Fiber Optics By Susan Wirsig

Transcription

1 Fiber Optics

2 Fiber Optics By Susan Wirsig Abstract Students learn the principles of buoyancy by building small divers in 2-liter soda bottles. Equipment 1. 2-Liter Soda Bottles w/cap 2. Pippettes 3. Hex Nuts 4. Hot Glue Gun 5. Electrical Wire 6. Scissors 7. Small Cup of Water Grade Level This activity is suitable for Elementary and Middle School Students State Standards Met Standard 1 Analysis, Inquiry, and Design Standard 4 Physical Setting and Living Environment

3 What Is It and What Is It Used For? Optical fibers were invented in They are extremely thin, wire-like threads made of glass. These wires are about the same diameter as a strand of your hair! Even though optical fiber is made of glass, it is extremely strong - stronger than steel. Fiber optics is the latest tool used in communication systems (telephones, computers, etc.). It uses light to transmit information over fiber optic cables instead of using electricity to transmit information over copper wires, which is the current method of transmitting information. Since light travels much faster than electricity, fiber optics is becoming very popular in the communications industry. Fiber optics is also being used in the medical industry. Doctors often use an instrument called an endoscope to look inside the human body without cutting it open. Endoscopes are narrow tubes containing optical fibers that can be inserted into a person s mouth and throat. Light shines inside and pictures are sent back for the doctors to study. 1

4 What Does It Look Like and How Is It Made? Fiber optic cables consist of a center core and an outside cladding. The core contains many threads of optical fibers bound together around a steel (or sometimes plastic) cable. The cladding is like a protective coat layered with aluminum, Kevlar (a nylon fiber), and polyethylene (a plastic). The cladding also minimizes light pulses from becoming weak as it travels long distances. Optical fibers are made in very clean rooms. The air in these rooms is filtered to remove as much dirt as possible. Optical fibers are made using a process known as modified chemical vapor deposition (MCVD). During this process, a hollow glass tube is placed on a rotating machine. As the glass rotates, it is heated by a torch that moves back and forth until the glass reaches 1600 degrees C. While the glass is heating, a special gas is pumped inside the tube which deposits a thin layer along the inside wall of the tube. The gas is then removed from the tube and the torch is heated to 2000 degrees C. The glass tube then collapses to form a solid glass rod. If the rod is flawless, it is reheated in a special furnace to 2200 degrees C. At this temperature, the rod melts and is then drawn into a hair like thin optical fiber up to 6 miles long. Properties of Glass 2

5 Almost all matter on Earth can be classified into one of three main states of matter: Solid, Liquid, or Gas. However, glass is an exception. Glass is both a solid and a liquid. Like other solids, glass has a definite shape and definite volume. However, in most solids, the atoms are organized in tidy, repeating patterns called crystals. Glass atoms are free flowing and not specifically organized, much like the way atoms are organized in a liquid. This disorganized arrangement of atoms gives glass some useful properties: 1. It is easy to form into different shapes. 2. It is good at dissolving other substances. Ordinary glass consists of a chemical called silicon dioxide. Quarts and beach sand are also silicon dioxide, but the atoms are in a crystal arrangement in these materials. Perfectly clear glass is used to create optical fibers for data communication. Since the glass does not have any impurities, information can be sent through optical fibers (bendable strips of glass the diameter of a human hair and miles long) as pulses of light. That means that information can travel around the world at the speed of light in glass ( km / second). 3

6 How does Fiber Optic Communication Work? Fiber-optic communications systems use pulses of light to carry information. For example, if you are typing in a message on your computer to send to a friend on the other side of the world the following steps occur: 1. As you type in your message an encoder inside the computer converts the text into binary code which is stored as electrical information. It is then converted to light pluses at the phone company. Binary code uses only two signals or digits. Zero represents when the light pulse is OFF and one represents when the light pulse is ON. 2. These light pulses travel along glass fiber optical cable at the speed of light. 3. At the receiving end, the pulses of laser light are converted back into electrical signals before they reach your friend s computer. When the electrical signals reach your friend s computer it goes through a decoder. This device converts the binary code into text. 4

