Many Modes - Multimode Fiber

Transcript

Mute and Chat – Instructions Use this button to send a chat message to the trainer Use this button to mute/unmute CCTV Fiber Principles Fiber Optic Advantages Long distances No cross-talk or short circuits High bandwidth EMI/RFI Immunity Signal security – much harder to “Tap-in” Flexible installation options Fiber Optic Advantages Video over Coax Signal ground connected to mains ground STOP Lightning & ground loop protection No Power Transmission 1 km Fiber 1 km Coax Cost-effective upgrades and system expansion Lightweight and small diameter Mainstream Uses for Fiber  Telecommunications  Data Communications  LAN/WAN  Security  Surveillance Video  Access control  Industrial/Factory Automation  Monitoring  PLC Controllers  Intelligent Transportation Systems  Signal control  Video Detection / Surveillance How does it work ? • Light is transmitted along hair-thin optical fibers by a series of internal reflections & Reflection Refraction 96% Air 4% Reflection 100% Glass 99.98% 100% Total Internal Reflection Multiple Reflections Air Glass Air Reflections in a Cylinder Air Glass Air Leakage due to Surface Defects contamination Air Glass scratch Air The Solution - Optical Cladding High Refractive Index Core Glass Lower Refractive Index Cladding Glass Surface Defects Air Air The Solution - Buffer Coating 62.5/125 Fiber Core Diameter (e.g. 62.5um) Cladding Diameter (e.g. 125um) Primary (buffer) coating Transmission Modes What is a Mode? Low Order Mode Different Ray, same Mode High Order Mode Many modes - Multimode Fiber Multimode Fiber Dispersion Modal Dispersion with Multimode Fiber Received Sent LED ON (1) LED ON (1) LED OFF (0) LED OFF (0) L E D Core Cladding Separate light paths (modes) Effect of Dispersion 1 0 1 0 1 0 1 1 0 1 0 1 0 1 50% decision level 1 ? 1 ? 1 ? 1 50% decision level Lost data Fiber Bandwidth Dispersion limits the maximum bandwidth capability of a fiber, which is measured in MHz.km. What does this mean? Fiber Bandwidth Suppose a fiber has a bandwidth of 15 MHz.km 3 km 5 MHz 1 km 15 MHz 2 km 7.5 MHz or any other combination of 15 / MHz = km Bandwidth Generalization/Comparison Volume of information transmitted is constant. In this case 6.0 MHz (standard color video) UTP Point at which there is a 3 dB loss. Coax (Half of Signal Strength Is Lost) Multimode Fiber 850 nm 1300 nm Singlemode Fiber .25 km 1 km 4 km Distance 10 km 35 km Multimode Tube Single-mode Tube Single-mode Fiber 9/125 Fiber Core Diameter (8.3um) Cladding Diameter (125um) Single-mode Fiber Dispersion in single-mode fibers is very small, and is determined by the characteristics of the transmitter emitter. Bandwidth of single-mode fiber is typically 50GHz.km In practice, the number of simultaneous channels that can be carried is limited by the electronics. The disadvantage of single-mode fibers is their very small core size (typically 8.3um), which necessitates high intensity & expensive lasers in the transmitter, and more precise connectors. Selecting Optics Multimode – Light Emitting Diodes (LED’s) - 850 nm – Edge Emitting LED’s (1300 nm) Singlemode – Edge Emitting LED’s (1300 nm) – Laser Diodes (1310 or 1550 nm) Industry Standard Fiber Sizes 125 m 50 / 62.5m Core 62.5/125 Multimode Fiber 125 m 9 m Core 9/125 Single-mode Fiber 75 m Human hair Fiber Transmission 100% Transmission 50% Exponential Decay 25% 12.5% 1 Km 2 Km 3 Km Distance 4 Km Fiber Attenuation 12 dB Attenuation 9 dB Slope equals Fiber Attenuation (dB/km) 6 dB 3 dB 0 dB 1 Km 2 Km 3 Km Distance 4 Km Fiber Spectral Response 20 10 7 850 nm Window 5 4 3 2 Fiber Attenuation dB/km 1.0 1300 nm Window 1550 nm Window 0.7 0.5 0.4 0.3 0.2 0.1 400 Human Eye Response 500 600 700 800 900 1000 1100 1200 1300 Light Source Wavelength (nm) 1400 1500 1600 Transmission Technologies Types of Transmission 1. Analog Transmission - intensity modulation (IM) (AM) - frequency modulation (FM) 2. Digital Transmission - transmission of analog video inputs - transmission of digital video inputs Analog Transmission Intensity Modulation Intensity or brightness of fiber optics emitter (LED) is varied in proportion to the level of the incoming signal. Receiver then produces an output which is controlled by the Automatic Gain Control (AGC) to produce an identical output. Fiber attenuation Tx Incoming signal Launched light intensity Rx Received light intensity Outgoing signal