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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 15 — Jul. 20, 2009
  • pp: 13031–13039
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Distributed feedback ring resonators for vertically emitting terahertz quantum cascade lasers

Lukas Mahler, Maria I. Amanti, Christoph Walther, Alessandro Tredicucci, Fabio Beltram, Jérôme Faist, Harvey E. Beere, and David A. Ritchie  »View Author Affiliations


Optics Express, Vol. 17, Issue 15, pp. 13031-13039 (2009)
http://dx.doi.org/10.1364/OE.17.013031


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Abstract

We present distributed-feedback Terahertz quantum cascade lasers operating in a double-metal ring waveguide. High power collimated emission in a single spectral mode is observed in the vertical direction. A double-slit configuration is employed to achieve both good electrical contacts and efficient power out-coupling. The optical properties of the devices are interpreted with the aid of finite element simulations.

© 2009 OSA

1. Introduction

2. Modeling

For the design of the ring resonator, we use a commercial finite element solver (Comsol Multiphysics) to solve Maxwell’s equation formulated as an eigenfrequency problem. A full three dimensional simulation is beyond the presently available computational power, not only because we consider resonators extending over many wavelengths (1mm vs. 30 μm), but also because THz QCLs use metallic layers for mode confinement, which are typically three orders of magnitude thinner than the free-space wavelength. Thus, the eigenfrequencies are here computed for a segment of the ring corresponding to one period, and, furthermore, the metallic layers are only taken into account through appropriately shaped boundaries, similarly to the simplification described in [19

19. L. Mahler, A. Tredicucci, F. Beltram, C. Walther, H. E. Beere, and D. A. Ritchie, “Finite size effects in surface emitting Terahertz quantum cascade lasers,” Opt. Express 17(8), 6703–6709 (2009). [CrossRef] [PubMed]

]. While this is useful for the design of the ring and grating in the top metallization, obviously it does not yield the eigenmodes with different periodicity or non-circular symmetry. For the latter, one would need to apply periodic boundary conditions with a non-zero phase. To compute the far-field, we extract both the magnetic and the electric near-field in a plane of the segment 2 µm above the grating, reconstruct the full near-field of the device with linear transformations, and apply the Stratton-Chu formula to obtain the far-field.

3. Fabrication and measurements

Devices were fabricated from the same wafer used in [19

19. L. Mahler, A. Tredicucci, F. Beltram, C. Walther, H. E. Beere, and D. A. Ritchie, “Finite size effects in surface emitting Terahertz quantum cascade lasers,” Opt. Express 17(8), 6703–6709 (2009). [CrossRef] [PubMed]

,20

20. L. Mahler, A. Tredicucci, F. Beltram, C. Walther, J. Faist, B. Witzigmann, H. E. Beere, and D. A. Ritchie, “Vertically emitting microdisk lasers,” Nat. Photonics 3(1), 46–49 (2008). [CrossRef]

], a 200 stage resonant-phonon structure. The wafer and a doped host substrate were covered with 10/300 nm of Ti/Au and wafer bonded using a thermo-compression method. The original substrate was then removed by a combination of lapping and etching. Rings of various diameters (910 to 1020 μm) were fabricated by optical lithography and lift-off in a thermally evaporated Ti/Au metallization. The top contact in the slit region was etched with a H3PO4/H2O2/H2O 3/1/50 solution with the metal as a self-aligned mask and a circular resist mask to maintain the contact layer on the inner circumference of the ring as an absorber. The use of Ti as an adhesion layer is crucial in order to prevent fast etching along the metal-semiconductor interface and thus metal lift-off. The ring mesas are etched with inductively coupled plasma (ICP), using a gas mixture of BCl3/Cl2/Ar with a photoresist mask and a Si carrier wafer. After substrate thinning, devices were soldered to copper bars with an In/Ag alloy and wire bonded. The number of bonds is a trade-off between uniform pumping and introduction of defects into the grating structure. We observed a dual mode spectrum in some devices with two bonds, which then became single mode upon adding another two bonds. This could be a consequence of non-uniform current densities along the ring. An alternative explanation could be that the bonds introduce additional defects into the grating structure and therefore change the spectral properties of the resonator. In future devices, the additional bond wires could simply be avoided by fabricating a thicker top metallization, which was only ~5/50 nm of Ti/Au in the present devices. Finally, devices were mounted on the cold finger of a continuous-flow liquid-helium cryostat for the measurement. Spectra were recorded with an f/1 Picarin lens and a Fourier transform infrared spectrometer in rapid scan mode, with a DTGS detector, and at the maximum resolution of 0.125 cm−1. Light-current curves were obtained with a Golay-cell with a 6 mm diameter PE-window positioned 30 mm away from the device surface (resulting in a maximum collection angle of ~6° from the vertical), while the devices were driven with an Avtech AVR-3HF-B power supply with a 35 Ω resistor in series. No collection optics was employed. The far-fields were obtained by spherically scanning a pyroelectric detector of 1 mm2 size at a distance of ~8 cm, while the device was driven with an Agilent 8114A and a transformer for impedance matching. The 25 mm diameter cryostat window was located 25 mm from the sample, equivalent to a maximum accessible angle of 26.5° with respect to the device axis.

