New silicon photonics integration platform enabled by novel micron-scale bends

Even though submicron silicon waveguides have been proposed for dense integration of photonic devices, to date the lightwave circuits on the market mainly rely on waveguides with micron-scale core dimensions. These larger waveguides feature easier fabrication, higher reliability and better interfacing to optical fibres. Single-mode operation with large core dimensions is obtained with low lateral refractive index contrast. Hence, the main limitation in increasing the level of integration and in reducing the cost of micron-scale waveguide circuits is their mm- to cm-scale minimum bending radius. Fortunately, single-mode rib waveguides with a micron-scale silicon core can be locally transformed into multi-mode strip waveguides that have very high lateral index contrast. Here we show how Euler spiral bends realized with these waveguides can have bending radii below 10 {\mu}m and losses below 0.02 dB/90{\deg} for the fundamental mode, paving way for a novel densely integrated platform based on micron-scale waveguides.Comment: 14 pages, 29 Refs., 5 Fig

Microphotonic silicon waveguide components

This thesis describes the design, simulation, fabrication and characterisation of microphotonic silicon waveguide components on silicon-on-insulator (SOI) substrates. The focus is on approximately 10 μm thick and single-moded (SM) silicon rib waveguides. In particular, simulation results are given for straight and bent Si waveguides, directional couplers (DCs), thermo-optically (TO) modulated Mach-Zehnder interferometers (MZI), and waveguide gratings. A new analytical SM condition for Si rib waveguides is proposed and the development of a new grating simulation algorithm is reported. The theoretical part of the work also involves inventions relating to multi-step patterning of Si waveguides, modulation of interferometric devices, and measurement of polarisation axes from waveguides and polarisation maintaining (PM) fibers. Clean room processing of waveguide chips is briefly described. Main process steps are photolithography, electron-beam lithography, thermal oxidation, oxide deposition, oxide dry etching and Si dry etching. Post-processing of the chip is also reported, including dicing, polishing, anti-reflection (AR) coating, fiber pigtailing and wire bonding. The development of fabrication processes for multi-step patterning, waveguide gratings and photonic crystal waveguides is reported, although the optical characterisation of devices based on these three processes is not included in the thesis. Experimental results are given for Si rib waveguides with different thicknesses (H) and widths (W). The minimum fiber coupling loss with H = 9 μm was 1.3 dB/facet without an AR coating. The AR coating reduced the coupling loss by 0.7-0.8 dB/facet. Minimum propagation loss for a 114 cm long waveguide spiral with H = 9 μm and W = 7 μm was 0.13 dB/cm. With H = 9 μm, the birefringence varied from 0.00063 to 15 dB. Furthermore, fast modulation with 15 dB extinction ratio (ER) is reported for TO MZI switches by using both traditional (10 kHz) and novel (167 kHz) modulation methods. Rise and fall times for single switching operations were pushed below 750 ns with 9 dB ER. The setups and methods used in measurements are described in detail, including a novel method for measuring the polarisation axes of waveguides and PM fibers.reviewe

Bilateral Vestibular Hypofunction in Quantitative Head Impulse Test : Clinical Characteristics in 23 Patients

OBJECTIVE: To explore clinical features of patients with bilateral vestibular hypofunction (BVH) verified in motorized head impulse test (MHIT). MATERIALS and METHODS: We examined clinical records of 23 adult patients (10 males and 13 females), whose gain of the vestibulo-ocular reflex in the MHIT was bilaterally lowered. Fifteen of 62 unilateral cochlear implant (CI) recipients routinely tested both pre-and postoperatively with the MHIT had BVH. Eight of 198 vestibular outpatients selected to the MHIT due to clinical causes had BVH. Clinical characteristics and a questionnaire regarding current sensations were analyzed. RESULTS: The mean gain +/- SD in the MHIT was 0.26 +/- 0.17 on the right and 0.26 +/- 0.14 on the left side. The mean gain in the CI recipients did not differ from that of vestibular outpatients (p>0.05). All outpatients with BVH suffered from oscillopsia, whereas only 46% of CI recipients experienced oscillopsia (p=0.048). Instability was more prominent (p=0.004) and quality of life further decreased (p=0.012) among vestibular outpatients compared with CI patients. Most common etiology for the BVH was meningitis. Other causes were either sudden or progressive loss of labyrinthine function, bilateral Meniere's disease, and ototoxicity. CONCLUSION: BVH is rare even in a specialized clinic. Vestibular outpatients were more disabled than CI recipients with the BVH.Peer reviewe

On classification in the case of a medical data set with a complicated distribution

Abstract In one of our earlier studies we noticed how straightforward cleaning of our medical data set impaired its classification results considerably with some machine learning methods, but not all of them, unexpectedly and against intuition compared to the original situation without any data cleaning. After a more precise exploration of the data, we found that the reason was the complicated variable distribution of the data although there were only two classes in it. In addition to a straightforward data cleaning method, we used an efficient way called neighbourhood cleaning that solved the problem and improved our classification accuracies 5–10%, at their best, up to 95% of all test cases. This shows how important it is first very carefully to study distributions of data sets to be classified and use different cleaning techniques in order to obtain best classification results.Peer reviewe

The Classification of Valid and Invalid Beats of Three-Dimensional Nystagmus Eye Movement Signals Using Machine Learning Methods

Peer reviewe

Low-error and broadband microwave frequency measurement in a silicon chip

Instantaneous frequency measurement (IFM) of microwave signals is a fundamental functionality for applications ranging from electronic warfare to biomedical technology. Photonic techniques, and nonlinear optical interactions in particular, have the potential to broaden the frequency measurement range beyond the limits of electronic IFM systems. The key lies in efficiently harnessing optical mixing in an integrated nonlinear platform, with low losses. In this work, we exploit the low loss of a 35 cm long, thick silicon waveguide, to efficiently harness Kerr nonlinearity, and demonstrate the first on-chip four-wave mixing (FWM) based IFM system. We achieve a large 40 GHz measurement bandwidth and record-low measurement error. Finally, we discuss the future prospect of integrating the whole IFM system on a silicon chip to enable the first reconfigurable, broadband IFM receiver with low-latency.Comment: 13 pages, 7 figure