WO2020188253A1

WO2020188253A1 - Additive manufacturing apparatus and method

Info

Publication number: WO2020188253A1
Application number: PCT/GB2020/050631
Authority: WO
Inventors: Philip Marsden; Kevin DOWTON
Original assignee: Unitive Design And Analysis
Priority date: 2019-03-15
Filing date: 2020-03-12
Publication date: 2020-09-24
Also published as: GB201903565D0; GB2582181A

Abstract

An apparatus is provided to enable the manufacture of optical fibre arrays. The apparatus is an additive manufacturing apparatus arranged to provide fused fibre optic arrays from a raw material to be deposited, the apparatus comprising, a print bed having a print bed surface arranged to support a raw material; a feed system arranged to receive the raw material from a raw material supply and deposit the raw material onto the print bed surface; a fusion heating member arranged to fuse the deposited raw material to the print bed surface, such that a portion of the deposited raw material is fused together with the print bed; a cleaving member arranged to cleave the raw material; a heat source having an adjustable temperature, and arranged to provide heat to the raw material and/or the deposited material and/or the print bed; wherein the raw material comprises optically structured material. The optically structured material is described as an optical fibre having a core and a cladding layer. The apparatus aims to achieve the manufacture of optical fibre structures which were previously impossible, impractical or overly costly to produce.

Description

Additive manufacturinq apparatus and method

Field of the Invention

The present invention relates to additive manufacturing systems, in particular to additive manufacturing systems for optics and optical devices.

Background to the Invention

Glass waveguides with cylindrical symmetry (more commonly called optical fibres) have potential uses in a countless number of applications, but their use in said applications is often hindered due to the impracticality of manufacturing optical fibre solutions tailored to the needs of the application. Current suboptimal manufacturing capabilities mean that tailored optical fibre solutions for a number of applications are either impossible, impractical, or are prohibitively expensive, time-consuming or manually intensive.

Optical fibres are typically created by drawing a thin structure from a larger structure (called a preform) by applying heat and tension to the larger structure. Imaging or spatially coherent structures can currently be formed by either assembling arrays of optical fibres and gluing them together or by drawing preforms assembled from single or multiple fibre preforms, and then fusing these together.

Fused arrays of fibres can then be machined and manipulated (with a very limited range of operations) into other shapes. This process is manual and very labour intensive.

Coherent optical fibre structures today fall into a number of limited categories. These can include:

Leached fibre bundles - used commonly in endoscopes and other imaging systems where flexibility is required;

Fibre optic faceplates - commonly used to transfer images from a displaced image plane to an image sensor. These can also be used to project an image from a light emitter such as an OLED display or backlit LCD. These are also commonly used where an imaging component needs to be protected from ionising radiation, such as in an X-ray detector; Solid fibre rod - commonly used to transfer illumination and images from one place to another. These work in a similar way to fibre optic faceplates, but can be carefully bent into shape with the aid of a heat. They are typically used with other free-space optical imaging components;

Coherent fibre optic tapers - these are typically constructed from thicker fibre optic faceplates which are heated in the middle and drawn out into a dual taper, similar to the way that a fibre taper is drawn. The dual taper can then be sawn in half, ground and polished, producing, two fibre optic tapers. Coherent fibre optic tapers are typically used for magnification or demagnification from compact imaging systems such as scintillation detection in electron microscopes; and

Coherent fibre optic inverters - these are typically used in night sights in firearms. It is interesting to note that these are difficult to source and are subject to International Traffic In Arms Regulations (ITAR).

These currently available structures carry a number of disadvantages which will now be discussed. All of these applications involve quite simple shapes. All of their shapes are limited in some way by the basic building blocks of the structure. These building blocks are invariably basic wound and leached fibre bundles and they are drawn and stacked on a faceplate block. They all have a limited bend radius. They typically have additional material in place for mechanical robustness and handling when processing. The fibre packing structure is not well controlled and is typically not aligned to the application. Bifurcations are not typically possible. The selection of materials is extremely limited due to large batch fabrication. This last limitation is especially important in environments where material properties are critical for requirements such as biocompatibility and ability to be effectively sterilised.

It is therefore desirable to provide an apparatus enabling the manufacturing of optical fibre solutions tailored according to the dimensional or property requirements of a variety of applications, in a quick, precise and cost-effective manner which may be more attractive to potential manufacturers and customers alike.

