Method and device for testing the properties of at least one splice in at least one optical waveguide

An optical waveguide splice (SP) is subjected for a prescribable test period to a tensile stress (F), while the light (SL) is launched upstream of the splice (SP) and light (EL) is coupled out downstream of the splice (SP) and the optical power (a) thereof is determined continuously as a function of the tensile stress (F).

BACKGROUND OF THE INVENTION 
The invention relates to a method and device for testing the properties of 
at least one splice in at least one optical waveguide. 
After a spliced joint of an optical waveguide has been finished, there is a 
practical interest in the extent to which the finished splice meets the 
requirements placed on it. However, to date the possibility of checking, 
for example, the mechanical properties of the finished splice has been 
only unsatisfactory. 
SUMMARY OF THE INVENTION 
It is the object of the invention to specify a way in which the properties 
of at least one finished optical waveguide splice can be checked reliably 
in a simple way in each case. In accordance with the invention, this 
object is achieved in a method of the type mentioned at the beginning when 
during a prescribable test period the splice is subjected to a tensile 
stress, during loading of the splice with the tensile stress, light is 
launched into the optical waveguide upstream of the splice and light is 
coupled out of the optical waveguide downstream of the splice, and the 
power of the coupled-out light is determined continuously as a function of 
the tensile stress. 
Owing to the fact that the respectively finished splice is subjected to a 
tensile stress and an optical power which is transmitted, that is to say 
transferred, via the splice is determined continously in the process as a 
function of this mechanical tensile loading, it is possible to acquire 
multifarious, detailed information on the properties, in particular 
mechanical characteristics, of the splice. Thus, for example, it becomes 
possible to make reliable statements on the quality of the core alignment 
and/or cladding alignment of the respective optical waveguide in the 
region of its splice, on the tensile strength, breaking strength and 
expansion behavior of said splice, etc. Since the coupled-out optical 
power is determined continuously as a function of the mechanical loading 
on the splice, it is possible not only to test the splice for the two 
states of "optical waveguide severed" or "optical waveguide not severed", 
but also to conduct an assessment which is much more finely graded. 
The invention also relates to a device for testing the mechanical 
properties of at least one splice in at least one optical waveguide, which 
is characterized in that at least one tension device is provided which 
subjects the splice to a tensile stress during a prescribable test period, 
in that a coupling device is provided upstream of the splice for launching 
light into the optical waveguide and a coupling device is provided 
downstream of the splice for coupling light out, and in that an 
evaluation/control device is provided which determines the power of the 
coupled-out light continuously as a function of the tensile stress. 
Other developments of the invention are specified in the dependent claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention and its developments are explained in more detail below with 
the aid of a drawing which shows an exemplary embodiment of a test or 
measuring device PE according to the invention. Represented by way of 
example in the sole FIGURE is an optical waveguide F1 having a finished 
splice SP which is produced, for example, by welding, by bonding or by 
means of other connections (for example a connecting sleeve) of the 
separate sections, preferably aligned with one another end face to and 
face of the optical waveguide F1 in the region of its disconnect point. In 
order to be able in the present exemplary embodiment to launch or couple a 
measuring light SL into the optical waveguide F1 from left to right as 
seen along a longitudinal axis, of the waveguide it is preferable to 
provide a first optical bending coupler BK1 at the transmitting end as a 
coupling device. For coupling purposes, the optical waveguide F1 is guided 
in a curved fashion around a bending mandrel or bending cylinder ZT1, 
which has a shape of a circular cylinder, of the bending coupler BK1. In 
this launching position the waveguide is retained or locked by a fixed 
holding device HV1. The holding device HV1 is indicated in the FIGURE only 
diagrammatically by a rectangular frame. The holding device HV1 is 
preferably formed by the basic holder of the bending coupler BK1. The top 
side of this basic holder, on which the bending mandrel ZT1 presses, 
expediently has a depression or trough resembling a segment of a circular 
arc for the purpose of accommodating the optical waveguide F1 in a defined 
fashion. The geometrical shape of this depression is matched to the 
bending mandrel ZT1, which has the shape of a circular cylinder. In 
detail, for the purpose of coupling the optical waveguide F1, the 
procedure is that in the open state of the bending coupler BK1 this 
optical waveguide is preferably inserted into a groove on the top side of 
the holding device HV1 and the bending mandrel ZT1 is moved downward in 
the direction of the hollow of the holding device HV1, with the result 
that the optical waveguide F1 is guided in a defined curved fashion and 
retained or fixed in a defined fashion. The optical waveguide F1 is 
therefore secured in a position by the bending coupler BK1 in the 
longitudinal direction (axial direction) and in the lateral direction, 
that is to say transverse to the axis. Further details on the coupling of 
an optical waveguide according to the principle of the bending coupler are 
provided, for example, in German Patent 34 29 947 C2 and the corresponding 
U.S. Pat. No. 5,040,866, where a device for launching light into an 
optical waveguide is described. 
