(research in collaboration with Prof. Jean-Claude Diels, University of New Mexico, Albuquerque, NM)
Lately, in the
field of optical gyroscopes, we often hear about slow and fast light
gyros. This started with a theoretical paper in 2000
; a recent paper offers an overview and extensive
references of theoretical research that has been done in this field
. The conclusion of the latter paper is that dispersion
manipulation of passive gyros
(e.g. Fiber Optics Gyros, FOG) does not lead to any improvement in
performance, as it was originally suggested. In contrast,
for the active laser gyro (Ring
Laser Gyro, RLG), a steep anomalous dispersion results in an increase
in sensitivity. This enhancement in sensitivity will indeed be at the
expense of noise and dead band, if one considers only cw laser gyros,
as it was done in . However, it was demonstrated that in
mode-locked operation, a ring laser gyro has no dead band if the pulse
crossing points are placed in a region that is free of backscattering
(air or ideally vacuum) . More of that below.
The above figure shows three ways to visualize, what is happening in a
rotating RLG. For simplification, a circular ring is assumed. A
clockwise (CW) and a counterclockwise (CCW) wave are generated. (c -
speed of light, R - radius, P - perimeter, A - area, λ=c/ν -
wavelength at rest, Ω - angular velocity of the RLG, Δν -
observed beat frequency)
RLG: Using a mode-locked ring laser gyro has the following
 U. Leonhardt and P. Piwnicki "Ultrahigh sensitivity of slow–light gyroscope" Phys. Rev. A 62 (2000) 055801, also available at arXiv.org.
 S. Schwartz, F. Goldfarb, and F. Bretenaker "Some considerations on slow and fast-light gyros" Opt. Eng. 53 (2014) 102706-1.
 M. Lai, J.-C. Diels, and M. Dennis "Nonreciprocal measurements in fs ring lasers" Opt. Lett. 17 (1992) 1535.
 James Hendrie, Matthias Lenzner, Hanieh Afkhamiardakani, Jean Claude Diels, and Ladan Arissian "Impact of resonant dispersion on the sensitivity of intracavity phase interferometry and laser gyros" Opt. Express 24 (2016) 30402.