Summary of the Invention

In accordance with a first aspect of the present invention, there is provided an additive manufacturing apparatus arranged to provide fused fibre optic arrays from a raw material to be deposited, the apparatus comprising, a print bed having a print bed surface arranged to support a raw material; a feed system arranged to receive the raw material from a raw material supply and deposit the raw material onto the print bed surface; a fusion heating member arranged to fuse the deposited raw material to the print bed surface, such that a portion of the deposited raw material is fused together with the print bed; a cleaving member arranged to cleave the raw material; a heat source having an adjustable temperature, and arranged to provide heat to the raw material and/or the deposited material and/or the print bed; wherein the raw material comprises optically structured material.

The term“structured material”, in the context of the present invention, would be understood by the skilled addressee as being a material having a structure to be maintained before, during and after the additive manufacturing process.

Preferably the structured material is pliable and comprises a flexible solid. The term “optically structured material” in the context of the present invention will comprise optically structured material such as an optical fibre having a core and a cladding layer. The structured material can comprise physical structures, filament structures and filaments having a chemical gradient structure.

The term“fused together with the print bed” will be understood in the context of the present invention to mean that the deposited raw material is made integral with, or merged with, the print bed, as distinguished from merely being layered above the print bed.

The invention comprises a new additive manufacturing based apparatus for the printing of fibre optic glass structures. In preferable embodiments, the optically structured material is an optical fibre comprising an optical fibre core and an optical fibre cladding layer surrounding the core. The invention is preferably arranged to fuse the deposited raw material to the print bed surface such that only the cladding layer, or a portion thereof, is fused to the print bed. During and following said fusion, preferable embodiments provide no diffusion of the cladding material into the core material, and therefore cause no change between short-range optical properties of the raw material and those of the final fused fibre optic array.

The present method preferably provides direct fusion of a cladding layer of an optical fibre raw material to a surface of a print bed, and/or to a cladding layer of a further optical fibre raw material. Such fusion is preferably performed using heat from the fusion heating member, which may be, or receive the heat from, the heat source. The heat may be used by the fusion heating member to bring the optical fibre raw material to a temperature similar to the Littleton Softening Temperature, permitting fusion between cladding layer and print bed surface, or between adjacent cladding layers. It has been identified that the present invention preferably prevents diffusion between cladding and core materials at the fusion temperature, thereby avoiding any effects of the invention on short-range optical properties of the core or cladding layer.

Overcoming limitations to the existing technology mean that structures beyond the typical end products of for example, image-transfer faceplates, tapers or leached fibre bundles should become available, and available beyond the finite number of standard dimension categories and limited range of properties currently available. The present invention preferably provides for the fusion of more than one optical fibre, such that the fibres collectively form a coherent fused fibre optic array having a well-defined input position and a well-defined output position relative to one another.

There are a number of applications for which the use of more tailored optical fibre solutions would pose a vast improvement in reliability, accuracy and efficiency of processes. The incorporation of optical fibres into such applications has, however, been previously hampered, or considered impractical, given the dearth of available solutions, or the unsuitability of standard size and property ranges.

The raw material optically structured material preferably comprises core characteristics and cladding characteristics appropriate to an end user requirement. The core characteristics may be understood by the skilled addressee to refer to: the core composition, which may include any suitable material and may further include any number of optical fibre dopants; the core diameter; the core refractive index; the core mode, which may be single mode or multimode; the core refractive index profile; the core numerical aperture; the core viscosity; the core tensile strength. The cladding characteristics may be understood by the skilled addressee to refer to: the cladding composition, which may include any suitable material and may further include any number of optical fibre dopants; the cladding diameter; the cladding refractive index; the cladding mode, which may be single mode or multimode; the cladding refractive index profile; the cladding numerical aperture; the cladding viscosity; the cladding tensile strength. During and following fusion with the present invention, preferable embodiments provide no diffusion of the cladding material into the core material, and therefore cause no change between said core or cladding characteristics of the raw material and those of the final fused fibre optic array. The apparatus preferably permits the precise laying down of optical fibres, preferably at speed, and preferably with the intention of producing optical fibre array shapes and/or sizes capable of high quality image transfer, which are preferably not possible to create using technology available prior to the present invention.

The apparatus preferably enables the design and development of fibre optic arrays tailored to end-user requirements i.e. products to fit the application and not as is possible currently, the other way around.

Preferably the apparatus of the present invention permits new design possibilities, which may preferably include new forms, including bends, splits, curves - preferably to enable images to be projected from below or the side. The apparatus preferably permits the creation of fused fibre optic arrays having input and output facets, wherein each said facet is preferably planar, and may be at an arbitrary orientation relative to one or more other of said facets. Preferably, across said facets, spatial coherence is maintained between each input to each output throughout and following the fusion process. As such, the present invention preferably permits the production of monolithic structures having input and output facets arranged in any configuration relative to one another, but always maintaining spatial coherence.

