Nowadays, communication has grown into a key area with a rapidly growing user community. The existing broadband users are overcrowded, and its faster speed has now become an essential parameter to meet the consumer’s expectations in the growing technology. As a result of our growth in computer technologies, high-speed processors are necessary, which provide simultaneous data computing with lower costs and a performance of more than 10,000 times quicker than electrical computers. Optics has become a more feasible alternative to electronics because of its greater speed. In this study, various methods of photonic crystals (PhCs) have been thoroughly examined, with essential properties and their benefits explained over previously identified methods (semiconductor optical amplifier and nonlinear waveguides) utilized to construct all-optical logic circuits. Particularly, evaluated a number of articles that covered topics including self-collimation effects, PhC waveguide intersection, and multi-mode interference with nonlinear effects. The merits and demerits of each technology are analyzed. Finally, concluded the major difficulties and the potential usage of every method. PhCs are used in logic circuits and devices for high data transmission. The performances of different types of logic gates based on PhC are studied.

The three important factors that affect the output power and temperature of fiber lasers (FLs) were investigated in a large mode area step-index FL under a high-power operation. Photodarkening (PD), quantum defect (QD), and background loss cause increases in the FLs temperature and reductions in beam quality, stability, and power. PD and background loss coefficients have different values for the signal (laser) or pump wavelength. But QD depends on the difference between the pump and the laser wavelength. By considering the PD attenuation in the rate equations, the effects of forward, backward, and bidirectional pump schemes on heat distribution agents were investigated. FL characters, including core and clad sizes, both side reflectors, and FL lengths in each heat generation agent, were studied in detail.

Computer-generated holography (CGH) is an ideal three-dimensional (3D) display technology, and head-mounted displays (HMDs) using CGH are expected to become the next-generation display devices without eye strain, which is called holographic HMDs (holo-HMDs). However, the CGH computational load is too much for a holo-HMD, which has limited processing power. We have devised a method that calculates the cylindrical object light on a sender, broadcasts the object light data to multiple holo-HMDs, and generates holograms matched to the planar display device on the holo-HMD. The cylindrical object light calculations, which take up most of the computational load, are performed on a high-performance computer with sufficient computational power. The cylindrical object light is transformed into an object light on the plane in accordance with the motion of the holo-HMD. The phase difference information between the complex amplitude distribution of the cylindrical object light and the object light on the plane corresponding to a free viewpoint position must be corrected. Using this method, objects placed near the center of the cylinder can be observed from a wide area, making it possible to support 3D image observation with multiple holo-HMDs. Experiments using an actual optical system demonstrated that planar transform was performed and that the computational load on a holo-HMD side was very small.

Random, time-varying blur due to atmospheric turbulence is known to significantly limit image quality. In division-of-time polarimeters, turbulence also randomly distorts the images that are used to infer the polarization content of the scene, leading to substantial Stokes image estimation errors. This research proposes a method to jointly estimate the full polarization properties of a scene along with the point spread functions (PSFs) for each imaging channel in the presence of isoplanatic turbulence. In particular, this research significantly expands on an existing algorithm, to include circular polarization in the framework of a generalized expectation maximization approach. The effectiveness of the approach is demonstrated on laboratory data using a surrogate phase screen placed near the entrance pupil of an imaging system.

Long-range target identification is well studied in the visible (Vis) and near-infrared (NIR) bands and more recently in the shortwave infrared (SWIR). The longer wavelength of SWIR (1 to 1.7 μm) improves target detection for both long ranges and under challenging atmospheric conditions because it is less limited by scattering and absorption in the atmosphere. For these reasons, SWIR sensors are proliferating on military platforms. The extended shortwave infrared (eSWIR) band spanning from 2 to 2.5 μm is not typically limited by diffraction, and as a result, the band benefits target acquisition both at long ranges and for degraded visual environments (DVEs). Theoretical and experimental data compare eSWIR with Vis, NIR, and SWIR for atmospheric transmission, reflectivity, illumination, and sensor resolution and sensitivity. The experimental setup includes two testbeds, each with four cameras. The first is a wide field of view (FOV) testbed matching FOV at 20 deg for each camera. The second is a narrow FOV telescope testbed to match instantaneous FOV for consistent resolution across all four bands at long ranges. Both the theory and experiment demonstrate advantages of using eSWIR for long-range target identification under DVEs.

