Panda-type Polarization-maintaining Fiber Research Articles

High sensitivity I-beam shaped polarization related vector curvature sensor with optical intensity modulation

This paper presents an innovative I-beam optical sensor combining Panda-type polarization-maintaining fiber (PMF) and thin-width polarization-maintaining photonic crystal fiber (PM-PCF), crafted using precision machining techniques like tapering and axially offset splicing. The study explores the impact of structural parameters on the device's optical performance using polarization mode coupling theory and assesses its effectiveness in vector curvature sensing, focusing on intensity sensitivity. A novel dual-parameter differential demodulation technique is proposed, achieving accurate bending angle measurements (error < 2°) through wavelength and intensity-curvature sensitivities. The experimental results highlight the device's impressive maximum intensity-curvature response of 9.36 dB/m−1. With notable responsiveness, low cross-talk, and robust polarization stability, this device holds substantial promise in the realms of fiber lasers and optical communications, serving as an ideal polarization-based, mechanically tunable optical device. Furthermore, it introduces innovative concepts and offers technological support for precision instrument measurements and related fields.

Fiber laser with dual-channel and a selectable comb filter based on Vernier effect of parallel-connected two Mach–Zehnder interferometers

We propose and demonstrate the implementation and application of a new configuration of an all-fiber comb filter based on the Vernier effect produced by parallel-connected two in-line Mach–Zehnder interferometers (MZIs). Each in-line MZI was fabricated by fusion splicing a section of panda-type polarization maintaining fiber (PMF) with peanut-shaped tapers between two single-mode fibers. These two in-line MZIs, respectively, form reference and sensing interferometers, which are parallel-connected by two 3-dB optical fiber couplers to realize the Vernier effect. By incorporating the proposed comb-filter into the erbium-doped fiber laser cavity, two output channels at 1533.2 and 1558.2 nm have been achieved. Further, the combination of the parallel-connected two in-line MZIs and polarization controllers (PC1 and PC2) promotes the lasing in a switchable and selective way. To the best of the authors’ knowledge, this is the first demonstration of a comb filter that employs paralleled two peanut-shaped MZIs in PMF. The experimental results indicate that the proposed filter has the potential to be used in communication systems.

Measurement of the birefringence variation induced by dihydrogen diffusion into a polarization-maintaining fiber.

We report continuous measurements of the transmission spectrum of a fiber loop mirror interferometer composed of a Panda-type polarization-maintaining (PM) optical fiber during the diffusion of dihydrogen (H2) gas into the fiber. Birefringence variation is measured through the wavelength shift of the interferometer spectrum when the PM fiber is inserted into a gas chamber with H2 concentration from 1.5 to 3.5 vol.% at 75 bar and 70°C. The measurements correlated with simulation results of H2 diffusion into the fiber lead to a birefringence variation of -4.25 × 10-8 per mol m-3 of H2 concentration in the fiber, with a birefringence variation as low as -9.9×10-8 induced by 0.031 μmol m-1 of H2 dissolved in the single-mode silica fiber (for 1.5 vol.%). These results highlight a modification of the strain distribution in the PM fiber, induced by H2 diffusion, leading to a variation of the birefringence that could deteriorate the performances of fiber devices or improve H2 gas sensors.

Highly birefringent one-air-hole panda fiber.

This Letter proposes a highly birefringent one-air-hole panda fiber, which is fabricated by corroding a single stress zone of the traditional panda-type polarization-maintaining fiber (PMF). An additional geometric asymmetry is induced in the fiber to increase the birefringence effect and enhance the light-matter interaction, which improves the performance of the sensor and the device applications of the special fiber. A theoretical and experimental analysis of the one-air-hole panda fiber demonstrates that the birefringence of the fiber can be of the order of 10-3, which is one order of magnitude higher than that of the traditional panda-type fiber. The corroded region provides a microchannel to be filled with a functional material to compose optical fiber sensors; a sample of a salt solution was filled into the microchannel to measure the refractive index with a sensitivity of 3760 nm/RIU (refractive index units).

Novel optical fiber Vernier immunosensor based on cascading Sagnac loops embedded with excessively tilted fiber grating for specific detection of canine distemper virus.

