Information throughput of photorefractive spatial solitons in the telecommunication range.

Photorefractive spatial solitons are attractive elements because they can be used as controllable optical interconnectors for all-optical devices. To our knowledge, until now their properties were investigated in terms of energy transportation. We suggest considering photorefractive spatial solitons as optically induced information channels. The experimental technique to measure the information throughput of photorefractive spatial solitons in accordance with Shannon's definition was developed and demonstrated by us. We experimentally demonstrated that in the wavelength range of 1520-1630 nm it can be estimated as large as approximately 90 Tbits/s. We also experimentally demonstrate a measurement of the group-velocity dispersion and show the limitation of the pulse transfer rate of the induced waveguides to approximately 6.2 THz.

Single-cavity, multiline laser system with large coherence length.

We present a new approach of generating the several wavelengths required for color holography with coherence lengths in the range of several meters. Our proposed laser system consists of an argon-ion laser, which is equipped with broadband optics. Its main lasing lines include 457, 488, and 514 nm. Sufficient coherence length is achieved by means of an intracavity etalon. We report single-frequency operation at several competing wavelengths and the successful recording of multicolor holograms with the described laser system.

Generation of 20-fs pulses by a prismless Cr(4+):YAG laser.

Ultrafast optical pulses shorter than 20 fs with 400-mW average power at a 110-MHz repetition rate have been generated by a Cr(4+):YAG laser with only double-chirped mirrors for dispersion compensation. The corresponding pulse spectrum has a peak intensity at 1450 nm and extends from 1310 to 1500 nm full width at half-maximum (FWHM). These pulses, which are believed to be the shortest generated to date from a Cr(4+):YAG laser, are only four optical cycles within the FWHM intensity width.

Integrated optical pickup system for axial dual focus.

We propose an optical pickup that acquires data from both layers of a dual-layer digital versatile disk simultaneously. An adaptive optical element that uses liquid crystals creates two axial foci separated by a spacing of 55 mum, which is the distance between the two layers. The spacing between the foci can be varied by the adaptive element. The separation of the reflected light into TE and TM polarized light, corresponding to each of the layers, is made by dielectric gratings that are characterized by high aspect ratios. Electron-beam lithography and reactive ion etching techniques were used to produce the submicrometer structures. All fabricated elements were assembled in a pickup system, whose properties were measured.

All-solid-state Cr:forsterite laser generating 14-fs pulses at 1.3 mum.

We report the generation of 14-fs pulses at 1.3mum with 80-mW average power at 100-MHz repetition rate by an all-solid-state Kerr-lens mode-locked Cr:forsterite laser. The laser spectrum covers wavelengths of 1230-1580 nm, with a FWHM of 250 nm. Since 1.3-mum wavelengths are close to the zero dispersion wavelength of Cr:forsterite, higher-order dispersion is the main factor limiting pulse durations. We use specially designed and fabricated double-chirped mirrors in combination with high-index PBH71 prisms to compensate for the intracavity dispersion over almost 300 nm.

Generation of 5-fs pulses and octave-spanning spectra directly from a Ti:sapphire laser.

Spectra extending from 600 to 1200 nm have been generated from a Kerr-lens mode-locked Ti:sapphire laser producing 5-fs pulses. Specially designed double-chirped mirror pairs provide broadband controlled dispersion, and a second intracavity focus in a glass plate provides additional spectral broadening. These spectra are to our knowledge the broadest ever generated directly from a laser oscillator.

Pulse compression over a 170-THz bandwidth in the visible by use of only chirped mirrors.

We report on double-chirped mirrors with custom-tailored dispersion characteristics over a bandwidth of 170 THz in the visible. The mirrors are used in a prismless compressor for a noncollinear optical parametric amplifier in the visible. The compressed pulses, characterized for the what is believed to be first time by use of the spectral phase interferometry for direct electric field reconstruction technique, display a nearly flat phase from 510 to 710 nm and have a duration of 5.7 fs.

Experimental control of unstable patterns and elimination of spatiotemporal disorder in nonlinear optics

A method based on Fourier filtered control signals for stabilization of unstable patterns in a nonlinear optical single feedback system is experimentally realized. The successful stabilization of the homogeneous solution and different stationary periodic patterns far above the pattern forming threshold as well as the elimination of spatiotemporal disorder above a secondary instability has been achieved. The temporal evolution of the control signal verifies the underlying philosophy of noninvasive control that changes only the linear stability of the systems' solution and not the solution itself.

Dynamics of formation and interaction of photorefractive screening solitons.

An experimental and numerical investigation of the dynamical, time-dependent effects accompanying the formation and interaction of two-dimensional spatial screening solitons in a photorefractive strontium barium niobate crystal is performed. These effects include initial diffraction, collapse to the soliton shape, the oscillation of beam diameters, beam bending, and the rotation, twisting, and turning of soliton pairs. The dynamics of complex spiraling of two incoherent solitons is considered in more detail.

Sub-two-cycle pulses from a Kerr-lens mode-locked Ti:sapphire laser.

Pulses shorter than two optical cycles with bandwidths in excess of 400 nm have been generated from a Kerr-lens mode-locked Ti:sapphire laser with a repetition rate of 90 MHz and an average power of 200 mW. Low-dispersion prisms and double-chirped mirrors provide broadband controlled dispersion and high reflectivity. These pulse durations are to our knowledge the shortest ever generated directly from a laser oscillator.

