Noise

Optical Communications

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

1. _____________ refers to any spurious or undesired disturbances that mask the received signal in a communication system.
a) Attenuation
b) Noise
c) Dispersion
d) Bandwidth

2. How many types of noise are observed because of the spontaneous fluctuations in optical fiber communication systems?
a) One
b) Four
c) Two
d) Three

3. ______________ is caused due to thermal interaction between the free electrons and the vibrating ions in the conduction medium.
a) Thermal noise
b) Dark noise
c) Quantum noise
d) Gaussian noise

4. A small leakage current still flows from the device terminals even if there is no optical power incident on the photo detector.
a) True
b) False

5. ___________ distribution provides the description the random statistics of light emitted in black body radiation.
a) Poisson
b) Cumulative
c) Probability
d) Bose-Einstein

6. The probability of zero pairs being generated when a light pulse is present is given by which of the following equation?
a) P(0/1) = exp(-Zm)
b) P(x) = exp (Zm)
c) P(y) = x (0) + x(1)
d) P(z) = P(-Zm)

7. The minimum pulse energy needed to maintain a given bit-error-rate (BER) which any practical receiver must satisfy is known as ___________
a) Minimal energy
b) Quantum limit
c) Point of reversed
d) Binary signaling

8. A digital optical fiber communication system requires a maximum bit-error-rate of 10-9. Find the average number of photons detected in a time period for a given BER.
a) 19.7
b) 21.2
c) 20.7
d) 26.2

9. For a given optical fiber communication system, P(e) = 10-9, Zm = 20.7, f = 2.9×1014, η = 1. Find the minimum pulse energy or quantum limit.
a) 3.9×10-18
b) 4.2×10-18
c) 6.2×10-14
d) 7.2×10-14

10. An analog optical fiber system operating at wavelength 1μmhas a post-detection bandwidth of 5MHz. Assuming an ideal detector and incident power of 198 nW, calculate the SNR (f = 2.99×1014Hz).
a) 46
b) 40
c) 50
d) 52

11. The incident optical power required to achieve a desirable SNR is 168.2nW. What is the value of incident power in dBm?
a) -37.7 dBm
b) -37 dBm
c) – 34 dBm
d) -38.2 dBm

12. In the equation given below, what does τstands for?

Zm = ηP0τ/hf

a) Velocity
b) Time
c) Reflection
d) Refractive index

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