Polarization-maintaining Fiber Research Articles

High fidelity amplification of radially-polarized laser in few-mode polarization-maintaining fiber amplifier

A high-power 20/400-μm few-mode polarization-maintaining (PM) fiber amplifier with a radially polarized output beam is firstly demonstrated and investigated. The reconstructed beam profiles and mode contents of the output laser were obtained using a numerical method. Experimentally, a home-made fiberized mode convertor was employed to convert the LP01 mode to be TM01 mode (radially polarized beam) with an average power of 2 W. In addition, the mode purity and polarization purity were 98.76%, and 98.5%, respectively. Based on a few-mode PM fiber amplifier, instead of the commonly used non-PM fiber amplifier, the radially polarized beam was scaled up to 192.1 W, while preserving the donut-shaped intensity distribution. The corresponding mode purity and polarization purity were measured to be approximately 97% and 98.2%, respectively, which indicates the polarization characteristic of the TM01 mode was preserved well. The beam quality factor (M2) was measured to be ∼2.2. Additionally, long-term stability in terms of both output power and polarization state were also verified experimentally. To the best our knowledge, this is the highest output power from a few-mode PM fiber amplifier laser system, while maintaining a high mode purity and a high polarization purity for radially polarized beam.

High sensitivity Sagnac interferometric temperature sensor using stress region refractiveindex modulation.

An all-fiber temperature sensor employing intentional refractive index modulation is experimentally demonstrated. The sensor consists of four sections of polarization maintaining fiber (FPMF) sandwiched between multi-mode fiber (MMF). The stress region of two sections of polarization maintaining fibers (PMFs) is aligned and then anti-clockwise rotates one PMF in 10deg angles while the other keeps still. Finally, the discharge proceeds. The remaining two PMFs are fusion spliced with the same method. Then the prepared FPMF-MMF structure is connected to the 3dB coupler to construct a Sagnac loop. The temperature sensitivity reaches 1.49nm/°C for a temperature range from 16°C to 55°C. The proposed temperature sensor with easy fabrication and good linearity in measuring temperature can be a promising candidate for various applications in environmental monitoring and industrial production.

Belt conveyor speed detection based on fiber-optic Sagnac interferometer vibration sensor

With their long transportation distance and high productivity, belt conveyors are characterized as the main equipment for bulk material transportation in coal mines and other key industries. However, its speed detection method has always been an engineering challenge under harsh working conditions. In this work, the elastic-optical effect of the polarization-maintaining fiber is used to design a fiber ring laser vibration sensing system based on a fiber-optic Sagnac interferometer vibration sensor and its packaging structure. The vibration detection is achieved by detecting the change in optical power at the working wavelength, and the belt conveyor speed measurement is completed by detecting the vibration frequency. With such a method, the belt conveyor speed measurement obtained a relative error of less than 1.88%. The proposed method bears the characteristics of anti-electromagnetic interference, intrinsic explosion-proof, and adapts to the harsh smoke and dust working environment, which has a wide range of application prospects in the fields of engineering, machinery, security, etc.

High-power, highly efficient, all-fiber wavelength-tunable polarization-maintaining Tm-doped fiber MOPA system

A 2 μm all-fiber wavelength-tunable polarization-maintaining Tm-doped fiber master oscillator power amplifier (MOPA) system is presented. We demonstrate an all-fiber ring cavity Tm-doped fiber master-oscillator (MO) with a tuning range of 60 nm (1959.9–2020.1 nm). The maximum output power of 82.4 mW is obtained at 1991 nm with the launched pump power of 16 W at 793 nm, corresponding to a slope efficiency of 10.8 % concerning launched pump power. Finally, through the first stage amplification, the power is successfully amplified to 38.92 W, the slope efficiency is about 31.4 %, and the polarization extinction ratio (PER) reaches 21.4 dB. Then a theoretical simulation is carried out to calculate the influence of different fiber lengths on the slope efficiency and output power of the amplifier stage when the pump power is increased to 420 W, which provides theoretical guidance for the subsequent experiments. Through the simulation, it is found that the output power will be greatly improved by choosing the appropriate fiber length and increasing the pump power.

Temperature and Twist Sensor Based on the Sagnac Interferometer with Long-Period Grating in Polarization-Maintaining Fiber.

