Abstract
Photonic integrated circuits (PIC) consist of functional optical building blocks, such as filters, modulators, photodetectors, that are connected with waveguides. In today's circuits, these connections are usually defined during the design of the chip, and therefore the functionality of the chip is limited to the original application for which it was designed. Programmable photonic circuits are changing this paradigm. In a programmable PIC, the light paths are configured at run time using a waveguide mesh that is interconnected with tunable couplers and electro-optic phase shifters [1]-[3]. As shown in Fig. 1, this can be done by organizing the couplers in either a forward-only waveguide mesh or a recirculating mesh. The former type is useful as universal linear interferometer [3] while the latter can also be configured to form interferometers or resonators for wavelength filtering [2]. This creates an optical equivalent to electronic field-programmable gate arrays. There are significant challenges on the path to realize fully functional programmable PICs. The tunable couplers and phase shifters that form the optical gates need to be very efficient, compact and introduce little or no optical loss, as the light needs to pass through a large number of them. Each of these actuators needs to be interfaced with an electronics driver, and in parallel, monitor detectors also need to be connected to readout electronics. The stability of these large circuits needs to be governed by control loops, and higher-level software routines are needed to define the actual functions. The benefits of having a general-purpose programmable chip are not to be underestimated: an off-the-shelf chip can dramatically reduce the development time for new photonic applications, and create a new ecosystem of photonic software. Related Research Topics
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