Segmented Cladding Fiber Research Articles

Single-Mode Segmented Cladding Chalcogenide Glass Fiber With Ultra-Large Mode Area

Small core size in conventional single mode step-indexed chalcogenide fiber could reduce the ability of mid-infrared (mid-IR) laser power delivery due to its limitation of power density. An effective way to solve the problem is to increase mode area with large core size, but this may degrade the beam quality. In this work, a novel mid-IR segmented cladding fiber (SCF) with leakage structure based on chalcogenide glasses was proposed to obtain large mode area, as well as single-mode condition. The leakage loss and effective mode area of the SCF was analyzed by optimizing the segment number <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> , duty cycle γ and core radius <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> . The results show that, when <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> =4, γ=75% and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> =33 μm, the mode area is more than 2000 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the wavelength range of 3-10 μm and the loss ratio of high order modes (LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ) to fundamental mode (LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> ) is more than 300, indicating the SCF can achieve single-mode operation with a large core. Then, a mid-IR SCF was fabricated via an extrude-and-stack technique based on chalcogenide glasses for the first time. The minimum fiber loss is 3.1 dB/m at 8.6 μm, the bend loss is 3 dB when bend radius is 6 mm. Compared with that in the traditional step-index single-mode fiber, it was found that, the mode area in SCF can be increased over 15 times. All these results demonstrate the SCF possesses the potential of high-power mid-IR laser transmission.

The Optimization of a Segmented Cladding Fiber via the Response Surface Methodology Approach for a Large Mode Area

In this work, we have proposed and optimized a segmented cladding fiber (SCF) with a large mode area (LMA) consisting of a uniform core and a double cladding. The outer cladding of the SCF consisted of a periodic alternation of high- and low-refractive-index segments, while the inner cladding consisted of a resonant layer of rods surrounded by high-refractive-index rings. The three geometrical parameters chosen as design variables were the (a) doped rod refractive index differences, (b) refractive index differences of rings, and (c) ring thickness. Using the Box–Behnken approach, we selected thirteen different design cases and modeled them numerically using the finite element method (FEM). In order to optimize the features of the proposed fiber, such as the effective mode area (EMA), we applied response surface methodology (RSM). The EMA of the optimal SCF was significantly improved and markedly enlarged to about 706 µm2 at a wavelength of 1.550 µm. Different properties of the optimized double-cladding octo-wing SCF (DC-OW-SCF), such as confinement losses in the core mode and the first higher-order mode, were studied. The DC-OW-SCF offers the advantages of feasibility in fabrication using the powder-in-tube (PIT) method and provides the possibility of utilization in compact amplifier devices and high-power fiber lasers.

Optimized segmented cladding fiber for extreme large mode area using latin hypercube sampling

In this paper a new design of octo-wing segmented cladding fiber (SCF) with a uniform core containing a ring and a non-uniform double cladding was proposed and optimized. The Latin hypercube sampling was applied to generate design cases as the input values for estimation of the objective functions as the output variables. Three physical parameters of the core assisted ring: thickness, radius, and refractive index difference were selected as the design variables. Twenty different design cases were numerically simulated by finite element method. To optimize the effective mode area (EMA) as the objective function, response surface methodology was applied. The fiber offers the single mode operation with a confinement loss ratio of over 100 between the fundamental mode (FM) and the higher order mode (HOM). Operating at the wavelength of 1.550μm, the EMA is significantly enlarged to about 884μm2. We have investigated the properties of the proposed optimized ring assisted SCF (RA-SCF) in terms of confinement losses of FM and first HOM considering a perfect matched layer. The proposed RA-SCF provides the potential applications in compact high power fiber lasers.

Large mode area multi segmented-trench crisscross fiber with resonance and leakage

In this paper, a multi segmented-trench crisscross fiber (STCF) is proposed. The multi STCF is designed from the segmented cladding fiber (SCF) and multi-trench fiber (MTF). A multi STCF is a SCF whose low index claddings are cut off by two layers of high index rings, then rotate the middle layer claddings. The high index rings are inserted into claddings to add the effect of resonance. The rotation of middle layer claddings makes the claddings distribution crisscross, thus restricting the excessive loss of core modes. Multi STCF is researched and compared to others four fibers with similar structures. The multi STCF has great advantages on large mode area and single-mode operation. When the bending radius is 20 cm, the multi STCF core radius can extend to 27 μm. And the mode area achieves 987 μm2 while simultaneously keeping large high order modes suppression. Multi STCF combines the resonance and leakage effects to adjust mode loss while enlarging the mode area. Besides, the fiber can also suit single-mode operation under certain heat load. This research has meaningful values on high power fiber lasers.

