Cascaded Fiber Bragg Gratings Research Articles

Switchable Dual-Wavelength Fiber Laser with Narrow-Linewidth Output Based on Parity-Time Symmetry System and the Cascaded FBG

In this paper, a dual-wavelength narrow-linewidth fiber laser based on parity-time (PT) symmetry theory is proposed and experimentally demonstrated. The PT-symmetric filter system consists of two optical couplers (OCs), four polarization controllers (PCs), a polarization beam splitter (PBS), and cascaded fiber Bragg gratings (FBGs), enabling stable switchable dual-wavelength output and single longitudinal-mode (SLM) operation. The realization of single-frequency oscillation requires precise tuning of the PCs to match gain, loss, and coupling coefficients to ensure that the PT-broken phase occurs. During single-wavelength operation at 1548.71 nm (λ1) over a 60-min period, power and wavelength fluctuations were observed to be 0.94 dB and 0.01 nm, respectively, while for the other wavelength at 1550.91 nm (λ2), fluctuations were measured at 0.76 dB and 0.01 nm. The linewidths of each wavelength were 1.01 kHz and 0.89 kHz, with a relative intensity noise (RIN) lower than −117 dB/Hz. Under dual-wavelength operation, the maximum wavelength fluctuations for λ1 and λ2 were 0.03 nm and 0.01 nm, respectively, with maximum power fluctuations of 3.23 dB and 2.38 dB. The SLM laser source is suitable for applications in long-distance fiber-optic sensing and coherent LiDAR detection.

A Comprehensive Study on EDFA Gain Flattening for WDM Transmission using Cascaded Fiber Bragg Gratings

The gain flattening of optical amplifiers plays a crucial role in optical Wavelength Division Multiplexing (WDM) communication systems, ensuring uniform amplification across all channels. This study focuses on investigating the gain flattening characteristics of Erbium-Doped Fiber Amplifiers (EDFAs) using cascaded Fiber Bragg Gratings (FBGs) in the C-band wavelength range. A comparative analysis of various optical amplifiers revealed that EDFA exhibited the highest gain variation, making it an optimal choice for gain flattening. The key parameters to achieve optimal EDFA gain flattening include the wavelengths of the channels, EDFA length, noise figure (NF), and the number of cascaded FBGs. Simulation experiments are conducted using Optisystem software (ver. 14.2) and the obtained results reveal that EDFA gain flatness can be achieved within the wavelength range of 1531 to 1533 nm, utilizing an EDFA length of 6 m and 12 cascaded FBGs. These findings contribute to the advancement of gain flattening techniques in optical WDM systems, enhancing their performance and reliability.

Performance enhancement of optical communication system with cascaded FBGs of varying lengths

In this paper, an optical communication system constructed with cascaded fiber Bragg gratings or fiber Bragg gratings (FBGs) of varying lengths capable of operating in the C-band is presented. Here, initially, a passive optical device formed with four cascaded FBGs of varying lengths is proposed and analyzed. Subsequently, the proposed device is kept in the optical communication system to reduce the spectral width of the source, thereby enhancing the system’s performance. Analytical formulation based on the transfer matrix method of an optical device is incorporated. The effect of such a device on the system performance at various operating distances is discussed. Further, the system performance is studied with the apodized FBGs in the passive optical device. At the end, we investigated the effect of incorporating the cascaded FBG structure in the system utilizing four-level pulse amplitude modulation or PAM-4 modulation . As per the simulation results, the proposed device has given a maximum reflectivity of 98.39 and a minimum FWHM of 0.175 nm for uniform FBGs. But with the apodized FBGs, an FWHM of 0.07 nm with a reflectivity of 59.81 has been achieved. Simulation results reveal that the system formed with the proposed device has given better performance up to a distance of 105 km compared to the absence of the device. At the maximum operating distance of the system with apodized FBGs, the Q-factor and bit error rate (BER) are recorded as 6.712 and 9.5321×10−12, respectively. Apart from the Q-factor and BER estimation, eye height is also used to estimate the system performance at various operating distances.

Optimization technology for DCF dispersion compensation based on cascaded fiber Bragg grating.

