A silicon-based photonic integrated circuit (PIC) chip combines silicon-based photonics and optical communications technologies by uniformly preparing, at a silicon layer on an insulating substrate using silicon on insulator (SOI), communications devices such as a laser, a modulator, and a detector that are prepared on different material substrates, and therefore, is an important technology for further promoting global informatization. The silicon-based PIC chip may input or output an optical signal in a coupling manner, so as to perform optical signal interaction with an external device. In a commonly used coupling manner, a grating coupler inputs an external optical signal into the silicon-based PIC chip, or outputs an optical signal inside the silicon-based PIC chip outside the silicon-based PIC chip in a diffraction manner using a top surface or a bottom surface of the silicon-based PIC chip as an incident surface.
A bandwidth of the grating coupler represents a spectrum range of an optical signal that can be coupled using the grating coupler. A higher bandwidth indicates a larger spectrum range of an optical signal that can be coupled and a greater amount of optical signal information that can be transmitted. However, a bandwidth of a conventional grating coupler in the prior art is always relatively low. For example, reference may be made to FIG. 1 for a top view of a conventional grating coupler in the prior art, and reference may be made to FIG. 2 for a normalized transmission spectrum of the conventional grating coupler in the prior art. The normalized transmission spectrum represents a correspondence between transmission energy of the grating coupler for an optical signal and a wavelength of the optical signal, that is, represents a correspondence between coupling efficiency of the grating coupler for the optical signal and the wavelength of the optical signal. A wavelength that has a smallest energy loss in the normalized transmission spectrum is a wavelength of the grating coupler that has highest coupling efficiency, and may be referred to as a coupling center wavelength of the grating coupler. In addition, when a wavelength of an optical signal more approximates to the coupling center wavelength, the grating coupler has higher coupling efficiency. It may be learned from FIG. 2 that, a coupling center wavelength of the conventional grating coupler shown in FIG. 1 is 1550 nanometer (nm), a wavelength range corresponding to 3 decibels (dB) energy is about 30 nm, and a spectrum range of an optical signal corresponding to the 3 dB energy, that is, a bandwidth of 3 dB is about 3.8 terahertz (THz). Therefore, a requirement for wide-spectrum optical communication is hardly met.