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One of the most important industrial applications of lasers is the treatment of materials. In this work pulsed Nd:YAG laser of wavelength (1064 nm) was used to precipitate the prepared solution of CuO nanoparticles in the form of thin films using energies (300, 400, 500 and 600 mJ) at a distance (10 cm) and for an irradiation period (20 s) for each energy. The optical properties of the material were examined, which include transmittance, absorbance and some other optical constants, in addition to calculating the optical energy gap and knowing the effect of increasing the laser energy on its values.

The effect of planar photonic crystal on CZTS/CdS solar cell is systematically investigated. The reflective properties of PhC ARC which consists of the periodic stack of ZnO and HfO2 with two numbers of periods having quarter wavelength thickness are analyzed. Similarly, the DBR having periodic stacks of HfO2 and ZnO dielectric layers with four numbers of periods having half wavelength thickness in CZTS/CdS solar cells are explored. Moreover, the results of the photovoltaic properties of CZTS/CdS solar cells are also analyzed. The outcome of the findings obtained from the computation using the transfer matrix method are very well agreeable with the recent literature. The planar (ZnO /HfO2)2 PhC ARC and (ZnO/HfO2)4 DBR has been expected to provide significant improvement in the performance of CZTS/CdS solar cells.

The cell-type continuous electromagnetic radiation system is a demonstration device capable of generating high-power millimeter electromagnetic waves of a specific wavelength and observing their effects on living organisms. It irradiates a biological sample placed in a 30 × 30 × 50 cm3 cell with electromagnetic waves in the 3.15-mm-wavelength region (with an output of ≥1 W) and analyzes the temperature change of the sample. A vacuum electronic device-based coupled-cavity backward-wave oscillator converts the electron energy of the electron beam into radiofrequency (RF) energy and radiates it to the target through an antenna, increasing the temperature through the absorption of RF energy in the skin. The system causes pain and ultimately reduces combat power. A cell-type continuous electromagnetic radiation system consisting of four parts—an electromagnetic-wave generator, a high-voltage power supply, a test cell, and a system controller—generates an RF signal of ≥1 W in a continuous waveform at a 95-GHz center frequency, as well as a chemical solution with a dielectric constant similar to that of the skin of a living organism. An increase of 5 °C lasting approximately 10 s was confirmed through an experiment.

The near-infrared (NIR) persistent luminescence materials (PLMs) can remain long-lasting luminescence after removal of the excitation light, which permits bioimaging with high sensitivity owing to the absence of background fluorescence interference from in situ excitation. Recently, the NIR PLMs have aroused intensive research interest in bioimaging. However, the optimal excitation wavelength of current NIR PLMs is located in the ultraviolet region with shallow tissue penetration, making it difficult to activate effectively in vivo, and seriously hindering their further application in bioimaging. Herein, we report a novel kind of Cr3+ ions and Y3+ ions co-doped NIR PLM, Zn1.3Ga1.4Sn0.3O4:Cr3+,Y3+ (ZGSCY), which emits NIR persistent luminescence at 696 nm. Compared with Zn1.3Ga1.4Sn0.3O4:Cr3+ (ZGSC) excited by the light with a wavelength in the biological window (>650 nm), after being co-doped with Y3+ ions, the NIR persistent luminescence performance of ZGSCY is significantly improved because of the increase of trap concentration in the matrix. In addition, we synthesized ZGSCY nanoparticles (NPs) by the combustion method, which exhibit excellent optical properties after being excited by the light with a wavelength in the biological window. After surface modification with PEG, the ZGSCY NPs present low cytotoxicity. Notably, due to the co-doping of Y3+ ions, the signal-to-noise ratio (SNR) of ZGSCY NPs in vivo imaging is about 1.8 times higher than that of the ZGSC NPs. Furthermore, the rechargeable in vivo imaging and passive tumor-targeted imaging are successfully achieved by activating with a light-emitting diode (LED, 659 nm) after intravenous injection of ZGSCY. Thus, this kind of NIR PLM with high excitation efficiency performance in the biological window is expected to promote its biomedical application in deep tissues.

Two dimensional (2D) Photonic crystals (PhCs) based cross waveguide structure (CWs) consisting of resonant cavity is investigated in this paper. Investigations are done using Two Dimensional Finite Difference Time Domain (2DFDTD) method. Transmission characteristics have been obtained for different radii of central rod placed at crossing point of two waveguides and number of regular rods surrounding central rod. Nonlinear behavior is also studied for different operating wavelengths.

The influence of neutron and gamma radiation on single mode fiber cables is experimentally conducted. Attenuation due to incident radiation is measured. Attenuation is determined by laser source and power meter in Africa Teleco Company, besides attenuation recovery is attained. The Gamma experiment is carried out within Egypt Mega Gamma1 in National Center for Radiation Research and Technology of Egyptian Atomic Energy Authority (EAEA). In this experiment, the cable is degraded by gamma radiation of doses 5KGy, 10KGy, 15KGy and 25KGy and dose rate of 1KGy/26.4 min. However the attenuation based on neutron degradation is executed in the second Egyptian Training Research Reactor (ETRR-2), in front of neutron beam facility (NBF) in ETRR-2 which has a flux of 1.5x107(n/cm2.sec). For both experiments, the experimental measurements are done at two different spectral wavelengths of 1310 nm and 1550 nm. A comparison between obtained results is investigated.