A cascaded fiber Bragg grating (FBG) structure is proposed to reduce the dispersion of optical signals in single-mode fibers. Using the OptiSystem software for simulation, the three compensation schemes (precompensation, postcompensation, and symmetric compensation) of dispersion-compensated optical fiber (DCF) are analyzed, and the results show that the best of the three schemes is the postcompensation structure. For the postcompensation scheme, the influence of the coding method and duty cycle on the system is analyzed, and then the fiber grating is cascaded behind the transmitter to obtain a narrow linewidth of the optical signal and minimize the reflectivity sidelobe, and a chirped fiber grating is connected in front of the receiver to compensate for the dispersion of the channel residue. With or without cascaded FBGs, system performance at different input powers and different transmission distances is discussed. The results show that cascading fiber gratings can improve the performance of the system.

Highly cascaded first-order sapphire optical fiber Bragg gratings fabricated by a femtosecond laser.

This Letter reports an innovative technique for fabricating large-scale, highly cascaded first-order sapphire optical fiber Bragg gratings (FBGs) using a femtosecond laser-assisted point-by-point inscription method. For the first time, to the best of our knowledge, this study successfully demonstrates a distributed array of 10 FBGs within highly multimode sapphire crystal fiber, made possible by employing a high-power laser technique to generate larger reflectors with a Gaussian intensity profile. These first-order FBGs offer advantages such as enhanced reflectivity, shorter fabrication time, and simplified spectral characteristics, making them easier to interpret compared with high-order FBGs. The FBGs' resilience and effectiveness are analyzed by subjecting them to temperature tests, proving their capacity for accurate temperature monitoring up to 1500°C-a testament to their suitability for harsh environments. This novel approach broadens the scope for sensing and communication applications in sapphire fibers, particularly under challenging conditions. The novelty of our work lies in successfully overcoming the limitations of previous designs by integrating a cascade of 10 FBGs in sapphire fibers, thereby enhancing multiplexing capabilities, minimizing overlapping of FBG peaks, and ensuring reliable temperature monitoring in industries and applications with thermal gradients.

High-Sensitivity Temperature Sensor Based on Transmissive Solc-Like Filter and Cascaded Fiber Bragg Grating

A high sensitivity temperature sensor is proposed, which is based on a cascade of transmissive Solc-like filter and fiber Bragg grating (FBG). The sensor combines rough measurement with precise measurement to expand the measurement range with high sensitivity. The Solc-like filter based on two spliced polarization maintaining fibers (PMFs) realizes high sensitivity measurement by Vernier effect. The mathematical model of transmission spectrum is established by Jones matrix, and the relationship between the splicing angle and the interference fringes is proved. And the experimental results demonstrate that the measurement range is expanded by 8 times after the filter is cascaded with the FBG. The highest sensitivity of the sensor is -57.35nm/°C in the range of -4.5°C~23.5°C and the resolution reaches 3.49×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> °C. In addition, the result demonstrates that the amplification factor and sensitivity increase as the measurement range wider, so the sensor has great application potential in high sensitivity temperature measurement.

Simultaneous measurement of trace dimethyl methyl phosphate and temperature using all fiber Michaelson interferometer cascaded FBG.

All fiber Michaelson interferometer cascaded fiber Bragg grating (FBG) sensor for simultaneous measurement of trace dimethyl methyl phosphate and temperature is proposed. One end of the four-core fiber (FCF) is spliced with a multimode fiber (MMF), the other end is flattened and evaporated with silver film to enhance reflection, and the Michelson interference structure is formed. The grating is engraved in the single-mode fiber (SMF) core and spliced with MMF, then the Michelson interference cascaded FBG, FBG-MMF-FCF sensor is obtained. The sensing film, MnCo2O4 is coated on the surface of FCF, and the structure, elemental composition and morphology of MnCo2O4 were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The sensitivity and the detection limit of DMMP are 86.44 dB/ppm and 0.1767 ppb, respectively. The response/recovery time is about 14/10 s. the temperature sensitivity can be compensated and calculated as 0.069 nm/°C. The sensor has good selectivity and stability, and has a good application prospect in high sensitivity detection of trace DMMP vapor.

