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Olivrodapsicologianigelbensonempdf ##TOP##

January 15, 2023

Olivrodapsicologianigelbensonempdf ##TOP##

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olivrodapsicologianigelbensonempdfHighly successful laser cavities require efficient coupling to an optical fiber through a small mode-size input aperture. High-power lasers generally have an array of power-receiving semiconductor diodes, such as laser diodes or a diode laser array, which produce the output beam. The effective coupling of the power from the laser diode to the output fiber requires low loss optical elements. It is highly desirable to have an output collimating lens which is placed as close as possible to the laser diode to reduce the overall size of the laser package. The positioning of the lens is adjusted to maximize the coupling into the optical fiber and to minimize the power loss between the lens and the diode.
It is also desirable to have a lens with high numerical aperture (NA) to produce a large mode-size at the output aperture. An ideal output collimating lens would have a NA of 1.0 and an effective focal length of about one-half the wavelength of the light in the fiber. An NA of 1.0 is well within the technically challenging limits of lens fabrication. However, there are many other cases where an NA of greater than 0.5 is needed. A lens with an NA of about 0.6 is widely used as a fiber collimator.
A lens with an NA of 0.66, created by C. M. Hopkins, et al., Electronics Letters, Vol. 10 (1974), pp. 95-96, has an annular zone as shown in FIG. 1. However, the geometry of the Hopkins device produces a mode size which is far too small for a useful device.
In a diode laser cavity of a linear array configuration, there must be a continuous waist between each pair of adjacent laser diodes. This waist usually has a minimum waist width less than the diameter of the optical fiber, and it is usually aligned along the longitudinal axis of the diode array. This minimum waist width depends on the output beam curvature and on the mode characteristics of the used fibers. As the laser diode power increases, the minimum waist width also increases.
It is known to provide a collimating lens close to the laser diode which focuses an output beam of the laser diode into a fiber; as the power of the diode increases, the effective focal length of the lens should be increased and the size of the waist of the lens should decrease in order to couple a larger fraction of the output



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