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4 Apr 2005

Volume 86, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 86, 142101 (2005); http://dx.doi.org/10.1063/1.1895476 (3 pages)

M. Hanke, T. Boeck, A.-K. Gerlitzke, F. Syrowatka, F. Heyroth, and R. Köhler
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Tuning of spontaneous emission of two-dimensional photonic crystal microcavities by accurate control of slab thickness

A. R. Alija, L. J. Martínez, A. García-Martín, M. L. Dotor, D. Golmayo, and P. A Postigo

Appl. Phys. Lett. 86, 141101 (2005); http://dx.doi.org/10.1063/1.1896427 (3 pages) | Cited 4 times

Online Publication Date: 29 March 2005

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We have found a blueshift in the cavity modes confined in two-dimensional photonic crystal microcavities when the thickness of the slab was varied uniformly by accurate dry etching. The shifts in the wavelength of the cavity modes were around 2 nm towards shorter wavelengths per nanometer reduced in the thickness of the slab. Three-dimensional plane wave expansion calculations showed that the observed shifts are inside the calculated photonic band gap of the structures. The variation in the energy position of the peaks with the thickness has been analyzed by three-dimensional finite difference time domain calculations for a one missing hole microcavity. This tuning of the emission wavelength with the change in the thickness slab shows the important effect of the third dimension in photonic crystals made out of semiconductor slabs and it can be of interest for its application in the final processed photonic devices like photonic crystal lasers.
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42.70.Qs Photonic bandgap materials
81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning

Transmission properties of terahertz pulses through an ultrathin subwavelength silicon hole array

Abul K. Azad, Y. Zhao, and W. Zhang

Appl. Phys. Lett. 86, 141102 (2005); http://dx.doi.org/10.1063/1.1897842 (3 pages) | Cited 37 times

Online Publication Date: 30 March 2005

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We demonstrate extraordinary THz transmission of an array of subwavelength apertures patterned on ultrathin highly doped silicon by reactive ion etching. The zero-order transmission spectra exhibit well-defined maxima and minima which are attributed to the excitation of surface-plasmon polaritons and Wood’s anomaly. The transmission anisotropy is investigated with respect to the orientation of the elliptical hole array in the frequency range from 0.2 to 3.5 THz, and we notice that the transmission increases significantly when the major axis of the elliptical hole is perpendicular to the polarization of THz beam. In addition, redshift and reduction in transmission amplitude are observed when the surrounding dielectric permittivity is increased.
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78.70.Gq Microwave and radio-frequency interactions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Electronic control of nonresonant random lasing from a dye-doped smectic A* liquid crystal scattering device

S. M. Morris, A. D. Ford, M. N. Pivnenko, and H. J. Coles

Appl. Phys. Lett. 86, 141103 (2005); http://dx.doi.org/10.1063/1.1885169 (3 pages) | Cited 9 times

Online Publication Date: 30 March 2005

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The electronic control of the excitation threshold for random lasing in a dye-doped smectic A* liquid crystal is demonstrated. Random lasing is the term given to the nonlinear amplification of light which is the result of feedback due to multiple scattering. With the application of an electric field the smectic A* phase forms a highly scattering texture for which the nonlinear amplification of light occurs at an excitation threshold of 10 μJ/pulse. In comparison, nonlinear amplification is not observed in the field induced homeotropic texture. As a result, a device has been conceived and demonstrated whereby random lasing is switched “on” or “off” with an applied electric field.
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42.79.Kr Display devices, liquid-crystal devices
42.55.Zz Random lasers
42.55.Mv Dye lasers
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Design, fabrication, and characterization of a two-dimensional photonic-crystal symmetric Mach-Zehnder interferometer for optical integrated circuits

Yu Tanaka, Yoshimasa Sugimoto, Naoki Ikeda, Hitoshi Nakamura, Kyozo Kanamoto, Kiyoshi Asakawa, and Kuon Inoue

