小芯径硫系玻璃光纤的制备及其非线性光学应用

通过动态蒸馏提纯技术制备了高纯Ge-As-Se和Ge-As-S硫系玻璃。采用两步棒管法拉制了以Ge-As-Se玻璃为纤芯、Ge-As-S玻璃为包层的小芯径阶跃折射率光纤,并使用飞秒激光抽运光纤测试了超连续谱的产生。以Al和GaCl_3分别作为除氧剂和C/H纯化剂可以有效消除玻璃中的C、H和O杂质。制备的Ge As Se/Ge As S光纤在2~9μm波段表现出优异的传输性能,光纤数值孔径约为1.3;采用重复频率为10.5 MHz、脉冲宽度为320 fs、中心波长为4.0μm、峰值功率为4.6 k W激光抽运长度为22 cm、芯径为6μm的光纤,获得了覆盖1.9~8.2μm、光谱平坦度为±10 d B、平均功率为4.5 m W的超连续谱。

Control of light scattering by nanoparticles with optically-induced magnetic responses

Conventional approaches to control and shape the scattering pattems of light generated by different nanostructures are mostly based on engineering of their electric response due to the fact that most metallic nanostructures support only electric resonances in the optical frequency range. Recently, fuelled by the fast development in the fields of metamaterials and plasmonics, artificial optically-induced magnetic responses have been demonstrated for various nanostructures. This kind of response can be employed to provide an extra degree of freedom for the efficient control and shaping of the scattering patterns of nanoparticles and nanoantennas. Here we review the recent progress in this research direction of nanoparticle scattering shaping and control through the interference of both electric and optically-induced magnetic responses. We discuss the magnetic resonances supported by various structures in different spectral regimes, and then summarize the original results on the scattering shaping involving both electric and magnetic responses, based on the interference of both spectrally separated （with different resonant wavelengths） and overlapped dipoles （with the same resonant wavelength）, and also other higher-order modes. Finally, we discuss the scattering control utilizing Fano resonances associated with the magnetic responses.

Diffractive photonic applications mediated by laser reduced graphene oxides

Modification of reduced graphene oxide in a controllable manner provides a promising material platform for producinggraphene based devices. Its fusion with direct laser writing methods has enabled cost-effective and scalable production for advanced applications based on tailored optical and electronic properties in the conductivity, the fluorescence and the refractive index during the reduction process. This mini-review summarizes the state-of-the-art status of the mechanisms of reduction of graphene oxides by direct laser writing techniques as well as appealing optical diffractive applications including planar lenses, information storage and holographic displays. Owing to its versatility and up-scalability, the laser reduction method holds enormous potentials for graphene based diffractive photonic devices with diverse functionalities.

柔性硫系玻璃光纤传像束的制备及性能研究

通过引入特征温度与硫系玻璃相匹配的高性能热塑性聚合物聚酰亚胺（PEI）作为光纤包层,结合复丝工艺制备了像素数为900的As2S3/PEI光纤传像束,表征了光纤的损耗、光纤束的断丝率、分辨率和串扰率。As2S3/PEI光纤在2~6μm波段传输性能优异,背景损耗约为0.5 d B/m,在S-H杂质对应的4.0μm波长的峰值损耗为3.5 d B/m。单丝直径为80μm、像素数为900的光纤束的断丝率为1%,分辨率为7 line/mm,串扰率为1%,通过此传像束得到了清晰的电烙铁红外图像。而且,将PEI溶于二甲基乙酰胺（DMAC）后使光纤束表现出很好的柔性。采用这种类似＂酸溶玻璃＂的可溶于特定溶剂的热塑性聚合物,作为过渡介质,结合复丝工艺有望制备出柔性高分辨率硫系玻璃光纤传像束。

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).

