Parallelized fiber Michelson interferometers with advanced curvature sensitivity plus abated temperature crosstalk.

In this Letter, we proposed a super sensitive optic-fiber curvature sensor with ultra-low temperature crosstalk based on Vernier effect and achieved it experimentally. This sensor composes a pair of parallelized 2CFMIs (2-core-fiber Michelson interferometers) in similar lengths, both of which are involved sensing, but there is a rotation angle between their cross-sections. When the rotation angle approaches 180°, the magnification factor for curvature sensitivity is doubled compared with conventional Vernier effect, while for temperature it is always 1. Therefore, advanced curvature sensitivity and abated temperature crosstalk can be realized simultaneously when demodulating Vernier envelops. The experiment results indicate that the curvature sensitivity of this sensor reached 214.533nm/m-1, and temperature crosstalk was as low as 0.000276m-1/∘C. The fabrication process is extremely flexible and repeatable, and the magnification factor of Vernier effect could be controlled conveniently.

Realizing torsion detection using berry phase in an angle-chirped long-period fiber grating.

We demonstrate the fabrication of an angle-chirped long-period fiber grating (ACLPFG) in a single-mode fiber via CO2 laser pulses. Because of the Berry phase introduced by the ACLPFG, the interference acquires an extra phase difference determined by the torsion of the device. By using that unique characteristic of the proposed device, a high sensitivity sine function torsion response is achieved. The torsion sensitivity is significantly improved, and the temperature crosstalk is effectively avoided by using the relative measurement technology. The torsion sensitivity is ~16 folds (~0.94 nm/ (rad/m)) higher than that of the normal long-period fiber grating (LPFG) with only ~0.006 nm/°C temperature crosstalk within the range of 25-80 °C, which is ~10 folds lower than that of the normal LPFG.

Concave-lens-like long-period fiber grating bidirectional high-sensitivity bending sensor.

A novel bidirectional high-sensitivity fiber-optic bending sensor based on the concave-lens-like long-period fiber grating (CLL-LPFG) is designed and demonstrated. The CLL-LPFG is composed by an array of arc-shaped grating planes, and accordingly, its refractive index modulation serves as a concave lens. As a result, the eigencladding mode of the device gets closer to the device surface than the conventional counterpart. Therefore, the proposed sensor provides a more sensitive result. The experimental results show that the bending sensitivities of the CLL-LPFG reach -32.782 nm/m-1 within the bending range of 0-2.08 m-1, which is about sixfold compared to the reported arts. The sensitivity can be potentially improved by optimizing the grating parameters, and the temperature characteristics of the CLL-LPFG can be used to manipulate the grating spectrum.

Microfiber interferometer with surface plasmon-polariton involvement.

We fabricated a microfiber interferometer with surface plasmon-polaritons (SPPs) involvement. Commonly, the SPPs are not involved in interference due to the mismatch momentum and ultrashort propagation distance. In this Letter, an absorber-doped microfiber is utilized for increasing the matched momentum (i.e., their modal projection), and as a result, an SPP is coherent with an end-fire method-stimulated hybrid SPP. A mathematical model is proposed for investigating the modal-projection-caused interference, and its results show that the proposed interferometer is very dependent on the polarization. Confirmation experiments were carried out, and a good agreement between theoretical predictions and experimental results was found. The proposed interferometer will potentially facilitate many SPP studies in directly related fields.

In-line polarization rotator based on the quantum-optical analogy.

An in-line polarization rotator (PR) is proposed based on the quantum-optical analogy (QOA). The proposed PR possesses an auxiliary E7 liquid crystal (LC) waveguide in the vicinity of the single-mode fiber (SMF) core. Because of the matched core size, the PR demonstrates good compatibility with the established backbone networks which are composed of conventional SMFs. With optimized parameters for the auxiliary waveguide, the PR offers a near 100% polarization conversion efficiency at the 1550 nm band with a bandwidth of ∼30 nm, a length of ∼4625.9 µm with a large tolerance of ∼550 µm, and a tolerance of the input light polarization angle and rotation angle of the E7 LC of ∼π/30 and ∼π/36 rad, respectively. The performance was verified by the full-vector finite-element method. The proposed PR can be easily fabricated based on the existing photonics crystal fiber manufacturing process, making it a potentially inexpensive device for applications in modern communication systems. Moreover, the QOA, compared with the previous supermode-theory design method, allows a designer to consider several waveguides separately. Therefore, various unique characteristics can be met simultaneously which is consistent with the trend of modern fiber design.

Fiber refractive index sensor based on dual polarized Mach-Zehnder interference caused by a single-mode fiber loop.

A novel refractive index (RI) sensor head is proposed and experimentally demonstrated in this paper. The proposed sensor head is composed of a segment of bared single-mode fiber and a fiber holder that is fabricated by a 3D printer. The mechanism of the sensor head is based on dual polarized Mach-Zehnder interference. According to the aforementioned mechanism, we derived that the RI responses of the resonance dips possess an exponential functional manner when the E field is along the fast or slow axes. In addition, based on the finite element method, we found that the resonance dips wavelength responses are more sensitive when the input E field is along the fast axis. A confirmation experiment was performed, and the results confirmed our hypothesis. The maximum arithmetic mean value of RI response is about 657.895 nm/RIU for the proposed sensor head when the ambient RI changes from 1.3350 to 1.4110. Moreover, in the case of the proposed liquid RI sensor head, aligning the E field along the fast axis is the potentially needed condition for polarization.

Photonic crystal fiber polarization rotator based on the topological Zeeman effect.

A photonic crystal fiber polarization rotator (PR) is proposed based on the topological Zeeman effect. The proposed PR is achieved by permanently twisting a segment of sixfold symmetric photonic crystal fiber with a matched length, and under the optimized parameters, the PR can offer an almost 100% polarization conversion ratio in the wavelength of 1.55-µm band (∼200 nm bandwidth) and a compact length of about 157 µm based on the numerical simulation result of the full-vector finite-element method. The proposed in-line PCF PR can be easily fabricated based on state-of-art PCF manufacturing, and it is a potential inexpensive candidate in the application of modern communication systems.

In-fiber torsion sensor based on dual polarized Mach-Zehnder interference.

This paper presents a novel optical fiber torsion sensor based on dual polarized Mach-Zehnder interference (DPMZI). Unlike the conventional fiber sensor, the proposed sensor is composed of a sensor part and a demodulator. The demodulator is made by a bared single mode fiber (SMF) loop, and the sensor part is a segment of a coated SMF placed before the loop. A mathematical model is proposed based on DPMZI mechanism and from the model when the sensor part is twisted, the E-field rotational angle will bring a quasi-linear impact on the resonance dip wavelength in their matched detecting range. A proof-of-concept experiment was performed to verify the theoretical prediction. From the experimental data, a sensitivity of -0.3703, -1.00962, and -0.59881 nm•m/rad is achieved with the determining range of 12.0936, 7.6959, and 10.4444 rad/m respectively. The sensor which is composed only of the SMF has the advantages of low insertion loss (~-2dB), healthy structure, low manufacture cost, and easy assembly and application.