A novel optical fiber Vernier effect (VE) biosensor based on cascading Sagnac loops embedded with excessively tilted fiber grating (ExTFG) is proposed for the label free and specific detection of canine distemper virus (CDV). The VE was realized by cascading two different Sagnac loops with similar free spectrum range (FSR), one of which was integrated with panda-type polarization maintaining fiber (PMF) as the reference loop, and the other was embedded with ExTFG as the sensing loop. Owning to the amplified function of the VE, the refractive index (RI) sensitivity of the proposed sensing structure reached -1914.89 nm/RIU, which is approximately 12 times higher than that of the single ExTFG based RI sensor. Furthermore, the ExTFG in sensing loop was modified by graphene oxide (GO) and bio-functionalized by the CDV monoclonal antibodies (anti-CDV MAbs) for the specific detection of the CDV. Experimental results show that the proposed optical fiber Vernier sensor could detect the CDV in buffer solution with concentration as low as 1 pg/mL, and the sensitivity was about -1.18 nm/[log(mg/ml)] in the concentration range of 1 pg/mL ~ 50 ng/mL. The excellent specific and clinical properties of the biosensor were verified by immunoassays for fetal bovine serum, Toxoplasma gondii, rabies virus and CDV serum in sequence. Due to the sensitivity amplification function of VE, dense comb spectrum of the Sagnac loop and the stable interference spectra maintained by the polarized light, the proposed biosensor possesses the combined advantages of high sensitivity, high Q-factor and high stability, which may have potential applications in biosensing fields.

Panda-type elliptical-core fiber with flat and low normal-dispersion at 1.5–2.5 µm

The panda-type polarization-maintaining fiber (PMF) with a heavily GeO2-doped elliptical core is proposed for the supercontinuum generation. An elliptical air hole is introduced into the core to tailor the dispersion and birefringence properties. The proposed fiber with an appropriate choice of parameters can exhibit a flat and near-zero normal-dispersion profile at 1.5–2.5 µm, and its birefringence reaches beyond 8.8 × 10−4 due to the combined effects of the stress-applying parts (SAPs) and elliptical core with an air hole. The linearly polarized flattened supercontinuum extending over one octave can be generated when the 0.1-ps linear-polarization pulse with the peak power of 100 kW at 1920 nm is injected into a 1-m-long proposed fiber and polarized along the principal axes.

A Panda fiber temperature sensor up to 900°C

The use of Panda-type polarization-maintaining (PM) fiber for the localized sensing of high temperatures was analyzed with simulations and experiments up to 900°C. Accuracy and repeatability of the results started to decline above 800°C. Fused silica optical fiber melts at 1700°C, which sets an ultimate limit for measurable temperatures. In practice, optical fiber birefringence restricts the maximum temperature to 1060°C where PM fiber loses its ability to maintain polarization. Three sensor fibers (4, 5 and 10 cm long) were spliced at 45° angles to input/output fibers and calibrated in an oven from room temperature to 850–900°C temperature range. Two superluminescent light-emitting diodes (SLEDs) were coupled together as a broadband light source. Birefringence-induced change of the polarization in the sensor fiber was measured with a polarization splitter and an optical spectrum analyzer (OSA) as a function of the wavelength. Temperature-dependent birefringence generates a sinusoidal reflection spectrum from the input polarization mode to the orthogonal output polarization mode. Temperature changes could be concluded from variations in these spectra. Finally, a small fusion device, NORTH, at DTU, Denmark was successfully used as a testbed to make sure that the sensors can handle transportation and the instrumentation required for vacuum operation and still produce sensible data from a harsh environment.

Sensing Characteristics of Polarization-Dependent Helical Long-Period Grating-Based Interferometer

We demonstrate an all-fiber Mach-Zehnder interferometer (MZI) by cascading a pair of helical long-period gratings (HLPGs) inscribed in a Panda-type polarization-maintaining fiber (PMF) using a CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -laser. By cascading two grating with different lengths, a serial of polarization-dependent MZIs with different free spectral ranges have been demonstrated. The maximum polarization-dependence loss of the MZI was measured to be more than 35 dB. Two orthogonal interference spectra corresponding to fast axis mode and slow axis mode can be observed. The sensing characteristics of the polarization-dependent MZI we investigated experimentally. For liquid level sensing, the maximum wavelength shifts of the fast and slow axis interference dips were measured to be 11.03 and 3.25 nm when the surrounding refractive index is 1.424 and the interference length is 12.0 cm, respectively. The fast and slow axis interference dips have good linearity and opposite response with the temperature and strain change, the measured temperature and strain sensitivities of the fast and slow axis interference dips were 103.43 pm/°C, −31.26 pm/°C and −2.13 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , 1.68 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , respectively. Based on the high polarization extinction ratio, narrow resonant bandwidth, and low insertion loss, the demonstrated MZI has potential application in polarization-dependent multi-parameter sensing or multi-channel polarization filter.

