David J. Olson

Electro-optic polymer modulators with 0.8 V half-wave voltage

We report the fabrication and test results for polymeric electro-optic modulators with a half-wave voltage of 0.8 V and a half-wave voltage-interaction length product of 2.2 V cm. These modulators employ an optical push–pull architecture and are made from poly(methylmethacrylate) with a high molecular hyperpolarizability polyene bridge-type chromophore. An electro-optic coefficient of 58 pm/V was obtained at a 1318 nm wavelength. The guest–host polymer system exhibited a thermal stability to 75 °C and a relatively stable nonlinearity at ambient conditions. The experimental results have demonstrated not only the sub-1 V half-wave voltage electro-optic polymer modulator but also the potential of polymeric electro-optic materials for photonic applications.

Push-pull poled polymer Mach-Zehnder modulators with a single microstrip line electrode

A push-pull structure has been realized for integrated Mach-Zehnder modulators based on a thermoset electrooptic polymer. The two modulator waveguide arms were poled in the opposite directions and covered by a single microstrip line electrode. This device structure can reduce the half-wave voltage by 50% without compromising wide-band frequency response. Efficient poling was achieved by using a compatible cladding material to lower the poling voltage, and by using a top cover piece and an inert gas to suppress air breakdown between the poling electrodes. Our fabricated devices exhibited the predicted 50% half-wave voltage reduction compared with non-push-pull devices fabricated on the same chip.

Double-end crosslinked electro-optic polymer modulators with high optical power handling capability

Integrated Mach–Zehnder and straight channel electro-optic modulators have been fabricated with a double-end crosslinked polymer containing amino-sulfone chromophores. The optical power handling capability of these modulators was tested at 1.32 μm wavelength and at input optical power levels compatible with commercial analog transmitters. At a cw peak intensity of 0.9 MW/cm2 inside the waveguide, the double-end crosslinked polymer waveguide modulators exhibited no observable increase in optical loss or degradation of nonlinearity during the experiment period. The poled polymer showed a long-term thermal stability of the electro-optic coefficient at 100 °C and photochemical stability at 633 nm wavelength.

Long-term stable direct current bias operation in electro-optic polymer modulators with an electrically compatible multilayer structure

The drift of the direct current (dc) quadrature bias voltage was monitored in electro-optic polymer Mach–Zehnder modulators for over 600 h. Traceable bias voltage was observed in polyurethane-Disperse Red 19 modulators. Electric field relaxation analysis showed that steady state dc and alternating current (ac) field distributions on polymer layers depended on the dielectric properties of the materials. The long-term bias stability of our modulators was originated from the low conductivity of the electro-optic polymer guiding layer. A concept of material electrical compatibility is introduced as a materials selection guideline for the fabrication of polymer modulators with the minimum bias drift.

Photoinduced molecular alignment relaxation in poled electro‐optic polymer thin films

The photoinduced nonlinearity decay in poled nonlinear optical polymer, polyurethane/Disperse Red 19, films was studied at wavelengths from 543 to 1320 nm. Electro‐optic gratings and waveguide modulators were used in measuring and monitoring material’s nonlinearity. No photoinduced nonlinearity decay was detected at near infrared wavelengths. However, the photoinduced relaxation rate increased approximately 5 orders of magnitude from 670 to 543 nm, as the excitation wavelength approaches π‐π* transition of the chromophores. The photoinduced chromophore reorientation was identified as the dominant relaxation mechanism.

Analysis of poling-induced polymer waveguide losses in push-pull Mach-Zehnder modulators

Poling induced losses of split-ground plane, push-pull polymeric electro-optic modulators have been investigated. Two sources of loss are found: loss due to the presence of oxygen and loss due to deforming the waveguide structure by large poling fields. Deformation is the most severe at the edges of the electrodes, where the electric field amplitude is largest. Experiments were done by poling waveguides with different architectures and poling in air and in an inert atmosphere. There is an apparent rapid increase in poling induced loss (to the 4th power) with poling voltage due to the presence of oxygen (up to 6.5 dB/cm for poling field of 170 V/micrometers ), whereas loss due to deformation increases linearly with poling voltage (up to 2.5 dB/cm). Oxygen-induced loss can be minimized by poling in inert atmosphere, while deformation induced loss can be minimized by optimizing device architecture.

