Temperature-independent curvature sensor based on tapered photonic crystal fiber interferometer

A temperature-independent highly-sensitive curvature sensor by using a tapered-photonic crystal fiber (PCF)-based Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. It is fabricated by sandwiching a tapered-PCF between two standard single mode fibers (SMFs) with the air holes of the PCF in the fusion splicing region being fully collapsed. The tapering of PCF is found to enhance the sensitivity significantly. Large curvature sensitivities of 2.81 dB/m⁻¹ and 8.35 dB/m⁻¹ are achieved in the measurement ranges of 0.36-0.87 m⁻¹ and 0.87-1.34 m⁻¹, respectively, with the resolution of 0.0012 m⁻¹ being guaranteed. The proposed sensor also shows negligible temperature sensitivity less than 0.006 dB/°C.     

Investigation of the dose-response relationship for road traffic noise in Assiut, Egypt

A field study has been carried out in urban Assiut city, Egypt. The goals of this study are: (1) to carry out measurements to evaluate road traffic noise levels, (2) to determine if these levels exceeds permissible levels, (3) to examine people’s attitudes towards road traffic noise, (4) to ascertain the relationship between road traffic noise levels and degree of annoyance. The measurements indicate that traffic noise noise levels are higher than those set by Egyptian noise standards and policy to protect public health and welfare in residential areas: equivalent continuous A - weighted sound pressure levels (L_A eq) = 80 dB and higher were recorded, while maximum permissible level is 65 dB. There is a strong relationship between road traffic noise levels and percentage of highly annoyed respondents. Higher road traffic noise levels mean that the percentage of respondents who feel highly annoyed is also increased.     

The temperature dependency of EDFAs in the 1480 nm pumping configuration

A theoretical study of the temperature-dependent gain and noise figure effects on erbium-doped fiber amplifiers (EDFAs) pumped at 1480 nm is investigated, solving the propagation equations related to two level systems. The solution of these equations is based on the population and temperature difference among amplification levels. The temperature-dependent propagation equation considered is used to determine the gain and noise figure effects on EDFAs. The population difference depends on pump and signal powers, Boltzmann factor K_B, cross-sections, noise figure (NF) and Er³⁺ concentration. The temperature-dependent gain and noise figure effect the EDFA length are numerically obtained for the temperature range of −20 °C to +60 °C. All of the analyses consist of the amplified spontaneous emission (ASE) effect.     

Temperature impact on mechanically induced long-period fiber gratings

The spectral response of mechanically induced long-period fiber gratings (MLPFG) to the ambient temperature variation was experimentally study. In the MLPFG setting, a pressure rig with aluminum grooved plates on standard telecommunication fiber was used. We found that a relatively low change in temperature can produce a severe impact on the characteristic parameters of the attenuation bands, such as a critical decrease in the contrast and fast shift saturation. When the temperature increases from −10 to 70 °C, all the bands are shifted toward longer wavelengths with a mean sensitivity of approximately 180 pm/°C from 0 to 40 °C in the near-linear region, then they present a flattened zone beyond this temperature. Meanwhile, the contrast of the attenuation bands rapidly decreases from the maximum value to 0 dB with a quasi-cosinoidal behavior. These results are important and have to be considered when MLPFG are applied in a medium with ambient temperature variation. Furthermore, we show that MLPFG can be used as low cost ambient temperature sensors through intensity based measurements.     

The impact of urban noise on primary schools. Perceptive evaluation and objective assessment

This paper aims to assess the impact of environmental noise in the vicinity of primary schools and to analyze its influence in the workplace and in student performance through perceptions and objective evaluation. The subjective evaluation consisted of the application of questionnaires to students and teachers, and the objective assessment consisted of measuring in situ noise levels. The survey covered nine classes located in three primary schools. Statistical Package for Social Sciences was used for data processing and to draw conclusions. Additionally, the relationship of the difference between environmental and background noise levels of each classroom and students with difficulties in hearing the teacher’s voice was examined. Noise levels in front of the school, the schoolyard, and the most noise-exposed classrooms (occupied and unoccupied) were measured. Indoor noise levels were much higher than World Health Organization (WHO) recommended values: L_Aeq,30min averaged 70.5 dB(A) in occupied classrooms, and 38.6 dB(A) in unoccupied ones. Measurements of indoor and outdoor noise suggest that noise from the outside (road, schoolyard) affects the background noise level in classrooms but in varying degrees. It was concluded that the façades most exposed to road traffic noise are subjected to values higher than 55.0 dB(A), and noise levels inside the classrooms are mainly due to the schoolyard, students, and the road traffic. The difference between background (L_A95,30min) and the equivalent noise levels (L_Aeq,30min) in occupied classrooms was 19.2 dB(A), which shows that students’ activities are a significant source of classroom noise.     

