Hongxi Zhang

Active organic-inorganic sol gel with high thermal stability for nonlinear optical applications

Second-harmonic generation and thermal stability of hybrid photosensitive sol-gel films doped with a side-chain electro-optic chromophore have been studied. Nonlinear optic coefficient d33 has been derived for the cross-linked and noncross-linked sol-gel films. The d33 of the cross-linked hybrid sol-gel film shows high stability at elevated temperature. No evident degradation in d33 was observed at 110 °C and only 20% of d33 decayed in 15 min at 180 °C. The results indicate that the film can meet the long-term stability requirement for optical components.

Low drive voltage Fabry-Pérot étalon device tunable filters using poled hybrid sol-gel materials

Nonlinear optical chromophore coupled hybrid sol-gel materials have been synthesized and incorporated in Fabry-Perot etalon devices (ED’s) using highly reflective distributed Bragg reflector mirrors. Etalon structures with indium tin oxide electrodes outside the ED cavity have been applied to reduce absorptive loss. Large tunability (∼0.75nm∕V), high finesse (∼235), and wide tunable range (>50nm) have been obtained. A transmitted light intensity isolation ratio of ∼35dB at ∼1550nm has been achieved at a low drive voltage of 10V. The electro-optic effect and inverse piezoelectric effect are discussed. The results indicate that such hybrid sol-gel ED’s are promising candidates for tunable filters in wavelength division multiplexing communication systems.

Hybrid Fabry-Pérot étalon using an electro-optic polymer for optical modulation

The authors present a Fabry-Perot etalon using an electro-optic (EO) polymer material as the nonlinear medium. The two electrodes used to apply voltage across the EO polymer include an indium tin oxide electrode outside the etalon cavity and a low-absorption indium oxide electrode inside the etalon cavity. High finesse (∼234) and a low insertion loss (∼4dB) have been obtained. An isolation ratio of 10dB and ∼10% modulation depth at 200kHz with 5V applied voltage have been achieved. These results indicate that EO polymer etalons are promising as spatial light modulators for information technology.

Electro-optic modulation in hybrid solgel doped with Disperse Red chromophore

An electro-optically active hybrid solgel doped with Disperse Red 13 has been developed by use of a simple solvent-assisted method. It permits a high loading concentration and has low optical loss at 1550 nm. A channel waveguide amplitude modulator has been fabricated by use of active and passive hybrid solgel materials. The device shows an electro-optic coefficient of 14 pm/V at 1550 nm and stable operation.

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

Fabry-Perot etalons using electro-optic (EO) organic materials can be used for devices such as tunable filters and spatial light modulators (SLMs) for wavelength division multiplexing (WDM) communication systems1-5 and ultrafast imaging systems. For these applications the SLMs 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 SLMs 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 In2O3 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.

Nonlinear optical and electro-optic properties of organic-inorganic hybrid sol-gels doped with chromophores

We report a systematic investigation on organic-inorganic hybrid sol-gels doped with nonlinear optical chromophores. The host is based on photosensitive sol-gels prepared from precursor of 3-(methacryloxy)propyl trimethoxysilane-zirconium (or aluminum) oxide (MAPTMS-Zr(Al)) hybrid system. The chromophores are incorporated into the hybrid sol-gels as both guest and side-chain. Second harmonic generation experiment has been conducted to optimize the poling parameters for the active sol-gel films and examine the stability of the second-order nonlinear optical coefficients. Electro-optic channel waveguides have been fabricated by direct ultra-violet (UV) exposure, direct blue laser writing, and reverse-mesa methods. Electro-optic effect of the waveguides is measured at 1550 nm. All the results show that the hybrid sol-gels are promising media for electro-optic devices for integrated optics in both performance and fabrication flexibility.

Solar powered wireless sensor systems for border security

A secure border necessitates the development of new technology for remote sensing and surveillance. We investigate and develop wireless sensor network systems consisting of spatially distributed sensor nodes that can monitor various environmental parameters including temperature, humidity, motion, and vibration, etc. The sensors, nodes and transceivers have low-power consumption and are powered by solar energy so that the systems can work over long time periods with minimal human intervention and maintenance. This paper presents the technology development, wireless sensor integration, power management, and communication architecture, as well as a demonstration of environmental monitoring.

Passive and active sol-gel integrated optics

The fabrication and device characteristics of passive and active hybrid sol-gels are presented. Waveguides, modulators and switches are fabricated