This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Device Types”.
1. ____________ converts the received optical signal into an electrical signal.
Explanation: A detector is an essential component of an optical fiber communication system. It dictates the overall system performance. Its function is to convert optical signal into an electrical signal. This electrical signal is then amplified before further processing.
2. The first generation systems of optical fiber communication have wavelengths between ___________
a) 0.2 and 0.3 μm
b) 0.4 and 0.6 μm
c) 0.8 and 0.9 μm
d) 0.1 and 0.2 μm
Explanation: The first generation systems operated at a bit-rate of 45 Mbps with repeater spacing of 10 km. It operates at wavelengths between 0.8 and 0.9μm. These wavelengths are compatible with AlGaAs laser and LEDs.
3. The quantum efficiency of an optical detector should be high. State whether the given statement is true or false.
Explanation: The detector must satisfy stringent requirements for performance and compatibility. The photo detector thus produces a maximum electrical signal for a given amount of optical power; i.e. the quantum efficiency should be high.
4. Which of the following does not explain the requirements of an optical detector?
a) High quantum efficiency
b) Low bias voltages
c) Small size
d) Low fidelity
Explanation: The size of the detector must be small for efficient coupling to the fiber. Also, ideally, the detector should not require excessive bias voltages and currents. The fidelity and quantum efficiency should be high.
5. How many device types are available for optical detection and radiation?
Explanation: Two types of devices are used for optical detection and radiation. These are external photoemission and internal photoemission devices. External photoemission devices are too bulky and require high voltages for operation. Internal devices provide good performance and compatibility.
6. The ___________ process takes place in both extrinsic and intrinsic semiconductors.
a) Avalanche multiplication
b) External photoemission
c) Internal photoemission
Explanation: During intrinsic absorption, the received photons excite electrons from the valence band and towards the conduction band in the semiconductor. Extrinsic absorption involves impurity centers created with the material. Generally, intrinsic absorption is preferred for internal photoemission.
7. ____________ are widely used in first generation systems of optical fiber communication.
a) p-n diodes
d) Silicon photodiodes
Explanation: The first generation systems operates at wavelengths 0.8 and 0.9 μm. Silicon photodiodes have high sensitivity over the 0.8-0.9 μm wavelength band with adequate speed, long term stability. Hence, silicon photodiodes are widely used in first generation systems.
8. Silicon has indirect band gap energy of __________________
a) 1.2 eV
b) 2 eV
c) 1.14 eV
d) 1.9 eV
Explanation: Silicon’s indirect band gap energy of 1.14 eV gives a loss in response above 1.09μm. To avoid this, narrower bandgap materials are used. Hence, silicon’s usefulness is limited to first generation systems and not for second and third generation systems.
9. Which of the following detector is fabricated from semiconductor alloys?
a) Photoconductive detector
b) p-i-n detector
d) Photoemission detectors
Explanation: The detectors fabricated from semiconductor alloys can be used for longer wavelengths. Photoconductive detector and hetero-junction transistor have found favor as a potential detector over a wavelength range of 1.1 to 1.6μm.
10. Silicon photodiodes provides high shunt conductance. State whether the given statement is true or false.
Explanation: Semiconductor photodiodes provide best solution for detection in optical fiber communications. Silicon photodiodes have high sensitivity, negligible shunt conductance and low dark current.
Sanfoundry Global Education & Learning Series – Optical Communications.
To practice all areas of Optical Communications, here is complete set of 1000+ Multiple Choice Questions and Answers.