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

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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

A power of perception seemingly independent of the five senses; keen intuition

sixth sense

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 informationTemperature,distance, speed, position,voice

Modern optical system

InformationOpticalSystem

Photo-electric Sensor

Analog Processing

Optical Processing

A/DComputer Digital processing

Fiber networks

light source

Out put

1.1 Telescope

1. Astronomical telescope (Kepler’s telescope)

Intermidiate imageInfiniteobject

fo -feEye

ObjectiveEyepiece

Air imageRetina

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 foca

l plane –afocal mode, Separation distance d=fo+fe

A real image on the retina

Practical mode: accommodation

Infiniteobject

distict vision distance

fo-fe

250mm

Instrumentmyopia

Eye

Retina

Objective Eyepieced

Instrument myopia

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 fr

ont of the eye

virtual image, invert image

d<fo+fe

2. Magnification

angular magnification

in afocal mode:

tan

'tan

objectofsizeAngular

imageofsizeAngularM telescope

EO f

y

f

y ''tan,

'tan

fo -fe

-y'θ θ '

E

Otelescope f

fM

h

D

Magnification:

The minus sign means that image is inverted

XP

EP

f

fM

E

Otelescope

EP(Entrance Pupil) XP(Exit Pupil)

Eye Relief-fefo

Parallel rays enter the objective next to uppers

Go through F, emerge from the eyepiece again parallel to

the axis

EO f

XP

f

EP

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

imageitsofsize

aperturetheofsizeMTelescope

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 n

ot reach the eyepiece!

VignettingField Lens

Eyepiece

Field Lens: No effectNo effect on Magnification

direct all rays passing through the last lens

reduce vignetting; increase the field of view

Hugens Eyepiece

Kellner EyepieceAberrations:Spherical aberration chromatic aberration — achromaticComaAstigmatismCurvature — planoscopic distortion — orthoscopic

Erfle Eyepiece high qulity for astronomical telescope

EF ff 2 )(2

1EF ffd

Field Lens

Huygens Eyepiece

Eye lens

d

Field Lens

Erfle Eyepiece

Eye lensd

Field Lens

Kellner Eyepiece

Eye lensd

Achromatic lens

Cemented doublet

5. Terrestrial telescope terrene: on the land, erect image

erecting system: Lens erector: rifle telescope Prism erector: prism binocular Galilean telescope

Porro prisms Pechan Prisms

x z

z

x

y

x

y

zz

x

y

6. Galileo’s telescope Galileo Galilei — Italian scientist

Upright image Low magnification: 2.5×~3.0×

Reason: Exit pupil is at the left side of eyepiece Short, opera glasses

-fe

fo

d

F

Positive objective Negative

eyepiece

EOEO ffffd )(E

O

f

fM

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: then:

From Gauss thin lens equation:

Exit pupil position:

Too short, difficult for aiming

mmfO 120 mmMff OE 158/120/

'

11

'

1

fss

mmfs

sfs

E

E 9.1615)15120(

15)15120('

EP(Entrance Pupil) XP(Exit Pupil)

Eye Relieffo fe

Erecting system:provide some magnification M=2X, then set

For erector: We get:

Image of EP through erector:

XP through eyepiece:

mmf 32mmfE 30

2/' ss

mms 5.3932)48120(

32)48120('1

mms

mms

96'

48

EP(Entrance Pupil) XP(Exit Pupil)

Eye Relieffe=30s'=96s=48fo=120

Erector

32

322

s

ss

mms 9.4530)5.393096(

30)5.393096('2

1.2 MicroscopeMicroscope: viewing small objectsTelescope: 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 hand-held, 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 objectiveprojects 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

Objective Magnification:

Eyepiece magnification:

Total Magnification:

-fefo

-T

y

Fo

Fo' Fe

-y'

OO f

T

y

yM

'

)(

250

250/'

/'

tan

'tan

mmfy

fyM

e

ee

eOeOmicroscope ff

TMMM

250

Image formation on Retina

do~25cm

Microscopy: History

Simple Compound

Microscopy: History

Microscopy: History

Microscopy: Importance Biomedical sciences: overall morphological features of specimens; quant

itative tool advances in fluorochrome stains and monoclonal antibody technique

s: 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 circuit

s

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 th

rough 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 im

aging, 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

Before adding lens A, The system is a telescope, the object is in distant

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:

then:

The combination of Lens A and L:

fL

f

-f A

-T

B

θ

θ '

lens Alens L

-S'

-f E

tan/'tantelescopeM

)250//('tan BM microscope

AL

L

t

m

fBf

S

B

fS

BM

M 250'250

250/

/'

)250/(

tan

E

L

AT

Am f

f

fM

fM

250250

0,111

dff

d

fff LALA

ff

T

f

ff

ffff

fM

E

L

ELE

Lm

250250)

11(

250

3.ExampleMicroscope for visual observation, for photography

Conditions:

photographic film is 60mm away from the eyepiece

Question: How much must the tube of microscope raised or lowered?

Solution:

from the Gauss thin lens equation

for the eyepiece:

for the objective:

The tube must raised:

5.12;160;16 EO MmmTmmf

mmmm

fE 205.12

250

mmsf

fss

E

EE 30

6020

)20)(60(

'

'

sfs

11

'

1

mmsf

fss

O

Ov 6.17

)16016(16

)16)(16016(

'

'

mmsp 7.17)1016016(16

)16)(1016016(

mm1.06.177.17

4.Numerical Aperture

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:

InNA sin0

1I2I

glasscover

objective

oil

0.1;0.1 NAno

0.1...6.1,5.1,2.1 NAno

Brighter and better image

Numerical Aperture

Measure of light gathering powerMeasure of light gathering power

Lenses;microscope objectives (where n may not be 1);optical

fibers …

Cover GlassCover Glass

ααgg

ααaa

AirAirOilOil

ααgg’’ααoo

nngg

N. A. = n sin N. A. = n sin αα

LensLens

OO

Collection Efficiency RevisitedWhich lens collects more light?

D =

5 m

mD

= 1

0 m

m

f = 10 mm

f = 10 mm

Rule of thumb:

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:

then it is the empty magnification

NA600M

NA600ionmagnificat Useful

diffraction limits the maximum M

1.3 Camera Lenses

The F/#

D

ff /#

•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

/#2

1

FNA

In many cases, the best coupling you can get occurs when you match the f/# between optical systems.

Realistic f/#’s: lens ~ 2fibers ~ 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 fi

eld are still severe • aperture can be no larger than f/16• slight improvement : using an achromatic meniscus, called “land

scape 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 typeF 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 tripletF number: f/D’=4.0~5.6Good correction for: spherical aberration, chromatic

aberrationGood 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: Standard lens: f=35~58mm Tele-photo lens: f>58mm Wide-angle lens: f<35mm Fisheye(sky lens): f<10mm Field of view: 160º

mmd 3.433624 22

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.ExampleA telephoto camera lens in the form of Galiean telescope t

ype

Condition:

Questions: (a) The focal length

(b) The actural physical length of camera

Solution:

(a)

(b)

The physical length = 100+30 = 130 mm

mmdmmfmmf 30,25,50 21

mmdff

fff 250

302550

)25)(50(

21

21

1

1'

f

df

h

h

f

vBV

mmf

dffvBV 100

50

3050250

1

1

VBV

Film plane

d

f 1

f

h h h'

H'

Homework

Problem: 1, 2, 4, 5, 7, 10