Optics and Electronics Flashcards

Optics and Electronics

• Many devices manipulate light, charge, or both.

• Optics: Techniques dealing with light, enabling tasks like recording images (cameras), direct observation (eyes), and detail enhancement (eyeglasses, magnifying glasses).

• Electronics: Techniques dealing with charge, facilitating storage (audio player memory), retrieval (computer), and recreation of sound (amplifier, headphones).

• Advances: Lasers revolutionized optics, and transistors revolutionized electronics, leading to optoelectronics.

• Optoelectronics: A combined field merging optics and electronics.

• Magnifying Glass:

  • Bends light rays inward.

  • Can magnify objects or project images onto surfaces.

Magnifying Glass Camera Experiment

• Objective: Project the image of a bright window onto a wall using a magnifying glass.

• Procedure:

  • Darken the room.

  • Hold the magnifying glass near the wall opposite the window.

  • Adjust the distance between the glass and the wall until a clear, window-shaped pattern of light appears.

• Observations:

  • Images of objects outside the window may also appear; adjust focus accordingly.

  • Images at different distances require adjustments to the lens position to achieve sharp focus.

• Key Questions:

  • How does lens position affect image sharpness?

  • Why can't all images be sharp simultaneously?

  • How do lens features affect image size and orientation?

  • How does blocking part of the lens affect the images?

  • Do objects at different distances form images simultaneously?

Chapter Itinerary

• Common Theme: Concentrating light to form small spots or images.

• Electronics: Representing, storing, manipulating, and using information as charge.

• Systems to be Examined:

  • Cameras: How lenses bend light to form images and their use in photography.

  • Optical Recording and Communication: The role of lasers and novel optical effects.

  • Audio Players: Basic electronic components integrated into computers and audio amplifiers, enabling portable music.

Cameras

• Cameras have simplified significantly since their invention.

• Basic Principle: Lenses project images onto light-sensitive surfaces.

• Key Considerations: Exposure, focus, and motion blur.

• Questions to Consider:

  • Why are camera lenses so complex?

  • How do longer lenses affect perceived distance?

  • What is the function of a camera's aperture?

  • Why do nearsighted and farsighted people need different eyeglasses?

Experiments

• Basic Setup: Use a simple lens (magnifying glass or farsighted eyeglasses) to project an image of a bright lamp onto white paper in a darkened room.

• Observations:

  • The image appears upside down and backwards.

  • The image becomes fuzzy when the lens is moved.

  • Only objects at a specific distance are in focus at any given lens position.

• Experiment 2 – Cardboard with a hole:

  • Procedure: Cover the lens with cardboard, leaving only a small center hole.

  • Observation: The image becomes darker but sharper over a range of distances.

  • Inference: Lens diameter and focus range are related.

Lenses and Real Images

• Real Image: A pattern of light projected in space or on a surface that replicates the original scene.

• Camera Lens: A transparent object that uses refraction to form images.

• Refraction: Bending of light as it passes through the lens (entering and exiting).

• Image Formation: Light from a point on an object converges to a point on the image sensor.

• Image Orientation: Real images formed by a single lens are inverted and backward.

• Converging Lens: Bends light rays toward each other, allowing image formation.

How a Converging Lens Works:

• Upper Ray: A horizontal ray from the flame bends downward as it enters and exits the lens, traveling towards the bottom of the image sensor.

• Lower Ray: A downward ray from the flame bends upward as it enters and exits the lens, traveling horizontally towards the bottom of the image sensor.

• Sharp Image:

  • Achieved only when the lens and sensor are at the correct distance.

  • Blurry if the sensor is too close or too far.

• Object Distance:

  • Distant objects: Light rays are nearly parallel, converging quickly near the lens, resulting in a smaller image.

  • Nearby objects: Light rays diverge rapidly, requiring the lens to bend them more to converge, resulting in a larger image farther from the lens.

