Photonics, Volume 11, Issue 1 (January 2024) – 99 articles

In the modern era, the secure transmission and storage of information are among the utmost priorities. Optical security protocols have demonstrated significant advantages over digital counterparts, i.e., a high speed, a complex degree of freedom, physical parameters as keys (i.e., phase, wavelength, polarization, quantum properties of photons, multiplexing, etc.) and multi-dimension processing capabilities. This paper provides a comprehensive overview of optical cryptosystems developed over the years. We have also analyzed the trend in the growth of optical image encryption methods since their inception in 1995 based on the data collected from various literature libraries such as Google Scholar, IEEE Library and Science Direct Database. The security algorithms developed in the literature are focused on two major aspects, i.e., symmetric and asymmetric cryptosystems. A summary of state-of-the-art works is described based on these two aspects. Current challenges and future perspectives of the field are also discussed. Full article

Analogous to the Poincaré sphere, a hybrid order Poincaré sphere is used to represent the ellipse field singularities (C-points). We study the tight focusing properties of generic bright and dark hybrid order Poincaré sphere beams in the presence of primary coma. The role of the polarization singularity index and handedness of the polarization of the hybrid order Poincaré sphere beams on the focused structure has been discussed. Results have been presented for the total intensity, component intensities, and component phase distributions for left- and right-handed bright and dark star and lemon types singularities. The presence of primary coma distorted the focal plane intensity distributions for both positive and negative index generic C-points. Coma is known to disturb the circular symmetry of the focal plane intensity distribution. Similarly in tight focusing polarization is known to disturb the symmetry. Therefore, a beam with structured and inhomogeneous polarization distribution tightly focused under the influence of coma is a fit case to study. It is found that the presence of primary coma aberration in the focusing system produces a positional shift of the high-intensity peaks and a reduction of the intensity on one side of the center. As the strength of the primary coma increases, the focal plane intensity distributions shift more and more toward the right from the initial position. Unlike the scalar vortex case, in the case of hybrid order Poincaré sphere beams, the focal plane intensity distribution undergoes rotation, as the helicity of the hybrid order Poincaré sphere beams is inverted, in addition to shifting. All the component phase distributions are found to be embedded with phase vortices of charge $\pm 1$. Full article

This article describes a novel electrochemical on-chip biosensor that utilises the anti-PSA antibody (Ab) and silver nanoparticles (AgNPs) to enhance the sensing and detection capability of the prostate-specific antigen (PSA) in the blood. The AgNPs are prepared, characterised, and applied to a silicon photonic on-chip biosensing receptor platform designed to enhance the accurate detection of PSA. The AgNPs were synthesised by a chemical reduction method using silver nitrate (AgNO₃) as the precursor. Transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersion X-ray spectroscopy (EDS), small angle X-ray scattering (SAXS), X-ray diffraction (XRD), and light microscopy were among the methods used in the characterisation and analysis of the AgNPs. Each stage of the immunosensor fabrication was characterised using cyclic voltammetry. The proposed immunosensor was applied in the detection of PSA, a prostate cancer biomarker, with a high sensitivity and a limit of detection of 0.17 ng/mL over a linear concentration range of 2.5 to 11.0 ng/mL. The immunosensor displayed good stability and was selective in the presence of interfering species like immunoglobulin (Ig) in human serum, ascorbic acid (AA), and diclofenac (Dic). The detectivity and sensitivity are significantly higher than previous reports on similar or related technologies. Full article

In this paper, the laser pulse time compression technique, based on stimulated Brillouin scattering (SBS) and passive laser–induced breakdown (LIB) series technology, is investigated. By doping a SiC nanowire in a CCl₄ solution of an LIB breakdown medium, the LIB generation threshold is reduced, and the stability of the LIB compression output is improved. When OD is 0.2, the output pulse width is 254.4 ps, and the corresponding energy conversion efficiency and pulse compression rate are 34.2% and 50.2%, respectively. Our experiment proves the feasibility of this scheme. Full article

