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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 23 — Nov. 8, 2010
  • pp: 23523–23528
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Saturable absorber Q- and gain-switched all-Yb3+ all-fiber laser at 976 and 1064 nm

Tzong-Yow Tsai, Yen-Cheng Fang, Huai-Min Huang, Hong-Xi Tsao, and Shih-Ting Lin  »View Author Affiliations


Optics Express, Vol. 18, Issue 23, pp. 23523-23528 (2010)
http://dx.doi.org/10.1364/OE.18.023523


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Abstract

We demonstrate a novel passively pulsed all-Yb3+ all-fiber laser pumped by a continuous-wave 915-nm pump laser diode. The laser was saturable absorber Q-switched at 976 nm and gain-switched at 1064 nm, using the method of mode-field-area mismatch. With a pump power of 105 mW, the laser iteratively produced a 976-nm pulse with an energy of 2.8 μJ and a duration of 280 ns, followed by a 1064-nm pulse with 1.1 μJ and a 430-ns duration at a repetition rate of 9 kHz. A set of rate equations was established to simulate the self-balancing mechanism and the correlation between the Q- and gain-switched photon numbers and the populations of the gain and absorber fibers.

© 2010 OSA

1. Introduction

A pulsed fiber laser could provide high peak power density with good flexibility that is useful for applications of medicine, nonlinear optics and efficient pumping of fiber lasers. Q-switched fiber lasers could be achieved using the conventional bulk Q-switches, such as acousto-optic modulators (AOM) [1

1. J. A. Alvarez-Chavez, H. L. Offerhaus, J. Nilsson, P. W. Turner, W. A. Clarkson, and D. J. Richardson, “High-energy, high-power ytterbium-doped Q-switched fiber laser,” Opt. Lett. 25(1), 37–39 (2000). [CrossRef]

,2

2. H. Zhao, Q. Lou, J. Zhou, F. Zhang, J. Dong, Y. Wei, and Z. Wang, “Stable pulse-compressed acousto-optic Q-switched fiber laser,” Opt. Lett. 32(19), 2774–2776 (2007). [CrossRef] [PubMed]

] and solid-state saturable absorbers [3

3. M. Laroche, H. Gilles, S. Girard, N. Passilly, and K. Aït-Ameur, “Nanosecond pulse generation in a passively Q-switched Yb-doped fiber laser by Cr4+:YAG saturable absorber,” IEEE Photon. Technol. Lett. 18(6), 764–766 (2006). [CrossRef]

,4

4. L. Pan, I. Utkin, and R. Fedosejevs, “Two-wavelength passively Q-switched ytterbium doped fiber laser,” Opt. Express 16(16), 11858–11870 (2008). [CrossRef] [PubMed]

]. A bulk Q-switch aligned in a fiber resonator generally comes with complexities of alignment, packaging and maintenance, and large losses of signal coupling into and out of the fiber cores. The internal Fresnel reflection caused by the air gaps between the bulk and the fibers could also lead to undesired wavelength competitions and noise by amplified spontaneous emission (ASE), especially in a high-gain Q-switched resonator. All-fiber Q-switched lasers with no air gap in the resonators have recently attracted the attention of researchers because of the relative small cavity loss and negligible internal Fresnel reflection that favor Q-switching operations in high-gain fiber resonators.

Sequential Q-switching in an all-fiber laser could be achieved actively using a piezoelectric transducer (PZT) [5

5. D. W. Huang, W. F. Liu, and C. C. Yang, “Q-switched all-fiber laser with an acoustically modulated fiber attenuator,” IEEE Photon. Technol. Lett. 12(9), 1153–1155 (2000). [CrossRef]

7

7. M. Delgado-Pinar, D. Zalvidea, A. Díez, P. Pérez-Millan, and M. V. Andrés, “Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating,” Opt. Express 14(3), 1106–1112 (2006). [CrossRef] [PubMed]

] and passively by a fiber-type saturable absorber Q-switch (SAQS) [8

8. L. Tordella, H. Dejellout, B. Dussardier, A. Saissy, and G. Monnom, “High repetition rate passively Q-switched Nd3+:Cr4+ all fibre laser,” Electron. Lett. 39(18), 1307–1308 (2003). [CrossRef]

17

17. A. Siegman, “Passive Saturable Absorber Q-switching,” in Lasers (University Science Books, 1986), Chap. 26.3, pp. 1024–1033.

