Expert System for the Design of Optical Fibre

8/3/2019 Expert System for the Design of Optical Fibre

1/13

Pergamon0 9 5 2 - 1 9 7 6 ( 9 5 ) 0 0 0 0 5 - 4

Engng Applic. Art i f . lntel l . Vol . 8 , No. 3 , pp . 319-331, 1995Copyrigh t 1995 Elsevicr Scicncc LidPrin ted in Grc at Bri t a in . Al l r ight s reserved0952-1976195 $9.50 + 0.00

Contributed PaperExpert System for the Des ign of Optical FibreCommunicat ions Links

K . P . DABKEMonash University, Australia

L . N . BINHMonash University, Australia

S. P. LAU*Extol Corporation, Malaysia

(Received Dece mber 1993 in revised form October 1994)The des ign o f an opt ica l f ibre com mu nicat ions netw ork i s a very knowledge-r ich dom ain , due to theeme rging nature of the art . Such opt ical f ibre syste ms are used in very large (e.g. global) to very sm allcom mu nicat ions networks , e .g . ins t rumenta t ion l inks . This pap er descr ibes an exper t sys tem, bu i l t toful f i l the twin n eeds o f a tutorial adv isor as w el l as a design consu l tant fo r the design o f sm all opt ical-f ibre netwo rks . On e par t o f the exper t sys tem i s a tu tor ia l in t roduct ion to the t erminology and bas icpr incip les o f the ar t o f the des ign o f op t ica l f ibre networks . The o ther par t i s a des igner' s consul tan twhich request s da ta f rom the inexper t user about the requirements o f the op t ica l f ibre netwo rk, andthen of fers design c hoices fo r opt ical sources, f ibr es and receivers o n the basis o f experient ialheurist ics , as wel l as well-establ ished ma them atical relat ions. The expe rt system is im ple me nted usinga very cheap (< $A us t 200) exper t -sys tem shel l which meets mo s t o f the needs o f th is applica tion . Theuse o f a ' shel l' a l lowed rapid bui ld ing o f the exper t sys tem in a f ew weeks b y an undergraduate s tudent(under academic guidance) s tar t ing f rom complete un fami l iar i t y w i th bo th the exper t -sys temme thodo logy and opt ica l- fibre t echnology. The induct ion faci l i ty o f the exper t -sys tem b ui ld ing too lwas used to translate device data and design decision tables into rules automatical ly, thus saving t imeand avoiding syntact ical errors.K e y w o r d s : O p t i c a l f i b r e c o m m u n i c a t i o n s , f i b r e o p t i c s , o p t o e l e c t r o n i c s d e s i g n , e x p e r t s y s t e m s ,ar t i f i c ia l in te l l igence , tu to r ia l

1 . I N T R O D U C T I O NI n i t i a l l y s e e n a s s c i e n t i f i c c u ro s i t i e s , l a s e r s o u rc e s a n do p t i c a l f i b r e s h a v e d e v e l o p e d i n t o a v e ry r a p i d l ye x p a n d i n g o p t o e l e c t r o n i c s t e c h n o l o g y f o r t h e b r o a d -b a n d c o m m u n i c a t i o n s s y s t e m s w h i c h n o w e n c i r c l e t h eg l o b e . ~3 M a j o r r e s e a r c h a n d d e v e l o p m e n t e f f o r t s b yt h e l e a d i n g c o m m u n i c a t i o n s o r g a n i z a t io n s o f t h e w o r l dh a v e p u t t h i s t e c h n o l o g y a t t h e d i s p o s a l o f c o m m u n i c a -t i o n s s y s te m d e s i g n e r s . I n m a n y c a s e s , t h e r e s e a r c h e r s /d e v e l o p e r s o f th e o p t o e l e c t r o n i c s t e c h n o l o g y b e l o n g t o* M s L a u w a s a s t u d e n t a t M o n a s h U n i v e r s i ty w h e n t h is w o r k w a s

carried o u t .Correspondence s h o u l d b e s e n t to : D r K . P . D a b k e , D e p a r t m e n t o fE l e c tr ic a l a n d C o m p u t e r S y s t e m s E n g i n e e r i n g , M o n a s hU n i v e r s i ty , C l a y t o n , M e l b o u r n e 3 1 6 8, A u s t r a li a .

t h e s e l a rg e c o m m u n i c a t i o n s o r g a n iz a t io n s . T h u s , m a j o rc o m m u n i c a t i o n s - s y s t e m d e s i g n e r s a n d o p e r a t o r s h a v ea c c e s s t o l e a d i n g e x p e r t s i n o p t o e l e c t r o n i c s , t o m e e tt h e i r d e s i g n n e e d s .H o w e v e r , t h e r a p i d d e v e l o p m e n t s i n t h e p r o d u c t s ,t e c h n o l o g y a n d a p p l i c a t i o n s o f o p t i c a l - f i b r e n e t w o r k so f t e n c r e a t e a s i t u a t i o n w h e r e s m a l l u s e r s w h o n e e dt h e m d o n o t h a v e a d e q u a t e f a m i l i a r i t y w i t h t h e t e r m i -n o l o g y , n o r t h e d e s i g n i n f o rm a t i o n a n d e x p e r t i s e t o u s et h e m e f f e c t i v e l y . C o n s u l t a n t s , w h o s e r v e t o d e l i v e rm a t u re t e c h n o l o g y t o s m a l l o rg a n i z a t i o n s , a l s o s u f f e rf r o m t h e s a m e d r a w b a c k o f u n f a m i li a r it y a n d i n e x p e r -i e n c e i n a r a p i d l y e x p a n d i n g a n d c h a n g i n g f i e l d .

T h e r e i s a n e e d t o d e l i v e r s u c h n e w t e c h n o l o g yd i r e c t l y f r o m r e s e a r c h / d e v e l o p m e n t s o u r c e s t o t h ee n g i n e e r o n t h e g r o u n d w h o i s a w a r e o f t h e p o t e n t i a l o f3 1 9


2/13

3 20 K . P . D A B K E et al.: OPTICAL FIBRE COMMUI,ICATIONSo p t o e l e c t r o n i c t e c h n o l o g y b u t u n a b l e t o t a p i n t o it f o r as m a l l a p p l i c a t io n . T o o v e r c o m e t h e p r o b l e m o f u n f a m i -l i a r i t y , s u c h a v e h i c l e m u s t d e l i v e r n o t o n l y t h e d e s i g ne x p e r t i s e b u t a l s o a n i n t r o d u c t i o n t o t h e t e r m i n o l o g y ,t o m a k e t h e u s e r f e e l c o n f i d e n t t h a t t u i s n e w v e h i c l e isg o i n g t o d e l i v e r s o m e t h i n g t h a t c o n f o r m s t o a n d c o m -p l e m e n t s t h e m a t e r i a l in j o u r n a l s a n d i n t h e m a n u f a c -t u r e r s ' l i t e r a t u r e .

2 . N E E D F O R A N E X P E R T S Y ST E MT h e n e e d t o d e l i v e r s u c h t u to r i a l a n d d e s i g n i n f o r -

m a t i o n f r o m a s o u r c e i n d e p e n d e n t o f s u p p l i er s /m a n u f a c t u r e r s w a s t h e m o t i v a t i o n b e h i n d t h e d e v e l o p -m e n t o f t h e e x p e r t s y s t e m d e s c r i b e d i n t h is p a p e r .

