Fabrication and inter-channel crosstalk analysis of polymer optical waveguides with W-shaped index profile for high-density optical interconnections

Abstract

For applications in high-density and high-speed optical interconnections, we propose to utilize polymer parallel optical waveguides (PPOWs) with so-called W-shaped refractive index profile in the core area. A W-shaped index profile is composed of a parabolic index distribution surrounded by a narrow index valley, followed by a cladding with a uniform refractive index. We expect that W-shaped index profiles contribute to decreasing the inter-channel crosstalk due to mode conversion in the waveguides. In this paper, we investigate how much the index difference of the index valley improves the crosstalk value. First, we fabricate polymer waveguides with various index profiles by changing the composition of the copolymer for cladding. We show the results that a 1-m long W-shaped profile PPOW has not only low propagation loss (0.027 dB/cm), but an inter-channel crosstalk (~-40 dB) lower than those of graded index (GI) core PPOW we previously fabricated. Next, we theoretically analyze the propagation loss and inter-channel crosstalk in polymer waveguides with different index profiles by means of a ray tracing model in which the light scattering effect is included. The calculation results indicate that the index valley surrounding each core works properly for preventing the power coupling from the cladding modes to the propagation modes, and consequently, very low inter-channel crosstalk is realized with W-shaped index profiles.

Near-infrared polymer Y-branch splitters with compact MMI structures for efficient power splitting

“…The index profile is a fundamental concept in optics, representing the variation of the RI across the cross-section of an optical waveguide. This profile plays a pivotal role in shaping the behavior of light propagation within the waveguide, influencing aspects such as mode confinement and propagation characteristics [33]. The index profile can be characterized through a power-law approximation [34], which can be represented the following equation:…”

Near-infrared polymer Y-branch splitters with compact MMI structures for efficient power splitting

“…The index profile is a fundamental concept in optics, representing the variation of the RI across the cross-section of an optical waveguide. This profile plays a pivotal role in shaping the behavior of light propagation within the waveguide, influencing aspects such as mode confinement and propagation characteristics [33]. The index profile can be characterized through a power-law approximation [34], which can be represented the following equation:…”

Analysis of interchannel crosstalk in multimode parallel optical waveguides using the beam propagation method

“…We have experimentally demonstrated that graded-index (GI) core polymer waveguides dramatically reduce the inter-channel crosstalk, compared to conventional step-index (SI) core waveguides [3][4][5]. However, the detailed mechanisms of inter-channel crosstalk in such multimode short-length waveguides have not yet been clarified.…”