Appl. Phys. Lett. 86, 141104 (2005); http://dx.doi.org/10.1063/1.1898431 (3 pages) | Cited 8 times

Online Publication Date: 30 March 2005

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We report on the design, fabrication, and optical characterization of a GaAs two-dimensional photonic-crystal-based symmetric Mach-Zehnder interferometer (PC-SMZ) aimed at all-optical switches in planar photonic integrated systems. The directional couplers that constitute the PC-SMZ interferometer prevent the occurrence of ring resonance which degrades the interference, and allow control pulses for the switching operation to be received. We show 50%- and 100%-power couplings from the transmission characteristics of the directional couplers, thus demonstrating their operation as 3-dB dividers in the PC-SMZ. We also show experimentally wavelength selectivity between signal and control pulses with a separation of ∼ 7 nm. These results indicate that the structure is promising as an all-optical switch when a nonlinear material such as a quantum dot is introduced into both arms of the interferometer.
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07.60.Ly Interferometers
85.60.Gz Photodetectors (including infrared and CCD detectors)

Regenerated surface plasmon polaritons

Tae-Woo Lee and Stephen K. Gray

Appl. Phys. Lett. 86, 141105 (2005); http://dx.doi.org/10.1063/1.1897427 (3 pages) | Cited 10 times

Online Publication Date: 30 March 2005

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We discuss a way to increase surface plasmon polariton (SPP) propagation lengths and intensities. It involves reflecting radiation loss back to the propagation surface, regenerating SPPs. This is achieved with a metal-dielectric structure, which is also designed to efficiently couple in external light. Flexibility in the design of the structure allows for optimization of SPP properties. Extensive finite-difference time-domain simulations, including coupling external light into the system, demonstrate the approach.
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68.49.-h Surface characterization by particle-surface scattering

Tetracene light-emitting transistors on flexible plastic substrates

C. Santato, I. Manunza, A. Bonfiglio, F. Cicoira, P. Cosseddu, R. Zamboni, and M. Muccini

Appl. Phys. Lett. 86, 141106 (2005); http://dx.doi.org/10.1063/1.1898429 (3 pages) | Cited 42 times

Online Publication Date: 31 March 2005

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We report on organic light-emitting (field-effect) transistors (LETs) fabricated on a flexible and transparent plastic foil (Mylar), acting both as substrate and gate dielectric. The foil is patterned on one side with bottom-contact gold source and drain electrodes, while a thin film of gold is evaporated on the opposite side of the foil to form the gate electrode. A vacuum sublimed tetracene film is employed as an active layer for charge transport and light emission. Atomic force microscopy shows that tetracene films have a good adhesion on Mylar and exhibit a granular structure. The transistor shows unipolar p-type behavior with mobilities typically of 5×10−4 cm2/V s. Drain-source current and electroluminescence have been simultaneously measured. Provided a suitable gate bias is applied, light emission occurs at drain-source voltages (Vds) above saturation. LETs on plastic substrates could open the way to flexible devices combining the switching function of a transistor and the light emission.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices
73.50.Dn Low-field transport and mobility; piezoresistance
78.60.Fi Electroluminescence
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)

Decay of photorefractive gratings in LiNbO3:Fe by neutron irradiation

G. Mandula, R. A. Rupp, M. Balaskó, and L. Kovács

Appl. Phys. Lett. 86, 141107 (2005); http://dx.doi.org/10.1063/1.1891298 (3 pages) | Cited 1 time

Online Publication Date: 31 March 2005

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The effect of neutron irradiation on photorefractive gratings in LiNbO3:Fe single crystals is studied experimentally. The observed phenomena result from the large effective cross section of math for thermal and cold neutrons and from the large number of the electrons excited to the conduction band by the high kinetic energy that is released during the neutron generated fission of math nuclei. The excited electrons erase the previously recorded holographic grating. The sensitivity threshold of the effect is better than 160 mSv (1.2×1010 cm−2 fluence) at neutron energy of 0.17 eV. Potential applications of the phenomena are discussed.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Dj Gratings
61.80.Hg Neutron radiation effects
61.82.Ms Insulators

