Chirped Fiber Bragg Grating Research Articles

Wavelength and pulse-number tunable ultrafast vortex fiber laser

We propose an all-fiber passively mode-locked laser emitting ± 1 order ultrafast optical vortex pulses with tunable wavelength and pulse-number, for the first time to the best of our knowledge. A home-made two-mode chirped fiber Bragg grating (TM-CFBG) is utilized to both select the higher-order mode and provide a relatively broad bandwidth to achieve ultrashort vortex pulses. The central wavelength of the vortex pulses can be tuned from 1552.23 nm to 1553.81 nm and the pulse duration reaches 6.31 ps. Through further simply controlling the cavity parameters, vortex pulses with different pulse-number are obtained as well. Moreover, the proposed laser exhibits pump hysteresis effect. This ultrafast vortex fiber laser with flexible tuning functions has potential applications in fields of optical communications, material processing, etc.

Novel Interrogation Method for Fully Distributed LCFBG Sensor Based on Microwave Photonic Filtering

A novel interrogation method for linearly chirped fiber Bragg grating (LCFBG) based fully distributed strain sensor which can simultaneously determine strain value and recognize position is proposed and experimentally demonstrated. Compared with the traditional distributed grating interrogation systems by analyzing the reflection spectrum of the LCFBG, the system is mainly based on frequency domain measurement from a microwave photonic filter (MPF) configuration, which has the features of fast responding and high resolution. By using this structure, when distributed strain is applied to the LCFBG, the reflective point on the LCFBG for a certain wavelength as well as the frequency response of the MPF will change. By detecting the resonance frequency shift of the MPF, the strain value can be achieved. Combined with the one-to-one correspondence between the wavelength and the spatial position of the LCFBG, the distributed strain profile along the LCFBG can be reconstructed. In a proof of concept experiment, interrogation of fully distributed grating sensors with ununiform strain distributions is experimentally demonstrated. A spatial resolution of ~0.2 mm over a gauge length of 27mm and a strain resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ &lt; 1\text{u}\varepsilon $ </tex-math></inline-formula> have been achieved.

Development and investigation of the sensitive element of the amplitude fiber-optic temperature sensor based on superimposed chirped Bragg gratings

In this paper we study an original technique for creating an amplitude temperature sensor based on n-pairs of chirped fiber Bragg gratings (CFBGs). The scalable design of the sensor allows to increase the range of the measured signal. The use of the amplitude interrogation technique ensures high speed, elementary nature of the scheme and simple operating conditions. The application of superimposed CFBGs as a sensitive element of an amplitude temperature sensor is investigated. As a result of the work, a method for measuring temperature with a fiber-optic sensitive element based on n-pairs of CFBGs is tested. Two superimposed CFBGs are inscribed in a standard telecommunication single-mode optical fiber using a KrF excimer laser system and Talbot interferometer. One of the superimposed structures is used as a reference element of the sensor and the second – as a sensitive element and is placed in a brass tube, where it is fixed on one side with an adhesive joint. The sensor has an accuracy of 0.48 °C and a sensitivity of 0.20 µW/°C for temperature measurement in the range of 30–70 °C. The results obtained are of great importance in the development of fiber-optic temperature control systems. Implementation of the sensor based on n-pairs of CFBGs allows scaling the power of signal, increasing the ability to detect a slight change in ambient temperature. The created sensor works according to the amplitude polling technique, which is characterized by high accuracy and speed of measurement, minimized scheme, simplified use and easy processing of the detected signal. In addition, the implemented interrogation method corresponds to the trend of developing low-cost fiber-optic systems without losing their main advantages.

Multimode polymer chirped fiber Bragg grating for shock and detonation velocity.

Shock and detonation velocities are today measured continuously using long silica chirped fiber Bragg gratings (CFBGs). These thin probes can be directly inserted into high-explosive samples. The use of a polymer fiber increases the sensitivity at low pressure levels when studying, for instance, shock-to-detonation transitions in wedge tests. The 22-mm-long multimode polymer CFBGs have, therefore, been manufactured and characterized. A first detonation experiment was realized on a narrow Formex strip using such a sensor. The feasibility is demonstrated, and the associated uncertainties, mostly coming from the use of a multimode fiber, are discussed.

