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 SiO<sub>2</sub>-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.
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.
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 SiO<sub>2</sub>-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.