SEMICONDUCTOR LIGHT EMITTING DEVICE

PURPOSE:To generate narrow beam width laser light by using a long external waveguide by providing a loss compensating unit which has an active layer for the external waveguide and by compensating the loss of light of the external waveguide by the loss compensating unit. CONSTITUTION:In a semiconductor light emitting device provided with a DFB laser unit 3 which emits single-wavelength laser light by pouring an active current Ia in the first active layer 1 and by selecting the light within a spectral width emitted from the first active layer 1 by using a diffraction grating 2 and an external waveguide 5 which makes the beam width of the laser light emitted from the DFB laser unit 3 narrow and is provided with a high reflecting mirror 4 on one end, a loss compensating unit 7 which provides the second active layer 6 for the above-mentioned external waveguide 5 is provided and the loss compensating unit 7 compensates the loss of light generated in the above-mentioned external waveguide 5. This semiconductor light emitting device can obtain the laser light wherein the beam width is made far narrower than that obtained by a conventional semiconductor light emitting device.