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Item type:Publication, Access status: without files , WDM-filters fabricated with hydrogenated amorphous silicon ring and racetrack resonatorsWavelength-division multiplexing filters are photonic key components for the distribution of multiple optical channels. Microring and racetrack resonators in add/drop configuration can be employed to perform the signal routing. In this work, low-loss hydrogenated amorphous silicon (a-Si:H) was employed as waveguide core material as it is transparent in the near infrared and can be fabricated at low costs and with low temperatures (<300°C) [1]. The advantages of using a high refractive index material like a-Si:H (n=3.48) as photonic layer are the low device footprint (<250μm 2 for eight channel ring resonators) and the large free spectral range (FSR) which supports multiple parallel channels and hence high optical bandwidth. Compared to SOI, the plasma deposition process is CMOS-backend compatible and the a-Si:H photonic layers can be directly deposited e.g. on top of integrated microchips at the last process steps. In this paper, four and eight channel WDM-filters which are based on cascaded racetrack and ring resonators are presented. The design, the fabrication, and the optical characterization are discussed. In order to match the desired filter characteristics the circumference length of each resonator was slightly tuned, whereas the gap separation between bus and ring waveguide were fixed. The photonic wire dimensions were chosen to be 480×200nm to ensure single-mode operation for the qTE-mode. The racetracks were designed with a radius of 20μm, a coupling gap of 300nm, and a straight coupling section of 6μm. The 5μm ring resonators were separated with a 150nm gap from the bus waveguides. The channel spacings were targeted to meet a 100-Ghz grid (0.8nm) which resulted in a successive length difference of 5.2nm for each resonator that was obtained by determining the group refractive index with FEM-simulations and numerical calculations. The measured FSRs of the racetracks are 4.6nm and 18nm for the ring resonators, respectively. Thus, four channel filters were fabricated with the racetracks and up to eight channel filters were realized with the microrings.Publicationtype: Conference Paper70 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On-chip sensing with high-Q amorphous silicon microdisk resonatorsIn this paper we present a low-loss hydrogenated amorphous silicon microdisk resonator which is employed for evanescent field refractive index sensing. The resonances of the whispering gallery modes have extinction ratios of <25dB and Q-factors up to 15000 when covered with aqueous solutions. The sensitivity of the microdisk sensor was experimentally determined to be 460nm/RIU for the qTM-mode with different concentrations of NaCl dispersed in deionized water. From the measurements the resonators intrinsic limit of detection was calculated to be LOD=3.3x10-4 and the minimum detectable amount of NaCl diluted in DI-water was determined to be 0.0375%. The early results prove that photonic microdisk resonators that are fabricated with low-loss hydrogenated amorphous silicon material can be applied in a variety of different areas for label-free lab-on-chip sensing, including chemical, medical and bio-sensing applications.Publicationtype: Conference Paper76 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Travelling wave resonators fabricated with low-loss hydrogenated amorphous siliconLow-loss hydrogenated amorphous silicon is employed for the fabrication of various planar integrated travelling wave resonators. Microring, racetrack, and disk resonators of different dimensions were fabricated with CMOS-compatible processes and systematically investigated. The key properties of notch filter ring resonators as extinction ratio, Q-factor, free spectral range, and the group refractive index were determined for resonators of varying radius, thereby achieving critically coupled photonic systems with high extinction ratios of about 20dB for both polarizations. Racetrack resonators that are arranged in add/drop configuration and high quality factor microdisk resonators were optically characterized, with the microdisks exhibiting Q-factors of greater than 100000. Four-channel add/drop wavelength-division multiplexing filters that are based on cascaded racetrack resonators are studied. The design, the fabrication, and the optical characterization are presented. © 2013 SPIE.Publicationtype: Conference Paper73 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Low-loss multilayer compatible a-Si:H optical thin films for photonic applicationsThis paper reports about hydrogenated amorphous silicon which can be employed as low-loss optical material for small footprint and cost-effective photonic integrated circuits. Basic waveguides, photonic wire based couplers, Mach-Zehnder interferometers, ring resonators and Mach-Zehnder assisted ring resonators were designed, fabricated, and optically characterised. The propagation loss of rib and photonic wire waveguides were determined to be 2 dB/cm and 5.3 dB/cm, respectively. The 90° bending losses of 5 μm curved photonic wires were determined to be 0.025 dB/90°. Three-dimensional tapers, which were fabricated without additional etching steps and were deposited on top of the fabricated photonic wires showed a net coupling loss of 4 dB/port. Multimode 3 dB-splitters were systematically investigated resulting in 49-51% splitting ratios. Mach-Zehnder interferometers that were realised with these splitters showed interference fringe depths of up to 25 dB for both polarisations. Compact ring resonators with 10 μm radius implemented as notch filters and in Mach-Zehnder coupled configurations provided extinction ratios of ≥20 dB and Q-factors up to 7500.Publicationtype: Journal Article132 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fabrication of freestanding SiO₂-membrane systems for thermo-optic adjusting of SOI photonic wiresPublicationtype: Journal Article25