Design of widely tunable semiconductor lasers usinggrating-assisted codirectional-coupler filters

The analysis and design of widely tunable semiconductor lasers using grating-assisted codirectional-coupler filtering in a vertical twin-guide structure are considered. An orthogonal coupled mode formalism is applied to obtain the important design parameters for the filter. It is shown that there is a tradeoff between tuning range and spectral purity when using this type of filter as an intracavity mode selector. Practical laser structures are presented, and design considerations and limitations are discussed for GaAs and InP material systems with lasing wavelengths around 0.98 and 1.55 μm, respectively