The measuring light SL is launched, preferably as tangentially as possible, 
into the core of the optical waveguide F1 by means of an optical 
transmitter OS, in particular a transmitting diode, in the curved region 
of the bending coupler BK1 and the light is transmitted beyond the 
finished splice SP to a second coupling device, in particular a second 
bending coupler BK2. The bending coupler BK2 is constructed in accordance 
with the bending coupler BK1. The optical waveguide F1 is guided in the 
coupler BK2 in a curved fashion or in the shape of an arc about a bending 
mandrel ZT2 which is approximately in the shape of a circular cylinder, 
and the waveguide is fixed in this coupling-out position by means of a 
diagrammatically indicated holding device HV2. The holding device HV2 is 
constructed in this case in a fashion analogous to the holding device HV1 
at the transmitting end. In particular, the device HV2 forms the basic 
holder, corresponding to the mandrel ZT2, of the coupling device. In this 
arrangement, the optical waveguide F1 is clamped in a defined way in the 
working position of the bending coupler BK2 between the bending mandrel 
ZT2 and the holding device HV2, with the result that it cannot be 
displaced or loosened in an uncontrolled fashion or automatically, 
particularly in the longitudinal direction. The same also holds if 
appropriate for the positioning of the waveguide transverse to the axis. 
An optical receiver OE, in particular a large-area photodiode, is 
positioned in the curved region of the bending coupler BK2 at the 
receiving end. This photodiode detects light components EL coupled out of 
the measuring light SL and feeds the former via a line L1 to an 
evaluation/control device AE which preferably operates in a digital and/or 
analog fashion. The evaluation/control device AE expediently has an 
arithmetic unit (not represented in the FIGURE) and a measured-value 
memory. In particular, the optical receiver can also be formed by a 
plurality of light-sensitive elements, in particular photodiodes, for 
example in the form of a measuring row or measuring field ("measuring 
array"). 
In order preferably to be able to test the mechanical properties of the 
finished splice SP, a tensile stress F is applied to the latter in the 
longitudinal direction. For this purpose, the test device PE has a tension 
device which pulls on the optical waveguide F1 along the longitudinal axis 
thereof with a force component which is directed away from the splice SP 
in the axial direction. The tension device, which acts axially on the 
optical waveguide F1, is formed in the FIGURE by, for example, an actuator 
SN, which can be moved in the longitudinal direction (axial direction) of 
the optical waveguide F1, and the fixed bending coupler BK1 at the 
transmitting end. In this arrangement, the actuator SN preferably receives 
its control signals via a line L5 from the evaluation/control device AE. 
The bending coupler BK2 at the receiving end is firmly attached to the 
actuator SN and can thus be displaced together with the latter in the 
axial direction, preferably rectilinearly. It is thus possible to use the 
actuator SN to move the bending coupler BK2 in the axial direction, and 
tis is indicated by a double arrow x. It is expedient for the actuator SN 
to have a stepping motor with an associated, axially displaceable slide. 
