Lotte Nagy

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

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.