The Influence of Network Topology on the Sensitivity of Fiber Bragg Grating (FBG) Sensors: Serial and Parallel Approaches

Anas Hambali Ahmad Abas1,2[0009-0003-2141-1108], Mohammad Syuhaimi Ab-Rahman1,3[0000-0002-7908-1688], I-Shyan Hwang4[0000-0002-8746-5294], Seri Mastura Mustaza1[0000-0002-7907-4197], Muhamad Hazwan Wahab1[0009-0005-3334-4728] and Norhidayah Ahmad1[0009-0009-3739-1977]

1 Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Malaysia

2 Faculty of Computing and Engineering, Quest International University, 30250 Malaysia

3 Electrical and Computer Engineering Program, Faculty of Engineering, Sohar University, PC:311, Sohar, Oman

4 Department of Computer Science and Engineering, Yuan Ze University, Taoyuan 32003, Taiwan
lncs@springer.com

Abstract. Sensing structures of Fiber Bragg Grating (FBG) are crucial for ensuring the precision and reliability of FBG-based monitoring systems in diverse applications such as structural health monitoring and industrial process control. This study investigates the sensitivity of serial and parallel FBG topologies to temperature and strain by simulating three FBG sensors in each arrangement using OptiSystem 21.0 software. Sensitivity calculations were performed using linear regression, where the Bragg wavelength shifts were measured against temperature and strain variations. Results indicate that the parallel FBG configuration significantly outperforms the serial configuration in terms of signal stability, power uniformity, and crosstalk. Specifically, the parallel topology demonstrated average temperature and strain sensitivities of 10.17 pm/°C and 1.11 pm/με, respectively, which are higher than those of the serial configuration (8.32 pm/°C and 0.89 pm/με). The parallel arrangement also exhibited lower standard deviations, indicating greater measurement stability, making it a better choice for applications demanding high sensitivity, low cross-sensitivity, and accurate measurement. These findings offer valuable insights for engineers and researchers in selecting the optimal FBG network topology for real-time monitoring in advanced optical networks, where precise and reliable sensing is paramount.

Keywords: Fiber Bragg Grating (FBG), Parallel and Serial Configuration, Optical Sensing Network, Sensitivity Analysis, Temperature and Strain Monitoring.

INTRODUCTION

Fiber Bragg Grating (FBG)-based sensors have gained significant attention in recent years for their application in structural health monitoring, aerospace, civil engineering, and industrial process control due to their high precision and robustness in harsh environments [1]-[2]. The underlying sensing principle of FBGs relies on modulating the refractive index along the optical fiber, enabling the reflection of specific wavelengths of light [3]. Changes in environmental parameters such as temperature, strain, and pressure cause shifts in the reflected wavelength, which can be precisely measured to monitor these variations [4]-[5]. This property has made FBG sensors ideal candidates for real-time monitoring of structural and environmental parameters in diverse applications.

Recent advancements in multiplexing techniques have enabled the development of distributed sensing systems, allowing multiple FBG sensors to be integrated into a single optical fiber [6]. The two main topologies used for sensor multiplexing are serial and parallel configurations. In a serial configuration, FBG sensors are arranged sequentially along the fiber, with a single light source used to interrogate all sensors, resulting in potential signal degradation, crosstalk, and attenuation [7]. In contrast, the parallel configuration places each sensor on a separate optical path, typically connected via an optical splitter, minimizing crosstalk and signal loss, thus offering a more stable and accurate measurement [8].

The study of these topologies has been central to many research efforts. For instance, the high efficiency of Passive Optical Networks (PONs) and their applications in network monitoring and management demonstrate the importance of reducing signal degradation and interference, which is analogous to the challenges faced in FBG-based systems [9]. Similarly, studies on survivability and protection in FTTH (Fiber to the Home) networks highlight the role of system reliability and resilience, which is crucial in the parallel FBG configuration where signal consistency is essential for long-term sensing applications [10]. Furthermore, next-generation optical access networks (NG-OANs) emphasize the challenges in ensuring network scalability and minimizing crosstalk, both of which are directly relevant to the design of effective FBG sensor systems [11].

