A monolithic widely tunable semiconductor laser based on a double-ring resonator is developed for use in a wavelength-routing switch. By using the double-ring resonator as a wavelength-selective filter, operation over a wide wave-length tuning range is achieved with a low tuning current. This low-tuning-current operation makes the laser very promising as a high-speed tunable light source for a wavelength-routing-based switch by effectively suppressing the thermal wavelength drift induced by current injection. In addition, the laser fabrication process is simpler compared to conventional distributed Bragg reflector tunable lasers. A tuning range of 50.0 nm, covering the entire C-band, is successfully demonstrated with an injection current of less than 5.2 mA. The wavelength drift caused by the thermal transients is less than 5 GHz.
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