Widely tunable laser diodes with vertically integrated Mach-Zehnder interferometer (VMZ)

Different design approaches and the corresponding fabrication technology of widely tunable lasers with vertically integrated Mach-Zehnder interferometer (VMZ) have been investigated with respect to the spectral selectivity and tuning performance. Calulations show for designs with InGaAsP bulk material as active region that a tuning range of 75nm and a side-mode suppression ratio (SSR) of more than 30dB are feasible. The tuning range can be further extended using multiple quantum well heterostructures as active regions. They enable tuning ranges covering the whole material gain spectrum, but with a reduced SSR. Due to the codirectional mode coupling of the laser, the use of an appropriate facet coating allows an enlargement of the SSR to more than 30dB even for the large tuning range designs. We present the different design concepts and discuss the theoretical data as well as the first experimental results of the corresponding VMZ-laser devices. The measured spectrum of the laser shows an SSR close to the theoretically predicted value.