Ultrafast all-optical phase switching enabled by epsilon-near-zero materials in silicon

Abstract

Transparent conducting oxides (TCOs) have emerged as both particularly appealing epsilon-near-zero (ENZ) materials and remarkable candidates for the design and fabrication of active silicon nanophotonic devices. However, the leverage of TCO’s ultrafast nonlinearities requires precise control of the intricate physical mechanisms that take place upon excitation. Here we investigate such behavior for ultrafast all-optical phase switching in hybrid TCO-silicon waveguides through numerical simulation. The model is driven from the framework of intraband-transition-induced optical nonlinearity. Transient evolution is studied with a phenomenological two-temperature model. Our results reveal the best compromise between energy consumption, insertion losses and phase change per unit length for enabling ultrafast switching times below 100 fs and compact active lengths in the order of several micrometers.

All-optical switching in epsilon-near-zero asymmetric directional coupler

“…In general, the following Drude model can quantify its permittivity dispersion profile 13 : where ε ∞ is high-frequency permittivity, γ is the damping frequency, ω is the angular frequency of light and ω p is plasma frequency. Here, we describe the static optical response of TCO with values from the references 23 , 25 , where ε ∞ = 5.5, γ = 3.35 × 10 13 rad s −1 , ω p = 2.85 × 10 15 rad s −1 . The real part of the permittivity has a zero-crossing at the wavelength of 1.55 μm.…”

“…These characteristics of ENZ TCO can provide possibilities for breaking the limitations of traditional all-optical waveguide logic gates. To date, all-optical ENZ switches are mostly based on metasurfaces 20 , 21 or bulk 22 structures, and the reported ENZ-related all-optical waveguide devices are mainly phase modulation designs 23 , 24 . Therefore, it is necessary to explore its form as all-optical switch in integrated photonic systems.…”

Reconfigurable photonics enabled by functional oxides

“…Furthermore, a quasi-continuous representation of the complex plane can be obtained by using an array of modulators with different lengths and driving voltages. A reconfigurable activation function based on such a hybrid waveguide modulator device has been recently proposed 14 . Reconfigurability is achieved by adjusting the driving voltage depending on the input optical power and two reconfiguration parameters.…”

Si-CMOS compatible epsilon-near-zero metamaterial for two-color ultrafast all-optical switching

“…Therefore, this opens up a new paradigm for photonic applications taking advantage of the linear and nonlinear properties [23][24][25][26][27][28][29] . In particular, Sicompatible ENZ materials that can be integrated with silicon photonics circuits significantly reduce the cost and manufacturing complexities.…”

“…In particular, Sicompatible ENZ materials that can be integrated with silicon photonics circuits significantly reduce the cost and manufacturing complexities. This would provide more efficient performance and new functionalities in hybrid integrated photonics devices concepts, i.e., logic analysis 28,30 . In this respect, transparent conducting oxides (TCOs) that are complementary metal oxide semiconductor (CMOS) compatible, such as indium-tin-oxide (ITO) and aluminum-doped zinc oxide (AZO), turn out to be relevant homogeneous ENZ materials operating at the telecom window as ultrafast photonics components 15,16,20,31,32 .…”