Ultrafast, all-optical control of modal phases in a few-mode fiber for all-optical switching

On the Hamiltonian form of cross-mode modulation in nonlinear optical waveguides

It is commonly believed that the Hamiltonian approach applies only to linear systems, or nonlinear systems with proper linearization procedures. In this Letter, we show that the Hamiltonian approach based on linear coupled-mode theory applies very well for cross-mode modulation, i.e., field variation of the probe light induced by a strong co-propagating pump light in a degenerate mode group. By deriving eigenvalues and eigenvectors of the nonlinear system, evolution of the probe light can be obtained, which agrees with numerical simulations of multimode nonlinear Schrödinger equations. Using the Hamiltonian approach, a simple approach for determining the pump mode for realizing arbitrary mode conversion is discussed. Two concrete scenarios of the optically induced vector mode conversions within the LP₁₁-mode group are further exemplified.

Low-power broadband all-optical switching via intermodal cross-phase modulation in integrated optical waveguides

We demonstrate the potential of all-optical switches in integrated waveguides based on intermodal cross-phase modulation between transverse modes. For this purpose, the differential phase between two transverse modes of a probe beam was altered by cross-phase modulation with a control beam propagating only in the fundamental mode. A switching behavior was accomplished by spatially filtering the resulting multimode interference of the probe modes, which changed depending on the control beam power. All-optical switching with a contrast of 82% at 1280 nm over a frequency range of 4.4 THz at 1.6 nJ was achieved, representing an improvement of the product of necessary power and waveguide length by a factor of nearly 2000 compared to similar experiments in graded-index fibers. Additionally, we show that the center wavelength of the switch can be tailored by changing the cross-sectional geometry of the waveguide or the involved probe modes.

Time-domain characteristics of ultrafast transverse mode switching based on Si nanowires

We investigate the potential of an ultrafast transverse mode switch based on silicon on insulator (SOI) platform for the switching applications in the spatial division multiplexing (SDM) systems. The impact of waveguide geometry, operation wavelength, pulse width of the pump and probe waves, as well as the temporal delay between the pulses are discussed with a special focus on the temporal switching windows of the switch. The optimized switching performances are further applied to a switching node in a hybrid optical time division-multiplexing (OTDM) and SDM system. The switching energy of the Si-based switch is shown to be potentially smaller than that of the Si₃N₄ based integration platform.

All-optical control of light on a graphene-on-silicon nitride chip using thermo-optic effect

All-optical signal processing avoids the conversion between optical signals and electronic signals and thus has the potential to achieve a power efficient photonic system. Micro-scale all-optical devices for light manipulation are the key components in the all-optical signal processing and have been built on the semiconductor platforms (e.g., silicon and III-V semiconductors). However, the two-photon absorption (TPA) effect and the free-carrier absorption (FCA) effect in these platforms deteriorate the power handling and limit the capability to realize complex functions. Instead, silicon nitride (Si₃N₄) provides a possibility to realize all-optical large-scale integrated circuits due to its insulator nature without TPA and FCA. In this work, we investigate the physical dynamics of all-optical control on a graphene-on-Si₃N₄ chip based on thermo-optic effect. In the experimental demonstration, a switching response time constant of 253.0 ns at a switching energy of ~50 nJ is obtained with a device dimension of 60 μm × 60 μm, corresponding to a figure of merit (FOM) of 3.0 nJ mm. Detailed coupled-mode theory based analysis on the thermo-optic effect of the device has been performed.