Simultaneous refractive index and temperature measurement using nested fiber balloon rings.

A simple all-fiber sensor based on nested fiber balloon rings (FBRs) for simultaneous refractive index (RI) and temperature measurement is proposed and demonstrated. The FBR is easily fabricated by properly bending a section of single-mode fiber. The FBR with a smaller bending radius is embedded in a bigger one. Because the two separate interference dips have different RI and temperature sensitivities, which are formed by individual FBRs, the RI and temperature can be simultaneously measured by interrogating the wavelength shifts of the two interference dips. This sensor has the advantages of convenient fabrication, economical materials, probe structure, and high sensitivity and can be a candidate for simultaneous measurement of RI and temperature.

Multi-channel optical fiber refractometer based on tree topology structure.

A multi-channel optical fiber refractometer based on S fiber taper (SFT) cascaded with fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The compact SFT acts as an in-line Mach-Zehnder interferometer (MZI) to be used as a band-pass filter (BPF) to tailor the FBG reflection, whose transmission spectrum is sensitive to the surrounding refractive index (SRI). Thus, the peak power of the FBG reflection is modulated by the SRI. The three-channel SRI monitor can be achieved by discriminating the different center wavelength and peak power variation of the FBG reflections. Experimental results show that the RI sensitivities of Channels 1, 2, and 3 are 345.54, 349.57, and 463.60 dB/RIU, respectively. Moreover, the temperature cross-sensitivity can be solved by interrogating the center wavelength of the FBG reflection.

Relative Humidity Sensor Based on No-Core Fiber Coated by Agarose-Gel Film.

A relative humidity (RH) sensor based on single-mode-no-core-single-mode fiber (SNCS) structure is proposed and experimentally demonstrated. The agarose gel is coated on the no-core fiber (NCF) as the cladding, and multimode interference (MMI) occurs in the SNCS structure. The transmission spectrum of the sensor is modulated at different ambient relative humidities due to the tunable refractive index property of the agarose gel film. The relative humidity can be measured by the wavelength shift and intensity variation of the dip in the transmission spectra. The humidity response of the sensors, coated with different concentrations and coating numbers of the agarose solution, were experimentally investigated. The wavelength and intensity sensitivity is obtained as -149 pm/%RH and -0.075 dB/%RH in the range of 30% RH to 75% RH, respectively. The rise and fall time is tested to be 4.8 s and 7.1 s, respectively. The proposed sensor has a great potential in real-time RH monitoring.

Improved Numerical Calculation of the Single-Mode-No-Core-Single-Mode Fiber Structure Using the Fields Far from Cutoff Approximation.

Multimode interferometers based on the single-mode-no-core-single-mode fiber (SNCS) structure have been widely investigated as functional devices and sensors. However, the theoretical support for the sensing mechanism is still imperfect, especially for the cladding refractive index response. In this paper, a modified model of no-core fiber (NCF) based on far from cut-off approximation is proposed to investigate the spectrum characteristic and sensing mechanism of the SNCS structure. Guided-mode propagation analysis (MPA) is used to analyze the self-image effect and spectrum response to the cladding refractive index and temperature. Verified by experiments, the performance of the SNCS structure can be estimated specifically and easily by the proposed method.

Analysis of Hollow Fiber Temperature Sensor Filled with Graphene-Ag Composite Nanowire and Liquid.

A hollow fiber temperature sensor filled with graphene-Ag composite nanowire and liquid is presented and numerically characterized. The coupling properties and sensing performances are analyzed by finite element method (FEM) using both wavelength and amplitude interrogations. Due to the asymmetrical surface plasmon resonance sensing (SPR) region, the designed sensor exhibits strong birefringence, supporting two separate resonance peaks in orthogonal polarizations. Results show that x-polarized resonance peak can provide much better signal to noise ratio (SNR), wavelength and amplitude sensitivities than y-polarized, which is more suitable for tempertature detecting. The graphene-Ag composite nanowire filled into the hollow fiber core can not only solve the oxidation problem but also avoid the metal coating. A wide temperature range from 22 ∘C to 47 ∘C with steps of 5 ∘C is calculated and the temperature sensitivities we obtained are 9.44 nm/ ∘C for x-polarized and 5.33 nm/ ∘C for y-polarized, much higher than other sensors of the same type.

Label-free assessment of replicative senescence in mesenchymal stem cells by Raman microspectroscopy.

Here, Raman microspectroscopy was employed to assess replicative senescence of mesenchymal stem cells (MSC). A regular spectral change related to the cell senescence was found in the ratio of two peaks at 1157 cm(-1) and 1174 cm(-1), which are assigned to C-C, C-N stretching vibrations in proteins and C-H bending vibrations in tyrosine and phenylalanine, respectively. With the cell aging, the ratio I1157 / I1174 exhibited a monotonic decline and showed small standard deviations, so that it can statistically distinguish between cells having slight changes in terms of aging. We propose that I1157 / I1174 can act as a characteristic spectral signature for label-free assessment of MSC senescence.

Multiwavelength erbium-doped fiber laser based on graphene oxide.

A multiwavelength erbium-doped fiber (EDF) laser based on graphene oxide (GO) has been proposed, to the best of our knowledge, for the first time, to generate an output of stable wavelengths. The structure mainly comprises a few layers of GO between two single-mode fibers incorporated into a capillary device and a Lyot comb filter. GO can show a good nonlinear optical effect, which is beneficial to suppress the mode competition caused by the EDF and stabilize the multiwavelength output. With assistance from the GO device, 11 stable simultaneous lasing signals with a power nonuniformity of about 1.5 dB are obtained. Wavelength spacing is about 0.42 nm and the linewidth of each wavelength is less than 0.07 nm.