Nuan Jiang

Transient reflectance spectra of adaptive filters based on dynamic population gratings

We propose a novel and practical method to exactly measure the transient reflectance spectra (TRS) of the adaptive filters based on dynamic population gratings. The modulating signals applied to the laser source play an important role. We specially designed a train of triangular amplitude modulated pulses with a small duty to modulate the laser frequency, and then the TRS was obtained from the grating responses to this pulse train. The measured half-zero-point bandwidths of the filter with and without 2.6 m cavity length are 20 and 60 MHz, respectively. Our research also indicates that the relatively high input power and a short cavity length may enhance the antiperturbation ability of lasers.

Numerical model of dual-wavelength erbium-doped fiber ring laser based on gain-equilibrium method

A novel numerical model of the dual-wavelength fiber ring lasers utilizing gain-equilibrium method is presented by developing the two level, homogeneous Giles model. To obtain the simulation method, the gain equilibrium condition is derived and modified to adapt to the iterative procedure in simulations. This condition is confirmed by both the numerical and experimental results, which indicate that the cavity losses of both wavelength channels play important roles in maintaining stable dual-wavelength emitting. The tolerant loss-bias is 0.05 dB in simulations and 0.4 dB in experiments, respectively. The difference between numerical and experimental results reveals that the inhomogeneous linewidth broadening of EDF contributes mostly to the improved power stability, but the loss vibrations play an important role in this effect.

Studies on technics and experiments of fused-tapered fiber grating coupler

This paper presents comprehensive research on fused-tapered Bragg reflection integrative FGC where high-quality and easy-fabricating are two main considerations. The technical procedure of FGC fabrication is fixed after a series of experiments. The possible factors that may determine the device performance were carefully analyzed. The fused-tapered FGC was successfully fabricated and a novel testing system was established. The adding and dropping functions of FGC were investigated experimentally.

Integrated polarization maintaining fiber polarized grating and its application in a fiber ring laser

Abstract. An integrated polarization maintaining fiber polarized Bragg grating is proposed, which achieves reflecting and polarizing functions simultaneously. This integrated polarized grating was designed to replace the traditional fiber polarizer and Bragg grating by a single fiber device, which may induce enormous performance promotion to optical fiber systems incorporating the two devices, such as fiber ring laser, some fiber sensing networks, etc. An integrated fiber polarized grating was fabricated, and the polarization states of both the reflection and transmission were measured. The temperature and strain responses were also tested which indicated sufficient stability. The integrated fiber polarized grating was then applied to the fiber ring laser, and results indicated that a robust single-longitudinal and single-polarization mode laser can be realized by utilizing this design type of integrated polarized grating.

Detecting mode hopping in fiber ring lasers by anisotropic dynamic gratings

We have demonstrated that a polarization-insensitive anisotropic dynamic grating can be used to detect accident mode hopping in long-cavity-length fiber ring lasers. The polarization-insensitive property of the grating is realized by a Faraday rotator mirror and validated experimentally. The mode hopping properties of a particular single-longitudinalmode erbium-doped fiber ring laser is examined by an anisotropic grating with 3-m long erbium doped fiber. When mode hopping occurs, the grating responds a negative intensity peak. Repeated measurement shows that the continuing cavity length wandering during the laser operation is the origin of the accident mode hopping when there is no modulation applied to the cavity length.

An integrated polarization-holding fiber polarizing grating based on side-polishing and metal film coating techniques

Optical fiber polarizer and grating are two widely used fiber components and in this paper we proposed an integrated polarizing grating fabricated in polarization-holding fiber, which achieves reflecting and polarizing functions simultaneously. A D-shaped multilayer grating waveguide model was established and the linearly polarizing principles in both reflection and transmission ports were presented. An integrated polarization-holding fiber polarizing grating was fabricated and the laser polarization states of incidence, reflection and transmission were all measured, showing that this integrated fiber device can achieve reflecting and polarizing functions simultaneously. The discrimination between the reflection and transmission was also investigated.

Research on fiber Bragg grating based on micro-fiber

Fiber Bragg grating sensors have been attracted more attention due to its excellent advantages, such as small size, light weight, low cost, immunity to electromagnetic interference, multiplexing and so on, which offer a widely application in optical sensing and communication field. Following the appearance of micro/nano-fiber (MNF), it is imperative to develop the manufactured technology of MNF devices, MNF Bragg gratings are the important passive device among these. In this paper, we simulate the effective refractive index in fiber core using two-layer model. Meanwhile, we present a new method to fabricate a 6μm diameter fiber Bragg grating through successive improvement of manufactured technology. The small cladding diameter fiber was obtained by immersing an optical photosensitive fiber in different concentrations of hydrofluoric acid solutions. Then a MNF is fabricated from the small cladding diameter fiber by drawing. Finally a 6μm-diameter fiber Bragg grating was written using phase mask technology with a higher reflection. The testing results of this grating showed a good agreement with the simulation.

An optimized design of a fiber optic hydrophone based on side-hole packaged

Fiber Bragg grating hydrophones exhibit exceptional properties for acoustic detection, oil exploration and other applications have been induced widely attention following the maturity of fiber grating fabricate technology. As the basic key point of optical fiber hydrophone array, hydrophone design has been focused on by many countries over the past two decades. In this paper, we present a design of fiber Bragg hydrophone based on side-hole packaged to enhanced sensitivity and optimize its parameters through theoretical approach. In our theoretical analysis, the radial and axial strain induced grating length changes are taken into account. The results show that the material parameters such as Possion ratio and Youngs modules and structural parameters like the position, diameter, ellipticity and number of the side-hole have significant effects on the sensitivity of the hydrophone. By optimizing these parameters, a high sensitivity can be achieved. This hydrophone is fabricated and experienced hydrostatic and dynamic sound pressure test. The experimental results are in good agreement with the theoretical results.