Spectral hole burning for pulse repetition frequency analysis

We demonstrate an optical processor based on spectral hole burning (SHB) that maps the carrier frequency into the time domain and the pulse repetition frequency (PRF) into the spatial domain by illuminating an SHB crystal with a signal beam that is scanned by a tilting mirror across a slice of the crystal. This time-to-space mapping makes it possible to measure signal envelopes with a resolution of . A signal with a pulsed envelope engraves a vertical absorption grating with a spatial periodicity given by the product of the PRF and the scan velocity. Reading the grating, which the crystal stores for up to T₁, with a collimated beam yields orders diffracted at angles proportional to the PRF, which are Fourier-transformed to produce spots displaced from the DC position by distances proportional to the PRF. Increasing the PRF increases the grating periodicity, causing the diffracted spots to move away from the DC position.     

Optical encryption with a reference wave in a joint transform correlator architecture

In this work we introduce a digital holographic configuration in a Joint Transform Correlator (JTC) architecture for encryption purposes. Conceptually, it is a Mach-Zender interferometer, with a JTC in one arm and a reference wave in the other. We describe the practical implementation of this architecture, along with experimental results that support the proposal. We analyze the noise influence caused by intensity saturation during image capture, and this information allows us a filtering process to reduce the information to be handled, with a consequent increase in the speed of the total procedure.     

Long-period fiber-gratings produced by exposure with a low-pressure mercury lamp and their sensing characteristics

A new production method of long-period fiber-gratings using neither a laser nor a fine-positioning system was proposed. A low-pressure mercury lamp emitting 254 nm ultraviolet light was used as a light source. Hydrogen-loaded Ge-B co-doped fiber was exposed to the emission of the lamp through an amplitude mask. A coupling loss up to 23 dB was obtained for a grating period of 212 μm. The maximum coupling loss for a grating period of 460 μm was 18 dB. The growth rate of the refractive index change by mercury-lamp exposure was 1.3 × 10⁻⁴/h. The temperature and strain characteristics were measured and compared with those fabricated by excimer-laser exposure. The temperature and strain sensitivities of long-period gratings with a period of 212 μm were higher than those of 460 μm. The temperature and strain sensitivities of those by mercury-lamp exposure were almost equal to those by excimer-laser exposure of the same fiber. The sensitivities of those by excimer-laser exposure of non-loaded fiber were higher than those of hydrogen-loaded fiber by mercury-lamp or excimer-laser exposures except for the temperature sensitivity of a grating period of 460 μm.     

Translocation of Biopolymer Chain Through a Nanopore: Coil--Helix Transition

The translocation dynamics of a single biopolymer chain through a nanopore in a membrane is investigated by taking the coil-helix transition into account. Based on the changing of the free energy due to the coil-helix transition, the mean first passage time T is obtained, and then the corresponding numerical simulations are presented under different conditions. It is shown that the coil--helix transition can significantly shorten the translocation time of the biopolymer chain. In addition, we also discuss the scaling behaviour for T with the chain length N and some related problems.     

All-Optical AND Logic Gate without Additional Input Beam by Utilizing Cross Polarization Modulation Effect

A novel design of all-optical AND gate is proposed by using cross polarization modulation effect in a semiconductor optical amplifier. In this scheme, an additional continuous-wave beam is not required as that in traditional scheme. AND output is obtained on either of two input signal wavelengths. The AND scheme is numerically simulated and experimentally demonstrated at a bit rate of 10 Gb/s successfully.     

Transmission intensity disturbance in a rotating polarizer

Random disturbance was observed in transmission intensity in various rotating prism polarizers when they were used in optical systems. As a result, the transmitted intensity exhibited cyclic significant deviation from the Malus cosine-squared law with rotation of prisms. The disturbance spoils the light quality transmitted through the polarizer thus dramatically depresses the accuracies of measurements when the prim polarizers were used in light path. A rigorous model is presented based on the solid basis of multi-beams interference, and theoretical results show good agreement with measured values and also indicate effective method for reducing the disturbance.     

Chern-Simons and WZW anomaly cancelations across dimensions

The WZW functional in D=4 can be derived directly from the Chern-Simons functional of a compactified D=5 gauge theory and the boundary fermions it supplants. A simple pedagogical model based on U(1) gauge groups illustrates how this works. A bulk-boundary system with the fermions eliminated manifestly evinces anomaly cancelations between CS and WZW terms.     

Potential Energy Surfaces of Nitrogen Dioxide for the Ground State

The potential energy function of nitrogen dioxide with the C2v symmetry in the ground state is represented using the simplified Sorbie-Murrell many-body expansion function in terms of the symmetry of NO2. Using the potential energy function, some potential energy surfaces of NO2（C2v, X^-^2A1）, such as the bond stretching contour plot for a fixed equilibrium geometry angle θ and contour for O moving around N-O （R1）, in which R1 is fixed at the equilibrium bond length, are depicted. The potential energy surfaces are analysed. Moreover, the equilibrium parameters for NO2 with the C2v, Cs and Dsn symmetries, such as equilibrium geometry structures and energies, are calculated by the ab initio （CBS-Q） method.     

Demonstration of a spatial-spectral holographic LIDAR range-Doppler processor

We present a new approach to laser interferometric Doppler and ranging (LIDAR) processing using spatial-spectral holography (SSH). In this approach, broadband optical signals from a random noise or frequency-modulated laser are transmitted and reflected off remote targets. The return signals interfere spatially and spectrally with a local copy of the original transmit signal in an SSH medium, resulting in spectral gratings that have a spectral period inversely proportional to the LIDAR target's range and a position proportional to the target's Doppler (or velocity). These gratings are subsequently read out by a slowly chirped source onto a parallel detector array, and the velocity and range of the targets are inferred. We present the theoretical framework that describes the function of the LIDAR processor, as well as proof-of-concept experimental results.     

Characteristics of the loss modulation of intracavity Raman-Nath acousto-optic devices

Acousto-optic loss modulators for applications in active mode-locking of lasers are discussed. We show that intracavity interference effects can either enhance or decrease the modulation efficiency. Optical, electrical, and acoustic measurements for the characterization of mode-locking devices are described.