An optical demodulator, comprising a first reflective mirror, a second reflective mirror, a third reflective mirror, and an optical splitter, wherein the first reflective mirror is located at one side of the optical splitter, and the second reflective mirror and the third reflective mirror are located at the other side of the optical splitter, wherein the optical splitter comprises two physically separate units: a first optical splitting unit and a second optical splitting unit; the first optical splitting unit is configured to split the input light for the first time, wherein the first path of light and the second path of light obtained through the splitting for the first time are emitted to the first reflective mirror and the second reflective mirror respectively; and the second optical splitting unit is configured to split for the second time the first path of light reflected back by the first reflective mirror, wherein the two paths of light obtained by splitting the first path of light are emitted to the first reflective mirror and the third reflective mirror respectively; split for the second time the second path of light reflected back by the second reflective mirror, wherein the two paths of light obtained through the splitting for the second time are emitted to the first reflective mirror and the third reflective mirror respectively; and split the two paths of light that are reflected back by the first reflective mirror and the third reflective mirror respectively and obtained by splitting the first path of light, and then make the split light to interfere with each other, so as to obtain and emit two paths of light with different phases, and split the two paths of light reflected back by the first reflective mirror and the third reflective mirror respectively and obtained by splitting the second path of light, and then make the split light to interfere with each other, so as to obtain and emit two paths of light with different phases; the first reflective mirror is configured to: reflect the first path of light to the second optical splitting unit after the splitting for the first time; reflect one of the two paths of light split from the first path of light to the second optical splitting unit after the splitting for the second time, so that the second optical splitting unit splits the two paths of light obtained by splitting the first path of light, and then makes the split light to interfere with each other, so as to obtain two paths of light with different phases; and reflect one of the two paths of light split from the second path of light to the second optical splitting unit, so that the second optical splitting unit splits the two paths of light obtained by splitting the second path of light, and then makes the split light to interfere with each other, so as to obtain two paths of light with different phases; the second reflective mirror is configured to reflect the second path of light to the second optical splitting unit after the splitting for the first time; and the third reflective mirror is configured to: reflect the other of the two paths of light split from the first path of light to the second optical splitting unit after the splitting for the second time, so that the second optical splitting unit splits the two paths of light obtained by splitting the first path of light, and then makes the split light to interfere with each other, so as to obtain two paths of light with different phases; and reflect the other of the two paths of light split from the second path of light to the second optical splitting unit, so that the second optical splitting unit splits the two paths of light obtained by splitting the second path of light, and then makes the split light to interfere with each other, so as to obtain two paths of light with different phases. reflect the first path of light to the second optical splitting unit after the splitting for the first time; reflect one of the two paths of light split from the first path of light to the second optical splitting unit after the splitting for the second time, so that the second optical splitting unit splits the two paths of light obtained by splitting the first path of light, and then makes the split light to interfere with each other, so as to obtain two paths of light with different phases; and reflect one of the two paths of light split from the second path of light to the second optical splitting unit, so that the second optical splitting unit splits the two paths of light obtained by splitting the second path of light, and then makes the split light to interfere with each other, so as to obtain two paths of light with different phases; reflect the other of the two paths of light split from the first path of light to the second optical splitting unit after the splitting for the second time, so that the second optical splitting unit splits the two paths of light obtained by splitting the first path of light, and then makes the split light to interfere with each other, so as to obtain two paths of light with different phases; and reflect the other of the two paths of light split from the second path of light to the second optical splitting unit, so that the second optical splitting unit splits the two paths of light obtained by splitting the second path of light, and then makes the split light to interfere with each other, so as to obtain two paths of light with different phases.