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Accepted papers to appear in an upcoming issue

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Pore-size dependent THz absorption of nano-confined water

Chi-Kuang Sun, Borwen You, Yu-Ru Huang, Kao-Hsiang Liu, Shusaku Sato, Akiyoshi Irisawa, Motoki Imamura, and Chung-Yuan Mou

Doc ID: 234712 Received 13 Feb 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: We performed THz absorption spectroscopy study on liquid water confined in mesoporous silica materials, MCM-41-S-18 and MCM-41-S-21 of two different pore sizes at room temperatures. We found that stronger confinement with a smaller pore size causes reduced THz absorption, indicating reduced water mobility due to confinement. Combined with recent theoretical studies showing that the microscopic structure of water inside the nanopores can be separated into a core water region and an interfacial water region, our spectroscopy analysis further reveals a bulk–water–like THz absorption behavior in the core water region and a solid–like THz absorption behavior in the interfacial water region.

Effects of multiphoton absorption on parametric comb generation in silicon microresonators

Ryan Lau, Alexander Gaeta, Yoshitomo Okawachi, and Michael Lamont

Doc ID: 235489 Received 03 Mar 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: We investigate theoretically parametric frequency comb generation in silicon microresonators at telecom and mid-infrared (MIR) wavelengths in the presence of multiphoton absorption and free-carrier effects using a modiffied Lugiato-Lefever model. We show that parametric oscillation may occur at MIR wavelengths, provided that the free-carrier lifetime is sufficiently short or the optical pump power is sufficiently low, but is inhibited at telecom wavelengths. In addition, we propose an etchless, air-clad silicon microresonator that enables an octave-spanning frequency comb in a completely passive device.

Secure optical GFBMC system based on cubic constellation masked method

Bo Liu, Lijia Zhang, and Xiangjun Xin

Doc ID: 236985 Received 27 Mar 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: A secure optical generalized filter bank multi-carrier (GFBMC) system with carrier-less amplitude-phase (CAP) modulation is proposed in the letter. The security is realized through cubic constellation masked method. Large key space and more flexibility masking can be obtained by cubic constellation masking aligning with the filter bank. An experiment with 18Gb/s encrypted GFBMC/CAP system is performed to demonstrate the feasibility of the proposed method.

Characterizing coherence vortices through the geometry

Alcenisio Silva, Eduardo Fonseca, and Cleberson Alves

Doc ID: 237634 Received 08 Apr 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: We produce experimentally and numerically coherence vortices and study the dependence of their bright ring area and dark region with their different orders. This is a linear dependence with slope proportional to the bright ring or dark area. We show that it is possible to obtain any order of coherence vortices, including the fractional ones, just by calculating the bright ring or dark area of vortices for the specific parameters of the incident beam.

Extraordinary transmission in optical Helmholtz resonators

Patrick Bouchon, Paul Chevalier, Emilie SAKAT, Jean-Luc Pelouard, Fabrice Pardo, and Riad Haidar

Doc ID: 238337 Received 17 Apr 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: Optical Helmholtz resonators have been adapted from acoustics designs for light absorbing structures, exhibiting extreme light confinement. Here, extraordinary transmission of light is theoretically demonstrated through symmetric optical Helmholtz resonators, comprising a cavity with two λ/500 narrow slits on either side. This device has appealing features to act as a spectral bandpass filter in the context of multispectral imaging, in particular its high angular tolerance due to the localized nature of the resonance. Besides, the cavity can be modeled as an inductor and the two slits as capacitors, the whole design acting as a LC circuit thus preventing any harmonic features.

Two-dimensional single-pixel imaging by cascaded orthogonal line spatial modulation

Randy Bartels and David Winters

Doc ID: 238426 Received 20 Apr 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: Two dimensional images are taken using a single-pixel detector by temporally multiplexing spatial frequency projections from orthogonal, time varying spatial line modulation gratings. Unique temporal frequencies are applied to each point in two dimensional space, applying a continuous spread of frequencies to one dimension, and an offset frequency applied to each line in the orthogonal dimension. The object contrast information can then be recovered from the electronic spectrum of the single pixel, and through simple processing be reformed into a spatial image.

