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Featuring a nontrivial coupling between the orbital angular momentum of light and spatially inhomogeneous polarization, hybrid-order Poincare sphere (HyOPS) beams have recently triggered numerous curiosities, especially in classical and quantum informatics. Despite much effort devoted to creating single HyOPS beam, it is still a formidable challenge to simultaneously harness multichannel and diverse HyOPS beams in a simple and efficient manner. Here, we propose a digitalized geometric phase optical element via photo-induced liquid crystal microstructures and demonstrate flexible and spin-controlled massive channels of HyOPS beams. By tuning the incident polarization, any state on up to 24 diverse HyOPSs is simultaneously mapped from common Poincare sphere in high efficiency and good energy uniformity. All experimental results match well with the theoretical predictions of such a planar multifunctional device. This adds an extra spatial degree of freedom to advanced light tailoring and may facilitate parallel optical trapping, high-capacity communication, and high-dimensional quantum entanglement.

The coding metasurface integrated with tunable materials offers an attractive alternative to manipulate the THz beam dynamically. In this work, we demonstrate a THz programmable metasurface based on liquid crystal. The phase profile on the metasurface could be dynamically manipulated by switching the “0” and “1” states of each element. The programmable metasurface could deflect the THz beam using the designed coding sequence, and a maximum deflection angle of 32° has been achieved. The presented design opens a route of beamforming for THz communication.

We experimentally demonstrate the use of a periodically poled LiNbO3 (PPLN) crystal to produce an ultra-long sub-diffraction optical needle via second-harmonic generation. When we input a radially polarized fundamental wave from a femtosecond laser, a sub-diffraction beam size of 0.45λSH and an ultra-long depth of focus (DOF) of 55λSH are experimentally realized, where λSH is the second harmonic wavelength. The lateral size of the second harmonic optical needle is reduced by a factor of 2 compared to the case using the fundamental wave. The compact experimental configuration can realize wavelength conversion and wave-front shaping simultaneously in a single PPLN crystal. In addition, the ultra-long DOF is potentially useful in observing thick samples. The unique characteristics of our second harmonic optical needle open the door for practical applications in super-resolution imaging and optical manipulation.

Terahertz (THz) metadevices featured by high-Q Fano resonance are applicable for ultrasensitive biodetection. The active tuning of Fano resonance further extends their applications to switching and filtering. Here, we propose a dynamic Fano cloaking in a liquid crystal (LC) integrated THz metasurface. The metasurface is composed of two-gap asymmetric split rings. Its Fano resonance is intensively dependent on the incident polarization. The Fano resonance occurs when illuminated by THz waves with polarization perpendicular to the gaps, while for parallel polarization, the Fano resonance vanishes, namely, the cloaking of Fano resonators. A 250-μm-thick LC layer functions as an integrated tunable polarization converter. Thus, the device can be electrically switched between the sharp Fano state and the high-transmission state. The modulation depth reaches over 50% in a broad frequency range of 660 GHz. This work may inspire various advanced active THz apparatuses for biosensing, switching, and filtering.Terahertz (THz) metadevices featured by high-Q Fano resonance are applicable for ultrasensitive biodetection. The active tuning of Fano resonance further extends their applications to switching and filtering. Here, we propose a dynamic Fano cloaking in a liquid crystal (LC) integrated THz metasurface. The metasurface is composed of two-gap asymmetric split rings. Its Fano resonance is intensively dependent on the incident polarization. The Fano resonance occurs when illuminated by THz waves with polarization perpendicular to the gaps, while for parallel polarization, the Fano resonance vanishes, namely, the cloaking of Fano resonators. A 250-μm-thick LC layer functions as an integrated tunable polarization converter. Thus, the device can be electrically switched between the sharp Fano state and the high-transmission state. The modulation depth reaches over 50% in a broad frequency range of 660 GHz. This work may inspire various advanced active THz apparatuses for biosensing, switching, and filtering.

Lithium niobate (LiNbO3) nonlinear photonic crystals have been widely used in nonlinear wave front modulation for the π-phase difference between the second-harmonic (SH) waves from positive and negative domains. Aided by optimizing algorithms, we can control the diffraction patterns of SH vortex beams by designing nonlinear fork gratings with supercell structures in LiNbO3 crystals. In experiment, we demonstrate that the diffraction energies can be equally distributed in each order or concentrated on certain orders, in agreement with theoretical designs. Potential applications include controllable vortex beam generation, nondestructive parallel vortex detection, and so on.

