Patent Description:
A microactuator is a type of microelectromechanical system (MEMS) that functions as an actuator.

It is desirable to provide a microactuator that is fast, easy to miniaturize, and requires low electrical voltage to operate. These characteristics are desirable for use cases such as optical coherence tomography.

<CIT> describes a method and apparatus for optical code reading using a MEM optical resonator having an integral photodetector. The resonator comprises a cantilever beam extending from a bimorph actuator. The cantilever beam may comprise depressions to control the beam's weight.

Jain et al. , (doi:<NUM>/j. <NUM>) describes a thermal bimorph micromirror with large bi-directional and vertical actuation. The design includes a silicon frame cantilevered from a substrate by bimorph beams.

<CIT> describes an electrothermal quadmorph microactuator.

<CIT> describes a 3D micromirror, reliant upon bi-morph actuators.

According to various, but not necessarily all, embodiments there is provided an apparatus comprising: a thermally-actuated microactuator configured to deflect a component in dependence on an applied stimulus; and an extender configured to increase deflection of the component by the microactuator, wherein the extender comprises one or more voids.

In some, but not necessarily all examples the extender has a void fraction of at least <NUM>%.

In some, but not necessarily all examples the extender comprises a framework of spaced members separated by one or more voids.

In some, but not necessarily all examples the length of the extender is at least <NUM>% of the length of the microactuator.

In some, but not necessarily all examples at least the extender is cantilevered.

The microactuator comprises a bimorph, wherein the bimorph comprises a first layer and a second layer, and wherein the first layer and the second layer have different coefficients of thermal expansion.

In some, but not necessarily all examples a portion of the first layer extends beyond the second layer, the extender comprising the portion of the first layer.

The first layer and/or the second layer is configured as a resistive heater.

In some, but not necessarily all examples the microactuator comprises at least one electrically isolating slot through the first layer and the second layer, and wherein the second layer comprises a direction change extending from one side of the slot to the other side of the slot.

The second layer comprises one or more discontinuities along its electrical length, for increased resistive heating at the one or more discontinuities than resistive heating of the second layer.

In some, but not necessarily all examples the microactuator is one of a plurality of microactuators of the apparatus, wherein the plurality of microactuators are arranged to enable deflection of the component about a plurality of axes.

In some, but not necessarily all examples at least a first pair of the plurality of microactuators is configured to enable rotation of the component about a first axis, and wherein at least a second pair of the plurality of microactuators is configured to enable rotation of the component about a second axis.

In some, but not necessarily all examples the apparatus comprises the component, wherein the component is an optical component. The optical component may be a reflector.

In some, but not necessarily all examples the reflector may be an optical mirror.

In some, but not necessarily all examples the apparatus comprises an optical coherence tomography system, wherein the optical component is positioned so that light from a light source of the optical coherence tomography system is incident on the optical component, and wherein the microactuator is configured to move the optical component in at least one direction relative to the optical coherence tomography system.

According to various, but not necessarily all, embodiments there is provided an apparatus comprising: a microactuator beam configured to deflect a component in dependence on an applied stimulus; and an extender configured to increase deflection of the component by the microactuator, wherein the extender comprises one or more voids.

The apparatus may be a microactuator apparatus.

The Figures illustrate an apparatus <NUM> comprising: a thermally-actuated microactuator <NUM> configured to deflect a component <NUM> in dependence on an applied stimulus; and an extender <NUM> configured to increase deflection of the component <NUM> by the microactuator <NUM>, wherein the extender <NUM> comprises one or more voids. The void fraction reduces mass and/or thermal mass of the extender <NUM>.

<FIG> schematically illustrates an example of an apparatus <NUM>. The apparatus <NUM> comprises the thermally-actuated microactuator <NUM> and the extender <NUM>. A combination of a microactuator <NUM> and an extender <NUM> may form a beam <NUM> (microactuator beam). The microactuator <NUM> is the part of the apparatus <NUM> configured to supply mechanical energy in dependence on the applied stimulus. The extender <NUM> does not supply actuation energy. For example, the extender <NUM> may be configured not to receive the stimulus.

