Narrowband Fiber Bragg Grating Research Articles

Towards real-time active imaging of greenhouse gases using tunable mid-infrared all-fiber lasers.

We report a tunable all-fiber laser emitting a maximum output power of 2.55W around 3240nm. The fiber laser cavity based on a fluoride fiber doped with dysprosium ions yields an efficiency of 42% according to the in-band launched pump power at 2825nm. Due to a custom piezoelectric fiber Bragg grating (FBG) package, mechanical strains applied to the narrowband FBG used as the input cavity coupler allowed for fast tuning of the emission wavelength over a spectral range of 1.5nm. This laser was deployed in the field in northern Québec (Canada) to assess its performances for remote sensing of methane in the presence of a significant amount of water vapor, i.e.,over a hydroelectric reservoir. The preliminary results acquired during this field campaign confirm the great potential of the proposed approach for the development of a real-time active imaging system of greenhouse gases.

Single-Longitudinal Mode Ytterbium-Doped Fiber Laser with Ultra-Narrow Linewidth and High OSNR Using a Double-Ring Passive Subcavity

A continuous wave (CW) ultra-narrow linewidth single-longitudinal mode (SLM) ytterbium-doped fiber laser (YDFL) based on narrowband fiber Bragg grating (NB-FBG) and double-ring passive subcavity (DR-PS) was studied. The filtering characteristics of the double-ring passive subcavity are analyzed theoretically, and it is used as a high-precision mode filter to eliminate the dense longitudinal mode and mode hopping of YDFL and ensure that the laser operates in the SLM state. Experimental results show that the laser has a central wavelength of 1030.052 nm at room temperature, an optical signal-to-noise ratio of up to 73 dB, and an ultra-narrow linewidth of 355 Hz. In addition, we measured the short-term and long-term stability of the laser, with wavelength and power fluctuations of less than 0.008 nm and 0.19 dB, respectively, over 120 min. As a result, we obtain SLM YDFL with high stability, ultra-narrow linewidth, and a high optical signal-to-noise ratio.

Gain‐clamping in L‐band zirconium–erbium co‐doped fiber amplifier with FBG based lasing control

AbstractIn this study, gain clamping performance in an L‐band zirconium‐erbium co‐doped fiber amplifier (Zr‐EDFA) with a very short length of heavily doped fiber and FBG based lasing control structure was presented. A simple gain clamping design based on a symmetrical narrow band C‐band fiber Bragg grating (FBG) pair addition was used in the L‐band Zr‐EDFA with bidirectionally pumping scheme. An L‐band gain of higher than 25 dB was obtained with a maximum noise figure (NF) of 5 dB in the conventional Zr‐EDFA design which was higher than the previous results obtained with forward pumping scheme. When a couple of narrow band FBGs at Bragg reflection wavelength of 1542 nm are used as the lasing mechanism for gain clamping in L‐band operation, small signal gain of Zr‐EDFA decreases, but on the other hand, the gain is clamped at almost 15.5 dB with a flattened gain spectrum along a dynamic range of 25 dB for the signal input powers between −30 and −5 dBm with the expense of 1.5 dB NF penalty.

Stable period-one oscillations in a semiconductor laser under optical feedback from a narrowband fiber Bragg grating.

Period-one (P1) oscillations in a semiconductor laser under optical feedback from a narrowband fiber Bragg grating (FBG) are numerically investigated. FBG feedback enhances the stability of P1 oscillations compared to the conventional mirror feedback in the form of P1 microwave linewidth and phase noise reduction and residual noise peaks suppression. In the proposed scheme, the FBG has a narrow bandwidth smaller than the laser relaxation oscillation frequency. Then it effectively suppresses the coherence collapse of the laser by filtered feedback. Hence it can keep the laser in P1 operation even under relatively strong feedback. Besides, a uniform FBG has a comb-filtered reflectivity spectrum with a main lobe surrounded by several side lobes. Hence it can limit the external cavity modes by each lobe. As a result, FBG feedback can reduce microwave linewidth and phase noise by sustaining stronger feedback power and improve side-peak suppression ratio (SPSR) by filtering external cavity modes. The effects of stabilization are enhanced by properly increasing grating bandwidth. By fine-tuning the feedback delay time, the microwave linewidth can be reduced to a local minimum which reveals the optimal locking between P1 frequency and one of the external cavity modes. Increasing the feedback delay time, the local minimum linewidth can be further reduced. FBG feedback reduces the microwave linewidth by up to more than an order of magnitude and improves the SPSR by up to more than two orders of magnitude than mirror feedback using the same delay time.

