Fiber Laser Sensor Research Articles

Highly sensitive adulteration detection in kelulut honey utilizing fiber Bragg grating technology with Q-switched pulse erbium-doped fiber laser and innovative spider silk substrate

The growing field of photonics has seen significant developments in optical pulse fiber-based sensing technologies. In this research, a novel fiber Bragg grating using a Q-switched erbium-doped fiber laser source and innovative spider silk as a base material is presented, specifically designed for the detection of adulteration in pure kelulut honey. Kelulut honey has attracted much attention from Malaysian researchers as it is a highly prized, versatile local health remedy. During the experimental setup, concentrations of the adulterant isoglucose ranging from 0 % to 8 % and 10–50 % were intentionally added to the pure kelulut honey. The sensor showed remarkable sensitivity and detected subtle shifts in both the wavelength and radio frequency spectrum. The experimental results obtained emphasize the effectiveness of the proposed sensor and demonstrate its exceptional sensitivity in detecting adulteration in pure kelulut honey. This inherent property makes the derived pulse fiber laser sensor a promising tool for various applications in clinical detection and diagnosis as well as in the food industry. The results presented here not only contribute to the field of photonics but also have the potential to advance the quality control and authenticity assessment of kelulut honey in various fields.

Humidity Sensing Using a Multimode Fiber Ring Laser with Thermal Compensation

We propose a multimode fiber laser sensor utilizing PI-SMF (polyimide-coated single mode fiber) for low-error relative humidity (RH) measurement, which is temperature compensated based on FBG. The PI-SMF in the laser cavity is used as a sensing element, and its length varies with humidity and temperature by volume-variation induced strain, which leads to frequency shift of the longitudinal mode beat frequency signal (BFS). When the 2000 MHz BFS is selected as the sensing signal, a RH sensitivity of −2.68 kHz/%RH and a temperature sensitivity of −14.05 kHz/°C are achieved. The peak shift of the FBG-based laser emission spectrum is only sensitive to temperature rather than RH with a temperature sensitivity of 9.95 pm/°C, which is used as the temperature compensation for RH measurements. By monitoring the response of the BFS and the laser wavelength, the cross-sensitivity effect of RH and temperature is overcome, and low-error RH measurement in the temperature range of 20 to 65 °C is realized with errors within ±0.67 %RH (25 to 85 %RH). The scheme does not require the design and production of complex structures and hygroscopic material coating processes, owning the advantages of simple structure, easy operation and high accuracy, and is expected to be practically applied in food safety and environmental monitoring.

Fiber Bragg gratings fabricated in fibers with different geometries by femtosecond laser written through the coating and their applications in strain sensing and fiber laser

Applications of the type-I fiber Bragg gratings (FBGs) written through the coating (TTC) in strain sensing and tunable distributed Bragg reflector (DBR) fiber lasers were demonstrated. We reported the principle of selecting the distance between the fiber and the phase mask when writing type-I TTC FBGs. Type-I TTC FBGs written in commercially available acrylate-coated fibers with various geometries and their strain responses were demonstrated. Results showed that the strain sensitivity of FBGs increases as the core-diameter decreases, probably due to the waveguide effect. In addition, a continuously tunable DBR fiber laser based on TTC FBGs was achieved with a wavelength tuning range of 19.934 nm around 1080 nm, by applying a strain of 0-21265.8 µɛ to the laser resonant cavity. The wavelength tuning range was limited by the splice point between the gain fiber and the passive fiber for transmitting pump and signal lasers. When the pump power was 100 mW, the relative intensity noises were −97.334 dB/Hz at the relaxation oscillation peak of 880 kHz and −128 dB/Hz at frequencies greater than 3 MHz. The results open a potential scheme to design and implement continuously tunable fiber lasers and fiber laser sensors for strain sensing with a higher resolution.

