A wavelength tunable laser includes: a heating layer, a dielectric layer, reflectors, a transport layer, a support layer, and a substrate layer. The heating layer is located above the transport layer; the transport layer is located above the support layer, and the transport layer includes an upper cladding layer, a waveguide layer, and a lower cladding layer from top to bottom; the reflector is located in the transport layer; the support layer has a protection structure, where the protection structure forms a hollow structure together with the transport layer and the substrate layer, and the hollow structure has a support structure; and the substrate layer is located below the support layer. The heating layer, the reflector, and a part of the transport layer form a suspended structure to prevent heat dissipation. Thus thermal tuning efficiency can be improved, and power consumption can be lowered.

A frequency comb generator including a semiconductor, wherein the semiconductor outputs a frequency comb in response to frequency mixing of an optical field and at terahertz field in the semiconductor using a high order sideband (HSG) mechanism. The frequency comb spans a bandwidth sufficient for self-referencing and may be used in optical clock applications, for example.

A wavelength-tunable laser includes a substrate, a waveguide layer over the substrate, and a cladding over the waveguide layer. The wavelength-tunable laser further includes an active layer in a part of the waveguide layer, and a tunable wavelength filter in at least one end region of the waveguide layer in a direction along which light is to be guided.