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Quantitative characterization of blood cells is very important for medical diagnosis and life science research. This study presents a novel label-free and high-throughput approach for analyzing flowing blood cells in a microfluidic channel by combining deep learning with partially coherent illumination-based diffraction phase microscopy (PCI-DPM). Diluted blood was injected into a microchannel and imaged with PCI-DPM, yielding high-contrast phase images for the blood cells. A modified YOLOv5-s neural network was used to perform automatic identification and analysis of blood cells in the phase image of PCI-DPM, revealing the diameter, dry mass, volumetric density, and speed of blood cells precisely. The proposed approach allows quick and accurate assessment of blood samples, providing valuable insights for patients in different pathological states, such as hematological disorders and infections. [ABSTRACT FROM AUTHOR]

In a recent article Babiker et al. (2024) claim that cylindrical vector beams (CVBs), also referred to as higher-order Poincaré (HOP) beams, possess optical chirality densities which exhibit 'superchirality'. Here we show that, on the contrary, CVBs possess less optical chirality density than a corresponding circularly polarized scalar vortex beam and that the 'superchiral' results are nonphysical. We also identify a number of issues concerning the derivation and general theory presented. [ABSTRACT FROM AUTHOR]

The lobster eye lens uses square channels to reflect and converge light. It has no fixed optical axis and possesses advantages such as a broad field of view (FOV) and no chromatic aberration. Moreover, lobster eye lenses based on microporous optics manufacturing technology have been successfully applied to the spatial detection of soft X-ray spectra. Based on the penetrability of hard X-rays, lobster eye lenses can detect the perspective of hidden targets, which can be applied to fields such as safety inspection and industrial flaw detection. This study proposes an algorithm for comprehensive analysis of the imaging ability of a hard X-ray lobster eye lens, focusing on the stray rays transmitted by high-penetration X-rays. The simulation results showed that the point-spread function of the off-axis FOV is different. With the increase in the photon energy, the enhanced superposition effect of the cross-arm decreases the image contrast. Both the simulated and experimental images show that the image contrast decreases as the photon energy increases. The image contrast can be improved by adding more Pb to the materials used to create the lobster eye lens owing to the strong attenuation ability of Pb to X-rays. These results can contribute to the improvement of lobster eye lenses in X-ray backscatter imaging. • Lobster eye lenses can detect the perspective of hidden targets using hard X-rays. • We analyse imaging of a large-field-of-view hard X-ray lobster eye lens. • The analysis focuses on the stray light transmitted by high-penetration X-rays. • The image contrast can be improved by adding more Pb. • Findings contribute to improving lobster eye lenses in X-ray backscatter imaging. [ABSTRACT FROM AUTHOR]

The advancement of lithography, mass spectrometry and other technologies is increasingly requiring the high-quality focusing of extreme ultraviolet (EUV) beams. Traditional transmissive optics are not suitable for focusing EUV beams due to the strong absorption of most materials. However, rapid developments of metasurfaces have led to breakthroughs in the research of EUV metalenses. Based on the hole-type unit structure proposed recently, we demonstrated the dual-wavelength achromatic metalens in the EUV working for wavelengths of 46.9 and 69.8 nm with a numerical aperture 0.05. Then the dispersion manipulation for the achromatic metalens is extended to three wavelengths 46.9, 60, and 69.8 nm. The simulation results suggest that the maximum relative focal shift from the designed focal length is 0.008 %, and the diffraction-limit focusing is achieved for all working wavelengths. This work could expand the means of the EUV optical field modulation. • Transmissive EUV metalens is designed for beam focusing. • The dual-wavelength achromatic metalens is demonstrated. • The dispersion manipulation for the metalens is extended to three wavelengths. [ABSTRACT FROM AUTHOR]

The laser-induced damage observed in optics has rendered compressor grating the most limited component in petawatt (PW) lasers, owing to the considerable challenges associated with manufacturing gratings possessing both a sufficiently high damage threshold and large dimensions. An asymmetric four-grating compressor (AFGC) based multistep pulse compressor method was proposed recently to alleviate the requirement of such gratings. The viability of AFGC is further investigated experimentally in SEL-100 PW frontend with spectral bandwidth of over 200 nm in this study. It is verified that the AFGC has the ability of beam-smoothing resulting from the introduced spatial dispersion. Meanwhile, the spatial dispersion scarcely impacts temporal contrast and focal spot of the output beam. By reducing the laser spatial intensity modulations from 2.0 to 1.3, the pulse energy capacity of the AFGC can be increased by more than 1.5 times through simple translation. The results mark a breakthrough toward experimentally renovating the grating compressor, and pave the way for a reliable and efficient constructions of 100 s PW lasers. [ABSTRACT FROM AUTHOR]

Conformal optics arose from the need for better aerodynamic performance. The Haack curve has the lowest air drag under given conditions. It has superior aerodynamic properties compared to hemispherical domes and quadric conformal domes. Most in line with the concept of conformal optics. But aberration correction is also the most difficult. At present, there is no research on this conformal dome with the best aerodynamic performance. Therefore, a new design method for the internal surface is proposed in this paper to reduce the fluctuation range of aberrations. This method can eliminate the position error on the detector, reduce the fluctuation range of coma and spherical aberration, and even suppress the sensitivity of the defocus-field curvature to the parameters change. A condition for eliminating astigmatism is also proposed for the conformal dome. The fluctuation range of astigmatism and the difficulty of corrector design are reduced by reasonably choosing the rotation center. The research of this paper is of great significance in improving the aerodynamic performance of conformal optical systems. • The aberration correction method for the Haack conformal dome is proposed, which has never been studied before. • An internal surface design method is proposed to eliminate the position error of the detector and reduce the aberration. • The rotation center of the smallest astigmatism fluctuation in the asymmetric conformal optical systems is derived. [ABSTRACT FROM AUTHOR]

