Tracking changes in a photonic integrated circuit is an essential task for many applications, such sensing or telecommunication systems. In particular, locking of laser to a microring resonator and tracking resonance shifts over time with high accuracy can improve several applications such as sensing and biosensing. In this work, we present a novel system to lock a laser to a silicon photonics microring resonance and track the changes in wavelength over time. An electronic digital feedback loop balances the power at outputs of the microring (at the through and the drop ports) by tuning finely the wavelength of the input laser. The silicon photonics chip is equipped with integrated photodiodes at each port of the microring. The low noise of photodiodes, together with the resolution of the tuning of the laser, allows achieving locking with less than 7 femtometers as residual noise at 1550 nm. The digital implementation of the feedback loop permits to reach bandwidth up to 1 kHz. Demonstration of the locking has been made with several different microring resonators, with Q-factor varying from 5000 to 60000.
Integrated Mach-Zehnder interferometers, ring resonators, Bragg reflectors or simple waveguides are commonly used as photonic biosensing elements. They can be used for label-free detection relating the changes in the optical signal in realtime, as optical power or spectral response, to the presence and even the quantity of a target analyte on the surface of the photonic waveguide. The label-free method has advantages in term of sample preparation but it is more sensitive to spurious effects such as temperature and refractive index sample variation, biological noise, etc. Label methods can be more robust, more sensitive and able to manipulate the biological targets.
In this work, we present an innovative labeled biosensing technique exploiting magnetic nano-beads for enhancement of sensitivity over integrated optic microrings. A sandwich binding is exploited to bring the magnetic labels close to the surface of the optical waveguide and interact with the optical evanescent field.
The proximity and the quantity of the magnetic nano-beads are seen as a shift in the resonance of the microring. Detection of antibodies permits to reach a high level of sensitivity, down to 8 pM with a high confidence level. The sizes of the nano-beads are 50 to 250 nm. Furthermore, time-varying magnetic fields permit to manipulate the beads and even induce specific signals on the detected light to easy the processing and provide a reliable identification of the presence of the desired analyte. Multiple analytes detection is also possible.
The complexity scaling of silicon photonics circuits is raising novel needs related to control. Reconfigurable
architectures need fast, accurate and robust procedures for the tuning and stabilization of their working point,
counteracting temperature drifts originated by environmental fluctuations and mutual thermal crosstalk from surrounding
integrated devices. In this contribution, we report on our recent achievements on the automated tuning, control and
stabilization of silicon photonics architectures. The proposed control strategy exploits transparent integrated detectors to
monitor non-invasively the light propagating in the silicon waveguides in key spots of the circuit. Local monitoring
enables the partitioning of complex architectures in small photonic cells that can be easily tuned and controlled, with
need for neither preliminary circuit calibration nor global optimization algorithms. The ability to monitor the Quality Of
of Transmission (QoT) of the optical paths in Photonic Integrated Circuits (PICs) is also demonstrated with the use of
channel labelling and non-invasive light monitoring. Several examples of applications are presented that include the
automatic reconfiguration and feedback controlled stabilization of an 8×8 switch fabric based on Mach-Zehnder
interferometers (MZIs) and the realization of a wavelength locking platform enabling feedback-control of silicon
microring resonators (MRRs) for the realization of a 4×10 Gbit/s wavelength-division-multiplexing transmitter. The
effectiveness and the robustness of the proposed approach for tuning and stabilization of the presented architectures is
demonstrated by showing that no significant performance degradation is observed under uncooled operation for the
We demonstrate non-invasive light observation in silicon photonics with a ContactLess Integrated Photonics Probe
(CLIPP), neither introducing appreciable perturbations of the optical field nor requiring photon tapping from the
waveguide. Light monitoring with sensitivity down to -30 dBm, across 40 dB dynamic range, in few tens of microseconds,
on TE and TM polarizations, and on monomode and multimode waveguides is achieved. Moreover, we show wavelength
tuning, locking and swapping of high-Q resonators assisted by the CLIPP that is integrated inside the microring. CLIPP
readout and feedback control is managed by a CMOS microelectronic circuit bridged to the silicon photonic chip.