Atomically thin optical lenses and gratings

Two-dimensional(2D)materials have emerged as promising candidates for miniaturized optoelectronic devices due to their strong inelastic interactions with light.On the other hand,a miniaturized optical system also requires strong elastic light–matter interactions to control the flow of light.Here we report that a single-layer molybdenum disulfide(MoS2)has a giant optical path length(OPL),around one order of magnitude larger than that from a single-layer of graphene.Using such giant OPL to engineer the phase front of optical beams we have demonstrated,to the best of our knowledge,the world’s thinnest optical lens consisting of a few layers of MoS2 less than 6.3 nm thick.By taking advantage of the giant elastic scattering efficiency in ultra-thin high-index 2D materials,we also demonstrated high-efficiency gratings based on a single-or few-layers of MoS2.The capability of manipulating the flow of light in 2D materials opens an exciting avenue towards unprecedented miniaturization of optical components and the integration of advanced optical functionalities.More importantly,the unique and large tunability of the refractive index by electric field in layered MoS2 will enable various applications in electrically tunable atomically thin optical components,such as micro-lenses with electrically tunable focal lengths,electrical tunable phase shifters with ultra-high accuracy,which cannot be realized by conventional bulk solids.

Integrated sources of photon quantum states based on nonlinear optics

The ability to generate complex optical photon states involving entanglement between multiple optical modes is not only critical to advancing our understanding of quantum mechanics but will play a key role in generating many applications in quantum technologies.These include quantum communications,computation,imaging,microscopy and many other novel technologies that are constantly being proposed.However,approaches to generating parallel multiple,customisable bi-and multi-entangled quantum bits(qubits)on a chip are still in the early stages of development.Here,we review recent advances in the realisation of integrated sources of photonic quantum states,focusing on approaches based on nonlinear optics that are compatible with contemporary optical fibre telecommunications and quantum memory platforms as well as with chip-scale semiconductor technology.These new and exciting platforms hold the promise of compact,low-cost,scalable and practical implementations of sources for the generation and manipulation of complex quantum optical states on a chip,which will play a major role in bringing quantum technologies out of the laboratory and into the real world.

Photonic microwave true time delays for phased array antennas using a 49 GHz FSR integrated optical micro-comb source[Invited]

We demonstrate significantly improved performance of a microwave true time delay line based on an integrated optical frequency comb source. The broadband micro-comb(over 100 nm wide) features a record low free spectral range(FSR) of 49 GHz, resulting in an unprecedented record high channel number(81 over the C band)—the highest number of channels for an integrated comb source used for microwave signal processing. We theoretically analyze the performance of a phased array antenna and show that this large channel count results in a high angular resolution and wide beam-steering tunable range. This demonstrates the feasibility of our approach as a competitive solution toward implementing integrated photonic true time delays in radar and communications systems.

Bragg-mirror-like circular dichroism in bio-inspired quadruple-gyroid 4srs nanostructures

The smooth and tailorable spectral response of Bragg mirrors has driven their pervasive use in optical systems requiring customizable spectral control of beam propagation.However,the simple nature of Bragg mirror reflection prevents their application to the control of important polarization states such as circular polarization.While helical and gyroid-based nanostructures exhibiting circular dichroism have been developed extensively to address this limitation,they are often restricted by the spectral inconsistency of their optical response.Here we present the fabrication and characterization of quadruple-gyroid 4srs nanostructures exhibiting bio-inspired Bragg-mirror-like circular dichroism:a smooth and uniform band of circular dichroism reminiscent of the spectrum of a simple multilayer Bragg-mirror.Furthermore,we demonstrate that the circular dichroism produced by 4srs nanostructures are robust to changes in incident angle and beam collimation,providing a new platform to create and engineer circular dichroism for functional circular polarization manipulation.

Experimental control of optical helicity in nanophotonics

An analysis of light–matter interactions based on symmetries can provide valuable insight,particularly because it reveals which quantities are conserved and which ones can be transformed within a physical system.In this context,helicity can be a useful addition to more commonly considered observables such as angular momentum.The question arises how to treat helicity,the projection of the total angular momentum onto the linear momentum direction,in practical experiments.In this paper,we put forward a simple but versatile experimental treatment of helicity.We then apply the proposed method to the scattering of light by isolated cylindrical nanoapertures in a gold film.This allows us to study the helicity transformation taking place during the interaction of focused light with the nanoapertures.In particular,we observe from the transmitted light that the scaling of the helicity transformed component with the aperture size is very different to the direct helicity component.