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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 250S ' 250 then: 250 250 f L 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 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