Microwave chips dependent devices constitute the cornerstone of many classical and emerging quantum technologies. To meet the demand for high-resolution, lossless, and fast wide-field imaging of microwave devices, we propose a wide-field microwave imaging method based on diamond nitrogen-vacancy center ensembles by combining continuous wave optically detected magnetic resonance technology with optical wide-field imaging technology. First, the optimal selection of laser parameters is achieved by measuring different laser powers. Then the accuracy of the wide-field microwave imaging technique is demonstrated by measuring the near-field imaging of the antenna surface at different microwave input powers and different microwave input frequencies. The spatial resolution of the imaging system is 5 μm over a field of view of 2400 μm × 1350 μm, and the optimal microwave precision measurement sensitivity is 5.6 μT / Hz^1/2. The above results are expected to provide a practical reference for applications such as fault diagnosis of highly integrated microwave circuits, antenna radiation profiling, and electro magnetic compatibility testing of integrated microwave circuits.

Structured light profilometry (SLP) is now widely utilized in noncontact three-dimensional (3D) reconstruction due to its convenience in dynamic measurements. Compared with classic fringe projection profilometries, multiple deep neural networks are proposed to demodulate or unwrap the fringe phase, and these networks utilize convolution layers to extract local features while omitting global characteristics. In this paper, we propose SwinConvUNet, a deep neural network for single-shot SLP that can extract local and global features simultaneously. In the network structure design, convolution layers are applied in shallow layers to extract local features, whereas transformer layers extract global features in deep layers, and an improved loss function by combining gradient-based structural similarity is employed to improve reconstruction details. The experimental results demonstrate that SwinConvUNet is more effective than the U-net model at decreasing learnable parameters while maintaining 3D reconstruction accuracy.

We propose a new solution for sensing a terahertz (THz) wavefront based on a THz reference-less shear interferometer. The key component of the experimental configuration of the proposed interferometer is a THz Ronchi phase grating (RPG). The RPG is custom designed and fabricated for a 0.28 THz source using mechanical milling on a block of high-density polyethylene with a computer numerical control machine. It acts as a shearing element that generates two diffraction orders, thereby, creating two laterally shifted copies of the investigated wavefront in the sensor plane where a THz camera is placed. The direction of the shear can be varied by rotating the grating. Since the grating is a phase grating, the diffraction efficiency is very high. The approach is verified experimentally by demonstrating interferograms of a spherical wave and wavefront reconstruction from five different shears using a gradient-based iterative process.

We proposed an innovative stereo camera pair calibration method suitable for traffic surveillance applications. In the method, we first split the sought parameters into two groups. The first group contains parameters that can be computed prior to the device being installed in the desired location, and we determine their values using already established methods. The second group contains parameters that need to be evaluated after the device is installed on-site, and we utilize calibration vehicles for their evaluation. We first localize the calibration vehicles by detecting and tracking their license plates in a series of stereo images; afterward, we exploit the known information about their speed and acceleration to compute the distances that they traveled between two frames; finally, we determine the internal and external stereo camera pair parameters by minimizing the difference between the computed and estimated distances while preserving the epipolar geometry. We evaluated the presented method on a task of measuring the distances that vehicles traveled between two consecutive frames. For this evaluation, we recorded a dataset containing almost 700 vehicles with trajectories that were recorded using prototype hardware and ground truth distance measurements that were obtained from a pair of single-beam LIDARs. The evaluation results were compared with the current state-of-the-art methods for long-distance stereo camera pair calibration and used in the application of the proposed method on the vehicle speed measurement task.

