Organic electro-optic polymer materials and organic-based hybrid electro-optic modulators

High performance electro-optic modulator,as the key device of integrated ultra-wideband optical systems,have be-come the focus of research.Meanwhile,the organic-based hybrid electro-optic modulators,which make full use of the advant-ages of organic electro-optic(OEO)materials(e.g.high electro-optic coefficient,fast response speed,high bandwidth,easy pro-cessing/integration and low cost)have attracted considerable attention.In this paper,we introduce a series of high-perform-ance OEO materials that exhibit good properties in electro-optic activity and thermal stability.In addition,the recent progress of organic-based hybrid electro-optic devices is reviewed,including photonic crystal-organic hybrid(PCOH),silicon-organic hy-brid(SOH)and plasmonic-organic hybrid(POH)modulators.A high-performance integrated optical platform based on OEO ma-terials is a promising solution for growing high speeds and low power consumption in compact sizes.

Progress in display technologies and their applications

This paper overviews some display technologies which play main roles on today′s display market. And new technologies which may be used for tomorrow′s display technologies have been discussed. New technologies will boost the development of display technologies.

The Transmission Modes and Losses of the Poled Nano-crystal and Polymer Composite PbTiO_3 / PEK-c Thin-film Waveguides

Composite thin films of PbTiO3 nano-crystals and high transparency polymer polyetherketone （PEK-c） for application of non-linear optical devices were prepared by spin coating. The size of PbTiO3 nano-crystals was estimated to be 30-40 nm using a transmission electron microscope. The refractive index and the mode propagation losses at 633 nm were measured using the prism coupling technique and improved photographic technique respectively. They were found to be 1.6545 and 2.00 dB cm^-1 （fundamental mode）,respectively. Moreover, it is observed that this loss is increased at higher mode indices.

Patterned Nanofoam Fabrication from a Variety of Materials via Femtosecond Laser Pulses

High-repetition-rate femtosecond lasers enable the precise production of nanofoam from a wide range of materials. Here, the laser-based fabrication of nanofoam from silicon, borosilicate glass, sodalime glass, gallium lanthanum sulphide and lithium niobate is demonstrated, where the pore size of the nanofoam is shown to depend strongly on the material used, such that the pore width and nanofibre width appear to increase with density and thermal expansion coefficient of the material. In addition, the patterning of nanofoam on a glass slide, with fabricated pattern pixel resolution of ~35 μm, is demonstrated.

Laser-Based Fabrication of Nanofoam inside a Hollow Capillary

Highly porous nanofoam can be fabricated via multiphoton ablation of a material by raster-scanning femtosecond laser pulses over the material surface. Here, we show the fabrication of nanofoam on the inside surface of a hollow silica capillary that has an inner and outer diameter of 640 and 700 μm respectively. A thin layer of nanofoam was fabricated over ~70% of the inner surface of the capillary. Ray-tracing simulations were used to determine the positional corrections required to account for refraction on the curved surface and also to explain the inability to fabricate nanofoam on the side walls of the capillary.

Universal silicon ring resonator for error-free transmission links

We report the design, fabrication, and characterization of a universal silicon PN junction ring resonator for C band error-free communication links operated up to 50 Gb/s with co-designed optical modulation and detection performance. The universal p-n junction ring device shows co-designed detection responsivity up to 0.84 A/W, in conjunction with a modulation efficiency of -4 V·mm and>8 d B optical modulation extinction ratio, enabling C band 50 Gb/s NRZ communication link with a bit error rate≤3×10^(-12).

High-speed silicon photonic electro-optic Kerr modulation

Silicon-based electro-optic modulators contribute to easing the integration of high-speed and low-power consumption circuits for classical optical communications and data computations.Beyond the plasma dispersion modulation,an alternative solution in silicon is to exploit the DC Kerr effect,which generates an equivalent linear electro-optical effect enabled by applying a large DC electric field.Although some theoretical and experimental studies have shown its existence in silicon,limited contributions relative to plasma dispersion have been achieved in high-speed modulation so far.This paper presents high-speed optical modulation based on the DC Kerr effect in silicon PIN waveguides.The contributions of both plasma dispersion and Kerr effects have been analyzed in different waveguide configurations,and we demonstrated that the Kerr induced modulation is dominant when a high external DC electric field is applied in PIN waveguides.High-speed optical modulation response is analyzed,and eye diagrams up to 80 Gbit/s in NRZ format are obtained under a d.c.voltage of 30 V.This work paves the way to exploit the Kerr effect to generate high-speed Pockels-like optical modulation.

