Self-Adaptive Perception of Object's Deformability with Multiple Deformation Attributes Utilizing Biomimetic Mechanoreceptors.

The perception of object's deformability in unstructured interactions relies on both kinesthetic and cutaneous cues to adapt the uncertainties of an object. However, the existing tactile sensors cannot provide adequate cutaneous cues to self-adaptively estimate the material softness, especially in non-standard contact scenarios where the interacting object deviates from the assumption of an elastic half-infinite body. This paper proposes an innovative design of a tactile sensor that integrates the capabilities of two slow-adapting mechanoreceptors within a soft medium, allowing self-decoupled sensing of local pressure and strain at specific locations within the contact interface. By leveraging these localized cutaneous cues, the sensor can accurately and self-adaptively measure the material softness of an object, accommodating variations in thicknesses and applied forces. Furthermore, when combined with a kinesthetic cue from the robot, the sensor can enhance tactile expression by the synergy of two relevant deformation attributes, including material softness and compliance. It is demonstrated that the biomimetic fusion of tactile information can fully comprehend the deformability of an object, hence facilitating robotic decision-making and dexterous manipulation.

Road Narrow-Inspired Strain Concentration to Wide-Range-Tunable Gauge Factor of Ionic Hydrogel Strain Sensor.

The application of stretchable strain sensors in human movement recognition, health monitoring, and soft robotics has attracted wide attention. Compared with traditional electronic conductors, stretchable ionic hydrogels are more attractive to organization-like soft electronic devices yet suffer poor sensitivity due to limited ion conduction modulation caused by their intrinsic soft chain network. This paper proposes a strategy to modulate ion transport behavior by geometry-induced strain concentration to adjust and improve the sensitivity of ionic hydrogel-based strain sensors (IHSS). Inspired by the phenomenon of vehicles slowing down and changing lanes when the road narrows, the strain redistribution of ionic hydrogel is optimized by structural and mechanical parameters to produce a strain-induced resistance boost. As a result, the gauge factor of the IHSS is continuously tunable from 1.31 to 9.21 in the strain range of 0-100%, which breaks through the theoretical limit of homogeneous strain-distributed ionic hydrogels and ensures a linear electromechanical response simultaneously. Overall, this study offers a universal route to modulate the ion transport behavior of ionic hydrogels mechanically, resulting in a tunable sensitivity for IHSS to better serve different application scenarios, such as health monitoring and human-machine interface.

Simulation analysis of high-order high-duty-cycle surface gratings.

High-order surface grating distributed feedback lasers are known to operate with a fundamental mode, narrow linewidth, high power, and high slope efficiency. The adoption of high-order surface gratings can avoid epitaxial re-growth necessary for the fabrication of conventional buried gratings, which simplifies the fabrication process and reduces device cost. It is essential for the design and optimization of device structure to clarify the influence of the change of grating structure parameters on grating characteristics (coupling and loss). Based on Lumerical's Mode Solutions and multiple grating samples, we evaluated the coupling and loss coefficients of surface gratings as a function of duty cycle, order, and V-groove topography. As the order increases, the duty cycle corresponding to the peak value of the grating coupling coefficient increases gradually and approaches one. The grating coupling coefficient decreases with increasing order but increases at some specific orders. At high duty cycles, the width of the grating groove corresponding to the peak of the coupling coefficient remains substantially in the range of 100-150 nm, which is close to the length of a quarter-wavelength in the grating groove filling material. Regarding the grating groove morphology, the fabrication difficulty of the V-shaped groove grating is obviously less than that of the rectangular groove grating, but its coupling coefficient is slightly smaller than that of the rectangular shaped groove grating of the same depth. The larger the V-shaped groove width, the smaller the peak coupling coefficient and the corresponding sidewall inclination will be. Losses decrease with increasing duty cycle and decreasing sidewall inclination of the V-groove.

Self-powered photodetectors with a position-controlled array based on ZnO nanoclusters.

