Tallinn University of Technology Laboratory exercise 2 of Fiber Optical Communication course FIBER OPTIC COMMUNICATION LINK LOSS, OSNR AND FEC PERFORMANCE Tallinn 2016
Please note that the OSA (Optical Spectrum Analyzer) must be switched on in the beginning of the laboratory exercise, as it needs time to warm up! Aim of the laboratory exercise: The aim of this laboratory exercise is to introduce the possibilities of using optical power budgeting and optical spectrum analyser (OSA) to estimate the performance of the optical communication link. In the laboratory exercise we will inspect attenuation on the links infrastructure (connectors, splices, length of the fibre), insertion losses (filters, splitters), simple amplification, forward error correction (FEC) performance and measure the optical signal to noise ratio (OSNR) with the OSA. After the laboratory exercise, students are expected to know the basics of the bower budgeting, OSA, FEC performance and evaluate the expected link loss and the link performance based on the OSNR values and FEC performance. The list of equipment is provided in the last section of this document. Preparation for the laboratory exercise Please note that sufficient preparation for this laboratory exercise is needed! The student is asked to study and prepare answers for preparation questions (see below) before coming to the lab exercise. The lab exercises are meant for practical introductory matter with real fiber optic devices and either lab report or defence of lab report is not necessary. Participation in the laboratory exercise is compulsory. In the beginning of each lab, these preparation questions are discussed through. If student fails completely without knowing any matter of correct answers, then student is asked to file a lab report with conclusions. Sufficient understanding of covered topics by these preparation questions is the basis of the successful completion of the lab exercise. Questions are following: 1. What should look like an ordinary fiber optic communication link? Please be able to draw it and explain your answer. 2. What is link power budget and why is it important? (See lecture 5) Also calculate power budget for the following problem: Make a power budget for the following fiber optical communication system with a transmission distance of 40 km. The maximum BER is 10-9 and the minimum system margin is 5dB. Data on the components used in the system are listed below: Transmitter: DFB laser, λ= 1.55 µm, output power = 10 mw (10 dbm), 7 db coupling loss to fiber Fiber: Single-mode, available in lengths of 7 km that is spliced together, attenuation = 0.4 db/km, dispersion = 20 ps/(km nm) Connectors: Loss = 1 db/connector (one at the transmitter and one at the receiver) Splices: Loss = 0.2 db/splice Detector: InGaAs-p-i-n, 1 db coupling loss from fiber Receiver sensitivity = -25 dbm for BER =10-9. 3. How one can measure the optical signal to noise ratio (OSNR) with OSA (Optical Spectrum analyzer)? (See Lecture 6 slide 24) 4. Why and how are the EDFAs (Erbium-doped fiber amplifiers) in the fiber optic communication links applied? (See Lecture 6 slide 3) 2
You can write your answers here: 3
8GSM D#01-D#32 IMPORTANT DISCLAIMER: Please note that before starting work with the laboratory equipment you are asked to confirm that you have read carefully the safety instructions for working in the lab and working with fiber optic communication equipment! 1 The Loss and OSNR measurement of the fiber optic link In the figure 1 is depicted fiber optic communication link that has been set up for laboratory exercise. Please introduce yourself the setup and devices of this communication link and make sure that it is connected in the same way as it is seen in the figure 1. SIGNAL FLOW DIRECTION MP1 MP7 MP8 Transmitter D#01 Transmitter D#03 Transmitter D#07 Transmitter D#12 D#01 D#02 D#03 D#04 D#05 D#06 D#07 D#08 D#09 D#10 D#11 D#12 D#09-D#12 D#05-D#08 D#01-D#04 C1 C2 C3 C4 C5 C6 C7 C8 8GSM D#01-D#32 8GSM module Nport output 95/5 S20 1) D20 amplifier input 2) midstage input 3)Midstage output 4) amplifier output 5) Rx direction monport 6) Tx direction monport MP2 MP3 MP4 MP5 MP6 D20 DCM module C1 C2 C3 C4 C5 C6 C7 C8 D#01-D#04 D#05-D#08 D#09-D#12 D#02 D#04 D#05 D#06 D#08 D#09 D#10 D#11 D#01 D#03 D#07 D#12 Receiver D#01 Receiver D#04 Receiver D#07 Receiver D#12 Figure 1 Laboratory fiber optic communication link setup, MP measuring point, WDM channel filters, 8GSM WDM group filters, 95/5 Power splitter module, S20 EDFA (Erbium-Doped Fiber Amplifier) Single Stage, D20 EDFA Double Stage (variable gain) Table 1 Table of measuring points MP Power level [dbm] Loss [db] Noise level [dbm ] OSNR [db] 1 Transmitter output power - 2 95/5 module Network port output power 3 S20 module output power 4 Fiber spool 2 output power 5 Fiber spool 3 output power (=D20 module input power) 6 D20 module output power 7 8GSM C-port output 8 C-port output power (=receiver input power) 4
Note that this system is capable of transmitting 32 DWDM channels in the presence of all the transmitters and receivers. In the figure 1 is shown only 4 transmitters to give you the idea of overall picture. In our current lab setup we also have 4 transmitters and 4 receivers present, but we are not going to use them all. After making sure that everything is connected as in the figure 1, switch on the transmitter and measure the signal, noise power and OSNR of the measuring points (MP) 1 and 2 with the OSA, fill in the table 1. After the signal is present before S20 module, switch on the amplifier S20 and measure the power levels at MP 3 to 5. Calculate the gain needed for D20 amplifier from the measured power budget. Adjust the gain from the interface and switch on the amplifier D20. Pay attention that you do not exceed the maximal permitted power level of the receiver! Measure the power, noise levels and OSNR at MP 6 to 8 with OSA. Calculate the Loss by power level differences between two measuring points. What is the measured link overall power budget and how much margin do you have to take into account if the receiver sensitivity level is -17 dbm? 2 FEC Performance Now make a study about FEC performance. Log in to the ADVA active shelf interface and explore the information given from the interface. Find the parameter of FEC performance. Study how the FEC performance will react to the amplifier D20 gain adjustment. Therefore adjust the gain of amplifier D20, measure the OSNR at the input of the receiver, take a reading of the FEC performance value and fill in the Table 2. Pay attention that you do not exceed the maximal permitted power level of the receiver! Table 2 FEC performance Amplifier D20 Gain[dB] OSNR [db] FEC performance [corrected errors] Optimal gain Disabled Attenuator and increased gain 5
List of equipment: Optical fibres and handling tools: One to three fibre spools in Lab environment (ITU-T G652 standard based fibre, ITU-T G.655 compliant Corning LEAF (Non-Zero Dispersion Shifted Fiber) and Corning Metrocore optical fibers) Fiberscope and necessary adapters Fibre cleaning equipment (cleaning cassette and cleaning sticks) Attenuators and patch cords/optical jumpers Optical WDM transmission equipment (including transmitters, receivers, amplifiers): 1 ADVA active shelf (SH7HU) 4x tuneable DWDM laser transponders WDM Channel filters (4-CSM) WDM Group filters (8-GSM) Power splitter (95/5 module) Erbium-doped Fiber Amplifier Single Stage (EDFA S20) Erbium-doped Fiber Amplifier Double Stage (EDFA D20) DCM Grating based module (DCM-G-60) DCM Fibre based module (DCM-F-80) Optical identification and measurement equipment: Optical Spectrum Analyser Powermeter 6