A compact digitally tunable seven-channel ring laser

A seven-channel ring laser was realized by monolithic integration of a compact 4/spl times/4 PHASAR (de)multiplexer with four amplifiers in InP. The PHASAR was fabricated using a double-etch technique, enabling a total size of the ring laser of only 1/spl times/1.5 mm/sup 2/. Light was coupled out via the outer array waveguides. Reflections are minimized by using mode filters and angled facets. Threshold-currents of 70 mA and a sidemode suppression ratio of 40 dB were measured. In principle, a ring laser with N amplifiers can produce 3N-3 different wavelengths.