A double-heterostructure laser diode is used as a Fabry-Perot-type optical amplifier. When biased at the operating point it has a gain coefficient of 50 cm−1, a loss coefficient of 4 cm−1 and a...

A double-heterostructure laser diode is used as a Fabry-Perot-type optical

amplifier. When biased at the operating point it has a gain coefficient of

50 cm−1, a loss coefficient of 4 cm−1 and a confinement factor of 0.9. The

length between Fabry-Perot endfaces is 350 μm and the reflectivities of the

endfaces are both 33%.

(a) What is the overall gain of this optical amplifier?

(b) If the reflectivities of both endfaces are made very small so that the device

acts as a traveling wave amplifier, but the current through the device is

kept to be the same as in (a), what is the overall gain?