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Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 12 — Jun. 4, 2012
  • pp: 13123–13128
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Q-switched induced gain switching of a two-transition cascade laser

Jianfeng Li, Tomonori Hu, and Stuart D. Jackson  »View Author Affiliations


Optics Express, Vol. 20, Issue 12, pp. 13123-13128 (2012)
http://dx.doi.org/10.1364/OE.20.013123


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Abstract

A gain-switched laser transition, of a two-laser-transition cascade laser, that is driven by the adjacent laser transition which is Q-switched is demonstrated using a Ho3+-doped fluoride fiber laser. Q-switching the 5I65I7 transition at 3.002 µm produces stable gain-switched pulses from the 5I75I8 transition at 2.074 µm; however, Q-switching the 5I75I8 transition produced multiple gain switched pulses from the 5I65I7 transition. The gain-switched pulses were measured to be of a similar duration to the Q-switched pulses suggesting that much shorter pulses of closer duration could be generated at pump power higher levels.

© 2012 OSA

1. Introduction

Gain switching is a convenient pulse generation technique allowing the generation of pulses with pulse durations spanning at least 6 orders of magnitude. As opposed to Q-switching which involves modulating the fractional power loss per round trip, switching the gain of laser transition, a traditional pulsing technique going back to the first demonstrations of lasers, involves directly modulating the population in the energy levels comprising the population inversion independent of the loss of the cavity. By modulating the injection current of semiconductor diode lasers [1

1. K. Y. Lau, “Gain switching of semiconductor injection lasers,” Appl. Phys. Lett. 52(4), 257–259 (1988). [CrossRef]

] for example, short pulses, down to a few ps duration, can be generated [2

2. Y. Arakawa, T. Sogawa, M. Nishioka, M. Tanaka, and H. Sakaki, “Picosecond pulse generation (<1.8 ps) in a quantum well laser by a gain switching method,” Appl. Phys. Lett. 51(17), 1295–1297 (1987). [CrossRef]

] and more recently, using optical pump pulses to excite fiber lasers [3

3. S. D. Jackson and T. A. King, “Efficient gain-switched operation of a Tm-doped silica fiber laser,” IEEE J. Quantum Electron. 34(5), 779–789 (1998). [CrossRef]

] the generation pulses of a few ns duration [4

4. M. Jiang and P. Tayebati, “Stable 10 ns, kilowatt peak-power pulse generation from a gain-switched Tm-doped fiber laser,” Opt. Lett. 32(13), 1797–1799 (2007). [CrossRef] [PubMed]

] has been demonstrated.

Cascade lasing of rare earth ion transitions allows the generation of a number of distinct emission wavelengths simultaneously, which may be an effective method to create power-scaled mid-infrared fiber lasers. Cascading lasing at 2.81 µm and 1.62 µm from Er3+ crystalline lasers [5

5. B. Schmaul, G. Huber, R. Clausen, B. Chai, P. Li Kam Wa, and M. Bass, “Er3+:YLiF4 continuous wave cascade laser operation at 1620 and 2810 nm at room temperature,” Appl. Phys. Lett. 62(6), 541–543 (1993). [CrossRef]

] for example relies on host materials that support less energetic phonons so that adjacent electronic transitions have sufficient luminescence efficiencies to allow a lasing threshold for each transition at a comparable level of pump power. To date, cascade lasing of fiber lasers has relied on low phonon energy fluoride glasses which are capable of supporting fluorescence from the near infrared [6

6. R. M. Percival, D. Szebesta, and S. T. Davey, “Highly efficient CW cascade operation of 1.47 and 1.82 µm transitions in Tm-doped fluoride fiber laser,” Electron. Lett. 28(20), 1866–1868 (1992). [CrossRef]

,7

7. G. Qin and Y. Ohishi, “Cascaded two-wavelength lasers and their effects on C-Band amplification performance for Er3+-doped fluoride fiber,” IEEE J. Quantum Electron. 43(4), 316–321 (2007). [CrossRef]

