Micromechanics-based digitally controlled tunable optical beam shaper

A digitally controlled programmable optical beam shaper that uses a two-dimensional (2-D) small-tilt micromirror device is introduced. The optical intensity profile at any spatial position can be independently modified by use of a macropixel, incorporated with binary pulse-width modulation. An experimental proof-of-concept optical beam shaper with a commercial 2-D digital micromirror device has shown that the spatial profile of a He-Ne laser beam can be digitally manipulated. Investigation of the analog intensity control showed 256-level nonlinear degamma behavior with a measured 24.5-dB optical contrast ratio and a 10-bit spatial resolution. The performance of this tunable optical beam shaper is limited by the dimensions of the micromirror, the intermirror distance, the size of the optical beam, the number of bits used to control the micromirror, the diffraction effect, and the quality of the imaging optical system.     

Increase of lifespan for glioma‐bearing rats by using minibeam radiation therapy

This feasibility work assesses the therapeutic effectiveness of minibeam radiation therapy, a new synchrotron radiotherapy technique. In this new approach the irradiation is performed on 9L gliosarcoma‐bearing rats with arrays of parallel beams of width 500–700 µm. Two irradiation configurations were compared: a lateral unidirectional irradiation and two orthogonal arrays interlacing at the target. A dose escalation study was performed. A factor of three gain in the mean survival time obtained for some animals paves the way for further exploration of the different possibilities of this technique and its further optimization.     

Influence of sintering temperature on microstructure,critical current density and pinning potential of superconducting Bi1.6Pb0.5Sr1.8Dy0.2Ca1.1Cu2.1O8+δ ceramics

The influence of sintering temperature on the microstructure, critical current density (J_C), pinning potential values (U₀) and flux pinning properties of Bi_1.6Pb_0.5Sr_1.8Dy_0.2Ca_1.1Cu_2.1O_8+δ superconductor has been investigated. The samples are prepared by the solid-state route and sintered at temperatures ranging from 846 to 860 °C. A systematic correlation between the sintering temperature, Lotgering index, J_C, U₀ and flux pinning properties has been found. The samples sintered at lower sintering temperature (846 °C) have more grain boundaries with smaller grains while those sintered at a higher temperature (856 °C) contain larger grains with good texturing. The flux pinning force (F_P) calculated from the field dependent J_C values shows that the irreversibility lines (IL) of the Dy-doped samples shift towards higher fields to different extents depending on the sintering temperature. The maximum value of F_P = 1697 kN m^?3 is obtained for the sample sintered at 846 °C and the peak position of F_P is obtained at 0.96 T as against 616 kN m^?3 and 0.52 T for the sample sintered at 856 °C. The U₀ values calculated by Anderson's function is maximum for the sample sintered at 846 °C. But the self-field J_C value of this sample is lower than that of the samples sintered at 856 °C. The samples sintered at 856 °C show best self-field J_C due to the improved microstructure. The changes in microstructure followed by very high enhancement of self-field J_C, J_C(B) characteristics, F_P and U₀ values within a narrow temperature range, are of great scientific and technological significance and the results are explained on the basis of microstructural variation with respect to sintering temperature, hole optimization and formation of point defects due to the doping of Dy atoms in Bi_1.6Pb_0.5Sr_1.8Dy_0.2Ca_1.1Cu_2.1O_8+δ system.     

Analysis of thermo-magnetic fluctuations above the glass-transition temperature in Bi1.6Pb0.5Sr2−xEuxCa1.1Cu2.1O8+δ (0.000 ≤ x ≤ 0.180) system

The resistivity of Bi_1.6Pb_0.5Sr_2−xEu_xCa_1.1Cu_2.1O_8+δ (0.000 ≤ x ≤ 0.180) superconductor has been measured as a function of temperature and magnetic field. The resistivity shows a glassy behavior even at higher temperatures and magnetic fields for the Eu-doped samples as compared with the Eu free sample. The values of glass-transition temperature [T_g], magnetic field dependent activation energy [U₀(B)] and the temperature and magnetic field dependent activation energy [U₀(B,T)] are found to be maximum for optimal doping levels (x = 0.135) which shows that the flux lines are effectively pinned in this sample. Also for temperatures below the superconducting transition temperature (T_C), a scaling of measured resistivity curves in magnetic field (B = 0.4 and 0.8 T) is obtained and this scaling is quite useful for better understanding of the behavior of the flux vortices in high temperature superconductors.     

Digitally controlled fault-tolerant multiwavelength programmable fiber-optic attenuator using a two-dimensional digital micromirror device

A digitally controlled multiwavelength variable fiber-optic attenuator using a two-dimensional digital micromirror device (DMD) is introduced. The results from an experimental four-wavelength (i.e., 1546.92, 1548.52, 1550.12, and 1551.72 nm) proof-of-concept attenuator indicate a 26-dB dynamic range and 11-bit resolution. The measured attenuator average coherent optical cross talk per wavelength channel is -38 dB , limited by the additive noise resulting from the nonideal isolation of the optical circulator and the attenuator module. The average optical loss for our experimental attenuator is 15 dB and is limited mainly by the visible-mode DMD that is used as a 1550-nm infrared window device. Our theoretical estimate of a <8-dB loss optimized attenuator can be used for equalization in multiwavelength fiber-optic communications with as many as 108 wavelengths.     