The present invention preferably permits the creation of monolithic arrays with input and output facets, whereby the array facets are constituted from two or more end facets of optical fibres of the array. These optical fibres may all be the same size or they may be varying sizes to suit a specific application. The structures/arrays may comprise fibres having varying optical fibre dimensions and optical fibre types.

The present invention may additionally permit the creation of monolithic objects with input and output facets providing a“one-to-many” or“many-to-one” configuration, i.e. a single input facet may transfer a spatial arrangement of light or image to two or more output facets, and vice versa. For example, a single imaging plane may be optically connected to two image sensors through a bifurcation structure produced using the present invention. As such, structures produced using the present invention are not limited to single input and output facets.

The present invention may additionally permit the creation of monolithic objects with arrangements of input and output facets wherein each input facet does not necessarily map directly to a corresponding output facet, but maps with a well-defined spatial coherence. For example, the present invention may be used to produce a structure or structures having a square grid array input facet, which could map to a corresponding line array at the output facet for use in hyperspectral imaging. As a second example, the present invention may be used to produce structure having a hexagonal grid array input facet, which could map to a corresponding circular array output facet for use in structured lighting. As such, the present invention is preferably arranged to achieve well-defined, but totally configurable, input to output mapping.

The fusion heating member of the present invention is preferably arranged to fuse bulk optical materials with waveguide/optical fibre material whereby the fusion occurs only between the cladding of the waveguide/optical fibre, and there is therefore no diffusion of material into or from the core material and hence the optical properties of the waveguide are unchanged, for example in terms of mode structure, number of modes and/or loss. The fusion heating member of the present invention therefore arranged to fuse optical fibre, but preferably only through cladding fusion.

The fusion process is preferably arranged to fuse, as the deposited raw material, step-index optical fibre or graded index optical fibre, wherein the optical mode of each fibre is preferably confined to the centre of the fibre. When the raw material is an optical fibre having a cladding layer of sufficient thickness (taken from the edge of the core to the opposing edge of the cladding layer), wherein sufficient cladding layer thickness is preferably greater than around 10pm, fusion between the deposited raw material and the print bed surface, or between adjacent deposited raw material, does not impact the optical waveguiding properties of the deposited raw material (preferably optical fibre). The minimum thickness of the fused cladding layers or cladding/print bed is limited to that where the optical field has fallen off by -20dB (1 %).

In preferable embodiments, the raw material being optical fibre, the fibre can be passive (comprising a simple core-clad structure) or active. The active component can be all optical, electro-optical, magneto-optical, chemical or biological. Examples may include lasers embedded in the optical fibre matrix, modulators embedded in the optical fibre matrix, chemical sensors embedded in the optical fibre matrix, and/or biologic sensors embedded in the optical fibre matrix encapsulated in raw material.

The apparatus may, in some embodiments, be arranged to apply a coating material to the fused fibre optic array, which may be applied to one or more, whole or partial, end facets of said array, or to individual ends of optical fibres within said array. The end facets or ends of the fibres may be coated post completion of fusion. The coating layer is preferably functional, the additional functional layer preferably being optical-sensing, electro-sensing, magneto-sensing, chemical sensing and/or or biologic sensing. For example the fused fibre optic array may be optimised for surface-enhanced Raman scattering (SERS). In such embodiments, one or more optical fibre ends of said array may be coated with a metal, which is preferably a noble metal, which may be deposited on the one or more optical fibre ends in nanoparticle form.

Using the present apparatus, the fibre arrangement of the fused fibre optic array may be customised and optimised for near-field illumination and imaging/sensing. For example, the fused fibre optic array may form a sensor, wherein a relatively large fibre can be deposited for use in the sensor for light field delivering, with a number of (potentially smaller) fibres deposited around this“delivery fibre” for signal collection. The smallest fibre may be around 6pm the largest around 500pm with core/clad ratios of 75/25 to 99/1 for the large, highly confined fibres. It is also preferably possible to provide a fused fibre optic array using the present invention wherein delivery of excitation light is performed unguided through the fused fibre optic array structure, with the fibre structure collecting only the resultant image. As such, the present apparatus is preferably arranged to produce a fused fibre optic array arranged to perform uniform bulk illumination.

The present apparatus therefore preferably enables the production of structures having one or more of the following improvements over and above currently available technology:

• inclusion of arbitrary bends and curves in a monolithic structure;

• creation of monolithic structures where the input plane and output plane are not parallel;

• creation of 'many to one' and 'one to many' structures;

• robustness (leeched fibre bundles typically degrade and break/catastrophically fail over time so are not robust);

• configurability to any type of glass (core-cladding combination);

• configurability of choosing raw materials for the application - e.g. sterilisability and biocompatibility;

• monolithic - no glue, no glue failure, avoiding limitations of free space optics; configurability of re-arranging the input and output geometry and dimensionality. The obvious example being to turn a 2D image into a 1 D projection for spectroscopic analysis (currently only possible by manual configuration); • configurability of alignment to specific pixel pitches (current systems use spatial oversampling, but this introduces loss); and/or

• suitable for just-in-time manufacturing (versus an 8-week lead-time for existing structures).

