Superstructured Fiber Bragg Grating Research Articles

Customized femtosecond laser-inscribed superstructure fiber Bragg grating: A novel approach to decoupling temperature and strain.

This paper introduces a novel technique to simultaneously measure temperature and strain using a single 5 mm femtosecond laser-inscribed superstructure fiber Bragg grating (SFBG). This SFBG enables improved spectral capabilities, resulting in side-resonances within the optical spectrum. The characteristics of the device depend on three key factors: the length of the SFBG, the inscribed FBG’s periodic perturbations, and the length of the uninscribed sections that compose the entire structure. Initially, mathematical expressions were derived to calculate the separation between the central peak and a resonance on each side, which plays a crucial role in determining the sensor’s response. Then, a series of complete simulations using OptiGrating software, and a theoretical analysis were performed to comprehend the functioning of this superstructure. Subsequently, the fabrication process employed a femtosecond laser following a point-by-point inscription. Finally obtaining a comprehensive study on the principle, design, simulation, and implementation of the proposed SFBG. The sensitivities of the central Bragg wavelength and the distance between central peak and first-order resonance when applying temperature and strain were calibrated. The results yielded sensitivities for the central Bragg peak of 10.58 pm/°C and 1.1598 pm/µɛ, while the peak-to-resonance distance had sensitivities of 0.3495 pm/°C and 0.03052 pm/µɛ. The different response of both magnitudes makes it possible to distinguish the contributions of strain and temperature within short distances, having the possibility to improve measurements in sensing applications. This study finally provides a critical insight into the design process, as it aligns with the theoretical expectations.

All-optical encryption/decryption of DmPSK signals with key steganography for photonic layer security.

In the 5th Generation Fixed networks (F5G) era, full-fiber-connected optical networks support emerging bandwidth-hungry services. However, optical networks are vulnerable to attack by tapping or other methods, which has been paid more and more attention in modern optical infrastructure. Therefore, optical Exclusive OR (XOR) encryption/decryption for advanced modulation formats used for F5G appears as one of the promising technologies to guarantee security. Some current solutions either leave potential security hazards because of the degenerate four-wave mixing and keys without special treatment or are cost-consuming due to employing multiple wavelengths and coherent receivers. In this paper, a novel all-optical encryption/decryption system for Differential m-Phase Shift Keying (DmPSK) signals occupying only a single wavelength with key steganography is proposed and simulated. The proposed system mainly consists of a generalized XOR (GXOR) part and a steganography part. We implement the GXOR part by the cascaded IQ Mach-Zehnder Modulators and the steganography part by the Equvilent-Phase-Shifted Super-Structured Fiber Bragg Grating (EPS-SSFBG). The numerical simulation results demonstrate that the GXOR implementation can achieve reconfigurable encryption/decryption of DQPSK (m = 4) or D8PSK (m = 8) signals merely with a single wavelength and a differential direct-detection receiver. And the EPS-SSFBG can enhance key security in a cost-efficient method as well. The system can work at the recorded bit rate of 260Gbps, which can be applied to enhance the photonic layer security in F5G and beyond.

Efficient photonics beam forming system incorporating super structure fiber Bragg grating for application in Ku band

We propose and demonstrate a photonic true-time delay beamforming system for a 1 × 4 linear phased array antenna, operating in the Ku-band, based on superstructured fiber Bragg gratings (SFBGs) with linearly rising equivalent chirps. The proposed beam-forming network operates at 18 GHz frequency, which is theoretically analyzed and simplified by simulated results. The SFBG has a distinct number of gratings in each beamforming path, which provides a large and progressive phase delay. The advantage of the proposed technique can be found in terms of its wavelength tunable scheme making the system squint-free. The proposed architecture is a true time delay optical beam forming a network, which enables squint-free beam steering of radio frequency (RF) signals. In this study, a technique known as double sideband modulation of multiple wavelengths is utilized to investigate the reflection quality of SFBG at various chirp rates. Taking into account that each segment of FBG consists of 50, 60, 70, and 80 gratings and phase shift section samples of each segment, the overall length of the SFBGs is calculated to be 2 cm, 2.4 cm, 2.8 cm, 3.2 cm, respectively, are used for calculating group delay. An equation in a closed form representing the corresponding dispersion is derived. SFBG group delay response is analyzed theoretically with required simulation to investigate the reflectance characteristics. All simulation work for designing the beam forming system is done on Optisystem version 19 and designing of Super structure fiber Bragg grating Optigrating version 4.2. The optically process wavelengths are detected by high speed dedicated photo-detector (PD) and delay response is investigated through array factor of each antenna. Errors in the fabricated SFBGs' group delay responses are examined also.

