Abstract: A method for fabricating an optical waveguide comprises: providing a sample of lithium niobate doped with magnesium oxide and having at least one grating of periodic domain inversion defined therein; applying a layer of metallic zinc to a surface of the sample over the at least one grating using sputter deposition; heating the sample in an atmosphere of pure oxygen to cause the zinc to indiffuse into the lithium niobate to form a waveguiding layer of increased refractive index under the surface of the sample; and using a dicing blade to cut two substantially parallel channels along a length direction of the at least one grating, to define a ridge waveguide between the two channels.

Abstract: A sample of nonlinear optical material for use in a nonlinear optical device contains a grating comprising alternating regions of inverted and non-inverted nonlinear coefficient of the material, with the regions separated by boundaries positioned such that the grating can provide quasi-phase matching of a selected nonlinear optical interaction, and compensate for phase mismatch arising from the Gouy phase shift of one or more focused optical beams involved in the interaction. The boundary positions can be calculated for second harmonic generation or optical parametric generation and oscillation.

Abstract: An optical waveguide device (10) comprises a planar substrate with a lower cladding layer (14), a core layer (16) and an upper cladding layer (18), a groove (20) in the substrate that extends at least into the core layer (16), and a waveguiding channel (22) in the core layer (16), wherein at least a part of the waveguiding channel (22), which may contain a Bragg grating, is sufficiently proximate to the groove (20) in the plane of the substrate for an evanescent field of light propagating in the waveguiding channel (22) to extend laterally into the groove (20). Material contained in the groove modifies the properties of the waveguiding channel, so that a sample of material can be analysed or an active material can be used to modulate the propagating light. The groove (20) can be made before the waveguide (22). The groove (20) can be made by cutting into the substrate with a saw and the waveguide (22) can be made by direct writing in the core layer (16) with an ultraviolet beam.

Abstract: A method of producing a planar substrate having waveguide channels, which method comprises: (i) providing a tube (6) of a substrate material; (ii) depositing silica layers (110) on the inside of the tube (6), the silica layers (110) being doped with a photosensitive material; (iii) drawing the tube (6) so that the cross-sectional size of the tube (109) is reduced; (iv) before or after the reducing of the cross-sectional size of the tube (6), causing the tube (6) to collapse into a flat shape by applying a low pressure to the tube, whereby the deposited silica layers together form a photosensitive silica layer (111); (v) cutting to required lengths the tube (6) which has been collapsed and reduced in cross-sectional size; and (vi) using laser writing to define waveguide channels in the cut lengths of the tube (6) and thereby to produce the planar substrate having the waveguide channels.

Abstract: A process for poling a ferroelectric material doped with a metal, which process comprises: (i) defining an electrode pattern on a ?z face of a crystal of the ferroelectric material doped with the metal; (ii) providing an electrode material; (iii) poling at a temperature of not more than 45° C.; and (iv) poling by a two-stage voltage-controlled application of electric field based on a first poling stage of domain nucleation and a second poling stage of domain spreading.

Abstract: A method of inducing a periodic variation of nonlinearity value in a sample of ferroelectric material comprises arranging a pair of electrodes on opposite faces of the sample, one electrode defining a desired pattern of nonlinearity variation, applying a pre-bias voltage across the sample for a predetermined time using the electrodes, the pre-bias voltage being less than the coercive field of the ferroelectric material; and after the predetermined time, applying a current-controlled poling voltage across the sample using the electrodes, to produce domain inversion in the sample according to the desired pattern of nonlinearity variation. The pre-bias voltage may be 75% of the coercive field or more, and applied for a pre-determined time between 1 and 100 seconds.

Abstract: A sample of nonlinear optical material for use in a nonlinear optical device contains a grating comprising alternating regions of inverted and non-inverted nonlinear coefficient of the material, with the regions separated by boundaries positioned such that the grating can provide quasi-phase matching of a selected nonlinear optical interaction, and compensate for phase mismatch arising from the Gouy phase shift of one or more focused optical beams involved in the interaction. The boundary positions can be calculated for second harmonic generation or optical parametric generation and oscillation.

Abstract: A method of inducing a periodic variation of nonlinearity value in a sample of ferroelectric material comprises arranging a pair of electrodes on opposite faces of the sample, one electrode defining a desired pattern of nonlinearity variation, applying a pre-bias voltage across the sample for a predetermined time using the electrodes, the pre-bias voltage being less than the coercive field of the ferroelectric material; and after the predetermined time, applying a current-controlled poling voltage across the sample using the electrodes, to produce domain inversion in the sample according to the desired pattern of nonlinearity variation. The pre-bias voltage may be 75% of the coercive field or more, and applied for a pre-determined time between 1 and 100 seconds.

Abstract: A process for poling a ferroelectric material doped with a metal, which process comprises: (i) defining an electrode pattern on a ?z face of a crystal of the ferroelectric material doped with the metal; (ii) providing an electrode material; (iii) poling at a temperature of not more than 45° C.; and (iv) poling by a two-stage voltage-controlled application of electric field based on a first poling stage of domain nucleation and a second poling stage of domain spreading.

