Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Gravitational lens wikipedia , lookup
Architectural lighting design wikipedia , lookup
Photoelectric effect wikipedia , lookup
Light pollution wikipedia , lookup
Bicycle lighting wikipedia , lookup
Daylighting wikipedia , lookup
Photopolymer wikipedia , lookup
Doctor Light (Kimiyo Hoshi) wikipedia , lookup
INTRODUCTION TO NETWORK CABLING MODULE 2 FIBER OPTIC-BASED SYSTEM Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Goal 2 Students will have an understanding of the basics of light to include speed, wavelength, frequency, intensity and attenuation. During this module students will be working with light sensors, emitters and optical power meters in support of module objectives. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Objectives: • • • • • • • • • • • • • • • • • • • • • • Define the characteristics of light to include: frequency and wavelength, speed, movement and amplitude Identify the speed of light as 300,000kps Identify that light slows down as it enters air or water Identify that the metric system is used for measurements in optics Define metric terms to include millimeter, micron and nanometer Identify that scientists use scientific notation to work with very large or very small numbers Convert numbers using scientific notation Given a sine wave, determine a wavelength measurement Define the terms: frequency and wavelength Describe the relationship between frequency and wavelength is inversely proportional Give examples of devices that use wavelengths and frequencies Define the Greek symbol, Lambda and what it represents Define that energy in the Electromagnetic Spectrum is measured by frequency or wavelength Identify the parts of the Electromagnetic Spectrum in terms of Radio, Visible, Non-Visible and Microwave Compare wavelengths and identify which has the lower frequency Identify that red is on one end of the visible spectrum and violet is on the other end Define the acronym ROYGBIV as the colors of the spectrum Given a color of light, identify its wavelength Define light as both the visible and the non-visible Use an infrared detector and check for the presence of non-visible light Identify that white light contains components of all visible wavelengths Take part in an experiment, observe and record the results of light with different wavelengths (4 SPOTS) Define light movement in terms of Reflection and Refraction Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Objectives (continued): • • • • • • • • • • • • • • • • • • • • Identify that most of what we see is the reflection of light Describe how we perceive the color of an object Identify incident angle, reflected angle and the normal line in terms of light reflection Identify that when light refracts it changes speed and direction Define Snell’s Law and give examples of how it applies to reflection and refraction Diagram how light reflects off a mirror and indicate which angles provide the strongest reflections Given an index of refraction chart, calculate the speed of light in a medium Describe which direction a refracted light wave travels when interfacing with materials of different indexes of refraction Describe how a Fresnel lens works to refract and focus light Define attenuation as loss of light over distance Define that attenuation is a ratio, a function of distance and wavelength Define that attenuation is measured in Decibels Define that decibels are a log expression Describe that 3 dB is a doubling of power Given a decibel to power conversion chart, determine what percentage of power is lost per dB Describe the operation of the power meter and light source Observe cautions when using a power meter and light source Use the subtractive or zero set method to measure the attenuation of an optical system Use a power meter and plot the light intensity of four optical sources Take part in an experiment, observe and record the results of an activity using light sources of different wavelengths measured with an 850nm power meter Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Introduction This course deals with the movement of light through strands of glass. These strands are only slightly larger then a human hair and they provide us with the ability to move large amounts of data. The use of these optical systems allows the connected world to operate. Optical systems provide for our computer networks, digital television and voice networks. Figure 2.1.1 Introduction to Network Cabling Fiber Optic-Based Systems Figure 2.1.2 2 Light and Optics Major corporations are laying thousands of miles of fiber in cities and even on the floor of the ocean. These pulses of light represent the heartbeat of technology. http://www.youtube.com/watch?v=cuxf6zBTO2g Before going too deeply into Fiber Optic technology, it is important to understand the basics of light. How fast does it move and at what wavelength? How does it bend when it travels through different materials? What is the difference between reflection and refraction? These are some of the questions that are addressed in this module. Introduction to Network Cabling Fiber Optic-Based Systems Figure 2.1.3 2 Light and Optics Light An optic technician needs to understand some of the fundamental characteristics of light and the fibers it moves through. These qualities are important to understand when you work with optical systems. Figure 2.2.1 The four characteristics of light are: Speed How fast is light moving and in what (air, water, outer space, etc.)