Polymer optical waveguide with multiple graded-index cores for on-board interconnects fabricated using soft-lithography

Abstract

We successfully fabricate a polymer optical waveguide with multiple graded-index (GI) cores directly on a substrate utilizing the soft-lithography method. A UV-curable polymer (TPIR-202) supplied from Tokyo Ohka Kogyo Co., Ltd. is used, and the GI cores are formed during the curing process of the core region, which is similar to the preform process we previously reported. We experimentally confirm that near parabolic refractive index profiles are formed in the parallel cores (more than 50 channels) with 40 microm x 40 microm size at 250-microm pitch. Although the loss is still as high as 0.1 approximately 0.3 dB/cm at 850 nm, which is mainly due to scattering loss inherent to the polymer matrix, the scattering loss attributed to the waveguide's structural irregularity could be sufficiently reduced by a graded refractive index profile. For comparison, we fabricate step-index (SI)-core waveguides with the same materials by means of the same process. Then, we evaluate the inter-channel crosstalk in the SI- and GI-core waveguides under almost the same conditions. It is noteworthy that remarkable crosstalk reduction (5 dB and beyond) is confirmed in the GI-core waveguides, since the propagating modes in GI-cores are tightly confined near the core center and less optical power is found near the core cladding boundary. This significant improvement in the inter-channel crosstalk allows the GI-core waveguides to be utilized for extra high-density on-board optical interconnections.

Crossed polymer optical waveguide for optical printed circuit board

“…4(b), the experimentally measured result of SI-core crossed optical waveguide which was previously reported in [9] is plotted. As can be seen, measurement result show a very good coincidence with the numerical result (waveguide loss is about 1.7 dB for 16 crossings, 3.4 dB for 48 crossings, which are indicated in [7] ). …”

“…However, in this paper, the index exponents p and q are set to be p = q = 40 for the SI profile, because we preliminary confirmed that ray paths similar to those in an SIcore (straight ray path in the cores and the total internal reflections at the core-cladding boundary) are obtained even if the index exponents p and q are as small as 40. Meanwhile, we set p and q to be 3.0 for the GI profile in this simulation, which is a typical value when we experimentally fabricate GIcore polymer waveguides [7] [8]. The refractive index profile approximated by Eq.…”

Graded-index core polymer optical waveguide circuit fabricated using a microdispenser for high-density on-board optical interconnects

“…Since the two monomers are three-dimensionally crosslinked, and form a copolymer, the concentration distribution of the two monomers is fixed, which leads to the refractive index profile. Therefore, the index profiles are quite stable at higher temperatures compared to the dopant-based GI-core polymer waveguides we previously reported [6], [8].…”

“…Thus, the waveguides have stepindex (SI) type square cores, so that all the propagating modes are confined in the core with the total internal reflection scheme. On the other hand, we have been fabricating polymer waveguides with graded-index (GI) cores and have proven that these waveguides have higher performance in transmission than conventional SI-core waveguides [6][7][8]. However, the GI waveguides were fabricated by heat-drawing a preform [6].…”

Large Optical Backplane With Embedded Graded-Index Glass Waveguides and Fiber-Flex Termination

“…1. In our work we address two problems: 1) Identifying a viable alternative to polymer waveguides [6] [7], as they are subject to higher optical losses in the wavelength ranges above 850 nm, like 980..1000nm and 1310/1550nm. Those wavelengths are of interest because of VCSEL/PD availability and emerging silicon photonics technologies.…”