A phase plate was fabricated on a quartz crystal using ion beam etching technique with a predesigned angular phase mask, which can modulate the phase of light illuminating the phase plate by 0 and π rad. Analyzed the field distribution of the diffracted light by angular diffraction theory, which shows the resulting beam is a superposition of two Laguerre-Gaussian(LG) beams with opposite topological charges. Illuminating the phase plate using the expanded beam with diameter 4 mm generates the superposition of two LG beams with the same radian index p=0 and opposite angular index l=20 and l=-20 By increasing the aperture of the illuminating beam, LG beam with higher p index can be acquired, while the l index remains opposite.