Modified superstructure fiber Bragg grating for a filter application

Performance of a modified superstructure fiber Bragg grating is carried out by; simulation using a Matlab and then by optisystem7. Results for these two simulations are compared with an experimental investigation for three special FBGs in addition to a standard one. These four FBGs have one, two, three, and four regions. For each region, Bragg wavelength is increased around 6nm, with constant spacing between every two regions. Laser reflectance (R) and transmittance (T) spectra and their corresponding number of peaks and their bandwidths are observed and analyzed in a constant temperature and strain. Results for this investigation indicate enhancement for the modified FBG to be an effective filter that can be employed for communication as well as sense. Filtering the transmitted signals could be satisfied in a simple and more efficiency than the traditional device.

Wavelength Dependent Odd Frequency Multiplication Based on a Superstructure FBG

In this letter, a photonic technique with wavelength tunable multiplication factor is proposed to generate odd multiple of modulating frequency. It is based on the cascading of two Mach-Zehnder modulators, super structured fiber Bragg grating, and a power combiner involving coherent heterodyne technique. Frequency tripling and quintupling of 10 GHz modulating signal have been demonstrated by tuning the wavelength of laser source and RF power control.The proposed scheme provides a simple method for photonic generation of widely tunable RF frequencies, and it has ability to change the multiplication factor by adjusting the wavelength of the laser source instead of tuning the passband frequency of the optical filter. The even multiplication capability of the proposed system can also be explored by changing the wavelength of the laser source.

Sensors of Encoding and Decoding Based on Superstructure Fiber Bragg Gratings Modulated in Amplitude and Phase for applications in systems OCDMA - 63 chip

ABSTRACTIn this paper, we report a series of incremental optical coding and decoding sensors using their respective fiber Bragg grating superstructure (SS-FBG). We performed a comparative study of the encoding/decoding bipolar and unipolar sequences using these grids. The modulation in the refractive index can be changed by discrete jumps in phase (± π) or variations in the amplitude of the specific grid regions. The aim of this study was to evaluate the performance of SS-FBG in autocorrelation and cross-correlation studies. This approach allows us to measure the quality of unipolar and bipolar coding and understand how the decoded signal can be affected by the presence of multiple users on the network. Each generated code is a Gold sequence for bipolar code 63chips and an M sequence for unipolar code 63chips. We use five different codes to represent the users, and we calculate through the signal/noise power ratio (SRNe) the energy used by a certain signal to interfere with a neighboring signal. Our results emphasize the accuracy and flexibility of Bragg gratings (FBG-SS) and showed that this technology is promising not only to Optical Code Division Multiple Access (OCDMA) but also for an extended variety of other optical processing applications.

Superstructure fiber Bragg gratings for simultaneous temperature and strain measurement

A new and simple fiber optic sensor based on a superstructure fiber Bragg grating (SFBG) for simultaneous temperature and strain measurement is proposed. The SFBG is a superimposed grating for which a long period fiber grating (LPG) and a fiber Bragg grating (FBG) is written in the same section of a Corning SMF-28 fiber. The reflection spectrum of the SFBG possesses two resonant peaks and a trough. By measuring the wavelength shift of the main resonant peak and the reflection power change of the trough, temperature and strain can be determined simultaneously. The accuracy of the sensor in measuring strain and temperature is estimated to be ±13.01 με in a range from 0 με to 1000 με and ±0.75 °C from 20 °C to 100 °C, respectively.

Investigations on highly sensitive fiber Bragg gratings with different grating shapes for far field applications

The Fiber Brag Grating (FBG) optical sensor is investigated with uniform fiber grating (UFBG), superstructure fiber Bragg grating (SFBG) and tilted fiber Bragg grating (TFBG) using Finite Difference Time Domain (FDTD). The effect of variation in Refractive Index (RI) on the far field pattern of the guided light, reflection and the transmission power spectra of the gratings have been observed. TFBG reported the best performance exhibiting maximum peak amplitude of far field is 0.218 a. u., followed by UFBG is 0.0467 a. u. and SFBG is 0.0383 a. u. Further, the coupling efficiency of the gratings has been calculated from the mode overlap integral. The TFBG reported the highest value of 5.622%. SFBG followed it with 0.466% and UFBG with 0.012%. The SFBG reported the maximum value of reflected power i.e. 1.9456dB which is 3 times to that of UFBG (0.6317dB) and 5.67 times to that of TFBG (0.3433dB).

