# Fiber Optic Device Testing Parameters (Video)

In this video, we will explain some of the most common parameters used in fiber optic device testing.

IEEE (ref. 10) defines insertion loss as:
“the total optical power loss caused by the insertion of an optical component such as a connector, splice or coupler.”
Insertion loss is:
The reduction in optical power between an input and output port of a passive component and is expressed in decibels
Insertion loss is defined as:
IL = -10 log (P1/P0)
P0 = the optical power launched into the input port
P1 = the optical power received from the output port
Insertion loss are called:
(1) Splitting loss in the case of optical fiber couplers
(2) Excess loss with other branching devices
Maximum/minimum insertion loss:
The upper/lower limit of the insertion loss over the entire operation wavelength range of the device
Typical insertion loss:
The expected value of the insertion loss measured at the specified center wavelength of the operating wavelength range

Return loss is the fraction of input power that is reflected back from the input port of a passive component
Return loss is defined as:
RL = -10log(Pr/Pi)
Pi = optical power launched into the input port
Pr = optical power received back from the same port
Return loss for fiber optic devices do not include the return loss contributions of connectors.

Reflectance is the ratio R of reflected power Pr to incident power Pi:
At a given port of a passive component
For given conditions of spectral composition, polarization, and geometrical distribution
Reflectance is expressed in decibels as:
R = -10log(Pr/Pi)
When referring to reflected power from an individual component, reflectance is the term preferred to return loss

Directivity is the ratio of the optical power launched into an input port to the optical power returning from any other port
Directivity has been referred to as near-end isolation or near-end crosstalk
Return loss is the ratio of optical power launched into an input port to the optical power returning from the same input port
Both directivity and return loss are expressed as positive decibels and are measured with all output ports optically terminated
Reflectance is the negative of return loss.
In many cases, reflectance and return loss are used synonymously
Minimum directivity and return loss are the power limits that apply over the entire operation wavelength range

Isolation is the measure of the decrease in optical power (decibels) resulting from the insertion of an isolator in its backward direction.
The launching port is the output port and the receiving port is the input port of the isolator
Isolation is given as:
BL = -10log(Pob/Pib)
Pob is the optical power measured at the input port of the isolator when Pib is launched into the output port
In operating conditions, Pib is the optical power reflected at the far-end optical circuit devices in the backward direction into the output port of the isolator being measured.

Operating Wavelength Range:
This is the specified range of wavelengths from λmin to λmax , within which a passive component is designed to operate

Polarization-Dependent Reflectance
The maximum variation of reflectance due to a change of the state of polarization over all states of polarization

Polarization-Dependent Loss (PDL)
The maximum variation of insertion loss due to a change of the state of polarization over all states of polarization