Heteroepitaxial Bi3Fe5O12/La3Ga5O12 films for magneto-optical photonic crystals

S. I. Khartsev and A. M. Grishin

Appl. Phys. Lett. 86, 141108 (2005); http://dx.doi.org/10.1063/1.1897077 (3 pages) | Cited 10 times

Online Publication Date: 31 March 2005

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Epitaxial La3Ga5O12 (LGG) garnet films and Bi3Fe5O12/La3Ga5O12 (BIG/LGG) heteroepitaxial film structures have been synthesized on the Gd3Ga5O12(GGG,111) single crystal. LGG films were grown by pulsed laser deposition technique whereas rf-magnetron sputtering was used to grow BIG films. LGG has a lattice constant 12.768 Å that is bigger than that in GGG (12.384 Å) and closer to that in BIG (12.626 Å). We demonstrate feasibility of integration lanthanum gallium garnet with a giant Faraday rotator Bi3Fe5O12 in magneto-optical photonic crystals. Heteroepitaxial Bi3Fe5O12(1.9 μm)/La3Ga5O12(300 nm)/GGG(111) structures show Faraday rotation as high as 5.74 deg/μm compared to 5.46 deg/μm in BIG/GGG at λ = 655 nm. Fitting LGG reflectivity spectra to Fresnel formulas yields LGG refractive index no = 1.981 compared to 1.963 in GGG at 655 nm. Dispersion of LGG refraction index follows Sellmeier formula no2 = 1+2.77/[1−(143 nm/λ)2] in the range from 400 nm to 1000 nm.
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81.15.Fg Pulsed laser ablation deposition
82.45.Mp Thin layers, films, monolayers, membranes

Terahertz wideband spectroscopic imaging based on two-dimensional electro-optic sampling technique

Mamoru Usami, Masatsugu Yamashita, Kazushiro Fukushima, Chiko Otani, and Kodo Kawase

Appl. Phys. Lett. 86, 141109 (2005); http://dx.doi.org/10.1063/1.1899259 (3 pages) | Cited 14 times

Online Publication Date: 1 April 2005

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We extended the bandwidth of a terahertz (THz) spectroscopic imaging system based on two-dimensional electro-optic sampling. By using an optical-rectification emitter, formed by a ZnTe crystal, a high-frequency component of more than 2.0 THz was detected. A calibration-free procedure with polarity inversion of the THz beam ensures us precise spectroscopy: the polarity was inverted by rotating the emitter crystal. The spatial patterns of the chemicals were extracted from the THz multispectral images in the extended spectral region.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.79.-e Optical elements, devices, and systems

Polarization-independent phase modulation using a polymer-dispersed liquid crystal

Hongwen Ren, Yi-Hsin Lin, Yun-Hsing Fan, and Shin-Tson Wu

Appl. Phys. Lett. 86, 141110 (2005); http://dx.doi.org/10.1063/1.1899749 (3 pages) | Cited 32 times

Online Publication Date: 1 April 2005

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Polarization-independent phase-only modulation of a polymer-dispersed liquid crystal (PDLC) is demonstrated. In the low voltage region, PDLC is translucent because of light scattering. Once the voltage exceeds a saturation level, PDLC is highly transparent and exhibits phase-only modulation capability. Although the remaining phase is not too large, it is still sufficient for making adaptive microdevices, such as microlens. A tunable-focus microlens for arrays using PDLC is demonstrated. This kind of microlens is scattering free, polarization independent, and has fast response time.
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61.30.Vx Polymer liquid crystals
42.70.Df Liquid crystals
42.70.Jk Polymers and organics
42.79.Hp Optical processors, correlators, and modulators
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.79.Bh Lenses, prisms and mirrors
42.86.+b Optical workshop techniques
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