To study the spatial spectrum characteristics of scattered light from a laser illuminated bubble curtain in the wake, the Monte Carlo model based on the single-bubble Mie scattering theory was used. The propagation process of each photon in the wake bubble group underwater was tracked, and the coordinates of the photon position reaching the receiving plane were recorded. The effects of propagation distance, bubble size, and bubble number density on the full-width at half-maximum (FWHM) of spatial spectrum of forward scattered light from wake bubbles were investigated. The results show that with the increase of the transmission distance, the bubble size and bubble number density increase, and the FWHM of the spatial spectrum decreases. This feature of spatial spectrum can be used as one of the criteria for ship wake identification.

The normal tracing angle measurement system based on Risley prisms can eliminate the influence of aberrations other than the dispersion of Risley prisms on the angle measurement accuracy. Although the traditional dispersion optimization method based on the extreme point can make the beam directions of different wavelengths more consistent after passing through the Risley prisms, the light intensity distribution that deviates from the extreme point wavelength causes the spot centroid to deviate from the target position, thus introducing the angle measurement error. In this paper, we propose a highly symmetry-glued achromatic Risley prisms optimization method for the needs of a normal tracing angle measurement system. Our method not only realizes the beam direction as closely as possible after the deflection of the Risley prisms but also compensates for the centroid error caused by the beam deviating from the central wavelength. ZEMAX simulation shows that, in the normal tracing angle measurement system, within the angle measurement range of ±700 ^″ and the light source wavelength range of 600 to 700 nm, the angle measurement error introduced by the dispersion of the optimized Risley prisms is not >0.01 ^″ .

The fiber bundle (FB) optical system is widely used in many fields, such as medical imaging and military reconnaissance, owing to its advantages of high design freedom, small volume, and light weight. The traditional theory for the optical transfer function is not suitable for such a discrete sampling optical system. Researchers have developed numerical calculation methods to analyze the imaging quality of the discrete sampling optical system, in which the geometric model needs to be established and the coupling region needs to be determined. We have developed a simple and computationally efficient imaging theory that is suitable for various combinations of FB and CCD detectors. The coupling modulation transfer function (coupling-MTF) of discrete sampling optical systems of square-arrangement fiber bundles (SFBs) and hexagonal-arrangement fiber bundles (HFBs) are analyzed. Simulation results demonstrate that although SFB has a higher coupling-MTF than HFB, the latter is more convenient in coupling alignment operation. Our results have proven the effectiveness and universality of the proposed theory, and it can be used to guide the system design.

The relative pose between the projector and screen in a phase-measuring deflectometry (PMD) setup can result in perspective distortion and intensity errors in the projected fringe patterns. These problems degrade the sinusoidal characteristics of the fringe patterns, thus increasing phase, slope, and height errors in the PMD measurement. To overcome these issues, inverse perspective distortion and intensity modification algorithms were developed and applied to computer-generated fringe patterns before projection. The inverse perspective distortion matrices were obtained using a single image of the projected grid distortion target. The pixel intensities in the generated fringe patterns were modified using the relationship between the generated and captured pixel intensity values in grayscale images of uniform intensity. Experiments were conducted to measure the surface topographies of spherical concave and convex mirrors using a monoscopic PMD setup. Based on the experimental results, the root-mean-squared (RMS) intensity and phase errors in the projected sinusoidal fringe patterns were reduced by about 90% after using the modified fringe patterns compared to the original fringe patterns. When comparing the measured and the theoretical heightmaps, the results in PMD measurement showed an 8% and a 14% reduction of the RMS height errors in concave and convex heightmaps, respectively. The effectiveness of the algorithms in improving the accuracy of projector-based PMD measurement was demonstrated successfully.

The digital micromirror device (DMD) is an array of tilting micromirrors, capable of high frame rates that are made possible by rapid changes of angular state. The rapid angular change of the mirrors is used to sweep an optical signal across a camera sensor, resulting in a version of a streak camera, capable of temporal dispersion of an optical signal. Using a single pixel or single line of pixels can produce a continuous temporal track, whereas a two-dimensional array of mirrors scans an intensity envelope across discrete diffraction orders. Temporal resolutions of 10nS have been achieved and used to measure laser pulse widths. Combining with a diffraction grating oriented orthogonally to the temporal dispersion enables temporal and spectral dispersion to be obtained simultaneously.

