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21 Jan 2008

Volume 92, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 92, 033101 (2008); http://dx.doi.org/10.1063/1.2830979 (3 pages)

Koichiro Zaitsu, Yosuke Kitamura, Keiji Ono, and Seigo Tarucha
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Green laser emission from monolithic II-VI-based pillar microcavities near room temperature

Carsten Kruse, Henning Lohmeyer, Kathrin Sebald, Jürgen Gutowski, Detlef Hommel, Jan Wiersig, and Frank Jahnke

Appl. Phys. Lett. 92, 031101 (2008); http://dx.doi.org/10.1063/1.2832644 (3 pages) | Cited 10 times

Online Publication Date: 22 January 2008

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We report on single-mode stimulated emission at a wavelength of 510 nm in monolithic high-Q ZnSe-based vertical-cavity surface-emitting laser (VCSEL) micropillars under optical excitation at 280 K. Calculations reveal the influence of polariton coupling and the dynamic detuning of the gain maximum to the cavity modes on the spectral characteristics of the VCSEL emission. In accordance with theory, we find a systematic decrease in threshold excitation energy for decreasing pillar diameter to a minimum value of 0.09 pJ for a pillar diameter of 1.2 μm as a combined effect of reduced active area and reduced mode volume in the microcavity lasers.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Color-converting combinations of nanocrystal emitters for warm-white light generation with high color rendering index

Sedat Nizamoglu, Gulis Zengin, and Hilmi Volkan Demir

Appl. Phys. Lett. 92, 031102 (2008); http://dx.doi.org/10.1063/1.2833693 (3 pages) | Cited 53 times

Online Publication Date: 22 January 2008

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Warm-white light emitting diodes with high color rendering indices are required for the widespread use of solid state lighting especially indoors. To meet these requirements, we propose and demonstrate warm-white hybrid light sources that incorporate the right color-converting combinations of CdSe/ZnS core-shell nanocrystals hybridized on InGaN/GaN LEDs for high color rendering index. Three sets of proof-of-concept devices are developed to generate high-quality warm-white light with (1) tristimulus coordinates (x,y) = (0.37,0.30), luminous efficacy (LE) = 307 lm/W, color rending index (CR) = 82.4, and correlated color temperature (CCT) = 3228 K; (2) (x,y) = (0.38,0.31), LE = 323 lm/W, CRI = 81.0, and CCT = 3190 K; and (3) (x,y) = (0.37,0.30), LE = 303 lm/W, CRI = 79.6, and CCT = 1982 K.
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42.72.-g Optical sources and standards
07.60.Dq Photometers, radiometers, and colorimeters
85.60.Jb Light-emitting devices

Overlap integral factor enhancement using buried electrode structure in polymer Mach-Zehnder modulator

Reem Song and William H. Steier

Appl. Phys. Lett. 92, 031103 (2008); http://dx.doi.org/10.1063/1.2827196 (3 pages) | Cited 6 times

Online Publication Date: 23 January 2008

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A buried coplanar waveguide (CPW) electrode for a polymer modulator is introduced in this letter. In this configuration, the electric and the optical fields are aligned and the overlap factor is enhanced. Thus, the poling efficiency can increase and Vπ decreases. Using two electro-optic polymers, Mach-Zehnder (MZ) modulators based on the buried electrode are demonstrated and compared to the in-plane CPW based MZ modulators. The measured Vπ’s of the buried CPW MZ’s are 6.7 and 4.3 V for CLD1 and AJL8 devices, respectively, which give the overlap×r33 products of 19 and 30 pm/V. This shows 20% improvement in the overlap×poling efficiency by using the buried electrode.
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07.60.Ly Interferometers
84.40.Az Waveguides, transmission lines, striplines
42.79.Hp Optical processors, correlators, and modulators
82.45.Fk Electrodes

Flexible metal grating based optical fiber probe for photonic integrated circuits

Stijn Scheerlinck, Dirk Taillaert, Dries Van Thourhout, and Roel Baets

Appl. Phys. Lett. 92, 031104 (2008); http://dx.doi.org/10.1063/1.2827589 (3 pages) | Cited 10 times

