Optical switch based on a fluid-filled photonic crystal fiber Bragg grating

Abstract

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...

Thermo-optic Characteristics of Micro-structured Optical Fiber Infiltrated with Mixture Liquids

“…Y. Yu and X. Li introduced a novel MOF temperature sensor based on liquid ethanol infiltrated into the cladding with the sensitivity of 0.315 dB/℃ [12]. Optical switches have been reported by Y. Wang and W. Jin based on fluid-filled MOF Bragg grating [13] or temperature-controlled hybrid micro-structured fiber [14], with the extinction ratio >30 dB via the temperature adjustment of ±5℃. They also investigated a thermo-optical switch based on the absorption of the filled fluid in combination with the interaction between the core mode and the excited "fluid rod" modes [15].…”

Improved bending property of half-filled photonic crystal fiber

“…An index-guiding PCF could be transform into a bandgap-guiding fiber by means of filling a high index material into the air holes [2,3]. Such a transformation in the fiber types may lead to various promising devices such as optical switches [4][5][6][7], tunable filters [8,9], attenuators [10], and dispersion compensators [11,12]. Compared with the indexguiding pure-silica PCFs, the bandgap-guiding fluid-filled PCFs are more susceptible to bend due to the low effective index mismatch between the fluid rod and the background silica [13][14][15][16].…”

Temperature-controlled transformation in fiber types of fluid-filled photonic crystal fibers and applications

“…Such an invertible transformation in the fiber types (PCF/PBF) may lead to many potential applications. Research [1][2][3][4][5][6] was, however, focused on the transformation from an index-guiding fiber to a bandgap-guiding fiber instead of an opposite process. In this Letter, we filled a fluid into the air holes of a solid-core PCF and investigated experimentally and theoretically an invertible fiber-type transformation from a PBF into an unideal waveguide and then into an index-guiding PCF via the thermo-optic effect of the filled fluid.…”

“…Many in-fiber devices such as switches [1][2][3][4], attenuators [5], and dispersion compensators [6] have been developed by filling liquid crystal, refractive-index-matching liquid, and other materials into the air holes to transform an indexguiding PCF into a photonic bandgap fiber (PBF). All of these functions are attributed to the bandgap changes resulting from the thermo-optic effect of the filled fluid and are usually operated within a limited wavelength range [1][2][3][4][5][6]. The fiber type transformation from a PCF into a PBF should be an invertible process resulting from increasing/decreasing the refractive index of the filled materials.…”

“…Such an invertible transformation in the fiber types (PCF/PBF) may lead to many potential applications. Research [1][2][3][4][5][6] was, however, focused on the transformation from an index-guiding fiber to a bandgap-guiding fiber instead of an opposite process.…”