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Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 7 — Apr. 7, 2014
  • pp: 8574–8584
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Leakage channel fibers with microstuctured cladding elements: A unique LMA platform

Sonali Dasgupta, John R Hayes, and David J Richardson  »View Author Affiliations


Optics Express, Vol. 22, Issue 7, pp. 8574-8584 (2014)
http://dx.doi.org/10.1364/OE.22.008574


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Abstract

We present a novel design of leakage channel fiber (LCF) that incorporates an air-hole lattice to define the modal filtering characteristics. The approach has the potential to offer single-mode, large mode area (LMA) fibers in a single-material platform with bend loss characteristics comparable to all-solid (LCFs) whilst at the same time providing significant fabrication benefits. We compare the performance of the proposed fiber with that of rod-type photonic crystal fibers (PCFs) and all-solid LCFs offering a similar effective mode area of ~1600μm2 at 1.05μm. Our calculations show that the proposed fiber concept succeeds in combining the advantages of the use of small air holes and the larger design space of rod-type PCFs with the improved bend tolerance and greater higher order mode discrimination of all-solid LCFs, while alleviating their respective issues of rigidity and restricted material design space. We report the fabrication and experimental characterization of a first exemplar fiber, which we demonstrate offers a single-mode output with a fundamental mode area ~1440µm2 at 1.06µm, and that can be bent down to a radius of 20cm with a bend loss of <3dB/turn. Finally we show that the proposed design concept can be adopted to achieve larger mode areas (> 3000µm2), albeit at the expense of reduced bend tolerance.

© 2014 Optical Society of America

1. Introduction

The industrial need for cost-effective and compact high power laser sources has driven the rapid development and commercialization of fiber laser technology, leading to the host of innovative products to be found in the market place today. Continuous wave fiber laser systems operating with multi-kW average powers and short pulse systems operating at peak powers of up to ~1 GW are now considered indispensable tools in a host of important application areas that include: industrial materials processing (e.g. for welding, cutting and marking), defense (e.g. for directed energy application and countermeasures), fundamental science (e.g. for generating laser-induced plasmas and particle acceleration), and medicine (e.g. for various imaging modalities and surgical procedures) [1

1. Y. Jeong, A. J. Boyland, J. K. Sahu, S. Chung, J. Nilsson, and D. N. Payne, “Multi-kilowatt single-mode ytterbium-doped large-core fiber laser,” J. Opt. Soc. Korea 13(4), 416–422 (2009). [CrossRef]

11

11. H. Meng, J. Liao, Y. Zhou, and Q. Zhang, “Laser micro-processing of cardiovascular stent with fiber laser cutting system,” Opt. Laser Technol. 41(3), 300–302 (2009). [CrossRef]

].

Central to the power scaling of fiber lasers has been the development of large mode area (LMA) fibers capable of supporting and sustaining the ever increasing power levels. Rare earth doped LMA fibers are essential to the development of the lasers themselves and passive variants are important in fiber-based delivery of the beam directly from the laser output to where the laser light is ultimately to be used (which is often over a distance much longer than the length of fiber used in the laser itself). While hollow core bandgap fibers have recently garnered a lot of attention for high power beam delivery applications [6

6. M. Petrovich, N. Baddela, N. Wheeler, E. Numkam, R. Slavik, D. Gray, J. Hayes, J. Wooler, F. Poletti, and D. Richardson, “Development of Low Loss, Wide Bandwidth Hollow Core Photonic Bandgap Fibers,” in Optical Fiber Communication Conference/National Fiber Optic Engineers Conference (Optical Society of America, 2013), paper OTh1J.3. [CrossRef]