We utilized a CO2 laser to carve long-period fiber gratings (LPFGs) on polarization-maintaining fibers (PMFs) along the fast and slow axes. Based on the spectra of LPFGs written along two different directions, we found that when LPFG was written along the fast axis, the spectrum had lower insertion loss and fewer side lobes. We investigated the temperature and twist characteristics of the embedded structure of the LPFG and Sagnac loop and ultimately obtained a temperature sensitivity of -0.295 nm/°C and a twist sensitivity of 0.87 nm/(rad/m) for the LPFG. Compared to the single LPFG, the embedded structure of the LPFG and Sagnac loop demonstrates a significant improvement in temperature and twist sensitivities. Additionally, it also possesses the capability to discern the direction of the twist. The embedded structure displays numerous advantages, including easy fabrication, low cost, good robustness, a wide range, and high sensitivity. These features make it highly suitable for applications in structural health monitoring and other related fields.

35 Core Polarization-Maintaining Multi-core Fiber for High Power Operation

This work presents a novel rod-type 35 core multi-core fiber design that is capable of overcoming the inherent lack of polarization maintenance in such structures. A polarization extinction ratio of 10.5dB is achieved.

High-sensitivity Simultaneous Demodulation of Multi-parameters in Polarization-maintaining Fibers Based on Brillouin Dynamic Gratings

High-sensitivity Simultaneous Demodulation of Multi-parameters in Polarization-maintaining Fibers Based on Brillouin Dynamic Gratings

Distributed phase-matching measurement for dynamic strain and temperature sensing based on stimulated Brillouin scattering enhanced four-wave mixing

A Brillouin dynamic grating (BDG) can be used for distributed birefringence measurement in optical fibers, offering high sensitivity and spatial resolution for sensing applications. However, it is quite a challenge to simultaneously achieve dynamic measurements with both high accuracy and high spatial resolution. In this work, we propose a sensing mechanism to achieve distributed phase-matching measurement using a chirped pulse as a probe signal. In BDG reflection, the peak reflection corresponds to the highest four-wave mixing (FWM) conversion efficiency, and it requires the Brillouin frequency in the fast and slow axes to be equal, which is called the phase-matching condition. This condition changes at different fiber positions, which requires a range of frequency injection for the probe wave. The proposed method uses a chirped pulse as a probe wave to cover this frequency range associated with distributed birefringence inhomogeneity. This allows us to detect distributed phase matching for birefringence changes that are introduced by temperature and strain variations. Thanks to the single shot and direct time delay measurement capability, the acquisition rate in our system is only limited by the fiber length. Notably, unlike conventional BDG spectrum recovery-based systems, the spatial resolution here is determined by both the frequency chirping rate of the probe pulse and the birefringence profile of the fiber. In the experiments, an acquisition rate of 1 kHz (up to fiber length limits) and a spatial resolution of 10 cm using a 20 ns probe pulse width are achieved. The minimum detectable temperature and strain variation are 5.6 mK and 0.37 με along a 2 km long polarization-maintaining fiber (PMF).

High-power long-picosecond pulse fiber laser at 2 μm with a narrow spectral width

Herein, stable mode-locked pulse trains with an ultra-narrow linewidth at the 2 μm region were obtained in a compact all polarization-maintaining fiber oscillator, which can directly deliver nearly transform-limited pulse with a duration of ∼105.6 ps and a spectral width of ∼86 pm. Relying on the multistage Tm-doped fiber amplifier chains, the output power of ∼19.42 W with a narrow linewidth and the maximum output power of ∼100.7 W were obtained, respectively. The narrow linewidth pulse laser may have the promising potential applications in mid-infrared spectroscopy and polymer processing.

Entanglement-enabled decoherence-free transmission of two-color photons through a single mode fiber.

We demonstrate decoherence-tolerant transmission of a Bell state through a single-mode fiber (SMF) using the photon frequency degree of freedom. To this end, a slightly non-degenerate polarization-entangled singlet, |Ψ -⟩=(|HV⟩-|VH⟩)/2, is localized at the SMF as the depolarization channel subject to random noise due to incessant fiber bending. Two-photon beats and quantum state tomography jointly verify the absence of collective decoherence, showing that |Ψ -⟩ is the sought-after one-dimensional decoherence-free subspace (DFS) pertaining to SMF. Efficient splitting and combining of photon streams in our DFS help outperform the DFS in time domain. This motivates us to attempt DFS-enabled fault-tolerant fiber transmission of biphoton qubits. Two-photon BB84 protocol is implemented in a polarization-maintaining fiber to which dephasing noise is relevant so that a two-dimensional DFS is appropriate. A low bit error rate 5.4% is achieved by encoding one-qubit information onto the biphoton state in spite of significant polarization fluctuation. Our scalable frequency-based DFS has a natural affinity for wavelength division multiplexing in fiber communication by design and as such is extensible to multi-particle entanglement.

