Andrew J. Waddie

Application of cooled spatial light modulator for high power nanosecond laser micromachining

The application of a commercially available spatial light modulator (SLM) to control the spatial intensity distribution of a nanosecond pulsed laser for micromachining is described for the first time. Heat sinking is introduced to increase the average power handling capabilities of the SLM beyond recommended limits by the manufacturer. Complex intensity patterns are generated, using the Inverse Fourier Transform Algorithm, and example laser machining is demonstrated. The SLM enables both complex beam shaping and also beam steering.

Design and fabrication of diffractive optical elements

An introduction to the design and fabrication of diffractive optical elements is presented. Design techniques for diffractive optic in the two theoretical design areas, the scalar and resonance domains, and the dominant methods of fabrications are described. Theoretical and experimental examples are given in each section.

Diffractive optical elements for high gain lasers with arbitrary output beam profiles.

We introduce a previously unreported laser cavity configuration, using a diffractive optical element (DOE) in place of the output coupler. Such a configuration allows the DOE to work both in reflection, as a mode shaping element, and in transmission as a beam shaper. Employing dual wavelength DOE optimization techniques and phase delays greater than 2pi, allows the two functions to be designed independently. Thus, an arbitrary output beam profile can be combined with a mode shape which maximizes energy extraction from the gain medium. Devices are designed and their performance modeled for a 1m cavity with 5mm diameter mirrors and a wavelength of 632.8nm. An element with 32 quantization levels and a maximum phase delay of 8pi in transmission produces high quality results.

Design and fabrication of nano-structured gradient index microlenses

We present a novel fabrication technology for nano-structured graded index micro-optical components, based on the stack-and-draw method used for photonic crystal fibres. These discrete structures can be described with an effective refractive index distribution. Furthermore we present spherical nano-structured microlenses with a flat facet fabricated with this method and designed using an algorithm based on the Maxwell-Garnett mixing formula. Finally we show theoretical verification by using FDTD simulations for a nano-structured lens as well as experimental data obtained in the microwave regime.

Three-dimensional nanoscale subsurface optical imaging of silicon circuits

Three-dimensional subsurface imaging through the back side of a silicon flip chip is reported with a diffraction-limited lateral resolution of 166nm and an axial performance capable of resolving features only 100nm deep. This performance was achieved by implementing sample-scanned two-photon optical beam induced current microscopy using a silicon solid immersion lens and a peak detection algorithm. The excitation source was a 1530nm erbium:fiber laser, and the lateral optical resolution obtained corresponds to 11% of the free-space wavelength.

Design and fabrication of diffractive elements for laser material processing applications

Diffractive optical elements have an important role to play in the provision of process adapted beam shaping for laser-materials processing applications. The design techniques and dominant methods of fabrication are described for intra-cavity and external beam shaping diffractive elements fabricated in a variety of dielectric and metallic materials for use with a wide range of laser sources. Theoretical and experimental examples are given in each section.

Nanostructured elliptical gradient-index microlenses

We show theoretical and experimental characterizations of a nanostructured gradient-index lens. The elliptical lens is a nonguiding element fabricated using the mosaic method, which is widely used for the fabrication of photonic crystal fibers. For the first time we show experimental data in the optics regime that confirm the effective medium approximation for discrete mosaic structures with subwavelength feature size. This opens the door for the development of general asymmetric gradient-index materials.

Broadband supercontinuum generation in normal dispersion all-solid photonic crystal fiber pumped near 1300 nm

We report on octave-spanning supercontinuum generation under pumping with 1360 nm, 120 fs pulses, in an all-solid, all-normal dispersion photonic crystal fiber. The fiber was drawn from thermally matched oxide soft glasses with a hexagonal lattice 35 µm in diameter, 2.5 µm solid core and pitch of Λ/d = 0.9. The fiber was designed for normal dispersion broadly flattened in the 1200–2800 nm range. Experimentally recorded supercontinuum spectrum covered a 900–1900 nm bandwidth and was reconstructed with good agreement using numerical modeling. To the best of our knowledge, this is the first report of an experimentally demonstrated octave-spanning supercontinuum bandwidth, reaching as far as 1900 nm in the all-normal dispersion regime.

Broadband infrared supercontinuum generation in hexagonal-lattice tellurite photonic crystal fiber with dispersion optimized for pumping near 1560 nm

We report on supercontinuum generation (SG) in a hexagonal lattice tellurite photonic crystal fiber (PCF). The fiber has a regular lattice with a lattice constant Λ = 2 μm, linear filling factor d/Λ = 0.75, and a solid core 2.7 μm in diameter. Dispersion, calculated from scanning electron microscope (SEM) image of drawn fiber, has zero dispersion wavelength (ZDW) at 1410 and 4236 nm with a maximum of 193 ps/nm/km at 2800 nm. Under pumping with 150 fs/36 nJ/1580 nm pulses, supercontinuum spectrum in a bandwidth from 800 nm to over 2500 nm was observed in a 2 cm long PCF sample, which is comparable to results reported for suspended core tellurite PCFs pumped at wavelengths over 1800 nm. Measured spectrum is analyzed numerically with good agreement, and observed spectral broadening is interpreted. To our best knowledge, tellurite glass, regular lattice PCFs for successful SG in this bandwidth have not been reported before.

Optoelectronic systems based on InGaAs–complementary-metal-oxide-semiconductor smart-pixel arrays and free-space optical interconnects

Free-space optical interconnects have been identified as a potentially important technology for future massively parallel-computing systems. The development of optoelectronic smart pixels based on InGaAs/AlGaAs multiple-quantum-well modulators and detectors flip-chip solder-bump bonded onto complementary-metal-oxide-semiconductor (CMOS) circuits and the design and construction of an experimental processor in which the devices are linked by free-space optical interconnects are described. For demonstrating the capabilities of the technology, a parallel data-sorting system has been identified as an effective demonstrator. By use of Batchers bitonic sorting algorithm and exploitation of a perfect-shuffle optical interconnection, the system has the potential to perform a full sort on 1024, 16-bit words in less than 16 mus. We describe the design, testing, and characterization of the smart-pixel devices and free-space optical components. InGaAs-CMOS smart-pixel, chip-to-chip communication has been demonstrated at 50 Mbits/s. It is shown that the initial system specifications can be met by the component technologies.