Abstract: A semiconductor laser diode (LD) has been disclosed, where the emission efficiency is independent on a thickness of the p-type cladding layer. The LD provides a first semiconductor region made of group III-V compound semiconductor material, a mesa region and a burying region. The burying region, disposed on the first region, buries the mesa region. The mesa region includes an active layer, a cladding layer with a first conduction type, another cladding layer with second conduction type and a contact layer with the second conduction type. The LD of the invention in the contact layer thereof contains aluminum (Al) and indium (In) for group III element, while, arsenic (As) for group V element.

Abstract: The present invention provides a light-emitting device with a quantum well structure comprising a barrier layer containing aluminum, gallium, indium and arsenic, which reduces the leak current flowing in the buried layer. The buried layer includes first and second buried layers stacked to each other and covers the sides of the quantum well structure. The barrier layer induces a tensile stress to lower the band gap energy, to increase the band gap wavelength ?BG greater than or equal to 1.0 ?m.

Abstract: A light-emitting device including an active region having a quantum well structure formed by a first barrier layer made of a first III-V compound semiconductor material that contains aluminum, gallium, indium, and arsenic, and a quantum well layer made of a second III-V compound semiconductor material. The device also includes a buried semiconductor region provided on sides of the quantum well layer. The first III-V semiconductor material has a band gap wavelength greater than 1 ?m.

Abstract: There is disclosed an optical switch for switching between a plurality of main light emitters respectively emitting light components having wavelengths different from each other and a backup light emitter adapted to replace any of the main light emitters, a light emitter switching method for switching from one failed main light emitter to a backup light emitter by using the optical switch the above switch and a light receiver switching method for switching from one failed main light receiver to a backup light receiver by using the above.

Abstract: There is disclosed an optical switch for switching between a plurality of main light emitters respectively emitting light components having wavelengths different from each other and a backup light emitter adapted to replace any of the main light emitters, a light emitter switching method for switching from one failed main light emitter to a backup light emitter by using the optical switch the above switch and a light receiver switching method for switching from one failed main light receiver to a backup light receiver by using the above.