The time-frequency characteristics of the transient response of dynamic gratings in erbium-doped fiber are different from stable gratings, which make it has great application value in the fields of fiber laser and optical fiber sensing. In consideration of the time domain characteristics, a time domain response model was built, which was based on metastable Er3+ population rate equation and light field transmission equation. The model simulated the process of establishing dynamic gratings in erbium-doped fiber with time sequence. And the theoretical results showed that the formation time of the dynamic grating gets shorter with higher pump power and shorter Erbium-doped fiber length within the effective length limits, which was consistent with the experimental results obtained by the so called “Strong light and weak light alternation” method except that the measured formation time decay ranges obviously migrated to lower pump power relative to the theoretical results. In consideration of the frequency domain characteristics, the transient two-wave mixing process was approximately simulated by using four-wave mixing equation. The transient reflectance spectra obtained through numerical calculation reflected the evolution rule of the dynamic gratings, which were coincident with the experimental results gotten by the rapid optical frequency modulation method. Under the condition of 1.8m Erbium-doped fiber, the experimental results showed that the turning saturated pump light power from the absorption type dynamic gratings to the gain type ones is about 0.05mW, the maximum relative reflectance variation of the gain dynamic gratings (3%) is 3 times of the absorption types. The measurement results have important references to the practical application of Erbium-doped fiber dynamic gratings.
With the development of networking technology and optical fiber sensor network technology, the use of optical fiber system to construct a large-scale, long distance optical fiber sensing network has become a hotspot of research. Optimizing the system to reach very long sensing ranges actually requires launching high pump and probe powers into the sensing fiber to provide a sufficient signal-to-noise ratio (SNR) on the measurements at the far end of the fiber. However, increasing the input power above a critical level excites undesired nonlinear effects such as the modulation instability (MI) and the stimulated Raman scattering (SRS), which deplete the pump and reduce the maximum sensing range of the system. Compared to SRS, MI shows a lower critical power and thus determines the maximum sensing range of a fiber sensor, so MI becomes the most important factor to limit the sensing range. In order to understand the MI in the system with the DFRA, we design a lot of experiments to test which factors will affect it in the system with distributed fiber Raman amplifier (DFRA) in this paper. From the threshold expression of MI and a lot of experiments, we found that the input power, the state of polarization, the phase and so on, have a significant impact on the system. According to the result of the experiments, we can find the Raman gain affects the MI and find some useful information for suppressing the MI in the later.
Mode instability acts as a common feature in single-frequency fiber ring lasers. The mechanism of coherence collapse by mode instability is theoretically analyzed and demonstrated with an unbalanced fiber Michelson interferometer utilizing phase modulation, which is illuminated by a single-frequency erbium-doped fiber ring laser. Multiform mode instability phenomena accompanied with coherence collapse are observed and discussed in detail by tracing the dynamics of the interference fringe visibility. The results show that mode instability would introduce extra phase noises like a false alarm to interferometric fiber optic sensing systems.
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.
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.
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.
The characteristics of dynamic gratings greatly affect the linewidth and mode hopping properties of ultra-narrow
linewidth erbium-doped fiber lasers. In this paper, we propose a novel method to estimate the temporal evolution of the
reflectance spectrum of the dynamic gratings recorded in EDF based on the transient effect of the erbium ions. An
experimental setup is also proposed to measure the reflectivity spectrum of the dynamic gratings utilized in lasers. The
experimental data are compared with the numerical results and their differences are analyzed. The experiment results
reveal some important transient characteristics of dynamic gratings in real lasers which are helpful to understand the
mechanism of mode hopping.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.