• Focusing:

  • Distant and nearby objects cannot be in focus simultaneously.

  • Compromise is possible for acceptable sharpness of multiple objects.

Check Your Understanding #1: Seeing the Lights

• Phenomenon: A magnifying glass held at the right distance above white paper will show an image of overhead lights.

• Explanation: The magnifying glass acts as a converging lens, creating a real image of the room lights by focusing the spreading light onto the paper.

Focusing and Lens Diameter

• Disposable Camera:

  • Simple design: Box with a lens projecting a real image onto the image sensor.

  • Fixed focus: Cannot adjust the distance between the lens and the image sensor.

  • Narrow lens: Small diameter lenses.

• Narrow Lens Benefits:

  • Eliminates the need for focusing.

  • Larger Depth of focus

• Wide Lens:

  • Gathers more light, but requires focusing.

Complex Cameras:

• Wider lenses: gather more light.

• Automatic focus: adjust lens-to-sensor distance.

• Internal diaphragm: Reduces aperture for greater depth of focus.

Lens Aperture: Light vs. Focus

• Narrow Aperture:

  • Imitates simple cameras - everything is almost in focus.

  • Large depth of focus.

  • Requires brighter scenes or longer exposures (less light).

• Wide Aperture:

  • Focusing becomes crucial.

  • Small depth of focus can be used creatively to blur backgrounds in portraits.

Camera Settings:

• Portrait: Sharp image with blurred background.

• Landscape: Sharp focus throughout the scene, requiring long exposures at narrow apertures.

• Sports: Brief exposures, potentially wide apertures, and shallow depth of focus.

Check Your Understanding #2: Portrait Photos

• Observation: Background is blurry in a photograph taken with a wide-open aperture.

• Explanation: Wide aperture makes focusing critical; the background focuses closer to the lens than the subject.

Focal Lengths and f-Numbers

• Focal Length: Distance between the lens and the real image of a very distant object.

  • Short focal length: Produces a small image near the lens.

  • Long focal length: Produces a larger real image on the sensor.

• Normal Lens: Allows objects in your central field of vision to fit onto the image sensor.

• Wide-Angle Lens: Shorter focal length than normal, resulting in a smaller but brighter image.

• Telephoto Lens: Longer focal length than normal, resulting in a larger but dimmer image.
  Object distance: distance between the lens and the object you’re photographing.
  Image distance: the distance between the lens and the real image it forms.

The Lens Equation

• \frac{1}{f} = \frac{1}{o} + \frac{1}{i}

  • Where:

    • f is the focal length of the lens,

    • o is the object distance,

    • i is the image distance.

• Implications:

  • For a distant object, the image distance is approximately equal to the focal length.

  • As the object moves closer, the image distance increases.

  • If the object is too close, no real image is formed.

f-Number

• Definition: Characterizes the brightness of the real image formed.

• Formula:

  • f\text{-number} = \frac{\text{focal length}}{\text{diameter}}

• Impact:

  • Smaller f-numbers indicate brighter images.

  • Increasing lens diameter decreases f-number.

  • Increasing focal length increases f-number.

• Diaphragm: Used to decrease the lens’s aperture and increase its f-number, reducing light but increasing depth of focus.

• Exposure Time: Must be increased as the f-number is doubled to compensate for reduced light.

Improving the Quality of a Camera Lens

• Complex Lens Systems: High-quality lenses consist of multiple elements functioning as a single lens.

• Chromatic Aberration: Different colors of light bend and focus at different distances.

  • Correction: Achieved using multiple lens elements with varying dispersion, forming an achromat.

• Anti-Reflection Coatings: Thin layers on lens elements that minimize reflections, often using interference effects.

• Zoom Lens: Adjusts effective focal length by moving elements, changing the size of the real image.

Check Your Figures #1: The Image of an Apple

• Scenario: The distance from an apple to a converging lens is twice the focal length.

