Abstract: A tunable laser includes an optical waveguide alternately including a gain waveguide portion and a wavelength controlling waveguide portion, and a diffraction grating. The diffraction grating includes a gain diffraction grating and a wavelength controlling diffraction grating. A wavelength controlling region is configured such that the wavelength controlling waveguide portion and the wavelength controlling diffraction grating are included therein. A gain region is configured such that the gain waveguide portion and the gain diffraction grating are included therein. The Bragg wavelength of the wavelength controlling region is longer than that of the gain region in a state in which current injection or voltage application is not performed for the wavelength controlling waveguide portion.

Abstract: A wavelength tunable laser is constituted by including a resonator composed of a pair of reflectors arranged to face each other, and inside the resonator, a SOA radiating a laser beam with a gain for a wide range of wavelengths, a transmission-type wavelength tunable filter having an asymmetric filter characteristic, and a phase controller controlling a phase of the laser beam resonating inside the resonator.

Abstract: A wavelength tunable laser device includes: a pair of reflection mirrors; a semiconductor element disposed between the pair of reflection mirrors, the semiconductor element integrating a region for providing an optical gain, a region having a wavelength tunable filter function and a phase control region; and an optical filter disposed between the semiconductor element and one of the pair of reflection mirrors, the optical filter having periodical transmission wavelengths. A wavelength tunable laser device is provided which is easy to be controlled and can be made compact.

Abstract: There is provided a phase control portion for controlling phase of a laser beam resonated in a resonator based on detected results by two optical detectors. The phase control portion adjusts the longitudinal mode positions by a feedback control so that a ratio of intensities detected by the two optical detectors comes to a predetermined reference value. To one of the optical detectors, part of a laser beam outputted from the resonator is irradiated as it is, whereas, to the other one of the optical detectors, part of the laser beam outputted from the resonator is irradiated after passing through an etalon. An FSR of the etalon is a double of that of another etalon in the resonator.

Abstract: A wavelength-selectable laser with a resonance region formed by two reflecting surfaces include a gain medium generating a laser beam, a first filter, and a second filter. The first filter has a first controllable transmission region and transmits a first predetermined wavelength region of the laser beam generated in the gain medium, the first predetermined wavelength region matching the first controllable transmission region. The second filter has a plurality of periodically arranged second transmission regions and transmits a second predetermined wavelength region of the laser beam transmitted by the first filter, the second predetermined wavelength region matching one of the second transmission regions.

Abstract: There are provided a wavelength selection device, a wavelength selection laser, and a tunable laser for suppressing adverse effects of non-selected light when selected light is obtained by the wavelength selection device. A linear polarizer is arranged on a side of the wavelength selection filter from which an incoming light enters, and a first faraday element and a second faraday element each for rotating the polarization of light by 45 degrees are arranged at respective locations between the linear polarizer and the wavelength selection filter, and between the wavelength selection filter and a reflection mirror for reflecting light having passed through the wavelength selection filter. After then incoming light has passed through the linear polarizer, selected light passes through the wavelength selection filter and is reflected by the reflection mirror, while non-selected light is reflected by the wavelength selection filter.

Abstract: A wavelength-selectable laser with a resonance region formed by two reflecting surfaces include a gain medium generating a laser beam, a first filter, and a second filter. The first filter has a first controllable transmission region and transmits a first predetermined wavelength region of the laser beam generated in the gain medium, the first predetermined wavelength region matching the first controllable transmission region. The second filter has a plurality of periodically arranged second transmission regions and transmits a second predetermined wavelength region of the laser beam transmitted by the first filter, the second predetermined wavelength region matching one of the second transmission regions.