A high-precision tunable single-frequency fiber laser (T-SFFL) at 1.5 μm based on self-injection locking is experimentally demonstrated. By virtue of an effective filtering and self-injection locking scheme, a stable single-longitudinal-mode operation of the fiber laser is obtained. The fine wavelength tunability is implemented by stretching a uniform fiber Bragg grating in the self-injection loop, and the laser wavelength is tuned from 1550.28 to 1560.40 nm with a tuning accuracy of less than 54 pm. In the whole tuning range of 10.12 nm, an output power of approximately 5 mW and an optical signal-to-noise ratio of 71 dB are synchronously obtained with this laser system. Additionally, the measured laser linewidth is less than 630 Hz and the relative intensity noise is lower than -149 dB/Hz at frequencies from 0.4 to 7.5 MHz. It is believed that this 1.5 μm high-precision T-SFFL can be a promising candidate for the optical communications system applications.

In this work, a modified square photonic crystal fiber (MS-PCF) architecture is exposed with ultra-high negative dispersion for communication window. The validation of the model is successfully performed by applying an efficient full-vector finite element method (FV-FEM) with anisotropic perfectly matched layers (PMLs) for precise simulation of PCFs. Additionally, waveguide dispersion engineering is accomplished by tuning the structural parameters of the MS-PCF. From the numerical investigation, negative dispersion behavior permits remarkable suppression rather than positive dispersion. It offers the high negative dispersion of −2357.54 ps/nm/km and Kerr nonlinearity (γ) of 74.68 W−1 km−1 simultaneously at the operating wavelength, λ = 1550 nm. Nevertheless, the designed fiber ensures the mono mode operation in the entire band of interest from λ = 1340 nm to λ = 1580 nm. MS-PCF with these outstanding optical performances has distinguished potency to be practiced as a dispersion compensating fiber in optical communication systems.

We firstly propose a roadmap for the design of high repetition rate (~100 MHz) Tm-doped ultrafast fiber laser with an emission wavelength above 2000 nm. This roadmap is confirmed by both theoretical simulation and experimental verification. The designed Tm-doped fiber oscillator not only operates in continuous wave regime with a broad tunable wavelength range of ~ 100 nm, but also in mode-locking regime with an emission wavelength > 2000 nm (up to 2020 nm). A 470-fs laser pulse with a pulse repetition rate of ~96 MHz and the maximum average power of 50 mW are achieved at the output wavelength of 2007 nm, matching well with the theoretical prediction. In a further step, the seed laser pulse is amplified to 3.3 W, accompanied by a Raman frequency shift of the output wavelength to 2346 nm. The homogeneous intense broadband spectrum with a bandwidth of 240-nm centered at 2200 nm is also observed.

We propose and demonstrate an overall non-mechanical spectrally steered laser rangefinder using the dispersion-tuned swept laser (DTSL) and a passive diffractive element. The DTSL has no mechanical moving parts, making it possible to achieve an inertial-free high wavelength sweeping speed. The inherent intensity-modulation characteristic of the DTSL allows the modulation phase-shift method to be applied, similar to that used for an amplitude-modulated continuous-wave (AMCW) rangefinder. Since the pulse repetition rate of the DTSL is chirped, standard signal processing techniques for AMCW are not applicable. In this paper, we propose a novel chirped amplitude-modulated phase-shift (CAMPS) method with a signal processing technique to obtain the phase-shift information from a chirped amplitude-modulated signal. As a proof of concept, we demonstrated the CAMPS LiDAR with an axial ranging resolution of ~50 m at a scanning speed of 10 kHz.

Theoretical limit of solar cell conversion efficiency given by Shockley and Queisser is calculated for the case that the cell is illuminated by solar radiation. If the input radiation is monochromatic, the efficiency can exceed the limit. The aim of our study is to experimentally demonstrate this theoretical prediction and to obtain the experimental results of spectral dependence of photovoltaic cell conversion efficiency. Conversion efficiencies of two types of Si photodiodes (equivalent to solar cells) are determined through the measurements of current–voltage characteristics as a function of the wavelength and the incident radiant power. As the theory predicts, it has been confirmed that the conversion efficiency is almost proportional to the wavelength and also to the logarithm of the incident radiant power. Also, it has been experimentally confirmed that the power conversion efficiency for long wavelength monochromatic radiation is higher than that for white radiation.

Opening new wavelength bands is the most economic step for further increasing the capacity of optical transmission links. Characteristics of different amplifier technologies for signal amplification in different wavelength bands are detailed. In particular, the suitability of these technologies for short-term and mid-term implementation is considered. An important criterion is the availability of qualified components, notably the required pump laser diodes. On this basis, solutions for the near-term and the mid-term are discussed.

