Exercise 3. Laser dynamics in a ring cavity
Consider a ring cavity like the one depicted in Fig. 3. Assume that the mirrors are perfectly reflective and that the small signal gain coeƯ icient is 1.2m-1. The saturated power of the amplifier is 100mW.
Figure 3. Layout of a ring cavity. The optical amplifier displays gain saturation for high input powers. The laser is initiated by a small amount of spontaneous emission radiation.
3.1 Neglecting cavity losses, design the output coupler so that it maximizes the output signal. Starting from a seed signal (equivalent to 0.1nW), analyze the evolution of the following parameters, in a roundtrip-by-roundtrip manner, and compare your results to the expectations from the theory:
a. Amplifier gain
b. Output power
c. Intracavity power
3.2 How do the steady state dynamics change when you consider that the amplifier also adds a small noise power of 0.1nW every round trip?