Microcrystal delivery instruments are pivotal to performing serial femtosecond crystallography experiments at the XFEL facilities. We present a novel sample delivery technique based on a micro-tubing reeling system (MRS). Despite the tiny size of the micro-tubing, the MRS device has the advantage of operating without real-time position adjustment of the tube to match with the XFEL pulses. Moreover, the applicable repetition rate is more flexible than the previously reported chip-based one-dimensional fixed target system. Full article

A question of physical importance is whether finite-energy spatiotemporally localized (i.e., pulsed) generalizations of monochromatic accelerating Airy beams are feasible. For luminal solutions, this question has been answered within the framework of paraxial geometry. The time-diffraction technique that has been motivated by the Lorentz invariance of the equation governing the narrow angular spectrum and narrowband temporal spectrum paraxial approximation has been used to derive finite-energy spatiotemporally confined subluminal, luminal, and superluminal Airy wave packets. The goal in this article is to provide novel exact finite-energy broadband spatio-temporally localized Airy solutions (a) to the scalar wave equation in free space; (b) in a dielectric medium moving at its phase velocity; and (c) in a lossless second-order temporally dispersive medium. Such solutions can be useful in practical applications involving broadband (few-cycle) wave packets. Full article

The prevalence of digital devices in modern society has raised concerns about the potential negative effects of blue-light emissions on eye health and biological rhythms. Research into blue light emissions from digital devices and their potential impact on eye health emphasizes the importance of understanding and quantifying the extent and scope of blue light emissions produced by commonly used screens (smartphones, tablets, and computers). The goal of this study was to implement a set of methodologies to analyze this emission. A comparative study specifically evaluated three popular Apple devices: the iPhone 12 mini^®, iPad Pro 12.9^®, and the MacBook Pro^®. The devices’ spectral power was measured using a spectroradiometer while displaying text and a game at different brightness levels. The laboratory measurements are compared to known solar irradiance, and all devices tested show blue wavelength peaks between 445 nm and 455 nm, with no expected immediate photobiological risk. We quantified the spectral emission from the three device categories and concluded that blue light levels should not significantly affect eye health. The measurements carried out indicated that the blue irradiance received by the human eye during one minute outdoors is greater than the blue light received by digital devices in approximately 24 h. This study also examines the effectiveness of blue-blocking lenses from well-known brands. The research highlights the importance of quantifying blue light emissions and understanding their potential impact on eye health, so appropriate measures can be developed to mitigate, if needed, adverse effects on ocular structures. A need to clarify the efficacy and usefulness of blue-blocking ophthalmic lenses still remains. Full article

High-quality silicon-based lasers are necessary to achieve full integration of photonic and electronic circuits. Monolithic integration of III–Vmicron lasers on silicon by means of the aspect ratio trapping (ART) method is a promising solution. To obtain sufficient optical feedback to excite the laser without introducing complex fabricating processes, we have designed a high-order surface grating on micron lasers which was epitaxially grown by the ART method and can be fabricated by common UV lithography. The performance of the grating was analyzed by the finite-difference time-domain (FDTD) method and eigenmode expansion (EME) solver. After simulation optimization, the etching depth was set to 0.6 μm to obtain proper reflection. The width of the slots and the slot spacing were selected to be 1.12 μm and 5.59 μm, respectively. Finally, we obtained results of 4% reflectance and 82% transmittance at a 1.55 μm wavelength at 24 periods. Full article

The nonlinear dynamics of nanolasers (NLs), an important component of optical sources, has received much attention. However, there is a lack of in-depth research into the high-quality chaotic output of NLs and their applications in chaotic secure communications. In this paper, we make the NLs generate broadband chaotic signals whose time-delay signatures (TDS) are completely hidden by a phase conjugate feedback structure. And in the two-channel communication scheme, we make the NLs achieve a combination of a low-latency high degree of synchronization and two-channel transmission technique, which enhances the security of message encryption and decryption. We also investigate the effects of system parameters, Purcell factor $F$, spontaneous emission coupling factor $\beta$, and bias current $I$ on the TDS, as well as the effects of parameter mismatch and injection parameters on chaos synchronization and message recovery. The results show that the phase conjugate feedback-based NLs can achieve the suppression of the TDS within a certain parameter range, and it can achieve high-quality synchronization and enhance the security of chaotic communication under appropriate injection conditions. Full article