In0.75Ga0.25As and In0.83Ga0.17As 320×256 short-wave infrared focal plane arrays (SWIR FPAs) with pixel pitches of 24 and 30 μm, extended cutoff wavelengths of 2.2 and 2.5 μm, low dark current densities of 5.2 and 21 nA/cm2, and high peak detectivities of 6×1011 and 6×1012 cmHz1/2W−1 are attained at 180 K, respectively. Lower 1/f noises and smaller knee frequencies are observed for the 2.2 μm FPA, indicates the dislocation defect-related trap states act as the major contributor for the 1/f noise. The non-uniformities of the dark signal and the dark noise are roughly the same for both FPAs at a short integration time of 1 ms (29% and 25% at 180 K, respectively) whereas are much smaller for the 2.2 μm FPA at longer integration times. Moreover, the dark current shot noise dominant integration time ranges are determined to be >20 and >2 ms for the 2.2 and 2.5 μm FPAs, respectively. Enhanced heat signature recording capability is also observed for wider SWIR spectral range while more effective suppression routes of dislocation defect must be incorporated for further improved sensitivity.

High-speed photodetector operating at 850 nm wavelength with a large diameter and high quantum efficiency is desirable to meet the growing demands of short-reach optical links for high-performance computing systems. Zero-bias operation of the high-speed photodetectors can reduce power consumption, minimize system complexity of the optical transceivers and reduce the radiation damage in a harsh environment. Traditional p-i-n photodetectors for 850 nm applications often require a high reverse bias to accelerate the carrier transport for high-speed data transmission. In this work, we demonstrate a high-speed and low dark current modified uni-traveling-carrier photodiode based on GaAs/AlGaAs at 850 nm wavelength operating under zero bias with a quantum efficiency of 73%. The 3-dB bandwidth of the 20 μm and 40 μm diameter devices is 22.5 GHz and 13.3 GHz, respectively. A clear eye pattern is demonstrated at a 25.8 Gbit/s data rate for the device under zero-bias operation. To the best of our knowledge, this photodetector demonstrates the highest 3-dB bandwidth among all the zero-bias 850 nm photodetectors reported to date.

Multiphysics modeling of a planar HgCdTe-based mid-wavelength infrared (MWIR) focal plane array with $3\,\mu$ m-wide pixels enlightens the role of surface plasmon-polaritons observed in gold nanorods arranged on its illuminated face. Simulations indicate that the proposed plasmonic detector, which employs a $1\,\mu$ m-thick absorber layer, exhibits a reduction of diffusive inter-pixel crosstalk by more than one order of magnitude with respect to more conventional, non-plasmonic detectors with a $5\,\mu$ m-thick absorber layer, without penalizing responsivity and achieving increased detectivity in the whole MWIR band by taking advantage of the absorber volume reduction.

This work investigates the spectral quantum efficiency and inter-pixel crosstalk of a MWIR-LWIR dual band, HgCdTe-based focal plane array (FPA) photodetector (MWIR and LWIR stand for mid- and long-wavelength infrared bands). Pixels are $\text{10}\,\mu$ m-wide with truncated pyramid geometry and separated by deep trenches. Three-dimensional combined full-wave electromagnetic and electrical simulations in the drift-diffusion approximation allowed to describe the complex, standing-wave-like spectral features resulting from the light interference and diffraction due to the pixels and illuminating beam aperture. The inter-pixel crosstalk for the MWIR operation demonstrated to be very sensitive to the trench depth, in contrast to the LWIR electrooptical response, left almost unchanged. The present work also investigates the causes of performance worsening in the two IR bands when pixel pitch is reduced to $\text{5}\,\mu$ m, hence well below typical LWIR wavelengths and close to the diffraction limited operation.

Bolometer sensors are prominent and excellent choice in technology because they do not need cooling. The trade-off between high sensitivity, fast response time, and strong light absorption is a key important challenge in bolometer sensors. Here, the bolometric effect for a high resistance sensitivity plasmonic sensing of total and profile infusion of radiation is studied for the proposed bolometer sensor based on plasmonic multilayer structure at 26° C. In the present study, by generating strong coupling condition between incident wave and surface plasmon polaritons (SPPs), a very narrow absorption spectra with high figure of merit (FoM) is achieved. The analytical model and numerical simulation are fulfilled based on the transfer matrix method (TMM) and 3-D finite-difference time-domain (FDTD), respectively. The narrow absorption spectra that generate by strong coupling with SPPs heats the silver thin film that leads to variation in temperature and supports TE surface mode. This temperature change rectifies the resistance of the metal thin film by the bolometric effect. So, optical characteristics of the proposed metasurface bolometer sensor, including quality factor (Q), sensitivity, and figure of merit (FoM) are calculated that Max sensitivity, FoM, and Q are 17.2 RIU-1, 530 and 434.5, respectively. Finally, we analytically simulate the temperature coefficient of resistance (TCR) in terms of wavelength and refractive index of analyte (na) that this resistance change can be monitored by an external electric model. The proposed plasmonic multilayer configuration is a very compact footprint structure that achieved high resistance sensitivity and FoM in comparison with any previous reports. This proposed thermal, optical, and electric plasmonic metasurface bolometer sensor can be used in different applications such as biophysics, biology, and environmental science.

