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 method of forming an optical fibre assembly, comprises providing a planar substrate made of a first material; positioning an optical fibre with an outer layer of a first glass material on a surface of the substrate to form a pre-assembly; depositing a further glass material such as silica soot onto the pre-assembly, over at least a part of the optical fibre and adjacent parts of the substrate surface; and heating the pre-assembly to consolidate the further glass material into an amorphous volume in contact with at least parts of the surface of the substrate and the outer layer of the optical fibre, thereby bonding the optical fibre to the substrate to create the optical fibre assembly.

Abstract: A method for compensating perturbed measurements comprises: obtaining measurements with respect to time of a signal representing a parameter modified by a perturbing influence and a signal representing the perturbing influence and storing the measurements for each time in a data array as parameter data and perturbation data respectively; for each of the parameter data and the perturbation data: fitting a mathematical model to the data with respect to time; determining an error between the model and the data at each time; storing the errors in the data array as normalised parameter data and normalised perturbation data respectively; fitting a mathematical model to the normalised parameter data against the normalised perturbation data to obtain a correlation function representing correlation between the parameter data and the perturbation data; using the correlation function to calculate a correction factor representing the modification of the parameter data by the perturbing influence; using the correction fac

Abstract: A method of controlling additive delivery during a bioreaction in a bioreactor comprises running a bioreaction in a bioreactor including adding additive into the bioreactor during spaced-apart feed events, where contents of the bioreactor equilibrate during a stabilisation period after a feed event; making in situ measurements of a bulk physical property of the bioreactor contents during the bioreaction to obtain process trend data; calculating a derivative of process trend data obtained over a measurement period beginning after a stabilisation period, the derivative being a metabolic rate index (MRI); and using the MRI to determine a time for starting a next feed event. A controller for a bioreactor and a bioreactor system are configured to operate according to the method.

Abstract: A method of forming an optical fibre assembly, comprises providing a planar substrate made of a first material; positioning an optical fibre with an outer layer of a first glass material on a surface of the substrate to form a pre-assembly; depositing a further glass material such as silica soot onto the pre-assembly, over at least a part of the optical fibre and adjacent parts of the substrate surface; and heating the pre-assembly to consolidate the further glass material into an amorphous volume in contact with at least parts of the surface of the substrate and the outer layer of the optical fibre, thereby bonding the optical fibre to the substrate to create the optical fibre assembly.

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: Apparatus (2) comprising a cylindrical substrate (4), and an integrated optical circuit which is provided on the cylindrical substrate and which comprises at least one optical waveguide (6). A process for producing the apparatus (2) is also disclosed.

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: A tunable filter device (2) comprising a waveguide containing a Bragg grating (4), and a planar substrate (6), the planar substrate (6) comprising a core (8), a first cladding (10) on a first side (12) of the core (8), and a second cladding (14) on a second side (16) of the core (8), the waveguide containing the Bragg grating (4) being positioned in the core (8), the planar substrate (6) being such that a part of the first cladding (10) is replaced with a liquid crystal (18), and the tunable filter device (2) being characterized in that the waveguide containing the Bragg grating (4) is ultraviolet light written, the first cladding (10) has a surface which is smooth, flat and uniform due to the waveguide containing the Bragg grating (10) being ultraviolet light written, and the liquid crystal (18) is in contact with the smooth, flat and uniform surface of the first cladding (10) whereby director orientation of the liquid crystal (18) is uniform, controlled and controllable.

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.