Design of transmission line driven slot waveguide
Mach-Zehnder interferometers 
and application to analog optical links

Abstract

Slot waveguides allow joint confinement of the driving electrical radio frequency field and of the optical waveguide mode in a narrow slot, allowing for highly efficient polymer based interferometers. We show that the optical confinement can be simply explained by a perturbation theoretical approach taking into account the continuity of the electric displacement field. We design phase matched transmission lines and show that their impedance and RF losses can be modeled by an equivalent circuit and linked to slot waveguide properties by a simple set of equations, thus allowing optimization of the device without iterative simulations. We optimize the interferometers for analog optical links and predict record performance metrics (V(pi) = 200 mV @ 10 GHz in push-pull configuration) assuming a modest second order nonlinear coefficient (r(33) = 50 pm/V) and slot width (100 nm). Using high performance optical polymers (r(33) = 150 pm/V), noise figures of state of the art analog optical links can be matched while reducing optical power levels by approximately 30 times. With required optical laser power levels predicted at 50 mW, this could be a game changing improvement by bringing high performance optical analog link power requirements in the reach of laser diodes. A modified transmitter architecture allows shot noise limited performance, while reducing power levels in the slot waveguides and enhancing reliability.

High-Speed, Low Drive-Voltage Silicon-Organic Hybrid Modulator Based on a Binary-Chromophore Electro-Optic Material

“…The EO coefficien r 33 can be obtained from the measured π-voltage U π of the push-pull MZM by using the relation [10], [33] U π = w slot λ c 2Lr 33 Γn 3 slot .…”

“…(1) The quantity w slot denotes the measured slot width, λ c is the wavelength of the optical carrier, L is the modulator length, n slot is the refractive index of the organic material in the slot, and Γ is the fiel interaction factor that is linked to the fraction of the optical power that interacts with the modulation fiel [10], [33] …”

“…This material system clearly outperforms conventional guest-host and neat dendritic materials. We demonstrate a record-high in-device EO coeffi cient of r 33 = 230 pm/V, which results in a low modulator voltage-length product of U π L = 0.52 Vmm. In addition we show that these modulators support data rates of up to 40 Gbit/s.…”

Low-power silicon-organic hybrid (SOH) modulators for advanced modulation formats

“…The fabricated slot width is w slot = 80 nm, and the rail width amounts to w rail = 240 nm. The transmission line consists of 200 nm thick aluminum strips in a ground-signal-ground (GSG) configuration [26]. The parts of the silicon slab which are overlapping with the aluminum are highly n-doped to achieve an Ohmic contact.…”

Silicon-organic hybrid (SOH) IQ modulator using the linear electro-optic effect for transmitting 16QAM at 112 Gbit/s

“…Thus a large and therefore efficient overlap is obtained between the electrical and optical mode. By attaching thin Si striploads to the optical WG an electrical connection is made to an RF coplanar waveguide (CPW), realized in a ground-signal-ground (GSG) configuration devised to have a 50 Ω impedance close to the RF source (similar to [20]). The active molecules (chromophores) of the nonlinear material are aligned during fabrication by applying a poling voltage (depicted in green) from one ground electrode to the next, which results in an orientation of the χ (2) nonlinearity in both slots (green arrows) that is asymmetric with respect to the signal electrode (S).…”