4. Results

Figure 2(a)
Fig. 2 (a) A SEM picture of a fabricated device. (b) Light-current characteristics of a ring with a diameter of 960 µm, driven with 800 ns pulses at 25 kHz repetition rate. The inset shows a spectrum on a logarithmic scale of the device driven with the above settings at a current of 1.8 A.
shows a fabricated device. The centers of the two slits belonging to one period have a spacing equal to 30% of the period, for which we compute a radiative efficiency of ~12% for the dominant resonance (see Fig. 1). Figure 2(b) shows the light-current characteristics of a device with a resonance frequency close to the maximum of the gain curve. 10 mW peak power are obtained at a duty cycle of 2%, with a slope efficiency of 25 mW/A. This is in good agreement with other lasers fabricated from the same growth, where 50 mW/A were observed from devices with ~24% computed radiative efficiency [20

20. L. Mahler, A. Tredicucci, F. Beltram, C. Walther, J. Faist, B. Witzigmann, H. E. Beere, and D. A. Ritchie, “Vertically emitting microdisk lasers,” Nat. Photonics 3(1), 46–49 (2008). [CrossRef]

]. Lasing ceases at 100 K, somewhat below the 130 K observed in unpatterned disk lasers. The inset shows the spectrum of the same device at a current of 1.8 A; the device is single mode with a side-mode suppression ratio of more than 20 dB. The same behavior was observed at all temperatures; only at currents just above threshold, we observed a second mode close to the dominant one. Figure 3(a)
Fig. 3 (a) Computed far-field of the device shown in Fig. 2. The angular position of the rings is determined by d/λ, where d is the ring diameter and λ the free-space wavelength. (b) Measured central portion of the emission far-field. Also shown is a spectrum taken prior to the far-field measurement. The insets show 3D plots of the corresponding panels.
shows the computed far-field for the mode shown in Fig. 1(a). For symmetry reasons, the field components interfere destructively on the device axis. The concentric rings in the far-field can be understood from an analysis following Young’s double slit experiment, considering the opposite ridges of the ring as two slits with anti-symmetric field distribution. Their angular position is determined by sin(2θ) = 2(n + 1/2)λ/d, where θ is the angle between device axis and free-space wavevector, λ is the free-space wavelength, and d is the device diameter. This explains why we expect a stronger divergence for our THz devices (λ/d≈1/10) than for the devices in [22

22. E. Mujagić, L. K. Hoffmann, S. Schartner, M. Nobile, W. Schrenk, M. P. Semtsiv, M. Wienold, W. T. Masselink, and G. Strasser, “Low divergence single-mode surface emitting quantum cascade ring lasers,” Appl. Phys. Lett. 93(16), 161101 (2008). [CrossRef]

], where λ/d≈1/100. The device from which we obtained the data of Fig. 2(b) was then mounted in a different setup to measure the far-field, where we also repeated the spectral measurements for verification. Results for the central cone (~15° from the vertical) of the far-field are shown in Fig. 3(b) with the laser nominally under the same driving conditions: a semicircular pattern with a relatively strong peak on one side was observed. The asymmetry could be due to the non-uniformly distributed mode along the ring, as discussed in detail below, or due to near-field distortions introduced by the asymmetric wire-bonding. We also note that the measured spectrum is no longer perfectly single-mode (see Fig. 3(b)), making the interpretation of the pattern even more complex.

