Grooming Middle East Cablers to Meet Ultra High-Speed FO Challenges

As published in the July Issue of SubTel Forum Magazine

By Greg Varisco and Shaheen Qamar
July 29, 2022

Lowering cost per unit of capacity is the goal while finding ways to increase both the security and reliability of the network.  This article is meant to focus on the optical design considerations using the most advanced methods, including utilization of space-division multiplexing (SDM) on our inter-regional fiber routes from Europe and across the Middle East to Near Asia (India) spanning distances of < 9,000 km. The route required we integrate the optical design of both the submarine and terrestrial segments to ensure sufficient optical signal to noise ration (OSNR) margin is maintained for the non-regenerated, end-to-end digital line segments (DLS).

 

Current technologyies require the use of pure silica core, large effective area, and ultra-low loss (ULL) fiber optic cable (FOC) both in the wet (subsea) and dry (terrestrial) segments of the network. While SDM employs more fibers to achieve a higher capacity system, the packaging of more ULL fiber pairs within the same diameter cable raises bending loss concerns, especially on the terrestrial segments. Then stretching amplified spans lowers system costs in both the submarine and terrestrial segments, but lowers the spectral efficiency and system capacity.

 

Therefore, sufficient consideration must be given to many factors to not limit the reach (non-regenerated distance) and capacity (bandwidth) of an ultra-high speed, long distance network. Fiber attenuation is an inherent and important factor, which is largely mitigated by using non-doped Pure Silica Core (PSC) fibers exhibiting a loss of 0.153 – 0.156 dB/Km. The recent developments in the fiber’s (preform) manufacturing process and enhancement in the glass drawing process have further improved the PSC fiber loss to an unprecedented 0.148 – 0.150 dB/Km. Other limiting factors are Chromatic Dispersion (CD); the dispersion caused by light of different wavelengths, and the Polarization Mode Dispersion (PMD) caused by the polarization of orthogonal modes of light traversing in the fiber. Pulse broadening due to chromatic dispersion and the variation of fiber attenuation with wavelength used to be the real issues with DWDM; however, with the advent of coherent transmission, advanced modulation schemes, use of Digital Signal Processors (DSPs) both at the transmission and receiver end and advanced error correction schemes have increased fiber reach and throughput manifolds.

 

Our approach to improving things focused on the integration of the subsea and terrestrial segments, where generally the subsea fibers perform better because of both lower span losses and lower repeater noise figure (NF), which caused us to look for improvements in the terrestrial segments to get a better match.

 

Grooming the Cablers

We worked closely with the renowned Cablers in the Middle East such as Middle East Fiber Company (MEFC), Riyadh Cable Group Company (RCGC), and Oman Fiber Optics (OFO) to construct and test FOC comprising of ULL fibers and to better understand the areas of improvement that could result in the better-installed performance both on fiber reach, capacity, and operational life perspectives. The FOC’s  installed in the harsh desert environments in the Middle East also need special manufacturing consideration to conform to Outside Plant (OSP) installation practices in the region either installing FOC direct burial, trench & lay method, and by air-jet blowing through the duct systems.

 

We discussed our requirements to locally manufacture and test a sample TEAS FOC drum with the above three Cablers and also with the ULL fiber supplier from the USA. They all agreed to support our initiative to manufacture a Test Cable Drum in their respective factories using the ULL fibers. We had ULL terrestrial FOC of various types locally manufactured and have tested concatenated cable sections to simulate repeater span distances to better understand the impacts.  We began to focus on several areas of improvement, increasing cable lengths on spools, without increasing spool diameters due to higher logistics costs, increasing section cable pull lengths thus reducing cable splices per span, and blowing outdoor fiber (both steel tape armored and double HDPE jacketed cables) through the metropolitan duct systems to reduce the number of fiber splices along a fiber span. Cablers are generally poised for certain cable spool sizes and cable lengths that reduce waste due to fiber spool lengths, which are generally supplied at 50 km. We discussed with the fiber supplier hand picking fiber spools of 50.4 Km lengths for up to 90% of the supply order to minimize wastage.  Increasing pull lengths must consider cable tensile strength to withstand cable installation strains incurred by the plowing machines and manual pulling, macro-bending considerations to coil the cables inside the manholes and handholes, and a few other factors like installing the outdoor cables in the right of way under the OHTL (Overhead Transmission Line) and installing two fiber cables in the same trench at different depths to attain a vertical diversity.

 

The selected Cablers fully cooperated with Cinturion and its General Contractor BTC Networks in realizing this initiative. The FOC drums were manufactured by all three Cablers; however, due to COVID-19 travel restrictions, only the fibers and cable testing could be realized with the Cablers in Saudi Arabia. Following is a walk-through of the BTC/Cinturion initiative to groom local Cablers to manufacture cost-effective ULL fiber cables using the local infrastructure resources, which could be deployed in TEAS and similar other projects and make them competitive as World-Class Cablers.

 

The Large Effective Area – Cutoff Shifted Fiber (LEA-CSF)

One of the fibers, which has raised serious interest in the minds of fiber optics designers of terrestrial networks is the Large Effective Area – Cutoff Shifted Fiber (LEA-CSF), which conforms to ITU-T G.654B/D/E recommendations. The G.654B/D Pure Silica Core (PSC) fibers specifically manufactured for submarine applications are used in the past; however, using a fiber made for submarine applications and planned to be for terrestrial applications poses many challenges. The ITU-T recommendation for terrestrial optimized PSC fiber are included in Table-E of ITU-T G.654, Nov-2016 publications and hence the name G.654E fiber, of which the Corning TXF fiber is a classical example. The G.654 fibers have a large effective area (A_eff) between 110-150 ?m². The OFS G.654B selected for the Test Cable drum has an effective area of 125 nm.

 

The submarine cable once installed in the ocean bed remains mostly relaxed, with very few cable cuts in its lifetime, and generally stays at a uniform temperature, whereas, the fiber optic cable installed on the land experience linear and angular stresses during installation, blowing & pulling through the duct systems, frequent fiber cuts and large temperature variation between the day and night if installed in the desert area. The submarine fiber shall therefore need to be optimized for terrestrial installations both on macro-bending and proof tests perspectives.

 

Cinturion wants to maintain a Cabled Fiber Loss (CFL) of 0.16 dB/Km both on the wet and dry segments to meet its transmission design objective of non-regenerated transmission links from end to end (India – Europe) and this is only possible if the FOC installed on the terrestrial segments also exhibits the same attenuation as in the subsea segments. The submarine cable has far fewer splices than the terrestrial fiber cable since a subsea amp spans (60-70 Km) is installed without a cable splice, whereas the terrestrial cable drums are limited in length (6-10 Km) depending on the fiber counts and cable armoring and therefore encounter more splices during installation and more fiber cut during the cable operational lifetime.

 

TEAS Test Cable Drums Production

Cinturion/BTC Networks selected and engaged two reputed Cablers in Saudi Arabia; MEFC (Middle East Fiber Company) and RCGC (Riyadh Cable Group Company) to manufacture a 96F Steel Armored Test Cable Drum of standard 6.0 Km length comprising 48 x G.654B and 48 x G.652D fibers and test optical, mechanical and geometrical parameters as per the mutually agreed Inspection & Test Plan (ITP). The G.654B fiber for manufacturing Test Cable Drums and both the Cablers imported G.654B fiber spools and used G.652D fibers from their preferred suppliers.

It was the first experience for both Cablers (MEFC & RCGC) to manufacture a Terrestrial FOC incorporating G.654 fibers so both Cablers cooperated with BTC/Cinturion and put their best Engineers & Technicians and Quality & Production managers to work with BTC/Cinturion Testing Team in carrying out the production and testing the FOC successfully. The Test Cable Drums were manufactured in the subject factories and preliminarily tested by the Cablers and BTC/Cinturion was formally invited to eyewitness the ITP tests.

 

Inspection & Test Plan

A suite of optical, mechanical, and geometrical tests was developed by BTC/Cinturion in coordination with both the Cablers to test the G.654B fibers for long-distance and ultra-high-speed network applications. The optical tests are generally called “fiber characterization,” and they include spectral attenuation, chromatic and polarization mode dispersion and optical return loss, etc. The manufactured FO Cable was also required to go through stringent mechanical stress and environmental tests as the TEAS cable is required to be installed underground installation strains of plowing machines and harsh desert environments in most parts of the terrestrial network between Oman and Israel passing through Saudi Arabia and Jordan.

