Optoelectronics and Photonics

This paper investigates and enhances unmanned aerial vehicle (UAV) relay-assisted free-space optics (FSO) optical wireless communication (OWC) systems under the effects of pointing errors (PEs) and atmospheric turbulences (ATs). The incorporation of UAVs as buffer-aided moving relays in the conventional FSO (CFSO) relay-assisted systems is proposed for enhancing the performance of PEs through AT. Using M-PSK (phase shift keying) and M-QAM (quadrature amplitude modulation), the impact of PEs on transmission quality is evaluated in this work. We evaluate and optimize the symbol error rate, outage probability (OP), and signal-to-noise ratio (SNR) for the UAV-to-ground station-based FSO communications systems. The spatial diversity-based relay-assisted CFSO systems can enhance the performance of the UAV-UAV FSO links. In this paper, a new FSO (NFSO) channel model for the hovering UAV-FSO OWC fluctuations under the PEs, AT effects, jitter, deviation, receiving an error, and wind resistan...

In this paper, we intend to extend the bandwidth capabilities of Mach-Zehnder Modulators (MZMs) to unprecedented heights by innovatively integrating
Lithium Niobate (LiNbO3) on Silicon-on-Insulator (SOI) platforms, thus exploring the frontier of high-speed optical communication. on Insulator
(SOI) technology, Our goal is to push the capabilities of Mach Zehnder Modulators (MZMs) to heights. By harnessing the electro optic properties of
LiNbO3 and leveraging the reliability and scalability of silicon photonics we aim to meet the increasing needs in data centers and high-performance computing
systems. Through a design process that involves integrating a thin film LiNbO3 substrate layer [1-4] both below silicon waveguides and optimizing
the thickness of these layers to 850 nm for the active region we've achieved a significant improvement in modulation efficiency. Our innovative device
architecture features structured gold electrodes that make use of the linear electro optic effect in LiNbO3 for low voltage high speed modulation. The
strategic placement of these electrodes along with a designed titanium adhesion layer ensures interaction with the optical mode leading to maximum
modulation depth with minimal insertion loss. By incorporating SiO2 as a buffer layer beneath LiNbO3 substrate and as a cladding layer above the silicon
core we've enhanced confinement and reduced propagation losses thereby boosting device performance. This design does not meet the requirements
for low power consumption aiming for efficiency at the femtojoule per bit level but also offers a scalable solution for compact integration on silicon
platforms. At the core of our design is the optimization of the setup, where we introduce gold electrodes with geometries to precisely regulate
the modulating electric field. This is enhanced by a titanium layer acting as an adhesion promoter meticulously crafted to preserve the structure of the
electrodes while maintaining optical performance of the modulator. By conducting simulations and practical validations we showcase the potential to
achieve bandwidths of up to 250 GHz setting a standard for non-resonant MZM performance in integrated photonics. This research does not signify an
advancement in optical modulation but also unlocks new possibilities for creating energy efficient high speed photonic electronic interfaces paving the
path for innovative optical connections in future technology.

We  investigate and  evaluate  the optical  performance  of high-and  low-RI cladding contrast Bragg fiber for two design wavelengths: 1550 nm (in the near-infrared  region)  and  632.8  nm  (in  the  visible  range).  In  order  to establish  a  connection  between  the  incoming  and  outgoing  light  waves using  the  transfer  matrix  technique,  the  boundary  matching  approach  is used. Less periodic cladding layers are needed to create a perfect photonic band gap (PBG), and the measured PBG in high RI cladding contrast Bragg fiber  (HRCCBF)  are  rather  large.  Both  low  refractive  index  and  high refractive  index  spectra  of  PBG  Cladding  contrast  Bragg  fiber  (LRCCBF) performance is very sensitive to the incoming light's optical path, or angle of  incidence.  One  way  to  find  out  how  sensitive  the  Bragg  fiber  is  for sensing applications is to measure the PBG's thickness or spectral shift. As the design wavelength increases, the spectral bandwidth of PBG with core RI  changes,  and  HRCCBF  seems  to  be  quite  sensitive  to  this  shift.  When taking  the Left  Band  Edge  (LBE)  and  the  Right  Band  Edge  (RBE)  into account,  LRCCBF  is  much  more  sensitive  than  HRCCBF,  making  it  the better choice for sensing applications.
Keywords:Bragg Fiber, Transfer Matrix Method, Photonic Band Gap, High Contrast, Design Wavelength