First and foremost, the core idea of the present invention is in the additive manufacture of structured glass, preferably acting as an optical waveguide, such as optical fibre, and preferably through cladding fusion without alteration of the waveguide properties of the optical fibre core. The term“cladding fusion” will be understood in the context of the present invention to mean the fusion of a cladding layer of an optical fibre to a substrate, such as the print bed surface or to a cladding layer of an adjacent optical fibre. The term“cladding layer” will be further understood to be a silica-based layer having immediate interface with the optical fibre core (or in the case of an“outer cladding layer”, immediate interface with an inner cladding layer), each said cladding layer having a refractive index properties arranged to form a waveguiding optical fibre core (or a waveguiding optical fibre inner cladding layer - in embodiments facilitating cladding modes) through internal reflection. The waveguiding function of the cladding layer will be understood to distinguish the term“cladding layer” from the term“coating layer”, wherein a“coating layer” is typically intended to provide protective, shielding, or other sensing properties to the optical fibre un-associated with wave guiding. In the case of“leached fibres”, a“coating” may be interpreted as a material used to temporarily combine optical fibres before being leached from the structure in the final product. The term “cladding fusion” in relation to the present invention will therefore be understood to distinguish the present invention from methods of “fusing” optical fibres using contrasting “coating fusion” methods. Preferably the apparatus of the present invention permits the printing of 1 -dimensional structured raw materials. The structures comprise optical fibres or optically structured material with a chemical gradient structure and/or chemically structured filament.

Preferably the feed system comprises any suitable system for feeding a single, or multiple, raw material entity (or entities, in a staggered manner or simultaneously) toward the print bed surface to be deposited. In preferable embodiments, the feed system comprises one or more guide members arranged to support the raw material on a surface thereon, and guide the raw material in a direction toward the print bed surface.

In preferable embodiments, the feed system may comprise the heat source and/or the fusion heating member. As such, elements of the feed system proximate or downstream of the heat source or fusion heating member are preferably comprised of a material resistant to the heat from the heat source, or a heat from the fusion heating member.

In preferable embodiments, the feed system comprises a channel, which may be enclosed, and arranged to convey the raw material from a channel input to a channel output, toward the print bed surface. The channel output may, in some embodiments, form a guide nozzle arranged to provide precise depositing of the raw material onto the print bed surface, or an adjacent deposited raw material, at a desired location. The raw material is preferably conveyed along the channel of the feed system under impetus from an active guide member of the feed system, which may be located upstream of, downstream of, or within the channel.

The channel is preferably proximate or adjacent to the heat source, wherein the heat from the heat source is arranged to pervade at least a portion of the channel in order to heat the raw material conveyed therethrough. The heat source may, in some embodiments, comprise a heating jacket surrounding the channel. In other embodiments, or additionally, the heat source may comprise an oven having a chamber housing the print bed. In some embodiments, the heat may also be provided from the heat source to the print bed.

In preferable embodiments the feed system comprises a first active guide member, a second passive guide member, and a guide nozzle. Preferably the first active guide member is driven by a motor. In such embodiments, the first active guide member may be a rotatable member arranged to rotate about an axis while supporting the raw material on a surface of the active guide member. Said rotation of the first active guide member is preferably driven by the motor. During rotation of the active guide member, the raw material may be urged, due to friction from the supporting surface of the active guide member, in a direction toward the print bed surface.

Preferably the second passive guide member is spring loaded. In such embodiments, the second passive guide member may be rotatable about an axis. In such embodiments, the second passive guide member may be rotatable under impetus from the raw material actively driven by the first active guide member, and supported on a surface of the second passive guide member. The second guide member is preferably biased in a direction toward the raw material by a spring, and is thus spring-loaded. In such embodiments, the second guide member is preferably moveable reciprocally along an axis perpendicular to the raw material, wherein the spring-loading provides gentle guiding of the raw material in a direction toward the print bed surface, without imparting excessive axial forces on the raw material. The rotatable first active guide member may additionally be supported on its axis by a low- friction bearing such that minimal resistance to the impetus of the raw material is exhibited, therefore permitting that guidance of the raw material causes minimal shear forces to be imparted from the second passive guide means to the raw material during rotation. In preferable embodiments, at least the supporting surfaces of the first and second guide member are coated with a compressive material arranged to impart minimal axial or shear forces to the raw material during feeding. Examples of suitable compressive materials may include soft rubber and similar polymeric materials. Preferably the first and second guide member each comprise a rotatable puck.