Doping dependent metal to insulator transition in the (Bi,Pb)-2212 system: The evolution of structural and electronic properties with europium substitution

The present work investigates the effect of europium substitution on the(Bi,Pb)-2212 system in the concentration range 0.5 ≤ x ≤ 1.0.Phase analysis and lattice parameter calculations on the powder diffraction data and the elemental analysis of EDX show that the Eu atoms are successfully substituted into the(Bi,Pb)-2212 system.Resistivity measurements(64-300 K) reveal that the system exhibits superconductivity at x ≤ 0.5 and semiconductivity at x > 0.5.With the complete suppression of superconductivity which is known to be a quasi-two dimensional phenomenon in these materials,a metal to insulator transition takes place at x = 0.6 and the predominant conduction mechanism is found to be variable range hopping between localized states,resulting in macroscopic semiconducting behaviour.The results of electrical and structural properties of the doped(Bi,Pb)-2212 compounds suggest that the decrease of charge carrier concentration and the induced structural disorder are the more effective and dominant mechanisms in the origin of the metal to insulator transition and suppression of superconductivity due to Eu substitution at its Sr site.     

Fault-tolerant polarization-insensitive photonic delay line architectures using two-dimensional digital micromirror devices

A binary multichannel photonic delay line (PDL) module is introduced that gives balanced loss switched states and a polarization-insensitive operation via the use of binary operation Digital Micromirror Devices (DMDs). Experimental demonstration of a DMD-based PDL architecture is performed for a 6.84-ns time delay design. Experimental results include a 25-beam feed interchannel crosstalk test indicating a <−60 dB optical interchannel crosstalk level for a 0.381 mm interchannel distance in the multichannel PDL. An average optical signal-to-leakage noise ratio of 35.33 dB is measured for this PDL. A butterfly design PDL optical architecture is proposed for minimizing loss and improving assembly accuracy. These DMD-based variable PDLs can be used in applications ranging from radio frequency (RF) fiber-optic signal processing systems to adaptive optics for astronomical and laser radar arrays.     

Field test studies of our infrared-based human temperature screening system embedded with a parallel measurement approach

This paper introduces a parallel measurement approach for fast infrared-based human temperature screening suitable for use in a large public area. Our key idea is based on the combination of simple image processing algorithms, infrared technology, and human flow management. With this multidisciplinary concept, we arrange as many people as possible in a two-dimensional space in front of a thermal imaging camera and then highlight all human facial areas through simple image filtering, image morphological, and particle analysis processes. In this way, an individual’s face in live thermal image can be located and the maximum facial skin temperature can be monitored and displayed. Our experiment shows a measured 1 ms processing time in highlighting all human face areas. With a thermal imaging camera having an FOV lens of 24° × 18° and 320 × 240 active pixels, the maximum facial skin temperatures from three people’s faces located at 1.3 m from the camera can also be simultaneously monitored and displayed in a measured rate of 31 fps, limited by the looping process in determining coordinates of all faces. For our 3-day test under the ambient temperature of 24–30 °C, 57–72% relative humidity, and weak wind from the outside hospital building, hyperthermic patients can be identified with 100% sensitivity and 36.4% specificity when the temperature threshold level and the offset temperature value are appropriately chosen. Appropriately locating our system away from the building doors, air conditioners and electric fans in order to eliminate wind blow coming toward the camera lens can significantly help improve our system specificity.     

Geometrical optics analysis for reduction of trapezoidal image distortion in a single prism-based optical fingerprint scanner

A single prism-based optical fingerprint scanner structure is mathematically analyzed by using geometrical optics approach. Important parameters including a tilting angle of the fingerprint accepting plane, a geometrical-optic distant difference, a trapezoidal image distortion, an object compression ratio, and an orientation of a two-dimensional image sensor are formulated for the first time in terms of all three angles of the prism and the prism material. In addition, based on our mathematical model, we propose to design all three angles of the prism in such a way that the plane accepting the fingertip observed from one side of the prism is normal to the optical axis of the system. In this way, the imaging plane is perpendicular to the optical axis, eliminating the trapezoidal image distortion and leading to ease of implementation. Experimental verification using three commercially available dispersion prisms made from three different glass materials and one prism based on our design concept shows that a prism with higher refractive index provides lower trapezoidal image distortion. The experimental data generally obeys our theoretical analysis.     

1 × N add-drop filter structures using one dense wavelength division multiplexing thin-film filter

This paper proposes 1 × N add-drop filter structures in which only one thin-film filter (TF) is used. Our key idea is based on a combination of an angle-multiplexing concept and the flexibility of the optical fiber to allow a multiwavelength optical beam hit the TF several times, each time at a different angle but same position. Due to the TF angle sensitivity, the desired wavelength optical beam corresponding to the incident angle is therefore spatially isolated from the main optical beam. Our first TF-based 1 × N add-drop filter structure is arranged in a reflective design in which N wavelength optical beams can be dropped out from the main channel. For our transmissive architecture, N − 2 channels are directed to their associated output terminals while the remaining λ_N−1 and λ_N wavelength optical beams are sent out at the same port. Experimental proof of concept for our reflective TF-based 1 × 3 add-drop filter using one off-the-shelf TF, a triple fiber-optic collimator, and an optical circulator separates two wavelength optical beams with their channel spacing of 0.8 nm from the main channel. In this case, measured optical losses of 0.67 dB, 1.66 dB, and 2.59 dB are obtained for the first, the second, and the remaining dropped wavelength optical beams, respectively. Optical crosstalk and polarization dependent loss of <−18 dB and <0.08 dB are also investigated, respectively.