Presenter: Roland Schlehuber. Fluke Networks

Transcription

1 Fiber optic theory and testing Presenter: Roland Schlehuber NE Distribution Sales Manager Fluke Networks

2 Agenda Trends and Performance Requirements in Fiber optics Fiber Inspection and Cleaning Tier 1 Optical Loss testing Encircled Flux Reflectance Tier 2 Optical Time Domain Reflectometer

3 Performance requirements 3

4 Growth Drivers 40/100 GB Ethernet Approved by IEEE in June 2010 The trend continues Higher Speeds Mb Me bps eters db Smaller Shorter loss Distances budgets Token Ring 4 Mb 10BASE- Ring Ring 4 Token FOI L Token 4 Mb Tok Mb ken 10BASE- 10BASE Ring E- 16 FOIL FOIL Token Toke FDDen I/TP Ring Ring PMD FDDI/T 10BASE- PMD PMD 10BASE TP TP FLSE- FL FL ATM AT ATM M Fibre Fibre Channe Channel nel 100BASE ASE- FX FX BASE-S 1000BAS SX SX 10GBASE E-SX SE- 10GBA S ASE- 40GBASE S SR4 SR4 SE- 100GBA 100GBA IEE AS EE AS E-SR10 E-SR ba 0 IEEE 802.3ba

5 Intrinsic Raleigh Scattering Splice Loss Fusion: core alignment Factors Affecting Signal Loss Mechanical: core alignment, dirt on end face, reflection Mode Field Diameter in Single Mode Fibers Numerical Aperture Mismatch in Multimode Fibers Connector Loss Mated Pair in coupler core alignment, dirt on end face, reflection

6 More Factors Affecting Loss Macrobending Bending radius ~ 2 15 mm Affects long wavelengths first Affected mostly by fiber design Microbending Bending radius ~ radius of core Can occur during optical fiber manufacturing process Can be induced during installation due to point pressures Affects all wavelengths, but increases slightly with wavelength Affected by Coating and Cable Design

7 Factors Affecting Performance Dispersion or pulse broadening

8 Effect of Dispersion FDDI Grade 62.5µ fiber 10 Gb/s Bit Period Laser Optimized 50µ fiber 10 Gb/s Bit Period Fiber Core Center Received pulse at 10 GB/s over 300 meters

9 Modal Dispersion Modal Dispersion (Multimode Fibers) Mode is quantum level in light pulse Each mode occupies different area of core Imperfect core structure causes modes to have different speeds Over-Filled Launch (OFL) Measurement Uses LED Completely fills all modes of multimode fiber Differential Modal Dispersion Measurement Uses Laser Injects pulses of light from one side of the core to the other at micron intervals Measures Pulse Intensity and Time of Arrival Effective Modal Bandwidth is determined from this test

10 Multimode Fiber Performance Fiber Type Bandwidth 850 nm) 1 GB/s Link Length (@850 nm) 10 GB/s Link Length (@850 nm) FDDI 62.5 µ m 26 m OM µ m 33 m OM2 50 µ m 82 m OM3 50 µ 1500 (2000)* ~1000 m * 300 m OM4 50 µ 3500 (4700)* ~1040 m * 400 m * * Effective Modal Bandwidth * Lengths unsupported by application standards * Formally stated by the IEEE. Some manufacturers specify more ( m) OM4 grade multimode fiber was approved in EIA/TIA 492AAAD on August 5, 2009

11 IEEE 10/40/100 Gigabit Limits 10GBASE-SR (850 nm laser) MBW Loss Distance 50 micron multimode fiber: db 300 m 50 micron multimode fiber: db 400 m 10GBASE-LX4 (1310 nm laser) 50 micron multimode fiber: db 300 m 50 micron multimode fiber: d 2.00 db 300 m singlemode fiber: 6.30 db 10 km 40GBase-SR4/100GBase-SR10 50 micron multimode fiber: db 100 m 50 micron multimode fiber: dB m 11

12 ANSI/TIA-568-C.0 Test Limit The allowable loss depends on: Number of adapters (connector pairs) Number of splices Length of fiber Wavelength measured You are permitted: 0.75 db per adapter (connector pair) BICSI limits this to 0.5dB 0.3 db per splice

13 ANSI/TIA-568-C.0 Test Limit You are permitted for multimode fiber 3.5 db per 850 nm 1.5 db per 1300 nm Maximum length of 2000 m Far longer than modern applications will allow You are permitted for singlemode fiber 1.0 db per 1310 nm and 1550 nm Inside Plant (ISP) 0.5 db per 1310 nm and 1550 nm Outside Plant (OSP) Maximum length of 3000 m Shorter than most singlemode applications will allow

