Dual-use on-chip polarizer based on straight silicon nitride platform

Silicon nitride (Si3N4) based optical platforms have been widely used in integrated photonics due to their low loss and simple processing characteristics. Polarizers working as polarization filters for purifying optical polarization and minimizing polarization crosstalk are important in integrated photonic devices. Here, we introduce a dual-use all-Si3N4 TE-pass integrated polarizer with a wide working bandwidth and a high polarization extinction ratio (PER) in a simple straight ridge waveguide structure. The polarization modulation properties of this on-chip Si3N4 polarizer were investigated analytically and experimentally. The fabricated polarizer can achieve an ultrahigh PER >40 dB and a broad operation bandwidth of ∼80 nm. The measured insertion loss is <1 dB in the wavelength range of 1540–1640 nm. Moreover, by covering it with a layer of high refractive index material, it becomes a waveguide for transmitting two orthogonally polarized modes with a loss of <1 dB. That is, this straight Si3N4 ridge waveguide structure can function as an on-chip polarizer as well as an optical waveguide.