We have investigated the influence of the poling process (poling temperature and poling field) on the second harmonic generation in PMMA doped with an azo dye. On the other hand, the dynamics of the poling, the thermal stability and the aging of the poled films have been studied.
Polymeric waveguides doped with nonlinear organic materials have been fabricated by pre- and post-doping techniques. High quality, low-loss planar waveguides have been produced with doping concentrations in excess of 30% by weight. Selective doping has been used to define simple monomode channel waveguide structures. Fast acting nonlinear behaviour has been observed using doped-polymeric waveguides, including nonlinear distributed waveguide coupling with surface relief gratings and intensity-dependent waveguide birefringence.
The method of optical mode coupling is used in the detection of the electro-optic response of monolayers and multilayers LB films. We show that this method represents a sensitive tool and a simple technique by which the second order non linear properties for different layers organization (Y or Z) may be quantified.
2-Cyclooctylamino-5-nitropyridine (COANP) is a new nonlinear optical crystal with point group symmetry mm2. It has been grown by a temperature difference solution growth technique. Its linear and nonlinear optical properties have been investigated. The refractive indices na = 1.699, nb = 1.847 and nc = 1.681 (at ? = 550 nm) and the nonlinear optical susceptibilities d31 and d33 (kw = 1.06 p.m) have been determined. Type I phase matching is possible at 1.064 Ilm. A peak conversion efficiency 71 = P2co/Pco = 3.6% has been observed with a 0.90 mm thick crystal and a fundamental power Pw = 560 W.
The operating characteristics of novel all-optical integrated optics devices based on strong nonlinearities are reviewed, as are all-optical guided-wave devices which are nonlinear extensions of well-known linear integrated optics devices. A comparison of how different material systems meet the requirements for all-optical guided-wave devices is also presented.
Second harmonic waves generated in the form of Cherenkov radiation from a 0.8μm diode laser in proton-exchanged LiNb03 waveguides have been observed. Low-loss and high-index waveguides were fabricated by using pyrophosphoric acid as a new proton source. Blue light of 1mW at 0.42μm was generated for a fundamental power of 65mW at 0.84μm at room temperature.
A new type of electrooptic modulator is presented. The modulation of optical waves is obtained by variation of one of the parameters ruling the excitation conditions of a guided mode, during the coupling of an optical beam into a planar structure. The performances obtained with a prism coupler are discussed.
The best optical detection sensitivities and the longest unrepeatered transmission spans for experimental systems at bitrates up to 2 Gb/s are now obtained using heterodyne detection techniques. In addition, the potential advantages of these techniques in multi-channel systems, for video distribution as well as for broad-band local network applications, are now being explored. Recently reported advances in theory and technique are reviewed and current problems and limitations are discussed.
This letter describes the effect of the intermodulation on the signal to noise ratio of a receiver employing in-phase and quadrature detection. Theoretical results are reported here for the case of an FDM signal made of six differential phase-shift keying (DPSK) modulated channels with a data rate of 2.4 Gbit/sec and employing a 3B4B line code.
The performance of switches and modulators for coherent systems is described. Emphasis is placed on enviromental stability and reliability of devices based on both Lithium Niobate and Electro-Optical Polymers. For hybrid opto-electronics Niobate devices offer the best performance and have proven reliability for applications in first generation systems. In the longer term hybrid systems using electro-optical polymer based active components are expected to outperform their monolithic semiconductor counterparts.
Results obtained with a square wave driven integrated optic frequency shifter fabricated in LiNbO3, and working at frequencies in excess of 20 MHz will be reported. Adjustment free operation of the device at 6328 Å in the presence of phase drift will be demonstrated. Polarisation independent operation is possible at this wavelength as a result of photo-refractive effects.
An experimental optical system with heterodyne detection has been designed and constructed. Particular attention has been paid to laser stabilisation and the requirement for optical isolation. The system also includes a microprocessor based controller for automatic signal and polarisation acquisition and tracking. A receiver sensitivity of -41 dBm has been achieved with standard DFB lasers. All the optical components used in the system are fitted with monomode fibre pigtails. This allows the system to be housed in a standard telecommunications equipment shelf of the type used in practical installations.
An optical coherent ten-channel distribution system with bit rates of 70 Mbit/s (nine channels) and 1.13 Gbit/s (one channel), corresponding to a TV and a High Definition TV (HDTV) digital signal, was built up 1 2 The main components of this laboratory system are reported.
The coupling of two waves in barium titanate is described in terms of scattering matrices derived from a vector coupled wave theory. Key mechanisms responsible for the processes of self-pumped phase conjugation and beam fanning are identified, and the role of reflections from the internal faces of the crystal are examined. The nonlinear effects observed in the crystal are considered in terms of theory and methods of controlling the photorefractive coupling strength in the crystal are considered. Applications for controlling the coupling in photorefractive crystals are also considered.
The photorefractive effect in 43 m crystals shows specific symmetries in its dependence upon wave polarizations and crystal orientation. We summarize them and use them to study the energy dependence of the photorefractive two-beam mixing in semi-insulating gallium arsenide and indium phosphide in the nanosecond regime at 1.06 μm.
We report signal beam amplification in degenerate two-wave mixing experiment at λ = 10.6 μm wavelength in nematic liquid crystals operating near the phase transition temperature. Theoretical results and experimental data are presented. We also present two and four-wave mixing experiments in Hg0.78Cdo.22Te at low temperature.
