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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 18 — Aug. 30, 2010
  • pp: 19242–19248
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Continuous-wave subwavelength microdisk lasers at λ = 1.53 µm

Zhijun Liu, Jeffrey M. Shainline, Gustavo E. Fernandes, Jimmy Xu, Jianxin Chen, and Claire F. Gmachl  »View Author Affiliations


Optics Express, Vol. 18, Issue 18, pp. 19242-19248 (2010)
http://dx.doi.org/10.1364/OE.18.019242


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Abstract

Subwavelength InGaAs/AlInAs microdisk lasers are demonstrated under continuous-wave optical pumping at a heat-sink temperature of 45 K. A 1.49 µm diameter, 209 nm thick microdisk lases in single-mode at a wavelength of 1.53 µm, which is identified as the whispering-gallery mode with the first radial mode number, the fifth azimuthal mode number, and a modal volume of 2.12(λ/n)3 according to our mode simulation.

© 2010 OSA

1. Introduction

In this paper, we examine the possibility of CW operation in subwavelength disk lasers. By using InGaAs/AlInAs heterostructures as the gain medium and optimizing the heat dissipation condition, we demonstrate the CW operation of subwavelength disk lasers at telecomm wavelength. A 1.49 µm diameter, 209 nm thick InGaAs/AlInAs disk is shown to lase in single-mode at a wavelength of 1.53 µm under CW optical pumping at 45 K.

2. Laser design and fabrication

The microdisks used in our experiments were fabricated on lattice-matched InGaAs/AlInAs heterostructures grown on InP substrate using solid-source molecular beam epitaxy (MBE) [16

16. J. Chen, O. Malis, A. M. Sergent, D. L. Sivco, N. Weimann, and A. Y. Cho, “In0.68Ga0.32As/Al0.64In0.36As/InP 4.5 µm quantum cascade lasers grown by solid phosphorus molecular beam epitaxy,” J. Vac. Sci. Technol. B 25(3), 913–915 (2007). [CrossRef]

]. The designed layer structure is sketched in Fig. 1(a)
Fig. 1 (a) Schematic epitaxial layer structure of our laser material. (b) Side-view and (c) top-view scanning electron microscope (SEM) images of an InGaAs/AlInAs disk on top of an InP pedestal.
, which is composed of six 9 nm-thick InGaAs quantum wells separated by 3 nm AlInAs barriers with two 60 nm-thick InGaAs cladding layers. The total thickness of the InGaAs/AlInAs layers is 209 nm. Electron beam lithography was used to define ~3 µm diameter PMMA circles on top of the sample, which acted as an etching mask. The sample was etched in an acid solution composed of HNO3/HBr/H2O with the ratio of 1:1:20. After wet-etching for ~40 seconds, which gives an etching depth of ~1.5 µm, disk cavities with diameters between 1.4 and 1.8 µm were formed. In order to avoid coupling of the optical mode into the InP substrate, selective wet-etching in a solution of HCl/H2O with the ratio of 1:2 was conducted at room temperature for ~1.5 hours to remove the InP around and below the InGaAs/AlInAs disks. A scanning electron microscope (SEM) image in Fig. 1(b) shows the side-view of a representative disk. The disk diameter is 1.49 µm. Its sidewall is vertical and the surfaces are smooth; these features are advantageous for improving the cavity Q factor and minimizing scattering losses. The underlying InP pedestal forms a mountain-like shape with a rough surface. Such a shape is different from multi-faceted shapes reported for quantum cascade disk lasers using the same material system [17

17. J. Faist, C. Gmachl, M. Striccoli, C. Sirtori, F. Capasso, D. L. Sivco, and A. Y. Cho, “Quantum cascade disk lasers,” Appl. Phys. Lett. 69(17), 2456–2458 (1996). [CrossRef]

,18

18. C. Gmachl, J. Faist, F. Capasso, C. Sirtori, D. L. Sivco, and A. Y. Cho, “Long-wavelength (9.5–11.5 µm) microdisk quantum-cascade lasers,” IEEE J. Quantum Electron. 33(9), 1567–1573 (1997). [CrossRef]

] due to different etching conditions and sample geometries. Figure 1(c) shows a top-view image of the disk. The pedestal is ~0.84 µm in diameter. This size is chosen as a compromise between effective heat sinking and prevention of optical mode coupling into the substrate.