Present    investigation    deals    with    the    electromagnetic    (EM)    wave propagation  through  the  asymmetrical  (distorted)  conventional  optical fiber and extended the investigation for the distorted multilayered hollow Bragg  Fiber.  For  this  purposed  theoretical  and  mathematical  are  well connected to investigate and further discuss the wave propagation through such distorted structure so that further many useful parameters like optical power, different losses, dispersion analysis, etc. can be computed easily by the  researchers  in  the  same  area.    In  present  study,  the  dispersion properties of an optical fiber with a little one-sided flattening are modelled using  a  straightforward  mathematical  approach  that  relies  on  coordinate transformation.  In  order  to  derive  the  modal  eigenvalue  equation,  we provide  the  boundary  condition  under  a  weak  guiding  condition  and choose  new  orthogonal  coordinates  that  are  suitable  for  the  suggested waveguide  construction.  Further,  a  distorted  Bragg  fiber  with  a  little flattened  distortion  is  anticipated  to  have  dispersion  characteristics  by comparing the fields at different boundaries.
Keywords:Distorted  Optical  Fiber,  Distorted  Bragg  Fiber,  Theoretical Modeling, Mathematical Modeling, Hankel Functions.

A five-layered Kretschmann configuration-based novel structure is designed for a highly sensitive surface plasmon resonance (SPR) sensor. An adhesion layer of magnesium oxide (MgO) is employed on the BK7 prism to avoid the adverse effects of metallic layers, which cause SPR broadening and a decrease in the resonance magnitude. A few layers of black phosphorus (BP) on top of the silver (Ag) metal layer are added to complete the structure, which becomes the BK7/MgO/Ag/BP configuration. The investigation is carried out using attenuated total reflection (ATR), while the widely used transfer matrix method (TMM) is applied to evaluate the performance of the SPR sensor. A separate analysis is performed using three thicknesses, 5 nm, 10 nm, and 15 nm of MgO, an optimized thickness of 40 nm of Ag, and eight layers of BP. The results revealed that the configuration BK7/MgO (10 nm)/Ag (40 nm)/BP (8 layers) delivers a maximum sensitivity (S) of 234°RIU−1. Moreover, the configuration BK7/MgO (5 ...

Quaternary LiNiVO 4 is a superb cathode material in lithium-ion batteries. There is, however, a lack of knowledge about the possibility of using it in other application areas. Therefore, the researchers attempted to fill in the knowledge gap regards to the possibilities of using it in other technologies. LiNiVO 4 thin films were sprayed using the spray pyrolysis technique. The investigated films have revealed interesting optical and optoelectrical properties. Besides, ethanol-sensing properties have been examined via DC measurements. The change in working temperatures is found to affect the degree of material's sensitivity. Furthermore, the effect of film thickness on a layer's sensibility has been tested. This has enabled us to explain the mechanisms of ethanol vapor interaction. In light of the obtained results, we could expect the rising of novel properties of these quaternary films. This would pave the way for using such interesting material in optoelectronic devices and/or gas sensors devices.

Novel thin films of CuInSn3S8 (CISS8) have been synthesized using the spray pyrolysis approach. This is the first time to prepare such interesting material which could be an up-and-coming candidate in the transparent conductive thin films family. Basic characterizations have been employed to inspect the nature and morphology of the deposited films. The film’s surface is quite uniform and homogeneous. Also, they are polycrystalline with a monoclinic structure. Furthermore, the network topology of CuInSn3S8 material has been investigated to understand its compactness nature. This has been achieved through evaluating several interesting indices such as density, molar volume, free volume percentage, packing density, compactness, and lone-pair of electrons. In addition, linear/nonlinear optical and optoelectrical properties have been studied. Films have revealed a wide energy gap that varies between (3.86 and 3.79 eV) with the direct optical transition. Moreover, they have presented high infrared reflectance, adequate optical transmittance within the visible spectrum, and the tendency of being n-type semiconductors. Besides, films have exhibited high values of optical conductivity and nonlinear optical parameters. A satisfactory linkage has been made betwixt all of the determined indices either the structural, network topology, and optical/optoelectrical ones. The obtained findings refer to the rising of a new star on the horizon of photovoltaic and optoelectronic applications fields.

Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy from fiber lasers. We develop a robust, scalable, and distributed digital control system with firmware and software integration for algorithms, to support the CPS application. We model CPS as a digital filter in the Z domain and implement a pulse-pattern-based cavity phase detection algorithm on an fieldprogrammable gate array (FPGA). A two-stage (2+1 cavities) 15-pulse stacking system achieves an 11.0 peak-power enhancement factor. Each optical cavity is fed back at 1.5 kHz, and stabilized at an individually-prescribed round-trip phase with 0.7 deg and 2.1 deg rms phase errors for Stages 1 and 2, respectively. Optical cavity phase control with nanometer accuracy ensures 1.2% intensity stability of the stacked pulse over 12 h. The FPGA-based feedback control system can be scaled to large numbers of optical cavities.

Negative curvature fibre (NCF) guides light in its core by inhibiting the coupling of core and cladding modes. In this work, an NCF was designed and fabricated to transmit ultrashort optical pulses for multiphoton microscopy with low group velocity dispersion (GVD) at 800 nm. Its attenuation was measured to be <0.3 dB.m-1 over the range 600-850 nm and the GVD was-180±70 fs 2 .m-1 at 800 nm. Using an average fibre output power of ~20 mW and pulse repetition rate of 80 MHz, the NCF enabled pulses with a duration of <200 fs to be transmitted through a length of 1.5 m of fibre over a tuning range of 180 nm without the need for dispersion compensation. In a 4 m fibre, temporal and spectral pulse widths were maintained to within 10% of low power values up to the maximum fibre output power achievable with the laser system used of 278 mW at 700 nm, 808 mW at 800 nm and 420 mW at 860 nm. When coupled to a multiphoton microscope, it enabled imaging of ex vivo tissue using excitation wavelengths from 740 nm to 860 nm without any need for adjustments to the setup .

w Gliwicach-fizyka techniczna. Obecnie jest adiunktem w Katedrze Optoelektroniki Wydziału Elektrycznego. W pracy naukowej zajmuje się projektowaniem i technologią wytwarzania elementów i układów optyki zintegrowanej do zastosowań w planarnych czujnikach światłowodowych pracujących w oparciu o spektroskopię pola zanikającego. Jest autorem i współautorem ponad 100 publikacji naukowych.

Three dimensional images were obtained using a single high numerical aperture hologram recorded in a high resolution photoresist with a table top α = 46.9 nm laser. Gabor holograms numerically reconstructed over a range of image planes by sweeping the propagation distance allow numerical optical sectioning that results in a robust three dimension image of a test object with a resolution in depth of approximately and a lateral resolution of 164 nm.

The influence of Na on Cu(In,Ga)Se2 (CIGS) solar cells was investigated. A gradient profile of the Na in the CIGS absorber layer can induce an electric field modulation and significantly strengthen the back surface field effect. This field modulation originates from a grain growth model introduced by a combination of alloy-hardening and pair-annihilation probabilities, wherein the Cu supply and Na diffusion together screen the driving force of the grain boundary motion (GBM) by alloy hardening, which indicates a specific GBM pinning by Cu and Na. The pair annihilation between the ubiquitously evolving GBMs has a coincident probability with the alloy-hardening event. PACS: 88. 40. H-, 81. 10. Aj, 81. 40. Cd,

Bladder cancer is among the most common cancers in the UK and conventional detection techniques suffer from low sensitivity, low specificity, or both. Recent attempts to address the disparity have led to progress in the field of autofluorescence as a means to diagnose the disease with high efficiency, however there is still a lot not known about autofluorescence profiles in the disease. The multi-functional diagnostic system &quot;LAKK-M&quot; was used to assess autofluorescence profiles of healthy and cancerous bladder tissue to identify novel biomarkers of the disease. Statistically significant differences were observed in the optical redox ratio (a measure of tissue metabolic activity), the amplitude of endogenous porphyrins and the NADH/porphyrin ratio between tissue types. These findings could advance understanding of bladder cancer and aid in the development of new techniques for detection and surveillance.

