ABSTRACT
Low-noise integrated all-optical wavelength converters that can be operated in short pulse regime are essential tools to overcome contention resolution in a modern communication network, based on wavelength division multiplexing. Any imperfect functionality in such devices causes non-ideal optical power transfer to the converted data pulses. All imperfections during the preparation and operation of the wavelength converters can be addressed to the waveguide inhomogeneity which distorts data pulses to be converted. This paper reports different waveguide inhomogeneity effects on the pulse distortion while using periodically poled lithium niobate waveguide as wavelength converters. Three types of [Formula: see text]-based nonlinear optical processes, including second harmonic generation, difference frequency generation, and cascaded second harmonic generation/difference frequency generation are numerically studied to show that any constant, linear, and quadratic waveguide inhomogeneity causes short pulse (down to 1 ns) distortion in such wavelength converters. In addition, it is shown that the reconstruction of [Formula: see text]-shaped generated pulses is possible, when suitable upside-down quadratic variations of obtained inhomogeneity are deliberately induced in the waveguide. Notably, for pulsed second harmonic generation, the generated pulse can be compressed using an upside-down quadratic phase mismatch.
ABSTRACT
Wavelength division multiplexing (WDM) using higher-order spatial modes such as orbital angular momentum (OAM) through a channelized bandwidth provides enhanced capacity communication systems. An all-optical wavelength converter is a key function in implemented WDM networks to overcome the wavelength contentions. In addition, a polarization converter provides efficient control on the state of polarization for encoded data channels in the optical networks. This paper proposes a novel versatile-designed integrated optical device with Ycut ridge lithium niobate photonic wire configuration that acts as a wavelength or polarization converter for data modulated on OAM. It is schemed in such a way that generates decomposed guided modes with a new wavelength and polarization via cascaded second harmonic generation/difference frequency generation (cSHG/DFG) and type-II DFG nonlinear interactions, respectively, where their desired relative phase is achieved by a linear electro-optical effect in the successive phase shifter part. The low loss ≤0.09 dB/cm, high purity (≥94%), and low voltage (≤4 V) of the high-speed proposed modulator enable its compatible operation in commercial wireless and fiber-based polarization-multiplexed WDM communication systems.
ABSTRACT
Recent studies demonstrated that the optical channels encoded by Orbital Angular Momentum (OAM) are capable candidates for improving the next generation of communication systems. OAM states can enhance the capacity and security of high-dimensional communication channels in both classical and quantum regimes based on optical fibre and free space. Hence, fast and precise control of the beams encoded by OAM can provide their commercial applications in the compatible communication networks. Integrated optical devices are good miniaturized options to perform this issue. This paper proposes a numerically verified integrated high-frequency electro-optical modulator for manipulation of the guided modes encoded in both OAM and polarization states. The proposed modulator is designed as an electro-optically active Lithium Niobate (LN) core photonic wire with silica as its cladding in a LN on Insulator (LNOI) configuration. It consists of two successive parts; a phase shifter to reverse the rotation handedness of the input OAM state and a polarization converter to change the horizontally polarized OAM state to the vertically polarized one. It is shown that all four possible output polarization-OAM encoded states can be achieved with only 6 V and 7 V applied voltages to the electrodes in the two parts of the modulator.