Preferably the heat source is arranged to heat the raw material to a raw material temperature, the raw material temperature being 0 - 1500 °C, preferably 650 - 800 °C, more preferably 500 - 550 °C. In such embodiments, the heat source may be, or comprise a component which is, positioned proximate or adjacent to a component of the feed system such that said heat is provided to the raw material as it is fed toward the print bed surface by the feed system.

Preferably the heat source is arranged to heat the print bed surface to a print bed surface temperature, the print bed surface temperature being 0 - 1500 °C, preferably 650 - 800 °C, more preferably 500 - 550 °C. More preferably in an embodiment the raw material temperature and the print bed surface temperature are substantially the same. In such embodiments, the heat source may be, or comprise a component which is, positioned proximate or adjacent to the print bed or print bed surface, such that said heat is provided to the print bed surface.

In some embodiments, the print bed and at least a portion of the feed system may be comprised within a chamber which is at least partially enclosed. The chamber may comprise walls having a component of the heat source comprised therein, or adjacent thereto. As such, the immediate environment of the print bed and said portion of the feed system may also be temperature-controlled. Said chamber may therefore form an oven around a “fabrication space” defined by the print bed surface and the vertical space thereabove. In the oven, said print bed surface temperature and/or the raw material temperature may be provided. Additionally, temperature within the oven may be controlled such that the rate of cooling of one or more layers of the fused fibre optic structure may be suitably regulated, either during or post fabrication. This may be important in order to maintain the integrity of, and thus the waveguide properties of, the individual deposited optical fibres of the fused fibre optic structure. Preferably the heat source comprises a heating element. Preferably the heating element comprises a wire arranged to transmit heat caused by electrical resistivity of the wire. Preferably the wire is arranged into a coil. Preferably the wire is comprised of a metal alloy. Preferably the metal alloy comprises at least one selected from the range: nickel; chromium; iron. Preferably the metal alloy is nichrome.

Preferably the apparatus further comprises a controller arranged to control at least one selected from the range: the print bed; the feed system; the fusion heating member; the cleaving member; the heat source. Control of the print bed will be understood in the context of the present invention as including at least control of one or more of: a position of the print bed on a horizontal plane and/or a vertical plane; an orientation of the print bed; a rotation of the print bed; and/or a temperature of the print bed. Other suitable forms of control of the print bed will be appreciated. Control of the feed system may include control of individual, or collectively two or more, elements of the feed system. Said control of the feed system will be understood in the context of the present invention as including at least control of one or more of: a feed rate of the feed system; a speed, such as rotational speed of a rotational element of the feed system, such as a rotational guide member; orientation or position of one or more elements or components of the feed system, such as an orientation or position of a channel outlet or guide nozzle relative to the print bed surface or deposited raw material; a temperature of the feed system, such as a temperature of the guide nozzle or channel. Other suitable forms of control of the feed system will be appreciated. Control of the fusion heating member will be understood on the context of the present invention as including at least control of one or more of: a position and/or orientation of the fusion heating member; a temperature of the fusion heating member. Control of the cleaving member will be understood on the context of the present invention as including at least control of one or more of: a position and/or orientation of the cleaving member; a temperature of the cleaving member. Control of the heat source will be understood on the context of the present invention as including at least control of one or more of: a position and/or orientation of the heat source; a temperature of the heat source. Such control, and particularly temperature control, may be regulated automatically as a result of feedback components and/or sensors, such as a thermostat. Temperature control may be automated in order to provide thermal cycling of components of the apparatus during manufacture of said fused fibre optic array. Preferably the print bed surface comprises a print bed surface material, wherein the print bed surface material comprises one selected from the range: silica glass; soda lime; borosilicate. Other examples of glasses include oxides of silica, barium, lead, sodium, potassium, boron, aluminium, calcium, magnesium, lithium, phosphorous, titanium, zirconium and glass families such as flint glass, crown glass, borosilicate glass, aluminosilicate glass, aluminoborosilicate glasses, alkali lead silicate glasses, alkali alkaline earth silicate glasses, lithium-aluminium silicate glasses, and their families.

Preferably the cladding layer of the raw material comprises the print bed surface material. Having the cladding material the same as the print bed material ensures that the structure has a robust substrate and also that there is strain-free adhesion between the substrate and the structure.

Embodiments will be appreciated wherein the fusion heating member is equal to, or comprised within or adjacent to, the print bed surface.

Preferably the print bed is arranged to move on a horizontal plane and/or a vertical plane, which may be, for example, provided for by an XY or XYZ platform and translational stage of the apparatus.