In any case we can observe that the device seems quite sensitive to operating conditions (pulse shape, optical feedback, temperature stability, bonding etc.), indicating low mode selectivity. To further investigate these aspects, far-field measurements were also performed in a much wider angular range along the horizontal axis. This was achieved measuring multiple far-fields, each taken after rotating the cryostat head by 15°, and joining them together. The absence of false peaks (originating from unwanted reflections, etc.) was verified by checking data collected in the same angular region for two different windows positions. Results are shown in Fig. 4(a)
Fig. 4 (a) Measured far-field of the same device as in Fig. 2(b), driven with 1.65 A, 330 ns pulses at 90 kHz repetition rate. Data are joined from measurements with different cryostat window positions. Under these pumping conditions, a maximum emission at 11/-18 degrees and a considerable angular spread of the power is observed. The black circle indicates the collection angle of the Golay-cell used for acquisition of the light-current characteristics. The colormap is the same as for Fig. 3. (b) Cross section of the computed far-field of the two modes depicted in Fig. 1(b): symmetric (red) and asymmetric (black). Surprisingly, the asymmetric mode presents a large radiating intensity also far from the vertical direction.
for the same device, though driven this time with shorter pulses (330 ns) at higher repetition rates. Apart from the lower signal-to-noise ratio implied by the time-consuming measurement technique, it is evident that, while a significant fraction of the emission is indeed observed in a relatively small angular spread near the vertical, some non-negligible signal is clearly detected at large angles as well, possibly a consequence of the presence of modes with an undefined phase relation with the grating. These would have a partially asymmetric character and, as shown in Fig. 4(b), the power radiating from the asymmetric mode shows a strong intensity also at large angle from the vertical. The central area of Fig. 4(a) is also qualitatively different from Fig. 3(b), further evidencing the sensitivity to driving conditions. More importantly, however, this intensity distribution is incompatible with the slope efficiency shown in Fig. 2(b), where 25 mW/A were observed within a small collection angle. In fact, assuming the optimistic case in which the Golay detector were aligned on the maximum intensity peak at 11/-18 degrees, and integrating the far–field intensity over the detector field of view (black circle in Fig. 4) for the power comparison, one obtains that the far-field of Fig. 4 would imply a radiative efficiency of at least 20%, even for the ideal internal quantum efficiency of 200 (equal to the number of stages). This provides clear further evidence that the laser oscillates on other modes under these pumping conditions. In Fig. 5
Fig. 5 (a) Light-current characteristics of a ring with a diameter of 990 µm, driven with 800 ns pulses at 12.5 kHz repetition rate. The inset shows a spectrum on a logarithmic scale of the device driven with the above settings at a current of 1.8 A. (b) Measured far-field of the same device. Except for the center ring, the computed far-field of Fig. 3(a) is reasonably reproduced. The non-continuous rings could be due to the bonds covering the grating. The area outside an angle of ~26° (black circle) is shielded by the cryostat window opening. The inset shows a spectrum of the device driven under the same conditions.
we present data for another device with a slightly larger diameter emitting at 3.21 THz. The reduced peak power of 4 mW, shown in Fig. 5(a) is expected from the spectral gain dependence observed in earlier device series [20

20. L. Mahler, A. Tredicucci, F. Beltram, C. Walther, J. Faist, B. Witzigmann, H. E. Beere, and D. A. Ritchie, “Vertically emitting microdisk lasers,” Nat. Photonics 3(1), 46–49 (2008). [CrossRef]

]. In this case, however, the device showed a more stable single-mode character in both set-ups. A far-field acquired at 1.7 A, where it was verified one mode dominated the spectrum, is reported in Fig. 5(b). We can now identify the ring shaped structure predicted; the centermost ring is however collapsed into a spot. The distortion could be due to the bonding wires disturbing the near-field, or to the device being slightly non-symmetric. We recall in fact that the near-to-far-field transformation is basically a Fourier transform, which means that a coherent, delocalized near-field leads to a narrow spot in the far-field, whereas small bright spots in the near-field lead to isotropic emission.

