With the development of optical interconnection and high-speed optical communication, electro-optic modulators have become a research hotspot. Silicon insulator materials have the advantages of compatibility with the complementary metal oxide semiconductor process, high integration, low power consumption, and high temperature resistance. There are several electro-optic modulators based on silicon materials. Electro-optic modulators with high modulation rate, compact size, and easy integration have been investigated previously, and the study on electro-optic modulators is crucial. Therefore, we design an electro-optic modulator with a reflective wall based on a one-dimensional photonic crystal nanowire cavity (PCNC). The modulator exhibits a high extinction ratio, large modulation bandwidth, and high modulation rate. Furthermore, it has a compact and simple structure and can easily to cascade other silicon photonic devices. With the development of integrated photonics in communication systems, the cascade of silicon photonic devices has a wider application prospect.
This study proposes a download-type electro-optic modulator with a reflective wall based on a silicon-on-insulator (SOI) one-dimensional PCNC. The main line waveguide, one-dimensional PCNC and download-type waveguide are used to form a download-type structure with a reflective wall. The duty cycle of the nanowire cavity decreases linearly from the center of the waveguide to the two ends, and doping is introduced at both sides of the modulator to form PN junctions. The finite difference time domain (FDTD) model in the optical simulation software Lumerical is used for simulation analysis. According to the free carrier dispersion effect in the silicon material, when the modulation voltage applied at both ends of the electro-optic modulator changes, the dielectric constant of the nanowire cavity material also changes. The refractive index change in the nanowire cavity produces a slight difference; hence, the resonant frequency of the cavity changes, i.e., the central wavelength of the electro-optic modulator shifts. Specifically, corresponding to the wavelength of 1550.01 nm, the addition or non-addition of the modulation voltage is equivalent to the “off” or “on” state of the modulator.
An electro-optic modulator with a reflective wall based on the SOI PCNC is proposed. The incident light is coupled into the one-dimensional PCNC after passing through the main line waveguide, and then coupled again to output through the download-type waveguide. The adjustments of the position and number of reflective circular holes in the main line waveguide and download-type waveguide are beneficial to improve the overall transmittance of the device. The nanowire cavity uses a gradual circular hole to confine the beam in the cavity. PN junction is generated by doping on both sides of the nanowire cavity, and a low bias voltage is applied to adjust the resonant wavelength of the nanowire cavity, to realize the “on” and “off” modulation of the optical signal at the working wavelength. 3D-FDTD is used to analyze the optical characteristics and electrical performance of the modulator. The results indicate that the electro-optic modulator can modulate the optical signal with the wavelength of 1550.01 nm, and the transmittances under the “off” and “on” states are 0.0037 and 96.34%, respectively (Fig.14). The modulation voltage is only 1.2 V, the insertion loss is 0.2 dB, the extinction ratio is 24 dB, and the size is only 54 μm2. The modulation frequency is 8.7 GHz, and the modulation bandwidth can reach 122 GHz, which implies that the proposed device has applications in optical communication and integrated photonics. In addition, after comparing the performances of the photonic crystal electro-optic modulators (Table 1), it is inferred that the proposed device exhibits excellent performance.
This study proposes a download-type electro-optic modulator with a reflective wall based on SOI one-dimensional PCNC. The downloadable structure of the reflection wall comprises a main line waveguide, one-dimensional PCNC, and downloadable waveguide. The doping method is introduced to form PN junctions at both sides of the modulator. Under the action of the modulation voltage, the refractive index of the silicon in the nanowire cavity changes, which triggers the migration of defect modes in the nanowire cavity; in addition, the “on” and “off” state modulations of the electro-optic modulator are realized. The electro-optical modulation is simulated and analyzed via the 3D-FDTD model in the Lumerical commercial simulation software. The simulation results demonstrate that compared with other electro-optical modulators based on nanowire cavity, the proposed electro-optical modulator has a higher extinction ratio, higher modulation bandwidth, higher modulation rate, compact and simple structure, and can easily be cascaded to other silicon photonic devices. The proposed electro-optic modulator exhibits a significant development and application value in the integrated photonics of optical communication.
