Thermo-optic modulator with ultra-high extinction ratio for low-loss silicon nitride integrated photonics

TL;DR

This work addresses the challenge of efficient, broadband, low-power modulation in silicon nitride photonics by introducing a thermo-optic phase shifter that uses a single-strip Ti heater with isolation trenches for C-band operation. A 2D FEM-based multiphysics design optimizes geometry to minimize the π-phase shift power, achieving a practical $π$-phase shift at about $65 mW$ with a $12 kHz$ bandwidth and an extinction ratio above $80 dB$, while preserving ultra-low propagation losses. The devices demonstrate compatibility with microring resonators exhibiting $Q$ factors up to $9.6×10^6$ and losses as low as $0.033$–$0.058$ dB/cm. Overall, the approach enables scalable, reconfigurable low-loss silicon nitride photonics suitable for quantum technologies, LiDAR, and high-performance photonic computing.

Abstract

Extremely low-loss silicon nitride integrated circuits is a potential platform for a growing number of frontier applications in quantum technologies, high-performance and analog computing, nonlinear optics, light detection and ranging (LiDAR), and biotechnologies. However, efficient optical modulation with a wide frequency response, high contrast, low power and scalable manufacturing remains one of the key challenges for silicon nitride integrated photonics. Here, we propose an integrated thermo-optic phase shifter with isolation trenches operating in the C-band. The fabricated thermo-optic modulator capable to achieve a $π$-phase shift shift at a power consumption of 65 mW, bandwidth of 12 kHz, and extinction ratio (ER) over 80 dB. Moreover, we systematically demonstrate its compatibility with low-loss silicon nitride photonic integrated circuits with microring resonators exibiting an average quality factor more than $5.9 \times 10^{6}$, which correspond to propagation loss of 0.058 dB/cm.

Figures (10)

• Figure 1: Comparison of the main characteristics of various phase shifting technologies: (a) MEMS; (b) Ferroelectrics; (c) Thermo-optics; (d) Plasma-dispersion; (e) Plasmonics; (f) Phase-change materials.
• Figure 2: Cross sections of various types of thermo-optic phase shifters: (a) Single-strip phase shifter; (b) Suspended single-strip phase shifter; (c) Phase shifter with folded waveguide; (d) PT-symmetry breaking phase shifter.
• Figure 3: (a) The 3D schematic of the phase shifter structure in unbalanced MZI architecture. (b) Cross-sectional view of the thermo-optic phase shifter.
• Figure 4: Parametric dependence of phase shifter performance on geometric factors. (a) Power consumption and heater temperature as functions of heater width and cladding thickness. (b) Power consumption and heater temperature as functions of heater width and height. (c) Heater temperature as a function of heater length. (d) Power consumption and heater temperature as functions of heater width and waveguide width.
• Figure 5: Dependence of phase shifter performance and field distribution on trench geometry. (a-b) Heatmaps of power consumption and corresponding heater temperature at the $\pi$-phase shift, both as functions of trench distance from the heater and trench depth. (c) Visualization of the electromagnetic field distribution within the phase shifter cross-section. (d) Temperature distributions in the optimized phase shifter cross-section.