Modulation Schemes
The correct modulation scheme for a given type of
fibre, transmission system, reach, channel density and data rate can
optimise performance and minimise complexity (cost). The 3 major
limiting factors are noise (OSNR), polarisation mode dispersion (PMD)
and chromatic dispersion (CD).
|
Name |
Description |
Spectral Efficiency |
OSNR Sensitivity |
PMD Tolerance |
CD Tolerance |
Electronics Complexity |
Photonics Complexity |
| |
|
bits/s/Hz |
dB/0.1nm |
ps |
ps/nm |
|
|
|
OOK or ASK |
On/Off Keying or Amplitude Shift Keying |
0.4 |
16~20 |
1 |
±15~50 |
Medium |
Low |
|
PSBT |
|
1 |
16~20 |
1~2.5 |
±50~150 |
Medium |
Low |
|
DPSK |
Differential Phase Shift Keying |
0.8 |
13~17 |
1~2.5 |
±12~100 |
Medium |
Low |
|
DQPSK |
Differential Quaternary Phase Shift Keying |
1.6 |
15~18 |
2~5 |
±35~200 |
Low |
Medium |
|
QPSK |
Quaternary Phase Shift Keying |
1.6 |
13~15.5 |
2~5 |
±35~200 |
Low |
High |
|
PM-DQPSK |
Polarisation Multiplexing DQPSK |
3 |
11~18 |
2.5~10 |
±140~800 |
High |
High |
|
PM-QPSK |
Polarisation Multiplexing QPSK |
3 |
11~15.5 |
2.5~10 |
±140~800 |
High |
High |
|
RZ |
Return to Zero |
Wider bandwidth but lower intensity which reduces the effects of
fibre nonlinearity - better at higher bit rates |
|
CS/RZ |
Carrier Suppressed Return to Zero |
|
|
NRZ |
Non Return to Zero |
Higher intensity but narrower bandwidth which reduces the effects
of chromatic dispersion - better at lower bit rates |
|
BPSK |
Binary Phase Shift Keying |
|
|
