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Iris defect texture inpainting is a challenging problem that is not only limited by a lack of research but also by requiring a higher degree of texture refinement than other types of images. In the field of image inpainting, most recent research has focused on designing improved encoder-decoder models. Solving the image blurring problem caused by autoencoder models has become a key factor in judging their merits. Generative adversarial networks were designed based on a hybrid attention generative adversarial network (Hybrid A-GAN) mechanism to repair missing iris textures. The generator is based on the encoder-decoder structure and introduces two attention mechanisms to enable obtaining the correlation between channels in the feature map and pixel importance in space, which enhances the network's ability to utilize feature information. Moreover, the improved jump connection effectively fuses the high-level features with the low-level features after weighting, which prevents the information loss caused by the downsampling process and enhances the image generation capability. In addition, the joint Wasserstein generative adversarial network-gradient penalty and L1 loss jointly guide network training, which further enhances network generation performance and ensures global consistency of the generated images. Extensive repair experiments and recognition experiments conducted on three publicly available datasets demonstrated that hybrid A-GAN has excellent repair capability and generalization performance. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we obtain SiGe quantum dots with the diameters and density of 15–20nm and 1.8×1011 cm−2, respectively, by 193nm excimer laser annealing of Si0.77Ge0.23 strained films. Under the excimer laser annealing, only surface atoms diffusion happens. From the detailed statistical information about the size and shape of the quantum dots with different annealing time, it is shown that the as-grown self-assembled quantum dots, especially the {105}-faceted dots, are not stable and disappear before the appearance of the laser-induced quantum dots. Based on the calculation of surface energy and surface chemical potential, we show that the {103}-faceted as-grown self-assembled quantum dots are more heavily strained than the {105}-faceted ones, and the heavy strain in the dot can decrease the surface energy of the dot facets. The formation of the laser-induced quantum dots, which is also with heavy strain, is attributed to kinetic constraint. [Copyright &y& Elsevier]

Broad-area lasers (BALs) have found applications in a variety of crucial fields on account of their high output power and high energy transfer efficiency. However, they suffer from poor spatial beam quality due to multi-mode behavior along the waveguide transverse direction. In this paper, we propose a novel metasurface waveguide structure acting as a transverse mode selective back-reflector for BALs. In order to effectively inverse design such a structure, a digital adjoint algorithm is introduced to adapt the considerably large design area and the high degree of freedom. As a proof of the concept, a device structure with a design area of 40 × 20 μm2 is investigated. The simulation results exhibit high fundamental mode reflection (above 90%), while higher-order transverse mode reflections are suppressed below 0.2%. This is, to our knowledge, the largest device structure designed based on the inverse method. We exploited such a device and the method and further investigated the device's robustness and feasibility of the inverse method. The results are elaborately discussed. [ABSTRACT FROM AUTHOR]

Photonic devices based on silicon waveguides are essential to versatile high‐performance and low‐cost photonic integrated systems. Extremely complex silicon photonic devices with hundreds or even thousands of degrees of freedom (DOF) are successfully designed and manufactured based on recent advances in data science and nanofabrication technology. At this level, conventional forward‐reasoning may no longer be suitable for designing high‐performance silicon photonic devices with novel functionalities since the light‐matter interaction is complex and non‐intuitive. Therefore, the timely development of sub‐wavelength silicon photonic devices that can precisely mold the flow of light is a critical and urgent issue requiring joint engineering and scientific efforts. In this paper, an inverse design strategy based on heuristic and gradient descendant algorithms, enabling the realization of large‐scale integrated devices is first introduced. Subsequently, the burgeoning deep learning technology, which offers a promising direction for the automation design of silicon photonics with a data‐driven approach, is discussed. Finally, the obstacles and prospects in this emerging research direction are revealed. Detail discussions from multiple perspectives are provided. This review aims to provide general guidance and a comprehensive reference for scientists developing photonic integrated systems. [ABSTRACT FROM AUTHOR]

