Fizoptika’s Fiber Optic Gyroscope (FOG) is a precise yet most miniature fiber optic rotation sensor. 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.
The gyro main frame is made of aluminum alloy or hard plastic to withstand a wide temperature range and high levels of vibration and shocks. Plastic housing option gives the gyroscope the lowest weight in its size.
Fizoptika’s FOGs are produced using the spliceless technology when the entire fiber optic assembly is fabricated from a single fiber length. The technology provides the highest quality of the assembly with ZERO excess loss due to the absence of joints between 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 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 open-loop FOG architecture is illustrated by the above Figure. 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).
The modulator is offset from the center of the coil to impress a relative phase difference between the counter-propagating light beams. 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 may be deduced from fundamental physical principles.
Bias immunity to acceleration (gravity) and vibration
Acceleration does not create any rotation like signal in the optical sensing coil. Therefore FOG output is naturally free of g, g2 components inherent in all mechanical gyros including MEMS. There is no vibration rectification error.
No dead zone or hysteresis
In the open loop gyroscope the rotational signal is directly detected. This linear signal conversion does not create any dead zone or hysteresis inherent in other gyro types (MEMS, laser gyros, closed loop gyros).
The time delay in the sensing coil is <2µs (light transmission time). The practical limit (<0.1ms) is due to the mechanical delay in the gyro frame (main frequency typically exceeds 2kHz).
Cross axis error
Due to its optical nature the FOG is a perfect single axis sensor. Cross axis sensitivity error does not exist.
Major Parts and Components
Analog Electronics Design
The open-loop sensor requires electronics to control SLD current and PZT voltage for signal conditioning and for precise demodulation of the interferometric signal after its conversion from the optical power to the receiver voltage.
Production Technology & Quality Control
Detailed information about fiber optic gyro production technology and quality control can be found here.