To investigate how the alignment of the metallic grating and the defects introduced by wire-bonding are affecting surface emission patterns, we need a model of the entire ring. To this end, we follow a recent work on electrically pumped photonic crystal devices [23

23. Y. Chassagneux, R. Colombelli, W. Maineults, S. Barbieri, S. P. Khanna, E. H. Linfield, and A. G. Davies, “Predictable surface emission patterns in terahertz photonic-crystal quantum cascade lasers,” Opt. Express 17(12), 9491–9502 (2009). [CrossRef] [PubMed]

], where the location of the bond-wires in surface emitting THz QCLs has been shown to be very important. The authors have successfully employed a 2D model to compute the resonances of their large devices and explain the surface emission patterns. The approach uses the effective refractive indices of both double-metal and slit region to mimic the device with a structure of infinite extension along the growth axis, which allows the use of a scalar differential equation in 2D. The magnetic field of the eigenmode in the non-metalized area is then considered to be the near-field. After checking this model to be consistent with Fig. 3(a), a misalignment between the center of the semiconductor ring and of the metallic grating was introduced, as well as four missing slits to simulate the bond locations, in order to model the device of Fig. 2(a). Figures 6(a,b)
Fig. 6 (a) Electric field along the growth axis computed in a 2D model for the device shown in Fig. 2(a). Slits are suppressed in the location of the bonding pads, and the grating is misaligned by 0.5/-1.5 µm in x/y direction. (b) Corresponding far-field, where the distortions are even stronger than those in the measured far-field (see Fig. 5(b)). (c), (d) Computed far-fields of a device with a grating misaligned by 1 µm in the x-direction, and of a symmetric device with 2 bonding pads on the x-axis respectively. Both deviations from a perfect device qualitatively change the surface emission pattern.
show the electric field of the obtained eigenmode and the corresponding far-field. The imperfections lead to a non-uniform mode distribution along the ring, which then translates into a spot-like emission pattern. As further examples, we also plot the computed far-fields of a device with a perfect grating misaligned by 1 µm, and a perfectly aligned grating with two defects on the x-axis. As expected, all deviations strongly modify the surface emission pattern. In any case, the general directionality of the power does not seem to be affected, in agreement with our experimental observations. We can also assume that the bond wires contribute to the near-field by enlarging the effectively radiating area, which would explain the fact that the spot observed in Fig. 5(b) is narrower than the spots in Fig. 6(b). This effect is of course not included in this simple model. While this approach proves very useful for the understanding of non-perfectly periodic devices, it does not yield the surface losses of a particular mode, and therefore also excludes the calculation of spectra like those shown in Fig. 1.

If the grating is even more shifted with respect to the waveguide, the ring segments have locally different eigenfrequencies. Figure 7
Fig. 7 (a) Resonances of segments of the same dimension, computed for two different radial positions of the grating. (b) Far-field of a device with the metallic grating misaligned with respect to the semiconductor ring by 2-3 um. Due to the effect shown in panel (a), the eigenfrequency is not constant along the ring. Indeed, the mode seems to be localized in the lower left part of the ring, thus the far-field is no longer determined by interference, but rather diffraction limited.
illustrates the consequences as observed in earlier devices. In places where the grating is shifted towards the outer radius of the mesa, the effective period seen by the mode is reduced. The resulting shift of the main resonance can be seen from the computed spectra in Fig. 7(a). Two segments are considered, on opposite sides of a ring with a grating misaligned by 2.5 µm. Because the difference in eigenfrequency is now of the order of the linewidth of the resonator, the mode becomes localized in only one part of the ring. Therefore, the interference effect between opposite ring sides previously described as causing the circular far-field is lost, as can be clearly seen in the measurements of Fig. 7(b).

