In this article, an Adiabatic Tapered Optical Fiber -- Fabry Perot (ATOF-FP) Sensor is introduced as a simple refractive index sensor. This FP Cavity relies upon reflection from two cleave ends of ATOF sensor’s arms. Its spectrum was investigated with Distributed Feedback (DFB) tunable laser and photo detector. With analyzing the change in Optical Transmission Power (OTP) versus refractive index changes, the sensitivity of ATOF was -66.21 dB/RIU. In addition, the visibility of FP was studied. Its RI sensitivity was -0.975 1/RIU. The sensor resolution was 2.3 × 10<sup>-5</sup> RIU with consideration of minimum detectable signal of acquisition system.
Mode splitting (MS) in whispering gallery microresonators provides excellent noise suppression in sensing signal compared to mode shifting. Here, we theoretically studied the ability of hollow bottle microresonators for detection of a single nanoparticle in air and water medium by MS phenomenon. To find out the optimum condition of sensor for nanoparticle (NP) detection, the effects of bottle geometry parameters, mode orders, and mode polarization state was investigated. The first radial transverse electric mode demonstrated the best sensitivity when the resonator radius and wall thickness were 10 and 0.3 μm, respectively. However, transverse magnetic modes manifested slightly better detection limit. In the air core hollow microbottle resonator (HMBR), the best detection limit of 3.1 nm radius for polystyrene NPs was achieved at an optimum condition of 30-μm resonator radius and 0.8-μm wall thickness. While MS could not be resolved in deionized water filled HMBRs for all of the investigated conditions at 1550 nm, changing the wavelength to 780 nm provided a detection limit of 15.1 nm in water. Furthermore, it is found that the sensitivity of HMBR is increased by at least two times in comparison with a microtoroid sensor. HMBRs are optofluidic platforms, so employing them could drastically enhance the applicability of microresonator-based systems for label-free NP detection.
In this paper, a new type of dynamic chemical etching is used to fabricate different fiber tips with different cone angles. It was done by controlling surface level of hydrofluoric acid relative to the fiber, with changing volume of the acid in the container using a syringe pump. Using this method the cone angle of the tip is effectively controlled and angles between 1° and 30° was obtained.
This article demonstrates an investigation and analysis of a tapered fiber fabrication using an etchant droplet method. To achieve precise control on process, a two-step etching method is proposed (using 48% concentration of HF acid and Buffered HF) which results in low-loss adiabatic tapered fiber. A spectrum analysis monitoring in addition to a microscopy system was used to verify the etching progress. Tapers with losses less than 0.4 dB in air and 4.5 dB in water are demonstrated. A biconical fiber taper fabricated using this method was used to excite the WGMs on a microsphere surface in aquatic environment.
In some of the optical fiber pressure sensors, the pressure on the fiber is converted to the strain along the fiber by a
mechanical transducer and the strain is measured. As the transducer causes many limitations in sensing process, we used
stimulated Brillouin scattering generated dynamic grating for distributed measurement of direct pressure without any
transducer in this paper. The sensitivity of the dynamic grating characteristic to the pressure loaded on the fiber for a two
side holes fiber is calculated, for the first time. The effects of the fiber parameters on the pressure sensitivity of dynamic
grating are discussed.
Ahigh pressure sensor based on an optical fiber micro sphere cavity Fizeau interferometer (MSC-FI) is presented in this
paper.The sensorwas fabricated by use of a fusion splicer. The achieved pressure sensitivity of MSC-FI sensor was in the
range of 500 to 7000pi to be 4×10<sup>-4</sup> nm/psi. With a 10 pm resolution for the wavelength shift detection, the resolution of
the device at room temperature for pressure measurement is to be 25 psi. This sensor can be used as a high pressure
sensor in downhole application.
We investigated the possibility the active DNAzyme formation of particular Guanine-rich oligonucleotide with
nonadiabatic tapered optical fiber (NATOF) sensor. These kinds of oligonucleotides can form stable four-stranded
structure called G-quadruplex in the presence of particular metal ions. Structural change of immobilized oligonucleotide
was detected by monitoring of transmission spectrum of the sensor. The formation of active DNAzyme formed was
confirmed by verifying enzyme activity. Result shows that the NATOF sensor has capability to detect intramolecular
structural changes and using this sequence as biorecognition molecule for fabricating fiber optic biosensor.
The numerical simulations of self-organization have been considered in the self-pumped phase conjugate compact
loop mirrors based on a photorefractive crystal PRC BaTiO<sub>3</sub> . We show that under optimal condition the
nonlinear reflection coefficient of such mirror achieves the maximum value 0.80 - 0.90 at the maximum
conjugate fidelity equal to 0.95 - 0.98. In this geometry the conjugate wave-front is generated due to scattering
from a dynamic hologram produced in the self-intersection region of the forward and backward beams. As a
result, the scenario of passing to unstable generation regimes in this case is the same as self-pumped loop phase-conjugate-mirror (PCM) but substantially differs from a single-crystal double PCM.