Workshop of Teaching Photonics &&@ 1 18 May 99, Cairo, Egypt

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- - Engineering Aspects in OFCS Curricula

Prof. Osman Lotfy EL-Sayed Cairo University

Introduction

Optical fiber transmission has revolutionized the telecom industry. In fact the pace of technological advances in the design of OFCS was so rapid

that, in less than two decades, the cost of transmission on transatlantic

submarine links has been reduced by more than two orders of magnitude.

Optical fiber systems established themselves as the preferred medium, not

only for large capacity backbones and global submarine links, but also for

CATV networks and high speed LAN's, MAN'S and WAN'S.

Furthermore the association of SDH technology with of 0.F transmission introduced new concepts in transmission network topology (O.F. rings) and transmission network management (robust, self-healing networks).

Continuous research in the fields of wave division multiplexing, erbium

doped fiber amplifiers, coherent OFCS, soliton propagation, mid infrared

fibers, integrated optoelectronics, photonic switching signals the dawn of all

optical telecommunication networks and makes OFCS one of the

cornerstones of the information age.

The potential and importance of OFCS has been recognized very early

by the author. A 5 day seminar was organized in Cairo University in

collaboration with researchers from the French Telecommunication Research

Center (CNET) in 1981. In 1983184 a postgraduate course on OFCS was

introduced in the frame of the Microwave Engineering MSc. courses of Cairo

University, Almost, simultaneously, OFCS figured among the first continuing

education programs offered by the National Telecommunication Institute. A couple of years later, it was introduced as an elective subject in the final year

program of the Dep. of Electronics and Telecommunications. During the

following decade, projects on OFCS accompanied the elective subject.

Workshop of Teaching Photonics .,&-, 18 May 99, Cairo, Egypt

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Course Objectives

. - One thing specific about OFCS is that it is rapidly evolving and that it

cuts across many advanced disciplines (quantum electronics, EM wave

propagation in dielectric WIG, Communications, Integrated optics and

optoelectronics). This puts a burden on the course instructor, as students are

more accustomed to segregated, specialized courses. Thus the primary

course objective was to provide an up to date, basic understanding of the

physical mechanisms governing the operation of the main system

components as well as an introduction to the analysis and design of optical

fiber systems (whether point-to-point or distribution).

With the introduction of OFCS in Cairo junction network (1985), it was

required to provide the students with practical engineering aspects that could

be an asset for them in their professional life.

In general the duties of a professional transmission engineer cover

some or all of the following fields:

1. The design of transmission networks subject to the performance

requirements stipulated by the ITU, the evolving service traffic needs

and the local constraints.

2. The development of RFP’S embodying this design.

3. The technical evaluation of the bids presented in response to the RFP.

4. The testing of system components using the RTM specified in the RFP.

5. The installation (or supervision of the installation) of the system and

seeing that the best practices are followed.

6. To commission the system.

7. To operate and maintain the system.

Thus the course was designed to cover the main engineering aspects

relevant to the specification, testing, installation, commissioning, operation

and maintenance of communication systems and components.

world of OFCS through a brief presentation of SDH technology,

Moreover the course was designed to introduce the students to the real

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The final objective was to give the students a good insight into system

issues (involving system economics) that would enable them to parameterize

OFCS according to type of application, capacity etc.

Specification of optical fibers and Cables

Classical textbooks on OFCS seldom refer to the concepts of

standards (including specifications, tolerances, reference test methods). Thus

our students are practically illeterate as far as ITU recommendations and

international standards are concerned.

Moreover, the textbooks. focus mainly their attention on the optical

properties of fibers and practically do not mention their mechanical properties

(which can be very important).

Furthermore, rarely does a textbook provide the engineer to be with a

thorough knowledge of O.F. connectors and the different standards available.

Finally classical textbook do not underline enough the importance of

RTM in optical fiber performance measurements.

In this respect, all along the course and more specifically during project

work the students are exposed to ITU -T recommendations (G 650-654)

pertaining to the geometrical and optical performance characteristics of MM &

SM fibers operating the different wavelength windows and the reference test

methods used. Supplementary information available in the section 6 of the

series G can also be of use to illustrate the practices of certain leading

telecom operators.

Furthermore, a good account of fiber mechanical properties under static

and dynamic loads, and the dermination of the level of fiber proof-testing to

ensure a fiber reliability commensurate with the system lifetime is presented.

Moreover the stresses experienced by cabled fibers due to the difference in

thermal expansion coefficients between silica and cable material, in the cases

of tight and loose buffer structures are presented.

Cable design considerations and cable basic structural requirements

are discussed. Typical cable designs for different applications: buried (directly

Workshop of Teaching Photonics 1 18 May 99, Cairo, Egypt

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or in duct), aerial (on poles or on high voltage lines), submarine (different

depthi.), indoor etc are presented. Tests for tensile strength, bending, torsion

and crushing are illustrated. The students are exposed to the t series of ITU-T

recommendations pertaining to the construction, installation and protection of

cable and other elements of outside plant (L 1-1 7).

System Design and Specification

The design of OFCS involves the specification of terminal equipment

involving speech coders, multiplex equipment, digital circuit multiplication

equipment, operation administration and management equipment. It is thus

essential to the student to have a brief overview of PDH AND SDH

technologies, and to understand the need for the operator of a link

management system. These equipment are specified in section 7 of the G

series of ITU-T recommendations.

As far as system design is concerned the student is confronted with the

basic requirements of a “good” system design namely:

1.

2.

3.

4.

5.

6.

7.

Ensuring end-to-end quality and availability targets specified by section

8 of the G series of the ITU-T recommendations all over the lifetime of

the system.

Provision for the “economic” growth in system capacity to cope with

traffic increases over the system life.

Fullfilling drop and insert requirements along the system route.

Ensuring the survivability of the network in case of cable cuts (use of

DXC’S and self healing rings).

Minimization of service disruption by appropriate cable design,

protection and laying procedure as well as the use of stand by systems.

Provision of comprehensive, user friendly link management systems.

Minimization of overall system cost (investment, operation and

maintenance cost).

Workshop of Teaching Photonics 18 May 99, Cairo, Egypt

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Conclusion

Although it might seem that all this information requires a long time to

be dispensed, it should be noted that it is “inserted” all along the course

without going into the details. The most important thing is to bring it to the

attention of the students, to discuss its rationale and to show them where to

get the details from.

It is evident that project work, provides a better opportunity to expose

the student to these concepts and to train their hand to their first “RFP”.

I think it is our duty toward our students to prepare them to their

professional life by reserving an appropriate part of the course to cover the

practical engineering aspects of optical fiber communication systems.