? Wavelength and Frequency Where does light fall in the electromagnetic spectrum? What color is it? What is the distance between peaks of the wave? Movement How does it travel or reflect? How does it interact in a substance, like glass or water? Amplitude How bright or intense is the light? How is the brightness reduced (fog, air, glass, etc.)? Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Speed Light is an electromagnetic wave that travels at a speed of 300,000 kilometers per second in a vacuum. That's 186,000 miles per second. The speed of light is the maximum speed limit of the universe. Nothing can travel faster than light! How fast is 300,000 kilometers per second? Figure 2.3.1 It is 670 million miles per hour. If you flew around the world in a jet, you could make the trip in about 38 hours. The space shuttle takes about an hour and a half. A beam of light can do it in 1/7 of a second. That's how fast. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Remember, this is the speed of light in a vacuum. As light passes through air it slows down. As it passes through denser materials, like water, it slows down even more. Light inside of a diamond slows down to a mere 300 billion miles per hour or less than half the speed it travels in air. Figure 2.3.2 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Light Math Optics deals with small strands of glass and even smaller wavelengths of light. The typical size of optical glass you will be working with is slightly larger than a human hair. The light that travels through these light waveguides is even smaller. In optics, the metric system is used. The basic unit of the metric system is the meter, which is a little longer than 39 inches. The meter represents one ten-millionth of the distance from the Equator to the North Pole. Divide a meter by a thousand and you get a millimeter. Divide a meter by a million and you get a micron. How small is that? One of your hairs is about 75 microns thick. The fibers you will be working with in this course are 125 microns in diameter. The micron has a special symbol, the Greek letter mu: µm. Even smaller than that is the nanometer, one-billionth of a meter. A nanometer is extremely small and is one billionth or 1,000,000,000 of a meter. A human hair is 10,000 times thicker than a nanometer. Wavelengths of light are measured in nanometers. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Converting one metric unit to another is easy because it's all decimals. All you have to do is shift the decimal point to the right or left. Prefix Meaning Number in 1 Meter deci- 10 10 decimeters centi- 100 100 centimenters milli- 1,000 1,000 millimeters micro- 1,000,000 1,000,000 micrometers nano- 1,000,000,000 1,000,000,000 nanometers Figure 2.4.1 NEW TERM Metric System - A universal scientific system of measurement. . Meter - The basic unit of the Metric System, about 39 inches (m). . Millimeter - One thousandth of a meter (mm). . Micron - One millionth of a meter. (symbol: µm) Also known as a micrometer. . Nanometer - One billionth of a meter. Also called a nanon. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Scientific Notation Look at the number below. On a separate sheet of paper, write this number down. 3,000,000,000,000,000,000,000,000,000,000,000,000,000,000 How long did it take you to write it? Check your work. Did you remember every single zero? It would be easy enough to miss one. Scientists work with large numbers like this, and very small numbers too. You can see that it would be hard to calculate with numbers like these. So scientists have developed a technique called scientific notation. It's a way of writing very large or very small numbers without using all the zeroes by manipulating decimal points. - A number expressed in scientific notation contains two parts: - A number greater than 1 but less than 10. A power of 10 that multiplies that number. This power of 10 represents the new location of the shifted decimal point. Here's an example: the number above, written in scientific notation, would be: 3 X 1042. Forty-two is the number of places you'd have to move the decimal point to the left to turn “3” into the number above. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Scientific Notation (continued) We can make a formula for scientific notation like this: A X 10B Here's how the formula works: Take the number you want to convert and move the decimal place to the left until the number is between 1 and 10. This number is A in the formula. Count the number of places the decimal point was moved and replace B with that number. So: 420,000,000,000 = 4.2 X 1011 (Move the decimal point 11 places to the left.) NEW TERM Scientific Notation - The way a scientist can quickly work with very large or very small numbers. Introduction to Network Cabling Fiber Optic-Based Systems Figure 2.5.1 2 Light and Optics Scientific Notation (continued) Scientific notation is used to make working with large numbers EASIER. Where: 5.13 X 100 = 5.13 5.13 X 108 = 513,000,000 But what if it's a very small number? You use the same formula, but you move the decimal point to the right and make "B" a negative number. Like this: 0.000979 = 9.79 x 10-4 0.000000000045 = 4.5 x 10-11 Remember the base number must be between 1 and 10. 0.000000000000000002 = 2 X 10-18 Figure 2.6.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Activity 2.1 Fundamentals of Light Match the terms to their definitions 1. 2. 3. 4. 