However, despite the extensive use of FBG sensors in these fields, limited studies have directly compared the sensitivity of serial and parallel FBG topologies [12], particularly in relation to temperature and strain. While the serial configuration offers simplicity and cost-effectiveness, it is often hampered by signal loss and interference. The parallel configuration, on the other hand, holds promise for overcoming these limitations by providing more independent and stable sensor measurements. This study aims to fill this gap by offering a comprehensive comparison of the sensitivity, stability, and crosstalk of serial and parallel FBG topologies, providing crucial insights into their performance in real-world applications.

THEORETICAL BACKGROUND

Fiber Bragg Grating (FBG) parameter

Each FBG sensor is modeled as a "Uniform Fiber Bragg Grating" element in the OptiSystem 21.0 software. The main parameters for the FBG simulation were carefully chosen to ensure consistency and accuracy across all simulations. The central Bragg wavelength (λB) is chosen to be 1550 nm, as this is a standard telecommunications wavelength which offers minimal fiber attenuation and a low dispersion rate in optical fibers [13]-[14]. The length of the diffraction grating was set at 10 mm, balancing between the grating reflectivity and spectral width, with the refractive index modulation (Δn) set to 1×10−4, corresponding to moderate reflection (approximately 90%). For each FBG, the effective refractive index (neff) is taken as 1.45 because assuming as a single-mode optical fiber. The apodization profile used was Gaussian to suppress sidelobes in the reflection spectrum, ensuring accurate sensing capabilities [15]. Furthermore, 100 discrete segments were used to model the grating ensuring the precision of the reflection spectra [16]. The sensors were designed to exhibit sensitivity to both temperature and strain, which are the two primary parameters for this study.

Network Topology Configuration

Serial Configuration

In the serial topology, multiple FBG sensors are arranged sequentially along a single optical fiber path. A continuous-wave (CW) laser source is connected to the input of the first sensor. The reflected signals from each sensor are transmitted sequentially through the network. Components such as optical circulators and wavelength division multiplexers (WDM) are employed to isolate the reflected signals based on each sensor's unique Bragg wavelength. This configuration, though simple and cost-effective, suffers from issues such as signal attenuation and crosstalk, particularly when sensors are closely spaced along the fiber.

The challenges of signal degradation and interference in serial configurations are critical in the context of optical access networks where efficient monitoring and management are essential for maintaining system performance [17]. For example, high-efficiency monitoring systems in Passive Optical Networks (PONs) have shown that minimizing signal loss and interference is vital for maintaining accurate network monitoring and improving system reliability [12]. This directly relates to the limitations faced by serial FBG configurations, where signal attenuation impacts sensitivity and the accuracy of measurements.

Parallel Configuration

In the parallel topology, each FBG sensor is placed in a separate branch of the optical fiber network, with the output from a CW laser split into multiple branches using an optical splitter. Each branch terminates at an individual FBG sensor, which allows each sensor to reflect light independently, reducing the potential for crosstalk and signal loss [18]. This topology ensures a more stable and reliable measurement by providing distinct optical paths for each sensor.

The advantages of the parallel configuration are particularly relevant in next-generation optical access networks (NG-OANs), where the need for scalability and minimal interference is paramount [19]. Studies on NG-OANs have emphasized the importance of designing systems that ensure minimal crosstalk and signal degradation to improve overall system reliability and performance, which are key considerations for parallel FBG sensor networks [20].

Temperature and Strain Sensitivity of FBG Sensors

FBG sensors are sensitive to changes in temperature and strain due to the shift in the Bragg wavelength (λB) in response to these environmental factors. The relationship between the Bragg wavelength shift and temperature is given by the formula derived from the study [21]:

ΔλB = λB (αΔT) (1)

where α is the coefficient of thermal expansion of the fiber and ΔT is the temperature change. For strain sensitivity, the shift in the Bragg wavelength can be expressed as the formula derived from [22]:

ΔλB = λB (pe Δϵ) (2)

where pe is the photo-elastic coefficient of the fiber and Δϵ is the applied strain.

METHODOLOGY

Simulation using Optisystem 21.0

Simulations were carried out using OptiSystem 21.0, which is a suitable platform for modeling complex optical networks. This software enables the integration of various optical components, making it ideal for simulating FBG-based sensor networks in both serial and parallel topologies. The goal of the simulation was to evaluate the sensitivity, signal stability, and crosstalk in different network configurations under controlled variations of temperature and strain.

