Abstract
Contrary to expectations, a measurement of the random walk in the ring laser
gyro (RLG) as a function of laser power P shows that it is not consistent with the
P<sup>1/2</sup> rule. In the experiment, the random walk and laser power are tested and
recorded at different discharge currents. The random walk decreases with increasing
power, but with a rate much less than the theoretical value according to current
literature. In order to solve the inconsistency above, we derive the expression for
the random walk in RLGs based on laser theory. Theoretical analysis shows that,
accumulating effects of lower energy level due to its limited lifetime lead to
additional quantum noise from spontaneous emission. Results show that the random
walk in the RLGs consists of two components. The former decreases with increasing
power according to the P<sup>1/2</sup> rule, whereas the other is power-independent. Thus
far, the power-independent quantum limit has not appeared in the literature;
therefore, the expressions for RLGs should be modified to describe the low-loss RLGs
exactly, where the power-independent term takes a relatively larger proportion. The
findings are significant to the further reduction of quantum limit in low-loss RLGs.
© 2012 Chinese Optics Letters
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