7 Before fiber optics was used, information was transmitted through copper electrical wires. Information was still converted into binary code, but the medium the digital data traveled through was not as fast. A single optical fiber can transmit as much information as can hundreds of copper electrical wires. Introductory Demo for Fiber Optic Communication Experiments Purposes: 1. Demonstrate total internal reflection 2. Demonstrate scattering by impurities. Equipment needed: 1. Hand held laser gal. Aquarium of water 3. 1 quart of milk 4. 2 X 1 pieces (2) of white poster board 5. big block of glass or plexiglass 6. flashlight or white light source. 5

8 Demonstration: 1. Transmission 2. Total internal reflection a) b) 6

9 3. Scattering by Impurities Optical Communication Experiment Introduction: Alexander Graham Bell invented the photophone, or what we know as the telephone. He used sunlight to transmit conversations without copper wire. This was a great breakthrough, showing that information contained in sound energy could be converted into light energy and back again. Light travels in straight lines in the absence of very strong gravitational fields. However, the farther it travels, the dimmer it gets. You can use mirrors to reflect light and transmit human 7

10 voices around corners, but this becomes difficult in the open air, where there are many objects which can interfere with the signal. Some examples are birds, people, cars, bugs, Many years after Bell, scientists found a way to get light to travel a great distance, around corners, and around other obstacles, using a medium called optical glass fibers. In this lab you are going to see how light signals can travel along glass fiber. Equipment for Experiments Part A and B: Lots of cable (disposable C. Pollock) Diagonal cutters (4) Optical microscopes (2) Stick matches Coffee cans with water (4) Black box light source with 12 ports (1) Fiber optics kit (voice link) Extra 9 V batteries (4) 900 ft. Optical fiber cable tape player and tape convex lenses 8

11 microscope Experiments Work in groups of two. Be sure to record your findings. Part A: Mechanical Properties of Optical Fibers 1. Take one fiber about 15 ft. Long and have a tug-of-war with your partner. What happened? Play with the fiber What happened? 2. Cut it up and look at the pieces under a microscope What does it look like? 9

12 3. Make a 1 foot long piece of fiber. Try to burn it with a match (be careful and hold it over the coffee can of water). Dunk the fiber in the water to cool it off. What happened? 4. Does the fiber float? 5. Bend a fiber as far as it will go, next to your ear. What happened? 10

13 Part B: Optical Properties of Optical Fibers 1. Stick one end of a fiber in the light box. What comes out of the fiber? 2. Bend the fiber in different ways and around corners. Any change in the light? Can you bend the fiber too much? Does the light spread after it comes out of the fiber? Try focusing it with a lens. 3. One student should place and hold a second fiber end-to-end with the fiber coming out of the lightbox. The second student should look for light coming out of the second fiber. Did you see light? 11

14 Try spitting on the fiber ends and then placing them together... better? 4. Remove the fiber from the light box. Is room light transmitted through the fiber? Do any colors transmit better than others? Cover one end with your finger, any change? 5. Hold one end of the fiber very close to this paper. Scan it back and forth across the written heading of this section. What happens to the brightness at the other end? Part C: Communication Using Light Signals (Work as a large group) 1. Connect one end of the black-cased 10 ft. Fiber cable to the receiver, and the other end to the transmitter. 2. Separate the receiver and transmitter by unrolling the cable 3. Turn the receiver on all the way. 4. Take turns depressing the switch on the transmitter and speaking into the microphone. 12

15 What happened? 5. Split into 3 groups: noisemakers, cable-switchers, and judges. Cable switchers will switch back and forth between the 10 ft. And the 900 ft. Cables, without the judges seeing. Noisemakers will make noise at constant volume Judges will determine whether there is a difference n the volume of sound from the receiver, when cables are changed 6. Re-attach the 10 ft. Cable to the receiver and transmitter 7. Start the tape playing into the microphone. What happens when the cable is bent further and further? Questions: 1. Why does the light follow the optical fiber around a curve instead of shining out through the side? What is total internal 13

16 reflection? Information can be carried by light along optical fibers. A light sensitive microchip has been invented that can read information from the optical fiber at the rate of 9 billion bits per second. Lets do some calculations to see how fast fiber optic cable really is. Get your calculators out! 2. A light pulse moves through optical fiber at a speed of km/s. (a) Convert this speed to km/h. (b) Rewrite this number in scientific notation. 3. Glass is also used on the space shuttle. Tiles made from heat resistant glass cover the underside of the shuttle to protect the astronauts during re-entry to the Earth s atmosphere. On reentry, the shuttle surface heats to 1260 degrees C. 14

