Brillouin ring laser

A method of providing stimulated Brillouin oscillation in an optical fiber, comprising:

• forming a loop in said fiber;
• optically closing said loop with a fiber optic directional coupler;
• and
• pumping said loop with light at a resonant frequency of said loop with sufficient intensity to cause Brillouin scattering.

A Brillouin ring laser rotation sensor, comprising:

• an optical fiber having first and second end portions with a loop portion therebetween;
• fiber optic coupling means for optically closing said loop portion, the length of said loop portion and the coupling constant of said coupling means selected to form a resonant cavity;
• means for detecting an optical signal;
• means, including a pump light source, for introducing first and second input pump lightwaves for propagation in opposite directions about said loop, said pump lightwaves at the resonant frequency of said loop, and having sufficient intensity to cause stimulated Brillouin scattering in said loop to provide first and second Brillouin waves which counter-propagate relative to said first and second pump lightwaves, respectively, and which resonate in said loop at a frequency less than said pump lightwaves, the frequency at which each of said Brillouin waves resonates changing in response to rotation of said loop portion to provide a frequency difference therebetween, indicative of the rotation rate of said loop portion;
• said fiber optic coupling means including means for coupling a fraction of said first and second Brillouin waves from said loop and for combining said Brillouin waves to form a Brillouin output wave, said Brillouin output wave having a beat frequency equal to the difference in frequency between said Brillouin waves;
• and
• means for guiding said Brillouin output wave to said optical signal detecting means, said detecting means detecting said beat frequency.

A method of sensing rotation, utilizing an optical fiber having first and second end portions with a loop portion therebetween, said method comprising:

• optically closing said loop portion utilizing a fiber optic directional coupler;
• selecting the length of said loop portion and the coupling constant of said coupler to form a resonant cavity;
• introducing first and second input pump lightwaves for propagation in opposite directions about said loop, said pump lightwaves at a resonant frequency of said loop, and having sufficient intensity to cause stimulated Brillouin scattering in said loop to provide first and second Brillouin waves which counter-propagate relative to said first and second pump lightwaves, respectively, and which resonate in said loop;
• rotating said loop to provide a frequency difference between said Brillouin waves;
• coupling a fraction of said first and second Brillouin waves from said loop;
• combining said Brillouin waves to form a Brillouin output wave, said Brillouin output wave having a beat frequency equal to the difference in frequency between said Brillouin waves;
• and
• detecting said beat frequency.

A Brillouin ring laser, comprising:

• a length of optical fiber having first and second end portions and forming a loop portion therebetween;
• a source for introducing light into the first end portion of said fiber for propagation through said loop to said second end portion;
• and
• means for optically closing said loop to cause light to circulate in said loop, said loop closing means having sufficiently low losses that said circulating light causes stimulated Brillouin oscillation in said loop when said light in said first fiber portion has an intensity of less than 10 mW.