High-precision fiber optic liquid level sensor based on fast Fourier amplitude demodulation in a specific range of spectrum

This study presents a fiber optic liquid level sensor (FOLLS) by acquiring information from the amplitude of spectral fast Fourier transform (FFT) in a specified narrow wavelength range. The sensing light path is simply formed by embedding a section of Panda-type polarization-maintaining fiber (PMF) into the sensing arm of a conventional Michelson interferometer (MI) structure. The output composite spectrum consists of two parts: the fine interference fringes due to MI optical path difference (OPD) and the envelope fringes stemming from the PMF’s birefringence. By applying liquid level variations on the sensing structure, shifts in envelope wavelength indicate a sensitivity of −0.193 nm/cm, and a liquid level resolution of 1 mm can be easily acquired. Furthermore, by demodulating the amplitude after spectral FFT in a specific narrow wavelength range, and intensity sensitivity of 1.906 dB/cm is achieved, leading to a greatly improved overall resolution of 0.03 mm in liquid level measurement. Besides, the sensing element is sealed and packaged by two sheets of silicone rubber, which can be thrown into liquid when in use, thus easing the sensor installation. Moreover, due to the proposed demodulation method, the sensor is insensitive to the light source power jitter, reference arm phase shift and optical spectral analyzer wavelength shift. Therefore, the merits of the proposed sensor include high precision, high stability, ease of installation, which are beneficial in pore water pressure and liquid level monitoring.

High extinction ratio elliptical core Panda-type polarization-maintaining fiber coil.

The polarization-maintaining performance of the traditional Panda-type polarization-maintaining fiber (PMF) coil is significantly affected by winding stress and temperature. Here, we present an elliptical core Panda-type PMF coil based on a fiber that employs both geometric and stress birefringence. The extinction ratio of the elliptical core PMF coil was found to be 20.13 dB at a temperature of 20°C, corresponding to an increase of 3.71 dB compared to the traditional Panda-type PMF coil. In addition, results from distributed polarization cross talk and gyroscope output tests also revealed a low sensitivity of the fiber to stress caused by the winding process and temperature. In summary, the proposed fiber coil has better polarization-maintaining ability compared to conventional coil and is promising for applications in high-precision optical fiber sensors.

Polarization-Maintaining Fiber Long-Period Grating Based Vector Curvature Sensor

We propose and demonstrate an optical fiber vector curvature sensor based on a long-period fiber grating (LPFG) inscribed in Panda type polarization-maintaining fiber (PMF) using CO2-laser heating and tapering system. The uniform heating approach removes the necessity of CO2-laser exposure alignment along the axis of PMFs during grating fabrication. A serial of PMF-LPFGs with grating period from 350 to 490 $\mu \text{m}$ with a step of 20 $\mu \text{m}$ have been fabricated experimentally. The curvature response of the fast and slow axis resonance dips for the LPFG with a period of 450 $\mu \text{m}$ was investigated in the curvature range from 0 to 4.137 m−1 at four bending orientations. The maximum curvature sensitivities were measured to be 9.26 and −6.89 nm/m−1 for the fast and slow axis LP15 modes, respectively. The sensor can achieve 2-dimensional bending direction recognition. The proposed grating has potential application as a vector curvature sensor.

High sensitivity strain sensor based enhanced polarized mode coupling and FBG sensitization

A highly sensitive strain sensor based on enhanced polarized mode coupling is proposed and demonstrated experimentally. The proposed Sagnac interferometric strain sensor comprises a segment of Panda-type polarization maintaining fiber (PMF) serving as a sensing component and a commercial fiber Bragg gratings (FBG) serving as a sensitizing component. The sensitization effect of FBG has been analyzed and demonstrated experimentally. The core of single mode fiber is intentionally collimated and fusion spliced to one stress applied zone built-in Panda type PMF to excite effectively the polarized mode. The spectra shift towards long wavelength with increasing strain. The measured strain sensitivity reaches up to 176 pm/με. The proposed fiber strain sensor characterizing simple fabrication and high sensitivity can be a good candidate in the field of strain measurements.

