Dual mode fiber-optic interferometer with circular-core fibers and birefringent modal filters and an interfering method thereof

A fiber-optic interferometer, comprising:

• a first dual-mode optical fiber for receiving a light input and exciting a first spatial mode and a second spatial mode;
• a first modal processor connected to said first dual-mode optical fiber for selecting said first spatial mode and said second spatial mode;
• a second dual-mode optical fiber connected to said first modal processor for propagating said first spatial mode and said second spatial mode, producing a phase shift (Δφ) between said first spatial mode and said second spatial mode in response to an external perturbation effect and producing a first light output interference pattern;
• and
• an analyzer having a polarization axis and connected to said second dual-mode optical fiber for adjusting said first light output interference pattern to produce a second light output interference pattern, so that said second light output interference pattern obtains an optimal contrast through an adjustment of said polarization axis.

A fiber-optic interferometer, comprising:

• a first dual-mode optical fiber for receiving a light input and exciting a first spatial mode and a second spatial mode, wherein said first and said second spatial modes are a fundamental and a second-order modes of an o-core dual-mode optical fiber respectively;
• a first modal processor connected to said first dual-mode optical fiber for selecting said first spatial mode and said second spatial mode;
• and
• a second dual-mode optical fiber connected to said first modal processor for propagating said first spatial mode and said second spatial mode, producing a phase shift (Δφ) between said first spatial mode and said second spatial mode in response to an external perturbation effect and producing a first light output interference pattern having a contrast.

An optical fiber interfering method for a fiber-optic interferometer, comprising steps of:

• providing a light;
• exciting a first spatial mode and a second spatial mode in response to said light;
• selecting and propagating said first and said second spatial modes through an environment having an external perturbation;
• producing a phase shift of said first and said second spatial modes in response to said external perturbation and producing a first light output interference pattern;
• adjusting said first light output interference pattern for producing a second light output interference pattern having an optimal contrast;
• and
• detecting said optimal contrast of said second light output interference pattern for obtaining said phase shift of said first and said second spatial modes.