Abstract
A high-performance broadband polarization-independent directional coupler is designed by using asymmetric-waveguides configuration on a silicon-on-insulator platform. Through the design of cascaded directional couplers, the coupling characteristics of the light with the orthogonally polarized transverse electric (TE) and transverse magnetic (TM) can be manipulated, so that the coupling strength could be equivalent between TE and TM polarizations within an ultra-broadband. Couplers with 50% splitting ratio are designed and simulated for operating in the wavelength range from 1450 nm to 1650 nm for both polarizations. Within the 100 nm wavelength range from 1500 nm to 1600 nm, the deviations of splitting ratio for TE polarization and TM polarization are $\pm$ 3.3% and $\pm$ 6.2%, respectively. And within the 200 nm wavelength range from 1450 nm to 1650 nm, the deviations for TE polarization and TM polarization are $\pm$ 9.0% and $\pm$ 7.8%, respectively. The footprint of this polarization-independent directional coupler is only 21 $\mu$ m × 1.6 $\mu$ m.
Highlights
Silicon-on-insulator (SOI) is considered to be an attractive platform for developing densely integrated optical devices using mature CMOS technology, which makes it possible to implement monolithic optoelectronic integrated circuits [1]
The incident light of dualpolarization is separated by using the polarization beam splitters (PBSs) [9]–[15] assisted with a polarization rotator (PR) [16]–[18] so that the directional coupler (DC) could work at a single polarization state
In order to make the output as a strip waveguide and facilitate the integration of the device, we flipped Fig. 1(a) as Fig. 5(a)
Summary
Silicon-on-insulator (SOI) is considered to be an attractive platform for developing densely integrated optical devices using mature CMOS technology, which makes it possible to implement monolithic optoelectronic integrated circuits [1]. The incident light of dualpolarization is separated by using the polarization beam splitters (PBSs) [9]–[15] assisted with a polarization rotator (PR) [16]–[18] so that the DCs could work at a single polarization state Such approaches will increase the system complexity, the device size and additional losses. In order to reduce the complexity and size, designing a polarization-independent DC is attracting more and more attention Another solution is based on the polarization-independent DCs with special waveguide structure, such as slot waveguides [19] and subwavelength-grating structures [20], [21]. The footprint of the device is only 21 μm × 1.6 μm
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