Optical loss characterization of polymer waveguides on halogen and halogen-free FR-4 substrates

Abstract

In order to characterize and optimize the overall link budget for an optical communication channel, the absorption loss of the waveguides must be well known, stable, and minimized. Research and characterization has been performed to ascertain the impact of the use of halogen vs. halogen free FR-4 circuit boards. Halogen is utilized within glass resin epoxy circuit boards as a flame retardant. An analysis of rectangular multi-mode polymer waveguide structures, with a fixed core dimension of 50 µm x 50 µm, was done to characterize the effects of the halogen FR-4 on the absorption loss. Thermal cycling times were varied in order to determine the relationship between heating of the polymer material, halogen diffusion into the optical cladding and core layer, and optical losses.

Optimal VIA Placement in Under Filled Embedded Multimode Waveguides

“…If one channel of a waveguide group is slightly longer than the other waveguides in the group, its coupling efficiency can be significantly less (1 -6 dB) than its neighbors leading to that channel to exceed the overall link budget. A change in index of refraction from heating of the board or aging of the material would additionally impact the coupling efficiency [6]. If the index of the board changes by 0.01, the optical path length changes by 1 mm per 10 cm length resulting in a new modal structure that is coupled to the optical VIA changing the coupling efficiency appreciably on the order of 1 -6 dB.…”

Optical Waveguides and Structures for Short Haul Optical Communication Channels within Printed Circuit Boards

“…If one channel of a waveguide group is slightly longer than the other waveguides in the group, its coupling efficiency can be significantly less (1-6 dB) than its neighbors leading to that channel exceeding the overall link budget. A change in index of refraction from heating of the board or aging of the material would additionally impact the coupling efficiency [47]. If the refractive index of the waveguide changes by 0.01, the optical path length changes by 1 mm per 10 cm length, resulting in a new modal structure that is coupled to the optical VIA changing the coupling efficiency appreciably on the order of 1-6 dB.…”

Multi-software modeling technique for field distribution propagation through an optical vertical interconnect assembly

“…After the core has been defined and cured, a top cladding layer is spun on and cured. The entire system is then baked again to remove the remaining solvent [11].…”