Download Holography

B.SC.II
PAPER-B
(OPTICS and LASERS)
Submitted by
Dr. Sarvpreet Kaur
Assistant Professor
PGGCG-11, Chandigarh
Holography
2
History of Holography
• Invented in 1948 by Dennis Gabor for use
in electron microscopy, before the
invention of the laser
• Leith and Upatnieks (1962) applied laser
light to holography and introduced an
important off-axis technique
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Conventional vs. Holographic
photography
• Conventional:
– 2-d version of a 3-d scene
– Photograph lacks depth perception or parallax
– Film sensitive only to radiant energy
– Phase relation (i.e. interference) are lost
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Conventional vs. Holographic
photography
• Hologram:
– Freezes the intricate wavefront of light that carries all
the visual information of the scene
– To view a hologram, the wavefront is reconstructed
– View what we would have seen if present at the
original scene through the window defined by the
hologram
– Provides depth perception and parallax
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Conventional vs. Holographic
photography
• Hologram:
– Converts phase information into amplitude
information (in-phase - maximum amplitude, out-ofphase – minimum amplitude)
– Interfere wavefront of light from a scene with a
reference wave
– The hologram is a complex interference pattern of
microscopically spaced fringes
– “holos” – Greek for whole message
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Creating Holograms
Reconstructing the image
Hologram :
Direct, object and conjugate waves
• Direct wave: corresponds to zeroth order grating
diffraction pattern
• Object wave: gives virtual image of the object
(reconstructs object wavefront) – first order
diffraction
• Conjugate wave: conjugate point, real image
(not useful since image is inside-out due to
negative phase angle) – first order diffraction
• In general, we wish to view only the object wave
– the other waves just confuse the issue
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Off-axis- Direct, object and conjugate waves
Use an off-axis system to record the hologram, ensuring separation of the three waves on reconstruction
Reference wave
Object
wave
Direct wave
Virtual image
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Conjugate
wave
Real image
Hologram – Reflection vs. Transmission
• Transmission hologram: reference and object waves
traverse the film from the same side
• Reflection hologram: reference and object waves
traverse the emulsion from opposite sides
View in Transmission
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View in reflection
Hologram: Wavelength
• With a different color, the virtual image will
appear at a different angle – (i.e. as a grating,
the hologram disperses light of different
wavelengths at different angles)
• Volume hologram: emulsion thickness >> fringe
spacing
– Can be used to reporduce images in their original
color when illuminated by white light.
– Use multiple exposures of scene in three primary
colors (R,G,B)
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Holography application
• A telephone credit card used in Europe has embossed
surface holograms which carry a monetary value. When the
card is inserted into the telephone, a card reader discerns the
amount due and deducts (erases) the appropriate amount to
cover the cost of the call.
• Supermarket scanners read the bar codes on merchandise
for the store's computer by using a holographic lens system to
direct laser light onto the product labels during checkout.
• Holography is used to depict the shock wave made by air
foils to locate the areas of highest stress. These holograms
are used to improve the design of aircraft wings and turbine
blades.
Holography application
• A holographic lens is used in an aircraft "heads-up
display" to allow a fighter pilot to see critical cockpit
instruments while looking straight ahead through the
windscreen. Similar systems are being researched by several
automobile manufactures.
• Researchers are developing the sub- systems of a
computerized holographic display.
• Holography is ideal for archival recording of valuables or
fragile museum artifacts.
• Optical computers, which use holograms as storage
material for data, could have a dramatic impact on the overall
holography market.
Holography application
• To better understand marine phytoplankton, researchers
have developed an undersea holographic camera that
generates in-line and off-axis holograms of the organisms. A
computer controlled stage moves either a video camera or a
microscope through the images, and the organisms can be
measured as they were in their undersea environment
• An interferogram (a sort of hologram) is a technique providing
a method of non-destructive analysis that determines
structural deformations in objects.
Holography application
• The using of ultrasound waves as main carriers of the
information creates opportunities for holography application in
a sound field visualization. This has a great practical
importance in:
- Undersea acoustics and hydrolocation;
- Defectoscopy;
- Medical diagnostics;
- Biological surveys
• The using of X-rays as main carriers of information creates
additional opportunities for holography method application in
biological, physical and chemical studies
Holography application
The using of γ –rays allows precise atomic and molecular
structural analysis:
(a)Holograms of a local
structure of crystallic Fe
(b) Estimated pictures of a
local structure of
crystallic Fe
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History of Fiber Optic
Technology
• People have used light to transmit info. for hundreds of years
• The invention of the laser prompted researchers to study the
potential of fiber optics
 send a much larger amount of data than telephone
• first experiment
 letting the laser beam transmit freely in air
& through different types of waveguides
• very large losses in the optical fibers prevented coaxial cables from
being replaced
 Decrease in the amount of light reaching the end of the fiber
Cont: History of Fiber Optic
Technology
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Early fibers had losses around 1,000 dB/km
In 1969, several scientists concluded that impurities in the fiber material
caused the signal loss
 Researchers believed it was possible to reduce the losses
By removing the impurities
researchersobserve the improvement
In 1970,(corning glass works)* made a multimode fiber with losses under
20 dB/km.
in 1972, the company made a high silica-core multimode optical fiber
with 4dB/km.
Nowadays, multimode fibers can have losses as low as 0.5 dB/km at
wavelengths around 1300 nm
*company
Introduction
• Optical fiber has a number of advantages over the copper wire
 since it is made glass or plastic
• light has a much higher frequency than any radio signal
 we can generate, fiber has a wider bandwidth
To carry more information at one time
Fiber Optics as a
Transmission Medium
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Information is carried through a fiber optic cable by transmitting pulses
of light (which is also an EM wave)!
