Comparison of macrobend losses in Single Mode Fibre (SMF) and Multimode Fibre (MMF)
Abstract
A comparison of macrobend losses in Single Mode Fibre (SMF) and Multimode Fibre (MMF) is
presented. The increased demand on information has seen optical fibres slowly replacing the use
of copper coaxial cables for signal transmission, and this, largely due to the high bandwidth and
speed of transmission, large carrying capacity and security offered by optical fibres. Signal
attenuation however remains a limitation to efficient and quality signal transmission and
macrobending is one of the loss mechanisms that contributes to this signal attenuation.
Appreciating the responses of the different optic fibres in use to macrobending is therefore
instrumental in ensuring macrobending contribution to overall attenuation in optic fibres is
minimum at all times. In this study the macrobend losses trends with bending diameter were
investigated for the SMF and MMF in similar experimental setups. To do this improvisions were
done for a light source using 555 timer astable multivibrator powering a green LED, a light detector using
an LDR in a Wheatstone bridge circuit and optic fibres off-cuts. Optic power was measured at the input
and output points of the optic fibres using the light detector in bend and straight conditions for
determination of signal attenuation in each case. The experimental measurement results show that
macrobending losses are more pronounced in a SMF than in a MMF. Characteristic values for
macrobending loss are 1268 dB/km for SMF compared to 1155 dB/km for MMF for bending
diameter value 4.19 cm. In the SMF macrobending loss trend showed an exponential variation
which agrees with work by previous authors. The contribution of macrobending loss in
multimode fibre attenuation was however minimal and therefore difficult to quantify. Results
also showed that MMF have a higher overall signal attenuation than SMF which justifies the use
of SMF in long distance signal transmission. Research findings confirm the significant
contribution of macrobending to optic fibre signal attenuation hence the need for careful
iv
consideration in installations for optimal operation of optic fibres. This would mean the choice of
optic fibre in any particular instance should consider the high attenuation in MMF not neglecting
the insignificant macrobending contribution of MMF to attenuation at any preferred wavelength
in order to obtain required transmission characteristics.
Sponsor
University of Zimbabwe,DAAD and the Research Council of ZimbabweSubject
Macrobending lossOptic Fibre
Bending diameter
Attenuation
Single mode fibre
Multimode fibre