Preferably the raw material supply is one selected from: an optical fibre drum; an optical fibre draw tower. In embodiments wherein the raw material is an optical fibre, the optical fibre may be fed by the feed system from a supply spooled around an optical fibre drum. As an example alternative, the present apparatus may be placed in-line with an optical fibre draw tower, with optical fibre being fed directly by the feed system as it is drawn from the draw tower.

Preferably the raw material supply is an optical fibre draw tower, and wherein the raw material is output from the optical fibre draw tower and provided directly to the apparatus.

Preferably there is a cutting or cleaving stage of the raw material supply, which may comprise a heated cleave process. For a heated cleave process, a temperature of around 800 °C to 1100 °C is preferable, with, in some embodiments, a temperature in excess of 1000 °C being desirable such that the glass raw material is heated to the fusion temperature (approximately at the Littleton Softening Point).

In accordance with a second aspect of the present invention, there is provided a method of additive manufacture of fused fibre arrays of optically structured material, the method comprising the steps of: a. providing an optical fibre having a core and a cladding layer; b. heating the optical fibre to an optical fibre temperature, wherein at the optical fibre temperature the optical fibre remains substantially solid;

c. feeding the heated optical fibre onto a print bed surface having a print bed surface temperature that is substantially the same as the optical fibre temperature;

d. fusing a portion of the heated optical fibre to the print bed surface, such that a portion of the optical fibre is merged and fused together with the print bed;

e. cleaving the heated optical fibre;

f. repeating steps c and d, and optionally step e, such that a layer or layer portion of optical fibre is deposited onto, and supported by, the print bed surface; g. heating the layer to the optical fibre temperature;

h. feeding the heated optical fibre onto the layer or a spacer layer or onto an orthogonal fibre spacer;

i. fusing a portion of the heated optical fibre to the layer, such that a portion of the optical fibre is merged and fused together with the layer;

j. cleaving the heated optical fibre;

k. repeating steps g to i, and optionally step j, such that a subsequent layer or layer portion of optical fibre is deposited onto, and supported by, the previous layer or layer portion;

L. repeating step k, such that a fused fibre optic array is provided.

Preferably steps b to I are performed in a heated chamber, such as, for example, an oven. In such embodiments, the heat source may be disposed within the heated chamber, within one or more walls of the heated chamber, or adjacent one or more walls of the heated chamber.

Preferably the optical fibre temperature remains constant throughout steps c to I.

Preferably the method further comprises a step, following step f, of: depositing a spacer element above the layer, wherein the spacer element covers at least a portion of the layer. In such embodiments, the method may further comprise subsequent steps of: heating the spacer element to the optical fibre temperature; feeding the heated optical fibre onto the spacer element; and fusing a portion of the heated optical fibre to the spacer element, such that a portion of the optical fibre is merged and fused together with the spacer element.

It will be appreciated that the steps of the method may be performed in any suitable order. For example, the steps of “heating” and“feeding” may be performed in any suitable order prior to the step of“fusing”, or two or more of these steps may be performed simultaneously. In other examples, a series sequential“feeding” steps may provide a one or more layered series of adjacent optical fibres (which may comprise a single layer on the print bed, or a series of stacked layers), subsequent to which“heating” and“fusing” steps may be applied to the one or more layers as a whole, to provide simultaneous heating to, and/or fusion of, the layer to the print bed, adjacent optical fibres to each other, and/or the adjacent layers to each other.

This printing technology preferably facilitates the creation of structures which were previously considered impossible. Bend radii are preferably limited only by the loss characteristics of the waveguide (or raw material) and not by the mechanical properties of the waveguide (or raw material).

Structures can preferably be made directly arbitrarily small or large to fit into a required footprint. The structures can also preferably be shaped to fit in around other components, fit inside other components and/or provide a mounting substrate for other components such as image sensors. The fibre packing arrangement can preferably be aligned to pixelated structures such as image sensors and displays. The fibre core size can preferably be optimised to feed into the centre of image sensor pixels, avoiding the need for micro-lenses and avoiding the dead space where the pixel fill fraction is low to get high speed and high dynamic range performance. Printing parameters can preferably be adjusted on the fly to adapt to different raw materials (which may optionally be glass) rapidly, preferably allowing for the printing from small batches of raw materials, dramatically increasing the range of possible raw material parameters.

