Theodore Sizer

Increase in laser repetition rate by spectral selection

An experimental and theoretical study into the use of Fabry-Perot etalons as static repetition rate upconverters outside the laser cavity is discussed. It is shown that the output repetition rate can be increased up to 12 times while maintaining high average power. >

Outdoor BLAST measurement system at 2.44 GHz: calibration and initial results

There are ever increasing demands for additional capacity in wireless communications to handle voice, data, and wideband Internet applications. These demands are constrained by the bandwidth that was allocated to wireless communications. The spectral efficiencies in present day wireless systems hover around 1 bit/s/Hz. Bell-labs Layered Space-Time (BLAST) is a communication technique for achieving very high spectral efficiencies in highly scattering environments using multiple transmit and receive antennas. A measurement campaign was undertaken to assess the BLAST gains in spectral efficiency in the suburban outdoor environment for stationary subscribers. The measurements employed directive antennas to better control interference from adjacent cells. The measurements were performed over a narrow band at 2.44 GHz with five transmitting and seven receiving antennas, respectively. Extensive calibration methods, assisted by simulations, were developed to assure accurate results for the BLAST capacities of the measured remote subscriber sites. Initial results indicate that BLAST capacities of C/sub B//spl ges/38 bits/s/Hz at 20% of the measured locations and C/sub B//spl ges/24 bits/s/Hz at 50% of these locations are feasible, for reasonable link parameters and negligible interference.

InxGa1−xAs/GaAs multiple quantum well optical modulators for the 1.02–1.07 μm wavelength range

We report the operation of strained‐layer InxGa1−x As/GaAs 50‐ and 100‐period multiple quantum well optical modulators at wavelengths ranging from 1.02 to 1.07 μm. Structures were grown on GaAs substrates, as well as on strain relief InxGa1−xAs buffer layers. Devices show favorable electrical characteristics and absorption contrasts up to 57% at the exciton peak. Optical modulation of a Nd:YAG laser is demonstrated, via operation of self‐electro‐optic effect devices at 1.064 μm.

Vertically grating-coupled ARROW structures for III--V integrated optics

We propose a new all-planar technology scheme for coupling active gain or absorbing regions to low-propagation-loss, large-mode passive regions using monolithic waveguides vertically directionally coupled with a grating in an antiresonant reflecting optical waveguide (ARROW) geometry. Basic aspects of the concept have been demonstrated by laser action in an InGaAsP/InP ARROW grown by hydride vapor phase epitaxy and optically pumped by a Nd:YAG laser. This is the first demonstration of interlayer vertical directional grating coupling in III-V waveguides.

Synchronous amplification of subpicosecond pulses

In high-gain dye amplifiers, the effective storage time of the gain medium is only a few hundred picoseconds. Therefore, efficient amplification of ultrashort pulses places a stringent requirement on the synchronization between the pump pulse and the pulse to be amplified. We present a technique of short pulse generation using a dye laser synchronously pumped by a frequency-doubled CW mode locked Nd:YAG laser. Pulses as short as 70 fs are produced. The short optical pulses are subsequently amplified with two different synchronous amplification schemes using 100 ps pulses to establish the gain in the dye amplifier stages. Subpicosecond pulses with energies from a few hundred nanojoules at 500 Hz to a few hundred microjoules at 7 Hz can be obtained.

InAsyP1−y/InP multiple quantum well optical modulators for solid‐state lasers

We report the operation of strained‐layer InAsyP1−y/InP multiple quantum well optical modulators at wavelengths compatible with solid‐state lasers such as neodymium‐doped yttrium aluminum garnet. A structure having 50 periods of 100 A InAsyP1−y quantum wells with 100 A InP barriers is described that has an exciton peak at 1.05 μm and a single pass transmission contrast ratio of 1.4. Favorable comparison is made to similar InxGa1−xAs/GaAs structures.

High‐speed absorption recovery in quantum well diodes by diffusive electrical conduction

We present here picosecond time‐resolved electroabsorption measurements in GaAs quantum well p‐i‐n diode structures. While the dynamics of the vertical transport is not completely understood at present, our data reveal the importance of the ‘‘lateral’’ propagation of the photoexcited voltage pulse over the area of the doped regions. We propose a two‐dimensional ‘‘diffusive conduction’’ mechanism, which predicts a fast relaxation of the electrical pulse, with time constants ranging from 50 fs to 500 ps, determined by the size of the exciting spot, the resistivity of the doped regions, and the capacitance of the intrinsic region.

Multiple quantum well light modulators for the 1.06 μm range on InP substrates: InxGa1−xAsyP1−y/InP, InAsyP1−y/InP, and coherently strained InAsyP1−y/InxGa1−xP

We compare InP‐based materials systems for multiple quantum well modulator application in the 1.06 μm wavelength range. Quantum well/barrier systems studied are the lattice‐matched system InxGa1−xAsyP1−y/InP, the strained system InAsyP1−y/InP, and the strain‐balanced system InAsyP1−y/InxGa1−xP. 50 period samples were grown on InP substrates by chemical beam epitaxy. We find the ternary systems to be better than the quaternary in terms of exciton peak sharpness. The InAsyP1−y/InxGa1−xP system was best overall, with our results suggesting that it is coherently strained to the InP substrate.

Growth of strain-balanced InAsP/InGaP superlattices for 1.06 μm optical modulators

Using a strain‐balanced growth approach, we show that the pseudomorphic InAsP/InGaP multiple quantum well structures, grown by chemical beam epitaxy, have superior material properties for 1.06 μm modulator application when compared to the strained InAsP/InP or the lattice‐matched InGaAsP/InP systems. The broadening in absorption edge due to dislocations in the strained system, or composition fluctuations in the lattice‐matched system as a consequence of growth temperature instability, can be greatly minimized. A strong reduction in the nonradiative recombination centers in the strain‐balanced InAsP/InGaP system has been observed.

Neodymium lasers as a source of synchronized high-power optical pulses

The recent considerable progress in the development of solid-state lasers, primarily neodymium-based lasers for use as sources of short, synchronized, high-power optical pulses, is reviewed. The amplification of femtosecond optical pulses using synchronous amplification techniques with these lasers has proved particularly applicable to experimentation. The authors also presents a laser design which combines several advantageous qualities into a single laser cavity. >