Simultaneous Detection of Magnetic Field and Temperature Using Micro-Nanofiber Cascaded Fiber Bragg Grating Structure

The monitoring of magnetic field plays an important role in aerospace, industrial production, and other fields. A novel sensor for simultaneous detection of magnetic field and temperature (MFT) by taking advantage of the micro-nanofiber Mach Zehnder interferometer (MZI) is proposed. Micro-nanofiber is formed by tapering single-mode fibers (SMFs). Furthermore, the MZI is cascaded to fiber Bragg grating (FBG) for the simultaneous detection of temperature. The structure is encapsulated in a glass tube filled with magnetic fluid (MF) to measure magnetic field intensity (MFI). FBG monitors temperature during MFI detection for the purpose of temperature compensation. By detecting the transmission spectra of FBG and MZI, it is possible to achieve simultaneous measurement of MFT. Experimental results show that the magnetic field sensitivity can reach 0.175 nm/Oe in the range of 0–133.5 Oe. The temperature sensitivity of the sensor is −0.486 nm/°C in the range of 30 °C–60 °C. The sensing structure has a detection limit of 3.09 Oe for MFI and 0.471 °C for temperature. The sensor has the characteristics of high sensitivity and compact size and can be used for dual-parameter measurements, which has broad application prospects in the fields of power systems and electromagnetic environment monitoring.

Wavelength Switchable Multi-Wavelength Erbium-Doped Fiber Laser Based on Polarization-Dependent Loss Modulation

We propose and demonstrate a novel and simple wavelength switchable multi-wavelength erbium-doped fiber (EDF) laser based on polarization-dependent loss (PDL) modulation with cascaded fiber Bragg gratings (FBGs) as the wavelength comb filter. PDL is generated and controlled by different polarization angles between the polarization state of each lasing line and the optical fiber polarizer in the laser cavity. The PDL modulation balances the difference between the total loss and the wavelength-dependent lasing gain. The relations among gain, loss, and laser output power under different PDL conditions are numerically analyzed on the basis of a simplified Giles model in an EDF laser system. Results show that multi-wavelength lasing lines can be built up by properly tuning the PDLs in different wavelengths. The amount of lasing lines can be switched by changing the PDL intensity in a certain wavelength. In an experiment, the PDL in that certain wavelength is modulated by utilizing four polarization controllable elements, each of which includes an FBG and a corresponding polarization controller (PC). One PC is used to control the polarization state of the reflected lasing line on the center wavelength of the FBG. A four-wavelength individually switchable EDF laser system is demonstrated by utilizing this wavelength switchable method, in which the switching operation for the single-, dual-, triple-, and four-wavelength laser output is verified. The experimental results are consistent with the theoretical results. All wavelength switching operations are conveniently controlled by merely adjusting the PCs. This simple structure and flexible wavelength switchable operations show that this multi-wavelength EDF laser has great potential in practical applications.

Switchable dual-wavelength Q-switched fiber laser based on sputtered indium tin oxide as saturable absorber

This paper demonstrate experimentally the generation of a stable switchable dual-wavelength Q-switched fiber laser. The pulsed fiber lasers is generated from deposited Indium Tin Oxide (ITO) saturable absorber (SA) on fiber ferrule, which is prepared by using DC Magnetron Sputtering. The deposited ITO SA is then being sandwiched in between the two fiber ferrules. A stable switchable dual-wavelength is generated by the aid of two cascaded fiber Bragg gratings (FBGs). To achieve a flexible switched in individual wavelength of 1532 or 1533 nm and simultaneously dual-wavelength fiber laser, the in line polarization controller is utilized to control the mode competition in the fiber laser cavity. The proposed fiber laser is capable of generating output at the pump power of 118.10 mW, centered at wavelength 1532 nm. The proposed design is having a repetition rate of 48.30 kHz and a pulse width of 5.22 µs. Similarly, at 1533 nm, it generates a repetition rate of 25.61 kHz and a pulse width of 7.72 µs. The output is also observed to remain unchanged over time, indicating high stability with the signal to noise ratio of 52.70 dB and 52.00 dB at wavelength 1532 nm and 1533 nm, respectively. The combination between ITO and cascaded FBG can offer a feasible and straightforward candidate for a multiwavelength fiber laser according to these results. Laser radar and terahertz generation may become a few of the potential fields that related to this work.