In this study, we have successfully demonstrated a high-energy subpicosecond Yb:YAG laser system based on chirped-pulse regenerative amplification. Our experimental results demonstrate a pulse energy of 3 mJ with a pulse duration of 829.8 fs and a repetition rate of 1 kHz. Additionally, we conducted an extensive investigation into the system’s recompression capability under various modulation and seeding conditions. Our findings suggest that the system can achieve effective recompression over a broad range of parameters, with the ability to compensate for a considerable degree of chirp. Our study provides valuable insights into the fundamental physic of high-energy laser systems and the performance characteristics of chirped-pulse regenerative amplification. Full article

A novel Yb-doped fiber design for improved lasing near 976 nm based on spectral filtering of the amplified spontaneous emission near 1030 nm was realized and investigated. A very sharp short-pass filter was implemented by adding appropriately chosen high-index absorbing rods into the silica cladding. In this case, the resonant interaction of the core mode with the high-index rod mode could be controlled by fiber bending, which allows for the precise adjustment of the stop-band position. It was shown that the utilization of Sm-doped absorbing rods allows one to achieve very high absorption of emission at unwanted wavelengths, but it also adds background losses for the pump near 915 nm and for the signal at 976 nm. Despite this fact, the improvement of efficiency in the 976 nm fiber amplifier, after shifting the stop-band to 1000 nm, was clearly demonstrated. Based on theoretical calculations, it was shown that, after optimizing the fiber parameters, a further twofold improvement in efficiency was possible despite the excess losses at the pump and signal wavelengths. Full article

Power unevenness, mainly induced by stimulated Raman scattering, has been a major problem in multi-band transmission systems, especially in the upcoming field-deployed 400 Gbit/s widened C band plus L band system for backbone long-haul and ultra-long-haul scenarios. To reduce the impact of power unevenness, we propose an automatic power optimization (APO) algorithm to guarantee reliable transmission for all channels, especially the channels at short wavelengths. The simulation results show that the power unevenness of output power after 5-span transmission in the C band is up to 11 dB before APO, while after APO is applied, it is greatly improved to less than 1.6 dB. To further investigate the performance of the APO scheme, we conduct a real-time 44 Tbit/s C+L transmission system over 1900 km G.654.E fiber utilizing 400 Gbit/s transponders. The experimental results show that the power unevenness has been effectively compensated from 12 dB to 4 dB in the entire 11 THz range, making the received optical signal-to-noise ratio relatively flat (3.4 dB). Moreover, the capacity and distance product of this system is 83.6 Pbit/s·km (44 Tbit/s × 1900 km), and to the best of our knowledge, this is a record capacity and distance product in the real-time single-mode fiber transmission system. Full article

The power conversion efficiency (PCE) of single-junction perovskite solar cells (PSCs) has reached 26.1% in small-scale devices. However, defects at the bulk, surface, grain boundaries, and interfaces act as non-radiative recombination centers for photogenerated electron-hole pairs, limiting the open-circuit voltage and PCE below the Shockley–Queisser limit. These defect states also induce ion migration towards interfaces and contribute to intrinsic instability in PSCs, reducing the quasi-Fermi level splitting and causing anomalous hysteresis in the device. The influence of defects becomes more prominent in large-area devices, demonstrating much lower PCE than the lab-scale devices. Therefore, commercializing PSCs faces a big challenge in terms of rapid decline in working performance due to these intrinsic structural defects. This paper provides a comprehensive review of recent advances in understanding the nature and the classification of defects, their impact on voltage losses, device parameters, intrinsic stability, and defect quantification and characterization techniques. Novel defect passivation techniques such as compositional engineering, additive engineering, post-treatments, dimensionality engineering, and interlayer engineering are also reviewed, along with the improvements in PCE and stability based on these techniques for both small-area devices and large-area roll-to-roll coated devices. Full article