• Where will the image form:
  \frac{1}{f} = \frac{1}{o} + \frac{1}{i}
  \frac{1}{i} = \frac{1}{f} - \frac{1}{o}
  \frac{1}{i} = \frac{1}{f} - \frac{1}{2f}
  \frac{1}{i} = \frac{1}{2f}
  i = 2f

• Answer: Image will form at a distance twice the focal length behind the lens.

Check Your Understanding #3: Bright and Sharp Photographs

• Observation: Sunny days lead to photos with large depth of focus, while dark days result in smaller depths of focus.

• Explanation: Bright conditions allow for smaller apertures with a greater depth of focus and vice versa.

Zoom Lenses

• 3 Groups of Lens Elements:

  • Group 1: Forms the first image.

  • Group 2: Forms a second image of the first image.

  • Group 3: Projects the third, real image onto the image sensor.

• Zoom process: Altering spacing between lens groups to vary object and image distances, changing image sizes.

Check Your Understanding #4: Not Such a Good Picture

• Scenario: Real image of a fluorescent light has blurry corners and rainbow colors.

• Explanation: The magnifying glass has chromatic aberration, spherical aberration, coma, and astigmatism.

Viewfinders and Virtual Images

• SLR (Single Lens Reflex) Cameras:

  • Allow lens changes to optimize for specific tasks.

  • Viewfinder displays the real image that will be projected onto the image sensor.

• Eyepiece Lens:

  • Forms a virtual image because the object distance is less than the lens’s focal length.

  • Magnifies the image, covering a wider portion of the field of vision.

• Fixed Lens Cameras:

  • Use electronic or optical viewfinders.

  • Optical viewfinders use lenses, mirrors, and prisms to produce a real-image; this real image is examined through a magnifying lens.

Check Your Understanding #5: Real and Virtual Images

• Observation: As a magnifying glass moves closer, an inverted image appears, becomes blurry, then an upright image appears.

• Explanation: The lens initially creates a real image near the eye, then a virtual image on the photograph's side of the lens.

Image Sensors

• Function: Record the light pattern projected by the lens.

• Mechanism: Both film and electronic image sensors use semiconductors to detect light when photons shift electrons.

• Photographic Film:

  • Silver halide crystals: Sensitive to light; when a photon strikes a crystal, it can free a silver atom.

  • Development: Silver particles transform entire silver halide crystals into metallic silver, forming a negative image.

• Color Photography:
  *Silver halide crystals are exposed to light through color filters, so that the film separately records its exposure to the three primary colors of light.

• Electronic Image Sensors:

  • Photodiodes: Diodes optimized to detect light and record the pattern of light in the real image.

  • Color information: Achieved by covering photodiodes with red, green, and blue filters.

Check Your Understanding #6: Foggy Photos

• Airport Screening:

  • Use X-rays to search for hidden items. Can damage film. How?

• Answer:

  • X-rays cause radiative transitions in the silver salt crystals and responds as though it was exposed to visible light.

Eyes and Eyeglasses

• Eye Structure: Lens and image sensor (retina).

• Focusing: The lens focuses real images on the retina by adjusting its focal length.

• Iris: Controls the amount of light entering the eye.

• Vision Correction:

  • Techniques: Laser surgery or eyeglasses/contact lenses.

  • Goal: Reshape and improve corneal surface to produce clear images.

• Farsightedness (Hyperopia):

  • Cause: Lens system has too long a focal length, the real images of nearby object focus too far away from the front of her eye

  • Correction: Converging lenses in eyeglasses shift the real image forward, focusing it correctly on the retina.

• Nearsightedness (Myopia):

  • Cause: Lens system has too short a focal length

  • Correction: Diverging lenses in eyeglasses create a virtual image closer to the eye, which the eye can then focus on the retina.

• Diverging Lens: Bends light rays apart, has a negative focal length, and is thinner in the middle than at the edges.