The bending coupler BK2 is preferably attached to this slide of the 
actuator SN. Since the optical waveguide F1 is firmly clamped in the fixed 
bending coupler BK2 at the receiving end, its splice SP is thus subjected 
to a tensile stress when the bending coupler BK2 is moved to the right, 
that is to say away from the fixed bending coupler BK1 at the transmitting 
end. Thus, it is expedient for the optical waveguide F1 to be retained in 
a stationary fashion at one end of the splice SP, while at the other, 
opposite end it is moved away from the splice SP by means of a tension 
device and thereby is rectilinearly stressed along its longitudinal axis 
between the two coupling devices, for example BK1, BK2. If appropriate, 
other relative movements are also possible between the two coupling or 
holding devices as long as it is possible to exert a tensile force on the 
splice in a defined way. Thus, in addition to or independently of the 
exemplary embodiment of the FIGURE it is also possible, for example, to 
assign to the bending coupler BK1 at the transmitting end an axially 
movable actuator in a fashion analogous to the actuator SN, at the 
receiving end, of the bending coupler BK2. 
The evaluation/control device AE now drives the actuator SN such that the 
bending coupler BK2 is moved away to the right from the splice SP. Since 
the optical waveguide F1 is fixed in a stationary fashion at the 
transmitting end, that is to say to the left of the splice SP, by the 
bending coupler BK1, in this process the waveguide F1 is subjected by the 
axial pulling movement exerted to the tensile stress F, that is to say is 
tensioned. The bending coupler BK2 is expediently moved away from the 
splice SP axially by the actuator SN as far as into a prescribable end 
position in such a way that the tensile stress F which comes to act on the 
splice SP continuously changes during a prescribable test period. The 
tensile stress preferably increases continuously during the actual test 
period up to a prescribable maximum value. In particular, in this case the 
tensile stress F can be increased, that is to say grow, linearly up to the 
prescribed maximum value. If appropriate, an exponential rise in the 
tensile stress F may also be expedient during the actual test period. As 
an alternative to this, the tensile stress F on the splice SP can 
preferably also be kept essentially constant during approximately the 
entire test period. Moreover, it may also be expedient to load the splice 
SP in addition to the actual test period, that is to say beyond the 
latter, for a prescribable residual period, doing so essentially by means 
of a constant tensile stress F, in particular the prescribable maximum 
tensile stress, before the optical waveguide F1 is untensioned or unloaded 
again. The splice SP is expediently subjected to at most a tensile stress 
of 30N, in particular of between 1 and 15N, preferably of between 1 and 
4.4N, as well as preferably of between 1.5 and 2N. The total test time 
(=actual test period+residual period) for the tensile stress loading is 
expediently selected at between 1 and 20 sec, in particular between 1 and 
10 sec, that is to say during this period the splice is under tensile 
loading. The possible residual period is preferably selected at between 1 
and 5 sec. 
At the same time, during the loading of the splice by means of the tensile 
stress F, the bending coupler BK1 is used to launch the measuring light SL 
continuously into the optical waveguide F1 upstream of the splice SP, and 
downstream of the splice SP, the components EL of the light, which has 
been transmitted or passed via the splice SP, are coupled out with the aid 
of the bending coupler BK2. In this process, the coupled-out power of the 
coupled-out light EL is determined by means of the evaluation/control 
device AE as a function of the respective tensile stress F. The power of 
the coupled-out light EL is preferably measured continuously or constantly 
in conjunction with a continuous change in the tensile stress F. Thus, 
depending on the respective tensile stress F acting on the splice SP, 
during the prescribable test period and/or the residual period, the 
optical power transmitted, that is to say transferred, via the splice SP 
is determined and made available for further evaluation in the 
evaluation/control device AE. 
The coupled-out optical power can be detected as a function of the 
respective tensile stress F, for example by an indicating measuring 
instrument MG, in particular a pointer instrument, which indicates the 
signal level coming from the evaluation/control device AE via a line L3. 
It is then possible, for example, to use the drop in the signal level 
below a prescribable minimum value for an acceptable splice, executed in a 
largely centered fashion, as a test criterion. 