In order to address the issue of large-aperture optical windows operating in wind tunnel environments with dynamic responses, the damping ratio between the vibration isolation device and the mass of the system was calculated by the passive vibration isolation principle. Two isolation models using circular rubber pads and rectangular rubber pads were proposed, and it was proven that the stiffness value of the circular rubber pad is superior to that of the rectangular rubber pad. A three-dimensional model of the optical window was established using finite element analysis software to simulate the working vibration environment of the optical window. Modal analysis and harmonic response analysis were carried out on the optical system with the isolation device installed, and the nodal data of the optical glass surface changes in the optical window were input into the Zemax 19.4 optical design software in the form of Zernike coefficients to calculate imaging quality evaluation indicators. Through finite element structural analysis of the optical window and evaluation of optical performance indicators, it was demonstrated that under the background of the wind tunnel working environment, the isolation performance of the circular rubber pad in the isolation device of the optical window is superior to that of the rectangular rubber pad. This study can provide a design basis for the isolation analysis methods and isolation measures of optical windows in wind tunnel working environments. These research results have implications for the development of large-aperture optical windows in high-speed wind tunnel applications. Full article

Extensive research has been devoted to spiral phase contrast imaging because of its notable capacity to enhance the edges of both phase and amplitude objects. We demonstrate a setup using ferroelectric liquid crystal (FLC) fork grating (FG) to enable switchable spiral phase contrast imaging within sub-milli-second responses. This system enables the electrical toggling between images featuring edge enhancement and those without it. The specially designed FLC FG generates a vortex beam while in a diffractive state and transmits a Gaussian beam when in a transmissive state. Using a two-step photo-alignment method, the produced FLC FG exhibits exceptional efficiency at approximately 35% and impressively rapid switching at around 307 μs. By introducing this method, we expand the potential applications of spiral phase contrast imaging, particularly in fields such as bio-sensing and photonics. Full article

We report on a 1064 nm master oscillator power amplifier (MOPA) system based on pulse-modulated laser diode seed sources combined with fiber preamplifiers and a Yb-doped tapered double-clad fiber (T-DCF) amplifier used as an all-fiber master oscillator and a two-stage side-pumped solid-state power amplifier. The combination of two master oscillators and a single power amplifier allowed us to obtain pulses with a duration ranging from 10 ns to 10 μs with energy up to 137 mJ at 100 Hz. For the first time, we demonstrate a widely tunable pulse duration and a solid-state MOPA system with over 100 mJ energy based on a T-DCF fiber seed laser. Full article

This article presents an analysis of an electro-optical up-converter relying on a semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI). The pulsed control signal is generated by an optical pulse clock (OPC) with a repetition rate of $f_s=$ 19.5 GHz. The intermediate frequency (IF) signal, which carries the modulation format known as quadratic phase shift keying (QPSK) at a frequency $f_{IF}$, is shifted at the output of the SOA-MZI to high outlet mixing frequencies ${nf}_s\pm f_{IF}$, where $n$ represents the harmonic order of the OPC. To examine the characteristics of the sampled QPSK signals, we employ the Virtual Photonics Inc. (VPI) emulator and evaluate them using significate metrics like error vector magnitudes (EVMs), conversion gains, and bit error rates (BERs). The up-mixing process is mainly achieved through the cross-phase modulation (XPM) effect in the SOA-MZI, which operates within a 195.5 GHz ultrahigh frequency (UHF). The electro-optical SOA-MZI up-converter demonstrates consistent uplifting conversion gains across the scope of the output mixing frequencies. The simulated conversion gain deteriorates from 38 dB at 20 GHz to 13 dB at 195.5 GHz. The operational efficiency of the electro-optical SOA-MZI design, employing the standard modulation approach, is also evaluated by measuring the EVM values. The EVM attains a 24% performance level at a data rate of 5 Gbit/s in conjunction with the UHF of 195.5 GHz. To corroborate our results, we compare them with real-world experiments conducted with the UHF of 59 GHz. The maximum frequency range of 1 THz is attained by increasing the OPC repetition rate. Ultimately, through elevating the control frequency to 100 GHz, the generation of terahertz replicas of the 4096-QAM (quadrature amplitude modulation) compound signal becomes achievable at heightened UHF, extending 1 THz, while maintaining a data transmission rate of 120 Gbit/s and upholding exceptional performance characteristics. Full article

