Integrated polarization-independent optical isolators and circulators on an InP membrane on silicon platform

In photonic integrated circuits (PICs), optical isolators and circulators are essential to prevent lasers from backreflections and to reroute the light flow. In this paper, an integrated polarization-independent device that can be operated as an optical isolator or an optical circulator, based on an InP membrane on silicon platform, is demonstrated. A ceriumdoped yttrium iron garnet die is adhesively bonded on a Mach-Zehnder interferometer, in combination with four polarization converters. The device shows maximum optical isolations of 27.0 dB for transverse-electric (TE)-mode input and 34.0 dB for transverse-magnetic TM-mode input. The device also works as a four-port optical circulator. Optical isolations of at least 18.6 dB and 16.4 dB are measured between each circulator port pair for TE- and TM-mode input, respectively. This work could remove the optical interfaces between laser and isolator for robust production. It also provides a step forward toward a multifunctional and high-density PIC