New OTDR Measurement and Monitoring Techniques · Coherent OTDR • Has found a niche market, testing submarine cables through EDFAs with the help of coupling devices installed in

New OTDR Measurement and Monitoring Techniques

Invited paper W3D.1 OFC 2014 Conference – San Francisco

Session W3D • Fiber Measurements and Characterization

ANDRE CHAMPAVERE

JDSU R&D FRANCE

© 20134JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 2

� Introduction

� Performance improvement trends

� Form factor evolution

� Smart solutions required

� Simplicity vs Complexity

� Capabilities in reserve

� Other OTDR technologies

� New OTDR embedded features

� Pluggable Transceiver embedded OTDR

� Non linear effect impact & new opportunity

� Conclusion

Content


Conventional Optical Time Domain Reflectometer - Principle

Pulse generatorLaser Diode

Coupler

Photodiode

I/O Connector

Time Base

t

DSP

Amplifier

Converter

A/D

To CPU & interfaces

( E/O converter)

( O/E converter)

G

� Single-end measurement

� Optical Pulse Response of the fiber

optic link

� Return signal due to fiber Rayleigh

backscatter and Fresnel reflection at

the interfaces (like connectors)

� Convert time to distance

� Display the signal in a log. scale

Fiber under test

distance L

Lin-to-Log

Sbs(z) = 5.log10(PW. P0 S. αs. 10 ( - αααα.z / 5)) = Cte - α .z

Pulse width (m)

Pulse peak power (W)

Fiber Backscattering factor

Fiber Rayleigh scattering coefficient (m-1)

Fiber Attenuation coefficient (dB/km)

Distance (km)


30 years of Optical Time Domain Reflectometry

Looking to the future, building on the past

80’s

• Performances�• Dimensions� *• Weight �• Mains –to Battery operation • Connectivity �• Display screen % �• Modularity �• Ease of use and user friendly software �

• Automated measurements �• Extension to other measurement types�

* Price�


OTDR performance – Dynamic Range

Dynamic range (DR) the SNR of the OTDR.

Signal can be improved by increasing the pulse energy.

� increasing peak power ( using optical amplifier then

using high power Lasers) reaching now the 1W limit

� increasing pulse width (20µs , 32.5µs) 2km (20µs)

not very often used and considered as the limit

� In addition, Laser Safety and minimum Pulsed Laser

duty cycle to consider

1 Watt limit

2

0

µ

s

m

a

x

250

km

Future DR improvements may be limited and not be based on pulse energy increase. Strong

demand is for medium and low pulse widths with higher DR.


OTDR performances – Dynamic Range & Resolution

Resolution/DR tradeoff, an old story.

• Dead zones divided by 10 in the last decades.

• Event dead zones down to a few tens of cm

• Attenuation dead zones down to a couple of

meters

• Access, FTTx , FTTA , Enterprise network

cannot benefit from DR at large pulse widths.

• PON networks have high budget loss on short

distances where 1µs and above are

prohibitory and shortest pulses don’t give

enough DR.

• Note: Singlemode fiber OTDRs. Typical Dynamic range versus pulse width at 1550nm Singlemode 3mn averaging time on G.652 fiber, taking into account pulse width and associated Bandwidth variation.

Still room for improvement. Today, measuring fiber attenuation after a 1:32 PON splitter

cannot be done at the shortest pulse widths.


� Event dead zone mainly linked to the pulse width (PW) and the OTDR receiver BW.

� Attenuation dead zone much more difficult to reduce

� Depending on event reflectance , the ADZ can be 3 to 6 times larger than EDZ.

� Shorter PW means higher deviation between reflection and Backscatter.

� In short pulse width mode,

� OTDR source spectral width impacts the dead zone due to CD

� Even fiber temperature can have an influence on distance accuracy

Attenuation dead zone (ADZ) still a challenge for OTDRs

<10cm EDZ

<50cm ADZ

Still strong push from customers to reduce OTDR dead zones

Single mode fiber measurement - Considering an PS/UPC typical reflectance


OTDR Form Factor and mechanical integration

Looking to the future, building on the past

Continuous improvement� Yesterday� Mainframe Connected to the

AC mains supply

� Up to 15kg, 30 to 50 liters in volume

� Non-modular then modular with plug-in modules

� Display 20% of the front panel

� Thermal printer, IEEE488 –GPIB , RS232, etc.

� Today� Mainframe restricted to niches

applications.

� Broad offer of sizes & performance

� Modular 5¨display OTDR less than 2 liters for about 1 kg

� Battery operation

� Touch screen, Twice more space % for display

� Rich offer of additional optical options USB, Ethernet, WIFI, etc.

� Tomorrow ?� Lesson learnt from mobile

and smart phone

� Down-sizing reducing display ?

� No OTDR trace ?

� Web enabled options

� More and more connectivity

� Virtualized ?

With an OTDR trace to display , the screen size will defined the smallest form factor.

ROI : Productivity is the ultimate goal to be clearly kept in mind.


Other OTDR technologies (temporary, limited success or limited to niche markets )

� Coherent OTDR

• Has found a niche market, testing submarine cables through EDFAs with the help of coupling devices installed in. Quite complex & dedicated to the application , expensive and still bulky units.

