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Optics Letters

Bill Corcoran, Zihan Geng, Valery Rozental, Arthur J Lowery
We propose occupying the guard bands in closely spaced WDM systems with redundant signal spectral components to increase tolerance to frequency misalignment and channel shaping from multiplexing elements. By cyclically repeating the spectrum of a modulated signal, we show improved tolerance to impairments due to add/drop multiplexing with a commercial wavelength selective switch in systems using 5%-20% guard bands on a 50 GHz DWDM grid.
March 15, 2017: Optics Letters
Giuseppe Vallone
Laguerre-Gauss (LG) modes represent an orthonormal basis set of solutions of the paraxial wave equation. LG modes are characterized by two integer parameters n and ℓ that are related to the radial and azimuthal profile of the beam. The physical dimension of the mode is instead determined by the beam waist parameter w<sub>0</sub>: only LG modes with the same w<sub>0</sub> satisfy the orthogonality relation. Here, we derive the scalar product between two LG modes with different beam waists and show how this result can be exploited to derive different expansions of a generic beam in terms of LG modes...
March 15, 2017: Optics Letters
Chuanchao Zhang, Wei Liao, Ke Yang, Taixiang Liu, Yang Bai, Lijuan Zhang, Xiaolong Jiang, Jing Chen, Yilan Jiang, Haijun Wang, Xiaoyu Luan, Hai Zhou, Xiaodong Yuan, Wanguo Zheng
A simple and convenient means of fabricating concave microlens arrays direct on silica glass by using the local fictive temperature modification of fused silica is presented. This method is based on the fact that an increased fictive temperature results in a much higher HF acid etching rate of fused silica. Combining the abrupt local fictive temperature enhancement by the CO<sub>2</sub> laser pulse and the subsequent etching by the HF acid solution, concave microlens arrays with high fill factors, excellent smoothness, and optical performance are generated on fused silica...
March 15, 2017: Optics Letters
M N M N Perera, D Schmidt, W E K Gibbs, S Juodkazis, P R Stoddart
This erratum reports a correction to Fig. 5 in the original manuscript, Opt. Lett.41, 5495 (2016)OPLEDP0146-959210.1364/OL.41.005495.
March 15, 2017: Optics Letters
Shichao Chen, Chengshuai Li, Yizheng Zhu
Sensitivity is a critical figure of merit to quantify measurement performance in quantitative phase imaging. It is affected by various noise sources in the system and by signal processing algorithms. Here we propose a three-level framework for sensitivity evaluation, including the Cramér-Rao bound (CRB), algorithmic sensitivity, and experimental sensitivity. Comparing the first two determines the theoretical efficiency of an algorithm, while inspecting the gap between the latter two reveals system efficiency...
March 15, 2017: Optics Letters
T Lipka, L Moldenhauer, L Wahn, H K Trieu
The large-scale and low-cost fabrication of high sensitivity sensors for the real-time detection of biochemicals and molecular substances opens up new opportunities in the areas of bioanalytic screening and medical diagnostics. Planar integrated photonic resonators that can be fabricated with a low footprint, in spatial and wavelength multiplexed arrangements, and that enable integration with microfluidics on the wafer scale have emerged as a promising sensing platform for these application fields. We realized an optofluidic and label-free biosensor that is based on hydrogenated amorphous silicon microring resonators embedded in silicon/glass microfluidic channels for analyte injection and biomolecule immobilization...
March 15, 2017: Optics Letters
Peng Zhao, Shikang Li, Xue Feng, Kaiyu Cui, Fang Liu, Wei Zhang, Yidong Huang
The relative phase shift among different components in the superposition of orbital angular momentum (OAM) states contains significant information. However, with existing methods of measuring the OAM spectrum, the phase term of the spectrum coefficient is hard to obtain. In this Letter, a mode-matching method is proposed to identify the complex OAM spectrum with a Mach-Zehnder interferometer and a charge-coupled device camera. It has the potential to extend the applications of OAM in scenarios sensitive to the phase factor, for instance, in imaging and quantum manipulation...
