In DFB lasers, the submode suppression ratio and the Bragg wavelength are determined by the coupling coefficient and effective refractive index of the grating, respectively. Both are sensitive to corrugation depth and width. In the conventional grating fabrication process using optical interference lithography and wet etching, the corrugation geometry is difficult to control. However, the ratio of the resist width to the period can be controlled by electron-beam direct writing and can be transferred to the substrate without severe undercut by reactive ion etching. Therefore, the depth and width of the grating groove can be optimized independently. Previously, 1.5-μm DFB lasers with second-order gratings have been fabricated using electron-beam direct writing and ion-beam milling.1 However, the resultant devices had a threshold current of 80-300 mA. Here we report the performance of λ/4-shifted 1.5-μm DFB-SIPBH lasers with first-order gratings defined by electron-beam lithography and reactive ion etching.
© 1989 Optical Society of AmericaPDF Article