We take H++CO as a prototype to analyze the effect of ion or proton collision on molecular orientation modulated by a two-color shaped pulse combined with the time-delayed terahertz (THz) pulse. Through examining the effect of ion collision on the molecular orientation, we found that when the impact parameter and collisional velocity have weak inverse influences on the maximal orientation degree, the appropriate two-color and THz field intensity employed can improve the molecular orientation degree. The carrier envelope phase and frequency of the THz laser pulse as well as the temperature also have certain influence on the collision-induced molecular orientation.

In amplitude-modulation-type electroholography, the binary-weighted computer-generated hologram (BW-CGH) facilitates the gradation-expressible reconstruction of three-dimensional (3D) objects. To realize real-time gradation-expressible electroholography, we propose an efficient and high-speed method for calculating bit planes consisting of BW-CGHs. The proposed method is implemented on a multiple graphics processing unit (GPU) cluster system comprising 13 GPUs. The proposed BW-CGH method realizes eight-gradation-expressible electroholography at approximately the same calculation speed as that of conventional electroholography based on binary computer-generated holograms. Consequently, we were able to successfully reconstruct a real-time electroholographic 3D video comprising approximately 180,000 points expressed in eight gradations at 30 frames per second.

To reduce the atmospheric turbulence-induced power loss, an AlexNet-based convolutional neural network (CNN) for wavefront aberration compensation is experimentally investigated for free-space optical (FSO) communication systems with standard single mode fiber-pigtailed photodiodes. The wavefront aberration is statistically constructed to mimic the received light beams with the Zernike mode-based theory for the Kolmogorov turbulence. By analyzing impacts of CNN structures, quantization resolution/noise, and mode count on the power penalty, the AlexNet-based CNN with 8 bit resolution is identified for experimental study. Experimental results indicate that the average power penalty decreases to 1.8 dB from 12.4 dB in the strong turbulence.

Due to the bandwidth limitation of the ultraviolet-C (UV-C) optical communication system and strong channel attenuation, it is difficult to transmit high-frequency signals. In this paper, the temporal ghost imaging (TGI) algorithm was first applied to the UV-C communication experimentally, and we realized the transmission of a 4 GHz signal through 95.34 MHz system bandwidth. The study indicates that the TGI algorithm can significantly improve the signal-to-noise ratio (SNR) compared with the on–off keying method. Our research provides a new approach for alleviating transmission frequency limitation due to poor SNR and insufficient hardware bandwidth.

In this work, a heavily Er-doped fiber with an 8 µm core diameter and a numerical aperture of 0.13 was prepared by the modified chemical vapor deposition (MCVD) technique combined with the sol-gel method. The background loss and absorption coefficient at 1530 nm were measured to be 20 dB/km and 128 dB/m, respectively. Thanks to the sol-gel method, the fiber showed a good doping homogeneity, which was confirmed through unsaturable absorption measurement. The net gains of three 25, 45, and 75-cm-long fibers were measured in the range of 1520 to 1600 nm, and the highest gain reached above 23 dB at both 1530 and 1560 nm in 25 and 75-cm-long fibers, respectively. The short-cavity laser performance was measured using centimeter-scale fibers. The maximum output power of 12 mW was demonstrated in a 6.5-cm-long active fiber with a slope efficiency of 20.4%. Overall, the prepared heavily Er-doped silica fiber is a promising item to be applied in a high-repetition-rate or single-frequency fiber laser.

Probabilistically shaped (PS) pulse amplitude modulation (PAM) is a promising technique for intra-data-center networks due to its superior performance, for which a low-complexity and cost-effective distributed matching method is critical. In this work, we propose an energy-level-assigned method to yield PS-PAM-4 signals with various bit rates based on variable probabilistic distributions. We experimentally demonstrate the proposed method in a 25 Gbaud PS-PAM-4 transmission over a bandwidth of approximately 10 GHz. Compared to a uniform PAM-4 system, the proposed multi-distributed PS-PAM-4 system approaches the hard decision threshold at a wide range of received optical power for different applications.