Polarization-resolved mode evolution in TMI-limited Yb-doped fiber amplifiers using a novel high-speed Stokes polarimeter.

In this work we have developed a high-speed Stokes polarimeter method based on simultaneous 4-channel imaging with a high-speed camera. Thus, current speed limitations of imaging polarimeters for wavelengths around 1 µm can be overcome, allowing a sub-ms polarization-resolved characterization of transverse mode instability (TMI). Additionally, the Stokes parameters of each individual mode are calculated by a simultaneous 4-beam mode reconstruction algorithm during post-processing and can be analyzed with unprecedented temporal resolution. We demonstrate the measurement capabilities of this polarimeter setup by characterizing TMI of a large-mode-area Yb-doped polarization maintaining (PM) fiber amplifier with 30 kHz video frame rate. Upon thorough characterization, we have found for the first time that at the onset of TMI in a PM fiber, the modal polarization states begin to oscillate on circular and elliptical trajectories at the same frequencies as the modal energy transfer occurs. The ability to measure the modal polarization states with sub-ms temporal resolution is key to developing a fundamental understanding and subsequently possible mitigation strategies of TMI in PM-fiber lasers.

4.6 kW linearly polarized and narrow-linewidth monolithic fiber amplifier based on a fiber oscillator laser seed

In this work, a record output power of 4.6 kW linearly polarized and narrow-linewidth fiber amplifier based on an optimized fiber oscillator laser (FOL) seed was realized by employing a homemade polarization-maintaining Yb-doped fiber (PMYDF), corresponding to a slope efficiency of 79.5% and a 3 dB linewidth of 0.3452 nm. Through an effective strategy relying on decreasing the transmission fiber length from 200 m to 120 m and adding a chirped and tilted fiber Bragg grating (CTFBG), the stimulated Raman scattering (SRS) effects were well-suppressed. By applying the forward combiner with the interconnection between the pump arms into the MOPA system, the MI threshold is increased by more than 560 W and the slope efficiency of the upgraded MOPA system is boosted by 5%. During the experimental process of power amplification, the polarization extinction ratio (PER) remains higher than 15 dB, and a near-diffraction-limited output beam at the laser power of 2980 W was measured with the M2x = 1.314 and M2y = 1.311.

Enhancing polarization maintenance and spectral filtering in negative curvature hollow-core fibers

A new design of polarization-maintaining and spectral filtering negative curvature hollow-core fiber tailored for the telecommunication bands in the near-infrared region is presented. The optical fiber, consisting of a six-tube silica structure, incorporates vertically nested tubes anchored radially by a pole structure. By contrast, standard nested tubes in the horizontal direction form the asymmetric fiber structure, which encounters birefringence. This unique fiber design not only preserves the polarization states of light but also exhibits frequency selective transmission exclusively in the vertical direction due to the pole structure. Through fiber design optimization, a transmission loss below 0.1 dB/km for spectrally filtered wavelengths is achieved, with birefringence on the order of 10−5 within the wavelength range of 1.45 µm to 1.60 µm. These results demonstrate significant improvements in terms of birefringence, distinct loss separation between horizontally and vertically polarized states, and a reduced number of spectrally filtered wavelengths compared to previously reported findings. The proposed fiber design holds untapped potential for applications requiring selective transmissions with specific polarization.

Tunable narrow-linewidth fiber laser based on an optically controlled tunable filter

A tunable narrow-linewidth fiber laser based on an optically controlled tunable filter is demonstrated. The filter consists of ytterbium-doped polarization-maintaining fibers (YD-PMF) and polarization-maintaining fibers (PMF), which are fused together with an angle offset of 90 degrees between their fast axes. This allows for the flexible adjustment of the wavelength of the laser by changing the pump power injected into the YD-PMF. A tuning range of 16.99 nm, spanning from 1547.87 nm to 1564.86 nm, has been achieved. The laser's linewidth and optical signal-to-noise ratio (OSNR) are approximately 300 Hz and over 32.38 dB, respectively. Additionally, the fluctuation in wavelength and power of the laser are kept to less than 0.02 nm and 0.14 dB within two hours, respectively.