AGC Benefits of Intensity Modulation • Simple, low cost electronics. • Reliable, easy to maintain & service. • Good performance. • Excellent value for money. Limitations of Intensity Modulation (AM) Light o/p - - Non-linearity of LED Signal I/p Electrical Interference (noise) Incoming signal Tx Rx Outgoing signal Analog Transmission Frequency Modulation Transmitter generates a high frequency carrier signal. Frequency of this carrier is varied according to level of incoming signal. Receiver amplifies and clips (to eliminate AM noise) then demodulates to recover the original signal. Tx Incoming signal Fiber attenuation Launched light intensity Received light intensity Rx Outgoing signal Benefits of Frequency Modulation • System is less dependent on LED linearity. • Transmission is immune to AM interference. • AGC operation does not restrict signal format. • Multiple carrier frequencies permit two or more signals to be multiplexed on to one fiber. • Can be used for transmission of either analog or data signals, or both. FM vs. AM SNR Performance Digital Transmission of Analog Signals Transmitter codes incoming signal into a series of 1’s and 0’s for transmission over the fiber. Receiver decodes the recovered 1’s and 0’s into the original signal. Tx Fiber attenuation A Incoming signal Rx D D Launched light intensity Received light intensity A Outgoing signal Analog to Digital Conversion Incoming Signal Sampled Signal (at 2x highest frequency) Signal Amplitude 3456789998643113456899875421234578987532112346789 Binary Coded Signal 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1001, 1000, 0110, 0100, 0011, 0001, 0001, 0011, 0100, 0101, 0110, 1000, 1001, 1001, 1000, 0111, 0101, 0100, 0010, 0001, 0010, 0011, 0100, 0101, 0111, 1000, 1001, 1000, 0111, 0101, 0011, 0010, 0001, 0001, 0010, 0011, 0100, 0110, 0111, 1000, 1001 Number of Digitization Bits • 8 bits - Surveillance CCTV 480 TV lines resolution (6 MHz video bandwidth) 55dB+ Video Signal/Noise ratio (S/N) 2% Differential Gain (Diff. Gain) 270 Mb/s (approx. 135MHz) transmission speed in fiber • 10 bits - Broadcast TV 560 TV lines resolution (7 MHz video bandwidth) 60dB+ Video Signal/Noise ratio (S/N) <1% Differential Gain (Diff. Gain) 400 Mb/s (approx. 200MHz) transmission speed in fiber Digital-Encoding Advantages True Broadcast Performance: - Can exceed all RS-250C short-haul transmission requirements Minimal Cost increase when compared to FM: - Best transmission quality vs. cost Eliminates Cross Talk and Inter-modulation. Very high immunity to RFI/EMI. Enhanced MTBF and reliability due to reduced parts requirement. (compared to FM) SNR, DIFF. PHASE & DIFF. GAIN are consistent from minimum path to maximum usable optical path loss. Digital-Encoding Disadvantages MULTIMODE OPERATION: - Distance/bandwidth limitations limit usable optical transmission distance. - Not available for low-cost 850 nm. Operation is only 1300 nm. FM vs. Digital SNR Performance 70 dB Digital Technology High Picture Quality 60 dB Good Picture Quality 50 dB Noisy Picture 25 miles (40 km) 31.25 miles (50 km) 37.5 miles (60 km) 43.75 miles (70 km) PTZ Dome - Video and Telemetry Data PTZ/Dome Camera Transmission Monitor PTZ/Dome Camera Coax T.P. Coax T.P. PTZ Keyboard PTZ Camera Transmission Monitor PTZ/Dome Camera Coax Coax Transmitter T.P. Optical Fibers Receiver T.P. PTZ Keyboard PTZ Camera Transmission Monitor PTZ/Dome Camera Coax Coax F.O. Transmitter Transmitter T.P. F.O. Receiver Optical Fiber Receiver T.P. PTZ Keyboard Single Fiber PTZ Transmission 850 nm Transmitter 850 nm Detector Video Data (Pan & Tilt) 1300 nm Detector 1300 nm Transmitter Single Fiber PTZ Transmission PTZ/Dome Camera Coax T.P. 1300 nm Transmitter 1300 nm WDM Coupler 850 nm Receiver 850 nm Single Fiber Bi-directional Transmission Monitor 1300 nm 1300 nm Coax Receiver WDM Coupler 850 nm 850 nm Transmitter T.P. PTZ Keyboard Cost Analysis Cost Comparisons 4 Coax Cables 4 video channels 4 video channels OR 4 video channels Tx Tx Tx Tx 4 fibers Rx Rx Rx Rx 4 video channels Tx 4 video channels OR 4 video channels Tx 1 fiber Cost Comparisons $/channel 4 channels per fiber Escalating Coax/ Repeater cost Breakeven Distance ?? Single channel per fiber Coax Cable >600m Distance (km) Contacts Francesco Della Mora – Regional Sales Manager [email protected] +34 673 488 922 Tom Exley – Technical Manager [email protected] +44 776 974 78 18