A real time digital vibration acceleration fiber sensing system based on a multi-carrier modulation/demodulation technique

A multi-longitudinal mode fiber laser sensor (MLMFLS) system based on digital modulation/demodulation technique for vibration acceleration detection is proposed. To the best of the authors’ knowledge, this is the first digital vibration acceleration demodulation system ever reported by a MLMFLS system. A few beat frequency signals (BFS) generated by the MLMFLS are used as signal carriers of applied vibration signals. Based on multi-channel digital down-conversion technique, the weak vibration signals modulated on the BFS are superposed by utilizing the digital universal software radio peripheral (USRP). The signal-to-noise ratio (SNR) of the output vibration signal is greatly enhanced. A spectral subtraction method is also utilized to improve the SNR of the demodulated vibration signal. The acceleration of the vibration signal is obtained after second order differential of the time domain vibration signal. By simply changing the position of window function of short-time Fourier transform, a real-time vibration frequency and acceleration sensing system is achieved. The measurement results demonstrated a minimum detectable acceleration of 0.03 g at vibration frequency of 1.0 Hz by the designed sensing system. It also has a simple structure, high signal-to-noise ratio and stability.

Demodulation of DBR Fiber Laser Sensors With Speckle Patterns

Demodulation of DBR Fiber Laser Sensors With Speckle Patterns

Liquid-crystal-based fiber laser sensor for non-invasive gas detection.

This Letter reports a new optical fiber gas sensor for measuring breath acetone. The sensor is based on photonic bandgap (PBG) mode laser emission sensing technology using liquid crystal (LC), which is combined with silica fiber and chiral nematic liquid crystal (CNLC), thus providing an ultra-compact, fast-response and simple-to-produce sensing system with a fast response that can accurately and quantitatively determine the concentration of respiratory acetone within the normal oral temperature range (35-38°C). Since LCs are affected by temperature, we propose a method that eliminates the influence of the temperature to solve the problem of the temperature influence when measuring gas. The detection of acetone leads to splitting of the dual laser peaks, with a linear correlation of 0.99. The sensor has a limit of detection of 65 ppm for acetone vapor and thus is suitable for breath acetone detection in diabetic patients.

Noise canceled graphene-microcavity fiber laser sensor for ultrasensitive gas detection

Optical microcavities offer a promising platform for highly efficient light–matter interactions. Recently, the combination of microresonators and 2D materials in the nanoscale has further enriched the optoelectronics of microcavity geometries, spurring broad advances including lasers, nonlinear converters, modulators, and sensors. Here, we report the concept of compact dual-laser cogeneration in a graphene-microcavity fiber, which offers a way to cancel the optical common mode noises. Driven by a single 980 nm pump, orthogonally polarized laser lines are generated in a pair of degeneracy breaking modes. The two laser lines produce a heterodyne beat note at 118.96 MHz, with frequency noise down to 200 Hz2/Hz at 1 MHz offset, demonstrating a linewidth of 930 Hz in vacuum. This compact device enables on-line and label-free NH3 gas detection with high resolution, realizing a detection limit on a single pmol/L level, and a capability to quantitatively trace gas–graphene interactions. Such a combination of graphene optoelectronics and microcavity photonics demonstrates a novel physical paradigm for microlaser control and offers a new scheme for in situ chemical sensing.

A micrometric deflection fiber laser sensor controlled by polarized light pumping

This work presents a study of a deflection laser sensor using a pump light source with different polarization states and shows that controlling the polarization state of the pump source can achieve better control in the tuning of an erbium-doped fiber laser. Laser tuning uses a selective wavelength filter manufactured using a thin core fiber section between two single-mode fibers, while the deflection is applied using an angular mechanism. In addition, the sensor was analyzed according to the wavelength shift of the laser emission as a function of the angular micrometric deflection, and a sensitivity of −33.01 pm µrad−1 was obtained in a dynamic range from 0 to 89.3 µrad with an adjustment parameter R 2 = 0.993 61. We achieved dual-wavelength tuning with gradual shifting and single-wavelength tuning from 1531.5 nm to 1547.7 nm. This sensor exhibits potential applications in the bionic and robotic detection fields owing to its high sensitivity, good linearity, simple fabrication, and low cost.

