Silicon photonics
Which correctly describes an edge coupler, which couples to optical fiber at the chip facet, compared with a grating coupler?
- AIt can be placed anywhere on the chip surface, but its coupling wavelength range is very narrow, only a few nm
- BIt needs no facet processing, but its loss varies greatly with polarization and it can pass only O-band light
- CIt readily achieves low loss over a wide wavelength range, but requires facet processing and is hard to measure on the wafer
Show answer and explanation
Answer: C. It readily achieves low loss over a wide wavelength range, but requires facet processing and is hard to measure on the wafer
An edge coupler couples a waveguide routed out to the chip edge to a fiber butted against it from the side. Because it does not rely on diffraction, its wavelength dependence is small, making it easy to obtain low loss of about 1–2 dB or less over a wide band spanning the O-band and C-band, and it also handles different polarizations more easily. In exchange, the chip must be cut out and its facet finished cleanly, it can be placed only at the chip edge, and it is hard to launch light into it on the wafer before dicing. Being placeable anywhere on the surface and measurable on the wafer are features of the grating coupler.