Experimental Setup

The simulation setup is designed to closely mimic real-world FBG sensing conditions. In the system, a continuous-wave (CW) laser was used to provide the input light to the FBG sensors. The CW laser is selected for its stable output and narrow linewidth, which is essential for accurately measuring small wavelength shifts caused by temperature or strain changes. The CW laser source was connected to the input of the first FBG sensor in both serial and parallel configurations.

In addition to the CW laser, a white light source was utilized in a complementary role, primarily for monitoring and evaluating the overall spectral response of the FBG sensors. While the CW laser was used for the direct excitation of the sensors, the white light source provided a broad spectrum for background theory and spectral analysis, particularly in monitoring spectral overlap or separation between adjacent FBGs in the network.

FBG Sensor Configuration

Three FBG sensors were modeled for both serial and parallel topologies. In the serial configuration, the sensors were arranged sequentially along a single optical fiber path. The CW laser was transmitted through the first sensor, with the reflected signals passing sequentially through the subsequent sensors. To isolate the reflected wavelengths from each sensor, optical circulators and wavelength division multiplexers (WDM) were employed, allowing for distinct channel separation for each sensor's reflection. This configuration emulates a typical serial FBG sensing system, which is commonly used in distributed sensing applications.

In the parallel configuration, each FBG sensor was placed in a separate optical branch. The output from the CW laser was distributed using an optical splitter, ensuring that each sensor received a dedicated path for signal reflection. This arrangement reduces crosstalk and signal degradation, as each sensor operates independently from the others. The reflected signals from each sensor were then measured independently using an optical spectrum analyzer (OSA) or re-multiplexed to a central receiver.

Temperature and Strain Variation

The primary objective of the simulation was to evaluate the sensitivity of the FBG sensors to temperature and strain variations. The temperature of each sensor was gradually varied from 0°C to 100°C in 10°C increments, while the applied strain was varied from 0 με to 2000 με in steps of 200 με. These parameters were chosen to mimic the range of environmental changes typically encountered in structural monitoring applications. During each simulation step, the reflection spectra from each FBG sensor were recorded using the optical spectrum analyzer (OSA). The peak reflected wavelength for each sensor was determined at every temperature and strain step, and the wavelength shift was calculated relative to the baseline wavelength.

The operating wavelength selection

The wavelengths 1310 nm, 1480 nm, 1550 nm, and 1625 nm are commonly used in optical communication systems, with each having distinct advantages. The 1310 nm wavelength is preferred for medium-range transmission due to its low dispersion and attenuation in optical fibers, making it suitable for distances up to 40 km. The 1480 nm wavelength is often used in optical amplification, particularly with Erbium-Doped Fiber Amplifiers (EDFAs), which enhance long-distance transmission by amplifying the 1550 nm signal. The 1550 nm wavelength is ideal for long-distance communication, offering the lowest attenuation in silica optical fibers, thus reducing the need for signal repeaters. Finally, the 1625 nm wavelength, used for monitoring purposes, is chosen to avoid interference with the primary transmission wavelengths and is particularly beneficial for long-distance network monitoring with minimal impact on data transmission. These wavelengths, while primarily relevant for network operation, also offer important context for FBG sensor applications, particularly in optical network systems.

Fig. 1. Design of Optical Network Configuration for Serial FBG Sensing

Fig. 2. Design of Optical Network Configuration for Parallel FBG Sensing

DATA COLLECTION AND ANALYSIS

Serial FBG Configuration

In the simulation of the serial FBG configuration with three gratings arranged sequentially, crosstalk analysis was conducted to evaluate the level of signal interference between adjacent sensors. The following table presents the actual signal power and unwanted leakage power for each FBG pair, along with the calculated crosstalk values in decibels (dB).

Table 1. Actual Signal Power, Leakage Power, and Crosstalk at Each Sensor in the Serial FBG Configuration

FBG	Actual Signal Power (dBm)	Leakage Power (dBm)	Crosstalk (dB) = 10·log10
FBG 1 → FBG 2	-3	-25	-22
FBG 1 → FBG 3	-3	-35	-32
FBG 2 → FBG 1	-6	-28	-22
FBG 2 → FBG 3	-6	-30	-24
FBG 3 → FBG 1	-9	-38	-29
FBG 3 → FBG 2	-9	-36	-27

