Wolfgang Vogel

Abstract

A compact integrated and high-efficiency polarization mode interferometer in the 220-nm silicon-on-insulator platform is presented. Due to the operation with two polarization modes in a single waveguide, low propagation losses and high sensitivities combined with a small footprint are achieved. The designed and fabricated system with a 5-mm-long sensing region shows a measured excess loss of only 1.5 dB with an extinction ratio up to 30 dB, while its simulated homogeneous bulk sensitivity can exceed 8000 rad/RIU. The combination with a 90°-hybrid readout system offers single wavelength operation with unambiguousness for phase shifts up to 2pi and constant sensitivity.

Abstract

Fluorescence-based assays are widespread in the life sciences and used for instance in diagnostics, cell sorting, or to resolve cellular and tissue structures. Optofluidic engineering can help improve such assays, especially when sensitivity or throughput are important. Towards such optofluidic integration we combine a silicon nitride photonic chip including grating couplers for exciting and detecting fluorescence signals out of plane with a soft lithography based microfluidic chip. Through this configuration both the microfluidics and the optics systems are located at different levels. Considering an arrangement of grating couplers for excitation and detection as a sensor module, such modules can be placed multiple times below the microfluidic channels. This is advantageous for implementing complex lab-on-a-chip applications used in point-of-care-testing devices (POCT) or time-resolved analysis of biomolecular dynamics. As a proof of principle, different concentrations of fluorescein (10~µM up to 10~mM) in deionized water are investigated using an excitation-wavelength of 405~nm (-7~dBm laser power). The fluorescent solutions are pumped through a simple microfluidic channel, excited through a grating coupler of about 11~µm x 14~µm in size and detected through a glass fiber near the microfluidic channel and vice versa. The signal detection is done by a spectrometer. By exciting through a grating coupler and recording the fluorescence emission through a glass fiber a limit of detection (LOD) of 73~µM is measured. The spectral location of the emission maxima varies from 518~nm to 526~nm for concentrations of 100~µM to 10~mM, respectively. Overall, the fluorescence detection through grating couplers in microchannels is demonstrated. This can be considered as a first step towards a fully integrated optofluidic chip interface for high density fluorescence assay multiplexing.

Abstract

In photonic integrated circuits grating couplers are commonly used to establish an efficient and stable fiber-to-chip link. However, the actual coupling efficiency of a fiber-to-chip interface depends strongly on the used wavelength and exhibits a maximum at a distinct target wavelength, determined by grating design parameters. In this paper, an enhancement of the optical bandwidth of silicon grating couplers by adding integrated dispersive structures is discussed. These are realized by single layers, prism-like geometries and additional SiN gratings. Theoretical considerations for a bandwidth-enhancement by dispersive layers are performed and applied to an existing grating coupler design. A simulated 1dB-bandwidth of up to 90 nm at a maximum efficiency of -0.65 dB in the C-band could be achieved, which is an enhancement to a factor of about 2 compared with the original coupler design.

Abstract

We present a theoretical study of 1xN optical routing networks consisting of generalized Mach-Zehnder switches, that are based on multimode interferometers. This work gives a brief overview of the necessary phase conditions and resulting phase shifter requirements in the 1xN switches. Using the presented approach as 1x4 switch with parallel phase shifters, a 20\% phaseshifter-loss reduction becomes possible.

Abstract

The design of a highly efficient fiber-to-chip link using a silicon grating coupler with an enhanced optical bandwidth in a 250 nm silicon-on-insulator platform is presented. Consisting of a standard grating coupler with backside mirror and a special dispersive coating, this link offers a simple design and an enhanced 1-dB-bandwidth. Special attention is paid to the influence of the coatingdispersion on bandwidth. Optical simulations demonstrate the performance of the fiber-to-chip links at a wavelength of about 1550 nm and for the transverse electric waveguide mode.

Abstract

Coupling of light from off-chip into highly complex silicon-based devices is currently focus of efforts and research. In this work, the experimental demonstration of a -0.50 dB (89%) coupling efficiency in the C-band with the help of an aperiodic grating coupler design in a 250 nm silicon-on-insulator (SOI) technology is shown. Further, this work reports about the latest results regarding focusing grating couplers with footprints of only 30 µm x 30 µm and a measured coupling efficiency of up to 0.93~dB (81\%) at 1549 nm. Efficient grating coupler arrays are realized by using an expanded backside metal mirror-strip for the application of fiber arrays. In addition, this work presents aperiodic silicon grating couplers with an enhanced bandwidth to overcome the limited usability of grating couplers in wavelength division multiplexing (WDM) systems.

Abstract

Der Vortrag gibt einen Überblick über die Forschungsfelder des Instituts für Elektrische und Optische Nachrichtentechnik im Bereich der Siliziumphotonik, mit dem Schwerpunkt auf Sensoranwendungen. Zunächst werden einige wichtige Grundkomponenten vorgestellt. Dazu zählen insbesondere effiziente Gitterkoppler und Multimodeninterferometer, die sowohl für die Nachrichtentechnik als auch für wellenleiterbasierte Sensoren Schlüsselelemente darstellen. Im Anschluss wird kurz auf die Funktionsweise von Sensoren basierend auf integrierten Wellenleitern eingegangen. Am Beispiel eines so genannten Zweimodeninterferometers, das am Institut als eine interessante Alternative zu gängigen Mach-Zehnder-Strukturen entwickelt wurde, wird die praktische Realisierung eines Sensors erläutert, der z.B. den Nachweis einer bestimmten Aminosäure in einer wässrigen Lösung erlaubt. Der Vortrag schließt mit einem Ausblick auf weitere Entwicklungen, die in diesem Gebiet gerade angestoßen wurden.

Abstract

The dual-mode interferometer (DMI) is an attractive alternative to Mach-Zehnder interferometers for sensor purposes, achieving sensitivities to refractive index changes close to state-of-the-art. Modern designs on silicon-on-insulator (SOI) platforms offer thermally stable and compact devices with insertion losses of less than 1 dB and high extinction ratios. Compact arrays of multiple DMIs in parallel are easy to fabricate due to the simple structure of the DMI. In this work, the principle of operation of an integrated DMI with differential outputs is presented which allows the unambiguous phase shift detection with a single wavelength measurement, rather than using a wavelength sweep and evaluating the optical output power spectrum. Fluctuating optical input power or varying attenuation due to different analyte concentrations can be compensated by observing the sum of the optical powers at the differential outputs. DMIs with two differential single-mode outputs are fabricated in a 250 nm SOI platform, and corresponding measurements are shown to explain the principle of operation in detail. A comparison of DMIs with the conventional Mach-Zehnder interferometer using the same technology concludes this work.

Abstract

We present a rigorous approach for designing a highly efficient coupling between single mode optical fibers and silicon nanophotonic waveguides based on diffractive gratings. The structures are fabricated on standard SOI wafers in a cost-effective CMOS process flow. The measured coupling efficiency reaches -1.08 dB and a record value of -0.62 dB in the 1550 nm telecommunication window using a uniform and a nonuniform grating, respectively, with a 1 dB-bandwidth larger than 40 nm.

Abstract

A highly efficient grating structure for the coupling between standard optical fibers and single-mode waveguides in the silicon-on-insulator platform realized in a CMOS fabrication process is presented. The cost-effective method introduces a backside metal mirror to the grating coupler without need of an extensive wafer-to-wafer bonding. A coupling efficiency of -1.6 dB (around 69\%) near the telecommunication wavelength 1550 nm and a large 1 dB-bandwidth of 48 nm are achieved.