Paint removal is an essential process in the industrial field. Laser technology provides an effective method of paint removal to replace traditional mechanical and chemical methods. This paper establishes a continuous wave (CW) laser thermal paint removal model based on heat conduction theory and Arrhenius’ law. The paint stripping process of epoxy paint film on the surface of 6061 aluminum alloy via CW laser was studied through simulation and experiment. We found that the carbonization of the paint film during the CW laser paint removal process will inhibit the laser paint removal process. Therefore, the paint removal efficiency of the CW laser is limited. The depth of CW laser paint removal increases linearly with the CW laser power density. However, during the CW laser paint removal process, due to the pyrolysis of the paint film and the reflection of the laser by the substrate, the surface temperature of the material first increases and then decreases. In addition, after laser paint removal, the surface roughness of the material after paint removal is reduced due to the melting of the base material. The model established in this article can provide a theoretical reference for studying the CW laser paint removal process. Full article

Antennas are important components in optical phased arrays. However, their far-field performance deteriorates when random phase noise is introduced because of fabricating errors. For the first time, we use a finite-difference time-domain solution to quantitatively analyze the far-field characteristics of Si and Si₃N₄ antennas considering process errors. Under rough surface conditions based on a fishbone structure, we find that the quality of the main lobe of the Si antenna deteriorates badly, with −0.87 dB and −0.51 dB decreases in the sidelobe level and 5.78% and 3.74% deteriorations in the main peak power in the φ (phase-controlled) and θ (wavelength-controlled) directions, respectively. However, the Si₃N₄ antenna is only slightly impacted, with mere 0.39% and 0.71% deteriorations in the main peak power in the φ and θ directions, respectively, which is statistically about 1/15 of the Si antenna in the φ direction and 1/5 in the θ direction. The decreases in the sidelobe level are also slight, at about −0.08 dB and −0.01 dB, respectively. Furthermore, the advantages of the Si₃N₄ antenna become more remarkable with the introduction of random errors into the waveguide width and thickness. This work is of great significance for the design and optimization of OPA chips. Full article

A multi-objective genetic algorithm approach is formulated to optimize the design of silicon-photonics complex circuits with contradicting performance metrics and no closed-form expression for the circuit performance. A case study is the interleaver/deinterleaver circuit which mixes/separates optical signals into/from different physical channels while preserving the wavelength-division-multiplexing specifications. These specifications are given as channel spacing of 50 GHz, channel 3-dB bandwidth of at least 20 GHz, channel free spectral range of 100 GHz, crosstalk of −23 dB or less, and signal dispersion less than 30 ps/nm. The essence of the proposed approach lies in the formulation of the fitness functions and the selection criteria to optimize the values of the three coupling coefficients, which govern the circuit performance, in order to accommodate the contradicting performance metrics of the circuit. The proposed approach achieves the optimal design in an incomparably short period of time when contrasted with the previous tedious design method based on employing Z-transform and visual inspection of the transmission poles and zeros. Full article

Breath is one of the most important physiological features of human life. In particular, it is significant to monitor the physical characteristics of breath, such as breath frequency and tidal volume. Breath sensors play an important role in the field of human health monitoring. However, an electronic breath sensor is not stable or even safe when the patient is in a Magnetic Resonance Imaging (MRI) system or during any oncology treatment that requires radiation and other high electric/magnetic fields. Fiber-optic-based sensors have attracted a considerable amount of attention from researchers since they are immune to electromagnetic interference. Here, we propose and demonstrate a fiber-optic-based relative-humidity (RH)-sensing strategy by depositing Ti₃C₂T_x nanosheets onto an etched single-mode fiber (ESMF). The humidity sensor function is realized by modulating the transmitted light in the ESMF using the excellent hydrophilic properties of Ti₃C₂T_x. Experiments show that the coated Ti₃C₂T_x nanosheets can effectively modulate the transmitted light in the ESMF in the relative humidity range of 30~80% RH. The sensor’s fast response time of 0.176 s and recovery time of 0.521 s allow it to be suitable for real-time human breath monitoring. The effective recognition of different breath rhythms, including fast, normal, deep, and strong breathing patterns, has been realized. This work demonstrates an all-optical Ti₃C₂T_x-based sensing platform that combines Ti₃C₂T_x with an optical fiber for humidity sensing for the first time, which has great promise for breath monitoring and presents novel options for gas-monitoring applications in the biomedical and chemical fields. Full article

