Michael J. Winningham

Single-mode fiber for high-power applications with small bend radii

A fiber design is proposed that addresses bend loss, high power and handleability concerns for fibers deployed in high power devices and associated pigtails. If bending is tight enough to leak power from the core into the glass cladding, a coating with a sufficiently low index traps this potentially dangerous power in the cladding. The coating is also designed to keep cladding power from damaging downstream devices and terminations. Loss due to tight bends is minimized by use of a glass design with a small mode-field diameter. This glass design further suppresses the high power failure mode. Over the high power coating is a thick layer of a toughened polymer coating which provides a significant increase in mechanical protection over most commercial coatings.

Analysis of single mode bent fiber failure under high power conditions

Optical fiber networks are being developed that require higher optical power levels. Examples include long haul communication with Raman amplification and fiber to the premises. Previous studies indicate that tightly bent optical fiber can mechanically fail when exposed to high optical power levels. In an extreme case where fiber is sharply bent and subjected to a power level of 1 to 2 W in the near-infrared wavelength window, optical fiber can fail in minutes. It also has been shown that time to failure decreases with increasing bend stress and optical power. This study is a further investigation of the physical events leading to failure. Previously we demonstrated that the optical signal that escapes the core of bent fiber passes into the coating, where a small amount is absorbed and converted to heat. As a result the coating can be heated to significant temperatures resulting in degradation over time. This paper focuses on several key aspects of the failure kinetics associated with bent fiber under high power. As a result of bending, optical power leaked from the core is distributed in the glass cladding and polymer coating. We have modeled this power distribution and compared it with measured temperature profiles in the coating. The results show that this redistribution of the power is key to establishing the distribution of temperature in the coating and ensuing degradation. This understanding is used to design glass and coating solutions for inhibiting this potential failure mode.