Twisted light, or orbital angular momentum (OAM) carrying light, has been gradually becoming an important subfield of nonlinear optics. Compared with ordinary light, its chiral phase front provides an additional interface for shaping the phase-matching condition of nonlinear interactions and in consequence reveals a feasible way to tailor light's transverse structure. Here, we explore the nonlinear propagation of twisted light during focused stimulated Brillouin scattering (SBS). Unlike ordinary light that will experience a time-reversal nonlinear reflection, OAM carrying light will break up into corresponding petal-like degenerate OAM modes that carry no net OAM, whereas the superposed OAM modes that carry no net OAM, as the input field, are still time–reversed in focused-SBS. This unexpected phenomenon, resulting from a unique OAM selection rule of noise-initiated SBS, gives more insight into the underlying principle of OAM conservation in electromagnetic interactions and provides an approach to shaping light via nonlinear propagation.

Liquid crystal q-Airy-plates with director distributions integrated by q-plates and polarization Airy masks are proposed and demonstrated via the photoalignment technique. Single/dual vortex Airy beams of opposite topological charges and orthogonal circular polarizations are directly generated with polarization-controllable characteristic. The singular phase of the vortex part is verified by both astigmatic transformation and digital holography. The trajectory of vortex Airy beams is investigated, manifesting separate propagation dynamics of optical vortices and Airy beams. Meanwhile, Airy beams still keep their intrinsic transverse acceleration, self-healing, and nondiffraction features. This work provides a versatile candidate for generating high-quality vortex Airy beams.

The band structure of surface plasmon polaritons (SPPs) on the Ag surface in the presence of gratings and SPP-based surface-enhanced Raman scattering (SERS) are investigated theoretically and experimentally. The SPP bandgap position can be tuned by geometric parameters. The SPP band edge dominates the SERS behavior. The template stripping process is introduced to reduce SPP propagation losses, improving SERS sensitivity by ∼40. Apart from flexibility and a moderate SERS enhancement factor of the order of 105–106, the SPP band structure is highly reproducible with a relative standard deviation of 10.9%. Our results open opportunities for SPP band structures to serve as SERS substrates.

Spiral holographic imaging in the Hong-Ou–Mandel interference scheme is introduced. Using spontaneous parametric down-conversion as a source of photon pairs, we analyze the joint orbital angular momentum spectrum of a reference photon and the photon encoding information of the object. The first-order interference of light beams in standard holographic imaging is replaced by the quantum interference of two-photon probability amplitudes. The difficulty in retrieving the amplitude and phase structure of an unknown photon is thereby avoided as classical interferometric techniques such as optical holography do not apply. Our results show that the full information of the object's transmission function can be recorded in the spiral hologram, which originates directly from the joint orbital angular momentum spectrum. This presents a lateral demonstration of compressive imaging and can potentially be used for remote sensing.

Based on nonlinear holography, we propose a 2D spirally poled LiNbO3 nonlinear photonic crystal that generates orbital angular momentum (OAM) states of second-harmonic (SH) waves. In this crystal, the generated SH waves from positive and negative domains have a π phase difference, which is used to compose a nonlinear Fresnel zone plate for an experimental demonstration of generating SH OAM states at the designed focusing spot. In addition, the crystal can be used to detect input OAM states of fundamental beams without significantly disturbing their wave fronts.

An inverted organic solar cell (OSC) device structure by incorporating pixelated speckle image holography carrier fringes (SIHFs) for efficient superimposed light harvesting is demonstrated. The proposed SIHF based OSCs yield an 18.2% increase in power conversion efficiency (PCE) compared to that of the flat control devices. Moreover, compared to the common two-dimensional (2D) periodic grating patterned OSCs, SIHF based devices achieve 7.8% higher short-circuit current (JSC) and 10.0% higher PCE. This observable improvement in PCE of SIHF based OSCs is mainly ascribed to the geometric effect due to the unique chaotic carrier fringes of SIHFs.

Self-healing and transverse accelerating optical vortices are generated via modulating Gaussian beams through subsequent liquid crystal q-plate and polarization Airy mask. We analyze the propagation dynamics of these vortex Airy beams, and find that they possess the features of both optical vortices and Airy beams. Topological charges and characteristics of nondiffraction, self-healing, and transverse acceleration are experimentally verified. In addition, vortex Airy beams with both topological charge and radial index are demonstrated and mode switch among Gaussian, vortex, vector, Airy beams and their combinations can be acquired easily. Our design provides a flexible and highly efficient way to generate unique optical vortices with self-healing and transverse acceleration properties, and facilitates prospective applications in optics and photonics.

