Pair Of Fiber Bragg Gratings Research Articles

Pulsed Yb³⁺-doped fiber laser operating at 1011 nm by intra-cavity phase modulation.

A 1011 nm pulsed Yb³⁺-doped fiber laser is experimentally demonstrated by employing a commercially available LiNbO₃ phase modulator (PM) in the linear cavity. The resonator is built up with a section of normal single-cladding Yb³⁺-doped fiber, a PM, and a pair of fiber Bragg gratings. Active mode-locked stable trains of pulses with 2 and 1.4 ns are generated at repetition rates of 30.2478 and 60.4956 MHz, respectively. The maximum average output power is 10.6 mW at pump power of 200 mW, with the slope efficiency of 13.3%. Relaxation-oscillation-modulated pulses with width of 2 μs are obtained at a repetition rate of 27.778 kHz.

Theoretical and Experimental Investigation of an Intensity-Demodulated Fiber-Ring-Laser Ultrasonic Sensor System

We theoretically and experimentally investigate the performance of an ultrasound detection system based on a fiber ring laser (FRL) whose cavity includes a pair of fiber Bragg gratings. The ultrasonic detection is achieved by the FRL power variations in response to the ultrasound-induced cold-cavity loss modulation of the FRL. The effects of key FRL parameters, including pump power, laser cold-cavity loss, and laser cavity length, on the system signal-to-noise ratio (SNR) performance have been investigated. It is found that the maximum SNR is achieved when the frequency of the ultrasound is the same as that of the FRL relaxation oscillation (RO). Harmonic generations are more prominent when the ultrasonic frequency is at the RO frequency and highly dependent on the strength of the ultrasonic signal. The analysis provides a useful tool for the understanding and optimization of such ultrasonic sensor systems.

Compact and Tunable Mid-IR Light Source Based on a Dual-Wavelength Fiber Laser

A compact, tunable mid-IR difference-frequency generation (DFG) light source based on a dual-wavelength fiber laser and a 5mol% MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal is developed and evaluated. An output power of 233 μW is achieved with a conversion efficiency of 0.1%/W. The mid-IR wavelength can be tuned between 3308 nm and 3314 nm by changing the temperature of a pair of fiber Bragg grating (FBG) taking as cavity mirrors in the dual-wavelength fiber laser from 26.5°C to 106.5°C.

Dual-Wavelength, Linearly Polarized All-Fiber Laser With High Extinction Ratio

We demonstrate a dual-wavelength linearly polarized all-fiber laser emitting 1- μm and 1.5- μm wavelengths with a total output power of 1.3 W. The laser consists of two pairs of fiber Bragg gratings (FBGs) fabricated on PM fibers to form a cavity and an Er/Yb co-doped fiber as a gain medium. A high extinction ratio of 23 dB is achieved using specially designed PM FBGs. The laser output has a narrow bandwidth of 26 pm at both 1057 and 1554 nm. When the dual-wavelength all-fiber laser is used to pump a PPLN crystal, the generation of mid-infrared emission at 3.3 μm is successfully demonstrated.

Monolithic Tm-Doped Fiber Laser at 1951 nm With Deep-UV Femtosecond-Induced FBG Pair

We report on a monolithic Tm-doped fiber laser emitting in the region <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{\rm 2}~\mu{\rm m}$</tex> </formula> . A pair of fiber Bragg gratings (FBGs) was written into the Tm-doped fiber using a two-beam interferometry and a deep ultraviolet (DUV) femtosecond laser source at 266 nm. Such a monolithic setup allows a simple setup of the laser made of a single fiber only. This configuration also offers greater reliability because fusion splices inside the resonator cavity could eventually generate failure in the laser cavity. To the best of our knowledge, this is the first rare-earth-doped fiber laser with an FBG pair written by DUV femtosecond laser radiation. Laser characteristics are presented as well as compared with the fiber laser with external FBGs conventionally spliced to the Tm-doped fiber. Dependence of the laser wavelength on the pump power is investigated in detail.

가변 페브리-페로 필터와 FBG를 이용한 광세기 기반 자기기준 광섬유 센서

본 논문에서는 자기기준 특성을 가지는 광세기 기반 광섬유 센서 구조를 제안하고 실험적으로 구현하여 성능을 제시한다. 제안하는 광섬유 센서는 광대역 광원(BLS), fiber Bragg grating (FBG), 가변 페브리-페로(Fabry-Perot) 필터, LabVIEW 프로그램으로 구성된다. 제안한 자기기준 광섬유 센서의 이론적인 해석을 통하여 측정 변수(Χ)와 보정 변수(β)를 정의하고, 이를 바탕으로 전달함수(Η)를 구한다. 또한 실험을 통하여 이론적인 해석의 타당성을 제시한다. 제안한 광섬유 센서 구조는 광대역 광원의 출력 광세기가 0 dB, 3 dB, 6 dB 감소해도 측정결과에 영향을 미치지 않는 자기기준 특성을 가진다. 또한 다른 특성의 FBG를 사용하여도 측정 가능하므로, 제안한 광섬유 센서 구조는 임의의 규격을 가진 FBG를 사용할 수 있다. 광원의 광세기가 감소하였을 때와 세 가지 다른 특성의 FBG 쌍을 이용하여 측정한 결과 이론적인 값과 잘 일치함을 보였다. 따라서 제안한 광섬유 센서는 자기기준 특성과 구성하는 FBG의 규격이 비교적 엄격하지 않아도 되는 장점을 가진다.

Narrow linewidth Yb-doped fiber laser at 1120 nm

A 974 nm laser diode pumped 1120 nm ytterbium (Yb)-doped fiber laser with all fiber components has been experimentally demonstrated. The resonator is composed of a normal single-mode Yb-doped fiber 1 m long and a pair of fiber Bragg gratings. Up to 21.6 mW of continuous-wave output power is generated when the launched pump power is 161 mW with an optical-to-optical conversion efficiency of 13.4%. The central wavelength is 1120.89 nm with a linewidth as narrow as 0.02 nm. Additionally, a similar fiber laser with a 2 m long gain medium displays a broadened linewidth. The results of the two fiber lasers are compared and discussed in the paper.

Mid-infrared chalcogenide glass Raman fiber laser

We report the first demonstration of a Raman fiber laser (RFL) emitting in the mid-infrared, above 3 μm. The operation of a single-mode As2S3 chalcogenide glass based RFL at 3.34 μm is demonstrated by using a low-loss Fabry-Pérot cavity formed by a pair of fiber Bragg gratings. A specially designed quasi-cw erbium-doped fluoride fiber laser emitting at 3.005 μm is used to pump the RFL. A laser output peak power of 0.6 W is obtained with a lasing efficiency of 39% with respect to the launched pump power.

Integrated hybrid Raman/fiber Bragg grating interrogation scheme for distributed temperature and point dynamic strain measurements

We propose and experimentally demonstrate the feasibility of an integrated hybrid optical fiber sensing interrogation technique that efficiently combines distributed Raman-based temperature sensing with fiber Bragg grating (FBG)-based dynamic strain measurements. The proposed sensing system is highly integrated, making use of a common optical source/receiver block and exploiting the advantages of both (distributed and point) sensing technologies simultaneously. A multimode fiber is used for distributed temperature sensing, and a pair of FBGs in each discrete sensing point, partially overlapped in the spectral domain, allows for temperature-independent discrete strain measurements. Experimental results report a dynamic strain resolution of 7.8 nε/√Hz within a full range of 1700 με and a distributed temperature resolution of 1°C at 20 km distance with 2.7 m spatial resolution.

Ultrahigh Resolution Multiplexed Fiber Bragg Grating Sensor for Crustal Strain Monitoring

We demonstrated a multiplexed fiber Bragg grating (FBG) sensor with static strain resolution of 10 nanostrain (nε) for crustal strain monitoring. Each sensor unit consists of a pair of identical FBGs for strain sensing and reference, respectively. A narrow linewidth tunable laser is used to interrogate the FBGs, and a cross-correlation algorithm is incorporated to demodulate the wavelength difference induced by strain. When no strain is applied, an ultrahigh wavelength precision corresponding to strain resolution of 3.3 nε was obtained, indicating the ultimate resolution of the sensor system. With a variable strain applied by a piezo-stage, strain resolution of 17.6 nε was demonstrated. When the sensor is adopted for the in situ monitoring of crustal deformation, the strain induced by oceanic tide is clearly recorded with a resolution of 10 nε, providing a potential tool for the geophysical measurements.