This paper presents a polarization descattering imaging method for underwater detection in which the targets have nonuniform polarization characteristics. The core of this method takes the nonuniform distribution of the polarization information of the target-reflected light into account and expands the application field of underwater polarization imaging. Independent component analysis was used to separate the target light and backscattered light. Theoretical analysis and proof-of-concept experiments were employed to demonstrate the effectiveness of the proposed method in estimating target information. The proposed method showed superiority in accurately estimating the target information compared with other polarization imaging methods.

We propose and demonstrate the generation of wideband chaos based on a dual-mode microsquare semiconductor laser with optical feedback. By adjusting the dual-mode intensity ratio and the feedback strength, wideband chaos covering more than 50 GHz in the RF spectrum is achieved. The standard and effective bandwidths of the chaotic signal are 31.3 GHz and 30.7 GHz with the flatness of 8.3 dB and 6.1 dB, respectively.

We demonstrate a high-resolution frequency-modulated continuous-wave dual-frequency LIDAR system based on a monolithic integrated two-section (TS) distributed feedback (DFB) laser. In order to achieve phase locking of the two lasers in the TS-DFB laser, the sideband optical injection locking technique is employed. A high-quality linear frequency-modulated signal is achieved from the TS-DFB laser. Utilizing the proposed LIDAR system, the distance and velocity of a target can be measured accurately. The maximum relative errors of distance and velocity measurement are 1.6% and 3.18%, respectively.

In this paper, we propose and demonstrate an adjustable-free and movable Nd:YVO4 thin disk laser based on the telecentric cat’s eye cavity. We design a V-shaped laser cavity containing two reflectors with Nd:YVO4 thin disks as the gain medium. The experimental results from the traditional plane-plane cavity, plane-telecentric cat’s eye cavity, and double telecentric cat’s eye cavity are compared. They show that plane-telecentric cat’s eye cavity laser can keep operating at the adjustable-free range of -6° to +6°, which is up to 60 times better than that of traditional plane-plane cavity. In the double telecentric cat’s eye case, the adjustable-free range is improved to -13° to +13°. Additionally, in the case of the double telecentric cat’s eye cavity, the output telecentric cat’s eye can achieve free movement within the horizontal range of ±20mm.

In this paper, we demonstrate a scheme to tailor both longitudinal and transverse modes inside a laser cavity and constitute an eye-safe single longitudinal mode Er:Y3Al5O12 (Er:YAG) vector laser. A q-plate is employed as a spin-orbital conversion element to modulate the transverse mode and obtain cylindrical vector beams. An optical isolator is employed as a non-reciprocal element for the ring cavity to enforce unidirectional operation and achieve single longitudinal oscillation. The characteristics of power, transverse intensity, and polarization spectrum of the output beams are observed. The observed typical single longitudinal mode and highly matched special polarizations prove the successful tailoring of both longitudinal and transverse modes.

In this Letter, we demonstrated the switchable single- and dual-wavelength femtosecond soliton generation in single-mode Er-doped fiber lasers with the usage of carboxyl-functionalized graphene oxide (GO-COOH) saturable absorbers (SAs) for the first time, to the best of our knowledge. The fiber laser generated a stable single-wavelength conventional soliton at 1560.1 nm with a pulse duration of 548.1 fs. The dual-wavelength solitons centered at 1531.9 nm and 1555.2 nm with a spacing of approximately 23 nm can be obtained by adjusting the pump power of the cavity. Our experimental results indicated the GO-COOH has great potential to be used in ultrafast fiber lasers as broadband SAs.

We proposed a periodic mid-infrared broadband chiral structure. Its unit cell consists of four indium tin oxide (ITO) helix subunits with different radii. The simulation results show that the flat-topped broadband circular dichroism (CD) can be achieved in the mid-infrared band by optimizing the parameters of helix structures. The simulation results also show that compared with the metallic (Ag and Au) helix structures, the ITO helix structure proposed exhibits evidently better broadband CD and optical activity, which provides a new idea for the design of broadband polarization state control devices in the mid-infrared band.

