Silicon photonics
Which is a correct reason it is difficult to integrate an optical isolator together with a laser on a silicon photonic circuit?
- APassing light in only one direction requires nonreciprocal effects, such as those of magneto-optic materials, which are hard to handle in CMOS processes
- BAn isolator is a device that amplifies light, and indirect-gap silicon cannot amplify light, so it would not work even if integrated
- CAn isolator is a device that converts light into electricity, and silicon cannot absorb telecom-wavelength light
Show answer and explanation
Answer: A. Passing light in only one direction requires nonreciprocal effects, such as those of magneto-optic materials, which are hard to handle in CMOS processes
An optical isolator passes forward-traveling light and blocks light coming back. When reflected light enters a laser from outside, lasing becomes unstable and its wavelength and output are disturbed, so isolators are sometimes used for protection. Nonreciprocity—light propagating differently depending on direction—cannot be obtained from ordinary waveguide materials and requires magneto-optic materials such as garnets that exhibit the Faraday effect in a magnetic field. Such materials are poorly compatible with CMOS processes, so approaches that do without an isolator are also used, such as low-reflection circuit design and lasers tolerant of back-reflection.