(Solved): 13.6 A double-heterostructure laser diode is used as a Fabry-Perot-type optical amplifier. When bia ...

13.6 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 $50{\mathrm{cm}}^{-1}$, a loss coefficient of $4{\mathrm{cm}}^{-1}$ and a confinement factor of 0.9 . The length between Fabry-Perot endfaces is $350\mu \mathrm{m}$ 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?