On-chip optical modulators, which are capable of converting electrical signals into optical signals, constitute the foundational components of photonic devices. Photonics modulators exhibiting high modulation efficiency and low insertion loss are highly sought after in numerous critical applications, such as optical phase steering, optical coherent imaging, and optical computing. This paper introduces a novel accumulation-type vertical modulator structure based on a silicon photonics platform. By incorporating a high-K dielectric layer of ZrO2, we have observed an increase in modulation efficiency while maintaining relatively low levels of modulation loss. Through meticulous study and optimization, the simulation results of the final device structure demonstrate a modulation efficiency of 0.16 V·cm, with a mere efficiency–loss product of 8.24 dB·V. [ABSTRACT FROM AUTHOR]

Highlights • S-shaped behavior in emission energy and a non-monotone evolution in spectral band width at low temperature were observed in AlGaInAs QW. • A highly negative linear correlation between FWHM and PL peak energy was exhibited in AlGaInAs QWs. • The above phenomena were attributed to lattice strain fluctuations due to thermal expansion coefficient difference and carriers' localization. • The thermal energies of photon-generated carriers moving from the band edges to localization centers were independent of annealing durations. Abstract A series of compressively strained AlGaInAs quantum well (QW) structures with different annealing treatment durations at 170 °C were investigated by temperature-dependent photoluminescence (PL). An abnormal S-shaped behavior in emission energy and a non-monotone evolution in spectral band width were observed at low temperature. A significant negative linear correlation between full width at half maximum (FWHM) and emission energy at different test temperature was exhibited in samples with different heat treatment durations. The highly linear relation demonstrated that the dependencies and relationships between PL peak energy and FWHM vs temperature are consistent. The anomalous blue shift and concomitant narrowing of FWHM in AlGaInAs QW were affected by lattice strain fluctuations due to the difference of thermal expansion coefficients between adjacent layers and strong carriers' localization at low temperature. [ABSTRACT FROM AUTHOR]

The surface Cs–O activation process directly determines quantum efficiency and stability of negative-electron-affinity photocathodes. To investigate the effects of excessive Cs and O supply on activation and to explore a more effective Cs–O activation recipe, Cs–O activation experiments of GaAs(100) photocathodes are carried out based on the current-driven solid Cs and O dispensers. By a comparison of differences in activation photocurrent, quantum efficiency, and photocurrent decay, it is found that the recipe of excessive O and non-excessive Cs is not suitable for activating GaAs photocathodes, while the recipe of continuous and completely excessive Cs along with intermittent and non-excessive O can achieve the most excellent photoemission performance, including the highest quantum efficiency in the long-wave threshold region and best stability under intense light irradiation after activation. Furthermore, this improved activation recipe with the least Cs–O alternating cycles is easier to operate. Combined with density functional calculations and dipole layer model, it is found that the activation recipe of completely excessive Cs and non-excessive O can form effective dipoles to the greatest extent, and avoid the direct interaction between As atoms and O atoms to form As–O–Ga oxides on the GaAs(100) reconstructed surface. [ABSTRACT FROM AUTHOR]

• An end-to-end unified iris recognition framework without normalization is proposed for more accurate iris segmentation and recognition. • MADNet combines multiple attention and improved skip connection to make better distinctions between iris and non-iris. • DSANet introduced spatial attention mechanism into the dense connection, which made the iris features of different samples more discriminative. • Plenty ablation experiments were used to demonstrate the effectiveness of MADNet and DSANet structures. • The proposed method can improve the performance of low-quality iris images that have not be provided the corresponding GT image most obviously. Due to their insufficient generalization ability, iris segmentation algorithms based on deep learning cannot accurately segment iris images without corresponding ground truth (GT) data. Moreover, prior to recognition, the segmented image requires normalization to reduce the influence of pupil deformation. However, normalization of nonconnected iris regions will introduce noise, thereby decreasing the recognition rate. This paper proposes an end-to-end unified framework based on deep learning that does not include normalization in order to achieve improved accuracy in iris segmentation and recognition. In this framework, a multiattention dense connection network (MADNet) and dense spatial attention network (DSANet) are designed for iris segmentation and recognition, respectively. Finally, numerous ablation experiments are conducted to demonstrate the effectiveness of MADNet and DSANet. Experiments on three employed databases show that our proposed method achieves the best segmentation and recognition performance on low-quality iris images without corresponding GT data. [ABSTRACT FROM AUTHOR]

