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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 4 — Feb. 24, 2014
  • pp: 4196–4201
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Gain-switching dynamics in optically pumped single-mode InGaN vertical-cavity surface-emitting lasers

Shaoqiang Chen, Akifumi Asahara, Takashi Ito, Jiangyong Zhang, Baoping Zhang, Tohru Suemoto, Masahiro Yoshita, and Hidefumi Akiyama  »View Author Affiliations


Optics Express, Vol. 22, Issue 4, pp. 4196-4201 (2014)
http://dx.doi.org/10.1364/OE.22.004196


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Abstract

The gain-switching dynamics of single-mode pulses were studied in blue InGaN multiple-quantum-well vertical-cavity surface-emitting lasers (VCSELs) through impulsive optical pumping. We measured the shortest single-mode pulses of 6.0 ps in width with a method of up-conversion, and also obtained the pulse width and the delay time as functions of pump powers from streak-camera measurements. Single-mode rate-equation calculations quantitatively and consistently explained the observed data. The calculations indicated that the pulse width in the present VCSELs was mostly limited by modal gain, and suggested that subpicosecond pulses should be possible within feasible device parameters.

© 2014 Optical Society of America

1. Introduction

Although the high reflectivity of distributed-Bragg reflectors (DBRs) may dramatically increase the photon lifetime of nitride-based blue VCSELs [6

6. S. Q. Chen, M. Okano, B. P. Zhang, M. Yoshita, H. Akiyama, and Y. Kanemitsu, “Blue 6-ps short-pulse generation in gain-switched InGaN vertical-cavity surface-emitting lasers via impulsive optical pumping,” Appl. Phys. Lett. 101(19), 191108 (2012). [CrossRef]

8

8. T. Someya, R. Werner, A. Forchel, M. Catalano, R. Cingolani, and Y. Arakawa, “Room temperature lasing at blue wavelengths in gallium nitride microcavities,” Science 285(5435), 1905–1906 (1999). [CrossRef] [PubMed]

], the intrinsic short length of cavities can still produce short photon lifetimes that are very useful for generating short pulses if there are appropriate designs for cavities. In fact, we previously demonstrated optical pulses as short as 6.0 ps from a gain-switched InGaN VCSEL [6

6. S. Q. Chen, M. Okano, B. P. Zhang, M. Yoshita, H. Akiyama, and Y. Kanemitsu, “Blue 6-ps short-pulse generation in gain-switched InGaN vertical-cavity surface-emitting lasers via impulsive optical pumping,” Appl. Phys. Lett. 101(19), 191108 (2012). [CrossRef]

], indicating that nitride-based blue VCSELs are indeed very good prospects for generating short pulses. However, lasing only occurred in multi-modes, which made it very difficult to quantitatively and theoretically analyze it. Consequently, generation dynamics of the 6 ps pulses was not clarified. A quantitative study of gain-switching dynamics is crucial to understand or design nitride-based gain-switched VCSELs that generate short output pulses. For this purpose, single-mode gain-switched pulses that are convenient for physical analysis are on demand.

In this paper, we obtained single-mode gain-switched short pulses from an InGaN VCSEL under impulsive optical pumping. We studied the lasing characteristics of the single-mode pulses through detailed measurements of pulse widths and delay times as functions of pump power. Single-mode rate-equation calculations with a nonlinear-gain model were undertaken to quantitatively analyze and also predict gain-switching dynamics. Quantitative simulations indicated that subpicosecond pulses could be generated in nitride-based VCSELs through structural improvements of the devices.

2. Experimental setup

3. Experimental results and discussion

The delay times and pulse widths of pulses with different pump powers are summarized in Fig. 3
Fig. 3 Delay times and pulse widths of gain-switched pulses with various pump powers. Dashed lines plot simulation results.
. It can be seen that the delay times and the pulse widths gradually decreased with increasing pump powers and then simultaneously stayed at certain values at pump powers over 100 μW. The shortest delay time was limited to 16 ps and the shortest pulse width was limited to 6.0 ps independently of the pump power. The power dependencies of the delay time and pulse width are similar to those in other gain-switched semiconductor lasers [10

10. S. Q. Chen, M. Yoshita, T. Ito, T. Mochizuki, H. Akiyama, and H. Yokoyama, “Gain-switched pulses from InGaAs ridge-quantum-well lasers limited by intrinsic dynamical gain suppression,” Opt. Express 21(6), 7570–7576 (2013). [CrossRef] [PubMed]

13

13. J. R. Karin, L. G. Melcer, R. Nagarajan, J. E. Bowers, S. W. Corzine, P. A. Morton, R. S. Geels, and L. A. Coldren, “Generation of picosecond pulses with a gain-switched GaAs surface-emitting laser,” Appl. Phys. Lett. 57(10), 963–965 (1990). [CrossRef]

]. These typical features indicate that gain switching indeed occurred in the VCSEL.