Instead of the indicating measuring instrument MG, or as a complement 
thereto, it is also possible to provide a displaying device ANZ, in 
particular a display, which via a line L2 continuously receives 
characteristics of the coupled-out optical power from the 
evaluation/control device AE as a function of the tensile stress F 
respectively acting on the splice SP. By way of example, in the FIGURE the 
displaying device ANZ continuously shows as a characteristic of the 
mechanical properties of the splice SP the attenuation a thereof (in dB) 
as a function of the continuously varying tensile stress F. For the sake 
of simplicity, the attenuation a is determined for a calibrated state of 
the measuring device PE, in which the absolute value of the optical power 
respectively launched into the optical waveguide is known and is therefore 
available as reference a quantity for the coupled-out optical power. 
The determination of the attenuation can be performed, for example, as 
described in the document DE 34 29 947 C2. Since the efficiency of the 
launching or coupling out of the light is not constant in practice in the 
case of bending couplers, by contrast the measurement of the attenuation 
is expediently carried out taking account of the air gap attenuation 
a.sub.b, present before the splicing operation, in accordance with the 
following formula: 
##EQU1## 
in which 
a.sub.s is the splice attenuation of the finished spliced joint, 
a.sub.b is the air gap attenuation, 
P.sub.b is the measured optical power after optimum alignment of the end 
faces of the optical waveguides with one another, but still before 
production of the spliced joint SP, and 
P.sub.a is the measured optical power after production of the spliced 
joint. 
Given cleaved surfaces of the end faces of the optical waveguides which are 
acceptably cut, that is to say are as smooth as possible, for example 
90.degree. cleaved surfaces, the normal result is an air gap attenuation 
of approximately 0.3 dB, in particular for monomode fibers. 
An acceptably constructed spliced joint is characterized, for example, by 
the preferably continuous attenuation curve NK in the displaying device 
ANZ. In simultaneous conjunction with an increase in the tensile stress F, 
for example, this curve rises slightly, that is to say with a low 
gradient, preferably first approximately exponentially, and then goes over 
into a virtually linear variation, approximately from the force value 
F=P1. As an example, the following is preferably suitable as test 
criterion: as long as the attenuation curve NK does not exceed a 
prescribable upper band or threshold SW as a still permissible, tolerable 
splice attenuation a until reaching a specific maximum value FM for the 
tensile stress F, the splice SP and/or the environment thereof is regarded 
as being "in order", that is to say pull-off resistant, and its 
attenuation is regarded as negligible. In this case, the actual test 
period is preferably determined by the length of time from the relatively 
low-tension initial state of the optical waveguide F1, in which F=0N 
(Newton) in approximate terms, up to the reaching of the maximum tensile 
stress loading, in which F=FM N (Newton). Not until the upper attenuation 
threshold a=SW is exceeded in the prescribed tensile stress range of F=0N 
to F=FM N is the splice SP regarded as being no longer acceptable, that is 
to say as "defective". During a tensile stress F of up to a maximum value 
FM of, for example, approximately 2 to 10N, the upper threshold SW for a 
still permissible splice attenuation a is expediently fixed at between 
0.02 and 0.5 dB. If the measured splice attenuation a exceeds the upper 
threshold SW inside the force range traversed from F=0N (Newton) to F=FM 
N, the splice SW is regarded as being not acceptably constructed. If, as 
the case may be, the tensile test even leads to severing of the optical 
waveguide F1 at the splice SP, the attenuation a increases abruptly 
(discontinuously) for this tensile stress, and this is indicated in the 
displaying device ANZ by the vertically extending curve SK marked with 
dots and dashes, for example for the tensile force P1. Since it is then 
virtually impossible for any more light to be transferred at the severed 
splice SP, the attenuation SK rises very sharply in practice, 
theoretically virtually as far as infinity. It is possible in this way for 
the tensile strength of the splice SP to be tested and, if appropriate, 
determined advantageously from the preferably continuous variation in the 
coupled-out optical power during loading which is accompanied by 
preferably continuous variation in the tensile stress F. 
Within the scope of the invention, "continuous determination" of the 
coupled-out optical power is preferably understood to mean that more than 
one measured value is acquired for the coupled-out optical power during 
the test period, that is to say the targeted or defined loading of the 
splice SP by means of the tensile stress F. In this case, the tensile 
stress F can, as explained above, vary continuously, that is to say 
constantly, or else can essentially remain constant. With particular 
preference, the recording and observing of the coupled-out optical power 
can be performed continuously over the entire test period (as in the case 
of the displaying device ANZ). If appropriate, it can also already be 
sufficient to record the coupled-out optical power by temporal sampling, 
that is to say subdivision of the test period. A plurality of discrete 
measured values a are then available for specific force values in the 
prescribed sampling interval within the tensile stress test interval from 
F=0N to F=FM N for the purpose of evaluation. 