Large lattice mismatched heterostructures In0.78Ga0.22As/GaAs were grown with a low-temperature (LT) InGaAs buffer. Misfit dislocation arrays were observed at the LT-buffer/GaAs interfaces. Transmission electron microscopy (TEM) was used to investigate the microstructures of the heterointerfaces. The relationship between misfit dislocations and strain relaxation at the interface was analysed. It was found that strain redistribution gives rise to the discrepancy of interfacial structure and misfit strain relaxation for different samples. The experimental results are in favor of the conclusion and confirm the analysis we proposed. [ABSTRACT FROM AUTHOR]

Wide-bandgap semiconductors are more advantageous for betavoltaic batteries due to their high conversion efficiency and strong radiation resistance. However, there has been little comprehensive analysis of how wide-bandgap semiconductors lead to efficiency improvements. In this work, we proposed a simulation model to predict the output performance of betavoltaic batteries based on 4H-SiC, hexagonal-GaN, and diamond, in which the Monte Carlo code and COMSOL Multiphysics software were combined. The energy deposition of a 63 Ni source in semiconductors and the electrical characteristics of p–n junctions were investigated and compared. Our simulation results showed that the mass density and atomic number of semiconductor materials will cause the difference in energy deposition distribution, further leading to the different electron–hole pair generation rates. Then, the internal efficiency of batteries is co-determined by the energy band structure, depletion region width, built-in potential barrier, and minority carrier lifetime. The batteries based on wide-bandgap semiconductors can achieve the larger open-circuit voltage, further leading to higher efficiency. Additionally, to optimize the energy converter structure, the output parameters were calculated with a variation of doping concentrations and thicknesses of each region. Under the irradiation of a 63 Ni source, the diamond-based battery with a p–n junction structure has the highest internal efficiency of 31.3%, while the GaN-based battery has the lowest one (16.8%), which can be attributed to the larger carrier recombination rate. [ABSTRACT FROM AUTHOR]

For the 63NiO-Si heterojunction betavoltaic nuclear battery, the energy deposition of the energy conversion material itself was simulated by Monte Carlo simulation, and the structure of the 63NiO-Si heterojunction was optimized based on the theoretical calculation results. When the thickness of 63NiO is 4 μm and the doping concentration of Si is 1 × 1015 cm−3, the short-circuit current density, open-circuit voltage, fill factor, and maximum output power density of the nuclear battery are 1.22 μA · cm−2, 3.17 V, 0.95, 3.67 μW · cm−2. In addition, the output performance of 63Ni/NiO-Si heterojunction betavoltaic nuclear cell was calculated in this study. Under the condition that the activity of the radioactive source and the thickness of NiO(63NiO) are the same in the two structures, the proposed structure (63NiO-Si) has greatly improved the output performance of the nuclear battery by reducing the energy lost from radioactive source self-absorption. [ABSTRACT FROM AUTHOR]

• A two-stage and two-discriminator generative adversarial network proposed for repairing irregularly incomplete iris images. • The two-stage generator and two-discriminator ensures the semantic information and texture information of the repaired images. • PC-Attention is proposed to further extract iris features. • Excellent repair performance on IITD, CASIA Iris Interval, and UBIRIS.V2 iris datasets. Due to the influence of the light source environment during image acquisition or the subject not fully opening their eyes, there are phenomena such as light spot interference, eyelash or eyelid occlusion in the iris area. This will cause the loss of effective iris information, ultimately affecting the success rate of recognition. To address the aforementioned issues, this paper introduces a Two-stage and Two-discriminator Generative Adversarial Network (TT-GAN) to restore irregularly incomplete iris images. The specific process is as follows: Firstly, TT-GAN employs gated convolution in place of ordinary convolution to more effectively extract image information; Secondly, TT-GAN incorporates a PC-Attention attention mechanism within the generator network to enhance the network's restoration capabilities; lastly, to ensure consistency in global and local semantic information of the repaired images, dual SN-PatchGAN discriminators are utilized. The experimental results based on three different spectral iris datasets, IITD, CASIA-Iris-Interval, and UBIRIS.V2, show that the repaired iris images significantly improve objective evaluation indicators compared to the incomplete iris images. Among them, TAR increased by 93.42 %, 68.41 %, and 59.72 %, respectively; EER increased by 27.17 %, 30.18 %, and 23.78 %, respectively; PSNR increased by 17.8712 dB, 18.818 dB, and 24.6053 dB respectively; SSIM increased by 0.0325, 0.0529, and 0.1337 respectively. [ABSTRACT FROM AUTHOR]

