The purpose of this paper is to present a new type of Optically Processing Element (OPE) based of the use of optical fibers as optical signal transmission medium

González Marcos, Ana

Martín Pereda, José Antonio

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Optical Programmable Processing Element Using Optical Fibers 
J.A. Martín-Pereda, A. González-Marcos, Ciudad Universitaria, Madrid, Spain 
The purpose of this paper is to present a new type of Optically-
Processing Element (OPE) based on the use of optical fibers as optical signal 
transmission medium. This device is able to process two signals, being its 
output two other logical signals. These outputs depend on two control inputs 
signals. Fourteen logic operations pairs are allowed with our circuit. Two 
nonlinear devices have been employed. The general scheme is shown in Fig. 1. 
A somehow similar all-optical programmable logic gate has been proposed 
previously [1], being one of the differences the transmission medium. The 
practical implementation of this gate [1] have shown one of the major 
problems with the technique of free-air transmission and on-axis addressing: 
all inputs need to be exactly collinear and of identical wavelength to 
produce the same characteristics for each input. As it will be shown these 
problems are not present in our system. Moreover our circuit is able to 
perform arithmetic operations such as addition, and to offer the possibility 
to implement an Optically-Programmable Digital Processor. 
Fig. 1 is a schematic of the optical configuration of this Optically-
Programmable digital circuit. Two optically bistable elements P and Q, 
described below, are used. The inputs to the circuit are two binary input 
signals, Ix and I2, and two holding or bias beams, g and h. These signals can 
be generated from common LED's, because no coherence requirements are needed. 
Signals Ix and I2 are fed to two optical fibers, combined by a 2 x 1 coupler 
and going through a single fiber. This combined signal is divided, with 
another 1 x 2 coupler, into two new optical fibers. Each one of these two new 
signals are again added to one bias beam, g or h. Signal going through path 
1, plus bias beam h, is the input of the optically bistable element Q. The 
output of this device is divided into two equal-intensity outputs, one going 
to the final port Oz and the other one, plus signal going through path 2, is 
incident on the nonlinear device P. The resulting signal from this element 
goes to the final port O r 
The optically bistable elements can be similar to the employed by 
Wherret et al. [1]. In our case, both devices P and Q act as logical 
processors without being completely independent. Any bistable device 
exhibiting the above indicated responses shown could be used to implement 
this kind of logic circuits. Examples include GaAlAs MQW devices [2], ZnSe-
based nonlinear interference filters [1] or liquid crystals based devices 
[3]. In our case, these behavior has been implemented optoelectronically. 
By an appropriate choice of the power levels of the two optical bias 
inputs, g and h, all of the fourteen two-output logic functions corresponding 
to the two-input optical signals can be produced. Table I shows the logic 
functions that can be generated. 
The main advantage of the present configuration is the possibility of a 
half adder, with an easy extent to a full-adder and a ripple carry-adder. 
This fact is of a great importance because the carry propagation in binary 
addition stands as a hindrance to the full utilization of the parallelism 
offered by optics. As it will be shown, the half adder is obtained on its 
basic configuration with the two controls signals to zero. Half-adder and 
Full-adder configurations are shown in Fig. 2.a-b, where M stands for the two 
bias inputs, q and h. 
Other advantages of this proposal are, besides the implementation of a 
full-adder and fourteen pairs of possible logic operations, the use of 
optical fibers as signal transmission medium. In this way, pulses from 
different sources can be combined by using fiber couplers. If this fact is 
374 
added to the smaller f iber losses, the device can opera te now at re la t ively 
lower power levels t h a t with other configurations. Timings can be easily 
adjusted by choosing the r ight fiber length. The whole system is now more 
efficient and rugged, reducing volume and cost. 
In summary, we have proposed a new type of optical processing element 
able to per form different logical operat ions. The nonlinear components a r e 
interconnected by optical f ibers . Hence, smaller losses a t the system a r e 
present . A limited amount of parallelism can be obtained with optical f iber 
bundles. Moreover, this configuration could easily be in tegra ted in order to 
obtain a more compact s t ruc tu re . 
REFERENCES 
1. B.S.Wherrett , Appl. Opt. 24, 2876 (1985); R.G.A.Craig, G.S.Buller, 
F.A.P.Tooley, S.D.Smith, A.C.Walker, and B.S.Wherrett , Appl. Opt. 29, 2148 
(1990). 
2. R.Fin, C.Hanson, A.Chavez-Pirson, H.M.Gibbs, G.Khitrova, N. 
Peyghambarian, T.Bowen, F.-Y.Juang, P.K.Bhattacharya, D.A.Weinberger, 
K.R.Evans, C.E.Stutz, and R.L.Jones, Opt. Eng. 28, 348 (1989). 
3. M.A.Muriel and J.A.Martín-Pereda, in Proc. of European Conf. on 
Optics, Optical Syst. & Appl. ECOOSA 84, (Amsterdam, 1984), p. 291. 
I. fe~~^X I 1 0 1 . ' 
(a) 
OPE 
FIG. 1.- Schematic of the Optical Programmable Processing Element (OPE) 
Table I. Possible output logic functions 
£ 
& 0 
g2 
(J 
f-,3 
4 
h 
0, i 
XOR 
NAND 
XOR 
AND 
OR 
h 
0 
o
 2 
AND 
ho 
0 
XJ
 1 
XOR 
NOR 
XNOR 
OR 
OR 
h 
i 
°2 
OR 
ll 1 
v«/ 
NAND 
NOR 
AND 
OR 
ON 
h 
2 
2 
ON 
h 
2 
n-1 
O o 
A n ^ 
¡M 
9 Ls2, 
0 = S ° 2 = C 
i n 
FIG.2.- (a) Half-adder (b) Ful l -adder 
375 


Optical programmable processing element using optical fibers

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Optical programmable processing element using optical fibers

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