Electro-optic modulator coupling loss improvement by tapering waveguides and fibers

Polymer based electro-optic (EO) modulators have the potential to provide low cost and lightweight alternative for antenna remoting and RF links because of their wide bandwidth (>100 GHz) and low drive voltage (V/sub /spl pi//<1 V) capabilities. Low noise figure and low power consumption systems require low insertion loss modulators. There are two major causes of loss in EO modulators: waveguide propagation loss (typically 1 dB/cm), and fiber-to-waveguide coupling loss. In this paper we investigate methods to minimize fiber-to-waveguide coupling loss which is mainly due to mode size mismatch. Pigtails using standard single mode fiber produce coupling loss on the order of 3 to 5 dB/connection. In order to improve mode size matching yet maintain low drive voltage, we incorporate waveguide and fibers tapers. Experimental results indicate improvement of up to 3 dB/connection (6 dB/device) using waveguide tapers, and up to 2 dB/connection (4 dB/device) using fiber tapers.

Microstrip line-slot ground electrode for high-speed optical push-pull polymer modulators

Optical push-pull poling and modulation can dramatically reduce the halfwave voltage of an electrooptic (EO) modulator [1–2].

Packaging and testing high-speed electro-optic polymer modulators

ABSTRACT Electrooptic polymer modulators demonstrate ultra-high frequency response to 1 1 0 GHz at chip level. To interconnect theseintegrated polymer waveguide devices to fiber-optic networks and to fully use their ultra-wide bandwidth capacity, apackaging technology that includes optical interfaces to standard fibers, electrode transitions to wideband coaxial cable connectors, and a stable mechanical enclosure is required. This paper summarizes TACANs efforts in high-speed electrooptic polymer modulator chip interfacing package. Fiber-to-waveguide pigtailing, mode mismatch loss reduction, andthe optimization of extinction ratio are important considerations for optical interfaces. Due to materials limitations and thelow driving voltage requirement, the waveguide mode size is often much smaller than that of a standard fiber which results inlarge mode mismatching loss. A fiber mode size conversion coupler has been developed to reduce the mode mismatchingloss. For microwave interfaces, the emphasis is on the electrode to coaxial cable connector transitions that include the use ofcommercial components and the test of connectorized circuits. The packaged electrooptic modulators were tested for theirperformance characteristics. Connector-to-connector frequency response of the electrode circuits, analog and digital signaltransmissions, long-term halfwave voltage stability, and DC bias stability have been tested using packaged electroopticmodulators.Keywords: Electrooptic modulators, electrooptic polymer, integrated optics, fiber mode size conversion coupler,optoelectronic device packaging

Polymer integrated modulators for photonic data link applications

Nonlinear optical polymers are gaining increasing research interests for high frequency photonic device applications, in particular, broadband modulators in commercial communication systems. the unique features of these materials allows the fabrication of integrated optical modulator chips that are compact, lightweight, and broadband at a low cost. With the advances in material synthesis and device fabrication, the application of polymer electro-optic modulators in commercial fiber-optic data links becomes increasingly realistic. We report our design, fabrication and packaging of polymeric integrated electro-optic Mach- Zehnder intensity modulators, as well as their test results including halfwave voltage, frequency response, optical insertion loss, on-off ratios, etc. We have inserted our packaged modulators into commercial fiber optical data links for applications tests. The standard tests procedures for the cable television industry are used and the results are compared to current commercial NTSC multi-channel cable television transmitter units with directly modulated lasers or LiNbO3 external modulators. The stability issues including thermal stability, photochemical stability and bias control stability have been investigated and will be discussed. The bottle-neck technical issues that may affect device design, fabrication, and applications will also be discussed.