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30 Jul 2012

Volume 101, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 101, 051103 (2012); http://dx.doi.org/10.1063/1.4738774 (4 pages)

Alec Rose, Da Huang, and David R. Smith
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Silicon nanomembrane based photonic crystal waveguide array for wavelength-tunable true-time-delay lines

Che-Yun Lin, Harish Subbaraman, Amir Hosseini, Alan X. Wang, Liang Zhu, and Ray T. Chen

Appl. Phys. Lett. 101, 051101 (2012); http://dx.doi.org/10.1063/1.4739003 (4 pages) | Cited 1 time

Online Publication Date: 30 July 2012

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We demonstrate a four-channel on-chip true-time-delay module based on a photonic crystal waveguide array. Using the photonic crystal taper to minimize the coupling loss, the delay lines with 1–3 mm long photonic crystal waveguides can operate up to a group index ng ∼ 23 without significant loss. The large group velocity dispersion enables continuous and wavelength-tunable time delays. Measurements show a highly linear phase-frequency relation, highest time delay up to 216.7 ps, and large tuning ranges of 58.28 ps, 115.74 ps, and 194.16 ps for 1–3 mm delay lines. The chip-scale true-time-delay module occupies only 0.18 mm2 area and can provide ±44.38° steering for an X-band phased-array-antenna.
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42.82.Et Waveguides, couplers, and arrays
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Extraordinary blueshift of a photonic crystal nanocavity by reducing its mode volume with an opaque microtip

T. Grosjean, A. El Eter, M. Mivelle, T.-Ph. Vo, A. Belkhir, C. Ecoffey, G. Le Gac, D. Nedeljkovic, A. Rahmani, C. Seassal, S. Callard, and F. Baida

Appl. Phys. Lett. 101, 051102 (2012); http://dx.doi.org/10.1063/1.4739492 (5 pages)

Online Publication Date: 30 July 2012

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We demonstrate a method to reduce the mode volume of optical micro/nanocavities by positioning an opaque microtip in close proximity of the structures. This concept is used to blueshift the resonance of an active photonic crystal nanocavity by up to 16 nm. This tuning range is shown to be about 10 times larger than the redshift achieved with a bare dielectric microtip of the same size and shape. By imagining materials or multilayered devices with the ability to become transparent and opaque under external control, the blue and redshifts of the resonance would become possible with a single perturbing device.
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42.70.Qs Photonic bandgap materials

Demonstration of nonlinear magnetoelectric coupling in metamaterials

Alec Rose, Da Huang, and David R. Smith

Appl. Phys. Lett. 101, 051103 (2012); http://dx.doi.org/10.1063/1.4738774 (4 pages) | Cited 2 times

Online Publication Date: 30 July 2012

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We demonstrate nonlinear magnetoelectric coupling in a varactor-loaded metamaterial at microwave frequencies. The nonlinear magnetoelectric coupling takes the form of second-harmonic generation in which incident magnetic fields at frequency ω drive an electric polarization at frequency 2ω. The magnitudes and phases of the generated signals from two nonlinear metamaterials are measured, verifying the dominant nonlinear process in each sample. We expect the metamaterial design employed in this letter to form the prototype for future investigations into nonlinear magnetoelectric coupling.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.15.Eq Optical system design
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Tunable degree of localization in random lasers with controlled interaction

Marco Leonetti, Claudio Conti, and Cefe López

Appl. Phys. Lett. 101, 051104 (2012); http://dx.doi.org/10.1063/1.4739942 (3 pages) | Cited 3 times

Online Publication Date: 31 July 2012

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We show that the degree of localization for the modes of a random laser (RL) is affected by the inter mode interaction that is controlled by shaping the spot of the pump laser. By experimentally investigating the spatial properties of the lasing emission we infer that strongly localized modes are activated in the low interacting regime while in the strongly interacting one extended modes are found lasing. Thus we demonstrate that the degree o localization may be finely tuned at the micrometer level.
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42.55.-f Lasers

Absorption spectroscopy using interference between optical frequency comb and single-wavelength laser

Keiichiro Urabe and Osamu Sakai

Appl. Phys. Lett. 101, 051105 (2012); http://dx.doi.org/10.1063/1.4742136 (4 pages)