In this study, we realize the high-power output of a single-mode 894 nm vertical-cavity surface-emitting laser (VCSEL) at high temperature. The effects of the dimensional parameters of oxide aperture and surface relief on the transverse mode and threshold gain of VCSEL were analyzed. Through collaborative optimization of the oxide aperture and relief, the VCSEL with 8 µm oxide aperture diameter and 5 µm surface relief inner diameter can operate at high temperature of 365 K with single-mode output power of 2.02 mW and side-mode suppression of 29.2 dB. [ABSTRACT FROM AUTHOR]

With the broad application of iris recognition systems, iris images acquired under cross-sensor and cross-spectrum conditions are increasingly common. Differences in the information stored in these images place high requirements for accuracy and robustness on cross-domain iris recognition algorithms, and current algorithms have not performed well in cross-domain iris recognition. Hence, we propose a dense squeeze and excitation network (DenseSENet) to extract common features in cross-domain iris images and use real-valued features for cross-domain matching. DenseSENet is a deep convolutional neural network based on an attention mechanism. It uses the batch normalization-rectified linear unit-Conv1 × 1 structure to increase the nonlinearity of the network and repeatedly uses features through dense connections to effectively prevent overfitting. The proposed dense squeeze and excitation structure extracts more accurate and stable features by learning the relations between channels and assigning corresponding attention values. The structure of global average pooling-fully connected-softmax is utilized to obtain compact and normalized real-valued feature templates to effectively reduce the size of the iris template. The proposed cross-domain iris recognition framework based on DenseSENet is end-to-end, which transforms the cross-domain matching problem to a many-to-one classification problem. Experiments are conducted on publicly available cross-sensor and cross-spectral iris databases. The results show that the proposed real-valued feature matching based on DenseSENet has better matching accuracy and robustness than the state-of-art cross-domain matching algorithm on two publicly available cross-sensor and cross-spectral iris databases. [ABSTRACT FROM AUTHOR]

This paper presents a simulation model to predict the performance of GaAs-based betavoltaic batteries with a p–n junction structure, in which the carrier transport and collection characteristics were studied. First, the electron–hole pair generation rate in the GaAs material under the irradiation of a 63Ni source was calculated using the Monte Carlo codes. Furthermore, by simulating the energy band structure, electric field distribution, and current density distribution in batteries with the finite element analysis software COMSOL Multiphysics, we analyzed the effects of structure parameters on the output performance. Our simulation results showed that the short-circuit current density (Jsc), open-circuit voltage (Voc), maximum output power density (Pm), and energy conversion efficiency (η) of the batteries are significantly affected by the thicknesses and doping concentrations of the p-region and n-region (Hp-GaAs, Hn-GaAs, Na, and Nd). The optimized GaAs-based battery with an Hp-GaAs value of 0.1 μm, an Hn-GaAs value of 9.9 μm, an Na value of 3.98 × 1016 cm−3, and an Nd value of 1 × 1015 cm−3 can achieve a Pm value of 0.080 μW/cm2. The related Jsc, Voc, and η values are 0.234 μA/cm2, 0.49 V, and 1.55%, respectively. When the top and bottom heavily doped layers are introduced, the Pm value of the battery is enhanced by 7.5% compared to that of the battery without heavily doped layers due to the formed drift fields. [ABSTRACT FROM AUTHOR]