In <FIG>, but not necessarily in all examples, the mechanical energy output by the microactuator <NUM> is resilient deflection. Resilient deflection implies that the microactuator <NUM> stays in its elastically deflected state while held in that state by actuation force and returns to its neutral equilibrium shape when the actuation force is released. Elastic deflection implies that the deflection is reproducible without causing plastic deformation. The applied stimulus may be configured to control curvature of the microactuator <NUM>, to cause the deflection. Therefore, the deflection may be a form of contortion that controls curvature. The applied stimulus may be electrical resistive heating as described herein, or another stimulus causing thermal actuation.

As shown, the beam <NUM> may be cantilevered, because a cantilever is more flexible than a beam supported at multiple locations along its length. In some, but not necessarily all examples, a beam <NUM> may comprise no more than one microactuator <NUM>. The microactuator <NUM> may be operably coupled to a component <NUM> to be actuated via the extender <NUM>. The beam <NUM> may at least partially support the component <NUM>. In the Figures, a fixed end <NUM> of the microactuator <NUM> is secured to a rigid body such as a substrate. The extender <NUM> is located to the free end of the microactuator <NUM>. The extender <NUM> terminates at a free end which is a tip region of the cantilever.

The component <NUM> is operably coupled to the free end of the extender <NUM>, for example at a tip region of the extender <NUM>. The component <NUM> may be coupled to the extender <NUM> via a separate coupling means (e.g. coupling member <NUM>) as illustrated, or alternatively the component <NUM> may be directly coupled to the extender <NUM>.

The coupling member <NUM> comprises the same or a different material from the extender <NUM>. The coupling member <NUM> may have a smaller cross-sectional area than the extender <NUM>. In some, but not necessarily all examples the coupling member <NUM> comprises a spring such as a serpentine spring.

In <FIG>, but not necessarily all examples, the component <NUM> is suspended from the ends of the beams 3a-3d by the coupling members 16a-16d. This floating method of supporting the component <NUM> reduces the energy required to deflect the component <NUM> and/or enables more degrees of freedom of deflection.

The extender <NUM> functions as a length-extending beam ('extender beam') to enable a reduced-length microactuator <NUM> without substantially reducing the range of deflection. Reducing the length of the microactuator <NUM> reduces the thermal response time of the microactuator <NUM>. Therefore, an applied stimulus can achieve the same range of deflection in a shorter time period. In this case, the tip region is moved by a similar distance as achievable with a full-length microactuator <NUM>.

In some, but not necessarily all examples the length L2 of the extender <NUM> is at least <NUM>% of the length of the microactuator <NUM>. The length L1 of the microactuator <NUM> may be some or all of the remaining span from the fixed end <NUM>. For the purposes of this disclosure, the span does not include the coupling member <NUM>.

The length L2 may be equal to or less than L1 within a suitable margin. Alternatively, L2 could be longer than L1.

<FIG> shows a top-down view of the example apparatus <NUM> of <FIG> shows that the extender <NUM> comprises one or more voids <NUM>, to reduce thermal mass of the extender <NUM>. A high thermal mass increases response times, defined as the time taken to reach steady state. This is because heat is conducted through the microactuator <NUM> to the extender <NUM>, so an extender <NUM> with a greater thermal mass would require a greater amount of heat to pass through the microactuator <NUM>, to achieve steady state. Therefore, it is desirable for the extender <NUM> to have the lowest possible thermal mass relative to that of the microactuator <NUM>. A technical effect of the one or more voids <NUM> is that response times are improved.

Thermal mass depends on mass, density and specific heat capacity, and in this case the void fraction reduces the mass of the extender <NUM>, and the effective density of the shape.

In some, but not necessarily all examples the void fraction of the extender <NUM> is at least <NUM>% and/or less than <NUM>%. Void fraction is a percentage/fraction of the volume of void space relative to the total volume of the extender <NUM>. This range provides an optimum compromise of: reduced response time due to a sufficient reduction in thermal mass; and sufficient mechanical stability.

The voids <NUM> may comprise accessible (open) voids as shown herein, and/or internal inaccessible voids.

<FIG> shows that the extender <NUM> may comprise a framework <NUM> of spaced members (20a-. 20n) ('frame members') separated by voids (22a-. 22n) where 'n' is the total number of members. The members are elongated and thin relative to the width of the microactuator <NUM>.

