiffracting few-cycle pulses were generated by microaxicons programmed into the phase map of a liquid-crystal-on-silicon spatial light modulator. As an example, the transfer of quick response code data with few-femtosecond pulses of a Ti:sapphire laser oscillator is reported. Data encoding in beam arrays via maps of temporal and spectral moments is proposed
Four-Wave-Mixing in Zirconia-Yttria-Aluminum Erbium Codoped Silica Fiber
Get PDFThe generation and characterization of the Four-Wave-Mixing (FWM) effect in an Erbium Doped Zirconia-Yttria-Alumino Silicate Fiber (EDZF) is described. The EZDF is fabricated from a conventional silica preform by Modified Chemical Vapour Deposition (MCVD) and also solution doping to add glass modifiers and nucleating agents, with the resulting preform annealed and drawn into a fiber strand with a 125 ± 0.5 µm diameter. A 4 m long EZDF with a propagation loss of 0.68 dB/m and an erbium concentration of 3000 ppm is used to investigate the FWM effect. The FWM power levels are measured to be approximately - 45 dBm at a region of 1565 nm and show good agreement with the theoretical predicted values. A non-linear coefficient of 14 W-1km-1 is also measured, along with chromatic and slope dispersion values of 28.45 ps/nm.km and 3.63 ps/nm2.km, which agree with the predicted values. The fabricated EZDF has many potential applications utilizing the FWM effect, including the generation of multi-wavelength outputs
High NA diffractive array illuminators and application in a multi-spot scanning microscope
Get PDFArray illuminators generating spots with high NA at high efficiency are presented. They are designed via application of high-NA scalar optics methods, and implemented as periodic binary phase structures. These array illuminators are used in a multi-spot scanning microscope for scanning large sample areas at high resolution with a relatively high resolution
Broadband photonic crystal antireflection
Get PDFBroadband antireflection layer have been fabricated by two dimensional (2D) photonic crystals (PCs) with tapered pillars on Si substrate. These PCs have been produced by interference lithography and reactive ion etching (RIE) techniques. The effect of depth and filling factor (FF) of the PCs on the reflectance magnitude and bandwidth has been investigated. The obtained reflectance was less than 1% in the broad spectral range from 400 to 2100 nm. Our numerically simulation shows the PC pillars slope has essential effect in the reduction of the reflection. However, our results show that the existence of RIE grasses in the PCs which are created in the RIE process have not been influenced in the performance of the antireflection layer which leads to simpler fabrication process
Spectral interferometry-based chromatic dispersion measurement of fibre including the zero-dispersion wavelength
Get PDFWe report on a simple spectral interferometric technique for chromatic dispersion measurement of a short length optical fibre including the zero-dispersion wavelength. The method utilizes a supercontinuum source, a dispersion balanced Mach-Zehnder interferometer and a fibre under test of known length inserted in one of the interferometer arms and the other arm with adjustable path length. The method is based on resolving one spectral interferogram (spectral fringes) by a low-resolution NIR spectrometer. The fringe order versus the precise wavelength position of the interference extreme in the recorded spectral signal is fitted to the approximate function from which the chromatic dispersion is obtained. We verify the applicability of the method by measuring the chromatic dispersion of two polarization modes in a birefringent holey fibre. The measurement results are compared with those obtained by a broad spectral range (500-1600 nm) measurement method, and good agreement is confirmed