Fiber Optic Gyroscopes
Another key application for SLED is in navigation systems, primarily those in avionics and aerospace that use fiber-optic gyroscopes (FOGs) to make precise rotation measurements ,. FOGs measure the Sagnac phase shift of optical radiation propagating along a fiber-optic coil when it rotates around the winding axis. When a FOG is mounted within a navigation system, it tracks changes in orientation. The basic components of a FOG, as shown in Fig. 11, are a light source, a single- mode polarization-maintaining (PM) fiber coil, a coupler and a detector. Light from the source is injected into the fiber in counter-propagating directions using the optical coupler. When the fiber coil is at rest, the two light waves interfere constructively at the detector and a maximum signal is produced at the demodulator. When the coil rotates, the two light waves take different optical paths that depend on the rotation rate. The phase difference between the two waves varies the intensity at the detector and provides information on the rotation rate. SLED
Fig. 11 Generic setup of a fiber optic gyroscope (FOG).
The key requirements for fiber optic gyroscopes are typically low cost, reduced form factor, low power consumption, long-term stability and high reliability. In the past, wavelength stability over time was a major drawback of semiconductor based broadband light sources like SLEDs compared with fiber-based light sources such as erbium-doped fiber-amplifiers.
EXALOS has a portfolio of products qualified for FOG applications that require extended operating temperature ranges, increased shock/vibrations levels and verified lifetimes due to their use in space environments. Examples of such products include uncooled free-space or fiber-coupled 820-nm SLEDs (EXS8310 or EXS8305, ) as well as cooled or uncooled transceiver modules with an integrated beam splitter and a receiver photodiode . SLED-Transceivers are particularly interesting when realized with a polarization-maintaining (PM) fiber output as they can be directly coupled to the fiber loop of the FOG, avoiding the complexity of realizing a PM fiber coupler. EXALOS’ SLED products have been qualified according to BELLCORE GR-468-CORE.