Silicon-based Optical Switch using Phase-change Materials
Creators: name: Chen, Xiaojun
Publisher: name: RMIT University
Year: 2025
Subjects: classificationCode: 400605
subject: Optical fibre communication systems and technologies
classificationCode: 510204
subject: Photonics, optoelectronics and optical communications

description: Recently, silicon integrated optical circuits have attracted intensive interests, thanks to the compatibility with the CMOS technology that enables mass production at low cost. The optical switch is an essential part of optical integrated circuits, with broad applications in optical communications and networks, optical computing, and sensing such as LiDAR. In general, the silicon integrated optical switch adopts thermo-optic or carrier dispersion effect to realize reconfigurable signal routing. However, the use of thermo-optic effect leads to high power consumption, and the carrier dispersion effect has the disadvantage of small refractive index change. In addition, both effects are non-latching, and hence, continuous power consumption is required even when switching is not needed. For overcoming these drawbacks, phase-change materials (PCMs) have been introduced into silicon integrated optical switches. However, prior works either had too small bandwidth, too high loss, too large size, or too few output ports, only two or even one. In this work, we first proposed a silicon-based optical switch with GST-enabled phase-shifting region. This optical switch is based on contra-directional couplers composed of two phase-shifted Bragg gratings. To minimize the impact of GST absorption loss, GST is only used in the phaseshifting area, and the switching function is achieved by changing the state of GST. Results show that the proposed device has a 3 dB operation bandwidth of about 163.2 GHz (1.394 nm) and an extinction ratio of about 19.06 dB for the drop port and about 20.25 dB for the through port. The loss at the central operation wavelength is about 1.3 dB and 1.04 dB for the through port and the drop port, respectively, and the largest loss over the entire operation bandwidth for these two ports is 1.66 dB and 2.35 dB. Furthermore, the optical switch is shown to be bi-directional, achieving similar performances when light propagates in the opposite direction. Compared with previous works, the proposed optical switch realizes wider operation bandwidth, higher extinction ratio and lower loss. After that, we proposed and studied a silicon-based optical switch based on the contra-directional coupler structure using Sb2Se3. The optical switch is non-volatile because of the material properties of Sb2Se3, and thanks to the property of Sb2Se3 that extremely low loss in both states over the entire C-band, this device has low loss. Results have shown that the proposed optical switch has a 3 dB operation bandwidth of 353 GHz (3.045 nm), and an extinction ratio of 26.9 dB and 14.7 dB for the through port and the drop port, respectively. The proposed optical switch has also demonstrated a low insertion loss, which is about 0.52 dB at the through port and about 1.03 dB at the drop port. In addition, we further proposed and studied the 1×3 optical switch based on the contra-directional coupler structure using Sb2Se3. Compared with conventional optical switches that have 2n ports, the proposed device enhanced the flexibility on the number of output ports to achieve more efficient operations. This optical switch also leverages the non-volatile extremely low loss material properties of Sb2Se3. Simulation results indicate that the proposed optical switch has an operation bandwidth of about 237 GHz (2.05 nm), with an extinction ratio of 14.3 dB for the through port and approximately 14.8 dB for the upper/lower drop ports. Additionally, the optical switch has shown an insertion loss of about 0.3 dB at the through port and about 1.3 dB at the upper/lower drop ports. Then, we proposed and studied a silicon-based 1×3 optical switch with a non-contact phase change control mechanism using Sb2Se3. Different from the previous work, this device can work with other materials with higher material loss in principle, although needs optimization for sure, but this is a good advantage. Moreover, its fabrication is less challenging, as the phase change materials is on sides. Results indicate that the proposed optical switch has an operation bandwidth of 96.6 GHz (0.8 nm), together with an extinction ratio of 13.1 dB for the through port and approximately 21.5 dB for the upper/lower drop ports. Additionally, the optical switch has shown an insertion loss of around 3.4 dB for the through port and the upper/lower drop ports.