Polarization-maintaining Fiber Research Articles

Single and Multiple Pulse Pattern Formation in All-Normal All-PM Yb-Doped Fiber Laser Using a Nonlinear Optical Loop Mirror

We report the evolution of single-pulse and multi-pulse in a mode-locked all polarization-maintaining fiber laser based on a nonlinear optical loop mirror (NOLM). The main parameters of the laser were determined by numerically simulating the relationship between the number of pulses and the basic parameters of each element. Experiments demonstrate generation of 1 to 6 pulses per cavity round trip. There is an unstable regime between the stable N and N + 1 pulses states when gradually increasing the pump power, while the intervals of the unstable regime shrink or even disappear when the direction of pump power variation is reversed. Our experimental results are different from those previously reported where the intervals of the unstable pulse regime are almost unchanged regardless of the pump power adjustment direction. We also describe how to obtain fundamental mode-locking from the multi-pulse state. The laser operated in the single-pulse regime shows excellent stability.

Temperature and vibration insensitive fiber optic vector magnetic field sensor

We propose and demonstrate a fiber optic vector magnetic field sensor based on the magneto-optical Faraday effect. The sensor has excellent environmental adaptability. Due to the polarization dependence of Faraday effect in polarization-maintaining fiber coil, the sensor uses two orthogonal polarization states to detect the direction and intensity of magnetic field. By establishing the magnetic sensitivity model of the sensor through the Jones matrix, we analyze the magnetic field-induced phase difference in the two orthogonal polarization states theoretically. Then the influence of environmental temperature and vibration on the output of the two polarization states of the sensor is analyzed, and the sensor can theoretically achieve complete suppression of environmental temperature and vibration errors. The experimental results show that the sensor sensitivity is 0.507 mV/mT. The directivity of the vector magnetic field sensor reaches 21 dB with the orientation error of ±0.4°. The sensor also has excellent robustness. It is insensitive to environmental temperature changes between 30 °C and 50 °C and environmental vibrations within 1 g. The suppression effect of environmental errors can reach 9.8 times with high anti-interference capability in experiments. The proposed sensor has potential applications in navigation, vehicle detection, and current sensing.

Multipoint pressure sensing at up to 900 °C using a fiber optic multimode interferometer

We demonstrate a multipoint optical fiber pressure sensor for high temperature operation using multimode interference. Each sensing element consists of a four-hole asymmetric multimode fiber acting as the pressure sensing fiber, spliced between two standard polarization-maintaining single mode fibers. Multiple sensing elements are serially connected for multipoint pressure sensing and demultiplexing is achieved using Fourier analysis. The spatial frequency associated with each sensing element is separated by having distinct optical path lengths. The pure silica material of the sensing fiber enables high-temperature operation. As a proof of concept, we demonstrate two-point pressure sensing at a temperature up to 900 °C with negligible crosstalk between the sensing elements and good stability. Our demonstrated sensor has potential applications in heavy industry where spatially resolved measurements of pressure at high temperature may lead to improvements in efficiency and safety.

Sagnac interferometer-based optical fiber strain sensor with exceeding free spectral measurement range and high sensitivity

Sagnac interferometer-based sensors have shown high sensitivity, but limited measurement range due to the free spectral range (FSR) limitation especially the higher the sensitivity. In this paper, we designed an optical fiber Sagnac interferometer with a polarization maintaining fiber (PMF) and a fiber Bragg grating (FBG) in the loop. The strain sensing performance was experimentally conducted. The PMF in the Sagnac interferometer showed a high strain measurement sensitivity with a limited measurement range due to the FSR. On the contrary, FBG in the Sagnac interferometer showed a low strain sensitivity but a large measurement range. By combining the PMF and FBG in a Sagnac interferometer, a high strain sensitivity of about 17.08 pm/µε with a large measurement range of 0–5187 µε was experimentally achieved. The method used in this paper can also be utilized to expand the sensing range in other interferometers. The proposed PMF and FBG constructed Sagnac interferometer shows the merits of simple structure, high sensitivity, and large measurement range, which make it a competitive candidate in strain monitoring.