Online Publication Date: 31 July 2012

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Optical frequency combs have the potential to be applied not only to frequency metrology but also to various spectroscopic measurements replacing incoherent wide-frequency band light sources and single-wavelength laser sources. In this study, we propose a system of absorption spectroscopy for single electronic transitions using the frequency-comb laser source. This spectroscopic method utilizes the interference between the probing frequency comb and an additional single-wavelength laser beam and detects power spectra of beat signals in the interfered laser beam. This method enables us to measure single-transition absorption spectra neither using a large-scale spectrometer nor scanning the laser-beam frequency.
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42.62.Fi Laser spectroscopy
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Polarization-sensitive photophoresis

Vladlen G. Shvedov, Cyril Hnatovsky, Niko Eckerskorn, Andrei V. Rode, and Wieslaw Krolikowski

Appl. Phys. Lett. 101, 051106 (2012); http://dx.doi.org/10.1063/1.4742137 (3 pages) | Cited 1 time

Online Publication Date: 31 July 2012

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We photophoretically trap spherical airborne particles using a single radially or azimuthally polarized laser beam and show that the trapping efficiency is significantly higher for the radial polarization. The demonstrated polarization sensitivity of the photophoretic force, which is caused by polarization-dependent reflection from the particles, adds additional flexibility to the optical micromanipulation of light absorbing particles in gaseous media.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.25.Ja Polarization
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
87.80.Cc Optical trapping

Extended Jones matrix method for oblique incidence study of polarization gratings

Li Tan, Jacob Y. Ho, and Hoi-Sing Kwok

Appl. Phys. Lett. 101, 051107 (2012); http://dx.doi.org/10.1063/1.4742146 (4 pages)

Online Publication Date: 31 July 2012

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A fast and accurate extended Jones matrix method for characterizing the transmitted field of polarization gratings at oblique incidence is reported. The far field diffraction properties of the mth order of the grating are determined by vectorial Fourier coefficients of the transmitted field. With this method, polar plots of the various transmission orders can be obtained. The dependence of viewing angle performance on the grating pitch and grating thickness is studied. Liquid crystal polarization gratings with different pitches were fabricated with azo-dye SD-1 as photoalignment material, by polarization holography. The experimental results show very good agreement with the calculated data.
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42.40.Eq Holographic optical elements; holographic gratings
42.79.Kr Display devices, liquid-crystal devices
42.86.+b Optical workshop techniques
42.30.Kq Fourier optics

A miniature ultrabright source of temporally long, narrowband biphotons

Chih-Sung Chuu, G. Y. Yin, and S. E. Harris

Appl. Phys. Lett. 101, 051108 (2012); http://dx.doi.org/10.1063/1.4740270 (4 pages)

Online Publication Date: 1 August 2012

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We demonstrate a miniature source of long biphotons utilizing the cluster effect and double-pass pumping in a monolithic doubly resonant parametric down-converter. We obtain a biphoton correlation time of 17.1 ns with a generation rate of 1.10×105 biphotons/(s mW) and an estimated linewidth of 8.3 MHz.
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42.65.Lm Parametric down conversion and production of entangled photons
42.50.-p Quantum optics

Strong two-photon fluorescence enhanced jointly by dipolar and quadrupolar modes of a single plasmonic nanostructure

Tianyue Zhang, Guowei Lu, Jie Liu, Hongming Shen, Pascal Perriat, Matteo Martini, Olivier Tillement, and Qihuang Gong

Appl. Phys. Lett. 101, 051109 (2012); http://dx.doi.org/10.1063/1.4742148 (5 pages)

Online Publication Date: 1 August 2012

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A single gold nano-cylinder presenting multipolar plasmon resonances to enhance two-photon fluorescence is investigated employing three dimensional finite-difference time-domain method. Cylinders of large dimension usually display dipolar and quadrupolar plasmonic resonances. We demonstrate that the dipolar resonance can couple with the incident light resulting in a large localized field enhancement which increases the molecular excitation rate. At the same time, the radiative quadrupolar mode overlaps with the emission band of excited fluorophores to assist the fluorescence emission due to an enhancement in the quantum efficiency. Such dipole-quadrupole jointly enhanced two-photon fluorescence exhibits exceptionally promise in brighter label design.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.Lp Collective excitations
78.55.Hx Other solid inorganic materials

