A.S. Greenblatt

Performance and modeling of broadband LiNbO/sub 3/ traveling wave optical intensity modulators

The design, fabrication and characterization of a traveling wave Ti:LiNbO/sub 3/ Mach-Zehnder interferometric modulator are discussed. The dependence of the velocity match condition on electrode thickness and wall angle is demonstrated experimentally and with finite element calculations. A set of test electrode structures is fabricated to study electrical losses in the modulator electrode. Loss coefficients are assigned to different sections of the device, and dielectric and radiative losses are shown to play an important role at high frequencies. This information is used in conjunction with finite-element calculations to develop accurate models for both the electrical and optical responses. The frequency dependence of the half-wave voltage is measured and shown to be in good agreement with a model. >

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).

Depolarized source for fiber-optic applications

Two diode-pumped Nd:YAG lasers are combined with their polarization vectors at 90° to each other to create a depolarized source suitable for propagation over long lengths of ordinary, low-birefringence single-mode fiber without a change in the polarization state. The source is demonstrated with an integrated-optical Mach–Zehnder interferometer and provides a constant −3-dB intensity input to the required linear input polarization state.

Ultrahigh-sensitivity fiber-optic strain and temperature sensor

We report ultrahigh-sensitivity static strain sensing (noise equivalent strain </=1.5n rms) by two fiber etalon cavities made from silica and fluoride fibers. The anomalous thermo-optic coefficient of fluoride glass fibers allows for determination of thermal and laser drift. This sensor is also capable of simultaneous strain and temperature measurement, with errors in strain and temperature of 6.4% and 0.68%, respectively.

Phase tuning by laser ablation of LiNbO/sub 3/ interferometric modulators to optimum linearity

Fast, accurate phase bias trimming of LiNbO/sub 3/ interferometric modulators by excimer laser ablation is reported. Phase angle measurements and correction were performed in situ on a previously fabricated, packaged modulator. Any angle can be precisely adjusted to 90 degrees (maximum linearity). Single-laser-pulse exposures on one interferometer arm caused changes in angle of 0.8-8 degrees , depending on laser fluence and the depth of the material removed.<<ETX>>

Thermal stability of bias point of packaged linear modulators in lithium niobate

The thermal stability of the bias point of packaged, passively biased, X-cut LiNbO/sub 3/ interferometric modulators is described. Absolute stability is assessed and a comparison is made of stability before and after laser ablation adjustment used to tune the bias point to linear operation (90/spl deg/ phase angle). Ablation is shown to be successful in setting the bias angle to /spl plusmn/1/spl deg/ of the desired value. The angle remained stable to a total variation of <5/spl deg/ over -25-+42/spl deg/C both before and after ablation. All the observed angular changes with temperature were in the range 0.02-0.09 deg//spl deg/C. The effect of humidity in the package on modulator stability is characterized and then minimized for the actual devices.

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.