Enhancement in the Gain of EDFA in Fibre Optic Communication

With the evolvement ofhigh speed and long distance data communication systems, conventional band erbium-doped fiber amplifiers (C-EDFAs) are getting more attention in recent times. Major advantage of the C-band EDFA is that it provides the user to realize a system with wide bandwidth of 40 nm. But, from the reported works, it is evident that for Gain enhancement in C-band using EDFA is reported with the use of multiple stages, multiple pumps, Gain flattening filters etc. However, these techniques suffered from high cost, complex techniques and low performance.Here enhancement process was done through the narrowband Fiber Bragg Gratings (FBG) or fiber reflectors mirrors. In this work, a conventional band erbium doped fiber amplifier is proposed with high gain and less noise figure by incorporating the two fiber bragg gratings (FBGs) for amplified spontaneous noise reinjection. Maximum ASE is emerged at 1565 nmfor the at -55 dBm carrier powers. Maximum gain is found out to be 48.16 dB with noise figure of 5.29 dBm.

Innovative fiber Bragg grating filter based on a graphene photonic crystal microcavity.

We propose a new model for a fiber Bragg grating (FBG) filter based on one-dimensional defective photonic bandgap structures, which operates within telecom windows. The device is realized in an asymmetric $ {{\rm SiO}_2}/{{\rm TiO}_2} $SiO2/TiO2 photonic crystal (PC) microcavity with the defect layer of the graphene disk placed in the center of the structure. The theoretical analysis of the optical properties of the narrowband FBG filter is given based on the combination of the density matrix approach with the transfer matrix method. The effect of the incident angle and the polarization of the probe field on the transmittance spectra is calculated. Also, tuning the filtering wavelength and the number of guided modes is performed by changing the properties of PC's defect layer. It is shown that depending on the ratio of the coupling fields' intensity, the probe field absorption can be minimized and even be amplified in $ {\lambda _0} = 1550\;{\rm nm} $λ0=1550nm. The results show very promising potential for fabrication of FBG filters operating in the near-infrared regime for light wave communications.

Multi-longitudinal mode fiber laser sensor system with high signal-to-noise ratio based on laser modes control.

A multi-longitudinal mode fiber laser sensor (MLMFLS) system with high signal-to-noise ratio (SNR) is proposed. To the best of authors' knowledge, this is the highest SNR ever reported by MLMFLS system. The laser sensor consists of a narrow-band fiber Bragg grating (FBG), erbium-doped fiber (EDF) and an optical reflector. The FBG controls the number of laser modes which excited by laser sensor. Beat frequency signals (BFS) modulated by applied measurand are generated by those laser modes and their SNR are controlled by the FBG. Measurement results show the BFS have SNR of 65.0 dB, accuracy of ± 2.0 με, and stability of 0.4 kHz, which demonstrate its high SNR, accuracy and stability.

Fiber Source for Pumping a Fiber-Optical Parametric Generator at ∼800 nm

The coherent anti-Stokes Raman spectroscopy (CARS) has attracted a great attention as non-invasive method of real-time monitoring of processes occurring in biological tissues and cells. It needs a special kind of optical source that would be compact, stable and low cost. We investigate a possibility of using highly-chirped dissipative soliton oscillator together with a narrowband fiber Bragg grating and all-fiber amplifier. Optical pulses with the duration of 85 ps and the peak power of 400 W were generated at the output of the fiber system with the repetition rate about 13 MHz. Developed source is suitable to pump a fiber optical parametric oscillator for CARS.