14 ANSI/TIA-568-C.0 Test Limit Example calculation of loss budget 850 nm: Adapters Splices Fiber = 2 * 0.75 db =0*03dB 0.3 = 0.1 km * 3.5 db Allowable loss = 1.50 db 000dB db 1.85 db

15 Smart Testing & Troubleshooting Eliminate common problems with good practices during installation and maintenance Verify continuity, polarity, adequate end-face condition with basic tools to ensure best termination and installation practices Perform complete cable certification per TIA-568C Basic certification (Tier 1) Extended certification (Tier 2)

16 Polarity Verification with a VFL A Visual Fault Locator (VFL) is good for polarity/continuity verification but Quality cannot be determined by any VFL! Which Link is better? 12 db Loss! 0.5 db Loss!

17 Two-Tier Testing Tier 1: OLTS (Optical Loss Test Set) Conforms to TIA B and TIA (Most closely simulates system) Measures the total loss of a fiber channel Verify polarity using OLTS or VFL Tier 2: OTDR (Optical Time Domain Reflectometer) t OTDR Trace can show segment lengths, connector locations and losses, and non-connector loss events Provides evidence that cable was installed without degrading events (e.g. bends, contaminated or damaged connectors or bad splices Is a single ended test 17

18 Test Example: Tier 1 (OLTS) 50/125 μm cabling Horizontal Cables TR X X 104 m backbone cable X X 3 m patch cord 102 m to the wall outlet MC X Backbone Cables Power Meter 2.00 db Light Source 2.60 db for 10GBase-SR per IEEE PMLS measures total link loss

19 Test Example: Tier 2 (OTDR) Horizontal Cables TR X X X MC X Backbone Cables OTDR characterizes link details

20 Event Map & Event Table from OTDR Event Map Event Table 20

21 Fiber inspection and cleaning 21

22 #1 Problem: Dirt! Contaminated connector end-faces: Leading cause of fiber link failures Particles of dust and debris trapped between fiber end faces cause signal loss, back reflection, and damaged equipment Many Sources of contamination: Equipment rooms & Telecommunication rooms in filthy environments Improper or insufficient cleaning tools, materials, procedures Debris and corrosion from poor quality adapter sleeves Hands of technicians i Airborne 22

23 Why Bother Inspecting End Faces? To Prevent Damage Debris will embed in glass when contaminated connectors are mated When embedded debris is removed, pit remains in glass as permanent damage Pits cause signal loss and back reflection Debris causes other damage such as chips and scratches 23

24 Inspection Images Good Connector Fingerprint on Connector Dirty Di t Connector C t Real images as captured from the Fluke networks Fiber Inspector

25 Automated Pass/Fail Analysis IEC Quantitatively assess the end face quality of a polished fiber optic connector What is a defect? Particles, pits, chips, scratches, embedded and loose debris, cracks, etc. Defects can be categorized into 2 groups: Scratches: permanent linear surface features Defects: all non-linear features detectable on the fiber, typically can be cleaned Pass/Fail results based on number of scratches and defects found in each measurement region of fthe fiber Core, cladding, adhesive layer and contact Adhesive Core Cladding Contact

26 How Automated Analysis Works IEC UPC MM spec PC polished connectors, multimode fibers Zone Name Scratches Defects Core No limit <= 3 um 0 > 3 um 2 <= 3 um None > 3 um No limit < 2 um No limit <= 5 um 5 from 2 um to 5 um Cladding 0 > 5 um None > 5 um Adhesive No limit No limit Contact No limit No >= 10 um Adhesive Core Cladding Contact

27 IPA vs. Hybrid Cleaners Isopropyl Alcohol (IPA) Must use as a minimum 98% IPA Anything less will leave a thin film behind, causing a change in reflectance. But IPA has issues Relatively slow evaporation result in halo effect There is a preference amongst professionals to move to hybrid cleaners. Hybrid Cleaners Evaporate much quicker Aremoreaggressiveatcleaning at Have antistatic properties Having a cleaner with an antistatic properties reduces the chance of dust being attracted to the end face of the connector. According to the EPA, the typically dust particle in the office is between 2 and 10 µm.

