Agilent Technologies 81610A, User Manual, Page: 43 / 118

Getting Started with Return Loss A Background to Return Loss Measurement
40
Agilent 81610A/11A/12A/13A/14A Return Loss Module, Fifth Edition
That is:
where:
The constants t
1
, t
2
, k
1
and k
2
are multipliers giving the proportion of
power transmitted through the coupler from the Input port to the
Output port and from the Output port to the sensor port respectively.
In other words, when optical power is input at the Output port, k
2
times that power is output at the sensor port. It is not necessary to
know the value for these constants, they can be eliminated later.
The constant s is a multiplier giving the scattering factor. The
scattering factor accounts for the directivity of the second coupler,
backscatter in the fiber, and reflections of connectors. The calibration
procedure helps you to eliminate the affect of these on return loss
measurements.
For “Making a Return Loss Measurement” on page 19 , the reflection
factor of the component is known. Here we refer to the reflection
factor as R
Ref
. This gives the following equation:
For “Measuring the Power when there are No Reflections” on page 37 ,
the value of the reflection factor is zero. This gives the following
equation:
For “Measuring the Reflections from the DUT” on page 38 , the value
of the reflection factor of the DUT is called R
DUT
. This gives the
following equation:
3 W
2
N
1
N
2
3
VUF
5 W
2
V0
+ =
0 W
1
3
6UF
=
F
1
W
2
W
1
----
N
1
N
2
=
F
2
W
2
W
1
----
V
=
3
⇒
F
1
0 5 F
2
0
+ =
(1)
3
5HI
F
1
0
5HI
5
5HI
F
2
0
5HI
+ =
(2)
3
SDUD
F
2
0
SDUD
=
(3)
3
'87
F
1
0
'87
5
'87
F
2
0
'87
+ =
(4)