In this work, we have substantially improved the measured signal-to-noise S/N ratio and Q-factors in a four-wave mixed  (FWM)  converted  wavelength  signal  in  a  dual  semiconductor  optical  amplifier  (SOA)  arrangement  by saturating  each  SOA  component  in  an  optical  fibre  communications  link.  The  results  show  considerable improvements in both measurands of the converted signal by virtue of SOA gain saturation.
Keywords: semiconductor optical amplifier (SOA), four-wave mixing (FWM), signal-to-noise ratio (S/N)

Solution-processed phototransistors can substantially advance the performance of image sensors. Phototransistors exhibit large photoconductive gain and a sublinear responsivity to irradiance, which enables a logarithmic sensing of irradiance that is akin to the human eye and has a wider dynamic range than photodiode-based image sensors. Here, we present a novel solution-processed phototransistor composed of a heterostructure between a high-mobility organic semiconductor and an organic bulk heterojunction. The device efficiently integrates photogenerated charge during the period of a video frame then quickly discharges it, which significantly increases the signal-to-noise ratio compared with sampling photocurrent during readout. Phototransistor-based image sensors processed without photolithography on plastic substrates integrate charge with external quantum efficiencies above 100% at 100 frames per second. In addition, the sublinear responsivity to irradiance of these devices enables a wide dynamic range of 103 dB at 30 frames per second, which is competitive with state-of-the-art image sensors.

This paper investigates and enhances unmanned aerial vehicle (UAV) relay-assisted free-space optics (FSO) optical wireless communication (OWC) systems under the effects of pointing errors (PEs) and atmospheric turbulences (ATs). The incorporation of UAVs as buffer-aided moving relays in the conventional FSO (CFSO) relay-assisted systems is proposed for enhancing the performance of PEs through AT. Using M-PSK (phase shift keying) and M-QAM (quadrature amplitude modulation), the impact of PEs on transmission quality is evaluated in this work. We evaluate and optimize the symbol error rate, outage probability (OP), and signal-to-noise ratio (SNR) for the UAV-to-ground station-based FSO communications systems. The spatial diversity-based relay-assisted CFSO systems can enhance the performance of the UAV-UAV FSO links. In this paper, a new FSO (NFSO) channel model for the hovering UAV-FSO OWC fluctuations under the PEs, AT effects, jitter, deviation, receiving an error, and wind resistan...

Glass composition ZnO-MnO2-B2O3 containing different contents of ZnO (0, 10, 20, 30, and 40, all in wt. %) were prepared by a popular melt-quenching method. The prepared glasses were characterized by xray diffraction (XRD) and differential thermal analysis (DTA) studies. Infrared (IR) and dielectric studies were also carried out for the prepared glasses. From DTA studies of these glasses, glass forming ability parameter, Kgl and other stability factors were calculated and presented. From IR studies, variations in intensities of various IR band positions were studied and presented. Parameters, which describe the insulating characteristics, such as dielectric constant, , dielectric loss, tan, and ac conductivity, ac were determined as a function of frequency (10 3 Hz to 10 5 Hz) and temperature (30 o C to 250 o C) and presented from the dielectric analysis of these glasses.

Physicoelectrical properties like density, dielectric properties, optical absorption and infrared absorption data are presented for borophosphate glasses doped with nickel ions. Standard samples of ZnO-B 2 O 3-P 2 O 5 glass system were prepared by the melt quenching technique in the compositional series containing 0.2, 0.4, 0.6, 0.8, and 1.0 mol % of nickel. The dc conductivity for these samples measured in the temperature range 473−623 K. The analysis of dc conductivity, electrical conductivity is affected by the structural change. The electronic conduction seems to be dominant in the higher concentration range. From the optical absorption and IR spectral studies, nickel ions prefer to occupy both tetrahedral and octahedral positions in the glass network; compare to tetrahedral, octahedral positions seems to dominate when the concentration of NiO is raised above 0.6 mol% in the glass matrix.

