Improvements in or relating to waveguides

Abstract

There is provided a cantilevered waveguide (1,101,301). The cantilevered waveguide having a flexible substrate (2,102,302) upon which a plurality of waveguide segments (6,106,306) are provided. The flexible waveguide also having one or more flexion elements (7,107,307). The flexion elements (7,107,307) having different material properties to the flexible substrate (2,102,302) so as to introduce a strain imbalance between the flexion element and flexible substrate when subjected to a stimulus such as heat or magnetic field. The strain imbalance inducing a flex in the flexible substrate.

Description

[0001] IMPROVEMENTS IN OR RELATING TO WAVEGUIDES

[0002] Technical Field of the Invention

[0003] The present invention relates to optical waveguides. In particular, but not exclusively the invention relates to cantilever waveguides.

[0004] Background to the Invention

[0005] In the fields of integrated nanophotonics, optical couplers are an extremely important component within any integrated nanophotonic circuits. Optical couplers allow light to be coupled from one conduit to another, typically from on-integrated photonic circuit conduits, such as waveguides, to off integrated photonic circuit conduits, such as optical fibres or free-space elements, and vice versa.

[0006] There are several known types of optical couplers used in integrated nanophotonics, one example being an on-chip grating coupler. Such a coupler comprises an optical grating formed into the integrated photonic circuit itself, so as to diffract light waves incident on the grating coupler and transfer them to a waveguide for use in said circuit.

[0007] Grating couplers can be fabricated at the same time as the waveguides themselves, and as they couple through the upper surface of the integrated photonic circuit, they enable significant space savings when opposed to other couplers, providing greater space efficiency, which is an important factor of integrated photonic circuit design. However, grating couplers only work effectively for a relatively small band of wavelengths. Additionally, the effectiveness of couplers is dependent upon the polarisation of the light.

[0008] Another known optical coupler is the edge coupler, where an optical fibre is physically coupled to the waveguide itself, allowing the transmission of light between the fibre and waveguide. Whilst these couplers function for a broad band of wavelengths, they require the integrated photonic circuit be cut or cleaved so as to allow the fibre to be coupled to the waveguide at the edge of the integrated photonic circuit. This complicates the integrated photonic circuit manufacture process. In addition, the space available on edge of the integrated photonic circuit is significantly less that the surface area of the chip. Also, in many cases the cut (or cleaved) facet requires polishing which further complicates the manufacturing process.

[0009] Another known example is the stressed cantilever waveguide, wherein a conventional waveguide is formed upon a flexible substrate which extends from a fixed end to a free end, allowing the waveguide to flex with the flexion of the substrate. In such devices, as the free end of the waveguide is flexed out of the plane of the integrated photonic circuit due to built-in stresses in the structure, it provides for coupling opportunities out of the plane of the integrated photonic circuit. The coupled light is then introduced into the plane of the integrated photonic circuit via the free end of the waveguide. However, owing to the requirements of the waveguides themselves (particularly the materials and dimensions thereof, especially that the waveguides add relative thickness to the overall structure in a direction transverse to the flex), the waveguides themselves are generally relatively inflexible compared to the substrate, and thus naturally limit the extent to which a cantilever waveguide can be flexed.

[0010] For a conventional stressed cantilever waveguide (i.e. a conventional waveguide is formed upon a flexible substrate, with stress elements incorporated into the structure), subjected to a I00K temperature change, the flexibility (measured in terms of the vertical movement of the free end) is around 8pm for a 400 nm x 1000 nm silicon nitride waveguide on a 100 nm thick, 100pm x 20pm silicon nitride cantilever substrate, for a stress is created by a deposited aluminium film that is fOOnm thick.

[0011] For a simple silicon nitride cantilever substrate of the same dimension (with no waveguide) and fOOnm thickness, again stressed by a fOOnm thick deposited aluminium film, the flexibility is around 78pm (again measured in terms of the vertical movement of the free end). It is therefore evident that conventional waveguides significantly reduce the flexibility of cantilevers, due to their rigid nature.

[0012] It is an object of the present invention to provide an improved cantilever waveguide which overcomes and / or ameliorates the above issues with known cantilever waveguides.

[0013] Summary of the Invention According to a first aspect of the present invention, there is provided a cantilever waveguide comprising: a flexible substrate extending along a cantilever major axis from a fixed end to a free end; a series of disconnected waveguide segments provided on the flexible substrate between the fixed and free ends so as to form a subwavelength grating waveguide; and one or more flexion elements provided on the flexible substrate, the one or more flexion elements configured to urge the substrate to flex in a direction transverse to the cantilever major axis.

[0014] Provision of a series of disconnected waveguide segments forming a subwavelength grating waveguide on the flexible substrate allows for the flexible substrate to flex in the regions between the segments. This can therefore increase the extent of flexion of the cantilever waveguide structure as a whole significantly compared to conventional cantilever waveguides.

[0015] To return to the example set out above (a conventional silicon nitride waveguide on a lOOnm thick 100pm x 20pm silicon nitride substrate), experimental data shows that provision of the disconnected waveguide segments which together form a subwavelength grating waveguide increases the flexibility by a factor of 8 (at least). In this specific example, a waveguide according to the present invention (with the subwavelength grating waveguide width (i.e. segment width) being lOOOnm, segment height of 400nm and a spacing / grating period of 430nm) achieved a flexibility (measured in terms of the vertical movement of the free end) of 70pm, as opposed to 8pm for a conventional cantilever waveguide.

[0016] The cantilever waveguide may be a single-mode waveguide. The cantilever waveguide may be a multi-mode waveguide.

[0017] The cantilever major axis may be defined by the cantilever waveguide when in a neutral (i.e. unflexed) position along the length of the cantilever. The transverse direction in which the cantilever waveguide flexes may be a direction that is substantially perpendicular to the plane in which the cantilever waveguide lies when in the neutral (i.e. unflexed) position.

[0018] The cantilever waveguide may extend between 1pm and 10mm from the fixed end to the free end. The width of the cantilever waveguide (i.e. the substrate width) may be between 1 m and 1mm. The segment width may be between 100 nm and 1 mm. The thickness of the cantilever waveguide (including the segments) may be between lOOnm and 100pm.

[0019] It will be understood by the skilled person that certain properties of the subwavelength grating waveguide will be dictated by the wavelength of the light to be transmitted therethrough. For example, longer wavelengths of light will require a wider and thicker subwavelength grating waveguide (and so the segments will necessarily be wider and thicker than for shorter wavelengths). The cantilever waveguide may be operable through a range of wavelengths between lOOnm to 10cm.

[0020] The width of the subwavelength grating waveguide (i.e. the segment width) may be between 10% and 1000% percent of the wavelength of the light transmitted therein. In a specific example of a single-mode waveguide, the width of the subwavelength grating waveguide (i.e. the segment width) may be between 10% and 100% of the wavelength of the light transmitted therein.

[0021] The thickness of the subwavelength grating waveguide (i.e. the segment height) may be between 10% and 1000% percent of the wavelength of the light transmitted therein. In a specific example of a single-mode waveguide, the thickness of the subwavelength grating waveguide (i.e. the segment height) may be between 10% and 100% of the wavelength of the light transmitted therein.

[0022] More specifically, the grating period Tig (also referred to as the ‘period’, ‘segment spacing’ or just ‘spacing’) of the waveguide must obey the below condition: where neis the effective refractive index of the Bloch mode of the grating waveguide, andois the free-space wavelength guided light within the waveguide. This ensures scatter-free, lossless wave-guiding.

[0023] As an example, for a silicon nitride waveguide transmitting light with a wavelength of 1550nm, the width of the subwavelength grating waveguide (i.e. the segment width) is lOOOnm, with a height of 400nm and a grating period of 430nm.

[0024] The fixed end of the cantilever waveguide may comprise a conventional waveguide to guide any light within the cantilever waveguide to / from an integrated photonic circuit.

[0025] The fixed end of the cantilever waveguide may be the point at which the cantilever waveguide is attached to a base structure upon which any integrated photonic circuit and / or external waveguide is formed. The base structure may be a second substrate onto which the cantilever waveguide is mounted. The base structure may be an unetched region of a base substrate upon which the flexible substrate was originally mounted (prior to the process of forming the cantilever waveguide). The second substrate maybe formed from a different material as the flexible substrate.

[0026] The flexible substrate and segments may be formed from the same material. The flexible substrate and segments may be formed of different materials.

[0027] The material may be silicon, silicon nitride, indium phosphide, gallium arsenide, indium gallium arsenide, indium gallium arsenide phosphide, diamond, germanium, lithium niobate or any other suitable materials as will be understood by the skilled person. It will be understood that, regardless of the material used for the flexible substrate, that the thickness of said flexible substrate must be sufficiently low to enable the flexible substrate to flex in response to the or each flexion element. It will also be understood by the skilled person that the waveguide and flexible substrate must necessarily have an appropriate refractive index distribution to support a guided optical mode.

[0028] Each individual segment (of the series of disconnected waveguide segments) may be integrally formed with the substrate. Each individual segment of the series of disconnected waveguide segments may be identical. In a specific embodiment, the series of disconnected waveguide segments extends along a line of symmetry of the cantilever waveguide, in a straight line between the fixed and free ends.

[0029] The segments may each be spaced equally far apart, to eliminate any scattering loss within the waveguide. Preferably, all segments are identical and equally spaced apart to ensure the scattering loss is minimised.

[0030] The subwavelength grating waveguide may extend from a point substantially at the fixed end of the cantilever waveguide. Alternatively, the subwavelength grating waveguide may extend from a point between the fixed and free ends of the cantilever waveguide. In a further alternative embodiment, the subwavelength grating waveguide may extend from a point which is further away from the free end of the cantilever waveguide than the fixed end.

[0031] The subwavelength grating waveguide may transition to a conventional waveguide at the point at which the subwavelength grating waveguide ends.

[0032] The or each flexion element may extend substantially the full distance between the fixed and free end of the cantilever waveguide. Alternatively, the or each flexion element may be provided at regular intervals between the fixed and free ends of the cantilever waveguide.

[0033] The or each flexion element may extend from a point substantially at the fixed end of the cantilever waveguide. Alternatively, the or each flexion element may extend from a point between the fixed and free ends of the cantilever waveguide. In a further alternative embodiment, the or each flexion element may extend from a point which is further away from the free end of the cantilever waveguide than the fixed end.

[0034] There may be one or more flexion elements provided symmetrically on either side of the series of disconnected waveguide segments.

[0035] In embodiments where the series of disconnected waveguide segments extends along a line of symmetry of the cantilever waveguide in a straight line between the fixed and free ends, there may be one or more flexion elements provided symmetrically on either side of the series of disconnected waveguide segments. In a particular embodiment, there is one flexion element provided symmetrically either side of the series of disconnected waveguide segments, each flexion element extending the full length of the cantilever waveguide (i.e. extending the full distance between the fixed and free end of the cantilever waveguide).

[0036] The or each flexion element may comprise a material having a different coefficient of thermal expansion to the flexible substrate. This enables the or each flexion element to expand or contract in relation to temperature changes, thereby urging the substrate to flex with the flexion element. This may result in a material having an inherent stress, which results in a fixed degree of flexion once a final temperature is reached. In such embodiments, the or each flexion element may extend the entire distance between the fixed and free ends of the cantilever waveguide.

[0037] Any such temperature changes may be positive or negative. The temperature change may vary between -50 K and +300K, dependent upon the materials from which the waveguide and flexion elements are formed (as will be understood by the skilled person). In some embodiments, the device may be cooled from an initially hotter state of manufacture. In such embodiments, the flexion elements may be deposited at a higher temperature, and the cooling of the flexion elements may provide the flexion which deforms the cantilever waveguide.

[0038] In other embodiments, the flexion elements may be deposited at a low temperature, and then externally heated so as to create flexion.

[0039] The or each flexion element may comprise a metal or alloy. The or each flexion element may comprise a ferromagnetic metal. This enables the or each flexion element to be moved by an externally applied magnetic field, and thereby urge the substrate to flex with the movement of the or each flexion element. In such embodiments, a field strength between 0.05 T and 5T may be applied, depending upon the level of flexion required and the properties (such as flexibility) of the cantilever waveguide itself.

[0040] The or each flexion element may comprise aluminium, nickel, gold, copper, platinum, titanium and tungsten.

[0041] The or each flexion element may have a length between 20% of the length of the cantilever and the full length of the cantilever. In embodiments where there are multiple flexion elements, the total length spanned by the flexion elements cumulatively may be within this range. The or each flexion element may have a width between 1% of the width of the cantilever and the full width of the cantilever. In embodiments where there are multiple flexion elements, the total width spanned by the flexion elements cumulatively may be within this range.

[0042] The cantilever waveguide’s flexion in a direction transverse to the cantilever major axis may be tuneable. The tuneability of the flexion may be achieved through temperature change. The tuneability of the flexion may be achieved through application of a magnetic field.

[0043] The tuneability may take the form of an alteration in the angle between the free and fixed ends, relative to the cantilever major axis (in its neutral, unflexed position). The tuneability may take the form of an alteration in the height of the free end relative to the cantilever major axis (in its neutral, unflexed position).

[0044] In one embodiment, the flexion may be tuneable to the extent that the free end of the cantilever waveguide is substantially perpendicular to the cantilever major axis.

[0045] According to a second aspect of the present invention, there is provided a reinforced cantilever waveguide array comprising: at least one cantilever waveguide in accordance with the first aspect of the present invention, the or each cantilever waveguide having a common cantilever major axis and at least one strut extending from the or each cantilever waveguide and transverse to the common cantilever major axis so as to restrict flexion of the or each cantilever waveguide about an axis transverse to both the common cantilever major axis and flex direction of the or each cantilever waveguide.