Highly stable and wavelength-switchable single-longitudinal-mode Tm3+-doped fiber laser with a specially-designed tri-coupler dual-ring filter

A single-longitudinal-mode (SLM) Tm3+-doped fiber laser (TDFL) with a narrow linewidth, less than 8 kHz, is proposed and demonstrated. A superimposed polarization-maintaining fiber Bragg grating (SI-PM-FBG), a specially-designed tri-coupler dual-ring (TCDR) cavity filter, and a section of unpumped Tm3+-doped fiber are combined to realize output lasing with SLM operation for each wavelength channel in 2 µm band. The design, fabrication, and characterization of the TCDR filter are demonstrated in detail. The proposed four-wavelength-switchable TDFL can be switched among fifteen lasing states, including four single-wavelength, six dual-wavelength, four triple-wavelength, and one quadruple-wavelength operations by adjusting the drop-in polarization controller. The experimental results show that the four SLM single-wavelength lasings are all with a relative intensity noise below − 113.06 dB/Hz at frequencies above 2 MHz, and the wavelength and output power fluctuation below 0.02 nm and 0.40 dB whihin 60 min, respectively. Four lasing wavelengths at 2048.28, 2048.71, 2049.05, and 2049.52 nm exhibit good wavelength and power stability and can maintain SLM operation.

Linear-cavity Er-doped fiber mode-locked laser with large wavelength tunability.

A linear-type wavelength-tunable all-polarization-maintaining fiber mode-locked laser is proposed for the first time, to our knowledge, and is implemented with an Er-doped fiber and polarization-maintaining fiber components. The tuning range of the center wavelength is from 1533.7nm to 1565.6nm. The linear-type configuration makes the proposed laser simpler and more compact, allowing it to achieve the highest repetition rate of 126.5MHz among C-band wavelength-tunable mode-locked lasers due to its short cavity length. Also, its polarization-maintaining fiber components provide reliable operating robustness. The significant wavelength tunability and high repetition rate of the proposed laser can be expected to make it an attractive resource for various applications, including optical communications, broadband spectroscopic LIDAR, and high-precision ranging.

Influence of position deviations on the performance of 80 dB adjustable polarization extinction ratio generator

This paper constructed an 80 dB adjustable polarization extinction ratio (PER) generator based on coaxial rotating polarization-maintaining fiber (PMF). The position deviations of PMF may lead to the deterioration of PER by affecting the energy coupling of the two axes. The quantitative relationship between PER and different position deviations is determined by simulations and experiments, and the PER uncertainty is analyzed. The axial distance has no influence on PER. The influences of lateral misalignment and angle deflection are a square exponential relationship, which is negligible below 50 dB and increases drastically above it. The expanded uncertainties (k = 2) in the ranges of 50 to 60 dB, 60 to 70 dB and 70 to 80 dB are about 0.2 dB, 0.6 dB and 2.7 dB, respectively. This paper provides a reference for the research of ultra-high PER traceability and other optical fiber technologies.

Optical Phase/Frequency Demodulation Using Polarization-Maintaining Fiber Bragg Gratings

Conventional techniques for demodulating phase/frequency-modulated (PM/FM) optical signals either require a sophisticated frequency-stable laser or employ a discriminator with poor characteristics. Here, we present a simple, compact, and robust technique featuring high linearity over a wide bandwidth and low background noise. Our technique exploits the reflection characteristics of fiber Bragg gratings written in polarization-maintaining fibers to create a frequency discriminator, which is able to convert PM/FM signals into intensity-modulated (IM) signals. A simple theoretical analysis is presented to highlight the advantages of the scheme. Experimentally, the transfer characteristics of the demodulator are characterized, yielding a linear FM-to-IM conversion slope of 1.238 mV/Hz in a 0.2-nm (∼25 GHz) bandwidth. Highly linear operation up to an FM-modulation index of 1.2 has been achieved. Background-free operation is shown by demonstrating negligible carrier leakage and a 10-dB IM rejection. Finally, high fidelity in demodulating arbitrary PM/FM optical signals is demonstrated with a correlation coefficient of 0.99 and a confidence of almost 100%. This simple yet efficient technique can potentially find applications in optical communications, microwave photonics and radar/lidar technologies.

Regeneratively mode-locked optoelectronic oscillator.

