Compact High Power Fiber Lasers Research Articles

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.

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.

A bend-resistant double-trench fiber with leakage channels for HOMs suppression

A double trench fiber with parabolic-profile core (PPDTF) and leakage channels (LC-PPDTF) is proposed in this paper. Due to the leakage channels, the loss of the higher-order modes (HOMs) is enhanced dramatically while the fundamental mode is hardly affected. High loss ratio (>400) of the higher-order modes to the fundamental mode is achieved in a wide range of bend radius and bend orientation at wavelength 1.06μm. The highest loss ratio reaches 2211, which is 62% higher than that of ordinary PPDTF without leakage channels. A large mode area of more than 450 μm2 hardly varies with the bend radius is realized. The fiber with a 100 μm core diameter and a mode area over 1284 μm2 is also presented. This fiber design shows great potential in compact high-power fiber lasers and amplifiers.

Bend-resistant side-leakage photonic crystal fiber with large-mode-area

A bend-resistant side-leakage photonic crystal fiber with large-mode-area (LMA) is proposed. Simulation results demonstrate that the robust single-mode operation is obtained thanks to an extremely high loss ratio (the minimum loss of high order modes to the loss of fundamental mode (FM)) at the wavelength of 2 μm while the bend radius is as small as 10 cm. Meanwhile, the FM suffers a low bend loss of 0.006 dB m−1 with an effective mode area exceeding 2000 μm2. The bend-resistant performance can be maintained over a broad range of wavelengths from 1.75 to 2.5 μm. Except for a wide waveband, a large tolerance for bend radius is also obtained. The fiber is able to operate under single-mode operation within a range of bend radius from 9 to 24 cm. LMA and single-mode operation under a small bend radius make this fiber have great potential in developing compact high power fiber lasers.

Bending characteristic of large-mode-area fibers with uniaxial crystal material cladding

Abstract A large-mode-area (LMA) fiber with uniaxial crystal material cladding is proposed in this paper. The modified refractive index of the cladding is derived, and bend-induced characteristics of a fiber with cladding made of potassium dihydrogen phosphate (KDP) are numerically investigated using Finite Element Method (FEM). The simulation results indicate that effective mode area (Aeff) of the KDP-cladding fiber with maximum core radius of 21 μm is up to 785.58 μm2 that is 19 μm2 greater than that of conventional silica-based LMA fiber with maximum core radius of 22 μm. Furthermore, single-mode length of this KDP-cladding fiber is 3 m shorter than that of conventional silica-based fiber, and it is helpful for suppressing nonlinear effects. Results suggest that KDP-cladding fiber can effectively mitigate bend-induced mode area compression, maintain the high beam quality and reduced nonlinear effects. These excellent properties of the proposed LMA fibers are potential for developing a compact high power fiber laser and amplifier system.

Bend-resistant low bending loss and large mode area single-mode fiber with low NA

• We have designed a novel low bending loss and large mode area single-mode fiber with low NA. The proposed fiber can provide high leakage loss ratio (776) between the high-order modes (HOMs) and fundamental mode (FM). • The bending loss of FM and HOMs as function of number of trenches is researched in the paper. The bending loss and effective mode area will decrease as number of trench increase. Without ring and trench in core and cladding, the bending loss of FM and HOM are small and that cannot realize the single-mode operation. Loss ratio is smallest in all of fibers. • The HOMs suppression is better than the traditional step-index fibers (SIF). Furthermore, bending loss can be reduced to about 0.0074 dB/m which is lower than previous study. Effective mode area can achieve 744.49 μm 2 at 15 cm bending radius. This fiber design shows great potential in developing compact high-power fiber lasers and amplifiers. A novel design of trench in cladding with resonant ring is proposed in this paper. Performances of proposed fiber have been numerically investigated by the finite element method with a perfectly matched layer boundary. Simulation shows that the proposed fiber can provide high leakage loss ratio (776) between the high-order modes (HOMs) and fundamental mode (FM) which is beneficial to realize robust single-mode operation to enhance the transverse mode instabilities at a wavelength of 1080 nm. The HOMs suppression is better than the traditional step-index fibers (SIF). Furthermore, the bending loss can be reduced to about 0.0074 dB/m due to the trench in the cladding, and the effective mode area can achieve 744.49 μm 2 at 15 cm bend radius, which is also beneficial to improve transmission efficiency. The advantage of an all-solid structure along with a much simpler fabrication process makes our approach very suitable for realizing very large mode area fibers for high power fiber laser application.

