Brillouin sensing using polarization pulling

A polarization pulling sensor configured to separate amplified probe light from background probe light, the polarization pulling sensor comprising:

• a first modulator configured to receive an optical beam and generate pump pulses;
• a first amplifier configured to:
• receive the pump pulses from the first modulator, and
• amplify the pump pulses;
• a second modulator configured to receive the optical beam and to produce a plurality of sidebands based on the optical beam, wherein the sidebands are shifted by approximately a Brillouin frequency;
• a filter configured to select a lower sideband in the plurality of sidebands, thereby producing a probe signal;
• a second amplifier configured to amplify the lower sideband, thereby generating an amplified lower sideband;
• a first polarization controller configured to receive the amplified pump pulses from the first amplifier;
• a second polarization controller configured to receive the amplified lower sideband from the second amplifier;
• a microscopy apparatus coupled to the first polarization controller and to the second polarization controller, wherein the microscopy apparatus is configured to receive the amplified pump pulses generated by the first amplifier and the amplified lower sideband generated by the second amplifier;
• a beam splitter aligned to the second polarization controller, wherein the beam splitter is configured to receive the lower sideband from the microscopy apparatus, wherein the second polarization controller is adjusted to minimize light reflected at the beam splitter, thereby discarding most of the probe light in the absence of a stimulated Brillouin scattering (SBS) interaction;
• a third modulator configured to receive:
• an oscillator signal, and
• modulate the probe signal using the oscillator signal, thereby providing a modulated probe signal;
• and
• a polarization pulling detector configured to:
• receive the amplified lower sideband and the modulated probe signal,
• detect an interference signal, and
• record an amplitude of the interference signal as a function of a probe frequency, thereby providing a measurement of a Brillouin gain spectrum, wherein a center of the Brillouin gain spectrum provides a measurement of a Brillouin frequency of the microscopy apparatus.

A polarization pulling sensor configured to separate amplified probe light from background probe light, the polarization pulling sensor comprising:

• a first modulator configured to receive an optical beam and generate pump pulses;
• a first amplifier configured to:
• receive the pump pulses from the first modulator, and
• amplify the pump pulses;
• a first polarization controller configured to receive the amplified pump pulses from the first amplifier;
• a second modulator configured to receive the optical beam and to produce a plurality of sidebands based on the optical beam, wherein the sidebands are shifted by approximately a Brillouin frequency;
• a filter configured to select a lower sideband in the plurality of sidebands, thereby producing a probe signal;
• a second amplifier configured to amplify the lower sideband, thereby generating an amplified lower sideband;
• a second polarization controller configured to receive the amplified lower sideband from the second amplifier;
• a fiber under test (FUT) coupled to the first polarization controller and to the second polarization controller, wherein the FUT is configured to receive the amplified pump pulses from the first polarization controller and the amplified lower sideband from the second polarization controller;
• a beam splitter aligned to the second polarization controller, wherein the beam splitter is configured to receive the amplified lower sideband from the FUT, wherein the first polarization controller is adjusted to maximize probe light reflected at the beam splitter to maximize a polarization pulling effect, and wherein the second polarization controller is adjusted to minimize light reflected at the beam splitter, thereby discarding most of the probe light in the absence of a stimulated Brillouin scattering (SBS) interaction;
• a third modulator configured to receive:
• an oscillator signal, and
• modulate the probe signal using the oscillator signal, thereby providing a modulated probe signal;
• and
• a polarization pulling detector configured to:
• receive the amplified lower sideband and the modulated probe signal,
• detect an interference signal, and
• record an amplitude of the interference signal as a function of a probe frequency, thereby providing a measurement of a Brillouin gain spectrum, wherein a center of the Brillouin gain spectrum provides a measurement of a Brillouin frequency of the FUT.