In this paper we study, both experimentally and by theory, a new nonlinear dynamic in multimode optical fiber where intermodal four-wave mixing (IM-FWM) and Kerr-induced nonlinear mode coupling (NLC) are strongly interacting. We show that presence of phase-matched IM-FWM and strong nonlinear mode coupling results in an unprecedented saturable mode conversion in the FWM anti-Stokes beam. We investigate the evolution of modal conversion as a function of fiber length and show that the result of this novel nonlinear dynamic is a controllable, length independent mode conversion. Our theoretical calculations suggest that the converted anti-Stokes beam can also be amplified via IM-FWM. We observe a mode conversion with an efficiency as high as 90 percent.
We report fabrication of a high pressure optical fiber sensor by using a fat long period fiber grating (FLPFG) for
downhole applications. The pressure sensitivity of the bare optical fiber is low so we have designed a mechanical
transducer for increasing the pressure sensitivity and possibility of installation the sensor in downhole. The pressure
along the longitudinal direction changes the physical characteristic of the FLPFG and result in shifting the resonance
wavelength. The FLPFG sensor has been installed on transducer and the pressure sensitivity of the fiber sensor has been
measured. Since the temperature changes can affect the FLPFG output, the high pressure vessel was isolated and the
temperature was kept constant during the experiment. Pressure sensitivity of the FLPFG sensors has been measured by
increasing the pressure from 1500 psi to 10000 psi in steps of 700 psi which is equal to -1.04 pm/psi. With a 10 pm
resolution for the wavelength shift detection our OSA, detection limit of our device at room temperature for pressure
measurement is calculated to be 10 psi.
A nonadiabatic tapered optical fiber sensor was utilized for studying of bimolecular interactions including DNA-DNA
and DNA-Drug interaction. This work presents a simple evanescent wave sensing system based on an interferometric
approach, suitable to meet the requirements of lable-free sensor systems for detecting biomolecular interactions. We have
demonstrated the measuring refractive index and the real time detection of interactions between biomolecules.
Furthermore basic experiments were carried out, for detecting the hybridization of 25-mer DNA with an immobilized
counterpart on the surface. The overall shift after the successful DNA hybridization was 9.5 nm. In this work, a new
approach for studying DNA-drug interactions was successfully tested. Nicotine as a carcinogenic compound in cigarette
smoke plays an important role in interaction with DNA. Different concentrations of nicotine were applied to observe the
Longmuir interaction with DNA.
We report fabrication of a high pressure nonadiabatic tapered optical fiber (NATOF) for downhole applications by using a
mechanical transducer. The mechanical transducer has been used for increasing the pressure sensitivity and possibility of
installation the sensor in downhole. The NATOF is fabricated by heat pulling method, utilizing a CO2 laser. The limit of
detection of the NATOF was 15 psi.