]. Passive Q-switching using a SAQS fiber is of particular interest because of the relative advantages of holding up very large roundtrip gain before Q-switching and no extra electric driving circuit required. Nevertheless, the drawback is the eligibility of a SAQS fiber that is restricted to a certain laser medium in a limited wavelength range where the absorption cross section (σa) of the SAQS is larger than the emission cross section (σe) of the laser gain medium. This threshold criterion of saturable-absorber Q switching results in a difficulty in finding suitable SAQS fiber materials, especially for a laser medium that has a very large σe at the desired Q-switching wavelength.

Most SAQS fibers to date are silicate fibers doped with rare earth ions, such as Tm3+ for erbium fiber lasers 1.57-1.6 μm [9

9. T.-Y. Tsai, Y.-C. Fang, and S.-H. Hung, “Passively Q-switched erbium all-fiber lasers by use of thulium-doped saturable-absorber fibers,” Opt. Express 18(10), 10049–10054 (2010). [CrossRef] [PubMed]

], Ho3+ for thulium fiber lasers at 2 μm [10

10. S. D. Jackson, “Passively Q-switched Tm(3+)-doped silica fiber lasers,” Appl. Opt. 46(16), 3311–3317 (2007). [CrossRef] [PubMed]

], and Tm3+, Sm3+, Ho3+, bismuth (not rare earth) for ytterbium fiber lasers at the wavelengths of 1055-1090, 1085, 1050-1160 and 1125 nm, respectively, where the Yb3+ fiber has a relatively small σe [11

11. P. Adel, M. Auerbach, C. Fallnich, S. Unger, H.-R. Müller, and J. Kirchhof, “Passive Q-switching by Tm3+co-doping of a Yb3+-fiber laser,” Opt. Express 11(21), 2730–2735 (2003). [CrossRef] [PubMed]

14

14. V. V. Dvoyrin, V. M. Mashinsky, and E. M. Dianov, “Yb-Bi pulsed fiber lasers,” Opt. Lett. 32(5), 451–453 (2007). [CrossRef] [PubMed]

]. Recently, we demonstrated all-fiber erbium lasers passively Q-switched with erbium fibers, using a mode-filed-area (MFA) mismatch method [15

15. T.-Y. Tsai, Y.-C. Fang, Z.-C. Lee, and H.-X. Tsao, “All-fiber passively Q-switched erbium laser using mismatch of mode field areas and a saturable-amplifier pump switch,” Opt. Lett. 34(19), 2891–2893 (2009). [CrossRef] [PubMed]

,16

16. T.-Y. Tsai and Y.-C. Fang, “A self-Q-switched all-fiber erbium laser at 1530 nm using an auxiliary 1570 nm erbium laser,” Opt. Express 17(24), 21628–21633 (2009). [CrossRef] [PubMed]

] that successfully enhanced the photon density through the SAQS fiber and thereby eased the SAQS threshold criterion. These methods are applicable to the 3-level laser media that can also serve as 2-level saturable absorbers, such as a 915-nm pumped Yb3+ fiber lasing at 976 nm.