 

The Inspection & Test Plan (ITP) covered the full spectrum of visual, optical, geometrical, and mechanical tests of G.654B fibers. There were certain fiber tests whose results were provided by the fiber suppliers with each G.654B fiber spool and only the results of those tests were reviewed, whereas most of the fiber and cable tests were eyewitnessed by BTC/Cinturion Team. All G.654B and G.652D fibers in the 96F Cable drum underwent the following optical, mechanical and geometrical test regimes.

1. Optical Tests

Reviewed

• Mode Field Diameter For G.654B Fibers
• Cutoff Wavelength for G.654B Fibers
• Mode Field Diameter For G.652D Fibers
• Cutoff Wavelength for G.652D Fibers
• Zero Dispersion Wavelength for G.652D Fibers
• Zero Dispersion Slope for G.652D Fibers

Witnessed

• Chromatic Dispersion (CD) For G.654B Fibers @ 1550nm
• Chromatic Dispersion (CD) For G.652D Fibers @ 1550nm
• Polarization Mode Dispersion (PMD) For G.654B Fibers
• Polarization Mode Dispersion (PMD) For G.652D Fibers

2. Mechanical Tests

Reviewed

• Proof Test For G.654B Fibers IEC-60793-1-30
• Proof Test For G.652D Fibers IEC-60793-1-30

Witnessed

• Tensile Strength Test                                IEC-60794-1-21, E1A
• Crush Test                                IEC-60794-1-21, E3
• Impact Test                                IEC-60794-1-21, E4
• Bend Test                                IEC-60794-1-21, E11
• Repeated Bending Test                                IEC-60794-1-21, E6
• Torsion/Twist Test                                            IEC-60794-1-21, E7
• Temperature Cycling Test                               IEC-60794-1-22, F1
• Water Penetration Test                                IEC-60794-1-22, F5B

3. Geometrical Tests

Reviewed

• 654B Fiber Cladding Diameter
• 654B Cladding Non Circularity
• 654B Core/Cladding Concentricity
• 654B Coating/Cladding Concentricity

Witnessed

• FO Cable Outer Diameter
• Inner Sheath Thickness
• Outer Sheath Thickness
• Steel Tape Thickness

4. Additional Tests

In addition to the standard tests specified above, the following Optical Tests were specifically required to be conducted to qualify the manufactured 96F TEAS FOC for deployment in the TEAS Project. The Cablers were asked to include the following supplementary Optical Tests and their test results, test conditions, test limits, tolerances, etc. in the ITP and also in the Test Reports for BTC/Cinturion reference and record.

1. Simulated Span Loss

The TEAS inter ILA spacing was required to be simulated in a single drum by splicing and cascading 12 x G.654B fibers from different tubes to simulate the span distance. Three (3) fibers from each fiber tube containing G.654B fibers were selected and serially spliced to simulate 3 x 6 = 18 Km fiber sections. The four (4) such fiber sections were then serially spliced to simulate the required span length.

• The length of the simulated span was measured with an OTDR in decimal KMs
• The span loss was measured by a laser source and optical power meter in dBs at 1550nm
• The attenuation profile was viewed and traced by an OTDR
• The splice loss of each splice was measured with an OTDR bi-directionally in dBs at 1550nm
• The individual splice loss didn’t exceed 0.05 dB
• The average splice loss of each splice shall as calculated in dBs
• The cumulative splice loss for all splices was calculated in dBs

1. Cabled Fiber Loss

The Cabled Fiber Loss (CFL) was calculated as follows and shown in a snap at the end of this article:

• The span loss of the simulated 72 Km span was calculated in dBs
• The cumulative splice loss was subtracted from the calculated span loss
• The resultant span loss was divided by the span length to get the CFL in dB/Km
• The CFL didn’t was found to be less than 0.16 dB/Km for both A- B and B-A directions

1. Macro-Bending Loss

The Macrobending Loss was calculated to verify G.654B submarine optimized fibers' suitability for terrestrial applications from the macro-bending perspective. The macro-bending loss values and test requirements for G.654B (submarine optimized) fiber and for G.654E (terrestrial optimized) fiber are indicated in Table-5 and Table-2 of ITU-T G.654 (Nov-2016) publications respectively. The objective of this test is to judge how close the G.654B fiber is to the G.654E fiber from the macro-bending loss perspective.

