Frequency converter implementing an optical analogue of the cosmological redshift

According to general relativity, the frequency of electromagnetic radiation is altered by the expansion of the universe. This effect–commonly referred to as the cosmological redshift–is of utmost importance for observations in cosmology. Here we show that this redshift can be reproduced on a much smaller scale using an optical analogue inside a dielectric metamaterial with time-dependent material parameters. To this aim, we apply the framework of transformation optics to the Robertson-Walker metric. We demonstrate theoretically how perfect redshifting or blueshifting of an electromagnetic wave can be achieved without the creation of sidebands with a device of finite length.