Thermoluminescence (TL) characteristics of X-ray irradiated pure and doped with four different rare earth ions (viz., Pr 3+ , Nd 3+ , Sm 3+ and Eu 3+) lithium borate glasses mixed with the three different modifiers ZnO, CaO and CdO have been studied in 303-573 K. All the pure glasses have exhibited single thermoluminescence peak at 382, 424 and 466 K, respectively. When these glasses are doped with different rare earth ions no additional peaks are observed but the glow peak temperature of the existing glow peak shifted gradually towards higher temperatures with gain in intensity of thermoluminescence light output. The area under the glow curve is also found to be maximum for Eu 3+ doped glasses. The glasses containing CdO as modifier have exhibited the maximum thermoluminescence light output. The trap depth parameters associated with the observed thermoluminescence peaks have been evaluated using Chen's formulae. The possible use of these glasses in radiation dosimetry has been described.

PbO-B 2 O 3 glasses containing different concentrations of MoO 3 ranging from 0 to 4 mol% were prepared. The dielectric properties (constant 3 0 , loss tan d, a.c. conductivity s ac over a range of frequency and temperature and breakdown strength) of these glasses have been studied. The results of these studies were analyzed with the aid of data on optical absorption, magnetic susceptibilities, ESR and IR spectra of these glasses. The analysis suggests that the molybdenum ions exist in Mo 5C state with Mo(V)O 3K complexes that act as modifiers in addition to Mo 6C state with MoO 4 and MoO 6 structural groups in these glasses. Further the Mo(V)O 3K complexes were identified to exhibit dipolar relaxation effects.

The development of modern electronics bases on the usage of the materials of refined properties. One of the group of materials displaying such properties are smart materials. In contrast to traditional materials, the smart ones change their properties under the influence of external forces. Owing to that, they simultaneously perform the function of a sensor and actuator. The sine qua non of having such properties is the appearance of nonlinear effects. The work involves the results of measurements and analyses of nonlinear dielectric properties of a wide range of ferroic crystals. The nonlinear properties of ferroelectrics with continuous or discontinuous ferroelectric phase transitions and ferroelectric relaxors were presented and compared. Among relaxors both canonic relaxors, i.e. the ones in which a spontaneous macroscopic structural phase transition does not take place, and those in which spontaneous phase transitions do occur were considered. The results obtained for ferroelec...

III-Nitride light emitting diodes (LEDs) are the backbone of ubiquitous lighting and display applications. Imparting directional emission is an essential requirement for many LED implementations. Although optical packaging 1 , nano-patterning 2,3 and surface roughening 4 techniques can enhance LED extraction, directing the emitted light requires bulky optical components. Optical metasurfaces provide precise control over transmitted and reflected waveforms, suggesting a new route for directing light emission. However, it is difficult to adapt metasurface concepts for incoherent light emission, due to the lack of a phase-locking incident wave. In this Letter, we demonstrate metasurface-based design of InGaN/GaN quantum-well structures that generate narrow, unidirectional transmission and emission lobes at arbitrary engineered angles. We show that the directions and polarization of emission differ significantly from transmission, in agreement with an analytical Local Density of Optical States (LDOS) model. The results presented in this Letter open a new paradigm for exploiting metasurface functionality in light emitting devices. Light emitting diodes (LED) are rapidly enabling solid-state solutions to commercial lighting applications. Imparting unidirectionality to LEDs is a challenging, problem with a host of applications 5-7 awaiting a scalable solution. Directional emission is naturally observed in lasing systems, 13,14 where all of the resonators are emitting coherently. By modifying the local density

Due to high demand of debris free and high conversion efficiency target for EUV lithography source, We introduce in this article Low-density nanomaterials tin dioxide and tin mono oxide targets for this source. The targets were prepared by refluxing and hydrothermal methods using SnCl2. 2H2O as a precursor. SnO2 spheres like and SnO sheets like images were observed from scanning electron microscopy. The crystal structures of SnO2 and SnO were confirmed by X-Ray diffractions. EUV signal from SnO target at low Nd:YAG energy pulses were more stronger than SnO2.

