Search

Simulating micro bending loss of SMF through a simple model and contrasting simulated curve and experimental results, confirm that the microbend loss is the main cause of hydrogen-loaded fiber fusion bubbles loss. There is a good linear relationship between the refractive index of liquid and normalized light intensity among the range from 1.3325 to 1.3562. Therefore, we propose a kind of low cost, high resolution optical fiber refractive index sensor.

We describe and analyze the coupling strength apodization effect among the three co-directional guided modes using the supermodes theory. The propagation condition is related to the two phase matching distribution induced by two long period co-spatial gratings. It is seen that one input mode can be converted into other two modes with one mode having two peaks at its transmission spectrum. Through adopting suitable apodization functions and adjusting the maximum coupling apodization strength from 100 to 1500, the frequency space between the two peaks in one converted mode can be tuned nearly linearly from 336 GHz to 5400 GHz. Moreover, the other converted mode which has one peak and maximum output power around the central frequency can be used in the transmission operation mode. This kind of design can form the basis for a new generation of optical filtering and mode converting.

A novel and simple optical fiber structure with a section of no-core fiber for measuring relative humidity (RH) is presented. Moisture-sensitive materials HEC/PVDF are used to form the hydrogel coating on the no-core fiber by dip impregnation method. Under different humidity conditions, the humidity induced refractive index changes on the outside coating of no-core fiber will lead to the variations of the optical output power. The different lengths of no-core fiber are tested at the two wavelengths of 1310 nm and 1550 nm, respectively. The results show that the structure with 2 cm no-core fiber has a higher RH sensitivity of 0.196 dB/%RH at 1310 nm and a better linearly response when the RH is lower than 75%. Furthermore, the optical output powers are measured with the rise and drop of RH, and the four times repetition are also recorded, which all demonstrate the good stability and repeatability of our proposed structure.

A simple and compact interferometer structure based on no-core fiber (NCF) and fiber Bragg grating (FBG) is proposed for simultaneous measurement of surrounding refractive index (SRI) and temperature. Two methods of measurement may be used here: 1) the sensing information can be analyzed by the wavelengths shift of the NCF-based interferometer and one arbitrarily FBG-reflected modes, or 2) they can be solely extracted through both wavelength and power of each FBG reflected mode. Moreover, experimental results indicate that the SRI sensitivity of the FBG reflected core mode is up to 160.23 dB/RIU at a range from 1.3330 to 1.3780, which is the highest value to our knowledge.

A novel method for simultaneous measurement of refractive index and temperature based on a small core and cladding diameters thinned fiber Mach–Zehnder interferometer (MZI) using singlemode-multimode-thinned-multimode-singlemode (SMTMS) fiber structure is proposed. Experiments indicate that the selected two interference orders have sensitivities of −16.1936 nm/RIU and 0.0534 nm/°C, and −23.0473 nm/RIU and 0.0575 nm/°C, respectively, among RI range from 1.3325–1.3720 and temperature range from 22 °C–82 °C. We can thus use the coefficient matrix of these two peaks to simultaneously determine the surrounding refractive index and temperature. The fabrication is easy, safe and cost effective, includes only the fusion splicing, making the device properly attractive for practical sensor applications.

In this letter, we propose and demonstrate a novel and simple method for simultaneous measurement of refractive index and temperature using all-fiber in-line single-mode-multimode-thinned-single-mode (SMTS) fiber structures based on a small core and cladding diameters thinned fiber Mach–Zehnder interferometer (MZI). The principle of operation relies on the strong effect of the core and cladding mode interference of the thinned fiber through the employing of a multimode fiber. By measuring the shifts of the attenuation peak wavelengths of the two arbitrarily selected interference orders in the transmission spectrum, we can simultaneously measure the refractive index and temperature surrounding the sensor. Results indicate that the selected two interference orders have sensitivities of −2.85 × 10 −3 RIU with 3.49 × 10 −1 °C, and −1.12 × 10 −3 RIU with 4.07 × 10 −1 °C respectively at RI range from 1.3325 to 1.3715 and temperature range from 24 °C to 84 °C. The fabrication is easy, safe and cost effective, and includes only the fusion splicing, making the device properly attractive for physical, biological and chemical sensing in practical applications.

A novel singlemode-multimode-thinned-singlemode (SMTS) fiber structure based Mach-Zehnder interferometer (MZI) is proposed for measurements of liquid level and refractive index (RI). We observe that the liquid RI information can be provided from the sensitivity of the interference peak shifts. Furthermore, by measuring the certain wavelength shift, the liquid level can be measured accordingly. A 9.00 mm-long thinned fiber with core/cladding diameters of around 4.5/80 μm is used. The wavelength of 1538.7228 nm exhibits a water level sensitivity of -175.8 pm/mm, and refractive index sensitivity of -1868.42 (pm/mm) / RIU, respectively. Moreover, the fabrication process is very simple and cost effective.

In this paper, a novel and compact configuration of stable multiwavelength generation with a uniform wavelength interval is proposed for the first time to our knowledge. It employs a mode-locked fiber laser using a carbon nanotube and spectrum-slicing technique. A flat rectangular optical output spectrum is demonstrated by adjusting the dispersion value of the fiber-loop cavity and the pump power. With a fiber Fabry-Perot filter, 33 wavelengths with 0.2 nm spacing are obtained among the power uniformity of 2.3 dB. Moreover, the variations of output power at each wavelength are all less than 0.1 dB, which implies excellent stability of the whole structure.

We propose and demonstrate a thinned fiber based Mach-Zehnder interferometer for multi-purpose sensing applications. The sensor head is formed by all-fiber in-line singlemode-multimode-thinned-singlemode (SMTS) fiber structure, only using the splicing method. The principle of operation relies on the effect that the thinned fiber cladding modes interference with the core mode by employing a multimode fiber as a mode coupler. Experimental results showed that the liquid refractive index information can be simultaneously provided from measuring the sensitivity of the liquid level. A 9.00 mm long thinned fiber sensor at a wavelength of 1538.7228 nm exhibits a water level sensitivity of -175.8 pm/mm, and refractive index sensitivity as high as -1868.42 (pm/mm)/RIU, respectively. The measuring method is novel, for the first time to our knowledge. In addition, it also demonstrates that by monitoring the wavelength shift, the sensor at a wavelength of 1566.4785 nm exhibits a refractive index sensitivity of -25.2935 nm/RIU, temperature sensitivity of 0.0615 nm/°C, and axial strain sensitivity of -2.99 pm/με, respectively. Moreover, the sensor fabrication process is very simple and cost effective.