] to the mid-infrared [8

8. M. Pollnau, Ch. Ghisler, G. Bunea, M. Bunea, W. Lüthy, and H. P. Weber, “150 mW unsaturated output power at 3 μm from a single-mode-fiber erbium cascade laser,” Appl. Phys. Lett. 66(26), 3564–3566 (1995). [CrossRef]

10

10. T. Sumiyoshi, H. Sekita, T. Arai, S. Sato, M. Ishihara, and M. Kikuchi, “High-power continuous-wave 3- and 2-μm cascade Ho3+:ZBLAN fiber laser and its medical applications,” IEEE J. Sel. Top. Quantum Electron. 5(4), 936–943 (1999). [CrossRef]

] and cascade lasing on up to three transitions has been demonstrated [11

11. J. Schneider, “Mid-infrared fluoride fiber lasers in multiple cascade operation,” IEEE Photon. Technol. Lett. 7(4), 354–356 (1995). [CrossRef]

,12

12. M. Pollnau, Ch. Ghisler, W. Lüthy, H. P. Weber, J. Schneider, and U. B. Unrau, “Three-transition cascade erbium laser at 1.7, 2.7, and 1.6 microm,” Opt. Lett. 22(9), 612–614 (1997). [CrossRef] [PubMed]

]. Cascade lasing reduces the thermal load by creating large photon conversion efficiencies which is particularly important in low phonon glasses which typically have relatively poor thermo-mechanical characteristics [13

13. S. D. Jackson, M. Pollnau, and J. Li, “Diode pumped erbium cascade fiber lasers,” IEEE J. Quantum Electron. 47(4), 471–478 (2011). [CrossRef]

].

In this paper, we demonstrate a new gain-switching process whereby modulation of the population inversion of a transition is produced from the forced modulation of an adjacent transition of a two transition cascade. We show using cascade lasing of a Ho3+-doped fluoride fiber laser at 3 µm and 2.1 µm, that by Q-switching one transition of the cascade, the energy levels of the adjacent transition are sufficiently modulated to cause gain-switched pulsing. Gain-switched pulses of a similar duration to the Q-switched pulses can be produced with a time delay between pulses that is dependent on the pump power and repetition rate of the Q-switch.

2. Experiment setup

3. Results and discussion

Figure 3
Fig. 3 Measured pulse width, Pw, of the 5I65I7 and 5I75I8 transitions as a function of the repetition rate, Rp at three launched pump powers. The inset shows the time delay, Δt, between 5I65I7 and 5I75I8 pulses as a function of Rp at three launched pump powers.
shows the repetition rates providing stable pulse generation and the corresponding pulse widths of the pulses for each transition at three launched pump powers. The gain-switched pulses were generated at the same repetition rate as the Q-switched pulses; multiple Q-switch and gain-switch pulsing occurred when the repetition rate of the AOM was lower than 30 kHz; unstable pulsing occurred when the repetition rate of the AOM was larger than 70 kHz. The width of the Q-switched and gain-switched pulses shortened with increasing pump power and lengthened significantly with increasing repetition rate. The inset to Fig. 3 shows the time delay, Δt, between the Q-switched and gain-switched pulses as a function of repetition rate and launched pump power. The time delay decreases and increases near linearly with the launched pump power and repetition rate, respectively. The shortest time delay of 2.2 µs occurred at a repetition rate of 30 kHz and at maximum launched pump power.

