Virtual cavity in distributed Bragg reflectors.

We show theoretically and experimentally that distributed Bragg reflector (DBR) supports a surface electromagnetic wave exhibiting evanescent decay in the air and oscillatory decay in the DBR. The wave exists in TM polarization only. The field extension in the air may reach several wavelengths of light.

Anti-waveguiding vertical-cavity surface-emitting laser at 850 nm: From concept to advances in high-speed data transmission.

Oxide-confined vertical cavity surface emitting lasers (VCSELs) with anti-waveguiding AlAs-rich core presently attract a lot of attention. Anti-waveguiding cavity enables the maximum possible optical confinement of the VCSEL mode ("λ/2 design"), increases its oscillator strength and reduces dramatically the optical power accumulated in the VCSEL mesa regions outside the aperture. VCSEL designs are suggested that favor single transverse mode operation.

Astigmatism-free high-brightness 1060 nm edge-emitting lasers with narrow circular beam profile.

1060 nm high-brightness vertical broad-area edge-emitting lasers providing anastigmatic high optical power into a narrow circular beam profile are demonstrated. Ridge-waveguide (RW) lasers yield record 2.2 W single-transverse mode power in the 1060-nm wavelength range under continuous-wave (cw) operation at room temperature with excellent beam quality factor M ≤ 2.

Frequency-shifted light storage via stimulated Brillouin scattering in optical fibers.

A method for storing optical data pulse sequences, frequency shifted with respect to the original data pulse frequency, is theoretically described and experimentally demonstrated. Data pulses are converted into long-living acoustic waves via stimulated Brillouin scattering in optical fiber by counterpropagating write pulses of one frequency, and later they are retrieved by read pulses at a different frequency giving rise to frequency-shifted stored pulses. The shifted frequency is governed by the phase-matching condition between the read pulse and the acoustic wave, which can be satisfied using birefringent fibers.

Toward the subdiffraction focusing limit of optical superresolution.

A superresolving three-zone plate is applied to a Fresnel diffractive lens. It is shown that for radial incident polarization this combination produces a focal spot approaching superresolution allowed subdiffractive limit of 0.36lambda/NA for focusing.

Coherent-absorber mode locking of solid-state lasers.

We study solid-state laser mode locking in the self-induced transparency regime of an intracavity absorber. Depending on the absorber dephasing, pulse energy, and resonator dispersion, we find stable coherent 2pi -pulse operation, pulse splitting, oscillatory pulse shapes, and smooth transition to incoherent saturable-absorber mode locking.

Supercontinuum generation and pulse compression in hollow waveguides.

We present a theoretical study of temporal and spectral characteristics and pulse compression in hollow waveguides, using a global approach to dispersion without application of the slowly varying envelope approximation. A novel ultrawide self-phase modulation-induced spectral-broadening regime with spectra covering almost 3 octaves is predicted for a pressure at which the group-velocity dispersion parameter is small and anomalous. Compression to subcycle pulses by an appropriate broadband modulator and pulse shortening without chirp control by a spectral filter are studied.

Pulse compression without chirp control and frequency detuning by high-order coherent Raman scattering in impulsively excited media.

It is shown that phase-locked pulses as short as 3 fs can be generated by coherent scattering in impulsively excited Raman media without the necessity of external phase control. The underlying mechanism, temporal characteristics, spectra, phase relations, physical limitations owing to competition processes, and precompensation of dispersion by the hollow waveguide window are studied analytically and numerically without the use of the slowly varying envelope approximation and with a global approach to dispersion. Additionally, the large frequency shifts in both the Stokes and anti-Stokes directions of as much as half the carrier frequency raise the possibility of generating widely tunable ultrashort pulses.

Chirped-pulse stimulated Raman scattering in barium nitrate with subsequent recompression.

We report a 30% internal conversion efficiency for the first Stokes pulse in stimulated Raman scattering of femtosecond pulses that are dispersively stretched to 250 ps, obtained by use of an all-solid-state laser system. A transfer of the linear chirp is observed, leading to a Raman pulse duration of 190 fs after recompression. Compressed pulse energies of 80 muJ at a repetition rate of 1 kHz are obtained, with a potential for an easy increase to more than 150 muJ.

Third-order dispersion impact on mode-locking regimes of Yb-doped fiber laser with photonic bandgap fiber for dispersion compensation.

Novel features in stretched-pulse and similariton mode-locked regimes of Yb-doped fiber laser with photonic bandgap fiber used for dispersion compensation are found by means of numerical simulations. We show that the mode-locked pulse may become shorter with increasing third-order dispersion. Analytical estimations explain observed behavior through resonant interaction of the main pulse with dispersive waves involving both resonant sidebands and zero-group-velocity dispersion waves.

Slow and fast light via SBS in optical fibers for short pulses and broadband pump.