Finally, it can also, if appropriate, be particularly expedient to follow 
up on a continuously changing tensile stress force which has possibly been 
acting on the splice SP by additionally loading this splice by means of a 
constant tensile stress such as, for example, by means of F=FM N 
(=extended tensile stress loading test). The coupled-out optical power at 
the receiving end is detected as continuously as possible throughout the 
duration of this constant loading as well, that is to say the optical 
power is determined more than once, in particular continuously, during 
this residual period as well. 
Owing to the fact that a measured value is provided more than once for the 
coupled-out optical power during the tensile stress loading, it becomes 
possible for the properties of the splice SP to be assessed with a much 
finer resolution, that is to say much more finely graded. This 
advantageously enables the assessment of the "internal" transmission 
characteristics and mechanical qualities of splices which, although they 
do not as yet become severed under the action of the predetermined tensile 
stress values exerted, are nevertheless defective. 
Instead of the splice attenuation a, it is therefore possible for further 
multifarious and detailed information, preferably relating to the 
mechanical and, if appropriate, optical properties, pertinent to the 
splice SP, to be obtained from the recorded optical power as a function of 
the respective tensile loading F which is present. Thus, the 
evaluation/control device AE can advantageously reliably determine from 
the coupled-out optical power in the bending coupler BK2 multifarious 
characteristics such as, for example, the quality of the core glass 
alignment and/or cladding glass alignment in the region of the splice SP, 
and the tensile strength, breaking strength and expansion behavior of the 
latter, etc. Thus, for example, checking of the alignment of the coupling 
point (splice), which can even be satisfactorily pull-off resistant as the 
case may be, is also advantageously rendered possible. The outer cladding 
glass alignment and/or the core glass alignment can preferably be checked. 
For example, if, as the case may be, there is a defective alignment in the 
fiber cladding structure, a transverse force can possibly additionally 
become active on the splice SP during drawing in the axial direction. This 
transverse force leads in the micro range to a displacement of the core 
regions, which depending on the core alignment can lead to an increase in 
the attenuation (in the case of well aligned cores) but also to a decrease 
in the attenuation (in the case of poorly aligned cores). Checking of the 
core-to-core alignment is thereby advantageously rendered possible. 
On the other hand, it is not only statements concerning the core alignment 
which are rendered possible, but additionally, or independently thereof, 
possibly also statements concerning the quality of the alignment of the 
outer buffer tube or the cladding glass of the optical waveguide. For 
example, in the case of an optical waveguide having a concentricity error 
there would be an outer offset nevertheless in the case of exact core 
alignment. Given tensile loading of this splice there would also be a 
change in the transmitted light, the advantageous result being the 
formation of a type of "sensor" for the alignment quality of the opposing, 
separated sections of the optical waveguide F1 at the splice SP. 
Furthermore, it can be expedient, as the case may be, to send light which 
is polarized (preferably linearly or circularly polarized) via the splice 
to be tested while the latter is loaded with the tensile stress F. It is 
possible thereby to make detailed statements on the direction of the 
forces acting in the immediate vicinity of the coupling point after 
analyzing the polarization of the light when the light is coupled out at 
the receiving end, that is to say downstream of the splice SP. 
Specifically, joints or coupling points having a possible offset (core 
and/or cladding glass offset), in particular, are mostly somewhat 
sensitive with respect to temperature changes or curvature loading 
(bending crush resistance). This resistance is generally undesired 
(exception: sensor technology). Since such coupling points (splices) are 
particularly sensitive to transmitted light in the case of tensile stress, 
and thus cause a change in attenuation, they are therefore advantageously 
easy to identify and reject. 