In 1964, just a few years after the invention of the laser, a fluid velocity measurement based on the frequency shift of scattered light was made and the laser Doppler technique was born. This comprehensive review paper charts advances in the development and applications of laser Doppler vibrometry (LDV) since those first pioneering experiments. Consideration is first given to the challenges that continue to be posed by laser speckle. Scanning LDV is introduced and its significant influence in the field of experimental modal analysis described. Applications in structural health monitoring and MEMS serve to demonstrate LDV's applicability on structures of all sizes. Rotor vibrations and hearing are explored as examples of the classic applications. Applications in acoustics recognise the versatility of LDV as demonstrated by visualisation of sound fields. The paper concludes with thoughts on future developments, using examples of new multi-component and multichannel instruments.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A five-layered Kretschmann configuration-based novel structure is designed for a highly sensitive surface plasmon resonance (SPR) sensor. An adhesion layer of magnesium oxide (MgO) is employed on the BK7 prism to avoid the adverse effects of metallic layers, which cause SPR broadening and a decrease in the resonance magnitude. A few layers of black phosphorus (BP) on top of the silver (Ag) metal layer are added to complete the structure, which becomes the BK7/MgO/Ag/BP configuration. The investigation is carried out using attenuated total reflection (ATR), while the widely used transfer matrix method (TMM) is applied to evaluate the performance of the SPR sensor. A separate analysis is performed using three thicknesses, 5 nm, 10 nm, and 15 nm of MgO, an optimized thickness of 40 nm of Ag, and eight layers of BP. The results revealed that the configuration BK7/MgO (10 nm)/Ag (40 nm)/BP (8 layers) delivers a maximum sensitivity (S) of 234°RIU−1. Moreover, the configuration BK7/MgO (5 ...

Various configurations have been conceived and tested for improvement of the gain and noise figures in Erbium doped fiber amplifiers (EDFA’s). Single pass (SP), double pass (DP), triple pass (TP) and quadruple pass (QP), are employed in the investigation. The highest gain and highest noise figure (NF) of 54dB and 7dB respectively are obtained at -50 dBm input power with 90 mW pump power using the QP configuration, while and the lowest gain of 23dB and lowest NF of 3dB are obtained at -50 dBm input power with 90 mW pump power for SP configuration.

We report an accurate and simple numerical matrix technique for the analysis of ARROW (anti‐resonant and reflecting optical waveguides). All the relevant parameters for the structure of the ARROW have been studied. The accuracy of the method has been established by comparing results with previously reported exact results. The technique proves to be a powerful tool for the design of complicated devices on the ARROW, thereby providing an accurate design tool for scaling a large number of devices on the ARROW chip.

Two types of monomers, 4,4 0-(hexafluoroisopropylidene) diphthalic anhydride and 4,4 0-oxydianiline, were employed to synthesize poly(amic acid) (PAA) as a precursor of polyimide (PI). Through the addition of modified metallocene cyclic olefin copolymer (mCOC), PAA/mCOC composites were formed. PI/mCOC composites were obtained through a blade coating and multistep thermal curing process. The structure of the prepared PI/mCOC composites was characterized through Fourier transform infrared spectrometry. The results showed that the copolymerization of PAA and modified mCOC improved thethermal stability and hydrophobic and electrical properties of the PI/mCOC composites. The formation of a network structure between PI and modified mCOC considerably reduced the mobility of PI molecules, thereby improving the glass transition temperature and thermal properties of the composite. The thermal and hydrophobic properties were improved by increasing the mCOC grafting ratio. V

We present the first chip-scale &quot;integrated optical driver&quot; (IOD) that can interrogate with a sensing coil to realize an interferometric optical gyroscope. The chip comprises a light source, three photodiodes, two phase modulators and two 3-dB couplers within an area of 4.5 mm&lt;sup&gt;2&lt;/sup&gt;. This allows for a significant reduction in size, weight, power consumption and cost of optical gyroscopes.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Nano-crystalline gadolinium doped tin oxide thin films were prepared by the spray pyrolysis method. The effect of doping concentration on its micro-structural, optical and gas sensing properties was reported. The grain size of the prepared films ranges from ~13 to 28 nm. The effective doping of gadolinium was confirmed by EDX and elemental mapping. The optical transmission and band gap were reduced as the concentration of doping increases. The electron concentration, Hall coefficient, and refractive index were examined. High gas sensing of ammonia was observed and the effect of doping concentration was reported.