28 Cleaning with IBC Cleaners IBC OneClick Cleaners for cleaning different end faces/connectors no training required 1.25 mm LC and MU connector and end faces 2.5 mm SC, ST, FC, E2000 connector and end faces MPO/MTP connector and end faces Cleans Ports on devices and patch panels as well as Cords.with an adapter D l i i l ffi i t f l i Dry cleaning is less efficient for cleaning grease (dried skin oil) than wet cleaning with a solvent and swabs/cleaning cubes

29 Cleaning With a Solvent Pen Start with a clean, lint-free wiping surface every time Material left exposed accumulates ambient dust Material used once should not be used again Use a minimal amount of specialized solvent Important that solvent be removed after cleaning Move the end-face from the wet spot into a dry zone Cleaning with a saturated wipe will not fully remove solvent Cleaning with a dry wipe will not dissolve contaminants and can generate static, attracting dust Proper handling and motion Apply gentle pressure with soft backing behind cleaning surface Hold end-face perpendicular to cleaning surface No figure-8 motion as that s for polishing only Inspect both end faces of any connection before Inspect both end-faces of any connection before insertion If the first cleaning was not sufficient, then clean again until all contamination is removed

30 Tier 1 OLTS testing

31 What Is Done Today Sadly, many folks are setting a reference this way? db Issues You have no idea what the loss is in the adapter Whatever it is, it s subtracted from your measurement The uncertainty is horrendous negative loss

32 What Is Done Today So you end up with this y db x db z db Measurement = x + y + z -? Issues You have no idea what the loss is in the adapter Whatever it is, it s subtracted from your measurement The uncertainty is horrendous negative loss

33 What Is Done Today Let s take an example 0.75 db Issues You have no idea what the loss is in the adapter Whatever it is, it s subtracted from your measurement The uncertainty is horrendous negative loss

34 What Is Done Today Let s take an example 0.1 db 0.3 db 0.3 db Issues Measurement = = db You have no idea what the loss is in the adapter Whatever it is, it s subtracted from your measurement The uncertainty is horrendous negative loss

35 The Right Way: 1-Jumper Reference I measure how much power is leaving this cord. I measure how much power is leaving this cord. After setting the reference disconnect at the input only. Disconnecting the output connectors at ANY time after setting reference invalidates said reference.

36 The Right Way: 1-Jumper Reference I know how much power is leaving this cord. I know how much power is leaving this cord.

37 The Right Way: 1-Jumper Reference I know how much power is entering the link I know how much power is entering the link. I measure the power LEAVING the link and I know the I measure the power LEAVING the link and I know the power ENTERING the link. Therefore, I know the loss of the link with the smallest uncertainty.

38 Verifying The Test Cords After setting the reference and adding the known good receive jumpers at the input ports, test them and save the results to ensure correct loss measurements. * ISO/IEC db for Multimode 0.2 db for Singlemode ANSI/TIA-568-C db? * This can be up to 0.15 db for LC Manufacturers 0.50 db? Do not use off the shelf fiber cords for testing!

39 Encircled flux 39

40 Test equipment #1, loss is 1.06 db Launch Conditions

41 Test equipment #2, loss is 0.66 db Launch Conditions Same test cords! 1.06 db vs db?

42 Traceable Calibration Only the power meter is calibrated to traceable standards The optical source has no traceable calibration Traceable calibration No traceable calibration That s why there is a standard to specify the source output launch condition: Encircled Flux

43 What Is a Launch Condition? The light source s launch condition determines how and where the light is distributed within the fiber. Cladding Core Source 1 Over filled Loss: Too high Source 2 Encircled Flux Compliant Loss: Just Right Source 3 Under filled Loss: Too Low

44 EF Assessment Improvement ANSI/TIA B August 2010 (Current Standard) EF specifies power throughout core using multiple control radii. EF provides tight tolerance on mode power distribution in the outer radii enabling improved agreement between EF-compliant test instruments. EF reduces the variability to less than 10% between 2 different light sources.

45 What about a VCSEL launch? A VCSEL is a type of multimode 850nm laser Like most lasers it is typically underfilled All lasers suffer from what is commonly called speckle Speckle causes a non-uniform launch condition Loss measurements may be noisy due to speckle Standards do NOT allow VCSELs for multimode fiber certification

46 An LED Is Required for MM Testing Excerpt from TIA B and IEC VCSELs and other lasers have very small spectral widths, only an LED can meet this requirement

47 TIA-TSB-4979 Titled: Practical Considerations for Implementation of Multimode Launch Conditions in the Field TSB = Telecommunications System Bulletin Not an official standard An advisory document Chances are will end up in ANSI/TIA-568-D.3 Helps users understand Encircled Flux and the options for implementing it

48 Option 1 Practical Implementation of EF Use an external mode controller

49 Option 1 Practical Implementation of EF Replaces the mandrels Mode controllers

50 Practical Implementation of EF Option 2 -Matched source and test reference cord

51 Reflectance: The silent killer of high speed networks 51

52 What Is Reflectance? When light moves from a medium of a given refractive index n1 into a second medium with refractive index n2, both reflection and refraction of the light may occur. These Fresnel reflections are what you see when looking at a window. Caused by the refractive index difference between air and glass. If not too bad, you can still see through the glass. An air gap between the end faces of a fiber also cause Fresnel reflections to occur.