Band-edge transitions in hexagonal boron nitride epilayers

S. Majety, X. K. Cao, J. Li, R. Dahal, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 101, 051110 (2012); http://dx.doi.org/10.1063/1.4742194 (4 pages) | Cited 2 times

Online Publication Date: 1 August 2012

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Hexagonal boron nitride (hBN) epilayers have been synthesized on sapphire substrates by metal-organic chemical vapor deposition (MOCVD). These MOCVD grown epilayers exhibit highly efficient band-edge photoluminescence (PL) emission lines centered at around 5.5 eV. The results represent a remarkable improvement over the optical qualities of hBN films synthesized by different methods in the past. It was observed that the emission of hBN at 10 K is about 500 times stronger than that of high quality AlN epilayers. Polarization-resolved PL spectroscopy revealed that hBN epilayers are predominantly a surface emission material, in which the band-edge emission with electric field perpendicular to the c-axis (mathemi⊥math) is about 1.7 times stronger than the component along the c-axis (mathemi‖math). This is in contrast to AlN, in which the band-edge emission is known to be polarized along the c-axis, (mathemi‖math). Time-resolved PL measurements revealed a decay lifetime of around 4.3 ns at 10 K for the dominant band-edge transition line. The present result together with the ability of p-type doping of hBN represents a major step towards the realization of hBN based practical devices.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.47.jd Time resolved luminescence
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Highly sensitive x-ray detectors in the low-energy range on n-type 4H-SiC epitaxial layers

Krishna C. Mandal, Peter G. Muzykov, and J. Russell Terry

Appl. Phys. Lett. 101, 051111 (2012); http://dx.doi.org/10.1063/1.4742741 (4 pages) | Cited 2 times

Online Publication Date: 2 August 2012

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Schottky diodes on n-type 4H-SiC epitaxial layers have been fabricated for low-energy x-ray detection. The detectors were highly sensitive to soft x-rays and showed improved response compared to the commercial SiC UV photodiodes. Current-voltage characteristics at 475 K showed low leakage current revealing the possibility of high temperature operation. The high quality of the epi-layer was confirmed by x-ray diffraction and chemical etching. Thermally stimulated current measurements performed at 94–550 K revealed low density of deep levels which may cause charge trapping. No charge trapping on detectors’ responsivity in the low x-ray energy was found.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.65.Cf Surface cleaning, etching, patterning
85.30.Kk Junction diodes

Transmission properties of double-gap asymmetric split ring resonators in terahertz region

F. Miyamaru, S. Kubota, T. Nakanishi, S. Kawashima, N. Sato, M. Kitano, and M. W. Takeda

Appl. Phys. Lett. 101, 051112 (2012); http://dx.doi.org/10.1063/1.4739945 (5 pages)

Online Publication Date: 2 August 2012

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We investigated the electromagnetic properties of the metamaterials that consist of double-gap split ring resonators (SRRs) in the terahertz region. We found that varying the position of one gap with respect to the other causes the resonant frequency of the SRRs to shift over a broad range. This frequency shift is attributed to the change in the combined capacitance that consists of two capacitances of gaps connected in series and an additional capacitance connected in parallel to the others. Our findings are also verified by obtaining good agreement between experiments and simulations.
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84.40.Az Waveguides, transmission lines, striplines
84.40.-x Radiowave and microwave (including millimeter wave) technology

All-optical time-stretch digitizer

A. M. Fard, B. Buckley, S. Zlatanovic, C.-S. Brès, S. Radic, and B. Jalali

Appl. Phys. Lett. 101, 051113 (2012); http://dx.doi.org/10.1063/1.4742173 (5 pages) | Cited 2 times

Online Publication Date: 2 August 2012

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We propose and demonstrate an all-optical time-stretch digitizer for real-time capture of ultrafast optical signals, beyond the bandwidths achievable by electronics. This approach uniquely combines four-wave mixing and photonic time-stretch technique to slow down and record high-speed optical signals. As a proof-of-concept, real-time recording of 40-Gb/s non-return-to-zero on-off-keying optical data stream is experimentally demonstrated using a stretch factor of 54 and 1.5-GHz back-end electronic bandwidth. We also report on the observation of dispersion penalty and its mitigation via single-sideband conversion enabled by an optical bandpass filter. Our technique may provide a path to real-time capture of ultrahigh-speed optical data streams.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Ci Filters, zone plates, and polarizers

