Low Loss Devices fabricated on the Open Access 3 μm SOI Waveguide Platform at VTT Srivathsa Bhat, Mikko Harjanne, Fei Sun, Matteo Cherchi, Markku Kapulainen, Ari Hokkanen, Giovanni Delrosso, Timo Aalto VTT Technical Research Centre of Finland, 02044 Espoo - Finland e-mail: srivathsa.bhat@vtt.fi ABSTRACT In this paper, the latest results on some of the building block devices and components fabricated on VTT's PIC platform, that is based on 3 μm thick Silicon-On-Insulator (SOI) waveguides [1], is presented. As part of the plans in developing the platform further, AWG and Echelle grating (EG) designs, with insertion loss in the range of 1-3 dB, and an extinction ratio reaching up to 35 dB have been designed and fabricated as part of the recent MPW run, and the measurement results are presented. Novel 45 o vertical coupling TIR mirrors have also been realized (with AR coating) as a new building block on this platform, and have been integrated with the waveguides. The measured coupling losses to/from lensed fibers are below 0.5 dB, which are better in comparison to the coupling loss from the etched facets at the edges of the chip (~ 1 dB). The main advantages of this thick SOI platform are low loss, dense integration, polarization independent and broadband operation, high optical power throughput, and smooth transition from prototyping to volume production. Open access via multi-project wafer (MPW) runs, dedicated process runs, prototyping and small-to-medium volume production services are provided. Keywords: Thick SOI Platform, AWG, Echelle Grating, Fiber-Coupling Mirrors, Low-Loss, Polarization Independent. 1. INTRODUCTION While the VTT 3 um platform sounds ‘thick’ for any single-mode (SM) operation or for any dense integration, this is very well realized from a combination of rib-waveguide (SM operation) and strip waveguide (dense integration) geometries [2], and the ability to couple adiabatically between the two. In addition, small footprints are achieved using Euler bends [3], and the platform is low loss (0.1 dB/cm) for broadband operation from 1.2 to 4 um. In addition, the platform also supports hybrid integration of active devices, heterogenous germanium photodetectors, thermo-optic heaters, and has a better mode-matching for coupling to tapered fiber, or for coupling to fiber via interposer. Some of the building blocks that are recently developed and optimized will be discussed in the following sections. 2. BUILDING BLOCKS DEVICES AND COMPONENTS VTT 3 μm SOI platform has its unique advantages, and various building block are being developed, and the design optimized, to support this platform. As part of a recent MPW process run, several multiplexer designs such as AWG, EG, and MZI, for varied design parameters such as channel spacing and channel count, have been included and successfully fabricated. Among these, and to demonstrate the low loss and high extinction characteristics, a 400 GHz channel spaced 1 x 11 channel AWG design, and two EG designs, with channel spacing of 800 GHz and 100 GHz, and channel count of 1 x 5 and 1 x 8 respectively have been presented. Other than that, novel vertical coupling mirrors have been successfully fabricated, measured, and the analysed results are presented below. 2.1 Multiplexing elements – AWG & EG Multiplexers are crucial for dense integration of channel wavelengths on a chip, and for larger channel counts, the usual way to do this is with AWG and EG. While AWG has the advantage in terms of easy scaling up of the channel count for low channel spacing values, EG is more compact and better suited for larger channel spacing with a comparatively lower channel count. Both AWG and EG designs are fabricated as part of the VTT MPW process run, and the measured characteristics are presented below. Schematic of the 1 x 11 channel AWG design for TE polarization with 400 GHz channel spacing centred at ITU 38 (1546.92) in the DWDM grid, and the measured transmission characteristic are shown in Fig.1. The insertion loss of the channels for TE is in the 1.2-2.0 dB range, and the extinction ratio is over 35 dB. Although, the bend waveguides within the AWG are not designed for TM, the insertion loss is in the 1.9-2.4 dB range, and with an extinction of about ~ 25 dB respectively. Similarly, the microscope images of two of the EG designs, centered around 1550 nm, are shown in Fig.2. The specifications of the design are shared there-in, and the transmission plots, presented in Fig.3. Both designs have