[0046] The reinforced cantilever waveguide array of the second aspect may comprise any or all of the optional features of the cantilever waveguide according to the first aspect of the present invention as required or as desired.

[0047] The or each strut may be formed from the same material as the flexible substrate. The or each strut may be formed from a different material to the flexible substrate. In embodiments with more than one cantilever waveguides, there may be at least one strut extending between each adjacent pair of cantilever waveguides.

[0048] The or each strut may extend perpendicularly to the or each cantilever waveguide.

[0049] The struts may be placed sufficiently far from the or each waveguide so as to not disturb or interfere with the optical signal. In certain embodiments, the struts are placed at least one width of the waveguide away from the waveguide itself.

[0050] It will be understood that the size and number of struts will depend upon the desired flexion and strength of the reinforced array. For example, an increased number of thicker struts will increase the strength of the array, at the expense of flexibility, whereas fewer, thinner struts will add less strength to the array, but will enable a higher degree of flexibility.

[0051] According to a third aspect of the present invention, there is provided a method for manufacturing a cantilever waveguide, the method comprising: providing a flexible substrate extending from a fixed end to a free end; wherein a series of disconnected segments have been formed onto the flexible substrate between the fixed and free ends, the segments thereby forming a sub wavelength grating waveguide; and depositing a material onto the flexible substrate onto the first substrate to create one or more flexion elements.

[0052] The cantilever waveguide produced by the method of the third aspect may be a cantilever waveguide according to the first aspect of the present invention. In particular, the cantilever waveguide produced by the method of the third aspect may comprise any or all of the optional features of the cantilever waveguide according to the first aspect of the present invention as required or as desired.

[0053] The method of the third aspect may also be suitable for producing a reinforced cantilever waveguide array according to the second aspect of the present invention. In particular, the reinforced cantilever waveguide array as produced by the method of the third aspect may comprise any or all of the optional features of the reinforced cantilever waveguide array according to the second aspect of the present invention as required or as desired. In one embodiment, the deposition of the material onto the flexible substrate onto may occur prior to the cantilever being formed in respect of the waveguide. Alternatively, the deposition of the material may occur after the cantilever has been formed (i.e. when the substrate already extends between a fixed and free end).

[0054] The flexible substrate and series of disconnected waveguide segments may be formed together. In such embodiments, the flexible substrate and series of disconnected waveguide segments may be etched from a single membrane. The etching process may include applying a mask to the waveguide core and the regions that will become the series of disconnected waveguide segments, and etching away the unmasked regions of the membrane, and subsequently removing the mask.

[0055] The cantilever of the flexible substrate may be formed after the disconnected waveguide segments have been formed. In such embodiments, the single membrane from which the flexible substrate and segments are formed may be suspended as part of a wafer material. The segments may then be formed from the suspended membrane, with a final etch then performed to release the substrate from the wafer and provide the cantilever.

[0056] Where the method is used to produce a reinforced cantilever waveguide array, the struts thereof may be formed together with the flexible substrate and series of disconnected waveguide segments. In such embodiments, the struts, flexible substrate and series of disconnected waveguide segments may be etched from a single membrane. The etching process may include applying a mask to the waveguide core and the regions that will become the series of disconnected waveguide segments and the struts, and etching away the unmasked regions of the membrane, and subsequently removing the mask.

[0057] The etching of the substrate and series of disconnected waveguide segments may be performed whilst the membrane is mounted upon a cladding material. The cladding material may be an oxide. The cladding material may be a polymer or other dielectric.

[0058] Alternatively, the membrane may be suspended. In such embodiments, the single membrane may be formed from a larger wafer. The wafer may comprise two membranes sandwiching a wafer material therebetween. The membranes may be formed from silicon, silicon nitride, indium phosphide, gallium arsenide, indium gallium arsenide, indium gallium arsenide phosphide, diamond, germanium, lithium niobate, or any other suitable materials as will be understood by the skilled person. The wafer material may be silicon, silicon-on-insulator, indium phosphide, gallium arsenide, or a combination of these.

[0059] The suspended membrane may be formed by etching away the wafer material underneath the membrane. This etching of the wafer material may be enabled by a window being formed in the opposing membrane (i.e. the membrane which is part of the wafer material that is not the membrane that will be suspended).

[0060] The etching may be a wet etch. In such cases, the wet etchant may be heated KOH, TMAH, NaOH, HC1 or HF. The etching may be a dry etch. In such cases, the dry etchant may be fluorine-based plasma, chlorine-based plasma, bromine-based plasma, HF vapour or XeF2 vapour. The etching may be anisotropic. The etching may be isotropic.

[0061] In a specific embodiment, the wafer material may comprise two Silicon Nitride (SiN) membranes sandwiching a silicon wafer. In this specific embodiment, the suspended membrane may be formed via the following process: opening a window into the opposing SiN membrane, anisotropically etching the silicon wafer in a heated KOH bath so as remove the Silicon wafer and thereby suspend the SiN membrane.

[0062] In alternative embodiments, the substrate and series of disconnected waveguide segments may be formed from a silicon membrane mounted upon an oxide layer, the oxide layer being removed later so as to provide a cantilever.

[0063] The deposition of the material may be performed using a conventional thin film deposition process. Examples of such deposition techniques are thermal evaporation and electron beam evaporation, as will be understood by the skilled person. According to a fourth aspect of the present invention, there is provided a protected cantilever waveguide assembly comprising: a cantilever waveguide provided on a base substrate, wherein the cantilever waveguide is within a contiguous mass of optically clear material.

[0064] Provision of the cantilever waveguide within such a contiguous mass allows thereby protects the waveguide from damage. It also provides for simple and robust construction.

[0065] As used herein optically clear indicates that a material is transparent or substantially transparent. Such transparency extends at least to light within the wavelength range suitable for guiding using the cantilever waveguide or for at least a selected subset of that range.

[0066] The cantilever waveguide of the fourth aspect may comprise any or all of the optional features of the cantilever waveguide according to the first aspect of the present invention as required or as desired.

[0067] The teachings of the cantilever waveguide of the fourth aspect, optionally including any optional features thereof may be applied to the cantilever waveguides of the second aspect of the present invention as required or as desired.

[0068] The cantilever waveguide may comprise a waveguide formed upon a flexible substrate which extends from a fixed end to a free end. Such a substrate allows the waveguide to flex with the flexion of the substrate. The waveguide may comprise an elongate element defining an optical path extending between the fixed end and the free end of the flexible substrate.

[0069] The cantilever waveguide may be formed on the base substrate. The cantilever waveguide may have a fixed end mounted on or supported by a base substrate. The base substrate may comprise one or more components optically coupled to the cantilever waveguide. The base substrate may comprise a device or form part of a device. The device may be an integrated photonic circuit.

[0070] A cantilever major axis may be defined along the length of the cantilever waveguide when in a neutral (i.e. unflexed) position. The cantilever waveguide may be configured to project a selected distance from the base substrate upon which it is provided. The cantilever waveguide may be configured to have a selected flex in a direction transverse to the major axis. The flex may be configured to meet any particular requirements. In some embodiments, the flex may be such that the free end of the cantilever waveguide is substantially perpendicular to the cantilever major axis. In some such embodiments, configuration of the flex may be achieved by controlling the temperature or magnetic field applied to the cantilever waveguide.

[0071] In embodiments, where the fixed end of the cantilever waveguide is mounted on the base substrate, the fixed end may comprise or be coupled to a conventional waveguide. This enables light to be guided between the cantilever waveguide and the conventional waveguide and thereby facilitates use of the cantilever waveguide to couple light into and / or out of a device provided on or connected to the base substrate.

[0072] The contiguous mass of optically clear material may encompass the cantilever waveguide. The contiguous mass of optically clear material may be provided on the base substrate. The contiguous mass of optically clear material may comprise a dome or blob. The contiguous mass of optically clear material may comprise a regular or irregular polyhedron.

[0073] The optically clear material may be a different material to the cantilever waveguide. The optically clear material may be a polymer. The optically clear material may comprise an adhesive or resin. The optically clear material may be an epoxy resin. Suitable optically clear materials for the contiguous mass include but are not limited to optical adhesive, conformal silicon dioxide, glass microlenses, a combination of these or the like.

[0074] The optically clear material may be curable. In such embodiments, the optically clear material may be cured by ultraviolet (UV) light, heat or any other suitable technique.

[0075] In some embodiments, the optically clear material may be provided within a housing. The housing may define an interior chamber. In such embodiment, the interior chamber may be filled with the optically clear material.

[0076] The housing may be provided on the same base substrate as the cantilever waveguide. The housing may have an external shape corresponding to a regular or irregular polyhedron. The housing may have a curved exterior. The skilled person will understand that the housing could have a variety of shapes as necessitated by the geometry of the base substrate upon which the cantilever waveguide is provided.

[0077] The housing may be formed from an optically opaque material. In such embodiment, the housing may comprise an opening provided within the optically opaque material. Alternatively, in such embodiments, the housing may comprise a window of optically clear material provided within the optically opaque material. The skilled person will of course appreciate that it may also be possible to form a housing from a suitable optically clear material.

[0078] In one embodiment, the housing may comprise one or more side walls defining an end opening. In such embodiments, the end opening can facilitate the filling of the housing with optically clear material and / or for light to enter / exit the cantilever waveguide. In such embodiment, the side walls may be at least as tall, or taller, than the distance the cantilever waveguide projects from the base substrate upon which it is provided. In some such embodiment a window may be fitted over the opening.

[0079] The housing may be formed from any suitable material. Suitable materials include but are not limited to silicon, glass, polymer, metals or the like.

[0080] Where the housing comprises a window, the window may comprise a sheet of material. The window may be formed from any suitable optically clear material. Suitable optically clear materials for the window include but are not limited to silicon nitride, silicon dioxide, sapphire, silicon, diamond, compound semiconductors such as InGaAs or the like.

[0081] The cantilever waveguide may comprise a part of a cantilever waveguide array. The cantilever waveguide array may comprise two or more cantilever waveguides each having a common cantilever major axis. The cantilever waveguide array may comprise at least one strut extending from the or each cantilever waveguide and transverse to the common cantilever major axis so as to restrict flexion of the or each cantilever waveguide about an axis transverse to both the common cantilever major axis and flex direction of the or each cantilever waveguide. The or each strut may be formed from the same material as the flexible substrate. The or each strut may be formed from a different material to the flexible substrate.

[0082] In embodiments with more than one cantilever waveguides, there may be at least one strut extending between each adjacent pair of cantilever waveguides.

[0083] The or each strut may extend perpendicularly to the or each cantilever waveguide.

[0084] The struts may be placed sufficiently far from the or each waveguide so as to not disturb or interfere with the optical signal. In certain embodiments, the struts are placed at least one width of the waveguide away from the waveguide itself.

[0085] It will be understood that the size and number of struts will depend upon the desired flexion and strength of the reinforced array. For example, an increased number of thicker struts will increase the strength of the array, at the expense of flexibility, whereas fewer, thinner struts will add less strength to the array, but will enable a higher degree of flexibility.

[0086] The waveguide may comprise one or more flexion elements provided on the flexible substrate, the one or more flexion elements configured to urge the substrate to flex in a direction transverse to the cantilever major axis.

[0087] The or each flexion element may extend substantially the full distance between the fixed and free end of the cantilever waveguide. Alternatively, the or each flexion element may be provided at regular intervals between the fixed and free ends of the cantilever waveguide.

[0088] The or each flexion element may extend from a point substantially at the fixed end of the cantilever waveguide. Alternatively, the or each flexion element may extend from a point between the fixed and free ends of the cantilever waveguide. In a further alternative embodiment, the or each flexion element may extend from a point which is further away from the free end of the cantilever waveguide than the fixed end.

[0089] There may be one or more flexion elements provided symmetrically on either side of the waveguide. The or each flexion element may comprise a material having a different coefficient of thermal expansion to the flexible substrate. This enables the or each flexion element to expand or contract in relation to temperature changes, thereby urging the substrate to flex with the flexion element. This may result in a material having an inherent stress, which results in a fixed degree of flexion once a final temperature is reached. In such embodiments, the or each flexion element may extend the entire distance between the fixed and free ends of the cantilever waveguide.

[0090] The or each flexion element may comprise a metal or alloy. The or each flexion element may comprise a ferromagnetic metal. This enables the or each flexion element to be moved by an externally applied magnetic field, and thereby urge the substrate to flex with the movement of the or each flexion element. In such embodiments, a field strength between 0.05 T and 5T may be applied, depending upon the level of flexion required and the properties (such as flexibility) of the cantilever waveguide itself.

[0091] The or each flexion element may comprise aluminium, nickel, gold, copper, platinum, titanium and tungsten.

[0092] The or each flexion element may have a length between 20% of the length of the cantilever and the full length of the cantilever. In embodiments where there are multiple flexion elements, the total length spanned by the flexion elements cumulatively may be within this range.

[0093] The or each flexion element may have a width between 1% of the width of the cantilever and the full width of the cantilever. In embodiments where there are multiple flexion elements, the total width spanned by the flexion elements cumulatively may be within this range.