Since the coupled-out optical power is preferably analyzed continually, in 
particular continuously, as a function of the mechanical loading in the 
axial direction, that is to say a combined tensile test/optical power test 
is continuously carried out, not only a "binary" test with two states of 
"optical waveguide severed" or "optical waveguide not severed" is rendered 
possible, but also, advantageously, so is a much more finely graded 
assessment of the splice SP. Thus, on the basis of the measurement curve 
NK recorded by way of example in the displaying device ANZ, a multiplicity 
of measured attenuation values are available, for example, during the 
states of "stress-free" (tensile stress F=0N) up to maximum tensile stress 
F=FM N for the purpose of assessing the splice quality. Consequently, it 
is also advantageously possible to identify as defective splices which, 
although they do not sever under the action of the tensile stress force, 
do already represent an impermissibly high attenuation point with respect 
to message transmission. 
It may also be expedient, as the case may be, to subject the splice SP to a 
completely different force diagrams during a prescribable test time. Thus, 
for example, the tensile stress F can be constant during a specific 
(period) test time, or else can be increased linearly, exponentially or in 
some other way up to a prescribable maximum value, for example FM. 
Thereafter, the respective splice such as, for example, SP can further, if 
appropriate, be exposed for a specific residual period to a maximum, 
constant tensile force for the purpose of a continuous loading test. 
In addition to or independently thereof, the splice SP can, if appropriate, 
also be subjected to a tensile stress F in such a way that the optical 
waveguide F1 is subjected to a bending stress between the bending coupler 
BK1 and the bending coupler BK2. In this case, the optical waveguide F1 is 
firstly retained in a fixed fashion on both sides of the splice SP by the 
bending coupler BK1 and by the bending coupler BK2 in such a way that the 
optical waveguide section between the two coupling devices is preferably 
essentially free from stress. By means of a bending device BV, which can 
be displaced transverse to the axis, that is to say transverse to the 
longitudinal axis of the optical waveguide F1, something which is 
indicated by a double arrow y, the optical waveguide F1 is then bent and, 
in the process, exposed to a tensile loading in the longitudinal direction 
and to a bending loading transverse thereto. Suitable as a bending device 
BV is, for example, a mandrel in the shape of a circular cylinder or a 
bending cylinder, of which a segment in the shape of a semicircular 
cylinder is indicated by dots and dashes in the figure. The bending device 
BV can preferably be driven via a line L4 by the evaluation/control device 
AE in a defined way and be displaced transverse to the axis in the 
y-direction (preferably at right angles to the x-direction). 
The test device PE according to the invention and/or the associated test 
method according to the invention can advantageously also be used to test 
the mechanical properties of a multiple splice such as can be present, for 
example, in the case of an optical-fiber ribbon having at least one or 
more individual fibers or individual optical waveguides. In the left-hand 
part of the figure, the approximately rectangular outer sleeve of an 
optical-fiber ribbon BL1 is indicated by dots and dashes and then omitted 
in the remaining part of the figure for the sake of clarity. The 
optical-fiber ribbon BL1 has, for example, three optical waveguides F1 to 
F3 with the associated splices SP, SP2 and SP3. Checking of the mechanical 
properties of the splices SP2 and SP3 is then performed separately in a 
fashion analogous to the procedure in the case of the splice SP for each 
individual optical waveguide F2 and F3, that is to say selectively in 
terms of a fiber. If appropriate, each individual optical waveguide can 
also have more than one splice to be tested. In particular, the method 
according to the invention also then permits the testing of more than one 
splice simultaneously. 
The test device PE according to the invention is preferably a component of 
a single or multiple optical waveguide splicer, an attenuation test set or 
other optical waveguide test apparatus. 
