Four Input, Voice and Data Communication through

IETE Journal of Education

ISSN: (Print) 0974-7338 (Online) Journal homepage: http://www.tandfonline.com/loi/tije20

Four Input, Voice and Data Communication through Single Optical Fiber Channel M Murugan & N K Srivastava To cite this article: M Murugan & N K Srivastava (2002) Four Input, Voice and Data Communication through Single Optical Fiber Channel, IETE Journal of Education, 43:2, 71-78, DOI: 10.1080/09747338.2002.11415765 To link to this article: http://dx.doi.org/10.1080/09747338.2002.11415765

Published online: 26 Mar 2015.

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Date: 27 November 2015, At: 20:27

JETE Journal of Education Vol 43, No 2, April-June 2002, pp. 71-78

Four Input, Voice and Data Communication through Single Optical Fiber Channel M MURUGAN AND N K SRIVASTAVA

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Electronics & Telecommunication Engineering Department. Pravara Rural Engineering College Loni, Ahmednagar 413 736. India.

In modern trends it has become necessary to transmit voice as well as data signals using a single channel. The communication system we have devised here transmits three voice signals and one data signal on a single fiber optic channel. The optic fiber we have used is a single mode step index plastic fiber of 1m length and 1 mm diameter using time division multiplexing (TOM) technique where each signal is transmitted only for brief period of time. This system finds extremely large number of applications in education, industries, railways, medicine, tourism, etc. This system has been designed for four channels, of which three are audio channels and one is data channel. It is a simplex system i.e., communication is always in one direction. The transmitter does not function as receiver and vice versa.

NE of the principal interests of human beings has been to device communication systems for sending messages from one distant place to another. Many forms of communication systems have appeared over the years. In conventional systems the signal is both attenuated and distorted with increasing distance. A phenomenal increase in voice and data communication has caused a corresponding increase in the demand for more economical and larger capacity communication system. The use of glass or plastic fibers as means of communication [1, 2] has caused a technical revolution in the communication industry. The latest trend is to transmit voice as well as data signals using a single channel [3].

Analog Multiplexer Switch (c) Gating Signal Generator (d) FSK Modulator (e) Optical Transmitter

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(b)

(a) Pre-amplifier The audio signal, used as base band, is first preamplified using two-stage transistor amplifier (Fig 1b). First stage is a common emitter (CE) amplifier (BC547B). The 0/P of the first stage is taken from the collector of the transistor and supplied to the base of the 2nd PNP (BC557B) transistor which is in common collector (CC) configuration. The final output is fedback to the first stage in order to stabilize the gain. The voltage gain of this two- stage amplifier is set to be around 50.

The basic blocks of the communication system consist of a transmitter and a receiver connected by an optical fiber. The transmitter uses four inputs in which three are audio signals and one data signal from the serial port (RS 232) of the PC.

(b) Analog Multiplexer Switch

Transmitter Section

A quad bilateral switch - IC CD4066A (Fig 2a) is used for time division multiplexing (TDM) f4-6]. Each of the analog switches in lC CD4066A is controlled by the four outputs (00 -0 3 ) of the sampling signal generator (Johnson's Counter CD40 17 A (Fig l b, 2a, 2b)) of 8kHz each. The output of all four analog switches are supplied to the OR-ing circuit formed by four diodes (1N4148) whose cathodes are shorted to obtain a single multiplexed output (Fig lb). This output is supplied to the optical transmitter circuit and then to the optical source for transmission.

This section consists of

(c) Gating Signal Generator

WORKING PRINCIPLE Figure la shows the block diagram of the voice and data communication using optical fiber system. A single mode step index fiber of 1-meter length with the core diameter of 1 mm has been used. The method of communication is 'simplex'. The four-channel optical communication system consists of the following blocks.

(a)

Pre-amplifier

The gating or sampling signals required to control the analog multiplexer switches are generated using an

Paper No 47-A; Copyright© 2002 by the IETE.

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Finally the output of this second OP-AMP is given to IC MC1488 through a diode 1N4148 (Fig 4b). The diode cuts off negative peaks in the input and supplies positive pulses to IC MC 1488, which is a quad line driver, designed to interface data terminal equipment with data communication equipment. The output of MC1488 is given to the serial communication port (RS232) of PC through a 25-pin DIP connector.

(e) Audio Power Amplifier The three audio outputs taken from the demultiplexer switch IC CD4066A (Fig 3a) are applied to volume control pots. (I OK each). Each output signal is givc::,n to a low power audio amplifier consisting of IC MC34119 (Fig 4c). This is low power audio amplifier capable of driving speaker loads of 8Q and more. The output power can be greater than 25 mW with gain adjustable between OdB to 46dB with very few external components. Transmission Line

attenuation single mode step index fiber has been designed and tested. It is a simplex system i.e., communication is always in one direction. IR-LED has been used as a light source and a phototransistor as a receptor. The system transmits three voice signals and one data signal on a single fiber optic channel. Alternative designs that can be considered are: (a) the system can be made into a full duplex type by building transmitter-receiver pairs on both sides of the channel. (b) If an optical detector of larger band-width (B.W.) is used, the number of signals to be transmitted can be increased. The sampling rate for TOM can also be increased which will reduce the quantization error. Quantization error can be further minimized by using frequency division multiplexing technique.

REFERENCES I.

L B Jeunhomme, Single-Mode NY Marcel Dekker 1983.

2.

CD4066A COS/MOS Quad Bilateral Switch, Digital Integrated Circuits, RCA Solid State Division, File Number 769, USA, 1976 Texas Instruments Data Sheets, Bulletin Number DLS 12632, Oct 1978. H Taub & DL Schilling, Principles of Communications Systems Second Edition, Me Graw Hill Book Company. NY 1971. A B Carlson, Communication Systems, Me Graw Hill Book Company, NY 1968. B Y Kim & H J Shaw, Multiplexing of Fiber-Optics Sensors, optics News Nov 1989. A Dewey, Analysis and Design (~f Digital Systems with VHDL, PWS Publishing Company, Boston 1997. J F Wakerly, Digital Design (3rd Edition), Prentice Hall, Upper Saddle River (NJ) 1999. J D Archer, Manual Of Fiber Optics Communication. STC Components Ltd London 1986. Texas Instruments Data Sheets, Bulletin Number DLS 11688, March 1972- Revised March 1976. B Culshaw & J Dakin, 1988, Optical Fiber Sensors, vol I; ibid 1989, vol II. HP data sheet: 5091-2921 E (I 0/91 ), 1991.

3. 4.

The transmission line used here is a low attenuation, single mode step index plastic optical fiber with 1mm diameter core [12]. It is sheathed in a black polyethylene jacket with standard simplex connectors and has a wide temperature range. The optical fiber receives optical signals from the IR LED on one end and transmits it to optical detector on the other end (Fig 1a). The optical fiber used is HFBR-RNS001 which belongs to HFBR-RIEXXYYY series of Hewlett Packard fiber optic cables [12]. Though this fiber has more losses compared to glass fiber, it is used because it is economical.

5. 6. 7. 8. 9. 10. II.

CONCLUSION

77

12.

Fiber Optics,

A fiber optic communication system using low

AUTHORS M Murugan graduated in Electronics and Communication Engineering from University of Madras in 1989 and received his Masters in Electronics & Telecommuincation (Spl: Micrwave) Engineering from University of Pune in 2001. Presently, he is working as Asst. Prof & incharge HOD of Electronics/E & TC Engineering Department of Pravara Rural Engineering College, LONI (MS). Having over 12 years of experience in teaching, his recent interests are in the areas of Microwave and Optical Communication.

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