The sensitivity of the receiver is specified by the incident
optical power required to reliably receive a transmission. It
is dependant on the responsivity of the photo detector and
the gain of the amplifiers. The purpose of the measurement
was to find correct parameters for the amplifier gain to give
highest sensitivity. The sensitivity of the receiver can then
be used to specify required output power of a transmitter for
communication links of a specified range.
The photo detector used for the sensitivity measurement has
a relatively fast response, this however comes at a cost of a
lower noise immunity due to interference from ambient light
sources. In the future the detector is to be replaced with a
component matched to the emission of the transmitter having a
similar response time but much tighter matching to the channel
wavelength. Therefore during the sensitivity measurements the
receiver was shielded from oscillating ambient sources such as
fluorescent lights. The transmitters used to measure sensitivity
were VCSELs developed by colleagues within the research
consortium. The optical output power of the VCSELs used
in the testing was previously measured to be 100μW at a
divergence of 20 degrees.