Hermetic Optical Fiber Iodine Frequency Standard

Philip Light, James Anstie, Fetah Benabid, and Andre Luiten

Doc ID: 240157 Received 04 May 2015; Accepted 19 May 2015; Posted 19 May 2015  View: PDF

Abstract: We have built an optical frequency standard based on interrogating iodine vapour that has been trapped within the hollow core of a hermetically-sealed kagome-lattice photonic crystal fiber. A frequency-doubled Nd:YAG locked to a hyperfine component of the P(142)37-0 ¹²⁷I₂ transition using modulation transfer spectroscopy shows a frequency stability of 3×10^-11 at 100 seconds. We discuss the impediments in integrating this all-fiber standard into a fully optical-fiber based system, and suggest approaches that could improve performance of the frequency standard substantially.

Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies

Sean Knight, Stefan Schoeche, Vanya Darakchieva, Philipp Kuehne, Jean-Francois Carlin, Nicolas Grandjean, Craig Herzinger, Mathias Schubert, and Tino Hofmann

Doc ID: 237567 Received 08 Apr 2015; Accepted 18 May 2015; Posted 18 May 2015  View: PDF

Abstract: The effect of a tunable, externally coupled Fabry-P\'{e}rot cavity to resonantly enhance the optical Hall effect signatures at terahertz frequencies produced by a traditional Drude-like two-dimensional electron gas is shown and discussed in this communication. As a result, the detection of optical Hall effect signatures at conveniently obtainable magnetic fields, for example by neodymium permanent magnets, is demonstrated. An AlInN/GaN-based high electron mobility transistor structure grown on a sapphire substrate is used for the experiment. The optical Hall effect signatures and their dispersions, which are governed by the frequency and the reflectance minima and maxima of the externally coupled Fabry-P\'{e}rot cavity, are presented and discussed. Tuning the externally coupled Fabry-P\'{e}rot cavity strongly modifies the optical Hall effect signatures, which provides a new degree of freedom for optical Hall effect experiments in addition to frequency, angle of incidence and magnetic field direction and strength.

Tilt-tuned etalon locking for tunable laser stabilization

Bradley Gibson and Benjamin McCall

Doc ID: 237963 Received 14 Apr 2015; Accepted 18 May 2015; Posted 18 May 2015  View: PDF

Abstract: Locking to a fringe of a tilt-tuned etalon provides a simple, inexpensive method for stabilizing tunable lasers. Here, we describe the use of such a system to stabilize an external-cavity quantum cascade laser; the locked laser has an Allan deviation of approximately 1 MHz over a one-second integration period, and has a single-scan tuning range of approximately 0.4 wavenumbers. The system is robust, with minimal alignment requirements and automated lock acquisition, and can be easily adapted to different wavelength regions or more stringent stability requirements with minor alterations.

Nonlinear compression of ultrashort-pulse thulium-based fiber laser to sub-70 fs in Kagome photonic crystal fiber

Martin Gebhardt, Christian Gaida, Steffen Hädrich, Fabian Stutzki, Cesar Jauregui, Jens Limpert, and Andreas Tünnermann

Doc ID: 236358 Received 18 Mar 2015; Accepted 16 May 2015; Posted 18 May 2015  View: PDF

Abstract: Nonlinear pulse compression of ultrashort pulses is an established method for reducing the pulse duration and increasing the pulse peak power beyond the intrinsic limits of a given laser architecture. In this proof-of-principle experiment we demonstrate nonlinear compression of the pulses emitted by a high repetition rate thulium-based fiber CPA system. The initial pulse duration of about 400 fs has been shortened to <70 fs with 19.7 μJ of pulse energy, which corresponds to about 200 MW of pulse peak power.

Multiwavelength phase-shifting digital holography selectively extracting wavelength information from wavelength-multiplexed holograms

Tatsuki Tahara, Ryota Mori, Shuhei Kikunaga, Yasuhiko Arai, and Yasuhiro Takaki

Doc ID: 235146 Received 23 Feb 2015; Accepted 16 May 2015; Posted 18 May 2015  View: PDF

Abstract: Multiwavelength phase-shifting digital holography that selectively extracts wavelength information from wave-length-multiplexed holograms is presented. Specific phase shifts are introduced for respective wavelengths to remove the crosstalk components and to extract only the object wave at the desired wavelength from the holograms. Object waves in multiple wavelengths are selectively extracted by utilizing 2π ambiguity and the subtraction procedures based on phase-shifting interferometry. Numerical results show the validity of the proposed technique in case of du-al-wavelengths. The proposed technique is also experimentally demonstrated.