A regeneratively mode-locked optoelectronic oscillator is proposed to realize multi-mode phase locking in optoelectronic oscillators by coupling a modulating signal generation loop. To verify the feasibility of the scheme, a numerical simulation model is established. In addition, a proof-of-concept experiment is demonstrated in a single-loop optoelectronic oscillator with a 2.2 km polarization-maintaining single-mode fiber, using an electric amplitude modulator/Mach-Zehnder modulator as an active mode-locking device. The generated microwave pulse signal has a center frequency of 10 GHz and a repetition rate of 95 kHz. We believe this scheme can provide a new approach to overcome the problem of detuning between the modulating frequency and the mode spacing during long-term operation.

Research on performance of fiber twist sensors based on reflective microfiber couplers

Fiber twist sensors based on reflective microfiber couplers (RMCs) with two different fiber types are proposed and investigated. The single-mode fiber RMC (S-RMC) is fabricated by fusing and tapering two single-mode fibers and then connecting two fibers to form a Sagnac loop. The polarization-maintaining fiber RMC (P-RMC) is fabricated by the same method but consist of a segment of polarization-maintaining fiber. The S-RMC and the P-RMC achieve twist sensitivity of 2621.08 (a.u.)/(rad/m) and 2355.59 (a.u.)/(rad/m), respectively. For S-RMC, the wavelength and intensity fluctuations are <0.1 nm (0.05 nm/°C) and 0.2 dB (0.01 dB/°C) at temperatures ranging from 25 °C to 45 °C, respectively. The S-RMC has the characteristics of high twist sensitivity and linearity, thermal stability, low loss as well as easy fabrication.

Simultaneous Strain and Temperature Discrimination in 18650 Li-ion Batteries Using Polarization-Maintaining Fiber Bragg Gratings

In this work, a fiber Bragg grating (FBG) sensor network inscribed in a polarization-maintaining (PM) fiber is proposed to proceed with a multipoint simultaneous temperature and strain discrimination in different locations (positive and negative terminals, and middle) on a cylindrical Li-ion battery. The birefringence property of the PM fibers, together with FBG sensors, allowed such an application using only one fiber line fixed to the edges of the battery. The battery was subjected to two different charge/discharge cycles, one with nominal charging and discharging conditions (1.00 C and 1.13 C, respectively) and another with abusive conditions (1.88 C for charge and 2.39 C for discharge). The PM-FBG sensors registered maximum temperature and strain variations at the end of the abusive discharge process of the battery; the positive terminal achieved a 28.7 ± 0.3 °C temperature variation, while the center achieved 221 ± 10 με strain variation. The results indicate a different strain variation behavior in the middle location when compared to the negative and positive terminals, as well as a higher temperature variation in both terminals when compared to the middle location. The use of PM-FBG sensors successfully demonstrates their feasibility in locally tracking and discriminating strain and temperature shifts in a battery surface. To our knowledge, this is the first study using the application of PM-FBG sensors to monitor and discriminate critical safety parameters in Li-ion batteries.

GHz-repetition-rate fundamentally mode-locked, isolator-free ring cavity Yb-doped fiber lasers with SESAM mode-locking.

A novel fundamentally mode-locked, GHz-repetition-rate ring cavity Yb-doped femtosecond fiber laser is demonstrated, which utilizes polarization-maintaining gain fiber and is enable by SESAM mode-locking. Thanks to the isolator-free structure, the ring cavity laser is operated bidirectionally and the two polarization-multiplexed output pulse trains are demonstrated synchronous. As a result, tunable waveforms one of which is with reduced pedestal and shorter pulse width in comparison with each individual, are generated by combination of the two orthogonal-polarized output pulses. Furthermore, a similar ring cavity structure that generates GHz picosecond pulses is demonstrated. We believe such high-repetition-rate polarization-multiplexed mode-locked fiber lasers could find further uses in various applications in need of gigahertz repetition rate and tunable waveforms.