We present the structural design and polarization-maintaining performance of solid-core anti-resonant fiber with two nested circular tubes in 3 m wavelength for the first time, to the best of our knowledge. Numerical simulation results indicated that laser fundamental mode could be obtained by filling the specially designed fiber model with materials of different refractive indices to form the completely solid configuration. We calculated the bend loss of fiber to demonstrate the preferable birefringence performance and outstanding light-confining ability. With the structural deformations from resonant tubes, the birefringence coefficient was enhanced significantly from 210-5 to 6.9310-5, which was of great importance in the polarization sensitive systems. In particular, when nested circular tubes were moved to introduce deformations, the confined loss difference in two orthogonal polarizations was calculated more than two orders of magnitude, which was the desirable result to promote the fabrication of the linear polarizer in 3 m wavelength.

In this work, we carry out theoretical investigation of the dispersion relationship both with the radius of the microsphere cavity and wavelength for the first two radial-order mode based on the theory of microcavity dispersion. The results show that the size of the microcavity corresponding to the zero dispersion point of the higher order mode is larger than that of lower order mode at the certain wavelength. The microsphere cavities with slight deformations, which have rich modes and high Q values, have been fabricated and optical frequency comb (OFC) in them with small size is realized by means of mode coupling. We have achieved OFC in cavities as small as 105 m in diameter by assistance of the theoretical study. The total dispersions are -7.1 MHz in 1550 nm and -14.2 MHz in 1310 nm, which are both in the normal dispersion region.

Purpose: To compare the light transmittance property of seven currently used intraocular lens (IOL) models by spectrophotometer data.Methods: Light transmission spectra of seven IOL models were assessed with a spectrophotometer. The transmittance properties were analyzed in 1 nm units from 350 nm wavelength to 800 nm.Results: Three ultraviolet filtering IOL models (ZCB00, XC1-SP, and AT LISA 809M) showed nearly full transmittance of the light from 400 to 500 nm, while steeply attenuating light with shorter wavelengths in various degrees. Three blue-light filtering IOLs (yellow-tinted IOLs; XY1, SN60WF, and TNFT00) showed a slow-sloped increase of light transmission between 400 to 500nm. Among the three, XY1 showed different degree of inclination, showing a steeper slope than SN60WF and TNFT00. The violet-light filtering IOL (ZFR00V) showed a rapid increase of the transmission at around 435 nm wavelength, which is similar to ultraviolet filtering IOLs.Conclusions: The seven different IOLs measured showed different characteristics of light transmission depending on the properties of each material and color. Blue-light filtering IOLs tend to blocked a wide range of wavelength up to 500 nm, but rather were not effective at the range of 400 to 430 nm. Violet-light filtering IOL showed advantages in filtering the high-energy wavelength, around 430 nm, having a potential risk to retina and allowing the transmission of useful blue and green wavelength which is necessary for a better scotopic contrast sensitivity.

In this paper, a low sidelobe-level (SLL) circularly-polarized (CP) leaky-wave antenna with A-shaped elements is proposed based on substrate integrated image guide (SIIG). The A-shaped CP radiating element consists of a horizontal LP structure and a vertical LP structure. The horizontal LP wave and the vertical LP wave can be excited by a pair of inclined transversal metal strip patches and a longitudinal metal strip patch respectively. Their phases are orthogonal and amplitudes can be controlled to be equal by adjusting the tilted angle of the horizontal LP structure and the length of the vertical LP structure. Moreover, the longitudinal metal strip patch is modified to the V-shaped strip patch, which can realize the field cancellation, thereby achieving the boresight radiation for such a leaky-wave antenna. Furthermore, a low SLL is realized by controlling the aperture-field distribution to obtain the desired amplitude distribution and the relatively small axial ratio (AR). In addition, because of the short waveguide wavelength of the SIIG, this feed line can be used to achieve the small interelement spacing and element size, thereby realizing the short length of the array. The measured peak gain of this antenna is 12.3 dBi and the SLL is 19.1 dB.

In this study, a multicolor-tunable Eu3+/Bi3+:Y2Zr2O7 transparent ceramic was successfully fabricated using vacuum sintering technology for the first time. The single-phase ceramic showed a pore-free structure and highest transmittance of 67% at 1200 nm. To reveal the luminescence properties of the obtained samples, photoluminescence (PL) tests were performed. Upon combining the green emission (centered at 475 nm) from Bi3+ and the red emission (centered at 629 nm) from Eu3+, bright, white light was observed in both the single-phase Eu3+/Bi3+:Y2Zr2O7 phosphors and transparent ceramics (λex = 302 nm). Furthermore, upon changing the excitation wavelengths, strong red (λex = 250 nm) and orange (λex = 365 nm) emissions were also observed at room temperature. The PL spectra and International Commission on illumination (CIE) coordinate diagram show that white light with CIE (0.3528, 0.3121) can be easily achieved. Combined with their excellent high-temperature performance and good mechanical properties, Eu3+/Bi3+:Y2Zr2O7 transparent ceramics have promising potential as white-light-emitting materials.

