Fibre-Optical Features of a Glass Sponge Some Superior Technological Secrets Have Come to Light from a Deep-Sea Organism

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brief communications Fibre-optical features of a glass sponge Some superior technological secrets have come to light from a deep-sea organism.

odern technology cannot yet com- between the spicule and air (Fig.1d,right). shows, for example, that sodium ions are pete with some of the sophisticated These biological fibres therefore resem- present throughout the spicules,particularly Moptical systems possessed by bio- ble commercial telecommunication fibres, in the core. Although sodium ions (and logical organisms1–3. Here we show that in that they are made of the same material many other additives) are desirable fibre- the spicules of the deep-sea ‘glass’ sponge and have comparable dimensions, as well as optic dopants, they present a manufacturing Euplectella have remarkable fibre-optical similar refractive indices for the high-index challenge, for example by causing devitrifi- properties, which are surprisingly similar to core and a low-index cladding. They also cation at high temperatures. those of commercial telecommunication function as efficient single-mode, few-mode Our results suggest the intriguing possi- fibres — except that the spicules themselves or multi-mode waveguides, depending on bility that the spicules of Euplectella,beyond are formed under normal ambient condi- the optical launch conditions. structural anchorage support, could also tions and have some technological advan- The principal weakness of commercial provide a highly effective fibre-optical net- tages over man-made versions. optical fibres is that they fracture as a result of work, which may be useful in distributing The skeleton of the hexactinellid class of crack growth, whereas the spicules’ lamellar light in its deep-sea environment. This illu- sponges is constructed from amorphous, layers, connected by organic ligands at the minating sponge should also shed light on hydrated silica3–6. Euplectella builds an intri- fibre’s exterior, provide an effective crack- low-temperature, biologically inspired pro- cate cage (Fig. 1a), which typically houses a arresting mechanism and enhance fracture cesses that could give rise to better fibre- mating pair of shrimp (hence its nickname, toughness6,8,9. Another superior feature of optical materials and networks. ‘Venus flower-basket’) and is composed of a the spicules is their formation under ambi- Vikram C. Sundar*, Andrew D. Yablon†, lattice of fused spicules4 that provide extend- ent conditions, a process that is regulated John L. Grazul*, Micha Ilan‡, ed structural support. by organic molecules10,11. This ambient- Joanna Aizenberg* A network of anchorage spicules temperature process, unlike the high-tem- *Bell Laboratories/Lucent Technologies, (basalia) extend outwards in a crown-like perature manufacture of man-made fibres, Murray Hill, New Jersey 07974, USA formation. These spicules are generally 5–15 allows the structure to be doped with special- e-mail: [email protected] cm long and 40–70 m in diameter; their ized impurities that improve the refractive †OFS, Murray Hill, New Jersey 07974, USA native cross-section is homogeneous and index and therefore the wave-guiding prop- ‡Department of Zoology, Tel Aviv University, they have no structural boundaries. Under erties. Our preliminary elemental analysis Tel Aviv 69978, Israel stress or etching,the spicules reveal a charac- teristic layered morphology6 and cross-sec- a b tional variations in composition that appear as three distinct regions: a pure silica core of about 2 m in diameter that encloses an organic filament; a central cylinder that has the greatest organic content of the three; and a striated shell that has a gradually decreas- ing organic content and which is glued together by organic films (Fig.1b). We anticipated that the spicules’rich sub- structure should be reflected in their optical properties as well. Indeed, interferometric c refractive-index profiling7 revealed three regions that correspond to the three regions of structural composition (Fig. 1c): a core with high refractive index that is comparable to (or higher than) that of vitreous silica; a cylinder of lower refractive index that sur- 1.46 core rounds the core; and an oscillating pattern with progressively increasing refractive 1.45 index at the outer part of the spicule. Figure 1 Structure and fibre-optical properties of spicules in the 1.44 cladding cladding To determine whether this typical ‘core- sponge Euplectella. a, The glass sponge, showing the basket-like cladding’ refractive-index profile endows cage structure and basalia spicules (arrow). Scale bar, 5 cm. 1.43 b, Mechanically cleaved spicules show three structural regions. OF, Refractive index the spicules with wave-guiding properties, 1.42 SS CC SS we investigated their transmission charac- organic filament; SS, outer striated shell; CC, central cylinder. Inset: –30–20 –10 0 10 20 30 teristics. We found that embedded spicules smooth cross-section of a stress-free spicule. c, Interferogram Radial position (µm) act as single- or few-mode waveguides — (top) and corresponding refractive-index profile (bottom) of a that is, light waves are effectively confined spicule. Dashed line indicates the refractive index of vitreous silica. d to the core,where refractive index is highest d, Wave guiding by individual spicules upon coupling with white (Fig. 1d, left). When light was coupled into light. Spicules embedded in epoxide act as single-mode or few- free-standing spicules, they functioned as mode waveguides (left); free-standing spicules act as multi-mode multi-mode fibres, with most of the waveguides (right). Scale bar, 10 m. Further details are available light filling the entire cladding, because from the authors. of the enhanced refractive-index contrast

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Previous models of language dynamics bilingual societies do, in fact, exist. But the Competing financial interests: declared none. have focused on the transmission and evolution of syntax, grammar or other structural Figure 1 The dynamics of lan- properties of a language itself 2–7. In contrast, guage death. Symbols show the ab the model we describe here idealizes lan- proportions of speakers over time 0.9 0.7 guages as fixed, and as competing with each of: a, Scottish Gaelic in Sutherland, Scotland9; b, Quechua in Huanuco, other for speakers. For simplicity, we also s = 0.33 s = 0.26 assume a highly connected population, with Peru; c, Welsh in Monmouthshire, no spatial or social structure, in which all Wales10; d, Welsh in all of Wales, speakers are monolingual. from historical data10 (blue) and a Consider a system of two competing lan- single modern census11 (red). Fit- guages,X and Y,in which the attractiveness of ted curves show solutions of the a language increases with both its number of model in equation (1), with para- speakers and its perceived status8 (a parame- meters c, s, a and x(0) estimated 0 0 ter that reflects the social or economic by least absolute-values regres- 1880 2000 1930 2030 opportunities afforded to its speakers). Sup- sion. Where possible, data were Year pose an individual converts from Y to X with obtained from several population cd a probability, per unit of time, of Pyx(x,s), censuses collected over a long 0.14 0.5 where x is the fraction of the population timespan; otherwise, a single speaking X, and 0s1 is a measure of X’s recent census with age-structured Fraction of minority speakers relative status. A minimal model for lan- data was used (although errors are s = 0.40 s = 0.46 guage change is therefore introduced, the size of which are reflected in the differing fits in d). s = 0.43 Using the fraction of Catholic dx — yPyx(x,s) xPxy(x,s) (1) masses offered in Quechua in Peru dt as an indicator, we reconstructed an approximate history of the lan- 00 where y1x is the complementary frac- guage’s decline. 1900 2020 1900 2020 tion of the population speaking Y at time t. Year By symmetry, interchanging languages