Biomedical Engineering Reference
In-Depth Information
A
0
2
2
Out
C
0
1
Attenuator
1
3 dB
Polarizer
3
0
3
B
Hybrid optical gates
NAND
OR
A
B
Out
A
B
Out
0
0
0
0
1
1
1
0
0
0
0
0
1
1
1
1
1
1
1
1
1
0
1
1
Initial conditions
Gate 1
180° Out of
phase
Gates 2 and 3
In phase
180° Out of phase
0
1
0
2
0
3
0
2
0
3
C
A
B
Out
Out
on
off
off
off
on
on
on
on
on
off
off
off
off
on
on
on
on
off
on
on
off
on
on
on
on
off
on
on
off
off
on
off
on
(c)
on
on
off
off
off
on
on
FIGURE 3.16 (continued)
(c) Hybrid MZI gate.
the Pockels effect, the relationship between the inputs “A” and “B” and
the output will be exclusive—or (XOR) or inverse XOR logic functions, as
described by the truth tables in Figure 3.16. One should note that the output
polarizer selects only the parallel polarized control signal for the output.
This has implications for the concept of cascading the basic Double-Y gate to
implement other logic functions.
Several combinations of cascaded Double-Y type gates can be considered
in order to implement all basic logic functions. Review of Figure 3.16a shows
that three logic f
unct
ions are accounted for by the basic Double-Y gate. Two
of these are the
XOR
and XOR functions. In addition, it can be seen that by
using the gate in either of the above initial phase modes (i.e., in-phase or 180°
out-of-phase) an inversion of the “A” input can be obtained by leaving the
“B” input “off” or “on,” respectively. This is indicated by the dashed boxes
in the truth tables.
Figure 3.16b shows a cascaded gate that produces either the NOR or AND
function, depending on the setting of the B
⊥
input. A few of the possible
problems that could be encountered in the operation of this gate are the split-
ting of the A input power and the length of the A
⊥
guide. Both of these factors
can make the proper phase changes and synchronization difficult to obtain.
These problems can be overcome with proper design control. Another prob-
lem is the extended length of the device; however, this would be reduced in
accordance with reductions in the length of the single Double-Y gate.
Search WWH ::
Custom Search