Crosstalk values ranging from -20 dB to -30 dB indicate a moderate level of signal interference, consistent with typical results for serial FBG arrangements with closely spaced wavelength intervals. More negative (lower) values reflect reduced leakage and, consequently, better signal isolation between sensors. This crosstalk phenomenon occurs when the reflected signal from one FBG falls within the wavelength range of a neighboring FBG, resulting in signal contamination and reduced measurement accuracy. In the context of serial configurations, this issue becomes more pronounced due to optical interactions and wave mixing along the fiber path. These findings highlight the inherent limitations of serial FBG configurations in terms of signal isolation and the accessibility of sensors located further along the chain. Therefore, to enhance the efficiency and reliability of FBG sensing systems, alternative configurations such as parallel arrangements which minimize crosstalk should be considered.

Parallel FBG Configuration

The simulation data for the parallel Fiber Bragg Grating (FBG) configuration indicates a lower level of crosstalk compared to the serial configuration, although some variations and irregularities. The following table displays the actual signal power and unwanted leakage power for each FBG pair, along with the corresponding crosstalk values in decibels (dB).

Table 2. Actual Signal Power, Leakage Power, and Crosstalk at Each Sensor in the Parallel FBG Configuration

FBG pair	Actual Signal Power (dBm)	Leakage Power (dBm)	Crosstalk (dB) = 10·log10
FBG 1 → FBG 2	-3	-38.5	-35.5
FBG 1 → FBG 3	-3	-40.2	-37.2
FBG 2 → FBG 1	-3.5	-36	-32.5
FBG 2 → FBG 3	-3.5	-34.8	-31.3
FBG 3 → FBG 1	-4	-39	-35
FBG 3 → FBG 2	-4	-33.5	-29.5

The observed crosstalk values mostly fall within the range of -29 dB to -37 dB, indicating better signal separation and minimal interference between sensors in the parallel arrangement. However, a few higher leakage values, such as the -29.5 dB recorded from FBG 3 to FBG 2, reflect possible imperfections caused by factors such as connector losses, fiber bending, or external signal disturbances. The low crosstalk between FBG1–FBG3 in the parallel configuration can be explained by a few key factors. First, the sensors are spaced further apart, which helps prevent their reflected wavelengths from overlapping and reduces interference. The Bragg wavelengths of the sensors are also carefully separated to ensure the signals from each sensor remain distinct and easy to identify. Minor variations in the actual signal power of each FBG also simulate real-world conditions, where factors such as fabrication inconsistencies and environmental fluctuations can affect the received signal strength. Overall, these results confirm that the parallel FBG arrangement offers advantages in reducing crosstalk compared to the serial configuration, making it a more suitable choice for sensing applications that demand high sensitivity and signal accuracy.

Crosstalk Analysis (Serial vs Parallel)

Fig. 3. Comparison Graph of Crosstalk in Serial and Parallel Configurations

The crosstalk levels between sensors are highly different in the serial and parallel configurations of the FBGs. The curve in figure 3 reveals that the average crosstalk corresponding to the serial configuration vary higher from -20 dB to -30 dB and the parallel configuration varies lower between -29 and -37 dB, which is a rather stable value.The key reason for this discrepancy stems from the intrinsic properties of both configurations. In the serial architecture, the optical signal is forced to travel through each FBG one after another in sequence, causing an accumulation of power losses, and interference between reflexed signals, which in turn gives rise to stronger crosstalk. By contrast, the parallel configuration allows every FBG to directly and independently access the optical signal, minimizing the interference between sensors, resulting in higher S/N ratio. The plot also shows that the crosstalk has a trend to be larger for the FBGs that are at the middle and at the end positions in the serial structure, while in the parallel structure, there is a low and uniform cross talk between the FBG couples. This highlights the superiority of the parallel configuration in signal stability and reliability, especially for the sensing which requires high sensitivity and accuracy detection.

RESULT AND DISCUSSION

Serial FBG Sensing Configuration

In the serial FBG configuration, the reflection spectrum exhibits significant signal degradation due to accumulated insertion losses as illustrated in Figure 6.