• 780 nm DFB laser based on surface isolation grooves. • Periodic p-electrode realize SLM output (SMSR greater than 36 dB). • Ultra wide tuning range (17.5 nm). • Cost-effective fabrication method(i-line). • The outpower is over 130 mW. Widely tunable distributed feedback (DFB) lasers based on surface isolation grooves were developed using i-line lithography. Periodic p-electrodes on mesas enabled the realization of a great tunability. It is to be mentioned that, our device reached a wavelength tuning range of approximately 17.5 nm by only one pair of electrodes under both temperature and current variation with the help of order hop. A single longitudinal mode with continuous-wave output power reached up to 132.8 mW/facet for a drive current of 400 mA at 20 °C. The side-mode suppression ratio reached 36.25 dB. The wide tuning range and the simple fabrication steps promise our device an immense potential as light source in many applications such as atomic clocks and gas sensing. [ABSTRACT FROM AUTHOR]

A widely tunable distributed feedback Bragg (DFB) laser diode based on surface isolation grooves has been produced by i-line lithography. Periodic p-electrodes on the mesas realize a single longitudinal mode output. The maximum continuous wave output power of the uncoated device was 145.3 mW/facet at 500 mA, and the maximum side-mode suppression ratio was over 37 dB. Experimentally, the laser diode could be tuned from 899.9 to 907.7 nm from 15 ∘ C to 35 ∘ C. The 3 dB linewidth was 920 MHz at 20 ∘ C for an injected current of 300 mA. The method of fabricating the tunable DFB laser diode has great potential for many applications, such as in light detection and ranging (LiDAR) devices. • Tunable distributed feedback Bragg laser diode based on surface isolation grooves. • Cost-effective fabrication method using photolithography (i-line). • Periodic p-electrode on mesas enable realization of single longitudinal mode output. • Tunability was in the range of 899.9 to 907.7 nm in a temperature range of 10 °C. • The 3 dB linewidth was 920 MHz at 20 °C for an injected current of 300 mA. [ABSTRACT FROM AUTHOR]

[Display omitted] • An improved activation recipe is proposed to enhance NIR response of InGaAs photocathode. • Performance difference of Cs/O and Cs/NF 3 activated InGaAs photocathodes is studied. • The interaction of 1064 nm and 405 nm light source with activated surfaces is investigated. • The NIR enhancement mechanism is clarified through in-situ experimental characterization. To enhance the near-infrared response of InGaAs photocathodes, we proposed an improved activation recipe, including conventional Cs/O or Cs/NF 3 activation with white light and a subsequent re-activation with 1064 nm light. In-situ activation, re-activation and characterization were performed to investigate the relationship between the spectral response and the emitting surface. Multiple activation experiments demonstrated that re-activation illuminated by the 1064 nm light after conventional Cs/O activation effectively enhanced the spectral response in the near-infrared range, e.g., by a factor of 2–6 at 1064 nm, and this recipe had no enhancement effect on the spectral response of the Cs/NF 3 activated samples. After Cs/O activation, the surface barrier of the activation surface was further optimized through the interaction of the 1064 nm light with the activated surface during re-activation. The minor optimization of the surface barrier could significantly improve the tunneling probability of the electrons excited by the near-infrared light. Moreover, the 1064 nm near-infrared light in re-activation could not be replaced by ultraviolet-blue light, as the interaction of ultraviolet-blue light with the activated surface had minimal effect on the surface barrier. [ABSTRACT FROM AUTHOR]

