ANSWERS TO QUESTIONS Q1. THROUGH Q28.

A1. An electro-optic device that accepts optical signals from an optical fiber and converts them into electrical signals.
A2. Amplifier.
A3. Receiver sensitivity.
A4. The range of optical power levels over which the receiver operates within the specified values. It usually is described by the ratio of the maximum input power to the sensitivity.
A5. It is a transducer that converts an optical signal into an electrical signal. It does this by generating an electrical current proportional to the intensity of incident optical radiation.
A6. High.
A7. The semiconductor positive-intrinsic-negative (PIN) photodiode and avalanche photodiode (APD).
A8. Silicon, gallium arsenide, germanium, and indium phosphide.
A9. The current produced when photons are incident on the detector active area.
A10. The ratio of the optical detector's output photocurrent in amperes to the incident optical power in watts.
A11. Reverse-biased.
A12. The leakage current that continues to flow through a photodetector when there is no incident light.
A13. Increase.
A14. Small.
A15. Fast transit time.

A16. Because fiber optic communications systems operate at low optical power levels.
A17. The electrons initially generated by the incident photons accelerate as they move through the APD active region. As these electrons collide with electrons in the semiconductor material, they cause a fraction of them to become part of the photocurrent.
A18. By increasing the reverse-bias voltage.
A19. The preamplifier.
A20. Receiver sensitivity, bandwidth, and dynamic range.
A21. Thermal noise, dark current noise, and quantum noise.
A22. Noise.
A23. Increased.
A24. Dark current and quantum noises.
A25. The high-impedance amplifier and the transimpedance amplifier.
A26. Transimpedance.
A27. For high-data-rate applications and for low- or moderate-data-rate applications where receivers with extremely low sensitivities are required.
A28. To smooth the amplified signal to remove some of the high frequency noise before the signal is further processed.