Wenshen Wang

DEMONSTRATION OF 110 GHZ ELECTRO-OPTIC POLYMER MODULATORS

Electro-optic modulation up to 113 GHz has been demonstrated using traveling wave polymer modulators. The modulation signal was directly detected at 1.3 μm using a laser heterodyne system with an external-cavity tunable semiconductor laser. The device optical response variation, as a function of frequency over the whole W band, was within 3 dB. A well-matched coplanar probe was used to launch W band millimeter wave driving power into the microstrip line electrode on the device. Based upon these measurements, high speed electrodes with integrated millimeter wave transitions had been fabricated and tested.

Fabrication and characterization of high-speed polyurethane-disperse red 19 integrated electrooptic modulators for analog system applications

The fabrication and characterization of polymeric electrooptic modulators, made of a thermally crosslinkable polyurethane with Disperse Red 19 side chains, are summarized in this paper. Straight channel and Mach-Zehnder modulators have been fabricated, packaged and tested for the fiber-optic analog transmission system applications. Device performances including halfwave voltage, insertion loss, on-off ratio, and modulation frequency responses were measured. Long-term halfwave voltage stability, dc-bias voltage stability, and optical power handling capability at 1.3-/spl mu/m wavelength were investigated. A carrier-to-noise ratio of 53 dB and 80-channel television transmission have been demonstrated using the packaged polymer modulators.

Optical heterodyne detection of 60 GHz electro‐optic modulation from polymer waveguide modulators

An optical heterodyne technique has been used to demonstrate electro‐optic modulation up to 60 GHz, the highest reported to date, in polymer waveguide modulators. The frequency response of the device from 40 to 60 GHz was obtained by measuring the frequency down converted modulation signal with a low frequency photodetector. No rolling‐off was identifiable from the measured device response, indicating no fundamental material limitations in this frequency range for the polymer material which we used. Such an optical heterdyne system can be a powerful tool for modulator characterization at millimeter wave frequencies because of its high sensitivity and low frequency demands on photoreceivers.

Traveling wave electro‐optic phase modulator using cross‐linked nonlinear optical polymer

We report the fabrication and characterization of a high frequency traveling wave electro‐optic phase modulator made from thermally cross‐linked polyurethane‐Disperse Red 19 polymers. The device has been fabricated using a three layer structure with an integrated 50 Ω microstrip line circuit. The straight channel optical waveguides were defined laterally by standard photolithography and oxygen reactive ion etching. The measured half‐wave voltage was in good agreement with that extrapolated from the second harmonic generation measurements. Optical modulation was observed directly on a spectrum analyzer up to 18 GHz. Long‐term evaluation over an extensive length of time found no observable loss of performance.

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.

GHz bandwidth GaAs light-emitting diodes

Double-heterostructure GaAs/GaAlAs light-emitting diodes (LEDs) have been fabricated with the emitter regions beryllium doped to 2×1019 and 7×1019 cm−3. The 7×1019 cm−3 doped emitters have an internal quantum efficiency of 10% and an optical modulation bandwidth of 1.7 GHz. The steady-state optical output power versus the input current shows an external efficiency of 2.5 μW/mA. The 2×1019 cm−3 emitters have internal quantum efficiencies as high as 80%, but a reduced cutoff frequency. The external quantum efficiency reaches 10 μW/mA. These high-speed LEDs are produced by reducing the radiative lifetime to 100–250 ps without significantly degrading internal quantum efficiency. The current results on heavily beryllium-doped LEDs exhibit, to the best of our knowledge, the highest external efficiencies to date for such high doping and efficiencies close to that observed for lower-doped LEDs.

40-GHz polymer electrooptic phase modulators

A broad-band high-frequency traveling wave electrooptic phase modulator made from stable nonlinear optical polymers has been tested. Using a 1.319-/spl mu/m light source, single-mode operation was achieved with high-input optical power, resulting in improved modulation depths and signal-to-noise ratios. The high-frequency optical modulation was observed up to 40 GHz using external microwave mixers. Direct optical-heterodyne detection of electrooptic phase modulation has also been demonstrated with high sensitivity at 40 GHz. The devices were tested with 10/sup 5/ W/cm/sup 2/ power density for 21 hours, and have showed no observable decay in nonlinearity.<<ETX>>

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.

High-isolation photonic microwave mixer/link for wideband signal processing and transmission

We have proposed, analyzed, and demonstrated a high-isolation photonic microwave mixer using an integrated, dual-stage balanced-bridge Mach-Zehnder modulator. The proposed balanced photonic microwave mixer provides not only high isolation between radio frequency (RF) signal and local oscillator (LO) ports, but also excellent isolation between intermediate frequency (IF) and RF/LO ports without any filters. In this paper, the structure, principle, and operation settings are discussed in detail. Experimental results showed >60 dB electrical isolation between RF and LO ports and >50 dB isolation between IF and RF/LO ports in a demonstrative photonic microwave mixer. This device can extend the bandwidth of a modulator and have wide applications in RF photonic links where RF signal conversion and processing are required.