Multiwavelength DFB laser array utilizing combined effect of ridge width and ridge tilt

DFB laser arrays are of interest for application in high capacity fibreoptic communication systems employing wavelength division multiplexing (WDM). The comb of wavelengths produced from such an array must be accurately controlled, both in absolute wavelengths and wavelength separation between channels. The main issue in laser arrays is the mechanism used to control the lasing wavelength. By far the most popular method for wavelength control is to vary the grating pitch. This can be done by various techniques such as direct E-beam writing, E-beam generated phase mask or by the use of stepped holographic exposure. It is also possible to control the wavelength by varying the modal index of the waveguide structure. Selective area epitaxy can be used to laterally control the active layer thickness thereby controlling the modal index. On the other hand, we have explored and demonstrated a much simpler method of mode index control by sequentially incrementing the ridge widths in the laser array as well as incrementing the tilt angle of the laser ridge. This method is novel and very attractive because it uses a uniformly grown wafer and involves fewer processing steps. In the paper, the results of this scheme are described.