Engineered optical activity of fiber modes for spectral measurements

It has been theoretically known that orbital-angular momentum (OAM) modes of optical fibers can be combined to exhibit so-called “optical activity.” Optical activity is an inherent property of chiral materials (such as sugar water), where linearly polarised light input into the material rotates as it propagates down the material. By measuring this rotation, one can learn the properties of the material (such as the amount of optical activity and hence the material’s concentration). This optical activity effect will also cause the polarization to rotate as light’s wavelength is changed. This effect is typically tiny in most chiral materials. However, since we are able to engineer this property in an optical fiber, where the mode can travel very long distances, this effect gets amplified. As a result, one can deduce the wavelength (color) of light by simply measuring the amount of rotation of the polarization of light at the output of the fiber. This leads to a new way to make very high resolution spectrometers that can decipher the wavelength of light down to sub-picometer accuracy. Misty Farrell mfpenn@bu.edu 617-358-3795