Zhan Gao

Polymer optical fiber for large strain measurement based on multimode interference

This Letter reports a polymer optical fiber (POF) based large strain sensor based on the multimode interference (MMI) theory for the application of structural health monitoring. A section of POFs is sandwiched between two silica single mode fibers to construct a single-mode-multimode-single-mode structure that produces a MMI spectrum. The strain sensing mechanism of the device was investigated and experimentally verified. A large dynamic range of 2×10(4) με (2%) and a detection limit of 33 µε have been demonstrated.

Fiber ring laser interrogated zeolite-coated singlemode-multimode-singlemode structure for trace chemical detection

Zeolite thin films were synthesized on the claddingless multimode portion of a singlemode-multimode-singlemode (SMS) fiber structure to construct a chemical vapor sensor. The zeolite-coated SMS structure was inserted into a fiber ring amplifier to produce a laser line. Combining the strong molecular adsorption capability of the nanoporous zeolite and the high signal-to-noise ratio of the fiber laser, the device was demonstrated for chemical vapor sensing with a low detection limit.

Long-Period Grating Inscribed on Concatenated Double-Clad and Single-Clad Fiber for Simultaneous Measurement of Temperature and Refractive Index

In this letter, a kind of long-period fiber grating (LPFG) that is capable of simultaneous measurement of temperature and surrounding refractive index (RI) is fabricated and demonstrated. The compact LPFG is written on a piece of spliced standard single-mode fiber (SMF) and double-clad fiber (DCF) with the CO2 laser point-by-point irradiation technique. The LPFG section in the DCF is solely sensitive to temperature, while the section of the LPFG in the SMF is sensitive to both temperature and surrounding RI. After temperature and RI calibration, the LPFG has been used to measure the RI change of ethylene glycol with the change of temperature to demonstrate its capability for dual parameter simultaneous measurement.

Radio frequency interrogated actively mode-locked fiber ring laser for sensing application

This paper proposes an actively mode-locked fiber ring laser for sensing applications. Mode-locking of the laser is achieved by driving an electro-optic amplitude modulator at an RF corresponding to the fundamental beat frequency between the longitudinal modes. The change of the cavity length produces a frequency comb around the beat frequencies. The frequency separation of the comb is found to be linearly proportional to the cavity length change. The sensing mechanism of the device is shown. Temperature measurement is demonstrated using the proposed actively mode-locked fiber ring laser.

High order mode long-period fiber grating refractive index sensor based on intensity measurement

Long-period fiber gratings have been used for refractive index measurements under different conditions. Normally, this kind of sensor is based on measuring resonance wavelength shift with respect to different refractive index environments. As high order mode long period fiber gratings are attracting more attention, a new methodology based on intensity measurement of turning points is introduced, which involves simple experiment setup and straightforward demodulation process compared with wavelength shift based method. By using CO2 laser point by point irradiation method, high order mode gratings working at turning point can be easily fabricated. This type of grating has a very high sensitive response to surrounding refractive index, which can be used in chemical, medical and bio applications. In this paper, high sensitive refractive index sensor is demonstrated based on high order mode using intensity measurement. Phase match curve and couple mode theory are combined to analyze the intensity response to refractive index change at turning point of LPFG. This sensor is also demonstrated as an effective refractive index based glucose sensor with a range from 0 to 40 mM concentration of glucose solution, which can fulfill the medical requirement.

Refractive-index insensitive long-period fiber gratings point-by-point inscribed by CO 2 laser for fiber sensors and lasers

This paper reports a long-period fiber gratings(LPFG) fabricated on a double-clad fiber (DCF) by the CO2 laser point-by-point technique. The LPFG is tested by measuring temperature and refractive index (RI) of different liquids. The results show that the LPFG inscribed on the DCF has no measurable sensitivity to external RI but has a high sensitivity for temperature. The measured temperature sensitivity is ~0.11 nm/oC, about 10 times higher than that of conventional FBGs. Such LPFGs can be used as a modulator in fiber lasers or temperature/strain sensors in applications where the surrounding RI is prone to variation, such as simultaneous measurement of the temperature and RI of chemical reactions.

Hydrogen Sensor based on Palladium Coated SMS Fiber Structure

We have developed a new optical fiber hydrogen sensor with palladium thin film coating on SMS fiber structures. The sensor performance is studied in detail.