We propose and demonstrate the use of the cost-effective electric arc writing method for the all-fiber cylindrical vector beam (CVB) and orbital angular momentum (OAM) beam generation in few-mode fibers (FMFs) for the first time to the best of our knowledge. We show that this technique enables the writing of long-period fiber gratings (LPFGs) with pitch values as small as 238 μm, which is required in some high-index contrast specialty fibers tailored for the stable guiding of CVB and OAM modes. Conversion efficiencies around 81% are measured for three different symmetric CVBs. The polarization-dependent properties of the fabricated gratings are elucidated, and we report a polarization-dependent loss of about 2.5 dB across the different CVBs. By means of a fabricated LPFG, we further demonstrated the all-fiber generation of the OAM states with topological charge (±1) at the output of the FMF. The results are relevant to the fields of space-division multiplexing, optical sensors, and optical tweezers that would benefit from a compact source of quality CVB and OAM beams of high average optical power.
An optical setup was devised for the Electrical engineering undergraduate course “Photonic devices” where students were introduced to a simple visible diode laser based method of measuring the refractive indices of liquid samples in a transparent quartz cuvette placed on a computer-controlled rotating stage. When setting the cuvette at a small angle with respect to the incident laser beam, the light transmission through the cuvette results in a small mm-scale deflection of the laser path. The evaluation of the sample’s refractive index hinges on measuring the beam displacement. Moreover, by positioning the cuvette at normal incidence and recording the optical power after passing through various liquid samples (e.g. distilled water, maple syrup) and comparing with a reference (empty cuvette), students learn to estimate the attenuation coefficients of the substances by taking into account the contribution of the multiple Fresnel reflections. Finally, the same optical setup is also used by students to perform the “knife-edge” technique for the characterization of the beam profile emitted by the visible diode laser used in the setup. The proposed setup was implemented in the fall 2018 where undergraduate students were able to practice optical alignment and implement the concepts of material refractive indices and attenuation, as well as revisit the Gaussian beam theory taught in-class.
In some fruits and vegetables, it is difficult to visually identify the ones which are pest infested. This particular aspect is important for quarantine and commercial operations. In this article, we propose to present the results of a novel technique using thermal imaging camera to detect the nature and extent of pest damage in fruits and vegetables, besides indicating the level of maturity and often the presence of the pest. Our key idea relies on the fact that there is a difference in the heat capacity of normal and damaged ones and also observed the change in surface temperature over time that is slower in damaged ones. This paper presents the concept of non-destructive evaluation using thermal imaging technique for identifying pest damage levels of fruits and vegetables based on investigations carried out on random samples collected from a local market.
We report an experimental demonstration and characterization of dynamic Brillouin gratings (DBGs) in a 5m
long polarization-maintaining fiber (PMF) using heterodyne detection. The dependence of DBG reflectivity on
the Brillouin gain and on the pumps and the probe powers is studied and reported.
The broad objective of this paper is to study the surface of the corroded metals by using proximity sensor which works
on the principle of light scattering by objects. The present work discussed a simple low cost sensor design making use
of plastic optical fiber. The sensor used is insensitive to source fluctuation and can detect surface roughness of the
metals. The average surface roughness of the samples in different concentrations of acidic medium has been studied
using the sensor. The reflected light intensity from the surface of sample metals was collected and measured as a
function of lateral distance to estimate the roughness of the surface. The results have been compared with the stylus
measurements.
The paper presents a proximity sensor based on plastic optical fiber as tilt sensor. Discrete and continuous response of
the sensor against change in tilt angle of the setup is studied. The sensor can detect tilt angles up to 5.70 and the achieved
sensor sensitivity is 97mV/0 .
The design and packaging of simple, small, and low cost sensor heads, used for continuous liquid level measurement using uniformly thinned (etched) optical fiber Bragg grating (FBG) are proposed. The sensor system consists of only an FBG and a simple detection system. The sensitivity of sensor is found to be 23 pm/cm of water column pressure. A linear optical fiber edge filter is designed and developed for the conversion of Bragg wavelength shift to its equivalent intensity. The result shows that relative power measured by a photo detector is linearly proportional to the liquid level. The obtained sensitivity of the sensor is nearly −15 mV/cm .