A self-powered ultraviolet (UV) photodetector (PD) with a position-controlled array based on zinc oxide (ZnO) nanoclusters (NCs) has been proposed. The structure of the special array makes it possible to reduce the light loss and improve the light trap. The PD innovatively modifies the structure of ZnO PDs, which is distinguished from other traditional devices. The results demonstrate that the ZnO NC array can spontaneously generate the carrier and successfully achieve the detection at zero bias under the radiation of UV light. In this study, the structure is fabricated with two different substrates of silicon (Si) and GaN. At zero bias voltage, the Si-based PD under 365 nm shows the responsivity and external quantum efficiency (EQE) reaching up to 14.1 mA/W and 4.79%, respectively, and the responsivity of the GaN-based detector can be obtained up to 59.9 mA/W; its parameter of EQE is 20.04%, the photocurrent is 10-5A, and the on/off ratio is 174. Our findings indicate that this structure of the device has potential for applications that require detection of light.

Tunable mode-locked fiber laser based on nonlinear multimode interference with double offset-splicing step-index few-mode fiber.

A tunable mode-locked all-fiber Yb-doped laser with a double offset-splicing step-index few-mode fiber (DOS-SIFMF) is demonstrated, to the best of our knowledge, for the first time. The structure of DOS-SIFMF, which constructs a micro Mach-Zehnder interferometer as a consequence of introducing offset splicing, has characteristics of both a saturable absorber and filter and is more accessible to obtain mode-locking operation in an all-normal dispersive region. The results of simulation show that interference with fewer modes is more reliable to acquire mode-locking operation of the fiber laser. The central wavelength, spectrum, and pulse widths are 1032 nm, 6.15 nm, and 28.8 ps, respectively. The output pulse in time and spectrum domains can be tuned in the range of 168.7 ps and 10.7 nm, respectively. This structure has effects of both mode-locking and filtering, showing potential application in communication and sensing. Furthermore, the influence on mode number to interference is generally discussed in the end.

High directionality of surface radiation for surface emitting distributed feedback lasers.

Improving the directionality of surface radiation is the key to increase the output power and the differential quantum efficiency of grating-coupled surface-emitting distributed feedback lasers. We proposed a scheme to realize the high directionality of surface radiation. In the structure, the second-order grating is fabricated on the p-side of the epitaxial wafer. A SiO2/Si3N4 multilayer reflector arranged above the grating is used to redirect the upward-diffracted beam. The design of the intermediate layer between the grating and the reflector is an important part of achieving high directionality, because the adjustment of its thickness can be used to phase the redirected light with the downward-diffracted light. The calculation results show that the directionality of this structural scheme can reach more than 98% which meets the device requirements. This design provides a reference for surface-emitting distributed feedback lasers with high performance and high stability.

All-fiber high-power spatiotemporal mode-locked laser based on multimode interference filtering.

Multimode interference (MMI) has been considered to be critical and investigated extensively in mode-locked laser based on single transverse mode systems, whereas there are few researches related to three-dimensional nonlinear dynamics within lasers. In this paper, we demonstrate all-fiber high-power spatiotemporal mode-locked (STML) laser by optimizing MMI filtering, where we find that the MMI filtering plays an important role in counteracting the coupling of high-order modes and improving output power of STML laser. The results under weak coupling condition when the length of graded-index multimode fiber (GIMF) is integral multiple of beat length show that the oscillator generates dissipative soliton pulses at 1036.86 nm with pulse width of 5.65 ps, and the slope efficiency of pump-signal is up to 10.3% with average power/energy of 215 mW/6 nJ, which is the highest among all-fiber STML lasers in normal dispersion regime. Besides, the multiple-soliton of STML, including multiple pulses and harmonic mode-locking can be observed in the experiment. Our work significantly broadens the dimensions of design for all-fiber high-power STML and makes them much more accessible for being put into applications.

High-power distributed feedback lasers with high-order surface curved gratings.

