This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Receiver Noise”.

1. Which are the two main sources of noise in photodiodes without internal gain?
a) Gaussian noise and dark current noise
b) Internal noise and external noise
c) Dark current noise & Quantum noise
d) Gaussian noise and Quantum noise

2. The dominating effect of thermal noise over the shot noise in photodiodes without internal gain can be observed in wideband systems operating in the range of ________
a) 0.4 to 0.5 μm
b) 0.8 to 0.9 μm
c) 0.3 to 0.4 μm
d) 0.7 to 0.79 μm

3. A silicon p-i-n photodiode incorporated in an optical receiver has following parameters:

Quantum efficiency = 70%
Wavelength = 0.8 μm
Dark current = 3nA
Incident optical power = 150nW.
Bandwidth = 5 MHz

Compute the photocurrent in the device.
a) 67.7nA
b) 81.2nA
c) 68.35nA
d) 46.1nA

4. In a silicon p-i-n photodiode, if load resistance is 4 kΩ, temperature is 293 K, bandwidth is 4MHz, find the thermal noise in the load resistor.
a) 1.8 × 10-16A2
b) 1.23 × 10-17A2
c) 1.65 × 10-16A2
d) 1.61 × 10-17A2

5. ________________ is a combination of shunt capacitances and resistances.
a) Attenuation
b) Shunt impedance
d) Thermal capacitance

6. ______________ is used in the specification of optical detectors.
a) Noise equivalent power
b) Polarization
c) Sensitivity
d) Electron movement

7. A photodiode has a capacitance of 6 pF. Calculate the maximum load resistance which allows an 8MHz post detection bandwidth.
a) 3.9 kΩ
b) 3.46 kΩ
c) 3.12 kΩ
d) 3.32 kΩ

8. The internal gain mechanism in an APD is directly related to SNR. State whether the given statement is true or false.
a) True
b) False

9. ____________ is dependent upon the detector material, the shape of the electric field profile within the device.
a) SNR
b) Excess avalanche noise factor
d) Noise power

10. For silicon APDs, the value of excess noise factor is between _________
a) 0.001 and 0.002
b) 0.5 and 0.7
c) 0.02 and 0.10
d) 1 and 2

11. __________ determines a higher transmission rate related to the gain of the APD device.
a) Attenuation
b) Gain-bandwidth product
c) Dispersion mechanism
d) Ionization coefficient

12. _________________ APDs are recognized for their high gain-bandwidth products.
a) GaAs