Heterojunction polarization beam splitter based on self-collimation in photonic crystal

Polarization beam splitter (PBS) is an important device in optical system, in which the optical signal can be separated into two mutually orthogonal polarized light and transmit along different paths. It is difficult for the traditional PBS to meet the needs of the modern optical integrated systems because of its low transmission efficiency and high dependence on the incident angle. Therefore, it is necessary to design more efficient and compact PBSs. In recent years, photonic crystals have attracted more attention due to their ability to manipulate photon motion. In this paper, a photonic crystal PBS with a non-orthogonal heterojunction structure is proposed, which is based on the self-collimation effect and bandgap properties of photonic crystal. The proposed PBS structure is composed of two square lattice photonic crystals with the same lattice constant and different air hole radii in silicon (Si), in which the beam can be self-collimated and propagate without diffraction, and the polarization separation of and transverse electric (TE) mode from transverse magnetic (TM) mode is realized at the interface. The self-collimation effect can be used to control the transmission of light in order to realize the general light guiding of the waveguide, and it can greatly reduce the difficulty in manufacturing process because of no additional defects introduced. The splitting properties, transmission properties and polarization extinction ratio of the PBS are numerically simulated and analyzed by using Rsoft software combined with the plane wave expansion method and the two finite-difference time-domain method. It is shown that a high efficiency and a large separating angle for TE and TM modes in a wide frequency range 0.275-0.285(a/ ) can be achieved. The transmission efficiency is above 88% for both TE and TM modes, and the extinction ratios are more than 26.57 dB for TE mode and 17.50 dB for TM mode, respectively. This structure can be applied to the transmission system of terahertz band: a=26 m, the size is 572 m546 m, and the separation of TE mode from TM mode can be achieved in a wavelength range of 91-95 m. A PBS for optical communication system can be also designed by using the same structure: n=3.48, a=426.25 nm, and the proposed PBS is only 9.38 m8.95 m in size, which can separate these two polarization beams in a wavelength range of 1511-1579 nm. What is more, the proposed PBS based on photonic crystal is simple and easy to integrate, which has important application value in optical communication technology.