Optical filter comprising: - a liquid crystal cell comprising two electrodes (13, 14), facing each other, each of the two electrodes (13, 14) being covered by an alignment layer, and separated by a cell gap (d) and a cholesteric liquid crystal mixture inserted between the two electrodes (13, 14); - the liquid crystal cell being configured to apply a voltage between the two electrodes (13, 14); - the cholesteric liquid crystal mixture comprises a chiral dopant and a dual frequency liquid crystal host material, wherein the chiral dopant has a helical twisting power higher than or equal to 100 μm -1, the dual frequency liquid crystal host material having a refractive index birefringence lower than 0.2 in the visible range, the dual frequency liquid crystal host material having a cross-over frequency (f c) lower than 10 kilohertz, - the liquid crystal cell having a reference Bragg reflection mode with a planar structure and a reference Bragg reflection wavelength in the spectral range between 300 nm and 900 nm when the applied voltage is null and when the applied voltage is modulated at a frequency higher than a high frequency limit (f H), and wherein the cholesteric liquid crystal mixture has a high frequency range where the liquid crystal mixture has a dielectric anisotropy that is independent from frequency and negative, the high frequency range extending above the high frequency limit (f H), the high frequency limit (f H) being lower than 100 kHz, - the liquid crystal cell has a first Bragg reflection mode with an unwound planar structure and a first Bragg reflection wavelength, when the applied voltage is higher than a threshold voltage, the threshold voltage being lower than 100 V, and the applied voltage is modulated at another frequency comprised in an intermediate frequency range which is above the cross-over frequency (f c) and below the high frequency limit (f H), where the liquid crystal mixture has a dielectric anisotropy that varies with frequency and is negative, and the first Bragg reflection wavelength being different from the reference Bragg reflection wavelength. - a liquid crystal cell comprising two electrodes (13, 14), facing each other, each of the two electrodes (13, 14) being covered by an alignment layer, and separated by a cell gap (d) and a cholesteric liquid crystal mixture inserted between the two electrodes (13, 14); - the liquid crystal cell being configured to apply a voltage between the two electrodes (13, 14); - the cholesteric liquid crystal mixture comprises a chiral dopant and a dual frequency liquid crystal host material, wherein the chiral dopant has a helical twisting power higher than or equal to 100 μm -1, the dual frequency liquid crystal host material having a refractive index birefringence lower than 0.2 in the visible range, the dual frequency liquid crystal host material having a cross-over frequency (f c) lower than 10 kilohertz, - the liquid crystal cell having a reference Bragg reflection mode with a planar structure and a reference Bragg reflection wavelength in the spectral range between 300 nm and 900 nm when the applied voltage is null and when the applied voltage is modulated at a frequency higher than a high frequency limit (f H), and wherein the cholesteric liquid crystal mixture has a high frequency range where the liquid crystal mixture has a dielectric anisotropy that is independent from frequency and negative, the high frequency range extending above the high frequency limit (f H), the high frequency limit (f H) being lower than 100 kHz, - the liquid crystal cell has a first Bragg reflection mode with an unwound planar structure and a first Bragg reflection wavelength, when the applied voltage is higher than a threshold voltage, the threshold voltage being lower than 100 V, and the applied voltage is modulated at another frequency comprised in an intermediate frequency range which is above the cross-over frequency (f c) and below the high frequency limit (f H), where the liquid crystal mixture has a dielectric anisotropy that varies with frequency and is negative, and the first Bragg reflection wavelength being different from the reference Bragg reflection wavelength.