An enhanced WDM optical communication system using a cascaded fiber Bragg grating

In this paper, a cascaded fiber Bragg grating (FBG) system is proposed to reduce the dispersion in the optical signal in single mode optical fibers. This consequently enhances the system performance, which is evaluated by the bit error rate (BER) and quality factor (Q-factor). The proposed model consists of four uniform cascaded FBGs connected at the transmitter to get narrow linewidth, Δλ, of the optical signal, which is a major cause of the delay. The Optisystem7 is used to simulate the proposed model in a WDM system with and without the model for distance 200 km. The system parameters are investigated showing an enhanced performance with 12%, including eye diagram, Q-factor and BER. A 10−6–10−10 BER is achieved with a quality factor in the range 7–14, including the effects of fiber length, input power and FBG length.

EDFA gain flattening using fiber Bragg gratings employing different host materials

In this paper, erbium-doped fiber amplifier (EDFA) gain flatness is studied using cascaded fiber Bragg gratings (FBGs) with different numbers. The gain characteristics are investigated in reference to the wavelength, EDFA length, erbium ion density, and erbium radius. Three host materials are used: conventional silica, fluoride, and alumino-germanosilica, depending on their absorption and emission cross section areas. The convectional silica exhibits a high gain of 38.5 dB before flattening with an in-band gain of 6.5 dB. After flattening, the gain is dropped to 29 dB with a relative gain difference of 1.3% with 10 FBGs. The bandwidth of 28.42 nm is realized with 20 and 10 FBGs while the 30 FBGs configuration achieves a slightly lower value of 25 nm. The fluoride as host material depicts a lower gain after flattening of 12 dB, minimum relative gain difference of 10% with 30 FBGs and bandwidth of 28.42 nm. The alumino-germanosilicate depicts the highest gain of 30 dB with 28 nm bandwidth flattened with a relative gain difference of 1% at 30 FBGs configuration.

High-precision differential measurement of dye concentration based on two cascaded fiber Bragg gratings.

A high-precision differential detection system based on two cascaded fiber Bragg gratings (FBGs) is proposed to detect dye concentration. In this system, two low-quality common FBGs are connected in a series, and one is corroded by 20% hydrofluoric solutions for 210 min. A novel demodulation method-differential measurement-is proposed to improve the sensitivity of the sensor. The working point is not in the central but in the waist region of the reflection spectra of the etched FBG, which has the best sensitivity and minimal nonlinearity (∼0.018%). After adopting the differential measurement, the detection precision of the dye concentration has been obviously improved. According to our analysis, the theoretical limit sensitivity of the sensor can reach 7×10-4ppm.

A Cascade Fiber Optic Sensors for Simultaneous Measurement of Strain and Temperature

A simple and compact cascade fiber optic sensor for simultaneous measurement of temperature and strain is proposed and demonstrated in this letter. The structure consists of a short section of a PANDA fiber and a cascaded fiber Bragg grating (FBG). A Sagnac interferometer was formed in the PANDA fiber by tip coating the gold film. The sensitivities of the PANDA fiber and FBG for the temperature and strain are different, which makes the sensor to have the ability to measure strain and temperature simultaneously. Experimental results show that the maximum errors for the temperature and strain measurements are 0.22 °C and 21.7 μϵ , respectively. Based on its simple fabrication process and compact size, the sensor described in this letter could be a competitive candidate in remote sensing for the simultaneous measurement of temperature and strain.

High-sensitivity refractive index and temperature sensor based on cascading FBGs and droplet-like fiber interferometer

In this paper, a highly sensitive refractive index (RI) and temperature sensor based on two fiber Bragg gratings (FBGs) cascaded with a droplet-like fiber interferometer (DLFI) is proposed and experimentally demonstrated. The DLFI was fabricated by mechanically bending a section of coating-stripped single-mode fiber. As the surrounding RI changes, the transmission spectrum of the DLFI shifts, which causes the intensity difference of the two FBGs change. Whereas, the temperature change induces a Bragg wavelength shift of the FBGs. Thus, RI and temperature can be simultaneously measured by the senor through monitoring the intensity-difference change and the wavelength change. In our experiment, the proposed sensor exhibits a RI sensitivity of 385.2 dB/RIU (refractive index unit) in the range of 1.3388–1.3998, which is the highest in RI sensors based on intensity demodulation so far. Meanwhile, the temperature sensitivity is 11 pm/℃ in the range of 25–70 ℃.