O p t i c a l c o m m u n i c a t i o n s s y s t e m s a r e r e q u i r e d f o r av a r i e t y o f a p p l i c a ti o n s . T h e s e r a n g e f r o m t h e l o n g-d i s t a n c e t e r r e s tr i a l a n d u n d e r s e a l i n k s f o r t e l e c o m m u -n i c a t i o n s , t o s h o r t a n d f i x e d - l e n g t h s e c t i o n s in l o c a la r e a n e t w o r k s . T h e r e q u i r e m e n t s f o r o p t i ca l c o m p o -n e n t s t o f o r m t h e l i n k s w o u l d v a r y s i g n i f i c a n t l y b e t w e e nt h e s e a p p l ic a t i o n t y p e s . F u r t h e r m o r e , m a n u f a c t u r e r s o fo p t o - e l e c t r o n i c c o m p o n e n t s o f f e r d if f er e n t p r o d u c t sf r o m t i m e t o t i m e . S e l e c t i o n o f t h e o p t i c al c o m p o n e n t sf o r a s p e c i f ic o p t i c a l l i n k r e q u i r e s a n a p p r o p r i a t e c h o i c eo f a c o m b i n a t i o n o f d e v i c e s fo r s h o r t - o r l o n g - d i s t a n cea p p l i c a t i o n , a s w e l l a s a m i n i m i z a t i o n o f th e c o s t o ft h e s e c o m p o n e n t s . I t is t h e r e f o r e e x p e c t e d t h a t a ne x p e r t a d v i s e r , t o g u i d e t h e d e s i g n e r s o f o p ti c a l c o m -m u n i c a t i o n s y s t e m s , w o u l d p r o v i d e n o t o n l y t h ed e c i s i o n - m a k i n g p r o c e s s f o r t h e s y s t e m d e s i g n , b u t a l sod e f i n it i o n s o f a n d t u t o r i a l h e l p a b o u t t h e r e l e v a n tt e c h n o l o g y .A n e x p e r t s y s t e m i s a c o n v e n i e n t v e h i c l e f o r d e l i v e r-i n g s u c h n e w t e c h n o l o g y . I t i s a s p e c if i c a p p l i c a t i o n o fa r t i f i c i a l i n t e l l i g e n c e a n d k n o w l e d g e - b a s e d s y s t e m s . A ne x p e r t s y s t e m i s a s u r r o g a t e e x p e r t i . e . it i s c o m p u t e rs o f t w a r e w h i c h a c t s l i k e a h u m a n e x p e r t ; i t a s k s q u e s -t i o n s , g i v e s a d v i c e , e x p l a i n s t h e a d v i c e a n d i n a v e r yl i m i te d w a y m a y e v e n l e a r n f r o m p a s t e x p e r i e n c e . 4

I n o r d e r t o a c t a s a s u r r o g a t e e x p e r t , a n e x p e r ts y s t e m n e e d s t h e f o l l o w i n g m a j o r c o m p o n e n t s :

1. Knowledge base: T h i s i s t h e s t o r e o f e x p e r tk n o w l e d g e e x p r e s s e d i n s o m e s u i t a b l e f o r m ,s u c h a s r u l e s , f r a m e s , e t c .2. Infere nce engine: T h i s c o n t r o l s t h e q u e r y i n g a n dd e d u c t i o n p r o c e s s s o a s t o r e a c h t h e r e q u i r e dc o n c l u s i o n .3. Use r interface: T h i s r e c e i v e s q u e r i e s a n d p r o b -l e m d a t a f r o m t h e u s e r , a n d s u p p li e s a n s w e r s /a d v i c e a s w e l l a s a n e x p l a n a t i o n a b o u t t h ea d v i c e t o t h e u s e r .4. Program interfaces: T h e s e p r o v i d e l i n k s t oo t h e r p r o g r a m s s u ch a s d a t a b a s e , s p r e a d s h e e t sa n d t h o s e w r i t t e n i n F o r t r a n , C , e t c . S o m ee x p e r t s y s t e m s h a v e a ' r u l e s f r o m e x a m p l e s 'f a c i li t y ( c a l l e d i n d u c t i o n ) s o t h a t c o d i n g o f th e

k n o w l e d g e b a s e i s a u t o m a t e d t o s o m e e x t e n t .T h e d e v e l o p m e n t o f t h e a b o v e c o m p o n e n t s o f th e

e x p e r t s y s t e m f o r t h e d e s i g n o f o p t i c a l f i b r e l i n k s i sr e p o r t e d i n th i s p a p e r .2 .1 . Know ledge-base organiza t ion

T h e k n o w l e d g e b a s e c o n s is t s o f f a c ts a n d r e l a t io n sb e t w e e n f a c t s , e . g . r u l e s . T h u s , k n o w l e d g e c o n s i s t s o ff a ct s ( o f t e n p u b l ic k n o w l e d g e ) a n d t h e i r i n t e r - re l a t i o n s ,k n o w n t o t h e e x p e r t s .

T h e K B o r g a n i z a t i o n d e c i d e s h o w t h e f a c t s a n d t h e i rr e l a t i o n s t o e a c h o t h e r a r e t o b e r e p r e s e n t e d a n dg r o u p e d . T h e f o l l o w i n g l is t s h o w s a v a r i e t y o f w a y s i nw h i c h t h i s i s d o n e , a n d t h e i r c h a r a c t e r i s t i c s .Knowledge representat ion

- - L o g i c a l e x p r e s s i o n s m o s t f o r m a l ( p r e c i s e )b u t u n s t r u c t u r e d

- - R u l e s - - O b j e c t - a t t r i b u t e -v a l u e t r i p l e t s

- - F r a m e s - - B l a c k b o a r d s - - S e m a n t i c n e t w o r k s h ig h ly s t r uc t u r e d b u t

l e a s t f o r m a l .T h e e x p e r t - s y s t e m b u i l d i n g t o o l e m p l o y e d i n t h i s

p r o j e c t ( V P X ) h a s a n i n d u c t i o n f a c i l i t y . I t a c c e p t sd e c i s i o n t a b l e s a n d ' i n d u c e s ' r u l e s a u t o m a t i c a l l y i n t h ec o r r e c t s y n t a x. T h e a u t o m a t i c a l l y i n d u c e d r u le s ( i d e n t i-c a l i n f o r m a t a n d s y n t a x t o t h e h a n d - c r a f t e d r u l e s ) a r ei n t h e f ai rl y s t a n d a r d " I F . . . T H E N . . .E L S E " f o r m , a n d a r e e as y to r e a d a n d m o d i fy w i th o u ta n y s p ec i a l k n o w l e d g e o f c o m p u t e r l a n g u a g e s.

T h e i n d u c t i o n t o o l i s f a ir l y p e r c e p t i v e b e c a u s e a n yr e p e a t e d p a t t e r n s i n th e d a t a a r e r e c o g n i s e d a n d c a n b ea s s i g n e d a n i n t e r m e d i a t e n a m e t o s a v e r e p e a t e d e n u -m e r a t i o n o f t h e s a m e c o n d i t i o n s in t h e " I F " p a r t o f th er u l e s . T h i s s a v e s m e m o r y , a n d a v o i d s t h e c o n f u s i o nw h i c h m a y b e c a u s e d b y m u l t i p l e r e p e t i t i o n o f th e s a m ec o n d i t i o n s i n m a n y r u l e s .

I f n e c e s s a r y , d a t a s t o r e d i n s p r e a d s h e e t s a n d d a t a -b a s e s c a n b e a c c e s s e d b y a n e x p e r t s y s t e m a s p a r t o f t h e' a c t io n ' r e s u l ti n g f r o m t h e T H E N p a r t o f t h e r u l e s.T h u s d a t a o n o p t o e l e c t r o n i c c o m p o n e n t s m a y b e s t o r e da s a s p r e a d s h e e t a n d t h e a p p r o p r i a t e c e ll s, r o w s o rc o l u m n s o f t h e s p r e a d s h e e t c a n b e a c c e s s e d b y i d e n ti f y -i n g th e k e y t o th e s e c e l l s, r o w s o r c o l u m n s f r o m t h eu s e r - s up p l i e d d a t a . S u c h d a t a t h e n b e c o m e s p a r t o f t h ek n o w l e d g e a v a i l a b l e t o t h e e x p e r t s y s t e m , a n d c a n b eu s e d f o r f u r t h e r d e c i s i o n - m a k i n g .

V e r y c o m p l e x k n o w l e d g e s t r u c t u r e s m a y n e e d t o u s ek n o w l e d g e - b a s e r e p r e s e n t a t i o n s o t h e r t h a n r u l e s e . g .o b j e c t - a t t r i b u t e - v a l u e t r i p l e t s , f r a m e s , b l a c k b o a r d sa n d s e m a n t i c n e t w o r k s . H o w e v e r , i n a r a t h e r t e c h n i c a la r e a s u c h a s o p t o e l e c t r o n i c s , s u c h c o m p l i c a t i o n sa p p e a r e d u n n e c e s s a r y , a n d r u l e s p r o v e d t o b e a na d e q u a t e f o r m o f k n o w l e d g e r e p r e s e n t a t io n .