The finite depth of focus (DOF) of a focusing lens gives rise to the degradation of lateral resolution at defocused positions. Consequently, the generation of a needle-shaped beam with sub-diffraction size and extended DOF can break through this limitation, but few studies have effectively balanced these two characteristics. In this paper, we propose a method based on the stochastic parallel gradient descent (SPGD) algorithm for designing multi-ring diffractive optical elements (DOEs) to produce the needle-shaped beam, which maintains a super-resolution and uniform spot within a large extended DOF range. Numerical simulations and experimental results have validated that our method can extend the DOF by 14 times longitudinally and reduce the lateral resolution to 73% of Airy spot, while maintaining up to 92% uniformity of the beam diameter. Furthermore, we demonstrate that the DOF of the needle-shaped beam extends with the increase of the number of rings and phase levels within the DOE. Our work provides an effective strategy for the design of DOF-extended DOE and it is anticipated to find potential applications in microscopy and three-dimensional imaging, photolithography, and optical manipulation. • Needle-shaped beam with super-resolution spot and large depth of focus. • Stochastic parallel gradient descent algorithm based optimization for diffractive optics. • Extremely high uniformity of the beam diameter within the extended depth of focus range. • Tunability of the needle-shaped beam through varying parameters within the diffractive optical element. [ABSTRACT FROM AUTHOR]

А 3D CFD model coupled with wave optics model for laser beam propagation is used to calculate the performance of a hydrocarbon-free K end pumped flowing-gas diode pumped alkali amplifier (DPAA). The K DPAA efficiency and output beam quality were calculated as a function of various parameters and the results were compared with those calculated for end pumped Rb DPAA with hydrocarbon-free buffer gas. For moderate pump intensity, both the efficiency and beam quality deteriorate at low gas velocity. The efficiency strongly depends on the pressure of the buffer helium, reaching a maximum at pressure close to atmospheric and falling with a further increase in pressure. The maximum efficiency of the K DPAA (∼0.45) is approximately 4 times higher than that of the Rb one, achieved at the same optimal pump power of 5 kW. Addition of CH 4 to the He buffer in the K DPAA decreases the amplifier efficiency and reduces the beam quality. [ABSTRACT FROM AUTHOR]

Solitons have been the focus of intense research since their discovery in the nineteenth century and have revolutionized various fields of science and technology, leading to groundbreaking advancements in nonlinear dynamics, optics, communications, and other disciplines. As we are commemorating the 50th anniversary of the discovery of optical solitons, this article aims to provide the contributions of the scientific community in India towards advancement in this domain, shedding light on the fundamental properties, and applications of solitons through diverse theoretical models and analytical approaches in different physical systems, such as in optical fibers, Bose–Einstein condensates, plasma etc. This article is a tribute to the late Prof. Porsezian, a pioneering figure in the world of 'Optical Soliton'. This article is a compendium of notable scientific contributions from the Indian community to the field of Soliton Physics. ▪ • It's a tribute to the late Prof. Porsezian for his contribution to soliton research. • It intends to showcase Indian community's major contributions in soliton research. • Breakthroughs and notable works across the globe, mainly from India was highlighted. • Various solitons, from fibers to diverse media, were discussed in this article. [ABSTRACT FROM AUTHOR]

Wilhelm's law of stress optics establishes the relationship between stress and refractive index in elastic birefringence effect, and the relationship between birefringence optical path difference (BOPD) and principal stress under uniaxial stress can be given according to it. BOPD can be measured and calculated based on photo-elastic principle and spectrometric method, and now the measurement system of BOPD has been designed and realized for getting quantitative result. In the previous research work of the laboratory, BOPD of single acrylic sample with internal stress was measured and analyzed for evaluating internal stress level, however, there were few studies involving BOPD superimposition issue. BOPD superimposition has been studied by means of the measurement system including quarter wave plate, and it not only can give BOPD result of acrylic sample but also help determine whether internal stress is tensile or compressive after uniaxial stress direction is identified. BOPD superimposition can give more useful information on internal stress. The theoretical analysis of BOPD superimposition is discussed, the verification is illustrated and the application of BOPD superimposition in acrylic sample testing is introduced in this article. • Study the possible forms of birefringence optical path difference (BOPD) superimposition from a theoretical perspective. • Design and realize the measurement system for verification and application of BOPD superimposition. • Provide a good solution for uni-axial stress direction identification by the measurement system. • Besides BOPD result, it can also help determine the tensile and compressive properties of uni-axial stress. • Suitable for various transparent materials, such as PMMA, PVC and PE. [ABSTRACT FROM AUTHOR]

We theoretically study a technique for a broadband nonreciprocal wave retarder whose quarter-wave plate phase retardation is the same in forward and backward directions. The system is built using a number of sequential nonreciprocal wave plates. The proposed device can also be utilized to create a broadband optical diode, which consists of two achromatic quarter-wave plates, one reciprocal and the other non-reciprocal, that are sandwiched between two polarizers aligned in parallel. • Broadband composite nonreciprocal polarization wave plates. • Broadband optical isolators. • Nonreciprocal wave retarder. • Nonreciprocal optics. [ABSTRACT FROM AUTHOR]

Cross Polarization is explicitly obtained in the two cases Gaussian and Bessel light beams using the elegant Mukunda–Simon–Sudarshan rule for transition from scalar optics to vector wave optics. Unlike other studies, we obtain the results without solving the Maxwell equations. [ABSTRACT FROM AUTHOR]

