For the past two decades, fiber optics technology has been under development in the Army, Navy, and Air Force for applications, which range from fiber optic payout dispensers for air, land, and marine vehicles to fiber optic sensors for vehicle-navigation and environmental sensing and monitoring. Teleoperated weapon systems have been designed to provide the soldier with operator standoff capability, non-line-of-sight targeting, precision kill capability, with unmatched bandwidth. The Government/industry team conducted tremendous research efforts in developing a reliable fiber optic dispenser design, which is part of the data transmission link between a launch platform and a weapon. This paper reviews the advanced fiber optic technology, which includes automated fiber winding, and pack mechanics and payout dynamics models for producing stable fiber optic payout dispensers and thermally symmetric fiber optic gyroscope coils for operations in military environments. Also, non-destructive fiber optic techniques for measuring distributed strain and temperature in wound fiber packs will be discussed. The findings of the novel technique adopted for fiber pack quality verification are also discussed. Finally, the results of research efforts that are underway to develop low cost, high performance, miniature fiber optic gyroscopes for use in tactical weapon systems are presented.
The report is a review of work one-dimensional photonic band gap (PBG) materials, carried out by the Quantum Optics Group at the US Army Aviation and Missile Command during the past few years. This work has benefited from national and international collaborations between academic, industrial, and governmental research organizations. The research effort has benefited from a multifaceted approach that combined innovative, theoretical methods with fabrication techniques in order to address the physics of structures of finite length, i.e., the description of spatio-temporal linear and nonlinear dynamics and boundary conditions. In this work we will review what we consider three major breakthroughs: (a) the discovery of transparent metals; (b) discovery of critical phase matching conditions in PBG structures for second harmonic and nonlinear frequency conversion; (c) development of a PBG true time delay device.
Our report addresses linear and nonlinear wave propagation in PBG materials, one-dimensional structures in particular. Most investigators generally address two and three-dimensional structures. We choose one-dimensional systems because in the past they have proven to be quite challenging and have pointed the way to the new physical phenomena that are the subject of this report. In addition, one-dimensional systems can be used as a blueprint for higher dimensional structures, where the work is necessarily much more computationally intensive, and the physics much less transparent as a result.
Step-wise two-photon excitation studies are useful for the development of upconversion lasers and infrared quantum counter devices. Our recent experimental results on erbium doped materials revealed efficient violet upconversion emission under diode laser excitation. Latest experiments on infrared quantum counter studies are also discussed. Different energy upconversion phenomena and the upconversion laser development are also reviewed in detail. A discussion is given on the estimation of excited state absorption cross sections.
Recently, we have demonstrated a picosecond all-optical switch, which also functions as a partial all-optical NAND logic gate using a novel polydiacetylene that is synthesized in our laboratory. The nonlinear optical properties of the polydiacetylene material are measured using the Z-scan technique. A theoretical model based on a three level system is investigated and the rate equations of the system are solved. The theoretical calculations are proven to match nicely with the experimental results. The absorption cross-sections for both the first and higher excited states are estimated. The analyses also show that the material suffers a photochemical change beyond a certain level of the laser power and its physical properties suffer radical changes. These changes are the cause for the partial NAND gate function and the switching mechanism.
Inducing efficient visible light emission from silicon (Si) and understanding the underlying physics have long defined fascinating scientific and technological challenges. We present a comprehensive study on the origin and nature of red to ultraviolet (UV) light emission from Si quantum dots (QDs). We report the strongest quantum confinement (QC) effects to date and find that: (i) light emission can be stable in ambient and continuously tunable from the red to the UV through a single mechanism, i.e., QC, (ii) the energy gap increases from QC with decreasing size (Eg(d)- 1.14 ∝1/41.4) to energies significantly greater than previously observed (3.80 eV), (iii) the lowest optical transition remains predominantly indirect despite strong QC in small QDs (~14 Å diameter), and (iv) these properties can apply to QDs with and without a surface oxide layer. These results agree well with calculations that go beyond effective mass approximations. Visible light emission can also result from localized traps and may be mistaken for quantum confined emission.
The crystal growth technique and associated optical characterizations of polydiacetylene PTS , poly bis(p-toluene sulfonate) of 2,4-hexadiyne-l,6-diol, are reviewed in this paper. The commonly observed defects such as twinning and cracking and their origins are analyzed. Two factors were found to significantly decrease the density of defects and improve the quality. First, the monomer crystal was grown reasonably quick consistent with single crystal growth to reduce polymerization. Second, the polymerization rate was reduced dramatically for the 10% to 90% conversion region for a smooth conversion by reducing the polymerization temperature. The absorption spectrum, typical Z-scans for measuring the optical nonlinearity, and SEM pictures of the surfaces are given as measures of the optical quality of the PTS crystals.