Asymmetric frequency multiplexing topological devices based on a floating edge band

Topological photonics provides a platform for robust energy transport regardless of sharp corners and defects.Recently,the frequency multiplexing topological devices have attracted much attention due to the ability to separate optical signals by wavelength and hence the potential application in optical communication systems.Existing frequency multiplexing topological devices are generally based on the slow light effect.However,the resulting static local spatial mode or finely tuned flat band has zero-group velocity,making it difficult for both experimental excitation and channel out-coupling.Here,we propose and experimentally demonstrate an alternative prototype of asymmetric frequency multiplexing devices including a topological rainbow and frequency router based on floating topological edge mode(instead of localized ones);hence the multiple wavelength channels can be collectively excited with a point source and efficiently routed to separate output ports.The channel separation in our design is achieved by gradually tuning the band gap truncation on a topological edge band over a wide range of frequencies.A crucial feature lies in that the topological edge band is detached from bulk states and floating within the upper and lower photonic band gaps.More interestingly,due to the sandwiched morphology of the edge band,the top and bottom band gaps will each truncate into transport channels that support topological propagation towards opposite directions,and the asymmetrical transportation is realized for the frequency multiplexing topological devices.

Fully integrated and broadband Si-rich silicon nitride wavelength converter based on Bragg scattering intermodal four-wave mixing

Intermodal four-wave mixing(FWM)processes have recently attracted significant interest for all-optical signal processing applications thanks to the possibility to control the propagation properties of waves exciting distinct spatial modes of the same waveguide.This allows,in principle,to place signals in different spectral regions and satisfy the phase matching condition over considerably larger bandwidths compared to intramodal processes.However,the demonstrations reported so far have shown a limited bandwidth and suffered from the lack of on-chip components designed for broadband manipulation of different modes.We demonstrate here a silicon-rich silicon nitride wavelength converter based on Bragg scattering intermodal FWM,which integrates mode conversion,multiplexing and de-multiplexing functionalities on-chip.The system enables wavelength conversion between pump waves and a signal located in different telecommunication bands(separated by 60 nm)with a 3 dB bandwidth exceeding 70 nm,which represents,to our knowledge,the widest bandwidth ever achieved in an intermodal FWM-based system.

Topological transformation and free-space transport of photonic hopfions

Structured light fields embody strong spatial variations of polarization,phase,and amplitude.Understanding,characterization,and exploitation of such fields can be achieved through their topological properties.Three-dimensional(3D)topological solitons,such as hopfions,are 3D localized continuous field configurations with nontrivial particle-like structures that exhibit a host of important topologically protected properties.Here,we propose and demonstrate photonic counterparts of hopfions with exact characteristics of Hopf fibration,Hopf index,and Hopf mapping from real-space vector beams to homotopic hyperspheres representing polarization states.We experimentally generate photonic hopfions with on-demand high-order Hopf indices and independently controlled topological textures,including Néel-,Bloch-,and antiskyrmionic types.We also demonstrate a robust free-space transport of photonic hopfions,thus showing the potential of hopfions for developing optical topological informatics and communications.

Multidimensional optical tweezers synthetized by rigid-body emulated structured light

Structured light with more extended degrees of freedom(DoFs)and in higher dimensions is increasingly gaining traction and leading to breakthroughs such as super-resolution imaging,larger-capacity communication,and ultraprecise optical trapping or tweezers.More DoFs for manipulating an object can access more maneuvers and radically increase maneuvering precision,which is of significance in biology and related microscopic detection.However,manipulating particles beyond three-dimensional(3D)spatial manipulation by using current all-optical tweezers technology remains difficult.To overcome this limitation,we theoretically and experimentally present six-dimensional(6D)structured optical tweezers based on tailoring structured light emulating rigid-body mechanics.Our method facilitates the evaluation of the methodology of rigid-body mechanics to synthesize six independent DoFs in a structured optical trapping system,akin to six-axis rigid-body manipulation,including surge,sway,heave,roll,pitch,and yaw.In contrast to previous 3D optical tweezers,our 6D structured optical tweezers significantly improved the flexibility of the path design of complex trajectories,thereby laying the foundation for next-generation functional optical manipulation,assembly,and micromechanics.