Multiple-input single-output (MISO) have extraordinary propagation properties, making it possible to further improve the performance of underwater wireless optical communication (UWOC). In this paper, a tilted MISO-UWOC system consists of a beam array and an aperture averaged detector, academically called multiple-input aperture-average (MIAA) systems, are proposed. Different from the original approach where beams are parallel to each other, the tilted approach has a series of multiple beam transmitters individually aimed at the receiver. The MIAA systems are extensively compared to single-input single-output (SISO) systems on scintillation index and SNR for various oceanic turbulence conditions and system configurations by wave optics simulation (WOS). Our results reveal that tilted MIAA systems show tremendous advantages over the parallel MIAA systems including the reduced scintillation and the improved signal to noise ratio (SNR) under the same configuration. The obtained results can be useful for the UWOC system design. [ABSTRACT FROM AUTHOR]

Dispersion problem has always constrained the development of see-through near-eye displays with diffractive waveguide. Here, we propose a design method and optical systems for one-layer achromatic surface microstructure composed with a triple-carved-sub-grating. The triple-carved-sub-grating with specified period is designed based on rigorous coupled wave theory, corresponding to Red (R), Green (G) and Blue (B) wavelengths, respectively. The surface microstructure with period of 18.9um is realized by synthesizing the three sub-gratings together, and it is verified numerically that the diffractive angle of R, G, and B wavelengths is 35°under the normal incidence of TE polarization, which imply that the surface microstructure diffracts the certain RGB wavelengths achromatically. A diffraction waveguide with achromatic surface microstructure is also modeled to analysis the stray light and color correction, and the results indicate that the diffraction waveguide transmits image with little stray light. Via proper duplication it could be utilized as the combining optics of diffractive-waveguide near-eye display and head-up display because of its light and compact features. [ABSTRACT FROM AUTHOR]

Controlling the polarization state of light is an important research region in optics due to its enormous potential. Conventional polarization converters inevitably express huge size and low efficiency, which run counter to the requirement of modern optics. Herein, a frequency-dependent multi-functional metasurface is proposed and researched to design a broad-band and high-efficiency reflective-type polarization converter at near-infrared band. Based on the simulation results, 90 ° polarization convertor and quarter wave plate can be realized at different wavelengths. The broad-band 90 ° polarization convertor will transform gradually to a broad-band quarter wave plate by increasing the "coupling gap" at the long wavelength region, and the functionalities of 90 ° polarization convertor and quarter wave plate can always be kept at the short wavelength region. Our results can provide a guide to design the ultrathin optical polarization converters. • The 90 ° polarization convertor (CPC) and quarter wave plate (QWP) can be realized at different wavelengths. • The broadband CPC (QWP) can be obtained in the near infrared region. • The CPC and QWP can be transformed into each other by adjusting the "coupling gap". [ABSTRACT FROM AUTHOR]

Abstract Based on the demand for the stability of the Mach–Zehnder optical interferometer, we proposed and designed a system that can achieve fast and precise locking at any phase point in one period. The locking system is simple and is easy to operate. The core elements are an electro-optic modulator (EOM), which can generate different phase shift on the vertically polarized light and horizontally polarized light, and a PID feedback. The experimental results show that for the MZ interferometer, the system can achieve fast, accurate and long-term locking at any phase point. The accuracy of the phase lock can be controlled within 1.05°or 0.0029 λ with the intensity of the interference beams of 0.335 mW. This locking technology can be applied in the field of precision measurement in the future. [ABSTRACT FROM AUTHOR]

In traditional optical imaging, the imaging results are often affected by the scattering of light, resulting in image blurring and other problems. Imaging through scattering media has always been an important research direction in the field of optics. In this paper, on the basic of the speckle autocorrelation imaging method using memory effect, a new speckle reconstruction method is proposed, which improves the phase recovery part in the traditional method, and forms a subsection optimization phase recovery algorithm (SSO). Experimental results show that, the proposed method has large improvement in speckle reconstruction speed, and the quality of the reconstructed image is obviously higher than that of traditional method in fast imaging. Meanwhile, this method is more stable and has better robustness to noise. • A parameter named Error Rate of Fourier Amplitude (EROA) is introduced to judge the accuracy of phase in a single iteration. • A Subsection Optimization (SSO) phase-retrieval algorithm is proposed to realize faster speckle reconstruction. • An indicator named Mean-Square-Error of Amplitude (MSEA) is designed to control the iteration times. [ABSTRACT FROM AUTHOR]

Abstract Sol–gel derived ormosil gel glass can act as matrix for different functional molecules or nanomaterials due to its many advantages. Gold and silver colloidal nanoparticles have great application potential in nonlinear optical field due to their ultrafast optical response. In this letter, the nanocomposites of gold nanorods and ormosil gel glass were prepared by a solvent-assisted dispersing process and characterized by UV–vis spectra, TEM, XRD and optical limiting measurement. The results showed that these gold/ormosil nanocomposites could preserve optical limiting property of gold nanorods and had enhanced thermostability due to thermostable silica matrix. Such nanocomposite material of metal-doped gel glass matrix could be considered as a promising candidate for optical limiter against tunable laser. [ABSTRACT FROM AUTHOR]

