We study self-injection locking of DFB laser through ring fiber optic resonator in the different regimes. Experimentally measured transmitted and reflected from fiber cavity powers at undercoupled, critically coupled, and overcoupled regimes are properly coincide with the calculated values. Significant reduction of locked laser linewidth was observed. For the free running laser, the full-width at half-maximum linewidth was equal to 2.55 MHz assuming that line shape is Lorentzian. Meanwhile the self-injection locked DFB laser demonstrates linewidth equal to 2.5 KHz for undercoupled and critically coupled regimes and about two times more for overcoupled one.
Several potentially conducting polymers, optically nonlinear polymers, and biomaterials contain heterocyclic structures. Reduction of the energy band gap of a conjugated polymer is a topic of considerable interest due to the possible elimination of doping in the preparation of highly conductive polymers. Control of the energy gap value of a polymer by molecular design could modify its optical, electronic and optoelectronic properties. Thiadiazoles and their derivatives are the structural basis of some of these polymeric materials. The results of the calculation of the HOMO-LUMO gap, the dipole moment and polarizability of thiadiazole oligomers in vacuo and in the presence of solvents are reported. The calculations are based on density functional theory using a specially tailored model chemistry. The potential utility of these materials for the development of chemical sensors is discussed.
We present results of measurements of fiber bend loss caused by soft and swellable materials with perturbation periods of 1 mm to 20 mm. We used swellable materials that have different moduli of Young. We show that the swell of soft materials causes the pure bend loss that increases when the period rises. We show that the higher modulus of Young the higher the loss caused by swellable materials. These results may be used to choose suitable materials and construction for assembling a fiber optics sensor based in the bend loss.
Several potentially conducting polymers, optically nonlinear polymers, and biomaterials contain heterocyclic structures. Reduction of the energy band gap of a conjugated polymer is a topic of considerable interest due to the possible elimination of doping in the preparation of highly conductive polymers. Control of the energy gap value of a polymer by molecular design could modify its optical, electronic and optoelectronic properties. Thiadiazoles and their derivatives are the structural basis of some of these polymeric materials. The results of the calculation of the HOMO-LUMO gap, the dipole moment and polarizability of thiadiazole oligomers in vacuo and in the presence of solvents are reported. The calculations are based on density functional theory using a specially tailored model chemistry. The potential utility of these materials for the development of chemical sensors is discussed.
This work describes the performance of a new optical distributed sensor. This new sensor is capable of detecting and locating liquid hydrocarbon leakage on long pipelines. It is an improvement over the current fiber bending distributed sensors that use a polymeric filament that interacts with an optical fiber by means of a helicoidal wire. When a liquid or gas compatible with the polymeric filament within this type of sensor comes in contact with it, the liquid is absorbed and causes the swelling of the filament and the concomitant compression of the optical fiber against the helicoidal wire. This phenomena cause the fiber to bend and generate an increase on the optical attenuation signal that travels through the fiber. The signal attenuation permits the detection of a specific liquid presence in the vicinity of the sensor and the reflection of the same signal allows to pinpoint the location of this event. The new sensor has the following advantages over similar devices: a) the swelling of the polymeric filament is conducted in a preferential direction permitting to concentrate the osmotic pressure towards the optical fiber. This improves significantly the response speed of the sensor. b) The fiber is placed within a capillary channel located eccentrically in the polymer filament; therefore, no additional protection is needed to prevent damage to the fiber. Of even greater importance, the signal attenuation provoked by stress and deformations due to direct contact of the fiber with the helicoidal wire is avoided. And finally, c) an optimal bending period that take in count the polymer nature to improve the sensor response was found and employed. An experimental prototype of this sensor was fabricated using a multimode optical fiber attached to a polybutadiene filament. The experimental results confirm the benefits of this new design.
In this work we decided to show the behavior about the bend loss caused by soft and swellable materials. The principal measurements of fiber bend loss caused by soft and swellable materials were done with perturbation periods of 1 mm to 20 mm, because we needed to be close in the range of small curture. We used soft materials that have different moduli of Young. To accomplish this measure, we used single mode and multimode fibers. We had to watch the behavior over range of wavelength 1400nm to 1600nm with different radii of curvature. We would like to point out that the material that has the highest modulus of Young causes the highest loss. Ours results show that the highest attenuation and fastest sensor operation can be achieved at respectively long periods of perturbation, more than 10 mm in our experiments.
The paper presents distributed fiber optic bending sensor for petroleum hydrocarbon detection based on COFDR technique. Sensitive polymer, which effectively swells under hydrocarbon influence, was employed in order to introduce bending losses in hydrocarbon presence. In this work we used lumped reflectors, namely fiber Bragg gratings, placed between distributed sensitive elements. Proposed design of the sensor utilises the principle of truly distributed detection with discrete localisation of perturbation. We have demonstrated that the COFDR technique with bending based chemical sensor is capable to detect hydrocarbon presence within a few minutes for 20-cm perturbation-length with spatial resolution up to 0.5 meters.
In this paper, we present a new fiber optic Bragg grating sensor for petroleum hydrocarbon leak detection. The developed sensor includes fiber section with imprinted in the fiber core Bragg grating covered by special polymer material. This polymer reversibly swells under hydrocarbon influence and strains the fiber section with the Bragg grating inside. As a result of the fiber elongation, the Bragg wavelength shifts to aside longer wavelength. Experimentally demonstrated shift of the grating resonant wavelength was more than 2 nm for 20-min gasoline influence, which significantly exceeds a shift due to possible environmental temperature variation and the width of the grating reflection spectrum, which was about 0.5 nm. The paper presents also the results of the swelling-behavior test of the loaded and unloaded sensitive polymer material under liquid and vapor gasoline influence and the results of the theoretical and experimental investigation of the hydrocarbon sensor performance.
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