Sagnac Interferometric Temperature Sensor Based on Boron-Doped Polarization-Maintaining Photonic Crystal Fibers

A sensitive temperature sensor was demonstrated using boron-doped polarization-maintaining photonic crystal fiber (PM-PCF) as a Sagnac interferometer (SI). This boron-doped PM-PCF combines both the geometric birefringence introduced by the PCF structure design and the stress birefringence introduced by the boron-doped stress-applying parts. However, we found that the stress birefringence dominates the total birefringence of the sensor by numerical analysis. In the experiments, the fabricated sensor exhibited the highest temperature sensitivity of −1.83 nm/°C within the wide temperature range of 28~76 °C. The temperature sensitivity was mainly derived from the stress birefringence of boron-doped PM-PCF SI. These findings provide some support for the designation of high-precision temperature sensors.

Tunable and switchable erbium-doped fiber laser based on the parallel filter of the FBGs embedded in Sagnac ring and the in-line MZI

A tunable and switchable erbium-doped fiber laser (EDFL) based on the parallel filter is proposed and experimentally verified. The parallel filter is composed of two branches. One branch is double fiber Bragg gratings (FBGs) embedded in Sagnac ring filter, which can realize the selection of two wavelengths; the other branch is an in-line Mach Zehnder interferometer (MZI) filter, which is composed of a 10 cm polarization-maintaining fiber (PMF) fused in the middle of single mode fibers (SMFs) with spheres at both ends, which can realize the selection of five wavelengths. When the parallel filter is inserted into the fiber laser cavity and the polarization controllers (PCs) are adjusted, the laser excitation from single-wavelength to quadruple-wavelength can be realized, including 7 different single-wavelength laser states, 16 different dual-wavelength laser states, 11 different triple-wavelength laser states and 2 different quadruple-wavelength laser states. In addition, the intervals of the dual-wavelength laser states are relatively regular, and the dual-wavelength laser intervals are obtained every ∼ 2 nm from 7 nm to 18 nm. And the optical signal-to-noise ratios (OSNRs) are more than 43 dB, and the highest OSNR is 60 dB. Finally, by changing the temperature applied to the FBG, tunability of dual-wavelength intervals can be achieved with a range of 1.1 nm. Due to the variety of lasing laser states of the fiber laser, easy switching, and regular intervals between the dual-wavelength laser states, the fiber laser proposed can be better applied to wavelength division multiplexing (WDM)system.

Hybrid structure polarization-maintaining hollow-core photonic bandgap fiber with anti-resonant tubes and silicon layers.

A novel-hybrid structure polarization-maintaining 19-cell hollow-core photonic bandgap fiber (HC-PBGF) is proposed. Robust single-mode characteristic is achieved by introducing six anti-resonant tubes into the core of 19-cell HC-PBGF. A high birefringence at the level of 10-3 is achieved by adding silicon layers into the y-direction tubes. The higher-order mode extinction ratio (HOMER) is greater than 4.71 × 107, and the high birefringence can be improved to 5 × 10-3. In the waveband from 1530 nm to 1595 nm, the single-mode, high birefringence performance can be effectively maintained even under a tight bending radius of 5 mm.

Abundant dynamics of group velocity locked vector solitons from Er-doped fiber laser based on GO/PVA film

Abstract With the insertion a segment of polarization-maintaining fiber (PMF) inside the cavity, abundant dynamics of group velocity locked vector solitons (GVLVSs) in Er-doped fiber laser have been investigated by using graphene oxide/polyvinyl alcohol (GO/PVA) film as a saturable absorber (SA). The generated Kelly sidebands in emission spectra reveal peak-valley or valley-peak alternation and slightly shift in two orthogonal components, which are the characteristics of GVLVSs. Through proper adjustment of polarization controllers (PCs) inside the EDFLs cavity, versatile vector soliton dynamics such as polarization locked GVLVSs (PL-GVLVSs), polarization rotation GVLVSs (PR-GVLVSs), dual wavelength GVLVSs, bound state GVLVSs, bunch GVLVSs and harmonic mode-locking GVLVSs (HML-GVLVSs) have been observed. The separation between two emission peaks from the dual wavelength GVLVSs was controlled by the Lyot filter and related to the insertion length of PMF inside the cavity. Unlike PL-GVLVSs, the period-doubling phenomenon has been found in two orthogonal components of the PR-GVLVSs. Besides, the bound state GVLVSs were generated showing strongly modulated interference fringes in emission spectrum. For the bunch and HML GVLVSs, the number of solitons inside the cavity increased with the pump power, and it showed the quintuple solitons and the 7th HML-GVLVSs at the highest pump power.

