Linearly Chirped Fiber Bragg Grating Research Articles

Modified CFBG-based approach for chromatic dispersion compensation in high speed DWDM links.

Chromatic dispersion (CD) is a major concern in high speed fiber optics communication systems. This work presents an efficient optical compensation technique with reduced complexity to mitigate CD effects in single mode fiber (SMF) at high data rates. The proposed method includes a post-dispersion mitigation system using a single linear chirped fiber Bragg grating (CFBG) with tanh apodization. Here, various parameters of CFBG, such as grating length, effective refractive index, and apodization function, are optimized to achieve effective CD compensation. Then, the system is extended to a 16-channel WDM link with each channel carrying data at 25Gbps over 100km. The simulation results show that the proposed model enhances the system performance while minimizing overall system complexity. The proposed system is also compatible with the prevailing fiber optics networks. The results are consistent with the findings published in recent studies.

Distributed strain interrogation with a linearly chirped fiber Bragg grating based on an optoelectronic oscillator.

A novel distributed strain sensor method, to the best of our knowledge, based on a linearly chirped fiber Bragg grating (LCFBG), which can simultaneously determine the strain value and ascertain the position, is proposed and experimentally demonstrated. Different from the traditional distributed grating interrogation system via analyzing the optical spectrum of an LCFBG, the system is mainly based on the frequency domain measurement by using an optoelectronic oscillator (OEO) structure, which has the characteristics of fast response and high resolution. Based on this structure, when the distributed strain is applied to the LCFBG, the frequency response of the OEO for a reflective point of a certain wavelength will change. The strain value can be obtained by detecting the frequency shift of the OEO. Combined with the one-to-one correspondence between the wavelength and the spatial position of the LCFBG, the exact position of the strain point can be determined. In a proof-of-concept experiment, interrogation of fully distributed grating sensors with nonuniform strain distributions is demonstrated experimentally. A spatial resolution of ∼3µm over a gauge length of 53mm and a strain resolution of <1µε have been achieved.

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.

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.

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.

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.

Sensitivity-improved fiber optic current sensor based on an optoelectronic oscillator utilizing a dispersion induced microwave photonic filter.

An optoelectronic oscillator (OEO)-based fiber optic current sensor (FOCS) with greatly improved sensitivity is proposed and experimentally demonstrated. A microwave photonic filter (MPF) induced by the dispersion effect of a linearly chirped fiber Bragg grating (LCFBG) is used to select the frequency of the OEO oscillating signal. A two-tap MPF formed by a polarization multiplexed composite cavity is cascaded to achieve a stable single mode oscillation. When the current changes, the magneto-optic phase shift induced by Faraday effect will be introduced between the left and right circularly polarized lights transmitted in the reflective sensing unit. The magneto-optic phase shift is converted to the phase difference between the optical carrier and sidebands through a LiNbO3 Mach-Zehnder modulator. This phase difference is the decisive factor for the center frequency of the cascaded MPF as well as the oscillating frequency. Therefore, the current can be measured in the microwave frequency domain, which can improve the interrogation speed and accuracy to a large extent. The experimental results show that the oscillating frequency shifts up to 407.9 MHz as the current increases by 1 A.

Demonstration of super‐Gaussian apodized linearly chirped fiber Bragg grating for efficient beam steering in Ku‐band applications

This paper demonstrates a photonics-based wideband TTD beamforming network employing super-Gaussian apodised chirped fibre Bragg grating (SGFBG) of different length (each having a central wavelength of 1550 nm) such as 5, 4.5, 4, 3.5, 3, 2.5, 2 and 1.5 cm as well as varying chirp rate, which can be used as variable TTD lines for controlling the radiation angle of PAA (the main lobe radiated by the PAA can be steered squint-free between 0 ° and ± 69 ° ) suitable for continuous beamforming at microwave frequencies in Ku-band (12–18 GHz). The experimental demonstration shows the effect of change in laser wavelength on delay incurred within the reflected light from the SGFBG. This delay in the modulated optical signal will be converted into delayed microwave signal feed to a respective element of PAA after passing through the photodetector. Finally, the time-delayed microwave signal feeded to each element of PAA will be responsible for tilt in microwave signal compared to the horizontal direction. The novelty of the proposed SGFBG as compared to linearly chirped fiber Bragg grating (LCFBG) is in terms of reduction in ripples in the delay spectrum which will lead to exact delay introduction in the optical signal.

