IMPROVEMENT OF OPTICAL FIBER COMMUNICATION SYSTEM USING A
PARALLEL INTERFACE CIRCUIT
By:
S. S. Elwakeel, H. A. Jawad, K. I. Hajim
Department of Physics, College of Science, Sudan University of Science and Technology, P.O.Box: 407, Khartoum.
KEYWORDS:
Laser, detector optical fiber and interface.
ABSTRACT
A certain parallel interface circuit for an optical fiber system was designed and
built. A suitable software was built and tested. The performance of each part of the
system was tested.
The final form of the circuit was tested individually. The complete system
including the parallel interface circuit was examined applying a case study. The
performance of the system was good within the acceptable experimental error.
‫لقد تم في هذا البحث بناء وتصميم دائرة موائمة متوازية لتستخدم في نظام نقل المعلومات بواسطة ا‬
:‫الملخص‬
‫ تم اختبار كل مكونات الدائرة وقد تمت دراسة أحد التطبيقات الفيزيائية باستخدام هذه الدائرة وقد‬.‫األلياف البصرية‬
:‫اشتملت الدراسة على‬
‫ثم تحويل‬.‫تسليط ضوء ليزري عبر الليف البصري ليستقبل من الطرف اآلخر بواسطة كاشف ضوئي‬
‫ تم‬.‫ ُمررت الفولتية التماثلية عبر دائرة الموائمة لتحول إلى فولتية رقمية‬.‫هذا الضوء الليزري إلى فولتية تماثلية‬
.‫استعراض هذه الفولتية الرقمية على شاشة الكمبيوتر باستخدام برنامج صمم لهذا الغرض‬
INTRODUCTION
During the past years, a new technology has become increasingly accepted in
the field of communication transmission via optical fiber cables. In contrast to copper
cable technology, the signals are transmitted optically with the aid of optical
waveguides also called optical fibers[1]. They have many advantages, such as: high
capacity, low cost per channel, light weight and small size[2].
Stored data can easily displayed from receiver when it is required.
A
special medium to capture the data and convert it to signals understood by computer is
needed. This medium is called interface card. The analog signal is to be converted to
digital signals and then to be displayed on the screen by certain software.
The benefits got from interface personal computer with the environments are:
high speed in processing, low cost of (PC), high degree of reliability in (PC),
availability of external storage medium and availability of input and output devices [3].
There are three methods for connecting computer with the out side word:
Serial interface, direct interface, and parallel interface.
A serial communication is the technique that allows one computer to be
connected to another device by sending data through a transition media and receiving
data on another and has a great importance because of its flexibility[4]. Various
devices such as plotter, modem, mouse and of course a printer can be connected to the
serial interface[5].
The common type of the direct interface is the plug in card, which fits into a
free expansion slot in the computer, and its main advantages are: low cost, high speed,
and easily connected.
Finally, the parallel interface is quicker[4] and cheaper. It works by sending
data through collection of eight wires at once, unlike the serial interface, parallel
interface can send an entire byte of data at once by using eight data wires.
For all these advantages of PC and optical fiber, recent work was concentrated
on the construction of parallel interface circuit for the use of optical fiber system.
MATERIALS AND METHODS
The Optical Fiber System: consists of a light source which is a cw laser diode:
manufactured by Phillips Company, with optical power of 5 mw, wave length of 0.67
μm[8], which is corresponding to the aperture of the used optical fiber with low loss,
and it also corresponding to the response of the used optical detector. It is pumped by
current flow through the device[8].
The Optical Fiber: Is a single mode polymethylmetacrylate (PMMA) Fiber, which has
suitable characteristics for diffusion of light, low cost and also has a little attenuation
at the wavelength of 0.67 μm.
The Optical Detector: Is a PN detector, which is suitable for the wavelength of the laser
used. A suitable electronic circuit is design and built to operate this detector.
A certain parallel interface circuit is designed and constructed related to the
requirement of the used optical system. The interface unit consists of: operational
amplifier, resistances, diodes, capacitors, analog to digital converter, tri-state buffer
and decoder[7] manufactured by Texas Company. The lay out of the interface circuit is
illustrated in (Fig. 1)[6]. The performance of each part of the circuit is tested via a
Cathode Ray Oscilloscope and multimeter including, the buffer, the operational
amplifier, the diode and the analog to digital converter input and output.
Fig. (1): The Used Optical Communication System
Light from light source passes through an optical fiber in analog form and then
received by the detector[6], which converts this analog light into analog voltage then
an analog voltage passes through interface circuit, which convert this voltage into a
digital voltage by certain software. The system setup is shown in (Fig. 2).
[7]
Pin (9)
Pin(8)
Pin (2)
Fig. (2): The Parallel Interface circ
RESULTS AND DISCUSSION
The test results have shown that the performance of all the electronic chips is
corresponding to chips specification.
Software is writing for interface circuit control and then it is tested. Written
results of the software are shown in (Table 1). The input is in binary code while the
output is in decimal code.
Table (1): The Software Test
0000
0001
0011
0111
1111
Lines
0000
0000
0000
0000
0000
Output Signals in Decimal
0
1
3
7
15
0000
0000
0000
0000
0000
The software output has the same binary input, which indicates that the
software is successfully worked.
The results of the interface circuit determine either the design is successfully
working or not. (Table 2).
Table (2): The Interface Circuit Test
Decimal input
0
1
2
3
4
5
6
7
8
9
10
Decimal output
0.06
1.01
1.9976
2.9976
.4
.5
5.9976
6.9976
7.9976
8.9976
9.9963
The results obtained from the interface circuit test showed that the
measurement of the designed circuit seems to be faithful in transferring the input
signal proportional with the operating voltage of the Analog to Digital Converter.
From the results of the interface circuit, we notice that the error is approximately
ranging from 0.001v to 0.004v.
After completing the interface circuit test, the optical fiber system is
reconnected as a case study for the system. The results are listed in (Table 3).
Table (3): The Physical Interface Results
The input signal (V)
0
0.1
0.3
0.5
0.9
1
The buffer o/p
(V)
0
0.1
0 .3
0.5
0.9
1
The op-amp
(V)
0
1
3
5.01
8.85
9.81
The D. c o/p
(V)
0
1.03
3.00
4.88
8.6
9.61
The digital o/p(V)
0
1.028
2.9976
4.878
8.5987
9.5987
Notice: The ADC zero is ½ LSB (1.22 mV), full Scale is 11/2 LSB.
CONCLUSION
The present study concludes that the constructed parallel interface circuit for
the used optical fiber system is performing successfully. The experimental error
ranges from 0.001v to 0.004v is acceptable for range operation.
REFERENCES
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Physica Department Indian Institute of Technology, New Delhi, India.
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Technicians, First edition, Mc Graw. Hill, San Diego community collage
California, California PP: [90].
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[551].
6- Leot Courses (2001). Introduction To Laser, U.S, PP: [6].
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Litho, England, Britain, PP: [60].
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