Abstract A ternary molybdenum tungsten selenide (MoWSe 2) alloy is proposed and demonstrated as a saturable absorber (SA) to induce Q-switching in the 1. 0 μ m , 1. 5 μ m and 2. 0 μ m regions. The MoWSe 2 based SA is fabricated by mechanical exfoliation and sandwiched between two fiber ferrules to complete the fiberized SA assembly. The MoWSe 2 -SA is integrated into ytterbium, erbium and thulium-doped fiber laser cavities, and stable self-starting Q-switched pulses are observed at 1038 nm, 1554 nm and 1964 nm respectively. Maximum repetition rates at 120.2 kHz, 48 kHz and 61.5 kHz are observed at these wavelengths, along with corresponding pulse widths as narrow as 0.96 μ s, 1.9 μ s and 2.4 μ s respectively. These results validate the performance of MoWSe 2 as a broadband SA for Q-switching operation, offering new opportunities of ternary transition metal dichalcogenide alloys in future photonics devices. Highlights • Ternary MoWSe 2 alloy demonstrated as a saturable absorber. • Able to generate stable Q-switched pulses in 1.0 μ m, 1.5 μ m and 2.0 μ m region. • Laser output with operating wavelength at 1038 nm, 1554 nm and 1964 nm. • Repetition rates at 120.2 kHz, 48 kHz and 61.5 kHz achieved in YDFL, EDFL and TDFL. • Pulse widths of 0.96 μ s, 1.9 μ s and 2.4 μ s achieved in YDFL, EDFL and TDFL. [ABSTRACT FROM AUTHOR]

Abstract We derive and discuss a quasidistribution for phases in line of earlier investigations of quasidistributions in quantum optics and their sampling. We illustrate it for classical and quantum fields as well as at the quantum–classical border generated by nonlinear optical processes, such as optical parametric process and Raman scattering. A new nonclassical property of optical fields related to their phases is derived. [ABSTRACT FROM AUTHOR]

Abstract In lensless digital holography the resolving power is limited by factors such as the finite size of recorded area, pixel dimensions and sampling rate of digital acquisition system. These factors acts as a filter that discards high-frequency components with useful information about the analyzed object. In the present work, we propose a method to overcome these limitations to proving the resolution recovery in digital in-line holography by utilizing adjustable magnification in a compressive sensing framework. Here, we model the sensed field as low-pass filtered and projected on a Fresnel base with adjustable magnification and use sparse regularization in an inverse problem approach to image reconstruction. Our method enhances image reconstruction resolution from a single recorded hologram with magnification independent of parameters such as propagation distance and wavelength of light, which enables to be used in applications like multi-wavelength digital holography. In addition, this technique offers high noise immunity and eliminates typical problems of holographically reconstructed images such as twin image and speckle. Therefore, we demonstrate by simulations and experimentally results that our approach significantly improves the quality of reconstructed images when compared with conventional techniques. Highlights • An approach for holographic magnification using compressive sensing is proposed. • The technique enables holographic reconstruction even from very noisy holograms. • Improves resolution on magnified image reconstructed from a single hologram. • Reduces typical holography problems such as speckle, twin image and aliasing. [ABSTRACT FROM AUTHOR]

Abstract A novel multi-wavelength continuous Thulium-doped fibre laser incorporating a microfibre coil resonator based on black phosphorus (MCR-BP) material has been successfully fabricated and demonstrated. A twelve-wavelength spectrum with 0.54 nm channel spacing has been achieved by simply adjusting the pump source power. A single peak extinction ratio of more than 40 dB was observed. The superior performance of the MCR-BP described in this article compared to conventional MCR based fibre lasers can be attributed the inclusion of the Black Phosphorous Material. The enhanced lasing is primarily due to the twin properties of the MCR-BP device combining a comb-like filter effect and a four-wave-mixing (FWM) effect caused by the nonlinearity of black phosphorus. The experimental results indicate that the novel device can be successfully used as a comb filter and an FWM source to realize a multi-wavelength continuous fibre laser due to the low cost and ease of fabrication of the MCR-BP device. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a back propagation neural network-based function approximation scheme is proposed to provide the capacity of the nonuniform quantization (FABP) in intensity modulated direct detection-based optical filter bank multicarrier (IMDD-FBMC) system. In the means of leveraging this scheme, the quantization noise can be reduced to further improve the ratio of Signal-to-Quantization noise, namely SQNR. Further, with the help of the nonlinear programming, the optimal quantization levels are accurately calculated. And, to validate the feasibility of our method, the simulation and experiment investigation are conducted on the 10-Gb/s transmission system with optical order offset quadrature amplitude modulation based optical orthogonal frequency division multiplexing (OQAM-OFDM) signals through 80-km fiber. Results verified that, our scheme can achieve the error vector magnitude (EVM) improvement of ∼ 2.0% and received sensitivity improvement of at least 2 dB in the same quantization bit case compared with uniform quantization scheme. [ABSTRACT FROM AUTHOR]

Abstract In this paper, deep learning as a novel algorithm is proposed to reduce the noise of the fringe patterns. Usually, the training samples are acquired through experimental acquisition, but these data can be easily obtained by simulations in the proposed algorithm. Thus, the time cost used for the whole training process is greatly reduced. The performance of the proposed algorithm has been demonstrated through the analysis on the simulated and real fringe patterns. It is obvious that the proposed algorithm has a faster calculation speed compared with existing denoising algorithm, and recovers the fringe patterns with high quality. Most importantly, the proposed algorithm may provide a solution to other denoising problems in the field of optics, such as hologram and speckle denoising. [ABSTRACT FROM AUTHOR]

Abstract We propose a polarization modulator (PolM) -based optical vector network analyzer (OVNA) with extended measurement bandwidth. The combined use of the PolM, a polarization controller (PC) and a polarizer performs phase-and-intensity hybrid modulation of optical signal with double-sideband (DSB) modulation. The ratio between phase and intensity modulations is controlled by the PC, leading to different modulation formats. The frequency response of a device-under-test (DUT) can be obtained by processing the results of two measurements under two arbitrarily different modulation formats. The significance of this work lies in that the measurement of a DUT with bandpass response can be simply achieved, which is a huge challenge for the conventional single-sideband (SSB)-based OVNAs. In addition, the measurement bandwidth is doubled compared with the conventional SSB-based OVNA. Moreover, the PolM-based OVNA can avoid the bias drifting problem using conventional Mach–Zehnder modulator (MZM)-based scheme. The proposed method is theoretically and experimentally demonstrated. A proof-of-concept experiment is carried out and a DUT with bandpass response is successfully measured using the proposed scheme. [ABSTRACT FROM AUTHOR]