The determination of the splice attenuation can also be performed in this 
case, if appropriate, as described in U.S. Pat. No. 5,078,489, whose 
disclosure is incorporated herein by reference thereto and which claims 
priority from DE 38 28 604 A1, for example. Thus, the so-called "LID" 
system ("Light Injection and Detection") described there can likewise be 
used to check the splice. What is understood there is a measurement system 
in which in a first measurement operation, the measurement signal 
(measuring light) of a first transmitter is measured at the output of an 
optical medium (such as, for example, an optical waveguide) in a first 
measurement receiver. In a second measurement operation, the measurement 
signal (measuring light) of a second measurement transmitter at the other 
end of the optical medium is measured in the opposite direction in a 
second measurement receiver. In a third measurement operation, the 
measurement signal (measuring light) of the first measurement transmitter 
is further measured upstream of the optical medium by means of the second 
measurement receiver, and in a fourth measurement operation the 
measurement signal of the second measurement transmitter is measured in 
the first measurement receiver. The attenuation of the optical medium can 
essentially be determined in the manner of a relative measurement from the 
four measured values thus obtained. The measurement transmitters and 
measurement receivers are advantageously coupled out by means of bending 
couplers. It is then particularly preferred for the respective bending 
couplers for transmitting and receiving, that is to say the coupling 
devices (compare BK1, BK2 in the FIGURE) to be integrated in the tension 
device, for example, formed by HVI, HV2, SN. 
The following procedure for checking the mechanical properties of a splice 
is preferably expedient in practice: 
Two optical waveguide sections to be connected to one another are prepared 
at their end faces which are to be spliced with one another, inserted into 
the splicer, in particular the fusion-welding apparatus, and aligned with 
one another end face on and the splicing operation (in particular welding 
operation) is started. The splicer measures the splice attenuation after 
splicing, in particular welding. 
An optical waveguide spliced in such a way advantageously remains in the 
splicer for the purpose of tensile testing according to the invention. The 
tensile test is started, the splicer simultaneously being checked as to 
whether the two interconnected optical waveguide sections are correctly 
inserted into the holding system. The measurement system, which is 
provided for determining the attenuation, is preferably integrated in the 
holding systems required for the tensile test in order to fix the optical 
waveguide sections, with the result that it is also advantageously 
possible to monitor the correct manipulation of the insertion operation. 
The measurement system thus automatically recognizes whether the test 
object (optical waveguide) has been correctly inserted and gives the user 
appropriate instructions as the case may be. Subsequently, the measurement 
system measures the intensity level of the light transmitted via the 
unloaded splice, which can be taken as reference quantity for subsequent 
attenuation measurements during the tensile test. 
The actual tensile test is then preferably started with a temporally 
varying tensile stress, in order to test the mechanical properties of the 
finished splice. During the tensile test, the power level of the light 
transmitted via the splice is observed permanently, that is to say 
constantly or continuously. It can be expedient to terminate the tensile 
test immediately if the level of the transmitted light changes more 
strongly than a prescribed limit. If, for example, a change in 
attenuation, in particular an increase in attenuation, of approximately 
0.05 to 0.2 dB is registered, the tensile test is broken off and the 
splice is regarded as impermissible. If, by contrast, the tensile test 
proceeds regularly over a permanently set total test time, that is to say 
without exceeding the prescribed, maximum permitted change in attenuation, 
the splice is assessed as being "acceptable". It is normal here to select 
a test time of between 1 sec and 20 sec, in particular 1 and 10 sec, 
preferably between 1 and 5 sec. As a result, it is advantageously rendered 
possible to specify in percent or, if appropriate, even in absolute terms 
the change in attenuation which results with respect to the coupled-out 
optical power before carrying out the tensile test, that is to say in the 
largely unloaded state of the splice. Thus, it is possible to use the 
transmitted level to detect changes in attenuation by virtue of the 
mechanical loading. Finally, it is possible if appropriate further to 
undertake an additional measurement of the level of the transmitted light 
after the tensile test for the purpose of additional monitoring. 
Since the splice is loaded under tension and at the same time the optical 
power respectively transferred via the splice is determined continuously 
as a function of the tensile stress, which in particular is varying, the 
actual, mechanical properties of the splice and of its environment can 
preferably be assessed much better than, for example, in the case of the 
customary visual monitoring of the splice alone. Tensile testing is thus 
preferably carried out in combination with the measurement of the optical 
power, in particular the measurement of the splice attenuation. In other 
words, the respectively finished splice is preferably exposed to a 
temporally varying tensile force, and in the process the change in the 
optical power transmitted (transferred) via the splice is simultaneously 
observed, that is to say in particular measured and provided for further 
evaluation.