Abstract

The mid-infrared wavelength region (MIR, 3-15 µm) has a large potential for sensing applications, as many molecules have strong fundamental absorption lines in this range. However, the high-cost and bulky MIR technology has prevented a real breakthrough so far. The development of MIR photonic integrated circuits in group IV platforms can provide a crucial step towards large scale applications, with ring resonators expected to play an important role. Several resonators operating in the MIR have been demonstrated in silicon-based platforms. In particular, high Q-factors have been reported in silicon-on-insulator [1] and silicon-on-sapphire [2] which, however, have high losses beyond ~3.5 and ~6.5 µm, respectively. On the contrary, the transparency window of germanium-based chips can go up to 15 µm [3,4]. Until recently, however, only Q-factors in the order of 10³-10⁴ were reported in germanium-based integrated resonators [9]. Here we demonstrate a pure germanium ring resonator which, for the first time in any integrated germanium-based platform, reaches a Q-factor beyond 10⁵.

© 2023 IEEE