CWDM Networks Reference Poster CWDM/DWDM Standards REFERENCE POSTER CWDM Testing CWDM Characteristics • Affordable alternative for bandwidth increase • Limited maximum distance • Can be easily overlaid on existing infrastructure • Typical transmitter output power : 5 dBm Future of CWDM Networks Construction/Fiber Qualification Test Test Instrument Connector cleanliness according to IEC and IPC standards Inspection probe with automatic pass/fail analysis software ORL measurement ORL testers, OTDR Fiber, connector, splice loss CWDM OTDR Channel power and wavelength check Channel analyzer, CWDM-calibrated power meter Wavelength assignment testing CWDM OTDR, channel analyzer Turn-Up and Provisioning Maintenance and Troubleshooting Future of CWDM Networks: Hybrid Networks or DWDM over CWDM CWDM WL 1470 nm 1490 nm 1510 nm 1530 nm 1550 nm 1570 nm 1590 nm 1610 nm • Typical signal power at receiver : > -25 dBm ITU-T G. 694.2—Spectral Grids for WDM Applications: CWDM Wavelength Grid • 18 wavelengths defined by ITU-T, though usually only 8 or 16 are used DWDM WL • Transmitter drift tolerance: ±6-7 nm • Channel spacing: 20 nm • Increase network capacity by replacing a CWDM card by a DWDM card • Single CWDM channel now supports 8 or 16 wavelengths Channel Number Central Wavelength (nm) 1 1271 2 1291 3 1311 4 1331 5 1351 6 1371 7 1391 8 1411 1431 1451 11 1471 12 1491 13 1511 14 1531 15 1551 16 1571 17 1591 18 1611 • No amplification = no noise = no need to measure optical signal-to-noise ratio (OSNR) Channel analyzer, OSA Is Your Network CWDM-Ready? In most CWDM networks, C-band and L-band are used where attenuation is pretty flat with wavelength. If more than eight wavelengths are required, the S-band must be used where attenuation varies a lot, around the water peak at 1383 nm. Therefore, an appreciation of spectral loss is required. By utilizing an OTDR with four wavelengths including 1383 nm, a simple calculation yields the loss across the whole CWDM range. • Spectral testing: channel analyzers won’t work. Basic optical spectrum analyzers (OSAs) without OSNR capabilities can analyze both CWDM and unamplified DWDM wavelengths without the extra cost of full OSAs. Basic OSAs provide the best fit for the technician to test DWDM over CWDM. CWDM Testing with iOLM 0.6 Calculated Fiber Spectral Attenuation 0.5 Attenuation (dB/km) 9 10 Channel wavelength, power drift testing Using a multipulse approach to ensure maximum accuracy, the iOLM enables any technician to test individual CWDM channels at the touch of one button. Measured Fiber Losses by an OTDR 0.4 A Pos. 0.3 0,0000 Len. Link ORL: 0.0 1250 Fiber Attenuation (dB/km) O-Band 1260-1360 E-Band 1360-1460 2.0 C-Band L-Band S-Band 1530- 15651460-1530 1565 1625 Water Peak 1.5 1270 1290 1310 1330 1350 1370 1390 1300 1350 1400 1450 1500 Wavelength (nm) 1550 1600 Head-End/CO 40.00 0.5 1 OADM 1530 nm 10 20 30 40 50 60 70 1600 Wavelength (nm) 5,1338 5,0547 10,534 km Global pass/fail status 19,684 dB 32,50 dB Pass 3 25.00 1500 5,2818 Connectors are key components that interconnect all network elements. This is why maintaining them is essential to ensuring that the equipment will operate at maximum performance and catastrophic network failures will be avoided. OADM 1550 nm 30.00 ITU-T G.652 Fibre 25,265 1610 nm Properly inspecting a fiber-optic cable can prevent a slew of problems, saving you time, money and pains. 45.00 1410 1430 1450 1470 1490 1610 1510 1530 1550 1570 1590 1400 76,4 km 65,962 ‘AN OUNCE OF PREVENTION IS WORTH A POUND OF CURE’ 2 1300 60,908 Fiber Connector Inspection CWDM Testing: CWDM OTDR 35.00 1200 55,774 1650 Calculated fiber spectral attenuation from model. 