], here we seek a fiber design that is applicable to fiber lasers and amplifiers, which require a rare-earth doped silica glass core. Besides supporting a large fundamental mode (FM) area, state-of-the-art LMA fibers also need to be able to provide a number of critically important practical features. These include robust single-mode output, low fundamental mode loss and low bend loss sensitivity. Indeed, in the majority of commercially relevant cases a compromise needs to be struck between the use of fibers offering the maximum possible effective area and those offering better performance with regards to these more practical issues. Such considerations are beginning to significantly constrain system performance – particularly in the pulsed fiber laser area where nonlinear effects associated with high peak powers are the dominant consideration. Consequently, new approaches to LMA fibers offering different opportunities for trade-off between the key properties listed above are critical to the further development (and deployment) of fiber laser technology. For completeness, we note that the active management of beam distortion due to thermal load and optical nonlinearity through fiber design are also emerging topics [12

12. W. W. Ke, X. J. Wang, X. F. Bao, and X. J. Shu, “Thermally induced mode distortion and its limit to power scaling of fiber lasers,” Opt. Express 21(12), 14272–14281 (2013). [CrossRef] [PubMed]

]. However, these issues are beyond the scope of the current paper.

Rod-type Photonic Crystal Fibers (PCFs) have been very successful in offering large mode areas [13

13. J. Limpert, N. Deguil-Robin, I. Manek-Hönninger, F. Salin, F. Röser, A. Liem, T. Schreiber, S. Nolte, H. Zellmer, A. Tünnermann, J. Broeng, A. Petersson, and C. Jakobsen, “High-power rod-type photonic crystal fiber laser,” Opt. Express 13(4), 1055–1058 (2005). [CrossRef] [PubMed]

,14

14. J. Limpert, O. Schmidt, J. Rothhardt, F. Röser, T. Schreiber, A. Tünnermann, S. Ermeneux, P. Yvernault, and F. Salin, “Extended single-mode photonic crystal fiber lasers,” Opt. Express 14(7), 2715–2720 (2006). [CrossRef] [PubMed]

], however such fibers are extremely bend loss sensitive and the need to keep them rigid and straight means the typical device length is limited to ~1m, which restricts their application in many real-life systems. Similar limitations govern the more recently reported large pitch fibers that can to a large extent be considered a subset of rod-type PCFs, although they have been shown to exhibit very large mode areas up to ~8600µm2 [15

15. F. Jansen, F. Stutzki, T. Eidam, J. Rothhardt, S. Hädrich, H. Carstens, C. Jauregui, J. Limpert, and A. Tünnermann, “Yb-doped Large Pitch Fiber with 105µm Mode Field Diameter,” in Optical Fiber Communication Conference/National Fiber Optic Engineers Conference, (Optical Society of America, 2011), paper OTuC.

]. Thus, LMA fibers offering a certain degree of bend tolerance are highly desirable, and leakage channel fibers (LCFs) have attracted a lot of attention in this regard. Unlike the rod-type PCFs that are based on the endlessly single-mode feature of PCFs [16

16. T. A. Birks, J. C. Knight, and P. S. Russell, “Endlessly single-mode photonic crystal fiber,” Opt. Lett. 22(13), 961–963 (1997). [CrossRef] [PubMed]

], LCFs exploit the large differential leakage loss of the modes in a leaky fiber structure to achieve single mode output along with low bend loss for considerably large mode areas [17

17. L. Dong, X. Peng, and J. Li, “Leakage channel optical fibers with large effective area,” J. Opt. Soc. Am. B 24(8), 1689 (2007). [CrossRef]

]. The initial reports of LCFs showed their potential to offer mode areas of ~1500µm2 with a critical bend radius of 20 cm [17

17. L. Dong, X. Peng, and J. Li, “Leakage channel optical fibers with large effective area,” J. Opt. Soc. Am. B 24(8), 1689 (2007). [CrossRef]

]. However, in spite of such remarkable performance, the use of large air holes (hole diameter > 30µm) to define the leakage channels and their inevitable collapse/distortion during splicing/end termination renders air-hole LCFs impractical. A solution was proposed in the form of all-solid LCFs in which the air holes were replaced by F-doped rods [18

18. L. Dong, T. Wu, H. A. McKay, L. Fu, J. Li, and H. G. Winful, “All-glass large-core leakage channel fibers,” IEEE J. Sel. Top. Quantum Electron. 15(1), 47–53 (2009). [CrossRef]