Design of Superstructure Fiber Bragg Grating With Efficient Mode Coupling for Simultaneous Strain and Temperature Measurement With Low Cross-Sensitivity

An efficient fiber-optic sensor based on a superstructure fiber Bragg grating (SFBG) for simultaneous strain and temperature measurement is numerically and experimentally demonstrated. The stain-insensitivity property of a specific LPG resonance band has been used to overcome the effect of cross-sensitivity. The strain sensitivities of the FBG and LPG peaks of the proposed SFBG sensor have been obtained as 0.79 and −0.41 pm/ $\mu \varepsilon $ , and their temperature sensitivities are found as 8.67 and 40.13 pm/°C, respectively. The resolutions for the strain and temperature measurements have been noted as $\pm 12.83~\mu \varepsilon $ and ±1.02 °C based on the wavelength resolution of an optical spectrum analyzer (FBG peak: 0.01 nm; LPG peak: 0.1 nm) and the deviations of measured values from applied ones of measurands. The proposed sensor has shown good agreement between the applied and measured measurands with good linearity and reduced cross-sensitivity.

Using Finite Element and Eigenmode Expansion Methods to Investigate the Periodic and Spectral Characteristic of Superstructure Fiber Bragg Gratings.

In this study, a numerical simulation method was employed to investigate and analyze superstructure fiber Bragg gratings (SFBGs) with five duty cycles (50%, 33.33%, 14.28%, 12.5%, and 10%). This study focuses on demonstrating the relevance between design period and spectral characteristics of SFBGs (in the form of graphics) for SFBGs of all duty cycles. Compared with complicated and hard-to-learn conventional coupled-mode theory, the result of the present study may assist beginner and expert designers in understanding the basic application aspects, optical characteristics, and design techniques of SFBGs, thereby indirectly lowering the physical concepts and mathematical skills required for entering the design field. To effectively improve the accuracy of overall computational performance and numerical calculations and to shorten the gap between simulation results and actual production, this study integrated a perfectly matched layer (PML), perfectly reflecting boundary (PRB), object meshing method (OMM), and boundary meshing method (BMM) into the finite element method (FEM) and eigenmode expansion method (EEM). The integrated method enables designers to easily and flexibly design optical fiber communication systems that conform to the specific spectral characteristic by using the simulation data in this paper, which includes bandwidth, number of channels, and band gap size.

Optical Fiber Sensor Based on Second-Order Superstructure Fiber Bragg Grating

Optical Fiber Sensor Based on Second-Order Superstructure Fiber Bragg Grating

Optical Fiber Sensor Based on Second-Order Superstructure Fiber Bragg Grating

Optical Fiber Sensor Based on Second-Order Superstructure Fiber Bragg Grating

Three dispersion compensation methods for radio-over-fiber system

This paper introduces three different dispersion compensation methods based on superstructure fiber Bragg grating (SSFBG) and an injection distributed feedback (DFB) laser. First, an SSFBG with a nonlinearity group delay spectrum was designed to achieve tunable dispersion compensation. Second, an approach is pro- posed for realizing single-sideband modulation with an optimum optical carrier to sideband ratio for maximizing the transmission performance of a radio-over-fiber (RoF) system based on a strong optical injection-locked DFB laser. Finally, a broadband chromatic dispersion compensation scheme using an optical phase conjugator based on a DFB semiconductor laser is proposed and experimentally demonstrated in RoF links. © 2015 Society of Photo-

An efficient method for determining transmission characteristics of superstructure fiber Bragg grating and its use for multiparameter sensing

We propose an efficient approach for determining the transmission characteristics of periodic superstructure fiber Bragg grating (SFBG). In the analysis, the core mode and circularly symmetric cladding modes have been considered for mode coupling. The fiber Bragg grating (FBG) sections and phase shift sections of SFBG have been formulated using coupled-mode equations. The transfer matrices for both the sections have been determined using finite difference method. The modulation of transmission characteristics of SFBG under the perturbation of multiple physical parameters (e.g. strain, temperature etc.) have been investigated numerically. We have simulated the transmission characteristics of SFBG under the simultaneous application of strain & temperature in the range of 0 to 1200μɛ and 30 to 90°C. The results obtained show a good agreement when compared with experimental data.

Performance comparison of proposed 3-d coherent spatial-phase-time coding/decoding with super structured fiber Bragg grating-based optical CDMA systems

In this paper, performance comparison in terms of bit error rate (BER) of proposed WDM compatible optical CDMA system incorporating 3-D spectral-phase-time encoding/decoding to a 7 chip-super-structured fiber Bragg grating (SSFBG)-based optical code division multiple access (OCDMA) system is investigated. Coding and decoding using binary [0, π] phase chips is demonstrated for six users at 5 Gb/s, and a single coded signal is separated with acceptable bit-error rate ≤10−9. In our proposed optical CDMA system encoding and decoding is done by converting hadamard codes (used for conventional CDMA system) to phase codes. It is then compared with two optical pulse retiming and reshaping systems incorporating super structured fiber Bragg gratings (SSFBGs) as pulse shaping elements. Simulation results show that with all input bands having same sample rate, size data rates our proposed codes with even larger number of channels perform better in terms of eye opening & BER.