Efficient ultrafast laser writing with elliptical polarization

Photosensitivity in nature is commonly associated with stronger light absorption.It is also believed that artificial optical anisotropy to be the strongest when created by light with linear polarization.Contrary to intuition,ultrafast laser direct writing with elliptical polarization in silica glass,while nonlinear absorption is about 2.5 times weaker,results in form birefringence about twice that of linearly polarized light.Moreover,a larger concentration of anisotropic nanopores created by elliptically polarized light pulses is observed.The phenomenon is interpreted in terms of enhanced interaction of circularly polarized light with a network of randomly oriented bonds and hole polarons in silica glass,as well as efficient tunneling ionization produced by circular polarization.Applications to multiplexed optical data storage and birefringence patterning in silica glass are demonstrated.

Controlled generation of picosecond-pulsed higher-order Poincaré sphere beams from an ytterbium-doped multicore fiber amplifier

Higher-order Poincarésphere(HOPS) beams with spatially variable polarization and phase distributions are opening up a host of unique applications in areas ranging from optical communication to microscopy.However, the flexible generation of these beams with high peak power from compact laser systems remains a challenge. Here, we demonstrate the controlled generation of HOPS beams based on coherent beam combination from an Yb-doped multicore fiber(MCF) amplifier. Using a spatial light modulator to adaptively adjust the wavefront and polarization of the signals seeded into the individual cores of the MCF various structured beams(including cylindrical vector beams and first-and second-order vortex beams) were generated with peak powers up to 14 k W for ~92 ps pulses.

High Q-factor reconfigurable microresonators induced in side-coupled optical fibres

Recently,significant efforts have been devoted to enable light resonating inside various resonators for long time,leading to high Q factors.Achieving tunability of the free spectral range while maintaining high Q has been,however,challenging.

High-efficiency reflector-less dual-level silicon photonic grating coupler

We present the design and experimentally demonstrate a dual-level grating coupler with subdecibel efficiency for a 220 nm thick silicon photonics waveguide which was fabricated starting from a 340 nm silicon-on-insulator wafer.The proposed device consists of two grating levels designed with two different linear apodizations,with opposite chirping signs,and whose period is varied for each scattering unit.A coupling efficiency of-0.8 d B at1550 nm is experimentally demonstrated,which represents the highest efficiency ever reported in the telecommunications C-band in a single-layer silicon grating structure without the use of any backreflector or indexmatching material between the fiber and the grating.

Raman amplification at 2.2μm in silicon core fibers with prospects for extended mid-infrared source generation

Raman scattering provides a convenient mechanism to generate or amplify light at wavelengths where gain is not otherwise available.When combined with recent advancements in high-power fiber lasers that operate at wavelengths~2μm,great opportunities exist for Raman systems that extend operation further into the mid-infrared regime for applications such as gas sensing,spectroscopy,and biomedical analyses.Here,a thulium-doped fiber laser is used to demonstrate Raman emission and amplification from a highly nonlinear silicon core fiber(SCF)platform at wavelengths beyond 2μm.The SCF has been tapered to obtain a micrometer-sized core diameter(~1.6μm)over a length of 6 cm,with losses as low as 0.2 dB cm^(−1).A maximum on-off peak gain of 30.4 dB was obtained using 10 W of peak pump power at 1.99μm,with simulations indicating that the gain could be increased to up to~50 dB by extending the SCF length.Simulations also show that by exploiting the large Raman gain and extended mid-infrared transparency of the SCF,cascaded Raman processes could yield tunable systems with practical output powers across the 2–5μm range.

