1. Calculate the acceptance angle of single-mode fibre at wavelength 1.55um with parameters 2, 4 um core radius, fractional index contrast 0.03 and 1.45 refractive index.

2.In older-generation optical communications networks, LEDs were used as light sources.

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Explain why LEDs might not be the best option for fibre optics networks.

What improvements has the laser diode made to the network performance

3.Calculate the responsivity a p–i–n photodiode at 1.55 um and 1.3 um if its quantum efficiency is 80%.

Why is the photodiode less responsive at 1.55 um

4.How do you encode 4 bits per symbol in a single code?

Sketch the structure of a transmitter for multilevel modulation. Explain the roles of each part in the encoding process.

5.Depending upon the direction and wavelength of light propagation, an individual port may be used as an input port or output port.

What other features can this device support?

Answer to Question: ELG5381 Photonics Networks

Question 1

Question 2

LEDs are used for fiber optic communication networks.

LEDs aren’t the best choice, however. Because they emit incoherent radiation with a broad spectrum because they produce light by spontaneous emission, they can be difficult to read.

Because of this, LED-based transmitters cannot transmit data over a distance greater than chromatic diffusion.

LED transmitters cannot also be coupled into multimode fibre because the LED’s light is not directional.

Furthermore, the LEDs can only be used for a very small fraction of the light, making them less efficient.

Laser diode transmitters were invented to overcome the many limitations that LED transmitters had.

Laser diode transmitters have a higher output, which is why they are more efficient.

The output of a laser transmitter can be oriented, making it possible to use single mode fibers. This results in a higher level and longer distance transmission.

The coherent light output of laser diode transmitters means that light energy can only be transmitted in one frequency, which reduces the possibility of modal dispersion.

Both LEDs and laser dimers can be modulated by direct, but the latter has higher data rates.

Question 3

A p -i-n pixel photodiode’s response is defined as the ratio of the optical power input to the electrical output.

The wavelength in micrometers is where, and the quantum efficacy is there.

Responsivity of 1.3 micrometers

Responsivity is at 1.55 Micrometers

Higher responsivity will be observed when the wavelength exceeds 1.55 micrometers. Because responsivity has a direct proportional relationship to wavelength, it is possible to observe a higher responsivity.

Because of this, higher wavelengths are expected to have a higher response than those with smaller wavelengths.

Question 4

For multilevel modulation, quadrature-amplitude modulation is possible.

The transmitter figure shows that a 16QAM can encode 4 bits for each symbol.

The transmitter incorporates both phase modulation (and amplitude) modulation functions.

The 16-QAM transmitter uses 16 constellations points on the constellation quad.

Figure 1: The block diagram for a 16-QAM. Readinggrat, 2017.

The input data are divided into four channels (I, I’ Q, and Q).

Each channel’s bit rate is equal quarter of the input bitrate.

This is called f/4.

“The 2-4 level converters produce a 4-level pulse amplitude modulation signal (PAM), which modulates the quadrature carrier and in-phase carrier of the product modulators.

The linear summer merges outputs from Q and I channels, producing 16 desired output conditions.

Question 5

Multicasting can also be allowed in systems with multiple input port that direct a wavelength towards the output ports.

Multicasting of light signals can be possible when the output port is used for the output and the input ports serve as the output ports.

ReferencesReadinggrat. (2017). Quadrature Amplitude Modulation [Photograph]. Retrieved from

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