17 (a) How hot is boiling water in Celcius? (b) How many times warmer does the shuttle surface get than boiling water? 4. Light travels at a speed of km/h in glass (see question 2a above. As light travels through an optical fiber, it loses energy, this is partly because of impurities in the glass. This means that after a certain distance, the light signal becomes weak and must be powered up again. A repeater is used to boost the light signal after approximately every 30 km of travel. (a) Convert the speed of light in glass to km/s km 15

18 (b) The speed of light in a vacuum is km/s. How long does it take for light from the sun to reach the Earth? Your answer should be in seconds. c) The speed of light in air is almost the same as the speed of light in a vacuum. Assuming it is the same, how long would it take for a light message to get from Newfield to LA (approx km), if we sent it through the air? Ignore the earth s curvature. Your answer should be in seconds. d) Now suppose we send the message through an optical fiber. Assume no time is lost in the repeaters. How long will it take to send the message from Newfield to LA? Answer in seconds. e) How many times will the signal need to be boosted between NY and LA (how many repeaters are there)? f) Suppose you could shout loudly enough, so that you could be heard all the way from Newfield to LA. The speed of sound in air is 343 m/s at room temperature. How long would it take your shouted message to reach LA? Answer in seconds. 16

19 Lets Take A Look At Binary Code Computers, Music CDs, video games, digital TV's, and watches all use digital technology. A machine that uses digital technology gets its instructions in the form of numbers. These numbers are called binary code. Binary code uses series of 0s and 1s to represent tiny pieces of information, like a letter in the alphabet, a sound, a color, or a shape. For example, means the letter Z. Recall from the previous section that data must be converted into light signals in order to be transmitted over fiber optic cables. An ENCODER converts electricity into light pulses. Since both electricity and light have just 2 states, ON and OFF, this is easy. In electricity In light - 1 means the electricity is ON - 0 means the electricity is OFF. - 1 means the light is ON - 0 means the light is OFF. So the encoder sends light if the electricity is on and holds the light if the electricity is OFF. All rights Copyright 2003 CCMR Educational Programs. reserved. 17

20 The 0s and 1s used here are called Binary Digits (BITS for short). It is really just another way of counting. Any of the numbers we use (called DECIMAL numbers) can be converted into binary numbers. Think about the way we count. We have ten digits, starting at 0 and ending with 9. When we count, what digits do we use once we have used 0 to 9? Well, we use 0 to 9 again, only we put a 1 in front of them, giving us 10 to 19. This process keeps going and our decimal system looks like this: 0,1,2,3,4,5,6,7,8,9 10,11,12,13,14,15,16,17,18,19 20,21,22,23,24,25,26,27,28,29 90,91,92,93,94,95,96,97,98,99 THEN 100,101,102,103,104,105,106,107,108,109 The same method is used in binary - but we only have 2 digits, 0 and 1. So once we run out of digits, we start counting again, placing a 1 in front, giving us 10, 11. This process continues and the binary system looks like this: 0,1 10,11 100, , ,

21 Converting Binary to Decimal Think again about the way decimal numbers work. Each digit in a decimal number represents a power of 10: The number means 1 X X X 10 4 X 1 OR 1 X X X X 10 0 which is = 1674 In binary, each digit represents a power of 2. The number means 1 X X X X 2 0 OR 1 X 8 1 X 4 0 X 2 1 X 1 which is = 13 19

22 So the number 1101 in binary is equivalent to 13 in decimal. Convert the following numbers to decimal to crack the code and uncover a new fact about glass!

