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6 Jun 2011

Volume 98, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 233101 (2011); http://dx.doi.org/10.1063/1.3597211 (3 pages)

Yu-Jung Lu (呂宥蓉), Hon-Way Lin (林弘偉), Hung-Ying Chen (陳虹穎), Yu-Chen Yang (楊右丞), and Shangjr Gwo (果尚志)
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Observation of phase shifts in a vertical cavity quantum dot switch

C. Y. Jin, O. Kojima, T. Kita, O. Wada, and M. Hopkinson

Appl. Phys. Lett. 98, 231101 (2011); http://dx.doi.org/10.1063/1.3596704 (3 pages) | Cited 4 times

Online Publication Date: 6 June 2011

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We have studied the possibility to utilize semiconductor quantum dots (QDs) as an optical phase shifter within a vertical geometry for ultrafast information processing. From theoretical analyses, an optical phase nonlinearity in QD structures has been predicted which can be enhanced through the use of an vertical optical cavity. Asymmetric cavity structures with 16/30 periods of GaAs/AlGaAs layers for the front/back mirrors have been fabricated to demonstrate a practical device with significant nonlinear characteristics for optical switching. A phase shift of 18° has been initially observed with a tilted pump scheme. This observation paves the way toward a Mach–Zehnder optical switch using QDs inside a vertical cavity.
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42.79.-e Optical elements, devices, and systems
42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics
78.67.Hc Quantum dots

High-performance quantum cascade lasers with wide electroluminescence ( ∼ 600 cm−1), operating in continuous-wave above 100 °C

Kazuue Fujita, Shinichi Furuta, Atsushi Sugiyama, Takahide Ochiai, Akio Ito, Tatsuo Dougakiuchi, Tadataka Edamura, and Masamichi Yamanishi

Appl. Phys. Lett. 98, 231102 (2011); http://dx.doi.org/10.1063/1.3596706 (3 pages) | Cited 4 times

Online Publication Date: 7 June 2011

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The authors report high temperature continuous-wave (cw) operations of broad-gain quantum cascade lasers based on the anticrossed dual-upper-state to multiple-lower-state design. The devices exhibit extremely wide electroluminescence (>600 cm−1) and subthreshold amplified spontaneous emission ( ∼ 570 cm−1) spectra at room temperature. Despite showing such broad electroluminescence spectra, the high-reflection coated, buried heterostructure lasers operating at 6.8 μm demonstrate a low threshold current density of ∼ 1.5 kA/cm2 and a high power of >500 mW with a high slope efficiency of ∼ 1.6 W/A in cw mode at 300 K. The maximum cw operating temperature of above 100 °C is achieved.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Real time demonstration of high bitrate quantum random number generation with coherent laser light

T. Symul, S. M. Assad, and P. K. Lam

Appl. Phys. Lett. 98, 231103 (2011); http://dx.doi.org/10.1063/1.3597793 (3 pages) | Cited 6 times

Online Publication Date: 7 June 2011

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We present a random number generation scheme that uses broadband measurements of the vacuum field contained in the radio-frequency sidebands of a single-mode laser. Even though the measurements may contain technical noise, we show that suitable algorithms can transform the digitized photocurrents into a string of random numbers that can be made arbitrarily correlated with a subset of the quantum fluctuations (high quantum correlation regime) or arbitrarily immune to environmental fluctuations (high environmental immunity). We demonstrate up to 2 Gbps of real time random number generation that were verified using standard randomness tests.
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03.67.Hk Quantum communication

Resilience of gated avalanche photodiodes against bright illumination attacks in quantum cryptography

Z. L. Yuan, J. F. Dynes, and A. J. Shields

Appl. Phys. Lett. 98, 231104 (2011); http://dx.doi.org/10.1063/1.3597221 (3 pages) | Cited 6 times

Online Publication Date: 8 June 2011

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Semiconductor avalanche photodiodes (APDs) are commonly used for single photon detection in quantum key distribution. Recently, many attacks using bright illumination have been proposed to manipulate gated InGaAs APDs. In order to devise effective countermeasures, careful analysis of these attacks must be carried out to distinguish between incorrect operation and genuine loopholes. Here, we show that correctly operated, gated APDs are immune to continuous-wave illumination attacks, while monitoring the photocurrent for anomalously high values is a straightforward countermeasure against attacks using temporally tailored light.
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85.60.Dw Photodiodes; phototransistors; photoresistors
03.67.Dd Quantum cryptography and communication security

Tuneable polaritonics at room temperature with strongly coupled Tamm plasmon polaritons in metal/air-gap microcavities

C. Grossmann, C. Coulson, G. Christmann, I. Farrer, H. E. Beere, D. A. Ritchie, and J. J. Baumberg

Appl. Phys. Lett. 98, 231105 (2011); http://dx.doi.org/10.1063/1.3597304 (3 pages) | Cited 2 times

