Ultra-high suppression microwave photonic bandstop filters

A bandstop radio frequency(RF)filter can enhance the capabilities of RF communication systems by removing unwanted signal components such as distortion,or interference.In modern cognitive radio systems,frequency agile filters are desired to block interferers with dynamically changing frequencies and powers.These filters should be tunable over a broad frequency range,and they should be capable of suppressing very strong signals with a high resolution.To simultaneously meet these requirements with traditional RF filters are highly challenging.Microwave photonic(MWP),a technology that primary deals with the generation,distribution,and processing of high speed RF signals using photonic techniques and components,is promising for creating frequency agile RF filters.However,traditional MWP filters are lacking the high resolution and peak suppression exhibited by state-ofthe-art RF electrical filters.We recently introduced a new class of MWP notch filter which is free from this limitation.This scheme allowed the creation of anomalously high suppression MWP notch filter from virtually any kind of optical resonance,irrespective of its type(gain or absorption),or its magnitude.This enabled,for the first time,simultaneous optimization of the MWP filter resolution,peak attenuation,and frequency tuning range.In this paper,we present the analysis of notch filter response creation using the novel sideband processing technique.We thenshow the applicability of this technique to a wide range of optical filters.We compare simulated and experimental results of the notch filter response created using three types of optical filter commonly used in MWP signal processing,namely stimulated Brillouin scattering(SBS),an integrated optical ring resonator(ORR),and a phase-shifted fiber Bragg-grating(FBG).

Multidimensional synthetic chiral-tube lattices via nonlinear frequency conversion

Geometrical dimensionality plays a fundamentally important role in the topological effects arising in discrete lattices.Although direct experiments are limited by three spatial dimensions,the research topic of synthetic dimensions implemented by the frequency degree of freedom in photonics is rapidly advancing.The manipulation of light in these artificial lattices is typically realized through electro-optic modulation;yet,their operating bandwidth imposes practical constraints on the range of interactions between different frequency components.Here we propose and experimentally realize all-optical synthetic dimensions involving specially tailored simultaneous short-and long-range interactions between discrete spectral lines mediated by frequency conversion in a nonlinear waveguide.We realize triangular chiral-tube lattices in three-dimensional space and explore their four-dimensional generalization.We implement a synthetic gauge field with nonzero magnetic flux and observe the associated multidimensional dynamics of frequency combs,all within one physical spatial port.We anticipate that our method will provide a new means for the fundamental study of high-dimensional physics and act as an important step towards using topological effects in optical devices operating in the time and frequency domains.

Thermo-optically tunable spectral broadening in a nonlinear ultra-silicon-rich nitride Bragg grating

Spectral tunability methods used in optical communications and signal processing leveraging optical,electrical,and acousto-optic effects typically involve spectral truncation that results in energy loss.Here we demonstrate temperature tunable spectral broadening using a nonlinear ultra-silicon-rich nitride device consisting of a 3-mm-long cladding-modulated Bragg grating and a 7-mm-long nonlinear channel waveguide.By operating at frequencies close to the grating band edge,in an apodized Bragg grating,we access strong grating-induced dispersion while maintaining low losses and high transmissivity.We further exploit the redshift in the Bragg grating stopband due to the thermo-optic effect to achieve tunable dispersion,leading to varying degrees of soliton-effect compression and self-phase-modulation-induced spectral broadening.We observe an increase in the bandwidth of the output pulse spectrum from 69 to 106 nm as temperature decreases from 70℃ to 25℃,in good agreement with simulated results using the generalized nonlinear Schrödinger equation.The demonstrated approach provides a new avenue to achieve on-chip laser spectral tuning without loss in pulse energy.