Jose J. Sanchez-Mondragon

SPATIAL SOLITONS IN PHOTOREFRACTIVE BI12TIO20 WITH DRIFT MECHANISM OF NONLINEARITY

The analysis performed shows that in cubic photorefractive crystals (of Bi12SiO20 and GaAs type in particular) with drift (‘‘quasilocal’’) mechanism of optical nonlinearity spatial soliton propagation can be observed for reasonable external dc electric fields 10–15 kV/cm. These photorefractive solitons which can be excited at very low cw laser power are stable in a broad region of signal(soliton)/incoherent(spatially uniform) intensity ratio, and allow easy switching from bright to dark type. Original experimental results of self‐channeling of submicrowatt HeNe laser beam in a cubic Bi12TiO20 sample under external dc field are presented.

Fiber-optic sensor for liquid level measurement

A novel (to the best of our knowledge) liquid level sensor based on multimode interference (MMI) effects is proposed and demonstrated. By using a multimode fiber (MMF) without cladding, known as no-core fiber, liquids around the MMF modify the self-imaging properties of the MMI device and the liquid level can be detected. We show that the sensor exhibits a highly linear response with the sensing range and multiplexed operations easily controlled by just modifying the length of the no-core fiber. At the same time, we can measure the refractive index of the liquid based on the maximum peak wavelength shift. We can also use the sensor for continuous and discrete liquid level sensing applications, thus providing a liquid level sensor that is inexpensive with a very simple fabrication process.

Experimental evidence of modulation instability in a photorefractive Bi(12)TiO(20) crystal.

We present experimental results on the propagation of an interference pattern of two He-Ne laser beams of unequal amplitudes through a photorefractive Bi(12)TiO(20) crystal in the presence of drift nonlinearity. The phenomenon that we have observed is the focusing of the fringes as the nonlinearity of the crystal is increased. We show that such a phenomenon can be quantitatively interpreted in the framework of modulation instability theory.

(1 + 1)-Dimension dark spatial solitons in photorefractive Bi12TiO20 crystal

Abstract The generation of (1 + 1)-dimension photorefractive spatial dark solitons by 180° phase or amplitude jumps is reported. Experiments are performed in a cubic photorefractive Bi 12 TiO 20 crystal under an external dc electric field at the wavelength of the cw HeNe laser (633 nm). The waveguiding properties of the generated dark solitons are investigated using another HeNe (or semiconductor) cw laser probe beam.

Observation of interaction forces between one-dimensional spatial solitons in photorefractive crystals

We propagate two coherent and parallel beams of a He-Ne laser through a Bi(12)TiO(20) photorefractive crystal in the presence of drift nonlinearity. Our experimental results demonstrate that the beams attract or repel each other according to their initial phase difference. They attract each other when they are initially in phase and they repel each other when they are initially out of phase. These experimental results agree with numerical predictions recently published.

Electromagnetic oscillations in a multilayer spherical stack

We examine the waveguide properties of a spherical stack: a system of optical layers deposited onto the microsphere substrate, with arbitrary ratios between thicknesses of layers and a wavelength of initial electromagnetic radiation. Frequency dependencies of the reflection coefficient and impedance of the stack are studied. An appropriate matrix formalism is developed to generalize the matrix method well-known for the plane case, to the case of the spherical layer geometry. The material losses and random deviations of thicknesses of layers are taken into account. The quarter-wave length layers are studied in details. Our numerical calculations have revealed the narrow gap of a transparency in a zone of high reflectance of a stack under the suitable parameters.

Torsion Sensing Characteristics of Mechanically Induced Long-Period Holey Fiber Gratings

We present the spectral transmission response of a long-period holey fiber grating mechanically induced in two different twisted holey fibers. We have found that each resonance wavelength of the grating splits when the holey fiber is twisted prior pressure application. The new upper and lower resonance wavelengths show an opposite symmetrical shift that increases proportionally with the induced twist ratio, and it does not depend on tuning and twist direction. The shift observed in the splitting of the peaks in the mechanically induced long-period holey fiber grating is higher than that obtained in standard single-mode fibers and its sensitivity depends of the transverse structure of the holey fiber. High sensitivity is observed in the fiber with asymmetrical cladding structure. These results are important in the design of new torsion sensors based in long-period holey fiber gratings.

Fiber Optic Sensor for High-Sensitivity Salinity Measurement

A highly sensitive salinity sensor based on a two-core optical fiber is demonstrated for both high- and low-concentration regimes. Salinity of several aqueous solutions is measured in the ranges from 0 to 5 mol/L and from 0 to 1 mol/L with sensitivities of 14.0086 and 12.0484 nm/(mol/L), respectively. The achieved sensitivity is ~19 times higher than that recently reported for polymide-coated photonic crystal fibers.

Electromagnetic eigenoscillations and fields in a dielectric microsphere with multilayer spherical stack

We analyze numerically the spectrum of the eigenfrequencies and the electromagnetic eigenfields distribution in the spherical microsphere coated by the multilayered dielectric spherical stack in the optical frequency range. The general eigenfrequency equation is derived. The eigenfrequencies values are calculated versus the number of layers in the stack. We have found what Q factor can reach the large values for the eigenfrequency in the range of strong reflectivity of the stack (stop band). The eigenfrequencies laying beyond the stop band are unstable with respect to changing the number of layers, and such frequencies have low Q factors. The eigenfrequencies inside stop band are stable and their Q factors exponentially increase with the growth of the number of layers in stack until the saturation because of an influence of material losses in layers. The explicit calculation of the radial distribution of the electromagnetic eigenfields confirms that the energy of field is concentrated in the deepest part of the layered system. The confinement of the energy of optical eigenoscillations takes place in such states. The field amplitudes of oscillations decrease exponentially with a removal from the center of resonator up to external boundary. Therefore, the influence of the nonlinearity must be most substantial in the central part of the dielectric microsphere. We analyze several representative geometries: a dielectric sphere, a metallic sphere with the deposited stack on both of them.

Interferometric measurements of the photoinduced refractive index profiles in photorefractive Bi12TiO20 crystal

Abstract By direct interferometric measurement in Bi 12 TiO 20 under external DC electric field, we demonstrate that the steady-state photorefractive lens produced by the laser beam with the initial circular cross-section is essentially anisotropic: its focusing strength along the direction of the applied electric field is remarkably higher. Experimental data are supported by computer simulations and analytical results.