Using a strong nonlinear saturation absorption effect is one technique for breaking through the diffraction limit. In this technique, formation of a dynamic and reversible optical pinhole channel and transient superresolution is critical. In this work, a pump–probe transient detection and observation–experimental setup is constructed to explore the formation process directly. A Ge₂Sb₂Te₅ thin film with strong nonlinear saturation absorption is investigated. The dynamic evolution of the optical pinhole channel is detected and imaged, and the transient superresolution spot is directly captured experimentally. Results verify that the superresolution effect originates from the generation of an optical pinhole channel and that the formation of the optical pinhole channel is dynamic and reversible. A good method is provided for direct detection and observation of the transient process of the superresolution effect of nonlinear thin films.

Atomically thin MoS₂ films have attracted significant attention due to excellent electrical and optical properties. The development of device applications demands the production of large-area thin film which is still an obstacle. In this work we developed a facile method to directly grow large-area MoS₂ thin film on SiO₂ substrate via ambient pressure chemical vapor deposition method. The characterizations by spectroscopy and electron microscopy reveal that the as-grown MoS₂ film is mainly bilayer and trilayer with high quality. Back-gate field-effect transistor based on such MoS₂ thin film shows carrier mobility up to 3.4 cm² V^?1 s^?1 and on/off ratio of 10⁵. The large-area atomically thin MoS₂ prepared in this work has the potential for wide optoelectronic and photonic device applications.

We propose an ultra-simple dual-channel configuration for simultaneously evaluating two branches of a multifunctional integrated optic chip (MFIOC). In the configuration, the MFIOC is employed as a beam splitter to construct the demodulation interferometer together with a 2 × 2 fiber coupler. Interference happens between polarization modes traveling through different channels of the MFIOC. The cross-couplings of each channel are respectively characterized by the interference peaks which distribute on opposite sides of the central interference peak. Temperature responses of the MFIOC are experimentally measured from ?40°C to 80°C. Results show that the proposed configuration can achieve simultaneous dual-channel transient measurements with resolution of ?90 dB and dynamic range of 90 dB. In addition, the two channels of the configuration have consistent measuring performance, and the two branches of the MFIOC have different responses to temperature variation.

In this work pulse generation in both the 1.5 and 2 μm spectral ranges using a graphene oxide (GO)-paper-based saturable absorber in Er- and Tm-doped fiber lasers is presented. The article describes the fabrication method of GO paper and its characterization. The performance of both lasers is discussed in detail. Stable, mode-locked operation provides 613 fs and 1.36 ps soliton pulses centered at 1565.9 and 1961.6 nm in Er- and Tm-doped fiber lasers, respectively. Furthermore, scaling of spectral width, and hence the pulse duration, by increasing the number of GO paper layers in the Er-doped laser is described. The versatility and simplicity ofGOpaper fabrication combined with the possibility of scaling the optical spectrum full width at half-maximum are essential features that make it a good candidate for ultrafast low-power mode-locked lasers operating in different spectral regions.

We study through electromagnetic modeling the absorption of light of a given wavelength in an array of horizontal InP nanowires of diameter less than 100 nm. Such absorption is performed most efficiently by using polarized light and by exciting a coupled optical resonance in a sparse array. In that case, we excite a resonance in the individual nanowires and couple the resonances in neighboring nanowires through a lattice resonance of the periodic array. At such a resonance, an array with nanowires of 80 nm in diameter can absorb more than eight times more strongly than a tight-packed array, despite containing a seven times smaller amount of the absorbing InP material.Nanophotonics and photonic crystals

A method for optimizing the spectral distortion of an ultrafast pulse in a polarization-maintaining picosecond linear-cavity fiber laser with a one-stage fiber amplifier is proposed and demonstrated. The mechanism of control of the spectral distortion in the fiber system has been investigated. The experimental and theoretical results illustrate that the filtering effect of a fiber Bragg grating can effectively decrease the spectral oscillatory distortion accumulated by self-phase modulation. Injected into a Nd:YAG regenerative amplifier, the ultrafast pulse could produce high pulse energy of 1.2 mJ at a repetition rate of 1 kHz.

