PCT/SG2019/050519 WO 2020/081014 tunable element further comprises one or more resistive heating pads formed proximate to the second waveguide section. The first and third waveguide sections are formed from a first material and the second waveguide section is formed from a second, different material and the second material is more thermo-optically sensitive than the first material. [0006] A first aspect provides a tunable element for an optical waveguide device, the tunable element comprising: a first waveguide section formed from a first material; a second waveguide section formed from a second material and arranged to receive light coupled from the first waveguide section; a third waveguide section formed from the first material and arranged to receive light coupled from the second waveguide section; and one or more resistive heating pads proximate to the second waveguide section, wherein the second material is more thermo-optically sensitive than the first material. [0007] A second aspect provides a tunable optical waveguide device comprising one or more tunable elements described herein. [0008] A third aspect provides an optical phased array comprising one or more tunable elements as described herein. [0009] A fourth aspect provides a method of fabricating a tunable element for an optical waveguide device, the method comprising: forming a first waveguide section and a third waveguide section from a first material; forming a second waveguide section from a second material; forming at least one layer of cladding material on the second waveguide section; and forming one or more resistive heating pads on top of a layer of cladding material and proximate to the second waveguide section, wherein the second material is more thermo-optically sensitive than the first material. [0010] The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention. [001 1] Embodiments of the invention will be described, by way of example, with reference to the following drawings, in which: [0012] FIGs. 1A and 1B show schematic diagrams of two example tunable waveguide devices; [0013] FIGs. 2A, 2B and 2C show schematic diagrams of a known tuning element for use in a tunable waveguide device; [0014] FIG. 3A is a schematic diagram of a first example improved tuning element for use in a tunable waveguide device; [0015] FIGs. 3B, 3C and 3D show cross-sections through three different variants of the improved tuning element shown in FIG. 3A; [0016] FIG. 3E shows a further cross-section through an improved tuning element shown in Brief Description of the Drawings