Optical Pulse Shaping with an Electro-optic Modulator and Quadratic Electronic Feedback

Abstract

A digital optical repeater employing an electro-optic modulator and nonlinear electronic feedback provides optical bistability at a smaller value of the received optical power. The switching time is improved by increasing the local oscillator power and the overall gain of the feedback loop. The spread of the received optical pulses may be effectively reduced, leading to a considerable reduction in the intersymbol-interference power penalty. An optical amplification results in an improved system gain that exceeds the degradation due to a slight extinction penalty.     

Effects of chromatic dispersion on microwave and millimetre wave carrier transmission in optical fibres

Abstract

A new formalism for the analysis of optical (phase) noise in fibre-optic communication links is presented. The formalism is applied to an amplitude modulated millimetre-wave (or microwave) link with chromatic dispersion. A realistic link model is described and rigorously solved. In general, the power spectrum of the output signal consists of a ‘comb’ of spectral components with centre separation equal to the modulation frequency. Each spectral component contains a smooth ‘noise’ curve and a narrow spike which represents a modulated field component (carrier). With the new method it is possible to compute each spectral component and, consequently, the full power spectrum. From the power spectrum one can compute quantities relevant to the link design, in particular the carrier-to-noise ratio. Several graphs are presented, showing the power spectrum and the carrier-to-noise ratio for different values of the modulation frequency, link dispersion and modulation index. Several conclusions regarding the millimetre-wave fibre-optic link are dis-cussed.     

On calculating the reflectance and transmittance of light for a simple thick grating structure

Abstract

This paper presents a formulation for calculating the reflectance and transmittance of classical light for a simple structure that contains a rectangularly shaped line grating layer that lies atop a thick transparent or weakly absorbing substrate layer. It is assumed that the substrate thickness is sufficiently large and non-uniform that when the light traverses it is averaged over a large surface area, the averaged field is considered as losing phase coherence and intensities can be added. It is assumed that the optical properties of the media in the various homogeneous regions of the structure are complex, local, linear, isotropic, and non-magnetic. This kind of structure has important applications in the metrology of linewidths for the semiconductor integrated circuit industry.     

Wigner–Ville distribution based diffraction phase microscopy for non-destructive testing

ABSTRACT

The paper proposes an approach for non-invasive measurement of displacement derivatives and defect identification using an optical interferometric technique based on diffraction phase microscopy. Our approach relies on the application of Wigner–Ville distribution method in diffraction phase microscopy for directly extracting the phase derivative information, which is subsequently utilized for non-destructive deformation metrology. In addition, the proposed method offers good computational efficiency and robustness against noise for fast defect inspection. The performance of the proposed method is validated by experimental results.     

Scattering measurements on curved rough surfaces

Abstract

A theoretical model is developed to examine light scattered from a curved optical surface with a defined surface form. The contribution of the surface form to scattering patterns is separated from that of the surface roughness. Experiments are carried out on a curved surface. Measurements are analysed and compared with theoretical calculations. The power spectrum density function and the autocorrelation function of the surface roughness are recovered from the measured scattering pattern.     

Intracavity Optical Bistability Driven by Squeezed Light from a Parametric Amplifier

Abstract

We describe the theory of optical bistability when atoms are collectively excited within the cavity of a parametric oscillator. Both optical bistability and parametric amplification can squeeze significantly the cavity-field quantum noise. When they are coupled together we find significant changes both on the mean value bistability and on the spectrum of squeezing as the parametric coupling increases. These are calculated directly from the appropriate master equation for the density matrix using a quantum distribution function (positive P) to develop Fokker—Planck and Ito equations.     

Optical pattern recognition in motion acquired scenes using a binary joint transform correlation

Abstract

The problem of detecting patterns in moved scenes is analysed. The correlation when the input scene presents a relative motion with respect to the recording system image is studied analytically and an original method for detecting patterns by means of a binary joint transform correlator is presented. The method is based on the compensation of the sign errors introduced in the joint power spectrum by the transfer function of the degradation. Two alternatives to determine the sign of the transfer function are demonstrated: the first is based on an algorithm to extract information from the Fourier spectrum of the blurred image and the second method determines the sign errors by post-processing the correlation. Digital simulations and optical results are provided.     

2.35 μm LEDs for measuring methane

GaAlAsSb/GaInAsSb/GaAlAsSb double-heterostructure LEDs emitting in the region of the 2.35 μm absorption band of methane have been developed for fast gas analyzers. Different designs of double heterostructures based on the solid solution GaInAsSb were studied. Continuous-wave optical power of 1.2 mW was achieved. The methane absorption spectrum for the LED radiation is presented. Pis’ma Zh. Tekh. Fiz. 24, 72–79 (January 26, 1998)     

Analysis of beam properties in the neighbourhood of a double-heterostructure laser source

Abstract

The power density distribution and beam characteristics of double-heterostructure lasers with very thin active layers in the neighbourhood of the light source are evaluated by using a plane wave spectrum approach and a second-moment order theory for diffracted scalar light beams. It is shown that the evanescent waves contribute to shape the power density when the distance is smaller than the emission wavelength λ or of the order of λ. It should be noted that the optical fields deeply penetrate into the cladding layers when the thickness of the active layer is much smaller than the emission wavelength λ.     