2. Experiments

Figure 1
Fig. 1 Schematic design of a self-balancing passively Q- and gain-switched all-Yb3+ all-fiber laser.
depicts the schematic design of a passively Q- and gain-switched ytterbium all-fiber laser system. The laser was CW-pumped by a 915-nm laser diode (LD) through a 915/976-nm WDM coupler that protected the LD from the 976-nm pulses leaked out of the high-reflectivity (HR) FBG. The 976-nm resonator consisted of a HR FBG, a FBG of 11%R, a large-core ytterbium gain fiber with a calculated fundamental mode field diameter (MFD) of 7 μm and an ytterbium SAQS fiber with a relatively small MFD of 3.5 μm. The gain fiber was 30 cm long with absorption strength of 75 dB at 976 nm. The SAQS fiber was 110 cm long with 976-nm absorption strength of 36 dB. A 915/976-nm WDM was located between the gain fiber and the SAQS to prevent the SAQS from the 915-nm pump. The SAQS was also the gain medium in the 1064-nm intracavity formed with a HR FBG and a FBG of 80%R. The resonator lengths of 976 and 1064 nm were about 10 and 3 meters, respectively. The output 976-nm and 1064-nm pulses were separated by a 976/1064-nm WDM and detected by two InGaAs photo-detectors that were connected to an oscilloscope.

The MFA ratio of 976 nm between the gain fiber and the SAQS was about 4, which caused a calculable transmission loss near 2 dB and an enhanced photon density in the SAQS. When the laser reached the threshold, the enhanced photon density induced a quick bleaching of the SAQS, followed by a passively Q-switched 976-nm pulse. Figure 2
Fig. 2 The manifolds of the 2F5/2 and 2F7/2 levels of Yb3+ fibers, and the correlation between the gain fiber Q-switched at 976 nm and the SAQS fiber gain-switched at 1064 nm (or 1 to 1.1 μm).
illustrates the correlation of the lasing and absorption between the manifolds in 2F5/2 and 2F7/2 of the gain fiber and the SAQS. Because of negligible σe at 0.9-0.97 μm and σa at 1-1.1 μm, an Yb3+ resonator is considered a quasi-three-level laser at 976 nm and quasi-four-level laser at 1064 nm.

Figure 3
Fig. 3 (a) Sequentially saturable absorber Q-switched pulses (signal above) and gain-switched pulses simultaneously detected and monitored on an oscilloscope. (b) Single pulsing of 976 and 1064 nm observed in a minor scale. The time spacing between the 976- and 1064-nm pulses was 1.1 μs with a standard deviation of 0.04 μs.
shows sequential Q- and gain-switched pulses at Rrp ~9 kHz that were detected and simultaneously monitored by a two-channel oscilloscope. The wavelengths of the two outputs were verified to be individually 976 nm and 1064 nm by an Oriel Cornerstone monochromator. The time spacing between the Q- and gain-switched pulses, ΔTs, was 1.1 μs with a standard deviation of 0.04 μs. The pulse of 976 nm had a full width at half maximum (FWHM) of 280 ns, an estimated energy of 2.8 μJ and a peak power of 10 W. Correspondingly, the pulse of 1064 nm had a pulse width of 430 ns, an energy of 1.1 μJ and a peak power of 2.6 W. Figure 4
Fig. 4 (a) Normalized 976-nm pulse repetition rate, pulse energy and width relative to the applied CW pump power. (b) Normalized time spacing (ΔTs) between the pulses of 976 and 1064 nm, 1064-nm pulse energy and width relative to the CW pump power.
presents the measured output characteristics of the 976- and 1064-nm pulses, the Rrp, and ΔTs, relative to the applied 915-nm CW pump power from 72 to 105 mW.

3. Modeling and simulation

A set of four rate equations Eq. (1-4) are modified based on Siegman’s three rate equations [17

17. A. Siegman, “Passive Saturable Absorber Q-switching,” in Lasers (University Science Books, 1986), Chap. 26.3, pp. 1024–1033.