Online Publication Date: 23 January 2008

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An optical probe for photonic integrated circuits is proposed and demonstrated. The device is based on a single-mode fiber containing a subwavelength period metal grating on the facet. When approaching an integrated waveguide, light can be efficiently coupled between probe and waveguide without the need for integrated coupling structures, paving the way for wafer-scale circuit testing. A nanoimprint-and-transfer process were developed for fabricating this probe in a single step. We report 15% coupling efficiency between a gold grating fiber probe and a 220 nm×3 μm silicon-on-insulator waveguide and demonstrate testing of an integrated microring resonator using two probes.
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42.81.Pa Sensors, gyros
42.79.Dj Gratings
42.82.Et Waveguides, couplers, and arrays
42.82.Bq Design and performance testing of integrated-optical systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.87.-d Optical testing techniques

A miniature tunable coupled-cavity laser constructed by micromachining technology

H. Cai, A. Q. Liu, X. M. Zhang, J. Tamil, D. Y. Tang, Q. X. Zhang, and C. Lu

Appl. Phys. Lett. 92, 031105 (2008); http://dx.doi.org/10.1063/1.2831912 (3 pages) | Cited 2 times

Online Publication Date: 23 January 2008

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This letter presents a miniature tunable coupled-cavity laser by integrating a Fabry-Pérot chip, a gain chip and a deep-etched parabolic mirror using micromachining technology. The mirror is to actively adjust the gap between chips, enabling the optimal mode selection. Single-mode operation with a tuning range of 16.55 nm and a side-mode-suppression ratio of >25.1 dB is demonstrated. The device overcomes phase mismatching and instability problems encountered in conventional fixed-gap coupled-cavity lasers.
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42.60.Fc Modulation, tuning, and mode locking
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.82.-m Integrated optics

Wide-ridge metal-metal terahertz quantum cascade lasers with high-order lateral mode suppression

Jonathan A. Fan, Mikhail A. Belkin, Federico Capasso, Suraj P. Khanna, Mohamed Lachab, A. Giles Davies, and Edmund H. Linfield

Appl. Phys. Lett. 92, 031106 (2008); http://dx.doi.org/10.1063/1.2835202 (3 pages) | Cited 15 times

Online Publication Date: 23 January 2008

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Terahertz quantum cascade lasers with wide-ridge metal-metal waveguides are prone to lasing in high-order lateral modes, which reduce the maximum light output power from these devices. We have demonstrated, theoretically and experimentally, that the output power can be improved severalfold by introducing “side absorbers” into the waveguide structure, which enforce lasing in the TM00 mode with minor temperature performance deterioration. Lasers without side absorbers operate up to 168 K, a current record for devices processed using indium/gold wafer bonding.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Multiple exciton generation and electrical extraction from a PbSe quantum dot photoconductor

Sung Jin Kim, Won Jin Kim, Yudhisthira Sahoo, Alexander N. Cartwright, and Paras N. Prasad

Appl. Phys. Lett. 92, 031107 (2008); http://dx.doi.org/10.1063/1.2835920 (3 pages) | Cited 32 times

Online Publication Date: 23 January 2008

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Multiple exciton generation and subsequent electrical extraction from a thin film photoconductive device constructed from PbSe nanocrystal quantum dots are demonstrated. The hydrazine treatment of the PbSe film drastically improves the conductivity of the film while maintaining excellent optical and structural film quality. The effects of multiple exciton generation and electrical extraction (electrons collected per photon absorbed) were quantified as a function of incident photon energy from 1.55 to 3.1 eV. The multiple carrier extraction (>100%) was observed at photon energies greater than 2.8 times of the quantum dot bandgap with ∼ 210% measured at 4.4 times the bandgap.
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85.60.Bt Optoelectronic device characterization, design, and modeling

Rabi splitting and ac-Stark shift of a charged exciton

M. Kroner, C. Lux, S. Seidl, A. W. Holleitner, K. Karrai, A. Badolato, P. M. Petroff, and R. J. Warburton

Appl. Phys. Lett. 92, 031108 (2008); http://dx.doi.org/10.1063/1.2837193 (3 pages) | Cited 16 times

Online Publication Date: 23 January 2008

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The Rabi splitting of the negatively charged exciton in a single InGaAs quantum dot is observed in resonance transmission spectroscopy. We use a pump laser excitation to drive strongly the unpolarized trion transition in a quantum dot and detect its modified absorption spectrum with a second weak probe laser. By tuning the pump laser near resonance, we observe an ac-Stark effect dispersion, with a power dependent Rabi splitting on resonance, both signatures of a strongly coupled two level system. Although the pump and probe laser fields are resonant with the same transition, we do not observe all features in the Mollow spectrum. We combine the results of pump probe with saturation spectroscopy data to deduce the individual contributions to the low power linewidth.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.35.Pq Charged excitons (trions)
78.67.Hc Quantum dots
78.20.Jq Electro-optical effects