The present work proposes a simple low cost sensor head design making use of FBG sensor, for the measurement of
liquid level. The sensor head consists of a lever, a buoyancy tube and an FBG. The lever is used to transfer the buoyancy
force due to change in liquid level to the FBG resulting in shift in Bragg wavelength. The Flexibility of this design
enables to measure the liquid level in an open or closed tank. The arrangement shows that liquid level sensitivity is high
and is 10.7pm/mm.
The performances of two liquid level sensors based on Fiber Bragg grating are studied. The Fiber Bragg gratings (FBG) are sensitive to strain and temperature. We investigate on enhancement of strain sensitivity of the FBG for liquid level measurement. Two different sensor heads arrangement are fabricated to exploit the strain sensitivity of FBG and use it for the liquid level measurement. The measurement sensitivity of a FBG based fiber optic liquid level sensor can be improved by controlling the parameter such as diameter of the FBG.
An intensity based fiber optic liquid level sensor for continuous measurement is described. The sensing principle is based on intensity of reflected light which is disturbed by the change in proximity of the fiber probe and the reflector. A Mechanical CAM is used in the sensing arrangement. It converts the rotatory motion into a linear displacement. As the liquid level raises, rotation of the CAM takes place and the CAM follower connected to it moves linearly. A reflector which is attached to the end of the CAM follower reflect the incident light. As the displacement of reflector occur the intensity of reflected light also changes and is a measure of change in liquid level. The prototype designed sensor can sense liquid level upto 17cm. The proposed sensor can find potential applications in transportation and process industries.
In this work half the length of the single FBG is chemically etched and the un-etched half is glued on a cantilever. The response of the grating is investigated as a function for buoyancy force on the cantilever due to liquid level and temperature. Simultaneous measurement of liquid level and temperature is achieved from the coefficients of liquid level and temperature sensitivities obtained from the experimental results.
This study focused on the development of high sensitivity pressure sensor based on reduced clad FBG encapsulated
in a stainless steel cylinder, partially filled with silicon rubber. The sensor works by means of transferring radial or
lateral pressure into an axially stretched- strain along the length of the FBG. The experiment is carried out using two
different FBG's have core/clad diameters of 9/125μm (FBG1) and 4/80μm (FBG2). FBG2 is chemically etched to reduce
the cladding diameter which significantly enhances the pressure sensitivity. The shift of the Bragg wavelength in
response to applied pressure is monitored with an optical spectrum analyser (OSA). The measured pressure sensitivity of
FBG2 and FBG1 are found to be 5.85 x 10-2 MPa-1 and 2.07 x 10-2 MPa-1, which are approximately 18870 and 6677
times respectively higher than that can be sensed with a bare FBG. A very good linearity is observed between Bragg
wavelength shift and pressure. This compact, low cost and robust design of the sensor can find applications in the areas
of low and medium pressure measurement.
A single mode fiber optic vibration senor is designed and demonstrated to monitor the vibration of a simply
supported beam. A rectangular beam (length 30.8 cm, width 2.5cm and thickness 0.5mm) made of spring-steel is
arranged as simply supported beam and is made to vibrate periodically. To sense the vibrations a telecommunication
fiber is chemically etched such that its diameter reaches 50μm and is glued using an epoxy at the centre of the beam. A
broadband light (1550nm) is launched into Fiber Bragg Grating (FBG) through a circulator. The light reflected by the
FBG (1540.32nm) is coupled into the centre etched fibre through the circulator and is detected by photodiode connected
to a transimpedance amplifier. The electrical signal is logged into the computer through NI-6016 DAQ. The sensor
works on transmission power loss due to the mode volume mismatch and flexural strain (field strength) of the fiber due
to the bending in the fiber with respect to the bending of the spring-steel beam. The beam is made to vibrate and the
corresponding intensity of light is recorded. Fast Fourier transform (FFT) technique is used to measure the frequencies of
vibration. The results show that this sensor can sense vibration of low frequency accurately and repeatability is high. The
sensor has high linear response to axial displacement of about 0.8 mm with sensitivity of 32mV/10μm strain. This lowcost
sensor may find a place in industry to monitor the vibrations of the beam structures and bridges.
