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We describe widely tunable lasers incorporating microring resonators. By using a double-ring-resonator-coupled filter, a wide wavelength tuning range is achieved with a low tuning current. A double-ring-resonator-coupled tunable laser has series-connected microring resonators in the laser cavity. A tuning range of 50 nm is achieved with injection current of less than 5.2 mA. This low injection current reduces the frequency drift caused by thermal transients to less than 5 GHz. We also describe an integrated filtered feedback tunable laser consisting of a Fabry-Perot (FP) laser and integrated filtered feedback sections. In this device, the filter section is removed from the laser cavity. The device exhibits a 24-nm tuning range with a side-mode suppression ratio of 50 dB. The frequency drift is less than 1 GHz because the longitudinal mode of the laser is mainly determined by the FP laser section. We have also developed a filter-free widely tunable wavelength converter by monolithically integrating a tunable laser and a wavelength converter based on a semiconductor optical amplifier. Wavelength conversion for a 10-Gb/s nonreturn-to-zero signal is also demonstrated, tunable over a 40-nm range.