Detailed Description

Specific embodiments will now be described by way of example only, and with reference to the accompanying drawings, in which:

FIG. 1 shows a viscosity vs temperature plot for four example raw materials suitable for use with the present invention;

FIG. 2 provides a schematic view of an example feed system suitable for an apparatus according to the first aspect of the present invention;

FIG. 3 provides a sectional view of an example feed system and print bed for use suitable for an apparatus according to the first aspect of the present invention; FIG. 4 provides an isometric view of an example print bed and cleaving member of an apparatus according to the first aspect of the present invention;

FIG. 5 provides an isometric view of a fibre optic array suitable for manufacture using an apparatus according to the first aspect of the present invention;

FIG. 6 illustrates the front view of the structure of FIG. 5 fabricated according to the first aspect of the invention; and

FIG. 7 illustrates an alternative structure fabricated according to a first aspect of the invention.

The diagram in FIG. 1 shows the viscosity vs temperature plot for four different glasses (soda lime glass, borosilicate glass, 96% silica glass, and fused silica). The essential elements of additive manufacturing of structured glass fibres are captured in this plot. To maintain the structure of the glass, it is important to stay well below the melting point temperature (T_m) and, in preferable versions, below the working point temperature. To achieve fusion, it is important to ensure that the raw material is above the raw material temperature. In particular for fusion it is the aim to heat the glass to the fusion temperature (approximately at the Littleton Softening Point).

The glass enters the oven below To arriving at the print bed some fraction above T_g. As the fibre starts to lie on the print bed it is thermally cycled. The exact temperature of the cladding is likely to approach the working point temperature. At this point adjacent cladding structures and/or substrate materials fuse together holding the glass fibre in place.

Referring to FIG. 2, the fibre feed system can be described. The feed system 10 takes the fibre 20 from a drum or draw tower (not shown) and drives it into the oven and fabrication space. The feed system 10 is driven by a stepper motor 30 to provide fine control and rubber pucks 40 and 50 are provided downstream of the stepper motor. Pucks 40, 50, provide mechanical control, the pucks comprise one driver; one idler and the pucks grip the fibre sufficiently to draw and feed the fibre into the oven. Damage to the surface of the fibre must be kept to a minimum to eliminate scatter losses and poor fusion. The pucks 40, 50 comprise soft rubber so that damage is kept to a minimum. The feed system has provision for sourcing the optical fibre from a drum or optionally from a draw tower. Optical fibre is typically coated in a polymer when taken from the draw tower. This prevents surface damage when it is wound onto a drum. For pristine glass delivery with the best surface quality, the machine can be linked to a small fibre draw tower which runs quasi-synchronously with the print feed ensuring the best material quality.

The fibre 20 cannot be simply squeezed onto the print bed 60 bed like in other additive manufacturing processes. The angle of attack, the tackiness of the print bed surface 70 and the speed of attack are all controlled carefully to ensure rapid adhesion and minimal feedback back up through the nozzle 80 to the feed pucks 40, 50. The print bed surface arrangement is shown in FIG. 3.

With reference to FIG. 3 it can be seen that the design of the fibre lay up can be controlled and managed. Indeed the fibre lay up is the key to getting robust structures. Glass fusion requires close-packed stacking. Hermetic sealing introduces an additional critical laying up requirement. The other driving requirements are then the entry and exit facets of the final monolithic light guiding structure. The fibres lay up design may have one or more entry facets and one or more exit facets.

Fibre cleaving is illustrated in FIG. 4. The fibre 20 needs to be cleaved at the end of print run so that the print bed 60 can move to the next start position for the subsequent fibre run. The cleave needs to be clean, rapid, not send a shockwave up the feed nozzle and not leave any debris on the print bed 60. This is achieved by dropping the end of the fibre onto a heated wire 80, around 1000 ° C. The heated wire melts the fibre at the point of contact forcing it to both cleave and droop and drop out of the current print scope.

The first layer of fibre is fused to the print bed with the aid of nichrome coil heaters which are located above the print bed. The temperature of this additional heat source is static and carefully controlled. These heaters also ensure that subsequent layers are fused to the first layer.

The print bed 60 itself is chosen to be a planar glass material to which the print material can be adhered. This is matched to have a similar temperature-viscosity characteristic as the material being deposited. The temperature of the print bed is controlled by the heat elements on the oven wall. Since the material is structured, standard geode and Additive Manufacturing file formats do not contain sufficient information to describe how to produce the structures. A new file format for 1 D raw material printing such as a print description (or an addition to the AMF standard) adds the core : cladding ratio and fibre diameter along with a set of 3D point trajectories through which the fibres need to pass.

An annealing step is described here as the structure, when formed, contains both the stress of the original fibre and the stress built into the new structure. In fact, the act of fusion can change the in-built stress characteristic. The fibre structure requires a careful cooling temporal profile to prevent it from cracking or shattering.

