Temperature and refractive index sensing characteristics of an MZI-based multimode fiber–dispersion compensation fiber–multimode fiber structure

We proposed an optical fiber sensor with simple multimode fiber (MMF)–dispersion compensation fiber (DCF)–multimode fiber structure based on Mach–Zehnder Interferometer (MZI) and researched its temperature and refractive index (RI) sensing characteristics. The sensing principle is based on the interference between core and cladding modes of DCF due to the large core diameter mismatch. Spectral analyses demonstrate that the transmission spectrum is mainly formed by the interference between the dominant excited cladding mode and core modes. The experimental results show that the proposed sensor has high temperature sensitivity of 0.118 nm/°C in the range of 20–250 °C and RI sensitivity of 66.32 nm/RIU within the linear sensing range of 1.33–1.39 RIU. Therefore, the characteristics of compact size, low cost, easy fabrication, high sensitivities, and good anti-interference ability make this sensor have extensive application prospects.     

Optical fiber relative-humidity sensor with evaporated dielectric coatings on fiber end-face

An optical fiber relative-humidity sensor (OFRHS) with evaporated dielectric coatings is proposed and demonstrated. The sensitive coatings, composed of multilayers of Ti₃O₅ and SiO₂, form an extrinsic Fabry–Perot cavity on the distal end of the multimode fiber. As the effective refractive index of the porous coatings were correlated with the change of ambient Relative-humidity (RH), which will at last result in the shift of interference fringe. By monitoring the drift of reflected interference fringe under different RH levels, the information about RH of the environment under test can be extracted. Experimental results show that the average sensitivity is 0.43 nm/% RH when environmental RH changes from 1.8% RH to 74.7% RH. The proposed sensor was proved to be high repeatability, little hysteresis and especially highly sensitive to lower moisture measure.     

Concentration sensor based on a tilted fiber Bragg grating for anions monitoring

The ubiquity and importance of anions in many crucial roles accounts for the current high interest in the design and preparation of effective sensors for these species. Therefore, a tilted fiber Bragg grating sensor was fabricated to investigate individual detection of different anion concentrations in ethyl acetate, namely acetate, fluoride and chloride. The influence of the refractive index on the transmission spectrum of a tilted fiber Bragg grating was determined by developing a new demodulation method. This is based on the calculation of the standard deviation between the cladding modes of the transmission spectrum and its smoothing function. The standard deviation method was used to monitor concentrations of different anions. The sensor resolution obtained for the anion acetate, fluoride and chloride is 79 × 10⁻⁵ mol/dm³, 119 × 10⁻⁵ mol/dm³ and 78 × 10⁻⁵ mol/dm³, respectively, within the concentration range of (39–396) × 10⁻⁵ mol/dm³.     

A highly nonlinear photonic quasi-crystal fiber with low confinement loss and flattened dispersion

We proposed a novel photonic quasi-crystal fiber with near-zero flattened dispersion, highly nonlinear coefficient, and low confinement loss by using the dual concentric core structure. By optimizing the structure parameter, the proposed photonic quasi-crystal fiber can achieve a nonlinear coefficient larger than 33 W⁻¹ km⁻¹ and near-zero flatten dispersion of 0 ± 3.4 ps/nm/km with a near-zero dispersion slope of 8.5 × 10⁻³ ps/nm²/km at the wavelength of 1550 nm. Near-zero flattened dispersion and low confinement loss in the ultralow order of 10⁻⁷ dB/m are simultaneously obtained in the wavelength range from 1373 to 1627 nm. Furthermore, two zero dispersion wavelengths can be achieved in a wide wavelength ranger from 1373 to 1725 nm. From the point of view of practical fabrication, the influence of deviation of each air hole diameter within 3% of imperfections on dispersion, nonlinearity, and is discussed to verify the robustness of our design.     

Long-period grating inscription in hydrogen-free SMF-28 fiber by high-repetition-rate femtosecond UV pulses

Using femtosecond UV (258 nm) pulses, generated at high-repetition-rate (50 kHz), we managed to record high-quality long-period gratings in a number of fibers, including a standard telecommunication one, SMF-28. Along with the main grating, connected to the refractive index change in the fiber core, at the relatively high intensity of the inscribing UV radiation, I ～ 1.5 TW/cm², we recorded the formation of an additional long-period grating, based on the refractive index change induced in the fiber cladding. We have compared the temperature sensitivity and the thermal stability of both gratings.     