Bend-resistant octo-wing silica segmented cladding fiber with high index rings

We have proposed a novel segmented cladding fiber (SCF) design and the bending effects were investigated in detail. The proposed SCF with large mode area properties has a uniform circular core and octo-wings of rods with higher refractive index than the silica segments in the cladding. While the high index octo-wings improved the waist of the electrical field distribution of the fundamental mode (FM), the lower index segments enabled SCF to be bend-resistant. We numerically investigated the light guiding properties through the proposed SCF by using finite element method with a perfectly matched layer. SCF was investigated in terms of effective mode area, confinement loss in bent state and it was shown that the proposed SCF is insensitive to the bending angle. By applying high index rings around the rods in octo-wings and optimizing the structure, we obtained an effective mode area as large as 715 µm2 at the wavelength of 1.55 µm with a relatively large loss ratio between FM and first higher order mode of about 137. Effective single mode operation was achieved at a tight bending radius of 10 cm over a wide wavelength range from 1 µm to 1.7 µm. The novel proposed SCF gives the advantages of fabrication feasibility by the method of powder-in-tube process. Octo-wing SCF could be applied for compact amplifiers and high power fiber lasers.

Silica Segmented Cladding Fiber Design and Its Fabrication Using a Powder-in-Tube Technique

A new design of segmented cladding fiber (SCF) was proposed and fabricated in silica glass. The silica glass SCF had a central core and hexagonal wings with higher refractive indices than silica cladding. The proposed SCF was analyzed numerically in terms of the confinement loss and the effective mode area using finite element method (FEM). In experiments, SCF preform was prepared by a stack-and-draw method using two types of pre-drawn rods: silica rods for the cladding and Al-doped silica rods for the higher refractive index segments and the central core. The latter was fabricated in the powder in tube (PIT) process by optimizing the heating cycles and the bubble removal during the sintering process. Light guidance along the SCF was experimentally confirmed and its intensity patterns in the near-field at the wavelengths 0.980 m and 1.550 m were characterized. With the proposed SCF, all silica SCF fabrication feasibility was confirmed, which can open a new alternative for large mode area fibers.

Segmented Cladding Fiber With a High-Index Ring in Core for Wideband Single-Mode Operation in Any Bending Orientation

A resonant-ring-assisted large mode area segmented cladding fiber (RR-SCF) with a high-index ring in the core is proposed. Numerical investigations of the effects of the high-index ring on the leakage losses of guiding modes, mode area, and electric field distribution of FM of the proposed fiber show the high-index ring not only increases the ratio of the loss between the fundamental mode (FM) and the higher-order modes (HOMs) but also improves the electric field distribution of the FM to be flat. By taking these advantages of the high-index-ring-assisted core, the effective single-mode (SM) operation is achieved in the proposed fiber bent in any orientation, which makes up the defect of the conventional RR-SCF that the SM output is affected by the bending orientation. Meanwhile, the mode area is enlarged. Furthermore, the effects of the heat load, duty cycle, bending, and operation wavelength on the fiber performance are analyzed. The results show single-mode operation in all bending orientations with a mode area larger than 824 μm2 can be achieved at a tight bending radius of 15 cm to 16 cm when the operating wavelength ranges from 1.06 μm to 1.76 μm. This fiber shows great potential in high-power fiber lasers.

Resonant-ring assisted large mode area segmented cladding fiber with high-index rings in core

This paper proposes a modified segmented cladding fiber with two-layer high-index rings in the core. The inner high-index ring helps to increase the loss ratio between the higher-order modes (HOMs) and the fundamental mode (FM) to achieve single-mode operation. The outer high-index ring is beneficial to improve the waist of the electric field distribution of the FM to enlarge the mode area. The simulation results show thanks to the joint defect of these two-layer high-index rings, the defect of the RR-SCF that cannot provide single-mode operation in all bending orientations is made up. Effective single-mode operation is achieved at a tight bending radius of 15 cm when the operating wavelength ranges from 1.06 μm to 1.58 μm. The mode area of the fiber operating at 1.06 μm is markedly enlarged to 835 μm2. This new fiber shows great potential in compact high-power fiber lasers and amplifiers.

