Yinghua Qi

Cross-linkable bromo-fluorinated poly(arylene ether ketone)s for photonic device applications

A series of novel cross-linkable bromo-fluorinated poly(arylene ether ketone)s have been synthesized and used to fabricate photonic devices. The polymers, prepared by polycondensation reactions of decafluorobenzophenone with mixtures of bisphenols in different ratios, exhibit excellent solubility in common organic solvents and can be easily cast into optical-quality thin films by spin coating. The materials are thermally stable with decomposition temperatures (Td, 5% weight loss) over 450 degrees C and have high glass transition temperatures (Tg) in the range of 164 degrees C-178 degrees C. By controlling the bromine content of the polymers, the refractive index can be precisely controlled over a range as wide as 0.07. The material has excellent design flexibility, low optical loss (0.4-0.6 dB/cm at 1550 nm), a low birefringence (2-3 x 10(-3)), and is suitable for use in wavelength sensitive photonic devices based on arrayed waveguide gratings.

Polymer wavelength division multiplexers based on bromo-fluorinated poly(arylene ether ketone)

Photonic devices based on novel bromo-fluorinated poly(arylene ether ketone)s have been prepared. In these materials, the intrinsic optical losses at 1550 nm, due to the absorption of hydrocarbon bond overtone vibration, have been minimized by replacing H in the C-H bonds with Br or F, thereby shifting the overtone absorption to a longer wavelength. Typical optical slab losses of these materials are ~ 0.5 dB/cm at 1550 nm. In addition these materials have high thermal stability (5 wt% loss at temperature greater than 450°C), and are easily processed at temperatures lower than those previously reported for other poly(arylene ether)s (< 200°C). High quality waveguides have been fabricated using standard photolithographic processes. A thin film of silicon dioxide deposited by rf sputtering or e-beam evaporation on the polymer surface was used as a mask for reactive ion etching. Data on the design, fabrication and characterization of wide-band wavelength division multiplexers are reported. The devices exhibit on-chip losses of 7 dB including the fiber to chip coupling loss, output uniformity of ± 0.5dB and central wavelength thermal sensitivity lower than 0.06 nm/oC. Optimization of devices through material properties and fabrication process parameters is discussed.

Polymer photonic devices using fluorinated poly (arylene ether ketone)

Polymeric materials have been widely used for the fabrication of photonic devices, in particular for applications in short haul optical networks employing coarse wavelength division multiplexing (CWDM). However, the molecular design and processing of polymeric materials to have all the properties required for the fabrication of high performance photonic devices continue to present challenges. This paper presents data on the design, fabrication and characterization of waveguide devices using novel fluorinated poly(arylene ether ketone) materials. These materials exhibit low optical loss (slab loss ~ 0.5 dB/cm at 1550 nm), high thermal stability (1 wt% loss at temperatures up to 430 °C), and are easily processed at temperatures lower than those previously reported for poly(arylene ether)s (< 200 °C). High quality waveguides have been fabricated using standard photolithographic processes. Issues affecting polymer layer and device birefringence and optical loss have been investigated, including molecular structure, processing conditions and substrate selection. Coupling devices sensitive to waveguide dimensions have been designed and fabricated, and their output compared to numerical simulations. Characterization of these devices allows further optimization of the materials and the waveguide process and assists with the design of more complex polymer photonic components.

Fabrication of waveguide devices by UV photopatterning of fluorinated poly"arylene ether ketone…s containing tetrafluorostyrol moieties

This work demonstrates waveguide devices based on a novel photocrosslinkable fluorinated poly(arylene ether ketone). A new molecular design has enabled waveguide fabrication to be achieved for the first time using this kind of polymer, through direct UV patterning and a wet-etch process, which is faster and more convenient and economical than the process based on standard reactive-ion etching that has been applied to previously reported poly(arylene ether ketone) materials. High-quality waveguides with smooth, well-defined sidewalls have been produced, and optical splitter devices based on directional coupling are demonstrated. Optical characterization of these devices suggests that the waveguide quality is comparable to that of waveguides fabricated using a dry-etch process, and the experimental data obtained from the fabricated optical splitters are in excellent agreement with theoretical predictions.

Design, synthesis, and properties of cross-linkable fluorinated poly(arylene ether ketone)s

Novel cross-linkable highly fluorinated and bromo-fluorinated poly(arylene ether ketone)s have been prepared by low temperature copolymerization reactions of a tetrafluorostyrol-containing bisphenol with 4,4’-(hexafluoroisopropylidene)diphenol /4,4’-isopropylidenebis(2,6-dibromophenol) and decafluorobenzophenone in the presence of calcium hydride and cesium fluoride. The resultant polymers had high molecular weights and linear structures. Tough, flexible and transparent thin films of these polymers can be readily formed by both solution casting and spin-coating techniques. Fine-tuning of the refractive indices of these polymers has been achieved by either adjusting the feed ratio of bisphenols or the introduction of bromine atoms into the polymer structures. The refractive index of the polymers showed a linear dependence on the bromine content and could be tuned over a range of 0.07. The polymers exhibited low optical losses of less than 0.5 dB/cm at 1550 nm and can be cross-linked by both thermal and photo processes. These polymers represent promising candidates for use as both core and cladding materials in the fabrication of optical waveguide devices.

In situ second harmonic generation measurements of poled fluorinated polymer films

New fluorinated poly(arylene ether sulfone)s (FPAES) and poly (arylene ether ketone)s (FPAEK) with two types of NLO chromophores as pendant groups were obtained by a polycondensation reaction carried out using very mild reaction conditions. The glass transition temperature (Tg) of these copolymers is between 168 and 190°C. The SHG intensity was measured during thermal corona poling : the dipole orientation starts at 100°C, and reaches a maximum at 160°C, which is lower than Tg. During cooling of the film under the applied electric field, we observed an unusual drop of the SHG intensity starting at 120°C and reaching 70 % of the maximum value. The physical origin of this drop has been investigated and is possibly attributable to a secondary phase transition of the copolymers. Despite this decrease, d33 coefficients measured after poling vary between 2 and 15 pm/V at 1907 nm fundamental wavelength, depending on the first hyperpolarisability of the NLO chromophore. The dipole orientation of all these copolymers is very stable provided the temperature of the films is kept below the temperature threshold of 120 °C, which is below the Tg of the polymers.

Photopatternable fluorinated poly(arylene ether ketone) for optical waveguide devices

Fluorinated poly(arylene ether)s are attractive for the fabrication of optical waveguide devices for photonic applications due to their low optical attenuation and high thermal stability. A variety of waveguide devices have been fabricated in these polymers through thermal crosslinking followed by a reactive ion etch process. This work reports on the use of a novel fluorinated poly(arylene ether ketone) incorporating tetrafluorostyrol groups for photo-crosslinking. This new molecular design allows sufficient photosensitivity to fabricate waveguides through a UV direct patterning and wet-etch method, offering a fast, convenient and economic approach to making polymer photonic devices. Data concerning the polymer molecular structure and choice of suitable photo-initiators for the fabrication of the devices are presented in this paper. Based upon the optical and thermal properties of the resultant materials it appears that similar degrees of polymer crosslinking can be achieved using the photo-curing process as those using a thermal crosslinking process. High quality waveguide devices with smooth, well-defined sidewalls are demonstrated. Optical characterization of these devices suggests that the waveguide quality is comparable to that of waveguides fabricated using a dry etch process.