Although four voids 22a-22d are shown in <FIG>, the extender <NUM> may be regarded as comprising one or more voids <NUM>. The number of voids <NUM> is dependent on the specific implementation. However, having multiple spatially distributed voids <NUM> can provide greater mechanical strength against bending and/or twisting than having only one large void <NUM>. In the Figures, the framework <NUM> defines a matrix pattern of voids 22a-22d arranged in a plurality of rows and a plurality of columns, such as 2x2 or 5x2.

In the Figures, but not necessarily in all examples, the frame members comprise first members 20a-20c, and one or more second cross-members 20d-20e interconnecting two or more first members 20a-20c. The first members 20a-20c may be relatively long members and the cross-members 20d-20e may be relatively short members. A void <NUM> is the internal area defined by three or more of the members 20a-20e, in cross-section view.

<FIG> shows a plurality of parallel first members 20a-. 20n, separated across the width of the microactuator <NUM>. Alternatively, as shown in <FIG>, fewer than all of the first members 20a-20c may be parallel.

The extender <NUM> may form either a quadrilateral shape of <FIG> or a different polygonal shape such as a triangular shape of <FIG>, in the length-width plane of the extender <NUM>. The edges of a void <NUM> may form a quadrilateral, triangular or other polygonal shape, or even an irregular shape depending on the manufacturing method. The edges of a void <NUM> may form a closed shape as shown, to improve mechanical stability against bending and/or twisting.

A cross-member 20d may be provided at a location along the span of the first members, to further improve rigidity. In <FIG>, a further cross-member 20e is provided at the free end/tip region of the extender <NUM>, to improve rigidity. By contrast, in <FIG> there is no requirement for a cross-member 20e at the free end of the extender <NUM> because the first members 20a-20c converge and interconnect at the free end, forming an acute angle therebetween.

<FIG> shows an example of a void-less extender <NUM>, for comparative purposes.

In <FIG>, but not necessarily all examples, the microactuator <NUM> comprises a bimorph. A bimorph is a structure used for actuation which comprises at least two active layers. The bimorph comprises a first layer <NUM> and a second layer <NUM>. The first layer <NUM> has a first coefficient of thermal expansion. The second layer <NUM> has a second, different coefficient of thermal expansion. It would be appreciated that one or more intermediate layers could be provided between the first layer <NUM> and the second layer <NUM>.

In an implementation, the first layer <NUM> comprises polysilicon, and the second layer <NUM> comprises gold. This pairing has a high thermal diffusivity as well as a significant difference in thermal expansion coefficients. Thermal diffusivity is a key factor in controlling heat dissipation and therefore the thermal response time of actuation.

In some examples, chromium, nichrome, aluminium or copper may be used instead of gold, among other possibilities that are generally, but not always metals.

In some examples, silicon dioxide, SU-<NUM> or tungsten may be used instead of polysilicon, among other possibilities that are either metals or nonmetals.

Example first layer <NUM> - second layer <NUM> pairings include: silicon dioxide - chromium; silicon dioxide - aluminium; SU-<NUM> - nichrome; tungsten - aluminium; tungsten - copper; or copper-aluminium.

SU-<NUM> is composed of Bisphenol A Novolac epoxy dissolved in an organic solvent (usually gamma-butyrolactone GBL or cyclopentanone), and up to <NUM>% by weight of mixed Triarylsulfonium/hexafluoroantimonate salt.

In some, but not necessarily all examples, the materials chosen may have thermal diffusivities no less than <NUM>-<NUM> m<NUM>/s, therefore excluding materials such as SU-<NUM>, nichrome and silicon dioxide and preferring materials such as polysilicon or metals. Polysilicon has the additional advantage of reduced fatigue compared to metals, to increase durability.

If electrical current is to be passed through one layer of the bimorph to act as a heater, then nonmetal-metal such as polysilicon-metal represents a better pairing than metal-metal combinations which may require electrical isolation between the layers.