Blazed subwavelength grating coupler

Short-wavelength mid-infrared(2–2.5 μm wave band) silicon photonics has been a growing area to boost the applications of integrated optoelectronics in free-space optical communications, laser ranging, and biochemical sensing. In this spectral region, multi-project wafer foundry services developed for the telecommunication band are easily adaptable with the low intrinsic optical absorption from silicon and silicon dioxide materials. However,light coupling techniques at 2–2.5 μm wavelengths, namely, grating couplers, still suffer from low efficiencies,mainly due to the moderated directionality and poor diffraction-field tailoring capability. Here, we demonstrate a foundry-processed blazed subwavelength coupler for high-efficiency, wide-bandwidth, and large-tolerance light coupling. We subtly design multi-step-etched hybrid subwavelength grating structures to significantly improve directionality, as well as an apodized structure to tailor the coupling strength for improving the optical mode overlap and backreflection. Experimental results show that the grating coupler has a recorded coupling efficiency of-4.53 dB at a wavelength of 2336 nm with a 3-dB bandwidth of ~107 nm. The study opens an avenue to developing state-of-the-art light coupling techniques for short-wavelength mid-infrared silicon photonics.

Classical imaging with undetected photons using four-wave mixing in silicon core fibers

Undetected-photon imaging allows for objects to be imaged in wavelength regions where traditional components are unavailable. Although first demonstrated using quantum sources, recent work has shown that the technique also holds with classical beams. To date, however, all the research in this area has exploited parametric downconversion processes using bulk nonlinear crystals within free-space systems. Here, we demonstrate undetectedphoton-based imaging using light generated via stimulated four-wave mixing within highly nonlinear silicon fiber waveguides. The silicon fibers have been tapered to have a core diameter of915 nm to engineer the dispersion and reduce the insertion losses, allowing for tight mode confinement over extended lengths to achieve practical nonlinear conversion efficiencies(-30 dB) with modest pump powers(48 m W). Both amplitude and phase images are obtained using classically generated light, confirming the high degree of spatial and phase correlation of our system. The high powers(>10 nW) and long coherence lengths(>4 km) associated with our large fiber-based system result in high contrast and stable images.

Ultralow-loss geometric phase and polarization shaping by ultrafast laser writing in silica glass

Polarization and geometric phase shaping via a space-variant anisotropy has attracted considerable interest for fabrication of flat optical elements and generation of vector beams with applications in various areas of science and technology.Among the methods for anisotropy patterning,imprinting of self-assembled nanograting structures in silica glass by femtosecond laser writing is promising for the fabrication of space-variant birefringent optics with high thermal and chemical durability and high optical damage threshold.However,a drawback is the optical loss due to the light scattering by nanograting structures,which has limited the application.Here,we report a new type of ultrafast laser-induced modification in silica glass,which consists of randomly distributed nanopores elongated in the direction perpendicular to the polarization,providing controllable birefringent structures with transmittance as high as 99% in the visible and near-infrared ranges and >90% in the UV range down to 330 nm.The observed anisotropic nanoporous silica structures are fundamentally different from the femtosecond laser-induced nanogratings and conventional nanoporous silica.A mechanism of nanocavitation via interstitial oxygen generation mediated by multiphoton and avanlanche defect ionization is proposed.We demonstrate ultralow-loss geometrical phase optical elements,including geometrical phase prism and lens,and a vector beam convertor in silica glass.

Reflective chiral meta-holography: multiplexing holograms for circularly polarized waves

By allowing almost arbitrary distributions of amplitude and phase of electromagnetic waves to be generated by a layer of sub-wavelength-size unit cells,metasurfaces have given rise to the field of meta-holography.However,holography with circularly polarized waves remains complicated as the achiral building blocks of existing meta-holograms inevitably contribute to holographic images generated by both left-handed and right-handed waves.Here we demonstrate how planar chirality enables the fully independent realization of high-efficiency meta-holograms for one circular polarization or the other.Such circular-polarization-selective meta-holograms are based on chiral building blocks that reflect either left-handed or right-handed circularly polarized waves with an orientation-dependent phase.Using terahertz waves,we experimentally demonstrate that this allows the straightforward design of reflective phase meta-holograms,where the use of alternating structures of opposite handedness yields independent holographic images for circularly polarized waves of opposite handedness with negligible polarization cross-talk.