On-line temperature measurement using single-ended distributed cascading fiber Bragg gratings-based Brillouin optical fiber sensor

In this study, we report a novel method of on-line distributed temperature measurement in optical fibers. The method is based on a cascading fiber Bragg gratings (FBGs) single-ended Brillouin optical time-domain analyzer (BOTDA). This proposal applies the cascading FBGs both as a reflector and an optical filter to improve the signal-to-noise ratio of the single-ended BOTDA. Experimental results show that a 75 km sensing range with 3 °C temperature resolution and 5 m spatial resolution are achieved.

Optic fiber temperature sensor based on cascading fiber Bragg gratings

In this paper, we demonstrate a novel method of distributed temperature sensing in optical fibers. The method is based on cascading fiber Bragg gratings (FBGs) single-ended Brillouin optical time-domain analyzer (BOTDA). This proposal applies the cascading FBGs both as a reflector and an optical filter to improves the measurement. Experimental results show that a 75-km sensing range with 3°C temperature resolution and 5 m spatial resolution are achieved.

Simultaneous acoustic and magnetic measurement using cascaded fibre Bragg grating

Abstract A fibre-optic sensor is proposed to conduct acoustic and magnetic measurements simultaneously. The sensor consists of two cascaded fibre Bragg gratings (FBGs), one of which is inserted into a magnetic extension bulk (TbDyFe (Terfenol-D)). This is to conduct the magnetic measurements while the other conducts the acoustic measurements. In this research, some pre-processing has been used to improve the sensitivities of the sensor. Side-band filtering technology-based intensity interrogation is used for the acoustic detection, and wavelength interrogation is used for the magnetic measurement. The results of the present study indicate that the sensor is able to measure acoustic and magnetic simultaneously within a considerable range.

Large Mode Area Pr3+-Doped Chalcogenide PCF Design for High Efficiency Mid-IR Laser

We propose a novel design of a photonic crystal fiber made of praseodymium (Pr3+)-doped chalcogenide glass with single mode operation beyond 4 $\mu \text{m}$ . Our design has an enlarged Pr3+-doped core diameter of 60 $\mu \text{m}$ . The field area of the emitted fundamental mode is about 3160 $\mu \text{m}^{2}$ at 4.5 $\mu \text{m}$ and 2050 $\mu \text{m}^{2}$ at a pump wavelength of 2.04 $\mu \text{m}$ . This large mode field area not only reduces the nonlinear effects but also increases the possible pump power before the damage threshold. The selected laser layout avoids fabrication difficulties associated with cascaded fiber Bragg gratings in Pr3+-doped chalcogenide glass fibers. The proposed design also increases the laser efficiency by using the overlap of the emission cross sections of Pr3+ in the transitions (3F2, 3H6 $\to$ 3H5 and 3H5 $\to$ 3H4) to enable both transitions to simultaneously produce a single coherent mid-infrared wavelength. The simulation results reveal that more than 64% of slope efficiency could be achieved at 4.5 $\mu \text{m}$ for a fiber loss of 1 dB/m.

Dual-wavelength ring-cavity continuous-wave fiber laser based on semiconductor optical amplifier

A dual-wavelength fiber ring-cavity laser based on InP/InGaAsP multi-quantum wells semiconductor optical amplifier is proposed and experimentally demonstrated. The proof of concept device consists of a semiconductor optical amplifier with InP/InGaAsP multi-quantum wells structure as the gain medium and two intracavity cascaded fiber Bragg gratings as wavelength selector by changing their operation temperature. The results demonstrate the new concept of dual-wavelength fiber laser based semiconductor optical amplifier with InP/InGaAsP multi-quantum wells structure and the technical feasibility.