Alexander Bekker

Broadband second‐harmonic generation in SrxBa1−xNb2O6 by spread spectrum phase matching with controllable domain gratings

We have demonstrated, for the first time to our knowledge, second‐harmonic generation for a broad input wavelength range of 750–1064 nm in SrxBa1−xNb2O6 crystals, with a controllable spread spectrum of quasiphase matching. Second‐harmonic conversion efficiencies of up to ∼1% were observed. This was done without any temperature or angular tuning of the crystal. The phase matching was obtained by inducing alternating ferroelectric domains in the crystal in real time, using a novel fixing process which is based on screening. The broadband capability of the conversion is allowed by a spread in the range of the domain widths.

Dispersion-mode pulsed laser

A new self-consistency condition in pulsed lasers with strong intracavity dispersion imposes dispersion modes with specific cavity-length dependent pulse rates, utilizing pulse-train self-imaging properties of a temporal Talbot effect. We give an experimental demonstration of such a laser operation, using a long fiber cavity. We also demonstrate temporal Talbot imaging of a train of short pulses that propagate along large distances of dispersive fibers.

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.

Image and hologram fixing method with SrXBa 1− XNb 2 O 6 crystals

We demonstrate a new fixing method with Sr(x)Ba(1-x)Nb(2)O(6) crystals. This is done by inducing ferroelectric domains in the crystal in real time, by a screening mechanism. Images or their holograms can be recorded in small separate locations in the crystal. This crystal pixelization permits the recording of many pictures and their individual readout and erasure.

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.

OPTICALLY INDUCED DOMAIN WAVEGUIDES IN SRXBA1-XNB2O6 CRYSTALS

Optically induced refractive index patterns, which can be used for waveguides, were formed in SrxBa1−xNb2O6 crystals using an erasable fixing mechanism, based on domains formation by the screening effect. The sign and strength of the refractive index change of the fixed waveguides was controllable by an applied electric field. Fixed patterns are shown to allow the storage of many spatially multiplexed holograms.

Experimental demonstration of localization in the frequency domain of mode-locked lasers with dispersion

Mode-locked lasers with intracavity dispersion are experimentally shown to exhibit localization behavior in their frequency domain. The localization, with its typical exponential spectrum structure, is analogous to that which occurs for the quantum kicked rotor. The experimental demonstration of our optical kicked rotor is done with a long mode-locked dispersive fiber laser. The localization effect sets a basic limit on the spectrum bandwidth and the minimum pulse width in such lasers. It also provides a special experimental test bed for the study of optical kicked rotors and localization effects.

Many-Body Photonics

Researchers are using statistical mechanics to uncover thermodynamic-like properties in optical systems. This unique research direction could have far-reaching implications for photonics.

Cavity-resonance-activated wavelength selectable fiber and diode lasers

Summary form only given. Wavelength-controllable components, such as laser sources, which can operate at several selectable wavelengths, can be very attractive for many applications, especially for dynamic wavelength division multiplexing (WDM) networks in fiber optic communication. It is difficult to obtain fiber lasers and even diode laser-based systems with several wavelengths, which can be tuned and selected at high speeds. We report on wavelength selectable fiber and diode lasers, which can operate at each of several chosen wavelengths, with the possibility of switching between them at high speeds. The obtained selection time was /spl sim/5 ns for the diode laser system and /spl sim/150 ns for the fiber laser. The method is based on mode-locking or cavity-resonance-operated wavelength selection (CROWS). It is done by applying the suitable mode-locking frequency of a multiple-length fiber laser cavity, formed by multiple successive fiber grating reflectors, each with a different Bragg wavelength. It allows selection and high speed switching between these wavelengths. Such lasers can be useful for dynamic wavelength division multiplexing (WDM) in fiber optic networks.

Classical condensation of light pulses in a loss trap in a laser cavity

We present an experimental demonstration of condensation in a many-light-pulse system in a loss trap (loss well) in a one-dimensional laser cavity. The route to condensation is similar to Bose–Einstein condensation in a potential trap (potential well), but classical. The pulses, their loss levels, and the noise-induced power distribution take the role of “particles”, “energy” levels, and quantum-thermal population-statistics, respectively. The multipulse system is formed by high harmonic active mode-locking modulation and the trap by an envelope modulation. The experiment is done with an erbium-doped fiber laser. Condensation is shown to occur when the loss trap has near the lowest-loss pulse a power law dependence with exponent smaller than 1, as the theory predicts.