Hi-Bi Fiber Research Articles

Ultra-broadband flat-top circular polarizer based on chiral fiber gratings near the dispersion turning point.

Based on the dual-resonance principle around the dispersion turning point, a scheme of chiral long-period fiber gratings (CLPGs) formed by twisting a high-birefringence (Hi-Bi) fiber is herein proposed to realise ultra-broadband flat-top circular polarizers. The coupling bandwidth is approximately seven times larger than that of traditional CLPGs. In addition, by introducing chirp characteristics in these CLPGs, an ultra-broadband flat-top circular polarizer with ∼200 nm@3 dB was conveniently achieved. Subsequently, by optimising the chirped CLPGs, a circular polarizer with a bandwidth extinction ratio of approximately 30 dB and a high level of ∼100 nm at 1 dB was realised. It was shown that the mode-controlling performances of the CLPGs can be remarkably improved, which has significant applications in light-field regulation. Finally, for the first time, it was proved that the CLPG cannot generate a vortex beam.

Polarization properties of a fiber optic loop mirror

In this work, we present the spectral polarization properties of a fiber optic loop mirror (FOLM) which includes a 50/50 coupler and 25-cm long highly birefringent (hi-bi) fiber. The modulation depth of the reflection/transmission spectra can be adjusted by twisting the hi-bi fiber at the splices by means of two azimuth rotators (AR). The results show that the polarization properties of the reflection strongly depends on the angle rotation. We found that it is possible to obtain reflection spectral polarization independence for any modulation depth with the proper parameters. The experimental behavior was confirmed by numerical simulations based on the Jones matrix formulation.

High Enhancement Strain Sensor Based on Vernier Effect Using 2-Fiber Loop Mirrors

In this letter, a strain sensor with high sensitivity enhancement using a special case of Vernier effect is presented. The sensor configuration is composed of two-fiber loop mirrors in a cascaded configuration with opposite strain responses when individually characterized. Thus, the enhanced Vernier effect is explored, which is the most sensitive of three possible cases Vernier effect. Here, the Vernier response depends on the difference between the sensitivities of each Hi-Bi optical fiber. In addition to this, the fundamental and the first harmonic were also explored. The results obtained are a strain sensitivity of (13.3 ± 0.3) pm/ $\mu \varepsilon $ for the carrier, (80.0 ± 0.3) pm/ $\mu \varepsilon $ or the Vernier envelope of the fundamental case and (120 ± 1) pm/ $\mu \varepsilon $ for the Vernier envelope of the first harmonic. The first harmonic could achieve a magnification factor of 8. Considering that the optical interrogation system allows a minimum resolution of 0.02 nm, the minimum measurement step achievable is $0.2~\mu \varepsilon $ . This work proves the possibility of applying the concept of enhanced Vernier effect to fiber loop mirrors, obtaining higher sensitivity than a standard fiber loop mirror alone. Besides, the sensitivity can be increased through the usage of harmonics of the Vernier effect. Moreover, the use of large interferometers allows a better discretization of the envelope, which implies a greater ease of analysis.

Simultaneous measurement of temperature and refractive index using microfiber knot resonators in Hi-Bi fiber loop mirrors

Based on the large evanescent field of microfibers, a novel fiber sensor using a microfiber knot resonator embedded in a Hi-Bi fiber loop mirror is proposed for simultaneous measurement of the temperature and refractive index of solutions. Due to the different responses of the microfiber knot resonator and fiber loop mirror to temperature and refractive index variations, the fiber sensor can measure temperature and refractive index simultaneously by utilizing the sensitivity matrix. The experimental measurements show that the sensitivities of the microfiber knot resonator and the fiber loop mirror to temperature are 5.6 pm/°C and −464.1 pm/°C, respectively. The sensitivity of the microfiber knot resonator to the refractive index of dilute solutions is 116 nm/RIU. The sensor has a higher sensitivity to refractive index variations than LPGs and has potential for use in the field of biochemistry.

Tunability of Hi-Bi photonic crystal fiber integrated with selectively filled magnetic fluid and microfluidic manipulation.