Structured light illumination (SLI) systems can measure a target’s two-dimensional height profile. High-quality imaging in SLI systems is typically dependent upon well-focused optical systems that can be difficult to achieve due to the nonlinear nature of defocus. We present the quad target method (QTM), a simple and fast alignment technique that linearizes defocus for SLI projectors. This linear response provides a clear zero crossing along the optical axis to minimize any focus ambiguity and maximize projector focus quality. QTM creates the linearization by sampling the field at two locations along the optical axis using a quad target, which is a diffuse target with two different heights in opposing quadrants. To maximize feedback speed, QTM can estimate the current focus position using only a single image by measuring the contrast of projected sinusoidal fringes on the quad target. QTM was tested using a commercial SLI system and compared with a published phase shifting reconstruction technique. The nonlinear defocus behavior was efficiently linearized as evidenced by focus estimation accuracies over a broad range of QTM variables.

We theoretically discuss the group delays induced by the transverse-magnetic polarized light penetrating a Weyl semimetal (WSM) film. It is shown that the transmitted group delay τ_ps emerges because of the nonzero off-diagonal components of the dielectric constant tensor. In particular, the transmitted group delays τ_pp and τ_ps are enlarged significantly at the epsilon-near-zero (ENZ) frequency, where steep phase changes occur due to the sharp changes of the transmission coefficients | t_pp | and | t_ps | . More importantly, the tunable ENZ effect can be effectively obtained with Fermi energy, so the giant enhanced group delays at various frequencies can be readily realized. The enhanced group delays also show the adjustability of WSM thickness, incident angle, and Weyl node separation. Our findings supply easy and available methods to realize the adjustable enhanced group delays with a WSM.

Graphene nanoribbons (GNRs) and graphene hybrid photodetectors were demonstrated in the middle- and long-wavelength infrared (MWIR and LWIR, respectively) regions. Graphene transistors were prepared using Si substrates with an SiO₂ layer and source and drain electrodes. Single-layer graphene fabricated by chemical vapor deposition was transferred onto the substrates to form a channel; the GNR was formed on this channel by solution dispersion. The formation of graphene and the GNR was confirmed by position mapping of the Raman spectra. The photoresponse was measured in the MWIR and LWIR regions, and was found to be drastically enhanced for devices with the GNR when compared with those without it. Although the devices without the GNR could not respond at temperatures higher than 15 K, those with the GNR could be operated at temperatures up to 150 K. This was attributed to photogating by the GNR layers that absorbed the MWIR and LWIR radiation, leading to a significant temperature change. These results can potentially contribute toward developing high-performance and broadband IR graphene-based photodetectors.

Wavefront aberration is an essential factor that significantly affects the image quality of an optical system. We proposed a comprehensive method to determine the wavefront aberration of a deformed optical component caused by clamping forces. First, the displacement of the elements on the optical component, induced by external forces, is calculated using ANSYS software. Then, the deformation surface is fitted with an aspherical surface to obtain Zernike coefficients. Finally, the wavefront aberration is obtained from Zemax using the Zernike coefficients and the parameters of the optical component. An experimental study on a spherical mirror is carried out to verify the accuracy of this method. A Zygo interferometer is used to measure the actual wavefront aberration of the deformed mirror. The result indicates a good agreement between the theoretical calculation and the experimental data, with a variation of <10 % for various applied forces. Our finding provides a meaningful and reliable method for designing and selecting reasonable mounting structures to ensure the image quality of an optical system.

