# Symmetry-free tm-doped photonic crystal fiber with enhanced mode area

Enrico Coscelli, Carlo Molardi, Annamaria Cucinotta, Stefano Selleri

Research output: Contribution to journalArticle

12 Citations (Scopus)

### Abstract

Thulium-doped fiber lasers have recently attracted a growing interest because of the possibility to combine emission around 2 $\mu$m with the high beam quality and compactness provided by the fiber medium. A key factor for power scaling of these devices, especially if operation in the short-and ultrashort-pulse regime is desired, is the availability of active fibers capable of joining large effective area and robust single-mode guiding. The strong thermo-optic effect originating from the large quantum defect of Tm ions hinders the possibility to easily find a design with such features, strongly improving the confinement of high-order modes and shrinking the mode area of the fundamental one. In this paper, a rod-type double-cladding photonic crystal fiber with inner cladding properly designed without any mirror symmetry in the cross-section is presented, and its guiding properties are thoroughly analyzed by means of numerical simulations, taking into account the effects of thermally-induced refractive index change. The results have shown that, with a careful choice of the structural parameters, the proposed fiber is capable of ensuring effective high-order mode suppression and effective area up to 3800 2 when operating under heat load of about 300 W/m.

Original language English 6709780 IEEE Journal on Selected Topics in Quantum Electronics 20 5 https://doi.org/10.1109/JSTQE.2014.2299636 Published - Sep 1 2014 Yes

### Fingerprint

Photonic crystal fibers
Laser modes
photonics
fibers
Fibers
symmetry
Thulium
crystals
Beam quality
Fiber lasers
Ultrashort pulses
Joining
thulium
Optics
Refractive index
Mirrors
void ratio
Availability
fiber lasers

### Keywords

• single-mode regime
• thulium-doped fibers

### ASJC Scopus subject areas

• Atomic and Molecular Physics, and Optics
• Electrical and Electronic Engineering

### Cite this

Symmetry-free tm-doped photonic crystal fiber with enhanced mode area. / Coscelli, Enrico; Molardi, Carlo; Cucinotta, Annamaria; Selleri, Stefano.

In: IEEE Journal on Selected Topics in Quantum Electronics, Vol. 20, No. 5, 6709780, 01.09.2014.

Research output: Contribution to journalArticle

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AU - Cucinotta, Annamaria

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AB - Thulium-doped fiber lasers have recently attracted a growing interest because of the possibility to combine emission around 2 $\mu$m with the high beam quality and compactness provided by the fiber medium. A key factor for power scaling of these devices, especially if operation in the short-and ultrashort-pulse regime is desired, is the availability of active fibers capable of joining large effective area and robust single-mode guiding. The strong thermo-optic effect originating from the large quantum defect of Tm ions hinders the possibility to easily find a design with such features, strongly improving the confinement of high-order modes and shrinking the mode area of the fundamental one. In this paper, a rod-type double-cladding photonic crystal fiber with inner cladding properly designed without any mirror symmetry in the cross-section is presented, and its guiding properties are thoroughly analyzed by means of numerical simulations, taking into account the effects of thermally-induced refractive index change. The results have shown that, with a careful choice of the structural parameters, the proposed fiber is capable of ensuring effective high-order mode suppression and effective area up to 3800 2 when operating under heat load of about 300 W/m.

KW - Double-cladding photonic crystal fibers

KW - single-mode regime

KW - thulium-doped fibers

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