Abstract We report on a fiber-based, Yb-doped, ultrafast laser system capable of outputting 100 W average power at a repetition rate of 500 kHz. The system uses chirped pulse amplification, employing a custom-made pulse-stretching fiber and a grating based compressor, to generate highly energetic, 330 fs pulses at 1030 nm. A diode-pumped photonic-crystal rod delivers amplification of pulses up to 400 μJ while maintaining near diffraction-limited mode quality. The system is highly robust and offers excellent short and long term power stability. [ABSTRACT FROM AUTHOR]

Abstract An information hiding scheme for visual cryptography based on optical moiré-pixel matrix is introduced in this paper. The hiding information is formed by black and white unit square visual moiré-pixels with half of the period of a visual moiré pattern. The moiré-pixels can be accurately determined by designing the parameters in the original gratings. To verify the designed information hiding scheme, we experimentally conduct the sharing gratings to decrypt the information by using ordinary low-cost digital printing. The concealment of the sharing gratings is good to ensure the confidentiality. Both the simulation and experimental results show that the provoked scheme can afford enough security demand, yielding that the moiré-pixel matrix is a flexible platform for cryptographic security. Highlights • Novel scheme for visual cryptography combining moiré pattern and pixel matrix. • Simple encryption and high-quality decryption is provided. • Provides a low-cost and flexible platform for cryptographic security. [ABSTRACT FROM AUTHOR]

Abstract A Gray code mapping scheme is proposed to reduce coding penalty for probabilistically shaped 9QAM. The carrierless amplitude and phase modulation (CAP) probabilistically shaped 9QAM with the Gray code mapping scheme is experimentally investigated in a single carrier intensity modulation/direct detection (IM/DD) transmission system. The experiment results show that the proposed 9QAM with Gray coding has a gain of 0.034 bits/symbol and 0.111 bits/symbol over 9QAM without Gray coding and star-8QAM at a received optical power of -5.5 dBm, respectively. All of the three modulation formats have the same spectral efficiency (SE) equal to 3 bits/symbol. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we design and numerically analyze the performance of electrostatic doping (ED) assisted junction-less optical phase shifter loaded silicon Mach–Zehnder (MZM), which is realizable on the 220 nm SOI platform. The proposed phase shifter contains a vertical metal–insulator–semiconductor (MIS) junction and a lateral metal–semiconductor (MS) junction. Change in the refractive index profile inside the rib waveguide, which supports the phase shifter is achieved by altering the concentration of free carriers via the plasma dispersion effect. Numerical simulation using a commercially available TCAD tool and mode solver are used to estimate the performance of the proposed modulator. Two different sets of materials are used as electrodes to realize the MIS–MS charge plasma diode. In one design, gold (Au) and silver (Ag) is used as the electrode materials, while the other design utilizes palladium (Pd) and aluminum (Al) as the electrode materials. The performance of the proposed modulator(s) is extensively studied both in the steady state and transient state. A complete analysis of the chirp and nonlinear distortion for the proposed modulator are also presented in the paper. Results predict that a maximum of 15.4 dB dynamic extinction ratio (ER) is achievable with a minimum of 3.2 dB insertion loss (IL). The proposed modulator is expected to provide a maximum of 30.3 Gbps operating speed with 22.2 GHz of 3-dB electro-optical bandwidth. Simulation result predicts that the worst case dynamic energy per bit for the proposed ED assisted MZM is approximately 54.4 fJ/bit. [ABSTRACT FROM AUTHOR]

Abstract A novel photonic approach to generate frequency and bandwidth multiplying dual-chirp microwave for application in dual-band radar system is proposed using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator. The proposed approach is based on optical frequency multiplying and polarization selection. In the approach, the baseband signal and RF signal are injected into the DP-QPSK modulator to generate optical broad spectra and sidebands respectively. By adjusting the bias points of the DP-QPSK modulator, after polarization selection and optical to electrical conversion, frequency-quadrupling bandwidth-octupling and frequency-double bandwidth-quadrupling or frequency-tripling bandwidth-sextupling and frequency-fundamental bandwidth-doubling dual-chirp signals can be generated in the single structure respectively. The proposed approach is verified by simulations. Dual-chirp microwaves with central frequency–bandwidth of 32 GHz-8 GHz, 16 GHz-4 GHz or 24 GHz-6 GHz, 8 GHz-2 GHz are generated in the two ports respectively. Their autocorrelation results manifest good pulse compression capabilities. The central frequency, bandwidth, chirp rate and time duration can be tuned independently. The generated dual-chirp signals show good performance on the range-Doppler coupling and can significantly improve the range-Doppler resolution in dual-band radar system. [ABSTRACT FROM AUTHOR]

Abstract Optical logic devices are the fundamental building blocks for optical computing. In this paper, a compact optical logic device based on plasmonic waveguides is designed and investigated numerically. The proposed structure consists of ring resonators coupled to a metal–insulator–metal(MIM) waveguide. The finite-difference time-domain (FDTD) simulation and coupled-mode theory (CMT) analysis both reveal that typical plasmon-induced transparency (PIT) phenomena can be observed when the refractive index of the rings is changed. Based on the proposed structure, 2 bits and 3 bits input optical logic devices with high intensity contrast ratio (ICR) are devised and demonstrated, while the output logic states "1" and "0" are represented by the high and low levels of optical power. By changing the incident light at different wavelengths, the proposed structure can implement the two basic functions of logical operation: AND gate and NOR gate. The proposed devices are suitable for on-chip optical computing and can also be used in wavelength division multiplexing (WDM) systems. [ABSTRACT FROM AUTHOR]

