A wavelength tunable laser configured for thermal tuning by changing the temperature of a DBR reflector, comprising: a heating layer, a transport layer, a DBR reflector a support layer, and a substrate layer, wherein: the heating layer is located above the transport layer; the transport layer is located above the support layer, and comprises an upper cladding layer, a waveguide layer, and a lower cladding layer from top to bottom; the reflector is located in a part of the transport layer; the support layer is located between the transport layer and the substrate layer, and has a protection structure and a support structure which is a portion of the support layer that is arranged underneath the part of the transport layer that comprises the reflector, wherein the protection structure forms a hollow structure together with the transport layer and the substrate layer, and the support structure is arranged in the hollow structure; and the substrate layer is located below the support layer, wherein: there are gaps between the part, comprising the reflector, of the transport layer and materials on two sides of the transport layer, to form a suspended structure; within a length range of the reflector in a first direction, the gaps completely isolate the suspended structure in a horizontal direction from the materials on the two sides of the transport layer, so that the suspended structure is not connected to the materials on the two sides of the transport layer; and the first direction is a transmission direction of light in the waveguide layer, wherein, within the length range of the reflector, the suspended structure has a width varying along the first direction, characterised in that a support structure of a large size is disposed below a wider part of the suspended structure, and a support structure of a small size is disposed below a narrower part of the suspended structure. the heating layer is located above the transport layer; the transport layer is located above the support layer, and comprises an upper cladding layer, a waveguide layer, and a lower cladding layer from top to bottom; the reflector is located in a part of the transport layer; the support layer is located between the transport layer and the substrate layer, and has a protection structure and a support structure which is a portion of the support layer that is arranged underneath the part of the transport layer that comprises the reflector, wherein the protection structure forms a hollow structure together with the transport layer and the substrate layer, and the support structure is arranged in the hollow structure; and the substrate layer is located below the support layer, wherein: there are gaps between the part, comprising the reflector, of the transport layer and materials on two sides of the transport layer, to form a suspended structure; within a length range of the reflector in a first direction, the gaps completely isolate the suspended structure in a horizontal direction from the materials on the two sides of the transport layer, so that the suspended structure is not connected to the materials on the two sides of the transport layer; and the first direction is a transmission direction of light in the waveguide layer, wherein, within the length range of the reflector, the suspended structure has a width varying along the first direction, characterised in that a support structure of a large size is disposed below a wider part of the suspended structure, and a support structure of a small size is disposed below a narrower part of the suspended structure.