O. Horn

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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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.

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

We present a novel quartz cantilever for frequency-modulation atomic force microscopy (FM-AFM) which has three electrodes: an actuating electrode, a sensing electrode, and a ground electrode. By applying an ac signal on the actuating electrode, the cantilever is set to vibrate. If the frequency of actuation voltage closely matches one of the characteristic frequencies of the cantilever, a sharp resonance should be observed. The vibration of the cantilever in turn generates a current on the sensing electrode. The arrangement of the electrodes is such that the cross-talk capacitance between the actuating electrode and the sensing electrode is less than 10(-16) F, thus the direct coupling is negligible. To verify the principle, a number of samples were made. Direct measurements with a Nanosurf easyPPL controller and detector showed that for each cantilever, one or more vibrational modes can be excited and detected. Using classical theory of elasticity, it is shown that such novel cantilevers with proper dimensions can provide optimized performance and sensitivity in FM-AFM with very simple electronics.

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.

Three-electrode self-actuating self-sensing quartz cantilever: Design, analysis, and experimental verification

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.

Amorphous Silicon as High Index Photonic Material

The elasto-optic and the thermo-optic effect in silicon nanowires is demonstrated using Mach-Zehnder interferometers. The nanowires are placed on undercut SiO2 membranes which can be deflected electrostatically.

Thermo-optic and elasto-optic tuning of silicon nanowires

An optic switch of SOI-nanowires with a very low power consumption of less than 1 mW is presented. The nanowires are placed on freestanding electrostatically deflectable SiO2-membranes to tune them thermo-optically and elasto-optically.