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The structural control of the monofilament fiber cross‐sectional architecture is a well‐established method for imparting its active functionality. Resulting from a thermal draw, the fiber device, until recently, is expected to be a cross‐sectionally scaled‐down and axially scaled‐up replica of its preform. However, thermal draw is a melt‐shaping process in which the preform is heated to a viscous liquid to be scaled into a fiber. Thus, it is prone to capillary instabilities on the interfaces between preform cladding and materials it encapsulates, distorting the fiber‐embedded architecture and complicating preform‐to‐fiber geometry translation. Traditionally, capillary instabilities are suppressed by performing the draw at a high‐viscosity, large‐feature‐size regime, such that the scaling of the preform into the fiber happens faster than a pronounced instability can develop. It is discovered recently that highly nonlinear, at times even chaotic capillary instabilities, in some fluid dynamic regimes, become predictable and thus engineerable. Driven by ever‐growing demand for enhancing the fiber‐device functionality, piggybacking on a capillary instability, instead of suppressing it, establishes itself as a new material processing strategy to achieve fiber‐embedded systems with user‐engineered architecture in all 3D, including the axial. Considering this development, the notable emerging methodologies are cross‐compared for designing 3D fiber‐embedded architectures.
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Cross-sectional refractive-index variations in fiber Bragg gratings measured by quantitative phase imaging
Unexpected micrometer-scale patterns in the induced refractive index of various commercial fiber Bragg gratings (FBGs) are observed in the cross-sectional fiber directions, which are in addition to the expected periodic variations along the fiber axis. These measurements were made using 3D tomographic deconvolution phase microscopy, a type of quantitative phase imaging. The cross-sectional patterns observed are shown to exhibit a variety of appearances, including fringes normal to the fiber axis and radial blades, the details apparently depending on the FBG writing method.
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- Award ID(s):
- 1915971
- PAR ID:
- 10127414
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Letters
- Volume:
- 45
- Issue:
- 1
- ISSN:
- 0146-9592; OPLEDP
- Format(s):
- Medium: X Size: Article No. 53
- Size(s):
- Article No. 53
- Sponsoring Org:
- National Science Foundation
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