Silicon photonics
When light travels 5 mm through a silicon waveguide with a propagation loss of 2 dB/cm, which is closest to the fraction of optical power remaining at the output?
- AAbout 79%
- BAbout 90%
- CAbout 50%
Show answer and explanation
Answer: A. About 79%
5 mm is 0.5 cm, so the loss is 2 dB/cm × 0.5 cm = 1 dB. The loss L in dB and the transmittance T are related by T = 10^(−L/10); 10^(−0.1) ≈ 0.79, so about 79% remains. It is handy to remember that 3 dB is roughly half and 10 dB is one-tenth. About 90% corresponds to a loss of 0.5 dB, and about 50% to a loss of 3 dB. Using dB turns the multiplication of each component's transmittance into addition, making it easy to total the losses of multiple components.