Noise abatement schemes for shielded canyons

Access to quiet areas in cities is important to avoid adverse health effects due to road traffic noise. Most urban areas which are or can become quiet (L_A,eq < 45 dB) are shielded from direct road traffic noise. By transfer paths over roof level, many road traffic noise sources contribute to the level in these shielded areas and noise abatement schemes may be necessary to make these areas quiet. Two real life shielded courtyards in Göteborg have been selected as reference cases for a numerical investigation of noise abatement schemes. The selected areas are modelled as canyons with a road traffic noise source modelled outside the canyon by a finite incoherent line source, which is more realistic than both a coherent and an incoherent line source of infinite length. The equivalent sources method has been used for the calculations. For all studied noise abatement schemes in the shielded canyon, the reductions are largest for the lower canyon observer positions. Façade absorption is the most effective when placed in the upper part of the canyon and can typically yield a reduction of 4 dB(A). Constructing 1 m wide walkways with ceiling absorption reduces the level typically by 3 dB(A). These effects are most effective for narrower canyons. For treatments at the canyon roof, reductions are independent of the canyon observer position and amount to 4 dB(A) for a 1 m tall screen and 2 dB(A) for a grass covering of a saddle roof. Downward refracting conditions increase the levels for the lower canyon observer positions and higher frequencies. For sources located in canyons, abatement schemes therein are more effective for noise reduction in the shielded canyon than similar abatement schemes in the shielded canyon itself, given that all contributing source canyons are treated.     

Gain clamped L-band EDFA with forward–backward pumping scheme using fiber Bragg grating

The paper proposes a novel two stage L-band erbium doped fiber amplifier with forward–backward pumping scheme for transmission of 32 wavelength division multiplexed (WDM) channels. It is gain clamped with an in-line fiber Bragg grating (FBG) to provide flat gain over 45 nm by restricting and reutilizing amplified spontaneous emission (ASE). We demonstrate that it provides an efficient small signal gain with minimum noise figure of over 20 dB and 5.5 dB, respectively, in the L-band region (1565–1610 nm) by comparing with its forward and backward pumped counterparts with fixed Er³⁺ fiber length of 20 m for −30 dBm/channel input power. We also obtain the gain and noise figure dependence as a function of each of the Er³⁺ fiber lengths, pump power (both 1480 and 980 nm), and temperature. Hence a 10 nm region (1580–1590 nm) has been acknowledged where temperature variations become constricted for 30 °C variations (15–45 °C).     

The thermo-optical variable optical attenuator based on SOI

A thermo-optical variable optical attenuator was studied based on silicon on insulator (SOI) substrate waveguide. It is composed by the single-mode waveguide, taper waveguide, multi-mode waveguide, and inclined electrode. By adjusting the applied voltage on the inclined electrode it can achieve continuously variable attenuation of the output light. The results we studied show that when the applied voltage is about 4.7 V (the corresponding power is 233 mW), the variation of the waveguide's core temperature is about 33 °C, the refractive index changes more than 5.0 × 10⁻³ and the attenuation will reach 35 dB, and the response time is only 35 μs.     

Tunable polymer waveguide Bragg filter fabricated by direct patterning of UV-curable polymer

Tunable polymer wavelength filters are demonstrated using a silicon-nitride grating which gives high refractive index contrast with polymers. The polymer waveguides are defined using direct patterning of a liquid-state UV-curable polymer by proximate-contact lithography technique. The wavelength filter exhibits a narrow bandwidth of less than 1.0 nm and a transmission dip of more than −15 dB. The peak wavelength is shifted over 10 nm in the temperature range of 25-70 °C and the thermal tuning efficiency is −0.212 nm/°C.     

Design and performance of an open jet wind tunnel for aero-acoustic measurement

This paper presents the design and performance of an open jet, blow down wind tunnel that was newly commissioned in the anechoic chamber at the ISVR, University of Southampton, UK. This wind tunnel is intended for the measurement of airfoil trailing edge self-noise but can be extended to other aeroacoustic applications. With the primary objectives of achieving acoustically quiet and low turbulence air jet up to 120 m/s through a 0.15 m × 0.45 m nozzle, several novel noise and flow control techniques were implemented in the design. Both the acoustical and aerodynamic performances of the open jet wind tunnel were examined in detail after its fabrication. It is found that the background noise of the facility is adequately low for a wide range of exit jet velocity. The potential core of the free jet is characterized by a low turbulence level of about 0.1%. Benchmark tests by submerging a NACA0012 airfoil with tripped and untripped boundary layers at 0° and 10° angles of attack respectively into the potential core of the free jet were carried out. It was confirmed that the radiating airfoil trailing edge self-noise has levels significantly above the rig noise over a wide range of frequencies. The low noise and low turbulence characteristics of this open jet wind tunnel are comparable to the best facilities in the world, and for its size it is believed to be the first of its kind in the UK.     