5. Conclusions and perspectives

We have demonstrated a promising new technology for high power THz QCLs. In future devices, one should further reduce the grating misalignment to the submicron range, but also increase the thickness of the top-metallization to 200-300 nm, in order to ensure a completely symmetric device, both from an electrical and an optical point of view. Finally, the technology employed in [17

17. S. Kumar, B. S. Williams, Q. Qin, A. W. Lee, Q. Hu, and J. L. Reno, “Surface-emitting distributed feedback terahertz quantum-cascade lasers in metal-metal waveguides,” Opt. Express 15(1), 113–128 (2007). [CrossRef] [PubMed]

] to separate the bonds from the grating would eliminate the mode distortions due to the bond pads. More recent heterostructures [9

9. S. Kumar, Q. Hu, and J. Reno, “186 K operation of terahertz quantum-cascade lasers based on a diagonal design,” Appl. Phys. Lett. 94(13), 131105 (2009). [CrossRef]

,24

24. G. Scalari, M. I. Amanti, M. Fischer, R. Terazzi, C. Walther, M. Beck, and J. Faist, “Step well quantum cascade laser emitting at 3 THz,” Appl. Phys. Lett. 94(4), 041114 (2009). [CrossRef]

] show slope efficiencies up to 60 mW/A in double-metal FP resonators. According to our simulations, a ring resonator with a first order grating, together with a slightly thinner waveguide (~10% of the free-space wavelength) should yield a radiative efficiency of 25%. Considering also the high collection efficiencies achieved, we indeed believe that slope efficiencies of up to 300 mW/A can be reached in these structures. Surface emission then allows large emitter areas by device parallelization, which should pave the way towards compact, narrowband THz sources at the Watt level.

Acknowledgments

We acknowledge SENTECH Instruments, Berlin, for assistance in performing the ICP-etching. This work was supported in part by the European Commission through the Research and Training Network “Physics of Intersubband Semiconductor Emitters” and the integrated project “Teranova”.

References and links

1.

R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Ritchie, R. C. Iotti, and F. Rossi, “Terahertz semiconductor-heterostructure laser,” Nature 417(6885), 156–159 (2002). [CrossRef] [PubMed]

2.

B. S. Williams, “Terahertz quantum-cascade lasers,” Nat. Photonics 1(9), 517–525 (2007). [CrossRef]

3.

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89(6), 061115 (2006). [CrossRef]

4.

A. W. M. Lee, Q. Qin, S. Kumar, B. S. Williams, Q. Hu, and J. L. Reno, “Real-time terahertz imaging over a standoff distance (>25 meters),” Appl. Phys. Lett. 89(14), 141125 (2006). [CrossRef]

5.

S. Kumar and A. W. M. Lee, “Resonant-phonon terahertz quantum-cascade lasers and video-rate terahertz imaging,” IEEE J. Sel. Top. Quantum Electron. 14(2), 333–344 (2008). [CrossRef]

6.

J. R. Gao, J. N. Hovenier, Z. Q. Yang, J. J. A. Baselmans, A. Baryshev, M. Hajenius, T. M. Klapwijk, A. J. L. Adam, T. O. Klaassen, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer,” Appl. Phys. Lett. 86(24), 244104 (2005). [CrossRef]

7.

H.-W. Hübers, S. Pavlov, A. Semenov, R. Köhler, L. Mahler, A. Tredicucci, H. Beere, D. Ritchie, and E. Linfield, “Terahertz quantum cascade laser as local oscillator in a heterodyne receiver,” Opt. Express 13(15), 5890–5896 (2005). [CrossRef] [PubMed]

8.

B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum-cascade laser at λ ≈ 100 µm using metal waveguide for mode confinement,” Appl. Phys. Lett. 83(11), 2124–2126 (2003). [CrossRef]

9.

S. Kumar, Q. Hu, and J. Reno, “186 K operation of terahertz quantum-cascade lasers based on a diagonal design,” Appl. Phys. Lett. 94(13), 131105 (2009). [CrossRef]

10.

