X. Yu

Evanescent Field Absorption Sensor Using a Pure-Silica Defected-Core Photonic Crystal Fiber

An evanescent field absorption sensing technique in liquid solutions is demonstrated using a microstructured photonic crystal fiber (PCF). Aqueous solution of cobalt chloride was infiltrated into all air holes of the PCF. The defected-core with a central hole in the PCF together with an increase in the surface volume with the evanescent field penetration into the air holes enhanced the liquid absorption sensitivity. The effects of solution concentration, detection directions, and PCF length on the absorption sensitivity are investigated experimentally. We have obtained a linear relationship between the evanescent field absorption and liquid concentration and also between the evanescent field absorption and PCF length. The absorption sensitivity using the longitudinal detection method is increased by more than 60 times compared with that using perpendicular measurement technique.

All-normal-dispersion passively mode-locked Yb-doped fiber ring laser based on a graphene oxide saturable absorber

We have demonstrated an all-normal-dispersion passively mode-locked Yb-doped fiber laser using a graphene oxide/polyvinyl alcohol (GO–PVA) saturable absorber without surfactant, for the first time to the best of our knowledge. The experimental results show that the pulse duration of the mode-locked lasers varies from 191xa0ps to 1.68xa0ns, while the cavity round trip time changes from 24 to 458xa0ns, through the variation of the cavity length. In addition, the proposed passively mode-locked fiber laser demonstrates a maximum average output power of 539xa0mW with a laser cavity length of 94xa0m, and the corresponding single pulse energy reaches 0.429xa0μJ. The proposed mode-locked fiber lasers with large chirp pulses may find potential applications in fiber chirped pulse amplification systems for micromachining, material processing and diagnostic applications.

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.

Silica-Based Birefringent Large-Mode-Area Fiber With a Nanostructure Core

Nanostructure photonic crystals with two-fold symmetry are introduced into a silica-based fiber core to induce high birefringence between the two nearly orthogonal fundamental modes. We theoretically study and provide our preliminary findings on the birefringence property of such fibers over a large wavelength range. A large-mode-area structure with a typical high birefringence in the order of is easily realized.

Long path-length axial absorption detection in photonic crystal fiber.

In this paper, we present a long path-length axial absorption detection method in photonic crystal fibers (PCFs). A PCF, also called a holey fiber or microstructured fiber, is an optical fiber which consists of a periodic array of very tiny and closely spaced air holes on the scale of 1 microm running through the whole length of the fiber. Here, a PCF with porous microstructures was used as a sample container for absorption detection. Light was guided by total internal reflection and propagated axially in the air holes of PCFs that were filled with the solution of the absorbing species by vacuum pumping. Excellent linearity was obtained for different sample concentrations, and high sensitivity was achieved due to the long optical path length. In addition, as the dimension of the PCF is small, the sample volume is greatly reduced. Moreover, due to its robustness, the PCF can be coiled up to keep the footprint small, making it suitable for microchip absorption detection. It can be widely used for both off-chip and on-chip detection of absorbing species, such as ions, alkaloids, and biomolecules.

Highly Sensitive Photonic Crystal Fiber-Based Refractive Index Sensing Using Mechanical Long-Period Grating

We experimentally demonstrate a novel refractive index (RI) sensor with the measurand infiltrated into the air channels of a single mode photonic crystal fiber (PCF). A tunable long-period grating is formed in a short length of PCF by use of the periodic mechanical pressure. Resonance shift with the change of the infiltrated liquid is observed with a sensitivity of 4.1times 10-6 RI unit in a refractive index range from 1.32 to 1.39. The thermal stability of the pure-silica-based PCF device shows a three times better performance compared with conventional single mode fiber.

Determination of the wavelength dependence of the coupling effect in twin-core microstructured polymer optical fibers

A simple and straightforward method is applied to experimentally obtain the wavelength dependence of the intercore beat length for two different types of twin-core microstructured polymer optical fiber. The results are compared with numerical calculations using a full-vectorial plane-wave expansion method, which shows good agreement.

Wavelength dependence of coupling in twin-core microstructured polymer optical fiber

Theoretical and experimental results are reported for a twin-core microstructured polymer fiber. A full-vectorial numerical method based supermode theory is applied in the symmetrical structure to obtain the interference between the even and odd modes. The wavelength dependence of the coupling length is measured, and compared to calculations using a full-vectorial numerical method. Both results show good agreement.

Evanescent field absorption detection in aqueous solutions using microstructured optical fibers

There is a growing interest in microstructured optical fibers (MOFs) for advanced sensors by infiltrating the air-holes with gas, liquid and polymers. The evanescent field overlap with infiltrations is enhanced compared with conventional fibers. The pure silica material is chemically and biologically inert, which well prevents the evaporation of water. Recently, liquid core waveguide cell has become widely used to minimize source light loss to the cell. However, the construction material Teflon® AF, is one of the most expensive commercial polymers. Moreover, it is highly gas permeable, causing problems of enhanced evaporation of water from the internal solution. In this paper, we demonstrate a novel and highly sensitive detection technique of Co2+ absorbance in aqueous solutions using two different structures of microstructured optical fibers (MOF). The evanescent field is numerically investigated in a systematic manner with the variation of structure parameters and wavelength. The effects of solution concentration, effective path-length, temperature stability and bending effect on the absorption sensitivity are explored and compared experimentally. The enhanced evanescent field from the second structure can achieve absorption sensitivity up to 1.6 Mol-1. The sensitivity using longitudinal detection method is at least sixty times higher compared with that using the perpendicular measurement technique

Evanescent field absorption sensor in aqueous solutions using microstructured polymer optical fiber

An axial absorption detection scheme is developed using a microstructured polymer optical fiber. Excellent linearity is obtained for absorbance against both concentration and length. The sensitivity is increased significantly compared with perpendicular direction measurement.