Asymmetric twin-waveguide design offers manufacturing efficiency

Hassaun Jones-Bey

Princeton University researchers have fabricated 1550-nm, multiquantum-well (MQW) distributed Bragg reflector (DBR) lasers using an asymmetric twin-waveguide (ATG) design to facilitate low-cost manufacturing.1 The ATG design is based on two vertically stacked waveguides that are strongly coupled but separated by a cladding structure (see figure). The devices were grown on an n-doped indium phosphide (InP) structure using a single-step gas-source-molecular-beam-epitaxy (GSMBE) process. Layers deposited during the single-step GSMBE process began with an InP buffer layer, followed by an indium gallium arsenide phosphide (InGaAsP) passive waveguide, an InP cladding layer, followed by an active waveguide built around three InGaAsP quantum wells, followed by an InP top cladding and an InGaAsP contact layer. The grating section was produced using a simple process of near-field holographic printing through a phase mask.

The researchers fabricated several devices with varying active-region lengths and varying placement of grating sections. The emission wavelength of these devices was 1543 nm and output powers exceeded 11 mW, with a side-mode suppression ratio in excess of 40 dB and a slope efficiency of 0.11 W/A when operated in pulsed mode. While the performance of the device is comparable to conventional discrete DBR lasers, the researchers say the twin-waveguide design provides compatibility with photonic integrated circuits. Stephen Forrest, who leads the Princeton research team, described the ATG approach as providing "a versatile integration platform by which many different photonic devices can be fabricated using a single growth step." For more details, contact Stephen Forrest at [email protected].

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In a DBR laser based on an ATG structure, the MQW active waveguide contains the optical mode of the gain section and tapers provide low-loss coupling into the underlying passive waveguide.