Another key SLED application 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 are a light source, a single mode polarization-maintaining 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. 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-based gyroscopes rely on the large bandwidth of the source to reduce both the scattering along the fiber and reflections at the facets of the internal optical components, which could decrease the sensitivity at very low rotation rates.

The key requirements for fiber optic gyroscopes (FOGs) 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.

At EXALOS, we have successfully overcome this drawback by developing SLEDs that are less sensitive to wavelength shifts induced by temperature or aging. Novel materials and material structures have made it possible to improve the wavelength stability of our devices by a factor of four compared with conventional devices. Further work is in progress with the target of achieving wavelength stabilities down to the 10 parts per million range. SLEDs with this performance will help to reduce the size and cost of FOGs substantially.

EXALOS has a portfolio of products qualified for Fiber Optic Gyroscope (FOG) applications that require extended operating temperature ranges, increased shock/vibrations levels and verified lifetimes due to their use in Space environments. Our SLED products have been qualified to BELLCORE GR-468-CORE.