Phonon-polaritons are studied both theoretically and experimentally in a one-dimensional two-component generalized quasiperiodic piezoelectric superlattice. The experimental observation of phonon-polaritons through dielectric abnormality is carried out at the microwave region. Some potential applications are discussed.

Dual-frequency addressed hybrid-aligned nematic (HAN) liquid crystal cell is demonstrated as a variable optical attenuator at 1.55μm wavelength. By controlling the low- and high-frequency electric field, the dual-frequency liquid crystal (DFLC) molecules can be reoriented parallel or perpendicular to the substrates so that the maximum obtainable phase modulation is doubled. In comparison to a homogeneous cell, the DFLC HAN cell shows a lower operating voltage and faster response time. Furthermore, the DFLC HAN cell exhibits three stable states that have some applications such as ternary photonic devices.

Tunable light switch using a photonic crystal fiber filled with nematic liquid crystal is demonstrated. The original band-gap-guiding fiber structure was transformed to a total internal reflection-guiding photonic crystal fiber by filling liquid crystal into the air core and cladding air holes. By applying external voltage to the liquid-crystal-filled fiber, we have demonstrated an electrically tunable fiber-optical switch with over 30dB attenuation at 60Vrms for a He-Ne laser beam. This liquid-crystal-filled photonic crystal fiber will find useful applications in fiber-optic communication systems.

We demonstrate hole-injection enhancement from Au into N,N′-bis-(1-naphyl)-N,N′diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) by inserting between them a plasma-polymerized fluorocarbon (CFx) buffer layer. Ultraviolet and x-ray photoemission spectroscopic study indicates that chemically tailoring the Au surface with CFx can reduce the hole-injection barrier to ∼1 eV with respect to bare Au. This effect is ascribed to the buildup of an interfacial electric field, arising from the molecular dipolar characteristic of CFx. The present results suggest that CFx can function as a hole-injection enhancement layer for organic optoelectronic/electronic devices which use a metallic anode.

The doping mechanism in organic-semiconductor films has been quantitatively studied via ultrahigh-sensitivity ultraviolet photoelectron spectroscopy of N,N-bis(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine (α-NPD) films doped with hexaazatriphenylene-hexacarbonitrile [HAT(CN)6]. We observed that HOMO of α-NPD shifts to the Fermi level (EF) in two different rates with the doping concentration of HAT(CN)6, but HOMO distributions of both pristine and doped amorphous α-NPD films are excellently approximated with a same Gaussian distribution without exponential tail states over ∼5 × 1018 cm−3 eV−1. From the theoretical simulation of the HAT(CN)6-concentration dependence of the HOMO in doped films, we show that the passivation of Gaussian-distributed hole traps, which peak at 1.1 eV above the HOMO onset, occurs at ultralow doping [HAT(CN)6 molecular ratio (MR) < 0.01], leading to a strong HOMO shift of ∼0.40 eV towards EF, and MR dependence of HOMO changes abruptly at MR ∼ 0.01 to a weaker dependence for MR...

Arbitrary vector beams (VBs) are realized by the designed polarization converters and corresponding vector-photoaligned q-plates. The polarization converter is a specific twisted nematic cell with one substrate homogeneously aligned and the other space-variantly aligned. By combining a polarization-sensitive alignment agent with a dynamic micro-lithography system, various categories of liquid crystal polarization converters are demonstrated. Besides, traditional radially/azimuthally polarized light, high-order and multi-ringed VBs, and a VB array with different orders are generated. The obtained converters are further utilized as polarization masks to implement vector-photoaligning. The technique facilitates both the volume duplication of these converters and the generation of another promising optical element, the q-plate, which is suitable for the generation of VBs for coherent lasers. The combination of proposed polarization converters and correspondingly fabricated q-plates would drastically enhance the capability of polarization control and may bring more possibilities for the design of photonic devices.

We propose a high-frequency traveling-wave integrated electro-optic modulator based on a periodically poled LiNbO3. The traveling velocity of the optical wave and the electrical wave velocity in the waveguide can be quasimatched due to the periodic structure. Using this design, a modulation frequency of several hundred GHz can be realized. Wide-bandwidth modulation is also achievable by employing an aperiodic domain grating.

