Showing papers on "Mode scrambler published in 1998"

Single-mode excitation of multimode fibers with ultrashort pulses.

Abstract: Single-mode excitation of step-index multimode fibers with light sources with short temporal coherence lengths is demonstrated. Multimode fiber designs with reduced microbending-induced mode coupling are described that allow the propagation of the fundamental mode over long lengths with negligible mode coupling even in the presence of tight fiber bends. At a wavelength of 1.56microm a fiber with a core diameter of 45microm can preserve the fundamental mode for a propagation length of ~20m . Such fibers allow coiling with a coil diameter as small as 7cm.

Mode mixing and power diffusion in multimode optical fibers

Abstract: Mode coupling and power diffusion in multimode optical fibers is considered. In particular, the mechanisms responsible for the coupling are investigated and their characteristic lengthscales explored. An appropriate local coordinate system is introduced in which arbitrary curvatures may be considered. Through an asymptotic analysis, the mode coupling equations are shown to reduce to a nonconstant coefficient diffusive equation for the power coupling. This power coupling is shown to be strongly driven by the degenerate mode structure of the multimode fiber.

Optical fiber polarization scrambler and operating parameter input method therefor

Abstract: An optical fiber polarization scrambler decreasing the degree of polarization (DOP) of light efficiently using at least two optical fiber birefringence modulators (10, 11) and an operating parameter input method for the same. Birefringence modulators are constructed with hollow cylindrical piezo devices (10, 11) and a strand of optical fiber (30) wound continuously on the outer walls of the piezo devices (10, 11). An angle between the birefringence modulators consisting of the optical fiber polarization scrambler is configured to compensate the effect of circular birefringence. A method for exactly configuring birefringence modulation frequency and birefringence modulation amplitude to achieve effective polarization scrambling for the optical fiber polarization scrambler is also provided.

Narrow-band-mode converting Fabry-Perot output coupler for fiber lasers

Abstract: Summary form only given. Tilted Bragg gratings have been demonstrated to be efficient mode converters in two-mode fibers. A pair of tilted Bragg gratings in a two-mode section of a single-mode fiber can be written in a way to become a nonreflecting narrow-band transmission filter. The latter device behaves like an ordinary Fabry-Perot with one exception: light is only reflected in the LP/sub 11/ mode and therefore not guided by the adjacent single-mode fiber. In this paper we present a Fabry-Perot device where mode conversion (LP/sub 01/-LP/sub 11/) is accompanied by mode reflection. The result is a narrow-band transmission and reflection at resonance used as an output coupler for fiber lasers.

Observation and discrimination of the mode patterns in a micron-sized hollow optical fiber and its synthetic measurements: far-field micro-imaging technique

Abstract: We report a far-field micro-imaging technique that is used for the observation and discrimination of the mode patterns in a micronsized hollow optical fiber as well as for the synthetic measurement of the fiber. By using an M-20x microscope objective lens, we obtained images, magnified by a factor of about 460, from the mode patterns at an output end facet of the hollow fiber with relative measurement accuracy better than 3%. This method can be used for clear identification of the mode patterns in the hollow fiber and detailed study of the relationship between the excitation conditions and the excited modes in the hollow fiber. Moreover, it is useful for the measurement of the geometrical sizes of the hollow fiber and fortesting the coupling efficiencies of the core and cladding modes in their mixed mode pattern. In addition, this method can be also used in the generation of a dark hollow laser beam with 10-^m dark-spot size and the measurement of the focused-spot size of a Gaussian laser beam with about 1-µrn diameter.

Optical communications system for transmitting signals via light conductors, has mode coupler or mixer for reducing dispersion at or after mode transition and before transmission path

Abstract: The system has a LED or laser (1) on the input side from which light is fed into a monomode fiber (3). A multi mode fiber (7) forms the transmission path (17). A transition from the monomode fiber to the multi mode fiber is arranged before the transmission path. The light wave transmission is based on an analogue data transmission. A mode coupler or a mixer (13) for reducing dispersion, especially mode dispersions, is arranged at the transition, or after it, and before the transmission path.

In multimode fiber-based single-mode amplifier

Abstract: An optical amplification system, comprising: a laser source (10) for generating an input beam having a nearly diffraction-limited mode; a multimode fiber amplifier (12); wherein said multimode fiber amplifier has a double jacket structure; wherein said multimode fiber amplifier (12) comprises a fiber core, wherein the active dopant of the multimode fiber amplifier (12) is limited in cross-sectional area which is substantially smaller than the fiber core area; coupled to a mode converter (14) for receiving the input beam and for converting the mode of the input beam to adapt to a fundamental mode of the multimode fiber amplifier (12), and for providing a mode-converted input beam into the multimode fiber amplifier (12), and to the multi-mode fiber amplifier (12) pump source (20), wherein said pump source (20) pumps the multimode fiber amplifier (12) optically, wherein said multimode fiber amplifier is pumped coat, and wherein said multimode fiber amplifier (12) provides at its output an amplified beam substantially in the fundamental mode with an M