A CMOS-compatible heterogeneous interferometer for chip-scale temperature sensing

• Published in: Applied physics letters 2022-12, Vol.121 (26)
• Main Authors: Payne, D. A., Matthews, J. C. F.
• Format: Article
• Language: English
• Subjects: Applied physics; Bend radius; Circuits; Figure of merit; Mach-Zehnder interferometers; Optical measurement; Photonics; Silicon nitride; Temperature sensors; Transverse electric modes; Waveguides
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0128130

We report a photonic temperature sensor with enhanced performance in both broad- and narrow-bandwidth optical measurements. The device consists of a heterogeneously integrated Mach–Zehnder interferometer with arms composed of silicon and silicon nitride waveguides whose thermo-optic coefficients differ by an order of magnitude. The waveguides are fabricated in distinct layers of a monolithic device and guide light in a single transverse-electric mode. The resulting small bend radii enable compact sensing of temperatures local to integrated photonic components with a device footprint of 580 × 410  μ m 2. Furthermore, the dual layers of the sensor enable overlaying of the spiral arms of the interferometer over each other or other photonic circuit components. We measure a sensitivity of 324 pm/K, an over threefold enhancement compared to the measurement of an asymmetric Mach–Zehnder constructed of silicon waveguides on the same device. We additionally define a useful figure of merit for the side-of-fringe measurement regime, which uses direct detection of a narrow linewidth laser and show that the reported device is also competitive on this metric.