3/13

K. P. DABKE e t a l . : OPTICAL FIBRE COMMUNICATION S 321

2 .2 . Inference eng ineThe inference engine controls the process and order

of querying and logical deduction, and thus gives theexpert system its decision-making ability. The type ofproblem determines the type of inference mechanismused. The most commo n types of inferencing strategiesused in expert systems are called 'backward chaining'(goal driven) and 'forward chaining' (data driven). TheVPX tool uses backward chaining.To cope with uncertain data, inference engines use avariety of methods of arriving at conclusions fromstated uncertainties in the data, and different reliabili-ties of the rules which allow the combination of suchuncertain data to reach conclusions. Techniques such asprobability theory, Bayes rule, certainty factors andfuzzy logic may be used to deal with inherently uncer-tain data. In this application of expert-system tech-niques to the design of optical-fibre communicationlinks it was not necessary to use uncertainty.Artificial neural networks (ANN) may be used tospeed the inferencing process, since inferencing isessentially a pattern-matching process. After appropri-ate and adequate training (which can take a long time),an ANN can recognise the pattern in the user supplieddata quickly to arrive at a conclusion. An ANN can alsobe used initially to generate patterns (and hence rules,etc.) from a collection of examples, e.g. of the bestdesigns from several designers.2.3. Application of expert systems to optoelectronicdesign

Expert systems may be designed to solve differenttypes of problems. Gevarter7 lists the following, whichrepresent the general consensus:

classification (including interpretation, diagnosis,debugging and use advice), design and synthesis,intelligent assistance, prediction from model-based reasoning, scheduling, planning, monitor-ing, (on- or off-line) control, digesting of infor-mation, and discovery.

Expert systems, with their components ~numeratedabove, are very useful tools for delivering expertise in anarrow specialization to users who are not experts inthe particular topic. A large number of expert systemshave been developed in the field of engineeringdesign ~-l in genera l, but those for optoelectronic engi-neering appear to be rare or non-existent. This paperaims to fill this gap. It should be useful to novice,inexperienced or occasional designers of optical fibrecommunications systems. The tutorial section could, ofcourse, be produced as a booklet or canned text dis-played by a computer. However, a guided search asprovided by an expert system (or other means) wouldallow an inexperienced user to obtain informationabout optoelectronic devices, and the design processshould reinforce the design recommendations providedby the expert system.EAAI 8 -3 -D

Though an advisor can be built using a number ofprogramming languages, including the logic or list pro-cessing languages such as PROLOG, LISP etc., use ofan expert-system building tool (often called an expert-system 'shell') makes the process of development andmaintenance of such a system much easier. Many shellsallow linkages with external programs if a particularpart of the task can be accomplished more effectively inthat way.

Rapid prototyping/development is particularly con-veniently done using an expert system shell as shown bythis example, as well as by previous experience. ~1-~2 Inthis case, the undergraduate student was unfamililarwith both expert-system technology and optoelectro-nics, but a short introductory session with each of thetwo academic supervisors with specialization in opto-electronics and expert systems respectively was enoughto get the student started on the project very quickly.

3. ARCHIT ECTURE OF OPTOELECT RONICE X P E R T S Y S T E M

This expert system was built as an aid in teaching anddoing design of optical communications systems. Henceits dual aims are:

1. a tutorial introduction to the terminology andtechnology of optical link design;2. design assistance for novice or infrequentdesigners.

The tutorial introduction to the terminology andcurrent technology helps to overcome the initialobstacle of unfamiliar ity with the details of optoelec-tronics for a novice user or a forgetful, infrequent usersuch as an underg raduate student. The second aim is tooffer expert assistance in the process of design, bymaking available currently accepted best practice,based on the experience of a human expert. Obviously,the opinion of the human expert whose knowledge isincoporated in the expert system biases the designpractice, but this is the same in a design office with ahierarchy of designers.

The expert system does have the additional possibi-lity of being able to incorporate the design expertise ofmore than one expert if such expertise is available.Where two or more experts differ, someone senior hasto adjudicate on the acceptable design, both in thedesign office and in an expert system. However, theexpert system can be built to make this choice clear to anovice or less-experienced user of the expert system,and to offer alternative designs for consideration.In the prototype expert system reported here, suchalternative designs are not incorporated, but they canbe without excessive additional effort. However, one ofthe authors is an experienced designer in this area andhence the knowledge incorporated in this expert systemis ec.~entiaily derived from multiple experts. Thisknowledge is collated and moderated by the exper-


4/13

322 K.P . DAB KE et al .: OPTICAL FIBRE COM MUNICATIONSi e n c e d d e s i g n e r in o r d e r t o p r e s e n t t h e d e s i gn m e t h o d o -l o g y a s a c o n s i s t e n t b o d y o f k n o w l e d g e .T h e e x p e r t s y s t e m r e p o r t e d h e r e i s f o r th e d e s i g n o fo p t ic a l c o m m u n i c a t i o n s s y s t e m s , b u t d o e s n o t i n c o rp o r -a t e t h e d e s i g n o f a n o p t i c a l a m p l i fi e r . I t is m a i n l y a i m e da t t h e s e l e c t i o n o f c o m p o n e n t s w h i ch m a k e u p a no p t i c a l c o m m u n i c a t i o n s s y s t e m . O p t i c a l a m p l i f i e rd e s i g n w o u l d b e a s u i t a b l e t o p i c f o r a s e p a r a t e p a p e r .T h e u s e o f o p t i c a l a m p l i f ie r s a n d w a v e l e n g t h m u l t i p le x -i n g t e c h n i q u e s w o u l d b e a m a j o r d e v e l o p m e n t i n t h en e x t g e n e r a t i o n o f o p t i c a l c o m m u n i c a t i o n s s y s t e m s .I n c o r p o r a t i n g t h e s e s p e c i a l i z e d c o m p o n e n t s a n d t h ee f f e c t s o f p h a s e n o i s e s in o p t i c a l s y s t e m s i n a n e x p e r ts y s t e m w o u l d c e r t a i n l y b e v e r y u s e f u l f o r a d v a n c e dd e s i g n e r s .3 . 1 . U s e o f i n d u c t i o n t o c r e a t e t h e k n o w l e d g e b a s e

T h e p r o d u c t i o n o f t h e k n o w l e d g e b a s e f o r t h e e x p e r ts y s t e m w a s m a d e e a s i e r b y u s i n g t h e i n d u c t i o n f a c i l i t yo f t h e e x p e r t s y s t e m s h e l l V P X . T h e a v a i l a b l e d e v i c ed a t a w a s p u t i n a s i m p l e t a b u l a r f o r m ( o f t e n , i t w a sa v a i l a b l e i n t h i s f o r m i n t h e f i r s t p l a c e ) a n d r u l e s w e r ei n d u c e d . T h i s r e d u c e d t h e e f f o r t r e q u i r e d i n w r i t in gr u l e s t o a m i n i m u m . T h i s t e c h n i q u e o f r e p r e s e n t i n ga v a i la b l e k n o w l e d g e i n t a b u l a r f o r m w h e r e v e r p o s s ib l ew a s u s e d t o i m p r o v e t h e p r o d u c t i v i t y o f r u l e - c r e a t i o nt h r o u g h o u t t h is p r o j e c t .T h e u s e o f t h e i n d u c t i o n f a c i l it y h a s t h e f u r t h e ra d v a n t a g e t h a t w h e n t h e m a n u f a c t u r e r ' s d a t a c h a n g e s ,o n l y t h e t a b l e o f t h is i n f o r m a t i o n n e e d s t o b e c h a n g e db e f o r e i n d u c i n g t h e n e w r u l e s . T h u s , s o f t w a r e m a i n t e n -a n c e b e c o m e s r e l a t iv e l y e a s y a n d c a n b e c a r r i ed o u t b yp e o p l e w i t h d i f f e r e n t b a c k g r o u n d s . A p e r s o n f a m i l i a rw i t h t h e s u b j e c t m a t t e r , a s w e ll a s t h e f e a t u r e s o f t h ee x p e r t s y s t e m s h e l l, c a n a d d o r m o d i f y k n o w l e d g e int a b u l a r f o r m , a n d c r e a t e o r m o d i f y t h e k n o w l e d g e b a s eu s i n g i n d u c t i o n . I f t h e p e r s o n d o i n g th e s o f t w a r e m a i n -t e n a n c e i s f a m i l i a r w i t h t h e s u b j e c t m a t t e r b u t n o t v e r yc o m f o r t a b l e w i t h t h e e x p e r t - s y s t e m s h e l l , s / h e c a n u s e at e x t e d i t o r t o m o d i f y o r c r e a t e r u l e s t o su i t c h a n g e dk n o w l e d g e .H o w e v e r , t h e c r y p t i c d a t a c o n t a i n e d i n t h e o r i g i n a lt a b u l a r f o r m i s n e v e r p r e s e n t e d t o t h e e n d u s e r a n dh e n c e t h e e n d u s e r i s s h i e l d e d f r o m i n c o m p r e h e n s i b l ed a t a . I f n e c e s s a r y , t h e e n d u s e r c a n e x a m i n e t h e a c t u a lE n g l i s h - l i k e r u l e s ( r a t h e r t h a n j u s t t h e c o n c l u s i o n s )d u r i n g c o n s u l t a t io n , i n o r d e r t o u n d e r s t a n d t h e p r o c e s so f d e d u c t i o n w h i c h l e d to t h e c o n c l u s i o n o r a d v i c e .3 . 2 . T u t o r i a l o n o p t o e l e c t r o n i c s