53 What Do Those Numbers Mean? Reflectance is the preferred term when characterizing a single connector or connection. It is a measure of the amount of power reflected by a connection. It includes one connection It is always negative. Smaller is better (e.g. -35dB is better than -20dB) Refl = 10log P reflected P incident Return Loss is the preferred term when characterizing an entire link It is a measure of the amount of power NOT reflected by a link. Includes all connections and fiber It is always positive. Bigger is better (e.g. +35dB is better than +20dB) P ORL = 10log P incident reflected

54 Why Should You Care? High reflectance causes increased Bit Error Rates (CRC errors) on the network Laser light reflected back into the transmitter increases the Relative Intensity Noise (RIN) of the laser. If the reflection is caused by contamination that results in Mode Selective Losses (e.g. caused by dirt) then Modal Noise is increased. Noise on the network increases Bit Error Rates (adversely affecting the user s experience)

55 Connector Types

56 Reflectance In Connectors If light sees a change in refractive index, there will be a reflection. The most common causes are: Air gap between the connectors Dirt/contamination Residue left behind by the cleaning solution In a perfect world, there would be no air gap between the mated connectors but in reality, there is always a small air gap, also known as undercut : The very best factory terminated connectors will have an undercut better than 50 nm (that s 0.05 µm). The amount of undercut you see will depend on your polishing technique.

57 No More Field Polishing! The quality of field polishing heavily depends upon operator s skill and the polishing process that is followed. They must have a good connector EVERY connector. Problems often encountered: Over polishing the connector (air gap, poor reflectance) Trying to save money or time by not replacing the final polishing paper on a regular basis (final polishing paper is only good for 5 polishes) Skipping the final paper because the Loss/Length testing will probably pass with a limit of 0.75 db per connector Achieving a low reflectance connection is harder than achieving a low loss connection. You can get away with some sloppy practices and still pass Loss/Length testing but OTDR testing will reveal the sloppy practices.

58 4G Fibre Channel with CRC Errors

59 Why We Suggest -35 db 8 Effects of Connector Reflectance on Total Optical Return Loss at 850nm fibre = 100m, 50um, 1.5 db/km Connectors = 4x, equal reflectance (x axis), 0.5 db loss Transceiver = 10GBASE-SR with 12 db return loss tolerance 9 1.7dB over limit if Connector Reflectance is -20 db Total Optical Ret turn Loss (db B) GBASE-SRSR ORL Limit i is 12 db No margin if Connector Reflectance is -30 db Connector Reflectance (db)

60 Tier 2 OTDR testing

61 Tier 2 OTDR Measurement Good example. Spikes are small (good reflectance). Launch + Receive Compensation enabled. Pass/Fail on loss and reflectance measurements for each connection.

62 Traces From Two Typical Multimode Links Link 01 Link 02 The height of the event indicates the amount of reflectance. Poor reflectance widens the deadzone. Short multimode links require shorter deadzones. Poor reflectance may cause negative loss. or the measurement may be impossible to make.

63 Event Table From Two Typical Multimode Links Link 01 Link 02 Unable to measure Excellent reflectance. Poor reflectance. The OTDR event table is generated from automatic analysis. The measured reflectance value may be inspected. Pass/Fail details may be inspected.

64 Multimode Links Digging Deeper The use of the receive fiber enables measurement of the receive event. The tailing caused by the poor reflectance limits the useful information available. Note the ghost caused by the poor reflectance.

65 Summary Do not Plug-and-Pray VFL testing is not testing Perform full Tier 1 Certification Testing Inspect and Clean Proper loss referencing (1-Jumper) Use test reference cords, not off the shelf jumpers Encircled Flux for multimode fiber Perform Tier 2 OTDR testing for Event Loss and Connector Reflectance Provides a rock solid testing strategy Inspect and Clean everything Use Launch and Tail Cords Strive for multimode connector reflectance <-35 db and singlemode connector reflectance <-40 db