• The test required a fiber spool of G.654B fiber of any measurable length
• The test further required a 30mm mandrel or a tube having a 30mm outer diameter
• The fiber loss of the G.654B fiber wound on the spool was measured with an OTDR at 1625nm
• 100 Turns of G.654B fiber were wound on a 30 mm outer diameter mandrel/tube
• The fiber loss was measured again with the same OTDR in dBs at 1625nm
• The difference in the first and second fiber loss readings was found less than 0.1 dB
• The difference in the first and second fiber loss reading of less than 0.1 dB (G.654E value) indicated OFS G.654B fibers' suitability for terrestrial application

 

1. Span Chromatic Dispersion

Chromatic Dispersion was required to be measured on the simulated span of 72 Km using a calibrated CD Test Set and applicable test procedure. The measured CD value at 1550 was found to be =/< 22 ps/Km-nm for several G.654B fibers and =/<18 ps/Km-nm for G.652D fibers nm selected from different fiber tubes.

1. Span Polarization Mode Dispersion (PMD)

Polarization Mode Dispersion was required to be measured on the simulated span of 72 Km using a calibrated PMD Test Set and applicable test procedure. The measured PMD value was found to be less than 0.01 ps/?km for several G.654B and G.652D fibers selected from different fiber tubes.

 

Fiber Cable Testing Team

BTC/Cinturion assigned a Team of highly experienced OSP & Transmission Engineers to eyewitness the Test Cable Drums in both MEFC and RCGC Cable Factories. Instead of using Cabler’s Test Equipment, BTC/Cinturion decided to get support from Vivai’s regional distributor Comtinu in providing the latest and calibrated Test Equipment for the G.654B and G.652D fibers testing at the cable factories. The Testing regimen took 3 days in each factory to eyewitness and conclude the tests.

 

Test Results

The test results achieved from testing both the Test Cable drums at the MEFC and RCGC cable factories were very promising. All the tests in the ITP were successfully conducted and eyewitnessed, in the presence of the BTC/Cinturion Testing Team. The following key optical, mechanical, and geometrical parameters of G.654B fibers were successfully validated qualifying both the Cablers to manufacture TEAS Type-1 (Steel Armored) and Type-2 (Non-Metallic Double HDPE Jacketed) and Type-3 (Ducted) FOC locally and installation by the selected OSP Contractors in Saudi Arabia and other countries.

1. All the key optical parameters G.654B selected fibers in the TEAS Test FO Cable drum were tested, eyewitnessed, and validated in MEFC and RCGC Cable Factories in Saudi Arabia:

 

1. All the key mechanical and geometrical parameters of G.654B selected fibers in the TEAS Test FO Cable drum were tested, eyewitnessed, and validated in MEFC and RCGC Cable Factories in Saudi Arabia:

 

Conclusion

The successful manufacturing and testing of TEAS FO Cable G.654B subsea fibers encapsulated in Terrestrial FOC in Saudi Arabia gave strong confidence to both BTC/Cinturion and the Cablers that such cables can be locally manufactured and remain competitive with FOC manufactured and imported from overseas.

 

TEAS FO Cables

 

About the Authors

Greg Varisco is CEO of Cinturion, building the Trans Europe Asia System- TEAS from Europe to India.  He has provided professional services to the telecom and energy industries for more than 30 years. His experience in developing and commercializing advanced subsea and fiber optic networks through the design, development, implementation, and operational phases. He has led the development of several international business initiatives in various companies (startups, turnarounds, public, private, and Fortune 100 organizations). Prior, he was occupied as the CEO of a new transatlantic network.

Shaheen Qamar of BTC Networks is a Lead FO Network Design Engineer providing consulting services on different technologies used in the terrestrial part of the TEAS Project. He has written major RFIs/RFQs/RFPs for the TEAS Project and is leading the BTC/Cinturion Technical & Bids Evaluation Team. Mr. Qamar has more than 30 Years of experience in designing and implementing high-capacity FO networks. He has supervised the design, engineering, and implementation of many NBN class long-distance FO networks in Saudi Arabia such as SNFN, B-ICON, and MFON, etc. spanning tens of thousands of kilometers. He has worked in the past with MOD, AT&T/Lucent, BTC Networks, ProCom, Mobily, and Saudi Ericsson and is currently based in Toronto, Canada.

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