The microdisks were measured in a micro-photoluminescence (µ-PL) apparatus. The samples were mounted in a low-temperature cryostat cooled with liquid helium. A diode-pumped Nd:yttrium–aluminum–garnet (YAG) laser with relatively long emission wavelength of 1064 nm was chosen as the pump laser for minimizing heat generation. The pump light was focused by a 50 × microscope objective with a 0.42 numerical aperture and a working distance of 1.7 cm to a spot size of ~5 µm on top of a single disk. The scattered light emission from the disk was collected by the same objective and then directed to a Horiba TRIAX spectrometer with a Peltier-cooled InGaAs photodiode array for recording the spectrum. The measurements were performed under CW optical pumping.

3. Testing results and analysis

Figure 3
Fig. 3 Emission spectra of a 1.49 µm diameter, 209 nm thick InGaAs/AlInAs disk at different pump intensities between 11.2 and 477.2 W/mm2. The spectra are vertically shifted for clear view.
shows the emission spectra of the 1.49 µm diameter, 209 nm thick disk under different pump intensities at a heat-sink temperature of 45 K. At low pump intensities, spontaneous emission from electron-hole radiative recombination in both the quantum well region and the InGaAs cladding layers are measured in the wavelength range from 1350 to 1550 nm. When the pump intensity increases beyond 276 W/mm2, a narrow peak appears at the wavelength of 1530 nm.

By fitting the emission peaks given in Fig. 3 to a Lorentzian function, the linewidths— defined as the full width at half maximum (FWHM)—are obtained and plotted in Fig. 4 a
Fig. 4 (a) Full width at half maximum (FWHM) of the emission peak versus reciprocal pump intensity. (b) Spectrally integrated intensity versus pump intensity. The two solid lines are fitted linear curves.
) as a function of the reciprocal pump intensity. The linewidth decreases from 3.8 to 1.2 nm as the pump intensity increases from 276 to 477.2 W/mm2. Figure 4(b) shows the spectrally integrated emission intensity as a function of the pump intensity. The curvature slope changes at the pump intensity of ~300 W/mm2, which indicates a threshold behavior. These observed linewidth narrowing and threshold behavior suggest that the emission corresponds to laser action. This laser emission was observed at temperatures up to ~55 K for CW pumping, and ~70 K for optical chopped pumping with 50% duty cycle. The pulsed laser performance with low duty cycle and short pump pulses were not determined in this work as limited by the pump laser source.

In order to understand the lasing behavior, we measured the photoluminescence from an unpatterned sample without a microdisk cavity. This spectrum is shown in the black curve in Fig. 5(a)
Fig. 5 (a) Photoluminescence of the laser material without cavity (black) and lasing spectra of two microdisks with diameter of 1.49 (red) and 1.54 (blue) µm. The triangles, referred to the right y-axis, are the calculated Q factors for TE1,6 and TE1,5 modes in the 1.49 (red) and 1.54 (blue) µm diameter disks. (b) Calculated spatial distribution of electrical field radial component in the cross-section of the disk and pedestal, and (c) magnetic field normal component in the disk plane for the TE1,5 mode in the 1.49 µm diameter disk.
. There are two emission peaks. The one covering wavelengths between ~1450-1600 nm is attributed to the emission from the InGaAs cladding layers, since this emission range agrees with the bandgap of bulk InGaAs at ~0.82 eV (1512 nm) [22

22. O. Madelung, Semiconductors: data handbook (Springer, 3rd edition, 2004), Chap. 2.

]. The second peak covering shorter wavelengths between ~1350-1500 nm is attributed to the emission from the InGaAs/AlInAs quantum wells, which have sizes resulting in quantum-confinement and therefore blue-shifted emission. The observed lasing at 1530 nm for the subwavelength disk laser with diameter of 1.49 µm, shown in the red spectrum in Fig. 5(a), appears at the longer wavelength shoulder of the InGaAs cladding emission peak. Therefore, the main contribution to optical gain is believed to be from the InGaAs claddings for this subwavelength laser. For a second disk laser with slightly larger diameter of 1.54 µm, its emission at 1454 nm as given by the blue spectrum appears at longer wavelength shoulder of the quantum well emission, which indicates that the quantum wells mainly contribute to the optical gain for this slightly larger disk. Therefore both quantum wells and cladding layers in our structure can provide optical gain for the lasing depending on the resonant wavelength position of the cavity modes.

