Pulse Characterization Technique Research Articles

Highly sensitive differential tomographic technique for real-time ultrashort pulse characterization

We demonstrate a highly sensitive real-time optical pulse characterization technique based on differential chronocyclic tomography. The spectral intensity and phase of the pulse under test are reconstructed analytically from two experimental traces measured simultaneously in the spectral domain. The high sensitivity and accuracy are made possible by lock-in detection of the differential spectra in the simplified chronocyclic tomography. An accuracy of approximately 0.04 rad of spectral phase recovery is achieved with a 10-Hz refresh rate and 10-microW sensitivity. We also show that the measurement technique is applicable to pulses as short as approximately 100 fs.

Highly sensitive direct characterization of femtosecond pulses by electro-optic spectral shearing interferometry.

We report what is to our knowledge the first experimental demonstration of spectral shearing interferometry by use of an electro-optic temporal phase modulator to generate the spectral shear. This approach achieves far better sensitivity than nonlinear optical pulse characterization techniques, including other versions of spectral shearing interferometry. Temporal phase modulation is conceptually simple and is implemented easily with telecommunication components. The technique is versatile, and a wide range of pulse durations can be measured with minimal changes in the setup. We demonstrate the accurate characterization of a 156-MHz train of 1540-nm pulses with durations ranging from 750 fs to more than 30 ps after various amounts of chirping, at average powers below 1 microW.

Measuring timing jitter with optical cross correlations

The use of optical cross correlations for characterizing timing jitter is investigated. Applications, limitations, and correspondence to radio frequency measurements are presented and clarified. The probability density function of the timing jitter of semiconductor mode-locked lasers is deconvolved from the cross-correlation measurements with the aid of pulse characterization techniques.

Accuracy criterion for ultrashort pulse characterization techniques: application to spectral phase interferometry for direct electric field reconstruction

We propose a procedure for the comparison of two ultrashort optical pulses based on the root-mean-square field error. This procedure supplies a practical criterion that allows one to test the accuracy of pulse characterization techniques. We apply this procedure to spectral phase interferometry for direct electric field reconstruction (SPIDER), a method that uses shearing interferometry in the frequency domain to measure ultrashort light pulses. Two novel reconstruction algorithms are described in detail, one based on the reconstruction of the spectral phase by concatenation, the other by integration. The range of validity of these algorithms and the influence of noise on the accuracy of the reconstruction are studied using the proposed criterion.

High-sensitivity pulse spectrogram measurement using two-photon absorption in a semiconductor at 15-�m wavelength

A femtosecond pulse characterization technique is developed using frequency-resolved optical gating based on the two-photon absorption in an InP crystal.The technique provides direct visual monitoring of pulse frequency chirping in the time-spectral domain for femtosecond pulses with a pulse energy as low as 3.8 pJ.Pulse chirping and pedestal wings of 10-GHz optical fiber solitons are characterized experimentally for the first time by this technique.

The criterion of pulse reconstruction quality based on Wigner representation

We propose a new criterion for the assessment of ultrashort pulse reconstruction quality. Our idea is based on the use of a two-dimensional Wigner representation of the electric field. This allows introducing a single measure to represent the quality of both phase and amplitude retrieval. The new criterion is employed to examine two contemporary pulse characterization techniques: FROG (Frequency Resolved Optical Gating) and SPIDER (Spectral Interferometry for Direct Electric-field Reconstruction). For SPIDER, the influence of reference pulse stretching on the quality of phase extraction is investigated. Next, we ascertain the limitations in the use of a Fabri-Perrot etalon in the SPIDER apparatus for producing delayed pulse replicas. For the FROG technique we examine the impact of the doubling crystal orientation on the quality of the amplitude-phase retrieval of sub-5-fs pulses. The introduced criterion is also applied to study the respective sensitivity of FROG and SPIDERto the limited phase-matching bandwidth of the non-linear medium and detector noise.

Generalized interferometric technique for ultrashort pulse characterization

A direct Young interferometric technique as a tool to determine ultrashort chirped Gaussian pulses characteristics is described: the intensity as a function of the order of the minima of the interference pattern depends on a function of the pulse characteristics. Effects related to modification of the functional forms of the shape and phase are computed, and the modulation in the intensity due to the finite size of the slits is deduced. A generalization of this technique, through measuring the minima intensity for an appropriately generated second harmonic pulse, permits the individual determination of the pulse width and chirp rate.