M. I. Amanti, M. Fischer, C. Walther, G. Scalari, and J. Faist, “Horn antennas for terahertz quantum cascade lasers,” Electron. Lett. 43(10), 573–574 (2007). [CrossRef]

11.

A. Wei Min Lee, Q. Qin, S. Kumar, B. S. Williams, Q. Hu, and J. L. Reno, “High-power and high-temperature THz quantum-cascade lasers based on lens-coupled metal-metal waveguides,” Opt. Lett. 32(19), 2840–2842 (2007). [CrossRef] [PubMed]

12.

L. Sirigu, R. Terazzi, M. I. Amanti, M. Giovannini, J. Faist, L. A. Dunbar, and R. Houdré, “Terahertz quantum cascade lasers based on two-dimensional photonic crystal resonators,” Opt. Express 16(8), 5206–5217 (2008). [CrossRef] [PubMed]

13.

O. P. Marshall, V. Apostolopoulos, J. R. Freeman, R. Rungsawang, H. E. Beere, and D. A. Ritchie, “Surface-emitting photonic crystal terahertz quantum cascade lasers,” Appl. Phys. Lett. 93(17), 171112 (2008). [CrossRef]

14.

Y. Chassagneux, R. Colombelli, W. Maineult, S. Barbieri, H. E. Beere, D. A. Ritchie, S. P. Khanna, E. H. Linfield, and A. G. Davies, “Electrically pumped photonic-crystal terahertz lasers controlled by boundary conditions,” Nature 457(7226), 174–178 (2009). [CrossRef] [PubMed]

15.

O. Demichel, L. Mahler, T. Losco, C. Mauro, R. Green, A. Tredicucci, J. Xu, F. Beltram, H. E. Beere, D. A. Ritchie, and V. Tamošinuas, “Surface plasmon photonic structures in terahertz quantum cascade lasers,” Opt. Express 14(12), 5335–5345 (2006). [CrossRef] [PubMed]

16.

J. A. Fan, M. A. Belkin, F. Capasso, S. Khanna, M. Lachab, A. G. Davies, and E. H. Linfield, “Surface emitting terahertz quantum cascade laser with a double-metal waveguide,” Opt. Express 14(24), 11672–11680 (2006). [CrossRef] [PubMed]

17.

S. Kumar, B. S. Williams, Q. Qin, A. W. Lee, Q. Hu, and J. L. Reno, “Surface-emitting distributed feedback terahertz quantum-cascade lasers in metal-metal waveguides,” Opt. Express 15(1), 113–128 (2007). [CrossRef] [PubMed]

18.

M. Schubert and F. Rana, “Analysis of Terahertz Surface Emitting Quantum-Cascade Lasers,” IEEE J. Quantum Electron. 42(3), 257–265 (2006). [CrossRef]

19.

L. Mahler, A. Tredicucci, F. Beltram, C. Walther, H. E. Beere, and D. A. Ritchie, “Finite size effects in surface emitting Terahertz quantum cascade lasers,” Opt. Express 17(8), 6703–6709 (2009). [CrossRef] [PubMed]

20.

L. Mahler, A. Tredicucci, F. Beltram, C. Walther, J. Faist, B. Witzigmann, H. E. Beere, and D. A. Ritchie, “Vertically emitting microdisk lasers,” Nat. Photonics 3(1), 46–49 (2008). [CrossRef]

21.

E. Mujagić, S. Schartner, L. K. Hoffmann, W. Schrenk, M. P. Semtsiv, M. Wienold, W. T. Masselink, and G. Strasser, “Grating-coupled surface emitting quantum cascade ring lasers,” Appl. Phys. Lett. 93(1), 011108 (2008). [CrossRef]

22.

E. Mujagić, L. K. Hoffmann, S. Schartner, M. Nobile, W. Schrenk, M. P. Semtsiv, M. Wienold, W. T. Masselink, and G. Strasser, “Low divergence single-mode surface emitting quantum cascade ring lasers,” Appl. Phys. Lett. 93(16), 161101 (2008). [CrossRef]

23.

