Rigorous Theory of Optical Trapping by an Optical Vortex Beam Jack Ng
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Generation of Vortex Optical Beams Based on Chiral Fiber-Optic Periodic Structures
sensors Article Generation of Vortex Optical Beams Based on Chiral Fiber-Optic Periodic Structures Azat Gizatulin *, Ivan Meshkov, Irina Vinogradova, Valery Bagmanov, Elizaveta Grakhova and Albert Sultanov Department of Telecommunications, Ufa State Aviation Technical University, 450008 Ufa, Russia; [email protected] (I.M.); [email protected] (I.V.); [email protected] (V.B.); [email protected] (E.G.); [email protected] (A.S.) * Correspondence: [email protected] Received: 22 August 2020; Accepted: 17 September 2020; Published: 18 September 2020 Abstract: In this paper, we consider the process of fiber vortex modes generation using chiral periodic structures that include both chiral optical fibers and chiral (vortex) fiber Bragg gratings (ChFBGs). A generalized theoretical model of the ChFBG is developed including an arbitrary function of apodization and chirping, which provides a way to calculate gratings that generate vortex modes with a given state for the required frequency band and reflection coefficient. In addition, a matrix method for describing the ChFBG is proposed, based on the mathematical apparatus of the coupled modes theory and scattering matrices. Simulation modeling of the fiber structures considered is carried out. Chiral optical fibers maintaining optical vortex propagation are also described. It is also proposed to use chiral fiber-optic periodic structures as sensors of physical fields (temperature, strain, etc.), which can be applied to address multi-sensor monitoring systems due to a unique address parameter—the orbital angular momentum of optical radiation. Keywords: fiber Bragg gratings; chiral structures; orbital angular momentum; apodization; chirp; coupled modes theory 1. Introduction Nowadays, the demand for broadband multimedia services is still growing, which leads to an increase of transmitted data volume as part of the development of the digital economy and the expansion of the range of services (video conferencing, telemedicine, online broadcasting, streaming, etc.). -
Beam Profiling by Michael Scaggs
Beam Profiling by Michael Scaggs Haas Laser Technologies, Inc. Introduction Lasers are ubiquitous in industry today. Carbon Dioxide, Nd:YAG, Excimer and Fiber lasers are used in many industries and a myriad of applications. Each laser type has its own unique properties that make them more suitable than others. Nevertheless, at the end of the day, it comes down to what does the focused or imaged laser beam look like at the work piece? This is where beam profiling comes into play and is an important part of quality control to ensure that the laser is doing what it intended to. In a vast majority of cases the laser beam is simply focused to a small spot with a simple focusing lens to cut, scribe, etch, mark, anneal, or drill a material. If there is a problem with the beam delivery optics, the laser or the alignment of the system, this problem will show up quite markedly in the beam profile at the work piece. What is Beam Profiling? Beam profiling is a means to quantify the intensity profile of a laser beam at a particular point in space. In material processing, the "point in space" is at the work piece being treated or machined. Beam profiling is accomplished with a device referred to a beam profiler. A beam profiler can be based upon a CCD or CMOS camera, a scanning slit, pin hole or a knife edge. In all systems, the intensity profile of the beam is analyzed within a fixed or range of spatial Haas Laser Technologies, Inc. -
Optical Vortex Sign Determination Using Self-Interference Methods
Optica Applicata, Vol. XL, No. 1, 2010 Optical vortex sign determination using self-interference methods PIOTR KURZYNOWSKI, MONIKA BORWIŃSKA, JAN MASAJADA Institute of Physics, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland We have proposed a simple method for determining the sign of optical vortex seeded in optical beam. Our method can be applied to any single optical vortex, also the one with topological charge magnitude higher than 1, as well as to the whole vortex lattice. The proposed method has been verified experimentally for all the cases. Keywords: optical vortex, interference, birefringence. 1. Introduction Optical vortices are singular lines in a phase distribution of a light field. Usually they are observed in planar cross section (on the screen) as dark points with undefined phase (vortex points) [1–3]. The wavefront takes characteristic helical form in the vicinity of the vortex line (Fig. 1) [1–4]. The twisted helical wavefront results a non-zero angular momentum carried by the beam with the optical vortex [3]. The wavefront’s helical geometry allows for vortex classification due to the helice handedness. We say that optical vortex may have ab Fig. 1. Left (a) and right (b) oriented helical wavefront. The light wave phase is undetermined along the axis of the helice. 166 P. KURZYNOWSKI, M. BORWIŃSKA, J. MASAJADA Fig. 2. Generally the vortex lines in a complex scalar field may have complicated geometry. Here, the line intersects the plane Σ twice. The phase circulation determined in plane Σ in the neighborhood of both intersection points circulates in opposite directions. -
Broadband Multichannel Optical Vortex Generators Via Patterned Double-Layer Reverse-Twist Liquid Crystal Polymer
crystals Article Broadband Multichannel Optical Vortex Generators via Patterned Double-Layer Reverse-Twist Liquid Crystal Polymer Hanqing Zhang 1, Wei Duan 1,2,*, Ting Wei 1, Chunting Xu 1 and Wei Hu 1,* 1 National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China; [email protected] (H.Z.); [email protected] (T.W.); [email protected] (C.X.) 2 School of Instrumentation and Optoelectronic Engineering, Beihang University, Beijing 100191, China * Correspondence: [email protected] (W.D.); [email protected] (W.H.); Tel.: +86-25-83597400 (W.D & W.H.) Received: 31 August 2020; Accepted: 27 September 2020; Published: 29 September 2020 Abstract: The capacity of an optical communication system can be greatly increased by using separate orbital angular momentum (OAM) modes as independent channels for signal transmission and encryption. At present, a transmissive OAM mode generator compatible with wavelength division multiplexing is being highly pursued. Here, we introduce a specific double-layer reverse-twist configuration into liquid crystal polymer (LCP) to overcome wavelength dependency. With this design, broadband-applicable OAM array generators are proposed and demonstrated. A Damman vortex grating and a Damman q-plate were encoded via photopatterning two subsequent LCP layers adopted with oppositely handed chiral dopants. Rectangular and hexagonal OAM arrays with mode conversion efficiencies exceeding 40.1% and 51.0% in the ranges of 530 to 930 nm, respectively, are presented. This provides a simple and broadband efficient strategy for beam shaping. Keywords: beam shaping; liquid crystals; orbital angular momentum; geometric phase 1. -
Making Optical Vortices with Computer-Generated Holograms ͒ Alicia V
Making optical vortices with computer-generated holograms ͒ Alicia V. Carpentier,a Humberto Michinel, and José R. Salgueiro Área de Óptica, Facultade de Ciencias de Ourense, Universidade de Vigo, As Lagoas s/n, Ourense, ES-32004 Spain David Olivieri Departamento de Linguaxes e Sistemas Informáticos, Universidade de Vigo, As Lagoas s/n, Ourense, ES-32004 Spain ͑Received 22 February 2007; accepted 16 June 2008͒ An optical vortex is a screw dislocation in a light field that carries quantized orbital angular momentum and, due to cancellations of the twisting along the propagation axis, experiences zero intensity at its center. When viewed in a perpendicular plane along the propagation axis, the vortex appears as a dark region in the center surrounded by a bright concentric ring of light. We give detailed instructions for generating optical vortices and optical vortex structures by computer-generated holograms and describe various methods for manipulating the resulting structures. © 2008 American Association of Physics Teachers. ͓DOI: 10.1119/1.2955792͔ I. INTRODUCTION optical tweezers that can trap neutral particulates,2 which re- ceive the angular momentum associated with the rotation of The phase of a light beam can be twisted like a corkscrew the phase.3 In nonlinear optics, waveguiding can be achieved around its axis of propagation. If the light wave is repre- inside the central hole.4,5 In astronomy the singularity can be ⌽ sented by complex numbers of the form Aei , where A is the used to block the light from a bright star to increase the amplitude of the field and ⌽ is the phase of the wave front, contrast of astronomical observations using optical vortex the twisting is described by a helical phase distribution ⌽ coronagraphs,6 which are useful for the search of extrasolar =m proportional to the azimuthal angle of a cylindrical co- planets. -
UFS Lecture 13: Passive Modelocking
UFS Lecture 13: Passive Modelocking 6 Passive Mode Locking 6.2 Fast Saturable Absorber Mode Locking (cont.) (6.3 Soliton Mode Locking) 6.4 Dispersion Managed Soliton Formation 7 Mode-Locking using Artificial Fast Sat. Absorbers 7.1 Kerr-Lens Mode-Locking 7.1.1 Review of Paraxial Optics and Laser Resonator Design 7.1.2 Two-Mirror Resonators 7.1.3 Four-Mirror Resonators 7.1.4 The Kerr Lensing Effects (7.2 Additive Pulse Mode-Locking) 1 6.2.2 Fast SA mode locking with GDD and SPM Steady-state solution is chirped sech-shaped pulse with 4 free parameters: Pulse amplitude: A0 or Energy: W 2 = 2 A0 t Pulse width: t Chirp parameter : b Carrier-Envelope phase shift : y 2 Pulse width Chirp parameter Net gain after and Before pulse CE-phase shift Fig. 6.6: Modelocking 3 6.4 Dispersion Managed Soliton Formation in Fiber Lasers ~100 fold energy Fig. 6.12: Stretched pulse or dispersion managed soliton mode locking 4 Fig. 6.13: (a) Kerr-lens mode-locked Ti:sapphire laser. (b) Correspondence with dispersion-managed fiber transmission. 5 Today’s BroadBand, Prismless Ti:sapphire Lasers 1mm BaF2 Laser crystal: f = 10o OC 2mm Ti:Al2O3 DCM 2 PUMP DCM 2 DCM 1 DCM 1 DCM 2 DCM 1 BaF2 - wedges DCM 6 Fig. 6.14: Dispersion managed soliton including saturable absorption and gain filtering 7 Fig. 6.15: Steady state profile if only dispersion and GDD is involved: Dispersion Managed Soliton 8 Fig. 6.16: Pulse shortening due to dispersion managed soliton formation 9 7. -
Multi-Vortex Laser Enabling Spatial and Temporal Encoding Zhen Qiao1†, Zhenyu Wan2†, Guoqiang Xie1*, Jian Wang2*, Liejia Qian1 and Dianyuan Fan1,3
Qiao et al. PhotoniX (2020) 1:13 https://doi.org/10.1186/s43074-020-00013-x PhotoniX RESEARCH Open Access Multi-vortex laser enabling spatial and temporal encoding Zhen Qiao1†, Zhenyu Wan2†, Guoqiang Xie1*, Jian Wang2*, Liejia Qian1 and Dianyuan Fan1,3 * Correspondence: [email protected]. cn; [email protected] Abstract †Zhen Qiao and Zhenyu Wan contributed equally to this work. Optical vortex is a promising candidate for capacity scaling in next-generation optical 1School of Physics and Astronomy, communications. The generation of multi-vortex beams is of great importance for Key Laboratory for Laser Plasmas vortex-based optical communications. Traditional approaches for generating multi- (Ministry of Education), Collaborative Innovation center of vortex beams are passive, unscalable and cumbersome. Here, we propose and IFSA (CICIFSA), Shanghai Jiao Tong demonstrate a multi-vortex laser, an active approach for creating multi-vortex beams University, Shanghai 200240, China directly at the source. By printing a specially-designed concentric-rings pattern on 2Wuhan National Laboratory for Optoelectronics and School of the cavity mirror, multi-vortex beams are generated directly from the laser. Spatially, Optical and Electronic Information, the generated multi-vortex beams are decomposable and coaxial. Temporally, the Huazhong University of Science and multi-vortex beams can be simultaneously self-mode-locked, and each vortex Technology, Wuhan 430074, China Full list of author information is component carries pulses with GHz-level repetition rate. Utilizing these distinct available at the end of the article spatial-temporal characteristics, we demonstrate that the multi-vortex laser can be spatially and temporally encoded for data transmission, showing the potential of the developed multi-vortex laser in optical communications. -
Lab 10: Spatial Profile of a Laser Beam
Lab 10: Spatial Pro¯le of a Laser Beam 2 Background We will deal with a special class of Gaussian beams for which the transverse electric ¯eld can be written as, r2 1 Introduction ¡ 2 E(r) = Eoe w (1) Equation 1 is expressed in plane polar coordinates Refer to Appendix D for photos of the appara- where r is the radial distance from the center of the 2 2 2 tus beam (recall r = x +y ) and w is a parameter which is called the spot size of the Gaussian beam (it is also A laser beam can be characterized by measuring its referred to as the Gaussian beam radius). It is as- spatial intensity pro¯le at points perpendicular to sumed that the transverse direction is the x-y plane, its direction of propagation. The spatial intensity pro- perpendicular to the direction of propagation (z) of ¯le is the variation of intensity as a function of dis- the beam. tance from the center of the beam, in a plane per- pendicular to its direction of propagation. It is often Since we typically measure the intensity of a beam convenient to think of a light wave as being an in¯nite rather than the electric ¯eld, it is more useful to recast plane electromagnetic wave. Such a wave propagating equation 1. The intensity I of the beam is related to along (say) the z-axis will have its electric ¯eld uni- E by the following equation, formly distributed in the x-y plane. This implies that " cE2 I = o (2) the spatial intensity pro¯le of such a light source will 2 be uniform as well. -
Performance Evaluation of a Thz Pulsed Imaging System: Point Spread Function, Broadband Thz Beam Visualization and Image Reconstruction
applied sciences Article Performance Evaluation of a THz Pulsed Imaging System: Point Spread Function, Broadband THz Beam Visualization and Image Reconstruction Marta Di Fabrizio 1,* , Annalisa D’Arco 2,* , Sen Mou 2, Luigi Palumbo 3, Massimo Petrarca 2,3 and Stefano Lupi 1,4 1 Physics Department, University of Rome ‘La Sapienza’, P.le Aldo Moro 5, 00185 Rome, Italy; [email protected] 2 INFN-Section of Rome ‘La Sapienza’, P.le Aldo Moro 2, 00185 Rome, Italy; [email protected] (S.M.); [email protected] (M.P.) 3 SBAI-Department of Basic and Applied Sciences for Engineering, Physics, University of Rome ‘La Sapienza’, Via Scarpa 16, 00161 Rome, Italy; [email protected] 4 INFN-LNF, Via E. Fermi 40, 00044 Frascati, Italy * Correspondence: [email protected] (M.D.F.); [email protected] (A.D.) Abstract: Terahertz (THz) technology is a promising research field for various applications in basic science and technology. In particular, THz imaging is a new field in imaging science, where theories, mathematical models and techniques for describing and assessing THz images have not completely matured yet. In this work, we investigate the performances of a broadband pulsed THz imaging system (0.2–2.5 THz). We characterize our broadband THz beam, emitted from a photoconductive antenna (PCA), and estimate its point spread function (PSF) and the corresponding spatial resolution. We provide the first, to our knowledge, 3D beam profile of THz radiation emitted from a PCA, along its propagation axis, without the using of THz cameras or profilers, showing the beam spatial Citation: Di Fabrizio, M.; D’Arco, A.; intensity distribution. -
Gaussian Beams • Diffraction at Cavity Mirrors Creates Gaussian Spherical
Gaussian Beams • Diffraction at cavity mirrors creates Gaussian Spherical Waves • Recall E field for Gaussian U ⎛ ⎡ x2 + y2 ⎤⎞ 0 ⎜ ( ) ⎟ u( x,y,R,t ) = exp⎜i⎢ω t − Kr − ⎥⎟ R ⎝ ⎣ 2R ⎦⎠ • R becomes the radius of curvature of the wave front • These are really TEM00 mode emissions from laser • Creates a Gaussian shaped beam intensity ⎛ − 2r 2 ⎞ 2P ⎛ − 2r 2 ⎞ I( r ) I exp⎜ ⎟ exp⎜ ⎟ = 0 ⎜ 2 ⎟ = 2 ⎜ 2 ⎟ ⎝ w ⎠ π w ⎝ w ⎠ Where P = total power in the beam w = 1/e2 beam radius • w changes with distance z along the beam ie. w(z) Measurements of Spotsize • For Gaussian beam important factor is the “spotsize” • Beam spotsize is measured in 3 possible ways • 1/e radius of beam • 1/e2 radius = w(z) of the radiance (light intensity) most common laser specification value 13% of peak power point point where emag field down by 1/e • Full Width Half Maximum (FWHM) point where the laser power falls to half its initial value good for many interactions with materials • useful relationship FWHM = 1.665r1 e FWHM = 1.177w = 1.177r 1 e2 w = r 1 = 0.849 FWHM e2 Gaussian Beam Changes with Distance • The Gaussian beam radius of curvature with distance 2 ⎡ ⎛π w2 ⎞ ⎤ R( z ) = z⎢1 + ⎜ 0 ⎟ ⎥ ⎜ λz ⎟ ⎣⎢ ⎝ ⎠ ⎦⎥ • Gaussian spot size with distance 1 2 2 ⎡ ⎛ λ z ⎞ ⎤ w( z ) = w ⎢1 + ⎜ ⎟ ⎥ 0 ⎜π w2 ⎟ ⎣⎢ ⎝ 0 ⎠ ⎦⎥ • Note: for lens systems lens diameter must be 3w0.= 99% of power • Note: some books define w0 as the full width rather than half width • As z becomes large relative to the beam asymptotically approaches ⎛ λ z ⎞ λ z w(z) ≈ w ⎜ ⎟ = 0 ⎜ 2 ⎟ ⎝π w0 ⎠ π w0 • Asymptotically light -
Arithmetic with Q-Plates
Arithmetic with q-plates SAM DELANEY1, MARÍA M. SÁNCHEZ-LÓPEZ2,*, IGNACIO MORENO3 AND JEFFREY A. DAVIS1 1Department of Physics. San Diego State University, San Diego, CA 92182-1233, USA 2Instituto de Bioingeniería. Dept. Física y Arquitectura de Computadores, Universidad Miguel Hernández, 03202 Elche, Spain 3Departamento de Ciencia de Materiales, Óptica y Tecnología Electrónica. Universidad Miguel Hernández, 03202 Elche, Spain *Corresponding author: [email protected] Received XX Month XXXX; revised XX Month, XXXX; accepted XX Month XXXX; posted XX Month XXXX (Doc. ID XXXXX); published XX Month XXXX In this work we show the capability to form various q-plate equivalent systems using combinations of commercially available q-plates. We show operations like changing the sign of the q-value, or the addition and subtraction of q-plates. These operations only require simple combinations of q-plates and half-wave plates. Experimental results are presented in all cases. Following this procedure, experimental testing of higher and negative q-valued devices can be carried out using commonly available q-valued devices. © 2016 Optical Society of America OCIS codes: (230.3720) Liquid-crystal devices, (230.5440) Polarization-selective devices, (120.5410) Polarimetry. http://dx.doi.org/10.1364/AO.99.099999 q-plates can be combined in order to generate equivalent devices of 1. INTRODUCTION different q-values to allow experimentation before purchasing the target devices. For example, two metasurface q-plate elements were Optical retarder elements with azimuthal rotation of the principal axes combined in [24]. The addition and subtraction of OAM was shown for are receiving a great deal of attention because they can create input circularly polarized light. -
Optics of Gaussian Beams 16
CHAPTER SIXTEEN Optics of Gaussian Beams 16 Optics of Gaussian Beams 16.1 Introduction In this chapter we shall look from a wave standpoint at how narrow beams of light travel through optical systems. We shall see that special solutions to the electromagnetic wave equation exist that take the form of narrow beams – called Gaussian beams. These beams of light have a characteristic radial intensity profile whose width varies along the beam. Because these Gaussian beams behave somewhat like spherical waves, we can match them to the curvature of the mirror of an optical resonator to find exactly what form of beam will result from a particular resonator geometry. 16.2 Beam-Like Solutions of the Wave Equation We expect intuitively that the transverse modes of a laser system will take the form of narrow beams of light which propagate between the mirrors of the laser resonator and maintain a field distribution which remains distributed around and near the axis of the system. We shall therefore need to find solutions of the wave equation which take the form of narrow beams and then see how we can make these solutions compatible with a given laser cavity. Now, the wave equation is, for any field or potential component U0 of Beam-Like Solutions of the Wave Equation 517 an electromagnetic wave ∂2U ∇2U − µ 0 =0 (16.1) 0 r 0 ∂t2 where r is the dielectric constant, which may be a function of position. The non-plane wave solutions that we are looking for are of the form i(ωt−k(r)·r) U0 = U(x, y, z)e (16.2) We allow the wave vector k(r) to be a function of r to include situations where the medium has a non-uniform refractive index.