The core of the open-loop fiber optic gyroscope (FOG) is the fiber optic sensing assembly. It comprises fiber optic sensing coil, phase modulator, two fiber optic couplers, fiber crystal polarizer, light-emitting SLD module and fiber ‘dead-end’. All components are made on a SINGLE fiber length using JOINTLESS manufacturing technology.
Fiber optic sensing coil is 100m (depends on the model) of specialty PM-fiber wound on a bobbin to form a quadrupole pattern. Constant low tension is applied to the fiber during winding to achieve uniform and symmetrical mechanical structure of the coil. This specialty very thin fiber (40µ diameter) was specially developed for production of fiber optic gyroscope.
Phase modulator is 0.5m fiber length wound on the side of a piezoelectric ring (PZT). The PZT is glued on a holder with a soft silicone. The holder works as an isolator to weaken mechanical coupling of PZT to the sensor main frame.
Fiber optic coupler is two fibers fused together and shaped as biconical tapers. The amount of optical cross-coupling depends on fusion length. To achieve predetermined coupling (3 dB), the corresponding signal is being measured continuously during coupler fabrication. The coupler is mounted on a quartz substrate to ensure mechanical and thermal stability.
Fiber-crystal polarizer is a fiber biconical taper cladded by birefringent crystal. The taper is fiber fragment where its diameter is made 5µ by fusion-tapering technique. The crystal is sodium nitrate grown on a mica substrate. The polarizer is mounted on a quartz substrate and covered with silicone gel to ensure mechanical and thermal stability.
Light emitting SLD module is an extremely bright and low-coherence light diode effectively coupled to the input fiber of the fiber optic assembly.
“Dead end” is a specially processed fiber end to eliminate back reflection.
An electronics board is required to drive the SLD and PZT for signal conditioning and for precise demodulation of the optical signal.
