Silicon photonics
When a silicon photonic circuit receives light from standard single-mode fiber, which is a correct reason polarization becomes an issue?
- AThe polarization in the fiber is not fixed, while silicon waveguides behave very differently depending on polarization
- BAfter passing through the fiber, light loses its polarization and can no longer propagate in a silicon waveguide
- CSilicon waveguides pass light the same way regardless of polarization, but the photodetector can detect only one polarization
Show answer and explanation
Answer: A. The polarization in the fiber is not fixed, while silicon waveguides behave very differently depending on polarization
Standard single-mode fiber does not maintain polarization, so fiber bending or temperature changes alter the polarization of the light arriving at the receiver. Meanwhile, in a flat silicon waveguide about 0.5 µm wide and about 0.22 µm thick, horizontally oscillating (TE) and vertically oscillating (TM) polarizations have very different effective indices and losses, and the characteristics of grating couplers and ring resonators also change with polarization. Solutions include devices that split light into two polarizations and rotate one of them, and two-dimensional grating couplers that handle both polarizations.