Michelson mode selector for spectral range stabilization in a self-sweeping fiber laser.

We report on spectral range stabilization in a self-sweeping laser by adding a narrowband fiber Bragg grating (FBG) to the output mirror in the Michelson configuration. The effects of FBG reflectivity and optical path difference in the Michelson interferometer on the laser spectral dynamics are investigated. Optimization of the interferometer allows us to demonstrate broadband (over 16nm) self-sweeping operation and reduction of the start and stop wavelength fluctuations by two orders and one order of magnitude (∼100 and 15 times) for start and stop bounds, respectively (down to several picometers). The proposed approaches significantly improve quality of the spectral dynamics and facilitate application of the self-sweeping lasers.

Fiber-Optic Acceleration Sensor on Duplex Fiber Bragg Structures

We propose an assessment of the possibility to use narrow-band fiber Bragg structures as the basis of a measuring system for an acceleration sensor (accelerometer). The assessment of applicability is carried out on the basis of mathematical and computer simulation and analytical assessments of the model's working capacity. We propose to solve the problem by transferring a signal from the optical (THz) to the radio frequency (GHz) range of measurements due to the theory and technology of radiophoton methods. The result is a significant increase in the signal-to-noise ratio. We suggest to use the measuring system based on two narrow-band fiber Bragg gratings with the following two properties: central frequencies are in the optical range, and a difference of central frequencies is in the radio frequency range of the spectrum. The optical signal obtained in the optoelectronic circuit is fed to a photodetector. An analysis of the resulting electrical signal allows to make a conclusion on the magnitude and direction of the force acting along the axis of the sensor sensitivity. The magnitude of the effective inertia force is directly related to the acceleration acting on the measuring system. We propose an approach to determine the magnitude of the effective force. The approach does not require measurement of the intermediate radio frequency, and determines the dependence of the effective force on the magnitude of the dual-frequency beats modulation factor. We propose to implement the design of the sensor in such a way as to minimize the effect of temperature deviations on the measuring system as a whole.

A Liquid-Level Sensing Technique Based on Differential Detection of Correlation Peaks From Broadband Chaos

A highly sensitive liquid-level sensing technique is proposed and experimentally demonstrated. Two narrowband fiber Bragg gratings (FBGs) with high reflectivity are used to filter out the two light signals from the broadband chaos. Two weak FBGs are served respectively as the liquid-level sensors at two different sensing points. The change of liquid-level will induce the wavelength shift of the weak FBGs, which can be demodulated through calculating the amplitude difference in the logarithm of two cascaded correlation peaks in the cross-correlation spectrum. Adopting the differential calculation of the cascaded correlation peak amplitudes can avoid the complex wavelength detection and enhance the robustness against the power variation of the broadband chaos. Our method can also support the simultaneous multiplexing and locating with high resolution from the time delays of the corresponding correlation peaks. Experimental results show that the liquid level changes linearly with the relative peak amplitude difference in the logarithm and the sensitivity is around 0.019/mm. The sensing resolution of liquid-level can reach at least 3 mm, and the relative resolution is around 0.055. Moreover, the real-time fiber fault monitoring can be achieved with a spatial resolution of around 2.8 cm, which improves the survivability in harsh environment.

