FBG Filter Research Articles

Long-period fiber grating sensor interrogation with single strain modulated FBG and harmonic analysis

Optical fiber sensors have been used in several applications due to their unique advantages, such as immunity to electromagnetic interference, small size, light-weight, and robustness, for example. Long-period fiber grating (LPFG) is a type of fiber sensor with great sensitivity to several parameters, including the surrounding refractive index. However, the challenge in using LPFGs lies in their interrogation, which relates the change in optical characteristics with the measurand. This paper presents a novel method for the interrogation of LPFG sensors. This method uses a single FBG attached to a vibrating piezoelectric component and harmonic analysis of the optical power reflected by the FBG filter to estimate the resonant wavelength of an LPFG. The method was simulated to process several arc-induced LPFG spectra and achieved results comparable to the baseline method for half of the test set and improved by roughly 5 times the accuracy and precision by limiting the dynamic range.

Random DFB-FL using apodized FBG and DFB-FL optical filters: a numerical performance evaluation

Random DFB-FL using apodized FBG and DFB-FL optical filters: a numerical performance evaluation

High-Precision Temperature-Compensated Magnetic Field Sensor Based on Optoelectronic Oscillator

We have proposed and experimentally demonstrated a high-precision and temperature-compensated magnetic field sensor based on two optoelectronic oscillators (OEOs) incorporating cascaded magnetostrictive alloy-fiber Bragg grating (MA-FBG) and FBG filters. The optical sources are provided by the reflection signals of two FBGs. The optical source wavelength is related to the overall time delay of the OEO loop which determines the oscillating frequency of OEO. The central wavelengths of MA-FBG and FBG change along with the magnetic field and temperature. Therefore, we can estimate the magnetic field and temperature by measuring the oscillating frequencies of OEOs, simultaneously. Besides, since two OEOs are grouped into a cross-referencing structure by wavelength division multiplexing under the same environment, the magnetic field sensor can reduce the influence of temperature. The proposed sensor for magnetic field and temperature with sensitivities of 250 Hz/Oe and 1.97 or 1.42 kHz/°C are achieved. The maximum measurement errors of magnetic field and temperature obtained are within 22 Oe and 0.2°C. The proposed scheme has merits of simplicity and compact configuration. It can realize high-speed and high-resolution measurement, which has potential applications in magnetic field sensing.

Hybrid transmission of unicast and broadcast signals without optical filter for WDM systems

Abstract This paper proposes and experimentally demonstrates the hybrid transmission of unicast and broadcast signals without using optical filters for the WDM systems. The dual-wavelength generated from a laser source are modulated by a phase modulator (PM) with a broadcast signal. Then, the central carriers and side-bands are separated by using a polarization beam splitter (PBS) and modulated with unicast data using Mach-Zender modulator (MZM). After combining side-bands (broadcast data) and central carriers (unicast data) using PBS, the hybrid data are transmitted through 25 km single mode fiber (SMF) to the remote node (RN). By probably adjusting the polarization controller (PC), the central carriers and side-bands are separated by PBS into two orthogonal polarization states. After transmission over 25 km SMF, the measured bit error rate (BER) curves and eye diagrams show that the performance of the proposed system is excellent to simultaneously transmit both unicast and broadcast signals. Moreover, only two modulators are required, which is cost-effective and also FBG or optical filter is not required due to sensitivity to temperature that decreases the system stability.

An 80 Gbps multi-band access radio over fiber link with single side band optical millimeter-wave dispersion-tolerant transmission without FBG and optical filter

We are presenting a new low-cost Single Sideband (SSB) modulated Radio-over Fiber (RoF) communication system for millimeter (mm)-wave multiband wireless communication at the frequencies of 40 GHz, 80 GHz and 120 GHz. Its principle lies in the Carrier Suppressed modulation through a nested dual electrode Mach–Zehnder Modulator (MZM) and product modulator based baseband signal decomposition. In this novel method, the optical signal is decomposed into different SSB signals using a power splitter and product modulators at the base station. This proposed method uses a different technique for a baseband signal decomposition from the existing method. The proposed signal decomposition technique has reduced the nonlinearities due to the FBGs. The proposed method is compared with the existing method in terms of BER, data rate and OSNR. The simulation results disclose that our proposed scheme outperforms the existing methods at a higher data rate of 80 Gbps with a minimum BER and privileged Q factor.

Optical sensing and monitoring architecture for pipelines using optical heterodyning and FBG filter

A novel model for pipeline optical sensor and monitoring unit is been proposed through this paper, which consist of fiber Bragg grating array functioning as sensor unit and base station consist of monitoring and transmission unit. Monitoring unit smartly converts optical signal to electrical signal through optical heterodyning and detects the variation of reflected central frequency of each FBG through data processing. Frequency spacing between reflected optical signals are elegantly adjusted so that number of peaks in electrical domain spectrum are equal to number of FBGs. This architecture is verified theoretically, successfully simulated and analyzed.

