An optical demultiplexer (200, 300), comprising: an electro-optic modulator configured to change, when the electro-optic modulator is in a first state, a polarization of light pulses having a first polarization and passing through the electro-optic modulator from the first polarization to a second polarization; a first mirror and a second mirror, wherein the electro-optic modulator is arranged in an optical trajectory between the first mirror and the second mirror for light pulses travelling in the optical trajectory between the first mirror and the second mirror to pass through the electro-optic modulator, wherein the first mirror and the second mirror are arranged in the optical demultiplexer (200, 300) such that the light pulses travelling in the optical trajectory between the first mirror and the second mirror are displaced perpendicular to a propagation direction of the light pulses between the first mirror and the second mirror during each round of travelling forth and back between the first mirror and the second mirror; and a first polarizing beam-splitter arranged in the optical trajectory between the first mirror and the electro-optic modulator, wherein the first polarizing beam-splitter is configured to: transmit light pulses having the first polarization, and reflect light pulses having the second polarization to remove the light pulses having the second polarization from the optical trajectory between the first mirror and the second mirror, wherein the first polarizing beam-splitter is configured to reflect the light pulses which are displaced with respect to each other perpendicular to the propagation direction onto different, respective output trajectories; wherein the optical demultiplexer (200, 300) further comprises a third mirror arranged at an end of the optical trajectory at normal incidence with respect to the optical trajectory at an end portion of the optical trajectory for reflecting light pulses to travel in the opposite direction between the first mirror and the second mirror. an electro-optic modulator configured to change, when the electro-optic modulator is in a first state, a polarization of light pulses having a first polarization and passing through the electro-optic modulator from the first polarization to a second polarization; a first mirror and a second mirror, wherein the electro-optic modulator is arranged in an optical trajectory between the first mirror and the second mirror for light pulses travelling in the optical trajectory between the first mirror and the second mirror to pass through the electro-optic modulator, wherein the first mirror and the second mirror are arranged in the optical demultiplexer (200, 300) such that the light pulses travelling in the optical trajectory between the first mirror and the second mirror are displaced perpendicular to a propagation direction of the light pulses between the first mirror and the second mirror during each round of travelling forth and back between the first mirror and the second mirror; and a first polarizing beam-splitter arranged in the optical trajectory between the first mirror and the electro-optic modulator, wherein the first polarizing beam-splitter is configured to: transmit light pulses having the first polarization, and reflect light pulses having the second polarization to remove the light pulses having the second polarization from the optical trajectory between the first mirror and the second mirror, wherein the first polarizing beam-splitter is configured to reflect the light pulses which are displaced with respect to each other perpendicular to the propagation direction onto different, respective output trajectories; transmit light pulses having the first polarization, and reflect light pulses having the second polarization to remove the light pulses having the second polarization from the optical trajectory between the first mirror and the second mirror, wherein the first polarizing beam-splitter is configured to reflect the light pulses which are displaced with respect to each other perpendicular to the propagation direction onto different, respective output trajectories; wherein the optical demultiplexer (200, 300) further comprises a third mirror arranged at an end of the optical trajectory at normal incidence with respect to the optical trajectory at an end portion of the optical trajectory for reflecting light pulses to travel in the opposite direction between the first mirror and the second mirror.