The wireless imaging radar need more orbital angular momentum (OAM) modes to irradiate targets alternately to obtain higher azimuth resolution. For that, this present paper investigates the fast-switching technique of radio frequency orbital angular momentum (RF-OAM) beam with the use of an optical-controlled system. Compared with the method using pure electrical device, the optical-controlled method offers conveniences in processing same-frequency radio signal, which will contribute to make the system compact. Moreover, the fast-responding speed of the optical device provide a fast speed of switching. The fast-switching system of RF-OAM beams with different mode and radiation direction is proposed and constructed, and proof-of-concept experiments are performed. The proposed system is realized by employing a program-controlled optical switch and the wavelength multiplexing technique integrated into an optical-controlled circular antenna array (CAA). In the demonstration experiments, the switching between +1-mode and -1-mode RF-OAM beams without steering control is detected within 20ms, then the system achieves the switching between a +1-mode OAM beam with radiation direction -3o and a -1-mode OAM beam with radiation direction 3o at the same rate.

This article presents an ultracompact bandpass filter (BPF) realized by slow wave substrate integrated groove gap waveguide (SW-SIGGW). The SW-SIGGW is composed of two layers of the dielectric substrate, in which periodic mushroom-type electromagnetic band-gap (EBG) unit cells are employed as packaging structures. The gap layer is realized by the upper substrate, and the via-patch mushrooms are designed on the lower substrate. Due to the slow wave structure in the form of periodical metallic via-holes designed on the lower substrate, the guided wavelength is reduced by about 52.8% compared with normal SIGGW. A dual-band resonator and a cascaded second-order BPF are designed based on SW-SIGGW. Compared with the conventional second-order SIGGW BPF, the proposed SW-SIGGW BPF achieves a 62.6% reduction in the area. By adopting vertical stacking technology, the area of the SW-SIGGW BPF is further miniaturized. The final area of the stacked SW-SIGGW BPF is only 18.7% of the conventional filter based on normal SIGGW without slow wave and stacked structure, which is very competitive for the room-limited applications. A prototype of the stacked SW-SIGGW BPF with 5.4% and 7.4% fractional bandwidths at 11.8 and 18 GHz is fabricated and measured. A good agreement between the measured and simulated results verifies the validity of the miniaturized design of SW-SIGGW BPF.

In this work, we fabricated and characterized 4 × 4 parallel flip-chip AlGaN-based micro-LED arrays with varied mesa diameters of 120 µm, 100 µm, 80 µm, and 60 µm. The reported micro-LED arrays have a maximum bandwidth of 380 MHz and a peak wavelength of ∼275 nm. It is found that the electrical and optical characteristics of AlGaN-based micro-LED arrays show strong size dependence for ultraviolet communication (UVC). The differential resistance increases from 28.8 Ω to 112 Ω, the external quantum efficiency (EQE) is increased by ∼30%, and the bandwidth doubles as the diameter of individual micro-LED decreases from 120 µm to 60 µm. Our research proves that tailoring the mesa size of parallel flip-chip AlGaN-based micro-LED arrays can further enhance its bandwidth and promote its application in UVC.

This manuscript comes up with a unique GaAs-filled elliptical core-based hexagonal cladding PCF that manifests ultra-high birefringence (Br) and non-linear coefficient (NLC). The distinct optical characteristics of the PCF are thoroughly simulated and analyzed by the finite element method (FEM) through the commonly available COMSOL Multiphysics software. The simulated findings confirm that using the high refractive index (RI) advantages of GaAs at the effective wavelength of 1.55 μ m , a high Br of 0.92 , as well as an ultra-high NLC of 2.06 × 10 6 W − 1 K m − 1 and zero-dispersion can be obtained. Besides, several primary optical properties, namely numerical aperture (NA), confinement loss (CL), power fraction (PF), dispersion, etc. are also discussed and investigated in depth in the propounded article. The zero-dispersion characteristic, as well as the high Br and ultra-high NLC of the advanced PCF model, make it a worthy candidate for extensive purposes, including biochemical detection, high nonlinear applications, supercontinuum generation, optical communication and other sensing applications.

A five-wavelength-switchable thulium-doped fiber laser with a fiber Bragg grating (FBG)-based five-channel transmitting Fabry-Pérot (F-P) filter and a multi-coupler based triple-ring cavity (CTRC) filter, is experimentally proposed. For the first time, a multi-channel F-P filter and specially-designed coupler-based compound cavity filter were combined to realize multi-wavelength-switchable operation, with single-longitudinal-mode (SLM) lasing for each wavelength channel in a 2 µm band fiber laser. The theoretical analysis of the CTRC filter and the principle for achieving SLM operation by corporately using the F-P filter and CTRC filter were presented in detail. The experimental results demonstrated the good performance of the proposed filters. Five lasing wavelengths (1941.13 nm, 1941.22 nm, 1941.30 nm, 1941.39 nm, and 1941.47 nm) were obtained with good switchability, and each operated in a stable SLM state. The OSNR of each lasing wavelength was higher than 50 dB, and the linewidths of all obtained wavelengths were less than 8 kHz.

A simple optically transparent absorber based on a double complementary structured layer of indium tin oxide (ITO) deposited polyethylene terephthalate (PET) film is presented. The structure showed more than 90% absorption from 2-4.5 GHz of the frequency with a thickness of 0.0847L (wavelength corresponding to the lowest frequency of absorption band). The computed absorptivity of the proposed structure is validated using the transmission line theory and measured experimentally as well. The structure has polarization insensitive response and is highly stable for oblique wave incidence over a wide angular range. This absorber can be conformally wrapped on a curved surface and reduces the radar cross-section (RCS) by more than 10 dB of a curve cylinder. This 10 dB RCS reduction covers almost the entire S-band of microwave frequencies. Optical transparency and flexibility of the proposed absorber make it suitable for a wide range of applications.

