Timo Lipka

Technische Universität Hamburg | TUHH · Institute of Microsystem Technology

Optical microcavity sensors are ideally suited for the development of optofluidic lab-on-chips and appear promising for application fields like drug development, bio-/chemical analyses, and medical diagnostics. In particular, planar integrated and low-footprint photonic sensors that are combined with microfluidics on wafer scale are attractive due...

The large-scale and low-cost fabrication of high sensitivity sensors for the real-time detection of biochemicals and molecular substances opens up new opportunities in the areas of bioanalytic screening and medical diagnostics. Planar integrated photonic resonators that can be fabricated with a low footprint, in spatial and wavelength multiplexed a...

We report on a lab-on-chip (LoC) sensor system based on integrated-optical resonators. The photonic components were realized in CMOS-process compatible amorphous silicon (a-Si:H) and the microfluidic interface enabling directed analyte transport was fabricated with soft-lithography technology. The developed sensor features optical resonators with d...

Low temperature deposited hydrogenated amorphous silicon (a-Si:H) is a promising material to fabricate compact photonic-electronic integrated circuits (PICs) in multiple layers. However, high refractive index contrast (HIC) photonic circuits are challenging in fabrication and even smallest deviations of the material quality or manufacturing have hu...

We present integrated-optic building blocks and functional photonic devices based on amorphous silicon-on-insulator technology. Efficient deep-etched fiber-to-chip grating couplers, low-loss single-mode photonic wire waveguides, and compact power splitters are presented. Based on the sub-μm photonic wires, 2 × 2 Mach-Zehnder interferometers and add...

We present energy-efficient optical add/drop multiplexers based on low-loss a-Si:H. The power for non-uniformity compensation is studied and the reduction by trimming is analyzed, resulting in record low metrics of sub-1mW consumption per 8-channel multiplexer.

Optical multiplexers are key components of modern data transmission systems that have evolved from long-haul fiber communication applications down to the photonic interconnect level on-chip which demand high bandwidths and low-power photonic links on small area. We present compact, energy-efficient, and high bandwidths optical add/drop multiplexers...

Large-scale integrated silicon photonic circuits suffer from two inevitable issues that boost the overall power consumption. First, fabrication imperfections even on sub-nm scale result in spectral device non-uniformity that require fine-tuning during device operation. Second, the photonic devices need to be actively corrected to compensate thermal...

A method to compensate for fabrication tolerances and to fine-tune individual photonic circuit components is inevitable for wafer-scale photonic systems even with most-advanced CMOS-fabrication tools. We report a cost-effective and highly accurate method for the permanent trimming of hydrogenated amorphous silicon photonic devices by UV-irradiation...

The precise detection of chemicals and biomolecules is of great interest in the areas of biotechnology and medical diagnostics. Thus, there is a need for highly sensitive, small area, and low-cost sensors. We fabricated and optically characterized hydrogenated amorphous silicon photonic resonators for label-free lab-on-chip biosensors. The sensing...

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-f...

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 experimental...

Wavelength-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 transparen...

The a-Si:H deposition process is systematically investigated in intrawafer and wafer-to-wafer experiments. Photonic ring resonators were studied within-chip and chip-to-chip, showing ±1.2nm resonance peak variations and deviations of 0.25% (intrachip) and 0.9%(interchip) for group index and FSR.

This 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 optical...

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.

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.

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.

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....

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-syste...

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...

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.

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.

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.

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...

In this paper a simple contact lithography with i-line or DUV is used for the production of photonic wires, which are additionally smoothed and shrunk by thermal oxidation.

Sophisticated electronic devices comprising sensitive microelectronic components have been installed in the close proximity of the 720 MeV superconducting electron linear accelerator (linac) driving the FLASH (Free Electron Laser in Hamburg), presently in operation at DESY in Hamburg. Microelectronic chips are inherently vulnerable to ionizing radi...