Ultra-Compact CMOS-Compatible Ytterbium Microlaser

Abstract

We demonstrate a waveguide-coupled trench-based ytterbium microlaser, achieving a sub-milliwatt lasing threshold and a 1.9% slope efficiency within an ultra-compact 40-µm-radius cavity while maintaining full compatibility with a CMOS foundry process.

High-Q-factor Al2O3 micro-trench cavities integrated with silicon nitride waveguides on silicon

“…In [13], we demonstrated a new type of micro-trench cavity, which has the advantages that it uses all silicon-photonicscompatible processing steps, is embedded in a silica cladding for robust form factor, has a nano-scale defined microcavity-waveguide gap for finely controlled and stable coupling, and can in principle accept any sputtered material as the resonator medium. Using this design we have demonstrated low threshold Yb-, Er-and Tm-doped aluminum oxide microlasers emitting at 1.0, 1.5 and 1.9 µm, respectively [13][14][15] and an athermal microcavity design using sputtered titanium dioxide as the resonator medium [16]. In [13] we reported Q factors of up to 5.7 × 10 5 at 1550 nm in undoped cavities, but we did not describe their design in detail or optimize their performance.…”

“…Figure 1 shows the aluminum oxide micro-trench cavity fabrication process. The processing steps are similar to those described in [13][14][15], but repeated here for clarity and to avoid confusion with small design differences. We fabricated the microcavity chips using a 300-mm CMOS foundry with a 65-nm technology node.…”

Broadband 2-µm emission on silicon chips: monolithically integrated Holmium lasers

“…In particular, integrated lasers beyond 2.0 μm are in demand due to the diminishing two-photon absorption of silicon [15,16] while also providing a new communication band for integrated systems [1]. Among the different methods to integrate lasers on a silicon photonics platform [17][18][19][20][21][22], deposition of rare-earthdoped Al 2 O 3 glass as gain medium [11,[22][23][24] and utilizing complementary metal-oxidesemiconductor (CMOS)-compatible silicon nitride (Si 3 N 4 ) cavities has proven to be effective for several key reasons. First, Si 3 N 4 has high transparency and low loss from near-IR into the mid-IR wavelength regime and is a mature wafer-scale waveguide platform already applied in passive and nonlinear silicon photonic devices [25][26][27].…”

“…Finally, the low thermo-optic coefficient of the host medium (Al 2 O 3 ) enables laser operation over a wide temperature range by providing good stability without active thermal control [41,42]. Rareearth-ion-based monolithic lasers integrated on a silicon platform have been demonstrated at 1.0, 1.5 and 1.9 µm wavelengths using ytterbium [24,43], erbium [14,22,23] and thulium [11,44] doped Al 2 O 3 glass as gain medium, respectively. However, to the best of our knowledge, monolithic integrated lasers beyond the 2 μm region have been minimally explored with no known demonstration of a holmium laser on a silicon photonics platform.…”

A Silicon Photonic Data Link with a Monolithic Erbium-Doped Laser

“…Using CMOS-compatible fabrication methods, rare-earth-ion-based monolithically integrated lasers have been demonstrated across near-infrared wavelengths at 1.0, 1.5, 1.8, 2.1 µm using ytterbium 52,53 , erbium 25,27,54 , thulium 37,55 , and holmium 56 doped Al 2 O 3 glass as gain media, respectively. These lasers use silicon-nitride (Si 3 N 4 ) cavities, as Si 3 N 4 has high transparency and low loss from near-IR to the mid-IR wavelength regime 57,58 .…”