Pulse Shaping Applications Research Articles

Instantaneous characteristics study of the diffracted and transmitted light of a staticphotorefractive reflection volume holographic grating read by an ultrashort pulselaser

The time-domain diffraction and transmission of reflectionvolume holographic gratings (RVHGs) recorded in photorefractiveLiNbO3 crystals are theoretically studied and compared with transmission volume holographicgratings (TVHGs) when they are illuminated by ultrashort pulse laser light. The modifiedKogelnik’s coupled-wave theory, combining the dispersion effect in the crystal, is used.The results show that larger diffraction intensity can be obtained by choosing alarger grating period, grating thickness and modulation index for a given pulseduration. The RVHG has higher diffraction intensity than the TVHG with thesame grating parameters. Also, it is found that the diffracted pulse of the RVHGand the TVHG shift in opposite directions along the time-axis. The values ofthe shifts are functions of the readout pulse duration and grating parameters.The overmodulation phenomenon appears in the diffracted pulse of the TVHGat high values of the grating thickness and refractive index modulation, but itdoes not occur in the RVHG. The results of our study can be used in choosingproper grating parameters for pulse shaping and signal processing applications.

Diffraction properties of multi-layer volume holographic gratings under an ultrashort pulsed beam with arbitrary temporal profiles

The diffraction properties of a system of multi-layer volume holographic gratings under an ultrashort pulsed beam with arbitrary temporal profiles are investigated using the multi-layer coupled wave theory. The dependence of the pulse profiles of the diffracted beams, diffraction bandwidth and the total diffraction efficiency of the multi-layer system on the temporal profiles of the input ultrashort pulse are investigated. The calculated results indicate that the temporal shape of the input pulsed beams is an important factor in the analysis of the propagation characteristics. The analysis of this paper will be valuable for the applications of pulse shaping, processing and filter.

Application of Nonuniform Transmission Lines to Ultra Wideband Pulse Shaping

The work presented in this letter demonstrates that nonuniform transmission lines (NUTLs) can be used for pulse shaping applications in ultra wideband pulsed systems and presents an approach to their design for this application. The pulsed waveforms generated are modified Hermite polynomials and encoded pulse trains thereof and are characterised by a broad bandwidth ranging from near DC to over 10 GHz and relatively long temporal duration in the region of nanoseconds. These pulses are more mathematically complex and at least three times higher bandwidth than previously has been reported in the literature. It is also believed to be the first time that modified Hermite polynomial pulses have been generated in practice. The NUTL design approach is verified by test structures fabricated on FR4 circuit board. The results demonstrate that NUTLs, which are completely passive structures, allow generation of complex pulse shapes in applications requiring fast, transient waveforms.

Spatial light modulator of 648 pixels with liquid crystal transparent from ultraviolet to near-infrared and its chirp compensation application

We fabricated a 648 pixel, two-dimensional spatial light modulator (SLM) with a transmittance of more than 85% in the wavelength region from 260 to 1,100 nm. The phase modulation characteristics of the liquid-crystal SLM were clarified. Furthermore, the SLM enabled us to compensate for chirp of 270 fs UV pulses and chirp of 120 fs near-IR pulses so that the former and latter pulse durations, respectively, were shortened to 35 and 25 fs. This suggests that the SLM can be utilized, in the UV to near-IR region, for the generation of monocycle optical pulses, pulse shaping, and other applications.

Diffraction study of volume holographic gratings in dispersive photorefractive material for femtosecond pulse readout

Based on the modified Kogelnik diffraction efficiency equation, the diffraction intensity spectrum and the total diffraction efficiency of volume gratings in photorefractive media are studied systematically. Taking photorefractive InP:Fe crystal as an example, the effect of the grating parameters and the pulse width on the diffraction properties are presented, in particular under the influence of crystal material dispersion. Under the combined effects, the diffraction pulse profiles and the total diffraction efficiency are shown. Also, the diffraction properties with and without crystal material dispersion are compared. These studies indicate that the properties of the diffraction beams can be controlled by the holographic grating parameters; this property can be used for pulse shaping applications.

