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Influence of Specimen Length and Launch Conditions on

Multimode Fibre Attenuation Measurement by Cut-back

Method

Liyan Zhang, Changfeng Yan, Xinben Zhang, Xufeng Yin, Rui Zhang, Runhan Wang, Jing Li
1.State Key Laboratory of Optical Fiber and Cable Manufacture Technology.
2.Yangtze Optical Fibre and Cable Joint Stock Limited Company. No.9 Optics Valley Avenue, Wuhan, Hubei, China 430073

1 Introduction Abstract: Influence of specimen length and launch conditions on multimode fibre attenuation
For the attenuation test of multimode measurement using cut-back method is studied. The oscillation phenomenon of attenuation
optical fibre and cable, there are several spectrum is found in short length fibre and the reason is analyzed.
standards which have established the test OCIS codes: (060.2300) Fiber measurements; (060.0060) Fiber optics and optical
requirements .[1-3] For all these standards, cut- communications
back method (or insertion loss method, which
in principle, is similar to the cut-back method) Figure 1. Schematic of the experimental setup for multimode fibre attenuation test
is the reference test method (RTM). However,
the launch condition requirements are different Figure 2 shows the measured attenuation as a including higher order modes, while EF and 70/70
among these standards, where IEC 60793-1-40 function of specimen length at different launch launch, which are underfilled launch, will excite less
specifies a 70/70 launch[1] while other standards conditions. It can be seen that, for both GI50 and higher order modes. For GI50 fibre shown in Fig.2 (a),
require Encircled Flux(EF) launch[2, 3].The BIMM fibre, as the specimen length decreases, the attenuation under EF launch condition is larger than
specimen length of multimode fibre and installed attenuation at 850nm increases, especially when 70/70 launch condition, while for BIMM fibre shown
cable are varied from 100m to several kilometers. the specimen length is less than 1km. The existence in Fig.2 (b), attenuation under EF launch condition
The varied specimen length and launch mode of more higher order modes in short fibres results is smaller than 70/70 launch condition. This may
would influence the attenuation result, which in higher attenuation. As the specimen length be caused by the different profile design of the two
the influence however hasn’t systematically gets longer, higher order modes are progressively fibres.
been reported before. In this paper, we studied decayed.
the attenuation measurement under three Figure 3 shows the attenuation spectrum of different
launch conditions, 70/70 launch, EF launch and For the same specimen length, different launch specimen length at different launch conditions for
overfilled launch (OFL), combined with different conditions result in different attenuation data. The GI50 fibre and BIMM fibre. Oscillation is found
specimen length(from 100m to 4.4km). Both attenuation value under OFL condition is larger in the attenuation spectrum and the amplitude
traditional graded index 50μm multimode (GI50) than the value under the other two conditions. The decreased as the specimen length increased. Under
fibre and bend-insensitive multimode (BIMM) reason is that OFL condition will excite all the modes each launch condition, we can see the wave peaks and
fibre are involved.
Figure 2. 850nm attenuation of three launch conditions as a function specimen length (a) GI50 fibre (b)
2.Experimental Setup and Procedure BIMM fibre
For 70/70 launch condition, limited phase space
launch is used to uniformly fill 70% of the test
fibre numerical aperture (NA) and 70% of the
test fibre core diameter. For overfilled launch, the
70%NA control and 70% launch spot control
are removed from the test setup. For EF launch,
a mode controller has been used before the fibre
sample to give a standard EF mode distribution [3].
The cut-back length is 2 meters as defined in the
standard [1].

The specimen length of each conditions are 100m,
150m, 300m, 550m, 1.1km, 2.2km and 4.4km
respectively. All of these fibres are coming from the
same fibre preform. The attenuation test under
each condition has been repeated for at least five
times and the average value is reported in this paper.
“Attenuation” in this paper represents the meaning
of attenuation coefficient (dB/km).

3.Experimental Results

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