A distributed feedback semiconductor laser comprising a substrate and, on such substrate, a double heterostructure formed by a confinement layer, an active layer, a guiding layer engraved to form a diffraction network, the active layer and the guiding layer being engraved to form a ribbon having a certain width and a certain thickness and a central portion of larger width and thickness, a metal electrode surmounting the assembly and enabling charges to be injected through the ribbon, wherein the metal electrode comprises two distinct portions forming a first electrode disposed above the central widened or thickened portion of the ribbon, the first electrode being connected to a first connection for the injection of a first current and a second electrode disposed above the rest of the ribbon and connected to a second connection for the injection of a second current.

A semiconductor laser device includes an electron carrying layer formed on a semiconductor substrate. An active layer which includes a first straight active layer region having a first width and a second straight active layer region having a second width is formed on the electron carrying layer. Here, the first straight active layer region is joined to the second active layer, the second width is narrower than the first width, and the active layer radiates laser light in response to an application of a voltage higher than or equal to a predetermined voltage. A hole carrying layer is formed on the active layer in contact with the active layer.

A semiconductor laser device has a periodic structure for distributively feeding back light. A waveguide for guiding light along the periodic structure is provided. A plurality of waveguide regions having a light confinement coefficient set to vary along the periodic structure and an equivalent amount of phase shift with respect to the phase of the periodic structure set to an integer multiple of .pi. are provided. The total phase shifting amount of light by the waveguide is set to a value different from an integer multiple of .pi..

A laser using a distributed phase shift structure is disclosed. The active medium is formed in the shape of a stripe having first and second surfaces and two ends. The stripe includes a large central portion and two end portions with the central portion being of different widths than the two end portions. A laser device which utilizes the active medium of the present invention further includes at least one P-guide layer and at least one N-guide layer, both having a higher bandgap energy than the active medium. The P-guide layer and the N-guide layer are located on opposing surfaces of the active medium. A current which is injected through the N-guide layer, the P-guide layer and the active medium induces single mode, narrow linewidth coherent light to issue from the active medium.

A wavelength selective resonant grating exhibits transmission resonances when a single gap between two sections of a split gratings is used to provide a phase shift which is not a quarter wavelength in length or .pi./2 in phase. When the phase is changed to non - .pi./2 values (or the gap differs from a quarter wave), the transmission resonance moves from the center of the stop band. Appropriate adjustments of the phase over a .pi. interval allow tuning of the resonance across the entire stop band. The resonant optical wavelength grating can, illustratively, be used as wavelength filter, wavelength monitor, or as part of an Add/Drop arrangement.