Fiber Optic Gyroscope: Open-loop Configuration

A fiber optic gyroscope (FOG) is an angular rate sensor which detects changes in orientation using the Sagnac effect. Fizoptika Malta FOG is a highly precision yet most miniature optical gyroscope. It comprises fiber optic “minimum configuration” sensing assembly and analog processing electronics. The FOG is a robust, reliable, maintenance-free electro-optical device offering all advantages of the optical sensing technology.

Fiber optic gyroscope spliceless technology diagram

The FOG is manufactured using the spliceless technology when the entire fiber optic assembly is fabricated from a single fiber length. Such technology provides ZERO optical excess loss due to the absence of joints between the components. The fiber is of a specialty (40µ) polarization maintaining type to suppress the effects of polarization state changes that occur in the fiber. By fine optical tuning the assembly acquires immunity to electromagnetic interference eliminating (for most applications) the need for heavy shielding. A single miniature analog PCB performs all necessary functions to process the optical signal and provide stability and precision conforming to the performance of the optical assembly.

The gyro main frame is made of aluminum or hard plastic to withstand a widest temperature range and highest levels of vibration and shocks.

Principle of Operation

The open-loop ‘minimum configuration’ architecture is employed.

The broadband light-emitting diode (SLD module) couples the light into an input/output fiber coupler (II).

Then the light passes through a polarizer and a spatial filter which ensure the reciprocity of the counter-propagating light beams through the fiber coil.

Another coupler (I) splits the two light beams in the fiber optic coil where they pass through a harmonic modulator (PZT).

After passing through the fiber coil, the two light beams recombine and pass back through the polarizer and are directed onto the photodetector. Synchronous demodulation behind the detector converts the rotationally-induced first harmonic signal into a rate proportional voltage.


Some general properties of the open-loop gyroscope (deduced from fundamental physical principles):

No dead zone or hysteresis

Instant response

Bias immunity to acceleration (gravity)