M.M. Howerton

Fully packaged, broad-band LiNbO 3 modulator with low drive voltage

A low drive voltage of /spl sim/5 V at 40 GHz has been achieved in a fully packaged, broad-band LiNbO/sub 3/ modulator. The excellent response is attributed to nearly perfect velocity and impedance matching, along with very long electrodes (41 mm), low electrode losses, and minimal packaging effects. Very accurate frequency-dependent drive voltages are obtained by the use of independent sets of measurements.

Low drive voltage, broad-band LiNbO/sub 3/ modulators with and without etched ridges

Frequency dependent drive voltage is reported in velocity matched, packaged, Mach-Zehnder interferometers, made on Z-cut, Y-propagating LiNbO/sub 3/, with and without etched ridges. Drive voltages of /spl sim/7 V at 40 GHz are demonstrated, with the etched ridge device showing a 1/2-1 V advantage. Microwave modeling allowed the extraction of the effects of dispersion in material properties, occurring near the acoustic resonance, on bandwidth and drive voltage.

Performance and modeling of advanced Ti:LiNbO/sub 3/ digital optical switches

High-performance Y-branch digital optical switches realized in Ti:LiNbO/sub 3/ are presented. Their switching response functions have been optimized in terms of switch voltage and crosstalk ratio. The optimization is based on analyzing different types of waveguide shaping and switching arrangements using coupled mode theory and computer simulations. Excellent switching characteristics are achieved with devices exploiting a specially shaped waveguide branch in a dilated switch arrangement. Demonstrated performances include switching voltage as low as 9 V with crosstalk suppression better than 45 dB and fiber-to-fiber losses as low as 4 dB. Polarization independence with crosstalk suppression better than 40 dB over a 1520- to 1570-nm wavelength range is achieved for any applied switch voltage greater than 18 V. These optimized digital optical switches have further demonstrated the capability to reshape electrical input signals at switching rates of several hundred megahertz.

Broad-band reflection traveling-wave LiNbO 3 modulator

A velocity matched traveling-wave Mach-Zehnder interferometer (MZI) in LiNbO/sub 3/ operating in reflection, is reported and drive voltages are compared to those for single-pass devices of the same length. The device achieves double-pass operation by simultaneously reflecting the optical and RF waves, Broad-band operation to 20 GHz with drive voltages from 0.5 to 1 V (<0.5 GHz) to /spl sim/4.5 V (at 20 GHz) is observed with the reflection device. This performance is superior to that of the single-pass device, which has drive voltages of 2.1 V (dc) to /spl sim/4.5 V (at 20 GHz).

Linear 1×2 directional coupler for electromagnetic field detection

A 1×2 directional coupler which can be used as an integrated optical electromagnetic field detector is described. Modulators have been formed from titanium‐indiffused lithium niobate waveguides operating at the 1.3 μm wavelength. Linear dynamic ranges of 74.3 dB with 190 μW light and 76.3 dB with 760 μW light were observed for separate devices. Voltage sensitivity measurements are in good agreement with theoretical predictions. A 3.1 μV rms sensitivity was obtained for a device with a 10 mm electrode length.

Investigations on short-path-length high-speed optical modulators in LiNbO/sub 3/ with resonant-type electrodes

Short-path-length resonant-type high-speed optical modulators are presented. To reduce the active electrode length and enhance modulation efficiencies, different types of resonant electrode structures were investigated using computer simulation tools. Electrical power coupling into the resonators was optimized with a variety of power-feeding circuits. Their resulting optical and electrical behaviors are compared with measurements on modulators fabricated in Ti:LiNbO/sub 3/. As a result, resonant-type optical modulators are presented that achieve a low voltage-length product of 25 V mm at 30 GHz in the 1.55-/spl mu/m wavelength range. Fiber-to-fiber loss of a fully packaged phase modulator with an active optical path length as short as 0.7 mm was 2.3 dB.

Low-biased fiber-optic link for microwave downconversion

Downconversion of microwave signals using fiber-optic links is investigated while low-biasing one modulator in a cascaded pair. Enhancement of the downconverted signal and variation of intermodulation distortion terms as a function of phase bias are studied theoretically and experimentally. Distortion is significant at high local oscillator powers needed to minimize conversion loss.

SBS suppression using a depolarized source for high power fiber applications

A depolarized source for fiber applications is demonstrated using a traveling wave LiNbO/sub 3/ phase modulator. The source suppresses stimulated Brillouin scattering (SBS) in the fiber when operated at high drive frequencies, enabling more power to be delivered to a remote location. The threshold for SBS is examined in detail using optical powers up to 150 mW and drive frequencies up to 4 GHz. A resonant enhancement technique is demonstrated which reduces the drive power requirement for frequencies <2 GHz by up to 7.6 dB.

High-speed optical modulator in LiNbO/sub 3/ with cascaded resonant-type electrodes

A high-speed optical modulator with cascaded resonant-type electrodes is presented. To reduce the drive power and switch voltage V/sub /spl pi// and to maintain high-modulation efficiencies, resonant reduced-length electrode structures were cascaded and integrated on LiNbO/sub 3/. Electrical power coupling into the resonators was realized by a single-input source distributed with electrical power dividers and delay lines. As a result, an optical modulator with four resonant-type cascaded electrodes was fabricated and characterized. This device, with a total active-electrode length as short as 3.4 (4 /spl times/ 0.85) mm, achieved a switch efficiency V/sub /spl pi///spl middot/ L of 68 V /spl middot/ mm at 25 GHz at 1.55-/spl mu/m wavelength, resulting in a drive power 8.7 dB less than that required for a traveling wave modulator with the same active length.

Reflective digital optical switch (RDOS) for DWDM optical network applications

A novel, high-performance, reflective digital optical switch for use in dense wavelength-division-multiplexed (WDM) network applications is presented. Highly reliable Ti-LiNbO/sub 3/ devices show high-speed polarization-independent reflection modulation with 30-dB ON-OFF ratios over a wavelength range from 1520 to 1570 nm.