Distributed Feedback Fiber Laser Research Articles

Distributed Feedback Fiber Laser Strain Sensor Technology

Distributed feedback fiber laser (DFB FL) sensors have been the subject of considerable research interest over the past decade, due primarily to their remarkable inherent strain sensitivity. Recent research has led to significant advances in both fundamental understanding of DFB FL devices and in practical performance outcomes in demanding real-world applications. Here, we provide an overview of the basic operating principles of wavelength division multiplexed DFB FL sensor systems and review the underlying theory of DFB FL.

ЭФФЕКТИВНАЯ СХЕМА НАКАЧКИ ЭРБИЕВОГО ВОЛОКОННОГО ЛАЗЕРА С РАСПРЕДЕЛЕННОЙ ОБРАТНОЙ СВЯЗЬЮ ДЛЯ ПОДАВЛЕНИЯ РЕЛАКСАЦИОННЫХ КОЛЕБАНИЙ

The scheme of erbium-doped distributed feedback fiber laser is proposed, which combines pumping schemes of the single frequency oscillator and optical signal amplifier. The scheme provides maximum efficiency of pump to signal conversion while minimizing the effect of relaxation oscillations on the output radiation parameters. In this scheme single-frequency fiber laser radiation power up to 30 mW achieved at the pump power of 600 mW at 980 nm. Amplified spontaneous emission was at the level of 0.08%. The magnitude of the relative intensity noise is — 140dB/Hz at frequencies more than 10 MHz and — 100dB/Hz at the peak of relaxation oscillations. The linewidth of the laser radiation is less than 1 kHz.

Graphene Q-switched distributed feedback fiber lasers with narrow linewidth approaching the transform limit.

A compact all-in-line graphene-based distributed feedback Bragg-grating fiber laser (GDFB-FL) with narrow linewidth of hundreds kHz is demonstrated and investigated in this study. Performing as an optical saturable absorber, graphene oscillates the initially kHz linewidth DFB-FL, and generates high-quality passively Q-switched pulses. Pumped with a 980 nm continuous-wave laser, the Q-switched GDFB-FL observes ~1 μs pulse durations, with pulse energies up to ~10 nJ and approaching the transform limit. The peak power is ~600 times higher than the original DFB-FL laser. By optimizing the cavity design and the graphene material, it is predicted that fast Q-switched pulses with more than MHz repetition rates and sub-100 ns pulse durations are achievable. Such transform-limited Q-switched GDFB-FLs with narrow linewidth of sub-MHz have long coherence length, good tunability, stability, compactness and robustness, with potential impact in optical coherent communications, metrology and sensing.

Effects of Intensity Noise in Digital Demodulation for Fiber Laser Sensor

Hydrophone array-based distributed feedback fiber laser (DFB FL) has a small size and large sensitivity; however, it also suffers from intensity noise completely. In this letter, a transfer function for intensity noise propagation through the use of a DFB FL sensor interrogation system is derived, basing on which a symmetric algorithm using $3\times 3$ coupler is improved. Both experimental and simulation data are provided to validate the model. A noise reduction of 20 dB is achieved.

Fiber-optic ultrasonic sensors and applications

Fiber-optic ultrasonic sensors possess the ability to detect ultrasonic waves by recovery of light intensity, wavelength, phase, and polarization. Compared with traditional electrical ultrasonic transducers, fiber-optic ultrasonic sensors have several merits, such as broadband response, high sensitivity, disturbance resistance, and good reusability, which are helpful to improve the reliability and efficiency of ultrasonic detection in underwater defense security, bioimaging, nondestructive inspection, and imaging of seismic physical models. To date, according to the principle, fiber-optic ultrasonic sensors can be classified into three types, including intensity modulation, fiber-optic interferometers and fiber gratings. For the intensity-modulated fiber-optic ultrasonic sensors, ultrasonic waves can be detected by measuring optical fiber coupling loss, fiber transmission-reflection loss, fiber reflection loss and fiber polarization loss. The phase difference in fiber-optic interferometers can be modulated by ultrasonic strain. According to the interference mechanism, fiber-optic interferometric ultrasonic sensors are generally based on Mach-Zehnder interference, Fabry-Perot interference, Michelson interference and Sagnac interference. For the ultrasonic sensors based on fiber gratings, the grating length is supposed to be shorter than the ultrasonic wavelength so that the ultrasonic stress presents constant along the fiber gratings. Currently, the approaches of spectral edge filtering and wavelength-matched filtering are utilized to transform optical signals into voltage signals, which highly depend on the slope of the grating spectra. Thus, the fiber gratings with extremely narrow 3-dB bandwidth, such as phase shifted fiber Bragg grating, are preferred for highly sensitive ultrasonic detection. Besides the fiber-optic passive sensing, the distributed feedback fiber laser and distributed Bragg reflector also exhibit outstanding advantages in ultrasonic detection. Fiber-optic ultrasonic detecting technique is one of the hot topics in international research community, which is an effective method to evaluate the microstructure and related mechanical properties, and detect the microcosmic and macroscopic discontinuities of solid materials. In this paper, three typical applications of ultrasonic detection, i.e., monitoring of smart structure and health, biomedical imaging, and imaging of seismic physical models are reviewed, respectively. Our group has been engaged in the research fields of fiber-optic geophones and ultrasonic sensors for seismic exploration for decades. Several fiber-optic ultrasonic sensors with smart packaging are proposed and also used for the scanning imaging of two physical models. In this paper we review the sensing mechanism, fabrication method, and current status of three types of fiber-optic ultrasonic sensors, respectively. Besides, the corresponding applications and technology challenges are also summarized. In particular, we present several kinds of home-made optical fiber ultrasonic sensors as a new technology applied in the imaging of seismic physical models. Overall, after decades of efforts, gratifying achievements have been achieved in the research of fiber-optic ultrasonic sensors. Further work needs to solve various technical issues, such as sensitivity, stability, structural microminiaturization, and multiplexing, etc. The next step will focus on the research issues in ultrasonic detection of seismic physical models, performance improvement, and multiplexing technology for distributed sensing. Miniaturization of fiber sensors and instrumentation of sensing system will also be the important research topic. The final objective of the research is to build a well integrated fiber-optic ultrasonic detecting system with high sensitivity and stability, networking construction, and proprietary intellectual property rights.

