Abstract
On-chip polarization manipulation is pivotal for silicon-on-insulator material platform to realize polarization-transparent circuits and polarization-division-multiplexing transmissions, where polarization splitters and rotators are fundamental components. In this work, we propose an ultracompact and high efficient silicon-based polarization splitter-rotator (PSR) using a partially-etched subwavelength grating (SWG) coupler. The proposed PSR consists of a taper-integrated SWG coupler combined with a partially-etched waveguide between the input and output strip waveguides to make the input transverse-electric (TE) mode couple and convert to the output transverse-magnetic (TM) mode at the cross port while the input TM mode confine well in the strip waveguide during propagation and directly output from the bar port with nearly neglected coupling. Moreover, to better separate input polarizations, an additional tapered waveguide extended from the partially-etched waveguide is also added. From results, an ultracompact PSR of only 8.2 μm in length is achieved, which is so far the reported shortest one. The polarization conversion loss and efficiency are 0.12 dB and 98.52%, respectively, together with the crosstalk and reflection loss of −31.41/−22.43 dB and −34.74/−33.13 dB for input TE/TM mode at wavelength of 1.55 μm. These attributes make the present device suitable for constructing on-chip compact photonic integrated circuits with polarization-independence.
Highlights
Bandwidth, and a typical mode evolution-based PSR is composed of a TM0-to-TE1 polarization rotator and a cascaded TE1-to-TE0 mode-order converter[10,12,13,14,15,16]
Compared with PSRs reported earlier, the present one has the shortest size since the input TE mode is directly coupled and converted to the output TM mode without some intermediate modes such as TE1 mode as a bridge used in many previous schemes[10,12,13,14,15,16,17,20,21,22,23], and the coupling and converting processes are reasonably combined together instead of using cascaded parts composed of separate splitters and rotators
For the input TE mode, it is firstly tending to the SWG region as it enters into the input SWG-tapered transition with its width being tapered from w2 to w5 in a period number of n1 since it cannot be well-supported by the input strip waveguide with its width being tapered from w1 to w3
Summary
Bandwidth, and a typical mode evolution-based PSR is composed of a TM0-to-TE1 polarization rotator and a cascaded TE1-to-TE0 mode-order converter[10,12,13,14,15,16]. Subwavelength gratins (SWGs), a grating pitch substantially smaller than the wavelength of light in the structure, behaving as a homogeneous media without diffraction effect, offer a new degree of freedom for the design of novel photonic devices since the effective index of the waveguide core can be engineered by changing the duty cycle[24,25] Based upon this unique feature, SWGs have been applied into a variety of photonic devices with enhanced performance, e.g., fiber-chip grating couplers[26], wavelength independent MMI couplers[27], waveguide crossings[28], power splitters[29], and other fundamental building blocks (SWG-based tapers[30,31], bends[32], DCs32, and microring resonators[33]). This is the first PSR reported so far whose footprint is less than 10 μm with reasonable performance
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