1.0 0.0 50,492 25,227 iOLM Link loss: ITU-T G. 652—Characteristics of a Singlemode Fiber and Cable 2.5 25,227 A 0.2 0.1 3.0 81,393 km B 80 Common Connector Issues 1470 nm 1490 nm EXFO Headquarters Tel.: +1 418 683-0211 Toll-free: +1 800 663-3936 (USA and Canada) Fax: +1 418 683-2170 info@EXFO.com www.EXFO.com 1510 nm ITU-T G.695—CWDM Optical Interfaces Dust/dirt residue • Provides optical parameter values for physical layer interfaces of CWDM applications with up to 16 channels and up to 10 Gbit/s EXFO serves over 2000 customers in more than 100 countries. To find your local office contact details, please go to www.EXFO.com/contact. © 2012 EXFO Inc. All rights reserved. Printed in Canada 1530 nm 20120640 Oily residue Dirty/damaged connector Connector Inspection and Maintenance Solutions FTB-200 12/11 Wet residue SAP1064097 OTDR trace showing the effects of the 1550 nm wavelength going through different OADMs. CWDM Testing: Spectral Analysis Topologies Connector Cleaning Supplies Fiber Inspection Probe and Display Fiber Inspection Probe on FTB Platform Connector Endface Analysis Software • Dry cleaning supplies • Inspects male and female connectors • Uses the platform screen; no need for additional display • Delivers clear-cut pass/fail verdict • Very secure, no direct eye exposure to laser radiations • Stores images for future reference • Guarantees a uniform level of acceptance (IEC and IPC standards-compliant) • Wet cleaning supplies • Cleaning kits Residential/Subdivisions Enterprise • Performs automated image analysis (when paired with analysis software) Cell Tower Where to Inspect/Clean The following items should always be on your inspection/cleaning list: (R)OADM • Patch panel (e.g., splitter cabinet) (R)OADM Splitter Head-End/CO • Test jumpers OSA trace of a four-CWDM channels. • Cable connectors Patch panel inspection. (R)OADM DWDM Backbone When to Clean (R)OADM CWDM MUX/DMUX CWDM Channel Add/Drop CWDM Channel Add/Drop The very first step is connector inspection. This applies to all testing phases–construction, activation and maintenance. Connectors should be cleaned only if the inspection reveals that they are dirty. CWDM Channel Add/Drop How to Clean a Single Fiber Connector with a Dry-Cleaning Method Each customer (enterprise or tower) receives a wavelength via an add/drop multiplexer (OADM). Scan and watch the video (EXFO.com/Connector2) Channel power for each CWDM wavelength measured with a channel analyzer. DWDM Networks Reference Poster Standards DWDM Dispersion Testing Network Topology • Dispersion is an important phenomenon that must be tested in DWDM networks to avoid bit errors. The longer the light path, the more dispersion there is. DWDM Characteristics • Best approach to maximize fiber capacity λλ1 1 • EXFO recommends dispersion testing for fiber span longer than 20 km. • Extensively used in metro, long-haul and ultra-long-haul networks λλ2 2 T1 Voice ITU-T G. 694.1—Spectral Grids for WDM Applications: DWDM Frequency Grid • Defines specific wavelengths (frequencies) allowed for 12.5 GHz, 25 GHz, 50 GHz and 100 GHz channel spacing Channel Spacing (GHz) Allowed Channel Frequencies (THz) 12.5 193.1 + n*0.0125 25 193.1 + n*0.025 50 193.1 + n*0.05 100 193.1 + n*0.1 Chromatic Dispersion (CD) λ3 T1/T3 PL SONET/SDH ATM Chromatic dispersion is a pulse broadening that occurs when different wavelengths of an optical pulse travel at different velocities in a fiber due to the variation of the fiber index of refraction with wavelength. DCM Ethernet Ethernet OADM OTN/G.709 Bidirectional Multiwavelength Optical Amplifier ESCON FC (n is a positive or negative integer including zero) Wavelength Services Polarization Mode Dispersion (PMD) T0 T Frequency (GHz) DCD WDM t PMD is a pulse broadening that occurs when different polarization modes (fast axis and slow axis) travel at different velocities due to fiber geometric imperfections or environmental constraints (heat, mechanical stress on the fiber like bends, etc.). PMD leads to differential group delay (DGD). 