In this paper we present theoretical and experimental analysis on Nd:YAG laser microwelding for pigtailing laser diode
transmitter through two ball lenses that are employed for effectively matching the elliptical mode field of the laser diode
with the circular on of the single mode fiber. The fiber attachment and the fixing of various coupling components have
been performed in what is so called active alignment process. The system continues measuring the coupled power during
the processes of alignment and attachment of various coupling components as well as the working distance and
misalignment tolerances optimizations. Results of theoretical modeling of laser weld penetration depth agree with the
experimentally measured results in the low laser pulse energy range. Moreover the laser pulse parameters such as,
duration, energy, number of pulse shoots as well as the focusing position over the workpiece and angle of laser pulse
incidence are found to have very significant effects on the weld yields and greatly affect the laser weld depth to width
ratio. Optimization of all the mentioned parameters found to be necessary for achieving strong laser microwelds with
more penetration and less width in the attachments of the sensitive optical components inside the packaged photonic devices modules.
Coupled 1X2 Single Mode Fiber (SMF-28e"R") has been successfully fabricated using a slightly unstable torch flame at a
temperature range of 800°C to 1350°C injecting hydrogen gas flowing at pressure of 1 bar. The coupling ratio and
coupling coefficient can be examined from 1% until 75%. In this paper, we compare the experimental results by using a
simple kinetic model of coupling coefficient where internal and external parametric functions are considered. This
equation is time independent and is then integrated over the direction of the coupling ratio range for various separation
fibers axis between two cores. The result shows that the separation between the cores significantly affects coupling
coefficient exhibiting exponential behavior. In the experiment the coupling coefficient gradient is significantly changed
towards the coupling ratio but in modeling it has a function of separation fiber axis and no power imposed. These
phenomena will determine the effects of power losses at coupling region where fabrications of coupled fibers are
demonstrated.
In this paper we present analysis on three different coupling systems, i.e., butt, single ball lens, and two ball lenses
between the tips of two coupled single mode fiber in semiconductor optical amplifier (SOA) module. The coupling
components inside the module can be aligned in an active alignment process and attached by means of dual beam from
an Nd: YAG laser welding system. The tips of the coupled fiber are ferruled inside metallic tubes to enable the
attachment to the substrates through saddle-shaped welding clips. Investigations of the variations of coupling efficiency
with the with working distance for the three schemes showed that two ball lenses is more efficient with coupling
efficiency of 75% followed by single ball lens at 55% and butt coupling mode at 20% maximum. In addition dual ball
lens configuration have shown to have better longitudinal tolerant even with an elliptical beam profile from the source
fiber. This is however not the case in single ball lens and butt coupling scheme. We also observe however the optimum
separation between the two lenses at in the range between 0.35 mm - 0.45 mm. This is to ensure the coupling efficiency
is the highest possible within the acceptable tolerant misalignments.
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.
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.
In this paper, the design of an optical fiber system for the monitoring of ventilation in a high way tunnel is presented. It employs a star topology for the sensing of dust and CO, at four levels of concentrations, 1.0-4.0 mg/cm3 and 100-400 ppm, respectively. A wavelength demultiplexer (employing an interference filter) is used for distinguishing between the signals from the dust/CO subsystems. A time division multiplexing scheme utilizing a single pulse technique is employed in detecting the dust signals. In the CO subsystem, a switching protocol permits the detection of the optical PCM signals from the sensors. A wind speed/dual direction sensor is spatially multiplexed with the above subsystems. A fiber optic system with eight sensor lines representing the dust/CO subsystems together with a single wind sensor line has been proposed. A laboratory model with four sensor lines has been constructed, and results from preliminary evaluation of the system are given.
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