The power dependencies of the delay time and pulse width of the gain-switched pulses were quantitatively simulated with a model of a single-mode-laser rate equation [10

10. S. Q. Chen, M. Yoshita, T. Ito, T. Mochizuki, H. Akiyama, and H. Yokoyama, “Gain-switched pulses from InGaAs ridge-quantum-well lasers limited by intrinsic dynamical gain suppression,” Opt. Express 21(6), 7570–7576 (2013). [CrossRef] [PubMed]

, 14

14. S. Q. Chen, M. Yoshita, T. Ito, T. Mochizuki, H. Akiyama, H. Yokoyama, K. Kamide, and T. Ogawa, “Analysis of gain-switching characteristics including strong gain saturation effects in low-dimensional semiconductor lasers,” Jpn. J. Appl. Phys. 51, 098001 (2012).

] given below to clarify the gain-switching dynamics and factors in the pulse-width limitations of the VCSEL.
dn2Ddt=ηP(t)hνmAΓmvgg1+εs2Ds2Dn2Dτr.
(1)
ds2Ddt=Γvgg1+εs2Ds2Ds2Dτp+mβn2Dτr.
(2)
g=g0(n2Dn02D)/[1+g0(n2Dn02D)gs].
(3)
Here, n2D is the two-dimensional carrier density in one quantum well, s2D is the two-dimensional photon density for all active layers, and g0 is the differential gain. ε is the gain compression factor, gs is the saturated material gain of the InGaN quantum well, and P(t) denotes the transient pumping power given by a Gaussian distribution with a pulse duration of 0.3 ps. η = 0.41 is the power absorption rate, m = 3 is the quantum-well period, and A = 2.5 × 10−5 cm2 is the spot size of the pump laser beam. L = 2.3 µm is the cavity length, n0 = 2.0 × 1012 cm2 is the transparence carrier density, and β = 0.03 is the spontaneous emission coupling factor. τr = 5 ns is the carrier lifetime, τp = 0.6 ps is the photon lifetime (also called the cavity lifetime), Γ = 4.6 × 10−3 is the confinement factor (estimated fromΓ=md/L, d is the quantum-well thickness), and vg = 1.1 × 10−2 cm/ps is the group velocity.

Differential gain g0, gain compression factor ε, and saturated material gain gs are the three main fitting parameters. Best agreement with the experimental results was obtained when a value for differential gain g0 = 2.0 × 10−10 cm, a very small value for gain compression factor ε = 2.0 × 10−16 cm2, and a high value for saturated material gain gs = 4.9 × 104 cm−1 were used. The order of saturated material gain was in very good agreement with the theoretical calculations [15

15. W. W. Chow and S. W. Koch, Semiconductor-Laser Fundamentals: Physics of the Gain Materials (Springer, 1999).

, 16

16. K. Domen, K. Kondo, A. Kuramata, and T. Tanahashi, “Gain analysis for surface emission by optical pumping of wurtzite GaN,” Appl. Phys. Lett. 69(1), 94–96 (1996). [CrossRef]

], and was considerably larger than the values for (In)GaAs lasers [10

10. S. Q. Chen, M. Yoshita, T. Ito, T. Mochizuki, H. Akiyama, and H. Yokoyama, “Gain-switched pulses from InGaAs ridge-quantum-well lasers limited by intrinsic dynamical gain suppression,” Opt. Express 21(6), 7570–7576 (2013). [CrossRef] [PubMed]

], indicating that the material gain of nitrides is indeed very large. The large gain of the nitrides was considered to have resulted from the three bands in the valence band close to the band edge and the large reduced-effective mass of each valence band [16

16. K. Domen, K. Kondo, A. Kuramata, and T. Tanahashi, “Gain analysis for surface emission by optical pumping of wurtzite GaN,” Appl. Phys. Lett. 69(1), 94–96 (1996). [CrossRef]

]. This reasonable value for the saturated gain of the nitrides we obtained and the good agreement between the experimental results and quantitative simulation demonstrated that the rate-equation model we used was indeed suitable to describe the gain-switching dynamics of InGaN VCSELs.