] for modeling the interaction between the Q- and gain-switched photon numbers, n1 and n2 (correspondingly at λ1 and λ2), the gain population of the gain fiber, Ng, and the absorption population of the SAQS, Na, as shown below:

dn1dt=(KgNgKaNaα1)×n1,
(1)
dn2dt=(Kg2Ngsα2)×n2,
(2)
dNgdt=RpNg+(pg1)NgTτ2pgKgn1Ng,
(3)
dNadt=NaTNaτ2pa(Kan1NaKg2n2Ngs).
(4)

The coupling coefficients Kg and Ka are defined to be σe1/(Agt1) and σa1/(Aat1), respectively, where σe1 and σa1, respectively, are the emission and absorption cross sections at λ1, Ag and Aa are the fundamental mode-field areas in the gain and SAQS fibers, respectively, and t1 is the one-way-trip transmit time of the Q-switched resonator. The coupling coefficient Kg2 is σe2/(Ag2t2), where σe2 is the σe at λ2, Ag2 is the mode-field area of λ2 in the SAQS fiber, and t2 is the one-way-trip transmit time of the gain-switched resonator. The factors α1 and α2 are the non-saturable cavity losses in the resonators of λ1 and λ2, respectively, Rp is the pump rate of Ng, and τ2 is the relaxation lifetime of the excited state 2F5/2 (~0.8 ms for Yb fiber). NgT and NaT are the total Yb3+ populations in the gain and SAQS fibers, respectively, and pg and pa are (1 + σa1/σe1) and (1 + σe1/σa1), respectively. Ng and Na are the factors for Q switching, defined to be Ng2-(σa1/σe1)Ng1 and Na1-(σe1/σe1)Na2, respectively. The gain population, Ngs, in the gain-switched resonator of λ2 has a time-independent relation with Na as

Ngs=1pa((1σa2σe1σe2σa1)NT(1+σa2σe2)Na).
(5)

4. Conclusion

We have demonstrated a passively Q- and gain-switched all-Yb3+ all-fiber laser at 976 and 1064 nm using the MFA-mismatch method. To the best of our knowledge, this is the first Q-switched ytterbium fiber laser demonstrated at 976 nm. With CW 915-nm pump power of 105 mW, a Q-switched pulse with an energy of 2.8 μJ and a width of 280 ns followed by a gain-switched pulse with 1.1-μJ and a 430-ns width was achieved at a repetition rate of 9 kHz. In addition, the rate equations of the Q- and gain-switched photon numbers and the populations of the gain and SAQS fibers were established to simulate the self-balancing mechanism and the pulse characteristics that were in good agreement with the experimental results. The rate equations and system simulation are helpful in providing understanding and further optimization of the laser system.

Acknowledgements

The authors are grateful for the financial supports from the National Science Council of Taiwan (Project No. NSC 99-2221-E-006-151) and the Industrial Technology Research Institute, Tainan, Taiwan (Project No. B200-99DE1).

References and links

1.

J. A. Alvarez-Chavez, H. L. Offerhaus, J. Nilsson, P. W. Turner, W. A. Clarkson, and D. J. Richardson, “High-energy, high-power ytterbium-doped Q-switched fiber laser,” Opt. Lett. 25(1), 37–39 (2000). [CrossRef]

2.

H. Zhao, Q. Lou, J. Zhou, F. Zhang, J. Dong, Y. Wei, and Z. Wang, “Stable pulse-compressed acousto-optic Q-switched fiber laser,” Opt. Lett. 32(19), 2774–2776 (2007). [CrossRef] [PubMed]

3.

M. Laroche, H. Gilles, S. Girard, N. Passilly, and K. Aït-Ameur, “Nanosecond pulse generation in a passively Q-switched Yb-doped fiber laser by Cr4+:YAG saturable absorber,” IEEE Photon. Technol. Lett. 18(6), 764–766 (2006). [CrossRef]

4.

L. Pan, I. Utkin, and R. Fedosejevs, “Two-wavelength passively Q-switched ytterbium doped fiber laser,” Opt. Express 16(16), 11858–11870 (2008). [CrossRef] [PubMed]

5.

D. W. Huang, W. F. Liu, and C. C. Yang, “Q-switched all-fiber laser with an acoustically modulated fiber attenuator,” IEEE Photon. Technol. Lett. 12(9), 1153–1155 (2000). [CrossRef]

6.

D. Zalvidea, N. A. Russo, R. Duchowicz, M. Delgado-Pinar, A. Díez, J. L. Cruz, and M. V. Andrés, “High repetition rate acoustic-induced Q-switched all-fiber laser,” Opt. Commun. 244(1-6), 315–319 (2005). [CrossRef]

7.