A novel low-profile circularly-polarized (CP) diversity patch antenna with extremely small edge-to-edge distance, reduced size and low mutual coupling is proposed under dual modes. Initially, the single microstrip patch antenna (MPA) is theoretically investigated by using characteristic mode analysis. It demonstrates that a large number of radiative modes, i.e. CM1 to CM7, are excited for the traditional MPA. By selecting its quarter patch configuration with shorting pins, only a few modes, i.e., CM2 and CM7, could be resonated for the quarter patch antenna (QPA). Meanwhile, their non-broadside radiated fields could be transformed into the broadside radiation. Particularly, the polarizations of CM2 and CM7 are maintained orthogonally with each other. Next, a linear slot is etched on the patch to reduce the magnitude ratio between |Eθ| and |Eφ| components. After that, the resonant frequency of CM7 is moved closely to that of CM2 for nearby 90o phase difference. With these arrangements, the compact CP performance is acquired by combining its CM2 and CM7. Furthermore, a pair of QPAs with CP diversity is deeply studied. The results prove that the antenna has successfully acquired both of left-handed CP (LHCP) and right-handed CP (RHCP) performances at dual ports. Moreover, the low mutual coupling between them is generated under extremely small spacing. In final, the proposed antenna is fabricated and tested. Both of LHCP and RHCP patterns are formed of around 4.785 GHz. Besides, the proposed antenna occupies the small overall volume 0.023λg3 (λg is the guided wavelength), that is only half of the traditional patch (0.045λg3), and maintains the isolation as high as about 24 dB under extremely small distance (0.3 mm).

Highly sensitive, simple and multiplex detection capabilities are key criteria of point-of-care (POC) diagnosis in clinical samples. Here, a simple and highly sensitive multi-analyte detection technique is proposed by using photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor that employs both internal and external sensing approaches. The proposed sensor can detect two different analytes simultaneously by the internal and external plasmonic micro-channels. The light propagation through the sensor is controlled by the scaled-down air-holes to excite the free electrons of the plasmonic metal layers. The light-guiding and sensing properties of the sensor is numerically analyzed by using the Finite Element Method (FEM). The proposed sensor shows the maximum wavelength sensitivities (WS) of 12,000 nm/refractive index unit (RIU), and 10,000 nm/RIU, for the internal and external sensing approaches, respectively, and corresponding resolution of 8.33×10-6 RIU and 1.0×10-5 RIU. Moreover, the hybrid sensor is applicable to detect unknown analyte refractive index (RI) in the range of 1.33 to 1.40 which covers extensively investigating analytes such as viruses, different cancer cells, glucose, proteins and DNA/RNA. Due to high sensing performance with multi-analyte detection capability, the proposed sensor can play a significant role to detect bio targets at the POC platform.

A double-layer metasurface is proposed to realize the low profile of a broadband dual-polarized antenna for cellular base-station applications. The proposed metasurface is formed by the two layers of printed metallic patch unit cells on either sub-strate surface to miniaturize the metasurface size and enhance de-sign flexibility by regulating the extent of electromagnetic coupling between the two layers. Despite the low profile of the antenna, a wideband operation is accomplished by operating the metasurface in the non-resonant region that facilitates wideband phase-com-pensation and its truncation to a finite dimension with an addi-tional transverse electric (TE) surface wave resonance. The guide-lines for the design of the surface is derived from a comparison of unit cell structures and an approach is introduced to correlate their potential with surface susceptibility parameters. A detailed parametric study addresses the critical concern on the overall di-mensions of the finite metasurface. A ±45° polarized dipole an-tenna with an overall thickness of 0.15λ0 (λ0 is the wavelength in free-space at the center operating frequency) is designed as exam-ple. The measured results show a |S11|≤ -10dB impedance band-width of 46.4% over the frequency range of 1.69-2.71 GHz with average boresight gain of 9 dBi with a ground plane of 1.1 λ0 × 1.1 λ0, well covering 2G (1.71-1.92 GHz), 3G (1.88-2.17 GHz) and LTE (2.3-2.4 GHz and 2.5-2.69 GHz) bands.

The study of refractive index provides the complete picture of material bodies with reference to their major properties like physical, chemical, optical, etc., and hence decides the behavior of the material body at macro level. Measurement of refractive index in small volume samples using a U-shaped extrinsic fiber optic sensor based on the principle of direct contact evanescent wave absorption can be employed to detect such information. In order to obtain such measurements, a U-shaped glass probe connected between a light transmitter and an optical detector using two PCS multimode optical fibers of the same diameters (200/230 μm) was developed and investigated in the present study. Liquid mixtures prepared using Toluene and Acetic acid taking at different proportions making total volume equivalent to 20 ml employing a two burette system. When the liquid mixtures are applied on the U-shaped probe the light reaching the detector from the source was shown varying depending upon the refractive index of the mixture. The changes in the transmitted power spectra were measured as a function of absorption of higher order evanescent wave modes at various refractive index values at different temperature levels ranging from 20 °C to 60 °C of the mixture and by repeating the experiment with various operating wavelengths (630 nm, 660 nm, 820 nm & 850 nm). The calibrated curves were plotted, which can be used to determine the refractive index of liquids at various temperatures with high degree of accuracy, precision and sensitivity measurements, exploiting all the benefits offered by the optical fiber communication systems.

