Enhancing Sensitivity of Ring Laser Gyroscopes and Accelerometers using Slow-Light Augmented Unbalanced Mach-Zehnder Interferometry

Currently, there is a need for very accurate inertial measurement units, based on rotation sensing and accelerometry. For a ring laser, which can be used for measuring rotation and acceleration, the measurement sensitivity is proportional to the minimum measurable frequency shift (MMFS), which is given by the geometric mean of the spectral width of the ring laser and the measurement bandwidth, for conventional detection. Here, we propose to use a Slow-light Augmented Unbalanced Mach-Zehnder Interferometer (SLAUMZI) to reduce the MMFS substantially. In a SLAUMZI, a medium with a large group index (GI) is inserted in one arm of the MZI. GI as high as ten million can be produced using electro-magnetically induced transparency (EIT). The SLAUMZI amplifies the fringes, resulting from a frequency scan, by a factor of the GI, compared to a regular unbalanced MZI. The factor of reduction in the MMFS is is given approximately by the ratio of the slow-light group index, and the finesse of the ring laser cavity, if the SLAUMZI and the cavity have similar dimensions. In a recent paper, we have reported verification of this mechanism, producing close agreement between theory and experiment, and demonstration of a reduction in MMFS by a factor of as much as ~twenty thousand. Under this proposal, we will investigate the feasibility of using this approach to realize an ultra-sensitive ring laser gyroscope and accelerometer. A ring cavity, incorporating a spring-mounted mirror, will produce two counter-propagating Rb Raman lasers, with a frequency difference matching the free spectral range of the cavity, to eliminate the lock-in effect. The difference and sum of the frequency shifts of the two lasers will be proportional to rotation and acceleration, respectively. If this cavity has a finesse of ten thousand, comparable to that of the best ring laser gyroscope, a GI of ten million would improve the sensitivity of rotation sensing and accelerometry by a factor of a thousand.