nan Saktioto

Mode matching for efficient laser diode to single mode fiber coupling

This paper presents some analysis for the matching between the elliptical mode field of 1550nm high power laser diode with the circular mode field of the single mode fiber in order to obtain high coupling efficiency with relaxed misalignment tolerances. Three coupling schemes namely Butt, single ball lens and double ball lenses coupling schemes have been employed in pigtailing the butterfly laser diode module using laser welding technique with dual beams from Nd:YAG laser welding system for the attachment of coupling components. The process of fiber attachment to laser diode and welding of various coupling components, such as lens holders, fiber ferrule and welding clips have been performed in what is so called active alignment process, where the system continues measuring the coupled power during the process of coupling and welding of coupling components in their holder to each other and to the main substrate. It has been found that double ball lenses coupling scheme is efficient and more effective for mode matching of highly elliptical (large divergence ratio) laser diode mode field with the circular mode field of a single mode fiber, whereas for small divergence ratios the single ball lens is adequate.

Laser-Induced Graphite Plasma Kinetic Spectroscopy under Different Ambient Pressures

The laser induced plasma dynamics of graphite material are investigated by optical emission spectroscopy. Ablation and excitation of the graphite material is performed by using an 1064nm Nd:YAG laser in different ambient pressures. Characteristics of graphite spectra as line intensity variations and signal-to-noise ratio are presented with a main focus on the influence of the ambient pressure on the interaction of laser-induced graphite plasma with an ambient environment. Atomic emission lines are utilized to investigate the dynamical behavior of plasma, such as the excitation temperature and electron density, to describe emission differences under different ambient conditions. The excitation temperature and plasma electron density are the primary factors which contribute to the differences among the atomic carbon emission at different ambient pressures. Reactions between the plasma species and ambient gas, and the total molecular number are the main factors influencing molecular carbon emission. The influence of laser energy on the plasma interaction with environment is also investigated to demonstrate the dynamical behavior of carbon species so that it can be utilized to optimize plasma fluctuations.

Growth dynamics and characteristics of fabricated Fiber Bragg Grating using phase mask method

In this paper, Fiber Bragg Gratings (FBGs) are written by photoinduced refractive index changes in optical fibers. Experimental setup and results are presented to show the growth dynamics and the characteristics of the FBG that are written using phase mask method with different exposure time. In this paper, the effect of various UV exposure times and pulse energy during fabrication onto the reflectivity and Bragg wavelength has been defined.

Effects of unstable torch flame for a fused single mode fiber

Coupled 1X2 Single Mode Fiber (SMF-28e®) is successfully fabricated using a slightly unstable torch flame at a temperature range 800°C to 1350°C by injecting hydrogen gas flowing at pressure of 1 bar. The fiber structure and geometry are investigated for both core and cladding before and after fusion. Coupled fiber is studied using Field Emission Scanning Electron Microscopy (FESEM) and Electron Dispersive X-Ray (EDX) System. The pulling length speed, coupling time, coupling coefficient and evolution of coupling ratio from 1% until 75% are examined to study the heating effects at the coupling region. The result shows that the core and cladding geometry of fiber are reduced 80-92%. Their structures are changed which are shown by the changes in the refractive indices. These phenomena have wide applications in industrial communications and sensors such as for optical switching and tunable filtering.

A tolerant coupling scheme for pigtailing laser diode module in active alignment process

A laser diode transmitter packaged in a butterfly module is coupled into a single mode fiber using double small ball lenses. The process of alignment and fixing of all the components inside the module is performed in an active alignment procedure, where the laser diode is powered and the output power is continuously measured during the alignment process of all coupling components to determine the optimum positions for maximum coupling efficiency and then fixed in their holders and to the main substrate by laser welding technique using dual beam Nd:YAG laser welding. The double ball lenses coupling scheme found to be very effective in mode matching between laser diode and single mode fiber. The axial, lateral and angular 1dB misalignment tolerances are enhanced for the transformed laser mode field radii in both X and Y directions. The experimentally measured coupling efficiency of the proposed coupling system was around 75% with a relaxed working distance (separation of the coupling system from the fiber tip) in the range of (2-4mm) by optimizing the separation between the two lenses as well as the separation between the first lens and the facet of the laser diode. The experimental results match very well with those obtained theoretically by employing ABCD ray tracing matrix.

