Reference no: EM132595052

Question 1

A semiconductor laser can attain a maximum optical gain of g_max = 2000 m^-1. The attenuation to light propagation in the semiconductor material, without amplification, is 600 m^-1.

(i) If the reflection coefficients of the cavity reflectors are R₁ = R₂ = 0.35, what is the minimum value for the length of the cavity that must be used for the laser?

(ii) If the cavity length is required to be L = 475 μm and R₁ = R₂ = R, what is the minimum value for the reflector value R?

Question 2

The longitudinal modes of a semiconductor laser emitting at a wavelength of 1.1 μm are separated in wavelength by 0.8 nm. The refractive index of the semiconductor is n = 3.6.

(i) Determine the length of the optical cavity.

(ii) If the loss coefficient of the semiconductor is 1000 dB/m, what is the minimum gain coefficient, in dB/m, required for lasing.

Note: The power reflectivity of a surface between two materials of refractive indices n₁ and n₂ is given by:

R = (n₂ - n₁/n₂ + n₁)²

Question 3

If this laser is required to produce a single mode output at a wavelength of 1.32 μm:

(i) If gratings are used for this purpose, determine the design pitch of the grating that must be used.

(ii) Indicate the reasons for the great interest in such single mode semiconductor lasers.

Question 4

The light-current characteristic of the semiconductor laser is shown in Fig. 1. Assume that the laser is biased at 25 mA and that the frequency of the modulating signal is within the laser bandwidth.
(i) If the modulating current has a peak value of 10 mA,
a) Plot the input current and output power as a function of time
b) Does the laser behave as a linear device for this modulating current? Why?
(ii) If the modulating current has a peak value of 20 mA,
a) Plot the input current and output power as a function of time
b) Does the laser behave as a linear device for this modulating current? Why?

Question 5

Semiconductor lasers and light emitted diodes are commonly found in optical communication systems. Which of these optical sources are preferred for long distance communication systems? Why?