Semiconductor saturable-absorber mirror assisted Kerr-lens mode-locked Ti:sapphire laser producing pulses in the two-cycle regime.

Pulses of sub-6-fs duration have been obtained from a Kerr-lens mode-locked Ti:sapphire laser at a repetition rate of 100 MHz and an average power of 300 mW. Fitting an ideal sech(2) to the autocorrelation data yields a 4.8-fs pulse duration, whereas reconstruction of the pulse amplitude profile gives 5.8 fs. The pulse spectrum covers wavelengths from above 950 nm to below 630 nm, extending into the yellow beyond the gain bandwidth of Ti:sapphire. This improvement in bandwidth has been made possible by three key ingredients: carefully designed spectral shaping of the output coupling, better suppression of the dispersion oscillation of the double-chirped mirrors, and a novel broadband semiconductor saturable-absorber mirror.

Analytic phase-factor equations for Talbot array illuminations.

Under specific circumstances the fractional Talbot effect can be described by simplified equations. We have obtained simplified analytic phase-factor equations to describe the relation between the pure-phase factors and their fractional Talbot distances behind a binary amplitude grating with an opening ratio of (1/M). We explain how these simple equations are obtained from the regularly rearranged neighboring phase differences. We point out that any intensity distribution with an irreducible opening ratio (M(N)/M) (M(N) < M, where M(N) and M are positive integers) generated by such an amplitude grating can be described by similar phase-factor equations. It is interesting to note that an amplitude grating with additional arbitrary phase modulation can also generate pure-phase distributions at the fractional Talbot distance. We have applied these analytic phase-factor equations to neighboring (0, pi) phase-modulated amplitude gratings and have analytically derived a new set of simple phase-factor equations for Talbot array illumination in this case. Experimental verification of our theoretical results is given.

Transient deformation measurement with electronic speckle pattern interferometry by use of a holographic optical element for spatial phase stepping.

We have used a computer-generated holographic optical element (HOE) with electronic speckle pattern interferometry to calculate the interference phase corresponding to the deformation of a test object from a single TV frame. The HOE is a modified crossed phase grating that introduces a known phase change between the +/-1 diffracted orders, without being translated. The progressive propagation of transient mechanical waves was measured with an rms precision of 2pi/30.

Annihilation of photorefractive solitons.

We investigate experimentally the interaction of two-dimensional solitary beams in photorefractive strontium barium niobate crystal. We show that simultaneous collision of many solitons can result in complete annihilation of some of them. This effect depends on the relative phases of the solitons and may be useful for application in the formation of multiport waveguide junctions.

Speckle reduction in laser projection systems by diffractive optical elements.

In laser projection systems the observer in the far field of the image points on the screen will recognize serious speckle noise. There are many methods to reduce or eliminate speckles in the near field by reducing or eliminating temporal or spatial coherence of the laser. But for the far field it is hardly possible to change the coherence properties of laser sources so that speckles will disappear. We propose a new method for eliminating speckles in the far field by using a diffractive optical element. The intensity modulation depth in the far-field speckle pattern can be reduced to a few percent while good beam quality is preserved.

Self-starting 6.5-fs pulses from a Ti:sapphire laser.

We demonstrate self-starting 6.5-fs pulses from a Kerr-lens mode-locked Ti:sapphire laser with 200-mW average output power at a pulse repetition rate of ~86 M Hz. This is to our knowledge the shortest pulse ever generated directly from a laser. For dispersion compensation we used a prism pair in combination with double-chirped mirrors, which balances the higher-order dispersion of the prism pair and therefore flattens the average total group-delay dispersion in the laser cavity. For self-starting mode locking we used a broadband semiconductor saturable-absorber mirror.

Design and fabrication of double-chirped mirrors.

We present an analytic design method for the reproducible fabrication of double-chirped mirrors to achieve simultaneously a high reflectivity and dispersion compensation over an extended bandwidth compared with those of standard quarter-wave Bragg mirrors. The mirrors are fabricated by ion beam sputtering. Use of these mirrors in a Ti:sapphire laser leads to 6.5-fs pulses directly out of the laser. The method can also be applied to the design of chirped-fiber gratings and general optical filters.

Enhancing the sensitivity of an adaptive holographic interferometer using non-Bragg diffraction orders.

The signal-to-noise ratio of the output of an adaptive holographic interferometer (AHI) based on a Bi(12)TiO(20) crystal is investigated. We show experimentally that the sensitivity of an AHI using the non-Bragg orders of diffraction in a thin photorefractive material is more than an order of magnitude greater than that of an AHI employing two-wave mixing in photorefractive volume holograms.

Parallel optical image addition and subtraction in a dynamic photorefractive memory by phase-code multiplexing.

We propose and demonstrate experimentally a method for utilizing a dynamic phase-encoded photorefractive memory to realize parallel optical addition, subtraction, and inversion operations of stored images. The phase-encoded holographic memory is realized in photorefractive BaTiO(3), storing eight images using Walsh-Hadamard binary phase codes and an incremental recording procedure. By subsampling the set of reference beams during the recall operation, the selectivity of the phase address is decreased, allowing one to combine images in such a way that different linear combination of the images can be realized at the output of the memory.