Optical fiber microfluidics technology can implement the mutual tune of the light field and fluid in micro-nano scale. In this paper, one core of high-birefringence photonic crystal fiber (Hi-Bi PCF) is used as a microfluidic channel. The birefringence of Fe3O4 nanofluid is experimentally and theoretically investigated by selectively infiltrating the magnetic fluid into the core of the Hi-Bi PCF. The presence of magnetic fluid alters the birefringence of the original Hi-Bi PCF and can be modulated by the intensity of the external magnetic field. The optical field distribution is simulated, and the birefringence of the Hi-Bi PCF with selective filling is approximately 6.672×10-4. The experimental results show that the structure has a highly linear response to the external magnetic field from 0Oe to 300Oe, and the sensitivity is 16.8pm/Oe with a high resolution of 1.19Oe. Due to several advantages such as all-fiber compact structure, low transmission loss, and high linear response, this device can find various applications, including weak magnetic field measurement with high accuracy, optical fiber gyroscopes, and magneto-optic modulators. Particularly, it also has important significance to realize the all-fiber microfluidic chip laboratory.

Distributed measurements of external force induced local birefringence in spun highly birefringent optical fibers using polarimetric OFDR.

We develop a local birefringence determination method of measuring the distribution of external force-induced birefringence in spun high-birefringence (HiBi) fiber (spun HiBi fiber) using polarimetric optical frequency domain reflectometry (P-OFDR). By constructing the similarity between the measured Mueller matrices and fiber under test (FUT) matrices using two input states of polarization, the total phase retardance caused by the local birefringence of FUT can be determined from the trace of the measured matrices. We measure the local birefringence of spun HiBi fibers from two different manufacturers and telecom SMF (G652.D) caused by bending, twist, and transverse stress using our presented P-OFDR system. From the experimental results, we find that bending- and twist-induced birefringences of spun HiBi fiber are much lower than those of standard SMF. More remarkably, the coating package influences the transverse stress induced birefringence of spun HiBi fibers significantly. These experimental results verify that our presented method is beneficial to evaluating and improving spun HiBi fibers' quality.

A Hi-Bi Ultra-Sensitive Surface Plasmon Resonance Fiber Sensor

In this paper, a simple, miniature, and highly sensitive photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor is proposed. The target analyte and the plasmonic material are at the outer surface of the fiber making practical applications feasible. A 30-nm gold (Au) layer supports surface plasmons. A thin titanium dioxide (TiO 2 ) layer is used to assist adhesion of Au on the glass fiber. The fiber cross section is formed purely by circular-shaped holes simplifying the preform manufacturing process. A high-birefringence (hi-bi) fiber is obtained by means of an array of air holes at the center of the fiber. A finite element method (FEM) is employed to analyze the surface plasmon properties of the proposed PCF-SPR sensor. By optimizing the geometric parameters, a maximum wavelength sensitivity (WS) of 25 000 nm/RIU and an amplitude sensitivity (AS) of 1411 RIU -1 for a dielectric refractive index (RI) range of 1.33-1.38 are obtained. Moreover, an estimated maximum resolution of 4 × 10 -6 and a figure of merit (FOM) of 502 are obtained that ensures high detection accuracy of small refractive index (RI) changes. Owing to its sensitivity and simple architecture, the proposed sensor has potential application in a range of sensing application, including biosensing.

Arbitrary Spectral Synthesis and Waveform Generation With HiBi Fiber Loop Mirrors

An arbitrary spectral synthesis scheme with parallel-connecting high-birefringence fiber loop mirrors (HiBi-FLMs) based on Fourier synthesis theory has been proposed and demonstrated. Three typical spectra of triangle, rectangle, and sawtooth shape have been synthesized by implementing only four HiBi-FLMs. The experimental results are in good agreement with theoretical simulations with goodness of fit of 0.9565. Furthermore, higher precise optical spectrum with narrower bandwidth can be obtained by adopting longer polarization-maintaining fiber and more sections of HiBi-FLMs. Besides, a typical application of arbitrary waveform generation has been implemented. By incorporating with frequency-to-time mapping, triangle- and sawtooth-shaped electrical pulses with repetition rate of 1 GHz and pulse width of ~860 ps have been generated.

