(1) splitting a laser beam output by an ultrafast pulse laser into two or more laser beams with equal power proportion via a splitting module, converging the two or more laser beams into a sample at an included angle θ less than 60° via a spatio-temporal synchronization module and a converging module, such that a first plasma grating is formed in the sample by interference of the two or more laser beams, the sample being fixed on an electronically controlled three-dimensional mobile platform;

(2) moving the sample in a longitudinal direction of a plane vertical to the first plasma grating to etch out a first prefabricated volume grating with an equivalent cross section to that of the first plasma grating;

(3) moving the sample laterally and keeping a distance from a focal point of the two or more laser beams to a front surface of the sample unchanged to form a second plasma grating at another position of the sample, an effective cross section of the first prefabricated volume grating partially overlapping with a cross section of the second plasma grating, then moving the sample in a longitudinal direction of a plane vertical to the second plasma grating to etch out a second prefabricated volume grating with an equivalent cross section to that of the second plasma grating; and

(4) repeating steps (2) and (3) n times to obtain a volume grating having a width W=n·w0, a length equal to a length L etched by each plasma grating in a cross section of the sample perpendicular to a propagation direction of the laser, and a depth equal to a length D of optical filaments of each plasma grating formed in the sample, wherein n represents a positive integer greater than 0, w0 represents an effective width of each plasma grating.