PCT/SG2019/050519 WO 2020/081014 Detailed Description [0029] Embodiments of the present invention are described below by way of example only. These examples represent the best ways of putting the invention into practice that are currently known to the Applicant although they are not the only ways in which this could be achieved. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples. [0030] As described above, a tunable waveguide device (e.g. an OPA or VOA (variable optical attenuator)) may, for example, be fabricated using the thermo-optic effect. Such a tunable waveguide device operates by splitting an optical path 102 into multiple optical paths 104, 106, each of the multiple optical paths comprising a separate waveguide, introducing a variable phase change into one or more of the optical paths (using one or more tuning elements 112 that rely upon the thermo-optic effect) and subsequently recombining light from some or all of the multiple optical paths. Any [0017] FIG. 3F is a schematic diagram of a second example improved tuning element for use in a tunable waveguide device; [0018] FIG. 3G is a cross-section through the improved tuning element shown in FIG. 3F; [0019] FIG. 4A is a schematic diagram of a third example improved tuning element for use in a tunable waveguide device; [0020] FIGs. 4B, 4C and 4D show cross-sections through three different variants of the improved tuning element shown in FIG. 4A; [0021] FIG. 4E shows a further cross-section through an improved tuning element shown in FIG. 4A; [0022] FIG. 4F is a schematic diagram of a fourth example improved tuning element for use in a tunable waveguide device; [0023] FIG. 4G is a cross-section through the improved tuning element shown in FIG. 4F; [0024] FIG. 5 is a schematic diagram of an example tunable waveguide device comprising a plurality of improved tuning elements; and [0025] FIGs. 6A, 6B, 6C and 6D show four different example methods of manufacture of an improved tuning element for use in a tunable waveguide device; [0026] FIGs. 7A, 7B, 7C and 7D show four different example methods of manufacture of an improved tuning element for use in a tunable waveguide device; and [0027] FIGs. 8A, 8B, 8C and 8D show four different example methods of manufacture of an improved tuning element for use in a tunable waveguide device. [0028] Common reference numerals are used throughout the figures to indicate similar features. FIG. 3A;