Question

Page 4 3. (a) Explain howa p-njunction can be used to make a diode laser. 4 marks (b) Sketch the ideal diode laser characteristic, indicating the spontaneous emission and stimulated emission regions and the threshold current. 2 marks State the threshold condition for laser action to occur in a laser diode of length L, absorption coefficient a, and gain coefficient y. The reflectivities of the cleaved planes of the laser diode are ri and F2 respectively. 1 marks Calculate the threshold forward current density required for lasing to occur in a diode laser with 1 1 In 2L = 10 cm-1 15 cm1. All symbols have their usual meanings. 3 marks B= 2.1 x 10-2 cm/A and a =

Answer 1

lasor diode foom Semicmduutor p.n Junehn diodes. foreword eleatrical h io's auross the la ser diode Couses the tuo species of Chorge Carrier holes cnd elechs o be "injeed from opposite stdes of vhe prn Junehan nto e deple tim regiom a subaset of the larger chsificotin of Light olp (pewery Spontoneouy emissieg rgim stimuloted emissien regin Current Trreshold Current cmly t a11 these emission Con be observed for a sem conduter laser reqwoements are sdtisfied stimuluted diode for Current evel belouo the fhershuld the emissm of the laser is spentoneou emissin. my for turent levels tigher them tue Current threinold the emissin is stimelokd Poation ut dain= exp (23) where the gaih coficient per unit leny thisgivenhy hain corfficient pes anit length m the case oftherhold tue fric tional losses heve to be egual fo the freutional gein so that ie Con define vhre shold geuin ttt R, R2 Thaeshold gain, 2L