Integrated electronic controller for dynamic self-configuration of photonic circuits

Abstract

Reconfigurable photonic integrated circuits (PICs) can implement arbitrary operations and signal processing functionalities directly in the optical domain. Run-time configuration of these circuits requires an electronic control layer to adjust the working point of their building elements and compensate for thermal drifts or degradations of the input signal. As the advancement of photonic foundries enables the fabrication of chips of increasing complexity, developing scalable electronic controllers becomes crucial for the operation of complex PICs. In this paper, we present an electronic application-specific integrated circuit (ASIC) designed for reconfiguration of PICs featuring numerous tunable elements. Each channel of the ASIC controller independently addresses one optical component of the PIC, and multiple parallel local feedback loops are operated to achieve full control. The proposed design is validated through real-time reconfiguration of a 16-channel silicon photonics adaptive universal beam coupler. Results demonstrate automatic coupling of an arbitrary input beam to a single-mode waveguide, dynamic compensation of beam wavefront distortions and successful transmission of a 50 Gbit/s signal through an optical free-space link. The low power consumption and compactness of the electronic chip provide a scalable paradigm that can be seamlessly extended to larger photonic architectures.

Fig. 1. Integrated electronic controller for reconfigurable photonic circuits.

a Schematic view of some examples of programmable photonic circuits that would greatly benefit from connection to a dedicated electronic control layer, capable of reconfiguring the optical functionality at run-time. b Microscope photograph of the custom electronic ASIC for real-time control of programmable PICs described in this work, highlighting its size and main internal sections. c Connection of two ASICs to a programmable photonic circuit, demonstrating the compact size of the complete assembly that ensures scalability to large-scale optical architectures

Fig. 2. Electronic chip design and characterization.

a Schematic view of the ASIC architecture for dynamic control of programmable photonic circuits. The ASIC features 8 parallel channels. b Measured ADC code for a wide range of input currents, that can be correctly detected thanks to the adaptive amplification mechanism. c Characterization of the actuator driver circuit: the square root compression of the DAC output (blue) results in a linearization of the heater dissipated power (red) with respect to the digital control value

Fig. 3. Silicon photonics 16-channel self-aligning universal beam coupler.

a Schematic view and b microscope photograph of the self-configuring optical beam coupler, made of a binary-tree mesh of 15 MZIs. A detail of a thermally-tunable MZI, featuring two actuators to completely steer the input light to one of the device outputs, is also reported. c Time transient of the PDs photocurrents when configuring the optical circuit, showing correct minimization when the ASICs are activated after 10 ms. The inset shows the evolution of the chip output power, which is correspondingly maximized in around 10 ms

Fig. 4. Experimental validation.

a Schematic view of the setup employed to introduce a static perturbation in the wavefront of a free-space beam. b Photograph, captured with an infrared camera, of the optical beam impinging on the beam coupler, when the SLM is off (left) and when it is used to perturb the free-space beam (right). c Optical power at the output port of the beam coupler for different SLM phase screens, showing its ability to perform real-time wavefront correction and beam reconstruction

Fig. 5. Real-time compensation of dynamic perturbations.

a Experimental setup employed to introduce a dynamic perturbation in the free-space propagation of the beam. b Temporal evolution, c probability density function, and d frequency spectrum of the received optical power when the ASICs are active (blue curves) or disabled (orange curves), demonstrating correct real-time compensation of the beam-front distortion performed by the electronically controlled photonic chip

Fig. 6. High-speed free-space optical transmission.

Eye diagrams of the received optical signal when transmitting a free-space beam modulated at 25 Gbaud both with a OOK and b PAM4 modulations, showing the transmission improvement when the adaptive receiver is dynamically operated