We address the behavior of a Y-laser junction, in which the fundamental modes generated by a twin-stripe semiconductor laser are guided for mixing. When the mode-locked laser emission of the pulses in-phase is launched in the waveguide, coherent combination of the modes in the junction is possible. Fast laser oscillations allow for a reduction in the waveguide angle, which serves to diminish transmission losses produced by bending. Shorter separation distances between stripes and reduced branch lengths also optimize the operation of the device.
In previous studies, it was shown that using a Y waveguide, a twin laser output signal could be mixed and coupled to a fiber. The need to adapt the dimensions of the Y waveguide and apply the more restrictive conditions of a coherent regime for laser emission and waveguide mixing, led us to try an MMI coupler to focus the output signal. Herein, ideal 2x1 MMI for this purpose are presented in schematic form. Using a TE mode approximated with Gaussian distributions for the twin laser output signal (the input signal to the MMI coupler), an optimally focused output signal requirement is considered. Possible longitudinal and width dimensions for the couplers are calculated. Similar values of the MMI refraction index to the laser magnitude values were assumed to avoid the drop in transmission produced by reflections at the boundary surface. We also assumed no air gap between the laser and MMI coupler. The functioning of these ideal devices for coherent and incoherent twin laser emission is discussed.
When a twin laser emits the mode fields in coherent form, a Y waveguide can be used to mix and focus the twin signals in the longitudinal axis of a fiber core. In best conditions of coupling, both modal fields are assumed to mix coherently in the waveguide junction. A general expression is derived for the coupling coefficient as a function of the longitudinal displacement between components and misalignments of vertical and angular errors. We show how the Y waveguide avoids the drop in coupling efficiency caused by the separation between main emitters and the longitudinal axis of the fiber, and calculate the coupling factors between each main signal and the signal transmitted through the furthest Y waveguide branch to estimate the order of magnitude of possible losses. The coupling efficiency between the TE fundamental mode field and one branch is compared with the expression obtained using the Gaussian approximation. The intensity transmitted by the whole system using a coupled twin-mode solution is analyzed, taking into account the general coupling coefficients between main stripe outputs and branches.
We considered a model in which two equal sources are symmetrically and vertically separated with respect to a central longitudinal axis, in which a Y-waveguide is placed to couple the two output signals to one fiber. Our aim was to establish the optimum considerations of coherently adding the Gaussian fundamental mode of this twin laser/s system transmitted in the junction waveguide. The coupling efficiency between each laser/s Gaussian output and each waveguide branch, and between the output waveguide and the fiber was calculated, avoiding waveguide rotations or vertical translations. For simplicity, equal minimum Gaussian waist width for each laser/s output and each waveguide branch was assumed. In addition, the fractional power transmission coupling (normalization) was numerically simulated.
To estimate the intensity transmitted by the entire twin laser - Y waveguide - fiber compound system, we used the coupling coefficient of an output laser beam and one branch of the waveguide (assumed equal for both signals in the twin laser/s array) as a weight factor for the field transmitted by the waveguide branch.
An ideal Y-waveguide for coupling to a fiber was designed to diminish coupling losses between the two output signals for a laterally coupled semiconductor twin laser.
Diabetes Mellitus is a chronic disease that is revealed with a lot of alterations due to factors such as an absolute or relative reduction of the insulin. It is usually accompanied by generalized arteriosclerosis and prepares for certain microvasculares pathologies such as retinopathy, nefropathy, and neuropathy. The first effects of diabetes in the retina seem to act on the capillaries. The functional modifications of the retinal circulation appear before the structural ones. These consist of the blood flux damage and the obligation of the hematorretinal barrier with extravasacy as can be proved in the fluorophotometry of the vitreous humor. Nowadays, medical treatments are more effective and only vitrectomy and photocoagulation are used in diabetic retinopathy. For that, the argon laser and the xenon arch are used. The treatment is usually spread panretine, with coagulation in a grid pattern around the eye, avoiding the macula and other vital structures, and treating the neoformed blood vessels. The rate of grave visual loss in the studies carried out with there techniques was 12 in relation to 28 in the non-treated cases. The most important factors of risk found, were the discal neoformed blood vessels and the hemorrhage of the vitreous humor. Adverse effects were found such as the reduction of visual sharpness and the contrition of the visual field, these are greater in patients treated with the xenon arch than in those treated with the argon laser.
One of the techniques for fiber-to-fiber connection is based on a basic interferometric method to obtain a holographic grating acting as a holocoupler. Holographic couplers can be used as memory systems storing information to achieve single or multiple fiber connections using a multiplexed hologram. This device works with high efficiency in short intervals of space and time. Applications can be extended, as well, to codify the stored information in a reflection configuration as a switcher system with a laser diode. The flexibility of this technique allows coupling of alternative focusing elements such as two GRIN lenses and other configurations. In order to develop this application in optoelectronic devices, the recording process must by carefully analyzed. The recording of the holograms has been already resolved for planar and spherical waves. Nevertheless, recordings with Gaussian waves require some conditions to be accounted for due to the width waist and divergence of the output beam of the laser source.
The phase profile of the wave scattered by a GRIN lens has been determined using the
eikonal approximation for the scattering amplitude. This wave acts as the object wave in a
holographic register to construct a GRIN holocoupler. Different geometries in the phase profile
distribution are presented as functions of the taper shape.
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