Diyun Huang

Broadband electro-optic polymer modulators with high electro-optic activity and low poling induced optical loss

A screening method is reported for electro-optic (EO) polymers with an emphasis on broadband device suitability. The method is based on comparing the signal from second harmonic generation (SHG) and the leak through current (LTC) during poling. Plots of the SHG and LTC are used to define high EO activity-low current poling windows that are critical for low driving voltage, broadband devices with relatively low optical loss. The screening procedure was used to select an EO polymer core that resulted in a 40Gbits∕s broadband modulator with a driving voltage of 1.3V and an insertion loss of <8dB.

Environmental Stress Testing of Electro–Optic Polymer Modulators

Low Vpi electro-optic (EO) polymer modulators were environmental stress tested at both the chip and packaged device level. Different top clad materials showed different results for high-temperature and temperature cycle testing, which is related mostly to coefficient of thermal expansion (CTE) mismatches and/or adhesion properties of the clads related to other materials in the devices stack and to the substrate and electrode materials. With thoroughly compatible cladding, devices that are thermally stable for over 5000 h at 85degC have been achieved. High optical power ( 500 mW @ 1550 nm) tests showed the photochemical stability of the EO polymer material in hermetically sealed packages. The results demonstrate that clad polymers and interactions between devices layers are of concern for achieving environmentally stable EO polymers modulators.

The effect of ligand conjugation length on europium complex performance in light-emitting diodes

Abstract Novel europium complexes containing either symmetrical or unsymmetrical diphenanthryl β-diketone ligands were synthesized and characterized. The ligand conjugation length has a profound effect on the spectral properties of the complexes and the device performance of the complexes as emitting dopants in light-emitting diodes. The unsymmetrical ligand has a longer conjugation, which red-shifts the absorption of the complex. The longer wavelength absorption facilitates the choice of host material that can efficiently transfer energy to the complex. However, the longer conjugation also results in a less efficient energy transfer from the ligand to the central Eu3+ ion.

Efficient emission from a europium complex containing dendron-substituted diketone ligands

A new europium (Eu) complex with dendron-substituted diketone ligands was synthesized and found to exhibit a photoluminescence efficiency of 45%. Double-layer light-emitting diodes based on polymer matrices doped with the Eu complex were fabricated. An electroluminescence external quantum efficiency of 0.80% was achieved when a copolymer containing side-chain carbazole and 1,3,4-oxadiazole groups was used as the matrix. The results are analyzed in the context of Forster energy transfer.

Achieving large electro-optic response: DH-type chromophores in both crosslinked systems and linear high-Tg systems

Drawing on the success of the DH6-polycarbonate system, new derivatives based on the DH bridge structure, bis-1,2-(dibutoxythiophene)vinylene have been synthesized and tested. The property-structure function has been investigated, showing that location of the trifluorovinylether (TFVE) crosslinker on the chromophore has an impact on electro-optic (EO) activity as well as stability. A crosslinked polymer, IMOH_PCT-R and a linear high glass transition (Tg) analog, IMOH_HT, in combination with various DH derivatives are discussed. The temporal stability data of these systems show comparable results for both crosslinked and linear polymers, furthering the argument that the Tg of the EO material is the critical parameter in determining device lifetime.

Material development and processing for electro-optic device systems

New crosslinked clad polymers were developed for electro-optic polymer modulators with special attention paid to properties such as refractive index tunability, optical loss, and conductivity. These cured polymers showed relatively low optical loss at 1550 nm and desirable conductivity. The clads were used to fabricate electro-optic devices having mode profiles closely matched to that of optical fibers in order to reduce insertion loss. A new hardmasking technique was developed to define Mach-Zehnder rib waveguides by photolithography and dry etching with high reliability and surface smoothness. The hardmasking technique demonstrated flexibility in defining waveguides made with electro-optic polymers having different reactivity towards etchant gasses.

Recent advances in commercial electro-optic polymer modulator

We present the state-of-art polymer-based electro-optic modulator, which, for the first time, can be used in real commercial systems. The devices work up to 100 Gbps and possess the Vpi as low as 1.6 V.

Low half-wave voltage modulators using nonlinear optical polymers

The optical and material properties of AJ309 electro-optic (EO) polymer were systematically studied with the objective to fabricate an optimized integrated device. Both bottom and top cladding materials were developed at Lumera to match the processibility of AJ309, and sustain high poling voltage needed for an effective poling process. A device fabrication process is developed. The degree of crosslinking of the EO polymer before poling is minimized by processing the top clad polymer at room-temperature. The UV-curable top clad has shown no detectable chemical damage to the EO polymer after the deposition process of the top clad, thus maintaining the integrity of the interface between top clad and AJ309 core. A 2.1 cm long active length Mach-Zehnder modulator with low half-wave voltage (Vπ) of 1.1 V @1550 nm was fabricated using the AJ309 EO polymer and in-house cladding materials. Other device parameters are also reported.

Development of side-chain NLO polymer materials with high electro-optic activity and long-term stability

The electro-optic coefficient and long-term dipole alignment stability are two major factors in the development of high performance NLO materials for the application of high-speed EO devices. We have developed a high performance non-linear organic chromophore and incorporated it into a crosslinkable side-chain polyimide system. The polymer was synthesized through stepwise grafting of the crosslinker followed by the chromophore onto the polyimide backbone via esterification. Different chromophore loading levels were achieved by adjusting the crosslinker/chromophore feeding ratio. The polyimides films were contact-poled with second-harmonic generation monitoring. A large EO coefficient value was obtained and good long-term thermal stability at 85°C was observed.

Systematic study of polymer wideband optical modulators: transition from intrinsic material characteristics to device performance

Low drive voltage Mach-Zehnder modulators were designed and fabricated using proprietary EO polymers with high electro-optic coefficients. We report on drive voltage and high-speed electrode parameters of modulators fabricated on silicon wafers with high yield. Special attention was paid to designing claddings to match the electro-optic core conductivity and dielectric constant. The r33 values measured on single layer thin films are compared with those resulting from drive voltage measurements on devices. Half-wave voltage measured on devices is compared with theoretical values derived from equations defined for poling of the core through bottom and top claddings. We compare results obtained from devices fabricated using commercially available UV-curable epoxies with devices fabricating using proprietary clad polymers developed at Lumera Corporation.