A novel design concept to reshape radiated fields of a slot antenna for improved bandwidth and stable radiation pattern is proposed. Initially, the radiated fields of the traditional slot antenna are theoretically studied using characteristic modes (CMs). The results demonstrate that its CM1, CM2, and CM3 are resonated of around 2.39, 4.78, and 7.17 GHz, respectively. For CM1 and CM3, both of them maintain the bidirectional radiation patterns. Whereas, the CM2 generates a radiation null in the broadside direction. Then, in order to utilize the nearby CM1 and CM2 for wide-bandwidth, the linear slot is properly folded so as to transform the non-bidirectional pattern of CM2 into the bidirectional one. After that, the narrow slot is reformed as the stepped scheme, thus reallocating these dual modes in proximity to each other. With these arrangements, the impedance bandwidth of the antenna is dramatically widened with two attenuation poles, while keeping a compact size and stable radiation pattern. Finally, the proposed antenna is fabricated and tested. Measured results show that the antenna without any extra feeding network has gained a wide-bandwidth (|S11

An efficient continuous-wave (CW) mid-infrared laser with a tunable wavelength range from 3 to 4.5 μm is demonstrated by using intracavity optical parametric oscillator (ICOPO). An optically pumped semiconductor laser (OPSL) is applied as the parent pumped laser gain medium to eliminate self-modulation effect caused by Nd-doped gain medium with ICOPO for fulfilling true CW emissions. Simultaneously, the OPSL gain chip with flip-chip packaging method can avoid mode hopping resulted from internal heat spreader etalon when strong depletion in ICOPO was achieved. The diode pump criteria of the OPSL is first investigated to prevent thermal roll over. By observing the spectral and temporal dynamics of the parent pumped OPSL with and without OPO operation, the true CW and mode-hop-free quality of the laser is verified. A low diode pump threshold of 2.67 W is obtained for the mid-IR idler emission and a total extracted idler power is 250 mW at a diode pump power of 8 W. Finally, the wavelength tunability is confirmed by adjusting the horizontal location of the multiple channel MgO:PPLN crystal, which indicated the feasibility of practical application in such a compact configuration.

In this study, the self-powered photodetector based on photovoltaic effect was obtained from BixFeO3 (x = 1, 1.3, 1.5, 1.7) films. In order to study the origin of the photovoltaic effect, the self-polarized structure and defect distribution of the films were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and piezoelectric force microscopy. In addition, the responsivity (1515 μA/W) and detectivity (1.35Χ1011 Jones) are achieved in the Bi1.5FeO3 film at zero bias after receiving 0.2 mW/cm2 of irradiation light in the wavelength of 500 nm. The rise and decay time of the photocurrent without bias reaches ∼6 ms and ∼15 ms respectively, and did not weaken after a 11 min cycling test. The self-polarized structure and defect dipoles play an important role in the photovoltaic effect of BixFeO3 self-powered photodetector. This work lays a foundation for applications in BixFeO3 self-powered photodetection.

In the article herein there is considered computation of temperature, deformation and pressure in engineering and building structures, using fiber Bragg grating (FBG). There has been studied fiber Bragg sensors in combination with the technology of far infrared range sensors, both for simultaneous temperature and deformation definition and for synchronous definition of temperature and pressure. Developed fiber-optic refractometric sensor for controlling technological and building structures health. Computations showed, that displacement change in percentage, in respect to the wavelength, varies for 5 temperature values from 20 to 100℃, which proves, that displacement changes linearly and proportionally to the wavelength, and it is connected with fiber plasticity, which increases along with temperature raise and boosts humidifying in fiber, consequently, displacement decreases.

This letter proposes a miniaturized wideband Butler matrix (BM) based on dual-layer half-mode substrate integrated waveguide (HMSIW) structure. By virtue of the excellent features of shorter guided wavelength, flatter in-band phase slope, and more compact size of HMSIW, simple and compact couplers and phase shifter are newly designed for BM. Finally, a BM prototype is designed, fabricated, and measured. Benefiting from the proposed structure, size miniaturization over 90% is achieved in comparison with the traditional single-layer substrate integrated waveguide (SIW) type.

The study of refractive index of liquids becoming increasingly popular in diverse areas to monitor chemical, pharmaceutical, food, scientific, biochemical, medical, etc. processes and procedures. In the present paper a low cost, simple, compact, reliable, robust, miniaturized and sturdy Refractive Index sensor is reported. It is configured by using a set of two multimode PCS fiber of 50 cm length in each, connected one to the source of wavelength 660 nm and other to a light detector. A glass rod drawn in the form of ‘U’, of compatible dimensions to that of two multimode fibers, was connected between source and detector by jointing to the remaining ends of the fibers, thus creating a sensing zone. Maintaining the binary liquids of Toluene and t-Butanol at the sensing zone at various temperatures, the light launched from source was monitored in the detector at the detector end. By forming relationship between index of refraction and power output at the temperature range of 10 °C to 60 °C, the sensor expected to be used to detect the index of refraction of liquids with maximum resolution of the order of 10-5 in the operating range from 1.36312nD to 1.50915nD.