A novel, to the best of our knowledge, broad-area distributed feedback laser with high-order surface curved gratings has been fabricated based on standard near ultraviolet lithography. The characteristics of increasing output power and mode selection are achieved simultaneously by using a broad-area ridge as well as an unstable cavity structure composed of curved gratings and a high-reflectivity coated rear facet. Suppression of high-order lateral modes is realized by setting current injection/non-injection regions and asymmetric waveguides. This DFB laser emitting around 1070 nm has achieved a spectral width of 0.138 nm and a maximum output power of 915 mW kink-free optical power. The threshold current and side-mode suppression ratio of the device are 370 mA and 33 dB, respectively. The simple manufacturing process and stable performance give this high-power laser broad application prospects in the fields of light detection and ranging, laser pumps, optical disk access, etc.

A Flexible Multimodal Sole Sensor for Legged Robot Sensing Complex Ground Information during Locomotion.

Recent achievements in the field of computer vision, reinforcement learning, and locomotion control have largely extended legged robots' maneuverability in complex natural environments. However, little research focuses on sensing and analyzing the physical properties of the ground, which is crucial to robots' locomotion during their interaction with highly irregular profiles, deformable terrains, and slippery surfaces. A biomimetic, flexible, multimodal sole sensor (FMSS) designed for legged robots to identify the ontological status and ground information, such as reaction force mapping, contact situation, terrain, and texture information, to achieve agile maneuvers was innovatively presented in this paper. The FMSS is flexible and large-loaded (20 Pa-800 kPa), designed by integrating a triboelectric sensing coat, embedded piezoelectric sensor, and piezoresistive sensor array. To evaluate the effectiveness and adaptability in different environments, the multimodal sensor was mounted on one of the quadruped robot's feet and one of the human feet then traversed through different environments in real-world tests. The experiment's results demonstrated that the FMSS could recognize terrain, texture, hardness, and contact conditions during locomotion effectively and retrain its sensitivity (0.66 kPa-1), robustness, and compliance. The presented work indicates the FMSS's potential to extend the feasibility and dexterity of tactile perception for state estimation and complex scenario detection.

Enhancing Q-Switched Fiber Laser Performance Based on Reverse Saturable and Saturable Absorption Properties of CuCrO2 Nanoparticle-Polyimide Films.

We demonstrate CuCrO2 (CCO) nanoparticle (NP)-polyimide (PI) composite film as a saturable absorber (SA) to regulate the output characteristics of passively Q-switched fiber laser at 1.55 µm. Based on the reverse saturable and saturable absorptions of the CCO NP-PI film, the passively Q-switched fiber laser expressed two stages with the increase of pump power for substantial performance enhancement. Reverse saturation absorption is observed to introduce appropriate cavity loss, which constructs effective pathways for promoting both the modulation depth and over threshold degree, as well as reducing the photon lifetime. In particular, our results realized the pulse duration and repetition rate compressing simultaneously for the first time. The second stage output laser exhibits a peak power of 1016 mW and a single pulse energy of 183 nJ, which are about 88 and 9 times higher than those of the first stage. Furthermore, the optical-optical conversion efficiency is up to 1270%. All of these can evidently demonstrate the importance of the appropriate cavity loss design for optimizing the Q-switched pulse laser output characteristics.

Research on the reconfigurable bottle beam based on adjusting the spot shape of the incident beam.

An optical system was designed that can generate a bottle beam with a reconfigurable function. The incident beam is produced by transmitting a circular Gaussian beam through the oblique circular aperture, effectively forming the elliptic beam spot. Due to the asymmetry of the elliptically limited Gaussian beam, the bottle beam with locally vanishing light intensity is generated after the optical system. The results show that the bottle beam can be opened and closed freely by the oblique circular aperture, which is of great significance to particle capture.

Polarization-stabilized tunable VCSEL with internal-cavity sub-wavelength grating.