We investigated a different approach to establish an optical multistability (OM) in quantum atomic systems. It is demonstrated that using two cavities in series configuration leads to a more flexible OM. The number of output intensities can be further than usual and each branch of OM diagram is controllable. In addition, we have specified necessary conditions to achieve this flexible OM. It is shown that the OM threshold and even the lengths of branches are adjustable. [ABSTRACT FROM AUTHOR]

As a deep and fine vertical via, through-silicon via (TSV) is a key factor in three-dimensional (3D) integrated circuit stack, which can pass through a silicon wafer or chip for 3D integration. TSV’s 3D profile metrology is one of the key issues in process control. In this work, we propose and demonstrate a non-destructive in situ measurement technology that can be used to measure the 3D geometric profiles of TSV with an aspect ratio of 10. The optical system designed by us can collect high-frequency signals, which contain the whole geometry information of the TSV in the pupil plane. This measurement is proven effective by analysing the high-frequency spectrum of the pupil plane. Our 3D measurement technology can measure TSV profile diameters as small as 5 μ m with an aspect ratio of 10:1. The measurement accuracy is ± 0.5% comparable with that of SEM measurements using the same sample. [ABSTRACT FROM AUTHOR]

Optics has been verified to play a significant role in the advancement of multiple-image hiding. However, due to the diversity and unrelatedness of hidden information, the quality and quantity of the secret images extracted cannot be guaranteed at the same time. Although various optimized methods have been proposed to enhance the capacity of the system by reducing the crosstalk between the extracted information, the extraction results still suffer from a low signal-to-noise ratio. Here, we propose the modified optical multi-image hiding method in phase cascade system with a physics-driven neural network (MIHNet). The multiple secret images are the only input to the MIHNet which is a physics-driven deep neural network to generate phase keys. The phase keys can independently reproduce the hidden images with higher quality in the Fresnel domain. Simulation results show that the hiding capacity of the proposed method is not only approximately twice that of our previous optimization algorithm (Shi et al., 2007), but also the signal-to-noise ratio of the extracted images are significantly improved. In addition, the feasibility of the proposed method is also demonstrated in metasurface holography. • The physics-driven deep neural network has better performance in estimating the phase keys. • The hidden capacity of the modified method is significantly improved compared to the previous optimized algorithm. • The proposed method can be used to guide the design of optical hiding system supported by metasurfaces. [ABSTRACT FROM AUTHOR]

The early work of the Femtosecond Optics Group at Imperial College on optical soliton generation in fibres is reviewed that commenced with studies of ultrashort pulse generation using high order soliton compression for the production of pulses of 18 fs. Also described are seminal studies of soliton Raman generation using long pulse pumping where evolution from modulational instability led to continuum generation and tunable femtosecond generation. Early investigations of seeding modulational instability for enhanced soliton generation and spectral extension are described, as is the work on seeding of noise, soliton generation from noise bursts and soliton generation from amplified noise bursts. The first study of femtosecond soliton amplification in Er fibre amplifiers is described as well as synchronous Raman amplification of solitons. Various schemes reviewing our investigations of adiabatic soliton compression and amplification are included for the generation of pulsewidth and wavelength tunable soliton sources in fully fibre integrated geometries. [ABSTRACT FROM AUTHOR]

Phase map filtering is considered an indispensable process in the measurement delivered by speckle interferometric optics. For recent measurements, quite a lot of scenarios require an optimized time consumption. A notable feature of the raw phase map is the 2 π modulo of the phase distribution, as retrieved by the inverse tangent operation. Instead of employing the filtering method directly on the phase fringe pattern, the wrapped phase is converted into the sine–cosine domain with its sine and cosine components, and then the filtering method is applied to them. However, it is the nature of the sine–cosine filtering framework that consumes approximately 70% calculation resources for the recalculation of the intermediate phase map and the sine/cosine components at every loop, which limits the temporal property of related measurement. To address the issues of efficiency and quality at the same time, a new filtering domain is proposed, namely the complex amplitude domain filtering framework. The filtering is conducted at the stage of recovering the complex amplitude without calculating the intermediate phase map at every loop. The merit of complex amplitude domain filtering is that it has a good filtering efficiency to remove the speckle noise, preserves the details of the sharp edge in the phase-wrapped area at the same time, and no additional phase shift is generated during the filtering. Most of the existing filters and strategies used in the sine–cosine filtering domain can be directly applied in the proposed complex amplitude domain. Preliminary experiments show that, compared to the sine–cosine domain filtering, the proposed complex amplitude domain filtering accelerates the filtering process by at least 40% at no cost of filtering quality, and particularly shows a better filtering performance with the partial differential equations (PDE) noise reduction method. • Speckle suppression speed at least 40% faster than filtering in sine–cosine domain. • Preserving details of sharp edges at phase jumping area in phase measurement. • Existing filters being readily and effectively applied in complex amplitude domain. • No artificial phase shift generated during complex amplitude domain filtering. [ABSTRACT FROM AUTHOR]

In this paper, a kind of dynamically tunable graphene metasurface which can act as a multi-band refractive index sensor or a four-state optical switch is proposed. Based on the plasmonic hybridization mechanism of a simple graphene ring array, this design exhibits dual-channel resonance modes to realize ultrahigh sensitivity for refractive index sensing, which is 4. 25 μ m /RIU at mid-infrared band and 11. 33 μ m /RIU at far-infrared band, respectively. The proposed design manifests an ultrabroad sensing range through tuning the Fermi level of graphene and a good insensitivity to the incident angle. In addition, we numerically demonstrate a reflective optical switch with the structure of dual-layer graphene disks which indicates that a four-state optical switch is achieved and the cut-off absorptivity is more than 98%. The concise structures are of high feasibility for fabrication and the results illustrate considerable potential in various applications including graphene optics and integrated photonic systems. • Concise and dynamically tunable graphene metasurface for multi-band sensing is proposed. • Ultrahigh sensitivity of 4.25/ 11. 33 μ m /RIU at mid-/far-infrared band is obtained. • Ultrabroad dynamic range and good insensitivity to incident angle are presented. • Four-state switch exhibits high cut-off absorptivity more than 98%. [ABSTRACT FROM AUTHOR]