We should comment that the decay tail of the gain-switched pulses could not be simulated well while most of the experimental results were quantitatively simulated with the rate equations. We can see that the decay tail at the end of the experimentally obtained pulses is much longer than that in the simulation results by comparing the pulse shape in the experiment with that in the simulation (shown as a dashed curve in Fig. 2(c)) with a high pump power of 200 μW. The decay time of the pulse with a high pump power should theoretically be mainly limited by the photon lifetime in the cavity of the VCSEL. Although the exact origin of the long tail is still unknown, the long tail should also be suppressed or removed to obtain even shorter gain-switched pulses.

7. Conclusion

In summary, a single-mode 6.0 ps blue pulse was generated by gain switching from an optically pumped InGaN VCSEL. Single-mode gain-switching dynamics in the VCSEL was quantitatively analyzed by both experimentally and theoretically investigating the pump-power dependencies of delay time and pulse width of gain-switched output pulses. The results from simulation demonstrated that subpicosecond short gain-switched pulses could be expected from nitride-based VCSELs by increasing the number of quantum wells and decreasing the cavity length. These results as well as the quantitative rate-equation model are expected to provide very significant reference values to future designs of samples and basic studies on nitride-based VCSELs.

Acknowledgments

This work was partly supported by Kakenhi grant no. 20104004 from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), no. 23360135 from the Japan Society for the Promotion of Science (JSPS), Japan Science and Technology-Core Research for Evolutional Science and Technology (JST-CREST) (FY2011–2016), and the Photon Frontier Network Program of MEXT in Japan.

References and links

1.

D. A. Parthenopoulos and P. M. Rentzepis, “Three-dimensional optical storage memory,” Science 245(4920), 843–845 (1989). [CrossRef] [PubMed]

2.

H. E. Pudavar, M. P. Joshi, P. N. Prasad, and B. A. Reinhardt, “High-density three-dimensional optical data storage in a stacked compact disk format with two-photon writing and single photon readout,” Appl. Phys. Lett. 74(9), 1338–1340 (1999). [CrossRef]

3.

K. Yamasaki, S. Juodkazis, M. Watanabe, H.-B. Sun, S. Matsuo, and H. Misawa, “Recording by microexplosion and two-photon reading of three-dimensional optical memory in polymethylmethacrylate films,” Appl. Phys. Lett. 76(8), 1000–1002 (2000). [CrossRef]

4.

S. Tashiro, Y. Takemoto, H. Yamatsu, T. Miura, G. Fujita, T. Iwamura, D. Ueda, H. Uchiyama, K. S. Yun, M. Kuramoto, T. Miyajima, M. Ikeda, and H. Yokoyama, “Volumetric optical recording using a 400 nm all-semiconductor picosecond laser,” Appl. Phys. Express 3(10), 102501 (2010). [CrossRef]

5.

S. Kono, T. Oki, T. Miyajima, M. Ikeda, and H. Yokoyama, “12 W peak-power 10 ps duration optical pulse generation by gain switching of a single-transverse-mode GaInN blue laser diode,” Appl. Phys. Lett. 93(13), 131113 (2008). [CrossRef]

6.

S. Q. Chen, M. Okano, B. P. Zhang, M. Yoshita, H. Akiyama, and Y. Kanemitsu, “Blue 6-ps short-pulse generation in gain-switched InGaN vertical-cavity surface-emitting lasers via impulsive optical pumping,” Appl. Phys. Lett. 101(19), 191108 (2012). [CrossRef]

7.

J. Y. Zhang, L. E. Cai, B. P. Zhang, S. Q. Li, F. Lin, J. Z. Shang, D. X. Wang, K. C. Lin, J. Z. Yu, and Q. M. Wang, “Low threshold lasing of GaN-based vertical cavity surface emitting lasers with an asymmetric coupled quantum well active region,” Appl. Phys. Lett. 93(19), 191118 (2008). [CrossRef]

8.

T. Someya, R. Werner, A. Forchel, M. Catalano, R. Cingolani, and Y. Arakawa, “Room temperature lasing at blue wavelengths in gallium nitride microcavities,” Science 285(5435), 1905–1906 (1999). [CrossRef] [PubMed]

9.

C. J. Chang-Hasnain, M. Orenstein, A. Von Lehmen, L. T. Florez, J. P. Harbison, and N. G. Stoffel, “Transverse mode characteristics of vertical cavity surface-emitting lasers,” Appl. Phys. Lett. 57(3), 218–220 (1990). [CrossRef]

10.

S. Q. Chen, M. Yoshita, T. Ito, T. Mochizuki, H. Akiyama, and H. Yokoyama, “Gain-switched pulses from InGaAs ridge-quantum-well lasers limited by intrinsic dynamical gain suppression,” Opt. Express 21(6), 7570–7576 (2013). [CrossRef] [PubMed]

11.

L. G. Melcer, J. R. Karin, R. Nagarajan, and J. E. Bowers, “Picosecond dynamics of optical gain switching in vertical cavity emitting lasers,” IEEE J. Quantum Electron. 27(6), 1417–1425 (1991). [CrossRef]

12.

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

13.

J. R. Karin, L. G. Melcer, R. Nagarajan, J. E. Bowers, S. W. Corzine, P. A. Morton, R. S. Geels, and L. A. Coldren, “Generation of picosecond pulses with a gain-switched GaAs surface-emitting laser,” Appl. Phys. Lett. 57(10), 963–965 (1990). [CrossRef]

14.

S. Q. Chen, M. Yoshita, T. Ito, T. Mochizuki, H. Akiyama, H. Yokoyama, K. Kamide, and T. Ogawa, “Analysis of gain-switching characteristics including strong gain saturation effects in low-dimensional semiconductor lasers,” Jpn. J. Appl. Phys. 51, 098001 (2012).

15.

W. W. Chow and S. W. Koch, Semiconductor-Laser Fundamentals: Physics of the Gain Materials (Springer, 1999).

16.

K. Domen, K. Kondo, A. Kuramata, and T. Tanahashi, “Gain analysis for surface emission by optical pumping of wurtzite GaN,” Appl. Phys. Lett. 69(1), 94–96 (1996). [CrossRef]

17.

T. Oki, K. Saito, H. Watanabe, T. Miyajima, M. Kuramoto, M. Ikeda, and H. Yokoyama, “Passive and hybrid mode-locking of an external-cavity GaInN laser diode incorporating a strong saturable absorber,” Appl. Phys. Express 3(3), 032104 (2010). [CrossRef]

OCIS Codes
(140.3570) Lasers and laser optics : Lasers, single-mode
(140.5960) Lasers and laser optics : Semiconductor lasers
(140.7090) Lasers and laser optics : Ultrafast lasers
(320.5390) Ultrafast optics : Picosecond phenomena

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: September 19, 2013
Revised Manuscript: November 7, 2013
Manuscript Accepted: February 3, 2014
Published: February 18, 2014

Citation
Shaoqiang Chen, Akifumi Asahara, Takashi Ito, Jiangyong Zhang, Baoping Zhang, Tohru Suemoto, Masahiro Yoshita, and Hidefumi Akiyama, "Gain-switching dynamics in optically pumped single-mode InGaN vertical-cavity surface-emitting lasers," Opt. Express 22, 4196-4201 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-4-4196