March 15, 2017: Optics Letters
Kalle Koskinen, Abdallah Slablab, Sasi Divya, Robert Czaplicki, Semen Chervinskii, Madanan Kailasnath, Padmanabhan Radhakrishnan, Martti Kauranen
We investigate bulk second-order nonlinear optical properties of amorphous indium selenide thin films fabricated by thermal evaporation. Such films are shown to exhibit strong and photostable second-harmonic generation (SHG). We report strong thickness dependence of the second-harmonic signals as characterized by the Maker-fringe method. The absolute value of the nonlinear susceptibility tensor of the film is addressed by analyzing the interference of SHG signals from the film and the glass substrate. The value of the joint non-diagonal component of the susceptibility is found to be 4 pm/V, which is comparable to that of widely used second-order nonlinear materials...
March 15, 2017: Optics Letters
Zhuopeng Xiao, B Li, Songnian Fu, L Deng, M Tang, Deming Liu
We demonstrate faster-than-Nyquist (FTN) transmission with a novel mitigation scheme of intercarrier interference. To the best of our knowledge, it is the first experimental demonstration of FTN PDM-16QAM transmission over standard single mode fiber (SSMF). Due to the use of maximum likelihood sequence detection and multi-input multi-output processing for severely overlapped Nyquist-PDM-16QAM carriers, 5.4-dB optical signal-to-noise ratio improvement is experimentally observed under the scenario of 2×16-GBd PDM-16QAM back-to-back transmission with a carrier spacing of 15 GHz...
March 15, 2017: Optics Letters
Nils Raabe, Tianli Feng, Mark Mero, Haochen Tian, Youjian Song, Wolfgang Hänsel, Ronald Holzwarth, Alexander Sell, Armin Zach, Günter Steinmeyer
Attosecond spectroscopy and precision frequency metrology depend on the stabilization of the carrier-envelope phase (CEP) of mode-locked lasers. Unfortunately, the phase of only a few types of lasers can be stabilized to jitters in the few-hundred millirad range. In a comparative experimental study, we analyze a femtosecond Ti:sapphire laser and three mode-locked fiber lasers. We numerically demodulate recorded time series of the free-running carrier-envelope beat note. Our analysis indicates a correlation between amplitude and frequency fluctuations at low Fourier frequencies for essentially all lasers investigated...
March 15, 2017: Optics Letters
Jonas Junker, Patrick Oppermann, Benno Willke
This note points out corrections to typographical errors in the published version of the article [Opt. Lett.42, 755 (2017)OPLEDP0146-959210.1364/OL.42.000755].
March 15, 2017: Optics Letters
Z Liu, M Ouali, S Coulibaly, M G Clerc, M Taki, M Tlidi
Complex spatiotemporal dynamics have been a subject of recent experimental investigations in optical frequency comb microresonators and in driven fiber cavities with Kerr-type media. We show that this complex behavior has a spatiotemporal chaotic nature. We determine numerically the Lyapunov spectra, allowing us to characterize different dynamical behavior occurring in these simple devices. The Yorke-Kaplan dimension is used as an order parameter to characterize the bifurcation diagram. We identify a wide regime of parameters where the system exhibits a coexistence between the spatiotemporal chaos, the oscillatory localized structure, and the homogeneous steady state...
March 15, 2017: Optics Letters
Zhaoyang Zhang, Danmeng Ma, Yiqi Zhang, Mingtao Cao, Zhongfeng Xu, Yanpeng Zhang
We experimentally generate a vortex beam through a four-wave mixing (FWM) process after satisfying the phase-matching condition in a rubidium atomic vapor cell with a photonic band gap (PBG) structure. The observed FWM vortex can also be viewed as the reflected part of the launched probe vortex from the PBG. Further, we investigate the propagation behaviors, including the spatial shift and splitting of the probe and FWM vortices in the medium with enhanced Kerr nonlinearity induced by electromagnetically induced transparency...
March 15, 2017: Optics Letters
Ning Jiang, Chenpeng Xue, Ding Liu, Yunxin Lv, Kun Qiu
We propose and numerically demonstrate a secure key distribution scheme based on the dynamic chaos synchronization of two external cavity vertical-cavity surface-emitting lasers (VCSELs) subject to symmetric random-polarization injections. By exchanging the random parameters that control the polarization angles of the driving injection, Alice and Bob can identify the time slots in which high-quality private chaos synchronization is achieved and independently generate a shared key from the synchronized polarization difference signals of their local VCSELs...