Computationally numerical experiment of carbon species densities for thermal plasma dynamic

The present work develops a computationally effective one-dimensional sub grid set in numerical integration for density formulation from thermal plasma. The model incorporates two-body and more collision effects throughout Carbon plasma using continuity equation. The carbon gas inter electrode gap is accelerated by the electric field to produce plasma. In this model the reaction processes of carbon species is identified. The extrapolation of species dominant in arc discharge process is critical issue in significant for predicting carbon nanostructure production. In this paper, we describe chemical kinetic models and their possibilities of carbon ion and neutral species production based on collisions and time dependence. The results show the reaction rate of Carbon ions calculated at 7.85 × 1028 m-3 s-1 while the temperature increment decreases, the reaction rate is up to 6.25 × 1027 m-3 s-1. The electron density reduces until 108 m-3 from initial condition at 1 atm. However, the electron density increases 1013 m-3 from 0.05 eV-0.3 eV. The ionization of Carbon reaction has been affected by pressure and temperature which gains a quantitative understanding of the density at equilibrium state.

Current densities effects in the focussing phase of a plasma focus device

Summary form only given. Current density plays an important role in the radiation produced by the system. Low and high current density will exhibit different characteristic, thus contribute to various outcomes. In this research, the effects of current densities of NX2 plasma focus device are explored by using Lee code. Lee code will be used to simulate the operation system of plasma focus device with neon, nitrogen, hydrogen and deuterium filling gas. The numerical experiments of each gaseous are carried out by using different range of pressures. The energy beams and current density were recorded, where the highest value obtained is in hydrogen medium with 204.6J and 3.1×109 Am-2. The plasma focus was characterized and the current density effects are observed for all filling gaseous.

Distribution Function for Nonlinear Potential Gradient High Pressure Plasma

The effect of carbon ion species distribution in arc discharge process becomes significant for the formation of carbon nanomaterial. It is essential to account for the velocity distribution of each carbon ion species to determine the greatest contribution from the kinetic energy possesses by each species that govern the binding energy for carbon formation. The resultant speed of the particle as a result of collisions determines the resultant force exerted by the particles which consider in non-conservative force. The variation of velocity distribution is investigated while the reaction rate for carbon species during kinematic process, the transient condition for carbon species is analyzed. Collision rate of carbon ion species is underway to derive carbon ion motion in electrode gap region where the external electric field is constant. The theoretical development has shown that at constant pressure and temperature, carbon ion species possess the resultant speed due to collision frequency affecting the distribution function quantified for each species.

Slow light in vertically coupled resonator of conical rod portion

Resonator structures have been proposed and modified as a method of reducing the group velocity of light for optical buffering in telecommunication field. This makes the characterization and optimization of the method become important to apply. In this paper, the characterization of vertically coupler resonator is modified by investigating its geometrical parameters. The modified models with conical rod portion as the slow light structure is described where the group velocity parameters are varied. The results found that the separation gap between fibers, lg and the rod radius, a are significant in reducing the group velocity of light through such a system in the case of lossless resonators.

Investigation of noise effects of CMS laser lineshape and frequency fluctuations

Lineshape and frequency fluctuations actually cause the optical field of current modulation semiconductor laser (CMS) laser beam to deviate from a pure sine wave [1]. This paper investigates the lineshape of a CMS laser for two distinct types of frequency noise. In the first case the investigation analyzes on the low-pass filter, the frequency noise level is a constant δo below a cutoff frequency but zero above this threshold. In the second case on high-pass filter the frequency noise level is a constant δo above a cutoff frequency but zero below this threshold. Investigations observed inspire us to focus for separation of the frequency noise spectrum into two regions wherein due to the effect of noise on the lineshape is radically different in the slow modulation area in a left side of the diagonal line where the noise contributes to the laser linewidth, with a Gaussian shape, and the other one the fast modulation area in a right side of the diagonal line, where the noise contributes only to the wings of the line (sidebands) and not to the linewidth, thus transforming the lineshape from Gaussian to Lorentzian.