Compact, repetition rate locked all-PM fiber femtosecond laser system based on low noise figure-9 Er:fiber laser

We demonstrate a compact femtosecond fiber laser system based on all polarization-maintaining (PM) fiber and fiber components integrated structure. The figure-9 oscillator which incorporated a nonlinear amplifying loop mirror in the cavity features a 103.4-MHz high repetition rate with up to 93.1 dB signal-to-noise ratio of the radio frequency spectrum, 0.0056% [1 Hz, 1 MHz] integrated root-mean-square amplitude noise at the fundamental repetition rate and 63.7-fs timing jitter [100 Hz, 1 MHz]. Meanwhile, the fundamental repetition frequency was also locked to a stable radio frequency reference by using a self-designed frequency actuator and a relative frequency stability of 2.1 × 10−12 at 1-s gate time was obtained. Moreover, benefitting from the large positive group-velocity dispersion and negative third-order dispersion at 1.5-μm wavelength band, we also achieved 48.2 fs compressed pulse duration as well as an amplified average power of 199 mW via one-stage all-PM fiber amplifier and compressor. At last, as a performance proof, by directly splicing 38-cm long PM highly nonlinear fiber to the pulse compressor, a broadband coherent supercontinuum spanning from 950 nm to 2150 nm was generated. Our all-PM fiber laser system is suitable for the further buildup of a low noise PM fiber optical frequency comb.

Flexible wavelength-, pulse-controlled mode-locked all-fiber laser based on a fiber Lyot filter.

In this paper, we report a flexible wavelength-, pulse-controlled mode-locked all-fiber laser based on a novel fiber optic Lyot filter. The wavelength, pulse duration and spectral bandwidth of passive mode-locked lasers can be tuned by controlling the polarization controller. The proposed Lyot filter was constructed by a single-mode fiber insertion between two polarization-maintaining fibers. The filter bandwidth and laser output tunability were based on the birefringence characteristics of the polarization-maintaining fibers. This all-fiber laser is simple and stable and can be used for various applications where width-tunable or wavelength-tunable pulses are necessary.

All-polarization-maintaining fiber optical frequency comb for the dispersion measurement of a microcavity

In this research, we demonstrate an optical frequency comb (OFC) based on a figure-9 laser and polarization-maintaining fibers to measure the dispersion of a microcavity. We adopt a multi-branch structure to obtain a broadband spectrum from 1,250 nm to 1,640 nm with 6-dB bandwidth. The single-mode power at each wavelength of the supercontinuum spectra is greater than 300 nJ, which assures the signal-to-noise ratio of the beat notes between the OFC and the diode laser. The frequency stability of the repetition rate is about 7.5 × 10–14 in an integration time of 1 s. This system allows us to extend the measurement bandwidth to 60 THz at the sub-megahertz resolution, which meets the requirements of the microcavity’s higher-order dispersion measurement.

Optical fiber temperature sensor with Vernier effect formed by Mach–Zehnder interferometer cascaded Sagnac interferometer based on Hollow-core photonic crystal fiber

This research proposes a Mach–Zehnder interferometer (MZI) based on hollow-core photonic crystal fiber (PCF) and a Sagnac interferometer (SI) based on polarization maintaining fiber (PMF). A stable reference interferometer is formed by using PCF which is insensitivity to temperature and the temperature monitoring is realized by using PMF which is sensitivity to temperature. The two interferometers are cascaded through a 3 dB optical fiber coupler to generate the Vernier effect by controlling the lengths of the two fibers, thereby improving the temperature sensitivity of the sensing structure. The length of PCF is 1.22 mm and PMF is 1.65 m, the experimental results show that the highest temperature sensitivity of 12.02 nm/°C is obtained. The proposed sensor not only has ultra-high temperature sensitivity, but also has scarcely response to physical quantities, such as refractive index, strain and so on. This sensor has reduced the generation of cross-talk in the measurement process, and has great application prospects in several fields.