We report an interesting study of electric-field-induced transformation from a single domain ferroelectric state to the multiple domain ferroelectric state in a KTa_1-xNb_xO₃ (KTN) crystal. Experimental results obtained using the confocal μ-Raman spectroscopy confirm the dynamic change of lattice structures induced by an external electric field. Furthermore, the dependence of relative permittivity on the applied voltage also indicates the transformation of ferroelectric states involving the processes of splintering, inversion, and re-formation of ferroelectric domains.

Microrobots-assisted drug delivery and surgery have been always in the spotlight and are highly anticipated to solve the challenges of cancer in situ treatment. These versatile small biomedical robots are expected to realize direct access to the tumor or disease site for precise treatment, which requires real-time and high-resolution in vivo tracking as feedback for the microrobots’ actuation and control. Among current biomedical imaging methods, photoacoustic imaging (PAI) is presenting its outstanding performances in the tracking of microrobots in the human body derived from its great advantages of excellent imaging resolution and contrast in deep tissue. In this review, we summarize the PAI techniques, imaging systems, and their biomedical applications in microrobots tracking in vitro and in vivo. From a robotic tracking perspective, we also provide some insight into the future of PAI technology in clinical applications.

We demonstrate comprehensive investigation of the injection locking dynamics of a backscattered Brillouin laser in silica whispering-gallery-mode microcavity. Via injection locking, the Brillouin laser acquires highly correlated phase with the seed laser, enabling ultra-narrow bandwidth, high gain, and coherent optical amplification. Also, for the first time, to the best of our knowledge, the injection locked Brillouin laser is utilized to implement all-optical carrier recovery from coherent optical data signals. We show that by using the injection locked Brillouin laser as a local oscillator for self-homodyne detection, high-quality data receiving can be realized, even without traditional electrical compensations for carrier frequency and phase drifts.

Tilted-pulse-front-pumping (TPFP) lithium-niobate terahertz (THz) pulse sources are widely used in pump-probe and control experiments since they can generate broadband THz pulses with tens of microjoules of energy. However, the conventional TPFP setup suffers from limitations, hindering the generation of THz pulses with peak electric field strength over 1 MV/cm. Recently, a few setups were suggested to mitigate or even eliminate these limitations. In this paper, we shortly review the setups that are suitable for the generation of single-cycle THz pulses with up to a few tens of megavolts/centimeter focused electric field strength. The THz pulses available with the new layouts pave the way for previously unattainable applications that require extremely high electric field strength and pulse energy in the multi-millijoule range.

The vector dynamics of solitons are crucial but easily neglected for realizing vortex solitons. In this Letter, we investigate the effect of vector dynamics on cylindrical vector beams (CVBs) implementation and propose a novel technical method to realize femtosecond CVBs based on vector-locked solitons, which are presented as group-velocity-locked vector solitons (GVLVSs) in the experiment. The outstanding vector properties of GVLVSs not only greatly improve the efficiency of solitons converted into CVBs and output power of CVBs (2.4 times and 4.1 times that of scalar solitons and vector change periodical solitons, with the purity of 97.2%), but also relax the obstacle of ultrafast CVBs from the fundamental frequency to the harmonic regime (up to 198 MHz) for the first time, to the best of our knowledge. This is the highest repetition rate reported for ultrafast CVBs based on passive mode-locking. The investigation of the influence of solitons vector dynamics evolution on the realization of CVBs provides guidance for the excellent performance of ultrafast CVBs.