<FIG> shows that a portion 32a of the first layer <NUM> may extend beyond the second layer <NUM>, the extender <NUM> comprising the portion 32a of the first layer <NUM>. The extender <NUM> is a continuation of the first layer <NUM> to reduce fabrication requirements. Alternatively, the extender <NUM> may be separately attached to the microactuator <NUM>, and/or as shown in <FIG> a thermally insulating element <NUM> such as silicon dioxide may be added between the microactuator <NUM> and the extender <NUM>. The extender <NUM> may comprise the same or different material as the first layer <NUM>. In some implementations, the extender <NUM> may comprise silicon oxide or silicon nitride.

In some, but not necessarily all examples, the first layer <NUM> and/or the second layer <NUM> is configured as a resistive heater. Configuring a layer as a resistive heater implies that electrical current flows through one or both of the layers, causing resistive heating dependent on the electrical resistivity of the material of the layer. The applied stimulus for thermal actuation may comprise an electrical current applied to at least the second layer <NUM>. Therefore, the bimorph material of the second layer <NUM> may be electrically conductive such as metal. Alternatively, the stimulus to the bimorph may be supplied indirectly via a separate material and/or layer.

<FIG> shows an example apparatus <NUM> wherein the component <NUM> is an optical component <NUM> such as a reflector. An example of a reflector is an optical mirror ('mirror' herein). The mirror may be a MEM mirror. The mirror may be flat or curved. However, aspects of <FIG> may be applicable for use with other optical components such as beam shaping optics, or non-optical components such as capacitor plates.

One or more of the plurality of microactuators 10a-10d of <FIG> have the characteristics described in relation to <FIG> including void-filled extenders 12a-12d, and are optionally implemented as described in relation to <FIG>.

In <FIG> a plurality of microactuators 10a-10d are arranged around the component <NUM> and oriented to enable deflection of the component <NUM> about a plurality of axes <NUM>, <NUM>. In some examples, deflection of the component <NUM> may comprise rotation in the form of tilting and/or tipping the component <NUM>. The axes <NUM>, <NUM> may be orthogonal to each other. Alternatively, the component <NUM> may be deflectable in one axis <NUM> or <NUM> only.

The apparatus <NUM> may be configured to convert deflection of one or more microactuators <NUM> into rotation of the component <NUM> about one or more axes <NUM>, <NUM>. For rotation about two axes <NUM>, <NUM>, at least a first pair 10a, 10c of the plurality of microactuators 10a-10d is configured to enable deflection of the component <NUM> about a first rotational axis <NUM>, and at least a second pair 10b, 10d of the plurality of microactuators 10a-10d is configured to enable deflection of the component <NUM> about a second rotational axis <NUM>. The first rotational axis <NUM> may be orthogonal to the second rotational axis <NUM>, and both axes <NUM>, <NUM> may be substantially coplanar with the mirror if the component <NUM> is a mirror.

In <FIG>, four microactuators 10a-10d are shown such that the pairs of microactuators 10a-10d do not comprise the same microactuators. The four microactuators 10a-10d may support the component <NUM> at four respective locations on the component <NUM>, wherein the four locations are angularly separated by <NUM> degrees relative to each other around the centre of the component <NUM>. Alternatively, at least three microactuators <NUM> may support the component <NUM> at three respective locations on the component <NUM>, wherein the three locations are angularly separated by <NUM> degrees relative to each other around the centre of the component and provide the same number of degrees of freedom as four support locations. In further examples, more than four microactuators <NUM> may be provided.

In the above examples it is assumed that the support locations are evenly angularly separated around the perimeter of the component <NUM>, however the support locations may be unevenly angularly separated in other examples.

Although <FIG> shows the microactuators <NUM> extending in different directions from each other, it is possible that at least some of the microactuators <NUM> could extend in substantially the same direction as other microactuators <NUM>.

A microactuator <NUM> may be curved up towards the mirror in its neutral equilibrium (non-actuated) state when no heat is applied, as shown in <FIG>. Heat may cause the microactuator <NUM> to deflect in a straightening direction, reducing its curvature. Alternatively, actuation may be configured to increase curvature based on the arrangement of the layers <NUM>, <NUM>.

As an alternative to <FIG>, the microactuator <NUM> may form another shape in its neutral non-actuated state, such as flat or curved downwards. Further, the actuation direction may be either upwards or downwards.

