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.
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
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.
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 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.