Engineering the optical properties of silicon using sub-wavelength structures

In most integrated optics platforms, including silicon-on-insulator, only minor modifications in refractive index are possible. The geometry of the waveguiding structure is thus the only degree of freedom for the design of devices. The use of sub-wavelength gratings (SWGs), i.e. structures that are small enough to suppress diffraction effects, enables local engineering of both refractive index and dispersion, thereby opening new possibilities for device design. Here we present some of the recent advances in refractive index and dispersion engineering using silicon SWGs, focussing on ultra-broadband and compact multimode interference couplers and directional couplersThis work was supported by the Spanish Ministerio de Ciencia (project TEC2009-10152), the European Mirthe project (FP7-2010-257980), and the Universidad de Málaga - Campus de Excelencia Internacional Andalucìa Tech

Re-inventing Multimode Interference Couplers Using Subwavelength Gratings

We use the concept of subwavelength grating (SWG) refractive-index-engineering to propose and experimentally demonstrate a reduced size, slotted 2x2 MMI coupler. We also present an ultra-broadband 2x2 MMI coupler which is based on SWG dispersion engineering.This work was supported in part by the Spanish Ministerio de Ciencia (project TEC2009-10152), a Formación del Profesorado Universitario scholarship (AP-2006-03355), the European Mirthe project (FP7-2010-257980) and “Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Toward optical coherence tomography on a chip: in vivo three-dimensional human retinal imaging using photonic integrated circuit-based arrayed waveguide gratings

In this work, we present a significant step toward in vivo ophthalmic optical coherence tomography and angiography on a photonic integrated chip. The diffraction gratings used in spectral-domain optical coherence tomography can be replaced by photonic integrated circuits comprising an arrayed waveguide grating. Two arrayed waveguide grating designs with 256 channels were tested, which enabled the first chip-based optical coherence tomography and angiography in vivo three-dimensional human retinal measurements. Design 1 supports a bandwidth of 22 nm, with which a sensitivity of up to 91 dB (830 µW) and an axial resolution of 10.7 µm was measured. Design 2 supports a bandwidth of 48 nm, with which a sensitivity of 90 dB (480 µW) and an axial resolution of 6.5 µm was measured. The silicon nitride-based integrated optical waveguides were fabricated with a fully CMOS-compatible process, which allows their monolithic co-integration on top of an optoelectronic silicon chip. As a benchmark for chip-based optical coherence tomography, tomograms generated by a commercially available clinical spectral-domain optical coherence tomography system were compared to those acquired with on-chip gratings. The similarities in the tomograms demonstrate the significant clinical potential for further integration of optical coherence tomography on a chip system

Development of a monolithically integrated, CMOS-compatible SiN photonics process flow for sensor and medical applications

Abstract: ams AG is a leading provider of sensing solutions developing semiconductor sensors in a wide variety of fields, with optical sensing as one of the key competences. Since integrated photonics is a promising technology for new sensor systems, ams AG has been developing processes for fully integrated CMOS-compatible photonic components based on Si3N4. This talk will provide an overview on the processing of basic photonic building blocks and their optical properties and performance. We will also give examples for applications in the fields of optical coherence tomography and opto-chemical gas sensing. In the 1980s photonics started its way for common use in telecommunication technology, using optical fiber technologies. In recent years, also a variety of photonic sensors has been proposed and developed. One of the major drawbacks of most of these photonic devices has been the lack of integration into existing (semiconductor) production processes, so far. This integration is feasible using SiN material systems to process monolithically integrated CMOS-compatible photonic sensors in the visible and near-infrared spectrum. We will present the basic processing steps for the SiN photonic technology, the development of some critical processing steps such as SiN deposition and SiN etching as well as several photonic components (waveguides, splitters, etc.) with their optical properties. One of the applications presented relates to optical coherence tomography (OCT), a fast growing imaging technique in ophthalmology. Drawbacks of existing OCT systems are their high costs as well as their bulkiness, which prevents a wider spread use of OCT systems. One way to overcome both cost and size issues is to integrate optical and electrical components on a single chip. Part of this work was carried out in the framework of the projects COHESION (funded by the Austrian Research Promotion Agency (FFG), no. 848588), OCTCHIP (funded by the EU’ Horizon 2020 research and innovation programme, no. 688173), and COLODOR (M-ERA.NET transnational Call 2015, funded by the Austrian Research Promotion Agency (FFG), no.854066, and the Bundesministerium für Bildung und Forschung, Germany)

Technological verification of size-optimized 160-channel silicon nitride-based AWG-spectrometer for medical applications

We present the technological verification of a size-optimized 160-channel, 50-GHz silicon nitride-based AWG-spectrometer. The spectrometer was designed for TM-polarized light with a central wavelength of 850 nm applying our proprietary “AWG-Parameters” tool. For the simulations of AWG layout, the WDM PHASAR photonics tool from Optiwave was used. The simulated results show satisfying optical properties of the designed AWG-spectrometer. However, the high-channel count causes a large AWG size with standard design approaches. To solve this problem we designed a special taper enabling the reduction of AWG structure by about 15% while keeping the same optical properties. The AWG design was fabricated and the measured spectra not only confirm the proposed size-reduction but also the improvement of optical properties of the size-optimized AWG