The plurality of microactuators 10a-10d of <FIG> may be the same as each other, or one or more aspects affecting responsiveness and/or deflection may differ. For example, the microactuators 10a-10d may be differentiated to provide a slow axis and a fast axis, depending on the use case. A slower axis can advantageously reduce power consumption. Additionally or alternatively, one axis may provide a different range of motion than the other.

In <FIG>, all the microactuators 10a-10d are below the component <NUM>. Alternatively, the microactuator beams supporting the component <NUM> may be located to either side the component <NUM> or above the component <NUM>.

<FIG> shows in more clarity how a resistive heater may be implemented. The second layer <NUM> comprises a first electrical terminal <NUM> such as a first conductive pad, and a second electrical terminal <NUM> such as a second conductive pad. The microactuator <NUM> provides an electrical length between the first electrical terminal <NUM> and the second electrical terminal <NUM> to resistively heat the bimorph. The first conductive pad and the second conductive pad may provide the fixed end <NUM> of the cantilever. The first conductive pad <NUM> and/or the second conductive pad <NUM> may be a continuation of the second layer <NUM> or a separate material. First electrical terminals 54a-54d and second electrical terminals 56a-56d may be provided for each corresponding microactuator 10a-10d. A single microactuator <NUM> implies a single pair of electrical terminals <NUM>, <NUM>.

An advantage of conductive pads, as shown in <FIG>, is easier electrical connection of the apparatus to other electronic circuitry, due to the large pad surface area. Techniques such as probing and wire bonding can be used.

The second layer <NUM> comprises a first leg 30a extending away from the first electrical terminal <NUM>, a direction change 30b changing the direction of the second layer <NUM> towards the second electrical terminal <NUM>, and a second leg 30c extending towards the second electrical terminal <NUM>. The direction change 30b may comprise a curve as shown, or a sharp turn. The first leg 30a, the direction change 30b, and the second leg 30c define the electrical length of the second layer <NUM>.

In <FIG>, but not necessarily all examples, the first leg 30a and the second leg 30c are parallel. The direction change 30b may be <NUM> degrees. More than one direction change 30b could be provided, if the microactuator <NUM> is wide. However, fewer direction changes reduce the chance of unintentional torsional deflections. In a further alternative example, no direction change 30b or second leg 30c is provided, and a flexible return wire may be used to close an electrical circuit.

<FIG> also shows that an electrically isolating slot <NUM> may be provided between the first leg 30a and the second leg 30c, to electrically isolate the first leg 30a and the second leg 30c from each other. The slot <NUM> may be through the second layer <NUM>, or through both the first layer <NUM> and the second layer <NUM> for additional isolation. In <FIG>, the slot <NUM> is elongated in a direction parallel to the first leg 30a and the second leg 30c. The direction change 30b of the second layer <NUM> extends widthwise from one side of the slot <NUM> to the other side of the slot <NUM>. The number of slots may depend on the number of direction changes and legs.

<FIG> also demonstrates that overall resistive heating may be increased by introducing one or more discontinuities <NUM> along the electrical length of the second layer <NUM>, if the material of the second layer <NUM> has low electrical resistivity, such as gold or copper. High electrical resistance is desirable so that a much lower applied voltage can achieve a same level of power dissipation. As shown in <FIG>, a plurality of discontinuities 31a-. 31n may be provided, such as ten discontinuities 31a-31j.

The illustrated discontinuities <NUM> extend widthwise across the whole width of the first leg 30a and/or the second leg 30c and/or the second layer <NUM>, presenting a break in the electrical length of the second layer <NUM>. A discontinuity <NUM> may be thin, presenting an electrical gap of only a few micrometres in the electrical length of the second layer <NUM>. Electrical current is forced to flow through the discontinuity <NUM> via different material at the discontinuities. The material at the discontinuities has a relatively-high-resistivity compared to the material of the second layer <NUM>. In some, but not necessarily all examples, the material at the discontinuities may be the material of the first layer <NUM>, which has higher electrical resistivity than the second layer <NUM>, therefore increasing overall resistance. In this example, it would be understood that portions of the first layer <NUM> and portions of the second layer <NUM> are configured for resistive heating, wherein the first layer <NUM> at the discontinuities <NUM> provides the dominant source of resistive heating due to greater resistivity of the first layer <NUM>.

