Question 1

3dB optical bandwidth is always ___________ the 3dB electrical bandwidth.

Accepted Answer

The 3dB optical bandwidth is typically larger than the 3dB electrical bandwidth because optical signals can carry more information and have a broader frequency range than electrical signals.

Question 2

A multimode graded index fiber exhibits a total pulse broadening of 0.15?sover a distance of 16 km. Estimate the maximum possible bandwidth, assuming no intersymbol interference.

Accepted Answer

C

Question 3

What is pulse dispersion per unit length if for a graded index fiber, 0.1?s pulse broadening is seen over a distance of 13 km?

Accepted Answer

Pulse dispersion per unit length is calculated by dividing the pulse broadening by the distance. Here, $0.1 \mu s = 100 ns$ over $13 km$, so $100 ns / 13 km = 7.69 ns/km$.

Question 4

Chromatic dispersion is also called as intermodal dispersion. State whether the given statement true or false.

Accepted Answer

Chromatic dispersion and intermodal dispersion are two different types of dispersion. Chromatic dispersion occurs due to the different speeds of light wavelengths through a medium, while intermodal dispersion happens in multimode fibers due to different paths (modes) that light can take, each with a different length.

Question 5

Chromatic dispersion is also called as intermodal dispersion. State true or false

Accepted Answer

Chromatic dispersion refers to the spreading of light in a fiber optic cable due to different wavelengths traveling at different speeds, while intermodal dispersion occurs when different modes of light travel at different speeds in a multimode fiber.

Question 6

The optical source used in a fiber is an injection laser with a relative spectral width ??/? of 0.0011 at a wavelength of 0.70?m. Estimate the RMS spectral width.

Accepted Answer

The RMS spectral width can be calculated using the formula: RMS spectral width = (??/?) * wavelength. Substituting the given values: 0.0011 * 0.70 µm = 0.00077 µm = 0.77 nm.

Question 7

In waveguide dispersion, refractive index is independent of

Accepted Answer

Waveguide dispersion occurs when the speed of a wave in a waveguide (such as an optical fiber) depends on its frequency for geometric reasons, independent of the medium's refractive index changes with wavelength.

Question 8

Intermodal dispersion occurring in a large amount in multimode step index fiber results in

Accepted Answer

Intermodal dispersion in multimode step index fibers causes different modes to travel at different speeds, leading to pulse broadening at the output.

Question 9

After Total Internal Reflection the Meridional ray

Accepted Answer

The answer of After Total Internal Reflection the Meridional ray
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Question 10

Consider a single mode fiber having core refractive index n1= 1.5.

Accepted Answer

The question seems to be asking for a specific value related to a single mode fiber with a core refractive index of 1.5, but without the context of what specific value (e.g., delay, speed, etc.) is being asked for, it's challenging to provide a direct answer. However, given the options, it appears to relate to a characteristic that could be measured in seconds (likely a delay or time difference). The correct choice among the provided options cannot be determined without additional context regarding the specific calculation or property being queried. The choice "B" is marked as correct based on the assumption that there might be a specific calculation or context in the original question that leads to this answer, but without more information, this is speculative.

Question 11

A 4 km optical link consists of multimode step index fiber with core refractive index of 1.3 and a relative refractive index difference of 1%. Find the delay difference between the slowest and fastest modes at the fiber output.

Accepted Answer

The delay difference between the slowest and fastest modes in an optical fiber is given by the formula: $\Delta \tau = \frac{L \cdot \Delta n}{c}$, where $L$ is the length of the fiber, $\Delta n$ is the difference in refractive indices between the core and cladding, and $c$ is the speed of light in vacuum ($3 \times 10^8$ m/s). The relative refractive index difference ($\Delta$) is given by $\frac{\Delta n}{n_1}$, where $n_1$ is the refractive index of the core. Therefore, $\Delta n = n_1 \cdot \Delta$.Given $n_1 = 1.3$, $\Delta = 1\% = 0.01$, and $L = 4$ km = $4000$ m, we find:$\Delta n = 1.3 \times 0.01 = 0.013$.Substituting these values into the delay difference formula:$\Delta \tau = \frac{4000 \cdot 0.013}{3 \times 10^8} = \frac{52}{3 \times 10^8}$ s.Converting to microseconds ($\mu$s) by multiplying by $10^6$, we get:$\Delta \tau = \frac{52}{300} \mu s \approx 0.173 \mu s$.

Question 12

A multimode step-index fiber has a core refractive index of 1.5 and relative refractive index difference of 1%. The length of the optical link is 6 km. Estimate the RMS pulse broadening due to intermodal dispersion on the link.

Accepted Answer

The answer of A multimode step-index fiber has a core...

Question 13

The differential attenuation of modes reduces intermodal pulse broadening on a multimode optical link.

Accepted Answer

Differential attenuation of modes can reduce intermodal pulse broadening by preferentially attenuating higher-order modes, which typically travel slower, thus reducing the spread in arrival times of different modes.

Question 14

The index profile of a core of multimode graded index fiber is given by-

Accepted Answer

The answer of The index profile of a core of...

Question 15

Intermodal dispersion in multimode fibers is minimized with the use of step-index fibers.

Accepted Answer

Intermodal dispersion is minimized with the use of graded-index fibers, not step-index fibers, because graded-index fibers have a refractive index that gradually changes across the diameter of the fiber, which helps to keep the light rays more closely together and reduces the spread in their arrival times.

Question 16

Estimate RMS pulse broadening per km due to intermodal dispersion for multimode step index fiber where length of fiber is 4 km and pulse broadening per km is 80.6 ns.

Accepted Answer

The answer of Estimate RMS pulse broadening per km due...

Question 17

Practical pulse broadening value for graded index fiber lies in the range of

Accepted Answer

Graded index fibers are designed to reduce pulse broadening by making the refractive index of the core decrease gradually from the center towards the outer edges. This design minimizes the difference in travel times for light rays taking different paths through the fiber. The practical pulse broadening value for graded index fibers typically lies in the range of 0.2 to 1 ns/km, which allows for high data rate transmission over longer distances without significant signal distortion.

Question 18

The nonlinear effects in optical fibers are large.

Accepted Answer

Nonlinear effects in optical fibers are generally small and become significant only at high power levels or over long distances.

Question 19

How many categories of nonlinear effects are seen in optical fibers?

Accepted Answer

The answer of How many categories of nonlinear effects are...

Question 20

Which of the following is not related to Kerr effects?

Accepted Answer

Stimulated Raman Scattering is not related to Kerr effects. Kerr effects, including self-phase modulation, cross-phase modulation, and four-wave mixing, are nonlinear optical effects related to the intensity of light. Stimulated Raman Scattering is a different nonlinear optical process that involves the interaction of light with vibrational modes of the medium.

Quiz 5: Fiber Optics and Dispersion