Error probability upper bound for perfect sequences implemented with super‐structured fibre Bragg gratings

The success of coherent optical code-division multiple-access (OCDMA) systems is strongly dependent on the optical encoder/decoder technology and on the selection of the correct OCDMA codes/sequences. For this reason, in this study, the authors present a method to implement perfect sequences with Super-Structured Fibre Bragg Gratings (SSFBGs). A new SSFBG power reflection model has been found. They have also derived a property that explains why the SSFBGs should use codes derived from m -sequences. Usually, OCDMA researchers try many different codes into SSFBGs in order to select the SSFBG encoders that result in lower error probability. In the authors work, they show that a SSFBG can be considered to be a perfect sequence encoder. For this reason, the codes written into the SSFBGs should be selected based on their new property. This property permits to design and select quickly the correct codes with low power contrast ratios. In addition, a new error probability upper bound, which is a function of the code family and of its power contrast ratio is also presented. With this new bound, it is not necessary to use an optical simulator to estimate the maximum bit error rate of an OCDMA system, if some power contrast ratios of the selected SSFBG code set are known.

40G-OCDMA-PON System With an Asymmetric Structure Using a Single Multi-Port and Sampled SSFBG Encoder/Decoders

In the hybrid optical code division multiple access (OCDMA) architectures using different types of optical encoder/decoder (E/Ds) between an optical line terminal and optical network units, a hybrid 40G-OCDMA-PON with a single multi-port and super-structured fiber Bragg grating (SSFBG) E/Ds is studied as a candidate system beyond next-generation PON stage 2 (NG-PON2). In this paper, we have developed uniformed and sampled SSFBG E/Ds with different refractive index profiles and have compared their code performances in a hybrid 40G-OCDMA-PON system. The experimental results show that the sampled profile improves the code dependent performances presented in many OCDMA systems. We have also demonstrated a full-duplex 4-user × 40 Gb/s hybrid OCDMA-PON system by applying the sampled SSFBG E/Ds. An asynchronous full-duplex 50 km transmission with a total capacity of 160 Gb/s (4-user × 40 Gb/s) has been achieved for the first time. Furthermore, we focus on major requirements in NG-PON2 and discuss several issues to introduce the hybrid 40G-OCDMA-PON for optical access networks.

Application of a novel SSFBG-based single-input multiple-output encoder/decoder to optical packet switching

We propose a novel superstructured fiber Bragg grating (SSFBG) based single-input multiple-output (SIMO) en/decoder, which can simultaneously process a group of independent optical codes with a specific permutation and combination of code patterns and spatially separate encoded and decoded signals into different optical paths. The number of optical codes processed by the SIMO en/decoder can be flexibly changed. We theoretically and experimentally investigate the coding performance of the SIMO en/decoder and discuss the unique features of the proposed device. In the experiment, we employ the SIMO en/decoder for optical label processing in an optical-code based optical packet switching system with the data rate of 10 Gbit/s and the packet rate of 312.5 MHz. The four-SSFBG based SIMO en/decoder are capable of simultaneously generating/recognizing four 31-chip 640 Gchip/s optical code based labels and distribute the labels into four designated destinations.

Use of Spectral Conditions to Separate Strain and Temperature Effects in Fibre Bragg Grating Sensors Embedded in Load-Carrying Anisotropic Laminates

This work presents a further development of the methods of simultaneous determination of temperature and axial strain using a single fibre Bragg grating (FBG). The reflected spectrum of composite-embedded FBG sensors has been analyzed in order to separate temperature and load effects. We found out that during the curing process of the laminates, a superstructure has been introduced on the FBG. Analyzing this effect, a temperature and strain separation was implemented by simply calculating and comparing the integrated intensity of the spectral response signal. A mathematical four-parametric model has been developed to calculate the reflected spectrum of a superstructured fibre Bragg grating. The mathematically achieved data has been evaluated with experimentally determined data from fibre Bragg gratings embedded in glass-fibre reinforced composite materials.

Tunable Microwave Photonic Filter With a Narrow and Flat-Top Passband

A frequency-tunable microwave photonic filter (MPF) with a narrow and flat-top passband implemented using a phase modulator (PM) and a superstructured fiber Bragg grating (SFBG) is proposed and experimentally demonstrated. The key component in the MPF is the SFBG, which is designed and fabricated based on the equivalent phase shift (EPS) technique. Two phase shifts are introduced, and the combination of the two phase shifts would lead to a flat-bottom notch in the reflection band. By incorporating the SFBG into the MPF, a frequency response with a narrow and flat-top passband is achieved. The reflection bandwidth and the notch width of the SFBG, which determine the frequency tunable range and passband width, can be controlled by the length and maximum index modulation (MIM) of the SFBG. An experiment is performed. An MPF with a 3 dB bandwidth of 143 MHz, a 20 dB bandwidth of 370 MHz, and a tunable range from 0.4 to 6.4 GHz is demonstrated.