� Commercial Correlation OTDR

� Good way to increase launched energy using a long code bits sequence. A commercial OTDR was introduced on the market by a key vendor without a real success.

� Photon counting

• Single-photon detection offers unmatched sensitivity. Getting no more than one photon is more complex than could appear. Demonstrate high resolution , works better at low backscatter level, cannot cover the full range linear-mode receiver of conventional OTDR that becomes more and more competitive on dead zones over the years.

� OFDR� Very powerful on very short distances ( mm ). Cannot really cover the measurement range of conventional OTDRs

� CD/PMD OTDR

� Single-ended commercial solutions have lost momentum due to limited performances (limited measurement points on one reflective event) in comparison to both-end measurement techniques like wavelength scanning, etc.

� Tunable OTDR� Several technical papers but not enough market interest on such wavelength agile OTDR. Possible use in WDM PON

monitoring. Multi-wavelength OTDR with Up to 18 wavelengths in a single platform for CWDM applications

� Up to 18 wavelengths in a single platform for CWDM applications

Conventional OTDRs are sold in 10s of thousands every year. Competing with and even dethroning it

is not at all imminent.


OTDR new embedded features to do more , quickly and efficiently

� Decreasing fiber network deployment costs , increasing test productivity by :

• integrated additional measurement capabilities to the OTDR

• Reducing fiber handling , limiting optical connections/disconnections , increasing test productivity

• Automating measurement sequences

• Automatic Pass/fail analysis

• Improving the speed and quality of the measurements

• Synchronization and data exchange when both end measurement needed

• Cutting the time spent testing , analyzing results, compiling test results , generating

reports, etc.

Cables with high fiber count , fiber characterization , One connection, one-touch automated measurement

Reducing overall test time , improving measurement quality all in a compact design.

More and more measurement capabilities to be added to the OTDR core part

OTDR

+ CW Source

+ Powermeter

+ BroadBand

Source

� IL

� ORL

� OTDR ( Loss, distance, R, ORL)

� CD/PMD/AP with Analyzer on the

far end side


Pluggable transceivers with embedded OTDR capabilities

OTDR-like functions added to SFP transceivers ,

� Testing at the traffic wavelength

� No additional fiber connection, simpler optical layout

� Different techniques in competition (correlation, pulsed, …)

� Different applications (In-service , Out-of-service, P2P, PON, etc…)

� Concession on OTDR performance in such a SFF

� Temptation to push objectives towards conventional OTDR techniques by adding HW.

� OTDR-like feature and Tx/Rx sharing failure mode,

� Often somewhere closer to a Reflective Fault locator rather than a real OTDR.

� Often dependent on the reflectance of the event

� Limited to location and presence of the active equipment.

� Non-pluggable embedded OTDRs are equipment agnostic , more physically intrusive but less data intrusive.

OTDR

� LD� Photodiode� Coupler � Connector� Electronics

� …

Tx/Rx

Attractive concept but still today challenging in terms of customer value.

Note Fiber cuts only , excluding Fiber Bending


Smarter and Smarter products

OTDR users do not want to waste their precious time� Connecting disconnected patch cords

� Configuring the OTDR , opening menus

� Analyzing details on the OTDR trace or results

� Storing traces and results

� Creating measurement report

� Transferring data ( connectivity)

� Coming back to the field redoing measurements when wrong set-up

� Waiting 3mn for “efficient” averaging time.

� … Reading the user manual

OTDR technology will be less and less visible moving from Product to Solution offers, by leveraging

Embedded intelligence


Complexity is changing sides

OTDR Designers

� Auto-config

� Auto-range

� Auto-meas.

� Ghost detection

� Bend detection

� Auto-Bidir

� Multi-λλλλ� Pass-Fail mode

� Results Exchange

� Auto-Store

� BiDir OTDR-LTS

Complexity Simplicity

1985 ……2014

INS

IDE

OU

TS

IDE

Still same rule for future improvement: More complex on the inside to be simpler on the outside

( user side). Higher dependency on automated events detection with optimal sensitivity

OTDR Users


Examples of “old new” OTDR applications

Single end bidirectional OTDR

Simultaneous bi-wavelength measurement

Fiber characterization used in Space Division multiplexing

MCF (Multicore fiber) OTDR

measuring crosstalk of multicore optical fibers ( inter-core crosstalk)

MCF (Multi-mode fiber) OTDR

several independent modes within a single core.

Misc.: MFD , Backscatter coefficient, ..