Pulse shaping and diffraction properties of multi-layers reflection volume holographic gratings

The multi-layers coupled-wave theory is extended to systematically investigate the pulse shaping and diffraction properties of a system of multi-layers reflection volume holographic gratings (MRVHG) under ultrashort laser pulse (ULP) readout. The combined effects that the grating parameters such as the number and thickness of layers and gaps between them and the pulse duration of the input ULP have on the pulse shaping properties are considered. The pulse profiles of the diffracted and transmitted beams, the diffraction bandwidth, and the total diffraction efficiency are presented. The calculated results we have derived permit an optimal choice of grating parameters for the pulse shaping and process applications.

Schrödinger solitons in left-handed SiO2–Ag–SiO2 and Ag–SiO2–Ag plasmonic waveguides calculated with a nonlinear transmission line approach

The existence of solitons in SiO2–Ag–SiO2 and Ag–SiO2–Ag plasmonic waveguides (PWGs) is investigated using a nonlinear transmission line approach. Both the SiO2–Ag–SiO2 and the Ag–SiO2–Ag, the former in its TM even mode and the latter in its odd mode, are shown to support bright solitons as solutions to the nonlinear Schrödinger equation. The SiO2–Ag–SiO2 even mode has low left-handed (LH) loss but is undesirably mixed with a right-handed mode, while the Ag–SiO2–Ag odd mode exhibits low-loss pure LH characteristics and is therefore the most suited mode for soliton propagation. Soliton PWGs may find applications in compact switching, pulse shaping, and pulse compressing devices.

All-Optical Signal Processing of Periodic Signals Using a Brillouin Gain Comb

The amplification of periodic signals using a Brillouin gain comb provides the opportunity to manipulate the amplitude and phase of a signal's individual spectral harmonics and, therefore, its temporal characteristics. In addition to obvious applications in pulse shaping, the approach offers new opportunities in the context of slow-light generation which include power-efficient Brillouin amplification of broadband periodic signals without delay, signal delay/advancement with relatively low gain variation, and fast-light generation accompanied by high levels of gain.

Pulse shaping properties of volume holographic gratings in anisotropic media

Based on a modified coupled wave theory, the pulse shaping properties of volume holographic gratings (VHGs) in anisotropic media VHGs are studied systematically. Taking photorefractive LiNbO(3) crystals as an example, the combined effect that the grating parameters, the dispersion and optical anisotropy of the crystal, the pulse width, and the polarization state of the input ultrashort pulsed beam (UPB) have on the pulse shaping properties are considered when the input UPB with arbitrary polarization state propagates through the VHG. Under the combined effect, the diffraction bandwidth, pulse profiles of the diffracted and transmitted pulsed beams, and the total diffraction efficiency are shown. The studies indicate that the properties of the shaping of the o and e components of the input UPB in the crystal are greatly different; this difference can be used for pulse shaping applications.

Analysis of an ultrashort pulsed finite beam diffracted by volume gratings

We obtain analytical solutions of the coupled wave equations that describe the Bragg diffraction of ultrashort pulsed finite beams by a thick planar grating, using two-dimensional coupled wave theory. The diffraction properties for the case of an ultrashort pulsed finite beam with Gaussian profiles in both the time and spatial domains are investigated. The spectral bandwidth of the diffracted beam, the Bragg selectivity bandwidth and the diffraction efficiency of the volume grating are influenced by the geometry parameter and the input bandwidth. Therefore extra attention should be paid to designing optical elements based on volume gratings for use with ultrashort pulsed waves in applications of pulse shaping and processing.

Demonstration of sharp switching from a power-symmetric NOLM and a polarizer

We demonstrate theoretically, experimentally and numerically that a steep all-optical transfer characteristic can be obtained from a power-symmetric NOLM, including a quarter wave retarder and highly twisted fibre, followed by a polarizer. We first develop a theoretical analysis to show that, if the input polarisation is chosen linear, then for a correct choice of the wave plate and input polarisation angles the transmission grows from zero with a 4dB/dB slope as power is increased, two times faster than can be obtained with a NOLM alone. An experimental study is then realised, which supports the theoretical results. Steep switching is demonstrated for reasonably low peak power levels that do not exceed 8W, less than one third of the NOLM critical power. In addition, using the same setup we demonstrate the possibility to obtain a sinusoidal transmission characteristic that cancels out for a particular nonzero value of input power, which can be easily adjusted simply through rotation of the wave plate and output polarizer. This setup would be very useful in the frame of optical pulse shaping and signal processing applications, among others.