Online Publication Date: 8 June 2011

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We report strong coupling between Tamm plasmons and excitons in III–V quantum wells at room temperature in ultracompact sample designs. A high refractive index contrast air-gap mirror together with optical Tamm states at a metal/semiconductor interface tightly confines the intracavity field leading to substantial local field enhancements. Angular-resolved reflectivity spectra give clear evidence for anticrossing in the dispersion relation. Room temperature Rabi splittings of 10 meV are found in excellent agreement with simulations. Electrical control of the polariton modes is realized without need for doped mirror layers. Such air-gap microcavities open innovative possibilites for electrically tunable microcavities and polaritonic microelectromechanics.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.35.-y Excitons and related phenomena

81 fJ/bit energy-to-data ratio of 850 nm vertical-cavity surface-emitting lasers for optical interconnects

P. Moser, W. Hofmann, P. Wolf, J. A. Lott, G. Larisch, A. Payusov, N. N. Ledentsov, and D. Bimberg

Appl. Phys. Lett. 98, 231106 (2011); http://dx.doi.org/10.1063/1.3597799 (3 pages) | Cited 5 times

Online Publication Date: 8 June 2011

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Extremely energy-efficient oxide-confined high-speed 850 nm vertical-cavity surface-emitting lasers for optical interconnects are presented. Error-free performance at 17 and 25 Gb/s via a 100 m multimode fiber link is demonstrated at record high dissipation-power-efficiencies of up to 69 fJ/bit (<0.1 mW/Gbps) and 99 fJ/bit, respectively. These are the most power efficient high-speed directly modulated light sources reported to date. The total energy-to-data ratio is 83 fJ/bit at 25 °C and reduces to 81 fJ/bit at 55 °C. These results were obtained without adjustment of driving conditions. A high D-factor of 12.0 GHz/(mA)0.5 and a K-factor of 0.41 ns are measured.
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42.62.-b Laser applications
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.81.Uv Fiber networks
42.82.Ds Interconnects, including holographic interconnects
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Type-II core/shell nanoparticle induced photorefractivity

Xiangping Li, Joel Van Embden, Richard A. Evans, and Min Gu

Appl. Phys. Lett. 98, 231107 (2011); http://dx.doi.org/10.1063/1.3596437 (3 pages)

Online Publication Date: 8 June 2011

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We demonstrate engineering the photocharge generation efficiency of nanoparticles on the nanometer scale by using a type-II band-gap structure. Compared to bare CdSe cores, the dispersion of type-II core/shell nanoparticles in photorefractive polymer led to an average 100% increase in photocurrents. An improvement to the refractive-index construction time, and a near 100% enhancement to the two beam coupling net-gain coefficients and four-wave mixing internal diffraction efficiencies have been achieved at moderate biases.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Hc Quantum dots
78.20.Mg Photorefractive effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Electrical injection, continuous wave operation of subwavelength-metallic-cavity lasers at 260 K

Kang Ding, Zhicheng Liu, Leijun Yin, Hua Wang, Ruibin Liu, Martin T. Hill, Milan J. H. Marell, Peter J. van Veldhoven, Richard Nötzel, and C. Z. Ning

Appl. Phys. Lett. 98, 231108 (2011); http://dx.doi.org/10.1063/1.3598961 (3 pages) | Cited 5 times

Online Publication Date: 8 June 2011

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We report continuous wave lasing operation at T = 260 K of subwavelength-metallic-cavities with semiconductor core encapsulated in silver under electric injection. The physical cavity volumes of the two lasers presented are 0.96λ3 (λ = 1563.4 nm) and 0.78λ3 (λ = 1488.7 nm), respectively. Longitudinal modes observed in one of lasers correspond to the Fabry–Perot cavity in the length direction. Such record high temperature operation of a subwavelength laser is of great importance for the development of small light sources in future integrated photonic circuits and other on-chip applications.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems

High-resolution heterodyne spectroscopy using a tunable quantum cascade laser around 3.5 THz

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, B. Klein, T.-Y. Kao, Q. Hu, and J. L. Reno

Appl. Phys. Lett. 98, 231109 (2011); http://dx.doi.org/10.1063/1.3599518 (3 pages) | Cited 7 times

Online Publication Date: 9 June 2011

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A frequency tunable terahertz heterodyne spectrometer, based on a third-order distributed feedback quantum cascade laser as a local oscillator, has been demonstrated by measuring molecular spectral lines of methanol (CH3OH) gas at 3.5 THz. By varying the bias voltage of the laser, we achieved a tuning range of ∼ 1 GHz of the lasing frequency, within which the molecular spectral lines were recorded. The measured spectra show excellent agreement with modeled ones. By fitting we derived the lasing frequency for each bias voltage accurately. The ultimate performance of the receiver including the resolution of noise temperature and frequency is also addressed.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
33.20.Bx Radio-frequency and microwave spectra