Fig. 4. Temperature sensitivity vs. Bragg Shift

Fig. 5. Strain sensitivity vs. Bragg Shift

The two linear graphs in Figure 4 and 5 depict the direct relationship between temperature, strain and the corresponding Bragg wavelength shift in Fiber Bragg Grating (FBG) sensors. The first graph demonstrates a linear increase in the Bragg shift with temperature, exhibiting a sensitivity of 10.17 pm/°C. This consistent relationship highlights the FBG sensor's capacity for precise detection of temperature variations. Similarly, the second graph illustrates a linear correlation between strain and Bragg shift, with a sensitivity of 1.11 pm/με. As strain increases, the Bragg shift follows a proportional rise emphasizing the sensor's effectiveness in monitoring strain. Both plots indicate that the parallel FBG sensor configuration offers stable and reliable responses to environmental changes, making it well-suited for real-time monitoring applications.

Fig. 6. Reflection Spectrum from Serial FBG Sensors Recorded by the Optical Spectrum Analyzer (OSA)

A large attenuation of the reflected signal power along the cascaded is observed in the optical spectrum from the serially lined Fiber Bragg Gratings (FBG) network. The first FBG has a peak power of about 5.755 dBm, which proves high transmittable of the optical signal fed into the first sensor. But the reflected power dramatically drops at the second and the third FBGs, for which they are −3.497 dBm and −12.886 dBm, respectively. This gradually diminished intensity signal is explained by the sum of accumulated insertion losses and intrinsic optical attenuation suffered by the fiber in serial structure.

The power fed into each following grating will however be lower as a part of the transmitted power is reflected back and the rest is subjected to losses by scattering, absorption and non-ideal reflections, which consequently diminishes the available power for the succeeding sensors. On the other hand, the inhomogeneous power distribution in a serial FBG series will result in lower sensitivity as well as lower signal-to-noise ratio (SNR) of a sensor at the downstream. The small shift and broadening of the observed spectra at the reflection peaks are attributed to the effects of the grating interaction and multiple reflections in the fiber.

These results illustrate the fundamental limitations of serial FBG sensor configurations on signal degradation and sensor performance coherence, emphasizing the requirement of complex schemes, such as parallel FBG arrangements, which can improve the measurement reliability and their performance efficiency.

Parallel FBG Sensing Configuration

In the parallel FBG configuration the reflection spectrum exhibits a more stable signal.

Fig. 7. Reflection Spectrum from Parallel FBG Sensors Recorded by the Optical Spectrum Analyzer (OSA)

This spectrum illustrated in Fig.7 displays the reflected output of three FBGs that are placed in parallel in an optical sensing network. Three reflection peaks appear at 1.614 µm, 1.624 µm, and 1.634 µm for the Bragg wavelengths of FBG 1, FBG 2, and FBG 3, respectively. Both FBGs reflect the light at almost the same power (2.43 dBm, 2.435 dBm, 2.431 dBm) with no obvious difference.

The wavelength spacing between the three FBGs has been well-designed not to cause spectral overlap. This is crucial in preserving the fidelity of each reflected signal and preventing spectral crosstalk. Therefore, different peaks can be discriminated more obviously, and the reliability of the system for simultaneous multipoint sensing is improved. In general, this spectrum validates that such parallel FBG configuration could give the consistent and stable reflection response, which will be applicable for high-performance multi-point sensing applications.

Eye Diagram Analysis

The eye diagram is an essential analytical tool in optical network systems, as it provides a visual representation of signal stability, noise, distortion, and jitter. By examining the shape and opening of the eye, the performance of data transmission can be more accurately assessed, including signal quality and bit error rate (BER).

Fig. 8. Eye diagram recorded by the BER analyzer for the series configuration

Fig. 9. Eye diagram recorded by the BER analyzer for the parallel configuration

Figure 8 shows the eye diagram for series FBG configuration, and Figure 9 shows it for parallel FBG configuration. As can be seen, the eye diagram of the parallel setup shows a larger, cleaner eye center, which implies a more stable signal and (to the higher) SNR. Closer inspection of the signal traces also reveals less crossover and better uniformity, each of which suggests a more limited timing jitter and distortion. The eye diagram for the series circuit in contrast shows distortion of the signals where the eye opening gets narrow and blurred. This is because the insertion loss, crosstalk and reflection power degradation add up, with an increased signal path from multiple sensors. These can cause high bit error and instability in the Data transmission.

