A length L.sub.1 of a first distributed Bragg reflector in a waveguide direction, a length L.sub.2 of a distributed feedback active region in the waveguide direction, a length L.sub.3 of a second distributed Bragg reflector in the waveguide direction, and a position x.sub.ps of a phase shift portion are set to satisfy correlations of x.sub.ps=L.sub.1+L.sub.2×α, L.sub.2(1−α)+L.sub.3>x.sub.ps, and 0.5<α<1. Further, the position x.sub.ps is a position of the phase shift portion in the waveguide direction with an end portion thereof on the first distributed Bragg reflector side set as an origin.

This application describes a wavelength-tunable laser apparatus, which reduces complexity of wavelength tuning of a laser. The laser includes a reflective gain unit, an optical phase shifter, a coupler, and a passive filter unit array. Furthermore, an output port of the reflective gain unit is connected to an input port of the optical phase shifter, an output port of the optical phase shifter is connected to an input port of the coupler, a first output port of the coupler is connected to an input port of the passive filter unit array, and a second output port of the coupler is an output port of the laser. The passive filter unit array includes a plurality of passive filter units, where any two of the plurality of passive filter units have different wavelength tuning ranges, and each filter unit has a linearly tunable wavelength.

The invention is concerned with a structured optical fibre sensor, comprising a light source (1), a detection system (2) and a Bragg grating optical fibre (3) connected to said source and said system. The light source is a wavelength-tunable laser emission device (1) comprising a cavity (CA) delimited by a first and a second Sagnac mirror (M1, M2). The cavity comprises an amplifying medium (AM) and a tunable spectral filter using the Vernier effect (F), said filter (F) comprising at least three resonant rings (R.sub.1, R.sub.2, R.sub.N−1, R.sub.N) arranged in cascade, each resonant ring integrating a wavelength-tunable reflectivity loop mirror (MBR).

In a first embodiment, an external cavity tunable laser, comprising a silicon photonics circuit comprising one or more resonators having one or more p-i-n junctions; wherein a voltage is applied to one or more of the p-i-n junctions. In a second embodiment, a method of operating an external cavity tunable laser, comprising sweeping out free-carriers from a resonator of the tunable laser by applying a voltage to a p-i-n junction of a waveguide of the resonator.

A semiconductor laser may include an active region having a longitudinal axis, a rear facet end and a front facet end. The front facet end emitting an output beam of the semiconductor laser. The semiconductor laser may include a plurality of diffraction gratings positioned along the longitudinal axis of the active region. The plurality of diffraction gratings including a first diffraction grating positioned proximate the rear facet end of the active region and at least one additional diffraction grating positioned longitudinally between the first diffraction grating and the front facet. The first diffraction grating having a first kappa value and the at least one additional diffraction grating having at least a second kappa value, the first kappa value being greater than the second kappa value.

Semiconductors lasers are disclosed having an active region having a longitudinal axis, a first facet end, and a second facet end. The second facet end emitting the main output beam of light from of the respective semiconductor laser. The first facet end may have a low-reflection coating. The first facet end may be non-perpendicular to the longitudinal axis of the active region. The semiconductor lasers may be distributed feedback (DFB) lasers having a plurality of diffraction gratings along the longitudinal axis of the active region. The plurality of diffraction grating may include a first diffraction grating positioned proximate the first end of the active region, a second diffraction grating positioned proximate the second end of the active region, and a third diffraction grating positioned between the first diffraction grating and the second diffraction grating. The first diffraction grating may be spaced apart from the third diffraction grating along the longitudinal axis of the active region by a first distance. The second diffraction grating may be spaced apart from the third diffraction grating along the longitudinal axis of the active region by a second distance. Each of the first distance and the second distance being greater than zero.

An optical semiconductor device includes a multi-quantum well layer including well layers and barrier layers alternately overlapping with each other, an optical confinement layer, and a guide layer interposed between the multi-quantum well layer and the optical confinement layer. Each barrier layer is an undoped layer and an outermost layer is one of the barrier layers. The optical confinement layer has a refractive index that is greater than that of the outermost layer and a band gap that is smaller than that of the outermost layer. The guide layer includes a first adjacent layer in contact with the outermost layer and the guide layer is thinner than the optical confinement layer. Each of the optical confinement layer and the guide layer is an n-type semiconductor layer. The first adjacent layer of the guide layer has a band gap that is larger than that of the optical confinement layer.

A surface-emitting laser, which is a ridge waveguide structure, including: a substrate, a first cladding layer, an active layer, a conductive layer, a second cladding layer; the Bragg gratings is etched on the surface of the ridge waveguide; the two upper electrodes are disposed on both sides of the ridge waveguide; two grooves are formed between the ridge waveguide and each of the two upper electrodes; the first waveguide cladding layer includes one or more current confinement regions; or a buried tunnel junction is formed in the second cladding layer for limiting current. The Bragg gratings comprise two first-order gratings and one second-order grating placed between two first-order gratings.

A beam positioner can be broadly characterized as including a first acousto-optic (AO) deflector (AOD) operative to diffract an incident beam of linearly polarized laser light, wherein the first AOD has a first diffraction axis and wherein the first AOD is oriented such that the first diffraction axis has a predetermined spatial relationship with the plane of polarization of the linearly polarized laser light. The beam positioner can include at least one phase-shifting reflector arranged within a beam path along which light is propagatable from the first AOD. The at least one phase-shifting reflector can be configured and oriented to rotate the plane of polarization of light diffracted by the first AOD.

The invention is concerned with a structured optical fibre sensor, comprising a light source (1), a detection system (2) and a Bragg grating optical fibre (3) connected to said source and said system. The light source is a wavelength-tunable laser emission device (1) comprising a cavity (CA) delimited by a first and a second Sagnac mirror (M1, M2). The cavity comprises an amplifying medium (AM) and a tunable spectral filter using the Vernier effect (F), said filter (F) comprising at least three resonant rings (R.sub.1, R.sub.2, R.sub.N−1, R.sub.N) arranged in cascade, each resonant ring integrating a wavelength-tunable reflectivity loop mirror (MBR).