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Optics Letters

Zhili Li, Zhen Wang, Fan Yang, Wei Jin, Wei Ren
We demonstrate mid-infrared photothermal interferometry (PTI) in a hollow-core fiber (HCF) for trace gas detection. Compared with free-space PTI, the optical intensity could be increased by orders of magnitude by confining the pump and probe lights in the hollow core. We coupled the pump light at 4.46 μm from a quantum cascade laser and the 1555.14 nm probe light into the HCF with a bore size of 200 μm. The HCF was filled with nitrous oxide (N2O) which has strong absorption at the pump wavelength. The probe light detects the N2O absorption-induced phase change in the HCF via a fiber-optic Mach-Zehnder interferometer...
September 15, 2017: Optics Letters
Haroon Asghar, John G McInerney
We demonstrate an asymmetric dual-loop feedback method to suppress external cavity side-modes induced in self-mode-locked quantum-dash lasers with conventional single- and dual-loop feedback. In this Letter, we report optimal suppression of spurious tones by optimizing the delay in the second loop. We observed that asymmetric dual-loop feedback, with large (∼8×) disparity in loop lengths, gives significant suppression in external-cavity side-modes and produces flat radio frequency (RF) spectra close to the main peak with a low timing jitter, compared to single-loop feedback...
September 15, 2017: Optics Letters
Di Zheng, Javier Madrigal, Hailan Chen, David Barrera, Salvador Sales
A simple, spectral-drift-insensitive interrogation scheme for a multicore fiber Bragg grating (FBG)-based directional curvature sensor is proposed. The basic principle is to transform the wavelength shift of FBGs into the reflected power variation, which is accomplished by utilizing a broadband source with a sinusoidal spectrum. The closed-form expression of the relationship between the reflected power of the FBG and the corresponding peak wavelength is derived for the first time, to the best of our knowledge; therefore, the peak wavelength of the FBG can be precisely interrogated by using a single photodiode...
September 15, 2017: Optics Letters
Xiaochen Zhou, Guangkui Qin, Long Wang, Zhuo Chen, Xiaoguang Xu, Youmei Dong, Alireza Moheghi, Deng-Ke Yang
We developed a waveguide liquid crystal display from a liquid crystal (LC)/polymer composite. It does not need polarizers or color filters. It is illuminated by color LEDs installed on its edge. The light produced by the edge LEDs is coupled into the display and then waveguided through the display. When the LC is in the transparent state, the incident light is waveguided through and no light comes out of the viewing side of the display. When the LC is in the scattering state, the incident light is scattered and comes out of the display...
September 15, 2017: Optics Letters
Yaxiao Lai, Yu Yu, Songnian Fu, Jing Xu, Perry Ping Shum, Xinliang Zhang
We propose and demonstrate a silicon-based spot size converter (SSC), composed of two identical tapered channel waveguides and a Y-junction. The SSC is designed for first-order mode fiber-to-chip coupling on the basis of mode petal separation and the recombination method. Compared with a traditional on-chip SSC, this method is superior with reduced coupling loss when dealing with a higher-order mode. To the best of our knowledge, we present the first experimental observations of a higher-order SSC which is fully compatible with a standard fabrication process...
September 15, 2017: Optics Letters
Elodie Boursier, Giedre Marija Archipovaite, Jean-Christophe Delagnes, Stéphane Petit, Guilmot Ernotte, Philippe Lassonde, Patricia Segonds, Benoît Boulanger, Yannick Petit, François Légaré, Dmitry Roshchupkin, Eric Cormier
We demonstrate phase-matched difference frequency generation in the emerging nonlinear crystal La3Ga5.5Ta0.5O14. Tunable wavelengths between 1.4 and 4.7 μm are generated by using femtosecond sources. We also report on the measurements of the optical damage threshold in the femtosecond regime and on the nonlinear refractive index n2.
September 15, 2017: Optics Letters
Hanyu Ye, S Chaitanya Kumar, Junxiong Wei, P G Schunemann, M Ebrahim-Zadeh
We report an optical parametric generator (OPG) based on the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched nanosecond Nd:YAG laser at 1064 nm with 25 kHz pulse repetition rate, the OPG can be tuned across 1721-1850 nm in the signal and 2504-2787 nm in the idler. Using a 40-mm-long crystal in single-pass configuration, we have generated a total average output power of up to ∼18  mW, with ∼5  mW of idler power at 2670 nm, for 2 W of input pump power...
