Optical Modulation via Guided-Mode Resonance in an ITO-Loaded Distributed Bragg Reflector Topped With a Two-Dimensional Grating

We are reporting the design procedure for a narrow-band ultra-low-power reflective optical modulator that operates at the critical coupling of an appropriately designed two-dimensional grating with the center frequency of a quarter wavelength distributed Bragg reflector (DBR). By sandwiching a three-layer stack of gated ITO/HfO2/ITO between the DBR and the grating, we can make the optical modulator operational, taking advantage of the tunable property of the ultrathin layer at the ITO/HfO2 interface accumulated by electrons under an ultra-low applied voltage (-0.1 V). The corresponding energy consumption is similar to 5.5 fJ/bit. Moreover, our simulations show that the capacitance limited modulation speed is more than 80 Mbps. Our numerical results also predict the influence of possible fabrication errors on the guided-mode resonance wavelength. This investigation shows that a +/- 3 nm deviation in the grating pitch affects the modulator performance profoundly. Furthermore, the numerical results demonstrate the modulation depth of similar to 24 dB is achievable for an appropriately designed modulator with an acceptable insertion loss of similar to 0.05 dB. This paper paves the way for developing next-generation optical modulators with high modulation depth, low insertion loss, and ultra-low energy consumption.