Transcript General Introduction of Optical

General Introduction of
Optical-electrical Information
Wu Lan
The purpose of this lesson
 Understanding the basic principals,
concepts, formulas, terms and applications
in optical engineering
 Improve the ability of professional English:
Reading, Listening, speaking, writing &
professional vocabulary
 Get the credits for your academic degree
Contents of this lesson
 Optical systems
 System evaluation
 Fiber optics
 Optical date processing
 Holography
 Light source and detectors
 Laser
 Image process
Requirements
 Read the text before and after the class
 Take necessary notes in the class
 Bring a dictionary with you in the class
 Finish the homework in English
 Be active in the class
 Small test or works in the class
 Examination in English
 Hope all of you to pass the final examination!!!!
Chapter 1
Optical system
 Information / knowledge
optical information ---- 80%
reading, watching, ...
vocal information: voice, acoustics
feeling information: sensors
touching, tasting, smelling
sixth sense
A power of perception seemingly independent of the
five senses; keen intuition
Men can not only see through naked eye, but also get visual
information with the aid of
tools
Optical System
The first important stage to get the visual information
 Optical information
image:
light modulation: encode and decode
light intensity:
light position:
light pattern: space:interference fringes
time: manipulate in phase
Optical information  other information
Temperature,distance, speed, position,voice
Modern optical system
Information
Optical
System
Photo-electric
Sensor
A/D
Computer Digital
processing
Fiber networks
light source
Analog Processing
Optical Processing
Out put
1.1 Telescope
1. Astronomical telescope (Kepler’s telescope)
Objective
Eyepiece
Air image
Intermidiate image
Infinite
object
Retina
Eye
fo
-fe
d
Two converging lenses
Object is at infinity, a air image in the right-hand focal plane of objective
Left-hand focal plane of the eyelens is the same with the right-hand
focal plane –afocal mode, Separation distance d=fo+fe
A real image on the retina
Practical mode: accommodation
Objective
Instrument myopia
Eyepiece
d
Infinite
object
Retina
Eye
fo
-fe
distict vision distance
Instrument
myopia
250mm
 Let the air image move inside the focal length of the eyepiece--defocus
 the air image is seen at the distance of most distinct vision, 25cm in
front of the eye
 virtual image, invert image
 d<fo+fe
2. Magnification
angular magnification
M telescope 
Angular size of image tan  '

Angular size of object tan 
h
D
in afocal mode:
θ
-y'
fo
 y'
tan  
,
fO
 y'
tan  ' 
fE
M telescope  
-fe
fO
fE
θ'
Magnification:
f O EP
M telescope  

f E XP
The minus sign means that image is inverted
EP(Entrance Pupil)
XP(Exit Pupil)
fo
-fe
Eye Relief
 Parallel rays enter the objective next to uppers
 Go through F, emerge from the eyepiece again parallel to
the axis
EP
XP

fO  f E
A Easy way to know the M of a Kepler’s Telescope
 Place a square aperture of know size in front of the
objective
 Aim the telescope at the sky or some other diffuse
target
 Hold a sheet of paper a short distance behind the
eyepiece and move it back and forth until the aperture
is in focus
 Measure the size of the image

size of the aperture
M Telescope 
size of its image
3. Specification of a telescope
Magnification × Entrance Pupil (mm)
Example: 6X30 : M=6 EP=30mm —> XP=EP/M=5mm
8X21 : M=8 EP=21mm
10X25: M=10 EP=25mm
10X50: M=10 EP=50mm
Limits to the Magnification:
hand shake for binocular: M< 10
diffraction limit: —> increase the EP in astronomical
telescope
4. Eyepiece
Vignetting: Light that can pass the objective but can
not reach the eyepiece!
Eyepiece
Vignetting
Field Lens
Field Lens: No effect on Magnification
 direct all rays passing through the last lens
 reduce vignetting; increase the field of view
 Hugens Eyepiece
fF  2 fE
1
d  ( fF  fE )
2
 Kellner Eyepiece
Huygens
Eyepiece
Field Lens
Eye lens
d
Aberrations:
Spherical aberration
chromatic aberration — achromatic
Coma
Astigmatism
Curvature — planoscopic
distortion — orthoscopic
 Erfle Eyepiece
high qulity
for astronomical telescope
Kellner
Eyepiece
Achromatic lens
Cemented
doublet
Field Lens
Eye lens
d
Erfle
Eyepiece
Field Lens
Eye lens
d
5. Terrestrial telescope
terrene: on the land, erect image
erecting system:
 Lens erector: rifle telescope
 Prism erector: prism binocular
 Galilean telescope
Porro prisms
x
Pechan Prisms
z
y
x
z
z
y
x
y
z
x
6. Galileo’s telescope
Galileo Galilei — Italian scientist
Positive
objective
Negative
eyepiece
F
d
-fe
fo
d  fO  (  f E )  fO  f E
M 
fO
fE
 Upright image
 Low magnification: 2.5×~3.0×
Reason: Exit pupil is at the left side of eyepiece
 Short, opera glasses
7.Example
Design a hunting rifle telescope(Kepler’s)
Exit pupil: iris pupil: 2~8mm, 3.75mm -- for daylight aiming
Magnification: 8× ; EP=8×3.75=30mm
Suppose: fO  120mm
then: f E  fO / M  120 / 8  15mm
From Gauss thin lens equation:
1 1 1
 
s' s f '
EP(Entrance Pupil)
XP(Exit Pupil)
Exit pupil position:
sf E
 (120  15) 15
s' 

 16.9mm
s  f E  (120  15)  15
Too short, difficult for aiming
fo
fe
Eye Relief
Erecting system:provide some magnification
then f E  30mm
set
M=2X,
f  32mm
For erector: s' / s  2
We get:
32 s
 2s 
s  32
EP(Entrance Pupil)
s  48mm
s'  96mm
XP(Exit Pupil)
Erector
Eye Relief
fo=120
s=48
s'=96
Image of EP through erector:
fe=30
 (120  48)  32
s1 ' 
 39.5mm
 (120  48)  32
XP through eyepiece: s2 '   (96  30  39.5)  30  45.9mm
 (96  30  39.5)  30
1.2 Microscope
Microscope: viewing small objects
Telescope: viewing distant objects
 Three goals:
 produce a magnified image of the specimen,
 separate the details in the image,
 render the details visible to the human eye or camera.
 Multiple-lens
designs with objectives and
condensers (compound)
 Simple single lens devices that are often handheld, such as a magnifying glass.
Compound Microscope
 Lens closest to the object:objective.
 Light from condenser, forms light cone
concentrated
onto
the
object
(specimen).
 Light passes through the specimen and
into the objective
 projects a real, inverted, and
magnified image of the specimen to
a fixed plane within the microscope:
intermediate image plane
Compound Microscope
 The objective: gathers light from each of
the various parts or points of the
specimen.
 focused close enough to the specimen so
that it will project a magnified, real image up
into the body tube.
 Distance between the back focal plane
of the objective and the intermediate
image is termed the optical tube length.
 mechanical tube length: distance between
the nosepiece (where the objective is
mounted) to the top edge of the observation
tubes where the eyepieces (oculars) are
inserted.
Compound Microscope
 Eyepiece or ocular: fits into the body
tube at the upper end
 Further magnifies the real image projected by
the objective.
 Eye of observer sees magnified image
as if it were at a distance of 10 inches
(25 centimeters) from the eye
 virtual image appears as if it were near the
base of the microscope.
 Photomicrography: enlarged real image
projected by the objective.
 projected on the photographic film in a
camera or upon a screen held above the
eyepiece.
1.Magnification of microscope
-T
y
Fo'
Fe
Fo
-y'
fo
Objective Magnification:
-fe
MO 
Eyepiece magnification: M e 
Total Magnification:
 y'
T

y
fO
tan  '  y ' / f e
250


tan   y ' / 250 f e (mm)
M microscope  M O  M e  
250  T
fO  fe
Image formation on Retina
do~25cm
Microscopy: History
Simple
Compound
Microscopy: History
Microscopy: History
Microscopy: Importance

Biomedical sciences: overall morphological features of specimens;
quantitative tool
 advances in fluorochrome stains and monoclonal antibody
techniques: explosive growth in the use of fluorescence microscopy
in both biomedical analysis and cell biology.
 optical microscope is most important in biomedical optic

Explosive growth in physical and materials sciences; semiconductor
industry,
 observe surface features of high-tech materials and integrated
circuits

Forensic scientists: hairs, fibers, clothing, blood stains, bullets, and other
items associated with crimes
Microscopy: Importance

Differences between biomedical and materials microscopy involves how
the microscope projects light onto the sample.
 Classical biological microscope: thin specimen; light is transmitted
through the sample, focused with the objective and then passed into
the eyepieces of the microscope. Diascopic
 For surface of integrated circuits: light passed through the objective
and is then reflected from the surface of the sample and into the
microscope objective. Episcopic

Biggest Problem in microscopy: poor contrast
 Light passed through very thin specimens or reflected from surfaces
with a high degree of reflectivity.
 Optical "tricks" to increase contrast: polarized light, phase contrast
imaging, differential interference contrast, fluorescence illumination,
darkfield illumination, Rheinberg illumination, Hoffman modulation
contrast, and the use of optical filters.
2.Derive the magnification of Microscope from telescope
lens A
f
-T
lens L
θ'
B
-S'
θ
fL
-f A
-f E
Before adding lens A, The system is a telescope, the object is in distant
M telescope  tan  ' / tan 
After adding lens A, and moving the object B to the focal point of lens A,
the intermediate image -S’ remain to be the same: M microscope  tan  ' /( B / 250)
M
tan 
 S'/ f
250 S '
250
then:
250
250 f




m
Mt
L
( B / 250)
B / 250
The combination of Lens A and L:
Mm 
Bf L
Mm  
fA
fA
 MT 
1
1
1
d



,
f
f A fL f A fL
250 f L 1 1
250 f L  f
250  T
(  )


fE
f fL
fE
f
fE f
fA

L
fE
d 0
3.Example
Microscope for visual observation, for photography
Conditions: f  16mm; T  160mm; M  12.5 
photographic film is 60mm away from the eyepiece
O
E
Question: How much must the tube of microscope raised or lowered?
250mm
Solution:
fE 
 20mm
12.5
from the Gauss thin lens equation
for the eyepiece:
for the objective:
sE 
1 1 1
 
s' f s
s' f E
(60)( 20)

 30mm
f E  s ' 20  60
sv 
s' f O
(16  160)(16)

 17.6mm
f O  s ' 16  (16  160)
sp 
(16  160  10)(16)
 17.7mm
16  (16  160  10)
The tube must raised:
17.7 17.6  0.1mm
4.Numerical Aperture
NA  n0 sin I
no: The index of the medium between cover glass and the
front lens of objective
I : The angle of total reflection at the glass-air boundary of
the cover
with air:
with oil:
no  1.0;
I1
NA  1.0
no  1.2, 1.5, 1.6 ...
NA  1.0
I2
objective
oil
cover glass
Brighter and better image
Numerical Aperture
Measure of light gathering power
Lenses;microscope objectives (where n may not be 1);optical
fibers …
N. A. = n sin α
Lens
Air
Oil
αo
α g’ α g
αa
ng
Cover Glass
O
Collection Efficiency Revisited
Which lens collects more light?
f = 10 mm
f = 10 mm
Rule of thumb:
Useful magnificat ion  600 NA
It is easy to go beyond this limit by
Using a higher-power eyepiece
projecting the image on a distance screen
result is merely a larger image but not the disclosure of
more detail
if:
M  600NA
then it is the empty magnification
diffraction limits the maximum M
1.3 Camera Lenses
The F/#
f
f /# 
D
•referred to as the “f-number” or speed
•measure of the collection efficiency of a system
•smaller f/# implies higher collected flux:
• f or D decreases the flux area
• f or  D increases the flux area
F/# and NA
1
NA 
2 F /#
In many cases, the best coupling you can get occurs when
you match the f/# between optical systems.
Realistic f/#’s:
lens ~ 2
fibers ~ 1.5
1.Single lens
 sixteenth century--biconvex lens
suffers from every types of aberration
No use
 eighteenth century--meniscus lens:
• concave side facing object
• an aperture stop in front of it,
• has not much astigmatism or coma
• spherical and chromatic aberration, distortion, and curvature of
field are still severe
• aperture can be no larger than f/16
• slight improvement : using an achromatic meniscus, called
“landscape lens.”
 twentieth century--aspherical plastic meniscus
• correction: spherical aberration
• control: chromatic aberration, coma, astigmatism
• left: curvature of field, distortion
• F number: f/D’=10~11
2. Rapid rectilinear lens
combination of two achromatic menisci, concave side
facing each other
symmetrical structure: control coma, distortion
cemented doublet: chromatic aberration
considerable spherical aberration, astigmatism or
curvature of field
F number: f/D’=8.0
3.Double Gauss type
 F number: f/D’=1.2~1.4
 good correction for:
spherical aberration, coma,
chromatic aberration, astigmatism, curvature, distortion
 standard lens for SLR(Single Lens Reflex) camera.
4.Taylor-Cooke triplet
 F number: f/D’=4.0~5.6
 Good correction for: spherical aberration, chromatic
aberration
 Good reduction for: coma, astigmatism, distortion,
curvature of field
 Zeiss Tessar
F number: f/D’=2.8
Excellent for aberration correction
4. Tele-photo lens, wide-angle lens
Standard lens: f~diagonal of the film
35mm film: d  242  362  43.3mm
Standard lens: f=35~58mm
Tele-photo lens: f>58mm
Wide-angle lens: f<35mm
Fisheye(sky lens): f<10mm
Field of view: 160º
6. Zoom lens
 derived from the Cook triplet’s structure
 Lens moving in the nonlinear way
controlled by cams or slots
cut into rotatable cylinder.
 Lagrange invariant
nyu=constant
n—reflective index
y—image size
u—slope angle of marginal ray
u↑ → y↓ , u ↓ → y ↑
 Aberration correction:
correction the aberration for each group
7.Example
A telephoto camera lens in the form of Galiean telescope
type
f 2  25mm, d  30mm
Condition: f1  50mm,
Questions: (a) The focal length
(b) The actural physical length of camera
Solution:
f1 f 2
( 50)( 25)

 250mm
f1  f 2  d
 50  25  30
(a)
f 
(b)
vBV h' f1  d
 
f
h
f1
vBV  f 
VBV
H'
h
h
f1  d
50  30
 250 
 100mm
f1
50
The physical length = 100+30 = 130 mm
h'
Film
plane
d
f1
f
Homework
Problem: 1, 2, 4, 5, 7, 10