[0094] The waveguide may be formed from optically transmissive material. The flexible substrate and waveguide may be formed from the same material. In such embodiments, the flexible substrate and waveguide may be integrally formed with the substrate. The flexible substrate and waveguide may be formed of different materials. Suitable materials include but are not limited to: silicon, silicon nitride, indium phosphide, gallium arsenide, indium gallium arsenide, indium gallium arsenide phosphide, diamond, germanium, lithium niobate or the like, as will be understood by the skilled person. It will be understood that, regardless of the material used for the flexible substrate, that the thickness of said flexible substrate must be sufficiently low to enable the flexible substrate to flex in response to the or each flexion element. It will also be understood by the skilled person that the waveguide and flexible substrate must necessarily have an appropriate refractive index distribution to support a guided optical mode.

[0095] In a specific embodiment, the waveguide may extend along a line of symmetry of the cantilever waveguide, in a straight line between the fixed and free ends. The waveguide may extend from a point substantially at the fixed end of the cantilever waveguide. Alternatively, the waveguide may extend from a point between the fixed and free ends of the cantilever waveguide. In a further alternative embodiment, the waveguide may extend from a point which is further away from the free end of the cantilever waveguide than the fixed end.

[0096] The waveguide may comprise a channel, tube or rod. The waveguide may comprise a subwavelength grating. The subwavelength grating may comprise a plurality of spring periods. The subwavelength grating may comprise a series of disconnected waveguide segments. The disconnected waveguide segments may be provided on the flexible substrate between the fixed and free ends. In such embodiments, each individual segment (of the series of disconnected waveguide segments) may be integrally formed with the substrate. In some such embodiments, each individual segment of the series of disconnected waveguide segments may be identical. In some such embodiments, the segments may each be spaced equally far apart. This can reduce or eliminate any scattering loss within the waveguide. In one preferred arrangement all segments are identical and equally spaced apart to ensure the scattering loss is minimised.

[0097] The subwavelength grating waveguide may transition to a channel, tube, rod or other conventional waveguide at the point at which the subwavelength grating waveguide ends.

[0098] The width of the subwavelength grating waveguide (i.e. the segment width) may be between 10% and 1000% percent of the wavelength of the light transmitted therein. In a specific example of a single-mode waveguide, the width of the subwavelength grating waveguide (i.e. the segment width) may be between 10% and 100% of the wavelength of the light transmitted therein.

[0099] The thickness of the subwavelength grating waveguide (i.e. the segment height) may be between 10% and 1000% percent of the wavelength of the light transmitted therein. In a specific example of a single-mode waveguide, the thickness of the subwavelength grating waveguide (i.e. the segment height) may be between 10% and 100% of the wavelength of the light transmitted therein.

[0100] More specifically, the grating period Tig (also referred to as the ‘period’, ‘segment spacing’ or just ‘spacing’) of the waveguide must obey the below condition: where neis the effective refractive index of the Bloch mode of the grating waveguide, andois the free-space wavelength guided light within the waveguide. This ensures scatter-free, lossless wave-guiding.

[0101] The subwavelength grating waveguide may transition to a conventional waveguide at the point at which the subwavelength grating waveguide ends.

[0102] According to a fifth aspect of the present invention there is provided a method of manufacturing a protected cantilever waveguide assembly of the type comprising a cantilever waveguide provided on a base substrate, wherein the cantilever waveguide is within a contiguous mass of optically clear material, the method comprising the steps of: providing a cantilever waveguide on a base substrate; applying a curable optically clear material to the cantilever waveguide such that the cantilever waveguide is within a contiguous mass of optically clear material; and curing the optically clear material.

[0103] The above method provides for simple and reliable construction of a protected cantilever waveguide assembly.

[0104] The method of the fifth aspect may include any or all features of the first, second and fourth aspects of the present invention, as desired or as appropriate. The optically clear material may be applied to the cantilever waveguide by any suitable means. In particular embodiments, suitable means of application include but are not limited to application with a micro-nozzle, chemical vapour deposition (CVD) or the like.

[0105] The optically clear material may be applied to a fixed end of the cantilever waveguide.

[0106] The optically clear material may be cured by any suitable technique. In particular embodiments, curing may be achieved by application of ultraviolet (UV) light, heat or the like.

[0107] The method may comprise the step of configuring the flex and / or projection of the cantilever waveguide from the base substrate. In such embodiment, configuring may be achieved by application of heat, a magnetic field or the like. In such embodiments, configuring may take place prior to curing. This can ensure that the flex and / or projection of the cantilever waveguide is maintained at the desired degree

[0108] The method may comprise the step of providing a housing on the base substrate. In some embodiments, the housing may be provided before the optically clear material is applied. In other embodiments, the housing may be provided after the optically clear material is applied. In such embodiments, the housing may be provided before the optically clear material is cured. In alternative such embodiments, the housing may be provided after the optically clear material is cured.

[0109] The method may comprise the step of fitting a window to the housing. The window may be fitted before the optically clear material is applied. Alternatively, the window may be fitted after the optically clear material is applied. In such embodiments, the window may be fitted before the optically clear material is cured. In alternative such embodiments, the window may be fitted after the optically clear material is cured. According to a sixth aspect of the present invention, there is provided an actuator arm comprising: a flexible substrate extending along a cantilever major axis from a fixed end to a free end; a series of disconnected waveguide segments provided on the flexible substrate between the fixed and free ends so as to form a subwavelength grating waveguide; and one or more flexion elements provided on the flexible substrate, the one or more flexion elements having a different coefficient of thermal expansion to the flexible substrate; wherein a light absorbing coating is provided on each of the segments that form the waveguide, the coating operable to absorb light within the waveguide, thereby heating the segments, substrate and flexion elements and thus varying the flexion of the actuator arm in response to light within the waveguide.

[0110] This therefore provides an actuator arm on the micro-scale that is lightweight and can be powered / controlled by supplying light, for instance through an optical fibre. An actuator arm according to the present invention may be operable to flex through at least a 180° angle.

[0111] It will be understood by the skilled person that the actuator arm could be used as a measurement arm, in that the actuation of the arm could be measured, and the actuation distance can be used to calculate the energy input into the actuator arm. This allows for the actuator arm to be used as part of a micro-sensor.

[0112] The cantilever major axis may be defined by the actuator arm when in a neutral (i.e. unflexed) position.

[0113] The transverse direction in which the actuator arm flexes may be a direction that is substantially perpendicular to the plane in which the actuator arm lies when in the neutral (i.e. unflexed) position.

[0114] The actuator arm may extend between 5 and 500pm from the fixed end to the free end. The actuator arm may have a width between lOOnm and 1mm. The thickness of the actuator arm (including the segments) may be between lOnm and 100|im. Particularly, the thickness of the actuator arm may be between lOOnm and 10|im.

[0115] It will be understood by the skilled person that the certain properties of the waveguide will be dictated by the wavelength of the light to be transmitted therethrough. For example, longer wavelengths of light will require a wider and thicker waveguide (and so the segments will necessarily be wider and thicker than for shorter wavelengths).

[0116] More specifically, the grating period 4g (also referred to as the ‘period’, ‘segment spacing’ or just ‘spacing’) of the waveguide must obey the below condition: where neis the effective refractive index of the Bloch mode, and Aois the free-space wavelength guided light within the waveguide. This ensures scatter-free, lossless waveguiding.

[0117] As an example, for a silicon nitride substrate transmitting light with a wavelength of 1550nm, the width of the waveguide / segments is lOOOnm, with a height of 400nm, a grating period of 430nm and a light absorbing coating thickness / height of between 10-20nm.

[0118] The fixed end of the actuator arm may comprise a coupling element to couple any light within the waveguide to an integrated circuit and / or light source. The fixed end of the actuator arm may comprise a coupling element to couple any light within the waveguide to an external waveguide. The integrated circuit may have the capability to guide and / or manipulate different wavelengths or polarizations of light. This allows the integrated circuit to control the actuation of the actuator arm, by manipulating the light therein.

[0119] The fixed end of the actuator arm may be the point at which the actuator arm is attached to a base structure upon which any integrated circuit and / or external waveguide is formed. The base structure may be a second substrate onto which the actuator arm is mounted. The base structure may be an unetched region of a base substrate upon which the flexible substrate was originally mounted (prior to the process of forming the actuator arm). The second substrate may be formed from a different material as the flexible substrate.

[0120] The flexible substrate and segments may be formed from the same material. The flexible substrate and segments may be formed of different materials.

[0121] The material may be silicon, silicon nitride, indium phosphide, gallium arsenide, indium gallium arsenide, indium gallium arsenide phosphide, diamond, germanium, lithium niobate, or any other suitable materials as will be understood by the skilled person. It will be understood that, regardless of the material used for the flexible substrate, that the thickness of said flexible substrate must be sufficiently low to enable the flexible substrate to flex in response to the or each flexion element. It will also be understood by the skilled person that the waveguide must necessarily have a higher refractive index than the surrounding material.

[0122] Each individual segment (of the series of disconnected waveguide segments) may be integrally formed with the substrate. Alternatively, the segments may be formed separately and later attached to the substrate. Each individual segment of the series of disconnected waveguide segments may be identical. In a specific embodiment, the series of disconnected waveguide segments extends along a line of symmetry of the actuator arm, in a straight line between the fixed and free ends.

[0123] The subwavelength grating waveguide may extend from a point substantially at the fixed end of the actuator arm. Alternatively, the sub wavelength grating waveguide may extend from a point between the fixed and free ends of the actuator arm. In a further alternative embodiment, the subwavelength grating waveguide may extend from a point which is further away from the free end of the actuator arm than the fixed end.

[0124] The subwavelength grating waveguide may transition to a conventional waveguide at the point at which the subwavelength grating waveguide ends.

[0125] The or each flexion element may extend substantially the full distance between the fixed and free end of the actuator arm. Alternatively, the or each flexion element may be provided at regular intervals between the fixed and free ends of the actuator arm. The or each flexion element may extent from a point substantially at the fixed end of the actuator arm. Alternatively, the or each flexion element may extend from a point between the fixed and free ends of the actuator arm. In a further alternative embodiment, the or each flexion element may extend from a point which is further away from the free end of the actuator arm than the fixed end.

[0126] In embodiments where the series of disconnected waveguide segments extends along a line of symmetry of the actuator arm in a straight line between the fixed and free ends, there may be one or more flexion elements on provided symmetrically on either side of the series of disconnected waveguide segments. In a particular embodiment, the is one flexion element provided symmetrically either side of the series of disconnected waveguide segments, each flexion element extending the full length of the actuator arm (i.e. extending the full distance between the fixed and free end of the actuator arm).

[0127] The or each flexion element comprises a material having a different coefficient of thermal expansion to the flexible substrate. This enables the or each flexion element to expand or contract in relation to temperature changes, thereby urging the substrate to flex with the flexion element. In some embodiments, the or each flexion element may extend the entire distance between the fixed and free ends of the actuator arm.

[0128] The or each flexion element may comprise a metal or alloy. The or each flexion element may comprise aluminium, nickel, gold, silver, copper, platinum, titanium, tungsten or the like.

[0129] The or each flexion element may have a length between 20% of the length of the actuator arm and the full length of the actuator arm. In embodiments where there are multiple flexion elements, the total length spanned by the flexion elements cumulatively may be within this range.

[0130] The or each flexion element may have a width between 1% the width of the actuator arm and 99% of the actuator arm. In embodiments where there are multiple flexion elements, the total width spanned by the flexion elements cumulatively may be within this range. The light absorbing coating may be provided on the distal surface of each segment relative to the flexible substrate. The light absorbing coating may be provided on the uppermost or top surface of each segment. The light absorbing coating may be provided on the flexible substrate in the gap between the segments. The light absorbing coating may comprise a metal or an alloy. The light absorbing coating may comprise chromium, tungsten, titanium, molybdenum or the like. The light absorbing coating may be formed of a different material to the or each flexion element.

[0131] The width and length of the light absorbing coating may be substantially the same as the width and length of the segments to which the coating is applied. In embodiments where the light absorbing coating is provided in the gap between segments, the width and length of the light absorbing coating in said gaps may be substantially the same as the width and length of the gaps themselves.

[0132] The thickness / height of the light absorbing coating may be dependent upon the wavelength of light which is being transmitted through the actuator arm (and hence absorbed into the light absorbing coating.

[0133] The thickness / height of the light absorbing coating may be between Inm and 100 nm. The thickness / height of the light absorbing coating may be between 0.1% and 100% the wavelength of the light being absorbed.

[0134] It will be understood by the skilled person that the light absorbing coating may be different for different contexts, so as to ensure the absorption of whichever wavelength of light is within the waveguide.

[0135] In some embodiments, the actuator arm may comprise one or more additional subwavelength grating waveguides. The or each additional subwavelength grating waveguide may not comprise a light absorbing coating. It will be understood that the or each actuator arm having a light absorbing coating and one or more additional subwavelength grating waveguides will function as a controllably flexible waveguide as the light within the or each additional subwavelength grating waveguide will propagate through the or each subwavelength grating waveguide, as opposed to being absorbed by the light absorbing coating. In this manner, the or each additional subwavelength grating waveguide may be operable to emit light from the free end of the actuator arm. This allows the emission of light from a range of angles via actuation of the actuator arm. This enables the actuator arm to be used in various contexts, for example laser atherectomies.

[0136] In actuator arms where there are provided at least one additional subwavelength grating waveguide, the or each additional subwavelength grating waveguides may be optically couple to a light source. The or each light source may be connected to an integrated circuit (optionally a photonic circuit). The integrated circuit may be the same integrated circuit as that which controls the light within the actuator arm (i.e. the subwavelength grating waveguide having the light absorbing coating). Alternatively, there may be a dedicated light source and / or integrated circuit for each of the actuator arm / s and the additional sub wavelength grating waveguide / s.