A discontinuity <NUM> may be provided by removing material of the second layer <NUM>, or by adding strips of different material with lower electrical conductivity at the expense of greater manufacturing time.

A discontinuity <NUM> is also significantly less complex to manufacture than varying the thickness of the second layer <NUM> to achieve a similar effect on electrical resistance.

In a study example, a <NUM>-micrometre length microactuator shown in <FIG> used gold as the second layer <NUM>. The gold had an electrical length of <NUM> micrometres due to a single direction change 30b. Discontinuities <NUM> were arranged in a pattern to increase the resistance from <NUM> ohms to <NUM> ohms.

<FIG> shows that the number of discontinuities 31a-31e in the first leg 30a and the number of discontinuities 31f-31j in the second leg 30c may be equal. Alternatively, the number of discontinuities <NUM> may be the same as <FIG> or different. The illustrated discontinuities <NUM> are evenly spaced along the electrical length, for even bimorph deflection, however they could be unevenly spaced to calibrate bimorph deflection. For similar reasons, the sizes of the discontinuities <NUM> may be the same or different.

In <FIG>, each extender 12a-12d supports the component <NUM> via a corresponding coupling member 16a-16d. <FIG> shows that a coupling member <NUM> coupling the component <NUM> to the extender <NUM> may comprise a low-mass spring. The cross-sectional area of the coupling member <NUM> may be no more than <NUM>% of the cross-sectional area of the extender <NUM>, and is significantly less than <NUM>% in <FIG> resulting in elastic spring-behaviour. In <FIG>, but not necessarily all examples, the coupling member <NUM> is a serpentine spring following a meandering path to the component <NUM>, with a plurality of direction changes. The serpentine path increases the elasticity of the coupling. The use of springs reduces rubbing or friction, resulting in behaviour more like an elastic hinge.

<FIG> is a graph of the results of a study example, testing the time response of the apparatus <NUM> of <FIG> for achieving a required deflection when a heating pulse is applied. The y-axis is normalized microactuator deflection from a base state and the x-axis is time.

A first line 60b in <FIG> plots the time response of a reference apparatus 60a comprising a full-length microactuator with no extender <NUM>. A second line 62b in <FIG> plots the time response of an improved apparatus 62a matching that of <FIG>. The improved apparatus 62a comprising the shorter microactuator <NUM> with the void-filled extender <NUM>. In the reference apparatus 60a, L1=<NUM> micrometres. In the improved apparatus 62a, L1=L2=<NUM> micrometres. The extender design of <FIG> was used, so that in the tested improved apparatus 62a, the void fraction was <NUM>%. The framework <NUM> made up <NUM>% of the volume of the extender <NUM>. The electrical power in each test was set to the value to achieve the required deflection. <FIG> shows that the response time is nearly halved in the improved apparatus 62a, demonstrating the advantages of the use of a shorter microactuator <NUM> with a void-filled extender <NUM> for applications that require fast response times.

A non-limiting example of an application that benefits from fast microactuator response times is optical coherence tomography. Optical coherence tomography is an imaging technique that uses low-coherence light to capture micrometre-resolution images (2D or 3D) from within optical scattering samples such as biological tissue. Optical coherence tomography can be used for medical imaging and nondestructive testing. Optical coherence tomography generally uses low-coherence interferometry, and usually the light is in the near-infrared spectrum.

Optical coherence tomography systems may be used for non-invasive health monitoring. Optical coherence tomography systems generally scan a laser at discrete points in a shaped (e.g. rectangular) array on the skin surface that is being scanned. A depth scan is performed at each array point by sweeping the wavelength. The scanned volume could be up to ten millimetres cubed or more, depending on factors such as required resolution and scanning speed. Back-scattered light is detected during each array point scan and provides structural and/or chemical composition information. It is desirable to perform this scan quickly, so that information is acquired as rapidly as possible, which aids in the usefulness and applicability of the approach. A related factor is that if a scan takes too long, a patient may move, and the scan is no longer accurate. Some fast MEMS-based techniques require high electrical voltage to maintain high scan rates. High required voltages is impeding the development of portable optical coherence tomography systems with handheld scanners. Some MEMS-based techniques are too slow when using lower electrical voltages. Aspects of the present apparatus <NUM> advantageously enables a scanning technique that is fast and requires low electrical voltage, to facilitate the development of portable (or nonportable) optical coherence tomography systems. The apparatus <NUM> could even be made wearable.