5. A. frequency B. amplitude C. speed of light D. micron E. meter C 300,000 kilometers per second D one millionth of a meter B intensity of light E 39 inches A color of light Calculate the following using scientific notation: 6. Blue light has a wavelength of 0.00000045 meters. How would a scientist define that number using scientific notation? X 10 -7 7. The speed of light is 186,000 miles per second. How would a scientist define that number using scientific notation? X10 5 8. A typical Fiber Optic network operates at 0.000000085 meters. Convert that number using scientific notation. X 10 -8 9. What would 6.8 X 1011 look like without scientific notation? 680000000000 10. What would 4.5 x 106 look like without scientific notation? 4500000 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Waves Light is a wave, so is sound and so is the energy sent to and from your cell phone. All of this wave energy is part of the electromagnetic spectrum. The electromagnetic spectrum includes all forms of electromagnetic waves from very long sound waves to very small gamma rays. A bass wave from a home theater can have a wavelength of over 50 feet while a gamma ray is measured in nanometers. Figure 2.8.1 Sound waves allow us to enjoy music. Introduction to Network Cabling Fiber Optic-Based Systems Figure 2.8.2 2 Light and Optics Waves (continued) X-rays let us see problems in our bodies. Figure 2.8.3 NEW TERM Electromagnetic Spectrum – All of the types of waves found in nature from sound to gamma rays. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Wave Math When measuring a wavelength, measure the distance where the wave repeats. You may measure from the peak of a wave to the next peak. You may also measure the points where the wave passes zero. In the diagram, A is the peak to peak distance and B is the point where the wave passes zero. The length of A is the same as the length of B. Either measurement is correct. Figure 2.9.2 Figure 2.9.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Frequency and Wavelength In the diagram, compare the waves and you will notice that the more waves there are, the less distance is between them. Lower frequencies have fewer waves! The length of the waves is longer! Figure 2.10.1 Higher frequencies have more waves! The length of the waves is shorter! Figure 2.10.2 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Frequency and Wavelength (continued) Frequency is the rate that a wave changes. Wavelength is the distance between like parts of a wave. • The higher the frequency, the shorter the wavelength. • The lower the frequency, the longer the wavelength. The scientific term that expresses this relationship is called: “inversely proportional.” As one variable gets larger, one gets smaller. NEW TERM Figure 2.10.3 Inversely Proportional - A relationship that when one variable goes up the other goes down. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Frequency and Wavelength (continued) For example, the frequency of the electrical voltage in your home is 60Hz. That means that it completes 60 cycles in one second. A WiFi and a Blue Tooth operate at 2.4 giga hertz. Giga-means one billion, so one Giga-Hertz means that the wave repeats one billion times in one second. Figure 2.11.1 Lambda, the Greek letter "λ" is used to represent wavelength. The power meter has a λ button that allows the user to select 850nm, 1310nm or 1550nm for testing different types of optical systems. NEW TERM Figure 2.11.2 Lambda - The Greek letter that represents wavelength. Figure 2.11.3 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics The Electromagnetic Spectrum The various types of waves are arranged by wavelength. Look at the diagram and notice that the spectrum runs from very long wavelengths (sound waves) to very short wavelengths (gamma rays). Notice that the visible light area is only a small part of the spectrum. Visible light is the only part of the spectrum we can see. White light is actually a combination of many colors, each of which has its own wavelength, ranging from violet at the low end, to red at the high end. We can not see ultraviolet waves but if exposed to them for too long we can get sunburn. We also can not see infrared light at the other end of the visible spectrum. Figure 2.12.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Light Wavelengths ROYGBIV You may have learned Roy G. Biv as a way to describe the visible spectrum. R O Y G B I V Red Orange Yellow Green Blue Indigo Violet Introduction to Network Cabling Fiber Optic-Based Systems Figure 2.13.1 2 Light and Optics Visible light The different colors of light have different wavelengths. These wavelengths are very small and range from 400 nanometers to 650 nanometers. Figure 2.13.2 Red waves have a wavelength of 650nm. They are about twice as long as violet waves. Infrared or the black area on the left of the scale is the area where fiber optical systems operate. Figure 2.13.3 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Non-Visible Light Energy whose wavelength is too long to see is "redder than red." Light with such long wavelengths is called "infrared" light. The prefix "infra-" means lower than; so infra-red means “lower than red.” Infrared light travels more easily through glass. It is the type of light used in fiber optical systems. To see continuity, a technician uses visible light. When Fiber Optic systems are operating, they use nonvisible light. The light source used in the course uses IR light. The light source puts out very intense light that can not be seen. Even though the light from the light source can not be seen, it is still present. Protect your vision and never look into a light source. Figure 2.14.