Polarization insensitive single mode Al2O3 rib waveguide design for applications in active and passive optical waveguides

Both passive and active, single mode, wavelength and polarization insensitive design of Al2O3 rib waveguides on SiO2 substrate is reported. Influence of the waveguide height, etch depth, waveguide width and operation wavelength to the mode number, mode size, birefringence and polarization sensitivity were analyzed with Beam Propagation Method. Design parameters for targeted properties are computed for waveguide widths ranging from 0 to 10 µm, and for etch depth ranging from 0 to 0.5 µm for fixed waveguide height of 0.5 µm. A design window for a fixed width of 3.5 µm and etch depths between 0.325 to 0.375 µm is identified for single mode, wavelength and polarization insensitive operation of Al2O3 waveguides on thermal oxide. A novel rib TE mode selective filter design is also suggested as an output of the numerical simulations

Simultaneous measurement of magnetic field and temperature based on magnetic fluid-clad long period fiber grating

Simultaneous measurement of magnetic field and temperature is proposed and experimentalized with a magnetic fluid-clad long period fibergrating structure. Magnetic fluid is used as the surrounding material of the long period fiber grating. Both of the wavelength and intensityof the spectral resonance valley of the proposed structure can be influenced by the applied magnetic field and ambient temperaturevariation. A two-parameter matrix method is proposed and utilized to measure the magnetic field and temperature simultaneously. Thelinear relationship between the corresponding wavelength shift/intensity variation and magnetic field/temperature change is obtained atcertain ranges of magnetic field and temperature, which is favorable for sensing applications

Accuracy of the subsurface damage parameters calculated by the finite difference algorithm

An important approach to characterize the full three-dimensional information of subsurface damage is to simulate the etching process of a sample reversely. The simulation starts from the morphology of the sample after the subsurface damage micro cracks being opened totally. During the etching experiment, it is possible for us to get the surface morphology at any moment. This paper presents a finite difference algorithm to simulate the morphology evolution during the etching process and then the surface’s morphology of the sample at a specific time can be obtained. Comparison between the simulated morphology and the measured one provides the clue of improving the precision of the finite difference algorithm. This method is kind of the fast calculation. In addition, the accuracy of this calculation of the corrosion model needs to be ensured. In order to improve the precision of calculation, the time interval should be set as the appropriate value by comparison and analysis. In this paper, the accuracy can be calculated through comparing the simulated result with the experimental result, and the maximum error of this method can be gained

Deterministic measurement and correction of the pad shape in full-aperture polishing processes

Full-aperture polishing is a significant process in fabricating large optical flats because it restrains Mid-Spatial Frequency errors and removes material quickly on the whole optic surface. Nevertheless, optical flats fabricated by full-aperture polishing generally fail to meet the stringent requirement of surface figure, which has to be corrected by sub-aperture polishing processes. Surface figure of optical flats in full-aperture polishing processes is primarily dependent on the pressure distribution uniformity which correlates intensively with the lap shape. At present, practical and precise means are urgently desired for measuring and correcting the lap shape, especially the polyurethane pad lap. In the study, we present a novel method for deterministic measurement of the pad shape. The method obtains the height of the pad at spirally distributed locations implemented by the revolution of the pad and translation of the laser displacement sensor. The pad shape in terms of matrixes whose elements representing the heights at the corresponding locations is then calculated by interpolation algorithm based on the obtained data. Further, we propose a method for deterministic correction of the pad shape utilizing a small conditioning tool. The dwell time algorithm and implementation strategy for the dwell time are provided for common full-aperture polishers. These solutions for the deterministic measurement and correction of the pad shape have been validated on a full-aperture polisher with polyurethane pad. The polishing experiments revealed that the optic surface figure was obviously improved

Optimized signal-to-noise ratio with shot noise limited detection in Stimulated Raman Scattering microscopy

