J. Amthor

Amorphous Silicon 3-D Tapers for Si Photonic Wires Fabricated With Shadow Masks

Three-dimensional taper structures made from plasma-enhanced chemical vapor-deposited hydrogenated amorphous silicon were evaluated by calculating the deposition profiles with a line-of-sight model and the corresponding mode profiles with a full-vectorial mode solver. The tapers were fabricated with shadow-masks made from KOH-etched Si wafers, and with the tapers light was coupled into 500-nm-wide photonic wires from lensed fibers.

Amorphous waveguides for high index photonic circuitry

Photonic wires, channel and rib waveguides as well as tapers were fabricated with amorphous silicon showing low propagation loss. Material analysis and RTA was carried out in order to tune the refractive index post deposition.

Amorphous silicon spot-size converters fabricated with a shadow mask

A rib-like spot-size converter was fabricated with a KOH etched shadow mask. The improvement in coupling and an expansion of the spot-size were evaluated with simulations and confirmed by transmission loss measurements.

Fabrication of Freestanding SiO

This work describes the design and fabrication of an electrostatically deflectable SiO2-membrane system with low-loss silicon-on-insulator (SOI) photonic wires. The photonic wires have been tuned thermo-optically and elasto-optically. A 10-mW thermo-optic switch is presented.

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We report about the fabrication and optical characterization of high Q hydrogenated amorphous silicon microdisk resonators in telecommunication C-band. High resonance peaks of >;30dB were achieved. Intrinsic Q-factors of 0.9×106 were measured with >;10dB extinction for qTM-modes.

-Membrane Systems for Thermo-Optic Adjusting of SOI Photonic Wires

Contact lithography with i-line (365 nm) or DUV (248 nm) is widely used in laboratories for prototyping. The achievable line width of 300 nm is sufficient for photonic wires, but a process with larger line width is more controllable. The sidewall roughness induced by the lithography and by the following etching steps results in high optical losses. Thermal oxidation is known to smoothen the silicon surface. The oxidation also consumes silicon, so that the photonic wire will shrink and a wider lithography linewidth can be applied. The silicon dioxide is used as a low loss cladding, which further reduces the refractive index contrast, so that the remaining roughness causes less losses. Single mode silicon nanowires with 500nm by 200nm cross section and optical losses of 2dB/cm were produced. The index contrast is still high enough for small bending radii for highly integrated photonic devices. Sharp branches used in Y-couplers can not be fabricated by this oxidation technique, due to the waveguide shrinkage. 3dB-couplers are easily realized by multimode interference (MMI)-couplers, with the output branches sufficiently apart. Using such couplers, Mach-Zehnder interferometers were fabricated. For electric contacts, the SiO2-cladding is locally removed and ZnO and Al electrodes are applied. The c-axis of sputtered ZnO grows preferentially perpendicular to the surface, which allows to utilize the electro optic effect.

High Q-factor hydrogenated amorphous silicon microdisk resonators

Low-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 20 dB 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.

Tunable silicon photonic wires fabricated by contact lithography and thermal oxidation

Silicon-on-Insulator (SOI) photonics has become an attractive research topic within the area of integrated optics. This paper aims to fabricate SOI-structures for optical communication applications with lower costs compared to standard fabrication processes as well as to provide a higher flexibility with respect to waveguide and substrate material choice. Amorphous silicon is deposited on thermal oxidized silicon wafers with plasma-enhanced chemical vapor deposition (PECVD). The material is optimized in terms of optical light transmission and refractive index. Different a-Si:H waveguides with low propagation losses are presented. The waveguides were processed with CMOS-compatible fabrication technologies and standard DUV-lithography enabling high volume production. To overcome the large mode-field diameter mismatch between incoupling fiber and sub-μm waveguides three dimensional, amorphous silicon tapers were fabricated with a KOH etched shadow mask for patterning. Using ellipsometric and Raman spectroscopic measurements the material properties as refractive index, layer thickness, crystallinity and material composition were analyzed. Rapid thermal annealing (RTA) experiments of amorphous thin films and rib waveguides were performed aiming to tune the refractive index of the deposited a-Si:H waveguide core layer after deposition.

Travelling wave resonators fabricated with low-loss hydrogenated amorphous silicon

In 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.

Amorphous Silicon as High Index Photonic Material

In this work a thermo-optic switch with very low power consumption of less than 1 mW is presented. The switch consists of a Mach-Zehnder-Interferometer whose arms are placed on free-standing SiO2-membrane cantilevers. The waveguides are monomode nanowires fabricated by DUV-contact lithography having losses of 2 dB/cm. Additionally, a membrane-system to tune the nanowires elasto-optically is shown.