[0137] In embodiments where there is a common integrated circuit for one or more actuator arms and / or additional subwavelength grating waveguides, the integrated circuit may be operable to manipulate the optical signals in the actuator arms and / or waveguides (as applicable) so as to deliver light and achieve different actuation / emission combinations. This may be achieved using known integrated circuit configurations. Examples of such known integrated circuit configurations include 2D grating arrays (i.e. polarization diversity couplers), Mach-Zehnder interferometers or arrayed- waveguide gratings (i.e. wavelength-division multiplexing devices).

[0138] In one embodiment, there is provided an actuator arm array comprising at least one actuator arm in accordance with the first aspect of the present invention, the or each actuator arm having a common cantilever major axis and at least one strut extending from the or each actuator arm and transverse to the common cantilever major axis so as to restrict flexion of each actuator arm about an axis transverse to both the common cantilever major axis and flex direction of the or each actuator arm.

[0139] The or each actuator arm array may comprise any or all of the optional features of the actuator arm according to the first aspect of the present invention as required or as desired. The or each strut may be formed from the same material as the flexible substrate. The or each strut may be formed from a different material to the flexible substrate.

[0140] The or each strut may extend perpendicularly to each actuator arm.

[0141] The struts may be placed sufficiently far from the segments so as to not disturb or interfere with the optical signal therein. In certain embodiments, the struts are placed at least one segment width away from the segments themselves.

[0142] It will be understood that the size and number of struts will depend upon the desired flexion and strength of the actuator arm array. For example, an increased number of thicker struts will increase the strength of the actuator arm array, at the expense of flexibility, whereas fewer, thinner struts will add less strength to the actuator arm array but will enable a higher degree of flexibility.

[0143] In actuator arm arrays with two or more actuator arms, there may be at least one strut extending between each adjacent pair of actuator arms.

[0144] In actuator arm arrays, in addition to the at least one actuator arm, the array may comprise one or more additional subwavelength grating waveguides. The or each additional subwavelength grating waveguide may not comprise a light absorbing coating a not have a light absorbing coating. It will be understood by the skilled person that, for actuator arm arrays with more than one actuator arm, only one actuator arm need have a light absorbing coating to enable the actuation of the array.

[0145] In actuator arm arrays where there are provided at least one additional subwavelength grating waveguide, the or each additional subwavelength grating waveguides may be connected to a light source. The or each light source may be connected to an integrated circuit. The integrated circuit may be the same integrated circuit as that which controls the light within the actuator arm. Alternatively, there may be a dedicated light source and / or integrated circuit for each of the actuator arm / s and the additional sub wavelength grating waveguide / s.

[0146] In embodiments where there is a common integrated circuit for one or more actuator arms and / or additional subwavelength grating waveguides, the integrated circuit may be operable to manipulate the optical signals in the actuator arms and / or waveguides (as applicable) so as to deliver light and achieve different actuation / emission combinations. This may be achieved using known integrated circuit configurations. Examples of such known integrated circuit configurations include 2D grating arrays (i.e. polarization diversity couplers), Mach-Zehnder interferometers or arrayed- waveguide gratings (i.e. wavelength-division multiplexing devices).

[0147] In this manner, the or each additional subwavelength grating waveguide may be operable to emit light from the free end of the actuator arm array. This allows the emission of light from a range of angles via actuation of the actuator arm array. This enables the actuator arm array to be used in various contexts, for example laser atherectomies.

[0148] According to a seventh aspect of the present invention, there is provided an actuator comprising an actuator arm in accordance with the first aspect of the present invention and one or more light sources optically coupled to the subwavelength grating waveguide of the actuator arm and operable to controllably introduce light into the waveguide so as to control actuation of the actuator arm.

[0149] The actuator arm which forms part of the seventh aspect may comprise any or all of the optional features of the actuator arm according to the sixth aspect of the present invention as required or as desired. The actuator may comprise an actuator arm array as discussed above.

[0150] It will be understood by the skilled person that (as with the actuator arm of the first aspect) the actuator of the second aspect could be used as a measurement device, in that the actuation of the or each arm of the device could be measured, and the actuation distance / s can be used to calculate the energy input into the actuator. This enables us of the actuator as a micro-sensor.

[0151] The light source may be operable to transmit light with wavelengths between 200nm and 20pm. The light source may be able to transmit a tuneable spectrum of wavelengths and / or polarizations of light, to allow the actuator to function with actuator arms with different properties.

[0152] The actuator arm may be detachable from the light source. This allows for cleaning and / or sterilisation of the actuator arm after use. This also enables the changing of the actuator arm for different purposes. For example, one actuator arm may have a greater range of motion than another (by having a longer distance between the fixed and free ends).

[0153] In actuators having an actuator arm array with two or more actuator arms wherein at least one of the arms does not have a light absorbing coating, the actuator may comprise a transparent shroud surrounding the actuator arm array so as to protect the array from external damage. The shroud may be in the form of a closed, hollow dome encapsulating the array, allowing full actuation thereof.

[0154] According to an eighth aspect of the present invention, there is provided a method for manufacturing an actuator arm according to the first aspect of the present invention, the method comprising: providing a flexible substrate extending from a fixed end to a free end, wherein a series of disconnected segments are formed on the flexible substrate between the fixed and free ends, the segments thereby forming a sub wavelength grating waveguide, and depositing a material having a different coefficient of thermal expansion to the flexible substrate onto the flexible substrate to create one or more flexion elements on the flexible substrate, and depositing a light absorbing coating onto a top surface of each segment.

[0155] The actuator arm produced by the method of the third aspect may be an actuator arm according to the first aspect of the present invention. In particular, the actuator arm produced by the method of the third aspect may comprise any or all of the optional features of the actuator arm according to the first aspect of the present invention as required or as desired.

[0156] The method of the eighth aspect may also be suitable for producing an actuator arm array as described above. In particular, the actuator arm array as produced by the method of the eighth aspect may comprise any or all of the optional features of the actuator arm array as required or as desired.

[0157] In one embodiment, the deposition of the material onto the flexible substrate onto may occur prior to the cantilever being formed in respect of the actuator. Alternatively, the deposition of the material may occur after the cantilever has been formed (i.e. when the substrate already extends between a fixed and free end).

[0158] The flexible substrate and series of disconnected waveguide segments may be formed together. In such embodiments, the flexible substrate and series of disconnected waveguide segments may be etched from a single membrane. The etching process may include applying a mask to the waveguide core and the regions that will become the series of disconnected waveguide segments, and etching away the unmasked regions of the membrane, and subsequently removing the mask.

[0159] The cantilever of the flexible substrate may be formed after the disconnected waveguide segments have been formed. In such embodiments, the single membrane from which the flexible substrate and segments are formed may be suspended as part of a wafer material. The segments may then be formed from the suspended membrane, with a final etch then performed to release the substrate from the wafer and provide the cantilever.

[0160] Where the method is used to produce an actuator arm array, the struts thereof may be formed together with the flexible substrate and series of disconnected waveguide segments. In such embodiments, the struts, flexible substrate, and series of disconnected waveguide segments may be etched from a single membrane. The etching process may include applying a mask to the waveguide core and the regions that will become the series of disconnected waveguide segments and the struts, and etching away the unmasked regions of the membrane, and subsequently removing the mask.

[0161] The etching of the substrate and series of disconnected waveguide segments may be performed whilst the membrane is mounted upon a cladding material. The cladding material may be an oxide. The cladding material may be a polymer or other dielectric.

[0162] Alternatively, the membrane may be suspended. In such embodiments, the single membrane may be formed from a larger wafer. The wafer may comprise two membranes sandwiching a wafer material therebetween. The membranes may be formed from silicon, silicon nitride, indium phosphide, gallium arsenide, indium gallium arsenide, indium gallium arsenide phosphide, diamond, germanium, lithium niobate, or any other suitable materials as will be understood by the skilled person. The wafer material may be silicon, silicon-on-insulator, indium phosphide, gallium arsenide, or a combination of these.

[0163] The suspended membrane may be formed by etching away the wafer material underneath the membrane. This etching of the wafer material may be enabled by a window being formed in the opposing membrane (i.e. the membrane which is part of the wafer material that is not the membrane that will be suspended).

[0164] The etching may be a wet etch. In such cases, the wet etchant may be heated KOH, TMAH, NaOH, HC1 or HF. The etching may be a dry etch. In such cases, the dry etchant may be fluorine-based plasma, chlorine-based plasma, bromine-based plasma, HF vapour or XeF2 vapour. The etching may be anisotropic. The etching may be isotropic.

[0165] In a specific embodiment, the wafer material may comprise two Silicon Nitride (SiN) membranes sandwiching a silicon wafer. In this specific embodiment, the suspended membrane may be formed via the following process: opening a window into the opposing SiN membrane, anisotropically etching the Silicon wafer in a heated KOH bath so as remove the Silicon wafer and thereby suspend the SiN membrane.

[0166] In alternative embodiments, the substrate and series of disconnected waveguide segments may be formed from a silicon membrane mounted upon an oxide layer, the oxide layer being removed later so as to provide a cantilever.

[0167] The deposition of the material may be performed using a conventional thin film deposition process. Examples of such deposition techniques are thermal evaporation and electron beam evaporation, as will be understood by the skilled person.

[0168] The deposition of the light absorbing coating may be performed using a thin film deposition technique. Examples of such deposition techniques are thermal evaporation and electron beam evaporation, as will be understood by the skilled person.

[0169] The deposition of the light absorbing coating may be performed prior to the deposition of the material which forms the or each flexion element. Alternatively, the deposition of the light absorbing coating may be performed after to the deposition of the material which forms the or each flexion element.

[0170] According to a ninth aspect of the present invention, there is provided a method of surgery comprising using an actuator arm in accordance with the sixth aspect of the present invention or an actuator in accordance with the seventh aspect of the present invention. The method of surgery may comprise performing a laser atherectomy.

[0171] According to a tenth aspect of the present there is provided a scanning actuator array comprising two actuators, the actuators each comprising a flexible substrate extending along a cantilever major axis from a fixed end to a free end; a series of disconnected waveguide segments provided on the flexible substrate between the fixed and free ends so as to form a subwavelength grating waveguide; and one or more flexion elements provided on the flexible substrate, the one or more flexion elements having a different coefficient of thermal expansion to the flexible substrate; a reflector operable to reflect light; wherein the reflector on a first actuator is operable to reflect an incident light beam onto the reflector on a second actuator.

[0172] Advantageously, by providing an actuator array according to the tenth aspect, an incident light beam can be reflected by both reflectors. As the reflectors are arranged on actuators the alignment of both reflectors can be changed, increasing the range of deflection in the incident light beam.

[0173] The actuators of the tenth aspect may be actuators according to the seventh aspect, optionally including optional features thereof, including where the actuator arm is an actuator arm according to the sixth aspect.

[0174] The first actuator may extend in a direction perpendicular to the second actuator. The first actuator may flex in a direction perpendicular to the second actuator. The first actuator may provide vertical sweep. The second actuator may provide horizontal sweep. A light absorbing coating may be provided on each of the segments that form the waveguide. The coating may be operable to absorb light within the waveguide. The coating may be operable to absorb light within the waveguide thereby heating the segments, substrate and flexion elements and thus varying the flexion of the actuator arm in response to light within the waveguide.

[0175] The flexion elements may be responsive to magnetic fields. The flexion elements may be responsive to changes in temperature.

[0176] The actuator array may comprise three optical fibres. A first optical fibre may be coupled to the waveguide of the first actuator. The first actuator may be mounted on the first optical fibre. The fixed end of the first actuator may be fixed to the first optical fibre. The first actuator may be mounted on the first optical fibre. The fixed end of the first actuator may be fixed to the first optical fibre. A second optical fibre may be coupled to the waveguide of the second actuator. A third optical fibre may be configured to direct the incident light beam onto the reflector on the first actuator.

[0177] The actuator array may comprise a collar. The collar may provide a base of the actuators. The optical fibres may extend through the collar. The collar may be cylindrical. The collar may have a diameter of between 100 pm and 1 mm, preferably between 200 pm and 600 pm, more preferably between 300 pm and 500 pm, for example 400 pm.

[0178] The actuator array may comprise a cap. The cap may be transparent. The cap may be transparent to the incident light beam (that is the cap may be made of a material with an optical transmission window at the wavelength of the incident light beam). The cap may be tubular. The cap may have a closed end. The cap may have an open end. The collar may be arranged in the open end of the cap. A seal may be formed between the collar and the open end of the cap. The collar and cap may define a cavity. The first and second actuators may be arranged in the cavity. By arranging the actuators in the cavity, the actuator array may be operable in liquid environments.

[0179] The actuator array may comprise a first light source. The first light source may be coupled to the first optical fibre. The first light source may have a first wavelength. The first light source may be a laser. The actuator array may comprise a second light source. The second light source may be coupled to the second optical fibre. The second light source may have a second wavelength. The second light source may be a laser. The first and second wavelengths may be the same. The first and second wavelengths may be different. The actuator array may comprise a third light source. The third light source may be coupled to the third optical fibre. The third light source may have a third wavelength. The third light source may be a laser.

[0180] The actuator array may comprise one or more controllers. The one or more controllers may be operable to switch the first light source between an emitting state and a non-emitting state. The one or more controllers may be operable to switch the second light source between an emitting state and a non-emitting state. The one or more controllers may be operable to switch the third light source between an emitting state and a non-emitting state. By actively controlling the first and second light sources the incident light beam can be scanned across a range of deflections, allowing the beam to be directed to a particular point. By actively controlling the third light source the incident light beam can be applied selectively.