Photothermal interferometry (PTI) with hollow core fibers (HCFs) have enabled highly sensitive spectroscopic gas sensors in an all-fiber format. Here we report remarkable improvement in the limit of detection of HCF-PTI, in terms of noise equivalent concentration (NEC), by exploiting the optical-phase-modulation amplifying (OPMA) effect of an HCF resonating cavity. By locking the wavelength of a 1550 nm probe laser to the resonance of a 10-cm-long HCF Fabry-Prot cavity with a finesse of ~700, OPMA of more than two orders of magnitude is achieved, which enables ultra-sensitive gas detection with large dynamic range. With 1654 nm, 1532 nm, and 761 nm pump lasers, we demonstrate detection of methane, acetylene, and oxygen with noise-equivalent-concentration of 15 parts-per-trillion (ppt), 2.7 ppt, and 0.56 parts-per-million (ppm), respectively. Further improvement in NEC is possible by use of a higher finesse cavity with a longer length of HCF. Extension of the technique to other gases, other types of phase or dispersion modulation-based sensors, and other optical resonating cavities is straightforward.

Design rules are proposed for UVA vertical-cavity surface-emitting laser diodes, and the modal gain and cavity properties are analyzed using an electro-optical numerical model. To achieve a low threshold current, it is important to align the gain-peak and resonance wavelengths, but the quantum-confined Stark effect makes that difficult because the former wavelength shifts with changing current density. The relationship between the gain peak and the injection current is discussed. Also, the quantum-well design affects the gain characteristics, and the gain properties with different quantum-well number, composition, and width are discussed.

Optical performances of 950 nm p-side up photonic crystal surface emitting lasers (PCSELs) with different types of air holes are numerically and experimentally investigated. Simulation results show an obvious distinction between effective index method and three dimensional finite-element method (FEM). Measured experiments including wavelength, threshold, and slope efficiency can well meet the FEM numerical predictions. It further reveals that the B mode dominates the laser action and the PCSELs accompanying with equilateral triangle and right isosceles triangle holes possess a lower threshold current and higher radiation than symmetric circle holes. The output power can be further enhanced by increasing the filling factor of air holes before the regrowth process.

The far-field interferometry is a well-established method of subsurface characterization, and it has traditionally been used to determine the dielectric properties and thickness of very low-loss subsurface materials, whose dimensions are comparable to the operating wavelength. However, this method is not very well suited for dielectrics with losses several orders high and, therefore, cannot be considered as a general method of subsurface characterization. In this article, we introduce a new idea of near-field interferometry, which can be used to characterize higher loss dielectrics with dimensions very low compared with the wavelength. It is shown that, in low frequencies, there is a noticeable variation in the field components with different medium dielectric properties and thickness, and these changes can be detected externally from near-field measurements by varying receiver distance and the operating frequency. The proposed method is tested on a lossy sea ice model in the presence of a horizontal electric dipole, and the variation in field magnitudes is observed for thickness up to 5 m. Since practical sea ice bulks have thicknesses of a similar range, the near-field interferometry appears to be a promising approach to determine sea ice thickness from noninvasive measurements.

We report Al0.3InAsSb/Al0.7InAsSb digital alloy n-barrier-n (nBn) photodetectors that operate in the 2-μm wavelength window. The AlxIn1-xAsySb1-y digital alloy material system exhibits near-zero valence-band offset, which is beneficial for nBn photodetectors. At 300 K these Al0.3InAsSb/Al0.7InAsSb nBn photodetectors have achieved specific detectivities of 1.7 × 10 10 and 3.0 × 10 10 Jones under 2-μm and 1.8-μm illumination, respectively. The dark current density at -0.5 V bias decreases from 3.1 × 10 -3 A/cm 2 at 300 K to 1.6 × 10 -10 A/cm 2 at 120 K, where the dominant dark current component is tunneling. The area-dependence of key performance parameters show that for mesa diameter ≤ 250 μm, surface defects assume a dominant role in the total noise.

Metal oxide-based plasmonics is an emergent field for which indium tin oxide (ITO) is a promising material. Improving the performance of ITO-based surface plasmon resonance (SPR) sensors requires a deeper knowledge of their optical and electrical properties. The effects of microstructural parameters and defects on mobility, which strongly influences SPR in the near-IR regime was explored. The proposed model incorporates different scattering mechanisms and non-parabolic conduction bands to obtain realistic values of mobility. The results show that larger grain sizes and higher carrier concentrations in ITO thin films improve SPR performance at near-IR wavelengths as low as 1300 nm

We present an X-ray-optical cross-correlator for the soft (> 150 eV) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature. Moreover, the cross-correlator can be employed on a 10 ps or 100 fs time scale featuring up to 50% total X-ray reflectivity and transient signal changes of more than 20%. (C) 2016 Author(s)., Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1331