Guiyun Kai

Highly birefringent elliptical-hole photonic crystal fiber with squeezed hexagonal lattice

We propose a novel polarization-maintaining index-guiding photonic crystal fiber (PCF). It is composed of a solid silica core and a cladding with squeezed-hexagonal-lattice elliptical air holes. Using a full-vector finite-element method, we study the modal birefringence of the fundamental modes in such PCFs. Numerical result shows that very high modal birefringence with a magnitude of the order of 10(-2) around 1550 nm has been obtained. Furthermore, large normal dispersion appears over a wide range of wavelengths in both orthogonal polarizations.

FBG-type sensor for simultaneous measurement of force (or displacement) and temperature based on bilateral cantilever beam

An improved FBG-type sensor for simultaneous measurement of force (or displacement) and temperature based on the bilateral cantilever beam (BCB) is proposed and demonstrated. The two parts of the beam are subject to opposite forces (or displacements) leading to a red shift for the part of the FBG subject to stretch and to a blue shift for the other one. An FBG bonded to the surface of the middle of the BCB is experimentally demonstrated to have a force sensitivity of /spl sim/1.046 nm/N, a sensitivity of the displacement-based strain of /spl sim/0.317 nm/mm, and a temperature sensitivity of /spl sim/0.190 nm//spl deg/C between 0/spl deg/C and 70/spl deg/C, respectively.

Stable room-temperature multi-wavelength lasing realization in ordinary erbium-doped fiber loop lasers.

A suppressant effect for mode competition of multi-wavelength lasing oscillations induced by deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL) was observed and experimentally investigated. Results show that the effect is helpful to obtain stable multi-wavelength lasing at room temperature in the EDFRL, which offers a new and simple approach to achieve stable multi-wavelength EDF lasing. Stable two- and three- wavelength lasing oscillations were achieved based on the effect in the ordinary EDFRL for the first time to our best knowledge. The multi-wavelength lasing oscillations were so stable integrated over smaller than 1 ms that the maximum power fluctuation over more than 30 minutes of observation was less than 0.1 dB and 0.5 dB for two-wavelength lasing with a spacing of 1.28 nm and 0.76 nm, respectively.

An embedded FBG sensor for simultaneous measurement of stress and temperature

An embedded fiber Bragg grating (FBG) sensor for simultaneous measurement of stress and temperature is proposed, where a uniform FBG is capsulated in a tapered polymer so that the grating is linearly chirped when the sensor is stressed. The value of applied stress and temperature can be obtained by measuring the chirp and central wavelength via a coefficient matrix. Experimental results demonstrate that the sensor has a stress sensitivity of 2.62/spl times/10/sup -3/nm/N and a temperature sensitivity of 0.108 nm//spl deg/C. Since the FBG is well protected and no sudden strain change is imposed on it, the sensor is expected to have an excellent reliability.

Simultaneous four-wavelength lasing oscillations in an erbium-doped fiber laser with two high birefringence fiber Bragg gratings.

A novel multiwavelength erbium-doped fiber laser configuration is proposed and demonstrated. The laser can produce simultaneous four-wavelength lasing oscillations with a minimum wavelength spacing of only 0.36 nm in C-band via using two fiber Bragg gratings written in high birefringence fiber, while ensuring fairly stable room-temperature operation. The laser can also achieve switching modes among four wavelengths by simple adjustment of two polarization controllers in the cavities. Theconfiguration is based on the polarization hole burning and overlapping cavities principle. The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.

L-Band switchable dual-wavelength erbium-doped fiber laser based on a multimode fiber Bragg grating

In this letter, a simple, switchable dual-wavelength erbiumdoped fiber laser operating in L-band is successfully proposed and demonstrated. The two wavelengths are specified by a Bragg grating formed in multimode fiber and the wavelength separation is 1.7 nm. The multimode section including the multimode fiber grating selects not only the lasing wavelengths but also the polarization states of the lasing lines. Stable dualwavelength operation can be achieved due to the spatial mode beating effect induced by a single-mode /multimode/ single-mode fiber combination structure. By simple adjustment of a polarization controller, the proposed laser can operate in stable dual-wavelength or switch between two wavelengths, all at room temperature.

Temperature-independent FBG-type torsion sensor based on combinatorial torsion beam

A new method of temperature-independent torsion measurement based on a combinatorial torsion beam is proposed and demonstrated. One half of the unique sensing fiber Bragg grating (FBG) is linked to a solid torsion beam, while the other is fixed to a less rigid part of the air-hole torsion beam. The spectral response of the FBG is split into two spectral peaks and the spectral separation of these peaks corresponds to applied torsion. In the measuring range from -40/spl deg/ to +40/spl deg/, torsion angle sensitivity is about 0.092 nm/degree and torque sensitivity is 2.076 nm/Nm, respectively.

Bend measurement with chirp of fiber Bragg grating

The first measurements of curvature with chirp of fiber Bragg grating are described. The grating is bonded at a slant onto the lateral surface of a beam and chirped by the bend-induced strain gradient. The bandwidth of the grating is proportional to the curvature of the beam and independent of temperature, resulting in a curvature measurement with a resolution of 0.036 m-1 within the range of 4 m-1. Simultaneously, the thermal response of the central Bragg wavelength provides a temperature measurement within the range of 0-45 °C.

Bragg grating resonances in all-solid bandgap fibers

Bragg gratings are fabricated in all-solid photonic bandgap fibers by forming a longitudinal periodic index modulation over the high-index rod lattice in the cladding. Due to its unique index-modulation pattern and the modal properties of the fiber, resonance couplings to the LP(01) supermodes (also known as high-index rod modes) are observed. The corresponding peak is located at the long-wavelength side of the Bragg wavelength and presents the highest depth. The asymmetric index profile over the high-index rods, which is induced by side UV illumination, leads to broadening of the supermode resonance peaks and variation with fiber orientation in the bend response of the fiber grating.

Ultraviolet-inscribed long period gratings in all-solid photonic bandgap fibers

Long period fiber gratings are fabricated in the cladding rods of all-solid photonic bandgap fibers (PBGFs) by point-by-point side UV illumination. Resonant couplings from fundamental mode to guided and radiative supermodes (rod modes), and bandgap-like modes are identified. We obtained a detailed insight over the modal and dispersive properties of the PBGF through a series of theoretical and experimental investigations on the spectral characteristics and the responses to temperature and high-index liquid of the LPGs.