Thermo-optic tuning of silicon nitride microring resonators with low loss non-volatile [Formula: see text] phase change material

Abstract

A new family of phase change material based on antimony has recently been explored for applications in near-IR tunable photonics due to its wide bandgap, manifested as broadband transparency from visible to NIR wavelengths. Here, we characterize [Formula: see text] optically and demonstrate the integration of this phase change material in a silicon nitride platform using a microring resonator that can be thermally tuned using the amorphous and crystalline states of the phase change material, achieving extinction ratios of up to 18 dB in the C-band. We extract the thermo-optic coefficient of the amorphous and crystalline states of the [Formula: see text] to be 3.4 x [Formula: see text] and 0.1 x 10[Formula: see text], respectively. Additionally, we detail the first observation of bi-directional shifting for permanent trimming of a non-volatile switch using continuous wave (CW) laser exposure ([Formula: see text] to 5.1 dBm) with a modulation in effective refractive index ranging from +5.23 x [Formula: see text] to [Formula: see text] x 10[Formula: see text]. This work experimentally verifies optical phase modifications and permanent trimming of [Formula: see text], enabling potential applications such as optically controlled memories and weights for neuromorphic architecture and high density switch matrix using a multi-layer PECVD based photonic integrated circuit.

Figure 1

(a) SEM image of a RR design variation with the PCM cell deposited on top. (b) Zoom in SEM image of a PCM cell highlighted in blue colour (c) Schematic of SiNx microring resonator partially covered with ${\text{Sb}}_2{\text{S}}_3$, with an inset showing a cross-section of the RR and the fundamental TE optical mode.

Figure 2

Simulated spectral shift from crystalline to amorphous for ${\text{Sb2}}_2{\text{S}}_3$-cell lengths ranging from 10 $\mu$m to 70 $\mu$m for a PCM thickness of 15 nm (green-dash line), 20 nm (blue-dotted line), 23 nm (purple dash-dot line), 25 nm (yellow-solid line) and optical measurement (red).

Figure 3

Measured ${\text{Sb}}_2{\text{S}}_3$ on SiN RR: (a) Q factor and (b) ER for PCM lengths ranging between 0 and 70 $\mu$m in amorphous (blue) and crystalline (red) states.

Figure 4

Experimental RR spectral shift for different temperatures, as indicated in the legends of: (a) Bare SiN RR before annealing (BA) (b) Bare SiN RR after annealing (AA) (c) Amp - ${\text{Sb}}_2{\text{S}}_3$ (d) Crys - ${\text{Sb}}_2{\text{S}}_3$ state at 1550 nm.

Figure 5

Normalised transmission of a RR AA (after annealing) partially capped with a crystalline ${\text{Sb}}_2{\text{S}}_3$ cell with a length of 120 $\mu$m using different optical powers in the waveguide (−5.9, −3.35 and −1.9 dBm) for a duration of 60 minutes.

Figure 6

Resonant wavelength of the exposed RR against the injected optical power in the waveguide (−5.9–5.1 dBm) for a duration of 60 minutes, cladded with a crystalline 120 $\mu$m long ${\text{Sb}}_2{\text{S}}_3$ cell.

Figure 7

Extracted $\mathrm{\Delta }{n}_{\mathit{eff}}$ of ${\text{Sb}}_2{\text{S}}_3$ in the crystalline state before and after each low-power exposure, as indicated in the legend (eye-guiding only).