To solve the issue of the contradiction between photovoltaic power generation and plant photosynthesis for sunlight demand, we propose a design method of multi-passband polymer multilayer optical structure. Using polycarbonate (PC) and polymethyl methacrylate (PMMA), two polymer materials with different refractive indices, the passband position and passband bandwidth are calculated and adjusted by the transmission matrix method and TFCalc software. A 450 nm, 660 nm, and 730 nm three-passband filter was realized by superimposing stacks of different band positions. The feasibility of the photovoltaic agriculture was confirmed by the power generation efficiency and the actual plant growth.

Using compressive sensing for imaging has many applications, and it is an important branch of computational imaging. In this Letter, freeform surfaces are introduced in the hardware optical system design of a compressive sensing imager. The system works under the medium wave infrared band and realizes a 16× compression with a field-of-view of 7.5°×6°. Good imaging performance is achieved in both the entire system and the freeform objective optics. Compared with the system using all spherical lenses, the volume of the freeform system is about 1/3 smaller, and the total transmittance is about 56% higher, which shows the benefits of using freeform surfaces for compressive sensing and computational imaging.

Vector vortex beams (VVBs) have attracted significant attention in both classical and quantum optics. Liquid crystal (LC), beyond its applications in information display, has emerged as a versatile tool for manipulating VVBs. In this review, we focus on the functions and applications of typical LC devices in recent studies on controlling the space-variant polarized vortex light. Manipulation of VVBs through patterned nematic LC optical elements, patterned cholesteric LC optical elements, self-assembled defects, and LC spatial light modulators is discussed separately. Moreover, LC-based novel optical applications in the field of quantum information are reviewed.

Quantum random access codes (QRACs) are important communication tasks that are usually implemented in prepare-and-measure scenarios. The receiver tries to retrieve one arbitrarily chosen bit of the original bit-string from the code qubit sent by the sender. In this Letter, we analyze in detail the sequential version of the 3→1 QRAC with two receivers. The average successful probability for the strategy of unsharp measurement is derived. The prepare-and-measure strategy within projective measurement is also discussed. It is found that sequential 3→1 QRAC with weak measurement cannot be always superior to the one with projective measurement, as the 2→1 version can be.

The analog photonics link (APL) is widely used in microwave photonics. However, in wideband and multi-carrier systems, the third inter-modulation distortion (IMD3) and cross-modulation distortion (XMD) will jointly limit the spurious-free dynamic range (SFDR) of links. In this paper, we experimentally present a linearized wideband and multi-carrier APL, in which the IMD3 and XMD are mitigated simultaneously by using artificial neural networks with transfer learning (TL-ANN). In this experiment, with different artificial neural networks, which are trained with the knowledge obtained from the two- or three-sub-carrier system, the IMD3 and XMD are suppressed by 21.71 dB and 11.11 dB or 22.38 dB and 16.73 dB, and the SFDR is improved by 13.4 dB or 14.3 dB, respectively. Meanwhile, compared with previous studies, this method could reduce the training time and training epochs to 16% and 25%.

We demonstrate a chip-scale scheme of Brillouin instantaneous frequency measurement (IFM) in a CMOS-compatible doped silica waveguide chip. In the chip-scale Brillouin IFM scheme, the frequency-to-power mapping process is achieved by one-shot detection without additional time averaging and implemented by lock-in amplification, which successfully detects the Brillouin gain of the doped silica waveguide chip in the time domain. A Costas frequency modulated signal ranging from 8 GHz to 9 GHz is experimentally measured, and the frequency measurement errors are maintained within 58 MHz.

Chalcopyrite Cu(In,Ga)Se2 (CIGS) thin films deposited in a low-temperature process (450°C) usually produce fine grains and poor crystallinity. Herein, different Ag treatment processes, which can decrease the melting temperature and enlarge band gap of the CIGS films, were employed to enhance the quality of thin films in a low-temperature deposition process. It is demonstrated that both the Ag precursor and Ag surface treatment process can heighten the crystallinity of CIGS films and the device efficiency. The former is more obvious than the latter. Furthermore, the Urbach energy is also reduced with Ag doping. This work aims to provide a feasible Ag-doping process for the high-quality CIGS films in a low-temperature process.