Broadband and tunable RF photonic phase shifter based on optical SSB modulation and FBG filtering

A broadband RF photonic phase shifter that can achieve the tunable phase shift with little RF power variation is presented. It is based on homodyne mixing technique. The beating between phase-modulated optical carrier and the first-order sideband can generate RF signal with desired phase shift. Results show the RF phase shifter can achieve a continuous 0–360° phase shift with low power variation at the frequency above 21.5GHz.

Optimal design of multichannel fiber Bragg grating filters using Pareto multi-objective optimization algorithm

A Pareto-based multi-objective optimization approach is proposed to design multichannel FBG filters. Instead of defining a single optimal objective, the proposed method establishes the multi-objective model by taking two design objectives into account, which are minimizing the maximum index modulation and minimizing the mean dispersion error. To address this optimization problem, we develop a two-stage evolutionary computation approach integrating an elitist non-dominated sorting genetic algorithm (NSGA-II) and technique for order preference by similarity to ideal solution (TOPSIS). NSGA-II is utilized to search for the candidate solutions in terms of both objectives. The obtained results are provided as Pareto front. Subsequently, the best compromise solution is determined by the TOPSIS method from the Pareto front according to the decision maker's preference. The design results show that the proposed approach yields a remarkable reduction of the maximum index modulation and the performance of dispersion spectra of the designed filter can be optimized simultaneously.

40 Gbps 100-km SSMF VSB-IMDD OFDM transmission experiment based on FBG filter

This work studies the transmission performance of vestigial-sideband (VSB)–IMDD OFDM system by theoretical analysis and numerical simulation. The analysis shows that the detrimental effect of dispersion-induced power fading can be effectively suppressed. The presence of positive and negative chirp of modulator will increase the dispersion-, chirp- and VSB optical filter-induced subcarrier to subcarrier intermixing interference (SSII), which significantly restricts transmission performance. Relatively lower order Gaussian optical filter has almost the same performance with ideal rectangular filter over 100-km SMF transmission and have better performance in less than 60-km transmission. Furthermore, we successfully transmit a 40Gbps, 16QAM, MZM-based VSB-IMDD OFDM signal through 100-km of uncompensated standard single mode fiber (SSMF) by using an economical FBG optical filter. The experimental results show that available bandwidth has been extended up to 10GHz after 100-km SSMF transmission.

Cross-Entropy Optimization for the Design of Triangular FBG Filter With Asymmetrical Spectrum

This letter reports the use of optimization methods to design triangular fiber Bragg grating (TFBG) filter with asymmetrical spectrum. In the optimization methods, TFBG synthesis problems are formulated as nonlinear objective functions, and stochastic optimization techniques are applied to search for index modulation profiles that minimize the difference between the synthesized and targeted spectra. However, the performances of traditional stochastic optimization techniques are affected by the initial guess. A poor initial guess may result in low-efficiency optimizations and easily get trapped into local solutions; in some cases, it may even lead to a false result. Accordingly, we introduce the use of cross-entropy optimization (CEO) in searching for the optimal index modulation profiles. CEO is an effective algorithm that solves various continuous multiextremal optimization problems and demonstrates robustness with respect to starting conditions. Computer simulation results show that the index modulation profiles obtained using the proposed method performed better compared with those obtained using the conventional covariance matrix adaptation evolution strategy (CMAES). In addition, CEO also provides a reliable convergence to the near-optimum solution. These findings indicate the CEO is more suitable than CMAES for the design of TFBG filters with asymmetrical spectrum for sensor applications.

Optical FBG filter with minimum group delay for WDM systems

The causality principle is taken into account to couple amplitude and phase of the reflection coefficient in a symmetric grating for the optimization purpose. The distortion functional for group delay minimization is proposed. The minimization of mean square group delay within the Bragg reflection band is carried out at fixed integral reflectivity. The optimal reflection coefficient with minimum phase distortion is found analytically. The described approach is shown to give the close to rectangular FBG filter with low group delay variation over the reflection band.

Dual-wavelength Brillouin ring-cavity fiber laser with tunable channel spacing

We experimentally demonstrate a dual-wavelength Brillouin fiber laser configured a pre-amplified Brillouin pump and FBG filter in a ring-cavity. The Brillouin laser can generate 21 Brillouin Stokes with 0.084 nm spacing, the first-Stoke has a peak power of 2.19 dBm. By adjusting the TLS wavelength and FBG’s reflection wavelength from circulating in the ring-cavity, the generated output dual-wavelength is stabile and the channel spacing is tunable, the widest and narrowest channel spacing obtained is approximately 1.12 nm (139 GHz) and 0.084 nm (10.5 GHz).

