
44-6 Optical
from the ideal, and the QE characterizes the ideality of the sensor. e QE of a photodiode is the ratio of
th
e
c
harge
p
airs
g
enerated
to t
he
i
ncident
p
hotons:
η
υ
=
I
p
/
/
q
P h
i
(44.5)
where
P
i
is the optical power incident on the photodiode
hυ
i
s
t
he
e
nergy
o
f
t
he
p
hotons
In
th
e
da
ys
of yo
re,
be
fore
LE
Ds
an
d
ca
librated
ph
otodiodes,
li
ght
in
tensity
wa
s
me
asured
wi
th
po
wer
me
ters
an
d
bo
lometers
. Wit
h
th
ese
de
vices,
th
e
me
asured
re
sponse
is pr
oportional
to th
e
en
ergy
of th
e
ph
otons,
as we
ll
as th
e
nu
mber
of ph
otons
. e
refore,
th
e
re
sponsivity,
R, is th
e
ra
tio
of th
e
ph
otocurrent
to t
he
i
ncident
o
ptical
p
ower
(
A/W):
R
I
P
= =
p
i
η
υ
q
h
(44.6)
Rea