The vertical cavity surface emitting laser (VCSEL)-based multimode optical transceivers enabled by pulse amplitude modulation (PAM)-4 will be commercialized in near future to meet the 400-Gbps standard short reach optical interconnects. It is still challenging to achieve over 56/112-Gbps with the multilevel signaling as the multimode property of the device and link would introduce the nonlinear temporal response for the different levels. In this work, we scrutinize the distortions that relates to the multilevel feature of PAM-4 modulation, and propose an effective feedback equalization scheme for 56-Gbps VCSEL-based PAM-4 optical interconnects system to mitigate the distortions caused by eye timing-skew and nonlinear power-dependent noise. Level redistribution at Tx side is theoretically modeled and constructed to achieve equivalent symbol error ratios (SERs) of four levels and improved BER performance. The cause of the eye skewing and the mitigation approach are also simulated at 100-Gbps and experimentally investigated at 56-Gbps. The results indicate more than 2-dB power penalty improvement has been achieved by using such a distortion aware equalizer. [ABSTRACT FROM AUTHOR]

We resolve the complex conjugate ambiguity in spectral-domain optical coherence tomography (SD-OCT) by using achromatic two-harmonic method. Unlike previous researches, the optical phase of the fiber interferometer is modulated by an achromatic phase shifter based on an optical delay line. The achromatic phase modulation leads to a wavelength-independent scaling coefficient for the two harmonics. Dividing the mean absolute value of the first harmonic by that of the second harmonic in a B-scan interferogram directly gives the scaling coefficient. It greatly simplifies the determination of the magnitude ratio between the two harmonics without the need of third harmonic and cumbersome iterative calculations. The inverse fast Fourier transform of the complex-valued interferogram constructed with the scaling coefficient, first and second harmonics yields a full-range OCT image. Experimental results confirm the effectiveness of the proposed achromatic two-harmonic technique for suppressing the mirror artifacts in SD-OCT images. [ABSTRACT FROM AUTHOR]

This paper proposes a vehicle positioning system using LED street lights and two rolling shutter CMOS sensor cameras. In this system, identification codes for the LED street lights are transmitted to camera-equipped vehicles through a visible light communication (VLC) channel. Given that the camera parameters are known, the positions of the vehicles are determined based on the geometric relationship between the coordinates of the LEDs in the images and their real world coordinates, which are obtained through the LED identification codes. The main contributions of the paper are twofold. First, the collinear arrangement of the LED street lights makes traditional camera-based positioning algorithms fail to determine the position of the vehicles. In this paper, an algorithm is proposed to fuse data received from the two cameras attached to the vehicles in order to solve the collinearity problem of the LEDs. Second, the rolling shutter mechanism of the CMOS sensors combined with the movement of the vehicles creates image artifacts that may severely degrade the positioning accuracy. This paper also proposes a method to compensate for the rolling shutter artifact, and a high positioning accuracy can be achieved even when the vehicle is moving at high speeds. The performance of the proposed positioning system corresponding to different system parameters is examined by conducting Matlab simulations. Small-scale experiments are also conducted to study the performance of the proposed algorithm in real applications. [ABSTRACT FROM AUTHOR]

We propose a general method for eliminating the reflection of waves in 2 dimensional photonic crystal waveguides (2D-PCWs), a kind of 2D material, by introducing extra scatterers inside the 2D-PCWs. The intrinsic reflection in 2D-PCWs is compensated by the backward-scattered waves from these scatterers, so that the overall reflection is greatly reduced and the insertion loss is improved accordingly. We first present the basic theory for the compensation method. Then, as a demonstration, we give four examples of extremely-low-reflection and high-transmission 90°bent 2D-PCWs created according to the method proposed. In the four examples, it is demonstrated by plane-wave expansion method and finite-difference time-domain method that the 90°bent 2D-PCWs can have high transmission ratio greater than 90% in a wide range of operating frequency, and the highest transmission ratio can be greater than 99.95% with a return loss higher than 43 dB, better than that in other typical 90°bent 2D-PCWs. With our method, the bent 2D-PCWs can be optimized to obtain high transmission ratio at different operating wavelengths. As a further application of this method, a waveguide-based optical bridge for light crossing is presented, showing an optimum return loss of 46.85 dB, transmission ratio of 99.95%, and isolation rates greater than 41.77 dB. The method proposed provides also a useful way for improving conventional waveguides made of cables, fibers, or metal walls in the optical, infrared, terahertz, and microwave bands. [ABSTRACT FROM AUTHOR]

We present a surface plasmon resonance sensor based on photonic crystal fiber filled with gold–silica–gold (GSG) multilayer nanoshells for measurement of the refractive index of liquid analyte. The GSG multilayer nanoshells, composed of a silica-coated gold nanosphere surrounded by a gold shell layer, are designed to be the functional material of the sensor because of their attractive optical properties. Two resonant peaks are obtained due to the hybridization of nanosphere plasmon modes and nanoshell plasmon modes. It is demonstrated that the resonant wavelength of the two peaks can be precisely tuned in 560–716 nm and 849–2485 nm, respectively, by varying the structural parameters of the GSG multilayer nanoshells in a compact, sub-200 nm size range. The excellent spectral tunability makes the sensor attractive in a wide range of applications, especially in biosensing in near-infrared region. Furthermore, the influences of the parameters on the performance of the sensor are systematically simulated and discussed. It is observed that the spectral sensitivities of 1894.3 nm/RIU and 3011.4 nm/RIU can be achieved respectively by the two resonant peaks in the sensing range of 1.33–1.38. The existence of two loss peaks also provides the possibility to realize self-reference in the sensing process. [ABSTRACT FROM AUTHOR]