Measurement of the Acoustic Relaxation Absorption Spectrum of CO2 Using a Distributed Bragg Reflector Fiber Laser

Reconstruction of the acoustic relaxation absorption curve is a powerful approach to ultrasonic gas sensing, but it requires knowledge of a series of ultrasonic absorptions at various frequencies around the effective relaxation frequency. An ultrasonic transducer is the most widely deployed sensor for ultrasonic wave propagation measurement and works only at a fixed frequency or in a specific environment like water, so a large number of ultrasonic transducers operating at various frequencies are required to recover an acoustic absorption curve with a relative large bandwidth, which cannot suit large-scale practical applications. This paper proposes a wideband ultrasonic sensor using a distributed Bragg reflector (DBR) fiber laser for gas concentration detection through acoustic relaxation absorption curve reconstruction. With a relative wide and flat frequency response, the DBR fiber laser sensor measures and restores a full acoustic relaxation absorption spectrum of CO2 using a decompression gas chamber between 0.1 and 1 atm to accommodate the main molecular relaxation processes, and interrogates with a non-equilibrium Mach-Zehnder interferometer (NE-MZI) to gain a sound pressure sensitivity of −45.4 dB. The measurement error of the acoustic relaxation absorption spectrum is less than 1.32%.

Fiber Laser Sensor Configurations for Refractive Index, Temperature and Strain: A Review

Fiber laser sensors have been present for almost four decades as versatile sensing devices with a simple demodulation process, high sensitivity, and competitive resolution. This work discusses the most representative fiber laser sensor configurations employed for detecting critical parameters such as temperature, refractive index, and strain. However, essential information about other interesting parameters that have been measured is considered in this manuscript. Concurrently, the sensing elements and principle operation are described. Furthermore, these configurations are analyzed in terms of their principle of operation, sensitivity, gain medium, and wavelength operation range. According to the literature reviewed, fiber laser sensors offer the possibility of new interrogation techniques and simultaneous, independent detection. Considering interferometric fiber sensors, the fiber laser sensors offer high brightness, good output power, and high resolution. As a result, it is demonstrated that fiber laser sensors are a robust alternative for multiple sensing applications.

Multiplexed optical fiber cell temperature sensing system with high sensitivity and accuracy.

A multiplexed fiber laser sensing system for cell temperature is proposed. To the best of the authors' knowledge, this is the first multilongitudinal mode (MLM) optical fiber laser sensor array designed for cell temperature sensing. A two-channel cell temperature sensing system with high sensitivity and real-time sensing capability is achieved. The temperature change of human hepatoellular carcinomas (HepG2) cells under the influence of exogenous chemical aflatoxin B1 (AFB1) can be monitored in real time. A fiber laser cavity consists of a pair of fiber Bragg gratings (FBGs) with matched central wavelengths and a piece of erbium-doped fiber (EDF). The static FBG is utilized for design of fiber laser cavity and laser modes selection. In comparison, the sensing FBG is used for cell temperature sensing. The sensing FBG has a length of 10mm and a diameter of . Beat frequency signals (BFS) are generated by MLM lasers after optical-to-electrical conversion at a photodetector. Frequency change of a BFS is closely related to the reflected wavelength change of the sensing FBG. Through frequency division multiplexing, two fiber laser cavities are designed in the sensing system for two-channel temperature sensing. Frequency shift of a BFS that represents temperature change of cells can be automatically recorded in seconds. A two-channel cell temperature sensing system is designed with high sensitivities of 101.62 and , respectively. The temperature change of HepG2 cells under the influence of exogenous chemical AFB1 is monitored in real time. The proposed system has the advantages of simple structure, high sensitivity, and two-channel sensing capability. Our study provides a simple and effective method to design a fiber laser sensor system without complex demodulation techniques and expensive optical components.

