<s>
A	O
guided	B-Device
ray	I-Device
(	O
also	O
bound	B-Device
ray	I-Device
or	O
trapped	B-Device
ray	I-Device
)	O
is	O
a	O
ray	B-Device
of	I-Device
light	I-Device
in	O
a	O
multi-mode	B-Device
optical	I-Device
fiber	I-Device
,	O
which	O
is	O
confined	O
by	O
the	O
core	O
.	O
</s>
<s>
For	O
step	B-Device
index	I-Device
fiber	I-Device
,	O
light	O
entering	O
the	O
fiber	O
will	O
be	O
guided	O
if	O
it	O
falls	O
within	O
the	O
acceptance	B-Device
cone	I-Device
of	O
the	O
fiber	O
,	O
that	O
is	O
if	O
it	O
makes	O
an	O
angle	O
with	O
the	O
fiber	O
axis	O
that	O
is	O
less	O
than	O
the	O
acceptance	B-Device
angle	I-Device
,	O
</s>
<s>
θ	O
is	O
the	O
angle	O
the	O
ray	B-Device
makes	O
with	O
the	O
fiber	O
axis	O
,	O
before	O
entering	O
the	O
fiber	O
,	O
</s>
<s>
The	O
quantity	O
is	O
sometimes	O
called	O
the	O
total	O
acceptance	B-Device
angle	I-Device
of	O
the	O
fiber	O
.	O
</s>
<s>
Light	O
that	O
enters	O
the	O
core	O
with	O
an	O
angle	O
below	O
the	O
acceptance	B-Device
angle	I-Device
strikes	O
the	O
core-cladding	O
boundary	O
at	O
an	O
angle	O
above	O
the	O
critical	O
angle	O
,	O
and	O
experiences	O
total	O
internal	O
reflection	O
.	O
</s>
<s>
This	O
treatment	O
is	O
necessary	O
when	O
considering	O
singlemode	B-Device
fiber	I-Device
,	O
since	O
the	O
ray	B-Device
model	O
does	O
not	O
accurately	O
describe	O
the	O
propagation	O
of	O
light	O
in	O
this	O
type	O
of	O
fiber	O
.	O
</s>
