Large core multimode fibers (MMF) in the range of 100-1000 μm core diameter are commonly used
with infrared lasers in medical, bio-photonics and other fiber optics applications. Angular misalignment of the laser
source to the multimode fiber can lead to unusual angular patterns at the exit of the fiber. The angular content of the
launch beam can result in under-filling, non-uniform angular filling, or over-filling of the MMF modes. Typically,
the beam condition optics at the distal end of the device has a limited impact on these angular modes. The result is
often loss of output power at the distal end or an uncontrolled angular and/or spatial distribution of light. We have
investigated angular misalignment perturbations of various fiber and coupling optics combinations in a medical laser
therapy device. We have quantified the resulting far field perturbations, as well as the resulting broadening of the
fiber output numerical aperture (NA). Angular misalignment may cause the development of so called "donut modes"
with highly inhomogeneous far field mode distribution, as well as a substantial NA broadening effect which may
impact therapy. We have shown that in order to avoid these perturbations, tight tolerancing of fiber coupling opto-mechanics
as well as a thorough alignment procedure is required.
The utilization of micro-optical components in systems for optical beam deflection and modulation offers the possibility for realization of miniaturized switches and scanners. As the required displacement of the micro-optical components for efficient beam manipulation is quite small, high speed actuators with small electrical power consumption can be used. We present micro-optical configurations and discuss their potential for the creation of different types of miniaturized switches. The combination of micro-optical components already available and semiclassical piezoelectric actuators leads to new types of switching and modulation systems for a very broad spectrum of applications.
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