Aspects of hole burning and spectro-temporal holography in molecular doped solids (Review)

The persistent spectral hole-burning (PSHB) phenomenon has been known since 1974. It is still an important research area for the study of the intimacy of complex molecular systems in the solid state, revealing high-resolution spectra, photophysics, photochemistry, and dynamics of molecular doped amorphous media, organic as well as inorganic. From another point of view, PSHB allows the engraving of any spectral structures in the inhomogeneous absorption band profile of molecular doped amorphous hosts or ion doped crystals cooled down to liquid helium temperatures. Therefore, a PSHB material is programmable in the spectral domain and consequently it can be transformed in an optical processor capable of achieving user-defined optical functions. Some aspects of both fields are illustrated in the present paper. Concerning the search for efficient PSHB materials, the hole-burning performances and the photophysics of polymer and xerogel based systems are compared. The problem of high-temperature persistent spectral hole-burning materials and the search for new frequency selective photosensitive systems for fast optical pulse processing at 800nm are considered. Regarding the points treated, inorganic hosts based on silicate xerogels or porous glasses have shown the best results. Moreover, by combining inorganic and organic capabilities or by grafting organic species to the host, hybrid xerogels have not yet revealed all possibilities. Also, the interest of two-photon materials for engraving spectral features with near-infrared or infrared light is developed. As an introduction to possible applications of PSHB material, the basics of spectro-temporal holography are remembered and a demonstrative experiment using a naphthalocyanine-doped polymer film is described, proving that the temporal aberration free recompression of ultrashort light pulses is feasible, therefore opening a way for applications in ultrashort light pulse shaping. Aspects for a comparison between cw hole-burning and femtosecond spectro-temporal experiments are considered, and prospects for coherent control of light fields or photochemical processes are also evoked.

Excitation and scattering of surface plasmon-polaritons on structured metal films and their application to pulse shaping and enhanced transmission

Using terahertz (THz) time-domain techniques, we measure the relative coupling and scattering characteristics of surface plasmon-polariton waves for rectangular cross-section grooves on a thick metal foil. This is accomplished by using a single subwavelength aperture surrounded by one or more annular grooves. A unique aspect of the measurement technique is that it allows one to discriminate between the contributions of each groove in the transmitted THz waveform. The measurements are obtained by using structures that contain either a single annular groove, for coupling measurements, or two concentric annular grooves, for scattering measurements. The basic approach should be extendable to other spectral ranges and applicable to different forms of surface electromagnetic waves. Using the aforementioned measurements, we demonstrate the ability to alter the pulse shape of the transmitted waveform using a single aperture surrounded by four annular grooves of varying dimensions. In addition to the value of this capability for pulse shaping applications, the basic technique allows for greater control of the transmission resonance lineshape related to enhanced transmission through a single subwavelength aperture.

Systematic Control of Nonlinear Optical Processes Using Optimally Shaped Femtosecond Pulses

This article reviews experimental efforts to control multiphoton transitions using shaped femtosecond laser pulses, and it lays out the systematic study being followed by us for elucidating the effect of phase on nonlinear optical laser-molecule interactions. Starting with a brief review of nonlinear optics and how nonlinear optical processes depend on the electric field inducing them, a number of conclusions can be drawn directly from analytical solutions of the equations. From a Taylor expansion of the phase in the frequency domain, we learn that nonlinear optical processes are affected only by the second- and higher-order terms. This simple result has significant implications on how pulse-shaping experiments are to be designed. If the phase is allowed to vary arbitrarily as a continuous function, then an infinite redundancy that arises from the addition of a linear phase function across the spectrum with arbitrary offset and slope could prevent us from carrying out a closed-loop optimization experiment. The early results illustrate how the outcome of a nonlinear optical transition depends on the cooperative action of all frequencies in the bandwidth of a laser pulse. Maximum constructive or destructive interference can be achieved by programming the phase using only two phase values, 0 and pi. This assertion has been confirmed experimentally, where binary phase shaping (BPS) was shown to outperform other alternative functions, sometimes by at least on order of magnitude, in controlling multiphoton processes. Here we discuss the solution of a number of nonlinear problems that range from narrowing the second harmonic spectrum of a laser pulse to optimizing the competition between two- and three-photon transitions. This Review explores some present and future applications of pulse shaping and coherent control.