Optical interferometric detection of ultrasonic signals at 7.5 MHz has been carried out at the rough surface of an aluminum sample. The distorted wavefront was reconstructed by optical phase conjugation leading to an increase of the light-gathering power of the interferometer.
Thin film systems composed of photoconducting elements (PC) and electroluminescent cells (EL) were investigated as AND- as well as OR-type logical gates. PC and EL elements were prepared by vacuum evaporation. The time functions of output signal in the form of the luminance of light emitted from the electroluminescent cell depending on the input signal (rectangular pulses of the light illuminating PC elements), at both constant and alternating voltage supplying the examined system were measured.
For the time being, Integrated Optics is able to produce a range of devices able of efficiently modulating phase, amplitude and frequency of guided waves in single mode structures implemented at the surface of active materials such as Lithium Niobate. In most of the cases, their basic principle relies on the interference pattern of two guided waves and the classical implementations of such modulators were mainly related to COBRA switch type directional couplers or to MACH ZEHNDER type interferometers. Only very recently a structure combining the coupled waveguides of a COBRA and the Y junction of the MACH ZEHNDER interferometer was designed. This paper is an analysis of the switching characteristics of this Y-fed directional coupler and of its high frequency modulation properties.
In this paper we present the capabilities of the silicon based integrated optics technology to be associated with microelectronics. Through the first device already achieved, we analyse what kind of poblems remains to solve and in what field of applications this association seems the more attractive.
The quantum well structures in semiconductor dominate many important application areas. Laser, loss modulator, optical bistable device, intersectionnal total reflection switch with high speed switching capabilities have been demonstrated. Polarization dependent absorption in waveguide structures, non linear transmission and voltage dependent absorption coefficient are investigated as a function of wavelength and quantum well structures. Results for GaAs/GaAlAs and InGaAs/InP Multiple Quantum Wells (MQW) structures are presented. Various device applications based on waveguide and 2D configurations are discussed.
A presentation of new theoretical results and of physical considerations will be given starting from a nonlinear model for semiconductor injection lasers. Particular attention will be devoted to the gain calculation, to the unphysical meaning of the superlinear approach commonly used for gain calculations and to the carrier lifetime dependence on the photon number.
Self-phase modulation (SPM) occuring at moderate power levels in single-mode fibers has important implications on long-range optical fiber transmission. Limitating and beneficial aspects of this fiber nonlinearity on future high-bit-rate optical communication systems will be discussed, including soliton propagation, power-dependent transmission bandwidth variations and modulational instability. On the other hand self-phase modulation can be the base for the realization of novel nonlinear optical fiber devices: Of most practical interest is its use for an optical pulse compression to pulsewidths in the femto-second range, or the realization of the so-called "soliton laser". In those fiber optic devices, however, the interaction of self-phase modulation with other fiber nonlinearities have to be taken into consideration.
Optical fibre waveguides with organic single crystal cores are receiving increasing attention for 'all-optical' devices such as amplifiers and wavelength shifters. This paper overviews the fabrication, design, optical assessment and both the predicted and currently realised performance of devices including second harmonic generators and, to a lesser extent, degenerate optical parametric amplifiers. Using guided wave interactions, existing materials have sufficient nonlinearity to show that efficient second harmonc generation (>50%) and high amplification gain (>35dB) are possible with devices a few cm in length when pumped by semiconductor diode lasers of just a few mW output power. Second harmonic generation can also be emitted in the radiation modes of the fibre waveguide. In this case, theory predicts a 1 mW output from a 10 mW pump laser in a 16 mm long device. Fabrication tolerances are much less severe than in the guided mode case, as phase matching is more easily achieved. Transparency in the clad glass may allow operation in the deep blue even for absorbing organic cores.
This paper presents measurements of Raman amplification utilising the 800cm 1 band of silica. Although higher gains are obtainable with other bands in silica, the size of the Stokes shift enables pump and signal lasers to operate in the l.3um and l.5um communications windows respectively. A maximum gain of 3dB is reported.
Using computer simulations, we examine various factors affecting the propagation of femtosecond pulses in single-mode optical fibers in the wavelength range of normal dispersion. In particular, we show that distortion and nonlinear chirping of the pulse can arise from such con-siderations as initial pulse asymmetry, higher-order dispersion and nonlinearity effects in the fiber, and higher-order dispersion from optical components such as grating-pair compressors. The effect of initial pulse chirp is also examined. In addition, we investigate intensity-dependent spectra of these propagating pulses. Our results indicate that the addition of both the cubic-dispersion term and the so-called shock term in the nonlinear Schro-dinger equation generate intensity-dependent pulse spectra that compare well with experiments. We also show that asymmetry in the input pulse can be a contributing factor responsible for asymmetric spectra. Finally, we show how the use of additional optical components can be utilized to compensate for cubic phase distortion pulse, leading to a fuller utilization of the pulse bandwith and state-of-the-art pulse durations.
The recent observation of efficient second-harmonic generation in glass fibers is a very exciting result. Fibers containing a small amount of phosphorous (and germania) doping in the core, that undergo an optical "preparation" process show efficient frequency-doubling. In this paper, a review is presented of some of the most important experiments reported in the literature, as well as a critical discussion of the models existent at present to explain the processes involved.
Experimental and theoretical investigations on Raman amplification in fibres have been carried out and simultaneous amplification and pulse compression observed. With a fibre design optimised for amplification high gain may be obtained at practical pump power levels.