A Programmable Mode-Locked Fiber Laser Using Phase-Only Pulse Shaping and the Genetic Algorithm

A novel, programmable, mode-locked fiber laser design is presented and numerically demonstrated. The laser programmability is enabled by an intracavity optical phase-only pulse shaper, which utilizes the same linearly chirped fiber Bragg grating (LC-FBG) from its two opposite ends to perform real-time optical Fourier transformation. A binary bit-pattern generator (BPG) operating at 20-Gb/s and producing a periodic sequence of 32 bits every 1.6 ns, is subsequently used to drive an optical phase modulator inside the laser cavity. Simulation results indicate stable programmable intensity profiles for each optimized user defined 32 code words. The laser operated in the self-similar mode-locking regime, enabling wave-breaking free operation. The programmable 32 bit code word targeting a specific intensity profile was determined using 100 generations of the genetic algorithm. The control of ultrashort pulse intensity profiles on the picosecond and femtosecond time scales is difficult. The process of stretching and compressing the pulse in the time domain allows for a slower BPG to impose a predefined phase modulation prior to pulse compression. This results in control over the fine features of the intensity profile of the compressed pulse on a picosecond or femtosecond time scale inside the laser cavity. The stability of the proposed scheme depends on the consistency and accuracy of the BPG rise and fall times in practice.

Demonstration of super-Gaussian apodized linearly chirped fibre Bragg grating for efficient beamsteering in Ku-band applications

This paper demonstrates a photonics-based wideband TTD beamforming network employing super-Gaussian apodised chirped fibre Bragg grating (SGFBG) of different length (each having a central wavelength of 1550 nm) such as 5, 4.5, 4, 3.5, 3, 2.5, 2 and 1.5 cm as well as varying chirp rate, which can be used as variable TTD lines for controlling the radiation angle of PAA (the main lobe radiated by the PAA can be steered squint-free between 0 ° and ± 69 ° ) suitable for continuous beamforming at microwave frequencies in Ku-band (12–18 GHz). The experimental demonstration shows the effect of change in laser wavelength on delay incurred within the reflected light from the SGFBG. This delay in the modulated optical signal will be converted into delayed microwave signal feed to a respective element of PAA after passing through the photodetector. Finally, the time-delayed microwave signal feeded to each element of PAA will be responsible for tilt in microwave signal compared to the horizontal direction. The novelty of the proposed SGFBG as compared to linearly chirped fiber Bragg grating (LCFBG) is in terms of reduction in ripples in the delay spectrum which will lead to exact delay introduction in the optical signal.

High-Resolution Fiber Optic Sensor based on Coated Linearly Chirped Bragg Grating

a fiber optic strain sensor is proposed and experimentally demonstrated using fiber Bragg grating (FBG) based interrogation scheme. Due to fast response time and better sensitivity of graphene oxide (GO) material, coated linearly chirped fiber Bragg grating (LCFBG) is used in this work. Interrogation scheme is used for the efficient strain sensing by placing LCFBG within the Sagnac loop (wavelength dependent receiver). The GO deposition is confirmed by ultraviolet–visible spectroscopy, atomic force microscopy (AFM), and field emission scanning electron micrograph (FESEM). Our proposed fiber optic strain sensor possesses better resolution, stable operation in the infra-red region. In addition, sensor demonstrates 5.25 με static strain and 0.645 με/√Hz dynamic strain resolutions, respectively.

Research on heterogeneous fiber grating spectrum separation based on transfer matrix and adaptive algorithm

To save the cost of the fiber grating sensing technology demodulation equipment and broaden the range of its detection application, one heterogeneous fiber grating spectrum separation (HFGPS) method based on transfer matrix and the adaptive algorithm is proposed. First, a theoretical mode of the HFGPS method is introduced. Second, simulation experiment on linearly chirped fiber Bragg grating (LCFBG) and fiber Bragg grating (FBG) is carried out to obtain the separation effect. After simulation experiment data analyses, relative errors between the separated spectrum signal and the heterogeneous original signal are no >5.29 % , which occurs at spectrum fringe region of FBG and LCFBG, and the separation algorithm can achieve single wavelength or multiwavelength mixing heterogeneous spectrum efficient separation with high precision. Lastly, the temperature calibration experiment is carried out on FBG temperature sensor and LCFBG to further verify the effect of the HFGPS method. After the temperature experiment data analyses, the result shows that sensitivity relative error of FBG between original and heterogeneous separated is 0.4%, and the HFGPS method can achieve heterogeneous spectrum efficient separation and has small influence on the detection performance of the FBG sensor. All these experiment data confirm that the HFGPS method can achieve effective heterogeneous spectrum separation with high precision and has certain practical application value.

