Fiber Ring Laser Sensor Research Articles

High-resolution temperature fiber ring laser sensor based on relative intensity noise measurement

High-resolution temperature fiber ring laser sensor based on relative intensity noise measurement

Fiber Ring Laser Sensor Based on Micro-Nano Fiber Interferometer and Highly Sensitive Detection of Gadolinium Nitrate

Fiber Ring Laser Sensor Based on Micro-Nano Fiber Interferometer and Highly Sensitive Detection of Gadolinium Nitrate

Temperature measurement with error suppression based on dual-wavelength fiber ring laser sensor

The sensors based on intracavity intensity modulation of fiber ring laser (FRL) have shown excellent performance in sensing resolution and detection limit, but suffer from large measurement errors. The measurement errors mainly result from the power fluctuation of pump source and environmental interference. Therefore, the methods of error suppression are of great significance for FRL sensors. In this paper, a temperature measurement method with error suppression is performed by a dual-wavelength FRL with an intracavity Sagnac interferometer. The sensing principle of single- and dual-wavelength FRL sensors have been analyzed. By the sensing manner of intensity difference of two excited wavelengths, the measurement error has been decreased from 0.443% to 0.066% compared with the single-wavelength configuration. The temperature sensitivity and measurement stability have been further discussed. This method can be extended to similar FRL sensors to suppress measurement errors.

A Fiber Ring Laser Sensor with a Side Polished Evanescent Enhanced Fiber for Highly Sensitive Temperature Measurement.

We demonstrate a highly sensitive and practical fiber-based temperature sensor system. The sensor is constructed based on a fiber ring laser (FRL) as well as a side-polished fiber filled with isopropanol. The laser cavity of the sensing part fiber is polished by the wheel fiber polishing system with residual thickness (RT) is selected to detect the temperature in the FRL. Thanks to the high thermo-optic coefficient of isopropanol, the sensitivity of the proposed temperature sensor could be effectively improved by filling isopropanol in the cost-less side polished single mode fiber. Refractive index (RI) of isopropanol changes with the surrounding temperature variation allowing high-sensitivity temperature sensing. Experimental results demonstrate that the side polished fiber can efficiently excite high-order cladding modes which enhance the modular interference increase the interaction between the evanescent wave and the isopropanol. Besides, the results show that the sensitivity can be as high as 2 nm/°C in the temperature range of 25–35 °C.

Temperature Sensor Based on Fiber Ring Laser With Cascaded Fiber Optic Sagnac Interferometers

A new temperature fiber ring laser (FRL) sensor based on a cascaded Sagnac loops fiber structure is proposed and experimentally demonstrated. The optical FRL sensor consists of cascaded Sagnac loops by inserting two polarization-maintaining optical fibers (PMF) with slightly different lengths. PMF with length of 56 cm and 75 cm are used in Sagnac loops as a filter and sensing unit in laser cavity. The working principle of the sensor is based on the phase shift (θ) caused by birefringence between two principal polarization modes and enhance the sensitivity by constructing a Vernier-scale. In an appropriate temperature range (25 °C - 31 °C), the detection sensitivity of FRL sensor based on a cascaded Sagnac structure is significantly higher than other FRL sensors. Thanks to the laser sensing system, the sensitivity can be modulated by changing the free spectral range (FSR). The experimental results show that the temperature sensitivity of the cascade Sagnac structure sensor is - 4.031 nm / °C, which is five times higher than that of FRL sensor base on the single Sagnac structure.

Strain- and Temperature-Sensing Characteristics of Fiber Ring Laser Sensor With Cascaded Fabry–Perot Interferometer and FBG

The strain- and temperature-sensing characteristics of fiber ring laser (FRL) sensors are studied comprehensively. The reflected sensing head, made up of spheroidal Fabry–Perot interferometer (FPI) concatenated with fiber Bragg grating (FBG), is inserted in the cavity of FRL acting as the laser intensity modulator and wavelength selector. The laser intensity is sensitive to temperature change while insensitive to strain, making the dual-parameter demodulation realizable without multivariate matrix by detecting the laser wavelength shift and the laser intensity variation, for the first time in our best knowledge. The comparable sensitivities of 1 pm/ $\mu \varepsilon $ and 24.9 pm/°C are detected in experiment for strain and temperature, respectively, with low detection limit (DL) of 0.87 $\mu \varepsilon $ and 0.035 °C, high $Q$ factor of 1140 and 7.07 $\times \,\,10^{5}$ . The high intensity and narrow linewidth of the sensor make it potentially great for application in long-distance sensing systems.