Tailoring chromatic dispersion in chalcogenide–tellurite microstructured optical fiber

We report fabrication of a highly nonlinear hybrid microstructured optical fiber composed of chalcogenide glass core and tellurite glass cladding. The flattened chromatic dispersion can be achieved in such an optical fiber with near zero dispersion wavelength at telecommunication wavelengths λ = 1.35–1.7 μm, which cannot be achieved in chalcogenide glass optical fibers due to their high refractive index, i.e. n > 2.1. We demonstrate a hybrid 4-air hole chalcogenide–tellurite optical fiber (Δn = 0.25) with flattened chromatic dispersion around λ = 1.55 μm. In optimized 12-air hole optical fiber composed of the same glasses, the chromatic dispersion values were achieved between −20 and 32 ps/nm/km in a broad wavelength range of 1.5–3.8 μm providing the fiber with extremely high nonlinear coefficient 86,000 km⁻¹W⁻¹. Hybrid chalcogenide/tellurite fibers pumped with the near infrared lasers give good promise for broadband optical amplification, wavelength conversion, and supercontinuum generation in the near- to mid-infrared region.     

Simultaneous measurement of strain and temperature based on a long-period grating with a polarization maintaining fiber in a loop mirror

Simultaneous measurement of strain and temperature using a long-period grating (LPG) and a polarization maintaining fiber (PMF) in a fiber loop mirror (FLM) is presented. The sensing head is formed by an LPG. The transmitted optical intensity from the FLM is linear with the variation of the strain. And the interference resonant dip has a blue shift with the increasing of the temperature. Experimental results show that the proposed sensor has the sensitivities of 0.0346 nm/°C and 1.82 × 10⁻³ dB/με within the strain range of 0–1300 με, respectively.     

A low power dissipation high-speed CMOS image sensor with column-parallel sigma–delta ADCs

A 60frames/s CMOS image sensor with column-parallel inverter-based sigma–delta (ΣΔ) ADCs is proposed in this paper. In order to improve the robustness of the inverter, instead of constant power supply, two buffers are designed to provide power supply for inverters. Instead of using of an operational amplifier, an inverter-based switch-capacitor (SC) circuit is adopted to low-voltage low-power ΣΔ modulator. Detailed analysis and design optimization are provided. Due to the use of the inverter-based ΣΔ ADCs, the conversion speed is improved while reducing the area and power consumption. The proposed CMOS image sensor has been fabricated with 0.18 μm CMOS process. The measurement results show that the random noise (RN) is 7e_rms⁻, the pixel conversion gain is 100 μV/e⁻. Since the measured full well capacity of the pixel is 25000e⁻, the CMOS image sensor achieves a 71 dB dynamic range (DR). The total power consumption at 60frame/s is 58.2 mW.     

The effect of annealing on the physical properties of thermally evaporated CuIn2n+1S3n+2 thin films (n=0, 1, 2 and 3)

In this study, the annealing effect on structural, electrical and optical properties of CuIn_2n+1S_3n+2 thin films (n=0, 1, 2 and 3) are investigated. CuIn_2n+1S_3n+2 films were elaborated by vacuum thermal evaporation and annealed at 150 and 250 °C during 2 h in air atmosphere. XRD data analysis shows that CuInS₂ and CuIn₃S₅ (n=0 and 1) crystallize in the chalcopyrite structure according to a preferential direction (112), CuIn₅S₈ and CuIn₇S₁₁ (n=2 and 3) crystallize in the cubic spinel structure with a preferential direction (311). The optical characterization allowed us to determine the optical constants (refractive indexes 2.2–3.1, optical thicknesses 250–500 nm, coefficients of absorption 10⁵ cm^?1, coefficients of extinction <1, and the values of the optical transitions 1.80–2.22 eV) of the samples of all materials. We exploited the models of Cauchy, Wemple–DiDomenico and Spitzer–Fan for the analysis of the dispersion of the refractive index and the determination of the optical and dielectric constants.     

On the performance of the 2D planar metamaterial structure

The performance of a 2D metamaterial (MTM) structure using finite element method (FEM) and transmission line model (TLM) is investigated in this paper. The size of the proposed unit cell is 4 mm × 4 mm to resonant around 12 GHz. The unit cell is constructed from a patterned patch and solid ground plane that are connected with via through an FR-4 substrate. The unit cell is characterized from 11 GHz to 14 GHz in terms of S-parameters, effective refractive index, and dispersion properties. It is found that the proposed unit cell behaves like unbalanced case of a passive constant k band elimination filter. Moreover, it is found that the unit cell exhibits no negative refractive index (NRI) over a wide range of frequencies; however, it shows a less than 1 refractive index over then same frequency range. A theoretical investigation based on TLM is developed to extract the values of the basic lumped, RLC, elements network.     

