Lecheng Li

All-fiber Mach-Zehnder interferometers for sensing applications

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.

Novel NCF-FBG Interferometer for Simultaneous Measurement of Refractive Index and Temperature

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.

Multiwavelength generation based on a mode-locked fiber laser using carbon nanotube and fiber Fabry–Perot filter

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.

Thinned fiber based Mach-Zehnder interferometer for measurements of liquid level and refractive index

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.