]. These LCFs offer optical mode characteristics at par with the air-hole LCFs and their properties can be tailored by controlling the index difference between the core and the cladding rods. For example, a larger index difference enables a higher effective index difference between the modes, a lower mode loss sensitivity to index variations and reduced losses at smaller hole diameter to pitch ratio. However, in practice, the material design space is quite limited in the all-solid LCFs. In our experience, one of the most challenging issues when incorporating elements drawn from brought-in F-doped silica is that of bubble formation during fiber draw [19

19. E. M. Dianov, K. M. Golant, V. I. Karpov, R. R. Khrapko, A. S. Kurkov, V. M. Mashinsky, and V. N. Protopopov, “Fluorine-doped silica optical fibres fabricated using plasma chemical technologies,” Proc. SPIE 2425, 53–57 (1994). [CrossRef]

]. We note that the low draw speeds typical of special fiber fabrication and the large combined surface area of the elements inside a stacked preform, provide potential for bubble formation, which results in issues of poor surface quality and localized defects that can severely compromise fiber quality. This may be especially important where a large index contrast is created using a glass in which the dopant is not in thermodynamic equilibrium as is the case for high concentrations of fluorine [19

19. E. M. Dianov, K. M. Golant, V. I. Karpov, R. R. Khrapko, A. S. Kurkov, V. M. Mashinsky, and V. N. Protopopov, “Fluorine-doped silica optical fibres fabricated using plasma chemical technologies,” Proc. SPIE 2425, 53–57 (1994). [CrossRef]

]. These considerations can limit the maximum material index difference that is practical in F-doped rods to ~10−3 although F-doped preforms with an index difference of ~2.3 × 10−2 are commercially available. In fact, to the best of our knowledge, the maximum material index difference reported in fabricated all-solid LCFs to date has been limited to 1.2 × 10−3. In contrast, the proposed design, referred to as the micro-clad LCF from hereon, obviates the aforementioned issues by exploiting the higher index contrast of silica/air and the simplicity of a single material structure.

The micro-clad LCFs are based on the ‘leakage channel’ concept but alleviate the design limitations of the conventional LCFs and rod-type fibers while offering the advantages of these two very successful concepts in their own right, through a single fiber design [20

20. S. Dasgupta, J. R. Hayes, C. Baskiotis, and D. J. Richardson, “Novel all-silica large mode area fiber with microstructured cladding element,” in SPIE Photonics West, LASE (San Francisco, 2013).

]. We present fabrication and characterization results of a first exemplar micro-clad LCF and compare its performance with equivalent all-solid LCFs and rod-type PCFs.

2. Fiber design concept and simulation results

2.1 Modal characteristics

2.2 Bend performance

Based on Fig. 2, we choose a LMA design that offers an effective area of ~1600μm2 at 1.05μm, with a FM and HOM loss of ~0.05dB/m and 1dB/m, respectively. We confirmed that there are no other HOMs with lower losses that could compromise the single-modedness of the fiber. Figure 3
Fig. 3 Optical mode profile of the (a) LP01 and (b) LP11 modes of the designed fiber at 1.05µm. We simulate only one half of the fiber to optimize computational time.
shows the power distribution of the LP01 and LP11 mode of the chosen fiber. We then study the bend performance of the design to analyze its feasibility for compact systems and in applications that require meter lengths of fiber (e.g. parabolic pulse amplifiers,delivery fibers). Bending the fiber in almost all LMA designs not only increases the loss of the M, it also reduces the FM effective area, and in extremely small bends, distorts the mode shape. Figure 4
Fig. 4 Change in FM effective area, FM loss and LP11 mode loss with varying bend radii. Fiber core radius = 25µm. Λ2 = 0.18; air hole diameter = 1µm.
illustrates the change in effective area and loss of the FM of the designed fiber in the bent configuration (Rc is the bend radius); assuming the bend to be along the XX’ plane (clf. Figure 1). Bending the fiber along the orthogonal YY’ plane yields losses that are in line with the qualitative observations for all-solid LCFs [21

21. T. W. Wu, L. Dong, and H. Winful, “Bend performance of leakage channel fibers,” Opt. Express 16(6), 4278–4285 (2008). [CrossRef] [PubMed]

]. Bend loss of the fiber is calculated using the equivalent index model defined in [22

22. D. Marcuse, “Influence of curvature on the losses of doubly clad fibers,” Appl. Opt. 21(23), 4208–4213 (1982). [CrossRef] [PubMed]

], which is implemented using the finite element solver COMSOL Multiphysics ®. Figure 4 shows that the fiber can be bent down to a radius of ~45cm while maintaining the FM loss below 1dB/m.