An aluminum gallium indium arsenic (AlGaInAs) material system is indispensable as the active layer of diode lasers emitting at 1310 or 1550 nm, which are used in optical fiber communications. However, the course of the high-temperature instability of a quantum well structure, which is closely related to the diffusion of indium atoms, is still not clear due to the system’s complexity. The diffusion process of indium atoms was simulated by thermal treatment, and the changes in the optical and structural properties of an AlGaInAs quantum well are investigated in this paper. Compressive strained Al0.07Ga0.22In0.71As quantum wells were treated at 170 °C with different heat durations. A significant decrement of photoluminescence decay time was observed on the quantum well of a sample that was annealed after 4 h. The microscopic cathodoluminescent (CL) spectra of these quantum wells were measured by scanning electron microscope-cathodoluminescence (SEM-CL). The thermal treatment effect on quantum wells was characterized via CL emission peak wavelength and energy density distribution, which were obtained by spatially resolved cathodoluminescence. The defect area was clearly observed in the Al0.07Ga0.22In0.71As quantum wells layer after thermal treatment. CL emissions from the defect core have higher emission energy than those from the defect-free regions. The defect core distribution, which was associated with indium segregation gradient distribution, showed asymmetric character. [ABSTRACT FROM AUTHOR]

Single-longitudinal-mode, gain-coupled distributed feedback (DFB) lasers based on high order surface gain-coupled gratings are achieved. Periodic surface metal p-contacts with insulated grooves realize gain-coupled mechanism. To enhance gain contrast in the quantum wells without the introduction of effective index-coupled effect, groove length and depth were well designed. Our devices provided a single longitudinal mode with the maximum CW output power up to 48.8 mW/facet at 971.31 nm at 250 mA without facet coating, 3dB linewidth ( < 3.2 pm) and SMSR ( > 39 dB). Optical bistable characteristic was observed with a threshold current difference. Experimentally, devices with different cavity lengths were contrasted on power–current and spectrum characteristics. Due to easy fabrication technique and stable performance, it provides a method of fabricating practical gain-coupled distributed feedback lasers for commercial applications. [ABSTRACT FROM AUTHOR]

We report a slotted high-order surface grating semiconductor laser without a multi-section design. A wide tuning range of 20 nm with side mode suppression ratios (SMSRs) larger than 30 dB is realized by controlling the temperature and the injection current. With a temperature variation of 30 °C, the wavelength tuning range is larger than 10 nm, in contrast to ∼3 nm for thermo-optic tuning range in other grating-based lasers. By analyzing the gain and the reflection spectrum of the device, we attribute this wide tuning range to the movement of the temperature-induced gain spectrum between the two adjacent Bragg reflection peaks of high-order surface gratings. This is a new method to realize the wide wavelength tuning range. • Realized a 20 nm widly tunable high-order surface grating semiconductor laser without a multi-section design. • Based on the temperature-induced gain spectrum shifting between two adjacent Bragg reflection peaks of the surface grating. • The parameters of the surface grating and the gain specturm of the device should be strictly controlled. [ABSTRACT FROM AUTHOR]

Single-longitudinal-mode end-emitting laser with 10 periods of metal slots at around 956 nm has been fabricated. 100 μm wide broad-stripe and ten periods of 9.5 μm periodicity metal slots are defined by i-line lithography and dry etching. Experimentally, continuous-wave power of 213 mW has achieved, at a slope efficiency of 520 mW/A, having a 3 dB spectrum width of less than 0.04 nm at 900 mA, and operating in a stable single longitudinal mode with the side-mode suppression ratio (SMSR) of 42 dB. We prove that metal slots introduce sufficient loss into the cavity to filter out the wanted mode, and is more efficient on our chip structure than traditional slot laser. This paper provides a new method for the realizing high power broad-stripe (~100 μm) laser and array with single longitudinal mode operation. [ABSTRACT FROM AUTHOR]

The two-step growth technique was introduced to solve the high lattice mismatch (5.6%) between In0.78Ga0.22As and GaAs substrate, and the mechanism of dislocation density reduction by a low-temperature buffer (LT-buffer) was investigated experimentally. For different thicknesses of LT-buffer layers, the surface morphology and microstructure were investigated, and the residual strain and dislocation density of the In0.78Ga0.22As epitaxial layer were studied by XRD, Raman spectroscopy and TEM. We proposed a mechanism explaining the dislocation density reduction during the two-step growth process by the LT-buffer. Also, the experimental results support our conclusion and verify the mechanism we presented. [ABSTRACT FROM AUTHOR]

