Fiber taper structures have been extensively selleck chemicals studied in SMFs and photonic crystal fibers [16,17]. For such applications more gradual tapers with smaller taper angles are preferred, because they are focused on reducing the insertion loss, while for abrupt tapers or larger taper angles, light in the core will be partially coupled into the cladding of the fiber as cladding modes. SMF typically supports only the fundamental mode (LP01) in the core, while the other higher order linear polarization modes mainly propagate as cladding modes. For the gradual fiber taper with small taper angle, the relative change in the taper radius is very small, so the main portion of the power remains in the LP01 mode and does not couple with other higher order cladding modes as it propagates along the taper.
But for an abrupt taper, Inhibitors,Modulators,Libraries the coupling occurs between the LP01 mode and the higher Inhibitors,Modulators,Libraries order cladding modes. In our experiment, a short but abrupt taper is made in the TCF to excite higher order cladding modes. Compared with the total length of the interferometer, the taper zone is small, yet is sufficient to enhance the sensing sensitivity.3.?Experiments and Discussion3.1. Sensor FabricationThe TCF used in our experiment is a commercial fiber (Yangtze Ltd., Wuhan, China). It has core/cladding Inhibitors,Modulators,Libraries diameters of 4.8/125 ��m, and the cut-off wavelength is 1,260 nm. An Ericsson fusion splicer (modal FSU 975), with a built-in core-offset attenuator program, was used to produce the lateral offset between the SMF and the TCF.
A C-band light source was used as the broad band source, and the output spectrum was monitored by an optical spectrum analyzer (OSA, Yokogawa, Inhibitors,Modulators,Libraries Japan) with wavelength resolution of 15 pm. The transmission spectra of the IMIs with different TCF lengths were measured and are shown in Figure Cilengitide 2. It can be seen that the free spectral range decreases with the increasing interference length. In addition, the interference spectra are a little inhomogeneous. This is because that more than one cladding modes are available in the interference pattern.Figure 2.Transmission spectra of the IMIs with different TCF lengths.The short taper in the TCF was made by using electric-arc-heating method, which can also be achieved by the same fiber fusion splicer with the built-in taper program. Figure 3(a) shows a photograph of the core offset between the SMF and the TCF, and the offset is approximately 5 ��m.
Figure 3(b) shows the typical photograph of taper region. The taper length and waist diameter Enzalutamide are 697 ��m and 91 ��m, respectively.Figure 3.(a) Photograph of the lateral core offset between the SMF and TCF, the offset is ~5 ��m; (b) The taper range in the TCF, L = 697 ��m, D = 91 ��m.3.2. RI Measurement and DiscussionAn IMI was fabricated with 38 mm length TCF, and was used as the sensor head.