X. Y. Dong

Cavity ring-down long-period fibre grating strain sensor

An exploratory study on a novel fibre long-period grating cavity ring-down strain sensor is proposed. By detecting the ring-down time at different strain levels, the performances of the strain sensor are investigated. The experimental results demonstrate that, by using this sensing setup, a high sensitivity of 1.261 ns/μe and a minimum detectable strain level of 9 μe could be achieved.

Temperature stability improvement of a multiwavelength Sagnac loop fiber laser using a high-birefringent photonic crystal fiber as a birefringent component

We experimentally demonstrate a temperature-stable multiwavelength erbium-doped fiber laser source using a high-birefringent photonic crystal fiber (HiBi-PCF) as the birefringent component of the Sagnac loop filter within the laser cavity. Three different high-birefringence (Hi-Bi) fibers are used in the loop filter to compare the temperature stability of the fiber laser systems: polarization-maintaining erbium-doped fiber (PM-EDF), panda Hi-Bi fiber, and HiBi-PCF. Because of the high birefringence and low temperature sensitivity of the HiBi-PCF, fiber length in the loop is greatly reduced and the temperature stability of the system is dramatically enhanced.

Application of an artificial neural network for simultaneous measurement of temperature and strain by using a photonic crystal fiber long-period grating

A general analysis of an inserted long-period grating in an air-clad photonic crystal fiber for temperature and strain measurement is presented. The temperature and strain can be detected simultaneously by using an artificial neural network. A simulation study was carried out with the data set generated by using theoretical strain and temperature sensitivities of the long-period gratings. It indicates that the maximum temperature error is 0.04 °C in the temperature range from 35 °C to 120 °C. At the same time, the maximum strain error is 2.7 µe in the strain range from 0 to 3000 µe.

Refractive index measurement using a photonic crystal fiber

An optical waveguide for measuring the change of refractive index (RI) by using a photonic crystal fiber is designed. The simulation results show that a variation of 3.5% refractive index unit (RIU) could shift the resonant wavelengths of 450 and 110 nm when the RIs of liquid are 1.5 and 1.7, respectively. The sensitivities of 8×10 -7 and 3.2×10 -6 RIU are thus able to be achieved for the RIs of liquid of 1.5 and 1.7, respectively.

Simultaneous measurement of temperature and strain by using photonic crystal fiber long period grating

A general analysis of an inserted LPG in air-clad PCF for temperature and strain measurement is presented. The temperature and strain can be detected simultaneously by matrix inversion. The maximum temperature errors are 3oC and 0.8oC in the temperature ranges from 35oC to 50oC and 90oC to 120oC, respectively. The corresponding maximum strain errors are 250με and 135με in the strain range from 0 to 3000με respectively.

High Resolution Biochemical Sensor by Using Photonic Bandgap Fiber

A PBG fiber based biochemical sensor has been demonstrated with a resolution better than Δn=7.3×10-6. It is based on the detection of the wavelength shift of the photonic-band-edge due to the refractive index variations.

A Wide Tunable Range Fiber Bragg Grating Filter

A simple, low cost setup was designed for tuning the Bragg wavelength for a uniform fiber Bragg grating (FBG). The tuning range was achieved by as much as 45.34 nm based on the principle of a rectangular beam of uniform strength in the simulation.

A tunable multiwavelength fiber laser source with an elliptical-core fiber Sagnac loop filter

A novel tunable multiwavelength erbium-doped fiber laser source based on a Sagnac loop filter is proposed and experimentally demonstrated. The filter, which is coupled together with the laser cavity, consists of a normal 3-dB fiber coupler, a polarization controller (PC1) and a segment of high-birefringence (Hi-Bi) fiber. The active gain medium, which is a polarization-maintaining erbium-doped fiber (PM-EDF) with an elliptical core, leads to possible multi-frequency lasing output at room temperature. In experiment, by changing the setting of the polarization controller (PC2), multiple frequency lasing lines with different wavelength spacing have been obtained. By applying some pressure to the PM-EDF, continuously tunable multiwavelength lasing output is achieved. Experimental results have shown several stable output lasing wavelengths with high extinction ratio at room temperature.

Refractive index measurement by using a photonic crystal fiber

An optical waveguide for measuring the change of refractive index by using a photonic crystal fiber is designed. The simulation results show that a variation of 0.032 refractive index unit (RIU) could shift the resonant wavelengths of 245nm and 68nm when the refractive indices of liquid are 1.5 and 1.7, respectively. The sensitivity for the refractive index measurement of about 1.3×10-6RIU is achieved.

Tunable photonic band gaps in a photonic crystal fiber

The transmission spectrum of a photonic bandgap fiber filled with low index material is investigated. A simple analytical model is developed to predict the position and bandwidth of the band gap in the wavelength domain with respect to the refractive index. The wavelength of the band gap has a blue shift and the bandwidth of the band gap becomes narrow with the increasing of the refractive index of the filled material. The degree of shifting of the band gap increases with the reduction of air-filling fraction of the photonic bandgap fiber.