Check Your Understanding #7: Keeping Up Your Image

• Question:

  • eyeglasses of a farsighted person can project a real image of a distant scene on a white wall. However, the eyeglasses of a nearsighted person produce no real image. Why not?

• Answer:

  • Nearsighted eyeglasses use diverging lenses, which bend light rays apart and don’t focus them together into a real image.

Optical Recording and Communication

• CD/DVD store representations of sound and light that it can use to recreate them on demand.

Representing sound and light

• Radio Wave Analogy:

  • Sound waves (density fluctuations in air) are represented analogously by changes in the amplitude (AM) or frequency (FM) of a radio wave.
    Analog Representation: A continuously variable physical quantity (radio wave) represents another (air density).
    Digital Representations a continuously variable physical quantity is first represented by a series of numbers, and then each of those numbers is represented by a set of physical quantities—a set of digits—each of which can have only a limited number of discrete values.

• Digital Representation:
  *Symbol: discrete physical qualities
  Binary uses 2 numbers
  Decimal uses 10
  binary is use full due to its ease of differentiating the too numbers
  Disadvantages of Analog:
  No noisy, any changes in physical quantity
  Advantage of Digital:
  Not noisy, dust and other imperfections have no effect on digital representations as long as the symbols can still be distinguished
  Extra symbols can be incorporated into the digital representation to correct for such reading errors

• Usefulness of Binary: Easier to work with 2 symbols (shiny/dull, charged/uncharged) than 10.

Check Your Understanding #1: New Math

• Question: What number does binary 10000001 represent?

• Answer: One hundred twenty-nine.

• Explanation:

  • It contains only 1 one hundred twenty-eight (27) and 1 one (20).

  • Since 128 1 1 is 129, that is the number represented by this binary value.

Digital Recording

• Audio Channels 2 on CD, independent

• Measurements: 44,100 times per second in CDs, recorded in binary form with 16 bits per measurement, positive and negative integers from 232,768 to 32,767.

• Audio DVDs can choose from several measurement rates,

• Audio DVDs can have multiple channels

• DVDs usually use compressed data

• CDs usually do not

• Encoding: Numbers are extensively reorganized before storage, allows reproduction even with disc damage.

• Redundancy: Information is duplicated so even if one copy is illegible, it can still be recreated.
  Damage that occurs along an arc is far more threanting than damage that occurs from center to edge of disk

The Structure of CDs and DVDs

• Standard Size: 120 mm diameter, 1.2 mm thick.

• CD: Clear on one side, sandwich of aluminum film, protective lacquer, and printed label on the other.

• DVD: Laminated from two 0.6 mm plastic discs with one, two, or four reflective layers.

Multiple layerts stacked in the between

Check Your Understanding #2: Cordless Clarity Away from Home

Cell phones transmit your voice in digital form. In general terms, how does this digital transmission work?
Your cell phone’s microphone converts the sound of your voice into a fluctuating current. This current is measured periodically and represented as a sequence of numbers. These numbers are then represented by radio waves and transmitted through space. The numbers eventually work their way to a receiving cell phone, where the radio waves are converted back into numbers and the num- bers are converted back into a fluctuating current. Finally, the current is amplified and sent through a speaker to create sound.

• More layers mean more information

• Layers so thin that they transmit some light

• Gold and Silicon layers are semitransparent

• Aluminum layers are mostly reflective
  Tiny Microscopic Pits Record Dat

• Track is a series of microscopic pits, as short as 0.83 μm long on a CD or 0.40 μm long on a DVD.

