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19 May 2008

Volume 92, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 92, 202101 (2008); http://dx.doi.org/10.1063/1.2927379 (3 pages)

Jasmin Aghassi, Matthias H. Hettler, and Gerd Schön
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Room temperature terahertz quantum cascade laser source based on intracavity difference-frequency generation

Mikhail A. Belkin, Federico Capasso, Feng Xie, Alexey Belyanin, Milan Fischer, Andreas Wittmann, and Jérôme Faist

Appl. Phys. Lett. 92, 201101 (2008); http://dx.doi.org/10.1063/1.2919051 (3 pages) | Cited 35 times

Online Publication Date: 19 May 2008

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We report on our progress in the development of a terahertz quantum cascade laser source based on intracavity terahertz difference-frequency mixing in a dual-wavelength mid-infrared quantum cascade laser with the active region engineered to possess giant second-order nonlinear susceptibility. In this letter, we demonstrate devices that operate in mid-infrared at λ1 = 8.9 μm and λ2 = 10.5 μm and produce terahertz output at λ ≈ 60 μm via difference-frequency generation with 7 μW output power at 80 K, 1 μW output at 250 K, and still approximately 300 nW output at 300 K.
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42.55.Px Semiconductor lasers; laser diodes
42.65.An Optical susceptibility, hyperpolarizability

Enhancing visibility and resolution in Nth-order intensity correlation of thermal light

De-Zhong Cao, Jun Xiong, Su-Heng Zhang, Lu-Fang Lin, Lu Gao, and Kaige Wang

Appl. Phys. Lett. 92, 201102 (2008); http://dx.doi.org/10.1063/1.2919719 (3 pages) | Cited 23 times

Online Publication Date: 19 May 2008

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The arbitrary Nth-order intensity correlation measurement with thermal light is both theoretically and experimentally investigated. In a double-slit interference scheme with thermal light, we compare the results for higher- and lower-order intensity correlation and demonstrate that the visibility of the interference pattern can be dramatically enhanced while the resolution can also be improved when the order N becomes larger. The experimental results are in agreement with our theoretical analysis.
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42.25.Hz Interference
42.25.Fx Diffraction and scattering
06.30.-k Measurements common to several branches of physics and astronomy

0.3 V drive voltage GaAs/AlGaAs substrate removed Mach–Zehnder intensity modulators

JaeHyuk Shin, Yu-Chia Chang, and Nadir Dagli

Appl. Phys. Lett. 92, 201103 (2008); http://dx.doi.org/10.1063/1.2931057 (3 pages) | Cited 3 times

Online Publication Date: 19 May 2008

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Push-pull driven Mach–Zehnder intensity modulators with a record low drive voltage of 0.3 V were realized in substrate removed very compact GaAs/AlGaAs optical waveguides at 1.55 μm. The modulator electrode is 7 mm long, corresponding to a drive voltage length product of 0.21 V cm. The modulation is due to linear electro-optic and carrier depletion effects and has a high speed potential. The propagation loss was 8 dB/cm, making moderately long devices possible.
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42.79.Hp Optical processors, correlators, and modulators
42.82.Et Waveguides, couplers, and arrays
07.60.Ly Interferometers

Gigahertz quantum key distribution with InGaAs avalanche photodiodes

Z. L. Yuan, A. R. Dixon, J. F. Dynes, A. W. Sharpe, and A. J. Shields

Appl. Phys. Lett. 92, 201104 (2008); http://dx.doi.org/10.1063/1.2931070 (3 pages) | Cited 34 times

Online Publication Date: 19 May 2008

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We report a demonstration of quantum key distribution (QKD) at gigahertz clock rates with InGaAs avalanche photodiodes (APDs) operating in a self-differencing mode. Such a mode of operation allows detection of extremely weak avalanches so that the detector afterpulse noise is sufficiently suppressed. The system is characterized by a secure bit rate of 2.37 Mbit/s at 5.6 km and 27.9 kbit/s at 65.5 km when the fiber dispersion is not compensated. After compensating the fiber dispersion, the QKD distance is extended to 101 km, resulting in a secure key rate of 2.88 kbit/s. Our results suggest that InGaAs APDs are very well suited to gigahertz QKD applications.
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03.67.Dd Quantum cryptography and communication security
85.60.Dw Photodiodes; phototransistors; photoresistors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Comparative study of electroabsorption in InGaN/GaN quantum zigzag heterostructures with polarization-induced electric fields