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References

  1. D. A. Parthenopoulos, P. M. Rentzepis, “Three-dimensional optical storage memory,” Science 245(4920), 843–845 (1989). [CrossRef] [PubMed]
  2. H. E. Pudavar, M. P. Joshi, P. N. Prasad, B. A. Reinhardt, “High-density three-dimensional optical data storage in a stacked compact disk format with two-photon writing and single photon readout,” Appl. Phys. Lett. 74(9), 1338–1340 (1999). [CrossRef]
  3. K. Yamasaki, S. Juodkazis, M. Watanabe, H.-B. Sun, S. Matsuo, H. Misawa, “Recording by microexplosion and two-photon reading of three-dimensional optical memory in polymethylmethacrylate films,” Appl. Phys. Lett. 76(8), 1000–1002 (2000). [CrossRef]
  4. S. Tashiro, Y. Takemoto, H. Yamatsu, T. Miura, G. Fujita, T. Iwamura, D. Ueda, H. Uchiyama, K. S. Yun, M. Kuramoto, T. Miyajima, M. Ikeda, H. Yokoyama, “Volumetric optical recording using a 400 nm all-semiconductor picosecond laser,” Appl. Phys. Express 3(10), 102501 (2010). [CrossRef]
  5. S. Kono, T. Oki, T. Miyajima, M. Ikeda, H. Yokoyama, “12 W peak-power 10 ps duration optical pulse generation by gain switching of a single-transverse-mode GaInN blue laser diode,” Appl. Phys. Lett. 93(13), 131113 (2008). [CrossRef]
  6. S. Q. Chen, M. Okano, B. P. Zhang, M. Yoshita, H. Akiyama, Y. Kanemitsu, “Blue 6-ps short-pulse generation in gain-switched InGaN vertical-cavity surface-emitting lasers via impulsive optical pumping,” Appl. Phys. Lett. 101(19), 191108 (2012). [CrossRef]
  7. J. Y. Zhang, L. E. Cai, B. P. Zhang, S. Q. Li, F. Lin, J. Z. Shang, D. X. Wang, K. C. Lin, J. Z. Yu, Q. M. Wang, “Low threshold lasing of GaN-based vertical cavity surface emitting lasers with an asymmetric coupled quantum well active region,” Appl. Phys. Lett. 93(19), 191118 (2008). [CrossRef]
  8. T. Someya, R. Werner, A. Forchel, M. Catalano, R. Cingolani, Y. Arakawa, “Room temperature lasing at blue wavelengths in gallium nitride microcavities,” Science 285(5435), 1905–1906 (1999). [CrossRef] [PubMed]
  9. C. J. Chang-Hasnain, M. Orenstein, A. Von Lehmen, L. T. Florez, J. P. Harbison, N. G. Stoffel, “Transverse mode characteristics of vertical cavity surface-emitting lasers,” Appl. Phys. Lett. 57(3), 218–220 (1990). [CrossRef]
  10. S. Q. Chen, M. Yoshita, T. Ito, T. Mochizuki, H. Akiyama, H. Yokoyama, “Gain-switched pulses from InGaAs ridge-quantum-well lasers limited by intrinsic dynamical gain suppression,” Opt. Express 21(6), 7570–7576 (2013). [CrossRef] [PubMed]
  11. L. G. Melcer, J. R. Karin, R. Nagarajan, J. E. Bowers, “Picosecond dynamics of optical gain switching in vertical cavity emitting lasers,” IEEE J. Quantum Electron. 27(6), 1417–1425 (1991). [CrossRef]
  12. K. Y. Lau, “Gain switching of semiconductor injection lasers,” Appl. Phys. Lett. 52(4), 257–259 (1988). [CrossRef]
  13. J. R. Karin, L. G. Melcer, R. Nagarajan, J. E. Bowers, S. W. Corzine, P. A. Morton, R. S. Geels, L. A. Coldren, “Generation of picosecond pulses with a gain-switched GaAs surface-emitting laser,” Appl. Phys. Lett. 57(10), 963–965 (1990). [CrossRef]
  14. S. Q. Chen, M. Yoshita, T. Ito, T. Mochizuki, H. Akiyama, H. Yokoyama, K. Kamide, T. Ogawa, “Analysis of gain-switching characteristics including strong gain saturation effects in low-dimensional semiconductor lasers,” Jpn. J. Appl. Phys. 51, 098001 (2012).
  15. W. W. Chow and S. W. Koch, Semiconductor-Laser Fundamentals: Physics of the Gain Materials (Springer, 1999).
  16. K. Domen, K. Kondo, A. Kuramata, T. Tanahashi, “Gain analysis for surface emission by optical pumping of wurtzite GaN,” Appl. Phys. Lett. 69(1), 94–96 (1996). [CrossRef]
  17. T. Oki, K. Saito, H. Watanabe, T. Miyajima, M. Kuramoto, M. Ikeda, H. Yokoyama, “Passive and hybrid mode-locking of an external-cavity GaInN laser diode incorporating a strong saturable absorber,” Appl. Phys. Express 3(3), 032104 (2010). [CrossRef]

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