Luping Yu

Large stable photoinduced refractive index change in a nonlinear optical polyester polymer with disperse red side groups

The photoinduced refractive index change of polyester with disperse red side groups was studied at several different wavelengths. This material exhibits a large photoinduced index change (0.3 at 633 nm) and in addition when poled has a sizable second‐order nonlinear optical effect. This index change was monitored over 1000 h and long‐term stability was demonstrated. Based on these results, a method using only photomasks to define channel waveguides and other patterns in such polymers was suggested and experimentally demonstrated. This photoinduced index change may have wide applications in integrated optical systems when these or other similar polymers are involved.

Picosecond nonlinear optical response of three rugged polyquinoxaline‐based aromatic conjugated ladder‐polymer thin films

We have fabricated the first optical quality polymer films of aromatic ladder polymers having an unbroken conjugated backbone, and find third‐order nonlinear susceptibilities two orders of magnitude larger than CS2. The nonlinearities respond in less than 6 ps. Although we find their space symmetry to agree with that expected for a nonresonant electronic nonlinearity, the mechanism may well depend on lattice motion. The polymers are stable and rugged at room temperature. We also develop and analyze a simple form of degenerate four‐wave mixing for the measurements, finding expressions for the effects of uncertainties in the spatial and temporal pulse profiles.

Large photoinduced birefringence in an optically nonlinear polyester polymer

A nonlinear optical polyester with disperse red side groups exhibited a stable photoinduced birefringence, from 0.14 at 850 nm to 0.21 at 633 nm, after exposure to linearly polarized short‐wavelength visible or ultraviolet light. Thin‐film wave plates, birefringent diffraction gratings and waveguides were written in this polymer using photoexposure. Thin‐ film wave plates of <1 μm thickness showed ≳π/4 phase delay and good temporal stability. A 9:1 diffraction efficiency ratio of the two polarization eigenmodes was measured from thin birefringent gratings. This ratio is in good agreement with the theoretical prediction obtained using a simple three‐level model.

Thermosetting nonlinear optical polymer: Polyurethane with disperse red 19 side groups

A new thermosetting second‐order nonlinear optical polyurethane polymer with disperse red 19 pendant groups was studied by second‐harmonic generation and electro‐optic modulation methods. The polymer can be crosslinked by thermal curing during electric field poling. The electro‐optic coefficient r13 measured with a Mach–Zehnder interferometer ranged from 5 pm/V at 800 nm to 13 pm/V at 633 nm. The polymer crosslinked during poling showed no significant decay of the nonlinearity at room temperature for thousands of hours. A long‐term thermal stability of the dipole alignment at an elevated temperature, 90 °C, was demonstrated. The thermosetting polymer showed improved alignment stability under ultraviolet exposure.

New polymers with large and stable second-order nonlinear optical effects

Second order nonlinear optical (NLO) polymers containing NLO moieties with large optical nonlinearities and a cross-linkable unit have been synthesized using difunctionalized disperse red dye. The enhanced second order NLO coefficients, X exp (2) of 250 pm/v for the first polymer and 500 pm/v for the second, were obtained at 532 nm using the corona poling method. The introduction of flexible chains into the polymer backbone is found to cause a decrease in glass transition temperature and, hence, a decrease in the stability of the second-order NLO effects.

Development of materials with enhanced optical non-linearity by control of ultrastructure

Abstract Copolymers incorporating rigid electroactive moieties and flexible segments have been synthesized in an effort to develop non-linear optical materials which can be processed into optical quality films. A variety of coupling linkages have been employed including ether, ester, amide, imine and azo linkages. Among the most attractive materials examined in this survey are heteroaromatic ladder and tetraazaannulene copolymers which yield optical non-linearities (ratioed to optical loss), χ (3) α of 10 −12 −10 −13 esu cm −1 and have desirable auxiliary properties of high laser damage threshold and fast optical switching (t ps for three-ring copolymer). Electron donating and withdrawing groups are conveniently incorporated and these have been observed to influence optical non-linearity. The copolymer approach yields linear optical spectra characterized by sharp band edges thus optimizing the window of transparency. Finally, it is noted that this approach yields excellent control of solubility and solution viscosity necessary for spin casting in the fabrication of thin films of uniform thickness.

Synthesis and Characterization of Third Order Nonlinear Optical Materials

New polymers incorporating a variety of electroactive moeities with defined π-electron conjugation lengths have been synthesized and characterized by degenerate four wave mixing (DFWM) techniques. The χ (3) /α values for these materials varied from 10 −12 to 10 −13 esu cm. This work has identified several promising structures with nonlinear optical activity including organometallic and purely organic materials. The preparation of composite materials has also permitted the measurement of χ (3) /α as a function of the electroactive unit concentration.

Recent advances in the synthesis and characterization of nonlinear optical materials: second-order materials

Abstract A major problem in utilizing second-order organic materials for device applications is the requirement for the assembly of these chromophores into a stable, noncentrosymmetric lattice. For certain applications, such as frequency doubling, a periodic noncentrosymmetric lattice may be desirable. In this presentation, we discuss the synthesis of such organic polymeric lattices and evaluation of modulators and doublers fabricated from resulting materials. The general approach is to develop soluble, processible precursor polymers which can be transformed into stable noncentrosymmetric lattices by electric field poling and subsequent photoinduced or thermally induced solid state crosslinking reactions. Photo-processing is utilized to generate periodic noncentrosymmetric lattices for quasi-phase-matched second-harmonic generation.

Nonlinear optics and optOcal micropatterning in polymers with disperse red 19 sidegroups

The nonlinear and linear optical properties of a group of polymers containing DR19 are reviewed. The thermal setting polymers have demonstrated large NLO coefficient and long term poling stability. Dry processed micro-patterning of the index of refraction and the birefringence has been demonstrated with sub-micron resolution.

Bipolaronic-enhanced third-order nonlinearity in organic ladder polymers

Third order nonlinear optical properties of organic ladder copolymer (POL) system is studied using degenerate four-wave mixing with picosecond laser pulse. Both the real and imaginary part of the third order nonlinear susceptibility (3) were determined by a new phase conjugate interferometric method over the wavelength range of 532 - 720 nm. From the space symmetry and wavelength dependence of -) we attribute the observed nonlinearity to the nonlinear photoexcitation of bipolarion states in this ladder copolymer system.