T o m e e t t h e t w o a i m s o f p r o v i d i n g a t u t o r ia l a n dg i v i n g d e s i g n a d v i c e , t h e e x p e r t s y s t e m o f f e r s a n i n i t ia lc h o i c e b e t w e e n a t u t o r i a l a n d d e s i g n a s s i s t a n c e . T h et u t o r i a l o p t i o n h a s t w o s u b - o p t i o n s o f :( a ) d e f i n i t i o n o f te r m s ;( b ) i l lu s t r a t iv e d e s i g n e x a m p l e .

D e f i n i t i o n o f t e r m s i s f u r t h e r b r o k e n d o w n i n t o a n

i n t r o d u c t i o n t o m a n y t o p i c s , s u c h a s s o u r c e , d e t e c t o r ,o p t i c a l f i b r e , d a t a m o d u l a t i o n a n d p r e - a m p l i f i e r .F u r t h e r e x t e n s i v e d e t a i l s a r e o f f e r e d f o r e a c h o f t h e s et o p i c s a n d t h e s e c a n b e s e l e c t e d f r o m c o n v e n i e n tm e n u s . T h e d e t a i l s o f t h e d e c i s i o n s t r u c t u r e o f t h eT U T O R I A L s e ct io n o f t h e e x p e r t sy s te m a r e s h o w n i nF i g . 1 . A t e a c h s t a g e o f th e t u t o r i a l , t h e o p t i o n t o e x i tf r o m t h e t u t o r i a l o r a n y o f i t s s u b - s e c t i o n s i s a v a i l a b l et o p r o v i d e a n e s c a p e f r o m a l a b y r i n t h o f b r a n c h i n gp a t h s i n t o t h e t u t o r i a l . T h i s is a n i m p o r t a n t f e a t u r e o f ag o o d u s e r i n t e r f a c e e s p e c i a l l y f o r a n o v i c e o r i n e x p e r -i e n c e d u s e r , w h o c a n f e e l o v e r w h e l m e d b y a n e v e r -b r a n c h i n g m e n u w i t h o u t t h e p r o v i s io n f o r r e t r a c in g t h ee a r l i e r s t e p s .

T h e I l l u s t r a t i v e D e s i g n o p t i o n i n t h e t u t o r i a l s e c t i o ni s a d e t a i l e d , s t e p - b y - s t e p , e i g h t - p a g e d e s i g n e x a m p l eg i v i n g a l l t h e d e t a i l s o f d e v i c e s e l e c t i o n a n d n u m e r i c a lc a l c u l a t i o n s .T h e d e t a i l s i n t h e s e c t i o n o n t e r m i n o l o g y w e r e

p r o v i d e d b y o n e o f th e a u t h o r s ( L N B ) w h o i s a n a c t iv er e s e a r c h e r i n t h e f i e ld o f o p t o e l e c t r o n i c s . T h e i n f o r -m a t i o n a b o u t c u r r e n t t e c h n o l o g y c o n t a i n e d i n t h et u to r i a l s e c ti o n w a s g a t h e r e d f r o m m a n u f a c t u r e r ' s c a t a-l o g ue s . C l e a r l y , s u c h i n f o r m a t i o n i s n o t c o m p r e h e n s i v eb u t g i v e s a n i n e x p e r i e n c e d u s e r t h e f l a v o u r o f t h ec u r r e n t s t a t e o f t h e a r t . T h e s e c t i o n o n i l l u s tr a t iv ed e s ig n e x a m p l e s w a s b a s e d o n s o m e a c t u a l d e si g n s, a n do n e x p e r i e n c e o f t e a c h i n g u n d e r g r a d u a t e s t u d e n t s t h et e c h n i q u e s o f o p t i c a l -f i b r e s y s t e m d e s i g n .3 . 3 . D e s i g n a s s i s t a n c e

I n th i s s e c t io n o f t h e e x p e r t s y s t e m , t h e u s e r i s a s k e dt o s u p p l y t h e f o l l o w i n g i n p u t s :1 . l e n g t h o f t h e o p t i c a l f ib r e l i n k ;2 . b i t r a t e , h e n c e b a n d w i d t h o f d a t a t r a n s m i s s i o n ;3 . a l l o w a b l e b it e r r o r r a t e ( B E R ) ;4 . m o d u l a t i o n f o r m a t .

T h i s d a t a d e t e r m i n e s t h e b a n d w i d t h - l e n g t h p r o d u c t( d e s i g n a t e d a s B o i n F i g . 2) a n d t h e m a x i m u m a l l o w a b l ei m p u l s e s p r e a d f o r a s i n g l e - m o d e o p t i c a l -f i b r e l in k . F o rs u c h a s i n g l e - m o d e f i b r e , u s e r - s u p p l i e d v a l u e s o f m a x i -m u m a t t e n u a t i o n a n d c h r o m a t i c d i s p e r s i o n l e a d t o t h ed e t e r m i n a t i o n o f m a x i m u m a l l o w a b l e s p e c t r a l w i d t ha n d t h e a l l o w a b l e m a x i m u m a n d m i n i m u m s o u r c e r i s et i m e .F o r a m u l t i -m o d e f i br e , t h e l e n g t h - b a n d w i d t h p r o d -u c t a n d m a x i m u m a t t e n u a t i o n a r e r e q u e s t e d f r o m t h eu s e r t o d e t e r m i n e , a s in t h e c a s e o f a s i n g l e - m o d e f i b r e ,t h e m a x i m u m a l l o w a b l e s p e c t r a l w i d t h a n d t h e a l l o w -a b l e m a x i m u m a n d m i n i m u m s o u r c e r is e ti m e . A nu p p e r l i m i t o f th e l e n g t h - b a n d w i d t h p r o d u c t B o o f 1 2 00M H z - K m is us e d t o d e t e r m i n e w h e t h e r a m u l t im o d e o rs i n g l e - m o d e f i b r e s h o u l d b e u s e d .F r o m t h e s e i n f e r r e d ( o r u s e r - s u p p l i e d , o v e r r i d i n g )v a l u e s o f s p e c t r a l w i d t h , s o u r c e r i s e t i m e a n d s o u r c eo u t p u t p o w e r a r e d e t e r m i n e d i n o r d e r t o s e l e c t a na p p r o p r i a t e p h o t o d i o d e . A d e c i si o n t o u se a P I N d i o d e


5/13

K. P. DABKE et al.: OPTICAL FIBRE COMMUNICATI ONS 323

IE X I T

T U T O R I A L

ID E F I N I T I O N I L L U S T R A T I V EO F T E R M S D E S I G N

II t I ISOURCE OPTICALFIBREDETECTOR

DATA RECEIVERMODULATION

SEPARATE FLOW CHARTSLABELLED ~ ETC.