M. Delgado-Pinar, D. Zalvidea, A. Díez, P. Pérez-Millan, and M. V. Andrés, “Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating,” Opt. Express 14(3), 1106–1112 (2006). [CrossRef] [PubMed]

8.

L. Tordella, H. Dejellout, B. Dussardier, A. Saissy, and G. Monnom, “High repetition rate passively Q-switched Nd3+:Cr4+ all fibre laser,” Electron. Lett. 39(18), 1307–1308 (2003). [CrossRef]

9.

T.-Y. Tsai, Y.-C. Fang, and S.-H. Hung, “Passively Q-switched erbium all-fiber lasers by use of thulium-doped saturable-absorber fibers,” Opt. Express 18(10), 10049–10054 (2010). [CrossRef] [PubMed]

10.

S. D. Jackson, “Passively Q-switched Tm(3+)-doped silica fiber lasers,” Appl. Opt. 46(16), 3311–3317 (2007). [CrossRef] [PubMed]

11.

P. Adel, M. Auerbach, C. Fallnich, S. Unger, H.-R. Müller, and J. Kirchhof, “Passive Q-switching by Tm3+co-doping of a Yb3+-fiber laser,” Opt. Express 11(21), 2730–2735 (2003). [CrossRef] [PubMed]

12.

A. A. Fotiadi, A. S. Kurkov, and I. M. Razdobreev, “All-fiber passively Q-switched Ytterbium laser,” 2005 Conference on Lasers and Electro-Optics Europe, p. 515.

13.

A. S. Kurkov, E. M. Sholokhov, and O. I. Medvedkov, “All fiber Yb-Ho pulsed laser,” Laser Phys. Lett. 6(2), 135–138 (2009). [CrossRef]

14.

V. V. Dvoyrin, V. M. Mashinsky, and E. M. Dianov, “Yb-Bi pulsed fiber lasers,” Opt. Lett. 32(5), 451–453 (2007). [CrossRef] [PubMed]

15.

T.-Y. Tsai, Y.-C. Fang, Z.-C. Lee, and H.-X. Tsao, “All-fiber passively Q-switched erbium laser using mismatch of mode field areas and a saturable-amplifier pump switch,” Opt. Lett. 34(19), 2891–2893 (2009). [CrossRef] [PubMed]

16.

T.-Y. Tsai and Y.-C. Fang, “A self-Q-switched all-fiber erbium laser at 1530 nm using an auxiliary 1570 nm erbium laser,” Opt. Express 17(24), 21628–21633 (2009). [CrossRef] [PubMed]

17.

A. Siegman, “Passive Saturable Absorber Q-switching,” in Lasers (University Science Books, 1986), Chap. 26.3, pp. 1024–1033.

OCIS Codes
(060.2310) Fiber optics and optical communications : Fiber optics
(140.3510) Lasers and laser optics : Lasers, fiber
(140.3540) Lasers and laser optics : Lasers, Q-switched

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: September 28, 2010
Revised Manuscript: October 20, 2010
Manuscript Accepted: October 21, 2010
Published: October 25, 2010

Citation
Tzong-Yow Tsai, Yen-Cheng Fang, Huai-Min Huang, Hong-Xi Tsao, and Shih-Ting Lin, "Saturable absorber Q- and gain-switched all-Yb3+ all-fiber laser at 976 and 1064 nm," Opt. Express 18, 23523-23528 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-23-23523