[0181] According to an eleventh aspect of the invention, there is provided a method of surgery using an actuator array according to the tenth aspect, optionally including any optional features thereof. The surgery may be a laser atherectomy.

[0182] Detailed Description of the Invention

[0183] In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

[0184] Figure 1 shows a perspective view of a partial cantilever waveguide according to the present invention in an unflexed position.

[0185] Figure 2 shows a cross-section view of a cantilever waveguide according to the present invention.

[0186] Figure 3 shows a side view of a cantilever waveguide according to the present invention in a flexed position. Figure 4 shows a perspective view of a reinforced cantilever waveguide array according to the present invention.

[0187] Figure 5 shows a cross-section of the cantilever waveguide at various stages (a)-

[0188] (e) of an exemplary manufacturing process of said waveguide.

[0189] Figure 6 shows a cross-section of the cantilever waveguide at various stages (a)-

[0190] (f) of an alternative manufacturing process of a cantilever waveguide.

[0191] Figure 7 shows a schematic cross-section of a protected cantilever waveguide assembly according to the present invention;

[0192] Figure 8 illustrates steps in an exemplary manufacturing process of the cantilever waveguide protector of figure 7, namely (a) application of optically clear material, (b) configuration of cantilever waveguide flex, and (c) curing of optically clear material; shows a perspective view of a housing for a protected cantilever waveguide assembly according to the present invention.

[0193] Figure 9 shows a housing for protected cantilever waveguide assembly in an alternative embodiment of the present invention.

[0194] Figure 10 shows a cross-section of an embodiment of a protected cantilever waveguide assembly comprising a housing as shown in figure 9;

[0195] Figure 11 illustrates steps in an exemplary manufacturing process of the cantilever waveguide protector of figure 10, namely (a) provision of cantilever waveguide, (b) mounting of housing, (c) application of optically clear material, (d) fitting of window;

[0196] Figure 12 illustrates an alternative step in an exemplary manufacturing process of the cantilever waveguide protector of figure 10, namely mounting of housing incorporating a window prior to the application of optically clear material.

[0197] Figure 13 shows a perspective view of a part of an actuator arm according to the present invention in an unflexed position. Figure 14 shows a cross-section view of an actuator arm according to the present invention.

[0198] Figure 15 shows a side view of an actuator arm according to the present invention in a flexed position.

[0199] Figure 16 shows a perspective view of an actuator arm array according to the present invention.

[0200] Figure 17 shows a schematic view of an actuator according to the present invention.

[0201] Figure 18 shows a cross-section of an actuator arm at various stages (a)-(e) of an exemplary manufacturing process of said actuator arm.

[0202] Figure 19 shows a cross-section of an actuator arm at various stages (a)-(f) of an alternative manufacturing process of said actuator arm.

[0203] Figure 20 shows a perspective view of an actuator arm according to the present invention.

[0204] Figure 21 shows a perspective view of an actuator array comprising a plurality of actuator arms of Figure 20.

[0205] Figure 22 shows a perspective view of the actuator array of Figure 21 with a cap.

[0206] In Figures 1 to 3, there is shown a cantilever waveguide 1. In the below description, any relative terms (upper, lower, top, bottom etc.) refer to the cantilever waveguide shown as oriented in figure 1.

[0207] The cantilever waveguide 1 is formed upon a flexible substrate 2, In this embodiment, the flexible substrate 2 is formed from silicon. It will be understood that alternative materials could be used for the flexible substrate 2. The flexible substrate 2, and hence the cantilever waveguide 1, extend from a fixed end 3 to a free end 4. The extension of the cantilever waveguide 1 between the fixed and free ends 3,4 when the substrate is in its unflexed form (i.e. as shown in figure 1) defines a cantilever major axis A. In this specific embodiment, the cantilever waveguide 1 extends approximately 100 pm from the fixed end 3 to the free end 4.

[0208] At the fixed end 3 of the cantilever waveguide 1, the flexible substrate 2 is mounted upon a base substrate 5. In this specific embodiment, the base substrate 5 is Silicon. It will be understood by the skilled person that alternative materials could be used for the flexible substrate 2. In this embodiment, the flexible substrate 2 and the base substrate 5 are each part of a conventional wafer material (not shown). The wafer material acts as a handle and mount for the cantilever waveguide 1, allowing operators to move the cantilever waveguide 1 without damaging the cantilever waveguide 1.

[0209] The cantilever waveguide 1 has, formed on an upper surface of the flexible substrate 2, a series of disconnected waveguide segments 6, with each segment 6 being spaced at regular intervals along the cantilever waveguide 1. In this embodiment, the segments 6 extend between the fixed end 3 and the free end 4. In this manner, the series of disconnected waveguide segments 6 extends the full length of the cantilever waveguide 1.

[0210] Together, the segments 6 form a subwavelength grating waveguide. Subwavelength grating waveguides are known in the art, and are capable of guiding light within the waveguide, whilst being formed of disconnected segments 6. Subwavelength grating waveguides comprise periodic structures arranged to frustrate diffraction of light transmitted therein, and thus behave like a homogeneous medium. This requires that the periodicity of the structure (in this case the series of disconnected waveguide segments 6) is sufficiently small such that It will be understood by the skilled person that the spacing of the segments 6 for any given embodiment will be configured such that the segments 6 can act as a subwavelength grating waveguide.

[0211] Within any subwavelength grating waveguide, light excites a Bloch mode, which propagates through the subwavelength grating waveguide. This allows for transmission of light throughout the waveguide.

[0212] In this embodiment, each segment 6 is formed integrally with the silicon which forms the flexible substrate 2, via etching from a silicon on insulator wafer material (see figure 5 and the associated description thereof below). Placed symmetrically either side of the series of disconnected waveguides segments 6 are a pair of flexion elements 7. The flexion elements 7 each extend from the fixed end 3 to the free end 4 of the cantilever waveguide 1. In this embodiment, the flexion elements each comprise a film of aluminium deposited directly onto the flexible substrate 2. It will be understood by the skilled person that an alternative material or materials could be used for the flexion elements 7.

[0213] As the material of the flexion elements 7 has different properties to the material of the flexible substrate 2, under particular conditions the flexion elements 7 will experience different stress forces to the flexible substrate 2. This differential stress can cause the cantilever waveguide 1 to flex, the direction of flex dependent on the nature of the differential stress. In the present example there is a difference between the coefficients of thermal expansion between the aluminium flexion elements 7 and the silicon flexible substrate 2. If the temperature of the cantilever waveguide 1 is raised, the silicon flexible substrate 2 expands more than the aluminium flexion elements 7. Accordingly, the cantilever waveguide 1 flexes in a direction toward the flexion elements 7 as shown in figure 3. In this manner, the degree of flexion can be tuned by applying differing temperature changes or by changing the material of the flexion elements 7 so as to change the temperature response.

[0214] In an alternative embodiment, the flexion elements 7 are each formed of nickel instead of aluminium. In such examples, the application of an external magnetic field can cause the nickel flexion elements 7 to experience a different stress to the silicon flexible substrate 2. As a result, the cantilever waveguide 1 can be caused to flex in a direction toward the flexion elements 7 as shown in figure 3. In particular, the flexion of the cantilever waveguide 1 can be tuned through application of a suitable external magnetic field. Again, it will be understood by the skilled person an alternative ferromagnetic material could be used in such an embodiment in place of nickel.

[0215] Finally, on the portion of flexible substrate 2 mounted above the base substrate 5 (i.e. the portion which is further away from the free end 4 than the fixed end 3), the subwavelength grating waveguide formed by the segments 6 transitions to a conventional channel waveguide 8. The channel waveguide 8 connects the subwavelength grating waveguide formed by the segments 6 to an integrated photonic circuit (not shown), which is also mounted upon the base substrate 5.

[0216] As shown in Figure 3, the cantilever waveguide 1 is capable of flexion in a direction transverse to the cantilever major axis A. In the orientation of figure 1 and 3, the flexion of the cantilever waveguide 1 occurs in the vertical direction, i.e. out of the plane in which the flexible substrate 2 (in its unflexed position) and integrated photonic circuit lies.

[0217] This enables the series of disconnected waveguide segments 6 to guide and, at the free end 4 of the cantilever waveguide 1, to transmit or received light (as required). This in turn allows for light to be transmitted or received (again as required) into the integrated photonics circuit to which the cantilever waveguide 1 is connected.

[0218] Turning to Figure 4, there is shown a reinforced cantilever waveguide array 10. The reinforced waveguide array 10 comprises three cantilever waveguides 1 as described above, each sharing a common cantilever major axis A’ , with a series of struts 11 extending between the cantilever waveguides 1. The struts 11 serves to prevent deformation of each cantilever waveguide 1 about an axis transverse to both the cantilever major axis A’ and flex direction of each cantilever waveguide 1.

[0219] The struts 11 are each generally cuboidal in form and connect the flexible substrates 2 of each cantilever waveguide 1 at an angle perpendicular to the direction of the subwavelength grating waveguide formed by the series of disconnected waveguide segments 6. In the exemplary embodiment of figure 4, there are ten struts 11, one each at the free and fixed ends 3,4 of each cantilever waveguide 1, and eight struts 11 at regularly spaced intervals therebetween.

[0220] Figure 5 shows a manufacturing process used to produce a cantilever waveguide 1 as described above. The view shown in figure 5 is the same cross section as in figure 2.

[0221] Initially, a three-layer material is provided, the material having an upper silicon membrane 20, an insulating layer 21 formed of silicon dioxide and a silicon handle 22, where the insulating layer 21 is sandwiched between the membrane 20 and handle 22 (as shown in fig. 5(a)). After this, a mask is applied to the membrane 20, and the membrane 20 is then etched (step 30). The masking and etching process removes the majority of the membrane 20, leaving a flexible substrate 2 and a series of disconnected waveguide segments 6 formed thereon in place of the membrane 20. In this embodiment, the etching step 30 is a plasma etch, as will be understood by the skilled person.

[0222] Following this, aluminium is deposited upon the substrate 2 using film deposition (step 31). The deposited aluminium forms a pair of flexion elements 7 upon the flexible substrate 2 as described above. Deposition is conducted at a temperature below the operational temperature of the waveguide.

[0223] Next (step 32), a pair of windows 23 are formed in the flexible substrate 2, by masking the non-window regions, and etching away the flexible substrate 2 in the unmasked regions. The windows 26 run along the entire length of the cantilever waveguide 1 and connect around one end thereof to form a ‘U’ shape, thereby defining the fixed and free ends 3,4. In this embodiment, the etching step 32 (as with the earlier etching step 30) is a plasma etch, as will be understood by the skilled person.

[0224] Finally (step 33), the insulating layer 21 beneath the flexible substrate 2 is etched away, leaving the cantilever waveguide 2 which extends from a fixed end 3 to a free end 4. This etching (step 33) is performed using a hydrofluoric acid vapour, though the skilled person will understand that alternative etching process can be used.

[0225] To produce the reinforced waveguide array 10 of figure 4, the process of figure 5 is performed for the desired number of waveguides 1 in parallel, with the masking and etching of the windows 23 (step 32) being altered to also mask the regions of the flexible substrate 2 which will become the struts 11.

[0226] In this embodiment, step 33 is performed as usual, thereby providing the desired number of cantilever waveguides 1 and the struts 11 therebetween, producing the reinforced waveguide array 10.

[0227] Figure 6 shows an alternative manufacturing process which can be used to create a cantilever waveguide. In this exemplary embodiment, the waveguide has a flexible substrate 2 and segments 6 formed of silicon nitride (SiN). The view shown throughout figure 6 is the same cross section as in figure 2. Initially, a three-layer wafer material is provided, the wafer having an upper silicon nitride membrane 40, an interior silicon wafer layer 41 and a lower silicon nitride membrane 42, where the interior silicon wafer layer 41 is sandwiched between the silicon nitride membranes 40,42 (as shown in fig. 6(a)).

[0228] After this, a mask is applied to the lower SiN membrane 42 and said membrane 42 is then etched (step 50). The masking and etching process removes a portion of the membrane 42, leaving a window 43 through which the interior Si wafer layer 41 is exposed. In this embodiment, the etching step 50 is a plasma etch, as will be understood by the skilled person.

[0229] Following this, a second etching (step 51) is performed, which removes the interior layer 41 in the region exposed by the window 43, until a lower surface of the upper membrane 40 is exposed, thereby suspending the membrane 40. It will be understood that the etchant which removes the interior layer 41 will have been chosen so as to be non-reactive against the silicon nitride membranes 40,42.

[0230] Next, a mask is applied to the membrane 40, and the membrane 40 is then etched (step 52). The masking and etching process removes the majority of the membrane 40, leaving a flexible substrate 2 and a series of disconnected waveguide segments 6 formed thereon in place of the membrane 40. In this embodiment, the etching step 52 is a plasma etch, as will be understood by the skilled person.

[0231] Following this, aluminium is deposited upon the substrate 2 using film deposition (step 53). The deposited aluminium forms a pair of flexion elements 7 upon the flexible substrate 2 as described above.

[0232] Finally (step 54), a mask is applied to the membrane / substrate 40, and the membrane / substrate 40 is then etched, so as to detach the substrate 2 from the reminder of the interior layer 41 and thereby provide a cantilever waveguide 1 as described above.

[0233] To produce the reinforced waveguide array 10 of figure 4, the process of figure 6 is performed for the desired number of waveguides 1 in parallel, with the masking and etching of the windows 43 (step 50) being altered to also mask the regions of the flexible substrate 2 which will become the struts 11. In such embodiments, the remaining steps 51 to 54 are performed as usual, thereby providing the desired number of cantilever waveguides 1 and the struts 11 therebetween, producing the reinforced waveguide array 10.