In this paper, a tunable VCSEL with internal-cavity sub-wavelength grating structure at 850nm was demonstrated. Utilizing the birefringence and anti-reflection characteristics of the sub-wavelength grating, the tunable VCSEL with wide wavelength tuning range and stable TE polarization mode was achieved. The relationships between the parameters of sub-wavelength grating and the transmittance/effective index of two polarization modes were analyzed. The tuning efficiency, polarization mode and wavelength tuning range of the tunable VCSEL with internal-cavity sub-wavelength structure were studied. Simultaneously, the MEMS cantilever structure with 'bowknot' shape on the end of the cantilever was designed, which can effectively avoid the concentration of stress distribution and reduce the maximum stress. The results show that the wavelength tuning range is 22.7nm, the peak output power is 1.6mW at 20°C, and the polarization suppression ratio is more than 20dB.

Thermal management of a semiconductor laser array based on a graphite heat sink.

Thermal analysis of a semiconductor laser array is carried out by establishing a packaging structure model of the array based on the use of copper as the base heat sink. A novel composite heat sink structure for a high-power semiconductor laser array with copper-implanted graphite microholes is proposed. The relationship between the location and quantity of microholes and the junction temperature of the semiconductor laser array is analyzed by numerical simulation. The packaging structure is found to effectively reduce the temperature generated by the semiconductor laser array in the process of operation, and the highest temperature is reduced by 4.52 K. Since the laser diode bar is composed of multiple emitters, the temperature of the intermediate emitters is higher than that of the edge emitters. The structure of the graphite heat sink is optimized to improve the temperature uniformity of the semiconductor laser array emitter. Without changing the parameters of the semiconductor laser array device, the temperature difference is calculated, and a reduction from 7.68 to 2 K is shown.

C-band wavelength tunable mode-locking fiber laser based on CD-SMS structure.

A wavelength-tuning passively mode-locked all-fiber laser based on cascaded dual single mode fiber-graded index multimode fiber-single mode fiber (CD-SMS) structure is proposed in this paper. The CD-SMS structure geometry, where two SMSs were fused together, and each of SMS was coined into the paddles of polarization controller (PC). By adjusting the orientation angle of the paddles, magnitude of the nonlinear phase shifts of the light can be controlled to realize mode-locking and filtering. Experimentally, mode locking was obtained based on the SMS structure with pulse duration of 930 fs at the central wavelength 1568 nm and FWHM bandwidth of 2.9 nm. The fundamental repetition rate obtained was 18.22 MHz. By inserting another SMS into the ring cavity, and make-up CD-SMS, the five main peaks of mode-locked pulses were tuned in the range of 1533-1573 nm was achieved by mechanically tuning the orientation angles of paddles of two PCs, the wavelength tuning range covers the whole C-band, reaching 40 nm. However, the tunable range is limited by gain bandwidth of erbium ion. The wavelength-tuning mode locked fiber laser based on CD-SMS provides a way to a wide range of tunable ultrafast lasers.

Emerging transparent conducting oxides material: 2-dimensional plasmonic Zn doped CuGaO2 nanoplates for Q-switched fiber laser.

A passively Q-switched Er3+ doped fiber laser has been realized by using Zn doped hexagonal CuGaO2 (CGZO) nanoplates (NPs) as a saturable absorber (SA) for the first time. The CGZO NPs SA film exhibits strong saturable absorption property, meanwhile with a small nonsaturable loss of 5.179%, and the modulation depth is up to 40.821%. A stable passively Q-switched laser, which was centered at 1559.75 nm, was achieved, and the threshold was as low as 42 mW. With an increase of the pump power from 42mW to 361mW, the pulse duration decreases from 36 µs to 1.71 µs, and the maximum output power of 12.1 mW is achieved. Particularly, the optical-optical conversion efficiency of the Q-Switched laser based on CGZO NPs reached 3.76%. Due to whispering-gallery-mode (WGM) resonance in CGZO NPs, the nonlinear optical response of CGZO NPs has been enhancement. These findings demonstrate that CGZO NPs are promising SA for fabricating high-efficiency and low-threshold pulse lasers.

Design of bottle beam based on dual-beam for trapping particles in air.