EXIT

r m _EX I T

rSPECTRAL

WIDTHEMISSION

WAVE-LENGTH

IP A R A M E T E RD E H N I T I O N

I IRISE POWERTIME OUTPUT

THRESHOLDCURRENT

S O U R C E

EXIT

LIGHTEMITrlNG

DIODE

]T Y P E O FS O U R C E

l LASER EXIT

/I I DFB FA BR Y- EXITLASER PEROT

LASER

SHORT LONG EDGE EXITWAVELENGTH WAVELENGTH EMITrlNG

LED LED LED

EX I T

DETECTORCAPACI- C1TANCE

RESPON-SIVITY

D E T E C T O RJ

P A R A M E T E RD E F I N I T I O N

II IDARK EXCESS

CURRENT NOISEFACTOR

MULTIPLIEDD A R K

CURRENT

PINPHOTODIODE

EXIT

iT Y P E O FD E T E C T O R

I AVALANCHE EXITPHOTODIODE

Fig. 1--Caption overleaf ,


6/13

324 K.P . DAB KE e t a l . : OPTICAL FIBRE COMMUNICATIONS

E X I T

IEXIT

O P T I C A L F I B R E

P A R A M E T E RD E F I N I T I O N

I JDISPER- MODE FIELD

SION DIAMETER

FT Y P E O F

F I B R EI

SINGLEMODE

NUMERICALAPERTURE

FIBREATTENUATION

U-CHROMATICDISPERSION

j

JINTER-MODALDISPERS-

SION

MATERIALDISPERSION

MULTI EXITMODE

JIEXIT BANDWIDTH

LENGTHPRODUCT

D A T A M O D U L A T I O N_ _

dEXIT

BITERRORRATE

rG E N E R A L

D E F I N I T I O NJ _ _

SYSTEM EXITRISETIME

rWAVEGUIDE EXITDISPERSION

MODULATIONFORMAT

I I IRETURN NON-RETURN EXITTO ZERO TO ZERO

I rBASELINE WANDER EXIT

R E C E I V E R

I IE X IT P H O T O D E T E C T O R

DESIGN NOISES EXIT

A M P L I F I E RC O N F I G U R A T I O NE

r iHIGH TRANS-

IMPEDANCE IMPEDANCE

IEXIT

Fig . 1 . F low chart for the tutoria l .

m u s t b e m a d e a t th i s st a g e a n d i f a P I N d i o d e i s n o ts e l e c t e d , a d d i t i o n a l i n f o r m a t i o n m u s t b e o b t a i n e d f r o mt h e u s e r t o f i n a l l y d e t e r m i n e t h e r e c e i v e r b a n d w i d t h ,r e c e i v e r s e n s i t i v i t y , m a x i m u m a l l o w a b l e e q u i v a l e n tn o i s e c u r r e n t a t t h e i n p u t o f t h e r e c e i v e r a n d t h e a c t u a ln o i s e c u r r e n t f o r t h e s e l e c t e d a m p l i f i e r d e s i g n .

A f t e r c h e c k i n g t h e f i b r e - l i n k o p t i c a l p o w e r a n d r i s e -t i m e b u d g e t s f o r t h e s e le c t e d d e s i g n , a d v i c e c a n b eo f f e r e d t o t h e u s e r t o i m p r o v e t h e s y s t e m u n d e r c o n -s i d e r a t i o n . T h e o v e r a l l p r o c e s s o f d e s i g n i s s h o w n i n t h ef low charts in Fig . 2 .

A t e a c h s t a g e o f d e d u c t i o n , m u c h t h e o r e t i c a l a n d


7/13

K . P . D A B K E e t a l . : O P T I C A L F I B R E C O M M U N I C A T I O N S 32 5t e c h n o l o g i c a l i n f o r m a t i o n m u s t b e a p p l i e d , t o d e d u c et h e a p p r o p r ia t e r e c o m m e n d a t i o n s . A s m e n t i o n e da b o v e , m u c h o f t h is k n o w l e d g e i n t h e k n o w l e d g e b a s ei s s t o r e d i n t a b u l a r f o rm s t o i n d u c e ru l e s . A s a m p l e o fs u c h t a b l e s i s i n c l u d e d i n t h e Appendix.F i g u re 3 s h o w s a b l o c k d i a g ra m o f a b a s i c o p t i c a lf i b r e l i n k . F i g u re s 4 , 5 a n d 6 s h o w t h e d e t a i l s o f t h em o d e l s o f t h e p h o t o d i o d e , h i g h - i m p e d a n c e p r e -a m p l i f i e r a n d t r a n s i m p e d a n c e p r e - a m p l i f i e r r e s p e c t i -v e l y , u s e d i n t h e o p t i c a l - f i b r e l i n k .F o r a c e r t a i n s e t o f p a r a m e t e r s o r d a t a f o r a n o p t i c a l-f i b r e c o m m u n i c a t i o n s l i n k , t h e r e a r e s e v e r a l o p t o e l e c -t r o n i c c o m p o n e n t s w h i c h m a y s a t is f y t h e s y s t e m sr e q u i r e m e n t s . H o w e v e r , d e p e n d i n g o n t h e b i t r a t e ,c e r t a in c o m b i n a t i o n o f o p t o e l e c t r o n i c c o m p o n e n t s c a nb e p r e - s e l e c t e d . A s e l e c t i o n g u i d e i s t h u s u s e d a s t h e

b a s i c ru l e s i n t h e k n o w l e d g e b a s e . S e v e ra l s e l e c t i o nr u l es f o r t h e s e c o m p o n e n t s , p r o v i d e d b y t h e m a n u f a c -t u r e r s , a r e c o m b i n e d i n t o a u n i v e r s a l g u i d e .I n f o r m a t i o n c a n b e d e d u c e d f r o m t h e s e g u i d e s b ya p p r o x i m a t i o n , s i n c e t h e y a r e t h e m s e l v e s a p p r o x i m a -t i o n s . Ex a m p l e s o f i n d u c t i o n t a b l e s o f e x t r a c t e d i n f o r -m a t i o n a r e s h o w n i n T a b l e s A 3 a n d A 4 o f t h eAppendix, f o r i i g h t w a v e s o u r c e s a n d p h o t o d e t e c t o r sr e s p e c t i v e l y .I n r e c e i v e r d e s i g n f o r i n t e n s i t y m o d u l a t i o n /d i r e c td e t e c t i o n ( I M / D D ) o p t i c a l - f i b r e s y s t e m s , t h e p r e -a m p l i f i e r c o n f i g u ra t i o n p l a y s a m a jo r p a r t i n d e t e rm i n -i n g t h e e q u i v a l e n t n o i s e c u r r e n t a t t h e i n p u t o f t h er e c e i v e r . T h e c h o i c e o f t h e r e c e i v e r i s n o t s t r a i g h t f o r -w a rd , b e c a u s e t h e r e i s a la rg e n u m b e r o f p o s s i b i l i ti e s ,d e p e n d i n g o n t h e t y p e s o f a p p l i c a t i o n s , s u c h a s o n -

U S E R I N P U T1 L E N G T H2 B I T R A T E3 B IT E R R O R R A T E4 M O D U L A T I O N F O R M A T

F I N D 1 S Y S E M R I S E T I M E2 M A X I M U M A L L O W A B L E

I M P U L S E S P R E A D

N O :

U S E R I N P U TI M A X I M U M A T T E N U A T I O N2 B A N D W I D T H - L E N G T H P R O D U C T ( B o )

F I N D tM A X . A N D M I N .S O U R C E R I S E T IM E

U S E R I N P U TI S P E C T R A L W I D T H2 S O U R C E R I S E T I M E3 S O U R C E O U T P U T P O W E R

I S E L E C A P N O T O D I O D E ]

U S E R I N P U TM A X . A T T E N U A T I O NC H R O M A T I C D I S -P E R S I O N

F I N DM A X A L L O W A B L ES P E C T R A L W I D T H

F i g . 2 . F l o w c h a r t f o r t h e o p t i c a l f i b r e s y s t e m d e s i g n a d v i s o r .