Bend resistant large mode area fiber with step-index core and single trench

Abstract A novel bend resistant large mode area fiber with step-index core and single trench in the cladding is proposed. Numerical results demonstrate that the largest effective mode area reaches up to 2460 μm2 at the wavelength of 2 μm when the bend radius is only 10 cm. To achieve the better performance of single mode, the loss ratio of the lowest loss of higher order mode to the highest loss of fundamental mode can reach up to 886 with a fundamental mode bend loss lower than 0.0083 dB/m through optimizing structure parameters. The circular symmetry of fiber structure makes it insensitive to the bending direction. Furthermore, this fiber structure can be also used to develop bend resistant large mode area fiber with high performance at the wavelengths of 1.06 μm and 1.55 μm. Due to large mode area, good single mode properties, small bend radius and insensitivity to bend direction, this fiber has the potential application for compact high power fiber lasers.

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.

Influence of quasi-periodic cladding on single mode behavior in a leakage channel fiber: Towards the enhancement of modal discrimination and low bending loss of the LP01 mode

A silica quasi-periodic clad leakage channel fiber (LCF) is proposed to enhance the mode filtering characteristics with large effective mode area (Aeff). In this work, we explore the fiber characteristics, namely, bending loss (BL), Aeff and differential loss for different micro-structured cladding LCF designs. Of the various LCFs, an octagonal core–octagonal quasi-periodic clad LCF provides a large loss ratio (>103) between fundamental mode (LP01 mode) and most competitive higher order mode (LP11 mode). Further, it exhibits a high BL of 66.48dB/m for LP11 mode by resonance mode filtering along with a bend induced modal discrimination at 1.05μm wavelength. The detailed numerical results reveal that the differential loss ratio goes high when the effective index of the second ring of eight sectional elements in a quasi-periodic cladding is scaled up and the Aeff increases when it is scaled down. Thus, the proposed octagonal core–octagonal quasi-periodic clad LCF exhibits a large mode area of 1161μm2, a low BL of 0.04dB/m for the LP01 mode and a high differential loss ratio of 1624 between LP11 and LP01 modes at a critical bending radius of 15cm with an air-filling ratio of 0.4. These interesting properties of the LCF could pave way for developing a compact high power fiber laser system.

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.

Bend Resistant Large Mode Area Fiber With Multi-Trench in the Core

A bend resistant large mode area fiber with multitrench in the core is proposed. Four layers of trenches with high refractive index are introduced to modulate the mode field distribution. Low refractive index trenches in traditional designs are replaced with pure silica trenches to reduce the difficulty of manufacture. Meanwhile, the core region with a refractive index higher than pure silica cladding conforms to the practical requirement for active fibers. Numerical investigations show that single mode operation with a mode field area of 1100 μm2 is achieved at a bend radius of 15 cm. This design shows the potential of mode field scaling for multitrench fibers and makes a contribution to compact high power fiber lasers.

Rectangle Lattice Large Mode Area Photonic Crystal Fiber for 2 $\mu$m Compact High-power Fiber Lasers

A rectangle lattice silica-host photonic crystal fiber with large mode area (LMA) is successfully fabricated for the first time. The introduction of rectangle lattice contributes to distinct leakage of second order modes and two large air holes provide an effective solution to suppress bend distortion. Numerical results demonstrate that a large mode field area (MFA) of 2500 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is achieved at the wavelength of 2 μm when the fiber is straight. While the fiber is bent to a radius of 30 cm, it confirms to single-mode (SM) operation conditions and the decrements of MFA at x polarization and y polarization are just 4.3% and 5%. Within a bend orientation angle of ± 10° and a wide wavelength range from 1.8 μm to 2.4 μm, the fiber can operate under single-mode (SM) conditions with low bend loss. LMA, SM operation, and small bend distortion make this fiber of great potential in developing 2 μm compact high-power fiber lasers.

Bending Orientation Insensitive Large Mode Area Photonic Crystal Fiber With Triangular Core

In view of the feasibility of fabrication and application, a bending orientation insensitive large mode area photonic crystal fiber with triangular core is proposed. This fiber structure breaks the limit of bend orientation angle and realizes single mode operation under any bending orientation angle at the bending radius of 30 cm. The mode field area of the fundamental mode at the wavelength of 1.064 μm achieves 1386 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the straight state and 1154 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at a bending radius of 30 cm, respectively. The decrement of the mode field area at the bent state is only 16.85% compared to that at the straight state. The large mode area at the bent state, small decrement of the mode field area, and low sensitivity of bending orientation make the fiber of great potential in compact high power fiber lasers.

Photonic Crystal Fiber With Large Mode Area and Characteristic Bending Properties

We report on a photonic crystal fiber with a large mode area designed for compact high power fiber lasers and amplifiers. The fiber suppresses higher order modes when bent around a 10-cm radius and enables single mode operation in small footprint laser and amplifier architectures. We experimentally confirm the peculiar bending properties of this fiber in its passive version, by reporting on the measurement results of fundamental mode loss in bent and straight fibers, and of the influence of the bending plane orientation on this fiber loss.