• The lengths of the pits and the flat “lands” that separate them represent numbers.
  Electromagnetic wave limit the disc due to not bieng able to detect things smaller tan wave length
  Laser and index of refraction affect size of wavelength
  The player detects a pit by bouncing light from the disc and determining how much of it reflects
  *light needs to interfere distructively
  Blu-ray players and discs, which first appeared in 2006, are based on a 405-nm laser.
  *Smaller wave length = smaller surface for ray, store more info

Check Your Understanding #3: The Blue-Light Special

Blu-ray disc players use blue lasers with a wavelength of 405 nm in air or vacuum. A CD player uses an infrared laser with a wavelength of 780 nm. How must the pit depths in the reflective layer of a Blu-ray disc compare to the pit depths in a CD?
*Answer: The pits in a Blu-ray disc must be about half as deep as those in a CD.
*Explanation: The pits in the reflective layer should be about a quarter of a wavelength deep so that light reflected from the bottom of a pit interferes destructively with light reflected from an adjacent flat region. Halving the wavelength of the laser light requires halving the depth of the pits to achieve destructive interference.

The Optical System of a CD or DVD Player
must measure the lenses
must follow track(automatic
autofocus
must be able to adjust based on the disc
laser diode= passes through several optical elements, reflects
special mirror = polarization beam splitter
measure the currents flowing through the detectors

laser diode = passes through through the beam splitter

• Beam splitter analyzes the light’s polarization and is applied with a special coating
  Light is diffracted and the beam is split due to being shined through such a small opening; the smaller the opening the worse is the speading.

Collimating used to stop the speading
Maintains constant diameter
Then passes through quater wave plate
*converts horizontally polarized light into vertically polarized light
ncircularly polarized light, the electric field actually rotates about the direction in which the light is traveling
The Plastic: 0.5mm thick
spot roughly 1 wavelength in diameter
beam waistis limited is limited, cannot be smaller than wavelength. Optical element are built and designed and fabrication, system does ad weel as it can
all these things is another examplle of diffraction, optical systen is diffraction limmilted
Then stikes photodiodes that use the reflection light intensity
Check Your Understanding #4::
that why there calle Laser Disc, its must be coherent so it can be focused
Optical Fibers guide light from 1 place to another.
two different glasses: a solid core of one glass surrounded by a cladding of the other glass
total internal reflection to refl ect perfectively
light tries to move from the inner glass core to the outer glass cladding, it’s reflected perfectly and thus can’t escape
light encounters the boundary between two materials with different indices of refraction, refraction causes that light to bend (Fig. 14.2.5). If the material it enters has a smaller index of refraction than the one it leaves, the light bends away from a line perpendicular to the boundary. The amount of this bend depends on the two indices of refraction and on the angle at which the light approaches the boundary. As long as the approach angle is steep enough, light will succee

Multi path: = pulse of stretching. Time is limited on fibers, gradedindex- multimode fiber
Check Your Understanding #5: When you look into an aquarium
surface has total internal reflecjtion
optical transmitter 1550nm= short pulse
optical fi ber, a lens and focused onto the receiver’s photodiode
erbium-doped fiber amplifiers (EDFAs), the amplifier duplicates photons and brightens the pulses
wavelength-division multiplexing -allows one fiber to carry far more information
Check Your Understanding #6 Why can’t you amplify at the end.
light weakens gradually as it passes through a long optical fiber, The glass absorbs many of these photons during their long passage through a fi ber, so they must be amplifi ed before their numbers become so small that there’s a chance that none of them makes it at all.

audio Players

Transiitors 1948 made electronics much
The drain and the source consist of a strongly doped n-type semiconductor. The MOSFET is effectively Off.
However, if more electrons could be coaxed into the channel somehow, those electrons would have to go into the channel’s conduction levels
Drawing extra electrons into the channel is the task of the metal-like gate.
*n-channel MOSFET’s name. N-channel refers to
*Metal-oxide-semiconducto
Check Your Understanding #1:
power and control
Enlarging the transistor and needing the positive charge to go with it
Storing digital sound information
Air and or music

RAM memory

Dynamic: charge will leak
Volatile -lose contents
Flash like Dynamic because each is stored with A MOSFET
Floating gate cannot can be removed until high currents applied
Magnetic disk have been high tech with lots of bits
Check Your Understanding #2