Experience from Chiral Photonics, Inc.

In most cases, microbending is considered a detrimental property of optical fibers and steps are taken by optical fiber manufacturers and optical system designers to reduce light propagation losses arising from this mechanism. The cumulative effect of microbends is to reduce the intensity of light propagating in the core along a given length of the fiber by causing light to scatter out of the fiber. In some cases people have used either periodic or random microbending, or a combination of these, in optical fibers to act as sensors of the surrounding environment. As a change in the local environment produces or relieves microbending in a fiber segment, the intensity of light from a light source coupled at one end of a fiber, propagating through the core of the fiber and reaching the other end of the fiber to be measured by a detector is a repeatable function of a target environmental parameter such as strain or temperature. It is the intensity of light that survives the effects of microbending which is generally of importance to those using optical fiber. To them the “lost” light is scattered out of the fiber. For lighting purposes, however, the scattering of light out of the fiber is what is most important. The control and repeatability of any desired luminous profile out of an LED fiber lamp is critical for both aesthetics and for large scale manufacturing. A microbending profile is difficult to repeat and is usually a result of stresses exerted on the fiber by the local environment. The profile is not permanently embedded in the fiber structure.

The technology pioneered at Chiral Photonics, Inc uses controlled microforming of optical fiber by passing it through a small oven or heater. The fiber is twisted as it temporarily melts in the oven. The twist profile along the length of the fiber can include sections of constant, accelerated and decelerated twist rates and becomes a permanent feature of the fiber structure. Twisting an optical fiber results in a helical structure if the fiber core is offset from the center of the device twist or if the core is not circular in shape. Depending on the original fiber core/cladding cross sectional profile and the twist method, all single helix, double helix, and multi-helix structures can be microformed along the fiber axis. These helical structures scatter light out of the fiber comparable to microbending except that new process introduces a controlled, permanent structure into the fiber, creating a new, mass scale manufacturable light filament replacement. The twist profile (or twist rate as a function of distance along the fiber axis) is selected so that substantially all the light coupled into the fiber from a LED source is scattered out of the fiber with luminous intensity along the length of the twisted fiber that is uniform or of some desired luminous profile. For a uniform luminous profile, since the amount of light intensity in the core decreases as a function of distance from the light source, the twist rate (turns/unit length) must increase accordingly so that the amount of light scattered per unit length along the fiber will remain constant.

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