Robert J. Deri

Comparison of Nd:phosphate glass, Yb:YAG and Yb:S-FAP laser beamlines for laser inertial fusion energy (LIFE) [Invited]

We present the results of performance modeling of diode-pumped solid state laser beamlines designed for use in Laser Inertial Fusion Energy (LIFE) power plants. Our modeling quantifies the efficiency increases that can be obtained by increasing peak diode power and reducing pump-pulse duration, to reduce decay losses. At the same efficiency, beamlines that use laser slabs of Yb:YAG or Yb:S-FAP require lower diode power than beamlines that use laser slabs of Nd:phosphate glass, since Yb:YAG and Yb:S-FAP have longer storage lifetimes. Beamlines using Yb:YAG attain their highest efficiency at a temperature of about 200K. Beamlines using Nd:phosphate glass or Yb:S-FAP attain high efficiency at or near room temperature.

Dynamic etch mask technique for fabricating tapered semiconductor optical waveguides and other structures

Using a novel dynamic etch mask technique and wet chemical etchants, we have produced semiconductor structures with tapered thicknesses, with horizontal slope angles as small as 0.9°. With this technique we have fabricated GaAs/GaAlAs rib optical waveguides in which the etch depth tapered from 0.2 to 1.0 μm over a distance of 50 μm, resulting in a 2× change in mode size, with an excess taper loss of less than 0.2 dB. The technique is capable of producing tapers in different orientations, at arbitrary locations on a sample, and appears to be useful for a wide variety of materials systems and devices.

Low‐loss multiple quantum well GaInAs/InP optical waveguides

Propagation losses as low as 0.24±0.06 dB/cm are demonstrated for single‐mode, GaInAs/InP multiple quantum well rib waveguides at 1.52 μm wavelength. We show that reproducibly low losses (≤0.6 dB/cm for rib widths ≥3 μm) can be maintained over a large chip area (9.4×5 mm2). Origins of the loss are discussed.

Quantitative analysis of integrated optic waveguide spectrometers

We show how scalar diffraction theory can be used to quantitatively evaluate insertion losses in integrated optic spectrometers based on planar waveguide and etched grating technologies. This approach is applied to optimize the loss-limited spectral operating range of these devices. We also show how limitations in the photolithographic process used for grating definition can result in appreciable spectrometer insertion losses.<<ETX>>

Optical power transfer in vertically integrated impedance-matched waveguide/photodetectors: physics and implications for diode-length reduction

We identify the physical basis of the irregular absorption (spatial transients) observed in vertically integrated and impedance-matched waveguide/photodiodes using numerical simulations. We then show how the mechanism underlying these transients can be exploited to design diodes 500% shorter than conventional evanescently coupled waveguide/photodiodes, in order to achieve low capacitance and high-speed operation.

Laser diode to single-mode fiber ball lens coupling efficiency: full-wave calculation and measurements.

We show that the coupling efficiency from a laser diode (LD) to an optical fiber through a ball lens can be calculated accurately using the exact solution to Maxwells equations for the scattering of a beam from a dielectric sphere. Our calculated results agree closely with coupling measurements from an asymmetric LD for two different ball lenses.

Multiwavelength parallel optical interconnects for massively parallel processing

We describe a multiwavelength, multifiber (parallel) optical interconnect based on multimode fiber ribbon cables with applications in massively parallel processing systems. By combining the benefits of parallel optics and coarse wavelength division multiplexing high aggregate throughputs are possible in a broadcast and select architecture that provides a single hop to all nodes. We identify the key components needed for such a system and report on our component development efforts for multiwavelength parallel optical interconnects. System components reported herein include a four-wavelength bit-parallel transmitter using a silicon optical bench and hybrid packaging, and two-port and three-port wavelength selective filter modules packaged to be compatible with mechanically transferable ferrule terminated ribbon cables. The transmitters were modulated up to 1.25 Gb/s with a bit-error rate better than 10/sup -12/ and no measurable power penalty due to multiple wavelength bit parallel operation. The filters exhibited insertion losses of between 1 and 2 dB and would support 10 nm spaced channels at -23-dB crosstalk.

GaAs/AlGaAs single‐mode optical waveguides with low propagation loss and strong optical confinement

Singe‐mode optical waveguides have been fabricated with a saturated bromine water etchant using single‐heterostructure GaAs/AlGaAs epitaxial material, with propagation losses as low as 0.6 dB/cm for 1.66 μm deeply etched ribs (Δneff≂2.4) and losses below 0.2 dB/cm for 0.23 μm shallowly etched ribs (Δneff =0.0067), measured at λ=1.5 μm.

GaAs/GaAlAs asymmetric Mach-Zehnder demultiplexer with reduced polarization dependence

A two-channel GaAs/AlGaAs asymmetric Mach-Zehnder wavelength demultiplexer with reduced polarization dependence was demonstrated. The device was fabricated on a single heterostructure comprising a 1.45- mu m-thick layer of GaAs on a 6.0- mu m-thick Ga/sub 0.85/Al/sub 0.15/As buffer layer. The epitaxial layers were grown by MOCVD (metalorganic chemical vapor deposition) on an n/sup +/ GaAs substrate. The single-mode rib waveguides, 3 mu m wide and 0.29 mu m high, were fabricated using standard photolithographic techniques followed by chemical etch and removal of the resist mask. Extinction ratios of 24.1 dB for transverse electric (TE) and 22.5 dB for transverse magnetic (TM) polarized light were measured on a device with an anti-reflection coating on its input and output facets. The active length of the device is approximately 6.5 mm and total loss of 1.1 dB was obtained in a 16-mm-long chip.<<ETX>>

Single‐mode semiconductor optical waveguides with large dimensions suitable for compact bend applications

We demonstrate a novel waveguide structure for realization of integrated optics with compact waveguide bends (radii≊1 mm), low propagation loss (0.45 dB/cm), and large guide dimensions (5 μm width) to facilitate input coupling. Experimental results using single‐mode GaAs/AlGaAs heterostructure guides at 1.52 μm wavelength are presented.