Fiber Sagnac Interferometer Research Articles

Vernier effect assisted sucrose sensor based on a cascaded Sagnac interferometer with no-core fiber.

We propose a sucrose concentration sensor by utilizing a fiber Sagnac interferometer with no-core fiber (SI-NCF) based on the Vernier effect. The Vernier effect is realized by introducing a single Sagnac interferometer (SI) with a similar free spectral range of SI-NCF. When the NCF is exposed to the external sucrose solution, the cladding state of NCF is changed, which induces the wavelength shift of the SI-NCF. The measured sucrose concentration sensitivity of a single SI-NCF is 2.97 nm/M, and the sensitivity can be improved to -13.84 nm/M with the assistance of the Vernier effect, which is 4.66 times of the single SI-NCF. The sensor has the advantages of high sensitivity, easy-fabrication and cost-effectiveness which can be applied in the field of the food industry, chemistry and agriculture.

Highly sensitive temperature and strain sensor based on fiber Sagnac interferometer with Vernier effect

A novel temperature and strain sensor based on fiber Sagnac interferometer (FSI) with Vernier effect is proposed and demonstrated experimentally. The FSI fabricated by fusion splicing a segment of thin polarization maintaining fiber (TPMF) with a coupler works as sensing. The Vernier effect is generated by cascading a polarization mode interferometer (PMI). The PMI is fabricated by fusion splicing a polarization maintaining fiber (PMF) with a polarizer. The suitable free spectral range (FSR) of the sensor is fabricated based on numerical simulation. The experimental results indicate that with the Vernier effect, the temperature sensitivity can be improved from −1.924 nm/°C to −32.830 nm/°C and the strain sensitivity can be improved from 25.9 pm/με to 407.32 pm/με. The measured amplification factors are about 17 and 16. The good performance of the FSI with the Vernier effect provides a new option in the temperature and strain sensing fields.

High-sensitivity optical fiber temperature sensor of cascaded FSI and MZI based on Vernier effect

A high-sensitivity optical fiber temperature sensor based on the Vernier effect of cascaded fiber Sagnac interferometer (FSI) and Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The FSI is composed of a 3 dB four-port coupler and a section of polarization maintaining fiber, which has high sensitivity and good stability as the sensing part. As the filtering part, MZI is made up of two three-port couplers by controlling the length of the two arms. The free spectral range (FSR) of these two interferometers is similar but not equal, so the cascade system can effectively amplify the temperature sensing sensitivity based on the vernier effect. The experimental results show that the temperature sensitivity of a single FSI is only −1.68 nm/°C, and the cascade system can amplify it to 14.30 nm/°C with a gain coefficient of 8.51, which is consistent with the theoretical results.

Ultrasensitive temperature sensor with Vernier-effect improved fiber Michelson interferometer.

A novel fiber Michelson interferometer (FMI) based on parallel dual polarization maintaining fiber Sagnac interferometers (PMF-SIs) is proposed and experimentally demonstrated for temperature sensing. The free spectral range (FSR) difference of dual PMF-SIs determines the FSR of envelope and sensitivity of the sensor. The temperature sensitivity of parallel dual PMF-SIs is greatly enhanced by the Vernier effect. Experimental results show that the temperature sensitivity of the proposed sensor is improved from -1.646 nm/°C (single PMF-SI) to 78.984 nm/°C (parallel dual PMF-SIs), with a magnification factor of 47.99, and the temperature resolution is improved from ±0.03037°C to ±0.00063°C by optimizing the FSR difference between the two PMF-SIs. Our proposed ultrasensitive temperature sensor is with easy fabrication, low cost and simple configuration which can be implemented for various real applications that need high precision temperature measurement.

Theoretical analysis of a microstructured fiber temperature sensor based on a Sagnac interferometer with a wide temperature measurement range

A temperature sensor with a wide measurement range and high sensitivity is proposed and analyzed. It is based on a microstructured fiber (MSF) Sagnac interferometer. The air holes were filled with ethanol by a full filling method. Increase of the birefringence and the sensitivity of the proposed sensor can be achieved by moving the two air holes on the left and right sides of the core. For an MSF with air hole diameters D1 = 0.8 μm, D2 = 0.6 μm, and D3 = 0.4 μm, pitch Λ = 2 μm, and distance R = 8.2 μm, when the length of the MSF is 0.274 cm, the simulation results show that the sensitivity of the proposed sensor can reach 14.7 nm/°C in the temperature range from 15 to 75 °C. This means that the length and sensing range of the MSF have a great influence on the sensitivity of our designed MSF temperature sensor. Because of the advantages of simple structure, high sensitivity, and wide temperature measurement range, the proposed temperature sensor has great application prospects in environmental temperature measurement.

