Optical measurement system

An optical measurement system is disclosed which enables rapid and repeatable measurement of insertion and return loss of each fiber in sequence of a multi-fiber connector 15 connected to an optical fiber ribbon 16 to be obtained without disturbing either the light source 17, 18 or detector components 19, 20 of the system. The system comprises a multi-channel optical switch 1 for connection to a light source 17, 18; 1.times.2 bi-directional splitters 2 each of which is optically coupled between one of the channels of the multi-channel optical switch and one fiber of a master multi-fiber connector 3, of which the geometry is known, for mating with a multi-fiber connector to be tested and, for connection to at least one detector for monitoring and recording the power reflected at the interface between a pair of optical fibers interconnected by the mating of the master multi-fiber connector and the multi-fiber connector under test, and a splitter 11 to which each of the bi-directional splitters 2 is also optically coupled.

BACKGROUND OF THE INVENTION 
This invention relates to an optical measurement system for determining the 
performance of a multi-fibre connector which is connected to an optical 
fibre ribbon and which is suitable for incorporation in a subscriber 
network. 
Two parameters generally used to determine the optical performance of a 
multi-fibre connector coupled to a length of optical fibre ribbon are the 
insertion loss and the return loss of each fibre in the connector. The 
insertion loss of an optical fibre in a connector when the optical fibre 
is connected to a fibre in another multi-fibre connector and the two 
multi-fibre connectors are mated together is defined as the proportion of 
input power that is transmitted along the output fibre. The return loss of 
an optical fibre in a multi-fibre connector when the optical fibre is 
connected to a fibre in another multi-fibre connector and the two 
multi-fibre connectors are mated together is defined as the proportion of 
input power that is returned along the input fibre due to reflection at 
the interface of the connected pair of fibres. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved optical 
measurement system by means of which can be obtained rapid and repeatable 
measurements of insertion and return loss of each fibre in sequence of a 
multi-fibre connector which is connected to an optical fibre ribbon and 
which is suitable for mating with a multi-fibre connector of complementary 
form, which measurements can be achieved without disturbing either the 
light source or the detector components of the system. 
According to the invention, the improved optical measurement system 
comprises a multi-channel optical switch suitable for connection to a 
source of light; a plurality of 1.times.2 bi-directional splitters each of 
which is directly optically coupled between one of the channels of the 
switch and one fibre of a master multi-fibre connector as hereinafter 
defined for mating with a multi-fibre connector to be tested and, for 
connection to at least one detector for monitoring and recording the power 
reflected at the interface between a pair of optical fibres interconnected 
by the mating of the standard multi-fibre connector and the multi-fibre 
connector under test, and a splitter to which each of said bi-directional 
splitters is also optically coupled. 
By a master multi-fibre connector is meant a multi-fibre connector of which 
the geometric and optical characteristics are clearly defined. 
For monitoring and recording the insertion loss of the optical fibres of a 
multi-fibre connector, the connector under test is mated to the master 
connector and the opposite end of the optical fibre ribbon connected to 
the connector under test is mated to at least one detector. For 
measurement of return loss of these optical fibers, the end of the optical 
fibre ribbon mated to said detector or detectors is unmated and so 
terminated that no light is reflected from this end, e.g. by a cell 
containing index matching liquid or semi-liquid. 
By means of the multi-channel optical switch each optical fibre in turn of 
the optical fibre ribbon connected to the multi-fibre connector under test 
can be tested to determine both its insertion loss and its return loss 
without disturbing either the light source or the detectors. Operation of 
the system may be effected manually but preferably the system is operated 
automatically under the control of a microprocessor. 
Each detector preferably includes means for automatic collation and 
analysis of the data received and recorded. 
The multi-channel optical switch preferably is suitable for connection to 
any one of at least two sources of light of wavelengths differing from one 
another, e.g. 1310 nm and 1550 nm, and in this case the splitter to which 
all the bi-directional splitters are optically coupled is preferably 
suitable for connection to at least two detectors, each appropriate to one 
of the sources of light.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2, the preferred optical measurement system 
comprises a multi-channel optical switch 1, eight 1.times.2 bi-directional 
splitters 2, a master multi-fibre connector 3 of which the geometry is 
known and a splitter 11 common to the bi-directional splitters. Each 
bi-directional splitter 2 is directly optically coupled to one of the 
channels 4 of the switch 1 by an optical fibre 5 which is fusion spliced 
at 6 to the channel and to one of the fibres 8 of an optical fibre ribbon 
7 connected to the master connector 3 by an optical fibre 9 which is 
fusion spliced at 10 to said optical fibre. Each of the bi-directional 
splitters 2 is also optically coupled to one optical lead 12 of a splitter 
11, common to the bi-directional splitters, via an optical fibre 13 which 
is fusion spliced at 14 to the optical lead. 
The optical switch 1 can be connected to either of two sources 17 and 18 of 
light, one having a wavelength of 1310 nm and the other having a 
wavelength of 1550 nm. The splitter 11 to which all the bi-directional 
splitters 2 are optically coupled can be connected to either of two 
detectors 19 and 20, each appropriate to one of the sources 17 and 18 of 
light. 
As will be seen on referring to FIG. 1, when using the optical measurement 
system for monitoring and recording the insertion loss between a pair of 
optical fibres interconnected by the mating of the standard multi-fibre 
connector 3 and a multi-fibre connector 15 under test, optical fibres of 
the optical fibre ribbon 16 connected to the multi-fibre connector 15 
under test are terminated by an adaptor 21 optically coupling the 
multi-fibre connector under test to a large area detector 22. 
As will be seen on referring to FIG. 2, when using the optical measurement 
system to monitor and record the return loss between the pair of optical 
fibres interconnected by the mating of the standard multi-fibre connector 
3 and the multi-fibre connector 15 under test, the adaptor 21 is 
disconnected from the large area detector 22 and is removed from the end 
of the optical fibre ribbon 16 and the free end of the optical fibre 
ribbon is immersed in an index matching gel 23 from which no light will be 
reflected. 
In use, before connecting up the optical measurement system as shown in 
FIGS. 1 and 2, the master connector 3 is connected direct to the large 
area detector 22 and values for reference power P.sub.1 for each fibre are 
recorded at both wavelengths by switching through each channel in 
sequence. Then, with the optical measurement system connected as shown in 
FIG. 1, the values of transmitted power P.sub.2 are recorded for each path 
in turn at both wavelengths. With the optical measurement system then 
connected as shown in FIG. 2, returned power values P.sub.3 for each path 
are recorded at both wavelengths. 
The insertion loss of each fibre path through the connector 15 under test 
is found from the equation: 
EQU Insertion Loss=P.sub.2 -P.sub.1 dB 
The return loss for each fibre path through the connector 15 under test is 
found from the equation: 
EQU Return Loss=P.sub.3 -P.sub.1 -X.sub.n dB 
where X.sub.n is the loss through the system travelled by the returned 
power, i.e. the loss through the couplers and fusion splices. This value 
can be calculated for each path in the system.