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We theoretically analyze and experimentally demonstrate improved half-wave couplers for widely tunable V-cavity lasers. An overlapping-image 6×6 MMI coupler and an aggregating-image 16×16 MMI coupler are investigated, which give optimal coupling phase and coefficient for achieving high single-mode selectivity in V-cavity lasers while producing a low loss. A single-electrode controlled tuning of 38 channels is achieved with channel spacings of 100 GHz and 150 GHz. By combining two single-electrode tuning segments at different temperatures, a wavelength tuning range of 52 channels from 1515 nm to 1585 nm is obtained, and the side mode suppression ratios (SMSRs) reach 45 dB.