Abstract
Inversely tapered spot size converter (SSC) is widely used to connect silicon waveguide with fiber in silicon photonics. However, the tapered structure may cause polarization rotation and further generate interference fluctuation in the transmission spectrum even of a straight waveguide. We analyzed the light propagation in a straight waveguide with SSC at the both ends with coupling matrix and transmission matrix methods. The analysis results matched with the phenomena we observed in the transmission spectrum. Combining the analysis with the measurement results, we calculated the polarization rotation efficiency of the SSC in different samples and analyzed the origin of the polarization rotation effect. Finally, we discussed the influence of the effect to the DP-QPSK signal and proposed several methods to release the impact.
Highlights
Silicon photonics is attracting more and more attention as the performance of the devices such as modulator and photo-detector on this platform approaching the traditional counterparts [1]
The cost of high integration is obvious: higher index-contrast corresponds to smaller mode size resulting in high coupling loss with single mode fiber
We find if there is polarization rotation effect in the spot size converter (SSC), the measured phenomena can be explained perfectly
Summary
Silicon photonics is attracting more and more attention as the performance of the devices such as modulator and photo-detector on this platform approaching the traditional counterparts [1]. The inversely tapered spot size converter (SSC) [2] is widely applied due to the simple structure and acceptable coupling loss. This taper structure may introduce problem in some situations, which is seldom mentioned in previous literature. The spectrum of the light source was measured by directly connecting the PC controller and inline polarizer. TE(TM)-TM(TE) denotes the measured TM(TE) component with TE(TM)-polarized input light. There are periodic fluctuations in both the TE and TM components regardless the polarization state of the input light in the spectrum, the polarization extinction ratio (PER) is much deteriorated compared with that of the source.
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