The fluctuation-dissipation relation in a resonantly driven quantum medium

Maria Erukhimova and Mikhail Tokman

Doc ID: 233481 Received 02 Feb 2015; Accepted 15 May 2015; Posted 19 May 2015  View: PDF

Abstract: We calculate the radiation noise level associated with the spontaneous emission of a coherently driven medium. The significant field-induced modification of relation between the noise power and damping constant in a thermal reservoir is obtained. The nonlinear noise exchange between different atomic frequencies leads to violation of standard relations dictated by the fluctuation-dissipation theorem. This result can cardinally modify the conditions of successful manipulations with nonclassical field states in EIT-based schemes which are attractive for realization of different quantum-information processing devices.

Optical Detection of Harmonic Oscillations in Fluorescent Dye-Loaded Microbubbles Ensonified by Ultrasound

Carolyn Schutt, Stuart Ibsen, Michael Benchimol, Mark Hsu, and Sadik Esener

Doc ID: 232767 Received 21 Jan 2015; Accepted 14 May 2015; Posted 15 May 2015  View: PDF

Abstract: A new optical contrast agent has been developed by exposing dye-loaded microbubbles to a rapid-cooling thermal treatment to homogenize the dye distribution across the surface. Ultrasound causes these microbubbles to oscillate in size which changes the self-quenching efficiency of the dye molecules creating a “blinking” signal. We demonstrate for the first time that these microbubbles can reproducibly generate 2nd, 3rd, and even 4th harmonic fluorescence intensity modulations in addition to the fundamental frequency of the driving ultrasound. Detecting these harmonic signals could produce a higher signal-to-noise ratio for fluorescence imaging in medical applications by allowing fundamental frequency interference and artifacts to be filtered out.

Dual-state dissipative solitons from an all-normal-dispersion Erbium-doped fiber laser: continous wavelength-tuning and multi-wavelength emission

Fu Songnian, Wu Zhichao, Chen Changxiu, Ming Tang, Shum Ping, and Dengming Liu

Doc ID: 237171 Received 02 Apr 2015; Accepted 14 May 2015; Posted 15 May 2015  View: PDF

Abstract: We propose and experimentally demonstrate switchable operation of dissipative solitons (DSs) in erbium-doped fiber laser (EDFL). By managing normal dispersion of laser cavity, the 3dB spectral bandwidth up to 8.1nm can be obtained with the help of semiconductor saturable absorber mirror (SESAM). Using an inline polarizer, the fiber laser can be separately operated at either wavelength-tunable or multi-wavelength emission. The central wavelength of DS can be continuously tuned from 1554nm to 1561nm with its spectra maintaining standard rectangular shape. Alternatively, triple-wavelength DSs at 1535nm, 1544nm, and 1553nm can be simultaneously obtained.

High power efficient SESAM-mode-locked Yb:KGW bulk laser

Alexander Rudenkov, Viktor Kisel, Anatoliy Pavlyuk, Alexander Kovalyov, Valeri Preobrazhenskii, Michail Putyato, Nataliya Rubtsova, Boris Semyagin, and Nikolai Kuleshov

Doc ID: 238140 Received 17 Apr 2015; Accepted 14 May 2015; Posted 15 May 2015  View: PDF

Abstract: High-power diode-pumped SESAM mode-lockedYb(5%):KGW bulk laser was demonstrated with high optical-to-optical efficiency. Average output power as high as 8.8W with optical-to-optical efficiency of 37.5% was obtained for Nm-polarized laser output with 162 fs pulse duration and 142 nJ pulse energy at pulse repetition frequency of 62MHz. For Np-polarization 143-fs pulses with pulse energy 139 nJ and average output power up to 8.6 W with optical-to-optical efficiency of 31% were generated.

Longwave infrared, single-frequency, tunable, pulsed optical parametric oscillator based on orientation-patterned GaAs for gas sensing

Antoine Godard, Quentin Clement, Jean-Michel Melkonian, Jean-Baptiste Dherbecourt, Myriam Raybaut, Arnaud Grisard, Eric Lallier, Bruno Gérard, Basile Faure, and Grégoire Souhaité

Doc ID: 236862 Received 25 Mar 2015; Accepted 12 May 2015; Posted 13 May 2015  View: PDF

Abstract: We demonstrate a nanosecond single-frequency nested cavity optical parametric oscillator (NesCOPO) based on orientation-patterned GaAs (OP-GaAs). Its low threshold energy of 10 µJ enables to pump it with a pulsed single-frequency Tm:YAP microlaser. Stable single-longitudinal-mode emission is obtained owing to Vernier spectral filtering provided by the dual-cavity doubly-resonant NesCOPO scheme. Crystal temperature tuning enables to cover the 10.3–10.9 μm range with a quasi-phase-matching period of 72.6 µm. A first step toward the implementation of this device in a differential absorption lidar is demonstrated by carrying out short-range standoff detection of ammonia vapor around 10.4 µnm. Owing to the single-frequency emission, interferences due to absorption by atmospheric water vapor can be discriminated from the analyte signal.

