Fast Electro-optics Research Articles

Compact slow-light waveguide and modulator on thin-film lithium niobate platform

Abstract Lithium niobate Mach–Zehnder modulators (MZMs) with compact footprint and fast electro-optics (EO) responses are highly demanded for the next-generation optical interconnect systems. Here, we demonstrate slow-light (SL) effect using a coupled Bragg resonator structure on the thin-film lithium niobate (TFLN) platform, and an ultra-compact SL-MZM with length L of ∼370 μm is also constructed. The fabricated SL waveguides show a large optical passband width of ∼8 nm, an insertion loss of 2.9 dB, and a maximal optical group index of 7.50, corresponding to 3.4 times as large as that of regular TFLN rib waveguide. The fabricated SL-MZM exhibits a large EO bandwidth of >50 GHz in an operating wavelength band of ∼8 nm as well. High-speed OOK transmissions at data rates of 64 Gbit/s and 80 Gbit/s are successfully achieved. To our best knowledge, it is first time to build SL waveguides and compact SL-MZMs with large EO bandwidths of >50 GHz on the monolithic TFLN platform.

Resonant Visible Light Modulation with Graphene

Fast modulation and switching of light at visible and near-infrared (vis-NIR) frequencies is of utmost importance for optical signal processing and sensing technologies. No fundamental limit appears to prevent us from designing wavelength-sized devices capable of controlling the light phase and intensity at gigaherts (and even terahertz) speeds in those spectral ranges. However, this problem remains largely unsolved, despite recent advances in the use of quantum wells and phase-change materials for that purpose. Here, we explore an alternative solution based upon the remarkable electro-optical properties of graphene. In particular, we predict unity-order changes in the transmission and absorption of vis-NIR light produced upon electrical doping of graphene sheets coupled to realistically engineered optical cavities. The light intensity is enhanced at the graphene plane, and so is its absorption, which can be switched and modulated via Pauli blocking through varying the level of doping. Specifically, we explore dielectric planar cavities operating under either tunneling or Fabry-Perot resonant transmission conditions, as well as Mie modes in silicon nanospheres and lattice resonances in metal particle arrays. Our simulations reveal absolute variations in transmission exceeding 90% as well as an extinction ratio >15 dB with small insertion losses using feasible material parameters, thus supporting the application of graphene in fast electro-optics at vis-NIR frequencies.

Fast electro-optics of a single self-assembled quantum dot in a charge-tunable device

The response of a single InGaAs quantum dot, embedded in a miniaturized charge-tunable device, to an applied GHz bandwidth electrical pulse is investigated via its optical response. Quantum-dot response times of 1.0 ± 0.1 ns are characterized via several different measurement techniques, demonstrating GHz-bandwidth electrical control. Furthermore, a novel optical detection technique based on resonant electron-hole pair generation in the hybridization region is used to map fully the voltage pulse experienced by the quantum dot, showing, in this case, a simple exponential rise.

Angle Selective Enhancement of Beam Deflection in High-Speed Electrooptic Switches

Fast electrooptic (EO) deflector switches (DSs) have high potential for applications in optical burst transport networks. EO properties of active materials used in the DSs can impose some limitations on their beam deflection efficiencies. Using a test setup with planar silica waveguide microlens arrays, thin-film ferroelec- tric oxide beam deflectors, and glass volume Bragg gratings, we demonstrate that the beam deflection angle can be increased by more than a factor of 5 for the same switching voltages. The tech- nology enables significant performance improvement of the fast EO DSs.

Fast Electrooptic Response Based on Defect Mode Switching in One-Dimensional Photonic Crystal Containing Nematic Liquid Crystal and Ferroelectric Liquid Crystal as a Defect Layer

Electrical tuning of defect modes in a one-dimensional photonic crystal has been demonstrated using a ferroelectric liquid crystal and a nematic liquid crystal as a defect layer in the periodic structure. The theoretical calculation based on a simple transfer matrix has been carried out, and the result has been found to agree with the experimental result. A high-speed electrooptic switching based on the tunable defect mode has also been demonstrated. The response time of the order of several tens microseconds in this defect mode switching has been realized at low driving voltage.

Electro-absorption and fast electro-optics in highly polar molecular crystals

Polar organic crystals show great promise for use in photonic devices such as electro-optic amplitude or phase modulators for telecommunication. We discuss the structural requirements for large electro-optic effects and demonstrate through high frequency electro-optic experiments that acoustic phonon contributions to the linear electro-optic effect can be neglected in the crystals presented here. The small effect of acoustic modes was found to result from a compensation between the effects of piezoelectric length change and elasto-optic contributions. Moreover, we show that the effects of electro-absorption and linear electro-optics can be well understood in the terms of the linear Stark effect.