Figure 4
Fig. 4 Synchronized output pulse trains for the Q-switched 5I75I8 pulse and gain-switched 5I65I7 pulse for the maximum launched pump power of 7.4 W. The inset shows the temporal pulse waveform for 5I65I7 and 5I75I8 transitions.
shows the output pulses for first-order Q-switching of the 5I75I8 transition and the resultant gain-switched pulses generated from the 5I65I7 transition; the inset to Fig. 4 shows the characteristics of each pulse at a repetition rate of 30 kHz and at maximum launched pump power. The Q-switched (5I75I8) pulse operated at a slope efficiency of 4.0% and threshold of 2.8 W had pulse duration of 300 ns, pulse energy of 6.1 µJ and a peak power of 20.4 W. After a time delay of 9.8 µs, multiple gain-switched (5I65I7) pulses were measured for all values of the repetition rate of the AOM. The gain-switched pulse durations were 720 ns, nearly twice the duration of the Q-switched pulse. The repetition rate providing stable Q-switched (5I75I8) pulses was 17 kHz to 47 kHz. The number of gain-switched pulses and time between them decreased with increasing repetition rate. The duration of the gain-switched and Q-switched pulses shortened with increasing pump power and increased with increasing repetition rate; the narrowest Q-switched and gain-switched pulse widths were 270 ns and 640 ns, respectively which was achieved at 17 kHz and 7.4 W launched pump power. The characteristics of the time delay between Q-switched and gain switched pulses was identical to the alternative switching arrangement; the shortest time delay of 7.6 µs was observed at 17 kHz and 7.4 W launched pump power.

The optical spectrum of the output at the maximum launched pump power for the Q-switched pulses and the corresponding gain-switched pulses is shown in Fig. 5
Fig. 5 Measured spectrum of the 5I65I7 laser transition at maximum pump power. The inset shows the measured spectrum for the 5I75I8 laser transition at maximum pump power.
. The Q-switched pulses arising from 5I65I7 (5I75I8) transition operated with a center wavelength of 3.002 µm (2.074 µm) and bandwidth of 16 nm (4.5 nm), while the gain-switched pulses arising from 5I65I6 (5I75I8) transition operated with a center wavelength of 2.986 µm (2.072 µm) and bandwidth of 13 nm (4 nm). The centre wavelength of the Q-switched pulse of a transition is longer than the corresponding gain-switched pulse of the same transition; the spectra of the Q-switched pulses are also broader. The gain-switched pulses were generated from cavities using feedback of approximately 4% Fresnel reflection that forces a higher threshold than the corresponding cavity generating Q-switched pulses. Thus the gain-switched transitions have a larger population inversion at threshold which allows the terminating Stark sub-level to be deeper in the lower laser level thus creating shorter emission wavelengths.

A gain-switched pulse has been produced by a Q-switched pulse of the adjacent transition of a two transition cascade. The gain-switched pulses from the lower transition rely on the excitation of the upper laser level from the emission of the Q-switched higher transition pulse. This process is fast which results in a single gain-switched pulse of similar duration to the Q-switched pulse. On the other hand, when the lower transition is Q-switched, the process of gain-switching the higher transition is more complicated. The upper laser level of the higher transition is continuously excited from the diode pump source; however the de-excitation of the lower laser level relies on the generation of the Q-switched pulse. After the generation of the lower transition Q-switched pulse, GSA is increased this creates greater localized excitation of the 5I6 level feeding the gain-switched pulse. There exists, therefore, a complex interplay between the excitation of the energy levels and pulse generation; we are currently constructing a numerical model to understand and further optimize this pulse generation technique. This mechanism can be transferred to passively Q-switched and mode-locked cascade lasers.

4. Conclusion

In this paper we have demonstrated the Q-switched pulse induced gain switching in a two-transition cascade laser. Using a Ho3+-doped ZBLAN fibre laser that was pumped with high power CW diode lasers emitting at 1.15 µm and operated cascade on two adjacent transitions emitting at 3 µm and 2.1 µm, gain-switched pulses as short as 460 ns at 2.07 µm were created from 350 ns Q-switched pulses at 3.002 µm. With optimized fibre and cavity parameters in conjunction with increased pumping, shorter pulses are envisaged. The pulse generation mechanism has potential applications in mid-infrared photonics and nonlinear optics.