Curvature sensor based on fiber ring laser with Sagnac loop

Abstract In this paper, a curvature sensor based on fiber ring laser with Sagnac loop is proposed and experimentally demonstrated. The Sagnac loop is inserted into a fiber ring laser used as the sensing element and the filter. The intracavity sensing is induced in the fiber laser with the filtering characteristic of the Sagnac loop modulated by the curvature. The intracavity sensing system is used to narrow the corresponding 3-dB band-width and enhance the resolution of the curvature sensor. With the intracavity intensity modulation method, the output power of the fiber ring laser sensor will change with an increase in curvature. The curvature range from 0 m−1 to 5.6865 m−1 has been measured and the highest curvature resolution of 6 × 10−8 m−1 is obtained. Based on the intracavity sensing system, the curvature resolution level has been enhanced from 10−4 m−1 to 10−8 m−1. The stability and measurement errors of the system are also studied and analyzed.

Simultaneous Measurement of Temperature and Relative Humidity Using a Dual-Wavelength Erbium-Doped Fiber Ring Laser Sensor

A fiber ring laser sensor setup utilizing fiber Bragg gratings (FBGs) for simultaneous measurement of ambient temperature and relative humidity (RH) is presented. Two FBGs are incorporated as tunable filters for a dual-wavelength laser emission, where one FBG was coated with polyimide (PI) in order to achieve sensitivity to RH changes, while the other bare FBG was used for temperature sensing. An increase in RH would induce a strain on the grating, which results in a variation in the resonance wavelength of the PI-coated FBG. This causes a shift in the laser emission wavelength. Being insensitive to RH changes, the bare FBG was employed to measure temperature. The dual-wavelength fiber ring laser sensor created, and thus allows to determine simultaneous measurement of RH and temperature. The RH sensitivities observed by the PI-coated FBG to RH and temperature are 3.6 pm/%RH and 12.15 pm/°C. The temperature sensitivity of the bare FBG was observed to be 9.6 pm/°C. The main advantage of the proposed setup is an optical signal to noise ratio (OSNR) higher than 55 db 3 dB bandwidth less than 0.02 nm, which points out efficient capabilities for both precise sensing and remote detection applications.

Highly sensitive dual-wavelength fiber ring laser sensor for the low concentration gas detection

A highly sensitive low concentration gas sensor based on dual-wavelength Erbium-doped fiber ring laser (EDFRL) is designed and demonstrated. The dual-wavelength lasing output is introduced by a tunable Fabry-Perot (F-P) filter and a fiber Bragg grating (FBG) due to the mode competition as they both share a same EDF gain medium. One wavelength at 1530.37 nm serving as the sensing element is inserted by a hollow core photonic crystal fiber (HCPCF) gas cell which can bring in much more power change when the cavity loss slightly varies while the other wavelength at 1532.38 nm acting as a reference. Experimental results show that the sensor can achieve a good linear response (R2 = 0.9864) to acetylene concentration variation and a minimum detection limit (MDL) of 10.42 ppmV at 20 s response time, which is the lowest to our best knowledge and improving 6.44 times than that of single-wavelength EDFRL based. Moreover, the absolute detected error induced by the power fluctuation (< 0.1 dB) is less than 1.78% over more than 300 s of observation.

Detection of dynamic signals from multiplexed SOA-based fiber-ring laser sensors.

A simple matched filter demodulation configuration for detecting dynamic signals from multiplexed semiconductor optical amplifier (SOA)-based fiber-ring laser sensors is investigated theoretically and experimentally. It is feasible for multiple points fiber Bragg grating sensing because the inhomogeneous broadening of the SOA source makes it possible to produce multimode lasing without mode competition. The best operating points for matched filter demodulation and the wavelength demodulation range are investigated. In the experiment, the simultaneous dual-channel detection of dynamic strains at high frequencies is presented by using piezoelectric transducers. An example application for simultaneous two-channel ultrasonic detection has been successfully demonstrated. The detection system design is simple, low cost, and high precision, making it attractive for applications in structure health monitoring.