Efficient diaphragm-based Fiber Bragg grating vacuum sensor

An efficient diaphragm-based fiber Bragg grating (FBG) vacuum sensor was designed, developed and experimentally demonstrated. The devised sensor was independently interrogated by spectral and intensity demodulation techniques. In spectral demodulation, a linear red-shift was observed in the Bragg spectrum with enhancement in the vacuum level with sensitivity and resolution of 18.5 p.m./mbar and 6.644 mbar, respectively. In intensity demodulation, a chirped fiber Bragg grating (CFBG) was used as an optical filter for the Bragg spectrum of the FBG which linearly varied reflected light intensity from the FBG with enhancement in vacuum level inside the chamber. The intensity demodulation was able to detect the pressure difference in the chamber from 67 mbar to 0.2 μbar with sensitivity and resolution of 1.40 nW/mbar and 6.41 mbar, respectively. The sensor offered 2000 times faster response time than the reference commercial vacuum gauge for intensity demodulations.

Femtosecond inscription of chirped fiber Bragg gratings and fiber Bragg grating arrays using a single uniform phase-mask

Chirped fiber Bragg gratings (CFBGs) and arrays of fiber Bragg gratings (FBGs) are inscribed with femtosecond pulses and a single uniform phase-mask (PM). The inscription setup includes an 800 nm NIR femtosecond laser, a PM, a defocusing spherical lens and a cylindrical focusing lens. The wavelength tunability is achieved by a defocusing lens, and movement of the PM. A first FBG is inscribed, followed by nine cascading FBGs, where each one is inscribed only after the movement of the PM and a movement of the fiber, thus allowing inscription on a fresh fiber section without overlapping. The transmission and reflection spectra of these ten cascaded FBGs are measured showing a spectral shift of ∼0.9 nm between each one, and a total shift of ∼8 nm. The transmission dip of each FBG is roughly −10 dB. The CFBG is inscribed with the same single uniform PM and with the same setup, but with different movement increments of the PM and fiber. The transmission and reflection spectra of the resulting CFBG are measured with a strength of ∼20 dB and a continuous bandwidth of ∼4.7 nm at FWHM. This yields a chirp rate of ∼1 nm/cm, while the full length of the CFBG is ∼45 mm.

Flexible demodulation for rotation-induced phase difference based on a phase-controlled microwave photonic filter.

High-performance demodulation of Sagnac effect is of great importance for rotation rate measurement in inertial navigation system. In this paper, we propose a flexible measurement of rotation rate based on a phase-controlled microwave photonic filter (MPF), which incorporates an orthogonal double-sideband (ODSB) modulator, a Sagnac loop, a linearly chirped fiber Bragg grating (LCFBG), a polarizer, and a photodetector. The ODSB modulator is used to generate optical carrier (OC) and first-order sidebands with mutually orthogonal polarizations. For the MPF, its central frequency can be tuned through changing the phase difference between the OC and first-order sidebands thanks to the dispersion of the LCFBG. Therefore, if the OC and first-order sidebands are separated by a polarization beam splitter and then travel along the Sagnac loop in opposite directions, the rotation-induced phase difference between them will lead to a shift on the frequency response of the MPF. Thus, two ways can be adopted to detect the rotation rate of the Sagnac loop for different applications: monitoring the frequency response shift of the MPF and measuring the power variation at a certain frequency. Besides, the measurement sensitivity can be easily adjusted to satisfy specific requirements by tuning a polarization controller or choosing a different operating frequency. An experiment is performed to validate the proposed scheme. The results show that the maximum frequency shift of the MPF can reach 1.7 GHz at a rotation rate of 1 rad/s, and a scale factor of 0.016 mW/(rad/s) is obtained at 4 GHz.

