An optical semiconductor device includes an active layer having a plurality of quantum dot layers. The plurality of quantum dot layers include: a first quantum dot layer doped with a p-type impurity; and a second quantum dot layer doped with an n-type impurity and having an emission wavelength different from that of the first quantum dot layer.

A photonic, integrated circuit chip can have a frequency comb laser configured to generate a plurality of wavelengths, a plurality of modulators, one respective modulator for each wavelength of the plurality of wavelengths, the plurality of modulators being aligned in series with each of the plurality of modulators being tuned to a respective one of the wavelengths of the plurality of wavelengths, a connector configured to convey a drive signal for each modulator of the plurality of modulators, a semiconductor optical amplifier configured to receive light exiting from the plurality of modulators, and a chip having present thereon the frequency comb laser, the plurality of modulators, and the semiconductor optical amplifier. The plurality of modulators can be configured to produce a single beam of time-interleaved, multiple-wavelength output laser light. A mobile system, such as a satellite, can also have the photonic, integrated circuit chip as a component thereof.

In an EADFB laser with an integrated SOA, a new configuration in which deterioration of optical waveform quality is solved or mitigated while taking advantage of characteristics that the same layer structure can be used and the manufacturing process can be simplified is shown. In an optical transmitter of the present disclosure, a carrier density is optimized depending on a light intensity inside the SOA and an amount of carrier consumption. The SOA is electrically separated into a plurality of regions, and a current is injected into each region independently. The divided SOA region is configured so that a length of the SOA region becomes shorter as a region is farther from an incidence end of the SOA. Further, for the divided SOA, an amount of carrier consumption increases as the SOA region is farther from the incidence end, so that a current injection amount is increased.

An integrated optical beam steering device includes a planar dielectric lens that collimates beams from different inputs in different directions within the lens plane. It also includes an output coupler, such as a grating or photonic crystal, that guides the collimated beams in different directions out of the lens plane. A switch matrix controls which input port is illuminated and hence the in-plane propagation direction of the collimated beam. And a tunable light source changes the wavelength to control the angle at which the collimated beam leaves the plane of the substrate. The device is very efficient, in part because the input port (and thus in-plane propagation direction) can be changed by actuating only log.sub.2 N of the N switches in the switch matrix. It can also be much simpler, smaller, and cheaper because it needs fewer control lines than a conventional optical phased array with the same resolution.

A photonic chip. In some embodiments, the photonic chip includes a waveguide; and an optically active device comprising a portion of the waveguide. The waveguide may have a first end at a first edge of the photonic chip; and a second end, and the waveguide may have, everywhere between the first end and the second end, a rate of change of curvature having a magnitude not exceeding 2,000/mm.sup.2.

An optical transmitter includes: a set of reflective semiconductor optical amplifiers (RSOAs) or other reflective gain media, a set of ring filters, a set of intermediate waveguides, a shared waveguide, a shared loop mirror, and an output waveguide. Each intermediate waveguide channels light from an RSOA in proximity to an associated ring filter to cause optically coupled light to circulate in the associated ring filter. The shared waveguide is coupled to the shared loop mirror, and is located in proximity to the set of ring filters, so that light circulating in each ring filter causes optically coupled light to flow in the shared waveguide. Each RSOA forms a lasing cavity with the shared loop reflector, wherein each lasing cavity has a different wavelength associated with a resonance of its associated ring filter. The output waveguide is optically coupled to the shared loop mirror and includes an electro-optical modulator.

A dual-ring-modulated laser includes a gain medium having a reflective end coupled to an associated gain-medium reflector and an output end, which is coupled to a reflector circuit through an input waveguide to form a lasing cavity. The reflector circuit comprises: a first ring modulator; a second ring modulator; and a shared waveguide that optically couples the first and second ring modulators together. The first and second ring modulators have resonance peaks that are tuned to be offset in alignment from each other to provide an effective reflectance having a flat-top response, which is aligned with an associated lasing cavity mode. The first and second ring modulators are driven in tandem based on the same electrical input signal, whereby the resonance peaks of the first and second ring modulators shift wavelengths in the same direction during modulation, and an effective reflectance stays within the flat-top wavelength range.

An optical transmitter includes: a splitter; a first optical modulator and a second optical modulator that modulate each of light beams split by the splitter; a first semiconductor optical amplifier (SOA) and a second SOA that are connected to a subsequent stage of the first optical modulator and a subsequent stage of the second optical modulator, respectively; a first detector and a second detector that detect light output intensity of the first SOA and light output intensity of the second SOA, respectively; a controller that sets gains of the first and second SOAs such that the first and second SOAs are equal in the light output intensity based on detection values of the first and second detectors; and a combiner that combines an output light beam of the first SOA and an output light beam of the second SOA.

A variable wavelength light source and an apparatus including the same are disclosed. The variable wavelength light source includes: a first waveguide; a second waveguide spaced apart from the first waveguide; a first optical amplifier including a first gain medium; and a second optical amplifier including a second gain medium that is different from the first gain medium.

An integrated optical beam steering device includes a planar dielectric lens that collimates beams from different inputs in different directions within the lens plane. It also includes an output coupler, such as a grating or photonic crystal, that guides the collimated beams in different directions out of the lens plane. A switch matrix controls which input port is illuminated and hence the in-plane propagation direction of the collimated beam. And a tunable light source changes the wavelength to control the angle at which the collimated beam leaves the plane of the substrate. The device is very efficient, in part because the input port (and thus in-plane propagation direction) can be changed by actuating only log.sub.2 N of the N switches in the switch matrix. It can also be much simpler, smaller, and cheaper because it needs fewer control lines than a conventional optical phased array with the same resolution.