Hw10-1_2 - density, J th . (d) If the pump current is 15mA,...

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2 Part B. Laser (Due: March 3, 2010, Wed) 5. Quaternary alloy In 1-x Ga x As y P 1-y , which is lattice-matched to InP, is used in making laser. The corresponding Eg is given by Eg =1.35-0.72y+0.12 y 2 (0 y 1) and x/y=0.45 (required for lattice matching). (a) Find the energy gap value if the desired lasing frequency is 193.3 THz. (b) Find the corresponding x and y value. 6. Review the discussion about laser rate equation and the work on the following problem. Assume a Fabry-Perot laser cavity has length=100 μ m, width=10 μ m, thickness=0.25 μ m, refractive index=3.5, and internal absorption α int =20cm -1 . The reflectivities of the two cavity end facets are 0.3 and 0.5, respectively. (a) Estimate the number of longitudinal modes and lateral modes between 1540nm and 1560nm. (b) Find the threshold gain of the cavity and the photon lifetime. (c) If the threshold current is I th =3mA. Find the corresponding threshold current
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Unformatted text preview: density, J th . (d) If the pump current is 15mA, what is the number of photons generated per second? 7. The laser threshold current has been reduced substantially since the inception of semiconductor laser in the 1960s. State what have contributed to this reduction. 8. If a laser has a threshold current at 15mA and a maximum output power 0dBm at 65mA. Assume the P-I curve is linear when operates above the threshold current. (a) Find an expression for the output power (in mW) with a sinusoidal input 40+5cos( ω t) mA. (b) If now the laser is not perfect with d 2 P/dI 2 | I=40mA =0.005 (W/A 2 ). Use Taylor series expansion for P(I)| I=40mA and then find the corresponding optical power (in mW) of the second harmonic term (at 2 ω ) and the 2 nd-order Harmonic Distortion (in dB). ~~ END ~~...
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