Yong Hyub Won

Synthesis and properties of nonlinear optical side chain soluble polyimides for photonics applications

Aromatic polyimides with side chain nonlinear optical chromophores have been investigated through a facile two-step synthetic route. First, various poly(hydroxy imide)s have been synthesized by direct thermal imidization of diaminophenol dihydrochloride salt and aromatic dianhydride monomers. The resulting polyimides bearing phenolic hydroxy groups were found to react easily with the terminal hydroxy group on the chromophores via the Mitsunobu condensation to give corresponding polyimides with high optical nonlinearities and good solubility in common organic solvents. Detailed physical properties showed that these polyimides have a molecular weight (M ω ) of 31,000 and high glass transition temperature above 220°C, ensuring a long-term alignment stability at elevated temperature. The electrooptic coefficients, r 33 , of the electrically poled polymer films were in the range 1.8-7.6 pm/V at 1.3 μm.

All-optical wavelength conversion using absorption modulation of an injection-locked Fabry-Perot laser diode

A novel all-optical wavelength converter based on the transverse-magnetic (TM)-mode absorption modulation of a Fabry-Perot laser diode (FP-LD) is proposed and demonstrated. An FP-LD shows absorption nulls for TM mode probe beam, which are red-shifted by an additional optical pump injection. Using this, the transmission of the continuous-wave probe beam can be optically controlled and wavelength conversion is, thus, achieved. The proposed scheme is simple and cost-effective, and can be used for very wide-range wavelength conversion. Bit-error-rate measurements at 2.5 Gb/s were performed, and the power penalties of 2 and 6 dB were observed, respectively, for noninverted and inverted wavelength conversion.

All-optical NRZ-to-PRZ converter at 10 Gb/s based on self-phase modulation of Fabry-Pe/spl acute/rot laser diode

We propose and demonstrate nonreturn-to-zero (NRZ) to pseudoreturn-to-zero (PRZ) data format conversion at 10 Gb/s based on transverse-magnetic (TM) mode absorption and self-phase modulation (SPM) in a Fabry-Pe/spl acute/rot laser diode (FP-LD). An FP-LD has absorption nulls for TM mode injected beam and the beam having NRZ data experiences SPM, which induces a frequency chirp at every rising edge and falling edge. By extracting the chirp components, all-optical NRZ-to-PRZ format conversion has been achieved. The resultant PRZ data gives well-defined 10-Gb/s clock signal. This method will be very useful in all-optical clock recovery of high-speed optical communication systems.

Second-order NLO polyamideimides based on functionalized stilbene derivatives: direct polycondensation and characterization

Abstract Polyamideimides having nonlinear optical (NLO)-active chromophores were synthesized by direct polycondensation of 4-[N,N′-bis(2-aminoethyl)amino]-4′-nitrostilbene (DANS-diamine) with oxy-bis[N-(4-phenylene)trimellitic imide] (BCI), N-(3-carboxyphenyl)-trimellitimide (BTI) and trimellitic anhydride chloride (TMAC). The direct polycondensation of NLO polyamideimides without a curing step may ameliorate the optical property of NLO polymers by reducing the optical propagation loss. The resulting polymers were highly soluble in aprotic polar solvents such as DMF, DMAc, NMP, etc. The NLO polyamideimides exhibited the inherent viscosity range of 0.14–0.33 dl g−1. Molecular structural characterization for the resulting polymers was achieved by 1H n.m.r., FTi.r. and u.v.-visible spectroscopies. The glass transition temperature for the resulting NLO polyamideimides was in the range 142–224°C and they showed thermal stability up to 260°C. The polymer solutions could be spin coated onto indium—tin-oxide (ITO) glass or quartz disc substrates to form optical quality thin films. The electro-optic coefficients (r33) at the wavelength of 1.3 μm, measured by a simple reflection method, for polymer thin films poled around the glass transition temperature were in the range 1.9–7.4 pm V−1.

Synthesis and characterization of NLO chromophores bearing poly(1,6-heptadiyne)s for electro-optic application

We utilized the metathesis reaction to synthesize a new type of multifunctional polymer that contains a conjugated backbone and a second-order NLO chromophore as a pendant group. The 1,6-heptadiyne derivatives bearing NLO chromophores were easily polymerized by using a metathesis catalyst to give corresponding polymers with large optical nonlinearities. Molecular structural characterizations for the resulting polymers were achieved by 1H- and 13C-NMR, FTIR, and UV-visible spectroscopies. Soluble polymers were obtained up to 72 mol % of chromophore monomer portion in the copolymer. These amorphous polymers exhibited good film-forming abilities and thermal stability. The electro-optic coefficient, r33, of the poled polymer films was in the range of 0.5–10.1 pm/V, and the nonresonant values of the third-order NLO coefficient, χ(3) was found to be about 10−11 esu.

Measurement of the linear electrooptic effect in poled polymer thin films with coplanar electrodes

The linear electrooptic (EO) effect of poled polymer thin film is measured in the coplanar-electrode structure. The optical geometry of the coplanar-electrode thin-film setup is analysed theoretically to find a relationship between the linear optical parameters and the EO modulation intensity. EO modulated intensity is measured as a function of the direction of incident light polarization relative to the macroscopic optic axis, also as a function of optical bias determined by quarter-wave plate. Comparison of experimental measurements with the theoretical analysis shows good agreement.

Optical Bistability of an Injection-Locked Single-Mode Fabry-Perot Laser Diode and Its Application to an Optical Filp-Flop

We investigate optical bistability of an injection-locked single-mode Fabry-Perot laser diode. Normal and reversed optical bistability curves are observed from the injection-locked laser. And the inverse bistability is used to implement an all-optical flip-flop with the high on-off ratio of over 35 dB.

Nonlinear optical moiety-doped polymers with improved optical properties for photonic devices

An electro-optic polymer guest-host system has been constructed and demonstrated. The polymer host is a polyimide (PIQ2200) and the guest chromophores are dimethyl (or diethyl) amino alkyl sulfone stilbenes. The alkylated-NLO moieties as guest chromophores have been modified, yielding new alkylated-NLO moieties. The higher content of alkylated-NLO moieties, compared to unmodified NLO moieties, was doped into a polyimide host system due to the improved solubility of new alkylated-NLO moieties. To the 40 wt%, the new alkylated- NLO moiety has been completely dissolved in the preliminary experiment, leading to the increase of refractive index by 0.0016. These polyimide-based guest-host systems exhibited a significant improvement in the thermal stability at high temperatures exceeding 250 degree(s)C. The electro-optic coefficient reported in the present study is 13 pm/V for the 40 wt% DASS-6- doped polymer system poled at the 135 V/micrometers . However, further increase up to 25 pm/V may easily be achieved by increasing the amount of guest moieties and/or the intensity of the poling field. This work presents new materials for photonic switching devices with low operating voltage.

All-Optical Flip-Flop With Inverted Output Based On Optical Bistable Fabry-Perot Laser Diode

An all-optical flip-flop with inverted output is presented. The flip-flop is realized based on the optical instability of injection-locked single-mode Fabry-Perot laser diodes. The operation principle is explained and experimental results are presented in this paper. The flip-flop with separate optical set and reset inputs had an on-off contrast ratio of over 35 dB.

All-optical flip-flop memory based on injection locked Fabry-Perot laser diode

We demonstrate all-optical flip-flop operation based on the bistability injection locked FP-LD. The proposed all-optical flip-flop consists of a slave FP-LD and a specially designed single mode FP-LD.