A novel method of integrating a total internal reflection (TIR) mirror into an optical waveguide embedded in a printed circuit board (PCB) was demonstrated for application in chip-to-chip optical interconnects. Plastic optical fiber (POF) was placed into channels that were mechanically machined into FR-4 composite plates. The TIR mirror was created by a second mechanical machining. The mirror loss was measured to be approximately −1.6 dB per reflection. The use of POF resulted in attenuation losses in the waveguide over an order of magnitude lower than what is obtainable with typical planar waveguides that are integrated into PCBs. Monte Carlo ray tracing was used to determine the theoretical efficiency of the system as well as cross talk between channels due to optical device alignment tolerances.
We demonstrate a modulated retroreflector that utilizes large-area multiple quantum well modulators on all three faces of a retroreflector. The large-area devices, fabricated by metalorganic chemical vapor deposition, are characterized in terms of the yield and leakage currents. A yield higher than that achieved previously using devices fabricated by molecular beam epitaxy is observed. The retroreflector module is constructed using a standard FR4 printed circuit board (PCB) technology, thereby simplifying the wiring issue. A high optical contrast ratio of 8.23 dB is observed for a drive of 20 V. A free-standing PCB retroreflector is explored and found to have insufficient angular tolerances (±0.5 deg). We show that the angular errors in the corner-cube construction can be corrected for using off-the-shelf optical components as opposed to mounting the PCBs on a precision corner cube, as has been done previously.
In recent decades, optical fiber has proven useful for many sensor applications. Specifically, fiber Bragg grating (FBG)
sensors have shown great utility for integrity management and environmental sensing of composite structures. One
major drawback of FBG sensors, however, is the lack of a robust, non-"pigtail" technique for coupling the embedded
FBG sensor to an external optical interrogation device. In this paper, a novel method of free space passive coupling of
light into FBG sensors has been investigated. Angled 45-degree mirrors integrated directly into fibers were used as an
input coupling technique. The approach was applied to both single mode and multimode glass fibers containing FBG's.
For multimode investigations, mirrors were integrated into graded-index multimode fiber by polishing the end face to a
45-degree angle. In single mode investigations, a novel method of coupling to the sensor via splicing and fusing a
multimode fiber to a single mode FBG was explored. Associated transmission spectra are shown for each method.
A novel method for passive coupling of light to optical communication links embedded in composite structures has been explored. The use of 45-deg-angled mirrors integrated directly in poly-(methylmethacrylate) fibers as an input node coupling technique was characterized under conditions of varying refractive index. Mirrors were integrated into the fiber through polishing of the endface to a 45-deg angle and then thermal evaporation of Ag metal. To explore angular tolerances and sensitivity to alignment errors, the efficiency of the node was characterized as a function of source position and angle of incidence. Coupling loss as low as −0.39 dB was measured for normal incidence while the input node was immersed in a fluid with refractive index of 1.33. Ray tracing simulations were used to model the coupling of light to fabricated input nodes and showed good agreement with experiments.
Novel methods for remote coupling of light into optical fibers embedded in composite structures has been explored. A
passive technique in which light is coupled via a 45° angled mirror manufactured at the end of a plastic optical fiber
(POF) was explored as well as an active technique in which a dye-impregnated POF was used to couple light to
immersed fibers without physical connectorization. The fibers were immersed in fluids with different refractive indices
to determine the effect of index on the coupling efficiency and simulate optical fibers embedded in a polymer composite.
The passive technique proved much more efficient with a maximum efficiency of 91.4% achieved in an index of 1.33.
The dye-impregnated POF was much less efficient with typical values ranging from 1%-2% for various indexes.