A fiber optic cable is a coaxial arrangement of glass or plastic material
of immense clarity (i.e., highly transparent)
A clear cylinder of optical material called the core is surrounded by
another clear wrapper of optical material called the cladding
These two materials are selected to have different indices of refraction
The fiber is surrounded by a plastic or teflon jacket to protect and stiffen
the fiber
Light is guided through the optical fiber by continual reflection from the
core-cladding boundary
This is made possible due to the different refractive indices of the core
and cladding materials
The index of refraction (n) of a material affects the angle by which a
light ray is bent while passing through the material
If the light incident on the core-cladding boundary is at a suitable angle,
then the light will be totally reflected from the boundary. This is called
total internal reflection
Beginning Of Fiber Optics
• Swiss Physicist Daniel Colladon Recognized
Light Guiding(1841)
How do They Work?
• Snell’s Law
n1 sin(1)=n2 sin(2)
The speed and wavelength of light change when entering
a different medium
• Index of Refraction (n=c/v c=speed of light in vacuum)
Total
Internal
Reflection
c=arcsin(n2/n1)
light is to enter the
second medium at
an angle greater
than critical angle
for TIR to occur
acceptance angle
 max=sin-1(n12-n22)1/2
Numerical Aperture(NA)=sin(acceptance
angle)
cladding index of refraction lower than core index of
refraction
Cross section of optical fiber cable
Core and cladding with
different indices of refraction
Core-cladding boundary
Optical Fiber
• Fiber is the medium to guide the light form
the transmitter to the receiver.
• There are two types:
– Multimode Fiber
– Single-Mode Fiber
Multimode Fiber
 In multimode fibers more than one light
transmitted at a time.
 Fiber diameter ranges from 50-to-100
micron.
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Multimode Fiber
 Multimode Fiber is divided into two types:
– Multimode Step-index Fiber
– Multimode Graded-index Fiber
Multimode Step-index Fiber
• Lights are sent at angles lower than the
critical angle or straight
• Any light angle exceed the critical angle
will cause it to penetrate through cladding.
• Obviously light with lower angle will reach
the end faster than others.
Multimode Step-index Fiber
• The difference in signals receiving time
result in unstable wave light at the
receiver.
• To avoid this problem there should be
spacing between the light pulses  but
this will limit the bandwidth.
• Used for very short distance
Multimode Graded-index Fiber
• In this mode reduce the problem with
Multimode Step-Index.
• All the beams reaching the receiver almost
at the same time.
• This can be done by slowing down the
ones with shorter distance.
• This is done in fiber implementation by
increasing its refractive index at the center
and gradually decreases it toward the
edges
Single-Mode Fiber
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Only one light is transmitted in the fiber.
Diameter ranges from 8.3 to 10 microns.
It has Higher transmission rate.
it can be used for longer distance.
Fiber Optics in The 20th Century
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Telephone Systems
Internet
Video Feeds
Medical Operations
Home Theater Systems
Losses in optical fibres
The predominant losses in optic fibres
are:
–absorption losses due to impurities in the fibre material
–material or Rayleigh scattering losses due to microscopic
irregularities in the fibre
–chromatic or wavelength dispersion because of the use of
a non-monochromatic source
–radiation losses caused by bends and kinks in the fibre
–modal dispersion or pulse spreading due to rays taking
different paths down the fibre
–coupling losses caused
by misalignment
& imperfect
Summer
Presentation
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surface finishes
Advantages of fiber optics
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Much Higher Bandwidth (Gbps) - Thousands of channels can be
multiplexed together over one strand of fiber
Immunity to Noise - Immune to electromagnetic interference (EMI).
Safety - Doesn’t transmit electrical signals, making it safe in
environments like a gas pipeline.
High Security - Impossible to “tap into.”
Less Loss - Repeaters can be spaced 75 miles apart (fibers can be
made to have only 0.2 dB/km of attenuation)
Reliability - More resilient than copper in extreme environmental
conditions.
Size - Lighter and more compact than copper.
Flexibility - Unlike impure, brittle glass, fiber is physically very flexible.
Disadvantages include the cost of interfacing equipment necessary to
convert electrical signals to optical signals. (optical transmitters,
receivers) Splicing fiber optic cable is also more difficult.
Disadvantages
• Different Signals
• New system required for Fiber Optics
Thank you
Any Question please
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Thank you!
SOURCES:
http://bsfp.media-security.ru/school2/10.htm
http://www.100top.ru/encyclopedia/article/?articleid=28743
http://www.holophile.com/history.htm
http://www.britannica.com/
http://www.litiholographics.com/technology/tech_producing.htm
http://vcs.abdn.ac.uk/ENGINEERING/lasers/laser1.jpg
http://www.holo.com/holo/book/book1.html
http://www.hmt.com/holography/
http://www.art-in-holography.org/
http://inventors.about.com/library/inventors/blholography.htm
Reference
http://www.wordiq.com/definition/Laser
http://www.asamnet.de/~birners/public_html/laser.html
http://vcs.abdn.ac.uk/ENGINEERING/lasers/lasers.html
Some links: lasers
http://www.lasersurplus.com/lasers.htm
http://www.midwest-laser.com/html/ilt5490a___ilt5470k.html
http://www.hhr-lasers.com/
http://www.coherentinc.com/
http://www.spectra-physics.com/
http://www.continuumlasers.com/
How lasers work
http://technology.niagarac.on.ca/courses/tech238g/Lasers.html
http://www.clf.rl.ac.uk/Public/index.htm
http://www.m2m.ecs.soton.ac.uk/Default.asp?id=283