Table 3. Eye Diagram Performance Metrics for Serial and Parallel FBG

Metric	Serial Configuration	Parallel Configuration
Q-Factor	4.21	7.83
Minimum BER	4.82 × 10⁻⁵	6.03 × 10⁻⁹
Eye Height (µa.u.)	45	92
Eye Width (UI)	0.72	0.96
Threshold Level	0.012	0.008

Based on Table 3, the eye diagram analysis confirms that the parallel FBG configuration offers superior signal integrity compared to the serial arrangement. A higher Q-factor (7.83) and lower bit error rate (6.03 × 10⁻⁹) indicate enhanced signal stability and transmission quality. Furthermore, the broader eye width (0.96 UI) and increased eye height (92 µa.u.) reflect improved timing precision and reduced distortion. These performance metrics underscore the parallel topology's suitability for high-reliability, multi-point optical sensing applications.

CONCLUSION

This study provides a comprehensive comparison of the serial and parallel FBG sensor architectures. While the serial configuration offers simplicity and cost-effectiveness for short-range networks, it is limited by signal degradation, crosstalk, and lower reflected signal power. In contrast, the parallel configuration, though more complex and requiring additional components, offers superior signal stability, reduced crosstalk, and enhanced flexibility, making it more suitable for large-scale, high-quality sensor applications. The parallel configuration demonstrated higher average sensitivities of 10.17 pm/°C for temperature and 1.11 pm/με for strain, compared to the serial configuration’s 8.32 pm/°C and 0.89 pm/με. These results were further supported by the eye diagram analysis, which showed that the parallel FBG configuration provides a wider, cleaner eye opening, higher Q-factor, and lower bit error rate, suggesting better signal integrity and less interference. While the serial FBG configuration may still be useful for applications with lower accuracy requirements, the parallel configuration is clearly more reliable for real-time monitoring and data transmission in modern optical systems. Future improvements in parallel FBG systems could focus on optimizing component orientation, ensuring balanced power distribution, and incorporating optical amplifiers or advanced signal processing to further enhance performance.

ACKNOWLEDGMENTS

The author would like to express sincere appreciation to the Faculty of Engineering and Built Environment (FKAB), Universiti Kebangsaan Malaysia (UKM), for the support and facilities provided in completing this research. Special thanks are also extended to the supervisor, Prof. Ir. Dr. Mohammad Syuhaimi Ab-Rahman, for his insightful feedback and constructive suggestions, which have greatly contributed to the successful completion of this study.

References

Siti Asma Che Aziz; Mohammad Syuhaimi Ab-Rahman; Kasmiran Jumari, “Customer access protection unit for survivable FTTH network,” 2009, doi: https://doi.org/10.1109/ICONSPACE.2009.5352668.

O. N. ⁎ Shoi Okagawa, Peter Bernus, “Realtime Health Monitoring of Composite Structures Using FBG Sensors,” Int. Fed. Autom. Control, vol. 55, no. 19, pp. 157–162, 2022, doi: https://doi.org/10.1016/j.ifacol.2022.09.200.

U. Senkans, J. Braunfelds, I. Lyashuk, J. Porins, S. Spolitis, and V. Bobrovs, “Research on FBG-Based Sensor Networks and Their Coexistence with Fiber Optical Transmission Systems,” J. Sensors, vol. 2019, 2019, doi: 10.1155/2019/6459387.

J. Qi, “A comparison study of the sensing characteristics of FBG and TFBG,” vol. 1, pp. 68–79, 2013, doi: 10.1108/02602281311294360.

M. S. Ab-Rahman, B. C. Ng, and K. Jumari, “Detecting faulty fiber with centralized failure detection system (CFDS) in fiber-to-the-home (FTTH) access network,” Opt. Appl., vol. 39, no. 2, pp. 241–250, 2009.

M. Zaynetdinov, E. M. See, B. Geist, G. Ciovati, H. D. Robinson, and V. Kochergin, “A fiber Bragg grating temperature sensor for 2-400 K,” IEEE Sens. J., vol. 15, no. 3, pp. 1908–1912, Mar. 2015, doi: 10.1109/JSEN.2014.2368457.

J. C. Yibeltal Chanie Manie, Peng-Chun Peng, Run-Kai Shiu, Yuan-Ta Hsu, Ya-Yu Chen, Guan-Ming Shao, “Enhancement of the Multiplexing Capacity and Measurement Accuracy of FBG Sensor System Using IWDM Technique and Deep Learning Algorithm,” J. Light. Technol., vol. 38, no. 6, pp. 1589–1603, 2020, [Online]. Available: https://opg.optica.org/jlt/abstract.cfm?URI=jlt-38-6-1589.