8/13

3 26 K . P . D A B K E e t a L : O P T I C A L F I B R E C O M M U N I C A T I O N S

12B- "" - NO- P IN .. .. . ~. . . . .~ D I O D E ~ . . . . .

YES q~U S E R I N P U T

l I D A R K C U R R E N T2 R E S P O N S I V I T Y

[ v F D : & MIN. REC EI - ~_A X .E R R IS E T IM E I - -

OU RC E RISETIMES O U R C E R I S E " I

Y E S +R E C E I V E R R I S E T I M E =

M I N . R E C E I V E R R I S E T IM E

F I N D :1 R E C E I V E R B A N D W I D T H2 R E C E I V E R S E N S I T I V I T Y3 M A X . A L L O W A B L E S O U R C E N O I SE4 N O I S E C U R R E N T F O R A L L P R E - S E L E C T E D A M P .

D E S I G N S

C O M P A R E N O I S E C U R R EN T S A N D S E L E C T A NA M P L I F I E R W I T H L O W E S T N O I S E C U R R E N T

C H E C K L I N K P O W E R A N D R I S E T I M E B U D G E T SF O R T H E S E L E C T E D S Y S T E M

G I V E N E C E S S A R Y A D V I C E T O I M P R OV E T H ET H E S Y S T E M U N D E R C O N S I D E R A T I O N

Fig. 2 - - c o n t i n u e d .

! USER INPUT ( AVA LAN C HE DIODE)~1 M U L T I P L I C A T I O N F A C T O R2 E X C E S S N O I S E F A C T O R3 D A R K C U R R E N T4 M U L T I P L I E D D A R K C U R R E N T5 R E S P O N S I V I T Y

R E C E I V E R R I S E T IM E= S O U R C E R I S E T I M E

T R A N S M I T T E R [/ ) / : ) / ; ' ~ , \ ) O P T I C A L F I B R Et2~/~/ - RECEIVER

Fig . 3 . Bas ic optical f ibre l i n k .

shore or undersea , l oca l or m etropo l i tan opt i ca l - f i brel inks, etc.

In the expert sy s tem for opt i ca l - f i bre com m uni ca t i ondes i gn presented here , the pre-am pl i f i er conf i gura t i onsse l ected by the adv i sor are res t r i c t ed to s i ng l e- s tagec o m m o n - e m i t t e r b i p o la r t ra n s is t or a n d c o m m o n - s o u r c eF E T a m p l if ie r s . H o w e v e r , u s e r s a r e g i v e n t h e c h o i c e t odes i gn the i r own rece i ver , i f des i red . A noth er res tr i c -

t i o n i n t h e a d v i s o r s e l e c t i o n i s t o c o n s i d e r o n l y pre-s e l e c t e d s il ic o n B J T o r F E T , s i li co n M O S F E T , a n dG a A s M E S F E T a s a m p li fy i n g d e vi ce s .In o r d e r t o c h o o s e f r o m a m o n g t h o s e p r e - s e l e c t e dpre-am pl i f i er des i gns , those w h i c h w o u l d r e s u l t i n th el o w e s t e q u i v a l e n t n o i s e c u r r e n t ( is L q , i n i ti a l ly o n l yd e s i g n s w i t h ( i N ) ~ l o w e r t h a n t h e m a x i m u m n o i s ecurrent ca l cu l a ted f rom the l i nk power b u d g e t a r e


9/13

K . P . D A B K E e t a l . : O P T I C A L F I B R E C O M M U N I C A T I O N S 3 27

i s

Fig . 4 . Pho tod iode m ode l .

0

PHOTODIODE

BIASINGRESISTOR

+ V

PRE-AMPLIFIERFig . 5 . H igh impedance p re -ampl i f i e r .

OUTPUT

considered. If none of these pre-selected designs satis-fies the allowable conditions, the design with lowest(iN)oq among the designs with noise current higher thanthe maximum allowable noise would be selected. Theinduction table for this decision is shown in Table A4 o fthe Appendix.After the selection of pre-amplifiers with equivalentnoise currents, the input impedance, including thephotodiode capacitance and hence the receiver band-width, together with the rise times of the transmitterand the total dispersion of the optical fibre are com-bined to confirm the satisfaction of the rise-time bud-get.

Rules are formulated to check that the final designmeets the desired performance in power and rise-time,and to give advice when necessary to improve the finaldesign. The induction tables and the flow chart forthese rules are given in the Appendix in Tables A5(a)and (b) and Fig. A2 respectively.

The expert system presented here also provides a'refreshing' procedure to provide users with an oppor-tunity to change the values of the parameters of thecomponents selected.

In implementing the optical-fibre link design, certain

+ VPHOTODIODE~

FEEDBACKRESISTOR

PRE-AMPLIFIERFig . 6 . Trans impedance p re -ampl i f i e r .

OUTPUT

design equations are required. Some of these wereimplemented indirectly, due to some restrictionsimposed by the expert-system development tool,VP-Expert. For example, the function x y is not avail-able, and the exponential and logarithm functions hadto be used to get around this deficiency.

Anoth er minor limitation imposed by the VP-Expertpackage is its inability to display and store numericalresults smaller than 10 -6 Scaling of variables was usedto overcome this problem.4. VERIFICATION AND EDUCATIONAL IMPACT

After creating the expert system, a few sample designproblems were submitt ed to it to verify that it producedthe expected design recomm endations. It was then usedfor an undergraduate, final-year honours electivecourse on "Optical fibre communications" taken byabout 35 students.

Because of the students' unfamiliar ity with the light-wave technology, effective design work required abrief reminder tutorial as a preliminary to the designprocess.

To make the students familiar with the design datasources, device data was made availale for a hand-crafted feasibility design. Students were required toread and interpret the given design specifications, andto find suitable components by consulting handbooks,databooks etc.

These feasible designs were checked and assessed bythe instructor before the students were allowed to usethe expert system to check detailed designs. Studentswere encouraged to use the expert system to check therise-time and power budgets for the componentsselected by them. The students were also encouraged toredesign the system using the expert-system advisor tosee if they could obtain a better /cheaper design startingfrom the given specifications.

The educational impact of the availability of theexpert system was very interesting to observe. In theprevious years, the design tasks had had to be limited tosimple, single tasks in order to arrive at a reasonabledesign in reasonable time. Design iterations were noteasy to perform.In contrast, the expert system allowed students toinvestigate several alternative designs in an iterativemanner, but without spending excessive effort or time.The reluctance to iterate the first or preliminary designwas overcome by the availability of the expert system.

The expert system not only allowed to students toexplore several alternative designs, but also gave thema better appreciation of the design process. Some of thestudents also explored the effects of changing some ofthe specifications or changing a component recom-mended by the expert system. Thus the expert systemallowed the students to develop a more matureapproach to design, and to get a better overview ofboth the design process and the resulting design.