Large dispersion-managed broadband high-energy fiber femtosecond laser system with sub 300 fs pulses and high beam quality output

We experimentally demonstrate a high-energy sub 300 fs polarization maintaining fiber chirped pulse amplification (CPA) system. The preamplifier is a monolithic fiberized system that uses two cascaded temperature-assisted dispersion-tuning broadband chirped fiber Bragg gratings (CFBGs) with a reflected bandwidth of 20 nm as stretchers. To make full use of the stretcher to lower the system’s nonlinearity accumulation, a homemade mode locked fiber laser with a spectral width of 14.8 nm (full width at half maximum) is selected as the seeder to offer a stretched pulse width of 1.69 ns. The main amplifier is based on a one-stage simple Yb:YAG single crystal fiber amplifier with an amplified output power of 40.6 W at a repetition rate of 200 kHz, and the beam quality is conserved in a single mode beam profile with beam quality of 1.246 and 1.142 in the horizontal direction and vertical direction, respectively. During amplification, the spectral gain narrowing effect is observed. To achieve the high-speed switch of the laser, an acoustical optical modulator (AOM) is inserted before the compressor to achieve high-speed turn-on/off control. The compressor is based on a diffraction grating pair with a groove density of 1600 line/mm to offer a dispersion match with the stretcher of the CFBGs. With the CFBG’s fine-tuned capacity of second-order dispersion and higher-order dispersion, the compressed average power of 29.6 W and pulse duration of 278 fs, corresponding to a pulse energy of 148 µJ and a peak power of 532 MW with ignoring the wings of the pulse, is obtained. The beam quality is well conserved after compression, and the beam quality is 1.250 and 1.196 in the horizontal direction and vertical direction, respectively. A power fluctuation of 0.1% (root mean square) and a beam pointing drift of 8.47 µrad/°C over 8 h are realized. This high peak power and high beam quality femtosecond laser is promising in science and industrial applications.

Arbitrary distance measurement without dead zone by chirped pulse spectrally interferometry using a femtosecond optical frequency comb.

We demonstrate an arbitrary distance measurement method by chirped pulse spectrally interferometry (CPSI) using femtosecond optical frequency comb (OFC). In this paper, the chirped fiber Bragg grating (CFBG) is used to investigate the mapping relationship between displacement and the center frequency of the chirped spectral interferogram. We overcome the direction ambiguity of dispersive interferometry (DPI) ranging and expand the range of distance measurement to 18 cm. Besides, we achieve a full range of dead-zone free ranging by introducing a variable optical delay line (VODL). And through principles simulation and experiment, it is demonstrated that the measurement accuracy is 12 µm in comparison with an incremental He-Ne laser interferometer and the minimum Allen deviation is 52 nm at an average time of 1.76 ms. Similarly, in the experiment with long-distance of ∼30m, the accuracy reaches 20 µm, and 2.51 µm repeatability is achieved under harsh environment.

FBG Sensor with enhanced resolution based on temporal spectroscopy and nonlinear effect

A unique technique to achieve high resolution interrogation of Fiber Bragg Grating(FBG) sensor based on dispersive time delay and Four wave mixing(FWM) effect is proposed. The wavelength shift induced by small strain or temperature on uniform FBG significantly enhances the time shift of the pulse reflected from linearly chirped fiber Bragg grating(LCFBG) by utilizing two stage FWM process in combination with wavelength–to-time mapping effect of LCFBG. The proposed scheme presents high robustness to power fluctuations in the system. A high strain sensitivity of 6.59 ps/με and temperature sensitivity of 72.5 ps/oC with corresponding strain and temperature resolution of 0.15 με and 0.01oC respectively is attained using the proposed scheme. The significance of the proposed scheme lies in enhancement of the time shift of the pulse without the usage of high dispersive device and simultaneous realization of temperature compensation and high strain sensitivity.

Dual resonance akinetic dispersive cavity swept source at 900 kHz using a cFBG and an intensity modulator

In this paper, a fast dual resonance akinetic optical swept source operating at 1550 nm is demonstrated. Instead of modulating the optical amplifier gain reported in our previous studies, here we employ a fiber intensity modulator as a mode-locking element. A chirped fiber Bragg grating is used to provide sufficient dispersion in the laser cavity. A tuning range of 25 nm is obtained for a sweep frequency of ≈900 kHz with a 6-dB drop-off in sensitivity at 2.6-mm optical path difference.

