Technical Field of the Invention
The present invention relates in general to ring laser gyroscope designs, and in particular to the use of Micro Electro-Mechanical System (MEMS) technology in ring laser gyroscope designs.
Description of Related Art
Ring laser gyroscopes (RLGs) are instruments that measure the angular rotation rate of a certain platform. An RLG typically includes a laser system designed and fabricated to work in a ring configuration. The most familiar form of an RLG is built using a helium-neon (HN) ring laser with a diameter in the range of 30 cm.
The operating principle of an RLG is based on the beating between two counter propagating beams of light in the ring laser cavity. At stationary state, the two beams travel the same distance around the cavity, and thus have the same operating wavelength (optical frequency). When the system is rotated with a certain specific angular rotation rate, one beam experiences a larger distance around the cavity than the other due to the Sagnac effect, and as a result, the two beams are generated at two different wavelengths. The optical path difference between the two beams is directly proportional to the rotation rate of the cavity, and similarly, the optical frequency difference. Such a difference can be detected as a beating frequency between the two waves propagating in the ring laser in the clockwise (CW) and counter clockwise (CCW) directions.
To reduce the cost and size of RLGs, semiconductor lasers have recently been suggested to be used. However, as the scale factor of the RLG is directly proportional to the area enclosed by the rotating beams, the miniaturization of the RLG by using integrated semiconductor ring laser technology may greatly affect its performance. Therefore, semiconductor lasers have been proposed to be used with an optical fiber ring to increase the area of the device, and consequently improve its scale factor and sensitivity.
One of the main problems in RLG systems is coupling and lock-in between the two propagating beams at low rotation rates. Due to the nature of the optical cavity, a scattering mechanism takes place at the reflector interfaces. Such scattering causes energy to be coupled from the CW beam to the CCW beam and vice-versa. This coupling can cause the two beams to be pulled to the same frequency in a phenomenon called mode locking, which seriously limits the sensitivity of RLG devices.
Various approaches to eliminate or reduce lock-in in RLG have been suggested in recent years. One approach uses a mechanical dithering mechanism as a DC bias for the rotation. However, this approach necessarily increases the size, weight and cost of the RGL.
Another approach introduces anisotropy in the ring using magnetic mirrors or phase modulation. Such an approach is based on using two or more reflectors, vibrating linearly in a certain synchronized mechanism. Yet another approach moves the reflectors in a tilting fashion. To eliminate the mechanical noise from the mechanical movement of the reflectors, a solution based on quantum well mirrors has also been proposed. However, all of these approaches utilize a volume optic configuration, which necessarily increases the size and cost of the RLG. In addition, due to the increased size, optical alignment and synchronization of the different mirror configurations may be difficult.
Therefore, there is a need for an RLG with a reduced size and cost that also reduces lock-in.