4. Conclusion

Acknowledgements

This work was supported in part by AFOSR, ARO, and by the WCU program of Seoul National University.

References and links

1.

K. J. Vahala, “Optical microcavities,” Nature 424(6950), 839–846 (2003). [CrossRef] [PubMed]

2.

W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,” Nature 424(6950), 824–830 (2003). [CrossRef] [PubMed]

3.

C. Manolatou and F. Rana, “Subwavelength nanopatch cavities for semiconductor plasmon lasers,” IEEE J. Quantum Electron. 44(5), 435–447 (2008)

4.

Y. Chassagneux, J. Palomo, R. Colombelli, S. Dhillon, C. Sirtori, H. Beere, J. Alton, and D. Ritchie, “Terahertz microcavity lasers with subwavelength mode volumes and thresholds in the milliampere range,” Appl. Phys. Lett. 90(9), 091113 (2007). [CrossRef]

5.

M. T. Hill, Y.-S. Oei, B. Smalbrugge, Y. Zhu, T. De Vries, P. J. Van Veldhoven, F. W. M. Van Otten, T. J. Eijkemans, J. P. Turkiewicz, H. De Waardt, E. Jan Geluk, S.-H. Kwon, Y.-H. Lee, R. Nötzel, and M. K. Smit, “Lasing in metallic-coated nanocavities,” Nat. Photonics 1(10), 589–594 (2007).

6.

M. A. Noginov, G. Zhu, A. M. Belgrave, R. Bakker, V. M. Shalaev, E. E. Narimanov, S. Stout, E. Herz, T. Suteewong, and U. Wiesner, “Demonstration of a spaser-based nanolaser,” Nature 460(7259), 1110–1112 (2009). [CrossRef] [PubMed]

7.

K. Yu, A. Lakhani, and M. C. Wu, “Subwavelength metal-optic semiconductor nanopatch lasers,” Opt. Express 18(9), 8790–8799 (2010). [CrossRef] [PubMed]

8.

M. P. Nezhad, A. Simic, O. Bondarenko, B. Slutsky, A. Mizrahi, L. Feng, V. Lomakin, and Y. Fainman, “Room-temperature subwavelength metallo-dielectric lasers,” Nat. Photonics 4(6), 395–399 (2010). [CrossRef]

9.

S. L. McCall, A. F. J. Levi, R. E. Slusher, S. J. Pearton, and R. A. Logan, “Whispering-gallery mode microdisk lasers,” Appl. Phys. Lett. 60(3), 289–291 (1992). [CrossRef]

10.

A. F. J. Levi, S. L. McCall, S. J. Pearton, and R. A. Logan, “Room temperature operation of submicrometre radius disk laser,” Electron. Lett. 29(18), 1666–1667 (1993). [CrossRef]

11.

Z. Zhang, L. Yang, V. Liu, T. Hong, K. Vahala, and A. Scherer, “Visible submicron microdisk lasers,” Appl. Phys. Lett. 90(11), 111119 (2007). [CrossRef]

12.

Q. Song, H. Cao, S. T. Ho, and G. S. Solomon, “Near-IR subwavelength microdisk lasers,” Appl. Phys. Lett. 94(6), 061109 (2009). [CrossRef]

13.

R. Perahia, T. P. M Alegre, A. H. Safavi-Naeini, and O. Painter, “Surface-plasmon mode hybridization in subwavelength microdisk lasers,” Appl. Phys. Lett. 95(20), 201114 (2009). [CrossRef]

14.

N. C. Frateschi and A. F. J. Levi, “Resonant modes and laser spectrum of microdisk lasers,” Appl. Phys. Lett. 66(22), 2932–2934 (1995). [CrossRef]

15.