High resolution measurement of refractive index with resistance to temperature crosstalk through an all fiber MZI-PMF structure

A simple cascaded structure composed of all-fiber Mach-Zehnder interferometer (MZI) and polarization-maintaining fiber (PMF) is proposed and experimentally demonstrated for simultaneous refractive index (RI) and temperature measurement. By splicing a section of thin no-core fiber (TNCF) between two conventional no-core fibers (NCFs) with large lateral offset, a part of the light in the MZI structure can interact directly with the external environment to obtain a high RI sensitivity. A Panda-type PMF is cascaded with the MZI to eliminate temperature crosstalk in the RI measurement. The experimental results show that the RI sensitivity of MZI is as high as −13862 nm/RIU, and the temperature sensitivities of MZI and PMF are −0.4 nm/℃ and 1.47 nm/℃, respectively. With the help of a sensitivity matrix, the change of RI and temperature can finally be demodulated. The RI and temperature resolutions of the cascaded structure can achieve 1.83 × 10−6 RIU and 0.014 ℃ respectively, to the best of our knowledge, which are the highest among all fiber structures without special materials coating or filling for simultaneous measurement. This structure presents outstanding advantages of easy fabrication, low cost and less sample consumption, which has great potential for integrated biochemical analysis systems.

High Sensitivity Polarimetric Optical Fiber Pressure Sensor Based on Tapered Polarization-Maintaining and Fiber Bragg Grating.

In this paper, we propose a high sensitivity polarimetric optical fiber pressure sensor (OFPS) using a polarization-diversity loop composed of a polarization beam splitter, polarization controllers, and a sensor head. The sensor head consists of 8-cm-long tapered panda-type polarization-maintaining fiber (PMF) and a fiber Bragg grating (FBG) directly spliced with PMF, and the sensor head is located inside a pressure chamber. A pressure-induced birefringence change due to the photoelastic effect can be greatly enhanced at the tapered section of PMF, thereby increasing the pressure sensitivity of the sensor head. The tapered PMF was fabricated using a fusion splicer, and the tapered length and center waist diameter of the tapered PMF segment were ~350 and ~56.82 μm, respectively. At the polarization-diversity loop, PMF is used as a birefringent element to create an interference spectrum due to polarization interference. A pressure-induced birefringence change of PMF results in a wavelength shift of the interference spectrum. Because the PMF birefringence also has a cross sensitivity to temperature, the FBG is utilized for the compensation of the temperature effect on it. The resonance wavelength of the FBG is sensitive to ambient temperature changes but insensitive to changes in pressure. This spectral response of the FBG can be used to compensate additional ambient temperature changes occurred at the sensor head. The pressure sensitivity of our sensor was measured as approximately -27.70 nm/MPa, and an adjusted R² value representing the sensor linearity was measured as ~0.9903 in a measurement range of 0-0.5 MPa. Our fabricated sensor exhibits the highest pressure sensitivity among previously reported polarimetric OFPS.

Temperature Sensor Employed TCF-PMF Fiber Structure-Based Sagnac Interferometer

A cost-efficient all fiber temperature sensor based on a Sagnac interferometer is proposed and experimentally demonstrated. The sensor proposed comprises a section of thin core fiber (TCF) in combination with Panda type polarization maintaining fiber (PMF). The key point is that the core of TCF is intentionally aligned to one of two stress areas of Panda type PMF in order to change the mode transmission. Then the prepared TCF-PMF fiber structure is built into a Sagnac loop. A well-defined spectrum is obtained and the fringe contrast reaches up to 28 dB. The dip wavelengths are employed to demonstrate the temperature characteristics. The experimental results show the transmission spectrum blue-shift with the temperature and sensitivity of -1.54 nm/°C is obtained. The proposed sensor has potential application in temperature measurement.

A novel photonic crystal fiber with high birefringence

A novel high birefringence photonic crystal fiber (PCF) was proposed and the properties of this type of PCF were investigated with full vector finite difference frequency domain method. According to the results of numerical analysis, the two orthogonally polarized states of the fundamental mode become non-degenerate in the fiber and show strong linear polarization. The polarization properties are strongly dependent on the structure parameters of this PCF. Through choosing suitable relative structure parameters, it may exhibit birefringence as high as the order of 10-2, at least one order of magnitude higher than that of the conventional D-type and panda-type polarization-maintaining fiber. It is shown that it may also exhibit ideal dispersion effect in a properly designed geometrical structure of PCF. So this type of PCF can be effectively used to fabricate polarization-preserving fiber and correlative fiber elements with special dispersion and polarization characteristics.