Refractive Index Fiber Laser Sensor by Using a Fiber Ball Lens Interferometer with Adjustable Free Spectral Range

In this work, a fiber laser refractometer based on a fiber ball lens (FBL) interferometer is proposed. The linear cavity erbium-doped fiber laser uses an FBL structure acting as a spectral filter and sensing element for determining the RI of a liquid medium surrounding the fiber. The optical interrogation of the sensor is the wavelength displacement of the generated laser line as a function of the RI variations. For the proposed FBL interferometric filter, the free spectral range of its wavelength-modulated reflection spectrum is adjusted to maximum in order to obtain RI measurements in a range of 1.3939 to 1.4237 RIU, from laser wavelength displacements in a range from 1532.72 to 1565.76 nm. The obtained results show that the wavelength of the generated laser line is a linear function of the RI variations on the medium surrounding the FBL with a sensitivity of 1130.28 nm/RIU. The reliability of the proposed fiber laser RI sensor is analytically and experimentally investigated.

Mode-Locked Fiber Laser Sensors with Orthogonally Polarized Pulses Circulating in the Cavity

Intracavity phase interferometry is a powerful phase sensing technique using two correlated, counter-propagating frequency combs (pulse trains) in mode-locked lasers. Generating dual frequency combs of the same repetition rate in fiber lasers is a new field with hitherto unanticipated challenges. The large intensity in the fiber core, coupled with the nonlinear index of glass, result in a cumulative nonlinear index on axis that dwarfs the signal to be measured. The large saturable gain changes in an unpredictable way the repetition rate of the laser impeding the creation of frequency combs with identical repetition rate. The huge amount of phase coupling between pulses crossing at the saturable absorber eliminates the small signal response (deadband). Although there have been prior observation of gyroscopic response in mode-locked ring lasers, to our knowledge this is the first time that orthogonally polarized pulses were used to successfully eliminate the deadband and obtain a beat note.

High-resolution strain fiber laser-sensor based on core-offset mach-zehnder interferometer

This paper presents an axial strain laser sensing setup based on a core-offset Mach-Zehnder interferometer (MZI). The core-offset MZI was implemented by fusion splicing of three segments of single mode fiber and was used as wavelength selective filter and sensing head. The experimental results show that in the strain range from 0 to 333.333 με, the laser wavelength emission shifts linearly from 1554 to 1557 nm, achieving a strain sensitivity of 5.2332 pm µε−1 and an R 2 value of 0. 9988. The laser emission has a linewidth of 20 pm and a single-mode suppression ratio of 45 dB. Furthermore, the fiber laser offers output power stability at room temperature, compactness, and robustness.

Wearable Optical Fiber Beat Frequency Digital Sensing System for Real-Time Non-Invasive Multiple Human Physiological Parameters Monitoring

An optical fiber beat frequency sensing system (BFSS) for multiple human physiological parameters monitoring is proposed. To the best of the authors' knowledge, this is the first BFSS ever reported for multiple human physiological parameters monitoring. By utilizing both fiber Bragg grating (FBG) and fiber laser sensor, not only a low frequency vibration detection with the lowest detectable frequency of 0.25 Hz can be achieved for respiration, heartbeat and pulse signals monitoring, but also human body temperature can be monitored at the same time. Two kinds of beat frequency signals (BFS) are generated in the sensing systems including both polarization laser modes' beat frequency (PMBF) signals and longitudinal mode beat frequency (LMBF) signals. The PMBF signal is utilized for respiration, heartbeat and pulse signals monitoring. Variational mode decomposition (VMD) algorithm is utilized to decompose the monitored time-frequency PMBF signals into single-component respiration, heartbeat and pulse signals. The central frequencies of those signals are obtained by fast Fourier transform (FFT). The LMBF signal is utilized for human body temperature sensing. Measurement results demonstrate that the wearable optical fiber beat frequency digital monitoring system has a simple structure, high signal-to-noise ratio (SNR), stability, accuracy and muti-parameters sensing capability including respiration, heartbeat, pulse and human body temperature without mutual interference.