Random Rotary Position Sensor Based on Fiber Bragg Gratings

In this paper a new rotary position sensing structure based on a pair of fiber Bragg gratings (FBGs) is experimentally demonstrated with capability of detecting rotating angle of a rotor which is rotated in arbitrary direction or rotated in the same direction infinitely. Moreover, owing to its miniature size, this structure can also be used for small rotary apparatus as a tiny rotating position sensor. The operation mechanism is mainly based on the difference between the wavelength shifts of two FBGs respectively due to the axial strain caused by bending the cantilever towards the angular direction corresponding to the rotating position of rotary shaft. A deviation of 1.1 degrees for rotary angle detecting is obtained.

Sensitivity Enhancement of Strain Sensing Utilizing a Differential Pair of Fiber Bragg Gratings

In strain measurement applications, the matched fiber Bragg gratings (FBG) method is generally used to reduce temperature dependence effects. The FBG parameters have to be designed to meet the requirements by the particular application. The bandwidth and slope of the FBG has to be balanced well, according to the measurement range, accuracy and sensitivity. A sensitivity enhanced strain demodulation method without sacrificing the measurement range for FBG sensing systems is proposed and demonstrated utilizing a pair of reference FBGs. One of the reference FBGs and the sensing FBG have almost the same Bragg wavelength, while the other reference FBGs has a Bragg wavelength offset relative to the sensing FBG. Reflected optical signals from the sensing FBG pass through two reference FBGs, and subtract from each other after the detection. Doubled strain measurement sensitivity is obtained by static rail load experiments compared to the general matched grating approach, and further verified in dynamic load experiments. Experimental results indicate that such a method could be used for real-time rail strain monitoring applications.

Characteristic analysis of a novel F-P interferometer based on a pair of FBGs with built-in LPFGs

The transmission characteristics of a Fabry-Perot (F-P) interferometer based on a fiber Bragg grating (FBG) pair with a built-in long-period fiber grating (LPFG) are theoretically analyzed, and the shift of transmission interference fringe as a function of environmental refractive index is acquired. The influence of the lengths of F-P cavity, LPFG and FBG on the transmission characteristics of the proposed interferometer has been numerically investigated, and the simulation results indicate that the sensitivity of refractive index reaches 2.27 10-6 for an optical spectrum analyzer (OSA) with a resolution of 1 pm.

Vibration Disturbance Localization Using a Serial Array of Identical Low-Finesse Fiber Fabry-Perot Interferometers

An optical fiber sensor system for localization of a vibrational disturbance along the fiber is presented. The sensor system is based on a serial array of identical Fabry-Perot interferometers, formed directly in the single mode SMF-28e fiber by pairs of fiber Bragg gratings with reflectivity of 0.04% each. Interferometers were interrogated by an intensity modulated distributed feedback diode laser. We present a signal processing algorithm for localization of a disturbed interferometer and experimental results for a serial array of 14 in-fiber interferometers. Simple sensor configuration and the use of low-frequency components make it potentially inexpensive and suitable for applications where continuous monitoring for appearance of vibrations is required.

Synchronous tunable wavelength spacing dual-wavelength SOA fiber ring laser using Fiber Bragg grating pair in a hybrid tuning package

A Dual-Wavelength Semiconductor Optical Amplifier (DW-SOA) based fiber ring laser with synchronous wavelength tunability is proposed and experimentally demonstrated. The SOA gain medium strongly suppresses mode competition, thus allowing stable dual-wavelength laser oscillation. The wavelength spacing of the two lasers can be tuned synchronously using a modified hybrid-tuning package incorporating a pair of Fiber Bragg Gratings (FBGs). The DW-SOA demonstrates a laser output with a wavelength spacing of between 0.10 and 8.30 nm (wavelength shift inequality of 0.08 to 0.75 nm). The relationship between the applied strain and wavelength shift of the two tuning modes is also analyzed.