Abstract: A method of producing a planar substrate having waveguide channels, which method comprises: (i) providing a tube (6) of a substrate material; (ii) depositing silica layers (110) on the inside of the tube (6), the silica layers (110) being doped with a photosensitive material; (iii) drawing the tube (6) so that the cross-sectional size of the tube (109) is reduced; (iv) before or after the reducing of the cross-sectional size of the tube (6), causing the tube (6) to collapse into a flat shape by applying a low pressure to the tube, whereby the deposited silica layers together form a photosensitive silica layer (111); (v) cutting to required lengths the tube (6) which has been collapsed and reduced in cross-sectional size; and (vi) using laser writing to define waveguide channels in the cut lengths of the tube (6) and thereby to produce the planar substrate having the waveguide channels.

Abstract: An optical waveguide device (10) comprises a planar substrate with a lower cladding layer (14), a core layer (16) and an upper cladding layer (18), a groove (20) in the substrate that extends at least into the core layer (16), and a waveguiding channel (22) in the core layer (16), wherein at least a part of the waveguiding channel (22), which may contain a Bragg grating, is sufficiently proximate to the groove (20) in the plane of the substrate for an evanescent field of light propagating in the waveguiding channel (22) to extend laterally into the groove (20). Material contained in the groove modifies the properties of the waveguiding channel, so that a sample of material can be analysed or an active material can be used to modulate the propagating light. The groove (20) can be made before the waveguide (22). The groove (20) can be made by cutting into the substrate with a saw and the waveguide (22) can be made by direct writing in the core layer (16) with an ultraviolet beam.

Abstract: An optical sensor comprises at least two planar Bragg gratings defined on a single substrate and arranged to receive light from a light source, each grating having a wavelength filtering response that varies with an effective modal index experienced by light propagating in the Bragg grating and a Bragg wavelength different to those of the other gratings, and at least one sample window overlying one or more of the gratings that can receive a sample of fluid that affects the effective modal index and response of the grating, the gratings filtering the light and outputting the filtered light for spectral analysis, from which the refractive index and related properties of the fluid can be determined. One or more of the gratings can be a reference grating used to compensate for temperature and other disturbances to the sensors. Gratings may have individual sample windows for testing separate fluid samples, or may share a common window so that a single fluid can be tested using several gratings.

Abstract: An optical sensor comprises a sensing element comprising a waveguide grating with a response that varies with an effective modal index experienced by light propagating in the grating and a sample window for receiving fluid which affects the effective modal index to modify the response, the sensing element arranged to receive light from a light source and to output the light after filtering; and an analyzing element comprising a second waveguide grating having a second response, and arranged to receive light output by the sensing element and to output the light after filtering for detection by an optical power detector. The combination of the two gratings converts changes in the wavelength of light output by the sensing element in response to the sample of fluid to changes in the amount of light, allowing the fluid index to be deduced from a measurement of optical power. The two elements may be fabricated on a single substrate to reduce errors from environmental disturbances such as temperature changes.

Abstract: A method of simultaneously defining a waveguide and grating in a sample of photosensitive material comprises providing a sample of material (24) having a region which is photosensitive to light of a specific wavelength, generating a spot of light (22) at the specific wavelength, the spot having a periodic intensity pattern of high and low intensity fringes, and a width which is related to the width of the channel, positioning the spot within the photosensitive region and causing relative movement between the sample and the light spot along the desired path of the waveguide/grating define a channel of altered refractive index by exposing parts of the photosensitive region to the light spot. Modulation of the light spot to produce multiple exposures produces a grating, while continuous exposure results in a uniform waveguide. These structures can be written in straight lines or around curves, and can be accurately overwritten, so that complex optical devices can be produced in a single fabrication step.

Abstract: A method of fabricating an optical waveguide (18) comprises providing a sample of lithium niobate (10) that has one or more periodically poled gratings made by electric field poling, applying a patterned surface layer of metallic zinc (16) to a z-face of the sample so that the layer (16) has a pattern corresponding to an intended pattern of waveguides (18) to be written int lithium niobate, and heating the sample to diffuse the metallic zinc (16) into the lithium niobate so as to form an optical waveguiding structure (18) within the sample.

Abstract: An optical sensor comprises at least two planar Bragg gratings defined on a single substrate and arranged to receive light from a light source, each grating having a wavelength filtering response that varies with an effective modal index experienced by light propagating in the Bragg grating and a Bragg wavelength different to those of the other gratings, and at least one sample window overlying one or more of the gratings that can receive a sample of fluid that affects the effective modal index and response of the grating, the gratings filtering the light and outputting the filtered light for spectral analysis, from which the refractive index and related properties of the fluid can be determined. One or more of the gratings can be a reference grating used to compensate for temperature and other disturbances to the sensors. Gratings may have individual sample windows for testing separate fluid samples, or may share a common window so that a single fluid can be tested using several gratings.