Current Mach–Zehnder switches primarily rely on the weak modulation of the refractive index (usually ∆n < 0.01) from the free-carrier dispersion or thermo-optic effects, resulting in a large footprintand high power consumption. By utilizing the dramatic difference in the optical refractive index and extinction coefficient between the crystalline and amorphous phases of Ge2Sb2Te5 (GST), we demonstrate an all-optical nonvolatile switch in microring resonators with extinction ratio up to 33 dB. To extent the operating bandwidth, we demonstrate compact (~30 µm), low-loss (~1dB), and broadband (over 30 nm with CT < –10 dB) 1 × 2 and 2 × 2 photonic switches using the PCM, based on the asymmetric directional coupler (DC) switch design bypassing the high loss associated with the crystalline state. GST possees much lower values of extinction coefficient in the wavelength region of >2 µm.
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