An optical reflective multiplexer chip (3, 42), comprising: a combiner (30, 420), a second external port (36, 421) constituting the output port of the combiner (30, 420), N third external ports (35, 422), N microring resonant cavities (34, 423), N polarization splitter-rotators (33, 424), N first waveguides (31, 425) being branch waveguides, and N second waveguides (32, 426) being branch waveguides, wherein N is a positive integer and is greater or equal to two, the N polarization splitter-rotators (33, 424) are in one-to-one correspondence to the N first branch waveguides (31, 425), the N polarization splitter-rotators (33, 424) are in one-to-one correspondence to the N second branch waveguides (32, 426) the N polarization splitter-rotators (33, 424) are in one-to-one correspondence to the N third external port (35, 422) and the N polarization splitter-rotators (33, 424) are in one-to-one correspondence to the N microring resonant cavities (34, 423); the combiner (30, 420) is connected to the N first branch waveguides (31, 425), the N second branch waveguides (32, 426), and the second external port (36, 421); each of the N polarization splitter-rotators (33, 424) is connected to a corresponding first branch waveguide (31, 425), a corresponding second branch waveguide (32, 426), and a corresponding third external port (35, 422); each of the N polarization splitter-rotators (33, 424) is configured to: receive polarized light from the corresponding third external port (35, 422), perform polarized splitting on the polarized light, and output the split polarized light to the corresponding first branch waveguide (31, 425) and the corresponding second branch waveguide (32, 426); wherein the N microring resonant cavities (34, 423) are coupled to a corresponding first branch waveguide (31, 425) and to a corresponding second waveguide (32, 426); each of the N microring resonant cavities (34, 423) is configured to: perform wavelength selection on the light transmitted to the corresponding first branch waveguide (31, 425) and the corresponding second branch waveguide (32, 426), output, through the second external port (36, 421) by using the combiner (30, 420); a part of the light passing the wavelength selection of the microring resonant cavity, and transmit the other part of the light back to the corresponding polarization splitter-rotator (33, 424) as reflective polarized light; and each of the N polarization splitter-rotators (33, 424) is configured to: perform polarized coupling on the reflective polarized light transmitted back by the corresponding microring resonant cavity, and output the coupled light from the corresponding third external port (35, 422). a combiner (30, 420), a second external port (36, 421) constituting the output port of the combiner (30, 420), N third external ports (35, 422), N microring resonant cavities (34, 423), N polarization splitter-rotators (33, 424), N first waveguides (31, 425) being branch waveguides, and N second waveguides (32, 426) being branch waveguides, wherein N is a positive integer and is greater or equal to two, the N polarization splitter-rotators (33, 424) are in one-to-one correspondence to the N first branch waveguides (31, 425), the N polarization splitter-rotators (33, 424) are in one-to-one correspondence to the N second branch waveguides (32, 426) the N polarization splitter-rotators (33, 424) are in one-to-one correspondence to the N third external port (35, 422) and the N polarization splitter-rotators (33, 424) are in one-to-one correspondence to the N microring resonant cavities (34, 423); the combiner (30, 420) is connected to the N first branch waveguides (31, 425), the N second branch waveguides (32, 426), and the second external port (36, 421); each of the N polarization splitter-rotators (33, 424) is connected to a corresponding first branch waveguide (31, 425), a corresponding second branch waveguide (32, 426), and a corresponding third external port (35, 422); each of the N polarization splitter-rotators (33, 424) is configured to: receive polarized light from the corresponding third external port (35, 422), perform polarized splitting on the polarized light, and output the split polarized light to the corresponding first branch waveguide (31, 425) and the corresponding second branch waveguide (32, 426); wherein the N microring resonant cavities (34, 423) are coupled to a corresponding first branch waveguide (31, 425) and to a corresponding second waveguide (32, 426); each of the N microring resonant cavities (34, 423) is configured to: perform wavelength selection on the light transmitted to the corresponding first branch waveguide (31, 425) and the corresponding second branch waveguide (32, 426), output, through the second external port (36, 421) by using the combiner (30, 420); a part of the light passing the wavelength selection of the microring resonant cavity, and transmit the other part of the light back to the corresponding polarization splitter-rotator (33, 424) as reflective polarized light; and each of the N polarization splitter-rotators (33, 424) is configured to: perform polarized coupling on the reflective polarized light transmitted back by the corresponding microring resonant cavity, and output the coupled light from the corresponding third external port (35, 422).