Biological Glass Fibers: Correlation between Optical and Structural Properties

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 101; no. 10; pp. 3358 - 3363
• Main Authors: Aizenberg, Joanna, Sundar, Vikram C., Yablon, Andrew D., Weaver, James C., Chen, Gang, Tyson, Anthony
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 09.03.2004; National Acad Sciences
• Subjects: Animals; Aquatic life; Biology; Bone fractures; Carbon; Chemical composition; Cladding; Condensation; Cylinders; Euplectella aspergillum; Fibers; Glass; Glass - chemistry; Light; Light refraction; Microscopy, Electron, Scanning; Microscopy, Interference; Molecular Structure; Optical fibers; Optical properties; Optics; Optics and Photonics; Physical Sciences; Physics; Porifera - chemistry; Porifera - ultrastructure; Refractometry; Silicon Dioxide - chemistry; Sponges
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0307843101

Biological systems have, through the course of time, evolved unique solutions for complex optical problems. These solutions are often achieved through a sophisticated control of fine structural features. Here we present a detailed study of the optical properties of basalia spicules from the glass sponge Euplectella aspergillum and reconcile them with structural characteristics. We show these biosilica fibers to have a distinctive layered design with specific compositional variations in the glass/organic composite and a corresponding nonuniform refractive index profile with a high-index core and a low-index cladding. The spicules can function as single-mode, few-mode, or multimode fibers, with spines serving as illumination points along the spicule shaft. The presence of a lens-like structure at the end of the fiber increases its light-collecting efficiency. Although free-space coupling experiments emphasize the similarity of these spicules to commercial optical fibers, the absence of any birefringence, the presence of technologically inaccessible dopants in the fibers, and their improved mechanical properties highlight the advantages of the low-temperature synthesis used by biology to construct these remarkable structures.