Fiber ring laser based on SMF–TCF–SMF structure for strain and refractive index sensing

An erbium-doped fiber ring laser with embedded Mach–Zehnder interferometer (MZI) is constructed and experimentally demonstrated for strain and refractive index (RI) measurement. The MZI consists of a segment of thin-core fiber sandwiched between two single-mode fibers and acts as both the sensing component as well as a bandpass filter to select the lasing wavelength. The strain sensitivity of ∼-0.97 pm/μϵ and RI sensitivity of ∼44.88 nm/RIU are obtained in the range of 0 to 1750 μϵ and 1.3300 to 1.3537, respectively. The high-optical signal-to-noise ratio of >50 dB and narrow 3-dB bandwidth of <0.11 nm obtained indicate that the fiber ring laser sensor is promising for high-precision strain and RI measurement.

Fiber ring laser sensor based on Fabry–Perot cavity interferometer for temperature sensing

A ring laser temperature sensor based on a novel reflective fiber Fabry–Perot (F–P) interferometer air cavity is proposed and experimentally demonstrated. The reflective F–P air cavity, which consists of a segment of glass capillary inserted between two single–mode fibers, is utilized as a sensing element as well as as a filter in the fiber ring cavity. As temperature increases, the reflection spectra of the F–P sensor move towards the longer wavelength, and then cause lasing wavelength shifts. By monitoring the variation of lasing wavelength, we obtain a temperature sensor system with a high temperature sensitivity of 0.249 nm °C−1, a narrow 3 dB bandwidth of 0.1514 nm, and a high signal-to-noise ratio of 52 dB. Moreover, it is convenient to fabricate the sensor head, and the stability is very good, giving it a wide range of applications.

Erbium-doped fiber ring laser sensor for high temperature measurements based on a regenerated fiber Bragg grating

ABSTRACTThis article presents an erbium-doped fiber ring laser for high temperature measurement with high accuracy. The proposed laser sensor employs a regenerated fiber Bragg grating (RFBG) as a sensor element. Through thermal treatments, the RFBG with enhanced thermal resistance was obtained. The laser emission optical spectrum presents good performance with a high optical signal-to-noise ratio of 58dB. Experimental results demonstrate a wavelength sensitivity to the temperature is 15.5 pm/ºC with the temperature range from 300ºC to 900ºC, and the correlation coefficient is 0.999. The results prove it is able to provide potential applications in high temperature measurement.

Real-Time Interrogation Technology for a Large-Scale Fiber-Ring Laser Sensor Array

A real-time interrogation technology for a large-scale fiber laser sensor array is proposed and experimentally investigated by employing a hybrid topological structure based on the wavelength- and frequency-division multiplexing techniques. In this system, a 2-D n × m sensor array is established by using a 1 × n coupler and n 1 × m couplers. All sensors are divided into n units by the 1 × n coupler. In each unit, there are m fiber-ring laser sensors with approximately the same wavelength and different beat frequencies due to different laser cavity lengths. Meanwhile, different units are characteristic of different operating wavelengths by splicing different fiber Bragg grating (FBG) as a reflector. Therefore, each sensor has a unique wavelength- and frequency-encoded information. All sensors can be interrogated by the combination of wavelength and frequency multiplexing technology. In the paper, a 4 × 4 sensor array is set up experimentally to verify the interrogation ability, and the sensing information of the strain and temperature has been successfully extracted. The experimental results show that the proposed interrogation system has the ability of real-time monitoring for a large-scale fiber laser sensor array.

High-sensitivity sucrose erbium-doped fiber ring laser sensor

We investigate a high-sensitivity sucrose sensor based on a standard erbium-doped fiber ring laser incorporating a coreless fiber (CF). A single-mode-coreless-single mode (SCS) structure with a very low insertion loss has been constructed. The SCS fiber structure performed dual function as an intracavity fiber filter and/or a sensing element. The gain medium (erbium-doped fiber) is pumped by a 975-nm wavelength fiber coupled diode laser. Laser emission around 1537 nm with −2 dBm peak output power is obtained when a CF in SCS structure has a diameter of 125 μm. The 3-dB line-width of the laser is <0.14 nm, which is beneficial to high precision sensing. The sucrose concentration varied from 0% to 60%, and the relationship between the lasing wavelength and the sucrose concentration exhibited linear behavior (R2=0.996), with sensitivity of 0.16 nm/% was obtained. To improve the measurement sensitivity, the CF is etched by hydrofluoric acid. The splice joint of etched CF with SMF is a taper, which improves its sensitivity to sucrose changes. An average sensitivity of 0.57 nm/% and a high signal-to-noise ratio of 50 dB make the proposed sensor suitable for potential applications.

