Abstract: An apparatus for laser processing a material including an optical fibre, at least one squeezing mechanism, and a lens. The optical fibre is a multimode optical fibre in which laser radiation propagates in a first optical mode and in a second optical mode. The squeezing mechanism includes at least one periodic surface defined by a pitch. The periodic surface is located adjacent to the optical fibre. The pitch couples the first and second optical modes together. The first optical mode is defined by a first mode order. The second optical mode is defined by a second mode order which is higher than the first mode order. The squeezing mechanism squeezes the periodic surface and optical fibre together with a squeezing force thereby coupling the first optical mode to the second optical mode.

Abstract: Apparatus for laser processing a material (11), which apparatus comprises a laser (1), an optical fibre (2), and a coupler (125), wherein: the laser (1) is connected to the optical fibre (2); the optical fibre (2) is such that laser radiation (13) is able to propagate along the optical fibre (2) in a first optical mode (21) having a first mode order (24), a second optical mode (22) having a second mode order (25), and a third optical mode (23) having a third mode order (26); the third mode order (26) is higher than the second mode order (25); and the second mode order (25) is higher than the first mode order (24); the apparatus being characterized in that: the coupler (125) is configured to switch laser radiation propagating in the first optical mode (21) to the laser radiation propagating in the second order mode (22); and the coupler (125) is configured to switch the laser radiation propagating in the second optical mode (22) to laser radiation propagating in the third order mode (23).

Abstract: An optical fibre (10) which has a first refractive index profile (61) that can be changed by heating to a second refractive index profile (62), at least one first dopant (7) for providing the first refractive index profile, at least one concealed dopant (8), and at least one mobile dopant (9), wherein the mobile dopant has a molar refractivity and is present in a concentration (19) such as to balance a change (146) in the first refractive index profile induced by the concealed dopant, and has a diffusion constant (16) greater than a diffusion constant (15) of the concealed dopant, so that heating of the optical fibre causes the mobile dopant to diffuse more quickly than the concealed dopant, thereby allowing the concealed dopant and the mobile dopant to change the first refractive index profile to the second refractive index profile.

Abstract: Apparatus (10) for laser processing a material (11), which apparatus comprises a laser (1) and a beam delivery cable (2), wherein: the laser (1) is connected to the beam delivery cable (2); the beam delivery cable (2) is configured to transmit laser radiation (13) emitted from the laser (1), and the laser radiation (13) is defined by a beam parameter product (4); and the apparatus (10) is characterized in that: the apparatus (10) includes at least one squeezing mechanism (5) comprising a periodic surface (6) defined by a pitch (7); a length (8) of optical fibre (9) that forms part of the laser (1) and/or the beam delivery cable (2) is located adjacent to the periodic surface (6); and the squeezing mechanism (5) is configured to squeeze the periodic surface (6) and the length (8) of the optical fibre (9) together with a squeezing force (12); whereby the beam parameter product (4) is able to be varied by adjusting the squeezing force (12).

Abstract: An optical fibre (10) which has a first refractive index profile (61) that can be changed by heating to a second refractive index profile (62), at least one first dopant (7) for providing the first refractive index profile, at least one concealed dopant (8), and at least one mobile dopant (9), wherein the mobile dopant has a molar refractivity and is present in a concentration (19) such as to balance a change (146) in the first refractive index profile induced by the concealed dopant, and has a diffusion constant (16) greater than a diffusion constant (15) of the concealed dopant, so that heating of the optical fibre causes the mobile dopant to diffuse more quickly than the concealed dopant, thereby allowing the concealed dopant and the mobile dopant to change the first refractive index profile to the second refractive index profile.

Abstract: Laser apparatus (1) comprising a reference source (2), a reference fiber (3), and at least one laser diode (4), wherein the reference fiber (3) comprises a core (5) having a refractive index n1 and a first cladding (6) having a refractive index n2, the first cladding (6) is surrounded by a second cladding (7) having a refractive index n3, the refractive index n1 is greater than the refractive index n2, the refractive index n2 is greater than the refractive index n3, the laser diode (4) emits laser radiation (8) that is guided through the first cladding (6) of the reference fiber (3), the reference source (2) emits reference radiation (9) that has a predetermined wavelength ?R (10), the reference radiation (9) is guided through the core (5) of the reference fiber (3) to the laser diode (4), and the reference radiation (9) that is guided through the core (5) of the reference fiber (3) to the laser diode (4) has a power (11) at the predetermined wavelength ?R (10), which power is greater than an injection lockin

Abstract: Apparatus for combining laser radiation (1) 5 which apparatus comprises a seed laser (2), a splitter (3), a plurality of amplifier chains (4), a reference amplifier chain (7), detection means (5). demodulator means (6), and phase control means (12), wherein each of the amplifier chains (4) comprises at least one optical amplifier (11), optical radiation (17) emitted from the seed laser (2) is split into the plurality of amplifier chains (4) by the splitter (3).