Characterization of ternary MgxZn1−xO thin films deposited by electron beam evaporation

Mg_xZn_1−xO (0≤x≤1) thin films were deposited on glass and quartz substrates by electron beam evaporation and effect of the Mg content of the film on its structural, optical and electrical properties were investigated. The structure, surface morphology, optical transmittance, band gap, refractive index and electrical resistivity were found to depend on the Mg content of the film. XRD data revealed that films were polycrystalline in nature. The structure of the films having Mg content in the range of 1–0.74 was cubic, mixed cubic-hexagonal phases for x=0.47 and hexagonal phase for x=0. The composition analysis showed that Mg content in Mg_xZn_1−xO film is high as compared to the corresponding target alloy. It was observed that the optical band gap increases from 3.3 to 6.09 eV, refractive index at 550 nm decreases from 1.99 to 1.75, transmittance increases from about 70% to 90% and electrical resistivity increases from 0.5 to 1.48×10⁶ Ω cm with the increase of Mg concentration in the film from 0 to 1. The results reported in this work are useful for window layer of solar cells and other optoelectronic devices.     

Tuning of an erbium-doped fiber ring laser based on heating a tapered fiber filter

An erbium-doped fiber ring laser (EDFRL) with wavelength tuning is reported. The laser has a Mach–Zehnder fiber interferometer (MZFI) based on tapers as an intracavity filter, which spectral interference transmission spectrum is modified by external refractive index changes induced by temperature variations in the 25–110 °C range. The MZFI is immersed in a glycerol solution, which refractive index is modified by controlled temperature changes, which allows the tuning of the laser wavelength determined by the interference fringes. Wavelength tuning of 12 nm was measured. This approach is very simple, portable and inexpensive over traditional methods to tune a fiber laser. In addition, the tuning mechanism do not require a solution replacement to operate.     

Temperature-independent accelerometer using a fiber Bragg grating incorporating a biconical taper

An intensity-modulated optical fiber accelerometer is proposed and experimentally demonstrated by using a fiber Bragg grating (FBG) incorporating a biconical fiber taper. Acceleration-induced microbending of the fiber taper region introduces various attenuation to the light, so that acceleration can be measured from changes of the optical power of the reflected light from the FBG. This power detection method reduces the cost and complexity of the sensor setup since only photodetector is required for the signal detection. In the static measurement, a relatively large range of 5g (g is gravity, equals to 9.8 m/s²) with sensitivity of 4.85 nW/g is achieved. Vibration measurements have also been carried out with a frequency up to 20 Hz. The proposed accelerometer is nearly independent of temperature because the reflected optical power of the FBG is insensitive to temperature.     

Proposal for highly birefringent broadband dispersion compensating octagonal photonic crystal fiber

In this paper, we propose and demonstrate a highly birefringent photonic crystal fiber based on a modified octagonal structure for broadband dispersion compensation covering the S, C, and L-communication bands i.e. wavelength ranging from 1460 to 1625 nm. It is shown theoretically that it is possible to obtain negative dispersion coefficient of about −400 to −725 ps/(nm km) over S and L-bands and a relative dispersion slope (RDS) close to that of single mode fiber (SMF) of about 0.0036 nm⁻¹. According to simulation, birefringence of the order 1.81 × 10⁻² is obtained at 1.55 μm wavelength. Moreover, effective area, residual dispersion, effective dispersion, confinement loss, and nonlinear coefficient of the proposed modified octagonal photonic crystal fiber (M-OPCF) are also reported and discussed.     

Solid-state sensing tip for zinc ion with double parallel optical fibers embedded in fluorescent hydrogel

A tip-shaped zinc ion solid-state sensor is made by two parallel optical fibers embedded closely in a sensing hydrogel film. The film is made of poly(2-hydroxyethyl methacrylate) (poly HEMA)hydrogel mixed with the selective fluorescent probe meso-2,6-Dichlorophenyltripyrrinone (TPN-Cl₂) with weight ratio of 0.025 wt%. A 405 nm laser output is sent from one fiber and the 622 nm fluorescence of the doped hydrogel is collected by the second fiber. Each fiber diameter is 370 μm (core is 300 μm), whose sum is roughly the tip diameter. The 0.4 cm by 0.5 cm tip has real-time response for zinc ion concentration over 10⁻⁶ M, with marginal signal for 10⁻⁷ M. The tip is inserted inside an oyster and successfully detects the zinc ions, showing that the sensor works in complex body fluid and tolerates certain mechanical stress. To show the potential application for medicine, the sensing film is applied for primary neuronal cultures. We report for the first time zinc ions release at concentration levels 10⁻⁶–10⁻⁷ M to the medium under stress conditions of ischemia, inflammation, and intoxication. Furthermore, this correlates with the zinc levels detected by biochemical assay. Such sensing tip has great potential for biomedical monitoring ex vivo or in vivo.     

