Testing Lorentz invariance using an odd-parity asymmetric optical resonator

We present the first experimental test of Lorentz invariance using the frequency difference between counter-propagating modes in an asymmetric odd-parity optical resonator. This type of test is $\sim {10}^4$ more sensitive to odd-parity and isotropic (scalar) violations of Lorentz invariance than equivalent conventional even-parity experiments due to the asymmetry of the optical resonator. The disadvantages of odd-parity resonators have been negated by the use of counter-propagating modes, delivering a high level of immunity to environmental fluctuations. With a nonrotating experiment our result limits the isotropic Lorentz violating parameter ${\tilde{\kappa }}_{\mathrm{tr}}$ to $3.4\pm 6.2\times {10}^{-9}$, the best reported constraint from direct measurements. Using this technique the bounds on odd-parity and scalar violations of Lorentz invariance can be improved by many orders of magnitude.

Figure 1

Asymmetric ring resonator with UV fused silica prism at Brewster’s angle ${\theta }_B$, showing counter-propagating modes.

Figure 2

The optical setup, showing the use of two AOMs to eliminate the need for an optical beat note.

Figure 3

Difference in resonant frequency of counter-propagating modes. Processed time series data (top) and spectral density (bottom). The middle graph are the values obtained for ${\tilde{\kappa }}_{\mathrm{tr}}$ from the data set split up into $\sim 2$ day portions.

Figure 4

Comparison of ${\tilde{\kappa }}_{\mathrm{tr}}$ determined by other experiments.