We have synthesized ternary InGaAs nanowires on (111)B GaAs surfaces by metal-organic chemical vapor deposition. Au colloidal nanoparticles were employed to catalyze nanowire growth. We observed the strong influence of nanowire density on nanowire height, tapering, and base shape specific to the nanowires with high In composition. This dependency was attributed to the large difference of diffusion length on (111)B surfaces between In and Ga reaction species, with In being the more mobile species. Energy dispersive X-ray spectroscopy analysis together with high-resolution electron microscopy study of individual InGaAs nanowires shows large In/Ga compositional variation along the nanowire supporting the present diffusion model. Photoluminescence spectra exhibit a red shift with decreasing nanowire density due to the higher degree of In incorporation in more sparsely distributed InGaAs nanowires.

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Influence of Nanowire Density on the Shape and Optical Properties of Ternary InGaAs Nanowires

In this paper, the basic principle of operation, design issues, limitations, recent developments and emerging research trends on wide-bandwidth lasers and modulators for radio-frequency photonic applications are reviewed. The topics covered are wide-bandwidth lasers, lumped and traveling-wave electroabsorption modulators, traveling-wave LiNbO/sub 3/, GaAs, and polymer modulators.

Wide-bandwidth lasers and modulators for RF photonics

Integrating the input and output waveguides with a multiple-quantum-well (MQW) electro-absorption (EA) optical modulator is shown to achieve ultra-high-speed modulation while keeping the total device length long enough for easy fabrication and packaging. Testing with fabricated modulators showed that a shorter modulation region results in a larger modulation bandwidth. The additional loss due to the waveguide integration was less than 1 dB. An optimized modulator showed a large modulation bandwidth of 50 GHz, a low driving voltage of less than 3 V, and a low insertion loss of 8 dB. A prototype module of this modulator had a bandwidth of greater than 40 GHz. Optimizing the MQW structure makes the modulator insensitive to polarization. These results demonstrate that MQW-EA modulators with integrated waveguides are advantageous in terms of fabrication, packaging, and ultra-high-speed modulation.

Ultra-high-speed multiple-quantum-well electro-absorption optical modulators with integrated waveguides

A method for growing In x Ga 1−x As epitaxial layer on a lattice mismatched InP substrate calls for depositing by organo-metallic vapor phase epitaxy, or other epitaxial layer growth technique, a plurality of discreet layers of InAs y P 1−y over an InP substrate. These layers provide a buffer. Each succeeding buffer layer has a distinct composition which produces less than a critical amount of lattice mismatch relative to the preceding layer. An In x Ga 1−x As epitaxial layer is grown over the buffer wherein 0.53≦x≦0.76. A resulting InGaAs structure comprises an InP substrate with at least one InAsP buffer layer sandwiched between the substrate and the InGaAs epitaxial layer. The buffer layer has a critical lattice mismatch of less than 1.3% relative to the substrate. Additional buffer layers will likewise have a lattice mismatch of no more than 1.3% relative to the preceding layer. The number of buffer layers is determined by the resulting bandgap desired in the InGaAs epitaxial layer, which, in turn, determines the composition of the In x Ga 1−x As epitaxial layer, and thus, the lattice mismatch.

Using a critical composition grading technique to deposit InGaAs epitaxial layers on InP substrates

This paper describes the design and demonstration of advanced 40-Gb/s return-to-zero (RZ) tunable all-optical wavelength converter technologies for use in packet-switched optical networks. The device designs are based on monolithic integration of a delayed interference Mach-Zehnder interferometer (MZI) semiconductor optical amplifier (SOA) wavelength converter with a sampled-grating distributed Bragg reflector tunable laser and an on-chip waveguide delay. Experimental results are presented demonstrating error-free wavelength conversion with 1-dB power penalty at 40-Gb/s data rates. By incorporating label modulation functionality on-chip along with a fast tunable 40-Gb/s wavelength converter, fully monolithic packet-forwarding chips are realized that are capable of simultaneous error-free wavelength conversion of 40-Gb/s payloads, remodulation of 10-Gb/s packet headers, and data routing through fast wavelength switching

Monolithic Wavelength Converters for High-Speed Packet-Switched Optical Networks

We report on a MQW electroabsorption modulator with tensile-strained wells. The device transmission is shown to be fully polarization insensitive, i.e. both in amplitude and phase. The modulation efficiency is over 20 GHz/V (bandwidth higher than 20 GHz and 1 V drive voltage) which is the highest figure of merit reported for any kind of polarization insensitive modulator. Full polarization independence is further demonstrated by 2.5 Gb/s transmission at 1.55 /spl mu/m over 475 km of standard fiber without penalty at 10/sup -9/ BER whatever the polarization. >

Full polarization insensitivity of a 20 Gb/s strained-MQW electroabsorption modulator

Selective area MOVPE growth of InP, InGaAs and InGaAsP using TBAs and TBP at different growth conditions

Hydrogen and nitrogen have been employed as carrier gases for the selective growth of InP-based materials on patterned substrates using tertiarybutyl-arsine (TBAs) and -phosphine (TBP) as alternative group-V sources at different reactor pressures. The properties of the deposited layers have been found to be mainly determined by the diffusion coefficient in the vapour phase, which increases by reducing the reactor pressure or using H2 instead of N2. A higher edge growth, combined with a smaller zone of enhanced growth and, where appropriate, In-enrichment near the masks was detected at atmospheric pressure deposition and for the use of N2, respectively. Furthermore a higher selectivity has been observed for both carriers at reduced reactor pressures and when using H2 instead of N2. Nitrogen as carrier gas offers an additional independent parameter to control the properties of selectively deposited layers and reduces the safety risks of the MOVPE process especially when being combined with less toxic group-V sources.

A. Mircea

Papers

Full polarization insensitivity of a 20 Gb/s strained-MQW electroabsorption modulator

Selective area MOVPE growth of InP, InGaAs and InGaAsP using TBAs and TBP at different growth conditions

The role of N2 and H2 as carrier gas on the selective area MOVPE of InP-based heterostructures using TBAs and TBP as group-V sources

Monolithic integration of strained layer multi-quantum well distributed feedback laser and external modulator by selective disordering