Formation energy of optically active Er3+ centers in Er doped GaN

C. Ugolini, I. W. Feng, A. Sedhain, J. Y. Lin, H. X. Jiang, and J. M. Zavada

Appl. Phys. Lett. 101, 051114 (2012); http://dx.doi.org/10.1063/1.4742196 (4 pages)

Online Publication Date: 2 August 2012

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Erbium doped GaN (GaN:Er) and low In-content InxGa1−xN (x∼0.05) epilayers were synthesized by metal organic chemical deposition. The 1.54 μm PL emission intensity was monitored for GaN:Er epilayers grown at different growth temperatures and utilized to establish a value of 1.8 ± 0.2 eV for the formation energy (EF) of the optically active Er3+ centers in GaN. The optically active Er+ centers are presumably Er and nitrogen vacancy (Er-VN) complexes. The experimentally measured value of the EF of the optically active Er3+ centers is about 0.98 eV larger than the calculated formation energy of Er ions at Ga sites; however, it is 1.1–2.2 eV lower than the formation energy of VN in GaN. Due to the large EF values, relatively high growth temperatures are required to improve the 1.54 μm emission efficiency in GaN:Er.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.jd Vacancies
68.55.ag Semiconductors
78.55.Cr III-V semiconductors

Controlling the photoluminescence of acceptor and donor quantum dots embedded in a nonlinear photonic crystal

Mahi R. Singh, Chris Racknor, and Daniel Schindel

Appl. Phys. Lett. 101, 051115 (2012); http://dx.doi.org/10.1063/1.4742197 (4 pages) | Cited 3 times

Online Publication Date: 2 August 2012

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We have studied energy transfer and photoluminescence in donor and acceptor quantum dots embedded in a nonlinear photonic crystal. The quantum dots are interacting with each other via the dipole-dipole interaction. The nonlinear photonic crystal modifies the dielectric constant of the hybrid system. Using the density matrix method, it is found that the energy transfer and photoluminescence in the donor quantum dot can be controlled by a pump field due to the nonlinearity of the photonic crystal. Additionally, our theoretical calculations agree with recent experiments. This hybrid system can be used to fabricate ultrafast switching and sensing nanodevices.
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78.55.-m Photoluminescence, properties and materials
78.67.Hc Quantum dots
81.07.Ta Quantum dots
42.70.Qs Photonic bandgap materials
77.22.Ch Permittivity (dielectric function)

Disorder-limited photon propagation and Anderson-localization in photonic crystal waveguides

N. A. Wasley, I. J. Luxmoore, R. J. Coles, E. Clarke, A. M. Fox, and M. S. Skolnick

Appl. Phys. Lett. 101, 051116 (2012); http://dx.doi.org/10.1063/1.4742743 (4 pages)

Online Publication Date: 3 August 2012

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We investigate the disorder-limited propagation of photons in photonic crystal waveguides in the slow-light regime. We use analysis of Fabry-Perot resonances to map the mode dispersion and extract the photon localization length. Propagation lengths are deduced to be limited to less than 20 μm for group index >50. Anderson-localized modes are observed at high group indices, when the localization lengths are shorter than the waveguide lengths, consistent with the Fabry-Perot analysis. The results have consequences for integrated quantum-dot single-photon circuits which rely on slow-light effects to enhance emission rates.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Electrical fine tuning of liquid crystal lasers

Jürgen Schmidtke, Gisela Jünnemann, Susanne Keuker-Baumann, and Heinz-Siegfried Kitzerow

Appl. Phys. Lett. 101, 051117 (2012); http://dx.doi.org/10.1063/1.4739840 (4 pages)

Online Publication Date: 3 August 2012

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We demonstrate high-precision, continuous, electrical tuning of a photonic band-edge laser based on a dye-doped cholesteric liquid crystal. A micro-patterned array of electrodes creates an electric field perpendicular to the cholesteric helix, which distorts the chiral order of the liquid crystal, thus shifting the resonant band edge modes. This configuration allows for smooth tuning of the laser emission in a wavelength range of about 3.5 nm, using low voltages (of the order of 10 V).
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42.55.-f Lasers
42.70.Df Liquid crystals
42.70.Qs Photonic bandgap materials
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