Table of contents

A novel quadrature interferometer based on Mach–Zehnder configuration and a 3 × 3 fibre coupler is presented. Measurements showing instantaneous extraction of both real and complex parts of the interferometric signal are described. The features of this quadrature interferometric platform are discussed with a focus on signal-to-noise ratio and optical power handling.

Illumination by pulses of second harmonic generation of picosecond Nd–YAG lasers at power densities of up to 200 MW cm⁻² has shown the appearance of photo-induced changes of the absorption in the transparent spectral range for lanthanum–gallium–sulfide–oxide (LGSO) glasses. Incorporation of the different rare-earth ions of 1% by weight substantially changes the observed photo-induced absorption. In particular, the additional photo-absorption is successively decreased by going from Nd³⁺ to Ce³⁺ rare-earth ions compared to the undoped LGSO glasses. Also, for Sm³⁺ ions with an enhancement of the pumping power density, it was even observed that the sign of the absorption changes. To explain the observed dependences, molecular dynamics and quantum chemical calculations were performed for the principal structural fragments of the glasses. The results observed allow us to consider the investigated materials as optically operated materials for the recording of information.

A simple method to monitor chromatic dispersion (CD) and polarization mode dispersion (PMD) simultaneously is proposed using two polarization-modulation pilot tones with different frequencies. It has been demonstrated that RF output power increases with group velocity delay (GVD) and differential group delay (DGD) and the power ratio of the two pilot tones increases with GVD and decreases with DGD, thus CD and PMD can be distinguished and monitored simultaneously.

Optical pumping of polymer films containing laser dyes results in emissions that exhibit spectral narrowing and wavelength shifting. Such films are fabricated on a substrate slice of silicon via a spin coating method. The thickness of the film is a few microns. The wavelength at peak intensity shifts in the short-wavelength direction as the number of pump laser pulse shots increases. Such blue shifts are abnormal: a red shift originating from the process of degradation of dye–polymer films was observed previously. An explanation for the blue-shift phenomenon is presented and the corresponding measured data supporting the explanation are provided.

To enhance the non-diffracting distance of propagation-invariant beams, fabrication of an axicon with large aperture diameter and height is essential. It is noted, however, that fabrication of continuous surface profile micro-optical elements with a large physical height (thick resist) is prone to various fabrication constraints and errors. We employ the kinoform technique to alleviate such problems in the fabrication of axicons. In this paper kinoform micro-axicons and kinoform micro-double-axicons are designed and fabricated employing electron beam lithography techniques to generate a Bessel beam and a self-imaged bottle beam with long non-diffracting distance. Furthermore, a detailed study of power conversion efficiency of kinoform structures is discussed.

The paper shows the design and results from a high speed, high resolution multi-channel scanner that can produce six separate angular outputs over a range of 4°. The design uses an absolute minimum of large optical components to achieve a scan length of 400 mm. Results are shown for ceramic tile surfaces. Speed and quantity of data collected are limited by the digitization electronics and computing available. The image quality is potentially limited by the precision of the scanner prism and by speckle from the monochromatic light source.

This paper concerns the problem of the optimization of parameters in acousto-optic image processing systems. The optimization was carried out with the purpose of obtaining the best performance and minimum driving power. A choice of optimal geometry of acousto-optic interaction in the crystal is discussed. Longitudinal aberrations in the device caused by dispersion of refractive indices of acousto-optic media are studied. Calculations prove that a specific choice of distances between optical elements in the device can reduce the aberration to a value less than the focal depth of a filtered image. Spectral analysis of radiation reflected from artificial test objects demonstrates operationaal capability of the imager.

Transmissions through a metallic film at near-infrared wavelengths with different surface corrugations on both sides are systemically studied. The calculations are performed by the three-dimensional finite-different time-domain method. Calculated results show that the transmissions are strongly dependent on the surface structures. Compared with other structures, the transmission for a film periodically drilled by cross air grooves are relatively larger. Transmission is enhanced more with symmetric conditions on both layers than the asymmetric case. The enhanced transmission can be explained by a competition between the absorption in the metal and enhanced transmission due to coupled surface plasmon resonance.

