Monolithic DWDM source with precise channel spacing

Abstract

We report a low-cost manufacturing approach for fabricating monolithic multi-wavelength sources for dense wavelength division multiplexing (DWDM) systems that offers high yield and eliminates crystal regrowth and selective area epitaxy steps that are essential in traditional fabrication methods. The source integrates an array of distributed feedback (DFB) lasers with a passive coupler and semiconductor optical amplifier (SOA). Ridge waveguide lasers with sampled Bragg side wall gratings have been integrated using quantum well intermixing to achieve a fully functional four-channel DWDM source with 0.8 nm wavelength spacing and residual errors < 0.13 nm. The output power from the SOA is > 10 mW per channel making the source suitable for use in passive optical networks (PONs). We have also investigated using multisection phase-shifted sampled gratings to both increase the effective grating coupling coefficient and precisely control the channel lasing wavelength spacing. An 8-channel DFB laser array with 100 GHz channel spacing was demonstrated using a sampled grating with two π-phase-shifted sections in each sampling period. The entire array was fabricated by only a single step of electron beam lithography.