The improved denoising algorithm of acoustic sensor based on linear optical fiber Sagnac interferometer

Abstract This paper is devoted to the study of an acoustic sensor system based on linear fiber optic Sagnac interferometer. An improved threshold denoising algorithm combined with the wavelet theory is proposed. Furthermore, a hybrid scheme based on the improved algorithm with bandpass filter is explored, and experimental verification of theoretical investigation is accomplished as well. Taking the measured speech signals as examples, the Allan variance of the signals can be reduced, while the class spacing criterion can be increased. It is of great significance for promoting the application of the fiber optic acoustic sensor system.

High‐sensitive temperature sensor based on ethanol‐filled elliptical‐core side‐hole fiber Sagnac interferometer

AbstractThe birefringence properties of two types of side‐hole fibers have been numerically studied, based on which a Sagnac fiber interferometer employing ethanol‐filled side‐hole fibers is proposed and experimentally demonstrated for high‐sensitive temperature measurement. Thanks to highly temperature‐sensitive refractive index of ethanol infiltrated in the air holes of side‐hole fibers, high‐sensitive temperature measurement could be realized by monitoring fiber‐birefringence‐induced resonance wavelength shift of the fiber Sagnac interferometer in response to environmental temperature variation. Experimental results show that within a temperature range of 26°C to 54°C, there exists some critical temperature point around 40°C, on both sides of which the resonance dips exhibit inverse temperature‐dependent shift behaviors. A temperature sensitivity of 1.10 nm/°C is experimentally achieved for our proposed side‐hole fiber Sagnac interferometer.

Fiber curvature sensor based on concave‐heterotypic cascaded fiber Sagnac interferometer

AbstractA fiber optical curvature sensor comprising a concave‐heterotypic cascaded fiber structure built into Sagnac loop is demonstrated experimentally. A section of multimode fiber is sandwiched between the single mode fiber and polarization maintaining fiber in order to construct the concave‐heterotypic cascaded fiber structure. The concave structure presented is used to effectively excite guided modes. The spectra of the proposed bending sensor will shift toward long wavelength with curvature. The measured the curvature sensitivity of 11.6 nm/m−1 has been achieved. The proposed curvature sensor characterizes cost‐efficient, simple fabrication process and can be used for health monitoring in civil engineering.

Sensing characteristics of photonic crystal fiber Sagnac interferometer based on novel birefringence and Vernier effect

In this paper, the sensing characteristics of a photonic crystal fiber (PCF) Sagnac interferometer based on flat-phase birefringence, zero-group birefringence and the Vernier effect have been studied. The temperature-sensitive liquid is filled into the air holes of the PCF. We realize flat-phase birefringence, by which the sensitivity can reach 4.9 nm/°C and 3.5 nm/°C. We find a new phenomenon in that there are more interference fringes appearing near the zero-group-birefringence wavelength with the environment changing. Highly sensitive sensors with −19.9 nm/°C and 28.6 nm/°C are obtained. We also demonstrate that two cascaded Sagnac interferometers based on PCF can realize the Vernier effect. The sensitivities are 1 nm/°C (single Sagnac interferometer) and 10.4 nm/°C (cascaded Sagnac interferometers), and the sensitivity is improved by more than 10 times. The sensitivity is inversely proportional to the difference between free spectral range (FSR)1 and FSR2, and the highest sensitivity reaches 23.2 nm/°C (−58 500 nm/RIU, resolution: 3.419× 10−7 RIU) by optimizing the PCF length in Sagnac interferometer 2. The average sensitivity based on two cascaded PCF Sagnac interferometers is up to −309 957 nm/RIU and the resolution is 6.453× 10−8 RIU as the refractive index of the analyte varies from 1.33 to 1.331, which is very competitive in the field of chemical sensing.

Tunable and switchable triple-wavelength ytterbium-doped fiber ring laser based on Sagnac interferometer with a polarization-maintaining photonic crystal fiber

A tunable and switchable triple-wavelength ytterbium-doped fiber laser (YDFL) based on a polarization-maintaining photonic crystal fiber (PMPCF) Sagnac interferometer is proposed and experimentally demonstrated. Owing to the large inhomogeneity of gain profile and simple two-level system of ytterbium-doped fiber, a tunable triple-wavelength lasing output is achieved with a tuning range of 1.6 nm. At room temperature, the maximum wavelength shift and peak power fluctuation are less than 0.018 nm and 0.64 dB, respectively. Moreover, the output lasing can be switched to single-wavelength lasing or dual-wavelength lasing through adjusting polarization controller. A tunable single-wavelength lasing with the side-mode suppression ratio above 50 dB is achieved from the wavelength of 1034.276 nm to 1038.314 nm. Two kinds of tunable dual-wavelength lasing with the tuning range of 3.2 nm are obtained in our experiment. In addition, the temperature stability is discussed by constructing the YDFL with PMPCF and conventional polarization-maintaining fiber (PMF), respectively. Experimental results demonstrate that the measured temperature sensitivity for PMPCF-based YDFL is 0.014 nm/℃, which is five times lower than that for PMF-based YDFL.