INVITED] Magnetic field vector sensor by a nonadiabatic tapered Hi-Bi fiber and ferrofluid nanoparticles

A magnetic field vector sensor based on super-paramagnetic fluid and tapered Hi-Bi fiber (THB) in fiber loop mirror (FLM) is proposed. A two-dimensional detection of external magnetic field (EMF) is experimentally demonstrated and theoretically simulated by Jones matrix to analyze the physical operation in detail. A birefringence is obtained due to magnetic fluid (MF) in applied EMF. By surrounding the THB with MF, a tunable birefringence of MF affect the transmission of the sensor. Slow and fast axes of this obtained birefringence are determined by the direction of applied EMF. In this way, the transmission response of the sensor is depended on the angle between the EMF orientation and the main axes of polarization maintaining fiber (PMF) in FLM. The wavelength shift and intensity shift versus EMF orientation show a sinusoidal behavior, while the applied EMF is constant. Also, the changes in the intensity of EMF in a certain direction results in wavelength shift in the sensor spectrum. The maximum wavelength sensitivity of 214 pm/mT is observed.

Tunable Ferrofluid Magnetic Fiber Sensor based on Nonadibatic Tapered Hi-Bi Fiber in Fiber Loop Mirror

An external magnetic field (EMF) fiber sensor by combining nanomagnetic fluid and Hi-Bi nonadiabatic tapered optical fiber in fiber loop mirror (THB-FLM) is demonstrated experimentally and theoretically. The polarization controllers (PCs) in FLM are adjusted to excite different cladding modes in the sensor. By variation of the PCs' settings, the sensitivity of the sensor to EMF in the range from 0 to 21 mT could be tuned from 255 to 402 pm/mT. As compared to the reported magnetic fluid (MF) based sensors, the achieved sensitivity of the proposed sensor, with only 0.1% of the volume concentration of MF nanoparticles, enhanced by 5.6 orders of magnitude relative to in-line nonadiabatic tapered optical fiber sensor. The detection limit of the THB-FLM to EMF in the range of 0 to 21 mT and 22 to 50 mT was 5 and 18.9 μT, respectively. Experimental results show that the sensitivity to the EMF increased with the order of the cladding mode. In addition to the EMF sensing capability, the proposed structure can simultaneously provide temperature information.

Experimental investigation of winding diameter effect on optical properties of Hi-Bi fiber with tin coating

Experimental investigation of winding diameter effect on optical properties of Hi-Bi fiber with tin coating

Monitoring the Etching Process of Hi-Bi Fiber Through a Fiber Loop Mirror

A method for monitoring the etching process of Hi-Bi fiber is proposed and demonstrated. The birefringence of the etching fiber is accurately calculated by tracking the shift of the interference spectrum in a high-birefringence fiber loop mirror interferometer. Then, the degree of etching can be inferred by the relationship between the etching-fiber birefringence and the fiber structure. A section of PANDA fiber is used as an example to experimentally demonstrate the proposed method. The results show that the calculated birefringence is consistent with the theoretical simulation. Furthermore, four different structural states, which reflected in four different rate of change, are presented in the whole etching process of PANDA fiber. This method has the advantages of easy realization, high precision, and repeatability, and it can be used in the preparation of Hi-Bi microfiber photonic devices.

Tunable Dual-Wavelength Thulium-Doped Fiber Laser Based on FBGs and a Hi-Bi FOLM

A tunable dual-wavelength thulium doped fiber laser is demonstrated experimentally. For the first time for the 2- $\mu \text{m}$ wavelength band we propose the independent tuning of the generated laser lines based on fiber Bragg gratings and the use of a Hi-Bi fiber optic loop mirror for the fine adjustment of the cavity losses to obtain stable dual-wavelength operation. Dual-wavelength laser generation with the laser lines separation in the range from 0.3 to 6.5 nm is obtained. The laser emission exhibits an optical signal-to-noise ratio better than 56 dB. Improved stability with output power fluctuations less than 1 dB is observed in dual-wavelength generation with equal power of lines.

Tunable narrow linewidth all-fiber thulium-doped fiber laser in a 2 µm-band using two Hi-Bi fiber optical loop mirrors

We propose an all-fiber Tm-doped fiber laser with a tunable and narrow laser line generated in a wavelength region of 2 µm. A single laser line with a linewidth below 0.05 nm, tunable in a wavelength range of 44.25 nm, is obtained. The laser linewidth and the discrete wavelength tuning range depend on the characteristics of the two fiber optical loop mirrors with high birefringence in the loop that forms the cavity. Dual-wavelength laser operation is also observed at tuning range limits with a wavelength separation of 47 nm. Alternate wavelength switching is also observed.

