Abstract

We designed, fabricated and characterised electrically injected quantum cascade lasers with photonic crystal reflectors emitting at terahertz frequencies (3.75 THz). These in-plane emitting structures display typical threshold current densities of 420 A/cm2 and output powers of up to 2 mW under pulsed excitation. The emission characteristics are shown to be robust, as with increasing current the emission remains singlemode with no drift in wavelength, this results from the narrow reflectivity band of the photonic crystal reflectors.

© 2005 Optical Society of America

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  22. Note that the point appears to be located at the �?M point in Fig. 1(a) and (b) due to a peculiarity of band folding in the reduced brillouin zone scheme where �?M fold onto �?M, but �?K, folds on to �?K, �?M,�?K
  23. The spacing between the modes can be seen clearly on the spectra taken at 0.8 A (blue line Fig. 5(b)). The optical path calculated from the sub-threshold Fabry-Perot fringes using an n gr = 3.9 is 1.3 mm that suggests that the highest reflectivity is at the cleaved facets.
  24. S. Mahnkopf, R. Marz, M. Kamp, G.-H. Duan, F. Lelarge and A. Forchel �??Tunable Photonic Crystal Coupled Cavity Lasers,�?? IEEE J. Quantum Electron. 40, 1306�??1314 (2004).
    [CrossRef]

Appl. Phys. Lett

M. Rochat, D. Hofstetter, M. Beck, and J. Faist �??Long-wavelength ( λ�?? 16 µm), room-temperature, single- frequency quantum-cascade lasers based on a bound-to-continuum transition,�?? Appl. Phys. Lett. 79, 4273�??4271 (2001).
[CrossRef]

Appl. Phys. Lett.

J. Faist, C. Gmachl, F. Capasso, C. Sirtori, D. L. Sivco, J. N. Baillargeon, and A. Y. Cho �??Distributed feedback quantum cascade lasers,�?? Appl. Phys. Lett. 70, 2670�??2672 (1997).
[CrossRef]

L. Mahler, R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, D. A. Ritchie, and A. G. Davies �??Single-mode operation of terahertz quantum cascade lasers with distributed feedback resonators,�?? Appl. Phys. Lett. 84, 5446�??5448 (2004).
[CrossRef]

D. Hofstetter, J. Faist, M. Beck, and U. Oesterle �??Surface-.emitting 10.1 µm quantum-cascade distributed feedback lasers,�?? Appl. Phys. Lett. 75, 3769�??3771 (1999).
[CrossRef]

G. Scalari, N. Hoyler, M. Giovannini, and J. Faist �??Terahertz bound-to-continuum quantum-cascade lasers based on optical-phonon scattering extraction�?? Appl. Phys. Lett. 86, 181101-3 (2005).
[CrossRef]

M. Meier, A. Mekis, A. Dodabalapur, A. Timko, R.E. Slusher, J. D. Joannopoulos, and O. Nalamasu �??Laser Action from two-dimensional distributed feedback in photonic crystals,�?? Appl. Phys. Lett. 74, 7-9 (1999).
[CrossRef]

CLEO Pacific Rim Tokyo Japan CTuE1-1

E. Kuramochi, M. Notomi, S. Hughes, L. Ramunno, G. Kira, S. Mitsugi, A. Shinya, and T.Watanabe �??Scattering Loss of Photonic Crystal Waveguides and Nanocavities induced by Structural Disorder,�?? CLEO Pacific Rim Tokyo Japan CTuE1-1 (2005).

IEEE J. Quantum Electron.

S. Mahnkopf, R. Marz, M. Kamp, G.-H. Duan, F. Lelarge and A. Forchel �??Tunable Photonic Crystal Coupled Cavity Lasers,�?? IEEE J. Quantum Electron. 40, 1306�??1314 (2004).
[CrossRef]

R. Ferrini, D. Leuenberger, M. Mulot, M. Qiu, J. Moosburger, M. Kamp, A. Forchel, S. Anand, and R. Houdré �??Optical Study of Two-Dimensional InP-Based Photonic Crystals by Internal Light Source Technique,�?? IEEE J. Quantum Electron. 38, 786�??799 (2002).
[CrossRef]

IEEE Trans. Microwave Theory Tech

P. H. Siegel �??Terahertz Technology�?? IEEE Trans. Microwave Theory Tech. 50, 910�??928 (2002).
[CrossRef]

J. Opt. Soc. Am. B

Nature

R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Richie, R. C. Lotti, and F. Rossi �??Terahertz semiconductor-heterostructure laser,�?? Nature 417, 156�??159 (2002).
[CrossRef] [PubMed]

Opt. Express

Opt. Lett.

Phys. Rev. B

M. Plihal and A. A. Maradudin �??Photonic band structure of two-dimensional systems: The triangular lattice,�?? Phys. Rev. B 44, 8565�??8571 (1991).
[CrossRef]

Phys. Rev. Lett

S. John, �??Strong localization of photons in certain disordered dielectric superlattices,�?? Phys. Rev. Lett. 58, 2486�??2489 (1987).
[CrossRef] [PubMed]

Phys. Rev. Lett.