Experimental realization of a reference-frame-independent decoy BB84 quantum key distribution based on Sagnac interferometer.

Quantum key distribution (QKD) can generate secure key bits between remote users employing the features of quantum physics. However, a shared reference frame is necessary for QKD systems in most scenarios. A reference-frame-independent (RFI) scheme can tolerate the reference frame drifting between legitimate remote users, which is significant in the operation of relative moving terminals such as satellites and aircraft. We design and experimentally demonstrate an RFI-BB84-QKD system by joint encoding with the polarization and orbital angular momentum states of the photons. We use self-compensating fiber Sagnac interferometers to perform high-speed polarization modulation, and q-plates to passively manipulate the rotation-invariant photon states, which makes the system feasible for high-speed operation using off-the-shelf components.

Highly Sensitive Torsion Sensor Based on Side-Hole-Fiber Sagnac Interferometer

A highly sensitive torsion sensor based on side-hole fiber (SHF) Sagnac interferometer is proposed and experimentally demonstrated in this paper. The theoretical analyses on sensing performances of the proposed interferometric sensor are in good accordance with their experimental measurement counterparts. Due to photo-elastic effect, the birefringence of SHF in the loop would vary with the torsional rate, giving rise to linear wavelength shift and sinusoidal power variation responses to torsion applied on the SHF. Based on the wavelength and intensity interrogations of transmission dips, the torsional sensitivities reach up to about 2.2 nm/(rad/m) and ±10 dB/(rad/m), respectively. Opposite wavelength shift responses for clockwise and counterclockwise torsion states equip the proposed sensor with good twisting direction distinguishability. Besides, the experimental results indicate that our proposed sensor has a low axial strain cross sensitivity of 4.3 pm/με. The side-hole-fiber-based interferometric torsion sensor possesses such desirable merits as high sensitivity, low axial strain cross sensitivity, good torsional direction distinguishability, and good mechanical robustness, ensuring its viability for practical use on torsion sensing occasions.

Refractive index sensor of a photonic crystal fiber Sagnac interferometer based on variable polarization states

Micron-sized holes distributed in the cross section of photonic crystal fibers allow the integration of the microfluidic analyte and fiber which makes it possible for rapid and effective chemical analysis. The innovation of this paper is that the polarization states of the fiber modes vary with the wavelength. The polarization directions of the two polarized modes are nearly 45 degrees with the horizontal direction at a certain wavelength, then the resonance wavelength will appear by a fiber Sagnac interferometer. The average sensitivity is up to −19040 nm/RIU as the refractive index of the microfluidic analyte varies from 1.33 to 1.37.

Research on temperature sensing characteristics with cascaded fiber Sagnac interferometer and fiber Fabry–Perot interferometer-based fiber laser

We have proposed and experimentally demonstrated a compact temperature sensor based on cascaded fiber Sagnac interferometer (FSI) and fiber Fabry–Perot interferometer (FFPI) with Vernier effect. The FSI is composed of a certain length of panda polarization-maintaining fiber and a 3-dB four-port coupler, whereas FFPI consists of two collimators and a wave plate. Both are used for temperature sensing, but where FSI is more sensitive to temperature than FFPI, the free spectral ranges of the two interferometers differ by 0.12 nm. The experimental results show that the temperature sensitivity is increased from −1.7 nm / ° C (single FSI) and 0.008 nm/°C (single FPI) to 10.28 nm/°C (cascade configuration), which is basically consistent with the theoretical analysis (10.82 nm/°C).

Selectively toluene-filled photonic crystal fiber Sagnac interferometer with high sensitivity for temperature sensing applications

Abstract In this paper, we theoretically and numerically investigate toluene-filled polarization maintaining photonic crystal fibers (PMPCFs) for temperature sensing application via Sagnac interferometer. We designed a PMPCF with a birefringence of 8.68 × 10−5, a relative birefringence sensitivity of 26% for 5 °C variation and sensitivity of −11 nm/°C around 25 °C. We study the effects of hole dimensions and fabrication imperfections on the performance of the proposed PMPCF and demonstrate that the PMPCF has a good toleration to any geometrical induced imperfections in the fabrication process of the fiber. Furthermore, we show that the spectral range of the sensor can be easily improved (to values larger than 137 nm) by decreasing the infiltration length of the PMPCF.

