International audienceWe present the first experimental demonstrations of stimulated Raman scattering in a liquid probed by the evanescent field of a tapered silica nanofiber. Raman scattering by a pure liquid, ethanol, or mixture of liquids, toluene diluted in ethanol, is investigated. Given the large choice of available materials for the medium surrounding the nanofiber, these demonstrations pave the way to the exploration of a new class of experiments and devices

Nanofibres can be produced with diameters smaller than the wavelength of the light they guide. In this regime, the guided mode presents a strong evanescent field well adapted to the excitation of "evanescent nonlinearities". We theoretically investigate such an evanescent nonlinearity: the Raman interaction between the evanescent field and a liquid surrounding the nanofibre. Our calculations demonstrate that the Raman conversion is obtained with nanofibre lengths an order of magnitude lower than those required for liquid core photonic crystal fibres.

We report the implementation of an in-fiber optical switch by means of filling a fluid into the air holes of a photonic crystal fiber with a fiber Bragg grating. Such a switch can turn on/off light transmission with an extinction ratio of up to 33 dB within a narrow wavelength range (Bragg wavelength) via a small temperature adjustment of ±5°C. The switching function is based on the temperature-dependent coupling between the fundamental core mode and the rod modes in the fluid-filled holes resulting from the thermo-optic effect of the filled fluid. An index-guiding PCF may be transformed into an all-solid photonic bandgap fiber (PBF) by filling highindex material into the air holes. Such an invertible transformation in the fiber types (PCF/PBF) has led to many switching applications [3][4][5][6]. These switches, however, usually turn on/off the light transmission over a broad wavelength range and cannot perform the switching function within a narrow wavelength range. In this Letter, we demonstrate a thermo-optic in-fiber optical switch produced by filling immersion oil into the air holes of a solid-core PCF in combination with an FBG. Such a switch can turn on/off light transmission within a narrow wavelength range (Bragg wavelength) as the result of the coupling between the fundamental core mode and the LP 01 -like mode in the fluid rods. A solid-core Ge-doped PCF (IPHT-252b5) with a core diameter of 4.1 m was employed in our experiments. Air holes of the PCF have an average diameter of 3.5 m and are arranged in a hexagonal pattern with an average pitch of 4.2 m. Other parameters of the PCF are listed in Table 1 of [7]. The PCF has a low transmission loss within a broad wavelength range, as shown in Fig. 1(a). The central region of the fiber core with a diameter of about 0.5 m was doped with a high concentration of germanium ͑36 mol.% ͒. The calculated refractive indices of the Ge-doped core and of the pure silica ͑SiO 2 ͒ cladding are Ϸ1.5039 and 1.4538, respectively, at a wavelength of 830 nm.As shown in Fig. 1(b), an FBG with a reflectivity of 45%, a Bragg wavelength of 829.76 nm, and a grating length of Ϸ6 mm was inscribed in the Ge-doped small-core PCF by the use of a 248 nm KrF excimer laser [8]. One end of the PCF with the FBG was spliced to a standard single-mode fiber (SMF) with a splice loss of Ϸ1.0 dB using the arc fusion splicing technique as reported in [9]. Another end of the PCF with a length of 300 mm was cleaved at a distance of 5 mm from the FBG and then placed in an immersion oil (n = 1.482 at room temperature; http:// www.niepoetter.de). Thus the immersion oil was filled into the air holes of the PCFs by means of the well-known capillarity action. The actual fluid-filled PCF including the FBG had a total length of Ϸ150 mm.Then we investigated the response of the fluidfilled FBG to the temperature change using a semiconductor Peltier cooler, a temperature controller (THORLABS TED200), and a specifically adapted FBG interrogation system [7]. As shown in Fig. 2(a), in the case of the temperatur...

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