This paper presents an analysis of several in-water algorithms developed using a large number of bio-optical data collected in Korean and neighbouring ocean waters. The upward and downward light fields measured in these waters were normalized to provide remote sensing reflectance (R_rs) from which the variations in sun-induced chlorophyll-a (Chl-a) fluorescence from phytoplankton biomass were analysed and the fluorescence line height (ΔFlu) was measured using a baseline method. ΔFlu measurements were related to in situ Chl-a concentrations (used as an index for quantifying the algal material) to obtain the ΔFlu(681), ΔFlu(688) and ΔFlu_(area) algorithms, which were compared with those from standard spectral ratios of the remote sensing reflectance, R_rs(444)/R_rs(554) and R_rs(490)/R_rs(554). Comparison revealed the correlation coefficients (r²) 0.88–0.90 for the fluorescence algorithms and 0.79–0.85 for the spectral ratios algorithms. A validation analysis using a new data set illustrated the merits of these algorithms in Case II waters. Fluorescence-based algorithms tended to reproduce in situ Chl-a concentrations (from 0.1 to 82 mg m⁻³), whereas standard spectral ratios algorithms gave inconsistent estimates, probably caused by the interference of inorganic sediment and dissolved organic matter in these waters. For measurements of the sun-induced Chl-a fluorescence signal in coastal waters, this study discusses the requirements and provides the optimal channels to be adopted in the design of the new generation ocean colour sensors planned in the near future.

The optical properties of a light filter consisting of a transparent dielectric matrix with inclusion of metallic nanoparticles of various shapes and sizes are investigated theoretically. By selecting distributions of nanoparticles, it is possible to achieve absorption of electromagnetic radiation in specified spectral regions of visible or near IR radiation. Such filters have narrow transition regions, high contrast and low fabrication temperature in comparison with well known absorption filters. A filter for absorption of optical radiation transparent in the infrared region and an infrared filter transmitting optical radiation are considered as examples.

We consider two frameworks: (i) the electromagnetic generalized Lorenz–Mie theory describing the interaction between an electromagnetic arbitrary shaped beam and a homogeneous, non-magnetic sphere, with an isotropic, linear, material and (ii) a quantum generalized Lorenz–Mie theory describing the interaction between a quantum eigen-arbitrary shaped beam and a quantum radial potential, in the case of inelastic interactions. We then demonstrate that electromagnetic scattering by an absorbing macroscopic sphere in the first framework is cross-sectionally equivalent to a superposition of two effective quantum processes in the second framework.

Passive Q-switching of a diode-pumped a-cut Nd:YVO₄ laser with Cr⁴⁺:YAG saturable absorber in a plano-concave cavity is experimentally studied. We find that, by adjusting the laser resonator to a nearly hemispherical geometry, stable and short Q-switched pulses can be obtained, though it has been theoretically predicted that the larger gain cross section of the laser crystal than absorption cross section of the absorber prevents good Q-switched operation for this laser, which is a failure to fulfil the second threshold condition. Success in achieving good Q-switched operation in this laser is connected with the occurrence of self-pulsation near the hemispherical resonator configuration. By using a concave mirror of 50 mm radius of curvature and pump power of 770 mW, stable laser pulses were obtained with pulse widths as short as 9.5 ns at a repetition rate of 10 kHz and peak power of 82 W.

The strong asymmetry in the emission of the fast and slow axes of semiconductor power lasers requires a significant optical beam transformation system to reach the parameters needed for micromachining, laser end-pumping and advanced applications. In this paper, a simple solution to this problem is proposed based on an array of cylindrical mirrors. Three examples of practical interest are considered, in which the compactness and effectiveness of the solution are demonstrated.