Y. Chassagneux, R. Colombelli, W. Maineults, S. Barbieri, S. P. Khanna, E. H. Linfield, and A. G. Davies, “Predictable surface emission patterns in terahertz photonic-crystal quantum cascade lasers,” Opt. Express 17(12), 9491–9502 (2009). [CrossRef] [PubMed]

24.

G. Scalari, M. I. Amanti, M. Fischer, R. Terazzi, C. Walther, M. Beck, and J. Faist, “Step well quantum cascade laser emitting at 3 THz,” Appl. Phys. Lett. 94(4), 041114 (2009). [CrossRef]

OCIS Codes
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(140.3490) Lasers and laser optics : Lasers, distributed-feedback
(140.3560) Lasers and laser optics : Lasers, ring
(240.6680) Optics at surfaces : Surface plasmons
(250.7270) Optoelectronics : Vertical emitting lasers
(140.5965) Lasers and laser optics : Semiconductor lasers, quantum cascade

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: May 12, 2009
Revised Manuscript: June 24, 2009
Manuscript Accepted: July 6, 2009
Published: July 15, 2009

Virtual Issues
July 17, 2009 Spotlight on Optics

Citation
Lukas Mahler, Maria I. Amanti, Christoph Walther, Alessandro Tredicucci, Fabio Beltram, Jérôme Faist, Harvey E. Beere, and David A. Ritchie, "Distributed feedback ring resonators for vertically emitting terahertz quantum cascade lasers," Opt. Express 17, 13031-13039 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13031