Cascaded third harmonic generation in lithium niobate nanowaveguides

Alexander S. Solntsev, Andrey A. Sukhorukov, Dragomir N. Neshev, Rumen Iliew, Reinhard Geiss, Thomas Pertsch, and Yuri S. Kivshar

Appl. Phys. Lett. 98, 231110 (2011); http://dx.doi.org/10.1063/1.3597627 (3 pages) | Cited 1 time

Online Publication Date: 9 June 2011

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We predict highly efficient third harmonic generation through simultaneous phase-matching of second-harmonic generation and sum-frequency generation in lithium niobate nanowaveguides, enabled due to strong modal dispersion. We demonstrate that the waveguide size which corresponds to phase-matching is also optimal for highest mode confinement and therefore for strongly enhanced conversion efficiency.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Gn Optical waveguides and couplers

To realize the optimal probe pulse length for detection of pulsed terahertz signal with spectral-encoding technique

Xiao-Yu Peng, Xin-Hai Zhang, Jing-Hua Teng, Hong-Cheng Guo, and Yong-Lim Foo

Appl. Phys. Lett. 98, 231111 (2011); http://dx.doi.org/10.1063/1.3598405 (3 pages)

Online Publication Date: 9 June 2011

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The approach to realize the optimal chirped probe pulse length for an arbitrary pulsed terahertz (THz) signal measured with the spectral-encoding technique was investigated by simulation. It was found that either the maximum positive peak or the absolute value of the strongest negative peak of the normalized difference between the probe spectrum modulated by THz signal and the background probe spectrum tended to be maximized when the probe pulse duration approached to the optimal value. The probe pulse length can be adjusted continuously with a pair of triangular dispersive prisms. THz signals from high-voltage biased air plasmas induced by femtosecond laser pulse were measured with minimum distortion using our simple method.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
84.40.-x Radiowave and microwave (including millimeter wave) technology

Low temperature near-field scanning optical microscopy on infrared and terahertz photonic-crystal quantum cascade lasers

I. C. Moldovan-Doyen, G. Xu, L. Greusard, G. Sevin, E. Strupiechonski, G. Beaudoin, I. Sagnes, S. P. Khanna, E. H. Linfield, A. G. Davies, R. Colombelli, and Y. De Wilde

Appl. Phys. Lett. 98, 231112 (2011); http://dx.doi.org/10.1063/1.3597411 (3 pages) | Cited 2 times

Online Publication Date: 10 June 2011

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We report the development of a scattering-type near-field scanning optical microscope (sNSOM) which operates at temperatures down to 100 K with a scanning range of up to 400 μm. We have used this sNSOM to map the electromagnetic near-field on mid-IR and terahertz (THz) surface emitting quantum cascade lasers with photonic-crystal resonators. Mid-IR devices operate at λ = 7.5 μm (40 THz) while THz devices operate at λ ≈ 110 μm (2.7 THz). The near-field images—in agreement with numerical calculations—demonstrate an instrument resolution of 100's nm.
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07.79.Fc Near-field scanning optical microscopes
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

The transition from a TEM-like mode to a plasmonic mode in parallel-plate waveguides

Jingbo Liu, Rajind Mendis, and Daniel M. Mittleman

Appl. Phys. Lett. 98, 231113 (2011); http://dx.doi.org/10.1063/1.3598404 (3 pages) | Cited 10 times

Online Publication Date: 10 June 2011

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We describe subwavelength-resolved measurements of the broadband terahertz field propagating inside a finite-width parallel-plate waveguide. We observe a transition in the spatial mode of the waveguide, in which the energy distribution shifts from the waveguide center to the edges with increasing frequency. This transition is surprisingly abrupt, and depends sensitively on the gap between the waveguide plates. These results may have important implications for a variety of terahertz experiments as well as in the design of optical systems and components in the visible and near-infrared regimes, which rely on plasmonic wave guiding.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Transition from strong to ultrastrong coupling regime in mid-infrared metal-dielectric-metal cavities

P. Jouy, A. Vasanelli, Y. Todorov, A. Delteil, G. Biasiol, L. Sorba, and C. Sirtori

Appl. Phys. Lett. 98, 231114 (2011); http://dx.doi.org/10.1063/1.3598432 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2011

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We have investigated the transition from strong to ultrastrong coupling regime between a mid-infrared intersubband excitation and the fundamental mode of a metal-dielectric-metal microcavity. The ultrastrong coupling regime is demonstrated up to room temperature for a wavelength of 11.7 μm by using 260 nm thick cavities, which impose an extreme subwavelength confinement. By varying the doping of our structures we show that the experimental signature of the transition to the ultrastrong coupling regime is the opening of a photonic gap in the polariton dispersion. The width of this gap depends quadratically on the ratio between the Rabi and intersubband transition energies.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
82.70.-y Disperse systems; complex fluids
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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