We presented the self-planar mesa structure for improving the performances of 850-nm oxide-confined vertical cavity surface emitting lasers (VCSELs). By employing the self-planar mesa, the maximum output power was increased from 8mW to more than 11mW, and the maximum wall–plug efficiency was improved from 26% to 36% for the VCSEL with an oxide aperture size of 13μm at 15°C. The thermal resistance was decreased from 1.16°C/mW to 0.94°C/mW. Thermal simulations about different mesa structures were carried out. And the enhanced lateral heat dissipation and current diffusion within VCSELs was considered to be the main reason for improved performances. [ABSTRACT FROM AUTHOR]

To obtain high-power semiconductor lasers with stable operation in a single longitudinal mode and improve the characteristics of the output beam, an end-emitting surface second-order metal grating distributed feedback (DFB) laser emitting at around 940 nm is fabricated. The characteristics of the uncoated devices with and without gratings are tested under room temperature continuous-wave conditions without any temperature-control device and compared. The devices with gratings achieve high powers of up to 385 mW/facet and a small lateral far-field angle of 2.7° at 1.5 A, have only 4.13 nm/A wavelength-shift, and 0.09 nm spectral linewidth at 600 mA, and operate in a stable longitudinal mode. Devices without gratings operate in multimode, with a larger lateral far-field angle (7.3°) and spectral linewidth (1.3 nm), although with higher output powers. Because of the integration of second-order metal gratings and their very high coupling capability, the output beam quality is improved greatly, the lasing wavelength is stable and varies slowly with changes in injection current, while the spectrum is narrowed dramatically, and the far-field angles are greatly reduced. This opens the way for the realization of watt-scale power broad-stripe (>100 μm) surface second-order metal grating end and surface-emitting DFB lasers and arrays with single frequency, single mode operation and high output beam quality. [ABSTRACT FROM AUTHOR]

To improve the lattice matching, quantum efficiency and response range of the transmission-mode GaAs-based photocathode, a novel photocathode with multilayer graded-band cascade emission layer is proposed. The one-dimensional steady-state continuity equations and finite-difference time-domain methods are utilized to obtain the quantum efficiency and optical absorption characteristics of the proposed photocathode, respectively. The results show that, the built-in electric fields generated by the varying-composition and varying-doping structure can assist the photoelectrons generated in the sublayer itself and the front sublayers to transport towards the emitting surface and escape to the vacuum. Compared with the conventional AlGaAs/InGaAs structure, the proposed structure possesses better lattice matching and enhanced quantum efficiency in the UV and NIR wavelength range. A three-fold increase of quantum efficiency can be realized at 400 nm and the theoretical quantum efficiency at 1064 nm can reach 2%. Besides, the integral absorptivity is increased by 6.8% in the visible wavelength range, and 12.9% in the NIR wavelength range. It is found that the increase of the thickness of AlGaAs sublayer and GaAs sublayer mainly reduces the quantum efficiency in the UV–Vis wavelength range. When the InGaAs sublayer is thin enough, the increase of thickness would enhance the quantum efficiency in the NIR wavelength range and deteriorate that in the UV–Vis wavelength range. This work can contribute to the performance improvement of UV–Vis–NIR broadband GaAs-based photocathode. • A transmission-mode photocathode with multilayer graded-band cascade structure is proposed. • The quantum efficiency model of the proposed multilayer structure is deduced. • The quantum efficiency and optical absorption characteristics are investigated. • The lattice matching, quantum efficiency and response range are improved. [ABSTRACT FROM AUTHOR]