Examples of structures fabricated according to the invention include fused fibre optic arrays, 90 ° bends, interlocked, spatially coherent Y junctions and the optical/image interleave of FIGs. 5 and 6 and the 90 ° bend or image corner shown in FIG. 7. FIG. 5 and FIG. 6 show spacers between alternating layers of the arra to permit the Y structure shown. The spacers are structured and could be fibres themselves.

It will be appreciated that the above described embodiments are given by way of example only and that various modifications thereto may be made without departing from the scope of the invention as defined in the appended claims. For example, one or more optical fibre layers can be envisaged arranged in layers in a packed arrangement. Alternatively strands of optical fibres may be arranged and fused together in part or portions of layers. Overlaid optical fibres may be created, although not necessarily forming strict planes, the overlaid fibres or filaments will still comprise depth and array characteristics.

Claims

1. An additive manufacturing apparatus arranged to provide fused fibre arrays from a raw material to be deposited, the apparatus comprising,

a print bed having a print bed surface arranged to support a raw material;

a feed system arranged to receive the raw material from a raw material supply and deposit the raw material onto the print bed surface;

a fusion heating member arranged to fuse the deposited raw material to the print bed surface, such that a portion of the deposited raw material is fused together with the print bed;

a cleaving member arranged to cleave the raw material;

a heat source having an adjustable temperature, and arranged to provide heat to the raw material and/or the deposited material and/or the print bed;

wherein the raw material comprises optically structured material.

2. An additive manufacturing apparatus according to claim 1 , wherein the feed system comprises a first active guide member, a second passive guide member, and a guide nozzle.

3. An additive manufacturing apparatus according to claim 2, wherein the first active guide member is driven by a motor.

4. An additive manufacturing apparatus according to claim 2 or claim 3, wherein the second passive guide member is spring loaded.

5. An additive manufacturing apparatus according to claim 2, claim 3 or claim 4, wherein the first and second guide member each comprise a rotatable puck.

6. An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the heat source is arranged to heat the raw material to a raw material temperature in the range from 0 - 1500 °C, preferably 650 - 800 °C, more preferably 500 - 550 °C.

7. An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the heat source is arranged to heat the print bed surface to a print bed surface temperature, the print bed surface temperature being a temperature in the range from 0 - 1500 °C, preferably 650 - 800 °C, more preferably 500 - 550 °C.

8. An additive manufacturing apparatus as claimed in claim 6 or claim 7, wherein the raw material temperature and the print bed surface temperature are substantially the same.

9. An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the print bed surface comprises a print bed surface material, wherein the print bed surface material comprises one selected from the range: silica glass; soda lime; borosilicate; oxides of silica, barium, lead, sodium, potassium, boron, aluminium, calcium, magnesium, lithium, phosphorous, titanium, zirconium and glass families such as flint glass, crown glass, borosilicate glass, aluminosilicate glass, aluminoborosilicate glasses, alkali lead silicate glasses, alkali alkaline earth silicate glasses, lithium-aluminium silicate glasses, and their families.

10. An additive manufacturing apparatus as claimed in claim 9, wherein the cladding layer of the raw material comprises the print bed surface material.

11. An additive manufacturing apparatus as claimed in any one of claims 8 to 10, wherein the print bed is arranged to move on a horizontal plane and/or a vertical plane.

12. An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the apparatus further comprises a controller arranged to control at least one selected from the range: the print bed; the feed system; the fusion heating member; the cleaving member; the heat source.

13. An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the raw material supply is one selected from: an optical fibre drum; an optical fibre draw tower.

14. An additive manufacturing apparatus as claimed in claim 13, wherein the raw material supply is an optical fibre draw tower, and wherein the raw material is output from the optical fibre draw tower and provided directly to the apparatus.

15. A method of additive manufacture of fused fibre arrays of optically structured material, the method comprising the steps of: a. providing an optical fibre having a core and a cladding layer;

b. heating the optical fibre to an optical fibre temperature, wherein at the optical fibre temperature the optical fibre remains substantially solid;

d. fusing a portion of the heated optical fibre to the print bed surface, such that a portion of the optical fibre is merged and fused together with the print bed; e. cleaving the heated optical fibre;

f. repeating steps c and d, and optionally step e, such that a layer or layer portion of optical fibre is deposited onto, and supported by, the print bed surface;

g. heating the layer to the optical fibre temperature;

h. feeding the heated optical fibre onto the layer;

j. cleaving the heated optical fibre;

L. repeating step k, such that a fused fibre optic array is provided.

16. A method as claimed in claim 15, wherein steps b to I are performed in an oven.

17. A method as claimed in claim 15 or claim 16, wherein the optical fibre temperature remains constant throughout steps c to I.

18. A method as claimed in any one of claims 15 to 17, wherein the step of cleaving the heated optical fibre is arranged wherein the cleave temperature is 800 - 1100 °C.