J. Shainline, S. Elston, Z. Liu, G. Fernandes, R. Zia, and J. Xu, “Subwavelength silicon microcavities,” Opt. Express 17(25), 23323–23331 (2009). [CrossRef]

16.

J. Chen, O. Malis, A. M. Sergent, D. L. Sivco, N. Weimann, and A. Y. Cho, “In0.68Ga0.32As/Al0.64In0.36As/InP 4.5 µm quantum cascade lasers grown by solid phosphorus molecular beam epitaxy,” J. Vac. Sci. Technol. B 25(3), 913–915 (2007). [CrossRef]

17.

J. Faist, C. Gmachl, M. Striccoli, C. Sirtori, F. Capasso, D. L. Sivco, and A. Y. Cho, “Quantum cascade disk lasers,” Appl. Phys. Lett. 69(17), 2456–2458 (1996). [CrossRef]

18.

C. Gmachl, J. Faist, F. Capasso, C. Sirtori, D. L. Sivco, and A. Y. Cho, “Long-wavelength (9.5–11.5 µm) microdisk quantum-cascade lasers,” IEEE J. Quantum Electron. 33(9), 1567–1573 (1997). [CrossRef]

19.

M. Oxborrow, “Traceable 2-D finite-element simulation of the whispering-gallery modes of axisymmetric electromagnetic resonators,” IEEE Trans. Microw. Theory Tech. 55(6), 1209–1218 (2007). [CrossRef]

20.

S. Nojima and H. Asahi, “Refractive index of InGaAs/InAlAs multiquantum-well layers grown by molecular-beam epitaxy,” J. Appl. Phys. 63(2), 479–483 (1988). [CrossRef]

21.

S. Adachi, “Optical dispersion relations for GaP, GaAs, GaSb, InP, InAs, InSb, AlxGa1-xAs, and In1-xGaxAsyP1-y,” J. Appl. Phys. 66(12), 6030–6040 (1989). [CrossRef]

22.

O. Madelung, Semiconductors: data handbook (Springer, 3rd edition, 2004), Chap. 2.

OCIS Codes
(140.5960) Lasers and laser optics : Semiconductor lasers
(140.3948) Lasers and laser optics : Microcavity devices

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: July 27, 2010
Revised Manuscript: August 20, 2010
Manuscript Accepted: August 23, 2010
Published: August 25, 2010

Citation
Zhijun Liu, Jeffrey M. Shainline, Gustavo E. Fernandes, Jimmy Xu, Jianxin Chen, and Claire F. Gmachl, "Continuous-wave subwavelength microdisk lasers at λ = 1.53 µm," Opt. Express 18, 19242-19248 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-18-19242