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Non-Visible Light (continued) Warning DO NOT LOOK INTO ANY FIBER OPTIC LIGHT SOURCE! Some remote controls use IR light to send signals to televisions or AVR’s. If a remote has to be pointed at the television or AVR then it uses IR light. The C-Tech IR detector card tests for IR light. NEW TERM Figure 2.14.3 Figure 2.14.2 Introduction to Network Cabling Fiber Optic-Based Systems Infrared light - Nonvisible light that is used in Fiber Optic systems. AVR - Audio Video Receiver. 2 Light and Optics Watch the demonstration with the C-Tech IR detector, the IR SPOT and the light source and power meter. Explain the demonstration and how IR light is detected. Show the movie and conduct the demonstration with the equipment listed. Demonstrate non-visible light, light source safety and line of sight for IR sources. Non-Visible Light_Power Light_Intensity SPOT Attenuation Z Video Video Video Video Introduction to Network Cabling Fiber Optic-Based Systems S Videos 2 Light and Optics Activity 2.4 Properties of Light 1. Describe the term inversely proportional. As one property goes up the other goes down 2. In the diagram below which letter represents wavelength? Circle your answer. 3. When wavelength goes up, frequency goes down. 4. Hertz is a measurement used for: a. speed b. weight c. wavelength d. frequency 5. Light travels fastest in a vacuum. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Activity 2.4 Properties of Light (continued) 6. It is important to remember that the operational wavelengths used in Fiber Optic communications are based on the light handling characteristics of: a.the environment b.the speed of light c.the fiber d.the laser 7. What does the Greek symbol "λ" mean? Lambda and or wavelength 8. What does the lambda button on the power meter do? Changeswavelengths 9. Give an example of a use of non-visible light. Remote controls, sources or any IR source 10. Which two of the following are a SPOT wavelength? a.650 b.745 c.850 d.1310 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Activity 2.3 Color and Wavelength Observe the SPOT demonstration and fill in the color and wavelength. Color Wavelength 1.SPOT number 1______ __________ 2.SPOT number 2______ __________ 3.SPOT number 3______ __________ 4.SPOT number 4______ __________ Have the students observe the demonstration or allow them to examine SPOTS and log results. Introduction to Network Cabling Fiber Optic-Based Systems Video 2 Light and Optics Light Movement Light rays always travel from the light source in straight lines, but the direction of those straight lines can be changed as the light passes through or strikes various substances. This change in direction of the light wave can occur in two patterns, either as reflection or refraction. Reflection is when light is redirected after bouncing off a substance. Refraction is when light enters a substance and its speed and direction changes. NEW TERM reflection – The description of light when it bounces off of a surface. Figure 2.18.2 refraction – The description of how light slows and bends as it enters a substance. Introduction to Network Cabling Fiber Optic-Based Systems Figure 2.18.1 2 Light and Optics Reflection Most objects don’t produce their own visible light. What we see most of the time is reflections of light off objects. Objects reflect light differently. Most of the light is absorbed by the object. Some of it is reflected. An orange appears orange because all wavelengths of light except orange are absorbed by the object. Mirrors reflect all visible wavelengths. Figure 2.19.1 Figure 2.19.2 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Reflection (continued) The diagram above shows light reflecting from a mirror. The incident ray strikes the mirror and reflects at the same angle. As shown above, the angles of incidence and reflection are the same. The angles are measured from the angle of the “normal line.” The normal line is a line perpendicular to the reflective surface. The law of reflection states that the angle of incidence is always equal to the angle of reflection. Figure 2.20.1 NEW TERM Angle of Incidence – The angle that light strikes a surface. Angle of Reflection – The path that reflected light travels; same as angle of incidence. Normal Line – A line that is perpendicular to a surface. Law of Reflection – This law states that the angle of incidence is equal to the angle of reflection. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Critical Angle All of the light is reflected back into a substance if the angle of incidence is less than the critical angle. The critical angle is the measurement of the angle of incidence to the normal line. The diagrams represent the interface of air and water. The air and water interface have a critical angle of 49 degrees. As the angle of incidence is increased all of the light is reflected at the interface. This phenomenon is known as total internal reflection because almost all of the light is reflected back into the substance. Figure 2.21.1 NEW TERM Critical angle – The angle that light begins to leave a substance at the interface. Below the critical angle more of the light leaves the substance. Total Internal reflection – When the incident angle allows most of the light to remain inside a substance. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Refraction and the Speed of Light When light refracts it changes speed and changes direction. Light does not travel the same speed in all substances. Light in outer space travels at the speed of light. When light enters the atmosphere, it slows down. If it was to travel through the ocean, it slows down even more. How light speeds up and slows down is shown (left) in the diagram of the raindrop. As the light enters the raindrop it slows down. As it leaves the raindrop it goes back to its original speed. Figure 2.22.1 Figure 2.22.2 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Index of Refraction When light enters transparent materials, it slows down as it travels through the material. Technicians use the term “index of refraction” to describe the speed of light in a medium. Index of refraction is the ratio of the speed of light and the speed in a substance. An index of refraction of 1 means the light is traveling at the speed of light. index of refraction = speed of light in a vacuum speed in the substance index of refraction of 2 means: 2 = 300,000/150,000 Medium Index of refraction Outer Space Air Ice Water Cranberry juice Shampoo Window glass Ruby Crystal Diamond 1.00 1.00029 1.309 1.333 1.351 1.365 1.5 1.770 2.00 2.417 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Index of Refraction (continued) The chart above shows the index of refraction in different substances. Light travels at its maximum speed in outer space. Light moves slower in air and even slower in ice. Using the chart, notice that light travels only half as fast in a crystal, compared to space. In space, light travels at 300,000 kilometers per second. In a crystal it moves at 150,000. Figure 2.23.1 NEW TERM Index of Refraction – The ratio of the speed of light in a vacuum to its speed in a substance. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Refraction and the Bending of Light When white light goes into a prism, the light is separated by wavelength because wavelengths refract at different angles. The same color or wavelength separation takes place in rainbows and glass. When a light ray enters a material with a higher index of refraction, it bends towards the normal. Figure 2.24.1 Figure 2.24.2 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Snell’s Law Snell's law explains how light bends as it moves from one substance to another. According to Snell’s Law, when light enters a substance with a higher index of refraction, the light bends towards normal. When light enters a substance with a lower index of refraction, it bends away from normal. The diagram below represents a glass rod suspended in air. The air has an index of refraction of 1 and the glass has an index of refraction of 1.4. The normal line is a line shown in the diagram. When light from the air enters the glass rod, it bends towards the normal. When light leaves the glass and enters the air, it bends away from the normal. Figure 2.25.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Snell’s Law (continued) Fishing birds take the bending of light into account. Because of refraction the fish appears closer than it really is. Figure 2.25.2 NEW TERM Snell's Law – The law that states how light refracts in a substance. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics The Fresnel Lens The refraction of light is the basis of the Fresnel (fray-NELL) lens. A Fresnel lens refracts the light and creates a focused light pattern. It amplifies the light as it captures and focuses it. The Fresnel lens has allowed light houses to operate and send a beam of concentrated light many miles out to sea. Fresnel’s invention has saved many ships from disaster. Figure 2.26.1 Figure 2.26.2 Figure 2.26.3 Figure 2.26.4 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Activity 2.5 Light Movement A. index of refraction F B. 300,000 km per second The slowing down and bending of light as it moves through different media. C Same as the angle of incidence. C. reflected angle E F. refraction An example of how light travels after it strikes an object and bounces off. G Describes how light bends towards or away from the normal line. A A number, that is always at least 1, that represents the ratio of how fast light travels in different substances. B The speed of light in a vacuum. G. Snell’s Law D D. Fresnel lens E. reflection Focuses light using refraction. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Light Amplitude The amplitude of light (scientists say intensity) is the brightness of the light or the amplitude of the wave. Wavelength measures the light wave from “side to side.” Amplitude measures the wave from “top to bottom.” The “taller” the wave, the greater the amplitude, the more intense the light. Attenuation Attenuation is the loss of light intensity over distance. A light signal cannot travel forever. Just as light from a flashlight or the headlights on a car get dimmer the farther away they are, the farther the signal travels the weaker it becomes. Figure 2.28.1 Look at the picture to the right. Notice that in fog the light does not travel as far as it would if it was a clear night. The picture demonstrates the attenuation of light. Figure 2.28.2 NEW TERM Attenuation – Loss of signal strength. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Attenuation There are three things to remember about attenuation and they are: Attenuation is a ratio of the original light intensity to the intensity of the measured light. When measuring light we measure how much the light is attenuated from the original light. Attenuation is a function of distance. The farther light travels the more it is attenuated. It may be possible to see a flashlight at 20 feet but impossible to see it at 20 miles. Attenuation varies depending on the wavelength of the light and what it is moving through. Attenuation varies with wavelength – some waves are not attenuated as much as others as they travel through different mediums like air or glass. Fiber Optics uses infrared light because there is less loss in the glass at that wavelength. Visible wavelengths or ultraviolet wavelengths will not travel as far in glass as IR wavelengths The photo to the left is of a simulated Fiber Optic cable. Note that the light is weaker as it travels to the right. The amplitude of the light is a function of distance, material and light wavelength. What other things do you notice while looking at the photo? Figure 2.29.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Attenuation of Sound Changes in amplitude in a light signal are measured in decibels (dB). The decibel is a way of measuring ranges of energy of any kind. For example, humans are capable of hearing a wide range of sound from a faint whisper to a loud noise. A single leaf falling to the ground is 3dB while thunder is 120dB. You would think that would mean that the thunder is 40 times louder than the falling leaf, but that’s not how decibels work. Thunder at 120dB is not 120 times louder than the falling leaf; it’s a trillion times louder. Figure 2.30.1 Figure 2.30.2 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Attenuation of Sound (continued) An engineering rule-of-thumb states that for every 3dB of change the power doubles or halves depending on whether the change is a positive or negative one. For example, suppose a light bulb is 100 watts. Three dB of attenuation will reduce it to 50 watts. A 3dB increase in the intensity of the signal will boost it to 200 watts. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Decibel to Power Conversion dB Power Out as a % of Power In 1 79% 2 63% 3 50% 4 40% 5 32% 6 25% 7 20% 8 16% 9 12% 10 10% 11 8% 12 6.3% 13 5% 14 4% 15 3.2% 16 2.5% 17 2% 18 1.6% 19 1.3% 20 1% 21 0.3% 22 0.1% 23 0.01% 24 0.001% % of Power Lost 21% 37% 50% 60% 68% 75% 80% 84% 88% 90% 92% 93.7% 95% 96% 96.8% 97.5% 98% 98.4% 98.7% 99% 99.7% 99.9% 99.99% 99.999% Remarks ----1/2 the power ----1/4 the power 1/5 the power 1/6 the power 1/8 the power 1/10 the power 1/12 the power 1/16 the power 1/20 the power 1/25 the power 1/30 the power 1/40 the power 1/50 the power 1/60 the power 1/80 the power 1/100 the power 1/300 the power 1/1000 the power 1/10,000 the power 1/100,000 the power Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Decibel to Power Conversion (continued) A fiber technician found a splice with 10dB of loss. How much light is lost in the splice? 90% What is the loss? 1/10 the power Figure 2.31.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics The Power Meter and Light Source The power meter and light source are used to measure light. The light source provides the light and the power meter measures the light at the other end of an optical cable. The following steps describe the controls of the light source and power meter. It is a simple task to set these units up and measure signal strength. Optical Light Source Figure 2.32.1 Provides Infrared light at 850nm. The ON button turns the unit on and the ON light will come on. Continuous or modulated Light sends steady or blinking light. If the ON light is blinking the unit is in the modulated light or blinking mode. Push the button until the ON light remains on steadily or continuously. Test with continuous light. A low battery light on the unit indicates when the battery needs to be changed. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics The Power Meter and Light Source (continued) Warning Do not look into the light source to see if it is working. Always assume that it is working and that it is putting out intense IR light that can not be seen. Even though you can not see it, this does not mean that it is not there and that it can’t harm your eyes. The optical light source has an ST type connector to connect to a Fiber Optic system. When connecting the light source use the ST to ST or ST to SC patch cord. Figure 2.32.2 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics The Optical Power Meter The purpose of the power meter is to measure the light from the light source after it has passed through the Fiber Optic system. It offers a variety of functions. It incorporates a power saving function to extend battery life. It allows you to select between dB and dBm. Although you will only be testing at 850nm, the power meter does have the ability to test 1310nm and 1550nm. There is also a "zero set" function, which allows a technician to measure loss without having to perform any mathematical calculations. Power On/Off – turns unit on or off. dB or dBm – The display will indicate which of these modes the power meter is in. In the dB mode the results are a ratio. In the dBm mode the power meter measures the loss of light from a standard milliwatt measurement. Figure 2.33.1 "λ" – the lambda button selects the wavelength to test. When testing, press the button until the display indicates 850nm. The light source provides light at a wavelength of 850nm. As you will learn in later modules the cables used in this course are also optimized for 850nm. Zero Set – this button zeros the meter display Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Activity 2.6 Power Meter and Light Source Demonstration Observe the demonstration and list the buttons on each device and their function. Show the demonstration and or demonstrate the functions of the power meter and light source. Introduction to Network Cabling Fiber Optic-Based Systems Video 2 Light and Optics Measuring Attenuation If you take a ruler and measure something six inches long, that’s a firm measurement. Six inches is six inches no matter what the circumstances. A measurement of 6dB always means a 6dB difference up or down compared to something else. Compared to what? Compared to a starting point that you choose. When you use a power meter, you take a first measurement to use as your starting point. This is a benchmark measurement. Then you use the meter to get a second reading on the cable you wish to test. Comparing these two measurements shows how much more or less power this cable passes than your benchmark. You don’t measure amplitude or intensity directly; you always measure it compared to a benchmark. Introduction to Network Cabling Fiber Optic-Based Systems Figure 2.35.1 2 Light and Optics Testing Methods There are two different methods you can use when testing and they are the subtractive or zero set. The subtractive method This method is especially useful when comparing the performance of one cable with another. The benchmark is the reading for the first cable. 1. 2. Turn on the power meter. Attach the first cable to the power meter and to the SPOT. 3. Turn on the SPOT and take the reading. 4. Replace the first cable with the second cable. 5. Take a reading for the second cable. 6. Subtract the first cable reading from the second cable reading. If the answer is a positive number, the second cable has more attenuation (lets less light through) than the first cable. If the answer is a negative number, the second cable has less attenuation (lets more light Introduction to Network Cabling Fiber Optic-Based Systems through) than the first. Figure 2.36.1 2 Light and Optics The Zero-Set Method This method is useful for comparing cables or comparing different light sources. It sets up a common benchmark to which everything is compared. 1. 2. 3. 4. 5. 6. 7. Turn on the power meter. Attach the cable and SPOT to the power meter. Turn on the SPOT. Zero out the power meter. This is the reference reading the “zero” condition. Attach the next cable or SPOT and turn on the SPOT. Take another reading. This method imitates a direct measurement. All readings are compared to the “zero” condition. Figure 2.37.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Activity 2.7 Measuring Attenuation Demonstration Watch the demonstration on testing methods and list the steps for each method. Video (S) This demonstration tests the attenuation of two different patch cables. This Demonstration also measures using adapters and sets a zero reference. Video (Z) Watch the demonstration or demonstrate measuring attenuation with subtractive and additive methods. Demonstrate how to connect and test cable systems Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Activity 2.8 Measuring the Attenuation of a Fiber Optic Cable Using a power meter and light source measure the attenuation of a patch cord. Use the checklist below and measure the attenuation of two Fiber Optic cables. CABLE ONE Type of Cable Method Used subtractive _____ zero set _____ dB loss _____ ST - ST, ____ SC - SC, ____ ST - SC, ____ Use the power to decibel conversion chart and indicate the approximate light loss in percentage. The approximate light loss at the end of the cable is about ___________ percent of the source. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Activity 2.8 Measuring the Attenuation of a Fiber Optic Cable (continued) CABLE TWO Type of Cable Method Used subtractive _____ zero set _____ dB loss _____ ST - ST, ____ SC - SC, ____ ST - SC, ____ Use the power to decibel conversion chart and indicate the approximate light loss in percentage. The approximate light loss at the end of the cable is about ___________ percent of the source. Students take turns measuring the attenuation and logging results of the patch cords in the student workstation. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Measuring Light The SPOTs have an On/Off switch on the left side. They have a button on the front that selects a steady or blinking light. The SPOTs have universal adapters and will accept either SC or ST optical connector. Do not measure attenuation when the SPOT is in the blinking mode. Test results will be unreliable. There are four SPOTS. •White •Blue •Red •IR To measure light intensity, follow these steps. Connect the cable from the SPOT to the power meter (power meter and SPOT ON). Select a wavelength (850nm). Turn the SPOT on and measure the light intensity on the power meter. Introduction to Network Cabling Fiber Optic-Based Systems Figure 2.40.1 2 Light and Optics Activity 2.9 Measuring Light Intensity Measure and record light intensity of the four SPOTS. Procedure: 1. Connect the cable from the SPOT to the power meter (power meter and SPOT ON). 2. Select a wavelength (850nm). 3. Establish a benchmark: zero the power meter using the blue spot as the light source. 