Lunlun Xian

Power-interrogated and simultaneous measurement of temperature and torsion using paired helical long-period fiber gratings with opposite helicities

A power-interrogated sensor which allows for simultaneous measurement of temperature and torsion is proposed and experimentally demonstrated, which is based on utilization of paired helical long-period fiber gratings (HLPG) with opposite helicities. Unlike most of the previous fiber grating-based sensing system, here the paired HLPGs are simultaneously used as both the sensing and the interrogating elements and thus the bulk and high-cost wavelength-interrogating device can be eliminated. Moreover not only the torsion but also the torsion direction can be determined simultaneously. The temperature sensitivity obtained is estimated to be ~41 pm/°C within a range of 20-150 °C, and the torsion responsivities obtained are ~-1.414 nm/rad/m and ~1.276 nm/rad/m, respectively within a rotation angle of -360°~360°.

Fabrication of Phase-Shifted Long-Period Fiber Grating and Its Application to Strain Measurement

Several kinds of phase-shifted long-period gratings (LPGs) have been fabricated using a high-repetitionrate CO₂ laser, where both the grating and the inserted phase shift are simultaneously produced in a commonly used single-mode fiber. Furthermore, using one of the fabricated phase-shifted LPGs, a temperature-insensitive sensor that allows for large axial strain measurement with a value up to 7600 με, is proposed and first demonstrated. Measurement accuracy for the strain ranging from 340 to 7600 με is estimated to be ±30 με, while the temperature is changed in a range of 20°C-140°C.

Calibration of a Phase-Shift Formed in a Linearly Chirped Fiber Bragg Grating and Its Thermal Effect

A novel scheme for quantitative calibration of a phase-shift formed in a linearly chirped fiber Bragg grating is numerically and experimentally demonstrated, which is based on the utilization of either a wavelength- or a power-interrogated fiber ring laser. Moreover, an application example of the proposed phase-shift FBG to temperature measurement has been proposed and experimentally demonstrated.

Phase-shift induced in a high-channel-count fiber Bragg grating and its application to multiwavelength fiber ring laser

A multichannel filter formed by the piezoelectric transducer (PZT)-induced phase shift in a phase-only sampled fiber Bragg grating (FBG) is experimentally demonstrated. The PZT-induced phase shift is stable and the magnitude of the induced phase shift is controllable. As an important application of this multichannel filter, a semiconductor optical amplifier (SOA)-based multiwavelength fiber ring laser is successfully demonstrated.

Cladding Mode Coupling in a Wide-Band Fiber Bragg Grating and its Application to a Power-Interrogated Temperature Sensor

Quantitative analysis for the cladding mode coupling in a linearly chirped fiber Bragg grating (FBG) with broad bandwidth is theoretically and experimentally demonstrated for the first time. It is found that due to the cladding mode effect, there exists a strong slope in the reflection spectrum, which could be larger than 5 dB within the 10-nm bandwidth of FBG. Based on this phenomenon, a novel temperature sensor working in the range of 17°C-181°C is first demonstrated by using a power-interrogation technique. Unlike most of the previous FBG-based sensors, here the proposed FBG is simultaneously utilized as both the sensing and the interrogating element.

Helical Long-Period Fiber Grating Formed in a Optical Micro/Nano Wire by Using a CO2 Laser

A novel kind of helical long-period grating formed in a optical micro/nano-wire, is firstly proposed and experimentally demonstrated, which may find applications to various photonic devices and high-sensitivity sensors.

Enhanced slow light in a phase-shifted multichannel fiber Bragg grating assisted by stimulated Brillouin scattering

Slow light is theoretically and experimentally demonstrated in a phase-shifted multichannel fiber Bragg grating (FBG) which has the ability not only to produce the slow-lights in multiple channels simultaneously but also to make the delay time tunable by changing the magnitude of the inserted phase shift. Phase shift is introduced into a phase-only sampled 51-channel FBG by utilization of a small piezoelectric transducer (PZT). On the other hand, the group delay of each channel can be further enhanced by incorporating stimulated Brillouin scattering (SBS).