Characterization of multimode linear optical networks

Multimode optical interferometers represent the most viable platforms for the successful implementation of several quantum information schemes that take advantage of optical processing.Examples range from quantum communication and sensing,to computation,including optical neural networks,optical reservoir computing,or simulation of complex physical systems.The realization of such routines requires high levels of control and tunability of the parameters that define the operations carried out by the device.This requirement becomes particularly crucial in light of recent technological improvements in integrated photonic technologies,which enable the implementation of progressively larger circuits embedding a considerable amount of tunable parameters.We formulate efficient procedures for the characterization of optical circuits in the presence of imperfections that typically occur in physical experiments,such as unbalanced losses and phase instabilities in the input and output collection stages.The algorithm aims at reconstructing the transfer matrix that represents the optical interferometer without making any strong assumptions about its internal structure and encoding.We show the viability of this approach in an experimentally relevant scenario,defined by a tunable integrated photonic circuit,and we demonstrate the effectiveness and robustness of our method.Our findings can find application in a wide range of optical setups,based on both bulk and integrated configurations.

X-parameter measurement on a GaN HEMT device: complexity reduction study of load-pull characterization test setup

Characterization of power transistors is an indispensable step in the design of radio frequency and mi- crowave power amplifiers. A full harmonic load-pull measurement setup is normally required for the accurate and comprehensive characterization of RF power transistors. The setup is usually highly complex, leading to a rela- tively high hardware cost and low measurement throughput. This paper presents X-parameter measurement on a gallium nitride （GaN） high-electron-mobility transistor and studies the potential of utilizing an X-parameter-based modeling technique to highly reduce the complexity of the harmonic load-pull measurement setup for transistor characterization. During the X-parameter measurement and characterization, load impedance of the device is tuned and controlled only at the fundamental frequency and is left uncontrolled at other higher harmonics. However, it proves preliminarily that the extracted X-parameters can still predict the behavior of the device with moderate to high accuracy, when the load impedance is tuned up to the third-order harmonic frequency. It means that a fundamental-only load-pull test setup is already enough even though the device is to be characterized under load tuning up to the third-order harmonic frequency, by utilizing X-parameters.

High-speed and broad optical bandwidth silicon modulator

A high-speed silicon modulator with broad optical bandwidth is proposed based on a symmetrically configured Mach- Zehnder interferometer. Careful phase bias control and traveling-wave design are used to improve the high-speed perfor- mance. Over a broadband wavelength range, high-speed operation up to 30 Gbit/s with a 4.5 dB-5.5 dB extinction ratio is experimentally demonstrated with a low driving voltage of 3 V.