MORPHIC: Programmable photonic circuits enabled by silicon photonic MEMS Wim Bogaerts a , Hamed Sattari b , Pierre Edinger c , Alain Yuji Takabayashi b , Iman Zand a , Xiaojing Wang c , Antonio Ribeiro a , Moises Jezzini d , Carlos Errando-Herranz c , Giuseppe Talli d , Kumar Saurav f , Marco Garcia Porcel e , Peter Verheyen g , Banafsheh Abasahl a , Frank Niklaus c , Niels Quack b , Kristinn B. Gylfason c , Peter O’Brien d , and Umar Khan a a Ghent University - IMEC, Photonics Research Group, Department of Information Technology,, Technologiepark-Zwijnaarde 126, 9052 Gent, Belgium b ´ Ecole Polytechnique F´ed´erale de Lausanne (EPFL), 1015 Lausanne, Switzerland. c KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden. d Tyndall National Institute, Lee Maltings Complex Dyke Parade, T12 R5CP Cork, Ireland e VLC Photonics S.L., Ed. 9B, D2, UPV, Camino de vera sn, 46022 Valencia, Spain f Commscope Connectivity Belgium, Diestsesteenweg 692, 3010 Kessel LO, Belgium g imec vzw. 3DSIP Department, Si Photonics Group, Kapeldreef 75, 3001 Leuven, Belgium ABSTRACT Keywords: Photonic Integrated Circuits, Silicon Photonics, Photonic MEMS, Programmable Photonics 1. INTRODUCTION Photonic integrated circuits (PIC) are becoming ever more complex. This evolution is fueled by increasingly mature fabrication processes for silicon photonics 1 and III-V PICs, 2 as well as better photonic circuit design capabilities. 3 Especially, technology platforms with a high refractive index contrast such as silicon can integrate thousands of building blocks on the same chip, boosting the level of complexity and functionality in a photonic circuit. Today, most PICs are custom designed with one particular application in mind. The optical waveguide connections on the chip are optimized at the design stage and implemented in physical paths on the chip. These so-called application-specific photonic integrated circuits (ASPIC) have similar benefits as electronic application- specific ICs (ASIC) in terms of ultimate performance, efficiency and power consumption. But the development of a new ASPIC is a costly proposition, as it takes a year to design, fabricate and test a new circuit. 1.1 Programmable PICs In contrast to ASPICs, the past few years have seen the emergence of programmable PICs. These photonic circuits are designed with flexibility in mind, allowing the user to configure the connectivity of the optical waveguides in the field using tunable waveguide couplers and optical phase shifters. 4 Conceptually, these photonic circuits are much more like an electronic field-programmable gate array (FPGA), in the sense that the connectivity can be programmed by the user through a software interface. On the photonic chip this software programming results in electronic actuation of the optical waveguides, redirecting the light along new waveguide paths so it can be processed in real time. Such programmable photonic circuits, which today are mostly implemented as waveguide meshes intercon- nected by tunable 2 × 2 couplers (e.g. implemented as a Mach-Zehnder interferometer), can be used to define connectivity matrices for optical routing by switching the couplers in cross or bar state. But when the tunable couplers are used in a partial coupling state, light can be routed along multiple paths, giving rise to interfero- metric circuits. In combination with optical phase shifters, these circuits can then project a linear combination Further author information: (Send correspondence to W.B.) W.B.: E-mail: wim.bogaerts@UGent.be, Telephone: 32 9 264 3324