Emre Sari, Tuncay Ozel, Aslı Koc, Jin-Woo Ju, Haeng-Keun Ahn, In-Hwan Lee, Jong-Hyeob Baek, and Hilmi Volkan Demir

Appl. Phys. Lett. 92, 201105 (2008); http://dx.doi.org/10.1063/1.2931696 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2008

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We present a comparative study on InGaN/GaN quantum zigzag structures embedded in p-i-n diode architecture that exhibit blue-shifting electroabsorption in the blue when an electric field is externally applied to compensate for the polarization-induced electric field across the wells. With the polarization breaking their symmetry, the same InGaN/GaN quantum structures redshift their absorption edge when the external field is applied in the same direction as the well polarization. Both computationally and experimentally, we investigate the effects of polarization on electroabsorption by varying compositional content and structural parameters and demonstrate that electroabsorption grows stronger with weaker polarization in these multiple quantum well modulators.
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85.30.Kk Junction diodes
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors

Systematic investigation of InAs/InP quantum-dash based lasers under external optical feedback

S. Azouigui, B. Dagens, F. Lelarge, A. Accard, D. Make, O. Le Gouezigou, K. Merghem, A. Martinez, Q. Zou, and A. Ramdane

Appl. Phys. Lett. 92, 201106 (2008); http://dx.doi.org/10.1063/1.2931703 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2008

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The tolerance to optical feedback of InAs/InP quantum dash-based lasers is reported for several structures exhibiting differing values of the linewidth enhancement factor and damping factor. An analysis of the onsets of coherence collapse is carried out based on the experimental dynamic parameters extracted for each structure. It is shown that the relevant significant parameter to explain the optical feedback tolerance for this low dimensional material system is the differential gain.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Band structure of terahertz metallic photonic crystals with high metal filling factor

Benjamin Reinhard, Garik Torosyan, and René Beigang

Appl. Phys. Lett. 92, 201107 (2008); http://dx.doi.org/10.1063/1.2929376 (3 pages) | Cited 1 time

Online Publication Date: 22 May 2008

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The excitation of resonant eigenmodes in two-dimensional metallic photonic crystals by incident terahertz pulses is both experimentally and numerically investigated. Transmission experiments are in excellent agreement with numerical calculations of the crystals’ photonic band structures and internal electromagnetic field patterns. The structures show large photonic band gaps in the terahertz spectral range and are highly polarization selective. At the resonant frequencies, transmittance is extraordinarily high despite the high metal filling factor.
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42.70.Qs Photonic bandgap materials
78.70.Gq Microwave and radio-frequency interactions

Room temperature terahertz emission from grating coupled two-dimensional plasmons

Y. M. Meziani, H. Handa, W. Knap, T. Otsuji, E. Sano, V. V. Popov, G. M. Tsymbalov, D. Coquillat, and F. Teppe

Appl. Phys. Lett. 92, 201108 (2008); http://dx.doi.org/10.1063/1.2919097 (3 pages) | Cited 20 times

Online Publication Date: 22 May 2008

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Room temperature terahertz (far infrared) radiation emission from double grating coupled GaInAs/AlGaAs/GaAs heterojunctions is reported. Theoretical calculations of plasmon absorption spectrum are performed using a first principles electromagnetic approach. They correctly reproduce the frequency range and overall shape of the main (broad-band) part of the experimental spectra. The results clearly indicate that important part of the observed room temperature terahertz emission spectra can be due to the radiative decay of hot two-dimensional plasmons in the grating structure.
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78.70.Gq Microwave and radio-frequency interactions
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.30.+q High-frequency effects; plasma effects
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.63.-b Electronic transport in nanoscale materials and structures
42.79.Dj Gratings

Energy transfer and enhanced luminescence in metal oxide nanoparticle and rare earth codoped silica

Neng Wan, Jun Xu, Tao Lin, Xiangao Zhang, and Ling Xu

Appl. Phys. Lett. 92, 201109 (2008); http://dx.doi.org/10.1063/1.2936842 (3 pages) | Cited 12 times

