Question

cavity? Q5. Single frequency lasers Consider a DFB laser operating at 1550 nm. Suppose that the re- fractive index n = 3.4 (InGaAsP). What should be the corrugation period A for a first order grating 9 = 1. What is A for a second order grating, 9 = 2. How many corrugations are needed for a first order grating if the cavity length is 2017 How many corrugations are there for q - 2? Which is easier to fabricate?

Answer 1

Bragg-wavelength Ag is given by the condition for in-phase interference =2A n On rearranging, A=q. 2n For q 1 = 1550 um A=1x 2x3.4 0.23 um Cavity length Number of corrugations is, Ncarugations Corrugation period L Namgations 50 μη 0.23 um =219 For q 2 1550 m A=2x 2x3.4 Ξ0.46 μπm Cavity length Number of corrugations is, carugations Corrugation period camugations 50 μη 0.46 um = 109 From the above results, the corrugation dimension (A)is larger and number of corrugations are smaller for q 2 which would be easier to fabricate