Polarization-dependent Four-wave Mixing Research Articles

Real-Time RF Multi-Dimensional Signal Switching Using Polarization-Dependent Optical Mixing

Real-time switching of RF signal properties, including phase, frequency, and amplitude, is essential for emerging high-speed RF systems to improve security, signal fidelity, and enhance data capacity. While it is easy to switch the amplitude of an RF signal at GHz speed, unfortunately, it is extremely challenging to perform phase or frequency switching of an RF signal with a fast switching time in the picosecond range. In this paper, a real-time RF signal switching technique is proposed and demonstrated based on polarization dependent four-wave mixing in a highly-nonlinear optical fiber. Due to the amplitude, phase, and frequency transparent property of four-wave mixing, the proposed scheme is capable of manipulating multidimensional RF signal of over tens of GHz frequency, and achieve frequency hopping and phase switching of a GHz RF signal. The switching time is not limited by the proposed temporal switching technique; instead, it is solely depending on the rise/fall time of the control signal itself. Furthermore, the generation of frequency hopping signal with a switching time of 50 ps, as well as simultaneously frequency and phase switching of a GHz RF signal have been experimentally demonstrated based on the proposed RF signal switching scheme.

All-optical logic operation of polarized light signals in highly nonlinear silicon hybrid plasmonic microring resonators.

All-optical logic operation is theoretically demonstrated by means of polarization-dependent four-wave mixing (FWM) processes in a highly nonlinear silicon hybrid plasmonic waveguide (HPWG) microring resonator. We design an ultra-compact (radii = 1 μm) microring resonator (MRR) that is realized by using a silicon HPWG with the capacity for subwavelength-bending. The HPWG exhibits very high confinement (Aeff~0.045 μm(2)) that can result in a remarkably high nonlinear parameter (γ~3000 W(-1) m(-1)), given a highly nonlinear gap material. By manipulating the polarization properties of the pump and signals with a very low electric field (|E|~10(8) Vm(-1)), all-optical NOT, NOR, and NAND logical operations are obtained through the FWM process. These compact all-optical nanoplasmonic devices are stable, fabrication simplified, and silicon on insulator (SOI) compatible.

Optical quasi logic gates based on polarization-dependent four-wave mixing in subwavelength metallic waveguides

All-optical quasi logic gates are demonstrated by means of polarization-dependent four-wave mixing (FWM) in metal-insulator-metal (MIM) waveguides filled with a Kerr nonlinear medium. By using finite-difference-time-domain (FDTD) methods, we perform a quantitative comparison of the FWM efficiency associated with different pump polarization states. By manipulating the core thickness and the polarization properties of the pump and signals, all-optical NOT, NAND, NOR, and NXOR logical functions are obtained.

Selection Rules and Symmetry Relations for Four-Wave Mixing Measurements of Uniaxial Assemblies

Uniaxial systems represent the next lowest symmetry below isotropic and are ubiquitous. The objective of the present work is to present a systematic foundation for interpreting polarization-dependent four-wave mixing measurements of oriented and aligned assemblies. Orientational averages connecting the molecular frame to the macroscopic frame in uniaxial assemblies were derived for several common molecular symmetry groups for coherent anti-Stokes Raman spectroscopy (CARS) measurements, coherent anti-Stokes two-photon spectroscopy (CATS) probing electronic transitions, resonant two-photon absorption (2PA), and traditional Raman measurements. First, the complete set of orientational averages connecting the molecular and macroscopic frames was compiled for the most general case of C1 molecular symmetry. Then, the orientational averages of a select few commonly occurring molecular symmetry groups (Cs, C2, C2v, and C3v) were explored in greater detail to illustrate the approach and to facilitate the interpretation of routine experimental measurements. One outcome of this analysis is the prediction of efficient electric dipole-allowed chiral-specific four-wave mixing in uniaxially oriented media.

Radiatively limited dephasing of quantum dot excitons in the telecommunications wavelength range

The extremely long dephasing time of excitons in strain-compensated quantum dots at telecommunications wavelengths was measured using a polarization-dependent four-wave mixing technique. The use of a 150-layer-stacked structure enabled them to measure a four-wave mixing signal with a high signal-to-noise ratio, in spite of the fact that a high-sensitive heterodyne detection was not used. The large anisotropy of the dephasing time indicates the dominance of the radiative recombination process on dephasing. By simultaneously measuring the radiative lifetime using a pump-probe technique, they could directly estimate pure dephasing with an accuracy of better than 0.1μeV.

Magneto-Optical Four-Wave-Mixing Studies of an Exciton–Biexciton System in a CdMnTe/CdTe/CdMgTe Single Quantum Well

Exciton and biexciton states in a CdMnTe/CdTe/CdMgTe quantum well were investigated by means of polarization-dependent four-wave mixing (FWM) measurements in magnetic fields up to 7 T. In co-linear and cross-linear polarization geometry, the FWM signals were strongly modified by the magnetic field, which was directed normal to the quantum-well plane. Very clear beat structures due to giant Zeeman splitting of the excitons were observed. In the co-circular (σ+,σ+) configuration, a high magnetic field induced a beat-like structure in an early delay-time region. Spectrally resolved FWM signals indicating an additional transition appeared at the 1.1 meV higher energy side of the exciton resonance. According to the spin selection rule, the oscillator strength of the triplet biexciton that consisted of two σ+ excitons was found to increase in magnetic fields.

Multiple, polarization diverse, idler wave generation in fibers from competing four-wave mixing processes

We report on a theoretical and experimental characterization of polarization-dependent four-wave mixing processes in highly nonlinear optical fibers. Two or three idler waves at different polarizations are experimentally generated in an optical fiber from the propagation of two wavelength-detuned, orthogonally-polarized pumps and a signal. Each idler wave results from a different four-wave mixing process involving the signal and one or both pumps. Orthogonally-polarized idler waves are demultiplexed in a polarization beam splitter with a cross-polarization suppression of over 17dB. The parametric process equations for this system are analytically solved and the efficiencies of the competing processes analyzed for the small pump detunings and identical pump powers. This experimental setup can be used in telecommunication systems for producing and selectively rerouting various copies of a data signal.

Excitons, biexcitons, and phonons in ultrathin CdSe/ZnSe quantum structures

The optical properties of CdSe nanostructures grown by migration-enhanced epitaxy of CdSe on ZnSe are studied by time-, energy-, and temperature-dependent photoluminescence and excitation spectroscopy, as well as by polarization-dependent four-wave mixing and two-photon absorption experiments. The nanostructures consist of a coherently strained ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ quantum well with embedded islands of higher Cd content with sizes of a few nanometer due to strain-induced CdSe accumulation. The local increase in CdSe concentration results in a strong localization of the excitonic wave function, in an increase in radiative lifetime, and a decrease of the dephasing rate. Local LO-phonon modes caused by the strong modulation of the Cd concentration profile are found in phonon-assisted relaxation processes. Confined biexcitons with large binding energies between 20 and 24 meV are observed, indicating the important role of biexcitons even at room temperature.