32 nm digitally tunable laser diode with a 0.58 nm wavelength grid using a vertically integrated Mach-Zehnder interferometer

A forward-coupling laser is presented that uses a monolithically integrated Mach-Zehnder interferometer (MZI) inside the laser cavity for discrete wide wavelength tuning. The electronically tunable MZI filter selects one individual mode out of the discrete Fabry-Ṕrot spectrum. The emission wavelength is thereby controlled by one current only. Internal reflections are a key issue for all forward coupling lasers as they limit the number of accessible modes. Employing an appropriate optical resonator design, the present laser structure overcomes this drawback and demonstrates full and regular wavelength accessibility across the free spectral range of 32 nm.