Mid-infrared optical modulator based on silicon D-shaped photonic crystal fiber with VO₂ material

Recently, photonic crystal fibers (PCFs) have become of significant interest due to their various applications, especially in the mid-infrared (mid-IR) regime. In this work, an optical mid-IR modulator based on silicon D-shaped PCF (Si-D-PCF) with vanadium dioxide (VO₂) as a phase changing material (PCM) is presented and analyzed. Thanks to the phase transition of the VO₂ material between insulating (ON) and conducting (OFF) states, the modulation process can be attained. The well-known full vectorial finite element method is utilized to numerically analyze the proposed design. Further, the propagation of light through the suggested structure is studied using the 3D finite difference time domain method. The optical losses of the fundamental TM mode supported by the Si-D-PCF structure in both ON and OFF states are investigated. The obtained results reveal that the extinction ratio (ER) of the reported modulator approaches 236 dB, while the insertion loss (IL) is less than 1.3 dB over the studied wavelength range 3-7 µm at a device length (L_D) of 0.5 mm. Additionally, the ER of the proposed modulator is higher than 56 dB through the whole studied wavelength range. Therefore, the proposed modulator could be utilized in photonic integrated circuits that require high ER, low IL, and large bandwidth. To the best of the authors' knowledge, this is the first time an infrared optical modulator based on Si-D-PCF with VO₂ material has been presented.