Tunable optoelectronic oscillator based on a polarization-dependent phase modulator cascaded with a linear chirped FBG

A tunable optoelectronic oscillator (OEO) based on polarization controlled frequency response shifting of a dispersion-induced microwave photonic filter (MPF) is proposed and experimentally demonstrated. The MPF consists of a phase modulator (PM), a linear chirped fiber Bragg grating (LCFBG), and polarization multiplexed dual loops. Thanks to the polarization properties of the LiNbO3 crystal, the center frequency of the MPF can be tuned by simply adjusting the polarization state of the optical signal, and a tunable optoelectronic oscillator is established. Compared to the previous structure, the expensive wavelength-tunable laser is not needed in the proposed structure. In addition, the instability of oscillation frequency caused by the bias drifts of the modulator is avoided. A pure oscillation signal with a tunable frequency range from 3.3 to 7.3 GHz is generated. The single-sideband phase noise of the oscillation signal is about −110 dBc/Hz at 10-kHz offset. During more than 30 min observation, the oscillation frequency drift is about 7 kHz.

Design and comparative performance evaluation of chirped FBG dispersion compensation with DCF technique for DWDM optical transmission systems

In this paper, we proposed an eight channels dense-wavelength-division-multiplexing (DWDM) optical transmission system using two different dispersion compensation techniques. Dispersion compensation mechanism limits the pulse broadening effects of transmitted signal in optical communication systems. To overcome pulse broadening effects, linear Chirped Fiber Bragg Grating (CFBG) and dispersion compensation fiber (DCF) schemes are modeled, analyzed and compared for investigate the performance of DWDM system. The proposed system is designed for 10Gbps using return-to-zero (RZ) modulation format with an erbium doped fiber amplifier (EDFA) over a channel length of 150 km single mode fiber (SMF) and 45 mm CFBG/30 km dispersion compensation fiber using Opti-System7.0 simulator. Performance of designed system is explore and compared in terms of eye-diagram, gain (dB), noise figure (dB), output power (dBm), output optical SNR (dB), bit error rate (BER) and Q-Factor by varying three different parameters which are channel length (km), input power (dBm) and attenuation coefficient (dB/km). It is observed that the CFBG gives the best performance as dispersion compensator for proposed DWDM long-haul transmission system.

A Chirp-Rate-Tunable Microwave Photonic Pulse Compression System for Multi-Octave Linearly Chirped Microwave Waveform

A chirp-rate-tunable microwave photonic pulse compression system for multi-octave linearly chirped microwave waveform (LCMW) is proposed in this paper. The key components are a dual-parallel Mach-Zehnder modulator (DPMZM) and a dispersive loop (DL) structure based on a linear chirped fiber Bragg grating. By controlling the output of the DL to change the accumulated group velocity dispersion, the chirp rate of the system can be tuned. By adjusting the wavelength of the optical carrier to select the single sideband modulated optical signal (positive or negative sideband), the chirp direction (down or up chirped) can also be tuned. The performance of the multi-octave LCMW pulse compression can be improved by eliminating the second-order harmonic distortion through configuring the bias voltages of the DPMZM. Detailed theoretical analysis is conducted. A verification simulation demonstrates the pulse compression of the multi-octave LCMWs with the chirp rates of 23.877, 11.939, 3.979, and -3.979 GHz/ns. In the proof-of-concept experiment, the matched chirp rates 23.229, 12.051, -22.568, and -11.355 GHz/ns are obtained. The multi-octave LCMW pulse compressions with the compression ratios of 14.3, 29.3, 15.0, and 28.6 are verified. The simulation and experiment results are in good agreement with the theoretical analysis.