Abstract: Laser apparatus (1) comprising a reference source (2), a reference fibre (3), and at least one laser diode (4), wherein the reference fibre (3) comprises a core (5) having a refractive index n1 and a first cladding (6) having a refractive index n2, the first cladding (6) is surrounded by a second cladding (7) having a refractive index n3, the refractive index n1 is greater than the refractive index n2, the refractive index n2 is greater than the refractive index n3, the laser diode (4) emits laser radiation (8) that is guided through the first cladding (6) of the reference fibre (3), the reference source (2) emits reference radiation (9) that has a predetermined wavelength ?R (10), the reference radiation (9) is guided through the core (5) of the reference fibre (3) to the laser diode (4), and the reference radiation (9) that is guided through the core (5) of the reference fibre (3) to the laser diode (4) has a power (11) at the predetermined wavelength ?R (10), which power is greater than an injection lockin

Abstract: In one embodiment, a photo-darkening resistant optical fibre includes a waveguide having a numerical aperture less than 0.15. The waveguide includes a core having a refractive index n1 and a pedestal having a refractive index n2, and wherein the fibre includes a first cladding having a refractive index n3 surrounding the pedestal, wherein n1 is greater than n2, n2 is greater than n3. The core includes silica, a concentration of alumina of between approximately 0.3 to 0.8 mole percent, a concentration of phosphate of substantially 15 mole percent, a concentration of ytterbium substantially in the range 20000 to 45000 ppm. The pedestal can include silica, phosphate and germania. The core can have substantially zero thulium dopant.

Abstract: In one embodiment, a photo-darkening resistant optical fibre includes a waveguide having a numerical aperture less than 0.15. The waveguide includes a core having a refractive index n1 and a pedestal having a refractive index n2, and wherein the fibre includes a first cladding having a refractive index n3 surrounding the pedestal, wherein n1 is greater than n2, n2 is greater than n3. The core includes silica, a concentration of alumina of between approximately 0.3 to 0.8 mole percent, a concentration of phosphate of substantially 15 mole percent, a concentration of ytterbium substantially in the range 20000 to 45000 ppm. The pedestal can include silica, phosphate and germania. The core can have substantially zero thulium dopant.

Abstract: Apparatus for combining laser radiation (1) 5 which apparatus comprises a seed laser (2), a splitter (3), a plurality of amplifier chains (4), a reference amplifier chain (7), detection means (5). demodulator means (6), and phase control means (12), wherein each of the amplifier chains (4) comprises at least one optical amplifier (11), optical radiation (17) emitted from the seed laser (2) is split into the plurality of amplifier chains (4) by the splitter (3).

Abstract: In one embodiment, a photo-darkening resistant optical fiber includes a waveguide having a numerical aperture less than 0.15. The waveguide includes a core having a refractive index n1 and a pedestal having a refractive index n2, and wherein the fiber includes a first cladding having a refractive index n3 surrounding the pedestal, wherein n1 is greater than n2, n2 is greater than n3. The core includes silica, a concentration of alumina of between approximately 0.3 to 0.8 mole percent, a concentration of phosphate of substantially 15 mole percent, a concentration of ytterbium substantially in the range 20000 to 45000 ppm. The pedestal can include silica, phosphate and germania. The core can have substantially zero thulium dopant.

Abstract: Apparatus for the industrial processing of a material by a fiber laser, which fiber laser emits optical radiation, the apparatus configured such that the optical radiation forms an optical power distribution on a surface of the material, including first and second optical powers which are located at respective first and second radii from a center of the optical power distribution and which are of substantially higher intensity than a third optical power which is located at a third radius from the center of the optical power distribution and which is smaller than the first and the second radii.