[0234] With reference to Figures 7 to 12, a protected cantilever waveguide assembly 60 is described. As the cantilever waveguides 1 flex out of the plane of the integrated photonic circuit they are substantially unsupported. They ability to flex can also render them quite fragile, as they form part of the integrated photonic circuit, a breakage in the cantilever waveguide 1 could result is the entire chip on which the integrated photonic circuit is provided needed to be replaced. This is time and cost intensive and inefficient. There is therefore an advantage in providing protection to the cantilever waveguides.

[0235] Figure 7 shows the protected cantilever waveguide assembly 60. The cantilever waveguide 1 is that described in relation to Figures 1 to 3, though, as will be appreciated by those skilled in the art, the teaching could be applied to other cantilever waveguides. Furthermore, whilst the examples below describe the protected cantilever waveguide assembly 60 in terms of a single cantilever waveguide 1, the skilled person will appreciate that the present invention could equally be applied to an example comprising a cantilever waveguide array 10 along the lines disclosed in relation to figure 4 and / or multiple separate cantilever waveguides I.

[0236] The assembly 60 comprises a contiguous mass of optically clear material 61, typically a resin, in particular examples, a curable resin. The contiguous mass is provided on a base substrate 5 upon which the cantilever waveguide I is provided. The cantilever waveguide I is provided within the contiguous mass 61. As illustrated, the contiguous mass 61 is generally in the form of a dome and encompasses the cantilever waveguide I. As the contiguous mass 61 is optically clear, it is transparent to wavelength / s of light transmitted and / or received by the cantilever waveguide I . In this specific embodiment, the optically clear material is a curable resin such as UV curable epoxy such as Dymax OP29.

[0237] Figure 8 illustrates how the assembly 60 can be manufactured. At a first step, a cantilever waveguide 1 on a base substrate 5 is provided. As illustrated in the example of figure 8a, a contiguous mass of optically clear material 61, in the form of a blob 62 from a suitable applicator for example a micro-nozzle 63, is applied to the cantilever waveguide 1. If the blob 62 is of sufficient size it will encompass the cantilever waveguide 1. Typically, internal forces within the optically clear material 61 will tend toward a substantially dome like form as shown in figure 9 and figures 8b and 8c. In preferred embodiments the blob 62 is initially applied to the fixed end 3 of the cantilever waveguide 1 and with additional material deposited the size of the blob 62 increases until it encapsulates the entire cantilever waveguide 1 (as denoted in figure 8a by a series of dashed semi-circles increasing in size. This is preferable because, given the size of the cantilever waveguide it can be fragile and application to the fixed end 3 (where it is more supported) reduces the risk of damage.

[0238] Turning to figure 8b, the flex of the cantilever waveguide 1 is configured. This can be achieved by applying heat 63 and / or a magnetic field 64 until the cantilever waveguide 1 is at a desired degree of flex.

[0239] The application of heat can cause the flex of the cantilever waveguide 1 to vary as a result of differential thermal expansion between different materials making up the cantilever waveguide 1. For example, between flexion elements 7 and the flexible substrate 2 as described previously.

[0240] The application of a magnetic field can cause the flex of the cantilever waveguide 1 to vary as a result of differential magnetic susceptibility between different materials making up the cantilever waveguide 1. For example, between flexion elements 7 and the flexible substrate 2 as described previously.

[0241] Turning to figure 8c, the optically clear material is cured, in this example by exposure to ultraviolet (UV) light 65. The skilled person will appreciate that other curing techniques may be applied where suitable. In this context, the skilled person will appreciate that heat curing techniques may not be appropriate in cases where the cantilever waveguide 1 is formed from multiple materials due to the possibility of differential thermal expansion changing the flex of the cantilever waveguide 1.

[0242] Turning now to figure 9, a housing 71 is shown. The housing 71 can be incorporated into an alternative embodiment of a protected cantilever waveguide assembly 70 according to the present invention, which is illustrated in figure 10. The provision of the housing provides additional protection for the assembly 70 against impacts and / or contaminants.

[0243] The housing 71 defines an interior space 72 between side walls 73, the housing having a top opening 74 and bottom opening 75 providing access to the interior space 72. In this example, the side walls 73 are arranged at right angles to define a cuboid exterior of the housing 71. Conversely, the inner faces of the side walls 73 are sloped such that the interior space 72 is shaped in a mesa form. In this example, to better accommodate the cantilever waveguide 1 or a coupled waveguide provided on base substrate 5, one side wall 73 is provided with a passage 76. As illustrated, the top of the housing 71 is provided with a window 77 of optically clear material. The window 77 covers the top opening 74, increasing impact and contamination protection, whilst allowing light to be transmitted to and / or received by the cantilever waveguide 1.

[0244] As shown in figure 10, the interior space is filled with a contiguous mass of optically clear material 61. As with protected assembly 60, the contiguous mass 61 encompasses the cantilever waveguide 1.

[0245] Figure 11 illustrates how the assembly 70 can be manufactured. At a first step, a cantilever waveguide 1 on a base substrate 5 is provided. Subsequently, as illustrated in figure 11b, the housing 71 is mounted on the base substrate 5. The housing 71 can be fixed in this position by any suitable technique, including, but not limited to use of an adhesive. As illustrated, the window 77 is not yet fixed to the housing 71, thereby providing access to the interior space 72 by way of the top opening 74. As illustrated in figure 11c, optically clear material 61 can then be introduced into the interior space 72 so as to encompass the cantilever waveguide 1. Subsequently, the window 77 can be mounted on top of the housing 71, to form the protected assembly 80 as illustrated in figure 12.

[0246] The skilled person will appreciate that equivalent steps to configuring the flex of the cantilever waveguide and / or curing the optically clear material as described in relation to figures 8b and 8c can be performed during manufacture of the protected assembly 80. These steps would occur after the optically clear material 61 is introduced into the interior space 72 in figure 11c but can occur before or after the window 77 is subsequently fitted. The skilled person will also appreciate that optionally the window 77 may be fitted to the housing 71 before it is mounted in position and / or before the optically clear material 61 is introduced into the interior space 72, as is illustrated in figure 12, indeed the window may be integrally formed with the housing. In such implementations, the optically clear material 61 is introduced into the interior space 72 by another opening such as passage 76. The skilled person will also appreciate that in further implementations, the housing 71 may be mounted in position after the optically clear material 61 is applied to the cantilever waveguide 1, i.e. after the step illustrated in figure 18a. To aid in this approach the interior space 72 may also be filled with optically clear material 61 and the two masses combined as the housing 71 is placed over the cantilever waveguide 1, this combined mass of optically clear material 61 can then be cured.

[0247] In Figures 13 to 15, there is provided a further embodiment of a cantilever waveguide 101 according to the present invention. The cantilever waveguide 101 shares a number of similarities with the cantilever waveguide of the first embodiment, and like features will be provided with like reference numerals, advanced by 100. In the present embodiment the cantilever waveguide 101 is configured as an actuator arm 100. In the below description, any relative terms (upper, lower, top, bottom etc.) refer to the actuator arm 100 shown as oriented in figure 13.

[0248] The actuator arm 100 is formed upon a flexible substrate 102. In this embodiment, the flexible substrate 102 is Silicon Nitride. It will be understood that alternative materials could be used for the flexible substrate 102. The flexible substrate 102, and hence the actuator arm 100, extend from a fixed end 103 to a free end 104. The extension of the actuator arm 100 between the fixed and free ends 103,104 when the flexible substrate 102 is in its unflexed form defines a cantilever major axis B (as shown in figure 13).

[0249] In this specific embodiment, the actuator arm 100 extends approximately 200pm from the fixed end 103 to the free end 104.

[0250] At the fixed end 103 of the actuator arm 100, the flexible substrate 102 is mounted upon a base substrate 105. In this specific embodiment, the base substrate 105 is silicon nitride. It will be understood by the skilled person that alternative materials could be used for the flexible substrate 102. In this embodiment, the flexible substrate 102 and the base substrate 105 are each part of a conventional wafer material (not shown). The wafer material acts as a handle and mount for the actuator arm 100, allowing operators to move the actuator arm 100 without damaging the actuator arm 100.

[0251] The actuator arm 100 has, formed on an upper surface of the flexible substrate 102, a series of disconnected waveguide segments 106, with each segment 106 being spaced at regular intervals along the actuator arm 100. In this embodiment, the segments 106 extend between the fixed end 103 and the free end 104. In this manner, the series of disconnected waveguide segments 106 extends the full length of the actuator arm 100.

[0252] Together, the segments 106 form a subwavelength grating waveguide. Subwavelength grating waveguides are known in the art, and are capable of guiding light within the waveguide, whilst being formed of disconnected segments 106.

[0253] Subwavelength grating waveguides comprise periodic structures arranged to frustrate diffraction of light transmitted therein, and thus behave like a homogeneous medium. Within any subwavelength grating waveguide, light excites a Bloch mode, which can propagate, reflect or scatter through the subwavelength grating waveguide. This allows for transmission of light throughout the waveguide. This requires that the periodicity of the structure (referred to herein as segments 106) is sufficiently small so as to be below the first Bragg reflection. It will be understood by the skilled person that the spacing of the segments 106 for any given embodiment will be configured such that the segments 106 can act as a subwavelength grating waveguide.

[0254] In this embodiment, each segment 106 is formed integrally with the silicon nitride which forms the flexible substrate 102, via etching from a single larger silicon nitride membrane (see figure 18 and the associated description thereof below).

[0255] Placed symmetrically either side of the series of disconnected waveguides segments 106 are a pair of flexion elements 107. The flexion elements 107 each extend from the fixed end 103 to the free end 104 of the actuator arm 100. In this embodiment, the flexion elements 107 each comprise a film of aluminium deposited directly onto the flexible substrate 102. It will be understood by the skilled person that an alternative material could be used for the flexion elements 107.

[0256] As the material of the flexion elements 107 has different properties to the material of the flexible substrate 102, under particular conditions the flexion elements 107 will experience different stress forces to the flexible substrate 102. This differential stress can cause the actuator arm 100 to flex, the direction of flex dependent on the nature of the differential stress. In the present example there is a difference between the coefficients of thermal expansion between the aluminium flexion elements 107 and the silicon nitride flexible substrate 102. If the temperature of the actuator arm 100 is raised, the silicon nitride flexible substrate 102 expands more than the aluminium flexion elements 107. Accordingly, the actuator arm 100 flexes in a direction toward the flexion elements 107 as shown in figure 15. In this manner, the degree of flexion can be tuned by applying differing temperature changes or by changing the material of the flexion elements 107 so as to change the temperature response.

[0257] It will be understood that a differential stress can be provided during the manufacturing process of the actuator arm 100, such that the actuator arm 100 can, if desired, have a neutral position which is pre-flexed. For example, the actuator arm 100 may, in the manufacturing process, be the subject of annealing, curing or physical forces which can provide a pre-flexure to the actuator arm 100.

[0258] Finally, on the portion of flexible substrate 102 mounted above the base substrate 105 (i.e. the portion which is further away from the free end 104 than the fixed end 103), the subwavelength grating waveguide formed by the segments 106 transitions to a conventional channel waveguide 108. The channel waveguide 108 connects the subwavelength grating waveguide formed by the segments 106 to an integrated photonic circuit (not shown), which is also mounted upon the base substrate 105.

[0259] Placed atop each segment 106 which together form the subwavelength grating waveguide is a light absorbing coating 109. In this example, the light absorbing coating 109 comprises a layer or pad of chromium. The chromium pads 109 are placed so as to overlap with the optical field within the subwavelength gating waveguide, and thereby absorb the light within the subwavelength grating waveguide. Whilst in this example, the light absorbing coating 109 comprises chromium, it will be understood that the this could be replaced by other suitable materials if required or desired.

[0260] Where the light within the waveguide is absorbed by the pads 109, the pads 109 will necessarily raise in temperature, as the energy from the light is absorbed. This temperature rise is conducted to the segments 106, flexible substrate 102 and flexion elements 107 in turn. As set out above, the difference between the coefficients of thermal expansion between the aluminium flexion elements 107 and the silicon nitride flexible substrate 102 thereby flexes the actuator arm 100. In this manner, the actuator arm 100 can be actuated by increasing or decreasing the intensity of the light transmitted therein: it will be understood that increasing the intensity of the light within the waveguide will increase the energy absorption and hence temperature change within the actuator arm 100.

[0261] As shown in Figure 15, the actuator arm 100 is capable of flexion in a direction transverse to the cantilever major axis B. In the orientation of figure 13 and 15, the flexion of the actuator arm 100 occurs in the vertical direction, i.e. out of the plane in which the flexible substrate 102 lies in its neutral position.

[0262] Turning to Figure 16, there is shown an actuator arm array 110. The actuator arm array 110 comprises three actuator arms 100 as described above, each sharing a common cantilever major axis B’, with a series of struts 111 extending between the actuator arms 100. The struts 111 serves to prevent deformation of each actuator arm 100 about an axis transverse to both the cantilever major axis B’ and flex direction of each actuator arm 100.

[0263] The struts 111 are each generally cuboidal in form and connect the flexible substrates 102 of each actuator arm 100 at an angle perpendicular to the direction of the subwavelength grating waveguide formed by the series of disconnected waveguide segments 106. In the exemplary embodiment of figure 16, there are ten struts 111, one each at the free and fixed ends 103,104 of each actuator arms 100, and eight struts 111 at regularly spaced intervals therebetween.

