9 Convergence and upgrade of optical networks
9.1 Convergence and upgrade of optical networks

Demand for higher information capacity and bit rates require upgrading existing optical systems or running more systems on one fibre. Coexistence of optical systems refers to CWDM and DWDM networks sharing the passive optical infrastructure.

## DWDM over CWDM

- CWDM
  - 8x10 Gbps channels - 1470 nm - 1610 nm.
- CWDM/DWDM
  - Replacement of the 5th channel in CWDM (1550 nm).
  - DWDM with 15x10 Gbps channels with 100 GHz spacing.
  - ∆Quality factor is changed by less than 0.1 dB.

Sample solution for DWDM over CWDM system – optical channels.

## Hybrid solutions

### Hybrid DWDM 10G/40G

- Initially 10G DWDM system
  - 15x10 Gbps, NRZ-OOK, 50 GHz spacing.
  - 6x80km SSMF (dual phase amplifiers, post-compensation).
- Hybrid DWDM 10G/40G with channel interleaving
  - Combining with 7x40 Gbps system.
  - Duobinary modulation, P-DPSK, RZ-DQPSK modulation formats.
  - Influence of 10 Gbps channels on 40 Gbps channels.
  - Cross Phase Modulation (XPM) problem.

Optical spectrum of DWDM with channel interleaving.

### Hybrid DWDM 10G/40G with safety band

Spectral split of 10G and 40G by safety band can help reducing the cross phase modulation from the 10G system.

Safety band (100 GHz) splitting two systems (RZ-DQPSK and P-DPSK 40G channels).