Classification of Radiation Source (1)

8. Introduction to Displays and
Imaging Systems
Radiation Sources
The origins of radiation:
Bohr’s atomic model:
Nucleus (protons+neutrons), surrounding orbits (electrons)
Electrons absorb energy to reach higher orbits
High  Low energy level + Radiation
Classification of Radiation Source (1)
1. Classification by Flux Output
-- Point source Eg. LED, small filament clear bulb
-- Area source Eg. Frosted light bulb
-- Collimated source Eg. Search light
-- Coherent source Eg. Laser
Classification of Radiation Source (2)
2. Classification by Wavelength and Color (in visible region)
-- Hue (色相) Eg. blue , red , green (color)
-- Saturation (飽和度或彩度) Eg. pink—red with less saturation (purity)
-- Intensity (強度) Eg. flux density of a radiating source
Note : Primary colors : Red (700nm) , Green (546nm) , Blue (440nm)
Note : Chroma (彩色度) : combination of hue and saturation
C=R+G+B , where G , R , B are primary flux component
Classification of Radiation Source (3)
3. Classification by radiation spectrum
-- Continuous spectrum Eg. thermally excited source incandescent bulb)
-- Line spectrum Eg. gas discharge and phosphorescent source (螢光)
-- Single wavelength Eg. source radiated only in a narrow band of wavelength
-- Mono chromatic source Eg. lasers
Classification of Radiation Source (4)
4. Classification by source excitation
-- Thermal excitation Eg. heating (incandescent bulb)
-- Electroluminescence (EL , 場致發光) Eg. LED
--Vacuum fluorescence Eg. CRT , TV tube , X-ray machine
-- Chato-luminescence (閃光發光) Eg. Low pressure gas-filled tube , plasma ,
gas discharge devices
-- Lasing Eg. Electroluminascedce and chemical exciting method
Classification of Radiation Source (4’)
Liquid Crystals
Three types of liquid crystals: Cholesteric, Nematic, and Smectic
Liquid Crystal Display (LCD)
LCD includes light source, liquid crystal, polarizer, color filter (CF), thin film
tansistor (TFT), and so on.
TFT controls orientation of liquid crystal, and
Black Matrix fills in the gap between color
Output Light Intensity Depending on
the Orientation of Liquid Crystal
Colorful Pixel
The pixels are addressed in rows
and columns, reducing the
connection complexity. The
column and row wires attach to
transistor switches, one for each
Controlling color filter to adjust the
transmissions of three primary
colors, one can obtain various colors.
Colorful Pixel (Cont’)
Overall Descriptions of TFT- LCD
TFT-LCD Component
Array/Cell Structure & Equivalent Circuit
Function of TFT Devices
• In the TFT-LCD, TFT
device acts as a switch to
conduct electric current
charging the LC capacitor
and storage capacitor.
• When the TFT device is
turned on, the signal is
written (recorded) into the
LC capacitor. With TFT
turned-off, the signal will
be locked on the LC
capacitor and prevent it
from being leaky.
Passive Matrix Liquid Crystal Display (PMLCD) and
Active Matrix Liquid Crystal Display (AMLCD)
Transmission/voltage Characteristics
Directional Characteristics
Response Time
For passive display (eg: LCD)
, 0  C 1
LB : backgroung luminance(cd/m2 )
Lo : object or source luminance(cd/m2 )
For active display (eg: LED)
, 1 C  
LB : backgroung luminance(cd/m2 )
Lo : object or source luminance(cd/m2 )
Note : To design a display with maximum contrast or contrast ratio
Brightness : Perception of Luminance
Plasma Display
Plasma display panel
Electroluminescent Source
Electroluminescence  Excitation of electron by electric field
+ Dielectric with embedded phosphor
Electroluminescent Source (cont’)
Source luminance is a function of (1) voltage (2) frequency (3) temperature
Eletroluminescent Display
Display cell (pixel) ~ 0.5  0.5mm - 0.25 0.25m m
(resolution : 3 lines/mm)
Number of pixel ~ 65,000 – 250,000 pixels
Electroluminescent dot matrix display
Electroluminescent display panel
Vacuum Fluorescent Source
Vacuum fluorescent 
high-speed electron + phosphor
Vacuum fluorescent display
Cathode Ray Tube (CRT)
Cathode Ray Tube (cont’)
Spatial Light Modulators (SLMs)
Spatial light modulator — SLM can modulate certain properties of wavefront
e.g., amplitude, intensity, phase, or polarization.
SLM  information-bearing element
Two major classes of SLM:
— electrically addressed SLM
— optically addresses SLM
Major applications of SLM:
— electro-optic system
— optical signal processing
— optical interconnection
— optical computing
Magneto-optic Modulators
Faraday effect: rotation of polarization by magnetic field
 = VBd
V: Verdet constant
B: magnetic field
d: travel distance in the medium
Operations of M-O Modulator:
— magneto-optic effect
— electrically addressed SLM
— binary amplitude/phase modulation
— switching speed: ~ 10 ns
— frame rate: 100-300 Hz (256256 pixels)
— spatial resolution: center-to-center distance between pixels 70 m
— contract ratio: 300:[email protected]
— transmittance: 5%
Pockel’s Readout Optical Modulators (PROMs)
Pockel’s effect:
n  E
n: induced birefringence
E: applied electric field
Operations of PROMs:
— Pockel,s effect (linear electro-optic effect) e.g., e-o crystal: BSO
— Optically addressed SLM (inconherent to conherent conversion/wavelength conversion)
— amplitude and phase modulation, and optical logic operation
— writing energy: 5~600 J/cm2
— spatial resolution: 100 lines/mm
— contract ratio: 10,000:1
— write-read-erase cycle: 30 frames/s (at video rate; write and erase times < 1ms)
Liquid Crystal Light Valves (LCLVs)
Operations of LCLV:
— twisted nematic liquid crystal
— optically addressed SLM
— inconherent-to-conherent converter/
wavelength converter
— amplitude and phase modulation
— writing energy: 10 J/cm2
— spatial resolution: 60 lines/mm
— contract ratio: 100:1
— readout time: 10 ms
Liquid Crystal Television (LCTV)
Operations of LCTV:
— twisted nematic liquid crystal (90o)
— electronically addressed SLM
— amplitude and phase modulation
— low cost and programmability
— writing energy: 10 J/cm2
— spatial resolution: (1) 640480 pixels
(2) center-to-center distance between pixels 50 m
— contract ratio: 100:1
— frame rate: 60 Hz
Microchannel Plate Spatial Light Modulators
Operations of LCTV:
— linear electro-optic effect (LiNbO3)
— optically addressed SLM
— inconherent-to-conherent converter/
wavelength converter
— very high sensitivity~30nJ/cm2
— spatial resolution: 20~50 lines/mm
— contract ratio: 1000:1
— writing time: 10 ms
Photoplastic Devices
Operations of photoplastic device:
— Charge  Exposure  Recharge  Develop Erase
— phase modulation/phase grating
— light sensitivity~ J/cm2
— spatial resolution: ~2000 lines/mm
— diffraction efficiency: ~ 10% @60 J/cm2
— lifetime: 300-2000 cycles
Deformable Mirror Array Devices (DMDs)
Operations of DMD:
— micro-mirror deformation
— electrically addressed 2-D phase modulator
— spatial resolution: (1) 128128 ~ 10001000 pixels
(2) 10 lines/mm
— frame rate: ~150 frames/s
— contrast ratio: ~100:1
Optical Disks
Operations of ODs:
— optical discs
— binary phase modulating SLM
— spatial resolution:
track separation: 1.6 m
width of a pit: 0.5~0.7 m
(typically, /NA1.55)
Photorefractive Crystals
Operations of Photorefractive Crystals:
— Photorefractive effect
— E-O crystals e.g., LiNbO3, BaTiO3, SBN
— light induced phase modulation
— refractive index grating:
n  n0(1-e-t/)
: photorefractive response time
n0: maximum refractive index change
t: exposure time
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