Tunable Chaotic External-Cavity Semiconductor Laser With Time-Delay Signature Suppression Including a Broadband Chirped FBG

A wavelength tunable chaotic external cavity semiconductor laser (ECSL) composed by a distributed-feedback laser diode (DFB-LD) and a broadband chirped fiber Bragg grating (CFBG), is proposed and experimentally demonstrated for generating tunable chaos signals with time delay signature (TDS) suppression. The experimental results show that by using a CFBG with a 3-dB reflection bandwidth of approximately 30 nm and a low dispersion of approximately 1.25 ps/nm, the chaotic ECSL can be tuned over a wide wavelength range, and the generated chaos possesses a low TDS of about 0.04. With the increase of the bias current of the DFB-LD, the chaotic ECSL is tuned towards long-wavelength direction, the effective bandwidth of the chaotic signal is extended, and the TDS of the chaotic signal remains effectively suppressed. To highlight the advantages of the proposed scheme, relevant experiments for the DFB-LD under fiber mirror feedback and fiber Bragg grating feedback are also performed and compared.

Fiber-optic amplitude bend direction and magnitude sensor

A variant of the implementation of a fiber-optic sensor for the direction and magnitude of the bend is proposed. Unlike existing spectral measuring systems, the solution under consideration involves the use of an amplitude polling technique which makes it possible to increase the speed of the sensor when using simpler and more affordable components. A sensitive element based on special diffraction structures consisting of pairs of chirped fiber Bragg gratings has been studied. The sensing elements are mounted on a tooling — a steel rod subjected to bending. The ability of the sensor to determine the magnitude and direction of bending in the deviation range from 0 to 30 mm was demonstrated with a standard deviation of the measured values from the real values of 0.536 mm. This measurement result is achieved by processing data obtained from three measuring devices and by the neural network with a hidden layer of 10 neurons and the sigmoid as the activation function. The research results are essential for modern monitoring systems. The implementation of the direction and magnitude of the bend sensor in the format of a fiber-optic device allows you to overcome the limitations of piezoelectric sensors, due to high noise immunity and resistance to environmental influences. The proposed technological solution makes it possible to avoid the spectral measurement technique that has become widely used in fiber-optic sensor systems. The use of an amplitude sensor for the magnitude and direction of bending will allow its use in devices where there is a need for precise positioning of control elements or structural components subjected to bending. Also, due to the measurement of the desired bending effect by estimating the optical power of the signal, the design of the sensor does not require the presence of a complex measuring device, and the sensor’s performance can be ensured using a cascade of inexpensive, but at the same time high-speed and durable photodetectors.

A 1060 nm stretched-pulse mode-locked wavelength-swept laser source providing an A-scan rate of 20 MHz

The laser source is the deciding factor in improving the rapid imaging of swept-source optical coherence tomography (OCT) systems. We introduce an intrinsically stable stretched-pulse mode-locking (SPML) laser operating a tuning range of over 92 nm at a center wavelength of 1060 nm. The laser provides variable A-line rates up to ~20 MHz as a function of the duty cycle. The cavity comprises a unidirectional ring cavity with matched positive and negative continuously chirped fiber Bragg gratings generating ± 556 ps/nm dispersion. We demonstrate the ability of the stretched-pulse mode-locking laser to provide rapid optical signals for optical coherence tomography. Finally, we highlight performance by displaying the 3D datasets acquired at > 19,487 × 103 A-lines/s as cross-sectional images, averaging the complex A-scan signals of the voxel, and examining the inter-frame phase variance without the need for trigger signals and a phase calibration method. By integrating three-dimensional coherence-based optical imaging into a video-rate, camera-like deployment using a high-speed digitizer, this laser may potentially leverage the use of optical coherence tomography of complex tissue dynamics in pre-clinical studies

Stable noise-like pulse generation from a NALM-based all-PM Tm-doped fiber laser.