This results in ~20% reduction in the effective area with ~75% confinement of the optical power within the notional core region. Tighter bends lead to a more significant reduction in the effective area and in addition to much higher FM propagation losses. Interestingly, bending the fiber does not seem to have a significant effect on the differential loss ratio although an optimum bending radius does exist that offers the largest ratio of loss between the FM and the first HOM. For even smaller bend radii, the loss ratio converges to a specific value (~7.2 in this case), depending on the fiber design.

2.3 Comparison with an equivalent all-solid LCF and rod-type PCF

2.4 Rare earth doping

Further depression of the core index increases the FM loss further and affects the bend sensitivity of the design. It is worthwhile to mention that although we simulated the scenario of a positive index difference (core index > silica glass) as well, which decreases the effective area, such a design would not be useful as the modes of the corresponding fiber would only support guided modes and would not offer any differential propagation loss/ mode filtering.

3. Fabrication and experimental results

3.1 Fiber characterization

Figure 7
Fig. 7 Fundamental mode image of the fabricated micro-clad LCF at a wavelength of 1.06µm.
shows the imaged facet of the fiber when light at a wavelength of 1.06µm was coupled to the input end of the fiber and the imaged output illuminated from the side in order to show both the transmitted mode and fiber structure. Without disturbing the setup, images were obtained with and without side illumination.

To estimate the mode field diameter (MFD), widths of the x and y Gaussians at the 13.5% height (1/e2) on the image were measured without side illumination and then scaled using the dimensions of the fiber structure. From this we estimate the effective area to be ~1440µm2. The most interesting aspect of the fabricated fiber was that even when it was loosely bent into a single turn of radius ~40cm, it was robustly single-moded and supported the FM only. A weak two-lobed HOM was observed only when the launch was highly offset from the center. We investigated this further as our simulations had predicted the existence of HOMs for the targeted design. SEM images of the fiber showed that the fiber matched our design reasonably well except that the air holes were somewhat larger (~1.65µm as compared to 1µm in the designed fiber). Consequently, we simulated the fabricated fiber with dimensions as obtained from the SEM images and our results showed that although the fabricated fiber supported the higher order LP11 mode, it was well separated from the FM in the effective index space with much higher confinement and bend loss. We did not observe the HOMs in our experiment, which was likely largely due to the fact that the fiber was excited with a Gaussian beam that would have favored the excitation of the fundamental mode.

4. Discussion

4.1 Fiber design for very large fundamental mode area (> 3000µm2)

5. Conclusion

In conclusion, we have presented a new design strategy that combines the desirable bending characteristics of all-solid LCFs with the splicing and handling advantages of single-material rod-type PCFs. The design allows for a greater flexibility in controlling the index difference between the core and the cladding through appropriate design of the microstructured cladding elements, which may also be easily individually altered to achieve polarization maintaining characteristics. We fabricated the first micro-clad LCF with FM effective area ~1440µm2 at 1.06µm and demonstrated its potential to offer compact high power fiber devices. We also showed that better mode discrimination and bending capability as compared to rod-type PCFs for very large effective areas exceeding 3000µm2 makes the proposed design highly attractive for achieving extremely large mode area fibers.

Acknowledgments

This work was supported by UK EPSRC through grant EP/H02607X/1 (EPSRC Centre for Advanced Manufacturing in Photonics)

References and links

1.

Y. Jeong, A. J. Boyland, J. K. Sahu, S. Chung, J. Nilsson, and D. N. Payne, “Multi-kilowatt single-mode ytterbium-doped large-core fiber laser,” J. Opt. Soc. Korea 13(4), 416–422 (2009). [CrossRef]

2.