We study theoretically the process of conversion of the topological charge of optical vortices upon their propagation in anisotropic and elliptical weakly guiding optical fibres. We demonstrate that in addition to the well-known mechanism of topological charge conversion due to the elliptical form of the fibre's cross-section such a conversion can also be caused by the spin–orbit interaction. We show that in strongly anisotropic fibres, in which the other mechanism is prohibited, this interaction leads to charge conversion of both linearly and circularly polarized optical vortices. We also apply our theory to the description of experiments on mode conversion in fibres (McGloin et al 1998 Appl. Opt. 37 469, Carpentier et al 2006 J. Eur. Opt. Soc. Rap. Publ.1 06031) and demonstrate that at the initial stage of fibre stressing the most probable reason of mode conversion is stress-induced photoelastic anisotropy of the fibre's core.

A theory is presented to show that dark and grey spatial solitons can be formed spontaneously in azobenzene-containing polymers (ACPs) with photoisomerization nonlinearity by simultaneously considering the angle hole burning (AHB) effect and the photoinduced molecular reorientation (PMR) effect. It shows that compared to that of the AHB effect, the contribution of the PMR to the formation of solitons is evident and cannot be ignored. It is found that the dependence of the width of this kind of solitons on the intensity of the light beam is similar to that of photorefractive solitons.

Rare-earth-containing oxide nanocomposites are prepared in a controlled fashion from porous GaAs templates. The initial porous GaAs network is replaced by a β-Ga₂O₃ one during annealing at temperatures from 500 to 900 °C. The impregnation of Eu and Er lanthanides from EuCl₃:C₂H₅OH and ErCl₃:C₂H₅OH solutions results in the formation of xenotime EuAsO₄ and ErAsO₄ microcrystals finely dispersed into the native oxide matrix. The 4f–4f intrashell transitions in Eu³⁺ and Er³⁺ ions ensure red and green emission from EuAsO₄ and ErAsO₄ nanophases. These nanocomposites may prove useful in future generations of optoelectronic and photonic devices.

Stochastic optimization is proposed for the pump absorption enhancement in double-clad fibres (DCFs). Monte Carlo forms of the Nelder–Mead (NM) method are proposed and benchmarked against a genetic algorithm (GA) and generalized pattern search (GPS) and mesh adaptive direct search (MADS) methods. A simple sampling NM variant offered the highest efficiency while MADS achieved global convergence with the highest probability in low dimensions. All algorithms examined are described within the pattern search frame while detailed pseudocode descriptions are given in structured functions. Smoothly perturbed patterns are proposed for implicitly constrained optimization in high dimensions. An improved Monte Carlo NM method, based on importance sampling and stochastically perturbed patterns, exhibited global convergence with higher efficiency than MADS in high dimensions. Many polymer and air outer cladding designs are optimized. A circular holey DCF with an optimally offset core and a single large solid-state hole with optimum offset, size and ellipticity offered 180% absorption enhancement over a conventional circular DCF with centred core.

We demonstrate a full-range parallel Fourier-domain optical coherence tomography (FD-OCT) in which a tomogram free of mirror images as well as DC and autocorrelation terms is obtained in parallel. The phase and amplitude of two-dimensional spectral interferograms are accurately detected by using sinusoidal phase-modulating interferometry and a two-dimensional CCD camera, which allows for the reconstruction of two-dimensional complex spectral interferograms. By line-by-line inverse Fourier transformation of the two-dimensional complex spectral interferogram, a full-range parallel FD-OCT is realized. Tomographic images of two separated glass coverslips obtained with our method are presented as a proof-of-principle experiment.

The durability of a liquid crystal (LC) modulator for use with a high power laser is measured at a wavelength of 808 nm. It is shown that the LC modulator can withstand a laser power density of 133 W cm⁻². For a laser power density greater than 133 W cm⁻² the phase transition is caused by the absorption of the material. In order to improve the durability, the absorption of glass, polyimide (PI), indium tin oxide and LC were measured. Results indicated that the phase transition of the nematic LC is mainly caused by the absorption of glass and PI. These results can be used for a LC modulator with nematic LC material, and it is important to use an LC modulator in optical systems with high power lasers.