23 A = 20 B = 15 C = 5 D = 34 E = 23 F = 21 G = 14 H = 7 I = 40 J = 12 K = 10 L = 17 M = 11 N = 28 O = 31 P = 45 Q = 35 R = 26 S = 18 T = 16 U = 32 V = 6 W = 72 X = 9 Y = 63 Z = 51 21

24 Experiment Microscopy The microscope allows us to view things at a very small level. Using a microscope we can see things that are very tiny and see smaller parts of a larger object. You will travel to 4 different stations to use various microscopes to view fiber optic cable. At each station you will be asked to answer some questions and document what you see and do. Remember good scientists take careful notes of their findings so they can be shared with other scientists. Station 1 Compare copper wire to fiber optic cable Optical fiber has many advantages over copper wires other electrical equipment and lightning storms do not cause interference, static or noise 22

25 repeaters are only needed every 30 km - unlike copper wires which require repeaters every 0.5 km to boost or reamplify energy it would take 256 pairs of copper wires to carry as much information as 1 pair of fiber optic cables it is more secure than copper wires - military information lines cannot be intercepted without being detected it weighs much less, and takes up less space it is also much more resistant to melting in building fires than is copper Using the Stereo Zoom Microscope, view the fiber optic cable and copper wire at various magnifications. Complete the chart below: 23

26 Material Magnification Words to describe Copper wire 7 X Sketch Fiber Optic Cable 7 X Copper wire 40 X Fiber Optic Cable 40 X List three main differences between the two samples as you have viewed them under the microscope

27 2. 3. Station 2 Single mode versus Multi mode There are two types of optical fibers - single mode and multi mode. Single mode fibers are used in long distance telephone lines and undersea cable. Its core is 10 micrometers in diameter and its cladding is 100 micrometers in diameter. Multi mode fibers are used in urban areas where signals are distributed from central switching systems. Its core is 50 micrometers in diameter and it s cladding is 125 micrometers in diameter. A MICROMETER is 1 millionth of a meter or 1 thousandth of a millimeter. 25

28 (a) Convert 10 micrometers into millimeters (b) Convert 50 micrometers into millimeters. (c) How much larger is the diameter of multi mode fiber core than the single mode fiber core (in millimeters)? Using the BH-3 Microscope, view single and multi mode fiber optic cable. Complete the chart below. 26

29 Material Magnification Words to describe Single mode 50 X Sketch Multi mode 50 X Single mode 100 X Multi mode 100X What are three differences you see between the single and multi mode fibers?

30 Station 3 3-D Stereo Pair Often scientists view objects in a 3-D Stereo Pair Microscope to calculate the 3 rd dimension of an object. After viewing it under the microscope they are able to make measurements. They then plug these measurements into a formula to get the 3 rd dimension. These calculations go far beyond the eight grade math level, so for our purposes we are just interested to see what the cable looks like under the microscope. Don t forget to accurately record your findings in the chart below: Object Words to Describe 3-D Sketch Fiber Optic Cable 28

31 Station 4 SEM The Scanning Electron Microscope The SEM is an amazing microscope that allows us to view things at a very, very, very small level... using electrons instead of light. In the stations above, you viewed things up to 100 times they appear in real life. An SEM can magnify an object times. The Scanning Electron Microscope is essentially a closed-circuit television system of some complexity. This is what happens: an object is scanned by a focused high-energy electron beam and the consequences of this interaction is viewed by the scientist on a computer screen. In order to get a clear view of the object (specimen) on the computer screen, the Scientist must prepare the specimen before putting it in the SEM. To prepare the specimen, the Scientist is going to coat it with gold palladium. This will provide a means of escape for electrons in the specimen that might interfere with view. But what would happen to the view if the specimen is not coated? This is what you are going to test. 29

32 Questions: 1. How does it look when the specimen is removed from the vacuum that coats it with gold palladium? What color is it? How has it changed? 2. What are the differences in the two specimens (one that is coated with gold palladium and one that isn t) when viewed in the SEM? 1. Tape your specimen here: 30

33 Steps To Completing Your Stain Glass Project 1. Get two copies of the pattern piece. 2. Cut the pieces out of one of the patterns using scissors. 3. Pick the glass you wish to use for your project. 4. Using the marker, trace each pattern piece on the glass. 5. Cut out the glass pattern pieces using the glass cutter. 6. Fit the cut glass pieces on to the pattern that wasn t cut up. Do they fit together like pieces to a puzzle? 7. Tape the edges of each glass piece with the copper tape. 31

34 8. Smooth down the edges of the copper using a popsicle stick. It is very important that all edges are affixed to the glass. Any loose edges may lift off the solder. 9. Use the solder iron to melt solder onto the glass. Start by soldering the glass pieces together at fixture points, then solder completely. Be very careful! The iron and solder are VERY hot and if they come in contact with your skin, it will leave a very serious burn Bend a small piece of wire into a loop to be used as a hook to hang your glass work. Solder the wire on the back of your project. 11. Clean up your work area. Put all broken glass in the glass disposal box. Use the brush and gloves to handle all glass pieces. 12. Unplug your iron and place it safely on the cooling rack. 32

35 Questions: 1. What did you notice about the properties of glass when cutting it? 2. How is cutting glass like swimming in water? 3. How is cutting glass different from cutting wood? Science Lab - Making Edible Glass Equipment: hot plate heavy pot with a lid water candy thermometer oven mitts 2 cups sugar 3/4 cup light corn syrup 1 tablespoon unsalted butter plate long wooden spoon drinking glass food coloring 33

36 flavoring cookie sheet greased with vegetable oil sturdy toothpicks Instructions: 1. Check the accuracy of your thermometer by bringing a half pot of water to a boil. Hold thermometer in center of boiling water for 2 minutes. Be careful, steam burns, use a mitt. Check the temperature of the thermometer while in the boiling water. Record the temperature: C. What temperature should the thermometer read? C. How many degrees do you need to add or subtract to correct the thermometer s reading? C. When doing the experiment, add or subtract it to the temperatures given to determine what your thermometer should read at each step. 34

37 2. Add the sugar, corn syrup, and butter to 1 cup of boiling water. Stir until ingredients dissolve. 3. Heat mixture to a boil without stirring. Cover and cook for three minutes. 4. Hold thermometer in syrup. Be careful, the syrup is very hot! 5. Remove syrup from heat. Scoop up a spoon of syrup and pour it onto the plate. What happened to the syrup? 6. Scoop another spoonful of hot syrup into a glass of cool water. What happened to the syrup? 35

38 7. Return syrup to heat without stirring and repeat steps 5 and 6 at the following temperatures: 112 C, 118 C, 121 C, 132 C. Complete the chart below: Temperature Desired Temp My Thermometer should read... Observation of the syrup 112 C 118 C 121 C 132 C 8. When syrup reaches 149 C, remove from heat. Cool to 71 C. This will take about 15 minutes. 9. Stir in color and flavor. 36

39 10. Set toothpicks on oiled cookie sheet. Pour a small amount of syrup around each. 11. Remove lollipops from cookie sheet as soon as they are firm. You have just made edible glass. Questions: 1. Most matter exists in one of three states. These three states of matter are: The Particle theory states: a. Solids are made up of an orderly arrangement of particles. Strong forces hold the arrangement together. b. Particles in liquids are held together in groups that are less orderly. Because particles are farther apart than the particles in a solid, the weaker attractive forces permit the particles to move around one another. 37

40 c. The attractions among the particles of gases are so weak hat individual particles are quite far apart, with a lot of space around them. This leaves the particles free to move in any direction. Complete the chart below: State Solid Shape (definite or indefinite) Volume (definite or indefinite) Particle Picture Liquid Gas 3. What happened to the particles in the syrup as it was heated up? 4. What state of matter was this syrup in step 7? 38

41 5. What happened to the particles in the syrup as it was cooled? 6. What state of matter was the syrup in at the end of step 10? 7. As you performed the experiment, the syrup solution went through changes in state. The liquid was heated and some of the solution changed into a gas. The change of state, where a liquid is changed into a gas is called. The liquid was also cooled and the solution changed into a solid. The change of state, where a liquid is changed into a solid is called. 39

42 Complete the Chart below: Name of Change From To Heat must be... melting solid liquid added freezing vaporization liquid added condensation liquid sublimation solid gas sublimation gas removed 8. At what temperature would it be easiest to make candy optical fibers? 10.What physical properties does your glass share with window glass? 40

43 Word Match 41

44 Word Search 42

45 Cross Word 43

46 Word Scramble 44

47 In (or Near Gallery 1): Corning Glass Museum 1. Most geologist think that most obsidian (natural glass) was blown out of these about years ago. 2. Name three obsidian objects on display that were fashioned by ancient people. A. B. C. 3. Archeologists believe that glass made by humans first developed in this western Asian country. Circle the probable answer. Mesopotamia (Iraq/Syria) Egypt China 4. People learned how to make a crude glass by melting special sand and plant ashes together and melting the mixture in a furnace. They chaped figures from it to bury with the dead. These figures are called? _ 45

48 5. What natural process caused the change in the appearance of ancient objects? 6. Techniques used to make glass objects varied. Name two of those glassmaking techniques. A. B. 7. In ancient times, the glassmaking process was probably protected. Only ruler and their friends could own glass objects. What substance did glass often equal in value? 8. What case is the first to contain transparent glass objects, and tell of its origins? 9. Case appears to be the first to show how shape, size and transparency began to be valued. 46

49 In (or Near Gallery 2): 10. This Roman glassmaking discovery was revolutionary? 11. Why? Clue: What happened to the value of glass? 12. The themes, or subjects, of the window display-cases are printed in white letters along their tops. Write two headings that suggest big changes in the lives of ordinary Romans because of the new glassmaking technology. A. B. 13. What fuel was used to melt the ingredients to make early glasses and metals? 14. Find Case 2. This part of the bird perfume bottle was broken so that the perfume could be sprinkled out. The. 47

50 15. A. What is a gladiator cup? B. They were made using this technique: 16. were the Roman s favorite animal. In (or Near Gallery 3): 17. A. Look at the large mosaic picture of the Empress Theodora. What clues tell you the religion practiced by these people? B. What tools would you need to determine how many small glass tiles make the picture? In (or Near Gallery 4): 18. Name the city-state whose luxury glass products were in great demand during the European Renaissance. 48

51 19. What method was used to make the small figures in Cases 50 and 51? 20. Six generations before, a famous American s family spelled its name differently on these decorative windows. Write the different spelling. 21. It s made of glass (of course). You can t see it, but you can see what holds it. Without it, chances are good that you would never have been born because your ancestors would have died. What is it? 22. A. Beginning in the 1820s, what happened to the price of glass produced by the machine press. B. Why? 23. The homed, beaded hat was made by these African tribal people: 24. Many trade beads were made in this European country. 25. A. Name three glass musical instruments on display

52 2. 3. B. They wrote music for glass instruments Glass were replacements for those damaged, or lost, in the Civil War. 27. Many of the containers in this gallery held either one of these two drugs This animal s head produced fuel to light streets. 50

53 In (or Near) Gallery 6; 29. Favorite playthings of the 19 th and early 20 th century child are displayed in case? 30. Case holds the curious Emperor. 31. The glass animals were used to. Around the Curve: 32. The two best known American Art Nouveau glass designers: A. B. 33. There are kinds of flowers found in the large colored-glass Tiffany window. 51

54 34. The name of the river in the window is the River. We are looking at it toward what direction? Circle your answer. North South East West 35. Name five different animal figures you find attached to the big beadedbear head. A. B. C. D. E. 36. List seven countries whose artist s works are displayed here. 52

55 Video Interactions 53

56 Digital Communications 1. What does it mean to digitize something? 2. What happens when you type a letter into the keyboard? 3. What else can you digitize besides keyboard letters and numbers? 4. How many 0 s and 1 s on a CD? 54

57 6. How is a picture or photo digitized? 7. How is video digitized? 8. How do you carry information from point A to B? 9. How does the speaker describe fiber optic cable? 55

58 10. Of what material is fiber optic cable made? 11. What is yet another method of sending information? 12. How is this method better than wires or fiber optics? 13. What do you think TV and videos will be like in the future? 56

59 Acknowledgements This unit was first designed and developed by Sheri Hanna and Sue Wirsig, Discover Program Directors, Kingston Ontario in The unit has been modified by the Cornell Center for Materials Research, Ithaca, New York in The following people have made considerable contributions to the modified version: David Picciotto, Graduate Student, Applied Physics Prof. Dieter Ast, Material Science and Engineering Prof. Michael Teter, LASSP John Hunt, Microscopy Facility Manager Don Knettles, Research Support Specialist Frank Starr, Corning Glass Museum Sue Wirsig, Educational Outreach Coordinator Also, special thanks to the staff and students at Newfield Middle school for their participation in this program. Optic Kits: 1. Purchased from Carls Electronics (PO Box 722 Leominster, MA 01453) 2. Designed by David Picciotto, made by Winn Tanner (CCMR) 57