Highly efficient broadband silicon nitride polarization beam splitter incorporating serially cascaded asymmetric directional couplers.
The implementation of a polarization beam splitter (PBS) on a silicon nitride platform remains challenging owing to its relatively low index. We therefore propose a silicon nitride PBS that exploits serially cascaded asymmetric directional couplers (ADCs) leading to a high polarization extinction ratio (PER) over a broad bandwidth. The ADC spatially routes incident light through polarization selective mode coupling under a small footprint of 112 um. The proposed PBS does not require an active phase control. It is thus effectively realized via a single step lithography process. The measured transverse electric and transverse magnetic PERs were determined to be above 23 dB and 10 dB over an 80 nm bandwidth, respectively, spanning l=1520 1600nm. The proposed device is thus anticipated to play a key role in providing polarization diversity in photonic integrated circuits.
Optics letters