A small and simple hydrostatic pressure sensor using fiber Bragg grating sensor for liquid level sensing is reported. The working principle of the sensor head design is based on transferring hydrostatic radial pressure to axial strain to the FBG. An FBG written in a fiber of diameter 50μm has been used for the measurement. The experimental result shows that sensitivity of the sensor can reach 23pm/cm of liquid column. The sensor can be useful in applications that involved with less hydrostatic pressure, like a tank with inflammable liquid in a fuel gas station.
A simple technique to discriminate the Strain and Temperature with a single Fiber Bragg Grating (FBG) at cryogenic
regime is presented in this paper. An uniform FBG is divided into two parts, one half is without coating (FBG1) and
other half is coated with Cyno-Acrylic Adhesive (FBG2). The measured temperature and strain sensitivities of the FBG1
are 4.05x10-6/K and 2.13x10-6/με and FBG2 are 1.39x10-5/K and 1.72x10-6/με respectively.
A fiber optic vibration sensor is demonstrated using bifurcated bundle fiber based on the principle of extrinsic
displacement sensor. An IR source is used along with glass fibers to avoid the effect of stray light in sensing. The
encapsulation of the sensor enables easy alignment, flexible handling and usage in harsh environments. The sensor is
capable of measuring the frequencies up to 650Hz with vibration amplitude resolution of 10μm, enough to monitor the
vibrations generated in heavy machines. The sensor is tested in the field to monitor the health condition of the diesel engine.
A temperature compensated liquid level sensor using FBGs and a bourdon tube that works on hydrostatic pressure is
presented. An FBG (FBG1) is fixed between free end and a fixed end of the bourdon tube. When hydrostatic pressure
applied to the bourdon tube FBG1 experience an axial strain due to the movement of free end. Experimental result
shows, a good linearity in shift in Bragg wavelength with the applied pressure. The performance of this arrangement
is tested for 21metre water column pressure. Another FBG (FBG2) is included for temperature compensation. The
design of the sensor head is simple and easy mountable external to any tank for liquid level measurements.
Fiber Bragg Gratings have been shown to have a much improved thermal sensitivity when coated by Polymethyle methacrylate (PMMA) at cryogenic regime has been proposed. The PMMA has large thermal expansion coefficients and acts as driving elements. It is coated on the FBG at room temperature and the FBG is under compression at lower temperatures. This allows a much wider tuning of Bragg grating as fiber can stand at more compression than tension. An overall sensitivity of 0.039nm/K in the 1550nm wavelength regime has been achieved and the Bragg wavelength has been tuned upto 8.97nm in the temperature range 77K to 303K.
An encapsulated fiber optic sensor head for the detection of level of fuel in a tank is presented. The design is
based on a concentric cam used along with a float and extrinsic intensity modulation of light. The sensor has been tested
for its performance to measure a fuel level range of 35cm and a sensitivity of 0.2316 volts/cm was observed during rise
in fuel level. The sensitivity and range of level sensing can be varied by varying the length of the connecting rod.
KEYWORDS: Heat flux, Remote sensing, Climatology, Linear filtering, Satellites, Solar radiation, Temperature metrology, Environmental sensing, Data modeling, System on a chip
Observational data from the Arabian Sea Monsoon Experiment (ARMEX-Phase IIA) in the southeastern Arabian Sea
(SEAS) showed intense warming with the SST up to 31.5°C during April-May 2005. Analysis of 5-day repeat cycles
of temperature and salinity profiles from an ARGO float (ID No. 2900345) in a 3°x1° box closer to ARMEX-II buoy
(8.3°N, 72.68°E) in the SEAS during January-September 2005 revealed evolution of warm pool (SST>28°C) in spring
2005. The Argo data derived D20 (depth of 20°C isotherm) showed the influence of remote forcing during January-May, and local wind forcing during southwest monsoon. Low salinity waters (<34.0) occupied the top 30 m during
January-February followed by temperature inversions (up to 0.5°C) in the 30-60 m depth range. From the peak spring
warming, the SST dropped gradually by 3.5°C by end-July with the advent of southwest monsoon followed by a
decrease in net heat gain upto 100 W/m^2. The merged weekly products of sea surface height anomalies and the NLOM
simulated surface currents showed complex surface circulation consisting of seasonal Lakshadweep High/Low in
winter/summer. The examined oceanic and atmospheric variables showed an intraseasonal variability with 41 to 63 day
period, coinciding with the Madden-Julian Oscillation.
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