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[nimsconfproc.pdf](https://mdr.nims.go.jp/filesets/db32824f-4be2-48ab-840d-233e9b52074b/download)

## Creator

[TODOROKI, Shin-ichi](https://orcid.org/0000-0003-3986-1900)

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[ACTIVE SOFT GLASS meets PASSIVE OPTICAL FIBERS](https://mdr.nims.go.jp/datasets/3ed0780b-9329-4444-8551-5f9bb4697f04)

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ACTIVE SOFT GLASS meets PASSIVE OPTICAL FIBERSS. TodorokiAdvanced Materials Laboratory, National Institute for Material Science1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanIntroductionOptical fibers have been playing an important role in developing optical communication systems. Two representa-tive examples are the fibers for long distance transmission and Er-doped fiber amplifiers (EDFA). Most of them aremade of silica glass, whose excellent thermal stability makes their manufacturing process simple with low cost. Asfor the glass materials other than silica glass, although they have a potential to exhibit unique optical properties,they also have a disadvantage that fiber drawing is harder because of their poorer thermal stabilities.As shown in Fig. 1(upper), fiber drawing process consists of several heating and cooling operations, in whichthe fiber preform is annealed near the temperature range for nucleation and crystal growth. Thus, fiber-drawablecomposition range is limited, as shown in Fig. 2 for example, where the glass can survive not to be precipitatedduring the heat treatment.In this study, a new fabrication method is proposed in order to expand the composition range of non-silicaglasses applicable for optical devices. The underlying idea is a hybridization of silica fiber and non-silica glasswith low softening temperature (soft glass) by one heating process to suppress precipitation (see Fig. 1(lower)).ExperimentalA small piece of zinc tellurite glass (xTeO2-(100 − x)ZnO, x = 80, 90, 100 in mol%) was melted on a Pt plate(10mm¤) with a heater. Two fibers were inserted into the glass melt from its side. Then, the plate is loweredto leave a small amount of the melt between the two ends. The fibers were immediately moved to an appropriateposition before the melt was solidified (see Fig. 3(a)[1]). The movement of the fibers and the heater described abovewas controlled by a personal computer and ends within few seconds. Transmittance of the laser light through thestructure (insertion loss) was measured by an optical multimeter (AQ-2140, Ando Electric Co.,Ltd.,λ = 1.31µm).TimeTemp.TmTxTsTgReforming DrawingMachiningMeltingIUNucleationFiber drawingIUTimeTemp.TmTxTsTgThis processCrystal GrowthTeO2ZnO Na2O806040202040608020406080Glass Formable  FiberdrawableUS Pat. 5,251,062Snitzer et al. (1992)This work• NTT made   Fibers by   +Bi2O3Figure 1: (left) Illustrations describing heating schedules during (upper) fiber drawing and (lower) this study.Characteristic temperatures are denoted asTm for melting,Tx for crystallization,Ts for softening andTg forglass transition. Temperature range for nucleation is located aboveTg (denoted as ’I’ in the figure) and crystalgrowth belowTm (’U’).Figure 2: (right) An example of composition range for tellurite glass fibers (closed marks) which are used forEr-doped fiber amplifiers. The compositions examined in this study is also plotted as open squares.Figure 3: Photographs of an optical coupling structure. (a, left) The diameter of the fiber is 125µm and thedistance between the two fiber end is about 0.6mm. (b, right) The fiber is bended in order to test its toughness. Thediameter of the coin is 22mm.Table 1: Properties of the glasses used in this study. Data source: O.V. Mazurin et al., Handbook of glass data.thermal expansion coefficient (×10−7/◦C) refractive indexSiO2 ∼6 1.4680TeO2-20ZnO (mol%) 170 2.08Results and DiscussionJoint structures were made without any apparent precipitation even for the compositions out of fiber-drawable re-gion as shown in Fig. 2. This structure is not so fragile if properly treated that the fiber segment can be bendedwithout fracture as shown in Fig. 3(b). Typical insertion loss value is 10dB/mm which is due to a lack of waveguidestructure in the tellurite glass segment. On the basis of reflection and insertion loss measurements and a bendingtest[2], however, it is proved that there’s no micro crystals in the quenched melt segment which cause light scatter-ing and/or stress concentration. Thus, the quenching rate of the melt in this fabrication technique is considered tobe 103 K/s[2].Although the thermal expansion coefficient of tellurite glass is 2-orders bigger than that of silica glass (seeTable 1), the fracture due to residual stress must be suppressed because the interface area is so small as sub-mm.The present fabrication technique has a potential to be applied to form a hybrid planar lightwave circuit and/ormicrocavity devices, in which lasing with ultra-low threshold is possible. Moreover, high refractive index of tellu-rite glass enables to capture light into microcavities efficiently. We are now planning to make such microcavitiesconnected with optical fibers.SummarySeveral nano liters of tellurite glass melt were inserted and quenched between two ends of silica glass optical fibersto form a new optical coupling structure, whose length was several hundred microns. No visible precipitates werefound even in the quenched melt of 100% TeO2. This means that we can use considerably wider range of glasscompositions to make these optical coupling structure compared with the range for making optical fibers.References[1] S. Todoroki, A. Nukui, and S. Inoue,J. Ceram. Soc. Jpn., vol. 110, no. 5, pp. 476–478, 2002.[2] S. Todoroki, A. Nukui, and S. Inoue, inThe International Symposium On Photonic Glasses, SPIE Proceedings,(Shanghai, China), Oct. 2002. (to be submitted).