Fiber Optics Communications Lecture One PDF

Fiber Optics Communications Lecture one Lecturer: Ahmed H. Al zaidy OVERVIEW OF OPTICAL FIBER COMMUNICATION Introduction Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an...

Fiber Optics Communications Lecture one Lecturer: Ahmed H. Al zaidy OVERVIEW OF OPTICAL FIBER COMMUNICATION Introduction Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. Fiber is preferred over electrical cabling when high bandwidth, long distance, or immunity to electromagnetic interference are required. This type of communication can transmit voice, video, and telemetry through local area networks, computer networks, or across long distances. Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Researchers at Bell Labs have reached internet speeds of over 100 petabit ×kilometer per second using fiber-optic communication. The process of communicating using fiber-optics involves the following basic steps: 1. creating the optical signal involving the use of a transmitter, usually from an electrical signal 2. relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak 3. receiving the optical signal 4. converting it into an electrical signal 1  Fiber Optics Communications Lecture one Lecturer: Ahmed H. Al zaidy Block Diagram of Optical Fiber Communication System Fig 1: Block Diagram of Optical Fiber Communication System Message origin: Generally message origin is from a transducer that converts a non-electrical message into an electrical signal. Common examples include microphones for converting sound waves into currents and video (TV) cameras for converting images into current. For data transfer between computers, the message is already in electrical form. Modulator: The modulator has two main functions:  It converts the electrical message into proper format.  It impresses this signal onto the wave generated by the carrier source. The distinct categories of modulation are used i.e. analog modulation and digital modulation. 2 Fiber Optics Communications Lecture one Lecturer: Ahmed H. Al zaidy Carrier source: Carrier source generates the wave on which the information is transmitted. This wave is called the carrier. For fiber optic system, a laser diode (LD) or a light emitting diode (LED) is used. They can be called as optic oscillators, they provide stable, single frequency waves with sufficient power for long distance propagation. Channel coupler: Coupler feeds the power into information channel. For an atmospheric optic system, the channel coupler is a lens used for collimating the light emitted by the source and directing this light towards the receiver. The coupler must efficiently transfer the modulated light beam from the source to the optic fiber. The channel coupler design is an important part of fiber system because of possibility of high losses. Information channel: The information channel is the path between the transmitter and receiver. In fiber optic communications, a glass or plastic fiber is the channel. Desirable characteristics of the information channel include low attenuation and large light acceptance cone angle. Optical amplifiers boost the power levels of weak signals. Amplifiers are needed in very long links to provide sufficient power to the receiver. Repeaters can be used only for digital systems. They convert weak and distorted optical signals to electrical ones and then regenerate the original digital pulse trains for further transmission. Another important property of the information channel is the propagation time of the waves travelling along it. A signal propagating along a fiber normally contains a range of fiber optic frequencies and divides its power along several ray paths. This results in a distortion of the propagation signal. In a digital system, this distortion appears as a spreading and deforming of the pulses. The spreading is so great that adjacent pulses begin to overlap and become unrecognizable as separate bits of information. 3 Fiber Optics Communications Lecture one Lecturer: Ahmed H. Al zaidy Optical detector: The information begin transmitted is detected by detector. In the fiber system the optic wave is converted into an electric current by a photodetector. The current developed by the detector is proportional to the power in the incident optic wave. Detector output current contains the transmitted information. This detector output is then filtered to remove the constant bias and then amplified. The important properties of photodetectors are small size, economy, long life, low power consumption, high sensitivity to optic signals and fast response to quick variations in the optic power. Signal processing: Signal processing includes filtering, amplification. Proper filtering maximizes the ratio of signal to unwanted power. For a digital syst5em decision circuit is an additional block. The bit error rate (BER) should be very small for quality communications. Message output: The electrical form of the message emerging from the signal processor is transformed into a sound wave or visual image. Sometimes these signals are directly usable when computers or other machines are connected through a fiber system. 4 Fiber Optics Communications Lecture one Lecturer: Ahmed H. Al zaidy Electromagnetic Spectrum The radio waves and light are electromagnetic waves. The rate at which they alternate in polarity is called their frequency (f) measured in hertz (Hz). The speed of electromagnetic wave (c) in free space is approximately 3 x 108 m/sec. The distance travelled during each cycle is called as wavelength (λ) frequencies; wavelength is often stated in microns or nanometers. 