Therefore, <FIG> illustrates an example of the apparatus <NUM>, wherein the apparatus <NUM> comprises an optical coherence tomography system <NUM> and an optical arrangement <NUM> comprising the optical component <NUM>. In some, but not necessarily all examples, the apparatus <NUM> may also comprise a controller <NUM> or a communication interface for communicating with a remote controller.

The optical coherence tomography system <NUM> comprises means for providing a beam of light to a sample <NUM> and means for receiving reflected light back from the sample <NUM>. The optical coherence tomography system <NUM> may also comprise means for combining the reflected light with reference light to enable the interference between the reflected light and the reference light to be analysed. For example, the optical coherence tomography system <NUM> may comprise an interferometer <NUM> and any other suitable means. The optical coherence tomography system <NUM> may comprise other elements that may enable light to be provided to a sample <NUM> and reflected light to be analysed to obtain an optical coherence tomography image. In some examples the integrated optoelectronic circuit may comprise one or more light sources <NUM> and one or more detectors <NUM>. The light source <NUM> may comprise a coherent light source such as a laser or any other suitable light source. The detector <NUM> may comprise one or more diodes such as a photodiodes. The electrical output of the detector <NUM> comprises information about the light reflected from the sample <NUM>. This can be processed to generate a three dimensional image of the sample <NUM>. The controller <NUM> may comprise: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the controller <NUM> at least to control the one or more microactuators <NUM>.

The optical component <NUM> may be a mirror. The optical component <NUM> is positioned so that light from the light source <NUM> of the optical coherence tomography system <NUM> is incident on the optical component <NUM>. The one or more microactuators <NUM> may be configured to move (e.g. rotate) the optical component <NUM> in at least one direction relative to the optical coherence tomography system <NUM>. The microactuators <NUM> may be operably coupled to the controller <NUM>. The microactuators <NUM> and the optical component <NUM> are configured to enable the light to be scanned in at least one direction to enable a multi-dimensional optical coherence tomography image to be obtained. The optical component <NUM> may be deflected to enable scanning of different array points.

The optical arrangement <NUM> and/or the optical coherence tomography system <NUM> may also comprise conventional optical elements (not shown) such as lenses or beam splitters/combiners to shape and focus light, and direct light between the functional components of the apparatus <NUM>.

For example, the component <NUM> could be an optical component for other applications that require fast movement, such as light detection and ranging (LIDAR). Alternatively, the component <NUM> could be other than an optical component, such as a capacitor plate. Features of the apparatus such as the extender may be applied to a microactuator beam configured to be actuated by another means than thermal actuation, such as magnetic actuation or electro-static actuation. This can provide advantages such as reducing the overall material mass required to span a particular distance, as the extender is lighter per unit length than many types of microactuator beam.

The term 'a' or 'the' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use 'a' or 'the' with an exclusive meaning then it will be made clear in the context. In some circumstances the use of 'at least one' or 'one or more' may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer and exclusive meaning.

The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

Claim 1:
An apparatus (<NUM>) comprising:
a thermally-actuated microactuator (<NUM>) configured to deflect a component (<NUM>) in dependence on an applied stimulus; and
an extender (<NUM>) configured to increase deflection of the component by the microactuator, wherein the extender comprises one or more voids (<NUM>),
wherein the microactuator comprises a bimorph, wherein the bimorph comprises a first layer (<NUM>) and a second layer (<NUM>), and wherein the first layer and the second layer have different coefficients of thermal expansion, wherein the first layer and/or the second layer is configured as a resistive heater, and wherein the second layer comprises one or more discontinuities (<NUM>) along its electrical length, for increased resistive heating at the one or more discontinuities than resistive heating of the second layer.