采用3×3耦合器的分布反馈式光纤激光传感器解调技术

采用3×3耦合器的分布反馈式光纤激光传感器解调技术

分布反馈光纤激光器阵列中外腔反馈特性研究

分布反馈光纤激光器阵列中外腔反馈特性研究

分布反馈式光纤激光水听器的声压灵敏度频率响应特性

分布反馈式光纤激光水听器的声压灵敏度频率响应特性

带加速度补偿的DFB光纤激光水听器

带加速度补偿的DFB光纤激光水听器

分布反馈式光纤激光水听器拖曳线列阵实验研究

分布反馈式光纤激光水听器拖曳线列阵实验研究

基于流固耦合作用的分布反馈式光纤激光水听器

基于流固耦合作用的分布反馈式光纤激光水听器

Random distributed feedback fiber laser at 2.1 μm.

We demonstrate a random distributed feedback fiber laser at 2.1μm. A high-power pulsed Tm-doped fiber laser operating at 1.94μm with a temporal duty ratio of 30% was employed as a pump laser to increase the equivalent incident pump power. A piece of 150m highly GeO2-doped silica fiber that provides a strong Raman gain and random distributed feedbacks was used to act as the gain medium. The maximum output power reached 0.5W with the optical efficiency of 9%, which could be further improved by more pump power and optimized fiber length. To the best of our knowledge, this is the first demonstration of random distributed feedback fiber laser at 2μm band based on Raman gain.

All-optical noise reduction of fiber laser via intracavity SOA structure.

We have designed a unique intracavity semiconductor optical amplifier (SOA) structure to suppress the relative intensity noise (RIN) for a fiber DFB laser. By exploiting the gain saturation effect of the SOA, a maximum noise suppression of 30 dB around the relaxation oscillation frequency is achieved, and the whole resonance relaxation oscillation peak completely disappears. Moreover, via a specially designed intracavity SOA structure, the optical intensity inside the SOA will be in a balanced state via the oscillation in the laser cavity, and the frequency noise of the laser will not be degraded with the SOA.

High-Resolution Sensor System Using a Random Distributed Feedback Fiber Laser

In this paper, high-resolution measurements using random distributed feedback fiber lasers have been attained. A phase-shifted fiber Bragg grating is used to detect temperature shifts with a resolution under 0.01 °C. Due to the longitudinal-modeless behavior and the inherent frequency stability of random fiber lasers, the resolution limit of conventional fiber lasers has been overcome. The frequency shift of the grating is measured in the electrical domain by beating an external laser source with the laser line generated. A second setup that measures axial strain without the need of temperature compensation is also proposed and validated, reaching an axial strain resolution under 0.2 μϵ.

Implementation of distributed feedback fiber laser sensor for acoustic measurements in hydraulic fracturing

A distributed feedback (DFB) fiber laser strain sensor was implemented to measure acoustic emission induced by the hydraulic fracturing process. A study of practical sensor mounting configurations and their characteristics was carried out to find a practical solution. Combining the suitable mounting configuration and ultrahigh strain sensitivity of the DFB fiber laser, the evolution of the hydraulic fracturing process was well monitored. This study shows that fiber lasers can be useful alternatives to piezoelectric sensors in the field of hydraulic fracturing for gas and oil extraction.

Statistical properties of radiation of multiwavelength random DFB fiber laser.