September 15, 2017: Optics Letters
Razvigor Ossikovski, Oriol Arteaga
We extend the original method of Yeh [J. Opt. Soc. Am.69, 742 (1979)JOSAAH0030-394110.1364/JOSA.69.000742] for calculating the reflection and transmission from anisotropic layered structures to media exhibiting not only dielectric, but also magnetic anisotropy, as well as optical activity. We likewise establish the relationship between the optical activity and gyration tensors from the two most used constitutive relations for optically active media and illustrate the extended Yeh's method on a practically important example...
September 15, 2017: Optics Letters
Kazi Tanvir Ahmmed, Hau Ping Chan, Binghui Li
We report a unique concept to implement a high-order mode pass filter using mode converters. Our proposed design method implements a high-order mode pass filter of any order, uses different mode converters available, and applies to a variety of planar lightwave circuit material platforms. We fabricate a broadband fundamental mode filter device using a Mach-Zehnder interferometer and Y-junctions to demonstrate our idea. The performance of the fabricated device is demonstrated experimentally in the wavelength range of 1...
September 15, 2017: Optics Letters
S Agustsson, G Bianchi, R Calabrese, L Corradi, A Dainelli, A Khanbekyan, C Marinelli, E Mariotti, L Marmugi, G Mazzocca, L Moi, L Ricci, L Stiaccini, L Tomassetti
We report on the direct experimental observation of the 7pP23/2→7dD2 optical transitions in 209 and 210 francium isotopes. By continuously monitoring the fluorescence emitted by the isotopes collected in a magneto-optical trap (MOT), the electric dipole transitions 7pP23/2→7dD25/2 of Fr209, not yet experimentally observed, and 7pP23/2→7dD25/2, 7pP23/2→7dD25/2 of Fr210 were detected as sub-Doppler depletion dips of the cold atom population. This approach allowed unambiguous identification of the excited state hyperfine structures, even in the absence of a large stable vapor...
September 15, 2017: Optics Letters
Naibo Jiang, Paul S Hsu, Jason G Mance, Yue Wu, Mark Gragston, Zhili Zhang, Joseph D Miller, James R Gord, Sukesh Roy
Two-dimensional (2D) Raman scattering at 10 kHz in non-reacting flow mixtures is demonstrated by employing a burst-mode laser with a long-duration pulse of about 70 ns and pulse energy of about 750 mJ at 532 nm. To avoid optical breakdown, the pulse width of the laser was varied in the range of 10-1000 ns. The effects of pulse shape, pulse energy, and harmonic conversion on 2D measurements are also studied. The applications of high-speed, single-shot, 2D imaging of CH4 and H2 jets in N2 at elevated pressures are demonstrated...
September 15, 2017: Optics Letters
A Aadhi, Varun Sharma, R P Singh, G K Samanta
We report on a high-power, continuous-wave source of optical vortices tunable in the mid-infrared (mid-IR) wavelength range. Using the orbital angular momentum (OAM) conservation of the parametric processes and the threshold conditions of the cavity modes of the singly resonant optical parametric oscillator (SRO), we have transferred the OAM of the pump beam at the near-infrared wavelength to the idler beam tunable in the mid-IR. Pumped with a vortex beam of order lp=1 at 1064 nm, the SRO, configured in a four curved mirror-based ring cavity with a 50 mm long MgO-doped periodically poled LiNbO3 crystal, produces an idler beam with an output power in excess of 2 W in a vortex spatial profile with the order li=1, tunable across 2217-3574 nm and corresponding signal beam in Gaussian intensity distribution across 1515-2046 nm...
September 15, 2017: Optics Letters
Kai Guo, Søren M M Friis, Jesper B Christensen, Erik N Christensen, Xiaodong Shi, Yunhong Ding, Haiyan Ou, Karsten Rottwitt
We derive from Maxwell's equations full-vectorial nonlinear propagation equations of four-wave mixing valid in straight semiconductor-on-insulator waveguides. Special attention is given to the resulting effective mode area, which takes a convenient form known from studies in photonic crystal fibers, but has not been introduced in the context of integrated waveguides. We show that the difference between our full-vectorial effective mode area and the scalar equivalent often referred to in the literature may lead to mistakes when evaluating the nonlinear refractive index and optimizing designs of new waveguides...
September 15, 2017: Optics Letters
Matteo Conforti, Fabio Biancalana
We introduce a new model that extends the Lugiato-Lefever equation to the description of multiple resonances in Kerr optical cavities. It perfectly agrees quantitatively (in both stationary and dynamical regimes) with the exact Ikeda map, even when using a small number of resonances. Our model predicts the onset of complex phenomena such as the recently observed super-cavity solitons and the coexistence of multiple nonlinear states. It will be of crucial importance for the analytical understanding of new nonlinear phenomena in Kerr cavities when the intensities or nonlinearities are high enough to be able to excite more than one cavity resonance...
