Smf 28

Figure 1 shows the schematic of line-by-line inscription of TFBGs. In our experiment, an oil-immersion lens with a magnification of 100× was used to focus the femtosecond laser. The wavelength of the femtosecond laser was 515 nm, the repetition rate was 1 kHz, and the pulse energy after oil-immersion lens was about 36 nJ. The period of grating (Λ) and the tilted angle (θ) were controlled by an electrical 3D translation stage. During inscription, the focus of the femtosecond laser translated from point A to point B. Then, the femtosecond laser was shut off, and the focus of the femtosecond laser moved to the beginning of the next line (point C in Figure 1). After the focus reached point C, the femtosecond laser switched on and began to generate the next line.
The relationship between these three points (A(x₁, y₁), B(x₂, y₂) and C(x₃, y₃)) is as follows: {y1=−y2=y3x2=2|y1|tanθ+x1x3=x1+Λ.
In order to cover the core diameter, the value of |y₁| is 16 μm. By varying the period of grating (Λ), the resonant wavelength could be tuned. Cladding mode coupling was affected by tilted angle (θ). In our experiment, TFBGs were inscribed on single mode fibers (Corning, SMF28). The number of the period was 3000. A sweeping wavelength laser (resolution: 6 pm, and wavelength range: 1503.4–1620nm) was used to record the transmission spectra.

First a micro-fiber with 1 μm in radius and 65 mm in length was fabricated from a standard single mode fiber (SMF-28, Corning) using the ame brushing method16 (link)22 (link). Then, the architecture of the proposed TBI as shown in Fig. 1(a) was constructed by adopting the micro-fiber. A plate of glass is adopted as the substrate to support the proposed TBI and ambient medium. In order to avoid evanescent field leaking from TBI into the glass substrate whose RI is higher than micro-fiber, a layer of low-index polymer (here, we use silica gel as the polymer, the RI of silica gel is 1.401, which is smaller than micro-fiber and glass substrate) was first coated on the glass plate. After this low-index polymer is cured, we put the fabricated TBI on the substrate. Then we coated the TBI expect for the sensing region by the same silica gel. After the silica is cured, the package is complete. The package would not only make the TBI robust, but also ensure the evanescent field is able to access the external medium. Figure 6 shows the schematic diagram of the packaged TBI.

The TFBGs, 1 cm long, were photo-inscribed in the core of a SMF-28 (Corning Inc., Corning, NY, USA) in order to fabricate the biosensors. This is a single-mode optical fiber with a diameter of 125 μm and a core of 8 μm that was hydrogenated prior to the inscription to enhance photosensitivity. The inscription procedure was based on the phase-mask technique involving the NORIA manufacturing system (Northlab Photonics, Nacka, Sweden), embedding an Argon Fluor deep UV-pulsed excimer laser (Excistar XS, Coherent Inc., Santa Clara, CA, USA), with a 500 Hz repetition rate, emitting at 193 nm, a phase-mask of 1100 nm period and the fibers with an 8° tilt angle with respect to the UV beam axis.

For grabbing force measurement, we utilized a 15 mm-long section of 125 μm-diameter communication-grade fused silica optical fiber (Corning, SMF-28) as the cantilever. As the support for applying the grabbing force, we also installed a 155 μm-diameter stainless steel wire (Small Parts) in parallel with the fiber. Then we measured the deflection of the fiber under an optical microscope (E-Zoom6, Edmund Optics) as the micro-tentacle wound around both the metal wire and optical fiber.

A non-degenerate photon pair is created via spontaneous four-wave mixing within a 200-m-long single-mode fiber (Corning, SMF-28), mediated by a pump laser under the relaxed phase-matching condition^{34 (link)}. The pump laser features a central wavelength of 1269.50 nm, a duration of 100 ps, and a peak power of about 1 W. The laser operates at a repetition rate of 20 MHz, electronically synchronized with the BS-FWM pump lasers. We employ two strategies to reduce the noise photons resulting from spontaneous Raman scattering. First, we cool the single-mode fiber by submerging it in liquid nitrogen, thereby reducing the population of excited state phonons. Second, we attach a polarizer to the output of the single-mode fiber and align the polarization direction of the pump to that of the polarizer. This is because the polarization state of the photon pair is parallel to that of the pump laser, while noise photons are unpolarized. The pump, signal, and idler photons are separated by bandpass filters with a bandwidth of 0.7 nm and centered at 1269.50, 1267.89, and 1271.11 nm, respectively. The setup ensures a pump rejection ratio exceeding 120 dB. The resultant coincidence-to-accidental ratio for the photon pair is 22.2 ± 1.1.

An FP interferometer was built within a 125 µm diameter fiber (SMF-28, Corning Inc., Corning, NY, USA). A lead-in SMF and a reflecting SMF were spliced to a silica capillary tube (CAP075/150/24T, Fiberguide Industries, Caldwell, ID) with a certain air gap separation between the two SMFs, as shown in Figure 1.
The inner diameter r_i of the tube was 75 µm, and the outer diameter r_o was 125 µm, the same as that of the SMF. A beam of incident light was reflected successively by the two SMF/tube interfaces. Two reflected light beams inferenced with each other and generated an interference pattern. When ambient pressure increased, the structure would deform to change the distance between two interfaces, and the interference pattern would shift accordingly.