Optically coupled cavities for wavelength switching

An optical bistable device which presents hysteresis behavior is proposed and experimentally demonstrated. The system finds applications in wavelength switching, pulse reshaping and optical bistability. It is based on two optically coupled cavities named master and slave. Each cavity includes a semiconductor optical amplifier (SOA), acting as the gain medium of the laser, and two pair of fiber Bragg gratings (FBG) which define the lasing wavelength (being different in each cavity). Finally, a variable optical coupler (VOC) is employed to couple both cavities. Experimental characterization of the system performance is made analyzing the effects of the coupling coefficient between the two cavities and the driving current in each SOA. The properties of the hysteretic bistable curve and switching can be controlled by adjusting these parameters and the loss in the cavities. By selecting the output wavelength (λ1 or λ2) with an external filter it is possible to choose either the invert or non-invert switched signal. Experiments were developed employing both optical discrete components and a photonic integrated circuit. They show that for 8 m-long cavities the maximum switching frequency is about 500 KHz, and for 4 m-long cavities a minimum rise-time about 21 ns was measured. The switching time can be reduced by shortening the cavity lengths and using photonic integrated circuits.

二极管泵浦1018 nm掺Yb双包层光纤激光器

We report a 1 018-nm ytterbium-doped double-clad fiber laser pumped by 970-nm diode. A pair of fiber Bragg gratings with reflectivities of 99.9% and 9% at a center wavelength of 1 018.9 nm are employed as cavity mirrors. The ytterbium-doped double-clad fiber is a 2.6-m-long Liekki fiber. Laser output power of 7.5 W at 1 018 nm is obtained under the pump power of 59.2 W. The overall slope efficiency of the fiber laser is about 16%. This low slope efficiency is mainly due to the incomplete absorption of the pump power.

A tunable and switchable single-longitudinal-mode dual-wavelength fiber laser with a simple linear cavity

A simple linear cavity erbium-doped fiber laser based on a Fabry-Perot filter which consists of a pair of fiber Bragg gratings is proposed for tunable and switchable single-longitudinal-mode dual-wavelength operation. The single-longitudinal-mode is obtained by the saturable absorption of an unpumed erbium-doped fiber together with a narrow-band fiber Bragg grating. Under the high pump power (>166 mW) condition, the stable dual-wavelength oscillation with uniform amplitude can be realized by carefully adjusting the polarization controller in the cavity. Wavelength selection and switching are achieved by tuning the narrow-band fiber Bragg grating in the system. The spacing of the dual-wavelength can be selected at 0.20 nm (approximately 25.62 GHz), 0.22 nm (approximately 28.19 GHz) and 0.54 nm (approximately 69.19 GHz).

Location of a time-varying disturbance using an array of identical fiber-optic interferometers interrogated by CW DFB laser

A novel technique for distributed detection and localization of vibrational disturbances is presented. It is based on a serial array of identical low-finesse Fabry-Perot interferometers interrogated at a fixed wavelength by DFB diode laser intensity modulated at 10 KHz. Interferometers are formed directly in the single mode SMF-28 fiber by pairs of fiber Bragg gratings with reflectivity < 0.05% each. A simple signal processing based on the Fourier transform of detected signals and evaluation of phases for different signal components enables localization of a perturbed interferometer with a high accuracy. In experiment, a localization accuracy of 10 meters has been demonstrated for 5 km long fiber after 1 s of averaging. The system has the capability of using well in excess of 100 interferometers in a single fiber channel. A simple sensor configuration and the use of low-frequency components make it potentially inexpensive and suitable for applications where a continuous monitoring of long structures has to be performed for appearance of vibrations.

Stable and spacing-adjustable multiwavelength Raman fiber laser based on mixed- cascaded phosphosilicate fiber Raman linear cavity

A novel multiwavelength Raman fiber laser based on the mixed-cascaded Stokes effects of phosphosilicate fiber is proposed and demonstrated experimentally. By using stimulated Raman scattering of both P(2)O(5) and SiO(2) along 1 km phosphosilicate fiber pumped with a 1064 nm double-clad fiber laser, the mixed-cascaded Raman linear cavity is formed by a pair of fiber Bragg gratings at 1239 nm, a polarization-maintaining fiber (PMF) Sagnac loop filter, and a conventional optical loop mirror. Up to 15-wavelength stable oscillations around 1320 nm are obtained with a wavelength spacing of 0.44 nm and power nonuniformity of less than 4 dB. By changing the length of the PMF in the Sagnac loop filter from 10 to 5.5 m, the wavelength spacing is adjustable from 0.44 to 0.8 nm. The extinction ratio of the laser is more than 30 dB. Excellent stability is also observed with a peak power fluctuation of less than 0.8 dB in 1 h.