Online Publication Date: 22 May 2008

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A significant enhancement of photoluminescence from Eu3+ embedded in SiO2 matrix is observed by codoping with wide band-gap In2O3 nanoparticles. The enhanced photoluminescence characteristics are strongly influenced by the postannealing temperature and the In3+ concentration. Synchronous scanning photoluminescence technique was used to understand the excitation and luminescence behavior in codoped silica films. Based on the experimental results, we argue that the enhancement of photoluminescence is associated with the effective energy transfer process from In2O3 nanoparticles to the charge transfer band of O2+–Eu3+ instead of the direct transfer to the rare-earth energy levels.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.72.Cc Kinetics of defect formation and annealing
61.72.up Other materials
81.40.Gh Other heat and thermomechanical treatments

Interband dot-to-well transitions in InAs/InGaAs dots in a well probed via photocurrent and electroluminescence spectroscopy

M. Defensor, V. Magusara, E. Estacio, C. Mateo, A. Somintac, and A. Salvador

Appl. Phys. Lett. 92, 201110 (2008); http://dx.doi.org/10.1063/1.2936082 (3 pages)

Online Publication Date: 23 May 2008

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Hole states of InAs/InGaAs dots in a well are optically probed by observing interband–quantum well (QW)–quantum dot (QD) transitions through photocurrent and electroluminescence (EL) spectroscopy. We find multiple sharp peaks with spacing in the range of 10–20 meV in between the expected QD and the QW signals. The spacing and the observed temperature dependent EL suggest that the features are brought about by transitions between the QW electron ground state and the QD hole states. The data extracted from these transitions provide experimental values for the QD hole confinement energies, which can potentially aid in the verification of theoretical models in QD structures.
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73.21.La Quantum dots
73.21.Fg Quantum wells
78.67.De Quantum wells
78.67.Hc Quantum dots
73.63.Kv Quantum dots
73.63.Hs Quantum wells

Wavelength selective coupler with vertical gratings on silicon chip

Kazuhiro Ikeda, Maziar Nezhad, and Yeshaiahu Fainman

Appl. Phys. Lett. 92, 201111 (2008); http://dx.doi.org/10.1063/1.2936862 (3 pages) | Cited 9 times

Online Publication Date: 23 May 2008

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We propose a wavelength selective coupler using vertical grating structure on silicon chip and discuss the operation principle and the analytic design procedure. The transmission spectra expected by the procedure agree with finite difference time domain simulation results. We then fabricate the designed wavelength selective coupler and demonstrate the expected operation. The available wavelength-division-multiplexing bandwidth of this device is not limited by free spectral range as in ring resonators. We also propose some applications of the wavelength selective coupler.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Random lasers with coherent feedback from highly transparent polymer films embedded with silver nanoparticles

Xiangeng Meng, Koji Fujita, Yanhua Zong, Shunsuke Murai, and Katsuhisa Tanaka

Appl. Phys. Lett. 92, 201112 (2008); http://dx.doi.org/10.1063/1.2912527 (3 pages) | Cited 14 times

Online Publication Date: 23 May 2008

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We report on observations of random lasers with coherent feedback in highly transparent polymer films embedded with silver nanoparticles. The hybrid materials were fabricated via in situ synthesis method, through which silver nanoparticles were precipitated by thermal treatment. Sharp peaks with linewidth ∼ 0.5 nm were observed to emerge on the broad emission background when the pump energy reached a threshold, together with unidirectional laser irradiation. Random lasers with coherent feedback induced by silver nanoparticles have been rarely reported, hence, we expect that this work will add an aspect to random lasers by using metal nanostructures to obtain coherent feedback.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems

Collinear second harmonic generations in a nonlinear photonic quasicrystal

Yan Sheng, Kaloian Koynov, Junhong Dou, Boqin Ma, Jingjuan Li, and Daozhong Zhang

Appl. Phys. Lett. 92, 201113 (2008); http://dx.doi.org/10.1063/1.2937210 (3 pages) | Cited 4 times

Online Publication Date: 23 May 2008

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LiNbO3 nonlinear photonic quasicrystal with octagonal symmetry was fabricated. The collinear quasiphase matched second harmonic generations at 22 wavelengths were observed. It is shown that not only the standard type quasiphase matching but also the recently proposed projection-based quasiphase matching plays an important role in these harmonic generations.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials
42.70.Mp Nonlinear optical crystals
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