Download Lecture 27

yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Astronomical spectroscopy wikipedia, lookup

Ultraviolet–visible spectroscopy wikipedia, lookup

Anti-reflective coating wikipedia, lookup

Harold Hopkins (physicist) wikipedia, lookup

Surface plasmon resonance microscopy wikipedia, lookup

Retroreflector wikipedia, lookup

Optical aberration wikipedia, lookup

Holography wikipedia, lookup

Magnetic circular dichroism wikipedia, lookup

Thomas Young (scientist) wikipedia, lookup

Optical coherence tomography wikipedia, lookup

Microscopy wikipedia, lookup

Nonimaging optics wikipedia, lookup

Nonlinear optics wikipedia, lookup

Ellipsometry wikipedia, lookup

Light wikipedia, lookup

Atmospheric optics wikipedia, lookup

Night vision device wikipedia, lookup

Polarizer wikipedia, lookup

Birefringence wikipedia, lookup

Lens (optics) wikipedia, lookup

Schneider Kreuznach wikipedia, lookup

Optician wikipedia, lookup

Design Realization
lecture 27
John Canny
Last time
Lenses reviewed: convex spherical lenses.
Ray diagrams. Real and virtual images.
More on lenses. Concave and aspheric lenses.
Fresnel optics:
 Lenses
This time
 More Fresnel optics:
 Lenticular arrays/diffusers
 Prisms
 Diffusers
 Holograms
 Polarization
Fresnel lenses
 Remove the thickness, but preserve
 Some artifacts are
introduced, but
are invisible for
large viewing areas
(e.g. diplays).
Lenticular arrays
 Many lenses printed on one sheet.
 Simplest version: array of cylindrical lenses.
 Used for budget 3D vision:
Lenticular arrays
 Simplest version: array of cylindrical lenses.
Lenticular arrays
 Lenticular screens are rated in LPI for lines
per inch. Typical range is 40-60 LPI, at
about $10 per square foot.
 Budget color printers can achieve 4800 dpi.
 At 40 LPI that gives 120 images in approx
60 viewing range, or 0.5 per image.
Lenticular stereograms
 By interleaving images from views of a
scene spaced by 0.5, you can achieve a
good 3D image.
 At 1m viewing distance, 0.5 translates to
1cm spacing between images.
 Eye spacing is about 6 cm.
 Diffusers spread collimated (parallel) light
over a specified range of angles.
 Can control viewing angle for a display.
 Gives sense of “presence” in partitioned
Geometric diffusers
 Arrays of tiny lenses (lenticular arrays).
 Can be cylindrical (diffusion in one direction
only), used in rear-projection screens.
 Surface etching. Using in shower glass,
anti-glare plastic coatings.
 Holographic surface etching: provides
tightly-controlled diffusion envelope.
 Low-quality surface finish(!) on plastics
gives diffusion effect.
Lenticular arrays
 Cylindrical arrays
 Diffusion in one direction only, same as the
arrays in lenticular stereograms.
 Used in rear-projection screens.
 Large angle: 30-90
Lenticular arrays
 Spherical arrays diffuse in both directions:
 Large angle: 30-90
 Homogeneous in all directions.
Rough surfaces
 Diffusion depends on the range of angles
on the surface. Surface should be irregular
but not too “sharp”.
 Arbitrary range of diffusion angles. 2-4
typical for anti-glare plastic coatings.
Material diffusers
 Tiny spheres embedded in clear polymer
with different refractive index.
 Can achieve wide range of diffusion angles.
 Simpler to manufacture than most surface
Example: Rear projection screens
 Combination of:
 Rear fresnel lens - concentrates light toward
central viewers
 Front lenticular screen – spreads light
 Diffusing material –
spreads light vertically
(by a smaller angle).
Fresnel prisms
 Similar idea to lenses. Remove the
thickness of the prism and stagger the
surface facets.
 Useful for bending light over a large area,
e.g. for deflecting daylight.
 Also used for vision correction.
An improvisation with Fresnel prisms
 Opposing prism arrays create an array of
TIR mirrors:
An improvisation with Fresnel prisms
 The array creates images of any point on
the opposite side – but only in crosssection. Two crossed arrays create images
in 3D.
An improvisation with Fresnel prisms
 Inverted images are formed in front of the
array, without the distortion effects of lenses.
An improvisation with Fresnel prisms
 Two such pairs invert the
image twice, producing a
right-sided, displaced
 Holograms are based on interference patterns
caused by the fine structure of the hologram.
 Production methods are generally complicated
and require:
A coherent laser light source
Collimating optics
Careful film processing
Lots of trial and error…
 E.g. white-light transmission hologram
setup from
Computer-Generated Holography
 Interestingly, there are many software
packages that can compute “CGH” holograms
(most standard optical CAD packages can do
 One of the simplest and most robust types of
hologram is the “Fraunhofer” hologram. The
hologram is a kind of Fourier transform of the
object. It can be accelerated using efficient
FFT software.
Computer-Generated Holography
 Current printers are at 4800 dpi, or about 5
microns, and produce binary images.
 Turning a printed image into a hologram
requires reduction down to optical
wavelengths (< 1 micron).
 e.g. Photograph with SLR camera with Fuji
“minicopy” film. The negative is the hologram.
Computer-Generated Holography
 Some commercial vendors will print
holograms from an image sequence (movie or
pan-around a fixed object): e.g.
 Remember that light is an electro-magnetic
wave with both electric and magnetic
components normal to its motion.
 Normal light has E (electric) components in all
directions, but it can be polarized under
certain conditions.
Polarization by reflection
Polarization by reflection
 This reflection profile is
typical for other
materials like water or
 Reflected “glare” is
typically mostly
horizontally polarized.
 Vertical polarized
sunglasses eliminate
much of it.
Polarization by absorption
 Dichroic materials exhibit different absorption
for transverse and parallel light polarizations.
The (artificial) polaroid material typically
transmits 80% of parallel light, but only 1% of
transverse light.
Circular Polarization
 Birefringent materials exhibit different
refractive indices (hence velocity) for the two
light polarizations.
 If a birefringent material is the right thickness,
the slower wave can be delayed exactly ¼
 Sending linearly polarized light into this layer
leads to elliptic polarization.
 If the polarizer axis is at 45 to the birefrengent
axis, the light will be circularly polarized.
 More Fresnel optics:
 Lenticular arrays/diffusers
 Prisms
 Diffusers
 Holograms
 Polarization