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Lasers and Integrated Optics M (ENG5298)
Semiconductor Lasers Assignment
You should prepare a report of not more than 3 pages addressing the points and questions set out
below. The report should be handed in to the Teaching Office by 1700 on Monday 18 November
2019.
Please note that late submissions will be subject to the penalties set out in the Code of Assessment.
(a) What is meant by mode locking in a laser?
(b) How would you design a 1.5 µm edge-emitting semiconductor laser to generate a 40 GHz pulse
stream? You should consider factors such as the length of the cavity, the refractive index of the
material, and indicate other typical dimensions of the device. How many wavelengths does the
cavity length correspond to?
(c) Develop a simple numerical model for the 1.5 µm laser you designed in part (b). Use it to
demonstrate how the addition of several longitudinal modes leads to the formation of pulses.
The model can be based on Python, MATLAB or similar, or even Excel.
Use the equation from the lecture notes:
𝐸(𝑡) = ∑𝐸𝑛 exp{𝑗[(𝜔0 + 𝑛𝛥𝜔)𝑡 + 𝜙𝑛]}𝑛
where 𝜔0 is an arbitrarily chosen resonant frequency of the cavity
and
𝑃 ∝ 𝐸(𝑡)𝐸∗
(𝑡)
(d) Using the model, show what happens when the phase angles of the modes are all set at zero.
(e) Show what happens when the modes have random phase angles.
(f) What happens when the modes have different amplitudes?
J. H. Marsh Nov 2019