3. A semiconductor laser has a total current that comprises a bias current IDc and a small signal ac current iac. The laser threshold current is 1th = 50 mA. When IDC = 75 mA and iac = 0, the laser output power is P = 2.5 mW. (a) What is the ac component of the modulated optical power at low frequencies when the laser is driven by a small signal current iac having a peak value of 10mA? 4.0 3.5 3.0 |P(t) = PDC + Pac cos(at) ас Optical Power (mW) 2.5 2.0 1.5 1.0 0.5 0 25 50 50 55 60 Threshold current ID (t) = 75 mA D'C = 75 mA + 10 mAxcos (wt) AC waveform Input current TIME 80 85 TIME Output Optical Power waveform 90 95 100 Current (mA)