E. Yablonovitch, �??Inhibited Spontaneous Emission in Solid-state Physics and Electronics,�?? Phys. Rev. Lett. 58, 2059�??2062 (1987).
[CrossRef] [PubMed]

Science

J. Faist, F. Capasso, D. L. Sivco, C. Sirtori, A. L. Hutchinson, and A. Y. Cho, �??Quantum Cascade Laser,�?? Science 264, 553�??556 (1994).
[CrossRef] [PubMed]

M. Beck, D. Hofstetter, T. Aellen, J. Faist, U. Oesterle, M. Ilegems, E. Gini, and H. Melchior �??Continuous Wave Operation of Mid-Infrared Semiconductor Laser at Room Temperature,�?? Science 295, 301�??305 (2002).
[CrossRef] [PubMed]

R. Colombelli, K. Srinivasan, M. Troccoli, O. Painter, C. F. Gmachl, D. M. Tennant, A. M. Sergent, D. L. Sivco, A. Y. Cho, and F. Capasso �??Quantum Cascade Surface-Emitting Photonic Crystal Laser,�?? Science 302, 1374�??1377 (2003
[CrossRef] [PubMed]

Other

K. Busch, S. Lölkes, R. B. Wehrspohn, and H. Föll Photonic Crystals: Advances in Design, Fabrication and Characterization (Wiley-VCH, Weinheim, 2004).

J. D. Joannopoulos, R. D. Meade, and J. N. Winn, Photonic Crystals: Moulding the Flow of Light (Princeton University Press, New Jersey, 1995).

Note that the point appears to be located at the �?M point in Fig. 1(a) and (b) due to a peculiarity of band folding in the reduced brillouin zone scheme where �?M fold onto �?M, but �?K, folds on to �?K, �?M,�?K

The spacing between the modes can be seen clearly on the spectra taken at 0.8 A (blue line Fig. 5(b)). The optical path calculated from the sub-threshold Fabry-Perot fringes using an n gr = 3.9 is 1.3 mm that suggests that the highest reflectivity is at the cleaved facets.

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Figures (6)

Fig. 1.
Fig. 1.

2D dispersion curves obtained from PWE calculations for TM polarised light through (a) a homogeneous medium n = 3.9 and, (b) and (c) a triangular PhC made of pillars, each with a refractive index difference Δn. The energy is given in reduced units u = a/λ where ‘a’ denotes the lattice constant and ‘λ’ represents wavelength. The fill factor is 0.4, the refractive index of the pillar is kept at n = 3.9. (b) Δn = 0.3, a weak refractive index contrast results in a splitting of the degeneracy of the high symmetry points. The circle highlights the stopband where lasing occurs in the ΓK direction. (c) Δn = 2.9 this refractive index contrast is strong enough to create full bandgaps, energy regions where the reflectivity remains high regardless of the direction of propagation in the PhC. (d) Sketch of the principal crystallographic directions in the square (triangle) lattices: ΓM and ΓX (ΓM and ΓK).

Fig. 2.
Fig. 2.

(a) Schematic of QCL laser bounded by a Single Plasmon Waveguide PhC. The red arrows show the direction of the light emission. The green stripe represents the active region, the blue the heavily doped region and yellow represents metal. The top and bottom contacts are labelled. (b) Cross-section of schematic shown in (a). The electric field intensity (red line) versus vertical distance from the surface of the QCL structure for the single plasmon waveguide structure, at the pillars/top contact area (c) and between the pillars (d). The optical mode overlap with the gain region at the pillars/top contact for the the single plasmon waveguide is Γ=0.35 [18]. The mode extends over 100 μm into the QCL substrate. (d) Shows also a second mode between the top gold layer and air (violet line, not to scale) which will be coupled into by the guided mode.

Fig. 3.
Fig. 3.

Schematic and Scanning Electron Microscope (SEM) images of a fabricated structure. (a) Schematic shows the top ‘A’ and bottom ‘B’ contacts and the ridge waveguide (below the top contact) bounded by four rows of PhC pillars ‘C’ on either side. (b) SEM image shows a top view of a ΓM orientated PhC-QCL, with a corresponding enlargement of the PhC area. (c) SEM image shows the cross section taken through the pillar structure after metal deposition. Good vertical sidewalls over the entire 15 μm depth are shown.

Fig. 4.
Fig. 4.

Results from a 4 row PhC-QCL in the ΓK directions a = 21 μm (a) Current voltage and output light peak power was measured by collecting the laser emission using a light pipe and sending it to a broadband, calibrated thermopile, and a series of light current curves for increasing temperatures. Lasing action upto liquid nitrogen temperatures is observed (temperature range 6 – 77 K). versus injected current with a current threshold, J th , = 421 A/cm2. (b) Series of high resolution spectra taken at different currents. Each current is marked on Fig. 4(a) with the corresponding symbol. The emission starts single mode at the lasing threshold and remains single mode with increasing current, moreover no wavelength drift with increased current is observed, until lasing roll over.

Fig. 5.
Fig. 5.

Results from a 4 row PhC-QCL in the ΓK directions with a = 21 μm. Sub threshold (a) Interferogram showing beating and (b) Optical spectrum, the spacing of the Fabry-Pérot fringes corresponding to an optical path length of 1.1 mm.

Fig. 6.
Fig. 6.

Results on a 4 row PhC-QCL in the ΓM directions with a = 21 μm (a) Current voltage and output light versus injected current showing a J th = 542 A/cm2. (b) Series of high resolution spectrum taken at different currents showing multi mode emission, a blue shift with increased current is seen due to the quantum confined Stark effect.

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