Three-Wavelength Fiber Laser Sensor With Miniaturization, Integration for the Simultaneous Measurement of Underwater pH, Salinity, Temperature, and Axial Strain

Three-Wavelength Fiber Laser Sensor With Miniaturization, Integration for the Simultaneous Measurement of Underwater pH, Salinity, Temperature, and Axial Strain

Strain and curvature optical fiber laser sensor based on an accurate RI-regulated FMF with high modal power balance

In this paper, a ring fiber laser sensor based on a three layered-core few modes fiber (TL-FMF) is proposed. The home-made TL-FMF is spliced with two pieces of single mode fiber (SMF) at both sides as the sensing and filtering component. In the TL-FMF, an intermediate with higher refractive index (RI) is sandwiched between a central dip and a sub-high RI layer. Due to the special RI, the TL-FMF has an equidistant modal effective RI difference and a balanced modal power of different modes, enabling a highly uniform interference spectrum. Then applying the TL-FMF in proposed ring fiber laser sensor, the sensing experimental results show that its sensitivities in strain and curvature are −2.78 pm/με and −6.17 nm/m−1, respectively, and shows an excellent characteristic of temperature insensitivity. This fiber laser sensor implements the dual-parameter measurement with anti-cross sensitivity, which offers a promising candidate in fiber fabrication monitoring, deformation measurement and bending detection.

Simultaneous measurement of vibration and temperature based on FBG and DBR fiber laser beat frequency digital sensing system

A fiber Bragg grating (FBG) and distributed Bragg reflection (DBR) fiber laser sensor combined digital sensing system for both vibration and temperature sensing is proposed. To the best of the authors’ knowledge, this is the first FBG and DBR fiber laser combined dual parameters digital sensing system ever reported. By utilizing both FBG and DBR fiber laser sensor, not only a low frequency vibration detection as low as 0.25 Hz can be achieved, but also temperature and vibration dual parameters sensing can be achieved. External vibration is applied on the FBG which is part of the DBR fiber sensor. The wavelength change of DBR fiber laser sensor’s polarization laser modes is controlled by the FBG. Frequency change of polarization laser modes’ beat frequency (PMBF) signal is closely related to the reflected wavelength change of the sensing FBG. Variational mode decomposition (VMD) algorithm is utilized to denoise the monitored time–frequency signal of PMBF and the denoised signal is fast Fourier transformed (FFT) to get the corresponding vibration frequency. By utilizing this method, extremely low frequency vibration signal can be accurately demodulated. Beat frequency signals (BFS) of multi-longitudinal mode lasers which are generated in the DBR fiber laser sensor are utilized for temperature sensing. Measurement results demonstrate that the dual parameters digital sensing system has an excellent low frequency vibration-sensing capability, simple structure, high SNR, stability and accurate dual parameters sensing without mutual interference.

Smart composite using fibre optic sensors for fluid flow characterization and temperature measurement

The paper presents the results obtained in simulation of how air flow type over a wing surface, laminar or turbid, is detected using a Distributed Feedback Fibre Laser (DFB-FL) sensor or a Long Period Grating Fibre Sensor (LPGFS). A comparison of the two sensors is made. The air flow type over a wing surface is important for improving the “green flight” to a large as possible extent. The “green flight” with a reduced fuel consumption is assured by laminar air flow. The DFB-FL or LPGFS constitutes the feedback loop of the aircraft automatization having the optimisation of wing “attack angle” as a main parameter. The DFB-FL or LPGFS can be used for simultaneous system temperature measurements. The simulation results are compared with experimental ones and a good agreement between the two kinds of data being observed.

Highly discriminative simultaneous measurement of level, refractive index and temperature of liquid by dual-wavelength fiber ring-cavity laser sensor

In this paper, a novel dual-wavelength fiber laser sensor is proposed and completed by the parallel configuration of modified fiber Bragg grating and modal interferometer. The stable lasing emissions are realized and the comprehensive tests are performed in terms of level, refractive index and temperature of liquid. By the demodulation of joint wavelength and intensity matrix, high-discriminative simultaneous measurement is achieved, and the obtained sensitivities are 19.88 pm/°C, 159.32 dB/RIU and 568 pm/mm, respectively, with the errors below 2.52 %. Additionally, the dynamic field tests are performed, and the limits of detection of 0.15 mm, 0.42°C and 9 × 10-4 RIU are experimentally verified.