Two high-order superfine comb filters based on HiBi Fiber Ring

Two high-order superfine comb filters based on HiBi Fiber Ring

Theoretical study on core-mode to radiation-mode coupling in chiral fiber long-period gratings

The chiral fiber long-period gratings (CLPGs) could be fabricated by twisting a high-birefringence (Hi-Bi) fiber. However, when it is immersed into a material whose refractive index (RI) is higher than that of the cladding, there exists a complicated coupling between the core modes and the radiation ones. In this paper, for the first time to our knowledge, we theoretically investigate the mode coupling characteristics in such a CLPG. It is found that, owing to a strong mode transfer from the co-handed core mode to continuous radiation ones under the phase-matching condition, the CLPG can be regarded as a broadband circular polarizer since only the cross-handed circularly polarized light is left when a linearly polarized light is injected. Furthermore, the influence of the RI of the surrounding medium on the bandwidth and extinction ratio of this circular polarizer is investigated in detail. As a result, a broadband all-fiber circular polarizer can be constructed. Considering its simple configuration, it might have some potential applications, such as filters, broadband polarizers, and sensors.

Optical Fiber Temperature and Torsion Sensor Based on Lyot-Sagnac Interferometer.

An optical fiber temperature and torsion sensor has been proposed by employing the Lyot-Sagnac interferometer, which was composed by inserting two sections of high-birefringence (HiBi) fiber into the Sagnac loop. The two inserted sections of HiBi fiber have different functions; while one section acts as the temperature sensitive region, the other can be used as reference fiber. The temperature and twist sensor based on the proposed interferometer structure have been experimentally demonstrated. The experimental results show that the envelope of the output spectrum will shift with the temperature evolution. The temperature sensitivity is calculated to be −17.99 nm/°C, which is enlarged over 12 times compared to that of the single Sagnac interferometer. Additionally, the fringe visibility of the spectrum will change due to the fiber twist, and the test results reveal that the fringe visibility and twist angle perfectly conform to a Sine relationship over a 360° twist angle. Consequently, simultaneous torsion and temperature measurement could be realized by detecting the envelope shift and fringe visibility of the spectrum.

PMD Emulator based on PZTs attached to pieces of an Hi-Bi fiber

In this paper we demonstrate the development of an adjustable and compact polarization mode dispersion (PMD) emulator device, based on piezoelectric actuators that squeezes a defined pieces of an Hi-Bi fiber. Using this device, the first and second order PMD (SOPMD) can be reproduced in a controlled and compact way, allowing its use as a reliable metrological reference for PMD compensators and for the study of several polarizations phenomena that can represent impairments to the high data transmission networks. This emulator was used to perform an analysis of the correlation between the PMD and SOPMD under different climate chamber temperature.

High resolution polarization-independent high-birefringence fiber loop mirror sensor.

In this work, two all polarization-maintaining (PM) high-birefringence (Hi-Bi) fiber loop mirrors (FLM) which are immune to external polarization perturbations are validated both theoretically and experimentally. Simplified and stable versions of classical FLMs were attained using a PM-coupler and by fusing the different Hi-Bi fiber sections with an adequate rotation angle between them. Since the polarization states are fixed along the whole fiber loop, no polarization controllers are needed. This simplifies the operation and increases the stability of the systems, which were also validated as ultra-high resolution sensors, experimentally obtaining a resolution of 6.2∙10-4 °C without averaging.

An in-line quasi-Sagnac interferometer based comb filter used for tunable multi-wavelength fiber laser

Abstract An in-line quasi-Sagnac interferometer comb filter based on high birefringence (Hi-Bi) fiber is proposed and experimentally demonstrated. This quasi-Sagnac interferometer is constructed by integrating a high-birefringence (Hi-Bi) fiber in between two fiber-coupled polarization controllers (PCs) followed by a fiber mirror. The filtering function is theoretically analyzed and simulated by the Jones matrix method. The extinction ratio and wavelength interval of the output spectrum can be flexibly adjusted by rotating the PCs. By only using a pump light source and gain medium, stable multi-wavelength lasing operation can be realized at room temperature. These advantages of tunable ability, switchable ability and good stability make the proposed filter to have broad application prospects in the field of tunable multi-wavelength fiber laser.