An all-polarization maintaining (PM) noise-like pulse (NLP) generation from a Tm-doped fiber oscillator based on nonlinear amplifying loop mirror (NALM) that incorporated with a phase shifter and a chirped fiber Bragg grating (CFBG) is experimentally demonstrated. The 3 dB bandwidth of the output spectrum is 25 nm at the central wavelength of 1950 nm, and the maximum output average power is 13.6 mW with the repetition rate of 3.25 MHz. The noise performances of the NLP are for the first time systematically examined, and it shows an improving tendency with the increasing of the output power. At an integration frequency range from 1 kHz to 1 MHz, the minimum estimated timing jitter and the rms RIN is 139 ps and 0.58%, respectively. In addition, the long-term stable operation of the laser is verified through monitoring the output spectrum and average power.

Optical frequency comb with tunable free spectral range based on two Mach-Zehnder modulators cascaded with linearly chirped fiber Bragg grating and phase modulator

Optical frequency comb with tunable free spectral range based on two Mach-Zehnder modulators cascaded with linearly chirped fiber Bragg grating and phase modulator

Inscription study of superimposed chirped fiber Bragg gratings

Inscription study of superimposed chirped fiber Bragg gratings

A reduced power budget and enhanced performance in a wdm system: a new fbg apodization function

The apodization profiles improve chirped fiber Bragg grating (CFBG) capability to compensate dispersion which enhances the performance of the wavelength division multiplexing (WDM) systems. In this paper, a new apodization profile is proposed to enhance performance and reduces the power budget for a WDM system. The newly apodization profile is implemented to a CFBG as a post compensator in a WDM system for 100 km. It is found the proposed profile enhances the performance and reduces the transmitted power at BER of 10−9. The evaluation of the proposed profile is compared with a previously published work. It is found the proposed profile enhances the Q-factor by 1.08%, decreases BER by 52.8%, and reduces the power budget by 4% than the related work.

A cascaded FBG scheme based OQPSK/DPSK modulation for chromatic dispersion compensation

The aim of this study is to present a proposed chromatic dispersion compensation model for single mode optical fiber. The proposed model consists of 4-stages of cascaded identical linear chirped fiber Bragg grating (CFBG) in post-compensation connection scheme. It is based on differential phase shift keying modulation format. To evaluate the performance of the proposed model, a comparative study is conducted using offset quadrature phase shift keying modulation technique. This comparative study includes four cases with and without using CFBG. For system performance evaluation, a 10 Gbps wavelength division multiplexing link is simulated at a distance of 70 km under conventional operating parameters. Optisystem 7.0 has been used for simulation and evaluation process. Quality factor (Q-factor) and bit error rate (BER) are used as evaluation metrics. The proposed model shows the best performance in case of using CFBG compared to the other cases. A maximum Q-factor of 7.22, and a corresponding minimum BER of 2.59 × 10−13are obtained. The proposed system performance is enhanced by at least 53% as compared to related work.

Performance comparison of TOPAS chirped fiber Bragg grating sensor with Tanh and Gaussian apodization

&lt;p&gt;In this work we &lt;span&gt;carried out a numerical simulation with software Optigrating for Apodization chirped fiber Bragg grating (CFBG) with TOPAS material to improve sensitivity sensor, it was found that CFBG with a grating length of 50 mm has advantages in terms of ripple factor, side lobe left (SLL), and side lobe right (SLR) with values of -0,998 and -10,5264 dB, respectively. While the 10 mm CFBG has a narrower full-width half maximum (FWHM) with a value of 0.4528 nm. Tanh and Gaussian apodization were arranged in the CFBG design, it was found that the Tanh linear-CFBG had a narrow FWHM but for the ripple factor and the main lobe and side lobes were not good enough compared to the Tanh Cubicroot-CFBG, and the same pattern was also obtained in the Gaussian apodization. The narrow FWHM indicates the accuracy in detecting temperature, as well as the suppression of SLL and SLR. for the effect of apodization on CFBG it was found that The Tanh Linear-CFBG design with TOPAS material has the highest sensitivity which is -51.76 pm/oC compared to other designs.&lt;/span&gt;&lt;/p&gt;