Acknowledgments

The authors acknowledge financial support from the Australian Research Council through the Discovery Projects and Centre of Excellence funding schemes. SJ acknowledges support from a Queen Elizabeth II Fellowship. This work was also supported by National Nature Science Foundation of China (Grant No. 61107037 and 60925019), China Postdoctoral Science Special Foundation (Grant No. 201003693).

References and links

1.

K. Y. Lau, “Gain switching of semiconductor injection lasers,” Appl. Phys. Lett. 52(4), 257–259 (1988). [CrossRef]

2.

Y. Arakawa, T. Sogawa, M. Nishioka, M. Tanaka, and H. Sakaki, “Picosecond pulse generation (<1.8 ps) in a quantum well laser by a gain switching method,” Appl. Phys. Lett. 51(17), 1295–1297 (1987). [CrossRef]

3.

S. D. Jackson and T. A. King, “Efficient gain-switched operation of a Tm-doped silica fiber laser,” IEEE J. Quantum Electron. 34(5), 779–789 (1998). [CrossRef]

4.

M. Jiang and P. Tayebati, “Stable 10 ns, kilowatt peak-power pulse generation from a gain-switched Tm-doped fiber laser,” Opt. Lett. 32(13), 1797–1799 (2007). [CrossRef] [PubMed]

5.

B. Schmaul, G. Huber, R. Clausen, B. Chai, P. Li Kam Wa, and M. Bass, “Er3+:YLiF4 continuous wave cascade laser operation at 1620 and 2810 nm at room temperature,” Appl. Phys. Lett. 62(6), 541–543 (1993). [CrossRef]

6.

R. M. Percival, D. Szebesta, and S. T. Davey, “Highly efficient CW cascade operation of 1.47 and 1.82 µm transitions in Tm-doped fluoride fiber laser,” Electron. Lett. 28(20), 1866–1868 (1992). [CrossRef]

7.

G. Qin and Y. Ohishi, “Cascaded two-wavelength lasers and their effects on C-Band amplification performance for Er3+-doped fluoride fiber,” IEEE J. Quantum Electron. 43(4), 316–321 (2007). [CrossRef]

8.

M. Pollnau, Ch. Ghisler, G. Bunea, M. Bunea, W. Lüthy, and H. P. Weber, “150 mW unsaturated output power at 3 μm from a single-mode-fiber erbium cascade laser,” Appl. Phys. Lett. 66(26), 3564–3566 (1995). [CrossRef]

9.

J. Schneider, “Fluoride fiber laser operating at 3.9 μm,” Electron. Lett. 31(15), 1250–1251 (1995). [CrossRef]

10.

T. Sumiyoshi, H. Sekita, T. Arai, S. Sato, M. Ishihara, and M. Kikuchi, “High-power continuous-wave 3- and 2-μm cascade Ho3+:ZBLAN fiber laser and its medical applications,” IEEE J. Sel. Top. Quantum Electron. 5(4), 936–943 (1999). [CrossRef]

11.

J. Schneider, “Mid-infrared fluoride fiber lasers in multiple cascade operation,” IEEE Photon. Technol. Lett. 7(4), 354–356 (1995). [CrossRef]

12.

M. Pollnau, Ch. Ghisler, W. Lüthy, H. P. Weber, J. Schneider, and U. B. Unrau, “Three-transition cascade erbium laser at 1.7, 2.7, and 1.6 microm,” Opt. Lett. 22(9), 612–614 (1997). [CrossRef] [PubMed]

13.

S. D. Jackson, M. Pollnau, and J. Li, “Diode pumped erbium cascade fiber lasers,” IEEE J. Quantum Electron. 47(4), 471–478 (2011). [CrossRef]

14.