Suppression of four-wave mixing in a 22 × 10 Gbps dense wavelength division multiplexed system by linearly chirped fiber Bragg gratings

A scheme comprising two linearly chirped fiber Bragg gratings (LCFBGs) is proposed to suppress four-wave mixing (FWM) effects in a 22×10 Gbps dense wavelength division multiplexed (DWDM) system employing dispersion shifted fiber with 0.2 nm channel spacing. The FWM reduction in our proposed scheme has been studied by varying the input signal power per channel from − 2 to + 10 dBm. The parameters of LCFBGs are optimized to obtain a maximum quality factor for all 22 channels. The proposed method is effective even at high input power (10 dBm) and provides a simple, cost effective way to improve the transmission performance in DWDM system.

High-Speed and High-Resolution Interrogation of a Strain and Temperature Random Grating Sensor

High-speed and high-resolution interrogation of a random fiber grating sensor based on spectral shaping and wavelength-to-time (SS-WTT) mapping, and pulse compression for simultaneous measurement of strain and temperature is proposed and demonstrated. In the proposed system, an ultrashort pulse is spectrum shaped by a high-birefringence (Hi-Bi) random grating (HBRG) to generate two orthogonally polarized spectra with a wavelength difference determined by the birefringence of the HBRG, which are then fed to a dispersive optical loop in which a linearly chirped fiber Bragg grating (LCFBG) is incorporated, to perform linear WTT mapping, to generate two temporally separated optical pulses, which are converted to two random electrical waveforms at a photodetector). Random pulse compression is then performed to increase the interrogation resolution. By measuring the time shifts of the temporally compressed pulses, the strain and temperature information is retrieved. An experiment is performed. The experimental results show that the proposed random grating sensor and its interrogation system can provide a strain and temperature resolution of 7.1 μϵ and 0.79 °C at an ultrahigh speed of 20 MHz.

Simultaneous interrogation of multiple fiber Bragg grating temperature sensors using a microwave photonic approach

In this paper, we demonstrate a microwave photonic (MWP) approach for interrogating multiple linearly chirped fiber Bragg grating (LCFBG) temperature sensors. The MWP interrogation system is based on an arrayed waveguide grating Sagnac interferometer, incorporating multiple LCFBG sensors, that is used to generate multiple chirped microwave waveforms whose characteristics are uniquely related to those of the LCFBGs. Compressing the generated microwave signals allows monitoring simultaneously and independently the shifts associated with applying temperature changes to each LCFBG in real time.

Fiber dispersion compensation in single side band optical communication system using ideal fiber Bragg grating and chirped fiber Bragg grating without DCF

In this paper, a 10 Gbps, single side band optical communication system is implemented with different dispersion compensation schemes. This paper proposes that dispersion compensation is fruitful with a linear chirped fiber Bragg grating, without a dispersion compensation fiber at higher input powers. Its performance is compared with fiber Bragg grating and DCF. Same global parameters are used for all simulations. The simulated transmission system has been analyzed by different performance parameters like Q factor, output RF power and eye diagram extinction ratio. The Q factor, output RF power and extinction ratio can be improved about by 21 dB, 3.5 dB, and 20 dB respectively. The simulations are conducted for higher input power from 0 dBm to 8 dBm and for fiber length from 20 km to 80 km. The BER in CFBG is 15 dB lesser than FBG. The CFBG shows better performance than conventional FBG. The signal delay is also the lowest in the method using CFBG. The Q factor and signal delay are also compared with CFBG, FBG, DCF and uncompensated system.

Tunable optoelectronic oscillator using a polarization division multiplexing emulator and a polarization modulator

This paper proposes a frequency-tunable optoelectronic oscillator (OEO) based on a single bandpass microwave photonic filter (MPF), which is implemented by a polarization division multiplexing emulator (PDME) with a tunable time delay difference between the two polarization states, a polarization modulator (PolM), a broadband optical source (BOS), and a linearly chirped fiber Bragg grating (LCFBG). The center frequency of the MPF can be shifted by adjusting the time delay difference between the two polarization states of the PDME. By incorporating the MPF into an OEO, the oscillation frequency of OEO is tuned. The proposed OEO is experimentally demonstrated. Frequency-tunable oscillation signals from 2.45 to 12.72 GHz are generated with their performance being investigated.