PWM‐Driven Thermally Tunable Silicon Microring Resonators: Design, Fabrication, and Characterization

Abstract

Ring resonators are one of the fundamental building blocks of advanced integrated optical circuits. They find applications as nonlinear optical elements, filters, sensors, and switches among others. Here, a comprehensive optimization framework and experimental results of thermally tunable microring resonators in silicon photonics is presented, with a focus on standard silicon photonic foundry processes. In order to minimize the total power consumption, the ring resonators are tuned by applying a pulse‐width‐modulated electrical signal to the heaters. The thermal performance of integrated silicon and metal heaters are investigated and compared using an effective model validated by the measurement results. The heater power consumption is minimized by optimizing heater cross section, resistance, and metal contact configurations. Using the multiproject wafer run developed at CEA‐LETI, it is demonstrated that a metal heater provides 30% lower power consumption compared to an integrated silicon one, reaching a power consumption of 27.53 mW per free spectral range. The measurements are in excellent agreement with the theoretically predicted thermal performance, with a deviation as low as 5%. The proposed framework, supported by the experimental results, will serve as a design guideline set that can be easily adapted for other thermo‐optic switches in future silicon photonic applications.

Design and Simulation of Thermo-Optic Phase Shifters With Low Thermal Crosstalk for Dense Photonic Integration

“…In other words, metal heaters are thermally more efficient than doped heaters. A similar conclusion was reported earlier in [26]. The simulated thermal efficiencies (calculated as power required for a phase shift of π) of the titanium and doped silicon heaters are 34.4 mW and 45.1 mW, respectively.…”

“…Being widely used to design thermal phase shifters within photonic integrated circuits, integrated heaters are important elements in silicon photonics. Practically, two types of integrated heater designs are possible in an SOI platform: a metal heater, just above the waveguide on top of the silicon dioxide (SiO2) layer [24]- [26] and doped silicon strips in close proximity to one side of the waveguide [26], [27]. A detailed discussion about the integrated heaters was provided in [28].…”

“…The temperature dependent phase change in the heated waveguide depends on the thermo-optic coefficient of both core (silicon) and cladding (silica) and it can be expressed as [26]:…”

“…This is because some amount of power is dissipated through the metal contacts and it also acts as a heat absorber, which further reduces the heater temperature. However, the design of the metal contacts can be optimized to reduce power consumption as described in [26].…”

A Review of Devices for Integrated Silicon Photonic Switches

“…Higher order rings have these features and are sensitive to fabrication variation: optical waveguide shape, coupling gap and thickness uniformity of the wafer. A review of MRRs is reported in [45]. Theoretical approach for coupled resonator optical waveguides (CROW) is reported in [42].…”