OPTI510R: Photonics Khanh Kieu College of Optical Sciences, University of Arizona kkieu@optics.arizona.edu Meinel building R.626
Important announcements Homework #2 is assigned, due Feb. 12 Travel to NSF Feb 26-27, pre-record lecture Mid-term exam on Feb 28 (open books/notes) Final exam on May 2 (tentative)
Fabry Pérot Interferometer
Fabry Pérot Interferometer
Sagnac Interferometer The sagnac sensor has the best sensitivity compared to other type of sensors.
Fiber Optics Gyroscope
Laser Gyroscope We can easily measure f beat with <1Hz precision. What would be the smallest rotation rate that we can measure using a ring Resonator with 1m radius?
There are many other interferometers Michelson Mach-Zehnder Sagnac Fabry-Perot Fizeau Twyman-Green Newton Nomarski
Diffraction and Devices Diffraction Overcoming the diffraction limit Diffraction gratings Ruled grating Holographic grating Volume grating Applications Tunable laser Spectroscopy Laser stabilization Pulse compression Volume grating
Diffraction Diffraction relies on the interference of waves emanating from the same source taking different paths to the same point on a screen Diffraction can be explained by interference Diffraction of a laser beam through a small circular hole (Airy disk) Young's double-slit interferometer Wikipedia
Diffraction and nature of light Need to be in the near field: Arago spot, Fresnel bright spot, or Poisson spot This experiment confirmed the wave nature of light! Wikipedia
Huygens Fresnel principle Near field and far-field diffraction Wikipedia
Diffraction limit How to overcome the diffraction limit?
Overcoming the diffraction limit
Overcoming the diffraction limit nobelprize.org
STED: Stimulated emission depletion nobelprize.org
STORM: Stochastic Optical Reconstruction Microscopy nobelprize.org
STORM: Stochastic Optical Reconstruction Microscopy nobelprize.org
STORM: Stochastic Optical Reconstruction Microscopy nobelprize.org
Diffraction Grating A periodic structure that diffracts light into different directions. Grating can be flat, concave, convex and arbitrary shape HeNe laser incident on a diffraction grating showing zero, first and second order beams
Diffraction Grating
Diffraction Grating
Basic equations Monochromatic source White light
Blazed grating Need: how to concentrate all the lights --- ---into one order? Solution: make the grating of right triangles with a braze angle. By tilting the slit faces to the normal of incidence of the desired order, grating efficiencies >90% can be achieved Blazed grating
Diffraction in Nature CDROM and DVD Blue Morpho butterfly Fossil Ammonite Peacock feather Opal Bug eyes
Grating fabrication-ruled grating Formed by physically writing grooves on a reflective surface with a diamond blade mounted on a ruling machine: Diamond milling Ruled grating High throughput and efficiency Maximum groove density of ---3600g/mm Good in IR and far IR Expensive
Grating fabrication-ruled grating
Grating fabrication-ruled grating Measured at Littrow configuration
Holographic grating Formed by interference lithography and etch Low stray light and dense groove spacing Lower reflectivity Maximum groove density of 6000g/mm Availability of non flat substrate Good in UV, short wavelength
Holographic grating Fringe locking controller locks the interference image to moving substrate by correcting stage error and interferometer phase error
Holographic grating Lightsmith transmission grating Excellent diffraction efficiency
Volume grating Diffraction efficiency ~99% Narrow bandwidth
Bragg mirrors 2 2 1 1 0 0 0 2 2 1 1 0, 2 / 2, 2 ) ( 2 d n n d n n c c k d n n d k B Constructive interference for two layers of a segment Bragg frequency
Fiber Bragg gratings Fiber laser reflector, filter, dispersion compensator
Fiber Bragg gratings High Power Fiber Lasers
Tunable Grating Microelectromechanical Systems (MEMS) spring comb drive actuator
Applications-Tunable laser Littrow configuration: light of desired wavelength is diffracted back along incident beam InAs/GaAs quantum dots laser Beam rotates as you tune!
Applications-Tunable laser Littman-Metcalf configuration: grating is kept at a fixed angle and a special mirror is rotated to tune the output wavelength. Output beam is aligned at grazing incidence with grating. First order diffracted beam is sent to retroreflector (mirror) that reflects beam back to itself. High efficiency for TM polarization (light polarized perpendicular to grooves). Output is the zeroth order reflected beam off the grating.
Applications-Laser stabilization
Applications-Spectroscopy Czerny-Turner Configuration two concave mirrors and planar diffraction grating more degrees of freedom, good coma correction at one wavelength M1: collimating light source M2: focus disperse light from grating asymmetrical geometry
Applications-Spectroscopy
Applications-Pulse compression Provide normal dispersion Compressed pulse
Applications-Pulse compression Schematic diagram of a chirped pulse amplification system
Optics of periodic structures Photonics crystal!
Questions for Thoughts Can you come up with a better way to overcome the diffraction limit? Can you create a new optics company making diffractive devices? Why there is a strong polarization dependence in diffraction efficiency for metal-coated ruled gratings? A compact device providing adjustable GVD with low loss? A diffraction grating with 100% diffraction efficiency and broad operating bandwidth?