We demonstrate the automatic thermal alignment of photonic components within an integrated optical switch. The WDM optical switch involves switching elements, wavelength de-multiplexers, interleavers and monitors each one needing independent control. Our system manages rerouting of channels coming from four different directions, each carrying 12, 200GHz spaced, wavelengths into eight add/drop ports. The integrated device includes 12 interleavers, which can act either as optical de-interleavers to split the optical signal into odd and even channels or as optical interleavers that recombine the odd and even channels coming from the switching matrix. Integrated Ge photodiodes are placed in key positions within the photonic integrated circuit (PIC) are serve for monitoring. An electronic integrated circuit (EIC) drives the photonic elements by means of dedicated heating circuits (824 on-board heater control cells, 768 for the switching elements and 56 for the interleavers and the mux/de-mux) and reads out the Ge diodes photocurrent through TIAs. We applied a stochastic optimization algorithm to align the spectral response of the interleavers to the ITU grid. We exploit the thermo-optic effect to shift the interleavers pass-band in a desired spectral position. The interleavers are provided with dedicated metallic heaters that can be operated in order to tune the interleaver response, which is typically misaligned due to fabrication inaccuracies. The experimental setup is made of a tunable laser coupled with one input port of optical switch. The optimization algorithm is implemented via a software to drive the EIC till finding the best heating configuration (on the two branches of the interleaver) on the basis of the monitor diode-feedback. This way, the even and odd wavelengths input in the interleaver are directed toward the wanted lines within the switching matrix. Our method has been used for aligning the micro-ring based switching elements in the PIC as well. In that case, the integrated Ge photodiodes have been used to align the photonic components in the PIC in order to enable different pathways for the routing or the broadcasting operation of the optical switch. With no bias applied to the heaters of the switching elements, the optical signal is expected to be maximum at the through port. When the micro-ring heaters are biased, the feedback controller finds the best set of heating values that minimize the optical power at the through port of the switching node. This way, the optical signal is coupled in the drop port and the node is enabled for switching. The algorithm, implemented in LabVIEW, converges over multiple instances and it is robust against stagnation. This work aims at enabling the automatic reconfiguration/restoration of the whole WDW optical switch.
In this work, we report on the modeling and the experimental characterization of a 6×400 GHz silicon Arrayed Waveguide Grating (AWG). The design of the device is based on the reduction of the background noise. The good characteristics of the AWG demonstrate that unwanted reflections have a detrimental role on its performance. We demonstrate a smoothing of the output channel shape of the AWG, as well as a reduction of the crosstalk level from −20.6(1) dB to −24.4(1) dB.
Array waveguide gratings (AWGs) are a key component in WDM systems, allowing for de-multiplexing and routing of wavelength channels. A high-resolution AWG able to satisfy challenging requirements in terms of insertion loss and X-talk is what is needed to contribute to the paradigm change in the deployment of optical communication that is nowadays occurring within the ROADM architectures. In order to improve the performances and keep down the footprint, we modified the design at the star coupler (SC) and at the bending stages. We evaluated how the background noise is modified within a whiskered-shaped SC optimized to reduce the re ectivity of the SOI slab and keep down back-scattered optical signal. A dedicated heating circuit has also been designed, in order to allow for an overall tuning of the channel-output. A high-performance AWG has also to cope with possible thermal-induced environmental changes, especially in the case of integration within a Photonic Integrated Circuit (PIC). Therefore, we suggested a way to reduce the thermal-sensitivity.