A. Malinowski, A. Piper, J. H. V. Price, K. Furusawa, Y. Jeong, J. Nilsson, and D. J. Richardson, “Ultrashort-pulse Yb3+-fiber-based laser and amplifier system producing >25-W average power,” Opt. Lett. 29(17), 2073–2075 (2004). [CrossRef] [PubMed]

3.

F. Röser, T. Eidam, J. Rothhardt, O. Schmidt, D. N. Schimpf, J. Limpert, and A. Tünnermann, “Millijoule pulse energy high repetition rate femtosecond fiber chirped-pulse amplification system,” Opt. Lett. 32(24), 3495–3497 (2007). [CrossRef] [PubMed]

4.

http://phys.org/news/2013-06-incoherent-combining-fiber-lasers-energy.html

5.

P. F. Moulton, “High power Tm:silica fiber lasers: Current status, prospects and challenges,” in CLEO/Europe and EQEC 2011 Conference Digest (Optical Society of America, 2011), paper TF2_3.

6.

M. Petrovich, N. Baddela, N. Wheeler, E. Numkam, R. Slavik, D. Gray, J. Hayes, J. Wooler, F. Poletti, and D. Richardson, “Development of Low Loss, Wide Bandwidth Hollow Core Photonic Bandgap Fibers,” in Optical Fiber Communication Conference/National Fiber Optic Engineers Conference (Optical Society of America, 2013), paper OTh1J.3. [CrossRef]

7.

S. D. Jackson, “Towards high-power mid-infrared emission from a fibre laser,” Nat. Photonics 6(7), 423–431 (2012). [CrossRef]

8.

D. J. Richardson, J. Nilsson, and W. A. Clarkson, “High power fiber lasers: Current status and future perspectives,” J. Opt. Soc. Am. B 27(11), B63 (2010). [CrossRef]

9.

T. Hoult, J. Gabzdyl, and K. Dzurko, “Fiber Lasers in Solar Applications,” in Solar Energy: New Materials and Nanostructured Devices for High Efficiency (Optical Society of America, 2008), paper STuC3.

10.

P. Kah, J. Lu, J. Martikainen, and R. Suoranta, “Remote laser welding with high power fiber lasers,” Engineering 05(09), 700–706 (2013). [CrossRef]

11.

H. Meng, J. Liao, Y. Zhou, and Q. Zhang, “Laser micro-processing of cardiovascular stent with fiber laser cutting system,” Opt. Laser Technol. 41(3), 300–302 (2009). [CrossRef]

12.

W. W. Ke, X. J. Wang, X. F. Bao, and X. J. Shu, “Thermally induced mode distortion and its limit to power scaling of fiber lasers,” Opt. Express 21(12), 14272–14281 (2013). [CrossRef] [PubMed]

13.

J. Limpert, N. Deguil-Robin, I. Manek-Hönninger, F. Salin, F. Röser, A. Liem, T. Schreiber, S. Nolte, H. Zellmer, A. Tünnermann, J. Broeng, A. Petersson, and C. Jakobsen, “High-power rod-type photonic crystal fiber laser,” Opt. Express 13(4), 1055–1058 (2005). [CrossRef] [PubMed]

14.

J. Limpert, O. Schmidt, J. Rothhardt, F. Röser, T. Schreiber, A. Tünnermann, S. Ermeneux, P. Yvernault, and F. Salin, “Extended single-mode photonic crystal fiber lasers,” Opt. Express 14(7), 2715–2720 (2006). [CrossRef] [PubMed]

15.

F. Jansen, F. Stutzki, T. Eidam, J. Rothhardt, S. Hädrich, H. Carstens, C. Jauregui, J. Limpert, and A. Tünnermann, “Yb-doped Large Pitch Fiber with 105µm Mode Field Diameter,” in Optical Fiber Communication Conference/National Fiber Optic Engineers Conference, (Optical Society of America, 2011), paper OTuC.

16.

