A projector, comprising: a laser module, for generating at least one laser beam; a lens module, comprising: a plurality of lenses (222_1, 222_2), wherein each of the lenses (222_1, 222_2) is arranged to receive one of the at least one laser beam to generate a collimated laser beam; and a plurality of diffractive optical elements (224_1, 224_2), wherein the diffractive optical elements (224_1, 224_2) correspond to the lenses (222_1, 222_2), respectively, and each of the diffractive optical elements (224_1, 224_2) is arranged to receive the collimated laser beam from the corresponding lens (222_1, 222_2) to generate an image, wherein at least two of the lenses (222_1, 222_2) have different focal lengths that correspond to different working distances of the projector, wherein the laser module comprises a plurality of laser diodes (312, 314, 322, 324), the laser diodes (312, 314, 322, 324) are arranged to generate a plurality laser beams to the lenses (222_1, 222_2), respectively, wherein the projector is designed so that the laser diodes can be sequentially turned on to generate the laser beams to the lenses (222_1, 222_2) and the diffractive optical elements (224_1, 224_2) to generate the images, respectively, and at least a portion of the images are overlapped. a laser module, for generating at least one laser beam; a lens module, comprising: a plurality of lenses (222_1, 222_2), wherein each of the lenses (222_1, 222_2) is arranged to receive one of the at least one laser beam to generate a collimated laser beam; and a plurality of diffractive optical elements (224_1, 224_2), wherein the diffractive optical elements (224_1, 224_2) correspond to the lenses (222_1, 222_2), respectively, and each of the diffractive optical elements (224_1, 224_2) is arranged to receive the collimated laser beam from the corresponding lens (222_1, 222_2) to generate an image, wherein at least two of the lenses (222_1, 222_2) have different focal lengths that correspond to different working distances of the projector, a plurality of lenses (222_1, 222_2), wherein each of the lenses (222_1, 222_2) is arranged to receive one of the at least one laser beam to generate a collimated laser beam; and a plurality of diffractive optical elements (224_1, 224_2), wherein the diffractive optical elements (224_1, 224_2) correspond to the lenses (222_1, 222_2), respectively, and each of the diffractive optical elements (224_1, 224_2) is arranged to receive the collimated laser beam from the corresponding lens (222_1, 222_2) to generate an image, wherein at least two of the lenses (222_1, 222_2) have different focal lengths that correspond to different working distances of the projector, wherein the laser module comprises a plurality of laser diodes (312, 314, 322, 324), the laser diodes (312, 314, 322, 324) are arranged to generate a plurality laser beams to the lenses (222_1, 222_2), respectively, wherein the projector is designed so that the laser diodes can be sequentially turned on to generate the laser beams to the lenses (222_1, 222_2) and the diffractive optical elements (224_1, 224_2) to generate the images, respectively, and at least a portion of the images are overlapped.