Brush electrodeposited silver indium selenide films and their optical characteristics

Silver indium selenide films were brush electrodeposited on tin oxide coated glass substrates at different substrate temperatures. The films were single phase with chalcopyrite structure. Optical absorption measurements indicated a band gap in the range of 1.20–1.30 eV with decrease of substrate temperature. Transmission spectra exhibited interference fringes. Using the envelope method, calculated values of refractive index at 850 nm decreased from 3.53 to 2.62 with decrease of substrate temperature. From the refractive index data, the value of N/m^⁎ was estimated to be in the range of 0.89–1.22. Optical data were analyzed by the single-effective oscillator model, and the single oscillator energy as well as the dispersion energy was estimated. The single oscillator energy decreased from 1.83 eV to 1.68 eV with the increase of substrate temperature. The dispersion energy increased from 5.42 eV to 12.25 eV with the increase of substrate temperature.     

Modeling of Ga1−xInxAs1−y−zNySbz/GaAs quantum well properties for near-infrared lasers

The aim of this work is to model the properties of GaInAsNSb/GaAs compressively strained structures. Indeed, Ga_1?xIn_xAs_1?y?zN_ySb_z has been found to be a potentially superior material to GaInAsN for long wavelength laser dedicated to optical fiber communications. Furthermore, this material can be grown on GaAs substrate while having a bandgap smaller than that of GaInNAs. The influence of nitrogen and antimony on the bandgap and the transition energy is explored. Also, the effect of these two elements on the optical gain and threshold current density is investigated. For example, a structure composed of one 7.5 nm thick quantum well of material with In=30%, N=3.5%, Sb=1% composition exhibits a threshold current density of 339.8 A/cm² and an emission wavelength of 1.5365 μm (at T=300 K). It can be shown that increasing the concentration of indium to 35% with a concentration of nitrogen and antimony, of 2.5% and 1%, respectively, results in a decrease of the threshold current density down to 253.7 A/cm² for a two well structure. Same structure incorporating five wells shows a threshold current density as low as 221.4 A/cm² for T=300 K, which agrees well with the reported experimental results.     

Design on a highly birefringent and highly nonlinear tellurite ellipse core photonic crystal fiber with two zero dispersion wavelengths

In this paper, a new photonic crystal fiber (PCF) with two zero dispersion wavelengths (ZDWs) based on the tellurite ellipse core is designed. The air holes in the cladding region have a V-shape distribution, which can increase the birefringence. By adjusting the size of tellurite ellipse core, different birefringence and nonlinearity coefficient can be obtained, and the dispersion can also be tailored. When the long axis of the tellurite ellipse core is 0.5 μm and the short axis is 0.25 μm, the birefringence of 7.66 × 10⁻² and nonlinearity of 3400 W⁻¹ km⁻¹ around 1550 nm are obtained. This PCF structure provides a way to get the high birefringence and nonlinearity at the same time, which can find extensive applications in the optical communication and sensor system.     

Theoretical analysis of characteristics for 2 μm Tm3+:Ho3+ co-doped silica fiber laser pumped by a 1550 nm fiber laser

We established a theoretical model of 2 μm Tm³⁺:Ho³⁺ co-doped silica fiber laser pumped by a 1550 nm fiber laser based on the rate-equation theory and performed the numerical simulation using Runge–Kutta algorithm and Newton–Raphson algorithm. The intracavity power distributions of both pump and laser of the Tm³⁺:Ho³⁺ co-doped silica fiber laser based on the Tm³⁺:Ho³⁺ co-doped silica fiber supplied by the National Optics Institute in Canada (NOIC) were obtained. The effects of the output reflectivity R₄(λ_s) at the output laser wavelength λ_s and the concentrations of Tm³⁺ and Ho³⁺ in the fiber on laser output performance were analyzed. In order to achieve a high laser output power, the optimal R₄(λ_s) of 0.13 was verified and the optimal Tm:Ho ratio of 1:2.4 was proposed. Finally, better output performance for the fiber laser based on the optimized Tm³⁺:Ho³⁺ co-doped silica fiber was obtained than the laser using the fiber supplied by the NOIC. This theoretical model and numerical simulation results will guide the fabrication of 2 μm Tm³⁺:Ho³⁺ co-doped all-fiber lasers pumped by 1600-nm-band (1500–1750 nm) Er³⁺:Yb³⁺ co-doped silica fiber lasers.     

Determination of structural and optical properties of gold phthalocyanine thin films using density functional theory

We determined some optical and electrical properties of thin gold phthalocyanine films. Calculations were performed in the framework of density functional theory using the full potential linear augmented plane wave method. Studies on the density of states and band structure yielded a bandgap energy (E_g) of approximately 2 eV. Two trap energy levels were observed at 0.9 and 1.3 eV. Analysis of the dielectric function and electric loss function revealed a plasmon oscillation at 1.8 eV. In addition, we determined static refractive index values in the x, y and z directions of n_0xx = 2.16, n_0yy = 1.66 and n_0zz = 2.07. The optical bandgap of gold phthalocyanine was estimated to be 0.97 eV. Calculations revealed strong absorption at 400–700 nm, which compares favorably with experimental results.