100 GHz Plasmonic Photodetector

Photodetectors compatible with CMOS technology have shown great potential in implementing active silicon photonics circuits, yet current technologies are facing fundamental bandwidth limitations. Here, we propose and experimentally demonstrate for the first time a plasmonic photodetector achieving simultaneously record-high bandwidth beyond 100 GHz, an internal quantum efficiency of 36% and low footprint. High-speed data reception at 72 Gbit/s is demonstrated. Such superior performance is attributed to the subwavelength confinement of the optical energy in a photoconductive based plasmonic-germanium waveguide detector that enables shortest drift paths for photogenerated carriers and a very small resistance-capacitance product. In addition, the combination of plasmonic structures with absorbing semiconductors enables efficient and highest-speed photodetection. The proposed scheme may pave the way for a cost-efficient CMOS compatible and low temperature fabricated photodetector solution for photodetection beyond 100 Gbit/s, with versatile applications in fields such as communications, microwave photonics, and THz technologies

Enhancing adoption of fodder technologies: how can an innovation systems perspective help?

We report a thin film phase modulator employing organic nonlinear optical molecules, with an electro-optic bandwidth of 1.25 THz. The device acts as a polarization sensitive broadband Pockels medium for coherent electric field detection in a dual wavelength terahertz time-domain spectroscopy setup in the telecom band at 1550 nm. To increase the sensitivity, we combine a three-dimensional bow-tie antenna structure with strongly electro-optically active molecules JRD1 in poly­(methyl methacrylate) supporting polymer. The antenna provides subwavelength field confinement of the terahertz wave with its waveguide gap with lateral dimensions of 2.2 μm × 5 μm × 4 μm. In the gap, the electric field is up to 150× stronger than in a diffraction limited space-time volume, such that an interaction length of only 4 μm suffices for the detection of fields below 10 V/m. This device is promising in the growing field of quantum optics in the terahertz, single photon terahertz detection, nonlinear imaging, and on-chip telecommunication

Data File 1: Harnessing nonlinearities near material absorption resonances for reducing losses in plasmonic modulators

Refractive Index of 75%HD-BB-OH and 25%YLD124 Originally published in Optical Materials Express on 01 July 2017 (ome-7-7-2168

Effect of Rigid Bridge-Protection Units, Quadrupolar Interactions, and Blending in Organic Electro-Optic Chromophores

A new organic electro-optic (EO) molecule was designed with two modifications aimed at increasing acentric order. The molecule is based on the well-known CLD donor-π bridge-acceptor template. The first structural modification introduces rigid aromatic fluorenyl and naphthyl site-isolation units (sterically bulky functional groups) to reduce aggregation. Site isolation units have been used in the past, but this is the first time that both the “front” and “back” of the CLD tetraene bridge have been modified with site-isolation units, and we had to introduce new synthetic methodology to do so. The second design element was the inclusion of cooperatively interacting aromatic dendron (HD) and fluoroaromatic dendron (FD) side groups to increase the acentric order. HD/FD units have previously been successfully used to increase EO performance, but we changed their location on the chromophore: they are attached to the donor and acceptor ends of the molecule to better match side chain ordering with the dipole moment of the molecule. Comparison chromophores were synthesized with alkyl (-MOM), hydroxyl (-OH), or HD units on the acceptor end of the molecule and either the traditional CLD bridge (T-bridge) or modified bridge (BB-bridge) for a family of eight chromophores. The HD/FD units increased glass transition temperature, <i>T</i>_g, by 4–21 °C, and the bulky bridge modification increased <i>T</i>_g by 27–44 °C, which is very beneficial as that results in extra thermal stability of the poling-induced acentric order. UV/vis absorbance spectroscopy shows that the site-isolation units reduce aggregation. Unfortunately, poor film formation of the neat materials precluded full chromophore evaluation in poling and <i>r</i>₃₃ experiments. The EO performance obtained for HD-BB-FD and HD-BB-OH was lower than expected, with <i>r</i>₃₃/<i>E</i>_p ≈ 1 nm² V^–2 at 1310 nm. We found that blending in 25 wt % YLD124 improved film-forming and poling efficiency. Due to the effect of blending and improved site isolation, <i>r</i>₃₃/<i>E</i>_p improved to 2.1–2.3 nm² V^–2 for 3:1 HD-BB-FD:YLD124, HD-BB-OH:YLD124, and HD-BB-MOM:YLD124, and <i>r</i>₃₃ as high as 351 pm V^–1 was obtained with 3:1 HD-BB-MOM:YLD124. Chromophore blends were also evaluated in plasmonic organic hybrid (POH) phase modulators with slot lengths of 5–20 μm. In POH devices, <i>r</i>₃₃ was as high as 325 pm V^–1 at 1260 nm and 220 pm V^–1 at 1520 nm. Overall, the increase in acentric order afforded by the HD/FD interactions was found to be small and resulted in no increase in <i>r</i>₃₃ due to the reduced number density. Ultimately, the increase in <i>r</i>₃₃/<i>E</i>_p afforded by the site isolation and blending resulted in a modest increase in <i>r</i>₃₃/<i>E</i>_p relative to YLD124, but combined with the increased <i>T</i>_g, the chromophore system is a significant improvement and points to an important design strategy