J. Li, D. D. Hudson, and S. D. Jackson, “High-power diode-pumped fiber laser operating at 3 μm,” Opt. Lett. 36(18), 3642–3644 (2011). [CrossRef] [PubMed]

OCIS Codes
(140.3480) Lasers and laser optics : Lasers, diode-pumped
(140.3510) Lasers and laser optics : Lasers, fiber

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: March 19, 2012
Revised Manuscript: May 14, 2012
Manuscript Accepted: May 21, 2012
Published: May 25, 2012

Citation
Jianfeng Li, Tomonori Hu, and Stuart D. Jackson, "Q-switched induced gain switching of a two-transition cascade laser," Opt. Express 20, 13123-13128 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-12-13123


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References

  1. K. Y. Lau, “Gain switching of semiconductor injection lasers,” Appl. Phys. Lett.52(4), 257–259 (1988). [CrossRef]
  2. Y. Arakawa, T. Sogawa, M. Nishioka, M. Tanaka, and H. Sakaki, “Picosecond pulse generation (<1.8 ps) in a quantum well laser by a gain switching method,” Appl. Phys. Lett.51(17), 1295–1297 (1987). [CrossRef]
  3. S. D. Jackson and T. A. King, “Efficient gain-switched operation of a Tm-doped silica fiber laser,” IEEE J. Quantum Electron.34(5), 779–789 (1998). [CrossRef]
  4. M. Jiang and P. Tayebati, “Stable 10 ns, kilowatt peak-power pulse generation from a gain-switched Tm-doped fiber laser,” Opt. Lett.32(13), 1797–1799 (2007). [CrossRef] [PubMed]
  5. B. Schmaul, G. Huber, R. Clausen, B. Chai, P. Li Kam Wa, and M. Bass, “Er3+:YLiF4 continuous wave cascade laser operation at 1620 and 2810 nm at room temperature,” Appl. Phys. Lett.62(6), 541–543 (1993). [CrossRef]
  6. R. M. Percival, D. Szebesta, and S. T. Davey, “Highly efficient CW cascade operation of 1.47 and 1.82 µm transitions in Tm-doped fluoride fiber laser,” Electron. Lett.28(20), 1866–1868 (1992). [CrossRef]
  7. G. Qin and Y. Ohishi, “Cascaded two-wavelength lasers and their effects on C-Band amplification performance for Er3+-doped fluoride fiber,” IEEE J. Quantum Electron.43(4), 316–321 (2007). [CrossRef]
  8. M. Pollnau, Ch. Ghisler, G. Bunea, M. Bunea, W. Lüthy, and H. P. Weber, “150 mW unsaturated output power at 3 μm from a single-mode-fiber erbium cascade laser,” Appl. Phys. Lett.66(26), 3564–3566 (1995). [CrossRef]
  9. J. Schneider, “Fluoride fiber laser operating at 3.9 μm,” Electron. Lett.31(15), 1250–1251 (1995). [CrossRef]
  10. T. Sumiyoshi, H. Sekita, T. Arai, S. Sato, M. Ishihara, and M. Kikuchi, “High-power continuous-wave 3- and 2-μm cascade Ho3+:ZBLAN fiber laser and its medical applications,” IEEE J. Sel. Top. Quantum Electron.5(4), 936–943 (1999). [CrossRef]
  11. J. Schneider, “Mid-infrared fluoride fiber lasers in multiple cascade operation,” IEEE Photon. Technol. Lett.7(4), 354–356 (1995). [CrossRef]
  12. M. Pollnau, Ch. Ghisler, W. Lüthy, H. P. Weber, J. Schneider, and U. B. Unrau, “Three-transition cascade erbium laser at 1.7, 2.7, and 1.6 microm,” Opt. Lett.22(9), 612–614 (1997). [CrossRef] [PubMed]
  13. S. D. Jackson, M. Pollnau, and J. Li, “Diode pumped erbium cascade fiber lasers,” IEEE J. Quantum Electron.47(4), 471–478 (2011). [CrossRef]
  14. J. Li, D. D. Hudson, and S. D. Jackson, “High-power diode-pumped fiber laser operating at 3 μm,” Opt. Lett.36(18), 3642–3644 (2011). [CrossRef] [PubMed]

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