Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 9

In a multiple quantum-well laser the temperature dependence of the differential or external quantum efficiency can be described by 57
where i ( T ) is the internal quantum efficiency, end is the mirror loss of the lasing cavity as given in Eq. (4.28), N w is the number of quantum wells, T th is the threshold temperature, w is the internal loss of the wells at T = T th and is a temperature-dependent internal- loss parameter. Consider a six-well, 350- µ m-long MQW laser having the following characteristics: w = 1.25 cm -1 , = 0.025 cm -1 /K, and T th = 303 K. The lasing cavity has a standard uncoated facet on the front ( R 1 = 0.31) and a high-reflection coating on the near facet ( R 2 = 0.96).
( a ) Assuming that the internal quantum efficiency is constant, use a computer to plot the external quantum efficiency as a function of temperature over the range 303 K T 375 K. Let ext ( T ) = 0.8 at T = 303 K.
( b ) Given that the optical output power at T = 303 K is 30 mW at a drive current of I d = 50 mA, plot the power output as a function of temperature over the range 303 K T 375 K at this fixed bias current.