We describe our set-up for Stimulated Raman Scattering (SRS) microscopy with shot noise limited detection for a broad window of biologically relevant laser powers. This set-up is used to demonstrate that the highest signal-to-noise ratio (SNR) in SRS with shot noise limited detection is achieved with a time-averaged laser power ratio of 1:2 of the unmodulated and modulated beam. In SRS, two different coloured laser beams are incident on a sample. If the energy difference between them matches a molecular vibration of a molecule, energy can be transferred from one beam to the other. By applying amplitude modulation to one of the beams, the modulation transfer to the other beam can be measured. The efficiency of this process is a direct measure for the number of molecules of interest in the focal volume. Combined with laser scanning microscopy, this technique allows for fast and sensitive imaging with sub-micrometre resolution. Recent technological advances have resulted in an improvement of the sensitivity of SRS applications, but few show shot noise limited detection.The dominant noise source in this SRS microscope is the shot noise of the unmodulated, detected beam. Under the assumption that photodamage is linear with the total laser power, the optimal SNR shifts away from equal beam powers, where the most signal is generated, to a 1:2 power ratio. Under these conditions the SNR is maximized and the total laser power that could induce photodamage is minimized. Compared to using a 1:1 laser power ratio, we show improved image quality and a signal-to-noise ratio improvement of 8 % in polystyrene beads and C. Elegans worms. Including a non-linear damage mechanism in the analysis, we find that the optimal power ratio converges to a 1:1 ratio with increasing order of the non-linear damage mechanism

Refractive index sensing setup based on a taper and an intrinsic micro Fabry-Perot interferometer

In this work, a refractive index sensor setup based on a biconically tapered fiber (BTF) concatenated to an intrinsic all-fiber micro Fabry-Perot interferometer (MFPI) is presented. Here, the power of the MFPI spectral fringes decreases as the refractive index interacts with theevanescent field of the BTF segment. Furthermore, it is demonstrated that the RI sensitivity can be enhanced by bending the BTF segment.Finally, it is shown that by using this sensing arrangement, at ~1.53 µm wavelength, it is possible to detect refractive index changeswithin the measurement range of 1.3 to 1.7 RIU, with a sensitivity of 39.92 dB/RIU and a RI resolution of 2.5 x 10􀀀^-3 RIU with a curvature of C = 18.02 m^-􀀀1

Academic innovation: are we truly ready for it?

Optics has been in the headlines this year due to the UN-sponsored International Year of Light 2015 (IYL 2015), and due to its presence in the 2014 Nobel Prize awards. The purpose of this article is to highlight the innovation-enabling elements that were behind the work of one of the Nobel Laureates - and the stream of innovations that followed, beyond the Nobel work. I will further, from this and my personal experience, expand some thoughts on the enabling elements of academic innovation and draw some conclusions - and, in particular, try and answer the question “How can academic success be repeated?â

Electromagnetic field intensity distribution along focal region of a metallic circular reflector covered with a plasma layer

Theoretical analyses has been carried out to study the deviation of the electromagnetic field intensity distribution in the focal region of a long metallic circular reflector that contains a uniform cold collisional plasma layer on its surface. The electromagnetic field intensity expressions along the focal region have been obtained using Maslov’s method. Maslov’s method is systematic procedure, which combines the simplicity of ray optics and the generality of transform methods. The derived analytical field expressions in the focal region have been solved numerically. The reflected and transmitted field intensity distributions from the plasma layer along the focal point were examined. The effects of some physical parameters such as the plasma frequency, the thickness of plasma layer and the effective collision frequency on the transmitted field intensity distribution along the focal region are studied. The results are found to be in a good agreement with results obtained using Kirchhoff’s approximation

Point diffraction interferometry to measure local curvatures and caustics of noisy wave fronts: Application for determining optical properties of fish lenses

The study of caustics is important because they contain information about the image formation properties of optical systems. In this work we use the concept of caustic as a set of focal points, and we have developed a second order approach theory to determine local slopes and curvatures of a wavefront emerging from an optical system. The method is based on the use of a point diffraction interferometer, and the analysis of the interferograms allows us to compute the focal region. Experimental results obtained with a plano-convex lens demonstrate the accuracy of the combined theoretical-experimental method here developed. Application to noisy wavefronts such as those produced by biological samples, specifically in crystalline lenses of fish eyes, are also exposed

Effect of heat treatment on optical properties of crosslinkable Azo Chromophore doped in poly amic acid

In this work, we have studied the optical properties of a crosslinkable poly amic acid containing Disperse Red 1. The thin films were cured at 130, 160 and 195 °C. The structural and optical properties of the doped films were investigated by using UV-VIS spectra, and Prism Coupling techniques. The composite crosslinks during poling rendering it totally insoluble. A r33 of 1.5 pm/v was obtained after poling