Efficient and Broadband Four‐Wave Mixing in a Compact Silicon Subwavelength Nanohole Waveguide

Abstract

In this paper, we propose a simple yet effective scheme by using a compact silicon subwavelength nanohole waveguide, which possesses a broadband and low-loss transmission. As the subwavelength nanoholes are periodically distributed along the silicon waveguide, the optical properties of this artificial material, such as the effective refraction index, the transmittance and the dispersion, can be engineered by varying the nanohole diameter and the period. By this means, an enhanced light intensity in the silicon area can be achieved in the nanohole waveguide, leading to an efficient and broadband FWM process. The mechanism we propose in this paper is different from the slow-wave effect reported in previous papers, [13,14] which enhanced the conversion efficiencies in 1D periodic photonic structures by leveraging the large group indices near the band edges. The nonlinearity of the silicon nanohole waveguide originates from the enhanced light intensity in the nonresonant silicon waveguide, thus enabling a broadband FWM process. For the nanoholes with a diameter of 100 nm and a period of 300 nm, a FWM conversion efficiency of −26.7 dB is observed in the experiment, showing a 12.5 dB improvement compared to a conventional silicon strip waveguide. Thanks to the broadband transmission and the negligible linear dispersion of the silicon nanohole waveguide, a 3 dB conversion bandwidth of 37 nm is experimentally demonstrated, which is limited by the optical amplifiers employed in the experiment.The proposed silicon nanohole waveguide is schematically illustrated in Figure 1a, which consists of a periodic array of subwavelength nanoholes in the center of the silicon waveguide. The propagation of the light in the waveguide is studied using the 3D finite-difference time-domain (3D-FDTD) method. In Figure 1b-d, the cross-section of the silicon waveguide is 480 × 220 nm 2 and the lengths of the silicon waveguide and the nanohole segment are 60 and 50 µm, respectively. The nanohole diameter d = 100 nm is used and kept constant while the period of the nanoholes is varied. The electric field distribution of the Bloch mode is mainly trapped in the air (silicon) area with the period a = 200 nm (a = 300 nm). Based on the previous study, [21] the band edge wavelength is dependent on the nanohole period. The normalized transmission spectra with two periods and different nanohole diameters are shown in Figure 1e,f, respectively. It can be seen that the band edges in both cases are away from the operating wavelengths (C-band) with the nanohole diameters ranging from 60 to 140 nm. Small Confining light in a small volume offers an effective approach to enhance the four-wave mixing (FWM) process. Recently, most efforts are devoted to improve the conversion efficiencies by using resonant structures. As a result, the bandwidths of the FWM conversions are typically limited to 1-2 nm. In this paper, a nonresonant silicon subwavelength nanohole waveguide is proposed to manipulate the field distribution of the propagating wave. The electromagnetic...

Enhanced Direct White Light Emission Efficiency in Quantum Dot Light‐Emitting Diodes via Embedded Ferroelectric Islands Structure

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