In-Fiber Mach–Zehnder Interferometer Based on Up-Taper Fiber Structure With Er3+ Doped Fiber Ring Laser

A robust optical fiber modal Mach–Zehnder (MZ) interferometer is proposed, which is embedded in a fiber ring laser system as a tunable filter to improve the detection limit (DL) due to its narrow full width half maximum (FWHM) and high signal-to-noise radio (SNR). The sensing element is composed of two cascaded up-taper joints fabricated by shoving fusion. After filtering, the laser spectrum possesses the sensing characteristics that the interferometer possessed. Temperature and refractive index (RI) are investigated as measurands in experiments and the response sensitivities are 92.1 pm/°C and 44.8 nm/RIU, respectively. Accordingly, the DLs for these two measurands are calculated as 0.19 °C and $3.86 \times {10^{ - 4}}$ (RIU). Moreover, the axis strain response is demonstrated to be much lower than many modal interferometers even under the help of fiber ring laser. Thus, the property contributes to the resistance of the outer force and disturbance. Compared to the simple sensing device, the proposed fiber ring laser sensor significantly improves the DL, which is one of the most crucial parameters. It is the first time to combine the fiber ring laser device with the up-taper MZ interferometer as far as we known. It is a feasible balanced way to improve the sensing capability without the expense of mechanical strength of sensing element.

Fiber Ring Cavity Laser Based on Modal Interference for Curvature Sensing

Fiber ring laser sensor for curvature measurement based on a single-mode–no-core–single-mode structure is proposed and experimentally demonstrated. Compared with the conventional curvature system, the proposed laser sensor system has a high optical signal-to-noise ratio and a narrow 3-dB bandwidth, which enables the system to monitor the variation of micro-bending more distinctly. In the experiment, changes in peak wavelength show a blue shift when the curvature varies from 0.1225 to 0.4062 $\text{m}^{-1}$ . The sensitivity of the curvature is about −22.33 nm/ $\text{m}^{-1}$ in the range of 0.2121–0.3463 $\text{m}^{-1}$ . The response to the temperature of the fiber laser sensor is also discussed, where temperature sensitivity of 9.23 pm/°C within the range from 10 °C to 100 °C is obtained.

Fiber ring laser sensor based on hollow-core photonic crystal fiber

We report an erbium-doped fiber ring laser intra-cavity sensor. Hollow-core photonic crystal fiber (HC-PCF) used as the gas absorption chamber is introduced into the laser cavity. When the HC-PCF is filled with gas, its absorption attenuation changes the cavity loss and the laser output. We use a modular NI PXI platform equipped with a programmable voltage and current source and a LabVIEW program to generate driving voltage for the tunable optical filter (TOF) to ensure high precision. The relationship between the concentrations of acetylene, coupling ratios, pump power and output power is theoretically and experimentally investigated. Different output spectra are measured by the optical spectral analyzer (OSA). A minimum detectable acetylene concentration (MDAC) of 5.4ppm has been experimentally achieved.

Study on a four-channel multi-longitudinal mode fiber-ring laser sensor array based on frequency division multiplexing

Combined with beat frequency demodulation technology, a four-channel multi-longitudinal mode fiber-ring laser (MMFRL) sensor array base on frequency division multiplexing (FDM) is proposed and experimentally investigated. The MMFRL sensor is formed using a fiber Bragg grating, a 3dB coupler and a section of erbium-doped fiber. Because the different cavity lengths of the fiber laser have different frequency intervals, the beat signal for each sensor is addressed using FDM technology. The proposed sensor array is experimentally validated. The responses of the beat frequencies shift to the strain are −0.584kHz/με@782.680MHz and −0.890kHz/με@1185.880MHz, which are in good agreement with the theoretical expectations. By using multiplexing technology, the cost of each sensor was greatly decreased. This is a very promising technique for use in large scale monitoring fields.

Multiplexed fiber-ring laser sensors for ultrasonic detection

We propose and demonstrate a multiplexing method for ultrasonic sensors based on fiber Bragg gratings (FBGs) that are included inside the laser cavity of a fiber-ring laser. The multiplexing is achieved using add-drop filters to route the light signals, according to their wavelengths, into different optical paths, each of which contains a separate span of erbium-doped fiber (EDF) as the gain medium. Because a specific span of EDF only addresses a single wavelength channel, mode completion is avoided and the FBG ultrasonic sensors can be simultaneously demodulated. The proposed method is experimentally demonstrated using a two-channel system with two sensing FBGs in a single span of fiber.