Incident Fundamental Mode Research Articles

Generation of squeezed states of light in arbitrary complex amplitude transverse distribution

The squeezed state is important in quantum metrology and quantum information. The most effective generation tool known is the optical parametric oscillator (OPO). Currently, only the squeezed states of lower-order spatial modes can be generated by an OPO. However, the squeezed states of higher-order spatial modes are more useful for applications such as quantum metrology, quantum imaging, and quantum information. A major challenge for future applications is efficient generation. Here we use cascaded phase-only spatial light modulators to modulate the amplitude and phase of the incident fundamental mode squeezed state. This efficiently generates a series of squeezed higher-order Hermite–Gauss modes and a squeezed arbitrary complex amplitude distributed mode. The method may yield new applications in biophotonics, quantum metrology, and quantum information processing.

Rayleigh backscattered radiation produced by an arbitrary incident mode in multimode optical fibers.

The recently developed diffraction technique of analytical investigation of the Rayleigh backscattering produced by an incident fundamental mode in a multimode optical fiber with an arbitrary refractive index profile is generalized to admit an arbitrary incident mode, either radial or azimuthal. The relative powers of all backscattered modes are determined with explicit formulas via the properly normalized transverse distributions of the incident and backscattered mode fields within the fiber cross section. The regularities conditioned by azimuthal indices are expressed via a universal set of coefficients, and dependences on the radial mode indices are estimated numerically. Excitation coefficients are shown to be symmetrical for any pair of incident and backscattered modes.

Influence of a variable Rayleigh scattering-loss coefficient on the light backscattering in multimode optical fibers.

The recently developed diffraction technique of analytical investigation of the Rayleigh backscattering produced by an incident fundamental mode in a multimode optical fiber with an arbitrary refractive index profile is supplemented by taking into account the Rayleigh scattering-loss coefficient, which could be variable within the fiber cross section. The relative changes in various radial and azimuthal modes' excitation levels, due to some typical radial dependences of this coefficient, are computed for the quadratic- and step-index fibers. It is stated that the excitation efficiency could either rise or decay for different modes. The effect of the variable Rayleigh scattering-loss coefficient is shown to be more noticeable in the fibers with a quadratic refractive index profile, whereas it is negligible in actual multimode step-index fibers.

Rayleigh backscattering from the fundamental mode in step-index multimode optical fibers.

The Rayleigh backscattering produced by an incident fundamental mode in a multimode step-index optical fiber was analyzed using a recently developed diffraction technique. The complete set of backward propagating modes, both radial and azimuthal, was determined and regarded. For this type of fiber, normalized mode functions were constructed in an explicit form, thus providing a unified power scale to characterize the relationships between various excited modes. The dependencies of the mode excitation efficiencies on the technical parameters of the fiber and the frequency of the launched radiation were studied. A comparison of the mode excitation efficiencies was performed with those in the fiber with quadratic refractive index profiles.

Rayleigh backscattering from the fundamental mode in multimode optical fibers.

Rayleigh backscattering produced by an incident fundamental mode in a multimode optical fiber is analyzed using a diffraction technique, with a full set of backward-propagating modes being taken into consideration. Explicit formulas are derived for mode excitation efficiency via radial distributions of the mode fields, and it is proved that only half-azimuthal modes are backscattered by the incident wave of a fixed polarization. Advanced analytical expressions are developed for fibers with a quadratic refractive-index profile, and mode groups of even numbers, composed of modes with equal propagation constants, are stated to be excited with equal efficiencies.

Intermode conversion in a near-field optical fiber probe

The propagation of light in metal-coated fiber probes used in scanning near-field optical microscopy is studied computationally by means of the cross-section method. In contrast to previous work focusing on the behavior of the HE11 mode in the vicinity of the end aperture of the probe, we trace the propagation of the incident fundamental mode of the optical fiber through the tapered probe. The transformation of the fiber mode into the probe modes, intermode conversion, and modes cutoff are consistently calculated. In particular, it is shown that in the conventional gradual tapered probe only a few percent of the input power are transformed into the HE11 mode which has the smallest cutoff radius. In addition, an easily manufacturable modification of the shape of the probe’s tip that can provide a tenfold enhancement in optical near-field intensity has been proposed.

Experimental investigation of the harmonic generation by waves over a submerged plate

Experiments in a wave flume have been performed to analyse the nonlinear interaction between regular gravity waves and a submerged horizontal plate used as breakwater. A new method, based on the Doppler shift generated by a moving probes, has been used to discriminate the incident fundamental mode and the reflected fundamental mode. The relationships of the reflection and transmission coefficients to the wave number at different submergence depth ratios are presented. The accurate discrimination, by this method, of the phase-locked and free modes allows the quantification of the higher harmonics generated by the breakwater and the analysis of the nonlinear interaction between the waves and the submerged plate. The transfer of energy from the fundamental mode to higher harmonics is very large in the cases of small submergence depth ratios. The vortices produced at the edges take part in the production of higher harmonics by interaction with the free surface but involve, at the same time, a dissipation process that increases the efficiency of the breakwater.

Effects of elastic heterogeneities and anisotropy on mode coupling and signals in shallow water

Coupled mode theory is applied to acoustic/elastic wave propagation in shallow water to examine the effects of lateral heterogeneities and transverse isotropy on mode coupling and signals. A numerical code is developed by applying the invariant imbedding technique to the coupled mode theory. From the code, the reflection and transmission matrices and the forward/backward-propagating wave fields in the frequency domain are generated for a range-dependent medium. The effect of transverse isotropy of bottom sediment layers is also considered. Time domain signals are synthesized with a 2-Hz bandwidth between 10 Hz and 12 Hz for the excitation by a unit line force and for an incident fundamental mode. The generation of higher overtones and the decay of the fundamental mode propagating in a range-dependent medium are clearly shown.

On the effect of the higher modes on the scattering of Love waves at the boundary of welded layered quarter-spaces

abstract In this paper, we investigate the effect of higher modes on the scattering of plane, harmonic Love waves, normally incident (from either side) upon the plane of discontinuity in the horizontally discontinuous structure consisting of welded layered quarter-spaces with a plane surface. We find that the effect of the higher modes on the scattering of an incident fundamental mode from hard into the soft medium is considerable for large impedance contrasts with or without body-wave conversion, and is negligible when the impedance contrast is low. Our results indicate that contributions from body-wave conversion are important in higher Love mode studies when there is large contrast in the elastic constants of the media on the two sides of the vertical plane of discontinuity.