Fred Ludwig Heismann

Automatic compensation of first order polarization mode dispersion in a 10 Gb/s transmission system

We demonstrate a novel, adaptive optical polarization mode dispersion equalizer in a 10-Gb/s transmission experiment. The equalizer comprises a fast electrooptic polarization transformer an adjustable differential polarization delay line, and a simple electric distortion analyzer for automatic feedback control.

Analysis of a reset-free polarization controller for fast automatic polarization stabilization in fiber-optic transmission systems

We analyze the operation of a reset-free polarization controller comprising three endlessly rotatable wave plates: a first quarter-wave plate followed by a half-wave plate and a second quarter-wave plate, which is rotated synchronously with the first quarter-wave plate. We show that for any arbitrary angular offset between the two quarter-wave plates; the controller allows continuous, reset-free transformations from any varying general input state of polarization into any general output state. An integrated-optic realization of this scheme on z-propagation LiNbO/sub 3/ offers control speeds that well exceed the speed of natural polarization fluctuations in standard single-mode fibers, thus allowing fast automatic polarization stabilization in fiber-optic transmission systems. >

High-speed polarization scrambler with adjustable phase chirp

We report on the operation and performance of a novel electrooptic polarization scrambler that is capable of generating any desired combination of optical phase and polarization modulation. The scrambler comprises a dual-drive Mach-Zehnder-type intensity modulator on lithium niobate and an external microoptic polarization splitter which combines the two complementary outputs of the integrated-optic intensity modulator in orthogonal polarization states. The modulation indexes of the sinusoidal phase and polarization modulation in the output light can be varied independently of each other via the amplitudes and phases of the two drive voltages to the Mach-Zehnder modulator. The scrambler has a 3-dB modulation bandwidth of 14 GHz and operates in the 1.5-1.6-/spl mu/m wavelength range with an overall fiber-to-fiber insertion loss of less than 5 dB. At 5 GHz modulation frequency and electric drive powers between 390-2030 mW, we demonstrate phase-chirped and chirp-free depolarization with a residual degree of polarization of less than 0.02 and continuously variable phase modulation to 2.3-rad peak phase deviation.

Tunable acoustooptic reflection filters in LiNbO/sub 3/ without a Doppler shift

A proposal is presented for an acoustooptic filter in LiNbO/sub 3/ without the Doppler shift, which is normally present in acoustooptic filters and which is undesirable as an intracavity element. This tunable filter has a significantly wider tuning range than previously demonstrated electrooptic filters. A structure incorporating an interdigital acoustic transducer, polarization filter, and single-mode optical waveguide is shown. The design presented works by cascading two acoustooptic filters with an intermediate polarizer, where the Doppler shift experienced in the first filter is precisely compensated for in the second filter. Hence, the output light of the two cascaded acoustooptic filters is not shifted in frequency, thus making the device suitable for applications inside a laser cavity. The filter with intermediate polarizer can be integrated with a single-mode waveguide and requires only a single interdigital acoustic transducer. Crystal symmetry and acoustic power considerations are treated in detail. >

Comparison study of the average transfer matrix of first- and second-order PMD

This paper presents numerical simulations of the transfer matrix of polarization-mode dispersion (PMD) in long optical fibers, wherein the average frequency dependence of this matrix is calculated conditioned on various given values of the differential group delay that is introduced between signal components in the two principal states of polarization (PSPs) and the second-order PMD parameter that characterizes frequency-dependent cross coupling between the PSPs. The results are then compared with four popular models of first- and second-order PMDs (F&SO-PMD), and it is found that none of them describes the average Jones matrix of F&SO-PMD with acceptable accuracy over the entire range of PMD parameters and optical bandwidth of interest. The differences between the various models and the simulation results are particularly large when the frequency-dependent cross coupling is large.

Improved Numerical Model for the Average Transfer Matrix of First- and Second-Order PMD

An improved model for the average transfer matrix of first- and second-order polarization-mode dispersion (F&SO-PMD) in optical fibers is derived from numerical simulations of the frequency dependence of the differential phase shifts and cross coupling between signal components that are transmitted in two principal states of polarization (PSPs). The mean differential phase shifts and cross-coupling phases are calculated for various given values of the differential group delay (DGD) and the second-order PMD parameter that characterizes the coupling between PSPs. It is found that the mean differential phase delays are equal to the DGDs only over a narrow optical bandwidth, beyond which they decrease with increasing frequency offset and in some cases even reverse sign. Similarly, the mean cross-coupling phases increase less rapidly with frequency than assumed in other popular models and always approach an asymptotic value, at which half of the optical power is coupled from one PSP to the other. Moreover, it is shown that these mean differential phase shifts and cross-coupling phases define a transfer matrix for F&SO-PMD that nicely predicts the average eye-opening penalties in return-to-zero-formatted digital optical signals that are transmitted in one of the two PSPs. These predictions are particularly accurate when the average polarization-dependent chromatic dispersion (PCD) is included in the PSP phases. Additional simulations of F&SO-PMD compensation reveal that the signal impairments caused by PCD, on average, are substantially smaller than those introduced by the cross coupling between PSPs

High - Speed Polarization Scrambler with Adjustable Frequency Chirp

High-speed polarization scramblers can substantially improve the performance of optically-amplified transoceanic lightwave systems by depolarizing the launched optical information signal, thus eliminating anisotropic gain saturation (polarization hole burning) in the erbium-doped fiber amplifiers [1]–[3].