A high-efficiency technique for optical vortex (OV) generation is proposed and demonstrated. The technique is based on liquid crystal fork gratings with space-variant azimuthal orientations, which are locally controlled via polarization-sensitive alignment layers. Thanks to the optical rewritability of the alignment agent and the dynamic image generation of the digital micro-mirror device, fork gratings can be instantly and arbitrarily reconfigured. Corresponding optical vortices carrying arbitrary azimuthal and radial indices are demonstrated with a conversion efficiency of 98.5%, exhibiting features of polarization control and electrical switching. The technique may pave a bright road toward OV generation, manipulation, and detection.

In this paper we present a novel nanoantenna (nantenna) design for energy harvesting. The nantenna has an “E” shape and is placed on a SiO₂ substrate. Its operation is based on the excitation of surface plasmon polaritons through the gold arms of the E shape. By varying the lengths and widths of the arms, two overlapping working bandwidths can be achieved. This results in a wideband behavior characterized by a full width at half-maximum of about 2.2 μm centered around 3.6 μm. Two orthogonal E nantennas are placed perpendicular to each other to realize a dual-polarized nantenna. This nantenna can receive the two incident polarizations at two separate gap locations with very high isolation. The proposed structure can be used in several energy harvesting applications, such as scavenging the infrared heat from the Earth and other hot objects, in addition to optical communications.crystals;Subwavelength structures, nanostructures;Resonance

Accurately measuring the differential molecular absorption cross section is the key to obtaining a high-precision concentration of atmospheric trace gases in a differential absorption lidar (DIAL) system. However, the CO₂ absorption line is meticulous at 1.6 μm, easily translating and broadening because of the change of temperature and pressure. Hence, measuring the vertical profile of atmospheric temperature and pressure to calculate the vertical profile of the CO₂ weight parameter is necessary. In general, measuring atmospheric temperature and pressure has a certain amount of uncertainty. Therefore, this study proposes the concept of a balanced on-line wavelength, where the differential molecular absorption cross section is larger and the CO₂ weight parameter is insensitive to the uncertainty of atmospheric temperature and pressure. In this study, we analyzed the influence of uncertainty on the CO₂ weight parameter at every preselected wavelength, as well as determined an appropriate wavelength near one of the absorption peaks. Our result shows that 1572.023 nm should be one of the appropriate balanced online wavelengths. The measurement errors of the mixing ratio of CO₂ molecule in this wavelength are only 0.23% and 0.25% and are caused by 1 K temperature error and 1 hPa pressure error, respectively. This achievement of a balanced on-line wavelength will not only depress the requirement of the laser’s frequency stabilization but also the demand for measurement precision of the atmospheric temperature and pressure profile. Furthermore, this study can achieve the exact measurement of the vertical profile of atmospheric CO₂ based on an independent differential absorption laser.

The influence of the axial relative motion between the target and the source on ghost imaging (GI) is investigated. Both the analytical and experimental results show that the transverse resolution of GI is reduced as the deviation of the target’s center position from the optical axis or the axial motion range increases. To overcome the motion blur, we propose a deblurring method based on speckle-resizing and speed retrieval, and we experimentally validate its effectiveness for an axially moving target with an unknown constant speed. The results demonstrated here will be very useful to forward-looking GI remote sensing.imaging;Image analysis

Chirped-pitch nanoscale circular surface-relief diffraction gratings were photoinscribed on thin films of a Disperse Red 1 functionalized material using a holographic technique. A truncated conical mirror splits and redirects a converging or diverging laser beam, resulting in an interference pattern of concentric circles with a chirped pitch that can be controlled by varying the wavefront curvature. The resulting circular gratings have a diameter of 12mm and have the advantage of being produced in a fast, single-step procedure with no requirement for a master grating, photomask, or milling equipment.

