A tunable laser includes a reflective semiconductor optical amplifier (SOA), a grating codirectional coupler, and a reflective microring resonator. The grating codirectional coupler and the reflective microring resonator are both formed on a silicon base. An anti-reflection film is disposed on a first end surface of the reflective SOA, and the first end surface is an end surface, coupled to a first waveguide of the grating codirectional coupler, of the reflective SOA. A second waveguide of the grating codirectional coupler is coupled to the first waveguide, a first grating is disposed on the first waveguide, a second grating disposed opposite to the first grating is disposed on the second waveguide, and the first grating and the second grating constitute a narrow-band pass filter. The second waveguide is connected to the reflective microring resonator.

Provided is a laser system that includes a laser head having a laser holder configured to house a laser beam and a lens for reflecting the laser beam at a predetermined wavelength, and a thermal-mechanical adjustment device disposed on the laser head and configured to adjust a temperature and an alignment of the laser beam, to maintain the predetermined wavelength of the laser beam.

A sweeping signal generating device includes a first converter that outputs a sweeping signal having a first offset value added to or subtracted from a sweeping standard level, a second converter that outputs an offset signal having a second offset value corresponding to the first offset value, and an adder circuit that adds the sweeping signal output from the first converter and the offset signal output from the second converter.

A technique for narrowing a linewidth of a plurality of lines of a coherent comb laser (CCL) concurrently comprises providing a mode-locked semiconductor coherent comb laser (CCL) adapted to output of at least 4 mode-locked lines; tapping a fraction of a power from the CCL from the laser cavity to form a tapped beam; propagating the tapped beam to an attenuator to produce an attenuated beam; and reinserting the attenuated beam into the laser cavity, where the reinserted beam has a power less than 10% of a power of the tapped beam. The reinsertion allows the CCL to be operated to output the mode-locked lines, each with a linewidth of less than 80% of the original linewidth. By propagating the tapped and attenuated beams on a solid waveguide, and ensuring that the secondary cavity is polarization maintaining, improved stability of the linewidth narrowing is ensured.

A technique for narrowing a linewidth of a plurality of lines of a coherent comb laser (CCL) concurrently comprises providing a mode-locked semiconductor coherent comb laser (CCL) adapted to output of at least 4 mode-locked lines; tapping a fraction of a power from the CCL from the laser cavity to form a tapped beam; propagating the tapped beam to an attenuator to produce an attenuated beam; and reinserting the attenuated beam into the laser cavity, where the reinserted beam has a power less than 10% of a power of the tapped beam. The reinsertion allows the CCL to be operated to output the mode-locked lines, each with a linewidth of less than 80% of the original linewidth. By propagating the tapped and attenuated beams on a solid waveguide, and ensuring that the secondary cavity is polarization maintaining, improved stability of the linewidth narrowing is ensured.

The present embodiment relates to a light-emitting device that enables reduction in attenuation or diffraction effect caused by a semiconductor light-emitting device with respect to modulated light outputted from a spatial light modulator, and the light-emitting device includes the semiconductor light-emitting device that outputs light from a light output surface and the reflection type spatial light modulator that modulates the light. The spatial light modulator includes a light input/output surface having the area larger than the area of a light input surface of the semiconductor light-emitting device, modulates light taken through a region facing the light output surface of the semiconductor light-emitting device in the light input/output surface, and outputs the modulated light from another region of the light input/output surface to a space other than the light input surface of the semiconductor light-emitting device.

There is provided a semiconductor optical integrated device having a DFB laser, an EA modulator, and an SOA monolithically integrated, and an output light intensity of the semiconductor optical integrated device is maintained constant. The semiconductor optical integrated device includes: a DFB laser; an EA modulator connected to the DFB laser; an SOA monolithically integrated with the DFB laser and the EA modulator on a same substrate and connected to an output end of the EA modulator; and an optical receiver disposed on an output end side of the SOA and having a same composition as the SOA. The optical receiver is configured to monitor change in a detection value according to an intensity of input light to the optical receiver such that drive currents flowing in the DFB laser and the SOA are feedback controlled.

Practical silicon-based light sources are still missing, despite the progress in germanium lasers, because both silicon and germanium are indirect-band semiconductors and inefficient at light generation. A tunable and single mode external cavity laser comprising: a gain medium for generating light between a reflective surface at one end of the gain medium; and a wavelength selective reflector at the other end of a laser cavity. A splitter disposed in the laser cavity includes an input port optically coupled to the gain medium, an input/output port optically coupled to the wavelength selective reflector, and an output port for outputting laser light at selected wavelengths. The wavelength selective reflector reflects light of one or more selected periodic wavelengths back to the gain medium via the input/output port, and passes light of non-selected wavelengths out of the laser cavity.

Higher power tunable lasers are feasible using photonics integrated circuit based external cavity laser configurations by using multiple RSOAs inside a single cavity to provide multiple on-chip coherent optical output at the same wavelength. The total collective output power in various output branches potentially adds up being higher than what commercial lasers can provide. Using multiple RSOA increases and distributes the number of gain materials, which keeps them in a linear regime and avoids available gain saturation, which thereby removes gain saturation limitation in optical amplifications.

Practical silicon-based light sources are still missing, despite the progress in germanium lasers, because both silicon and germanium are indirect-band semiconductors and inefficient at light generation. A tunable and single mode external cavity laser comprising: a gain medium for generating light between a reflective surface at one end of the gain medium; and a wavelength selective reflector at the other end of a laser cavity. A splitter disposed in the laser cavity includes an input port optically coupled to the gain medium, an input/output port optically coupled to the wavelength selective reflector, and an output port for outputting laser light at selected wavelengths. The wavelength selective reflector reflects light of one or more selected periodic wavelengths back to the gain medium via the input/output port, and passes light of non-selected wavelengths out of the laser cavity.