Design of a wavelength-locking circuit for Silicon-Photonics high-speed links with radiation-tolerant thermal control

Abstract Future High-Energy Physics (HEP) experiments will require optical data links capable of supporting multi-gigabit transmission rates under high radiation doses and tight power constraints. Silicon Photonics (SiPh) has emerged as a promising technology for these applications, offering high bandwidth, compact integration, and enhanced radiation tolerance. However, the resonant wavelength of SiPh micro-ring modulators (µRMs) is highly sensitive to temperature and process variations, requiring precise thermal stabilization to maintain resonance. To serve this purpose, µRMs are typically built with integrated heaters. This work presents the design of a radiation-tolerant Thermal Control Unit (TCU) for SiPh modulators, implemented in 28 nm technology. The proposed TCU senses the optical power trapped in each µRM through a photodiode and regulates the current flowing in the integrated micro-heater using a closed-loop control system. The architecture includes a current-input ΔΣ Analog-to-Digital Converter (ADC), a digital Proportional-Integral-Derivative (PID) controller, and a ΔΣ Digital-to-Analog Converter (DAC) with a high-power output driver. The system supports four independent control channels, enabling Wavelength-Division Multiplexing (WDM). Transistor-level simulations demonstrate that the ADC achieves approximately a 60-dB Signal-to-Noise Ratio (SNR), while the DAC and driver can deliver up to 80 mW of heater power with high resolution. The results confirm that the proposed TCU architecture enables precise and radiation-tolerant thermal control of SiPh modulators, providing a robust foundation for next-generation high-speed optical links in particle detector systems.