A new method for the long-term frequency stabilization of an opto-electronic oscillator (OEO) is proposed. All existing methods are based on the precise temperature stabilization of specific components of an OEO, for example, the optical fiber and the microwave band-pass filter. We propose a new method based on a feedback control loop that detects the oscillator frequency using a frequency discriminator and modifies the laser wavelength to keep the oscillator frequency constant using the fiber chromatic dispersion. With the proposed method we achieved a frequencytemperature coefficient of 0.2 ppm/K. Unlike previous methods, our method also compensates the effects of other unstabilized OEO components on the OEO's frequency. Other benefits are that there is no need for an accurate temperature stabilization of the optical fiber and mode hopping is prevented.

We present two stabilization methods for an optoelectronic oscillator. By using a frequency discriminator with a feedback control loop the long-term stabilization was improved and a frequency drift of 0.05 ppm/K was achieved without any fiber thermal stabilization. In addition, the phase-noise degradation as a result of the discriminator control loop was investigated. To the best of our knowledge, this has not been done before for this type of method. Our study revealed that a properly designed control loop does not increase the phase noise. The second stabilization method was used to increase the sidemode suppression ratio. This was achieved with an additional control loop in the form of an oscillator-loop phase modulation. In this way a 5-dB increase in the side-mode suppression ratio was recorded. The phase-noise degradation was less than 1 dB in the close-in region. The two methods were designed to operate simultaneously. This design provides both simplicity and cost effectiveness for the stabilized opto-electronic oscillator.

We study properties of a p-polarized surface plasmon polariton propagating circumferentially around a portion of a cylindrical interface between a vacuum and a metal, a situation investigated earlier by Berry (J. Phys. A: Math. Gen. 8 (1975) 1952). When the metal is convex toward the vacuum this mode is radiative and consequently is attenuated as it propagates on the cylindrical surface. An approximate analytic solution of the dispersion relation for this wave is obtained by an approach different from the one used by Berry, and plots of the real and imaginary parts of its wave number are presented. When the metal is concave to the vacuum, the resulting dispersion relation possesses a multiplicity of solutions that have the nature of waveguide modes that owe their existence to the curvature of the interface.

Two-terminal devices are building blocks for modern electronic systems. However, the typical two-terminal architecture can limit functionality and performance. Here we report a multifunctional three-terminal diode that consists of a traditional two-terminal gallium nitride-based p‒n diode with a monolithically integrated third terminal (Tt) composed of metal/Al2O3 dielectric layer directly on the p-layer. When the three-terminal diode operates as an emitter, the light intensity can be tuned by adjusting the bias applied to the Tt, and its modulation bandwidth can be increased from 160 MHz in the original p‒n diode to 263 MHz due to the integrated bias tee function enabled by the Tt. When it operates as a photodetector, both the applied voltage on the Tt and the incident light act as signal inputs that control the magnitude of output photocurrent, providing reconfigurable optoelectronic NAND and NOR logic gates.

Vascular responses were monitored to understand the role of the microvasculature in tumor destruction as a result of photodynamic therapy (PDT). Rats received an intravenous dose of 2 mg/kg Benzoporphyrin Derivative (BPD), at 20 min, 4 h, or 7 h before laser irradiation. With Photofrin (10 mg/kg), drug-light intervals were 20 min or 8 h. Jejunal blood vessels were exposed to 12 J/cm 2 at 690 nm (with BPD) or at 630 nm (with Photofrin). Optical Doppler tomography (ODT) was used to evaluate PDT-induced changes in vessel diameter and blood flow. At the shortest drug-light time interval (20 min), BPD-mediated PDT caused transient constriction of arteries, accompanied by decreased blood flow, followed by vasodilation until baseline was reached or overshoot occurred. Veins became occluded with no restoration of the vessel lumen. At longer drug-light intervals, vasoconstriction diminished and venodilation was observed. With Photofrin, vasoconstriction and venodilation increased with the drug-light interval. Application of a higher light dose (48 J/cm 2) resulted in irreversible hemostasis. ODT can be used to study changes in lumen diameter and blood flow, which are important diagnostic parameters of PDT.

