Ishac Kandas

Second harmonic generation in thin optical fibers via cladding modes

Since silica goes under the category of amorphous materials, it is difficult to investigate important processes such as second harmonic generation (SHG) in silica-based fibers. In this paper, we proposed a method for SHG relaying on cladding modes as pump modes. Cladding modes are introduced in optical fibers through tilted long period grating (T-LPG), where power of core mode is transferred into cladding modes. By functionalizing T-LPG with nonlinear coating, the interaction occurs between cladding modes and the coating material, consequently second harmonic signal (SHS) is generated with efficiency up to 0.14%.

Sensitivity improvement of reflective tilted FBGs

Tilted fiber Bragg gratings are used as energy couplers in which the core mode and cladding modes can be coupled together. Cladding modes have extensive importance in sensing applications due to their sensitive characteristics to the surrounding refractive index. The cladding modes are investigated theoretically by studying a three-layer model of optical fibers, whereas the core mode is investigated by studying a two-layer model of optical fibers. The analysis reveals that to increase the coupling of the energy transferred from the core mode to cladding modes, the cladding radius needs to be decreased. Such behavior is illustrated through studying the change in the electric field distribution and is used to improve the sensitivity of the sensing refractive index of the surrounding medium.

Parametric Study of Up-Conversion Efficiency in Er-Doped Lanthanide Hosts Under 780 nm/980 nm Excitation Wavelengths

Up-conversion is a process of converting low energy light photons to higher energy ones, which can be extensively used in many applications. This paper presents a detailed parametric study of the up-conversion process under different wavelength excitations—780xa0nm and 980xa0nm—showing the optical conversion mechanisms that affect the emitted light quantum yield efficiencies. The studied material is erbium-doped β-NaYF4 material, which is one of the most recently studied materials due to its low phonon energy. The studied simulation considers most processes and possible transitions that can take place between Er3+ ions. Einstein coefficients, which are the main parameters that are responsible for the transitions probabilities, are discussed in detail using Judd–Ofelt analysis. In addition, the effect of changing some parametric values is discussed, showing their optimum values that could improve the quantum yield efficiency. This model is very promising, and generic, and can be applied for any host material under any excitation wavelengths by varying the material-dependent parameters.

Solution of dispersion relations of multilayer optical fibers: a comprehensive study

The exact solution of the modal dispersion relation of multilayer optical fibers is very critical and complicated, especially in the case of complex refractive indices of some layers added to the fiber. In this paper, a different methodology is proposed to solve the complex dispersion relations for cladding modes, based on the well-defined proper expressions of electromagnetic fields in the different layers of optical fibers. An optical fiber, coated by a dielectric nonlinear layer, is analyzed using the exact four-layer model, and the results obtained are compared with those analyzed in the literature based on the approximate three-layer model, where the effect of the coating layer is neglected when solving the dispersion relation. The results obtained show a remarkable difference between the exact and the approximate values of the effective refractive indices of the cladding modes. Inappropriate values of the effective refractive indices strongly affect phase matching and coupling between modes, which are required in different applications such as second-harmonic generation. The proposed approach for solving general dispersion relations is also employed to obtain complex values of the effective refractive indices of the cladding modes for a five-layer optical fiber with a metallic thin film inserted between the nonlinear layer and the fiber cladding. Using the appropriate expressions that describe the electric field in the different dielectric and metallic layers of optical fibers, field distributions are displayed for some cladding modes.

Amendment performance of an apodized tilted fiber Bragg grating for a quasi-distributed-based sensor

In this work, the characteristics of reflectivity spectra produced inside a reflective-tilted fiber Bragg grating (R-TFBG) are investigated, seeking a remarkable performance that could be able to upgrade the sensitivity range for temperature-strain sensors of quasi-distribution type. We introduce an optimized performance through a comparative investigation among different evaluation parameters, such as core radius, tilt angle, and the elite selection of apodization profiles, in addition to the traditional parameters, such as grating length, L, and index modulation amplitude, Δn. Regarding the tilt angle, its increase affects the full width at half-maximum (FWHM) affirmatively, while having a negative impact on the maximum reflectivity. By controlling L and Δn, a compromised solution is achieved to retrieve the maximum reflectivity to be around 1.0. Regarding the sidelobes, the Kaiser profile is the best candidate that minimized the main sidelobe level (MSL) and raised the sidelobe suppression ratio (SLSR) at any tilt angle, while tanh apodization is the best choice from the perspective of raising the ramp down sidelobes asymptotic decay. The contrasts in the optimization process are examined through investigating the R-TFBG quasi-distributed sensors to be applied to a temperature-strain sensing system. The objective is to evaluate an assessment for the performance of a sensor system that extends the range and efficiency of temperature-strain ranges. Based on our analysis, the sensitivity range is upgraded for a temperature change to reach 179°C and for strain to be 3000 μϵ at a tilt angle of 10° with a FWHM of 0.063 nm, attenuation of -154u2009u2009dB for an MSL of 75.5%, and an SLSR of -60u2009u2009dB/nm.

Efficient apodized-TFBG for DWDM systems

This study is carried out to optimize the tilted fiber Bragg grating (TFBG) performance in the reflection mode. This optimization starts by controlling the tilt angle, that causes an intensive decrease in the full width at half maximum (FWHM) at the expense on the peak reflectivity. Grating tilt angle is compromised at 5° where a mutual point between narrower FWHM and unity peak reflectivity is achieved successfully. Then, different apodization profiles are applied with TFBG that yield a better performance concerning sidelobes. In general, the TFBG shows a better reflection spectrum when compared to regular FBG. The Nuttall apodization achieves the best performance. Asymptotic decay of 17 dB/nm, low main sidelobe strength (MSLS) of -206 dB, and a narrow FWHM around 0.16 nm were achieved.