Rx/TX two port OTDR

Many new solutions have been proposed over the years. Many ideas in reserve and still others to imagine

New OTDR measurement Technics

E-FOC91 Siemens Germany

1998

1991

JDSU ( formerly Schlumberger) OTDRs


Optical Network Test and monitoring gaining momentum

� Fiber cables are vital arteries that support Business activities

� Data center connectivity

� Critical finance exchange (banks & carriers clients)

� Critical data exchanges ( Military customers)

� low latency routes to support algorithmic trading requirements for financial and carrier customers

� Optical network security (Ex.: Intrusion/Fiber tapping)

� RFTS (Remote Fiber Test System) is gaining momentum ( In Service Out-of-Band & Out-of-Service)

� Keep network working 24/7/365

� Avoiding , minimizing outages ( Proactive maintenance)

� Reducing time to fix according to SLAs

� trimming installation time and reducing maintenance

costs ( Staffing expenses and cost).

time �� money

Photon � phomon

bits �� Bucks

100 Gb/s �� 100 GB/s

OTDR

Optical

switch

RFTS is increasing its customer value and the benefit it can bring


Lessons Learned :

� Need to add something that cost “nothing” to mark the fiber fare end (ONT side)

� Cannot count on ONT reflectance

� Initially difficult to determine in advance the expected return

� But much more fiber problems than initially expected ( several levels of subcontracting, cost pressure)

� ROI or Cost Of Non-Investment

Point-to-MultiPoint (P2MP) Monitoring (PON)

30cm

PON RFTS during construction phases offers value ( especially when no active

equipment in place)

Construction

Provisioning

Maintenance

Fiber length and attenuation at

different phases of the construction

ODN test before ONT connection

ONT vs ODN Fault demarcation

The sooner the problems detected the easier the repair

Avoids dispatching skilled technicians when the ONT has simply to be replaced

Reduced MTTR that can impact numerous subscribersDefective branch location

Accurate record in network inventory

Certified measurementAccurate record in network inventory

Measurement ODN length and budget

Avoids erroneous dispatches Certified measurement

Facilitates network maintenance

Customer benefitRemote Optical Network Monitoring


OTDR used outside the strict monitoring of fiber losses

� Today, Rayleigh scattering based Reflectometry is mainly used for local and distributed measurement of loss along optical cables.

� Using wavelength bend sensitivity , OTDR can extend its capabilities to sensing domain

� Distributed strain detection ( like microbend in dark soil)

� water detection

� intrusion detection (macrobend)

RFTS expanding its application coverage to telecom fiber cable sensing


Impact of non-linear effects and OTDR In-Service Out-of-Band Monitoring

In-Service Out-of-Band Monitoring in presence of EDFAs

� Interaction due to non-linear effects between Traffic & Test signal is not new.

� 15 years ago, introduction of new “Raman Resistant” OTDR with :

� Preferred counter-propagation to limit impact on signal ( depletion)

� Power transferred from signal to test wavelength makes ineffective optical filtering

� Capability to handle CW component in the OTDR receiver spectral BW

� In and Out-of-service reference trace ( RFTS applications)

OTDRs need to be resistant to traffic


Impact and opportunity when Distributed Raman Amplification

� DRA occurs along the fiber

� Sensitive to loss ( signal & pump)

� Connectors are critical points of failure

� Requires to check the link before System turn up

� Monitor to detect any degradation

� Associating OTDR with amplifiers is a solution

� But DRA makes the In-Service more challenging ( Gain ON/OFF)

OTDR should benefit from the deployment of Distributed Raman amplifiers in both In and

Out-of-Service mode.

Distributed Raman Amplification


Conclusions

OTDR for field applications :

• Remains the key tool for fiber optic network test.

• Still margin for performance improvement by incremental innovation

• Cost pressure may limit performance improvement by breakthrough innovation.

• OTDR will be smarter and smarter( complexity inside vs outside)

• Fiber Characterization built onto OTDR is a promising area

• RFTS/OTDR market pushed by:

• Its flexibility to cover the life of the network from construction to In-Service monitoring

• Security concerned

• DAS requiring Strict SLA between wireline and wireless operators

• High fiber density pushing automatic process

• Outsourcing that needs automatic and fast qualification tool

• Fiber expansion in emerging markets where there are many cables cut

• Deploying embedded OTDR with amplifiers is gaining interest

• Pluggable OTDR is still challenging

• More and more a versatile and a multi-faceted tool for the field test of fiber optic cables

• Still has still potential for new applications

OTDR a bright past and a promising future

References

[1] A. Champavere “Key OTDR Specification Relates to User’s Real Needs” Test & Measurement World, December 2000[2] V. Lecoeuche, A. Champavere Characterization Techniques for Installed Fibers OFC/NFOEC 2012 Conferences Los Angeles,2012

[3] A. Champavère “Technical challenges and new solutions of FTTX PON Fibre monitoring systems” OFMC 2009 , London[4] A. Champavere, J. Ponchon, “PON test systems - From theory to field deployments” (OFC/NFOEC 2011 Los Angeles, CA

[5] Daisuke Iida, Nazuki Honda, Hisashi Izumita, and Fumihiko Ito “Design of Identification Fibers With Individually Assigned Brillouin Frequency Shifts for Monitoring Passive Optical Networks” Journal of Lightwave Technology, Vol. 25, Issue 5, pp. 1290-1297 (2007)

[6] H. Schmuck and al. , "Embedded OTDR techniques for cost efficient fibre monitoring in optical access networks", ECOC 2006.

Documents

New OTDR Measurement and Monitoring Techniques · Coherent OTDR • Has found a niche market, testing submarine cables through EDFAs with the help of coupling devices installed in