Low-Voltage Organic Electro-Optic Modulators Using Transparent Conducting Oxides As Electrodes (23080)
A novel organic electro-optic modulator using transparent conducting oxide electrodes has been created by Northwestern University scientists. The modulator functions at significantly lower switching voltages than conventional metallic electrode modulators. Modulation frequencies of 10-20 GHz are potentially attainable with this new construct.
ADVANTAGE: Modulators fabricated with transparent conducting oxide (TCO) electrodes exhibit low optical loss and operate at significantly lower switching voltages than conventional devices. These properties promise significant increase in modulation frequency essential for high speed optoelectronic and photonic applications.
SUMMARY: Reduced switching voltage of electro-optic (EO) modulators below ~ 1V for RF photonics improves link gain of RF signals. Efforts to achieve lower switching voltages include synthesis of higher EO coefficient materials and use of new device configurations, however optimal properties have yet to be realized. This invention employs transparent conducting oxides as device electrode materials which provide low optical loss and adjustable conductivity compared to metallic electrodes. Thin film nonlinear EO materials inserted directly between the TCO electrodes (Figure 1) eliminates additional voltage drop from the top and bottom claddings and increases the electric modulation field of the EO material with significant reduction of the requisite modulator switching voltage. This arrangement allows use of thin TCO electrodes (~20-50 nm) resulting in 3-4 x greater electric field and 3-4 x lower switching voltage compared to conventional modulators.
Demonstration of the TCO modulator using a single straight waveguide configuration and 1.31 μm light exhibits the typical response (Figure 2). A half-wave voltage Vπ of 2.8 V for the 8 mm long waveguide employing an organic EO material with EO coefficient r =35 pm/V. The results indicate a 2 cm long push-pull Mach-Zehnder modulator with TCO electrodes and optimized poling should realize < 0.5 V switching voltage. Modulator configurations to minimize refractive index mismatch with organic waveguides are also feasible with TCO electrodes. Modeling studies indicate that achievable TCO conductivities > 50 S/cm, will afford modulators capable of operating above 20 GHz.
Tobin Marks, Jing Ma, Guoyang Xu, Seng-Tiong Ho
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