Nonlinearities of organic electro-optic materials in nanoscale slots and implications for the optimum modulator design

Abstract

The performance of highly nonlinear organic electro-optic (EO) materials incorporated into nanoscale slots is examined. It is shown that EO coefficients as large as 190 pm/V can be obtained in 150 nm wide plasmonic slot waveguides but that the coefficients decrease for narrower slots. Possible mechanism that lead to such a decrease are discussed. Monte-Carlo computer simulations are performed, confirming that chromophore-surface interactions are one important factor influencing the EO coefficient in narrow plasmonic slots. These highly nonlinear materials are of particular interest for applications in optical modulators. However, in modulators the key parameters are the voltage-length product U_πL and the insertion loss rather than the linear EO coefficients. We show record-low voltage-length products of 70 Vµm and 50 Vµm for slot widths in the order of 50 nm for the materials JRD1 and DLD164, respectively. This is because the nonlinear interaction is enhanced in narrow slot and thereby compensates for the reduced EO coefficient. Likewise, it is found that lowest insertion losses are observed for slot widths in the range 60 to 100 nm.

Ultra-high electro-optic activity demonstrated in a silicon-organic hybrid modulator

“…For plasmonic waveguides, even lower values down to UπL = 0.05 Vmm can be achieved [20]. However, while these devices feature large electro-optic bandwidths [21], they suffer from intrinsic propagation losses, which limit the range of practical device lengths to a few tens of micrometers [13,20]. This effect can be quantified by the product aUπL which combines the π-voltage Uπ, the phase shifter length L, and the waveguide propagation loss coefficient a measured in dB/mm.…”

Silicon-organic hybrid (SOH) Mach-Zehnder modulators for 100 GBd PAM4 signaling with sub-1 dB phase-shifter loss

“…The slightly reduced modulation efficiency is attributed to the fact that the EO chromophores near the slot walls are mostly oriented parallel to the sidewalls due to surface interactions. As a consequence, the volume fraction of perpendicularly aligned chromophores becomes smaller the narrower the slot is [7].…”

“…This trade-off leads to rather high loss-efficiency products, which amount to, e.g., aUπL = 5.8 VdB for best-in-class depletion-type phase shifters, which still feature substantial UπL products of 4.6 Vmm [6]. Much more efficient modulation is achieved in plasmonic-organic hybrid (POH) MZM, which combine plasmonic slot waveguides with highly efficient organic EO materials, and which offer ultra-small UπL products down to 0.05 Vmm [7] with unprecedented bandwidths of hundreds of GHz [8,9]. However, the plasmonic phase-shifter structure is intrinsically linked to strong optical absorption loss, which leads to aUπL products of more than 20 VdB [7].…”

“…Much more efficient modulation is achieved in plasmonic-organic hybrid (POH) MZM, which combine plasmonic slot waveguides with highly efficient organic EO materials, and which offer ultra-small UπL products down to 0.05 Vmm [7] with unprecedented bandwidths of hundreds of GHz [8,9]. However, the plasmonic phase-shifter structure is intrinsically linked to strong optical absorption loss, which leads to aUπL products of more than 20 VdB [7]. A modulator technology which simultaneously minimizes both the π-voltage-length product and the loss efficiency product is hence still lacking.…”

High‐Speed Modulator Based on Electro‐Optic Polymer Infiltrated Subwavelength Grating Waveguide Ring Resonator

“…The silicon‐organic hybrid (SOH) platform enables the marriage of the best of the two materials and thus has been receiving substantial attention. Compared to plasma dispersion, electro‐optic (EO) polymers have a remarkable EO coefficient (r33 > 400pm/V), ultrafast response speed (< 1 f s), small dispersion, and spin‐casting compatibility, which promise low‐power consumption, ultra‐high speed modulation, and ease of fabrication . Modulators with bandwidth over 100 GHz have been demonstrated, but their millimeter long device length defeats the purpose of chip‐scale integration .…”