Fizoptika fiber optic gyroscopes (FOGs) are fabricated using a specialized in-line technology. The basis of the technology is an exclusive 40-micron PM fiber with a number of distinctive optical and mechanical characteristics. The fiber maintains its optical guiding ability under high elastic or even plastic deformations. This makes possible the fabrication of various fiber optic components directly on a fiber length by shaping it at high temperatures when quartz glass becomes soft. The spliceless fabrication of the ring interferometer components (couplers, polarizer, SLD module) makes them naturally connected without optical losses.
For fiber shaping, a fusion-tapering technology and equipment were developed. During the couplers fabrication process the two fiber leads are held together by two moveable holders. A stabilized high-frequency arc discharge is applied to the fibers so that they melt together. Simultaneously, the fiber holders are moved apart so that a fused tapered region is formed. To ensure a low-loss coupler (polarizer), it is essential that the holders move apart in a straight line with no sideways motion or vibration. The speed of separation and heating length control the taper shape which in turn has a significant influence on the resulting loss. It is necessary to use an optimal arc length and arc current not to disturb the taper.
The quality of the single-mode fiber is extremely important. Its core and cladding must be highly circular and concentric with one another. Inferior quality fibers can result in high losses in the coupler.
It is also possible to monitor the coupler’s power splitting ratio during fabrication and to make a coupler with any required splitting ratio at a given wavelength.
The fabrication of the polarizer begins with a similar tapering process but with bigger elongation to achieve the fiber waist diameter of 5 microns. Next, the fiber waist is placed into the melted substance from which the birefringent crystal is grown around the fiber.
The soldering process is used to manufacture an SLD-module. The SLD chip and fiber lead are soldered to separate copper blocks. After precise mutual alignment the blocks are soldered to each other.
Assembling procedures are performed under the visual control. The conformation of the manufactured gyro sensor to its specification is verified at the functional test. The gyroscope scale factor is certified. An optional performance test or screening may be conducted for specific applications.
Both major technologies (fusion-tapering and soldering) produce temperature and mechanically stable components that bring the gyroscope reliable and stable performances in a wide range of environments.
The optical components are mounted on the gyro main frame and covered with protecting silicone gel. The electronics is mounted on the gyroscope cover (for some models – on the frame).
The accuracy of the FOG and its resistance to the environments are determined by the sensor’s design and components specifications. All purchased components and materials are subjected to the incoming quality test. While a fiber optic component is fabricated, its performance is automatically controlled and recorded. Provided the performance criteria are met, the next manufacturing step begins, so that a gyroscope with a nonconforming component does not come out of the production.