A visual indication of environmental humidity using a color changing hologram recorded in a self-developing photopolymer

Izabela Naydenova, Raghavendra Jallapuram, Vincent Toal, and Suzanne Martin

Appl. Phys. Lett. 92, 031109 (2008); http://dx.doi.org/10.1063/1.2837454 (3 pages) | Cited 15 times

Online Publication Date: 23 January 2008

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A reflection hologram for visual indication of environmental humidity has been studied. The hologram is recorded in a self-developing photopolymer and changes color when exposed to a change in humidity and is fully reversible. The range of color change, reversibility, and the response time of the hologram have been studied in a controlled humidity environment. Fully reversible holograms with response times from few seconds to tens of minutes have been designed. Extremely sensitive bright visual humidity indicators, capable of dramatic color change within a few seconds of breathing on them are demonstrated.
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42.70.Jk Polymers and organics
42.70.Ln Holographic recording materials; optical storage media
42.40.My Applications

1000 nm tunable acousto-optic filter based on photonic crystal fiber

K. S. Hong, H. C. Park, B. Y. Kim, I. K. Hwang, W. Jin, J. Ju, and D. I. Yeom

Appl. Phys. Lett. 92, 031110 (2008); http://dx.doi.org/10.1063/1.2806198 (3 pages) | Cited 11 times

Online Publication Date: 25 January 2008

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We report an all-fiber acousto-optic tunable filter based on a two-mode photonic crystal fiber. The properties of photonic crystal fiber allow us to demonstrate a notch filter tunable from below 700 to 1700 nm with a single acoustic transducer. The extreme dynamic range coupled with small insertion loss and fast response time ( ∼ 100 μs) makes this device promising for ultrawideband optical systems.
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42.81.Wg Other fiber-optical devices
42.79.Ci Filters, zone plates, and polarizers
42.79.Jq Acousto-optical devices
43.38.Zp Acoustooptic and photoacoustic transducers
42.70.Qs Photonic bandgap materials
42.81.Dp Propagation, scattering, and losses; solitons

Limitation of the electromagnetic cloak with dispersive material

Peijun Yao, Zixian Liang, and Xunya Jiang

Appl. Phys. Lett. 92, 031111 (2008); http://dx.doi.org/10.1063/1.2814039 (3 pages) | Cited 26 times

Online Publication Date: 25 January 2008

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Based on causality, the limitation of the electromagnetic cloak with dispersive material is investigated in this letter. The results show that perfect invisibility cannot be achieved because of the dilemma that either the group velocity Vg diverges or a strong absorption is imposed on the cloaking material. It is an intrinsic conflict which originates from the demand of causality. However, the total cross section can really be reduced through the approach of coordinate transformation. A simulation of finite-difference time-domain method is performed to validate our analysis.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
02.70.Bf Finite-difference methods

The use of a deformable photonic crystal for millimeter-wave beam steering

Shawn-Yu Lin, Zu-Po Yang, Mingfeng Chen, James A. Bur, A. Levitan, and Lester H. Kosowsky

Appl. Phys. Lett. 92, 031112 (2008); http://dx.doi.org/10.1063/1.2837620 (3 pages) | Cited 2 times

Online Publication Date: 25 January 2008

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Show Abstract
A deformable photonic band gap (PBG) material is theoretically proposed as a transmissive element for beam steering at 77 GHz. The deformation may be achieved by integrating microsprings (as spacers) into a one-dimensional PBG structure. This PBG material can produce a specific phase shift dependent on its spacer thickness. By varying the spacer thickness, we generate a continuous phase gradient across the element. Such a PBG device is experimentally realized, capable of beam deflection of up to ±15° and suitable for beam scanning for smart automobile radar application.
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42.70.Qs Photonic bandgap materials
42.60.-v Laser optical systems: design and operation

Design and fabrication of a line-defect bend sandwiched with air trenches in a photonic crystal platform

S. H. Tao, M. B. Yu, J. F. Song, Q. Fang, R. Yang, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 92, 031113 (2008); http://dx.doi.org/10.1063/1.2838337 (3 pages) | Cited 2 times

Online Publication Date: 25 January 2008

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A hybrid bend is designed and fabricated on the silicon-on-insulator system. The hybrid bend comprises a line-defect 120° bend sandwiched by double air trenches in a photonic crystal platform. The simulation and experimental results show that the hybrid bend has low insertion loss and large high-transmission bandwidth.
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42.79.Gn Optical waveguides and couplers
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