September 15, 2017: Optics Letters
Jianzhou Ai, Lulu Wang, Jian Wang
Chaos-based secure communication can provide a high level of privacy in data transmission. Here, we experimentally demonstrate secure signal transmission over two kinds of multimode fiber (MMF) based on electro-optic intensity chaos. High-quality synchronization is achieved in an electro-optic feedback configuration. Both 5  Gbit/s carrier-less amplitude/phase (CAP-4) modulation and 10  Gbit/s on-off key (OOK) signals are recovered efficiently in electro-optic chaos-based communication systems. Degradations of chaos synchronization and communication system due to mismatch of various hardware keys are also discussed...
September 15, 2017: Optics Letters
Jianjie Zhang, Huilian Ma, Hanzhao Li, Zhonghe Jin
A new record for high-finesse silica waveguide ring resonators (WRRs), to the best of our knowledge, is demonstrated experimentally. The achieved finesse and resonant depths of the silica WRR with a length of 7.9 cm and a diameter of 2.5 cm are 196.7% and 98%, respectively. In addition, the silica WRR chip is coupled with single-polarization fiber to improve the polarization extinction ratio (PER) and, thus, to reduce the polarization error. With the application of this high-finesse and high-PER WRR to the resonant micro-optic gyroscope (RMOG), a bias stability of 0...
September 15, 2017: Optics Letters
J C Liang, H C Wang
Nonlinear effects of photo-induced waveguides based on isomerization photochemistry are investigated. It is found that polarization information of the controlling light can be used to control the propagation of the signal light in all-optical waveguides, and an accurate and convenient light-controlling-light scheme is proposed, that is, controlling propagation of the signal light by synergic use of the intensity information and polarization information of the controlling light. The polarization dependence of optical nonlinearity is expected to enrich the connotation of the optical nonlinear effects and has theoretical significance and practical value...
September 15, 2017: Optics Letters
M Cavillon, P D Dragic, J Ballato
A model that predicts the material additivity of the thermal expansion coefficient in the binary silicate glasses most commonly used for present (GeO2-SiO2, P2O5-SiO2, B2O3-SiO2, and Al2O3-SiO2) and emerging (BaO-SiO2) optical fibers is proposed. This model is based on a derivation of the expression for the coefficient of thermal expansion in isotropic solids, and gives direct insight on the parameters that govern its additivity in silicate glasses. Furthermore, a consideration of the local structural environment of the glass system is necessary to fully describe its additivity behavior in the investigated systems...
September 15, 2017: Optics Letters
Xiaodan Pang, Oskars Ozolins, Richard Schatz, Joakim Storck, Aleksejs Udalcovs, Jaime Rodrigo Navarro, Aditya Kakkar, Gregory Maisons, Mathieu Carras, Gunnar Jacobsen, Sergei Popov, Sebastian Lourdudoss
Gigabit free-space transmissions are experimentally demonstrated with a quantum cascaded laser (QCL) emitting at mid-wavelength infrared of 4.65 μm, and a commercial infrared photovoltaic detector. The QCL operating at room temperature is directly modulated using on-off keying and, for the first time, to the best of our knowledge, four- and eight-level pulse amplitude modulations (PAM-4, PAM-8). By applying pre- and post-digital equalizations, we achieve up to 3  Gbit/s line data rate in all three modulation configurations with a bit error rate performance of below the 7% overhead hard decision forward error correction limit of 3...
September 15, 2017: Optics Letters
Svette Reina Merden Santiago, Yee Ann Wong, Tzu-Neng Lin, Chiao-Hsin Chang, Chi-Tsu Yuan, Ji-Lin Shen
We have developed a facile, fast, and one-step synthetic method to prepare graphene quantum dots (GQDs) simultaneously with nitrogen (N) doping via pulsed laser ablation. The N-doped GQDs (N-GQDs) with an average size around 3 nm and an N/C atomic ratio of 33% have been obtained. The N-GQDs emit blue photoluminescence (PL), where the PL intensity enhances as the N doping increases. The PL enhancement for the N-GQDs with a factor as high as 25 has been achieved as compared to GQDs. The origin of the PL enhancement in GQDs after N doping is attributed to the increased densities of pyridinic and graphitic N...
September 15, 2017: Optics Letters
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