The spatial variance of polarization state is an important indicator in diverse areas, such as optical biopsy and material characterization. Typically, the issue of polarization measurement has been addressed by dividing the signal up in space or in time. There are many techniques for division-of-space polarimeters that divide the input beam into multiple optical paths and project them simultaneously to different polarization analyzers in a spatial domain or a spectral domain. However, these methods need multiple optical polarization elements and an array of photodetectors (PDs). For the division-of-time polarimeters, the time sequential techniques are prone to loose measurement due to very limited sampling points and mechanical instabilities in the sampling. In general, these two kinds of polarization analyzers require multi-step measurements step by step or require multiple PDs, each targeting one of its vector components.
Several researchers in Wuhan National Lab for Optoelectronics, including Prof. Xinliang Zhang, Prof. Jianji Dong, and Dr. Hailong Zhou, etc. have put forward a tomographic polarization analyzer by polarization-mode-frequency mapping. The unknown light is decomposed into two orthogonal circularly polarized components, and converted to two orbital angular momentum (OAM) modes by a q-plate. Subsequently, we employ a time-varying spatial modulation to map the OAM modes to two beating signals with different frequencies. Finally, we complete tomographic reconstruction of the polarization state from the time-varying intensity collected by a PD. The time-varying spatial modulation can be achieved by a programmable device or a spinning object. Compared to the traditional methods, our scheme can directly measure the Jones matrix of light with high precision. Due to the high volume time sampling, our polarization analyzer can resist the systematic and random error in the tomographic reconstruction and offer a high-accuracy measurement.
This work has been on-line published in Optics Express on 26 June 2017 . Relative work was partially supported by National Natural Science Foundation of China (61622502 and 61475052). Full text can be viewed by
 Zhou H., Liu M., Dong J., et al. Tomographic polarization analyzer by polarization-mode-frequency mapping. Optics Express, 2017, 25 (13): 14023-14032.
Fig. 1. (a) Schematic diagram of the polarization analyzer. (b) Phase masks of the modulation function dependent on time.