Slow-light effect via stimulated Brillouin scattering (SBS) in single-mode optical fibers was considered for short probe pulses of nanosecond duration relevant to Gb/s data streams. Unlike recent estimations of delay versus pump based on steady-state small-signal approximation we have used numerical solution of three-wave equations describing SBS for a realistic fiber length. Both regimes of small signal and pump depletion (gain saturation) were considered.

Theoretical study of the effect of slow light on BOTDA spatial resolution.

Due to the resonant nature of Brillouin scattering, delay occurs while pulse is propagating in an optical fiber. This effect influences the location accuracy of distributed Brillouin sensors. The maximum delay in sensing fibers depends on length, position, pump and Stokes powers.

Ultra-short pulse operation of all-optical fiber passively mode-locked ytterbium laser.

The generation regimes of an all-fiber passively mode-locked ytterbium laser with intra-cavity photonic crystal fiber have been studied with the aim to provide recipes for obtaining chirp-free sub-picosecond pulses directly from the cavity. Small-beam area photonic-crystal fiber is used for dispersion compensation of the intra-cavity normal dispersion of b-doped and single-mode fibers as well as for spectrum expanding due to enhanced nonlinearity. Regions of the gain and fiber parameters near the generation threshold were found in both cases of normal and anomalous net intra-cavity dispersion, which provide a stable generation of ultra-short sub-picosecond pulses directly from the cavity.

Influence of transient phonon relaxation on the Brillouin loss spectrum of nanosecond pulses.

For pump-probe stimulated Brillouin scattering with a probe pulse of a few nanoseconds duration and with a finite DC level, the acoustic wave relaxation time varies with the pump power and the DC level. For a pump power of 1-6 mW, the acoustic wave relaxation changes from approximately 9 to 90 ns for polarization-maintaining fiber at a temperature of -40 degrees C for a 2 ns pulse width. When the pulse DC ratio of the probe varies from 10 to 20 dB, the acoustic relaxation time changes from 24 to 45 ns for single-mode fiber at 25 degrees C.

How to obtain high spectral resolution of SBS-based distributed sensing by using nanosecond pulses.

The ultimate spectral and spatial resolutions of distributed sensing based on stimulated Brillouin scattering (SBS) in optical fibers is shown for several-nanosecond Stokes pulses. Precise measurements of the local Brillouin frequency, with a spectral resolution close to the natural linewidth and, simultaneously, the spatial resolution of the pulse length are provided by AC detection of the output pump in the case of a finite cw component (base) of the Stokes pulse. Simulation examples of SBS-based sensing for fibers containing sections with different Brillouin frequencies are presented, demonstrating the high resolution of the sensing.

Enhancement of stimulated Brillouin scattering of higher-order acoustic modes in single-mode optical fiber.

Solving the elastic wave equation exactly for a GeO2-doped silica fiber with a steplike distribution of the longitudinal and shear velocities and density, we have obtained the dispersion, attenuation, and fields of the leaky acoustic modes supported by the fiber. We have developed a model for stimulated Brillouin scattering of these modes in a pump-probe configuration and provided their Brillouin gains and frequencies for an extended range of core sizes and GeO2 doping. Parameter ranges close to cutoff of the acoustic modes and pump depletion enhance the ratio of higher-order peaks to the main peak in the Brillouin spectrum and are suitable for simultaneous strain-temperature sensing.

Compression of single-cycle mid-infrared pulses by Raman-active molecular modulators.

We show theoretically how high-order stimulated Raman scattering in the impulsive pump-probe regime can be used for generation of single mid-infrared (MIR) single-cycle pulses. The propagation of MIR probe pulses in a hollow waveguide filled with a Raman-excited gaseous medium, with a probe delay in the maximum of the molecular oscillations, results in spectral broadening covering almost 2 octaves. The spectral phases of this broadening can be compensated for by use of an output glass window with anomalous dispersion in the MIR.

Phase relations, quasicontinuous spectra and subfemtosecond pulses in high-order stimulated raman scattering with short-pulse excitation.

High-order stimulated Raman scattering for pumping by ps and sub-ps pulses is studied in the frame of a time-domain approach without the slowly varying envelope approximation. Formation of pulse trains with sub-fs durations in the ps-pump regime is demonstrated using external phase compensation. For sub-ps excitation a novel broadening mechanism of Raman lines is predicted that leads to a quasicontinuous spectrum and permits one to generate single sub-fs pulses.

Higher-order phase dispersion in femtosecond Kerr-lens mode-locked solid-state lasers: sideband generation and pulse splitting.

The influence of higher-order phase dispersion on the pulse generation in femtosecond Kerr-lens mode-locked lasers for small net group-velocity dispersion is numerically analyzed. Depending on the third- and the fourth-order dispersion, we obtain the formation of spectral sidebands phase matched with the principal spectrum. At a relatively large amount of fourth-order dispersion pulse splitting arises, which leads to a quasi-steady-state multipulse operation regime of the Kerr-lens mode-locked laser.