Nanosecond mode-locked Tm-doped fiber laser based on graphene saturable absorber

The Tm-doped mode-locked pulsed fiber lasers, which are known for their wide applications in optical communication, laser medical system and special material processing, have attracted considerable interest as novel laser sources. Up to now, many reported Tm-doped mode-locked fiber lasers focused on emitting picosecond or femtosecond pulses at a few megahertz (MHz) repetition rate. Actually, due to the strong chirp, large pulse width, low peak power and little nonlinear phase accumulation characteristics in the process of power amplifier, nanosecond mode-locked fiber laser is a representative of ideal seed source in the chirped pulse amplification (CPA) system. However, nanosecond mode-locked fiber lasers are generally implemented with the kilometerlong cavity length, corresponding to the fundamental repetition rate of hundreds of kilohertz. Usually, fiber lasers with such a low repetition rate are not desirable in applications of laser material processing, nor medical treatment nor scientific researches. In this paper, we report a nanosecond mode-locked Tm-doped fiber laser with MHz repetition rate based on graphene saturable absorber (SA). As the SA, graphene has excellent optical properties, such as optical visualization, high transparency, ultra-fast relaxation time and nonlinear absorption. It is not limited by the band gap either because of its zero-band-gap structure. Therefore, graphene can be used as fast SA, with wide spectral range operated. Generally, graphene suitable for mode-locked fiber lasers can be produced by using chemical vapor deposition (CVD), liquid phase exfoliation and mechanical exfoliation. Since the CVD technique can obtain high-quality graphene with precisely controlled number of layers, it is always the first choice for the manufacture of graphene. In our work, monolayer graphene layers are grown on copper foils by CVD, and then transferred onto the end face of the fiber connector three times. Meanwhile, a narrow-band fiber Bragg grating is used to constrain longitudinal modes of the laser intra-cavity. By simply adjusting the pump power and the polarization angle of polarization controller, stable 2 μm nanosecond mode-locked pulses are obtained in a wide range from 3.8 ns to 94.3 ns at 3.8 MHz repetition rate. We believe that the results obtained will be helpful for investigating the CPA system at 2 μm.

Powerful narrow linewidth random fiber laser

In this paper, we demonstrate a narrow linewidth random fiber laser, which employs a tunable pump laser to select the operating wavelength for efficiency optimization, a narrow-band fiber Bragg grating (FBG) and a section of single mode fiber to construct a half-open cavity, and a circulator to separate pump light input and random lasing output. Spectral linewidth down to 42.31 GHz is achieved through filtering by the FBG. When 8.97 W pump light centered at the optimized wavelength 1036.5 nm is launched into the half-open cavity, 1081.4 nm random lasing with the maximum output power of 2.15 W is achieved, which is more powerful than the previous reported results.

Frequency doubling of Raman fiber lasers with random distributed feedback.

This Letter presents what we believe is the first experimental study of frequency doubling of a Raman fiber laser (RFL) with random distributed feedback (RDFB) in an MgO:PPLN crystal. We compared two laser configurations, each with a half-open cavity. The cavity contained either a broadband Sagnac mirror or a narrowband fiber Bragg grating (FBG). We found that spectral broadening in the studied configurations of the RDFB RFLs differed from that found in a conventional RFL with a linear cavity, as well as from each other. We also compared the second harmonic generation (SHG) efficiency for these three types of lasers. The highest SHG efficiency was obtained for the RDFB RFL with the FBG delivering >100 mW power at 654 nm.

Tunable and Switchable Narrow Bandwidth Semiconductor-Saturable Absorber Mirror Mode-Locked Yb-Doped Fiber Laser Delivering Different Pulse Widths**Supported by the National High Technology Research and Development Program of China under Grant No 2014AA041901, NSAF Foundation of the National Natural Science Foundation of China under Grant No U1330134, the Opening Project of Shanghai Key Laboratory of All Solid-State Laser and Applied Techniques under

The wavelength-tunable and switchable narrow bandwidth mode-locking operation is demonstrated in an all fiber laser based on semiconductor-saturable absorber mirror (SESAM). Two narrow-band fiber Bragg gratings centered at 1029.9 nm and 1032 nm respectively with a polarization controller inserted between them are used to realize the wavelength switchable between 1029.9 nm and 1032 nm. The laser delivers different pulse widths of 7.5 ps for 1030 nm and 20 ps for 1032 nm. The maximum output power for both could reach ~6.5 mW at single pulse operation. The output wavelength could be tuned to about 0.9 nm intervals ranging from 1030.2 nm to 1031.1 nm and from 1032.15 nm to 1033.7 nm with the temperature change of the fiber Bragg grating, respectively.