Near-field evanescent wave scattering from spatially deterministic and anisotropic medium

Jia Li, Liping Chang, and Zhefu Wu

Doc ID: 236982 Received 27 Mar 2015; Accepted 11 May 2015; Posted 14 May 2015  View: PDF

Abstract: The scattering of light waves by either spatially random or deterministic anisotropic medium has attracted substantial interest where the measurement of the internal structures of scatterers is concerned. However, to date, no literature has discussed the statistics of near-zone evanescent waves scattered by a spatially-deterministic anisotropic medium. Integral expressions are given to describe the behaviors of evanescent waves in the near-zone scattered field. The degree to which the intensity distributions of scattered light depends on the diffraction length of the scattering medium and the effective size of the scattering potential (ESSP) is also shown using numerical simulations. Potential applications of these finding include optical microscopy of nano-structure images on a sub-wavelength scale.

Discrete non-planar reflections from an ultrashort pulse written Volume-Bragg-Grating (VBG)

Daniel Richter, Christian Voigtländer, Ria Krämer, Jens Thomas, Andreas Tünnermann, and Stefan Nolte

Doc ID: 235895 Received 12 Mar 2015; Accepted 07 May 2015; Posted 18 May 2015  View: PDF

Abstract: In this letter we present a direct writing technique for two-dimensional-periodic VBGs in fused silica based on the phase mask technology, ultrashort laser pulses and three-beam-interference. An algorithm to predict the grating pattern and its diffraction behaviour under collimated, spectral broad illumination is developed. The predicted data are in good agreement with the measurements.

Effects of Phosphor Distribution and Step-Index Remote Configuration on the Performance of White Light-Emitting Diodes

Chung-Hao Chiang, Hung-Yi Tsai, Ting-Shi Zhan, Han-Yu Lin, Ying-Chien Fang, and Sheng-Yuan Chu

Doc ID: 232116 Received 09 Jan 2015; Accepted 01 May 2015; Posted 05 May 2015  View: PDF

Abstract: The phosphor-converted white light-emitting diode (pc-WLED) is fabricated by combining the CaSi2O2N2:Eu2+ and Ca2Si5N8:Eu2+ phosphors with the blue chip. Experimental results demonstrate that placing the red phosphor layer above the yellow one (Y down / R up type) which has the highest luminous efficiency is the preferable phosphor distribution for pc-WLEDs rather than Y up / R down type. This finding suggests that the extent of overlap between the emission spectrum of short emission-wavelength phosphors and the excitation spectrum of long emission-wavelength phosphors and lumen equivalent of them should be simultaneously taken into account as one seeks to study the optical characteristics of pc-WLEDs. Compared with common pc-WLEDs using silicone gel as the remote layer, a step-index remote configuration proposed herein exhibited a superior luminous efficiency because of the reduced Total Internal Reflection (TIR) and Fresnel loss.

Growth and diode-pumped laser operation of Pr$^{3+}$:β-(Y$_{0.5}$,Gd$_{0.5}$)F$_{3}$ at various transitions

Philip Metz, Daniel-Timo Marzahl, Christian Kraenkel, and Guenter Huber

Doc ID: 237466 Received 03 Apr 2015; Accepted 28 Apr 2015; Posted 08 May 2015  View: PDF

Abstract: We report on the crystal growth of the orthorhombic low temperature β-phase of (Y$_{0.5}$,Gd$_{0.5}$)F$_{3}$ (YGF) single crystals. The crystals were activated with trivalent praseodymium (Pr$^{3+}$) and characterized with respect to their ground state absorption and stimulated emission properties. Under InGaN-laser-diode pumping, laser oscillation was obtained at more than ten wavelengths in the green, orange, red, and dark red spectral region. In these initial experiments, output powers exceeding 100 mW and slope efficiencies between 10 \% and 30 \% were obtained. To the best of our knowledge, these results represent the first application of YGF crystals as laser host material for any active ion.

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