1micron (µ) = 1 Micrometer (1 x 10-6), 1 Nano (n) = 10-9 meter Fiber optics uses visible and infrared light. Infrared light covers a fairly wide range of wavelengths and is generally used for all fiber optic communications. Visible light is normally used for very short range transmission using a plastic fiber. Fig 2: Electromagnetic Spectrum 5  Fiber Optics Communications Lecture one Lecturer: Ahmed H. Al zaidy Advantages of Fiber Optic Transmission Optical fibers have largely replaced copper wire communications in core networks in the developed world, because of its advantages over electrical transmission. Here are the main advantages of fiber optic transmission. 1. Extremely High Bandwidth: No other cable-based data transmission medium offers the bandwidth that fiber does. The volume of data that fiber optic cables transmit per unit time is far great than copper cables. 2. Longer Distance: in fiber optic transmission, optical cables are capable of providing low power loss, which enables signals can be transmitted to a longer distance than copper cables. 3. Resistance to Electromagnetic Interference: in practical cable deployment, it’s inevitable to meet environments like power substations, heating, ventilating and other industrial sources of interference. However, fiber has a very low rate of bit error (10 EXP-13), as a result of fiber being so resistant to electromagnetic interference. Fiber optic transmission is virtually noise free. 4. Low Security Risk: the growth of the fiber optic communication market is mainly driven by increasing awareness about data security concerns and use of the alternative raw material. Data or signals are transmitted via light in fiber optic transmission. Therefore there is no way to detect the data being transmitted by "listening in" to the electromagnetic energy "leaking" through the cable, which ensures the absolute security of information. 5. Small Size: fiber optic cable has a very small diameter. For instance, the cable diameter of a single OM3 multimode fiber is about 2mm, which is smaller than that of coaxial copper cable. Small size saves more space in fiber optic transmission. 6. Light Weight: fiber optic cables are made of glass or plastic, and they are thinner than copper cables. These make them lighter and easy to install. 7. Easy to Accommodate Increasing Bandwidth: with the use of fiber optic cable, new equipment can be added to existing cable infrastructure. Because optical cable can provide vastly expanded capacity over the originally laid cable. And WDM (wavelength 6  Fiber Optics Communications Lecture one Lecturer: Ahmed H. Al zaidy division multiplexing) technology, including CWDM and DWDM, enables fiber cables the ability to accommodate more bandwidth. Disadvantages of Fiber Optic Transmission Though fiber optic transmission brings lots of convenience, its disadvantages also cannot be ignored. 1. Fragility: usually optical fiber cables are made of glass, which lends to they are more fragile than electrical wires. In addition, glass can be affected by various chemicals including hydrogen gas (a problem in underwater cables), making them need more cares when deployed under ground. 2. Difficult to Install: it’s not easy to splice fiber optic cable. And if you bend them too much, they will break. And fiber cable is highly susceptible to becoming cut or damaged during installation or construction activities. All these make it difficult to install. 3. Attenuation & Dispersion: as transmission distance getting longer, light will be attenuated and dispersed, which requires extra optical components like EDFA to be added. 4. Cost Is Higher Than Copper Cable: despite the fact that fiber optic installation costs are dropping by as much as 60% a year, installing fiber optic cabling is still relatively higher than copper cables. Because copper cable installation does not need extra care like fiber cables. However, optical fiber is still moving into the local loop, and through technologies such as FTTx (fiber to the home, premises, etc.) and PONs (passive optical networks), enabling subscriber and end user broadband access. 5. Special Equipment Is Often Required: to ensure the quality of fiber optic transmission, some special equipment is needed. For example, equipment such as OTDR (optical time-domain reflectometry) is required and expensive, specialized optical test equipment such as optical probes and power meter are needed at most fiber endpoints to properly provide testing of optical fiber. 7  Fiber Optics Communications Lecture one Lecturer: Ahmed H. Al zaidy Applications of Optical Fiber Communications Fiber optic cables find many uses in a wide variety of industries and applications. Some uses of fiber optic cables include 1. Medical: Used as light guides, imaging tools and also as lasers for surgeries 2. Defense/Government: Used as hydrophones for seismic waves and SONAR , as wiring in aircraft, submarines and other vehicles and also for field networking 3. Data Storage: Used for data transmission 4. Telecommunications: Fiber is laid and used for transmitting and receiving purposes 5. Networking: Used to connect users and servers in a variety of network settings and help increase the speed and accuracy of data transmission 6. Industrial/Commercial: Used for imaging in hard to reach areas, as wiring where EMI is an issue, as sensory devices to make temperature, pressure and other measurements, and as wiring in automobiles and in industrial settings 7. Broadcast/CATV: Broadcast/cable companies are using fiber optic cables for wiring CATV, HDTV, internet, video on- demand and other applications Fiber optic cables are used for lighting and imaging and as sensors to measure and monitor a vast array of variables. Fiber optic cables are also used in research and development and testing across all the above mentioned industries The optical fibers have many applications. Some of them are as follows: Used in telephone systems Used in sub-marine cable networks Used in data link for computer networks, CATV Systems Used in CCTV surveillance cameras Used for connecting fire, police, and other emergency services. Used in hospitals, schools, and traffic management systems. 8