In this study, we introduce a novel design of a remote edge-lit backlight structure featuring blue laser diodes (LDs). These LDs were integrated into a remote yellow phosphor layer on a light guide plate (LGP). Blue light emitted by the LDs passes through the LGP and spreads to the remote phosphor layer, generating white light output. Owing to the incorporation of a scattering layer between sequential LGPs, the remote edge-lit backlight structure facilitates the expansion of the output surface of the LGP by combining multiple individual LGPs. Two- and three-LGP remote edge-lit backlight structures demonstrated acceptable white illuminance uniformity. The proposed architecture serves as a viable solution for achieving uniform illumination in planar lighting systems using blue LDs; thus, this structure is particularly suitable for linear lighting or slender backlighting instead of display stand applications. Full article

The crosstalk of the small detection photosensitive elements test has always been the difficulty of research on infrared focal plane arrays (IRFPAs). With the decrease in the element size in the IRFPAs, the crosstalk of small detection photosensitive elements cannot be tested by the existing small spot method. In this paper, a novel eye hole method to realize the crosstalk of the small element IRFPAs test is proposed. The novel eye hole method is to make eye holes on the substrate. The transmittance of the eye holes in the substrate is 100%, while the transmittance of the other component in the substrate is 0. The substrate with the eye holes is fixed in front of small element IRFPAs to achieve the crosstalk of the small elements test. The filters selected by 9 elements and 25 elements as the eye hole unit are designed and prepared. The experimental results show that 25 elements are selected as the eye hole unit for the IRFPAs with the element size of 25 μm × 25 μm. The eye holes are formed tightly and repeatedly arranged. The crosstalk of the InSb IRFPAs with the element size of 25 μm × 25 μm by the novel eye hole method is 3.86%. The results are of great reference significance for improving the test level of small element IRFPA. Full article

This paper highlights the application of decomposition methods in Mueller polarimetry for the discrimination of three groups of barley leaf samples from Hordeum vulgare: Chlorina mutant, Chlorina etiolated mutant and Cesaer varieties in the visible wavelength at λ = 632.8 nm. To obtain the anisotropic and depolarizing properties of the samples under study, the additive and multiplicative decompositions of experimental Mueller matrices were used. We show how a rich set of anisotropy and depolarization parameters obtained from decompositions can be used as effective observables for the discrimination between different varieties of the same plant species. Full article

Laser-spot-location detection technology based on photodetectors is widely used in the aerospace, medical, military and communication fields. However, most of the current research focuses on continuous laser detection in the visible and near-infrared bands, and the real-time high-precision position detection of a long-wave infrared pulsed laser is lacking. In this paper, a spot-position detection system based on a four-quadrant detector is designed for a 10.6 μm CO₂-driven laser in extreme ultraviolet light source, and a second-order extended error compensation algorithm based on a Gaussian-spot model is proposed. Finally, the algorithm is verified and analyzed experimentally by a spot-position detection system under both focusing and defocusing conditions. The experimental results show that the root-mean-square error, maximum absolute error and average absolute error of the second-order error compensation algorithm are significantly reduced compared with the traditional algorithm, and the detection accuracy of the spot-position is better than 9 μm. The above results show that this spot-position detection system has obvious advantages and high accuracy, which can realize the high-precision real-time detection of a laser’s spot position to obtain accurate spot position information, provide feedback adjustments for subsequent beam pointing control, and provide a theoretical basis for the beam pointing stability of the extreme ultraviolet light source system. Full article

Testing accuracy is an essential factor in determining the manufacturing accuracy of aspheric mirrors. Because of the complexity of the null compensation test, the coherent stray lights generated by multiple reflections and transmissions between optical elements and the crosstalk fringes generated by the multi-beam interference of the reference light, test light, and stray lights are superimposed on the interference fringes, resulting in reduced testing accuracy. Focusing on this problem, a simulation analysis method for crosstalk fringes based on ray-tracing and multi-beam interference in interference testing is proposed. The coordinates, amplitudes, and phases of the test light and stray lights on the transmission sphere are traced, and the crosstalk fringes and interference testing fringes and their positions, sizes, and intensity information are simulated via multi-beam interference. The influence of crosstalk fringes on interference fringes is determined. An experimental optical path is built to verify the correctness of the crosstalk fringe simulation method. Full article

