Christophe Dorrer

Characterization of ultrashort electromagnetic pulses

Ultrafast optics has undergone a revolution in the past two decades, driven by new methods of pulse generation, amplification, manipulation, and measurement. We review the advances made in the latter field over this period, indicating the general principles involved, how these have been implemented in various experimental approaches, and how the most popular methods encode the temporal electric field of a short optical pulse in the measured signal and extract the field from the data.

Simultaneous temporal characterization of telecommunication optical pulses and modulators by use of spectrograms.

We demonstrate a simple technique for simultaneous and complete characterization of the optical pulses and temporal modulators commonly used in telecommunication. The electric field of a pulse and the response of a modulator are obtained from the analysis of the two-dimensional spectrogram of the pulse gated by the modulator. The measurement sensitivity is greatly improved compared with the conventional nonlinear optical techniques. Trains of picosecond pulses as weak as 10(-17)J are accurately characterized with an electroabsorption modulator as the temporal gate. The time-resolved transmission and phase of the modulator are also presented.

RF spectrum analysis of optical signals using nonlinear optics

We study a technique to measure the radio-frequency (RF) spectrum of an optical signal based on nonlinear optics. The conventional approach, based on fast photodetection and analysis of the generated photocurrent via electronics means, is replaced by a nonlinear interaction of the source under test with a quasimonochromatic source followed by an optical spectrum measurement. Our technique has the advantage of an all-optical measurement that can provide a much larger bandwidth than electronic alternatives. The properties of this diagnostic, such as resolution and bandwidth, are studied. Typical applications to the monitoring of optical signals are presented.

Linear optical sampling

We demonstrate the measurement of waveforms and eye diagrams at high bit rates by optical sampling using coherent detection. By simultaneously recording two orthogonal quadratures of the interference between the data stream and a sampling pulse with two balanced detectors, we are able to cancel the phase sensitivity inherent to linear optics. As the device is based on linear optics and square-law low-speed photodetectors, its sensitivity is 1000 times better than nonlinear optical sampling techniques, which makes it attractive for optical signal characterization and monitoring. This new diagnostic tool was used to measure eye diagrams at 10, 40, and 80 Gb/s, and is projected to operate at 160 Gb/s and higher.

Measurement of eye diagrams and constellation diagrams of optical sources using linear optics and waveguide technology

We demonstrate the characterization of optical sources with high sensitivity, high temporal resolution, and phase sensitivity using linear optical sampling. Eye diagrams and constellation diagrams are reconstructed using the interference of the source under test with a train of sampling pulses. This concept is implemented using a waveguide optical hybrid, which splits and recombines the sources and adjusts the phase between the recombined signals to provide optimal detection. This diagnostic is used to characterize on-off keyed (OOK) waveforms at rates up to 640 Gb/s and various phase-shift keyed (PSK) signals at 10 and 40 Gb/s.

Interferometric technique for measuring broadband ultrashort pulses at the sampling limit

We present a new technique for measuring ultrashort optical pulses by use of spectral phase interferometry for direct electric-field reconstruction that is suitable for large bandwidth pulses. The method does not require generation of a replica of the pulse to be measured and encodes the spectral phase information in a spatial interference pattern. A major advantage of this method is that the spectral sampling saturates the Whittaker-Shannon bound. Moreover, the technique allows for the characterization of some types of space-time coupling. An experimental demonstration of the technique is presented.

High-speed measurements for optical telecommunication systems

The field of high-speed measurements for optical telecommunication systems is reviewed. An emphasis is placed on diagnostics evaluating the temporal electric field of light, i.e., broadly speaking, those that temporally resolve the shape of the optical wave in these systems. Sensitivity to the electric field can be obtained via sampling techniques operating directly in the time domain or via indirect approaches. A survey of characterization techniques used to measure statistical representations of data-encoded sources and complete representations of periodic sources is presented and complemented by the description of experimental implementations and results

High-contrast optical-parametric amplifier as a front end of high-power laser systems

A high-contrast preamplifier based on optical-parametric amplification with a short pump pulse is demonstrated. A gain larger than 10(5) and measurement-limited contrast higher than 10(11) are obtained over a large temporal range extending within less than 10 ps of the peak of the pulse, because of the high instantaneous parametric gain provided by a short pump pulse in a nonlinear crystal. The energy gain and high contrast of this preamplifier make it a good seed source for high-power laser systems.

Complete temporal characterization of short optical pulses by simplified chronocyclic tomography

A new self-referencing technique to characterize the temporal electric field of a short optical pulse is presented. The group delay of the pulse is directly obtained from two projections of the Wigner-Ville function after rotation of the pulse in chronocyclic space. Implementation of the technique requires only quadratic temporal phase modulation and two spectrum measurements, from which the electric field is directly and unambiguously reconstructed without any assumption. A device based on these principles is used to characterize the electric field of a 2-ps optical pulse.

Design and analysis of binary beam shapers using error diffusion

An error diffusion algorithm is used to design binary pixelated beam shapers. Beam shapers based on pixels with transmission equal either to 0 or 1 can be synthesized with this deterministic algorithm to provide continuous intensity shaping after Fourier filtering. The capabilities of these shapers are studied for high-power lasers. A particular emphasis is placed on the influence of the feature size on the performance of the designed shapers, and it is shown that the transmission degradation is highly predictable for this algorithm. Simulations demonstrating the possibility of precompensating for feature size when designing intensity shapers are presented.