T. A. Birks, J. C. Knight, and P. S. Russell, “Endlessly single-mode photonic crystal fiber,” Opt. Lett. 22(13), 961–963 (1997). [CrossRef] [PubMed]

17.

L. Dong, X. Peng, and J. Li, “Leakage channel optical fibers with large effective area,” J. Opt. Soc. Am. B 24(8), 1689 (2007). [CrossRef]

18.

L. Dong, T. Wu, H. A. McKay, L. Fu, J. Li, and H. G. Winful, “All-glass large-core leakage channel fibers,” IEEE J. Sel. Top. Quantum Electron. 15(1), 47–53 (2009). [CrossRef]

19.

E. M. Dianov, K. M. Golant, V. I. Karpov, R. R. Khrapko, A. S. Kurkov, V. M. Mashinsky, and V. N. Protopopov, “Fluorine-doped silica optical fibres fabricated using plasma chemical technologies,” Proc. SPIE 2425, 53–57 (1994). [CrossRef]

20.

S. Dasgupta, J. R. Hayes, C. Baskiotis, and D. J. Richardson, “Novel all-silica large mode area fiber with microstructured cladding element,” in SPIE Photonics West, LASE (San Francisco, 2013).

21.

T. W. Wu, L. Dong, and H. Winful, “Bend performance of leakage channel fibers,” Opt. Express 16(6), 4278–4285 (2008). [CrossRef] [PubMed]

22.

D. Marcuse, “Influence of curvature on the losses of doubly clad fibers,” Appl. Opt. 21(23), 4208–4213 (1982). [CrossRef] [PubMed]

OCIS Codes
(060.2280) Fiber optics and optical communications : Fiber design and fabrication
(060.2400) Fiber optics and optical communications : Fiber properties
(060.2430) Fiber optics and optical communications : Fibers, single-mode
(060.4005) Fiber optics and optical communications : Microstructured fibers
(060.5295) Fiber optics and optical communications : Photonic crystal fibers

ToC Category:
Fiber Optics

History
Original Manuscript: November 21, 2013
Revised Manuscript: March 18, 2014
Manuscript Accepted: March 18, 2014
Published: April 3, 2014

Citation
Sonali Dasgupta, John R Hayes, and David J Richardson, "Leakage channel fibers with microstuctured cladding elements: A unique LMA platform," Opt. Express 22, 8574-8584 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-7-8574