Abstract: In one embodiment, a photo-darkening resistant optical fibre includes a waveguide having a numerical aperture less than 0.15. The waveguide includes a core having a refractive index n1 and a pedestal having a refractive index n2, and wherein the fibre includes a first cladding having a refractive index n3 surrounding the pedestal, wherein n1 is greater than n2, n2 is greater than n3. The core includes silica, a concentration of alumina of between approximately 0.3 to 0.8 mole percent, a concentration of phosphate of substantially 15 mole percent, a concentration of ytterbium substantially in the range 20000 to 45000 ppm. The pedestal can include silica, phosphate and germania. The core can have substantially zero thulium dopant.

Abstract: An optical fibre including a waveguide and at least one stress applying region is described. The waveguide is defined by a numerical aperture, and the stress applying region is defined by a depressed refractive index. The optical fibre is configured such that the waveguide supports at least two polarised fundamental modes, two polarized first second-order modes, and two polarised second second-order modes. The waveguide includes comprises a gain medium. The stress applying region, the waveguide and the disposition of the gain medium are such as to provide preferential guidance to at least one of the modes at an operating wavelength.

Abstract: Apparatus for dispersion compensating a signal (18) that propagates along a signal path (19), which apparatus comprises a grating (1) and a tuning means (2). The grating (1) is characterized by a wavelength operating range (3) and a group delay (4) that varies with wavelength (5), wherein the group delay (4) is equal at a plurality of pairs of wavelengths (6), (7) that are separated within the wavelength operating range (3), and wherein the grating (1) reflects each wavelength pair (6) from the same region (8) of the grating (1), and different wavelength pairs (7) from different regions (9) of the grating (1).

Abstract: Apparatus for filtering optical radiation at an operating wavelength (19), which apparatus comprises a grating (1) written into a waveguide (2), and which grating (1) has a first end (3), a second end (91), a first bandwidth (24), a maximum re-flectivity (29), a first group delay variation (17) defined with respect to the first end (3), and a second group delay variation (18) defined with respect to the second end (91), wherein the first and second group delay variations (17), (18) are with respect to the first bandwidth (24), the maximum reflectivity (29) is greater than 50%, the first group delay variation (17) is between 0.1 ps and 100 ps, and the second group delay variation (18) is between 0.1 ps and 100 ps.

Abstract: A method and apparatus for writing an apodised grating of improved quality into a photosensitive material using an interference pattern of fringe period gr. An unapodised part of the grating is written by exposing the photosensitive material with a succession of exposures separated from each other by an odd number of fringe periods and an apodised part of the grating is written by exposing the photosensitive material with a first set of N exposures, where N is an even number, separated from each other by an odd number of fringe periods, the first set of N exposures having a positive phase offset +&phgr; relative to the unapodised part of the grating and exposing the photosensitive material with a second set of N exposures separated from each other by an odd number of fringe periods, the second set of N exposures having a negative phase offset −&phgr; relative to the unapodised part of the grating.

Abstract: Methods for analyzing waveguide couplers are non-destructive, and comprise introducing probe light into a coupler; providing a source of perturbing radiation; presenting the coupling region of the coupler to the perturbing radiation to generate a temperature gradient across the waveguide, either from a direction so as to expose one waveguide before another waveguide and perturb the coupling region asymmetrically, or from a direction so as to expose the waveguides together and perturb the coupling region symmetrically; monitoring the power and/or phase of transmitted probe light, and repeating the presenting and monitoring along the length of the coupling region. Theoretical modeling shows that the transmitted probe light contains information from which can be derived the coupling profile, and power evolution and distribution along the coupling region, including location of the 50-50% points.

Abstract: An interferometer comprising a beam source (PM, M1, L1) of first and second light beams. The interferometer has a first arm that routes the first light beam via a first pair of mirrors (M4, M5) arranged at right angles to each other in the manner of a corner cube to reverse the direction of the first light beam and a second arm that routes the second light beam via a second pair of mirrors (M2, M3). The beam source (PM, M1, L1) and the second mirror pair (M2, M3) are mounted on a linear translation stage (P1). The first and second light beams are incident on a focusing element (L2) symmetrically about and parallel to its optical axis and then converge at an angle (&phgr;) to form an interference pattern. The symmetric, balanced configuration of the interferometer is retained under motion of the positioning element, which varies the separation (d) of the first and second light beams on the focusing element.