A. W. Qingtian Li, Zhiwei Jia, Longsheng Wang, Yuanyuan Guo, Pengfa Chang, Yuncai Wang, “Routes to broadband laser chaos with dynamics switching in a 1550-nm VCSEL laser subjected to optical feedback,” Opt. Express, vol. 33, no. 5, pp. 9695–9706, 2025, doi: https://doi.org/10.1364/OE.551461.

D. Kinet, P. Mégret, K. W. Goossen, L. Qiu, D. Heider, and C. Caucheteur, “Fiber Bragg grating sensors toward structural health monitoring in composite materials: Challenges and solutions,” Sensors (Switzerland), vol. 14, no. 4. MDPI AG, pp. 7394–7419, Apr. 23, 2014, doi: 10.3390/s140407394.

S. Ghoniemy, “Enhanced Time and Wavelength Division Multiplexed Passive Optical Network (TWDM-PON) for Triple-play Broadband Service Delivery in FTTx Networks.”

L. M. Peng, X. W. Li, W. H. Yang, and Y. C. Kim, “Investigation on reliability and scalability of an FBG-based hierarchical AOFSN,” Sensors, vol. 10, no. 4, pp. 2901–2918, 2010, doi: 10.3390/s100402901.

B. C. Ng, M. S. Ab-Rahman, A. Premadi, and K. Jumari, “High efficiency of PON network monitoring and management,” J. Netw. Syst. Manag., vol. 18, no. 2, pp. 210–231, 2010, doi: 10.1007/s10922-010-9158-9.

J. Zubia and J. Arrue, “Plastic Optical Fibers: An Introduction to Their Technological Processes and Applications,” Opt. Fiber Technol., vol. 7, 1011, doi: 10.1006rofte.2000.0355.

A. Sezer Hicyilmaz and A. Celik Bedeloglu, “Applications of polyimide coatings: a review,” SN Appl. Sci., vol. 3, no. 3, pp. 1–22, 2021, doi: 10.1007/s42452-021-04362-5.

M. Batumalay, A. Lokman, F. Ahmad, H. Arof, H. Ahmad, and S. W. Harun, “Tapered plastic optical fiber coated with HEC/PVDF for measurement of relative humidity,” IEEE Sens. J., vol. 13, no. 12, pp. 4702–4705, 2013, doi: 10.1109/JSEN.2013.2272329.

A. Méndez, “Fiber Bragg grating sensors: a market overview,” Third Eur. Work. Opt. Fibre Sensors, vol. 6619, p. 661905, 2007, doi: 10.1117/12.738334.

A. O. Yukihiro TOMINARI, Toshiki YAMADA, Takahiro KAJI, “Photochemical Stability of Organic Electro-Optic Polymer at 1310-nm Wavelength,” IEICE Trans. Electron., vol. E106-C, no. No.6, pp. 228–231, 2022, doi: 10.1587/transele.2022OMS0012.

H. Di Zhang et al., “High-sensitivity gas sensors based on arranged polyaniline/PMMA composite fibers,” Sensors Actuators, A Phys., vol. 219, pp. 123–127, Nov. 2014, doi: 10.1016/j.sna.2014.09.005.

X. Li, Y. Li, and Z. Wen, “300m optic fiber Bragg grating temperature sensing system for seawater measurement,” in Journal of Physics: Conference Series, 2011, vol. 276, no. 1, doi: 10.1088/1742-6596/276/1/012130.

M. S. Ab-Rahman, N. I. Shuhaimi, L. A. H. Azizan, and M. R. Hassan, “Analytical study of signal-to-noise ratio for visible light communication by using single source,” J. Comput. Sci., vol. 8, no. 1, pp. 141–144, 2012, doi: 10.3844/jcssp.2012.141.144.

B. Zhang, “Development of sandglass shape FBG sensor to reduce cross sensitivity effect,” Int. J. Opt., vol. 2013, no. 3, pp. 3–6, 2013, doi: 10.1155/2013/636987.

G. Luyckx, E. Voet, N. Lammens, and J. Degrieck, “Strain measurements of composite laminates with embedded fibre bragg gratings: Criticism and opportunities for research,” Sensors, vol. 11, no. 1, pp. 384–408, 2011, doi: 10.3390/s110100384.