Cleaning of SiC surfaces by low temperature ECR microwave hydrogen plasma

N-type 4H-SiC (0 0 0 1) surfaces were cleaned by low temperature hydrogen plasma in electronic cyclotron resonance (ECR) microware plasma system. The effects of the hydrogen plasma treatment (HPT) on the structure, chemical and electronic properties of surfaces were characterized by in situ reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). The RHEED results indicate that the structures of the films are strongly dependent on the treatment temperature and time. Significant improvements in quality of 4H-SiC films can be obtained with the temperature ranging from 200 °C to 700 °C for an appropriate treatment period. The XPS results show that the surface oxygen is greatly reduced and the carbon contamination is completely removed from the 4H-SiC surfaces. The hydrogenated SiC surfaces exhibit an unprecedented stability against oxidation in the air. The surface Fermi level moves toward the conduction band in 4H-SiC after the treatment indicating an unpinning Fermi level with the density of surfaces states as low as 8.09 × 10¹⁰ cm⁻² eV⁻¹.     

Broadband Er-Yb co-doped superfluorescent fiber source

In this paper, extensive experimental results on broad-band double cladding Er³⁺-Yb³⁺ co-doped superfluorescent fiber sources (SFSs), characterizing their output power, mean wavelength, and bandwidth (BW) stability with variations of pump power, pump wavelength, and fiber temperature, have been reported. For a 55-cm fiber, SFS power from 3.7755 (maximum BW condition of more than 80 nm) to 9.1837 mW (maximum power condition, BW is about 34 nm) has been achieved. The SFS mean wavelength dependence on pump wavelength is highly pump temperature sensitive, and can be reduced to zero in a chosen pump temperature field. The intrinsic variation of the SFS mean wavelength λ_m with fiber temperature is also measured, and a linear variation from 15 to 45 °C with a slop of −0.053 nm/°C for L_f = 100 cm and −0.04 nm/°C for L_f = 55 cm is found.     

Thermally tunable microfiber knot resonator based erbium-doped fiber laser

A compact and tunable erbium-doped fiber laser is demonstrated using a highly doped fiber and a microfiber knot resonator (MKR) structure which is laid on the surface of a small peltier. The MKR functions as both a reflector and a tunable filter where tunability is achieved by varying the temperature of the resonator by heating the peltier. A stable laser output is achieved at the 1533 nm region with an optical signal to noise ratio (OSNR) of 27 dB using a 65 mW of 980 nm pump power. The operating wavelength of the laser can be tuned from 1532.60 nm to 1533.49 nm as the temperature is increased from the room temperature of 24 to 90 °C. It is observed that the operating wavelength shifts to a longer wavelength as the temperature increases with an efficiency of 12.4 pm/°C. This is due to the thermally induced optical phase shift attributable to the changes in effective refractive index and optical path length of the MKR loop.     

Simultaneous measurement of strain and temperature with a long-period fiber grating inscribed Sagnac interferometer

A Sagnac interferometer with a long-period fiber grating (LPG) inscribed in the polarization-maintaining fiber (PMF) is proposed and experimentally demonstrated for simultaneous measurement of strain and temperature. Due to the different responses of the LPG and the Sagnac interferometer to strain and temperature, simultaneous measurement can be achieved by monitoring the wavelength shifts and the intensity changes of a resonance dip of the sensor setup. The experimental results show that the achieved sensitivities to strain and temperature are 6.4 × 10^− 3 dB/με and 0.65 nm/°C, respectively.     

Corrosion behavior of sputtered Cr-Si-Ni and Cr-Si-Ni-Al resistive films in 0.1 M NaOH

The corrosion behavior of magnetron sputtered Cr-Si-Ni and Cr-Si-Ni-Al resistive films had been investigated by means of the relative resistance change (ΔR/R), polarization measurements, AES, and SEM in 0.1 M NaOH solution at 25 °C and 50 °C, which simulated an alkaline environment. The results revealed that both the annealed Cr-Si-Ni and Cr-Si-Ni-Al films in Ar ambient exhibited good corrosion resistance and long-term reliability in 0.1 M NaOH solution at 25 °C, due to the formation of a protective oxide layer on the surface of two types of the films during corrosion. However, the corrosion properties of two types of the films became degraded rapidly with the solution temperature at 50 °C. The studies showed that the pro-formation of a protective oxide layer on the surface of two types of the films by annealing in air had an enhancing effect on the corrosion properties of the films in 0.1 M NaOH solution at 50 °C, and that Cr-Si-Ni-Al films by annealing in air had more improving effect on the corrosion resistance and long-term reliability than Cr-Si-Ni films.     