954 nm Raman fiber laser with multimode laser diode pumping

CW Raman fiber laser emitting at 954 nm under direct pumping by a high-power multimode laser diode at 915 nm is demonstrated. A cavity of the laser is formed with 2.5 km-long multimode graded-index fiber and two mirrors: highly reflective fiber Bragg grating (FBG) at one side and normally cleaved fiber end at the other side. The laser generates low-index transverse modes at the Stokes wavelength with output power above 4 W at a slope efficiency above 40%. It is shown that utilization of a narrowband FBG mirror with low reflectivity instead of the cleaved fiber end with Fresnel reflection leads to stronger spectral mode selection, but the generated power is reduced in this case.

Intensity-Modulated Optical Fiber Sensor for AC Magnetic Field Detection

An erbium-doped (Er3+) fiber optic laser is proposed for sensing alternated magnetic fields by measuring the laser intensity modulation. The sensor is fabricated using two partially overlapped narrow-band fiber Bragg gratings (FBGs) and a section of doped fiber in a Fabry–Perot configuration. Laser power stability and bandwidth are studied while changing the overlap. A bulk rod of TbDyFe, a magnetostrictive material, is glued to both the FBGs and the laser wavelength and power are modulated according to the magnetic field. Acquisition and processing are done using virtual instrumentation. Results have shown the possibility of detecting 11.18 $\mu \text{T}_{\mathrm {{rms}}}/\surd $ Hz for an alternating magnetic field of 4.17 mT $_{\mathrm {{rms}}}$ .

Distributed fiber sensing system with wide frequency response and accurate location

A distributed fiber sensing system merging Mach–Zehnder interferometer and phase-sensitive optical time domain reflectometer (Φ-OTDR) is demonstrated for vibration measurement, which requires wide frequency response and accurate location. Two narrow line-width lasers with delicately different wavelengths are used to constitute the interferometer and reflectometer respectively. A narrow band Fiber Bragg Grating is responsible for separating the two wavelengths. In addition, heterodyne detection is applied to maintain the signal to noise rate of the locating signal. Experiment results show that the novel system has a wide frequency from 1Hz to 50MHz, limited by the sample frequency of data acquisition card, and a spatial resolution of 20m, according to 200ns pulse width, along 2.5km fiber link.

All-incoherent wavelength conversion in highly nonlinear fiber using four-wave mixing

This work describes efficient and polarization insensitive, all-incoherent four-wave mixing wavelength conversion achieved within a short length of highly nonlinear fiber medium, created by using both spectrally sliced pump and probe channels from a single-amplified spontaneous emission source coupled to two narrowband Fiber Bragg grating (FBG) filters. This simple and cost-effective scheme is capable of generating a down-converted probe channel across a 17.2-nm wavelength span, while still maintaining a high conversion efficiency of around −22 dB and an optical-signal-to-noise ratio of ∼21 dB. The effects of pump power, FBG detuning, and polarization are also reported.

High-Power Thulium-Doped All-Fiber Superfluorescent Sources

Power scaling of broadband and narrowband thulium-doped all-fiber superfluorescent sources based on master-oscillator power-amplifier configuration is reported. For scaling the output-power of broadband superfluorescent fiber source, a stable low-power broadband superfluorescent fiber seed source and a two-stage cladding-pumped thulium-doped fiber amplifiers were adopted. The thulium-doped fiber power amplifier yielded 122 W of broadband superfluorescence output, and the wavelength range spanned from 1935-2075 nm with a full width at half maximum (FWHM) of 25 nm. To the best of our knowledge, this is the first demonstration of superfluorescence power exceeding 100 W from thulium-doped fiber amplifiers at 2 μm. In addition, we also investigate the power scaling of narrowband thulium-doped superfluorescent fiber source based on a tunable narrowband superfluorescent fiber seed source by selecting a small region out of a broadband superfluorescence spectrum using a narrowband fiber Bragg grating. The two-stage cladding-pumped thulium-doped all-fiber amplifiers were used directly to boost average power to 120 W, the center wavelength and the FWHM were 1963.5 and 1.2 nm, respectively. The presented high power broadband and narrowband superfluorescent fiber source could be of great interest and open up the prospect of many new applications such as laser materials processing and metrology.