[0264] Turning to Figure 17, there is shown an actuator 200. The actuator 200 comprises an actuator arm 100 as described above. The actuator arm 100 is connected, via the channel waveguide 108 upon the base structure 105, to a light source 221. In this exemplary embodiment of figure 17, the light source 221 is operable to transmit light through the channel waveguide 108 and into the actuator arm 100. As above, light within the actuator arm 100 can (dependent upon the wavelength of the light) be absorbed by the pads 109 of the actuator arm 100, and thereby actuate the actuator arm 100.

[0265] The light source 221 may be operably connected to and controlled by a control unit 222. The control unit 222 comprises a central processing unit 223, which is operably connected to the light source 221. The central processing unit 223 is operable to control the output of the light source 221 in response to control signals input by a user or in line with automated control signals in line with pre-programmed functions.

[0266] In this manner, the control unit 222 is able to adjust the properties of the light output by the light source 221, and hence the light within the subwavelength grating waveguide.

[0267] The control unit 222 is operable to transmit and receive data from a communication unit 224 to a corresponding communication unit 224a of an external control apparatus 222a. The external control apparatus 222a comprises its own central processing unit 223 a, and a user interface 225 a. The user interface 225 a is operable to display information regarding the state of the actuator arm 100. In some embodiments, the user interface 225a is also operable to receive user control inputs. In such embodiments, the central processing unit 223a of the external control apparatus 222a is operable, via the communication units 224,224a, to transmit the user control inputs to the control unit 222 of the actuator 200, which is then controlled according to the user control inputs.

[0268] Figure 18 shows a manufacturing process used to produce an actuator arm 100 as described above. The view shown in figure 18 is the same cross section as in figure 14.

[0269] Initially, a three-layer material is provided, the material having an upper silicon membrane 120, an insulating layer 121 formed of silicon dioxide and a silicon handle 122, where the insulating layer 121 is sandwiched between the membrane 120 and handle 122 (as shown in fig. 18(a)).

[0270] After this, a mask is applied to the membrane 120, and the membrane 120 is then etched (step 130). The masking and etching process removes the majority of the membrane 120, leaving a flexible substrate 102 and a series of disconnected waveguide segments 106 formed thereon in place of the membrane 120. In this embodiment, the etching step 130 is a plasma etch, as will be understood by the skilled person.

[0271] Following this, aluminium and chromium are deposited upon the substrate 102 using film deposition (step 131). The deposited aluminium forms a pair of flexion elements 107 upon the flexible substrate 102, and the chromium pads 109 form a light absorbing coating on the upper surface of the segments 106.

[0272] Next (step 132), a pair of windows 123 are formed in the flexible substrate 102, by masking the non- window regions, and etching away the flexible substrate 102 in the unmasked regions. The windows 123 run along the entire length of the actuator arm 100 and connect around one end thereof to form a ‘U’ shape, thereby defining the fixed and free ends 103,104. In this embodiment, the etching step 132 (as with the earlier etching step 130) is a plasma etch, as will be understood by the skilled person.

[0273] Finally (step 133), the insulating layer 121 beneath the flexible substrate 102 is etched away, leaving an actuator arm 100 which extends from a fixed end 103 to a free end 104. This etching (step 133) is performed using a hydrofluoric acid vapour, though the skilled person will understand that alternative etching process can be used.

[0274] To produce the actuator arm array 110 of figure 16, the process of figure 18 is performed for the desired number of actuator arms 100 in parallel, with the masking and etching of the windows 123 (step 132) being altered to also mask the regions of the flexible substrate 102 which will become the struts 111.

[0275] In this embodiment, step 133 is performed as usual, thereby providing the desired number of actuator arms 100 and the struts 111 therebetween, producing the actuator arm array 110.

[0276] Figure 19 shows an alternative manufacturing process which can be used to create an actuator arm 100. In this exemplary embodiment, the actuator arm 100 has a flexible substrate 102 and segments 106 formed of silicon nitride (SiN). The view shown throughout figure 19 is the same cross section as in figure 14.

[0277] Initially, a three-layer wafer material is provided, the wafer having an upper silicon nitride membrane 140, an interior silicon wafer layer 141 and a lower silicon nitride membrane 142, where the interior silicon wafer layer 151 is sandwiched between the silicon nitride membranes 140,142 (as shown in fig. 19(a)).

[0278] After this, a mask is applied to the lower SiN membrane 142 and said membrane 142 is then etched (step 150). The masking and etching process removes a portion of the membrane 142, leaving a window 143 through which the interior silicon wafer layer 141 is exposed. In this embodiment, the etching step 150 is a plasma etch, as will be understood by the skilled person.

[0279] Following this, a second etching (step 151) is performed, which removes the interior layer 141 in the region exposed by the window 143, until a lower surface of the upper membrane 140 is exposed, thereby suspending the membrane 140. It will be understood that the etchant which removes the interior layer 141 will have been chosen so as to be non-reactive against the silicon nitride membranes 140,142.

[0280] Next, a mask is applied to the membrane 140, and the membrane 140 is then etched (step 152). The masking and etching process removes the majority of the membrane 140, leaving a flexible substrate 102 and a series of disconnected waveguide segments 106 formed thereon in place of the membrane 140. In this embodiment, the etching step 152 is a plasma etch, as will be understood by the skilled person.

[0281] Following this, aluminium is deposited upon the substrate 102 using film deposition (step 153). The deposited aluminium forms a pair of flexion elements 107 upon the flexible substrate 102, and the chromium pads 109 form a light absorbing coating on the upper surface of the segments 106.

[0282] Finally (step 154), a mask is applied to the membrane / substrate 140, and the membrane / substrate 140 is then etched, so as to detach the substrate 102 from the reminder of the interior layer 141 and thereby provide an actuator arm 100 as described above. To produce the actuator arm array 110 of figure 16, the process of figure 19 is performed for the desired number of actuator arms 100 in parallel, with the masking and etching of the windows 143 (step 150) being altered to also mask the regions of the flexible substrate 102 which will become the struts 111.

[0283] In such embodiments, the remaining steps 151 to 154 are performed as usual, thereby providing the desired number of actuator arms 100 and the struts 111 therebetween, producing the actuator arm array 110.

[0284] In a further embodiment, two actuator arms 300 can be used in a scanning actuator array 301 as shown in Figures 19 to 21. The structure and flexing of the actuator arms 300 of this embodiment are substantially similar to the actuator arms 100 described with respect to Figures 13 to 17 and therefore the following description will use like terms and reference numerals, advanced by 200, to describe like features. Likewise, the two actuator arms 300 are structurally similar (differing only in their mounting, as will be described below) and thus only one will be described in detail.

[0285] Each actuator arm 300 is formed upon a flexible substrate 302. In this embodiment, the flexible substrate 302 is silicon nitride. It will be understood that alternative materials could be used for the flexible substrate 302. The flexible substrate 302, and hence the actuator arm 300, extend from a fixed end 303 to a free end 304. The extension of the actuator arm 300 between the fixed and free ends 303,304 when the flexible substrate 302 is in its unflexed form defines a cantilever major axis C (as shown in figure 12).

[0286] In this specific embodiment, the actuator arm 300 extends approximately 200pm from the fixed end 303 to the free end 304.

[0287] At the fixed end 303 of the actuator arm 300, the flexible substrate 302 is mounted upon an optical coupling 350 as will be expanded upon below.

[0288] The actuator arm 300 has, formed on an upper surface of the flexible substrate 302, a series of disconnected waveguide segments 306, with each segment 306 being spaced at regular intervals along the actuator arm 300. In this embodiment, the segments 306 extend between the fixed end 303 and the free end 304. In this manner, the series of disconnected waveguide segments 306 extends the full length of the actuator arm 300.

[0289] Together, the segments 306 form a subwavelength grating waveguide. Subwavelength grating waveguides are known in the art, and are capable of guiding light within the waveguide, whilst being formed of disconnected segments 306.

[0290] Subwavelength grating waveguides comprise periodic structures arranged to frustrate diffraction of light transmitted therein, and thus behave like a homogeneous medium. Within any subwavelength grating waveguide, light excites a Bloch mode, which can propagate, reflect or scatter through the subwavelength grating waveguide. This allows for transmission of light throughout the waveguide. This requires that the periodicity of the structure (referred to herein as segments 306) is sufficiently small so as to be below the first Bragg reflection. It will be understood by the skilled person that the spacing of the segments 306 for any given embodiment will be configured such that the segments 306 can act as a subwavelength grating waveguide.

[0291] In this embodiment, each segment 306 is formed integrally with the silicon nitride which forms the flexible substrate 302, via etching from a single larger silicon nitride membrane.

[0292] Placed symmetrically on either lateral edge of the flexible substrate 302 are a pair of flexion elements 307. The flexion elements 307 each extend from the fixed end 303 to the free end 304 of the actuator arm 300. In this embodiment, the flexion elements 307 each comprise a film of aluminium deposited directly onto the flexible substrate 302. It will be understood by the skilled person that an alternative material could be used for the flexion elements 307.

[0293] As the material of the flexion elements 307 has different properties to the material of the flexible substrate 302, under particular conditions the flexion elements 307 will experience different stress forces to the flexible substrate 302. This differential stress can cause the actuator arm 300 to flex, the direction of flex dependent on the nature of the differential stress. In the present example there is a difference between the coefficients of thermal expansion between the aluminium flexion elements 307 and the silicon nitride flexible substrate 302. If the temperature of the actuator arm 300 is raised, the silicon nitride flexible substrate 302 expands more than the aluminium flexion elements 307. Accordingly, the actuator arm 300 flexes in a direction toward the flexion elements 307. In this manner, the degree of flexion can be tuned by applying differing temperature changes or by changing the material of the flexion elements 307 (so as to have different coefficients of thermal expansion) so as to change the temperature response.

[0294] In alternative embodiments, a property other than thermal expansion may be used to induce the differential stress, for example the flexion elements may be comprises of nickel, or other magnetic material so as to induce a flex in the presence of a magnetic field.

[0295] It will be understood that a differential stress can be provided during the manufacturing process of the actuator arm 300, such that the actuator arm 300 can, if desired, have a neutral position which is pre-flexed. For example, the actuator arm 300 may, in the manufacturing process, be the subject of annealing, curing or physical forces which can provide a pre-flexure to the actuator arm 300.

[0296] On the portion of flexible substrate 302 mounted above the base substrate 305 (i.e. the portion which is further away from the free end 304 than the fixed end 303), the subwavelength grating waveguide formed by the segments 306 transitions to a conventional channel waveguide 308. The channel waveguide 308 connects the subwavelength grating waveguide formed by the segments 306 to an optical fibre as described below.

[0297] Placed atop each segment 306 which together form the subwavelength grating waveguide is a light absorbing coating 309. In this example, the light absorbing coating 309 comprises a layer or pad of chromium. The chromium pads 309 are placed so as to overlap with the optical field within the subwavelength grating waveguide, and thereby absorb the light within the subwavelength grating waveguide. Whilst in this example, the light absorbing coating 309 comprises chromium, it will be understood that the this could be replaced by other suitable materials if required or desired.

[0298] Where the light within the waveguide is absorbed by the pads 309, the pads 309 will necessarily raise in temperature, as the energy from the light is absorbed. This temperature raise is conducted to the segments 306, flexible substrate 302 and flexion elements 307 in turn. As set out above, the difference between the coefficients of thermal expansion between the aluminium flexion elements 307 and the silicon nitride flexible substrate 302 thereby flexes the actuator arm 300. In this manner, the actuator arm 300 can be actuated by increasing or decreasing the intensity of the light transmitted therein: it will be understood that increasing the intensity of the light within the waveguide will increase the energy absorption and hence temperature change within the actuator arm 300.

[0299] Finally, arranged on an upper surface of the flexible substrate 302 proximal to the free end 304 there is provided a reflector 310. The reflector 310 is a rectangular element with a reflective upper surface configured to reflect light within the operating wavelengths of the scanning array. In some embodiments the reflector 310 is a metallic film deposited along with the flexion elements 307 (and being comprised of the same material and simplifying manufacture); in other embodiments the reflector 310 is a metallic film deposited in a separate step to the flexion elements 307 (thereby allowing the material to be optimized for reflection); in yet further embodiments the reflector 310 may be a separate element bonded to the flexible substrate 302.

[0300] Turning to Figure 21, the scanning actuator array 301 is shown in greater detail.

[0301] The scanning actuator array 301 comprises a collar 320, the collar is a cylindrical body having a flat upper 321 and lower surfaces with a curved surface between. There collar is comprised of silicon and has a diameter of 400 m and a height of 300 pm. The collar 320 has three holes 322 extending between the upper 321 and lower surfaces. Arranged through these holes are three optical fibres 323, which terminate approximately 150 pm beyond the upper surface 321. From the lower surface the optical fibres 323 extend away to light sources and associated controllers (not shown). These light sources and controllers are similar to the light sources 221 and controllers 222 described with respect to a single actuator arm, adapted for a plurality of actuator arms, for example by comprising separate light sources for each optical fibre 323.

[0302] A first (rightmost as viewed in Figure 21) optical fibre 323 A is provided with first actuator arm 300 A mounted on its terminal end 324A at a 45° angle away from the place of the upper surface 321. The first optical fibre 323 A is optically coupled to the first actuator arm 300A via the conventional channel waveguide 308, such that light from the first optical fibre 323A is directed to the segments 306.

