DP Physics Questionbank
C.3 – Fibre optics
Description
Nature of science:
Applied science: Advances in communication links using fibre optics have led to a global network of optical fibres that has transformed global communications by voice, video and data. (1.2)
Understandings:
- Structure of optic fibres
- Step-index fibres and graded-index fibres
- Total internal reflection and critical angle
- Waveguide and material dispersion in optic fibres
- Attenuation and the decibel (dB) scale
Applications and skills:
- Solving problems involving total internal reflection and critical angle in the context of fibre optics
- Describing how waveguide and material dispersion can lead to attenuation and how this can be accounted for
- Solving problems involving attenuation
- Describing the advantages of fibre optics over twisted pair and coaxial cables
Guidance:
- Quantitative descriptions of attenuation are required and include attenuation per unit length
- The term waveguide dispersion will be used in examinations. Waveguide dispersion is sometimes known as modal dispersion.
Data booklet reference:
International-mindedness:
- The under-sea optic fibres are a vital part of the communication between continents
Utilization:
- Will a communication limit be reached as we cannot move information faster than the speed of light?
Aims:
- Aim 1: this is a global technology that embraces and drives increases in communication speeds
- Aim 9: the dispersion effects illustrate the inherent limitations that can be part of a technology
Directly related questions
- 16N.3.SL.TZ0.14b: Explain why graded-index fibres help reduce waveguide dispersion.
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16N.3.SL.TZ0.14a:
State the main physical difference between step-index and graded-index fibres.
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17M.3.SL.TZ1.8a.i:
State two advantages of optic fibres over coaxial cables for these transmissions.
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17M.3.SL.TZ1.8a.ii:
Suggest why infrared radiation rather than visible light is used in these transmissions.
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17M.3.SL.TZ1.8b:
A signal with an input power of 15 mW is transmitted along an optic fibre which has an attenuation per unit length of 0.30 dBkm–1. The power at the receiver is 2.4 mW.
Calculate the length of the fibre.
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17M.3.SL.TZ1.8c:
State and explain why it is an advantage for the core of an optic fibre to be extremely thin.
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17M.3.SL.TZ2.10a:
The diagram shows a ray of light in air that enters the core of an optic fibre.
The ray makes an angle A with the normal at the air–core boundary. The refractive index of the core is 1.52 and that of the cladding is 1.48.
Determine the largest angle A for which the light ray will stay within the core of the fibre.
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17M.3.SL.TZ2.10b.i:
Identify the features of the output signal that indicate the presence of attenuation and dispersion.
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17M.3.SL.TZ2.10b.ii:
The length of the optic fibre is 5.1 km. The input power of the signal is 320 mW. The output power is 77 mW. Calculate the attenuation per unit length of the fibre in dBkm–1.
- 20N.3.SL.TZ0.13: A single pulse of light enters an optic fibre which contains small impurities that scatter the...
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17N.3.HL.TZ0.15a:
Calculate the maximum angle β for light to travel through the fibre.
Refractive index of core = 1.50
Refractive index of cladding = 1.48 - 17N.3.HL.TZ0.15b: Outline how the combination of core and cladding reduces the overall dispersion in the optic fibres.
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18M.3.SL.TZ2.10b.i:
Calculate the maximum attenuation allowed for the signal.
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18M.3.SL.TZ2.10a:
An optic fibre of refractive index 1.4475 is surrounded by air. The critical angle for the core – air boundary interface is 44°. Suggest, with a calculation, why the use of cladding with refractive index 1.4444 improves the performance of the optic fibre.
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18M.3.SL.TZ2.10b.ii:
An amplifier can increase the power of the signal by 12 dB. Determine the minimum number of amplifiers required.
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18M.3.SL.TZ2.10b.iii:
The graph shows the variation with wavelength of the refractive index of the glass from which the optic fibre is made.
Two light rays enter the fibre at the same instant along the axes. Ray A has a wavelength of λA and ray B has a wavelength of λB. Discuss the effect that the difference in wavelength has on the rays as they pass along the fibre.
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18M.3.SL.TZ2.10c:
In many places clad optic fibres are replacing copper cables. State one example of how fibre optic technology has impacted society.
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18M.3.SL.TZ1.9a:
Calculate the critical angle at the core−cladding boundary.
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18M.3.SL.TZ1.9b:
The use of optical fibres has led to a revolution in communications across the globe. Outline two advantages of optical fibres over electrical conductors for the purpose of data transfer.
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18M.3.SL.TZ1.9c.i:
Draw on the axes an output signal to illustrate the effect of waveguide dispersion.
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18M.3.SL.TZ1.9c.ii:
Calculate the power of the output signal after the signal has travelled a distance of 3.40 km in the fibre.
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18M.3.SL.TZ1.9c.iii:
Explain how the use of a graded-index fibre will improve the performance of this fibre optic system.
- 18N.3.SL.TZ0.10b.iii: Suggest whether this fibre could be used to transmit information at a frequency of 100 MHz.
- 18N.3.SL.TZ0.10a.ii: The refractive indices of the glass and cladding are only slightly different. Suggest why this is...
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18N.3.SL.TZ0.10b.i:
Show that the longest path is 66 m longer than the shortest path.
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18N.3.SL.TZ0.10a.i:
Calculate n.
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18N.3.SL.TZ0.10b.ii:
Determine the time delay between the arrival of signals created by the extra distance in (b)(i).
- 19M.3.SL.TZ2.12biv: A signal consists of a series of pulses. Outline how the length of the fibre optic cable limits...
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19M.3.SL.TZ2.12biii:
Explain the shape of the signal you sketched in (b)(ii).
- 19M.3.SL.TZ2.12a: Outline the differences between step-index and graded-index optic fibres.
- 19M.3.SL.TZ2.12bii: An input signal to the fibre consists of wavelengths that range from 1299 nm to 1301 nm. The...
- 19N.3.SL.TZ0.9a: Describe why a higher data transfer rate is possible in optic fibres than in twisted pair cables.
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19N.3.SL.TZ0.9b(ii):
Determine the distance at which the signal must be amplified.
- 19N.3.SL.TZ0.9b(i): State one cause of attenuation in the optic fibre.