In the field of the active wavefront correction for off-axis telescopes, the sensitivity matrix and damped least squares method are widely employed to calculate the misalignment. Improper selection of the damping coefficient will lead to bad wavefront correction results. Moreover, the calculated misalignment is referenced on the optical coordinate system, which cannot be directly applied as the control quantity. The article has two innovative points to solve these problems. First, an adaptive damping least squares method is proposed. The method considers the mirror surface error, uses Python + Zemax cosimulation to perform closed-loop reverse verification, and selects the optimal damping coefficient. Simulation is carried out for verification. Second, the article deduces the mathematical relationship between the calculated misalignment and the mechanism control quantity. Based on the above research, the wavefront active correction experiment has been completed. The optical component is actively adjusted with the wavefront quickly converging to RMS = 0 . 055λ @ 632 . 8 nm. The results verify the correctness of the proposed method.

We examine the transmission characteristics of linear Gaussian array beams (LGABs) propagating through seawater to air considering oceanic and atmospheric turbulences. We derive the expressions of the mean-squared beam width and Rayleigh range of LGABs for the case of both coherent and incoherent combinations using stochastic wave theory and the extended Huygens–Fresnel principle. In addition, the properties of mean-squared beam width versus propagation distance are studied. Furthermore, the characteristics of the Rayleigh range versus the ocean turbulence parameters and beam number as well as the interval distance are investigated. In the seawater–air interface, the Rayleigh range of LGABs is up to three times higher than that of the underwater circumstance. Moreover, the Rayleigh range increases linearly with the increase of interval distance in a turbulent ocean and turbulent atmosphere. It can be concluded that the Rayleigh range is more affected by the rate of dissipation of turbulent kinetic energy and the rate of dissipation of mean-square temperature than by the parameter related to temperature and salinity.

The longitudinal mode distribution in the self-mode-locked (SML) laser with flexible reflectivity and a tilted mirror is investigated. First, the longitudinal mode characteristics of the SML laser are analyzed theoretically. Then by employing an intracavity etalon, the output mirror with different parameters is used for longitudinal mode manipulation in experimental research. By varying the reflectivity and tilting the output mirror, the longitudinal mode grouping and spectral shifting are observed. The experimental results show that, when the output mirror reflectivity decreases from 95% to 60%, the transmission peak linewidth of the intracavity etalon becomes narrower, and the number of the longitudinal mode selected by each transmission peak decreases from a maximum of 7 to a minimum of 1. When output mirror is tilted by +0.03 deg and −0.03 deg, the longitudinal mode wavelengths redshift and blueshift by 0.02 nm. The experimental results are in good agreement with the theory.

We propose an ensemble deep transfer learning (EDTL) method, which is a more refined multilayer feature extraction achieved by aggregating the convolutional layers of pretrained convolutional neural network models for joint optical modulation format recognition (MFR) and optical performance monitoring (OPM) in fiber-optic communication links. Modulation formats, such as quadrature phase shift keying, 16 quadrature amplitude modulation (QAM), and 64 QAM, are monitored for the optical signal-to-noise ratio (OSNR) range of 20 to 30 dB by considering the dispersive effects of chromatic dispersion from 0 to 1200 ps / nm and polarization mode dispersion from 10 to 70 ps in the fiber-optic transmission path. First, the generated constellation diagrams affected by the impairments are used to optimize and evaluate the pretrained models based on classification targets. Then the proposed EDTL model is designed by aggregating the feature extractor parts of the pretrained models; it is implemented in three phases, and the results are comprehensively studied. Further, data augmentation and aggregation methods are introduced to enhance the performance of joint MFR and OPM. The results obtained prove that the proposed model provides faster convergence of MFR and better identification accuracy of OSNR toward optical signal diagnostics in optical networks for efficient optical link monitoring.

Multiplane light conversion (MPLC) offers an alternative to adaptive optics for coupling a turbulence-corrupted free-space optical beam into single-mode fiber or waveguide. Recent published test results suggest that such a conversion device has comparable or better performance than an adaptive optics system. To better understand the device characteristics, simulations were conducted to quantify the power loss for different turbulence strengths and the number of Hermite–Gaussian modes used in the conversion process. The specific case studied is a prototype free-space laser communication system developed by the U.S. Army Research Laboratory. Simulation and statistical results of the conversion performance are reported. Analysis of a beam power combiner after MPLC is also discussed.