An optical system structure, consisting of a tunable bottle beam, was designed to capture micron absorbing particles in air. Using a 670 nm semiconductor laser as the light source, a bottle beam was formed with beam shaping elements, a double-axicon lens, and parabolic annular mirrors. Taking a particle of carbon nanoclusters as an example, the capturing effect of the bottle beam on a particle was analyzed. By adjusting the size of the bottle beam, the capture performance for particles of different radii could be optimized. When the optical power of the conical doughnut hollow beam was P=0.05 W, the composite bottle beam could capture a particle of carbon nanoclusters smaller than 237 µm.

1.6-µm-wavelength dissipative solitons mode-locked fiber laser based on the optimization of passive fibers distribution.

We present the results of numerical simulation of a dissipative solitons mode-locked fiber laser working over 1.6 µm. First, systematic and computationally intensive analysis of high-energy-pulse nonlinear phase shift of a fiber laser was conducted, and we numerically simulated dissipative solitons pulse evolution. In addition, we employed a method named A/B ratio to decrease B-integral by changing the distribution of passive fiber in the ring cavity. This method inhibited the accumulation of nonlinear phase shift and effectively enlarged the pulse energy from 0.8 nJ to 3.6 nJ. Finally, we optimized linear chirp of the pulse by using a designed larger-mode-area fiber, and ultimately a 2.82-kW, 650-fs pulse was obtained.

Reverse-bias-driven whispering gallery mode lasing from individual ZnO microwire/p-Si heterojunction.

In this paper, electrically driven whispering gallery mode (WGM) lasing was observed from ZnO single microwire (SMW)/p-Si heterojunctions operated at reverse bias. Current-voltage curve exhibits a non-ideal rectification characteristic with a turn-on voltage of about 0.8 V. When the reverse current of 20 mA was applied, several sharp lasing peaks with FWHM as narrow as ∼2 nm appeared in the spectra, which demonstrated that the gain was now large enough to enable the cavity resonant in ZnO SMW. The resonant process, lasing mode and quality factor (Q) were investigated via experiments and theory. The observed discrete lasing peak positions effectively matched the simulated lasing modes. The carrier transport process and light emission mechanism in heterojunctions are also discussed by energy band theory and interface defect.

Morphology and electrical characteristics of p-type ZnO microwires with zigzag rough surfaces induced by Sb doping.

Sb-doped p-type ZnO microwires with zigzag rough surfaces were synthesized by two zone chemical vapor deposition. The zigzag morphology characteristics analyzed by high resolution scanning electron microscopy and transmission electron microscopy show the existence of surface defects caused by Sb doping. The incorporation of Sb into a ZnO lattice induces lattice imperfection, which is the origin of the zigzag rough surface. Photoluminescence and electrical properties of the obtained Sb-doped ZnO microwires were determined. The crossed structure microwire-based p-n homojunction device was fabricated by applying as-synthesized Sb-doped p-type ZnO microwires and undoped n-type ZnO microwires. The doped microwires demonstrate reproducible p-type conduction and enhanced rectifying behavior with increasing Sb doping concentration. The results demonstrated that the optimizable optical and electrical characteristics, controlled by increasing the doping concentration, are reflected in the surface morphology changes which would be helpful for characterizing the doping effects in micro/nanoscale materials.

3 GHz passively harmonic mode-locked Er-doped fiber laser by evanescent field-based nano-sheets topological insulator.

In this paper, we report on the experimental observation of harmonic mode locking (HML) fiber laser based on evanescent field of tapered fiber using topological insulator (TI) Bi2Te3 saturable absorber (SA). The optical deposition method was adopted to fabricate the tapered fiber-based TISA. By significant nonlinear optical property of the tapered fiber TISA and high nonlinear fiber (HNLF), the fiber laser could operate at the pulse repetition of 3.125 GHz under 976 nm pump power of 148 mW, the pulse width of 1.754 ps, and the output power of 6.4 mW. Our results demonstrate that the tapered fiber TI device and HNLF can act as both high nonlinear optical component and SA in fiber lasers, and could also have better performance to achieve ultrashort pulses with ultrahigh repetition.