A comparative study and experimental observations of optical fiber sagnac interferometric based strain sensor by using different fibers

Abstract Designing of strain monitoring system is a vibrant topic for the researchers. Strain monitoring systems are required in various fields such as mechanics, aeronautics, metallurgy and health monitoring of complex structures etc. Researchers designed different strain monitoring systems based on requirements. In this paper, we have reported a comparative study of Optical Fiber Sagnac Interferometer (OFSI) based strain sensors using three different types of fiber, i.e Polarization Maintaining Fiber (PMF), Standard Photonic Crystal Fiber (PCF) and High Birefringence Photonic Crystal Fiber (Hi-Bi PCF). The transmission spectrums of the sensors were recorded using Optical Spectrum Analyzer (OSA). We have experimentally analyzed the response and sensitivity of the sensors at different applied strains. The experimental results show that the optical interferometric strain sensor using PMF is having highest sensitivity in comparison to other sensors.

Partial Discharge Ultrasound Detection Using the Sagnac Interferometer System.

Partial discharge detection is crucial for electrical cable safety evaluation. The ultrasonic signals frequently generated in the partial discharge process contains important characteristic information. However, traditional ultrasonic transducers are easily subject to strong electromagnetic interference in environments with high voltages and strong magnetic fields. In order to overcome this problem, an optical fiber Sagnac interferometer system is proposed for partial discharge ultrasound detection. Optical fiber sensing and time-frequency analysis of the ultrasonic signals excited by the piezoelectric ultrasonic transducer is realized for the first time. The effective frequency band of the Sagnac interferometer system was up to 175 kHz with the help of a designed 10 kV partial discharge simulator device. Using the cumulative histogram method, the characteristic ultrasonic frequency band of the partial discharges was between 28.9 kHz and 57.6 kHz for this optical fiber partial discharge detection system. This new ultrasound sensor can be used as an ideal ultrasonic source for the intrinsically safe detection of partial discharges in an explosive environment.

A high-sensitivity temperature sensor based on Sagnac interferometer employing photonic crystal fiber fully filled with ethanol

A high-sensitivity temperature sensor based on photonic crystal fiber Sagnac interferometer is proposed and studied. All holes of the PCF are filled with ethanol with capillarity. The cladding air holes are uniform arrangements. The two air holes around the core are removed to form new core modes with high birefringence. The sensitivities of the temperature can be up to −8.7657 and 16.8142 nm/ $$^{\circ }$$ C when temperature rises from 45 to 75 $$^{\circ }$$ C and the fiber length is 5.05 cm. And when temperature rises from 10 to 45 $$^{\circ }$$ C, the sensitivity can reach −7.848 and 16.655 nm/ $$^{\circ }$$ C with fiber length 2.11 cm. The performance of the selective-filled and the fully-filled PCF with temperature from 45 to 75 $$^{\circ }$$ C and fiber length 5.05 cm are analyzed and compared. The fully filling can better achieve PCF’s sensing performance. The simple structure and high sensitivities make the temperature sensor easy to achieve. The temperature sensor with high sensitivities and good linearity has great application value for environmental temperature detecting.

Sensitivity-enhanced temperature sensor by hybrid cascaded configuration of a Sagnac loop and a F-P cavity

A hybrid cascaded configuration consisting of a fiber Sagnac interferometer (FSI) and a Fabry-Perot interferometer (FPI) was proposed and experimentally demonstrated to enhance the temperature intensity by the Vernier-effect. The FSI, which consists of a certain length of Panda fiber, is for temperature sensing, while the FPI acts as a filter due to its temperature insensitivity. The two interferometers have almost the same free spectral range, with the spectral envelope of the cascaded sensor shifting much more than the single FSI. Experimental results show that the temperature sensitivity is enhanced from −1.4 nm/°C (single FSI) to −29.0 (cascaded configuration). The enhancement factor is 20.7, which is basically consistent with theoretical analysis (19.9).

Low-Drift Optoelectronic Oscillator Based on a Phase Modulator in a Sagnac Loop

A low-drift optoelectronic oscillator (OEO) is developed and experimentally shown. In the proposed OEO, a fiber Sagnac interferometer, including an optical phase modulator (PM) and a nonreciprocal bias unit, functions as an intrinsically drift-free intensity modulator. The phase noise of the proposed OEO is modeled in phase space, which is verified by experiments. Phase noise and frequency stability of the photonically generated microwave signals are measured. The single-sideband phase noise of the generated microwave signal is −106.6 dBc/Hz at 10-kHz offset from the 10.833-GHz carrier, with 120-fs rms timing jitter integrated from 1 kHz to 10 MHz. Frequency drift measurements show ±0.85-ppm maximum fractional frequency deviation over 35 h, mainly caused by drift of the fiber delay line.