1.9–2.4 μm Tunable Dual-Comb From a Polarization-Maintaining Single-Cavity Bidirectional Fiber Laser

1.9–2.4 μm Tunable Dual-Comb From a Polarization-Maintaining Single-Cavity Bidirectional Fiber Laser

1200-W all polarization-maintaining fiber GHz-femtosecond-pulse laser with good beam quality

In this work, we demonstrate a 1200-W average power all polarization-maintaining (PM) fiber ultrafast laser system operating at 1.0 µm. In accordance with the numerical modeling, the PM fiber laser system is designed and it delivers linearly-polarized femtosecond pulses at a 1.39-GHz fundamental repetition rate, with a maximum output power of 1214 W — to the best of our knowledge, the highest average power from all PM fiber ultrafast laser at 1.0 µm to date. The pulse width can be compressed to ∼800 fs with a beam quality of M2 < 1.1. This kilowatt-class all PM fiber laser system is expected to open new potential for high energy pulse generation through temporal coherent combination and laser ablation using GHz burst fs laser.

Mode attraction, rejection and control in nonlinear multimode optics

Novel fundamental notions helping in the interpretation of the complex dynamics of nonlinear systems are essential to our understanding and ability to exploit them. In this work we predict and demonstrate experimentally a fundamental property of Kerr-nonlinear media, which we name mode rejection and takes place when two intense counter-propagating beams interact in a multimode waveguide. In stark contrast to mode attraction phenomena, mode rejection leads to the selective suppression of a spatial mode in the forward beam, which is controlled via the counter-propagating backward beam. Starting from this observation we generalise the ideas of attraction and rejection in nonlinear multimode systems of arbitrary dimension, which paves the way towards a more general idea of all-optical mode control. These ideas represent universal tools to explore novel dynamics and applications in a variety of optical and non-optical nonlinear systems. Coherent beam combination in polarisation-maintaining multicore fibres is demonstrated as example.

Femtotesla 87Rb magnetometer based on a coaxial pump-probe beam delivery system

Advancements in highly sensitive and miniaturized spin-exchange relaxation-free atomic magnetometers have attracted significant attention. Although dual-beam magnetometers with high sensitivity have been developed, miniaturization while maintaining sensitivity remains challenging. In this study, we present a novel magnetometer configuration featuring a coaxial pump-probe beam delivery system facilitated by a single polarization-maintaining optical fiber. Utilizing polarized atoms to probe the diffuse central region of a ring pump beam, we achieved optimized performance through parameter adjustments, including the power of the pump and probe beams, modulation index, and other key factors. The magnetometer exhibited a remarkable sensitivity of 15 fT/Hz1/2. In addition, we introduced a novel method for evaluating the polarizability of alkali metals. The proposed magnetometer configuration shows considerable potential for advancing the field of highly sensitive miniaturized atomic magnetometers that are well suited for magnetocardiography (MCG) and magnetoencephalography (MEG) applications.

Polarization-Maintaining Fiber Loop Mirror Based Ultrasound Sensing Technique With Enhanced Signal-to-Noise Ratio

Polarization-Maintaining Fiber Loop Mirror Based Ultrasound Sensing Technique With Enhanced Signal-to-Noise Ratio

Switchable noise-like pulse generation in an all-polarization-maintaining thulium-doped fiber laser

In this paper, a tuning method based on temperature control of a piece of polarization-maintaining dispersion compensation fiber (PMDCF) is proposed in an all-polarization-maintaining (all-PM) thulium-doped fiber laser. The proposed tuning method simplifies the tuning parameter of the all-PM fiber laser, and various patterns of noise-like pulse (NLP) output can be realized only by adjusting the temperature of the PMDCF. The rectangular-shaped NLP, NLP bunches, the coexistence of rectangular-shaped NLP and NLP bunches, double rectangular-shaped NLP, and the switching between them are observed only through changing the temperature of the PMDCF, which helps to improve the research on the underlying physical mechanism of NLP. To the best of our knowledge, this is the first report of various patterns of NLP and their switching phenomena in an all-PM thulium-doped fiber laser.