Ultrafast laser direct writing of in-line polarizers based on nano-gratings

In-line polarizers play an important role in the emerging quantum computing, integrated photonics, and ultrafast science. However, to our knowledge, no one has actually used in-line polarizers based on nano-gratings (NGs) in those research fields. Here, we present a novel approach to write a fiber polarizer that utilizes nano-gratings directly within the fiber core for the first time to our knowledge. An optical fiber polarizer measuring 1 mm in length, 2.5 dB in polarization-dependent loss (PDL), and 2 dB in insertion loss was developed and initially utilized for the artificially saturable absorber nonlinear polarization evolution (NPE) experiment. In the experiment, several nonlinear transmission curves are measured. In-line polarizers based on nano-gratings are expected to be used in future integrated optical chips because of their small size and easy direct writing.