We propose an angular offset technique for launching optical signals into multimode fibers (MMFs) used in short distance optical fiber links. The signal is launched onto the angled facet of an MMF. The presented method shows better bandwidth enhancement in little power penalty. This method is simple and can be easily adopted in transmitters for high-speed MMF links.

The paper report new results of chromatic dispersion in Photonic Crystal Fibers (PCFs) through appropriate designing of index-guiding triangular-lattice structure devised, with a selective infiltration of only the first air-hole ring with index-matching liquid. Our proposed structure can be implemented for both ultra-low and ultra-flattened dispersion over a wide wavelength range. The dependence of dispersion parameter of the PCF on infiltrating liquid indices, hole-to-hole distance and air-hole diameter are investigated in details. The result establishes the design to yield a dispersion of 0+-0.15ps/ (nm.km) in the communication wavelength band. We propose designs pertaining to infiltrating practical liquid for near-zero ultra-flat dispersion of D=0+-0.48ps/ (nm.km) achievable over a bandwidth of 276-492nm in the wavelength range of 1.26 {\mu}m to 1.80{\mu}m realization.

In this article, we've theoretically investigated the application of selective liquid infiltration towards realizing birefringent Photonic Crystal Fiber (PCF) and its operation in the single mode region. Birefringence has been created in a symmetrical structure PCF by infiltrating liquid of certain refractive indices in diagonally opposite air-holes. Different air-hole fraction along with different infiltrating refractive indices has been considered towards studying the effect of the parameters towards birefringence and loss. Cutoff properties for different infiltrating liquid has been performed and it has been found that PCF infiltrated with higher Refractive Indices (RI) liquid is suitable for broader range of single mode operation. The present structure provides very low loss and that can also be minimized with higher number of air-hole rings without affecting the birefringent property. Tunability property of the infiltrating liquid for various temperatures has been studied. By varying the refractive indices of the infiltrating liquid the birefringence can be well tuned. Our research will be useful in designing a birefringent PCF from conventional symmetrical PCF by infiltrating liquids in two diagonally opposite air-holes and proper choice of PCF parameter for single mode operation at a desired wavelength of interest.

Conjugated polymers are increasingly exploited for biomedical applications. In this work, we explored the optical characteristics of conjugated polymers of variable chemical structures at multiple levels relevant to biological interfacing, from fluorescence yield to their influence on cellular membrane potential. We systematically compared the performance of conjugated polymer as cast thin films and as nanoparticles stabilized with amphiphilic polyethylene glycol-poly lactic acid-co-glycolic acid (PEG-PLGA). We assessed in both the dark and under illumination the stability of key optoelectronic properties in various environments, including air and biologically relevant physiological saline solutions. We found that photoreduction of oxygen correlates with nanoparticle and film degradation in physiologically relevant media. Using patch-clamp recordings in cell lines and primary neurons, we identified two broad classes of membrane potential response, which correspond to photosensitizer...

Dark-field microscopy is a standard imaging technique widely employed in biology that provides high image contrast for a broad range of unstained specimens1. Unlike bright-field microscopy, it accentuates high spatial frequencies and can therefore be used to emphasize and resolve small features. However, the use of dark-field microscopy for reliable analysis of blood cells, bacteria, algae, and other marine organisms often requires specialized, bulky microscope systems, and expensive additional components, such as dark-field-compatible objectives or condensers2,3. Here, we propose to simplify and downsize dark-field microscopy equipment by generating the high-angle illumination cone required for dark field microscopy directly within the sample substrate. We introduce a luminescent photonic substrate with a controlled angular emission profile and demonstrate its ability to generate high-contrast dark-field images of micrometre-sized living organisms using standard optical microscopy equipment. This new type of substrate forms the basis for miniaturized lab-on-chip dark-field imaging devices, compatible with simple and compact light microscopes.