Refractive index engineering in monolithic crystalline silicon with nanosecond laser pulses

Since the advent of waveguide writing in glasses with femtosecond lasers more than two decades ago [1], this three-dimensional (3D) refractive index engineering technique has increasingly evolved offering performances that are suitable for many applications (telecommunications, design of optical components, etc.). However, this method has no equivalent in silicon so far, representing a technological lock for further applications (e.g. ultrafast microelectronics, quantum computing, sensors). The origin of this limitation has been explained only recently by significant plasma effects which are inevitable for ultrashort laser pulses focused in the bulk of silicon [2]. To overcome these, studies have recently shed light on the possibility of modifying the crystalline phase of silicon with nanosecond pulses [3]. Thus, it is worth investigating the potential of this regime for refractive index engineering in this material.