Thermally Induced Mode Amplification Characteristics of Large Mode Area Segmented Cladding Fiber

A model of amplifier based on large mode area (LMA) segmented cladding fiber (SCF) is proposed. High order modes (HOMs) filtering effect and thermal-induced modal evolution characteristics are theoretically investigated by the few-mode steady state rate equations and heat conduction equation. Simulation results show that an amplifier based on ytterbium doped SCF presents much better HOMs suppression and mode beam quality than the amplifier based on conventional step-index fiber when achieving single-mode operation by coiling fiber. Furthermore, heat load generating in the core of ytterbium doped SCF can change the pre-designed refractive index profile through the thermo-optic effect, which induces evolution of mode amplification characteristics, including mode loss decreasing and mode area shrinking. And the co-pumping amplifier ytterbium doped SCF is more advantageous to get large mode area of fundamental mode at the output end, while single-mode operation is achieved much more effectively in the counter-pumping amplifier. These results can provide guidance in the design of high-power single-mode fiber amplifier based on rare-earth doped LMA-SCF.

Amplification characteristics in active tapered segmented cladding fiber with large mode area

Abstract A kind of tapered segmented cladding fiber (T-SCF) with large mode area (LMA) is proposed, and the mode and amplification characteristics of T-SCFs with concave, linear, and convex tapered structures are investigated based on finite-element method (FEM) and few-mode steady-state rate equation. Simulation results indicate that the concave tapered structure can introduce high loss for high-order modes (HOMs) that is advantageous to achieve single-mode operation, whereas the convex tapered structure provides large effective mode area that can help to mitigate nonlinear effects. Meanwhile, the small-to-large amplification scheme shows further advantages on stripping off HOMs, and the large-to-small amplification scheme decreases the heat load density induced by the high-power pump. Moreover, single-mode propagation performance, effective mode area, and heat load density of the T-SCF are superior to those of tapered step index fiber (T-SIF). These theoretical model and numerical results can provide instructive suggestions for designing high-power fiber lasers and amplifiers.

A bending-resistant large mode area pixelated trench assisted segmented cladding fiber

In this paper, a novel bend-resistant large mode area fiber with pixelated trench-assisted segmented cladding is proposed and investigated. This structure has large mode area and excellent higher order modes (HOMs) suppression. Numerical results show, when the bending radius is 20 cm and the operating wavelength is 1.06μm, the effective mode area of the fiber can reach 914μm2 and the loss ratio between lowest-HOMs and fundamental mode is larger than 100. In addition, the proposed optical fiber is insensitive to the bending direction. This fiber has great potential in high power fiber lasers and amplifiers.

Imaginary‐distance beam‐propagation method based on Yee's mesh in cylindrical coordinates

AbstractAn imaginary‐distance beam‐propagation method based on Yee's mesh (ID‐YM‐BPM) is developed in cylindrical coordinates, in which the mode number of the eigenmode field is strictly considered. The ID‐YM‐BPM is second‐order accurate with respect to the spatial mesh size. A segmented cladding fiber is analyzed, showing good agreement with other methods.

Bending-Resistant Design of a Large Mode Area Segmented Cladding Fiber With Resonant Ring

A novel design of segmented cladding fiber (SCF) with resonant ring is proposed in this paper. A high leakage loss ratio (>100) between the high-order modes (HOMs) and the fundamental mode can be achieved at wavelength 1.064 μm. The HOMs suppression is better than the traditional SCF. The numerical results show that the effectively single-mode operation with a mode area of 790 μm2 can be achieved at a bend radius of 15 cm. Besides, the fiber performance is insensitive to the bending orientation at the ranging of [−180°, 180°]. This fiber design shows great potential in developing compact high-power fiber lasers and amplifiers.

Design and analysis of a modified segmented cladding fiber with parabolic-profile core

A novel segmented cladding fiber structure is proposed in this paper for large-mode area properties. In this structure, a parabolic-profile core is surrounded by segmented cladding. It is called parabolic-profile core segmented-cladding fiber. The novel fiber has a better single-mode operation than segmented-cladding fiber. A large effective area of 980 µm2 is achieved. It is found that the effective-mode area does not vary with the changing of the bending radius. The bending performance does not change with varying the bending orientation.

Detailed study of bending effects in large mode area segmented cladding fibers.

This paper studies the bending effects on segmented cladding fibers (SCFs) in detail. Rod-type SCFs have offered large effective mode areas (EMAs) very successfully. The low-index segments in the design also enable the optical fibers to be bend-resistant. In this paper, the bending performance of the SCFs has been investigated by using the finite element method. The results indicate that SCFs can provide low-loss effective single-mode operation in a wide bandwidth under a bent configuration, due to the leakage losses of the higher-order modes (HOMs). A large ratio between the HOMs and the fundamental mode losses can be ensured, over a wide range of duty cycle, refractive index difference, and bending radius. Therefore, the required fabrication accuracy decreases. The mode loss ratio and EMA are independent of the bending orientation. Operating at 1550nm and 10cm bend radius, large EMA (754 μm2) is achievable with a large loss ratio (>30). The trade-offs between loss, EMA, and bending are studied. The structure has potential for compact high power fiber lasers, amplifiers, and beam delivery applications.

