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 fbeat 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 Volume grating  Laser stabilization  Pulse compression 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 Young's double-slit interferometer (Airy disk) 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

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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 Opal feather

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

Constructive interference 2k (n d  n d )  2 , k  2 / c for two layers of a segment 0 1 1 2 2 0 0

c0 n1d1  n2d2 Bragg frequency   , n  B 2n  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?