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What is the role of the transimpedance amplifier (TIA) placed right after the photodiode in an optical receiver?

  1. AIt converts electrical signals into changes in light intensity and sends them into the fiber without a modulator
  2. BIt converts the small current from the photodiode into a voltage signal that later stages can easily handle, and amplifies it
  3. CIt raises the reverse bias on the photodiode so that avalanche multiplication increases the light itself, improving sensitivity
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Answer: B. It converts the small current from the photodiode into a voltage signal that later stages can easily handle, and amplifies it

A photodiode outputs current according to light intensity, but at a received power of about 0.1 mW the current is also small, about 0.1 mA, too small for the decision circuit to handle as is. A TIA is an amplifier that converts input current into voltage, outputting a voltage whose magnitude depends on the feedback resistor value. It must combine a bandwidth of several tens of GHz with low noise, and it is placed right next to the photodiode to minimize the capacitance of the interconnect between them. Converting electrical signals into light is the role of the driver and modulator on the transmit side.

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More Silicon photonics questions

  1. Among methods of incorporating lasers into silicon photonic circuits, which correctly describes heterogeneous integration?
  2. Which is a correct reason it is difficult to integrate an optical isolator together with a laser on a silicon photonic circuit?
  3. Which correctly describes wavelength division multiplexing (WDM)?
  4. In CWDM (coarse wavelength division multiplexing) for data center optical transceivers, wavelengths are spaced 20 nm apart, for example 1271, 1291, 1311 and 1331 nm. What is the main reason for the wide spacing?
  5. For WDM in the C-band (around 1.55 µm), a frequency spacing of 100 GHz corresponds to roughly what wavelength spacing? (Δλ ≈ λ² × Δf / c, c = 3×10⁸ m/s)