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For high-speed links of a few m or more, such as those spanning racks, what is the main reason optical fiber has an advantage over copper cables and board traces?

  1. ALight travels more than 10 times faster than electrical signals in copper, nearly eliminating latency
  2. BOptical fiber also conducts electricity, so it can deliver power to equipment along with the signal
  3. CFiber loss barely depends on signal speed and is small, about 0.5 dB or less even over 1 km
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Answer: C. Fiber loss barely depends on signal speed and is small, about 0.5 dB or less even over 1 km

In copper wiring, skin effect and dielectric loss make loss increase with signal frequency, so higher speeds shorten reach. The equalizers and retimers used to compensate increase power consumption. In contrast, optical fiber loss is almost independent of modulation speed and small—about 0.35 dB/km at 1.31 µm and about 0.2 dB/km at 1.55 µm in single-mode fiber—and fiber is thin, light and immune to electromagnetic noise. Electrical signals in cables and boards also travel at about half to 80% of the speed of light, not much different from light in fiber (about two-thirds the speed of light).

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More Silicon photonics questions

  1. Which is a correct advantage of pluggable optical transceivers inserted into a switch's front panel?
  2. Which is a correct challenge of CPO (Co-Packaged Optics), which mounts the optical transmit/receive components in the same package as the switch IC?
  3. In CPO, an external laser source—placing the laser outside the switch IC package and supplying only light via fiber—is often considered. What is the main reason?
  4. Which correctly describes the concept of "linear drive" (called linear pluggable optics, LPO, etc.) in optical transceivers?
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