Sub-10-µm TM-selective optical switch using phase-matching control of absorptive Ge₂Sb₂Te₅ states

We propose a transverse-magnetic-selective (TM-selective) optical switch based on a bent directional coupler, utilizing the phase-change material (PCM) <i>G</i><i>e</i>₂<i>S</i><i>b</i>₂<i>T</i><i>e</i>₅ (GST). The device consists of two parallel bent silicon waveguides, with the GST embedded in the coupled waveguide. When the GST is in the amorphous state, the optical switch is in the ON state. The light of the TM mode is coupled from the ordinary silicon strip waveguide (SW) to the GST-Si hybrid waveguide (HW) and outputs from the Cross port. When the GST is in the crystalline state, the optical switch is in the OFF state. The light of the TM mode remains in the SW with minimal loss (<0.9<i>d</i><i>B</i>) and outputs from the Thru port. The proposed device has a compact footprint of 16µ<i>m</i>×3µ<i>m</i>, with a coupling length (<i>L</i><i>c</i>) of just 6.4 µm. It is unaffected by the transverse-electric (TE) mode, thus ensuring selective operation for TM polarization. At a wavelength of 1545 nm, the extinction ratio (ER) and insertion loss (IL) are 22.8 and 0.21 dB, respectively. The bandwidth is 32 nm when the ER is greater than 15 dB. The proposed device is expected to enhance the functionality of photonic integrated circuits and contribute to the advancement of reconfigurable optical transmission networks.