Realization of Optimal FBG Band–Pass Filters for High Speed HDWDM

The influence on FBG filters with different apodization profiles on WDM systems is evaluated numerically with OptSim 5.0 and FBGS 2.6 simulation programs at data transmission rate of 2.5 Gbit/s and 10.52 Gbit/s using 40 km of optical fiber. The realization of low insertion loss optical filter is one of key elements to ensure high speed dense WDM system and FBG filter with different apodization profiles influence on high speed dense WDM is enormous. Ill. 8, bibl. 5 (in English; summaries in English, Russian and Lithuanian).

FBG filter with minimal dispersion

An optimal filter for super-fast fiber-optic communication lines should cause minimal phase distortions. The simplest case of Bragg grating with a symmetric profile is considered. A distortion functional is presented, which is the mean square group delay over the Bragg reflection band at a fixed integral reflectivity. The functional is minimized analytically in the simplest limiting case. Numerical calculations confirm that the optimal reflection spectrum is realizable.

Broadband high-channel-count phase-only sampled fiber Bragg gratings based on spectral Talbot effect

A novel method of generating broadband high-count-channel optical filters in phase-only sampled fiber Bragg grating based on spectral Talbot effect is presented. Integer and/or fractional Talbot effects are examined using both Dammann and multi-level discrete phase-only sampling function. It is found that very high-count channels in a wide spectral band that covers the whole C band can be obtained with very limited number of discrete phase transitions in each sampling period. It provides a novel method for making high-channel-count FBG filters that is otherwise difficult or impossible using conventional discrete phase-only sampled FBGs.

1306 埋め込み新型光ファイバセンサを用いた振動・ひずみ同時測定(J14-2 知的材料・構造システム(2) 計測・モニタリングI,ジョイントセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

We have developed fiber optic strain and vibration sensors (FOSVS) suited for health monitoring of structures. A fiber optic gap sensor made of multi-mode fibers, broad-band light, two photo detectors and an FBG filter were used to compose the sensor system. The gap sensor was composed of a cantilever fiber and a reflector fiber. The axial strain of the sensor was measured from the reflected interfered signal. The amplitude of the transmitted signal through the reflector fiber was used to measure the transverse vibration of the cantilever fiber. In the present study, the sensors were embedded in epoxy plates and cantilever vibration tests were conducted. From the experimental and theoretical results, it appeared that the embedded FOSVS in specimens could measure dynamic strain and vibration of a vibrating cantilever plate simultaneously. From these results, it can be concluded that the FOSVS sensor has practical capability of simultaneous measurement of internal strain and vibration of materials.

Synthesis of long-period fiber gratings with a Lagrange multiplier optimization method

Based on the Lagrange multiplier optimization (LMO) method, a new synthesis approach for designing complex long-period fiber grating (LPG) filters is developed and demonstrated. The proposed synthesis method is a simple and direct approach. It was used to efficiently search for optimal solutions and constrain various parameters of the designed LPG filters according to practical requirements. The inverse scattering algorithm is a good tool for designing FBG filters; as well as for designing transmission-type fiber grating filters like LPGs. Compared to the results of the discrete layer-peeling (DLP) inverse scattering algorithm for LPGs, the synthesized LPGs, using the LMO approach, are more flexible and workable for the constraint conditions can be easily set in the user-defined cost functional, such as the limitation on the maximum value of the refractive index modulation and the parameters of the initial guess in LMO algorithm. Linear transmission LPG filters and EDFA gain flattening filters are synthesized and analyzed systematically by using the proposed method with different parameters. Moreover, as a variation-based method, we find that the convergence and the synthesized results of the LMO method are strongly dependent on the initial guess parameters.

Experimental demonstration and cascadability analysis of a tunable optical buffer based on a re-circulating loop consisting of optical SSB modulator and FBG filter

We demonstrate a tunable optical buffer with variable time delays for label switching applications using an optical single sideband modulator in a fiber Bragg grating-filter loop. This optical buffer realizes payload storage with optional wavelength conversion function, providing flexibility in packet router design. Small sensitivity penalty is observed in our experiment after the payload circulating in the buffer loop three times. The cascadability of the tunable optical buffer is investigated. We provide analysis of the optical signal to noise ratio degradation due to accumulated amplified spontaneous emission noise, and the penalty caused by loss ripple and group delay ripple of the fiber Bragg grating.

Individual switching of multi-wavelength lasing outputs based on switchable FBG filters

We demonstrate an individually-switchable multi-wavelength fiber ring laser using semiconductor optical amplifier with novel switchable band-pass filters. The switchable band-pass filter is based on a fiber Sagnac loop interferometer incorporating both fiber Bragg gratings and polarization controller. The proposed multi-wavelength fiber ring laser shows a high output performance of independent switching at arbitrary lasing wavelength and high extinction ratio for wavelength-division multiplexing source.

A polarization-maintained, ultranarrow FBG filter with a linewidth of 1.3GHz

A polarization-maintained ultranarrow FBG filter with a linewidth of 1.3GHz has been successfully fabricated by using a 15cm-long phase mask. A maximum reflectance of 65% and a side lobe suppression of 13dB were obtained by employing an apodization technique with slits.