Read the passage and answer the questions that follow on your understanding of the passage : Optical fibre communication is one among the new techniques have come up and are extensively used for communication purposes. The portion of the e.m. spectrum encompasses the optical region falls in the wavelength of 50 nm (Ultraviolet) to approximately 100 µm (Infrared) which includes visible light spectrum from 400 nm (Violet) to 700 nm (Red). The order of frequency corresponding to these wavelengths falls in the range 1014 to 1018 Hz. There are two types of transmission media used for optical communication i.e., atmospheric channel and guided wave channel. Out of the two, guided wave channel provide much more reliable and versatile medium of communication. The medium used for guided channels in optical range are non-metallic guides popularly known as optical fibre. The optical fibre link used for communication applications has several advantages over conventional copper cable links which makes possible to send much more data over long distances with negligible attenuation. Although some difficulties do exist in the making of optical fibre set and there are some challenges being faced yet this type of communication mechanism has made a great impact in the present scenario.
Following is not the usual classification of an optical fibre :
single mode graded index
Three classes are standard; single-mode graded index is the one that is not — option 2 — and the reason is that grading would have nothing to do.
| Class | Core | Usual? |
|---|---|---|
| Single mode step index | 8 – 10 µm | ✓ Long haul |
| Single mode graded index | — | ✗ |
| Multimode step index | 50 – 200 µm | ✓ Short, low cost |
| Multimode graded index | 50 – 62.5 µm | ✓ Building, data centre |
What grading is for. A graded index exists solely to cure intermodal dispersion — the pulse spreading that arises because different modes take paths of different length. Grading the profile lets the longer, off-axis paths run through lower-index glass where the light travels faster, so all the modes arrive at nearly the same instant.
Why that is pointless in single-mode fibre. A single-mode fibre supports exactly one mode — that is what its name means, and the condition
\(V=\dfrac{2\pi a}{\lambda}NA\lt2.405\)
is what enforces it. With one path there is no path-length difference, so intermodal dispersion is already zero. Grading the profile would add manufacturing complexity to solve a problem the fibre does not have.
What limits single-mode fibre instead is chromatic dispersion — different wavelengths within the source's linewidth travelling at slightly different speeds. Grading the index radially does nothing about that, since the effect is a property of the material and the waveguide as a whole rather than of the ray path. It is tackled differently: by narrow-linewidth laser sources, by operating near the 1310 nm zero-dispersion wavelength, and by dispersion-shifted or dispersion-compensating fibre — which do use tailored index profiles, but to move the zero-dispersion point rather than to equalise mode delays.
The classification in one line : the mode count is decided by the core diameter, and the profile is chosen only when more than one mode is present.
Hence, the classification that does not usually exist is single mode graded index.
Similar Questions
The core of an optical fiber has
The core diameter of single mode fiber is in the order of
Consider the following statements :
Losses in optical fibers are caused by
1. Impurities in the fibre material
2. Microbending
3. Splicing
4. Step index profileOf these statements :
Assertion (A) : Optical fibers have broader bandwidth compared to conventional copper cables.
Reason (R) : Low power LASER beams are considered to be very powerful as compared to high power ordinary light beams.
The following is true for the multimode graded index fiber :
1. The refractive index varies as a function of radial distance from the centre.
2. The refractive index undergoes sudden change at the cladding boundary.
3. It provides better bandwidth and the data rate than the multimode step index.
4. It provides the better bandwidth and data rate than single mode step index.A multimode step-index fibre has glass core (n1 = 1.5) and fused quartz cladding (n2 = 1.46), which one of the following is the value of acceptance angle ?
Which of the following are the cases of signal attenuation ?
1. Splicing
2. Intermodal Delay
3. Scattering
4. Chromatic Dispersion(A) Multimode fibre is less lossy than single mode
(B) The bandwidth of step index fibre is 50 MHz
(C) The graded index fibre has theoretically infinite bandwidth
(D) The step index fibre has numerical aperture of 0.2 to 0.5
(E) The graded index fibre has numerical aperture of 0.46 to 0.99Choose the most appropriate answer from the options given below :
If numerical aperture and fractional refractive index of an optical fibre are 0.22 and 0.012, respectively. The refractive index of core (µ1) and cladding (µ2) will be
An optical fibre has numerical aperture (NA) of 0.3 and refractive index $\eta_2$ of cladding material is 1.6. What is the refractive index of core material?
Important Questions from Optical Fiber
What is the relation between the refractive index of core n1 and cladding n2?
Graded index fiber is used to
In a multimode fiber (step index), number of modes passing at an operating wavelength of 1300 nm are 1000, the refractive index of the core is 1.50 and that of the cladding is 1.48. The value of core diameter is:
In optical fibers, the Rayleigh scattering is proportional to:
Fibre optic power meters have input for attaching fiber optic connector and detector:
