Computer-generated holograms with error compensation for recording phase-shifted DFB laser corrugations.
In a recent publication by Freude et al. it was shown that computer-generated holograms (CGH) of Lohmann type III with expansion of the amplitude dynamic (D), circular overflow correction (OFC), and one-step overall error compensation (EC) are useful for reconstructing and analyzing very complicated optical fields. Likewise, formerly we presented an example of a sinelike line grating with an in-between phase shift of 180 degrees ; such a structure is interesting as a simple illuminator for the photoresist masking of lambda/4-shifted semiconductor DFB lasers. This sixth-order grating was dimensioned to have P = 25.5 spatial periods of length Lambda = 6 xLambda(B), Lambda(B) = 0.223 microm for a total extension of y(K) = 33 microm when reconstructing the CGH at the encoding wavelength of 0.2578 microm. Now, after a change of the CGH program structure, we are able to generate and to reconstruct fourth-order gratings with P = 250, Lambda = 4 x Lambda(B), and y(K) = 224 microm reaching our present technological limit. We describe our production process and discuss the influence of the Talbot effect on the reconstruction. Finally, we give theoretical and practical limitations for the generation of such gratings.
W
W
Freude
H M
HM
Chen