Carlos R. Fernández-Pousa

The symmetric space and homogeneous sine-Gordon theories

Two series of integrable theories are constructed which have soliton solutions and can be thought of as generalizations of the sine-Gordon theory. They exhibit internal symmetries and can be described as gauged WZW theories with a potential term. The spectrum of massive states is determined.

Polarization beam splitters using polarization diffraction gratings.

We report a polarization beam splitter that uses polarization gratings written onto a zero-twist nematic liquid-crystal display. We show three configurations. The first two separate the diffracted light into two orthogonally polarized orders that are either linearly or circularly polarized. In the third configuration, we demonstrate a novel case for which the output is separated into two nonorthonormal polarization states. One component is linearly polarized and the second is circularly polarized.

Jones matrix method for predicting and optimizing the optical modulation properties of a liquid-crystal display

We present a simple technique for the calibration, prediction, and optimization of the optical modulation properties of a liquid-crystal display (LCD). The method is useful when there is no information about the internal fabrication parameters of the device (the orientation of liquid-crystal molecules, the twist angle, or the birefringence of the material). A complete determination of the LCD Jones matrix is accomplished by means of seven irradiance measurements for a single wavelength. This technique only requires two linear polarizers and one quarter-wave plate. Once the Jones matrix has been calibrated, the amplitude, phase, and polarization modulation response can be predicted. Therefore, it can be optimized through the control of the polarization configuration. The validity of the proposed method is experimentally probed. Finally, we present a particular application to produce phase-only modulation.

Integrable quantum field theories with unstable particles

Abstract A new family of S -matrix theories with resonance poles is constructed and conjectured to correspond to the Homogeneous sine-Gordon theories associated with simply laced compact Lie groups, where some of the resonance poles can be traced to the presence of unstable particles in the spectrum. These theories are unitary in the usual SS † =1 sense, they are not parity invariant, and they exhibit continuous coupling constants that determine both the mass spectrum of stable particles and the masses and the position of the resonance poles.

Semi-classical spectrum of the homogeneous sine-Gordon theories

Abstract The semi-classical spectrum of the homogeneous sine-Gordon theories associated with an arbitrary compact simple Lie group G is obtained and shown to be entirely given by solitons. These theories describe quantum integrable massive perturbations of Gepners G -parafermions whose classical equations-of-motion are non-abelian affine Toda equations. One-soliton solutions are constructed by embeddings of the SU (2) complex sine-Gordon soliton in the regular SU (2) subgroups of G . The resulting spectrum exhibits both stable and unstable particles, which is a peculiar feature shared with the spectrum of monopoles and dyons in N = 2 and N = 4 supersymmetric gauge theories.

Timing jitter smoothing by Talbot effect. I. Variance

A study of the stochastic description of the Talbot effect in the temporal domain under random timing jitter is presented. The relevant statistical quantity is the variance. The variance of a train of pulses, each one affected by random timing jitter, shows peaks in the edges of the pulses. When this train is Talbot-imaged, the variance becomes flattened along the unit interval corresponding to each pulse as a result of the dispersion of the individual pulses of the train. Fractional Talbot devices are also analyzed. In particular, it is shown that this smoothing effect also occurs in Talbot devices leading to N× repetition rates of the original train.

Polarizing diffraction-grating triplicators

We report experimental results with a reflective continuous anisotropic polarizing diffraction-grating beam splitter that produces three diffraction orders. The diffraction efficiencies and polarizations of the diffracted orders are controlled through the incoming polarization state and by use of a wave plate with arbitrary orientation located between the grating and a mirror. In particular, we show experimental evidence of a diffraction triplicator-a 100% efficiency diffractive device that generates three orders with equal power.

Generalized formulation and symmetry properties of reciprocal nonabsorbing polarization devices: application to liquid-crystal displays

We present a general formulation based on the Jones-matrix theory for reciprocal nonabsorbing polarization devices, including polarization interference filters and liquid-crystal displays. The development of this formulation is based on general symmetry conditions that relate the Jones matrix when the device is illuminated from the front side and from the back side. The application to liquid-crystal displays results in a constraint of the Jones-matrix elements, which represents a generalization of the existing models that explain their modulation properties.

Dual-Wavelength

We present a scheme for dual-wavelength operation of a diode-pumped Cr3+:LiCaAlF6 (Cr:LiCAF) laser with tunable frequency difference suitable for terahertz continuous-wave generation by heterodyne mixing in low-temperature-grown GaAs photomixers or intracavity nonlinear difference-frequency mixing. The laser is based on a double external optical feedback configuration to achieve spectral purity of the laser light through self-injection locking. The wavelength separation reported allows for a fully equalized dual-wavelength source between 0 and 9 THz in the 785-nm region.

{\rm Cr}^{3+}{\colon}{\rm LiCaAlF}_{6}

A technique is proposed to interrogate a distributed photonic sensor composed of seven standard fiber Bragg gratings in cascade. A microwave-modulated optical signal is launched into an FBG cascade and subsequently undergoes dispersion in standard single-mode fiber, so that the different Bragg wavelengths are mapped into the radio-frequency (RF) delays that determine the peaks in the electrical impulse response of the optical link. Shifts in Bragg wavelengths have been determined from the shifts in the impulse responses peaks by recording the links RF response in the range dc-20 GHz using a vector network analyzer (VNA), and then performing its inverse Fourier transform. A resolution of 14 pm is experimentally demonstrated after zero-padding the VNA traces.