An optical device includes: a waveguide array including a plurality of waveguides; and a pulse generator. The waveguides are arranged in a first direction and extend in a second direction intersecting the first direction. The pulse generator inputs, as an input light beam, a light pulse of light to each of the waveguides. The light has a frequency spectrum in air with a maximum peak at a frequency corresponding to a wavelength λ, and the full width at half maximum of the maximum peak is Δν. The waveguides propagate the input light beams in the second direction and emit part of the input light beams as emission light. The pulse generator adjusts the difference in phase between input light beams to be inputted to two adjacent waveguides of the plurality of waveguides to thereby change a first direction component of an emission direction of the emission light.