A distributed feedback laser comprising: waveguide (4) having a hologram (10) capable of emitting radiation mode light in upper and lower directions; first reflector (20) provided below said waveguide for returning said radiation mode light back to said waveguide; and second reflector (21A, 21B, 21C, 21D, 21E) provided above said waveguide for returning said radiation mode light back to said waveguide, intensity profile of said radiation mode light on said waveguide being non-uniform is disclosed. Also, by using 2nd- or higher-order diffraction gratings having an asymmetric cross-sectional configuration together with a reflection structure located at one side thereof, a highly directional optical isolator can be provided. Further, the present invention provides an optical functional element comprising: first waveguide which guides optical waves and has a grain or a loss, said waveguide having a hologram (202) capable of coupling with said optical waves guided by said waveguide to generate radiation mode light; amplifier (203) for amplifying said radiation mode light released from said first waveguide and releasing it; and first reflector (204) for reflecting said radiation mode light emitted from said amplifier back to said first waveguide.