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References

  1. K. J. Vahala, “Optical microcavities,” Nature 424(6950), 839–846 (2003). [CrossRef] [PubMed]
  2. W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,” Nature 424(6950), 824–830 (2003). [CrossRef] [PubMed]
  3. C. Manolatou and F. Rana, “Subwavelength nanopatch cavities for semiconductor plasmon lasers,” IEEE J. Quantum Electron. 44(5), 435–447 (2008)
  4. Y. Chassagneux, J. Palomo, R. Colombelli, S. Dhillon, C. Sirtori, H. Beere, J. Alton, and D. Ritchie, “Terahertz microcavity lasers with subwavelength mode volumes and thresholds in the milliampere range,” Appl. Phys. Lett. 90(9), 091113 (2007). [CrossRef]
  5. M. T. Hill, Y.-S. Oei, B. Smalbrugge, Y. Zhu, T. De Vries, P. J. Van Veldhoven, F. W. M. Van Otten, T. J. Eijkemans, J. P. Turkiewicz, H. De Waardt, E. Jan Geluk, S.-H. Kwon, Y.-H. Lee, R. Nötzel, and M. K. Smit, “Lasing in metallic-coated nanocavities,” Nat. Photonics 1(10), 589–594 (2007).
  6. M. A. Noginov, G. Zhu, A. M. Belgrave, R. Bakker, V. M. Shalaev, E. E. Narimanov, S. Stout, E. Herz, T. Suteewong, and U. Wiesner, “Demonstration of a spaser-based nanolaser,” Nature 460(7259), 1110–1112 (2009). [CrossRef] [PubMed]
  7. K. Yu, A. Lakhani, and M. C. Wu, “Subwavelength metal-optic semiconductor nanopatch lasers,” Opt. Express 18(9), 8790–8799 (2010). [CrossRef] [PubMed]
  8. M. P. Nezhad, A. Simic, O. Bondarenko, B. Slutsky, A. Mizrahi, L. Feng, V. Lomakin, and Y. Fainman, “Room-temperature subwavelength metallo-dielectric lasers,” Nat. Photonics 4(6), 395–399 (2010). [CrossRef]
  9. S. L. McCall, A. F. J. Levi, R. E. Slusher, S. J. Pearton, and R. A. Logan, “Whispering-gallery mode microdisk lasers,” Appl. Phys. Lett. 60(3), 289–291 (1992). [CrossRef]
  10. A. F. J. Levi, S. L. McCall, S. J. Pearton, and R. A. Logan, “Room temperature operation of submicrometre radius disk laser,” Electron. Lett. 29(18), 1666–1667 (1993). [CrossRef]
  11. Z. Zhang, L. Yang, V. Liu, T. Hong, K. Vahala, and A. Scherer, “Visible submicron microdisk lasers,” Appl. Phys. Lett. 90(11), 111119 (2007). [CrossRef]
  12. Q. Song, H. Cao, S. T. Ho, and G. S. Solomon, “Near-IR subwavelength microdisk lasers,” Appl. Phys. Lett. 94(6), 061109 (2009). [CrossRef]
  13. R. Perahia, T. P. M Alegre, A. H. Safavi-Naeini, and O. Painter, “Surface-plasmon mode hybridization in subwavelength microdisk lasers,” Appl. Phys. Lett. 95(20), 201114 (2009). [CrossRef]
  14. N. C. Frateschi and A. F. J. Levi, “Resonant modes and laser spectrum of microdisk lasers,” Appl. Phys. Lett. 66(22), 2932–2934 (1995). [CrossRef]
  15. J. Shainline, S. Elston, Z. Liu, G. Fernandes, R. Zia, and J. Xu, “Subwavelength silicon microcavities,” Opt. Express 17(25), 23323–23331 (2009). [CrossRef]
  16. J. Chen, O. Malis, A. M. Sergent, D. L. Sivco, N. Weimann, and A. Y. Cho, “In0.68Ga0.32As/Al0.64In0.36As/InP 4.5 µm quantum cascade lasers grown by solid phosphorus molecular beam epitaxy,” J. Vac. Sci. Technol. B 25(3), 913–915 (2007). [CrossRef]
  17. J. Faist, C. Gmachl, M. Striccoli, C. Sirtori, F. Capasso, D. L. Sivco, and A. Y. Cho, “Quantum cascade disk lasers,” Appl. Phys. Lett. 69(17), 2456–2458 (1996). [CrossRef]
  18. C. Gmachl, J. Faist, F. Capasso, C. Sirtori, D. L. Sivco, and A. Y. Cho, “Long-wavelength (9.5–11.5 µm) microdisk quantum-cascade lasers,” IEEE J. Quantum Electron. 33(9), 1567–1573 (1997). [CrossRef]
  19. M. Oxborrow, “Traceable 2-D finite-element simulation of the whispering-gallery modes of axisymmetric electromagnetic resonators,” IEEE Trans. Microw. Theory Tech. 55(6), 1209–1218 (2007). [CrossRef]
  20. S. Nojima and H. Asahi, “Refractive index of InGaAs/InAlAs multiquantum-well layers grown by molecular-beam epitaxy,” J. Appl. Phys. 63(2), 479–483 (1988). [CrossRef]
  21. S. Adachi, “Optical dispersion relations for GaP, GaAs, GaSb, InP, InAs, InSb, AlxGa1-xAs, and In1-xGaxAsyP1-y,” J. Appl. Phys. 66(12), 6030–6040 (1989). [CrossRef]
  22. O. Madelung, Semiconductors: data handbook (Springer, 3rd edition, 2004), Chap. 2.

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