Monolithic, wavelength-tunable QCL devices are provided which comprise a substrate, an array of QCLs formed on the substrate and an optical beam combiner formed on the substrate electrically isolated from the array of QCLs. In embodiments, the QCL devices are configured to provide laser emission in the range of from about 3 m to about 12 m, a wavelength tuning range of at least about 500 cm.sup.1, and a wavelength tuning step size of about 1.0 nm or less.

A wavelength tunable laser device includes: a laser cavity formed of a grating and a reflecting mirror including a ring resonator filter; a gain portion; and a phase adjusting portion. The grating creates a first comb-shaped reflection spectrum. The ring resonator filter includes a ring-shaped waveguide and two arms and creates a second comb-shaped reflection spectrum having peaks of a narrower full width than peaks in the first comb-shaped reflection spectrum at a wavelength interval different from that of the first comb-shaped reflection spectrum. One of the peaks in the first comb-shaped reflection spectrum and one of the peaks in the second comb-shaped reflection spectrum are overlapped on a wavelength axis, and a spacing between cavity modes is narrower than the full width at half maximum of the peaks in the first comb-shaped reflection spectrum.

A tunable laser for tuning a lasing mode based on light beams travelling through at least one block of channel waveguides with at least two tunable combs, includes: a frequency selective optical multiplexer comprising a first terminal for receiving/transmitting light, at least one block of channel waveguides, each channel waveguide having a reflectively coated first tail and a second tail, and an optical coupling element optically coupling the first terminal with the second tails of the channel waveguides of the at least one block of channel waveguides, each of the channel waveguides having a different length; a gain element generating a broad spectrum of light, the gain element coupling the first terminal of the frequency selective optical multiplexer with a reflective element.

A laser comprising a laser cavity formed by a first optical reflector, a gain region, a second optical reflector having a plurality of reflection peaks, and at least one optically active region. The first mirror may be a DBR or comb mirror and the second mirror may be a comb mirror. The spectral reflectance of the second optical reflector is adjusted at least partially based on an electric signal received form the optically active region such that only one reflection peak is aligned with a cavity mode formed by the first and second reflector.

An optical transmitter that includes a wavelength tunable laser diode (LD) with a narrowed emission linewidth is disclosed. The optical transmitter further includes a feedback unit and an optical attenuator. The feedback unit, receiving a portion of laser light of the wavelength tunable LD, generates feedback light by rotating the polarization of the laser light by 905, and returns thus generated feedback light in the wavelength tunable LD. The optical attenuator adjusts power of the feedback light to reduce a line wide of the laser light, or frequency noises thereof.

A tunable laser source includes a mirror, a tunable filter, and a semiconductor optical amplifier integrated device including first, second, and third semiconductor optical amplifiers between a first end face facing toward the tunable filter and a second end face facing away from the first end face. The first amplifier is closer to the first end face than the second and third amplifiers. The semiconductor optical amplifier integrated device further includes a partially reflecting mirror and an optical divider that are disposed between the first amplifier and the second and third amplifiers. The partially reflecting mirror is closer to the first amplifier than the optical divider. The optical divider includes first and second branches connected to the second and third semiconductor optical amplifiers, respectively. The tunable filter and the first amplifier are disposed in an optical path between the partially reflecting mirror and the mirror that form a laser resonator.

Monolithic, wavelength-tunable QCL devices are provided which comprise a substrate, an array of QCLs formed on the substrate and an optical beam combiner formed on the substrate electrically isolated from the array of QCLs. In embodiments, the QCL devices are configured to provide laser emission in the range of from about 3 m to about 12 m, a wavelength tuning range of at least about 500 cm.sup.1, and a wavelength tuning step size of about 1.0 nm or less.

In the prior art, tunable lasers utilizing silicon-based tunable ring filters and III-V semiconductor-based gain regions required the heterogeneous integration of independently formed silicon and III-V semiconductor based optical elements, resulting in large optical devices requiring a complex manufacturing process (e.g., airtight packaging to couple the devices formed on different substrates, precise alignment for the elements, etc.). Embodiments of the invention eliminate the need for bulk optical elements and hermetic packaging, via the use of hybridized III-V/silicon gain regions and silicon optical components, such as silicon wavelength filters and silicon wavelength references, thereby reducing the size and manufacturing complexity of tunable lasing devices. For example, embodiments of the invention may utilize hybridized III-V/silicon gain regions with ring filters on silicon form a tunable laser with efficient gain from the III-V region, while providing wide tunability, efficient tunability, and narrow linewidth due to the nature of the silicon rings.

An optical transmitter that narrows the linewidth of its output light is disclosed. The optical transmitter includes a wavelength tunable laser diode (LD) known as a CSG-DR LD integrated with a semiconductor optical amplifier (SOA) driven in a constant magnitude mode. The wavelength of the light output from the LD is determined by transmission through an etalon filter. The optical transmitter feeds the output of the etalon filter back to an injection current supplied to the LD to reduce phase noise inherently contained in the output light.

A semiconductor laser of the present invention includes: a waveguide structure including, in order, a first semiconductor layer, an active layer, and a second semiconductor layer; a p-type semiconductor layer disposed in contact with one side surface of the active layer; an n-type semiconductor layer disposed in contact with the other side surface of the active layer; a reflector optically coupled to one end of the active layer in a waveguide direction; a waveguide layer optically coupled to the other end of the active layer in the waveguide direction; a diffraction grating disposed on either one of a lower surface and an upper surface of the waveguide layer; and a refractive index control unit for changing a refractive index of the waveguide layer. Thus, the semiconductor laser of the present invention can provide a good high-temperature operation with a simple configuration.