Applied Optronics (United States)

A single-layer cholesteric film was fabricated using a pitch-gradient strategy, achieving broadband and polarization-selective reflection with stable optical properties. This simple and stack-free approach enables advanced photonic applications requiring both wide-spectrum reflection and selective circular polarization control.

For optical communication technologies, polarization control can be used to extend the dimension of data loading. However, most polarization controlling devices for optical communication suffer from severe dispersion, leading to signal loss. In this study, a hybrid-splay twisted liquid crystal (HST-LC) is utilized to achieve linear polarization rotation in the communication wavelength range (1260-1675nm). To make a HST-LC more practical for most optical applications, the twisting angle of the HST-LC is enlarged to optimize the voltage required for rotating the input linear polarization by 90°. Also, the rotation angle range is optimized to satisfy the essential requirement for polarization applications (covering 0° to 135°). Additionally, the achromatic modulation of linear polarization in the optical communication range is confirmed.

The growth of two-dimensional materials into three-dimensional geometries holds the promise for high performance hybrid materials and novel architectures. The synthesis of such structures, however, proceeds in fundamentally different flow regimes compared to conventional CVD where pressure differences and wall collisions are neglected. We here demonstrate the remarkable stability of graphene growth under varying fluid dynamic flow regimes. We investigate the growth process across different flow conditions using confined growth in refractory pores. Analysis of the growth rate reveals a transport-limited process which allows experimental determination of the gas diffusion coefficient. The diffusion coefficient was found to be constant for large pore dimension but scales with pore dimension as the pore size decreases below the mean free path providing clear evidence for previously predicted Knudsen molecular-flow conditions for atomic confinement. Surprisingly, changes to the flow conditions by two orders of magnitude do not cause qualitative changes of the graphene growth process. This unique behavior was attributed to rarefied flow conditions by scaling analysis and an analytical relation between growth rate and constriction could be extracted that proves accurate throughout the investigated conditions. Our results demonstrate a fundamentally different growth process compared to traditional CVD processes that is akin to atomic layer deposition and highlight the feasibility of high-quality 2D-material growth on 3D morphologies with ultra-high aspect ratios.

Diode lasers in the wavelength range of 630 to 740 nm are ideally suited for photodynamic therapy (PDT) and dermatological applications. Turnkey laser systems based on multiple discrete diode lasers offer significant advantages over other laser technologies, including dye, ruby and tunable lasers with respect to simplicity, cost, size reliability and maintenance. Applied Optronics Corp. has developed laser system platforms that permit the use of multiple diode lasers, each fiber-coupled to a single emitter, wired in series and mounted in a sealed aluminum module with its fiber bundle exiting and terminating in an SMA 905 connector. Low numerical aperture bundle fibers with core diameters less than 100 /spl mu/m permit the use of a large number of individually selected diode lasers to be used while maintaining a tight bundle packing ratio. The bundle output is re-imaged through an optical relay to decrease spot size while increasing numerical aperture. The laser system can use of wide variety of standard 400-1,000 micron, NA 0.37 PDT diffuser and other fibers. For PDT applications, light of a specific wavelength that is highly absorbed by a photosensitizer drug (dye) is required for optimal efficacy. Activation of the photosensitizer causes the release of singlet oxygen radicals that cause cell death. The photosensitizer is selectively absorbed by rapidly reproducing or abnormal cells (e.g., cancer cells) and, if a lesion or tumor can be exposed to the specific wavelength of light required, a cancerous tumor can be eliminated while preserving normal tissue. PDT has been largely successful as a treatment for cancer and pre-cancerous conditions in the lung, esophagus, oral cavity and skin. PDT is also being investigated for use in noncancerous treatment in ophthalmology for age related macular degeneration.

Summary form only given. 0.78 /spl mu/m, Al-free active-region, compressively-strained (/spl Delta/a/a=0.85%) InGaAsP quantum well diode lasers have been grown by MOCVD. Broad-stripe (100 /spl mu/m-wide) devices exhibit low threshold current densities, 290 A/cm/sup 2/ (L=1 mm), and cw front-facet output powers of 2.2 W.

This paper describes a mobile robot with acoustic- and vision-based intrusion detection capability. A difficult task for the robot is to distinguish between observed angular velocity of stationary versus moving objects. Techniques for extracting motion cues relevant to this task given angle-only object position measurements are given. Effectively, the motion cues compare perceived velocity (direction and magnitude) and angular momentum with that expected of stationary objects.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Phase-locked operation of an array of semiconductor lasers has been extensively studied in recent years [1-12] with the eventual goal of obtaining high power (several hundreds of milliwatts) into a single spatial lobe of radiation. Earlier, the studies were concentrated on the integration of two types of lasers, namely, gain guided [1,2,5,6,] and index guided [7] stripe geometry lasers into an array with different stripe widths and varied spacing between the stripes. Phase lock of these lasers can only be achieved with a proper combination of width, stripe spacing and driving current. A considerable amount of interest has since been focused on the study of conditions under which a single spatial mode with narrow divergence angle can be produced. At present there is no reproducible process that can be used to fabricate single lobe phase-locked semiconductor arrays. The main application of the semiconductor array now is to pump solid state lasers. In this case we do not require phase locking or single lobe far field. In this paper we report fabrication of a different kind of semiconductor laser array, i.e. incoherent laser array. The main features of the incoherent laser arrays are : 1) Low threshold index-guided laser elements, 2) Single lobe far-field pattern, 3) Low astigmatism, 4) Low current operation, 5) Densely packed and 6) Total electrical and optical isolation. We expect such laser arrays will have important applications in multi-head optical-disk reading and writing, multi-fiber optical communications and line of sight communications.

The cost-effective application of optical communications components requires that the product characterization measurements also predict the actual performance of the component in-situ, particularly for fundamental attributes such as attenuation. In this work, attenuation characteristics of individual components by several measurement methods were compared to the observed power reduction (loss) over a range of complexities of a practical LAN link topology for the ANSI X3T9.5 Fiber Distributed Data Interface (FDDI). The results clearly indicate the need to use quasi-steady-state measurement methods for LAN components, even when the total link length is less than 100 meters.