Compact computational spectrometer using a solid wedged low finesse etalon.

A novel, to the best of our knowledge, two-layer hybrid solid wedged etalon was fabricated and combined with a traditional imager to make a compact computational spectrometer. The hybrid wedge, comprised of ${{\rm Nb}_2}{{\rm O}_5}$ and Infrasil 302, was designed to operate from 0.4-2.4 µm. Initial demonstrations, however, used a complementary metal-oxide semiconductor (CMOS) imager and demonstrated operation from 0.4-0.9 µm with spectral resolutions ${\lt}\;{30}\;{{\rm cm}^{- 1}}$ from single snapshots. The computational spectrometer itself operates similarly to a spatial Fourier transform spectrometer (FTIR), but rather than use conventional Fourier-based methods or assumptions, the spectral reconstruction used a non-negative least-squares fitting algorithm based on analytically computed wavelength response vectors determined from extracted physical thicknesses across the entire two-dimensional wedge. This new computational technique resulted in performance and spectral resolutions exceeding those that could be achieved from Fourier processing techniques applied to this wedge etalon. With an additional imaging lens and translational scanning, the system can be converted into a hyperspectral imager.

High efficiency coherent beam combining of semiconductor optical amplifiers.

We demonstrate 40 W coherently combined output power in a single diffraction-limited beam from a one-dimensional 47-element array of angled-facet slab-coupled optical waveguide amplifiers at 1064 nm. The output from each emitter was collimated and overlapped onto a diffractive optical element combiner using a common transform lens. Phase locking was achieved via active feedback on each amplifier's drive current to maximize the power in the combined beam. The combining efficiency at all current levels was nearly constant at 87%.

High speed, high power one-dimensional beam steering from a 6-element optical phased array.

Beam steering at high speed and high power is demonstrated from a 6-element optical phased array using coherent beam combining (CBC) techniques. The steering speed, defined as the inverse of the time to required to sweep the beam across the steering range, is 40 MHz and the total power is 396 mW. The measured central lobe FWHM width is 565 µrad. High on-axis intensity is maintained periodically by phase-locking the array via a stochastic-parallel-gradient-descent (SPGD) algorithm. A master-oscillator-power-amplifier (MOPA) configuration is used where the amplifier array elements are semiconductor slab-coupled-optical-waveguide-amplifiers (SCOWAs). The beam steering is achieved by LiNbO(3) phase modulators; the phase-locking occurs by current adjustment of the SCOWAs. The system can be readily scaled to GHz steering speed and multiwatt-class output.

Diffractive coherent combining of a 2.5 kW fiber laser array into a 1.9 kW Gaussian beam.

Five 500 W fiber amplifiers were coherently combined using a diffractive optical element combiner, generating a 1.93 kW beam whose M(2)=1.1 beam quality exceeded that of the inputs. Combining efficiency near 90% at low powers degraded to 79% at full power owing to thermal expansion of the fiber tip array.

Active coherent beam combining of diode lasers.

We have demonstrated active coherent beam combination (CBC) of up to 218 semiconductor amplifiers with 38.5 W cw output using up to eleven one-dimensional 21-element individually addressable diode amplifier arrays operating at 960 nm. The amplifier array elements are slab-coupled-optical-waveguide semiconductor amplifiers (SCOWAs) set up in a master-oscillator-power-amplifier configuration. Diffractive optical elements divide the master-oscillator beam to seed multiple arrays of SCOWAs. A SCOWA was phase actuated by adjusting the drive current to each element and controlled using a stochastic-parallel-gradient-descent (SPGD) algorithm for the active CBC. The SPGD is a hill-climbing algorithm that maximizes on-axis intensity in the far field, providing phase locking without needing a reference beam.

Self assembly and optical properties of dendrimer nanocomposite multilayers.

Ultrathin multilayers are important for electrical and optical devices, as well as for immunoassays, artificial organs, and for controlling surface properties. The construction of ultrathin multilayer films by electrostatic layer-by-layer deposition proved to be a popular and successful method to create films with a range of electrical, optical, and biological properties. Dendrimer nanocomposites (DNCs) form highly uniform hybrid (inorganic-organic) nanoparticles with controlled composition and architecture. In this work, the fabrication, characterization, and optical properties of ultrathin dendrimer/poly(styrene sulfonate) (PSS) and silver-DNC/PSS nanocomposite multilayers using layer-by-layer (LbL) electrostatic assembly techniques are described. UV-vis spectra of the multilayers were found to be a combination of electronic transitions of the surface plasmon peaks, and the regular frequency modulations attributable to the multilayered film structure. The modulations appeared as the consequence of the highly regular and non-intermixed multilayer growth as a function of the resulting structure. A simple model to explain the experimental data is presented. Use of DNCs in multilayers results in abrupt, flat, and uniform interfaces.