March 15, 2017: Optics Letters
Mingming Nie, Qiang Liu, Encai Ji, Xuezhe Cao, Xing Fu, Mali Gong
We demonstrated the active shaping for a solid-state Nd:YVO<sub>4</sub> amplifier with a high average gain of 39.2 dB. The average output power was 8.3 W with respect to the input power of 1 mW. A range of common and useful pulse shapes was generated at the final output. In addition, a very flat square pulse was produced with a root-mean-square less than 3% in amplitude. A numerical method was proposed to realize active shaping without an experimental test for the Nd:YVO<sub>4</sub> amplifier, showing great potential for the design of lasers with both high peak power (>100  kW) and a desired pulse shape...
March 15, 2017: Optics Letters
Mohamed Haouat, Jorge Garcia-Sucerquia, Abdelhamid Kellou, Pascal Picart
This Letter presents an easy, fast, and efficient single-shot method to reduce speckle noise in digital Fresnel holography. In this method, several images from a single hologram are reconstructed by introducing spatial displacements in the Fresnel kernel. Spatial jitters produce images with different speckle positions. Averaging the set of numerically produced images leads to a strong reduction of speckle noise in both amplitude and phase difference images. The experimental results show the suitability of the proposed approach and confirm its applicability to digital holographic interferometry...
March 15, 2017: Optics Letters
Carsten Robens, Stefan Brakhane, Wolfgang Alt, Felix Kleißler, Dieter Meschede, Geol Moon, Gautam Ramola, Andrea Alberti
We have designed, built, and characterized a high-resolution objective lens that is compatible with an ultrahigh vacuum environment. The lens system exploits the principle of the Weierstrass sphere solid immersion lens to reach a numerical aperture (NA) of 0.92. Tailored to the requirements of optical lattice experiments, the objective lens features a relatively long working distance of 150 μm. Our two-lens design is remarkably insensitive to mechanical tolerances in spite of the large NA. Additionally, we demonstrate the application of a tapered optical fiber tip, as used in scanning near-field optical microscopy, to measure the point spread function (PSF) of a high NA optical system...
March 15, 2017: Optics Letters
E Mobini, A Rahimzadegan, R Alaee, C Rockstuhl
Patterned graphene, as an atomically thin layer, supports localized surface plasmon polaritons at mid-infrared or far-infrared frequencies. This provides a pronounced optical force/torque in addition to large optical cross sections and will make it an ideal candidate for optical manipulation. Here, we study the optical force and torque exerted by a linearly polarized plane wave on circular and oval graphene flakes (single layers of graphene). While the torque vanishes for circular flakes, the finite torque allows rotating and orienting oval flakes relative to the electric field polarization...
March 15, 2017: Optics Letters
Kutan Gürel, Valentin J Wittwer, Sargis Hakobyan, Stéphane Schilt, Thomas Südmeyer
We demonstrate the first diode-pumped Ti:sapphire laser frequency comb. It is pumped by two green laser diodes with a total pump power of 3 W. The Ti:sapphire laser generates 250 mW of average output power in 61-fs pulses at a repetition rate of 216 MHz. We generated an octave-spanning supercontinuum spectrum in a photonic-crystal fiber and detected the carrier envelope offset (CEO) frequency in a standard f-to-2f interferometer setup. We stabilized the CEO-frequency through direct current modulation of one of the green pump diodes with a feedback bandwidth of 55 kHz limited by the pump diode driver used in this experiment...
March 15, 2017: Optics Letters
Mao Ye, Ya Sha Yi
The subwavelength grating microlens has attracted much attention due to its variety of potential applications. Instead of the vertical sidewall profile normally considered by most recent works, a tapered sidewall profile is often obtained during current fabrication processes, especially during the fabrication of high aspect ratio structures. In this work, we have discovered that a tapered sidewall profile may have a significant destructive effect on the concentration properties of subwavelength concentrating lenses/metasurfaces...
March 15, 2017: Optics Letters
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