The dynamics of the electron in a homonuclear driven molecular ion

Abstract

The radiation diffused by a one-dimensional homonuclear molecular ion driven by a laser field is studied as a function of the time. When the photon energy is resonant with the energy gap between the ground and the first excited state, the electronic probability density is seen to undergo slow and deep oscillations between the two nuclei. Synchronous to such oscillations, deep modulations of the emitted power are observed. The period of oscillation is of the order of 10 optical cycles. Detection of the variation in the intensity of the emitted electromagnetic spectrum therefore brings information on the position of the electron in the molecule.     

Optical properties of binary composite materials with two nonlinear components

Abstract

A new formulation is presented for the calculation of effective dielectric magnitudes of two-component composites in which both components (the host matrix particles and the embedded particles) exhibit nonlinear behaviour of the Kerr type. It is predicted that, under certain conditions, two nonlinear component composites can exhibit optical bistable behaviour as a function of the shape and concentration of the embedded particles, the dielectric contants of the components, the intensity of the external electric field (power density) and the intrinsic third-order nonlinear optical susceptibilities χ⁽³⁾ _p and χ⁽³⁾ _m of the nonlinear components. It is also deduced that, as the power density increases, the effective third-order nonlinear optical susceptibility χ⁽³⁾ of the composite exhibits a clear transition from values close to χ⁽³⁾ _p (low power density) to χ⁽³⁾ _m (high power density). Therefore, it is shown that the optical response of binary composites dramatically changes at moderate and high power densities. A comparison is performed between the optical response of a real two nonlinear component composite and that of a composite with a single nonlinear component.     

Modeling of a vircator with internal TEM feedback

The Karat electromagnetic PIC code is used for computer modeling of a vircator with internal TEM feedback proposed by the authors. It is shown that the output power can be effectively controlled by varying the feedback length. Pis’ma Zh. Tekh. Fiz. 25, 89–94 (October 26, 1999)     

Wavelet analysis of short harmonics generated in presence of a two colour laser field

Abstract

The Morlet wavelet spectrum of the radiation emitted by a two level atom in presence of two laser pulses with very close frequency is obtained. The wavelet spectrum gives information on the time evolution of the full spectrum and of a particular line. The beating condition stimulates the atom to emit pulses of harmonics with duration of the order of a few optical cycles of the pumping radiation. Pulse trains of 3 optical cycles (FWHM) are observed.     

Analysis of Optical Pulse Distortion Through Clouds for Satellite to Earth Adaptive Optical Communication

Abstract

Clouds, if part of an optical communication channel, cause temporal widening and attenuation of optical pulse power. Space optical communication from satellite to earth (ground or airplane) occasionally involves clouds as part of the optical channel. Here, based upon Monte Carlo simulations, mathematical models are developed for the temporal characteristics of optical pulse propagation through clouds. These include temporal impulse response, transfer function, bandwidth, received energy and bode analysis. The method presented here can be used as an inclusive framework for developing other mathematical models of other characteristics of radiation propagating through clouds, as required. Several conclusions of this work are obtained. One is that simple prediction models can be applied to adaptive methods of optical communication. Another is that using shorter wavelengths such as 0·532 μm yields least temporal widening and maximum received power, and is thus preferable for optical communication. In addition, the simulation results strongly support the use of the double gamma function model to best describe optical pulse spread through clouds. This work is the first, to the best of the authors' knowledge, to present a comprehensive analysis of space optical communication through clouds.     

Coupled-wave Analysis of the Bragg Effect Waveguide Coupler

Abstract

A coupled-wave analysis is presented for the Bragg effect waveguide coupler. This device consists of a slanted volume phase grating which is integrated inside the lightguiding layer of an optical waveguide. The wave propagation is described by a set of leaky wave modes. Self-consistency relations are derived to determine the angular mode spectrum and the corresponding radiation loss coefficients. A maximum input coupling efficiency of 80% is predicted for an incident Gaussian beam. The power of a waveguide mode should be emitted into a single output beam reaching an efficiency of almost 100%.     

Study on the spectrum of phase fractal structure

Abstract

In this paper, the term of phase fractal structure is presented. The Cantor relief structure was designed and fabricated by photolithography. We derived its recurrence formulas for the Fourier spectrum function and pointed out that its power spectrum is composed of two parts, the spectrum for the main structure and the spectrum for the accompanying structure. The power spectrum of six concurrent generations and the experimental power spectrum are also illustrated and its characteristics are analysed.     

High-power broad-band single-mode InGaAsP/InP superluminescent diode

An InGaAsP/InP separate-confinement double heterostructure having a broad gain profile was used to fabricate superluminescent diodes having high optical power (40 mW), a broad radiation spectrum (65 nm at half-width), and low percent modulation (<1%). Using a cw pump current of 150 mA, 1mW of superluminescence radiation was obtained at the exit from a single-mode optical fiber. Pis’ma Zh. Tekh. Fiz. 25, 16–22 (August 12, 1999)     

Amplified spontaneous emission in distributed feedback active microcavities fabricated by the sol–gel dip-coating method

Abstract

Amplified spontaneous emission (ASE) is demonstrated in a distributed feedback (DFB) active microcavity, formed by rhodamine B molecules in a Bragg grating (BG). The BG was fabricated by alternately depositing titanium dioxide and silicon dioxide sol–gel thin films. The reflectance spectrum of BG simulated by the transfer matrix method was consistent with experimental results, demonstrating that the BG had good periodic structures. With rhodamine B molecules embedded, the ASE was observed from the DFB active microcavity in optical pumped conditions. The full-width-half-maximum and threshold of ASE were 7.5 nm and 0.2 mJ/pulse. The slope efficiency of 3% was measured. The DFB active microcavity is promising for low-cost ASE.