Various example embodiments relate to active optical fibers and devices using active optical fibers. An active optical fiber may comprise a central part surrounded by an annular active core. The fiber may have a tapered longitudinal profile such that the fiber comprises a single-mode portion and a multimode portion. The annular core may have low birefringence, obtained for example by rotating (spinning) the fiber preform during manufacture of the fiber. Refractive index of the annular core may be higher than the refractive indices of the central part and cladding layer(s) surrounding the annular core. The active optical fiber enables selective generation or amplification of light modes with orbital angular momentum (OAM). Furthermore, the fiber has a large mode field diameter (MFD) and it is not sensitive to internal heating or environmental influences.

An optical oscillator includes a first reflection part configured to reflect light of a first wavelength, a laser medium excited by excitation light of a second wavelength different from the first wavelength and configured to emit light of the first wavelength, a second reflection part configured to form an unstable resonator together with the first reflection part, the unstable resonator being configured to output annular laser light of the first wavelength, and a saturable absorption part disposed between the laser medium and the second reflection part and of which a transmittance increases with absorption of light of the first wavelength. When a power of the excitation light is indicated by P.sub.p (kW), and an inner diameter of the annular laser light is indicated by d.sub.i, and an outer diameter is indicated by d.sub.o, and d.sub.o/d.sub.i is a magnification m, the magnification m satisfies a.sub.0+a.sub.1 Log(P.sub.p)≤m≤b.sub.0+b.sub.1P.sub.p+b.sub.2P.sub.p.sup.2.

A laser device is provided for generating a helical-shaped optical wave and includes: (i) a gain region located between one first end defined by a first mirror and a second end defined by an exit region, (ii) a second mirror arranged so as to form with the first mirror an optical cavity including the gain region and a gap between the exit region and the second mirror, (iii) apparatus for pumping the gain region so as to generate the optical wave, wherein the laser device further includes at least one apparatus for shaping the light intensity and/or phase profiles of the optical wave and arranged for selecting at least one rotary-symmetrical transverse mode of the optical wave, the rotary-symmetrical transverse mode being chosen between those with a radial index equal to zero and with an azimuthal index being an integer with a module higher or equal to 1.

An optical oscillator according to an embodiment includes a first reflecting portion that transmits light having a first wavelength and reflects light having a second wavelength different from the first wavelength, a second reflecting portion that forms an unstable resonator together with the first reflecting portion and reflect light having the second wavelength, a laser medium that is disposed between the first reflecting portion and the second reflecting portion and emits light having the second wavelength due to incidence of light having the first wavelength, and a saturable absorption portion disposed on a side opposite to the first reflecting portion when viewed from the laser medium in the one direction, the first reflecting portion includes an incidence surface on which light having the first wavelength is incident, on a side opposite to the laser medium, a size of the second reflecting portion is smaller than a size of the first reflecting portion when viewed in the one direction, at least a part of a surface of the saturable absorption body on the side opposite to the laser medium includes a curved region curved toward the laser medium side, and the second reflecting portion is a dielectric multilayer film provided in the curved region.

The invention relates to a light injector element (20) comprising a body (21) extending according to a longitudinal axis (22), and a light source (23) placed facing an end (25) of the body (21), the light source (23) comprising a plurality of vertical-cavity surface-emitting laser (VCSEL) diodes, said plurality of diodes being arranged so as to form an emission surface (26) substantially perpendicular to the longitudinal axis (22) of the body (21).

The invention also relates to a photobioreactor (10) comprising such a light injector element (20).

A method for generating a spatially transformed optical output from a laser system, the method comprising: disposing a laser gain medium within a laser cavity structure; arranging an interferometric device to complete the laser cavity structure, wherein the interferometric device receives an input beam from laser oscillation in the laser cavity structure, splits the input beam into two sub-beams, and recombines the two sub-beams to provide an optical feedback beam to sustain laser oscillation; configuring the optical components that comprise the interferometric device to provide relative misalignment of the two sub-beams that are produced internally to the interferometric device; using at least a first output port of the interferometric device to provide an output beam of the laser system that due to the misalignment is a spatial transformation of the internal mode structure of the laser; and using at least a second output port of the interferometric device to provide the optical feedback beam to the laser cavity structure that sustains laser oscillation with a spatial structure that substantially preserves the internal mode structure of the laser. An apparatus which implements such a method is also provided.

A semiconductor light emitting element that can form a useful beam pattern is provided. A semiconductor laser element LD includes an active layer 4, a pair of cladding layers 2 and 7 between which the active layer 4 is interposed, and a phase modulation layer 6 optically coupled to the active layer 4. The phase modulation layer 6 includes a base layer 6A and different refractive index regions 6B that are different in refractive index from the base layer 6A. The different refractive index regions 6B desirably arranged in the phase modulation layer 6 enable emission of laser light including a dark line with no zero-order light.

The present disclosure relates to a three-dimensional cylindrical cavity-type laser system capable of supporting circumferential radial emission. A cylindrical ring waveguide provides optical confinement in the radial and axial dimensions thereby supporting a plurality of radial modes, one of a plurality of axial modes and a plurality of degenerate azimuthal modes. These modes constitute a set of traveling wave modes which propagate around the cylindrical ring waveguide possessing various degrees of optical confinement as quantified by their respective Q-factors. Index tailoring is used to tailor the radial refractive index profile and geometry of the waveguide to support radial modes possessing Q-factors capable of producing efficient radial emission, while gain tailoring is used to define a gain confining region which offsets modal gain factors of the modal constituency to favor a preferred set of modes supporting efficient radial emission out of the total modal constituency supported by the resonator.. Under appropriate pump actuation the selected modes produce circumferential laser radiation with the output surface comprising of the entire outer perimeter of the cylindrical ring waveguide. The design is applicable toward both micro-resonators and resonators much larger than the optical wavelength, enabling high output powers and scalability. The circumferential radial laser emission can be concentrated by positioning the cylindrical ring laser inside a three-dimensional conical mirror thereby forming a laser ring of light propagating in the axial dimension away from the surface of the laser, which can be subsequently collimated for focused using conventional optics.

Optical fiber structures for generating a single mode, saddle shaped output beam include first and second lengths of fiber. The first length of fiber has a first input end configured to receive a single mode gaussian beam. The second length of fiber has a second input end coupled to an output end of the first length of fiber. The second length of fiber includes a centrally located anti-guiding core and an annular guiding region coaxially encompassing the centrally located anti-guiding core.

A composite all optical-fibre based tapered photonic waveguide (110) including a single or multiple secondary waveguides (120) within or around a primary waveguide (118) is described. The composite optical fibre may also be termed a beam tailoring optical fibre (BT Fibre) (110). In use, at thelarger secondary end (114) both the primary waveguide (118) and the secondary waveguide/s (120) may guide modes at a particular wavelength. However, at the same wavelength, adiabatically tapering down the waveguides (118, 120) reduces the dimensions of the secondary waveguide/s (120) such that all the secondary waveguide/s (120) become effectively non-guiding at the smaller primary end (112), whilst the primary waveguide (118) still guides. In other words, the composite optical fibre is a spatially modulating optical fibre (110).