An artificial saturable absorber uses additive pulse mode-locking to enable pulse operation of an on-chip laser operation. Four different artificial saturable absorbers are disclosed. The first includes an integrated coupler, two arms each containing some implementation of the end-reflector, and a phase bias element in one arm. The second includes an integrated directional coupler, two integrated waveguide arms, and another integrated coupler as an output. The third includes an integrated birefringent element, integrated birefringent-free waveguide, and integrated polarizer. And the fourth includes a multimode waveguide that allows for different modes to propagate in such a way that the difference in the spatial distribution of intensity causes a nonlinear phase difference between the modes. These are just some examples of an on-chip fully integrated artificial saturable absorber with instantaneous recovery time that allow for generation of sub-femtosecond optical pulses at high repetition rates using passive mode-locking.

A distributed reflector (DR) laser may include a distributed feedback (DFB) region and a distributed Bragg reflector (DBR). The DFB region may have a length in a range from 30 micrometers (m) to 100 m and may include a DFB grating with a first kappa in a range from 100 cm.sup.1 to 150 cm.sup.1. The DBR region may be coupled end to end with the DFB region and may have a length in a range from 30-300 m. The DBR region may include a DBR grating with a second kappa in a range from 150 cm.sup.1 to 200 cm.sup.1. The DR laser may additionally include a lasing mode and a p-p resonance frequency. The lasing mode may be at a long wavelength side of a peak of a DBR reflection profile of the DBR region. The p-p resonance frequency may be less than or equal to 70 GHz.

A semiconductor laser source includes a partial-grating DFB laser with two laser electrodes, one over the grating and the other between the grating and one end of the laser. Constant laser currents flow into the waveguide through the electrodes (typically different from each other) and produce laser output. A wavelength discriminator, an optical detector, and a wavelength-control circuit act as a wavelength-control feedback mechanism to generate a wavelength control current that flows through one laser electrode or the other, or through both electrodes with opposite polarities. Phase noise on the laser output can be reduced at modulation frequencies exceeding several hundred kHz up to one or several tens of MHz or more. The laser-wavelength can be swept while exhibiting reduced phase noise.

A semiconductor laser comprising a single mode laser cavity having a stack of semiconducting layers defining a transversal p-n junction is provided. A plurality of electrodes are coupled to corresponding sections of the laser cavity along the longitudinal light propagation direction, each corresponding section defining one of an amplification section or a modulation section. One or more DC sources are coupled to the electrodes associated with the amplification sections to forward-bias the p-n junction above transparency, so as to provide gain in the associated amplification sections. One or more modulation signal sources are coupled to the electrodes associated with the modulation sections, and apply a modulation signal across the p-n junction below transparency, the modulation signal providing a modulation of an output optical frequency of the semiconductor laser. Each modulation section is operated in photovoltaic mode.

A directly modulated semiconductor laser whose optical output can be modulated by varying the transmittance of an end reflector of the laser cavity. In an example embodiment, the end reflector can be implemented using a lightwave circuit in which optical waveguides are arranged to form an optical interferometer. At least one of the optical waveguides may include a waveguide section configured to modulate the phase of an optical beam passing therethrough in response to an electrical radio-frequency drive signal in a manner that causes the transmittance and reflectance of the end reflector to be modulated accordingly. Advantageously, relatively high (e.g., >10 GHz) phase and/or amplitude modulation speeds of the optical output can be achieved in this manner to circumvent the inherent modulation-speed limitations of the laser's gain medium.

The first transmission line has a width perpendicular to a transmission direction. The first electrode has a width not exceeding the width. The first electrode is opposed to the first transmission line. The ground layer has a positional relationship with each portion of the first transmission line. The ground layer is next to the first transmission line on at least one side consisting of a first side along a thickness direction of the mounting substrate, and a second side and a third side with the first transmission line interposed therebetween. The first transmission line is bonded to the first electrode and has the width equivalently, at least, at a portion of the first transmission line. The portion equivalently has the positional relationship with the ground layer. The portion is next to the ground layer in an equivalent shape along the transmission direction.

A semiconductor optical device includes: a first conductive type semiconductor layer; an active layer; a second conductive type semiconductor layer including a ridge portion; a pair of first grooves, formed on bottom surfaces of both sides of the ridge portion and dividing the active layer; an optical functioning part including the first and second conductive type semiconductor layers, converting a state of light, and having a height higher than a height of the bottom surface of the ridge portion; and a second groove, at least a part thereof being formed on the optical functioning part, an end portion thereof being connected to the first groove, the second conductive type semiconductor layer being divided, and the maximum height of an inner wall surface thereof being higher than the maximum height of an inner wall surface of the first groove.

A system and method for providing laser diodes with broad spectrum is described. GaN-based laser diodes with broad or multi-peaked spectral output operating are obtained in various configurations by having a single laser diode device generating multiple-peak spectral outputs, operate in superluminescene mode, or by use of an RF source and/or a feedback signal. In some other embodiments, multi-peak outputs are achieved by having multiple laser devices output different lasers at different wavelengths.

An artificial saturable absorber uses additive pulse mode-locking to enable pulse operation of an on-chip laser operation. Four different artificial saturable absorbers are disclosed. The first includes an integrated coupler, two arms each containing some implementation of the end-reflector, and a phase bias element in one arm. The second includes an integrated directional coupler, two integrated waveguide arms, and another integrated coupler as an output. The third includes an integrated birefringent element, integrated birefringent-free waveguide, and integrated polarizer. And the fourth includes a multimode waveguide that allows for different modes to propagate in such a way that the difference in the spatial distribution of intensity causes a nonlinear phase difference between the modes. These are just some examples of an on-chip fully integrated artificial saturable absorber with instantaneous recovery time that allow for generation of sub-femtosecond optical pulses at high repetition rates using passive mode-locking.

A distributed reflector (DR) laser may include a distributed feedback (DFB) region and a distributed Bragg reflector (DBR). The DFB region may have a length in a range from 30 micrometers (m) to 100 m and may include a DFB grating with a first kappa in a range from 100 cm.sup.1 to 150 cm.sup.1. The DBR region may be coupled end to end with the DFB region and may have a length in a range from 30-300 m. The DBR region may include a DBR grating with a second kappa in a range from 150 cm.sup.1 to 200 cm.sup.1. The DR laser may additionally include a lasing mode and a p-p resonance frequency. The lasing mode may be at a long wavelength side of a peak of a DBR reflection profile of the DBR region. The p-p resonance frequency may be less than or equal to 70 GHz.