High Performance InP-Based Polarization Beam Splitter With Reverse Bias and Injection Current

Abstract

High performance InP-based polarization beam splitters (PBSs) with a symmetrical Mach–Zehnder interferometer (MZI) are theoretically and experimentally demonstrated. The p-i-n waveguide is exploited to employ the phase shifters in the two arms of the MZI. Injection current and reverse bias inducing electro-optic (EO) effects in each of the MZI arms are analysed in detail when the waveguides are aligned along both the [011] and $[ {01\bar{1}} ]$ directions. Results indicate that the birefringence from reverse bias help to realize the PBS combining with the polarization-independent carrier-induced refractive index change from the injection current. Theoretical prediction shows that the polarization extinction ratio (PER) is over 35 dB at 1550 nm for the PBSs with the waveguides aligned along both directions. Furthermore, the PBS with the waveguides aligned along the [011] direction can be adjusted more easily to work at the best operating point and get the higher birefringence which requires lower reverse bias exhibiting better performance across the C-band compared with the $[ {01\bar{1}} ]$ direction. The fabricated PBSs exhibit a PER over 19 dB (14 dB) in the wavelength range from 1525 to 1570 nm with one arm injected of 2.88 mA (0.2 mA) current and the other arm reversed biased at 5.63 V (7.89 V) when the waveguides aligned along the [011] ( $[ {01\bar{1}} ]$ ) direction. The PER of both PBSs is expected to be 20 dB across the C-band with the help of a birefringence contribution arising from inserting waveguide arms of different widths.