Silicon photonics
For optical transceivers, which correctly compares the parallel scheme, which sends one wavelength on each of four fibers, with the CWDM scheme, which combines four wavelengths onto one fiber?
- AThe parallel scheme needs only one fiber, but requires four lasers of different wavelengths plus a multiplexer and demultiplexer
- BThe parallel scheme needs no multiplexer or demultiplexer but requires many fibers; the CWDM scheme needs fewer fibers but requires a multiplexer and demultiplexer
- CThe CWDM scheme needs four fibers for transmission alone, but all the lasers can have the same wavelength
Show answer and explanation
Answer: B. The parallel scheme needs no multiplexer or demultiplexer but requires many fibers; the CWDM scheme needs fewer fibers but requires a multiplexer and demultiplexer
The parallel scheme (also called PSM) uses four single-mode fibers each for transmit and receive, eight in total, sending one lane of signal on each fiber with light of the same wavelength. It needs no multiplexer or demultiplexer, and the light from one laser can even be split and shared, but the number of fibers and multi-fiber connectors increases. The CWDM scheme needs only one fiber each for transmit and receive, two in total, making it easier to reuse existing cabling, but it requires four lasers of different wavelengths plus a multiplexer and demultiplexer. The two are chosen according to reach and cabling circumstances.