We demonstrate a high-peak-power and narrow pulse mid-infrared (MIR) laser with xenon-lamp pumping and La₃Ga₅SiO₁₄ (LGS) Q-switching on the Cr,Er:YAP crystal grown by Czochralski method. X-ray powder diffraction and x-ray rocking curves suggest the crystal has high crystalline quality. Segregation coefficients of the Cr^{3 +} and Er^{3 +} in the as-grown Cr,Er:YAP crystal are 4.96 and 1.07, respectively. The absorption and fluorescence spectra indicate that the Cr,Er:YAP crystal is a promising material for MIR laser by xenon-lamp pumping. The fluorescence lifetimes of the upper (I_11/24) and lower (I_13/24) laser levels are 0.86 and 3.57 ms, respectively. A maximum energy of 632 mJ is acquired at 5 Hz by xenon lamp pumping. By the LGS electro-optic Q-switching technology, single pulse energy of 148.6 mJ is achieved at 5 Hz with a pulse width of 35.4 ns and peak power of 4.2 MW. The results show that the LGS Q-switched Cr,Er:YAP crystal pumped by xenon lamp possesses potential application as a short-pulse and high-energy laser device.

We numerically demonstrated seven types of solitons in an anomalous dispersion erbium-doped fiber laser, including conventional soliton (CS), dissipative soliton (DS), dissipative soliton resonance (DSR), two- and triple-soliton bound states, and period doubling and period tripling solitons. We found that DSR is achieved when the net cavity dispersion is large. CS with a narrow pulse width is obtained in the near-zero dispersion region, and period doubling and period tripling solitons are achieved around CS by properly adjusting the polarization state. The large net cavity dispersion and high gain saturation energy contribute to the generation of DS. Furthermore, further increasing the gain saturation energy under specific dispersion condition enables DS to transform into two- and triple-soliton bound states, and bound states have smooth spectral profiles and steep edges similar to DS. Furthermore, the influence of the net cavity dispersion and gain saturation energy on pulse type is diagrammed intuitively.

Selective and noncontaminated surface polishing of titanium alloy implants is crucial in the biomedical field. We employed a pulsed laser as a localized and selective heat source and dilute phosphoric acid as a corrosion solution for laser chemical polishing (LCP) of medical Ti-6Al-4V titanium alloy surface. The effect of laser fluence on the removal groove morphology of titanium alloy surfaces was systematically studied, and the characteristics and mechanisms of material removal were further discussed. The results show that the groove morphology of the workpiece surface at different laser fluences can be classified into three categories, depending on the two-dimensional removal profile. The removal mechanism of LCP is a combination of laser etching and chemical corrosion, and chemical etching can completely remove the residues and melts produced by laser ablation. Finally, selective polishing of medical Ti-6Al-4V titanium alloy was achieved by setting appropriate process parameters. Moreover, the energy-dispersive x-ray spectroscopy analysis showed that there was no detectable chemical impurity contamination on the polished surface.

A high conservation efficiency periodically poled LiNbO₃ (PPLN) optical parametric oscillator (OPO) based on the plano-convex unstable resonant cavity is demonstrated. The OPO is pumped by a Q-switch quasi-continuous-wave Nd : YVO₄ with a wavelength of 1064 nm. The thermal effect of the nonlinear crystal and the mode distribution under the plano-convex cavity are analyzed. Through temperature tuning, the wavelength of the signal laser covers 1471.4 to 1510.4 nm. When the temperature is 30°C, the repetition rate is 30 kHz, and the pump power is 5.7 W. A PPLN-OPO based on a plano-convex cavity generates a 1471.4-nm laser with a maximum output power of 1.09 W and pulse duration of 17.14 ns. The highest pump-to-signal conversion efficiency is 28.71%. When the repetition rate is 40 kHz, the highest conversion efficiency of 29.29% is achieved at the pump power of 2.8 W.

The temperature measurement accuracy of the Raman distributed optical fiber temperature sensing system is an important metric. Aimed at the reduction of the temperature measurement error, which is caused by the noises in the sensor system, an improved wavelet modulus maximum method, which combine the 3sigm criterion with the traditional wavelet modulus maximum algorithm is proposed. In this proposed algorithm, the 3sigm value is used as the threshold for the highest decomposition layer of the wavelet modulus maximum method to judge whether it is a signal or noise, instead of using the ratio of the modulus maximum of the highest decomposition level to the number of decomposition levels to determine the threshold. We conduct distributed temperature measurement on a 10-km long multimode fiber, and analyze the experimental data by using the improved algorithm. The results show that the temperature measurement fluctuation obtained by improved method is 0.497°C on average. It is better than the 1.13°C that is obtained by the traditional wavelet modulus maximum algorithm. Compared with the traditional algorithms, the 3sigm criterion algorithm has improved the temperature measurement accuracy significantly. The improved algorithm provides a new idea for the selection of the threshold value, which makes the threshold selection more statistically.

The generation of a water window attosecond pulse with circular polarization is important for ultrafast research such as X-ray magnetic circular dichroism spectroscopy. In this paper, we propose a design method of broadband reflective quarter-wave plates in the water window region based on aperiodic Cr/Sc multilayer mirrors. Three broadband reflective quarter-wave plates are designed for achieving high circular polarization and circular reflection in the water window region with 10, 15, and 20 eV bandwidths. The results indicate that the reflected lights of the designed aperiodic Cr/Sc multilayer mirrors all show a more than 95% circular polarization degree and considerable circular reflection in their design band. The proposed broadband reflective quarter-wave plates can be used for controlling the polarization state of broadband water window region sources and generating the circularly polarized attosecond pulse by the linearly polarized water window region sources.

Compared with previous graphene-based optical modulators that can be tuned electrically with the Fermi level, all-optical modulators have attracted much attention due to their ultrafast and broadband response (bandwidth ≈ 200 GHz). To take advantage of hybrid plasmonic waveguides (HPWs) and the nonlinear response of graphene, we proposed all-optical absorption and phase modulators at the wavelength of 1.55 μm and E_F = 0.1 eV. The modulators consist of two different geometries, graphene on an HPW and graphene on a double-slot HPW. Compared with the previous graphene-based all-optical modulators, our design has a short-effective waveguide length and higher modulation depth. This was achieved through the incomparable integration of HPW optics and graphene photonics that can be used to design chip-scale, compact, and high-efficiency all-optical modulators.

In this paper, we have proposed an all-silicon and compact transverse electric (TE)-pass polarizer with large bandwidth and high polarization extinction ratio (PER), where the polarizer uses a semi-arc waveguide to cause polarization-dependent bending loss (PDBL). The combination of the subwavelength grating (SWG) and double adiabatic tapers serve as an equivalent cladding to get strengthened PDBL. The parameters of SWG and double adiabatic tapers are analyzed in detail to improve the performance of the device. In the proposed TE-pass polarizer, the injected fundamental TE mode (i.e., TE₀) gets protection and the injected fundamental transverse magnetic mode (i.e., TM₀) lets out. The footprint is only about 6 μm × 10 μm, which is substantially reduced compared with the previous counterparts. From the results, its bandwidth is as high as 228 nm (from 1.482 to 1.710 μm) with PER > 39 dB and low excess loss (EL < 1 dB), and it has an ultra-high PER of 42.5 dB and a low EL of 0.1 dB at 1.55 μm. In addition, large fabrication tolerances of 20 nm ( ± 10 nm) to the key structural parameters are analyzed.