High-temperature oxidation resistant (Cr, Al)N films synthesized using pulsed bias arc ion plating

(Cr, Al)N films were deposited by pulsed bias arc ion plating on HSS and 316L stainless steel substrates. With pulsed substrate bias ranging from −100 V to −500 V, the effect of pulsed bias on film composition, phase structure, deposition rate and mechanical properties was investigated by EDX, XRD, SEM, nanoindentation and scratch measurements. The high-temperature (up to 900 °C) oxidation resistance of the films was also evaluated. The results show that Al contents and deposition rates decrease with increasing pulsed bias and the ratio of (Cr + Al)/N is almost constant at 0.95. The as-deposited (Cr, Al)N films crystallize in the pseudo-binary (Cr, Al)N and Al phases. The film hardness increases with increasing bias and reaches the maximum 21.5 GPa at −500 V. The films deposited at −500 V exhibit a high adhesion force, about 70 N, and more interestingly good oxidation resistance when annealed in air at 900 °C for 10 h.     

Investigation of the effect of power ultrasound on the nucleation of water during freezing of agar gel samples in tubing vials

Nucleation, as an important stage of freezing process, can be induced by the irradiation of power ultrasound. In this study, the effect of irradiation temperature (−2 °C, −3 °C, −4 °C and −5 °C), irradiation duration (0 s, 1 s, 3 s, 5 s, 10 s or 15 s) and ultrasound intensity (0.07 W cm⁻², 0.14 W cm⁻², 0.25 W cm⁻², 0.35 W cm⁻² and 0.42 W cm⁻²) on the dynamic nucleation of ice in agar gel samples was studied. The samples were frozen in an ethylene glycol-water mixture (−20 °C) in an ultrasonic bath system after putting them into tubing vials. Results indicated that ultrasound irradiation is able to initiate nucleation at different supercooled temperatures (from −5 °C to −2 °C) in agar gel if optimum intensity and duration of ultrasound were chosen. Evaluation of the effect of 0.25 W cm⁻² ultrasound intensity and different durations of ultrasound application on agar gels showed that 1 s was not long enough to induce nucleation, 3 s induced the nucleation repeatedly but longer irradiation durations resulted in the generation of heat and therefore nucleation was postponed. Investigation of the effect of ultrasound intensity revealed that higher intensities of ultrasound were effective when a shorter period of irradiation was used, while lower intensities only resulted in nucleation when a longer irradiation time was applied. In addition to this, higher intensities were not effective at longer irradiation times due to the heat generated in the samples by the heating effect of ultrasound. In conclusion, the use of ultrasound as a means to control the crystallization process offers promising application in freezing of solid foods, however, optimum conditions should be selected.     

Luminescence property of Ce-doped silica decorated with S and Cl anions

Ce³⁺-doped silica was synthesized by sol-gel technique and was further decorated with S²⁻ and Cl⁻ anions through chemical exchange in controlled ambient at elevated temperature. The structure and optical property of samples were examined by X-ray diffraction spectrum, XPS pattern, reflection pattern, and photoluminescence patterns. There is a broad luminescence band at 445 nm under the excitation at 320 nm in the Ce³⁺-doped silica heat-treated in air at 1000 °C. The heat-treatment of the sample in vacuum at 800 °C can increase the intensity of luminescence but have no effect on the wavelength of luminescence. The decoration of S²⁻ and Cl⁻ anions cannot only increase the luminescent intensity but also shift the luminescent wavelength to shorter wavelength.     

60-GHz oxygen band: Precise experimental profiles and extended absorption modeling in a wide temperature range

The 60-GHz band of atmospheric oxygen was studied in the temperature range of −28° to +60 °C at atmospheric pressure by means of a resonator spectrometer with absorption-variation sensitivity of 0.002 dB/km. The experimental data obtained have sufficient signal-to-noise ratio to take second-order mixing into account, increasing the accuracy of the millimeter-wave propagation model (MPM). A refined set of mixing coefficients for the model is derived from the new data and presented. The fidelity of the new model to the spectrometer data is generally better than 2% between 54 and 65 GHz.     

Polymer waveguide thermo-optic switches with −70 dB optical crosstalk

To reduce the crosstalk of the polymer waveguide optical switches, waveguide attenuators are integrated with the switch on the same substrate. The switch and attenuator shares a single connected electrode which is controlled by a single current source. Due to the simple structure of the integrated attenuator, the device length is reduced to 10 mm so as to provide low insertion loss of 0.8 and 1.1 dB for 1300 and 1550 nm, respectively. Further radiation of the remained optical signal on the switch-off branch is induced by the integrated attenuator so that the switching crosstalk is reduced to −70 dB with an applied electrical power of 200 mW. The low crosstalk is maintained for the environmental temperature range of −10 to 55 °C.