• The VCSELs based on asymmetric confinement by oxide layer itself is an ideal solution to obtain polarization stability. • Theoretical simulations guide the selection of asymmetric oxidation apertures. • The oxidation time influences the asymmetry of oxide aperture. • The asymmetry of oxide aperture influences the state of the emitting mode. Given the high symmetry of vertical-cavity surface-emitting lasers (VCSELs) along their emission axis, these lasers demonstrate intrinsic polarization instability. In this study, we report the anisotropy oxide apertures of VCSEL formed by the unsymmetrical airflow distribution during the wet oxidation process. The polarization directions of VCSELs with anisotropy oxide apertures are well-controlled. VCSELs with oxide apertures of 2 μm × 4.6 μm achieve an orthogonal polarization suppression ratio of more than 20 dB and side-mode suppression ratio of more than 25 dB. In addition, an asymmetric far field distribution is observed, which can be ascribed to the asymmetric oxide apertures. [ABSTRACT FROM AUTHOR]

With the rapid development of deep learning, iris recognition methods based on deep learning are constantly being proposed. These methods generally consist of iris segmentation and normalization to more accurately locate iris regions and reduce the impact of iris feature changes caused by pupil expansion. We propose a non-segmentation (NS) iris recognition framework based on a deep learning classification model, which directly takes a raw image as input for feature extraction and recognition without performing iris segmentation and normalization. This method outperforms other methods. We proposed a non-segmentation network (NSNet). NSNet is a convolutional neural network (CNN) based on an attention mechanism that enhances the robustness and accuracy of the network by reusing features and assigning channel attention values. In addition, while ensuring the advanced performance of the network, it uses only 31 convolutional layers to complete iris feature extraction and recognition tasks in the NS iris recognition framework. Since the deep learning classification model cannot recognize that the category of an image is an untrained image category, we proposed a dual-threshold iris framework. In the proposed framework, all untrained image categories are classified as impostor classes, and the first threshold set in the proposed framework can effectively prevent impostors and eliminate inferior images. The proposed framework is suitable for the pursuit of more accurate, more robust, and safer private iris recognition scenarios. We conduct experiments with uniform parameter settings on four publicly available databases and shows that even in the challenging situation where a raw image is used as the input image, the proposed method is still the most advanced algorithm. Moreover, a series of ablation experiments were conducted to further confirm that the proposed framework has a higher accuracy, robustness, and generalizability through verification and discussion. [ABSTRACT FROM AUTHOR]

Single-longitudinal-mode gain-coupled distributed feedback (DFB) lasers based on high-order gain-coupled surface gratings emitting at 770 nm window are implemented. The periodic surface metal p-contact with insulated grating grooves realizes a gain coupled mechanism. Our devices provided a single longitudinal mode with the maximum CW output power up to 116.8 mW@400 mA with facet coated (HR>99%, AR<0.5%), 3 dB linewidth is 0.26 pm and SMSR is 36 dB. Due to easy-to-manufacture technology and stable performance, it provides a practical gain-coupled distributed feedback laser emitting at 770 nm region manufacturing method for commercial applications. • No secondary epitaxy and no complicated photo lithography techniques are used. • Using surface grating and periodic electrical injection. • Forming a gain coupling mechanism. • Fabricating a purely gain-coupled DFB laser at 770 nm. [ABSTRACT FROM AUTHOR]

AlGaInAs quantum well (QW) lasers have great potential in the application fields of optical communications and eye-safety lidars, owing to the advantages of good gain performance. A large amount of experimental evidence indicated that carrier dynamic affects the resonant frequency and modulation response performance of QW lasers. However, the mechanism of carrier dynamic in AlGaInAs QW structure is still ambiguous for complicated artificial multilayers. In this paper, the carrier dynamic of AlGaInAs QW structure was investigated by temperature-dependent time-resolved photoluminescence (TRPL) in the range of 14 to 300 K. Two relaxation times (a fast component and a slow one) have a major impact on the PL emission spectra of the AlGaInAs QW below 200 K. The carriers prefer a fast decay channel in the low temperature regime, whereas the slow one a higher temperature. An unconventional temperature dependence of carrier relaxation is observed in both decay processes. The carriers' lifetime decreases with the temperature increasing till 45 K and then increases with temperature up to 250 K. It is quite different from that in the bulk semiconductor. The mechanism of temperature-dependent carrier relaxation at temperatures above 45 K is a combination of dark state occupation and a nonradiative recombination process. [ABSTRACT FROM AUTHOR]