4. Measure the light intensity on the power meter for each of the four spots. Complete this checklist SPOT Color Wavelength --------------------- --------------------- --------------------- --------------------- Power meter Wavelength dB or dBM Modulate Yes/No ------------------------------- ------------------------------- ------------------------------- ------------------------------- Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Activity 2.9 Measuring Light Intensity (continued) Attenuation Reading ------------- ------------- ------------- ------------- Rank the SPOTS from strongest to weakest Strongest ------------- ------------- ------------- ------------- Weakest Graph your readings using the graph on the next page: Have students complete the checklist either by sharing the power meters and SPOTs or breaking into teams. Have students plot the chart on the following page. Encourage students to explain the resulting curve. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Do the different SPOTS vary in intensity across the spectrum? Do you notice a pattern? Can you explain the various readings? Refer to the chart on the next page as needed. Figure 2.42.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics The chart below is the response curve for the power meter at 850 nm. The reason that the SPOT readings vary is because the power meter has its strongest indication from the IR region. Areas outside of this range are attenuated, and measured by the power meter. Figure 2.43.1 Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Module Review The four characteristics of light are: •Speed •Wavelength and Frequency •Movement •Amplitude Light travels at 300,000 kilometers per second` in a vacuum. It slows down in air and even more in water. The index of refraction is a number that indicates the speed of light in a medium. The electromagnetic spectrum is a scale that shows all of the waves in nature. Some are extremely long waves and some are extremely short. Light, both visible and nonvisible is only a small part of the electromagnetic spectrum. Wavelength and frequency are inversely proportional as one goes up the other goes down. Non-visible light has a wavelength of 850nm or higher and shorter wavelengths of light are visible. Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics Module Review (continued) Remote controls and Fiber Optic systems use non-visible light. Light reflects off of surfaces and refracts in other mediums. When light reflects the angle of incidence equals the angle of reflection and if the angle of incidence is greater than the critical angle light reflects back into the medium from where it came. When light enters a medium with a higher index of refraction it bends towards the normal line. When light enters a medium with a lower index of refraction it bends away from the normal line. The amplitude of light is measured in dB and the loss of light is called attenuation. There are three attributes of attenuation and they are attenuation is a ratio, attenuation is a function of distance and attenuation varies by the wavelength of light. An attenuation of -3dB means halving of light. Power meters and light sources are used to measure the attenuation of light. The attenuation can be measured by either zero set or subtractive procedures Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics New Terms TERM DEFINITION Angle of Incidence Angle of Reflection The angle that light strikes a surface. The path that reflected light travels – same as angle of incidence. Loss of signal strength. Audio Video Receiver. The angle that light begins to leave a substance at the interface. Below the critical angle, more of the light leaves the substance. All of the types of waves found in nature from sound to gamma rays. Invented by Augustin Fresnel as a means to focus refracted light. The ratio of the speed of light in a vacuum to its speed in a substance. Non-visible light that is used in Fiber Optic systems. Attenuation AVR Critical angle Electromagnetic Spectrum Fresnel Lens Index of Refraction Infrared Light Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics New Terms (continued) TERM DEFINITION Law of Reflection This law states that the angle of incidence is equal to the angle of reflection. The basic unit of the measurement of the metric system, about 39 inches (m). A universal scientific system of measurement. One millionth of a meter, (symbol: µm). Also known as a micrometer. One thousandth of a meter (mm). One billionth of a meter. Also called a nanon. A line that is perpendicular to a surface. The description of light when it bounces off of a surface. The description of how light slows and bends as it enters a substance. The way a scientist can quickly work with very large or very small numbers. The law that states how light refracts in a substance. When the incident angle allows most of the light to remain inside a substance. Meter Metric System Micron Millimeter Nanometer Normal line Reflection Refraction Scientific Notation Snell's Law Total Internal Reflection Introduction to Network Cabling Fiber Optic-Based Systems Introduction to Networking Fiber Optic-Based Systems (Version 3.3) © 1998-2012 by C-Tech Associates, Inc. TRADEMARK ACKNOWLEDGEMENTS All Trademarks and Registered Trademarks are the property of their respective owners. Any oversight in acknowledging trademarks shall not be regarded as affecting the validity of any of these or as an infringement on them. ISBN# 0-9789769-7-5 Fiber Optics 3.3 Student Manual and CD 0-9789769-8-3 Fiber Optics 3.3 Student Manual, CD and Consumables 0-9826956-5-9 Fiber Optics 3.3 Instructor Manual and CD Introduction to Network Cabling Fiber Optic-Based Systems 2 Light and Optics QUESTIONS? Module Test Time! Introduction to Network Cabling Fiber Optic-Based Systems