[0303] A second (leftmost as viewed in Figure 21) optical fibre 323B is provided with a second actuator arm 300B mounted on its terminal end 324B via a coupling element 325. The second actuator arm 300B extends perpendicular to the second optical fibre 323B and to the direction in which the first actuator arm 300A extends. The second optical fibre 323B is optically coupled to the second actuator arm 300B via the conventional channel waveguide 308, such that light from the second optical fibre 323B is directed to the segments 306.

[0304] A third (central as viewed in Figure 21) optical fibre 323C provides an incident light beam (denoted by an arrow from the third optical fibre). The first 300A and second 300B actuator arms are aligned such that the incident light beam impinges the reflector of the first actuator arm 300A and is reflected to the reflector of the second actuator arm 300B from where it is directed to a target (not shown).

[0305] To protect the actuator arms 300 and thereby allow the scanning actuator array 301 to be used in liquid environments the array may be provided with a cap 330 as shown in Figure 22. The cap 330 is a cylindrical element having an open end 331 and a closed end 332. The cap 330 is comprised of a material which is optically transparent at the wavelength of the incident light beam. The open end 331 of the cap 330 is sized so as to engage with the collar 320 tightly, for example with an interference or transition fit. A seal is thereby provided between the collar 320 and cap 330 sealing a cavity 333 defined by an interior of the cap and the upper surface 321 of the collar. As an alternative to the interference or transition fit, or to complement it, the collar 320 and cap may be joined by an adhesive. The actuator arms 300 are arranged within the cavity 333.

[0306] The operation of the scanning actuator array 301 will now be described. As noted above, the incident light beam is emitted from the third optical fibre 323C onto the reflector of the first actuator arm 300 A from where it is reflected onto the reflector of the second actuator arm 300B and then towards the target (not shown). To aim the incident light beam at the target, the angles at which the light impinges the two reflectors can be vaired by sending light down the first 323A and second 323B optical fibres to heat the first 300A and second 300B actuators thereby inducing a flex. In this way the first actuator arm 300A can provide vertical scanning (relative to the orientation in Figure 21) as denoted by arrow F and the second actuator arm 300B can provide horizontal scanning (relative to the orientation in Figure 21) as denoted by arrow G.

[0307] Amongst other uses, the scanning actuator array 301 can be used in medical procedures, for example laser atherectomies. Advantageously, the use of the scanning actuator array as described therein allows for a more compact device than laser atherectomy device of the prior art and allow the surgeon great control of the procedure.

[0308] The one or more embodiments are described above by way of example only.

[0309] Many variations are possible without departing from the scope of protection afforded by the appended claims.

[0310] CLAIMS A cantilever waveguide comprising: a flexible substrate extending along a cantilever major axis from a fixed end to a free end; a series of disconnected waveguide segments provided on the flexible substrate between the fixed and free ends so as to form a subwavelength grating waveguide; and one or more flexion elements provided on the flexible substrate, the one or more flexion elements configured to urge the substrate to flex in a direction transverse to the cantilever major axis. A cantilever waveguide according to claim 1 wherein the cantilever major axis is defined by the cantilever waveguide when in a neutral (i.e. unflexed) position. A cantilever waveguide according to any preceding claim wherein the transverse direction in which the cantilever waveguide flexes is a direction that is substantially perpendicular to the plane in which the cantilever waveguide lies when in the neutral (i.e. unflexed) position. A cantilever waveguide according to claim 3 wherein the fixed end of the cantilever waveguide is the point at which the cantilever waveguide is attached to a base structure upon which any integrated photonic circuit and / or external waveguide is formed. A cantilever waveguide according to claim 4 wherein the base structure is a second substrate onto which the cantilever waveguide is mounted. A cantilever waveguide according to any preceding claim wherein the flexible substrate and segments are formed from the same material. A cantilever waveguide according to any preceding claim wherein the series of disconnected waveguide segments extends along a line of symmetry of the cantilever waveguide, in a straight line between the fixed and free ends. A cantilever waveguide according to any preceding claim wherein the subwavelength grating waveguide transitions to a conventional waveguide at the point at which the sub wavelength grating waveguide ends.

Claims

9. A cantilever waveguide according to any preceding claim wherein the or each flexion element extends substantially the full distance between the fixed and free end of the cantilever waveguide.

10. A cantilever waveguide as according to any preceding claim wherein the one or more flexion elements are provided on either side of the series of disconnected waveguide segments.

11. A cantilever waveguide as according to any preceding claim wherein the or each flexion element comprises a material having a different coefficient of thermal expansion to the flexible substrate.

12. A cantilever waveguide as according to any preceding claim wherein the or each flexion element comprises a ferromagnetic metal.

13. A cantilever waveguide as according to any preceding claim wherein the cantilever waveguide’s flexion in a direction transverse to the cantilever major axis is tuneable.

14. A cantilever waveguide as according to any preceding claim wherein the flexion is tuneable to the extent that the free end of the cantilever waveguide is substantially perpendicular to the cantilever major axis.

15. A reinforced cantilever waveguide array comprising: at least one cantilever waveguide in accordance with any of claims 1 to 14, the or each cantilever waveguide having a common cantilever major axis and at least one strut extending from the or each cantilever waveguide and transverse to the common cantilever major axis so as to restrict flexion of the or each cantilever waveguide about an axis transverse to both the common cantilever major axis and flex direction of the or each cantilever waveguide.

16. A reinforced cantilever waveguide array according to claim 15 wherein the or each strut is formed from the same material as the flexible substrate.

17. A reinforced cantilever waveguide array according to either claim 15 or 16, where there is more than one cantilever waveguide, and there is at least one strut extending between each adjacent pair of cantilever waveguides.

18. A reinforced cantilever waveguide array according to any of claims 15 to 17 wherein the or each strut extends perpendicularly to the or each cantilever waveguide.

19. A method for manufacturing a cantilever waveguide, the method comprising: providing a flexible substrate extending from a fixed end to a free end; wherein a series of disconnected segments have been formed onto the flexible substrate between the fixed and free ends, the segments thereby forming a subwavelength grating waveguide; and depositing a material onto the flexible substrate onto the first substrate to create one or more flexion elements.

20. A method according to claim 19 wherein the deposition of the material onto the flexible substrate onto occurs prior to the cantilever being formed in respect of the waveguide.

21. A method according to either claim 19 or 20 wherein the flexible substrate and series of disconnected waveguide segments are etched from a single membrane.

22. A method according to claim 21 wherein the etching of the substrate and series of disconnected waveguide segments is performed whilst the membrane is mounted upon a cladding material.

23. An actuator arm comprising: a flexible substrate extending along a cantilever major axis from a fixed end to a free end; a series of disconnected waveguide segments provided on the flexible substrate between the fixed and free ends so as to form a subwavelength grating waveguide; and one or more flexion elements provided on the flexible substrate, the one or more flexion elements having a different coefficient of thermal expansion to the flexible substrate; wherein a light absorbing coating is provided on each of the segments that form the waveguide, the coating operable to absorb light within the waveguide, thereby heating the segments, substrate and flexion elements and thus varying the flexion of the actuator arm in response to light within the waveguide.

24. An actuator arm according to claim 23 wherein the cantilever major axis is defined by the actuator arm when in a neutral (i.e. unflexed) position.

25. An actuator arm according to claim 23 or 24 wherein the transverse direction in which the actuator arm flexes is a direction that is substantially perpendicular to the plane in which the actuator arm lies when in the neutral (i.e. unflexed) position.

26. An actuator arm according to any of claims 23 to 25 wherein the fixed end of the actuator arm may comprise a coupling element to couple any light within the waveguide to an integrated circuit and / or light source.

27. An actuator arm according to any of claims 23 to 26 wherein the fixed end of the actuator arm is the point at which the actuator arm is attached to a base structure upon which any integrated circuit and / or light source is formed.

28. An actuator arm according to claim 27 wherein the base structure is a second substrate onto which the actuator arm is mounted.

29. An actuator arm according to any of claims 23 to 28 wherein the or each flexion element extends substantially the full distance between the fixed and free end of the actuator arm.

30. An actuator arm according to any of claims 23 to 29 wherein the light absorbing coating is provided on the uppermost or top surface of each segment relative to the flexible substrate.

31. An actuator arm according to any of claims 23 to 30 wherein the light absorbing coating comprises a metal or an alloy.

32. An actuator arm according to any of claims 23 to 31 comprising one or more additional sub wavelength grating waveguides.

33. An actuator arm according to claim 32 wherein the or each additional subwavelength grating waveguide is operable to emit light from the free end of the actuator arm.

34. An actuator comprising: an actuator arm in accordance with any preceding claim, and one or more light sources optically coupled to the subwavelength grating waveguide of the actuator arm and operable to controllably introduce light into the waveguide so as to control actuation of the actuator arm.

35. An actuator according to claim 34 wherein the light source is able to transmit a tuneable spectrum of wavelengths or polarizations of light, to allow the actuator to function with actuator arms with different properties.

36. An actuator according to either claim 34 or 35 wherein the actuator arm is detachable from the light source.

37. An actuator according to any of claims 34 to 36 wherein the actuator comprises one or more additional sub wavelength grating waveguides.

38. An actuator according to claim 37 wherein the or each additional subwavelength grating waveguide is optically coupled to a light source.

39. A method for manufacturing an actuator arm according to any of claims 12 to 33, the method comprising: providing a flexible substrate extending from a fixed end to a free end, wherein a series of disconnected segments are formed on the flexible substrate between the fixed and free ends, the segments thereby forming a subwavelength grating waveguide, and depositing a material having a different coefficient of thermal expansion to the flexible substrate onto the flexible substrate to create one or more flexion elements on the flexible substrate, and depositing a light absorbing coating onto a top surface of each segment.

40. A method according to claim 39 wherein the flexible substrate and series of disconnected waveguide segments are formed together from a single membrane.

41. A protected cantilever waveguide assembly comprising: a cantilever waveguide provided on a base substrate, wherein the cantilever waveguide is within a contiguous mass of optically clear material.

42. A protected cantilever waveguide assembly according to claim 41, wherein the cantilever waveguide comprises a waveguide formed upon a flexible substrate which extends from a fixed end to a free end.

43. A protected cantilever waveguide assembly according to claim 41 or 42, wherein the cantilever waveguide has a fixed end mounted on or supported by a base substrate.

44. A protected cantilever waveguide assembly according to claim 43, wherein the base substrate comprises one or more components optically coupled to the cantilever waveguide.

45. A protected cantilever waveguide assembly as according to claim 43 or claim 44, wherein a cantilever major axis is defined along the length of the cantilever waveguide when in a neutral (i.e. unflexed) position and the cantilever waveguide is configured to project a selected distance from the base substrate upon which it is provided and / or the cantilever waveguide is configured to have a selected flex in a direction transverse to the major axis.

46. A protected cantilever waveguide assembly according to any of claims 41 to 45, wherein the contiguous mass of optically clear material encompasses the cantilever waveguide.

47. A protected cantilever waveguide assembly according to claim 46, wherein the contiguous mass of optically clear material is provided on the base substrate.

48. A protected cantilever waveguide assembly according to any of claims 41 to 47, wherein the optically clear material is curable.

49. A protected cantilever waveguide assembly according to any of claims 41 to 48, wherein the optically clear material is provided within a housing.

50. A protected cantilever waveguide assembly according to claim 49, wherein the housing is provided on the same base substrate as the cantilever waveguide.

51. A protected cantilever waveguide assembly according to claim 49 or claim 50, wherein the housing comprises one or more side walls defining an end opening.

52. A protected cantilever waveguide assembly according to claim 51, wherein the side walls are at least as tall, or taller, than the distance the cantilever waveguide projects from the base substrate upon which it is provided.

53. A protected cantilever waveguide assembly according to claim 52, wherein a window is fitted over the opening.

54. A protected cantilever waveguide assembly according to any of claims 41 to 53, wherein the cantilever waveguide comprises a part of a cantilever waveguide array.

55. A protected cantilever waveguide assembly according to claim 54, wherein the cantilever waveguide array comprises at least one strut extending from the oreach cantilever waveguide and transverse to the common cantilever major axis so as to restrict flexion of the or each cantilever waveguide about an axis transverse to both the common cantilever major axis and flex direction of the or each cantilever waveguide.

56. A protected cantilever waveguide assembly according to one of claims 42 to 55, wherein the cantilever waveguide comprises one or more flexion elements provided on the flexible substrate, the one or more flexion elements configured to urge the substrate to flex in a direction transverse to the cantilever major axis.

57. A protected cantilever waveguide assembly according to any of claims 41 to 56, wherein the waveguide comprises a channel, tube, rod or a sub wavelength grating.

58. A protected cantilever waveguide assembly according to claim 57, wherein the subwavelength grating comprises a plurality of spring periods or a series of disconnected waveguide segments.

59. A method of manufacturing a protected cantilever waveguide assembly of the type comprising a cantilever waveguide provided on a base substrate, wherein the cantilever waveguide is within a contiguous mass of optically clear material, the method comprising the steps of: providing a cantilever waveguide on a base substrate; applying a curable optically clear material to the cantilever waveguide such that the cantilever waveguide is within a contiguous mass of optically clear material; and curing the optically clear material.

60. A method according to claim 59, wherein curing of the optically clear material is achieved by application of ultraviolet (UV) light and / or heat.

61. A method according to claim 59 or claim 60, wherein the method includes the step of configuring the flex and / or projection of the cantilever waveguide from the base substrate.

62. A method according to claim 61 , wherein configuring is achieved by application of heat and / or a magnetic field.

63. A method according to any one of claims 59 to 62, wherein the method comprises the step of providing a housing on the base substrate.

64. A method according to claim 63, wherein the method comprises the step of fitting a window to the housing.

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