Broadband Electro-Optical Crossbar Switches Using Low-Loss Ge2Sb2Se4Te1 Phase Change Material

This theoretical modeling and simulation paper presents designs and projected performance of non-volatile broadband on-chip 1 × 2 and 2 × 2 electro-optical switches operating in the telecommunication C-band and based on the silicon-on-insulator technological platform. These optical switches consist of an asymmetric two-waveguide directional coupler and a symmetric three-waveguide directional coupler, in which the optical phase change material Ge
₂
Sb
₂
Se
₄
Te
₁
(GSST) is the top cladding layer for one of the silicon strip waveguides. Reversible crossbar switching is attained by the amorphous (Am) to crystalline (Cr) and Cr-to-Am phase transitions in the GSST induced by heating the GSST in contact with an indium tin oxide (ITO) microstrip through Joule heating. We examined device performance in terms of mid-band insertion loss (IL), crosstalk (CT), and 0.3-dB IL bandwidth (BW). The 2 × 2 results were IL = -0.018 dB, CT <; 31.3 dB, and BW = 58 nm for the coupling length Lc of 15.4 μm, and IL = 0.046 dB, CT <; 38.1 dB, and BW = 70 nm for the coupling length Lc of 17.4 μm. Simulations of the 1 × 2 devices at 16.7-μm Lc revealed that IL = 0.083 dB and CT <; 12.8 dB along with an expanded BW of 95 nm. Thermal simulations showed that a 5-V pulse train applied to 10
¹⁹
-cm
^-3
doped ITO would produce crystallization; however, the process of amorphization required a 24-V pulse of 2.9-μs duration to raise the GSST temperature above the melting temperature of 900 K.