Diffraction study of photorefractive hologram under ultrashort pulse readout

Summary Based on the diffraction efficiency equation of Kogelnik, the diffraction effect of a cw photorefractive hologram under ultrashort pulse illumination is theoretically analyzed. We find that the recorded grating has the function of filter to the incident pulse beam. To fully reconstruct the incident pulse, the crystal width must be smaller and grating period must be larger. In this paper we also discuss the total diffraction efficiency of the hologram, and find that the total diffraction efficiency is functions of the crystal length, pulse duration and the grating period. The conclusion of our paper can be used in ultrashort pulse shaping application.

Adaptive control methods for ultrafast pulse propagation in optical fibers

Adaptive control in combination with ultrafast pulse shaping provides a compelling approach to harness events that occur on the fastest timescale available. This paper illustrates the application of adaptive pulse shaping to femtosecond pulse propagation at /spl lambda/=1550 nm in single-mode optical fibers. The approach is illustrated first by through a numerical simulation of the technique. An experimental demonstration is described. The propagation of /spl sim/200-fs pulses is successfully achieved in the nonlinear regime by suitably preshaping the input pulse using an adaptive feedback loop.

Iterative Fourier transform algorithm for phase-only pulse shaping

We demonstrate the adaptation of an iterative Fourier transform algorithm for the calculation of theoretical spectral phase functions required for pulse shaping applications. The algorithm is used to determine the phase functions necessary for the generation of different temporal intensity profiles. The performance of the algorithm is compared to two exemplary standard approaches. i.e. a Genetic Algorithm and a combination of a Simplex Downhill and a Simulated Annealing algorithm. It is shown that the iterative Fourier transform algorithm converges much faster than both alternative methods.

Femtosecond pulse shaping using spatial light modulators

We review the field of femtosecond pulse shaping, in which Fourier synthesis methods are used to generate nearly arbitrarily shaped ultrafast optical wave forms according to user specification. An emphasis is placed on programmable pulse shaping methods based on the use of spatial light modulators. After outlining the fundamental principles of pulse shaping, we then present a detailed discussion of pulse shaping using several different types of spatial light modulators. Finally, new research directions in pulse shaping, and applications of pulse shaping to optical communications, biomedical optical imaging, high power laser amplifiers, quantum control, and laser-electron beam interactions are reviewed.

Electrooptic nonlinear Fabry-Perot devices

A Fabry-Perot resonator containing an electrooptic element driven by the transmitted light can be used for a number of light processing operations. We describe the use of such devices for pulse Shaping, optical limiter, and optical logic applications. "Optical triode" operation is demonstrated. We also propose and demonstrate a new type of "high-nonlinearity" operation which permits multilevel optical logic and switching operations.

Optimum pulse shaping application of binary transversal filters used in satellite communications

The implementation of binary transversal filters (b.t.f.) is gaining wide acceptance, due to their operational adaptability to variable bit rates, their achievable high out-of-band attenuation and linear phase performance and to the recent availability of medium-scale integrated components such as charged-coupled devices.The design and evaluation results of a b.t.f. meeting the single channel per carrier Intelsat satellite communications specifications are presented, which are based on Mueller's synthesis method. The performance evaluation problems of these type of filters are also described and, in particular, emphasis is given to the following: out-of-band to in-band power ratio inaccuracies when wideband measurement techniques are employed, and the evaluation of the r.m.s. jitter of b.t.f. based on the jitter probability density function.