10/13

328 K.P . DABKE et al.: OP T ICAL FIBR E COM M UNICAT IONS

5 . C O N C L U S I O N ST h i s p a p e r h a s s h o w n t h a t f o r a f a s t - d e v e l o p i n g

t e c h n o l o g y s u c h a s o p t o e l e c t r o n i c s , e x p e r t - s y s t e m t e c h -n o l o g y i s a s u i t a b l e v e h i c l e f o r d i s s e m i n a t i o n o f c u r r e n tk n o w l e d g e i n a t u to r i a l f o r m , a n d f o r c o m b i n i n g i t w i t ht h e e x p e r t k n o w l e d g e r e q u i r e d f o r th e d e s i gn o f s u c hs y s t e m s u s i ng c u r r e n t t e c h n o l o g y .T h e s o f t w a r e v e h i c l e u s e d f o r t h is p u r p o s e c a n b ev e r y e c o n o m i c a l , a n d h e n c e a c c e s s i b l e t o a n o r g a n i z a -t i o n w h o s e m o n e t a r y a n d h u m a n b u d g e t i s f a ir l y s m a l l .E v e n s i m p l e a n d c h e a p e x p e r t - s y s t e m s h e l l s h a v ea d e q u a t e u s e f u l f e a t u r e s t o a ll o w im p l e m e n t a t i o n o f a ne x p e r t s y s t e m f o r a h i g h - t e c h a n d a d v a n c i n g t e c h n o l -o g y . F a m i l i a r i s a t i o n w i t h s u c h a s o f t w a r e t o o l i s n o tp a r t i c u l a r l y d i f f ic u l t , a n d a f t e r a b r i e f i n t r o d u c t i o n i tm a y b e u s e d b y m o s t e n g i n e e r s . L e a r n i n g o f a n e wc o m p u t e r p r o g r a m m i n g l a n g u a g e is n o t re q u i r e d. I na d d i t i o n t o u s i n g t h e e x p e r t s y s t e m f o r t u to r i a l a n dd e s i g n p u r p o s e s , a n i n t e r e s t e d e n g i n e e r c a n l o o k i n s i d et h e e x p e r t s y s t e m i n o r d e r t o m o d i f y i t t o i n d i v i d u a ln e e d s . T h e r u l e s o f d e s i g n in t h e k n o w l e d g e b a s e o f t h ee x p e r t s y s t e m a r e s u f f i ci e n tl y t r a n s p a r e n t t o a l l o w th i s.

T h e i n d u c t i o n f a c i li ty p r o v i d e d b y s o m e o f th ee x p e r t - s y s t e m b u i l d i n g t o o l s ( s h e l ls ) is a v e r y p o w e r f u lm e c h a n i s m f o r c o n v e r t i n g t a b l e s o f d a t a a n d d e c i si o ns t r u c t u r e s i n t o w o r k a b l e r u l e s . T h i s f a c i l i t y a l l o w s t h ee x p e r t - s y s t e m b u i l d e r t o b y p a s s m o s t o f t he p r o b l e m so f le a r n i n g t o w r i t e r u l e s , a n d l e a d s t o th e c r e a t i o n o fr u l e s f r e e o f s y n t a c t i c a l e r r o r s , e t c . , i n t h e p r o c e s s . T h i sm a k e s t h e m a i n t e n a n c e o f s u c h e x p e r t s y s t e m s fa i rl ys i m p l e , e v e n w h e n t e c h n o l o g i c a l k n o w l e d g e c h a n g e sf r e q u e n t l y .T h e h a r d w a r e p l a t f o r m r e q u i r e d t o r u n s uc h e x p e r ts y s t e m s i s a l s o v e r y e c o n o m i c a l a n d t h e r e f o r e t h ed i s s e m i n a t i o n o f te c h n o l o g i c a l e x p e r t i s e i s q u i te c h e a pi n r e l a ti o n t o t h e c o s t o f t h e s y s t e m b e i n g d e s i g n e d .

T h e p a r t i c u l a r e x p e r t - s y s t e m s h e l l u s e d w a s n o t p a r -t i c u l a r l y p o w e r f u l a n d l a c k e d o n e o r t w o f e a t u r e s , b u tt h i s d e f i c i e n c y w a s n o t a s i g n i f i c a n t p r o b l e m . O t h e rs i m i l a r l y i n e x p e n s i v e s h e l l s a r e a v a i l a b l e w i t h t h er e q u i r e d f e a t u r e s .

T h i s e x p e r t s y s t e m w a s u s e d a s a n a id t o r e v is i o n a n da s a t u t o r i a l i n 1 9 9 1 i n t h e c o u r s e o n o p t i c a l - f i b r ec o m m u n i c a t i o n s , a n d w a s f o u n d t o b e v e r y u s e f u l b yt h e s tu d e n t s . I t a p p e a r e d t o e n c o u r a g e t h e e x p l o r a t i o no f a l t e r n a t i v e d e s i g n s , a n d ' w h a t i f ' a n a l y s i s .

R E F E R E N C E S1. Hewlen-Packard Company, Optoelectronics Divisio n,Appl icat ions Engine er ing S ta ff . Optoelectronics/fiber-opticsApplicat ions Manual . Mc Gra w Hill , New York (1981).2. H enry P. S. Lightwave primer. IE E E J. Quant . Elect. QE-21,1862-1879 (1985).3. Jain V, K. and Gupta H. M. O ptical fibre l ink design. J. Opt.C o m m u n . 6, (2) 58-66 (1985).4. Waterman D. A. A Guide to Expert Sys tems. Addison-Wesley,Reading, MA (1986).5. Harmon P. and King D. Expert systems--Artificial Intelligence inbusiness. John Wiley & Sons, New Y ork (1985).

6. Winston P. H. and P rendergast K. A. ( E ds ) Th e A IBus iness--T he Commercial Use s of Art i fic ia l In te l ligence. "['heMIT Press, Cam bridge, MA (1986).7. Gevarter W . B. The nature and eva luation of comm ercial expertsystem s building tools. I E E E C o m p u te r 20, (5) 24-41 (1987).8. Pham D. T. (Ed.) Expert Systems in Engineering. IF SPublications/Springer-Verlag, Bedford, U.K. (1988).9. Liebow itz J. (Ed.) Expert Sys tem Applicat ions toTelecommunications. W iley-Interscience, U.S.A . (1988).10. Ericson E. C., Tra eger Ericso n L. and Minoli D. (Eds) Exper tSystems Applicatons in Integrated Network Management . Pub.Artech House Inc., Norwood MA, U .S.A. (1989).I1. Dabke K. P. and Thom as K. M. Expe rt system guidance forlibrary users. Li b r a r y H I TEC H 10, 53-60 (1992).12. Hand reck K., Dabk e K. P. and Conlon M. F. An expert systemfor transformer impulse test diagnosis, Engng Applic . Art i f .Intell. 4, 11-21 (1991).

A P P E N D I XD e c i s i o n T a b l e s f o r I n d u c i n g R u l e s i n t h e K n o w l e d g eB a s eT h e t w o t a b l e s g i v e n b e l o w a r e t y p i c a l r e p r e s e n -t a t i o n s o f te c h n i c a l k n o w l e d g e . T a b l e A 1 c o n t a i n sm a i n l y q u a l it a t iv e s y m b o l i c k n o w l e d g e , w h i le T a b l e A 2h a s q u a n t i t a t i v e k n o w l e d g e .N o t e : A l l v a r i a b l e s i n a V P X k n o w l e d g e b a s e m u s t b ec o n t i g u o u s c h a r a c t e r s t r in g s . T h i s r e q u i r e m e n t is m e tb y u si n g th e u n d e r s c o r e ( _ ) t o j o i n w o r d s w h i c h c o n v e yt h e m e a n i n g o f t h e v a r i a b l e s in E n g l i s h - l i k e s t r in g s .

T h e k n o w l e d g e b a s e in d u c e d f r o m t h e ta b u l a t e d t e x tf r o m T a b l e A 1 a b o v e a p p e a r s in Fi g. A 1 . N o t e t h a t th ef o u r c o l u m n s i n T a b l e A 1 y i e l d f o u r r u l e s ( R U L E 0 t oR U L E 3 ) . T h e i n d u c t i o n to o l a l s o p r o d u c e s t h e a p p r o -p r i at e q u es t io n s ( ' A S K ' ) , m e n u s f o r t h e ' C H O I C E S 'a m o n g t h e a l l o w a b l e a n s w e r s a n d s p e c if i e s t h e o b j e c t o ft he q u e r y ( ' A C T I O N S F I N D I n f o l ' ) . T o a id s o ft w a r em a i n t e n a n c e , a m o r e o b v io u s n a m e ( e . g . , f ib r e r e c o m -m e n d a t i o n ) c o u l d b e u s e d i n p l a c e o f ' i n f o l ' ( F i g . A 1 ) .