In the presented paper, the temporal and statistical properties of a Lyot filter based multiwavelength random DFB fiber laser with a wide flat spectrum, consisting of individual lines, were investigated. It was shown that separate spectral lines forming the laser spectrum have mostly Gaussian statistics and so represent stochastic radiation, but at the same time the entire radiation is not fully stochastic. A simple model, taking into account phenomenological correlations of the lines' initial phases was established. Radiation structure in the experiment and simulation proved to be different, demanding interactions between different lines to be described via a NLSE-based model.

Narrow-linewidth Q-switched random distributed feedback fiber laser

A narrow-linewidth Q-switched random fiber laser (RFL) based on a half-opened cavity, which is realized by narrow-linewidth fiber Bragg grating (FBG) and a section of 3 km passive fiber, has been proposed and experimentally investigated. The narrow-linewidth lasing is generated by the spectral filtering of three FBGs with linewidth of 1.21 nm, 0.56 nm, and 0.12 nm, respectively. The Q switching of the distributed cavity is achieved by placing an acousto-optical modulator (AOM) between the FBG and the passive fiber. The maximal output powers of the narrow-linewidth RFLs with the three different FBGs are 0.54 W, 0.27 W, and 0.08 W, respectively. Furthermore, the repetition rates of the output pulses are 500 kHz, and the pulse durations are about 500 ns. The corresponding pulse energies are about 1.08 μJ, 0.54 μJ, and 0.16 μJ, accordingly. The linewidth of FBG can influence the output characteristics in full scale. The narrower the FBG, the higher the pump threshold; the lower the output power at the same pump level, the more serious the linewidth broadening; and thus the higher the proportion of the CW-ground exists in the output pulse trains. Thanks to the assistance of the band-pass filter (BPF), the proportion of the CW-ground of narrow-linewidth Q-switched RFL under the relative high-pump-low-output condition can be reduced effectively. The experimental results indicate that it is challenging to demonstrate a narrow-linewidth Q-switched RFL with high quality output. But further power scaling and linewidth narrowing is possible in the case of operating parameters, optimization efforts, and a more powerful pump source. To the best of our knowledge, this is the first demonstration of narrow-linewidth generation in a Q-switched RFL.

High‐power random distributed feedback fiber laser: From science to application

A fiber laser based on random distributed feedback has attracted increasing attention in recent years, as it has become an important photonic device and has found wide applications in fiber communications or sensing. In this article, recent advances in high‐power random distributed feedback fiber laser are reviewed, including the theoretical analyses, experimental approaches, discussion on the practical applications and outlook. It is found that a random distributed feedback fiber laser can not only act as an information photonics device, but also has the feasibility for high‐efficiency/high‐power generation, which makes it competitive with conventional high‐power laser sources. In addition, high‐power random distributed feedback fiber laser has been successfully applied for midinfrared lasing, frequency doubling to the visible and high‐quality imaging. It is believed that the high‐power random distributed feedback fiber laser could become a promising light source with simple and economic configurations. image

All-Fiber Configuration Laser Self-Mixing Doppler Velocimeter Based on Distributed Feedback Fiber Laser.

In this paper, a novel velocimeter based on laser self-mixing Doppler technology has been developed for speed measurement. The laser employed in our experiment is a distributed feedback (DFB) fiber laser, which is an all-fiber structure using only one Fiber Bragg Grating to realize optical feedback and wavelength selection. Self-mixing interference for optical velocity sensing is experimentally investigated in this novel system, and the experimental results show that the Doppler frequency is linearly proportional to the velocity of a moving target, which agrees with the theoretical analysis commendably. In our experimental system, the velocity measurement can be achieved in the range of 3.58 mm/s–2216 mm/s with a relative error under one percent, demonstrating that our novel all-fiber configuration velocimeter can implement wide-range velocity measurements with high accuracy.

High-power ultralong-wavelength Tm-doped silica fiber laser cladding-pumped with a random distributed feedback fiber laser.

We demonstrated a high-power ultralong-wavelength Tm-doped silica fiber laser operating at 2153 nm with the output power exceeding 18 W and the slope efficiency of 25.5%. A random distributed feedback fiber laser with the center wavelength of 1173 nm was employed as pump source of Tm-doped fiber laser for the first time. No amplified spontaneous emissions or parasitic oscillations were observed when the maximum output power reached, which indicates that employing 1173 nm random distributed feedback fiber laser as pump laser is a feasible and promising scheme to achieve high-power emission of long-wavelength Tm-doped fiber laser. The output power of this Tm-doped fiber laser could be further improved by optimizing the length of active fiber, reflectivity of FBGs, increasing optical efficiency of pump laser and using better temperature management. We also compared the operation of 2153 nm Tm-doped fiber lasers pumped with 793 nm laser diodes, and the maximum output powers were limited to ~2 W by strong amplified spontaneous emission and parasitic oscillation in the range of 1900–2000 nm.