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We report a novel linear-in-wavenumber (k-linear) swept laser source based on an acousto-optic deflector (AOD). The AOD-based optical filter includes an acousto-optic deflector and a reflection grating. The laser may tune k linearly in wavenumber over time due to its appropriate configuration and is favorable for fast imaging because it avoids data resampling and recalibration, as are required in conventional swept source optical coherence tomography (SS-OCT). We achieved k-linearity with Pearson's r correlation coefficients of 0.99995 without and 0.99997 with optimization. The laser has a tuning range of 50 nm, a 3 dB swept range of 42 nm (FWHM), output power of 2.56 mW, 6 dB sensitivity roll-off depth of 0.941 mm, and central wavelength of 1064 nm at a scanning rate of ∼20 kHz. Scanning rate as high as ∼400 kHz is also achieved for this laser with the tuning range 49 nm, swept linearity of 0.99990, output power of 2.30 mW, and a 6 dB sensitivity roll-off depth 0.550 mm. SS-OCT imaging with linear-in-wavenumber swept laser is also demonstrated.