Vladimir Smulakovsky

Complete characterization of optical pulses by real-time spectral interferometry

We demonstrate a simple method for complete characterization (of amplitudes and phases) of short optical pulses, using only a dispersive delay line and an oscilloscope. The technique is based on using a dispersive delay line to stretch the pulses and recording the temporal interference of two delayed replicas of the pulse train. Then, by transforming the time domain interference measurements to spectral interferometry, the spectral intensity and phase of the input pulses are reconstructed, using a Fourier-transform algorithm. In the experimental demonstration, mode-locked fiber laser pulses with durations of approximately 1 ps were characterized with a conventional fast photodetector and an oscilloscope.

Compression of periodic light pulses using all-optical repetition rate multiplication

We propose a novel method for compression of periodic optical pulses based on all-optical repetition rate multiplication of pulses without requiring propagation in a dispersive delay line. The compression principle is explained using the temporal Talbot effect. The proposed method is demonstrated experimentally with the generation of ∼20 ps pulses from cw radiation of a laser diode. The repetition rate multiplication is performed with fiber Bragg gratings. The proposed method simultaneously implements two important requirements of many fields, for example, of optical communications: pulse compression and pulse repetition rate multiplication.

Experimental study of the stochastic nature of the pulsation self-starting process in passive mode locking

We present an experimental study of the probabilistic nature of pulsation self-starting in passively mode-locked lasers. It is a Poissonian process that results from a noise-activated switching barrier. The switching rate from cw operation to pulsation when the laser pump level is turned on has an exponential dependence that is inversely proportional to the square of the laser power.

Amplified-spontaneous-emission pumped raman fiber laser

We present a low-threshold Raman fiber laser at 1670nm, pumped for the first time by the ASE of an EDFA. The output was 340mW, 34% of the pump power, and the threshold (with another laser) 160mW.

Noise-mediated Casimir-like pulse interaction mechanism in lasers

Strongly pumped mode-locked lasers often form pulse bunches. Although several mechanisms of pulse interaction are known, none yields the experimentally observed long-range attraction. Here we demonstrate theoretically and experimentally a new pulse interaction mechanism mediated by the continuum noise floor that is a universal feature in multipulse passively mode-locked lasers. Long-range attraction is facilitated by the depletion of the gain by the pulses, leading to an inhomogeneous noise floor that biases the timing jitter of the pulses and produces an effective interpulse potential with stable pulse bunch configurations. The pulses attract by suppressing electromagnetic fluctuations, as do conductors in the Casimir effect of quantum electrodynamics. This enables manipulation and design of multipulse waveforms to ultimately make them useful for application of mode-locked lasers.

Experimental demonstration of nonlinear pulse propagation in a fiber Bragg grating written in a fiber amplifier

We study experimentally nonlinear propagation of sub-nanosecond optical pulses in a fiber Bragg grating written in a Ytterbium-doped fiber amplifier (YD-FBG). The magnitude and the sign of group velocity dispersion (GVD) in YD-FBG can be controlled by adjusting the fiber tension. In the case of anomalous GVD, pulse breakup was observed due to modulation instability. However, for the same input pulse power in the normal GVD regime, the output pulse duration was increased, and pulse breakup was not observed. The deterioration of pulse spectrum due to Raman and four-wave mixing effect was also reduced in the normal GVD regime. Since GVD in YD-FBG is six orders of magnitude higher than in standard fibers, the advantages of normal GVD in fiber amplifiers that were demonstrated in previous works for femtosecond and picosecond pulses can be exploited for amplifying sub-nanosecond pulses. The experimental results are in good agreement with numerical simulations. We have also demonstrated a gain coefficient enhancement by a factor of 1.7 due to slow-light propagation in the YD-FBG.

Measurement of resonant and nonresonant induced refractive index changes in Yb-doped fiber grating amplifier

We have measured the refractive index change (RIC) induced in a fiber Bragg grating (FBG) written in a Yb-doped fiber amplifier (YB-FBG) because of the amplifier pumping. The measurement was performed by exploiting the high sensitivity of the YD-FBG transmission to the RIC. We have separated between electronic and thermal contributions to the RIC based on the difference between the time-scales of the two effects. Because of high UV-induced loss in FBGs, the thermal contribution to the RIC is increased, in comparison with previously published work, where no grating was written in the fiber amplifier. The measurement method allows us to find the sign of each contribution to the RIC, and it requires only a few centimeters of fiber. Optimal pumping scheme for reducing the RIC in a YB-FBG is studied.

Casimir-Like Light Pulse Interaction Induced by Amplified Spontaneous Noise in Laser Cavities

We present a new mechanism for light pulse interaction in mode-locked lasers induced by amplified spontaneous noise. It is a time-light domain Casimir-like mechanism. We show experimental evidence for this unique effect.

Long Range Soliton Interaction Related to Sidebands Generation in Mode-Locked lasers

Soliton formation in passively mode-locked lasers is often accompanied with spectral sidebands. We find how the exact spectral shape of the sidebands affects the long range interaction between pulses in a fiber laser cavity.

Pulse-Quasi-Crystal Formation in Mode-Locked Lasers

Many-pulse formation in passively mode-locked fiber lasers is shown to exhibit self pulse crystallization phenomena. We present experimental demonstrations and theoretical thermodynamic-like modeling.