The paper proposes an equivalent optical scheme of an in-line digital holographic system for particle recording and a mathematical model that establishes a one-to-one correspondence between the dimensional and spatial parameters of a digital holographic image of a particle and the imaged particle itself. The values of the model coefficients used to determine the real size and longitudinal coordinate of a particle according to its holographic image are found by calibration. The model was tested in field and laboratory conditions to calibrate a submersible digital holographic camera designed to study plankton in its habitat. It was shown that four calibration measurements are sufficient enough to determine the model coefficients, and the developed design of the submersible digital holographic camera makes it possible to perform these measurements during the recording of each hologram. In addition, this neither requires data on the refractive index of the medium with particles nor on the parameters of the optical elements of the scheme. The paper presents the results of marine experiments in the Kara Sea and the Laptev Sea, as well as in fresh water in laboratory conditions and in Lake Baikal. The error in measuring the particle size in seawater without the use of the model is 53.8%, while the error in determining their longitudinal coordinates is 79.3%. In fresh water, the same errors were 59% and 54.5%, respectively. The error in determining the position of a particle with the use of the designed mathematical model does not exceed 1.5%, and the error in determining the size is 4.8%. The model is sensitive to changes in the optical properties of the medium, so it is necessary to perform calibration in each water area, and one calibration is quite sufficient within the same water area. At the same time, the developed design of the submersible holographic camera allows, if necessary, calibration at each holographing of the medium volume with particles. Full article

Silicon carbide (Sic) materials find wide-ranging applications in advanced optical systems within the aerospace, astronomical observation, and high-intensity laser fields. The silicon-modified Sic used in this study was created by depositing an amorphous silicon film on the surface of a Sic substrate using electron beam evaporation. Such hard and brittle materials often yield smooth surfaces when subjected to plastic removal. To address the issue of the removal depth of the surface plastic domain for silicon-modified Sic, we propose a method to calculate the indentation depth based on the critical load for the transition from plastic to brittle removal. We conducted a series of nanoindentation and nanoscratching experiments. The critical depth formula was validated through mechanical parameters such as hardness, elastic modulus, and fracture toughness, and the theoretical critical depth of the modified silicon layer was calculated to be 2.71 μm. The research results indicate that the critical load for obtaining the plastic-to-brittle transition point during the nanoindentation experiment is 886 mN, at which point the depth of plastic removal is 2.95 μm, closely matching the theoretical value. The measurements taken with an atomic force microscope near the critical load reveal a scratch depth of 3.12 μm, with a relative error of less than 5% when compared to the calculated value. This study establishes a solid foundation for achieving high-quality surface processing. Full article

This paper presents a phase retrieval algorithm that incorporates sparsity priors into total variation and framelet regularization. The proposed algorithm exploits the sparsity priors in both the gradient domain and the spatial distribution domain to impose desirable characteristics on the reconstructed image. We utilize structured illuminated patterns in holography, consisting of three light fields. The theoretical and numerical analyses demonstrate that when the illumination pattern parameters are non-integers, the three diffracted data sets are sufficient for image restoration. The proposed model is solved using the alternating direction multiplier method. The numerical experiments confirm the theoretical findings of the lighting mode settings, and the algorithm effectively recovers the object from Gaussian and salt–pepper noise. Full article

A concise and adaptive sidelobe suppression algorithm based on a least mean square (LMS) filter is proposed for pulse-compressed signals of a phase-sensitive optical time-domain reflectometer (Φ-OTDR) system. The algorithm is suitable for the denoising filtering process of phase coding OTDR (PC-OTDR) systems and mitigates the sidelobe effect due to matched filtering. In a simulation experiment, Rayleigh backscattering (RBS) signals including phase-coded pulse signals are generated and decoded to verify that the LMS algorithm can eliminate the sidelobes more effectively than the windowing method and the recursive least squares (RLS) method. Then, the PC-OTDR system is set up and combined with the LMS algorithm for positioning experiments. The results show that the peak side lobe ratio (PSLR) of the signals can reach −15.86 dB, which is 4.26 dB lower than the raw pulse compressed signal. Full article