The electro-optic effect of periodically poled optical superlattice LiNbO3 (PPLN) was studied. Because of the periodic electro-optic (EO) coefficient, the reciprocal vector of the periodic structure can be used to compensate for the phase mismatch between the ordinary and extraordinary waves, which is similar to the nonlinear optical frequency conversion process. If the quasi-phase-matching condition is satisfied, polarization of a light propagated in PPLN can rotate linearly with the applied electric field, which shows that PPLN may be used as a precise spectral filter or an EO switch.

Frequency tuning of optical parametric generators in periodically poled LiNbO3 by applying a periodic electric field was demonstrated. Remarkable wavelength change was achieved. The dependence of the wavelength shift on the applied field shows a linear relationship. The tuning rates exceeding 3 nm/(kV/mm) were obtained. The phenomenon of dispersion in electro-optic tuning was predicted. Possible applications were discussed.

A graphene-based electrical current sensor is proposed utilizing a microfiber coil resonator. Monolayer graphene sheet with a large sheet resistance is transferred onto the surface of a glass capillary rod. A microfiber is spirally wrapped around the graphene sheet to form a coil resonator. Heat generated from electrical current shifts the resonant wavelength because of the thermal effect in the microfiber resonator. The sensor exhibits a very good performance with a high sensitivity of 67.297 μm/A2, which is two orders of magnitude higher than that reported earlier. Our results show that microfiber-graphene-integrated devices have great potential for miniature and highly sensitive fiber sensors for monitoring electrical current.

In this paper, the Fe3O4/Au nanocomposites were fabricated and employed as surface-enhanced infrared absorption (SEIRA) substrates. The superparamagnetic nature of Fe3O4/Au nanocomposites makes them suitable for controlled magnetic manipulation. The infrared absorption enhancements of Fe3O4/Au composite were improved as the magnetic field intensity increasing both for mercaptobenzoic acid and nitrobenzoic acid probe molecules. When the magnetic field intensities increase to 280 mT, the infrared enhancement could raise up to 3.3 and 10.7 times for -SH and -NO2 groups, respectively. The enhancement is due to the synergy of localized surface plasmon resonance of Au and the magnetism of Fe3O4. Under the strong magnetic field, the superparamagnetic Fe3O4/Au nanoparticles are highly concentrated, leading to the increase number of SEIRA “active sites” and the surface density of Au nanoparticles. The synergistic effects of both Fe3O4 and Au nanoparticles make the composites an excellent SEIRA substrate. In additi...

Optical superlattice Er:LiNbO3 was fabricated by inducing a periodic ferroelectric domain structure into the crystal during the growing process. Because of the combination of the nonlinear optical properties of LiNbO3 and the spectral properties of Er3+, the crystal can simultaneously emit the second harmonic light through quasi-phase matching and the green light through upconversion at room temperature. Pumped by infrared diode lasers, violet-and-green and blue-and-green light generation was demonstrated in two samples. The detailed absorption spectrum and emission spectrum of upconversion were measured. The possible physical mechanism was discussed.

We report the 390 and 385 nm violet light generation by frequency doubling of a tunable 90 fs, 82 MHz Ti:sapphire laser in two optical superlattice LiNbO3 samples through third‐order quasiphase matching (QPM). With the average incident infrared light power of 770 mW, 9.7 and 2.9 mW output second‐harmonic lights were obtained without photorefractive damage. The QPM wavelength acceptance bandwidth measurement indicates that violet light generation with higher efficiency is possible.

A transmission silica phase mask grating was used to fabricate LiNbO3 wafer phase gratings by a single excimer pulse at 248 nm. The morphologies of the LiNbO3 wafer gratings were studied with an atomic force microscope as well as an optical microscope. The crystal structures of the gratings were characterized by x‐ray diffraction and three new crystal phases were found at the gratings’ surface besides the substrate phase of LN (110).

Optical superlattice LiNbO3 crystals with a modulation period number over 200 and a modulation period from 2.0 to over 15.0 μm were grown by the Czochralski method in a carefully designed asymmetric temperature field system. Measurements of the frequency doubling efficiency for generating light from blue to green were performed. The largest efficiency obtained was 24.0% for frequency doubling of a picosecond 980 nm fundamental light. The angle tuning tolerance of a LiNbO3 optical superlattice was measured to be over 10° of the incidence angle.

We have grown Nd:MgO:LiNbO3 crystals with periodic ferroelectric domain structures. Absorption and fluorescence spectra measured on these crystals showed little difference from those from Nd:MgO:LibO3 with uniform domain structures. Green fluorescence was generated by self‐frequency doubling in a cavity having great losses and pumped by a pulsed dye laser.