All-optical canonical logic units at 40 Gb/s using bidirectional four-wave mixing (FWM) in highly nonlinear fiber are proposed and experimentally demonstrated. Clear temporal waveforms and correct pattern streams are successfully observed in the experiment. This scheme can reduce the amount of nonlinear devices and enlarge the computing capacity compared with general ones. The numerical simulations are made to analyze the relationship between the FWM efficiency and the position of two interactional signals.

We proposed a new scheme of controlling second-harmonic generation by enhanced Kerr electro-optic nonlinearity. We designed a structure that can implement the cascaded Pockels effect and second-harmonic generation simultaneously. The energy coupling between the fundamental lights of different polarizations led to a large nonlinear phase shift and, thus, an effective electro-optic nonlinear refractive index. The effective nonlinearity can be either positive or negative, causing the second-harmonic spectra to move toward the coupling center, which, in turn, offered us a way to measure the effective electro-optic nonlinear refractive index. The corresponding enhanced Kerr electro-optic nonlinearity is more than three orders of magnitude higher than the intrinsic value. These results open a door to manipulate the nonlinear phase by applying an external electric field instead of light intensity in noncentrosymmetric crystals.

We propose a cross-talk-free integral imaging 3D display based on a pyramid pinhole array. The pyramid pinhole array is used to provide a point light source array. Since the generated point light source array is behind a transmission-type display panel that displays an elemental image array, the pseudoscopic problem can be resolved. By setting the appropriate parameters for the pyramid pinhole array, the cross talk can be eliminated. We experimentally verify the reconstruction of the orthoscopic and cross-talk-free 3D images using the proposed 3D display.

We propose and experimentally demonstrate a novel type of polarization rotator that is capable of rotating the polarization plane of a linearly polarized light at any desired angle in either broad or narrow spectral bandwidth. The rotator comprises an array of standard half-wave plates rotated at specific angles with respect to their fast-polarization axes. The performance of the rotator depends on the number of individual half-wave plates, and in this paper we experimentally investigate the performance of two composite rotators comprising 6 and 10 half-wave plates.

We report on the modification of the wettability of stainless steel by picosecond laser surface microstructuring in this paper. Compared with traditional methods, picosecond laser-induced surface modification provides a fast and facile method for surface modification without chemical damage and environmental pollution. As a result of treatment by 100 ps laser pulses, microstructures are fabricated on the stainless steel sample surface, contributing to the increase of the contact angle from 88° to 105°, which realizes a transformation from hydrophilicity to hydrophobicity. The morphological features of fabricated microstructures are characterized by scanning electron microscopy and optical microscopy.

The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip InGaN/GaN quantum well light-emitting diodes (LEDs) with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays was investigated by focusing on the effect of the packing density, packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having a hexagonal and close-packed monolayer microsphere array configuration for achieving optimum extraction efficiency, which translated into a 3.6-fold enhancement in light extraction compared to that for a planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns was also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.

Propagation properties of high-power fiber laser with high-order-mode (HOM) content are studied numerically for the first time to the best of our knowledge. The effect of HOM on the propagation property is evaluated by the power in the bucket (PIB) metric. It is shown that PIB is mainly dependent on HOM content rather than the relative phase between the fundamental mode and HOM. The PIB in vacuum is more than 80% when the power fraction of the HOM is controlled to be less than 50% at 5 km. The relative phase has an impact on the peak intensity position and concentration of the far-field intensity distribution. If an adaptive optics system is used to correct the peak intensity deviation, the results indicate that there exists a maximal value of PIB as relative phase increases. Such effect is weakened when propagating in turbulence. Compared to the laser beams without HOM, laser beams with HOM content are less influenced by the turbulence and can reduce average intensity fluctuation. The results may be useful in the design of a high-power fiber laser system.