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References

  1. Y. Jeong, A. J. Boyland, J. K. Sahu, S. Chung, J. Nilsson, D. N. Payne, “Multi-kilowatt single-mode ytterbium-doped large-core fiber laser,” J. Opt. Soc. Korea 13(4), 416–422 (2009). [CrossRef]
  2. A. Malinowski, A. Piper, J. H. V. Price, K. Furusawa, Y. Jeong, J. Nilsson, D. J. Richardson, “Ultrashort-pulse Yb3+-fiber-based laser and amplifier system producing >25-W average power,” Opt. Lett. 29(17), 2073–2075 (2004). [CrossRef] [PubMed]
  3. F. Röser, T. Eidam, J. Rothhardt, O. Schmidt, D. N. Schimpf, J. Limpert, A. Tünnermann, “Millijoule pulse energy high repetition rate femtosecond fiber chirped-pulse amplification system,” Opt. Lett. 32(24), 3495–3497 (2007). [CrossRef] [PubMed]
  4. http://phys.org/news/2013-06-incoherent-combining-fiber-lasers-energy.html
  5. P. F. Moulton, “High power Tm:silica fiber lasers: Current status, prospects and challenges,” in CLEO/Europe and EQEC 2011 Conference Digest (Optical Society of America, 2011), paper TF2_3.
  6. M. Petrovich, N. Baddela, N. Wheeler, E. Numkam, R. Slavik, D. Gray, J. Hayes, J. Wooler, F. Poletti, and D. Richardson, “Development of Low Loss, Wide Bandwidth Hollow Core Photonic Bandgap Fibers,” in Optical Fiber Communication Conference/National Fiber Optic Engineers Conference (Optical Society of America, 2013), paper OTh1J.3. [CrossRef]
  7. S. D. Jackson, “Towards high-power mid-infrared emission from a fibre laser,” Nat. Photonics 6(7), 423–431 (2012). [CrossRef]
  8. D. J. Richardson, J. Nilsson, W. A. Clarkson, “High power fiber lasers: Current status and future perspectives,” J. Opt. Soc. Am. B 27(11), B63 (2010). [CrossRef]
  9. T. Hoult, J. Gabzdyl, and K. Dzurko, “Fiber Lasers in Solar Applications,” in Solar Energy: New Materials and Nanostructured Devices for High Efficiency (Optical Society of America, 2008), paper STuC3.
  10. P. Kah, J. Lu, J. Martikainen, R. Suoranta, “Remote laser welding with high power fiber lasers,” Engineering 05(09), 700–706 (2013). [CrossRef]
  11. H. Meng, J. Liao, Y. Zhou, Q. Zhang, “Laser micro-processing of cardiovascular stent with fiber laser cutting system,” Opt. Laser Technol. 41(3), 300–302 (2009). [CrossRef]
  12. W. W. Ke, X. J. Wang, X. F. Bao, X. J. Shu, “Thermally induced mode distortion and its limit to power scaling of fiber lasers,” Opt. Express 21(12), 14272–14281 (2013). [CrossRef] [PubMed]
  13. J. Limpert, N. Deguil-Robin, I. Manek-Hönninger, F. Salin, F. Röser, A. Liem, T. Schreiber, S. Nolte, H. Zellmer, A. Tünnermann, J. Broeng, A. Petersson, C. Jakobsen, “High-power rod-type photonic crystal fiber laser,” Opt. Express 13(4), 1055–1058 (2005). [CrossRef] [PubMed]
  14. J. Limpert, O. Schmidt, J. Rothhardt, F. Röser, T. Schreiber, A. Tünnermann, S. Ermeneux, P. Yvernault, F. Salin, “Extended single-mode photonic crystal fiber lasers,” Opt. Express 14(7), 2715–2720 (2006). [CrossRef] [PubMed]
  15. F. Jansen, F. Stutzki, T. Eidam, J. Rothhardt, S. Hädrich, H. Carstens, C. Jauregui, J. Limpert, and A. Tünnermann, “Yb-doped Large Pitch Fiber with 105µm Mode Field Diameter,” in Optical Fiber Communication Conference/National Fiber Optic Engineers Conference, (Optical Society of America, 2011), paper OTuC.
  16. T. A. Birks, J. C. Knight, P. S. Russell, “Endlessly single-mode photonic crystal fiber,” Opt. Lett. 22(13), 961–963 (1997). [CrossRef] [PubMed]
  17. L. Dong, X. Peng, J. Li, “Leakage channel optical fibers with large effective area,” J. Opt. Soc. Am. B 24(8), 1689 (2007). [CrossRef]
  18. L. Dong, T. Wu, H. A. McKay, L. Fu, J. Li, H. G. Winful, “All-glass large-core leakage channel fibers,” IEEE J. Sel. Top. Quantum Electron. 15(1), 47–53 (2009). [CrossRef]
  19. E. M. Dianov, K. M. Golant, V. I. Karpov, R. R. Khrapko, A. S. Kurkov, V. M. Mashinsky, V. N. Protopopov, “Fluorine-doped silica optical fibres fabricated using plasma chemical technologies,” Proc. SPIE 2425, 53–57 (1994). [CrossRef]
  20. S. Dasgupta, J. R. Hayes, C. Baskiotis, and D. J. Richardson, “Novel all-silica large mode area fiber with microstructured cladding element,” in SPIE Photonics West, LASE (San Francisco, 2013).
  21. T. W. Wu, L. Dong, H. Winful, “Bend performance of leakage channel fibers,” Opt. Express 16(6), 4278–4285 (2008). [CrossRef] [PubMed]
  22. D. Marcuse, “Influence of curvature on the losses of doubly clad fibers,” Appl. Opt. 21(23), 4208–4213 (1982). [CrossRef] [PubMed]

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