Single sensor (pixel) signals require scanning of the sample in order to obtain spatial information. In this paper we show that using interference, optically induced signals can be reconstructed when recorded using interference pattern excitation, rather than a point illumination. This method reduces the need for dense scanning and requires a small number of scans, or can eliminate the need for scanning in some cases. It is shown that this method can be used in particular in 2D photo-acoustic imaging. [ABSTRACT FROM AUTHOR]

We report high efficiency linearly polarized Cerenkov radiation (CR) generation in a photonic crystal fiber with suspended rectangle core. The frequency up-conversion via the Cerenkov radiation upon pumping of Yb-doped femtosecond fiber laser is discussed in details. Experiment results show that the output spectrum contains, besides the infrared supercontinuum, intense green Cerenkov radiation around 536 nm, which carry about 43% of the pump energy at best. The influence of the high birefringence and dispersion character on the Cerenkov radiation generation is discussed. Experiment and simulation results indicate that the rectangle core photonic crystal fiber acts like single-mode single-polarization fiber at the pump wavelength. Only the pulse component along with the slow axis could be confined in the rectangle core well and release Cerenkov radiation efficiently. The Output green Cerenkov radiation is also demonstrated to be linearly polarized. Experiments results agree well with the theoretical predictions. [ABSTRACT FROM AUTHOR]

A novel photonic digital-to-analog conversion (PDAC) scheme, which is based on optical intensity weighting and multiplexing/summing of different wavelengths, is proposed. The employment of wavelength multiplexing in the system, which conducts the function of modulated light intensity summation, greatly simplifies the system complexity and improves the conversion speed/accuracy limited by large-area photo-detectors and associated electronics. A 4-bit PDAC with a conversion speed of 10 GS/s demonstrates the feasibility of the proposed scheme. In addition, the performance degradation induced by the limited extinction ratios of the applied electro-optic modulators, the synchronization errors among different wavelength channels, and the bit resolutions of the built system is also discussed. [ABSTRACT FROM AUTHOR]

888 nm pumped acousto-optic (AO) Q-switched laser with high output power and high efficiency under dual Nd:YVO 4 crystals configuration is firstly demonstrated and rate equations for dual-crystal lasers are further ameliorated and investigated. In continuous wave (CW) operation, we experimentally achieve a maximum output power exceeding 50 W. The global optical efficiency reaches 49.5% and the slope efficiency attains 55.5% via using a 1.5 at.% crystal with a 0.5 at.% crystal. In Q-switch operation, by utilizing double 0.5 at.% crystals, the global optical efficiency rises from 25.6% to 45.6% and the pulse duration varies from 26.2 to 42.4 ns when pulse repetition frequency (PRF) increases from 10 to 100 kHz. The measured beam quality factors M 2 at 100 kHz are 1.012 and 1.041 with 52.8 W output power in the two orthogonal directions respectively. [ABSTRACT FROM AUTHOR]

A new approach to a dispersive Michelson interferometer (DMI) is introduced. Rings of Equal Chromatic Order (RECO) are formed by a DMI illuminated by a white light source and crossed with an auxiliary dispersion spectrograph. The theoretical foundations are developed and then applied to different glass plates (BAK1, BK7, N-LAF35 and SK4) of thicknesses (12.101, 12.473, 9.930 and 6.602 mm), respectively. The sample is introduced in one of the arms of the interferometer. The refraction and dispersion of the samples are deduced from a single RECO interferogram. The refractive index and its variation are measured across the spectral range: 0.500–0.650 µm with relative errors of 10 −3 and 1.6 × 10 −4 , respectively. A good agreement between our measurements and reference data is found. [ABSTRACT FROM AUTHOR]

Grating based X-ray differential phase contrast imaging has found a large variety of applications in the last decade. Different types of samples call for different imaging energies, and efforts have been made to establish the technique all over the spectrum used for conventional X-ray imaging. Here we present a two-grating interferometer working at 8.3 keV, implemented at the bending magnet source of the IMX beamline of the Brazilian Synchrotron Light Laboratory. The low design energy is made possible by gratings fabricated on polymer substrates, and makes the interferometer mainly suited to the investigation of light and thin samples. We investigate polymer microspheres filled with Fe 2 O 3 nanoparticles, and find that these particles give rise to a significant visibility reduction due to small angle scattering. [ABSTRACT FROM AUTHOR]

Orbital angular momentum (OAM), an emerging and fascinating degree of freedom, has highlighted an innovation in communication and optical manipulation field. The beams with different OAM state, which manifest as the phase front “twisting” of electromagnetic waves, are mutually orthogonal, which is exactly what a new freedom applied to practical communication eagers for. Herein, we proposed a novel millimeter-wave OAM modulation technique by electrically optical phase controlling. By modulating OAM and phase of optical-millimeter-wave synchronously, the multi-modulation: quadrature orbital angular momentum modulation (QOM) communication system at W band is structured and simulated, allowing a 50 Gbit/s signal transmitting with bit-error rates less than 10 −4 . Our work might suggest that OAM could be compounded to more complex multi-modulation signal, and revealed a new insight into OAM based high capacity wireless and radio-over-fiber communication. [ABSTRACT FROM AUTHOR]