2.9979 x 108 Wavelength (nm) = Building Blocks/Components of a WDM Network DWDM Multiplexer/Demultiplexer λ1 λ2 2 Δt DCM = Dispersion Compensating Module OADM = Optical Add/Drop Multiplexer λ3 fast axis z, t Channel Spacing Conversion GHz 200 100 50 25 12.5 nm 1.6 0.8 0.4 0.2 0.1 slow axis DGD Optical Transport Network (OTN) How to Handle High PMD OAM&P CO ITU-T G.650.3—Test Methods for Installed Singlemode Optical Fiber Cable Links Transparency CO Splice loss, splice location, fiber uniformity and cable length OTDR Polarization mode dispersion PMD tester rn he Et 2 km 80 km Scalable Up to 100G FE C 80 km he rn et Core Network OTN/DWDM Et ORL tester CO Good section (acceptable) Bad section (must be replaced) ITU G.709 defines a stronger forward error correction for OTN, which can result in up to 6.2 dB improvement in signal-to-noise ratio (SNR). C CD tester Optical return loss CO FE Chromatic dispersion Frequency Test Instrument Attenuation High OTDR, OLTS, probes, OSA Optical channel power changes due to gain variations High OSA Frequency (or wavelength) deviation from normal High OSA et rn he Et 10-1 10-2 10-3 10-4 Et he rn et Impairment FE Common Failures in DWDM Networks Distributed PMD analysis breaks down the measurement results, effectively pinpointing the high-contributing sections of the link. C Traditional PMD measurement techniques provide a total link PMD value but do not locate which spans are causing the link to fail the test. 10 -6 Medium PMD tester, distributed PMD tester Four-wave mixing Medium OSA • Locates the fiber sections that are the main contributors of the total PMD of a link Amplified spontaneous emission noise from optical amplifier Medium OSA • Enables to isolate and repair only the worst PMD sections of the fiber cable and allows the cost-effective upgrade of a fiber network Chromatic dispersion, CD slope Medium CD tester 10-10 Reflection Medium OLTS, OTDR, probe 10-11 Laser noise Medium OSA 10-12 Interchannel crosstalk Medium OSA 10-13 Interferometric crosstalk Medium OSA 10-14 10-7 BER G.709 10-8 10-9 10-15 2 EXFO recommendation Source: Recommendation ITU-T G. 697. Optical Monitoring for DWDM Systems, Table 1—Optical Impairments. Uncorrected 10-5 Polarization mode dispersion High = 10 events per year Medium = 1 event per year Integrated Solution C OTDR FE Link attenuation 1 km et Inspection probe rn Test Instrument he Recommended Tests Connector endface inspection FEC et Core Network OTN/DWDM • Detailed tests should be carried out on a singlemode fiber for proper operation Et DWDM Testing 5.86 dB 6.2 dB 3 4 5 6 7 High-contributing PMD section. 8 9 Eb/No 10 11 12 13 14 15 BER vs Eb/No DWDM Spectral Testing • Spectral testing with an optical spectrum analyzer (OSA) is key to identifying many common types of failures in DWDM networks, as shown in the following table: Importance of OSNR Definition of Optical Signal-to-Noise Ratio (OSNR) Lower Bit Error Rate Higher OSNR Higher Quality of Service Less Errors in Transmission IEC Method and (R)OADMs IEC Method and 40G Signals • IEC method fails for signals that went through (R)OADMs • IEC method fails for 40G signals • It leads to an underestimation of the noise level • It leads to an overestimation of the noise level -5 CWDM -40 -10 Signal -45 OSNR vs. BER Typical Relationship dBm dBm -15 -20 -50 -25 OSNR 1.00E-03 -30 1.00E-05 -35 BER Channel analyzer Measure wavelength, power and noise Standard OSA DWDM over CWDM only OSA without OSNR DWDM Standard or in-band OSA 1553 1554 1530 1531 Without ROADMs Standard OSA With ROADMs In-band OSA 10G and below 1.00E-11 Real Noise Level IEC Noise Level IEC Noise Level Real Noise Level 1.00E-13 The Solution: In-Band OSNR 1.00E-15 The simplest case for an OSNR measurement is a single channel, as there is no interference coming from adjacent channels. Measure wavelength and power only -60 1552 1.00E-09 DWDM over CWDM -55 -40 1.00E-07 Noise Spectral Analysis Product Selection Guide 18 19 20 21 22 23 OSNR (dB) 24 25 26 27 • In-band OSNR method is required to measure 40G signals or signals that went through (R)OADMs • It consists in measuring the noise level inside the signal band, not out-of-band DWDM 40G In-band OSA
