opti510r: photonics
TRANSCRIPT
OPTI510R: Photonics
Khanh Kieu
College of Optical Sciences,
University of Arizona
Meinel building R.626
Important announcements
• Homework #2 is assigned, due Feb. 11
• Mid-term exam on Feb 27 (open books/notes)
Fabry Pérot Interferometer
Fabry Pérot Interferometer
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?
Laser Gyroscope
There are many other interferometers
• Michelson
• Mach-Zehnder
• Sagnac
• Fabry-Perot
• Fizeau
• Twyman-Green
• Newton
• Nomarski
• …
Question for thoughts
Can you come up with a new type of interferometer?
Can we explain interference by a different mechanism other than
waves?
New modulator design for optical communication?
What is the sharpest resonance that we can make?
Can you build a gyroscope that can measure the rotation of the earth
and would still cost <$100?
Can you build a company and then sell it for $100M?
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
Arago spot, Fresnel bright spot, or Poisson spot
Need to be in
the near field:
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
Bug
eyes
Opal
Grating fabrication-Ruled grating
Formed by physically writing grooves on a reflective surface
with a diamond blade mounted on a ruling machine:
Ruled grating
Diamond
milling
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
22110
0022110
,2
/2,2)(2
dndnn
n
c
ckdndnk
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
InAs/GaAs quantum dots laser
Littrow configuration: light of desired
wavelength is diffracted back along
incident beam
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
asymmetrical geometry
M1: collimating light sourceM2: focus disperse light from grating
Applications-Spectroscopy
Applications-Pulse compression
Compressed
pulse
Provide normal dispersion
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?