Optical modulation from an electro-optic polymer based hybrid Fabry-Pérot étalon using transparent conducting oxides

Fabry-Pérot étalons using electro-optic (EO) organic materials can be used for devices such as tunable filters and spatial light modulators (SLM's) for wavelength division multiplexing (WDM) communication systems^1-5 and ultrafast imaging systems. For these applications the SLM's need to have: (i) low insertion loss, (ii) high speed operation, and (iii) large modulation depth with low drive voltage. Recently, there have been three developments which together can enhance the SLM performance to a higher level. First, low loss distributed Bragg reflector (DBR) mirrors are now used in SLM's to replace thin metal mirrors, resulting in reduced transmission loss, high reflectivity (>99%) and high finesse. Second, EO polymer materials have shown excellent properties for wide bandwidth optical modulation for information technology due to their fabrication flexibility, compatibility with high speed operation, and large EO coefficients at telecommunication wavelengths. For instance, the EO polymer AJL8/APC (AJL8: nonlinear optical chromophore, and APC: amorphous polycarbonate has recently been incorporated into waveguide modulators and achieved good performance for optical modulation. Finally, very low loss transparent conducting oxide (TCO) electrodes have drawn increasing attention for applications in optoelectronic devices. Here we will address how the low loss indium oxide (In₂O₃) electrodes with an absorption coefficient ∼1000/cm and conductivity ∼204 S/cm can help improve the modulation performance of EO polymer Fabry-Pérot étalons using the advanced electro-optic (EO) polymer material (AJL8/APC). A hybrid etalon structure with one highly conductive indium tin oxide (ITO) electrode outside the etalon cavity and one low-absorption In ₂O₃ electrode inside etalon cavity has been demonstrated. High finesse (∼234), improved effective applied voltage ratio (∼0.25), and low insertion loss (∼4 dB) have been obtained. A 10 dB isolation ratio and ∼10% modulation depth at 200 kHz with only 5 V applied voltage have been achieved. These results indicate that such etalons are very promising candidates for ultrafast spatial light modulation in information technology.