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References

  1. J. A. Alvarez-Chavez, H. L. Offerhaus, J. Nilsson, P. W. Turner, W. A. Clarkson, and D. J. Richardson, “High-energy, high-power ytterbium-doped Q-switched fiber laser,” Opt. Lett. 25(1), 37–39 (2000). [CrossRef]
  2. H. Zhao, Q. Lou, J. Zhou, F. Zhang, J. Dong, Y. Wei, and Z. Wang, “Stable pulse-compressed acousto-optic Q-switched fiber laser,” Opt. Lett. 32(19), 2774–2776 (2007). [CrossRef] [PubMed]
  3. M. Laroche, H. Gilles, S. Girard, N. Passilly, and K. Aït-Ameur, “Nanosecond pulse generation in a passively Q-switched Yb-doped fiber laser by Cr4+:YAG saturable absorber,” IEEE Photon. Technol. Lett. 18(6), 764–766 (2006). [CrossRef]
  4. L. Pan, I. Utkin, and R. Fedosejevs, “Two-wavelength passively Q-switched ytterbium doped fiber laser,” Opt. Express 16(16), 11858–11870 (2008). [CrossRef] [PubMed]
  5. D. W. Huang, W. F. Liu, and C. C. Yang, “Q-switched all-fiber laser with an acoustically modulated fiber attenuator,” IEEE Photon. Technol. Lett. 12(9), 1153–1155 (2000). [CrossRef]
  6. D. Zalvidea, N. A. Russo, R. Duchowicz, M. Delgado-Pinar, A. Díez, J. L. Cruz, and M. V. Andrés, “High repetition rate acoustic-induced Q-switched all-fiber laser,” Opt. Commun. 244(1-6), 315–319 (2005). [CrossRef]
  7. M. Delgado-Pinar, D. Zalvidea, A. Díez, P. Pérez-Millan, and M. V. Andrés, “Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating,” Opt. Express 14(3), 1106–1112 (2006). [CrossRef] [PubMed]
  8. L. Tordella, H. Dejellout, B. Dussardier, A. Saissy, and G. Monnom, “High repetition rate passively 
Q-switched Nd3+:Cr4+ all fibre laser,” Electron. Lett. 39(18), 1307–1308 (2003). [CrossRef]
  9. T.-Y. Tsai, Y.-C. Fang, and S.-H. Hung, “Passively Q-switched erbium all-fiber lasers by use of thulium-doped saturable-absorber fibers,” Opt. Express 18(10), 10049–10054 (2010). [CrossRef] [PubMed]
  10. S. D. Jackson, “Passively Q-switched Tm(3+)-doped silica fiber lasers,” Appl. Opt. 46(16), 3311–3317 (2007). [CrossRef] [PubMed]
  11. P. Adel, M. Auerbach, C. Fallnich, S. Unger, H.-R. Müller, and J. Kirchhof, “Passive Q-switching by Tm3+co-doping of a Yb3+-fiber laser,” Opt. Express 11(21), 2730–2735 (2003). [CrossRef] [PubMed]
  12. A. A. Fotiadi, A. S. Kurkov, and I. M. Razdobreev, “All-fiber passively Q-switched Ytterbium laser,” 2005 Conference on Lasers and Electro-Optics Europe, p. 515.
  13. A. S. Kurkov, E. M. Sholokhov, and O. I. Medvedkov, “All fiber Yb-Ho pulsed laser,” Laser Phys. Lett. 6(2), 135–138 (2009). [CrossRef]
  14. V. V. Dvoyrin, V. M. Mashinsky, and E. M. Dianov, “Yb-Bi pulsed fiber lasers,” Opt. Lett. 32(5), 451–453 (2007). [CrossRef] [PubMed]
  15. T.-Y. Tsai, Y.-C. Fang, Z.-C. Lee, and H.-X. Tsao, “All-fiber passively Q-switched erbium laser using mismatch of mode field areas and a saturable-amplifier pump switch,” Opt. Lett. 34(19), 2891–2893 (2009). [CrossRef] [PubMed]
  16. T.-Y. Tsai and Y.-C. Fang, “A self-Q-switched all-fiber erbium laser at 1530 nm using an auxiliary 
1570 nm erbium laser,” Opt. Express 17(24), 21628–21633 (2009). [CrossRef] [PubMed]
  17. A. Siegman, “Passive Saturable Absorber Q-switching,” in Lasers (University Science Books, 1986), Chap. 26.3, pp. 1024–1033.

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