A strip titanium dioxide (TiO₂) waveguide is designed for highly coherent mid-infrared (MIR) supercontinuum (SC) generation. For the designed TiO₂ waveguide, three zero-dispersion wavelengths (ZDWs) are obtained through adjusting the waveguide structure parameters. The three ZDWs are located at 1.53, 3.96, and 5.43 μm, respectively. The nonlinearity coefficient γ is calculated as 1.12 W ^{− 1} m ^{− 1} at wavelength 3.1 μm. By optimizing the pump pulse parameters, the highly coherent MIR SCs are generated when the hyperbolic secant pump pulse with a duration of 80 fs, peak power of 1 kW, and wavelength of 3.1 μm is launched into the TiO₂ waveguide and propagated 4.2-mm in length. The obtained SC covers a wavelength range from 1.71 to 9.90 μm (more than 2.5 octaves). Our research results can find important applications in MIR photonics and spectroscopy, biophotonics, optical precision measurement, etc.

We study the impact of the surface roughness on the response of deeply etched silicon Bragg mirrors and resonators. The transfer matrix method is extended to account for the roughness in multilayered systems. The model is first verified numerically using the finite difference time domain (FDTD) method for surface roughness values up to 80 nm at a wavelength of 1550 nm. The response of the mirrors and filters having an RMS roughness of 30 nm is calculated by the developed model and compared with the numerical results of the FDTD results, and it shows a good agreement. Then the model results are compared with the experimental data of a Bragg mirror and filter, fabricated by the deep reactive ion etching Bosch process of silicon on an insulator wafer; they show a very good agreement in the insertion loss and 3-dB bandwidth due to the roughness model. Finally, the transmission, 3-dB bandwidth and quality factor of the optical filters based on single, double, and triple silicon layer mirrors are examined using the model and accounting for Gaussian beam excitation. The presented model can be used to guide the requirements on the fabrication quality of optical surfaces and the choice of the optimum number of layers.

In this paper, the particle swarm optimization (PSO) algorithm is used to optimize the performance of a radio over fiber system against cross-phase modulation (XPM) crosstalk by finding the optimum value of crosstalk by independently considering the range of various fiber parameters in the V band (40 to 75 GHz) and W band (75 to 110 GHz). Results show that, without using any optimization technique, the crosstalk is found to be minimum at the small frequency in both frequency bands. Without optimization, XPM crosstalk is found to be −62.2, −56.2, and −52.7 dB at 40 GH, 75 and 110 GHz, respectively, at the fiber length of 20 km, whereas after PSO, XPM crosstalk is −65.4 and −71.9 dB at 75 and 110 GHz, respectively, at the high fiber length of 50 km. After applying the PSO optimization technique, XPM crosstalk is optimized with the minimum at high frequencies in both frequency bands at large fiber lengths. It is found that XPM is optimized at different values of the dispersion parameter without the use of a dispersion-shifted fiber. Joint optimization is also done for the complete range of frequencies from 40 to 110 GHz, and optimized crosstalk is obtained independently at high frequencies and large fiber lengths in both frequency bands. From the results, it can be seen that a radio-over-fiber system can be designed by choosing a single-mode fiber with the optimized parameter value. The XPM crosstalk keeps increasing with the increase in the length of the fiber and frequency, and PSO was used to counter the crosstalk by optimizing the various fiber parameter values.

This paper proposes a method to study the transmission characteristics of ultraviolet turbulent channels, by considering the variation of atmospheric refractive index structure parameters along transmission paths. This method is adopted in a Monte Carlo simulation to analyze the transmission characteristics of ultraviolet light when the communication nodes are mobile. The analysis focuses on the influence of the moving speed and direction of the receiver on path loss under long-distance and atmospheric turbulence conditions. The simulation results show that, when the altitude increases, atmospheric refractive index structure parameters show a decreasing trend, and the path loss of the system decreases. With or without turbulence, when the receiver moves away from the transmitter in a horizontal plane, the received signal strength always decreases as the moving speed increases; and vice versa. When the receiver moves along the vertical axis, the signal strength increases as the moving speed increases. With the presence of atmospheric turbulence, the received signal strength attenuates significantly, compared with the case with no turbulence. When the receiver moves along the vertical axis, the path loss is higher compared with the situation when the receiver moves on the horizontal plane.