Poly(methyl methacrylate-co-9-anthrylmethyl methacrylate) (PMMA-AMA) LP-136 with various AMA contents was
prepared. The polymer was modified via Diels-Alder (D-A) type "click chemistry". In one approach, the side-chain was
grafted stepwise with maleimide-containing chromophore AJL-04 followed with N-phenylmaleimide (PI) to form LP-160. LP-160 was doped with 30 wt % of chromophore AJLS-102 to give electro-optic (EO) core polymer AJ-415. In the
other approach, all the pending AMA groups were modified with PI in one step to yield LP-165. Doping 33.7 wt %
AJLS-102 in LP-165 gives another core polymer AJ-416. The EO and material properties of both polymers were
systematically studied. Via careful selection of bottom and top cladding materials with proper optical and electrical
properties, Mach-Zehnder type modulators were fabricated based on both core materials. At the operational wavelength
of 1550 nm, modulator with AJ-415 core has half-wave driving voltage (Vπ) of 0.95 V and insertion loss of 19.1 dB,
while the best results from modulators with AJ-416 core are 0.75 V of Vπ and 17.1 dB of insertion loss. AJ-416 also has
the advantage over AJ-415 for building EO modulator with better processibility and long-term stability.
A major breakthrough in the area of organic electro-optic (EO) materials has been recently achieved. To go beyond the
oriented gas model limit for organic EO materials, new approaches of using nanoscale architecture control and
supramolecular self-assembly have been proved as a very effective method to create a new paradigm for materials with
very exciting properties. High-performance EO polymers were demonstrated by a facile and reliable Diels-Alder "click"
reaction for postfunctionalization and lattice hardening to improve EO activity and thermal stability. This type of "click"
chemistry paves the way to systematically study the relationship among EO activity, chromophore shape, and number
density of the chromophores. Reversible supramolecular interactions were also introduced to a new generation of EO
dendrimers and polymers to create self-assembled nano-objects, overcome strong intermolecular electrostatic
interaction, and improve their poling efficiency and stability. These self-organized EO materials were used as hosts in a
binary chromophore system to further improve chromophore number density and r33 value. With these novel approaches,
we succeeded in enlarging the full potential of organic NLO materials by a factor of 3~5 and developing a variety of
nano-structured organic EO materials with ultrahigh r33 values (>300 pm/V at the wavelengths of 1310 and 1550 nm,
more than 10 times that of LiNbO3) and excellent auxiliary property, such as thermal stability and optical transparency.
The success of these material developments has inspired the exploration of new device concepts to take full advantage of
organic EO materials with ultrahigh r33 values.
A novel broadband E-field sensor based on electro-optic polymer micro-ring resonator directly coupled to the core of optical fiber is proposed and demonstrated. A flat is made on the side of the optical fiber by polishing and an electro-optic polymer waveguide in the shape of a ring is placed on the polished flat. One side of the ring is directly above the core of the fiber and light is evanescently coupled between the fiber and the micro-ring. External electric fields change the index of refraction of the ring resonator and therefore its resonant wavelengths. The sensor is all dielectric without metal layers to distort the measured E-field. The resonance structure allows the sensor to potentially have much higher sensitivity than other electro-optic sensors based on interferometry or polarization modulation. Since electro-optic polymers have higher electro-optic coefficients, lower dielectric constants and faster electro-optic responses than inorganic crystals, higher sensitivity, lower invasiveness and higher bandwidth of E-field sensing can be expected. The sensor with EO polymer micro-ring directly coupled to side-polished fiber eliminates unreliable and possibly lossy fiber to waveguide butt coupling as well as the high propagation loss which comes from the long straight EO polymer waveguides. Unlike devices based on waveguide technology, a supporting substrate is not necessary in this device. This leads to sensors of small size and low disturbance to the measured electric field. In the proof-of-concept experiment, a sensitivity of 100 mV/m has been achieved at frequencies up to 550 MHz (limited by the measurement system) using
AJLS103 electro-optic polymer.
A series of side-chain electrooptic (E-O) polymers have been prepared by Diels-Alder reaction in a solid state and characterized for their nonlinear optical properties. A synthesized chromophore were easily attached to a pendent anthracenyl moiety functionalized on the poly(methylmethacrylate-co-anthrylmethylmethacrylate) thermally in the bulk films during the poling process without compromising E-O performances. We have also controlled a chromophore concentration to determine its critical loading density at which chromophore-chromophore electrostatic interaction occurs in the polymer matrix. The highest E-O coefficient was 110 pm/V for the 34 wt% of the doped chromophore in the polymer at the wavelength of 1.3 μm. A high loading density of chromophore was obtained without observing a severe phase separation in the polymer matrix by an AFM morphology study. This novel approach provides to demonstrate a strategy for developing highly efficient E-O materials with the full potential of a chromophore.