Design and analysis of a modified segmented cladding fiber with large mode area

This paper proposes a novel segmented cladding fiber structure for large mode area properties. In this structure a thin ring is placed between the high index core and nonuniform cladding. It is called Single-Ring Segmented-Cladding Fiber (SR-SCF). The novel fiber offers the possibility of single-mode(SM) operation from 1µm to 1.7µm with a large core diameter. With illustrations, the fiber has a better SM operation than segmented-cladding fiber (SCF) is demonstrated. A large effective area of 1000µm2 is achieved. The SM operation with very high suppression of the higher order modes can arise by 76%. Moreover, mode spacing between the adjacent modes (LP01 and LP11) is also improved significantly. Besides, the bending property is analyzed. It is found that the fiber is insensitive to bending angle ranging from −180° to 180° at bending radius of 30cm. The proposed fiber will play an important role in developing high power fiber laser, fiber amplifier and high power delivery application.

Segmented cladding fiber fabricated in silica-based glass

We report fabrication of a segmented cladding fiber (SCF) in silica-based glass. An SCF with a uniform core of pure silica and cladding of periodically arranged pure silica and fluorine-doped silica in an angular direction has been fabricated by using the stack-and-draw technique. The fabricated fiber has been characterized by capturing its near-field intensity pattern at 633 nm wavelength. The number of modes has been estimated from the captured near-field intensity pattern by using neural network analysis. A four-segment SCF of 30- μ m core diameter and 0.43% relative index differences between the high- and low-index segments shows few-mode operation by filtering out higher-order modes of an otherwise highly multimode fiber.

Design of segmented cladding fiber for femtosecond laser pulse delivery at 1550 and 1064 nm wavelengths

Segmented cladding fiber (SCF) is capable of single mode operation over an extended range of wavelengths while maintaining large mode area. In this paper we report the design of an SCF with mode area as large as 1,825 \(\upmu \hbox {m}^{2}\), suitable for delivery of high peak power femtosecond laser pulses at 1550 and 1064 nm wavelengths. An SCF with such a large-mode area is a few-moded fiber and its design requires careful choice of design parameters to have robustness against mode-coupling effects and bend loss. In this paper we address these issues and report a design of an SCF showing near distortion-free propagation of 100-fs, 53-kW peak power pulses at 1550-nm wavelength with 1,825-\(\upmu \hbox {m}^{2}\) mode area through fundamental mode. The same fiber can also deliver 250-fs, 15-kW peak power pulses at 1064-nm wavelength with 1,793-\(\upmu \hbox {m}^{2}\) mode area. The fiber has been analyzed by using the radial effective-index method in conjunction with transfer matrix method and the pulse propagation has been studied by solving the nonlinear Schroedinger equation by split-step Fourier method. Such a fiber would find applications in multiphoton microscopy and in biomedical engineering.

Birefringence analysis of segmented cladding fiber

We present a full-vectorial modal analysis of a segmented cladding fiber (SCF). The analysis is based on the H-field vectorial finite element method (VFEM) employing polar mesh geometry. Using this method, we have analyzed the circular SCF and the elliptical SCF. We have found that the birefringence of the circular SCF is very small (1.0×10(-8)). Birefringence of a highly elliptical SCF can be altered to some extent by the number of segments and duty cycle of segmentation in the segmented cladding. However, the change is not profound. The analysis shows that the circular SCF possesses low birefringence and that the segmented cladding does not add any significant birefringence in an elliptical fiber. This result strongly indicates that small deviations in the segmented cladding parameters arising from fabrication process do not significantly affect the birefringence of the fiber.

Fabrication of segmented cladding fiber by bicomponent spinning

AbstractFabrication of segmented cladding fiber (SCF) by bicomponent spinning was proposed in this article. In the new designed spin pack, we considered the high refractive component of cladding and core as a whole to control the cross section of the fiber. Quenching system in current bicomponent melting spinning system was modified according to the requirement of quenching fiber with a large size. The polymer SCF with required cross section was successfully fabricated using polycarbonate and polymethyl methacrylate. The transmission loss in the wavelength of 500–1000 nm was tested by the cut‐back method. The result showed that the transmission loss of the obtained fiber was comparatively high, being up to 30 dB/m. The output light pattern of the obtained fiber of 60 cm was collected by using a charge‐coupled device camera with laser light of 532 nm as the input. The output light pattern for the far field was a uniform circle and that for the near field was similar to the cross‐section designed. The results showed that the obtained fiber was still a multimode optical fiber because of the comparatively large refractive index difference between the two materials used. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers