The report presents a theoretical and numerical analysis of the sharp focusing of a displaced Laguerre-Gauss single-ring mode with circular polarization based on the Richards-Wolf formulas. Expressions for the amplitude of the field components in the focal plane are obtained, while the case of “+”-polarization is considered in more detail. In addition to the general expression, the formula for intensity along the horizontal axis is given separately. It is more convenient for determining the displacement parameters than tracking them from the intensity pattern. Expressions are given for calculating the displacement value based on the intensity profile of the longitudinal component for large values of the vortex order. It is shown that for explicit asymmetry visualization it is advisable to use modes with a small but non-zero number.
We analyze theoretically, numerically, and experimentally the spectral response of scattered light intensity from moving particles crossing the fringes of a Bessel beam. This response could be the basis of a simple technique to measure velocity.
Chiral materials possess circular dichroism property that leads to difference in absorption between left and right handed
circularly polarized beams. Using these materials in an optical system or measuring their properties causes transmission
impairments such as circular dichroism (CD). Using Jones matrix analysis we show the polarization independence in
transmission of a chiral element placed in a Sagnac loop interferometer containing a half-wave plate.
Keywords: Chiral, circular dichroism, Jones matrix, Sagnac loop interferometer
The extended depth of field of axicons is an advantage for imaging applications but comes with a degradation of image
quality. Image processing is proposed to solve this problem. In the present work, three types of refractive axicons are
examined for imaging applications: a linear axicon, a logarithmic axicon and a Fresnel axicon. Each one has its own
advantages: a linear axicon is simple, the Fresnel axicon is compact and has a potential low cost of production and the
logarithmic axicon generates nearly constant longitudinal intensity distribution which might ensure a more uniform
image quality along the focal length. Preliminary experimental measurements of the Point Spread Function (PSF) for
each one of these axicons were performed and are used to design digital filters to de-noise the images.
It is shown that an axicon telescope system preserves isotropy and scaling in both the transverse and longitudinal
directions as opposed to regular lens telescopes. Also, a coherent fiber optics imaging bundle was used with an axicon
lens permitting viewing with an extended depth of field as compared to using a fiber optics bundle with a regular lens.
The paper presents a proposal of multiorder varifocal moiré zone plates, which change their focal length because
of the lateral displacement of their two components with transmittances described by a cubic profile. The newly
introduced element turns out to be an intermediate solution of the hitherto existing elements, which are the
refractive Alvarez lens and its diffractive counterpart. Some of the expected properties of multiorder varifocal
moiré zone plates are discussed, as well as reasons, because of which this newly introduced set of elements can
be of interest in practical applications.
Nondiffracting or Bessel beams find applications in diverse fields like optical tweezers/spanners, microscopy, super-resolution
and optical coherence tomography. An axicon, energywise, is the most efficient method for generating a
diffraction-free beam. Yet one of the impediments to wide use of these optical elements is the cost related to the way
they are manufactured. Recently we proposed a novel optical element - Fresnel axicon (Opt. Lett. 31, 1890, 2006) -
which enables to overcome this problem while providing advantages such as compactness and very low bulk absorption.
Prototypes of the Fresnel axicon were manufactured. In the present work we report the first experimental results
characterising the optical properties of this novel device, which bridges the gap between diffractive axicons and their
refractive counterparts.
A novel type of waveguides utilizing simultaneously Bragg reflection and TIR (total internal reflection) for light confinement is proposed and studied. The BRAGGATIR waveguides combine the advantages of Bragg waveguides and lateral ARROWs (antiresonant reflecting optical waveguides) -- namely, large core sizes allowing easy and low loss fiber coupling and their reduced sensitivity to fabrication errors, with the properties of high index contrast ridge waveguides which tolerate small bending radius. Since the proposed waveguides have only one Fabry-Perot layer, they are more compact compared to the Bragg waveguides. Moreover, the large dispersion of the BRAGGATIR waveguides near the resonances may find applications in optical signal processing. Beam propagation method (BPM) and mode solver numerical simulations were performed and the bending losses of different waveguides, namely BRAGGATIR, ridge and ARROW, were compared for different bending radii down to 10 microns. The results demonstrate advantage of the proposed waveguides allowing very small radius ring resonators with large free spectral range and more compact integrated optics devices.
Progress in optical switching technology currently faces several major obstacles. One of these is high power consumption, which quickly multiplies in cascaded switch configurations. As well, many implementations have long switching speeds and large footprints. An improved compact 1x2 digital optical switch (DOS) in InGaAsP/InP is presented, with experimental results compared to numerical modeling. The Y-junction waveguide switch operation is based on reconfiguration of output waveguide arms by carrier injection at the electrodes. We present experimental results of DOS fabricated with InGaAsP cores having bandgaps of 1.2um, 1.3um, and 1.4um. The results are compared with calculations of refractive index change versus carrier concentration in the different InGaAsP alloys. Additionally, wafer layer structure and waveguide parameters were redesigned to decrease, respectively, power dissipation and optical confinement. Switching current is significantly reduced from greater than 100 mA to about 20 mA, which not only provides power savings, but also results in less thermal overshoot in the switched optical pulse. The DOS has a measured switching contrast ratio of better than 12.5 dB, with a transition time of less than 5ns. Polarization dependence of switching contrast is also explored.
A compact Y-junction waveguide switch with electrically reconfigurable output waveguide arms is demonstrated in InGaAsP/InP. Simulations indicate that the plasma effect or the thermo-optic effect can be used as the active switching mechanism, as corroborated by experimental tests. For the plasma effect the induced index change under the electrode, Δn, is negative. The Y-junction device has a measured switch contrast ratio ~ 20 dB, with a response time of ~ 5 ns. Using the thermo-optic effect Δn is positive and the observed contrast ratio is better than 10 dB. The highly localized nature of the thermal gradient in these devices yields thermo-optic switching into the hundred of nanoseconds range, several orders of magnitude faster than the overall thermal response time. This is the fastest thermo-optic switch reported to date. Fabrication of these switches, and in particular the use of O+-ion implantation to provide electrical isolation of the waveguide branches, is described.
We demonstrate Digital Optical Switches (DOS) on InP based on carrier-injection and on the quantum-confined Stark effect (QCSE). The active waveguide core is composed of either a double-heterostructure of InGaAsP for carrier-injection or a InGaAs-InGaAsP for reverse bias operation. O-Ion implantation was employed to isolate the branches of the DOS instead of the usual isolation by etching employed elsewhere.
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