High Performance Polarization Beam Splitter Based on Cascaded Directional Couplers Assisted by Effectively Anisotropic Structures

Abstract

A high performance polarization beam splitter (PBS) based on cascaded directional couplers (DCs) assisted by effectively anisotropic structures is proposed. The sub-wavelength grating (SWG) structures between the two coupled waveguides act as anisotropic metamaterial cladding to block/enhance light coupling for transverse electric (TE)/magnetic (TM) polarization. Cascading the DCs designed at different central wavelengths can improve the extinction ratio (ER) within the desired bandwidth or broaden the working wavelength bandwidth for TM polarization. Three design examples show the excellent performance of PBS with ER of >35 dB, 20 dB or 14 dB and loss of <0.12 dB, 0.4 dB or 0.8 dB over a bandwidth (BW) of 60 nm, 250 nm or 400 nm, which is difficult to achieve in any PBS structure reported before. The BW ER>20dB of the PBS based on the cascaded DCs increases by ∼11 times when compared with a single DC.

Polarization splitting directional coupler using tilted subwavelength gratings

“…On the contrary, inverse/non-linear algorithm designs achieve extremely short devices at expense of a complex design process and a limited low-loss bandwidth. However, arguably the most widely used mechanism for polarization splitting in integrated photonic chips is directional coupling (DC-PBS) [16][17][18][19][20][21][22][23][24][25][26]. These splitters can be classified in two categories, symmetric and asymmetric.…”

Ultra-Broadband Polarization Beam Splitter Based on Cascaded Mach-Zehnder Interferometers Assisted by Effectively Anisotropic Structures

“…Finally, the two fundamental polarizations are separated and the bandwidth mostly depends on the bandwidth of the MZI splitting 50:50 for the TM polarization. For this cascaded structure, it is convenient to use transfer matrix to calculate [19]. For a single DC with straight coupling length Lc in Fig.…”

“…In our previous work, by taking advantage of polarization-dependent evanescent wave control via the SWG as effectively anisotropic structures in the cascaded DCs, we have designed theoretically a PBS with ER > 20 dB and IL < 0.4 dB over a bandwidth of 250 nm [19]. In this paper, by using the cascaded MZIs assisted by SWG structures and two filters at the two outputs, we further improve the bandwidth and reduce the footprint of the PBS than before.…”

“…This DC consists of a normal DC and SWG structure in the coupling region. By inserting the SWG structure in the coupling region of a normal DC and selecting the period Λ1, the duty cycle of silicon ρ1 and the total number of periods N1 of the SWG structure, the decay rate of the TE polarization or the TM polarization can be suppressed or enhanced [19]- [21]. Therefore, when light travels in the coupling region in a DC, there is almost no coupling for the TE polarization but strong coupling for the TM polarization.…”

Two-dimensional extreme skin depth engineering for CMOS photonics

“…The concept is called extreme skin depth engineering, or e-skid . E-skid has been employed as cross talk suppression [7,8], and for high performance polarization splitting [9,10]. The e-skid features are created in the same processing step as the waveguide itself, allowing this to be an innate no-cost addition to any design.…”