Table A I. Decision table for inducing the rules in 'dcsign_default"related to the fibreth e_ l ib re thewavelength help_ l in fo 1multi_mode a_850 nm default com ponent librc 1mul t i _ mo d e b_ 1 3 0 0 m d efau l t _ co m p o n en t f ib re 2s i n g le_ mo d e b_ 1 3 0 0 m d efau l t _ co m p o n en t t ib rc 3s i n g le_ mo d e c_ 1 5 5 0 m d efau l t _ co m p o n e n t f ib re 4

Table A2. Decision tab le for inducing the rules in "design_default 'related to the data modulationsource r t max source r t minModulation max. source rise t ime m in . source rise t ime

non_ return_to_ zero 0.225*bit_ period O. ll25*bit periodre t u rn _ t o _ z e ro 1 ) .1 )5 * b i t _ p e r i o d 0 .0 2 5 * b i t _ p c r i o d


11/13

K. P. DABKE e t a l . : OPTICAL FIBRE COMMU NICAT IONS 329

Table A3. Decision table for inducing the rulesfor selecting the source ('design_component')--light source selection)

Length (km) bit_rate source_info


12/13

3 30 K . P . D A B K E e t a l . : O P T I C A L F I B R E C O M M U N I C A T I O N S

T a b l e A 5 ( a ) . D e c i s i o nt a b l e f o r i n d u c i n g t h e r u l e st o c h e c k d e s i g n b u d g e t( ' d e s i g n _ b u d g e t ' )l e n g t h l p o p t _ l e n g t h< = l e n g t h _ r t l e n g t h _ l p> l e n g t h _ r t l e n g th r tT h e t e r m s u s e d i n t h i s t a b lea n d s u b s e q u e n t t a b l e s a n di n F i g . A 2 a re d e f i n ed a tt h e e n d o f F i g . A 2 .

T a b l e A 5 ( b ) . D e c i s i o n t a b l e f o r i n d u c i n g t h e r u l e st o c h e c k d e s i g n b u d g e t ' d e s i g n _ b u d g e t ' _ r i s e t i m et h e _ f i b r e l e n g t h _ r ts i n g l e _ m o d e ( t ~ , - t ~ - t ~ ) l / 2 1 D ~m u l t i m o d e ( t ~ - t ~ ' / 't ; O - B w _ l _ p r o d u c t / 4 4 0T h e t e r m s u s e d i n t h i s t a b l e h a v e t h e f o l l o w i n gd e f i n i t i o n s : t ,v ~= r i se t i me sp ec i f i ed by t h e sy s t emb a n d w i d t h ; t ~ = s o u r c e r i s e t i m e ; t , ~ = r e c e i v e r r i s et i m e ; B w _ l _ p r o d u c t = b a n d w i d t h , le n g t h p r o d u c t .

START WITH A SOURC E OF SPECIFIEDRISE TIME, OPTICAL POWER& SPECT R A L W I DT HI~V

INPUT1 length_rt 2 length_lp j

CALCULATEopt_length

4 ,

system length= opt_lengthSELECT A M OR EECONOMICAL SOURCE

BUDG ETN OT M ET

RISE TIME < PICK NEWBUDG ET SOUR CESATISFIED RISE TIMEq ,BUDG ETN OT M ET

P O W E R / P I C K N E WB U D G E T < [ S O U R C ESA T I SFI ED POW ER

SELECTDIFFERENTSOURCE

r - - -i A 2 ~L . . . .

" - . N O PI CK HI G HER POW ERi n ew sp > -< o ld sp .~ ~ ' i OUTPUT OR A NEW" \ " " - I P O W E R S O U R CEY ES V

P I C K N E W P O W E RS O U R C E W I T H L O W E RP O W E R O U T P U T

NO J J ~ NO~ ~ e w n e w s _ r _ ~ new s_ width > ~ ,

'ES + r sELECT NEW] SOURCE WITH

P I C K N E W S O U R C E I / N A R R OW E Rl SPEC. WIDTH

F i g. A 2 . F l o w c h a r t f o r t h e r u l e s r e l a t e d t o d e s i g n b u d g e t . L e n g t h _ r t , d i s p e r s i o n l i m i t e d l e n g t h ; l e n g t h _ l p , a t t e n u a t i o n l i m i t e d l e n g t h ;o p t _ l e n g t h , m a x . o p e r a t i o n a l l e n g t h w i t h a n o p t o e l e c t r o n i c s c o m b i n a t i o n ; s y s te m l e n g t h , p h y s i c a l l e n g t h o f t h e o p t i c a l f ib r e l i n k ; ne w _ s p , n e ws o u r c e p o w e r o u t p u t ; o l d _ s p , o l d s o u r c e p o w e r o u t p u t ; n e w s r t , n e w s o u r c e r is e ti m e ; o l d s _ r _ t , o ld s o u r c e r is e t i m e ; n e w s _ w i d t h , n e ws p e c t r a l w i d t h ; o l d s _ w i d t h , o l d s p e c t r a l w i d t h .

A U T H O R S ' B I O G R A P H I E SK i s h o r D a b k e g r a d u a t e d w i t h B . E . a n d M . E . d e g r e e s f r o m M a h a r a j a S a y a j i r a o U n i v e r s i t y o f B a r o d a , I n d i a a n d o b t a i n e d h isP h . D . f r o m M o n a s h U n i v e r s i t y i n A u s t r a l i a i n 19 7 2. H i s c u r r e n t r e s e a r c h i n t e r e s t s a r e in th e a r e a s o f c o n t r o l s y s te m s ,n o n l i n e a r c h a o t ic s y s t e m s a n d t h e a p p l i c a t io n n o f A I a n d E S t o e n g i n e e r i n g p r o b l e m s . H e r e c e i v e d t h e F a c u l t y o f E n g i n e e r i n g


13/13

K. P. DAB KE e t a l . : OPTICAL FIBRE COMM UNICATIONS 331T each i n g Aw ard fo r 1 9 9 3 a t M o n ash Un i v e r s i t y . He h as been a v i s it i n g sc i en t is t a t Un i v e r s i t y o f S t u t t g a r t , Ca rn eg i e M el l o nUn i v er s i t y i n P i t t sbu rg h , U .S .A . an d T h e Ar t i f i c i a l In t e l l i g en ce S y s t ems S ec t i o n o f t h e T e l eco m Aus t r a l i a R esea rchL a b o r a t o r i e s i n M e l b o u r n e , A u s t r a l ia .L e N g u y e n B iu h r e c e i v e d a B . E . ( H o n s . ) a n d P h . D . , b o t h i n E l e c tr o n i c E n g i n e e r in g , f r o m t h e U n i v e r s it y o f W e s t e r n A u s t r a li ai n 1 9 7 5 an d 1 9 8 0 . S i n ce 1 9 7 5 h e h as p i o n eere d ex p er i m en t a l an d t h e o re t i ca l wo rk i n i n t eg ra t ed o p t i c s fo r o p t i ca l f ib r eco mmun i ca t i o n s , p a r t i cu l a r l y aco us t o - an d e l ec t ro -o p t i ca l d ev i ces i n g u i d ed wav e s t ruc t u res . R ecen t l y h e h as d ev e l o p ed an o v e l t ech n i que fo r an a l y z i n g an d sy n t h es i zi n g v e ry l a rg e p h o t o n i c c i r cu i ts an d o p t i ca l l ump ed n e t wo rk s . H i s r e sea rch g ro up i sp resen t l y exp e r i men t a l l y v e r i fy i n g t h eo r i e s r e l a t ed t o t h is i n v en t io n . D r B i n h h as p ub l i sh ed o v e r sev en t y r e sea rch p ap e r s injo u rn a l s an d co n fe ren ce p ro ceed i n g s an d h o l d s t wo p a t en t s i n o p t i ca l en g i n ee r i n g .S i en P e n g L a u c o m p l e t e d h e r B . E . d e g r e e i n th e D e p a r t m e n t o f E l e c tr i c al a n d C o m p u t e r S y s t e m s E n g i n e e ri n g , M o n a s hUn i v er s i t y i n 1 99 0 . S h e r e t u rn ed t o M al ay s i a a f t e r g r ad ua t i o n an d h as wo rk ed as a co m p ut e r sy s t ems en g i n ee r . He r exp er i en cei n c l ud es l o ca l a r ea n e t wo rk d es i g n , i mp l emen t a t i o n , ma i n t en an ce an d secu r i t y ag a i n s t v i ruses , f au l t s , e t c .

Documents

Expert System for the Design of Optical Fibre