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References

  1. R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Ritchie, R. C. Iotti, and F. Rossi, “Terahertz semiconductor-heterostructure laser,” Nature 417(6885), 156–159 (2002). [CrossRef] [PubMed]
  2. B. S. Williams, “Terahertz quantum-cascade lasers,” Nat. Photonics 1(9), 517–525 (2007). [CrossRef]
  3. H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89(6), 061115 (2006). [CrossRef]
  4. A. W. M. Lee, Q. Qin, S. Kumar, B. S. Williams, Q. Hu, and J. L. Reno, “Real-time terahertz imaging over a standoff distance (>25 meters),” Appl. Phys. Lett. 89(14), 141125 (2006). [CrossRef]
  5. S. Kumar and A. W. M. Lee, “Resonant-phonon terahertz quantum-cascade lasers and video-rate terahertz imaging,” IEEE J. Sel. Top. Quantum Electron. 14(2), 333–344 (2008). [CrossRef]
  6. J. R. Gao, J. N. Hovenier, Z. Q. Yang, J. J. A. Baselmans, A. Baryshev, M. Hajenius, T. M. Klapwijk, A. J. L. Adam, T. O. Klaassen, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer,” Appl. Phys. Lett. 86(24), 244104 (2005). [CrossRef]
  7. H.-W. Hübers, S. Pavlov, A. Semenov, R. Köhler, L. Mahler, A. Tredicucci, H. Beere, D. Ritchie, and E. Linfield, “Terahertz quantum cascade laser as local oscillator in a heterodyne receiver,” Opt. Express 13(15), 5890–5896 (2005). [CrossRef] [PubMed]
  8. B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum-cascade laser at λ ≈ 100 µm using metal waveguide for mode confinement,” Appl. Phys. Lett. 83(11), 2124–2126 (2003). [CrossRef]
  9. S. Kumar, Q. Hu, and J. Reno, “186 K operation of terahertz quantum-cascade lasers based on a diagonal design,” Appl. Phys. Lett. 94(13), 131105 (2009). [CrossRef]
  10. M. I. Amanti, M. Fischer, C. Walther, G. Scalari, and J. Faist, “Horn antennas for terahertz quantum cascade lasers,” Electron. Lett. 43(10), 573–574 (2007). [CrossRef]
  11. A. Wei Min Lee, Q. Qin, S. Kumar, B. S. Williams, Q. Hu, and J. L. Reno, “High-power and high-temperature THz quantum-cascade lasers based on lens-coupled metal-metal waveguides,” Opt. Lett. 32(19), 2840–2842 (2007). [CrossRef] [PubMed]
  12. L. Sirigu, R. Terazzi, M. I. Amanti, M. Giovannini, J. Faist, L. A. Dunbar, and R. Houdré, “Terahertz quantum cascade lasers based on two-dimensional photonic crystal resonators,” Opt. Express 16(8), 5206–5217 (2008). [CrossRef] [PubMed]
  13. O. P. Marshall, V. Apostolopoulos, J. R. Freeman, R. Rungsawang, H. E. Beere, and D. A. Ritchie, “Surface-emitting photonic crystal terahertz quantum cascade lasers,” Appl. Phys. Lett. 93(17), 171112 (2008). [CrossRef]
  14. Y. Chassagneux, R. Colombelli, W. Maineult, S. Barbieri, H. E. Beere, D. A. Ritchie, S. P. Khanna, E. H. Linfield, and A. G. Davies, “Electrically pumped photonic-crystal terahertz lasers controlled by boundary conditions,” Nature 457(7226), 174–178 (2009). [CrossRef] [PubMed]
  15. O. Demichel, L. Mahler, T. Losco, C. Mauro, R. Green, A. Tredicucci, J. Xu, F. Beltram, H. E. Beere, D. A. Ritchie, and V. Tamošinuas, “Surface plasmon photonic structures in terahertz quantum cascade lasers,” Opt. Express 14(12), 5335–5345 (2006). [CrossRef] [PubMed]
  16. J. A. Fan, M. A. Belkin, F. Capasso, S. Khanna, M. Lachab, A. G. Davies, and E. H. Linfield, “Surface emitting terahertz quantum cascade laser with a double-metal waveguide,” Opt. Express 14(24), 11672–11680 (2006). [CrossRef] [PubMed]
  17. S. Kumar, B. S. Williams, Q. Qin, A. W. Lee, Q. Hu, and J. L. Reno, “Surface-emitting distributed feedback terahertz quantum-cascade lasers in metal-metal waveguides,” Opt. Express 15(1), 113–128 (2007). [CrossRef] [PubMed]
  18. M. Schubert and F. Rana, “Analysis of Terahertz Surface Emitting Quantum-Cascade Lasers,” IEEE J. Quantum Electron. 42(3), 257–265 (2006). [CrossRef]
  19. L. Mahler, A. Tredicucci, F. Beltram, C. Walther, H. E. Beere, and D. A. Ritchie, “Finite size effects in surface emitting Terahertz quantum cascade lasers,” Opt. Express 17(8), 6703–6709 (2009). [CrossRef] [PubMed]
  20. L. Mahler, A. Tredicucci, F. Beltram, C. Walther, J. Faist, B. Witzigmann, H. E. Beere, and D. A. Ritchie, “Vertically emitting microdisk lasers,” Nat. Photonics 3(1), 46–49 (2008). [CrossRef]
  21. E. Mujagić, S. Schartner, L. K. Hoffmann, W. Schrenk, M. P. Semtsiv, M. Wienold, W. T. Masselink, and G. Strasser, “Grating-coupled surface emitting quantum cascade ring lasers,” Appl. Phys. Lett. 93(1), 011108 (2008). [CrossRef]
  22. E. Mujagić, L. K. Hoffmann, S. Schartner, M. Nobile, W. Schrenk, M. P. Semtsiv, M. Wienold, W. T. Masselink, and G. Strasser, “Low divergence single-mode surface emitting quantum cascade ring lasers,” Appl. Phys. Lett. 93(16), 161101 (2008). [CrossRef]
  23. Y. Chassagneux, R. Colombelli, W. Maineults, S. Barbieri, S. P. Khanna, E. H. Linfield, and A. G. Davies, “Predictable surface emission patterns in terahertz photonic-crystal quantum cascade lasers,” Opt. Express 17(12), 9491–9502 (2009). [CrossRef] [PubMed]
  24. G. Scalari, M. I. Amanti, M. Fischer, R. Terazzi, C. Walther, M. Beck, and J. Faist, “Step well quantum cascade laser emitting at 3 THz,” Appl. Phys. Lett. 94(4), 041114 (2009). [CrossRef]

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