Sebastian Lourdudoss

Monolithically integrated InP-based photonic chip development for O-CDMA systems

This work discusses photonic integration efforts toward developing an InP-based monolithically integrated photonic chip for optical code-division multiple-access (O-CDMA) system applications. The chip design includes the colliding pulsed mode (CPM) locked laser, the Mach-Zehnder interferometer-based threshold detector (MZI), and the monolithic O-CDMA encoder/decoder chip based on array-waveguide-gratings and phase modulator arrays. The compact 4 /spl times/ 1 cm monolithic chip can replace a complex and large O-CDMA setup based on bulk optics. The integration technique involves active-passive integration using dry etching, metal organic chemical vapor deposition growth, and lateral hydride vapor phase epitaxy regrowth technologies. The fabricated CPM showed stable 1.54 ps modelocked laser output, the MZI showed excellent O-CDMA threshold detection, and the O-CDMA encoder showed Walsh-code O-CDMA encoding. Further, the fabricated devices showed excellent planarity, which accelerate our progress toward monolithic integration of O-CDMA systems.

Hydride vapor phase epitaxy revisited

The salient features of hydride vapor phase epitaxy (HYPE) process in the fabrication of optoelectronic devices are demonstrated by combining the state of the art results of several groups working in this field.

An investigation on hydride VPE growth and properties of semi-insulating InP:Fe

Growth of highly resistive semi-insulating InP : Fe has been achieved by the Hydride VPE technique in an ambient consisting mostly of nitrogen. After dealing with some thermodynamic considerations pertinent to InP:Fe growth, the experimental growth parameters are described. It is shown that various amounts of iron can be introduced into the InP crystal just by varying the temperature of the iron source. The crystal quality of the grown material is estimated to be good by etch pit density and x-ray diffraction analyses. Current-voltage behaviour and capacitance studies on ann+-SI-n+ structure are explained by invoking the theory of current injection in solids by Lampert and Mark: the experimental current densities at the threshold of each observed regime are compared with the theoretically derived current densities; in the absence of current injection, the measured capacitance is found to be the same as the geometrical capacitance.

Thermal strain in indium phosphide on silicon obtained by epitaxial lateral overgrowth

High-resolution x-ray diffraction reciprocal lattice mapping and low-temperature photoluminescence (PL) were used to study the thermal strain in InP layers grown on Si (001) substrate by hydride vapor-phase epitaxial lateral overgrowth (ELO) technique. Good agreement is found between the PL and x-ray measurements. We show that strain in the grown ELO InP/Si layers is affected by the aspect ratio (width to height ratio) of the ELO InP layer. Almost strain-free InP layer with high crystallographic quality is obtained on Si substrate, which is similar to that of a homoepitaxial InP layer.

Modulation response measurements and evaluation of MQW InGaAsP lasers of various designs

Results from modulation measurements of 40 high-speed multi quantum well (MQW) lasers ((lambda) equals 1.55 micrometer) of various designs are presented. By fitting the careful calibrated measurements, both magnitude and phase, to an analytical transfer function we were able to determine if a certain laser was limited by thermal effects, parasitic-like effects, or nonlinear gain effects. We found that most of the devices in the study were limited by thermal effects and/or contact parasitics. The parasitics were found to be determined by the width of the high-doped contact layer and cladding layers below the metallic contact. It was also found that a high doping of the separate confinement heterostructure (SCH) layers decreases the damping of the relaxation peak since it facilitates the carrier transport. Improved contact design and high doped SCH-layers resulted in modulation bandwidths of around 24 GHz.

1.55 μm buried heterostructure laser via regrowth of semi-insulating InP:Fe around vertical mesas fabricated by reactive ion etching using methane and hydrogen

A GaInAsP/InP Fabry-Perot-type buried-heterostructure quantum well laser operating at 1.55 μm has been realized utilizing iron-doped semi-insulating InP around vertical mesas fabricated by reactive ion etching using methane and hydrogen. A maximum cw output power of 19 mW has been achieved on as-cleaved chips of 300 μm length with a quantum efficiency of 21% per facet. Threshold currents lie between 20 and 25 mA. As low as 2 Ω series resistance has been measured despite an ohmic contact area not exceeding that of the 2-μm-wide mesa. A 3 dB bandwidth of 7.5 GHz at 12 mW output power is obtained from the small-signal frequency modulation measurements.

Epitaxial lateral overgrowth of InP on Si from nano-openings: Theoretical and experimental indication for defect filtering throughout the grown layer

We present a model for the filtration of dislocations inside the seed window in epitaxial lateral overgrowth (ELO). We found that, when the additive effects of image and gliding forces exceed the d ...

Monolithic InP 100-Channel

We demonstrate monolithic integration of a 100-channel arrayed-waveguide grating (AWG) with 10-GHz channel spacing and 100 optically controlled Michelson-interferometer-based phase and amplitude modulators. The high-resolution AWG showed better than -15-dB crosstalk, and the modulator extinction ratio was better than 20 dB with either electrical or optical modulation control. The twin-integrated devices comprise a 50-mm diameter InP wafer with 1200 independent optoelectronic components.

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We report on successful spectral phase encoding and decoding operation in a pair of monolithically integrated InP encoder chips, each consisting of an arrayed waveguide grating (AWG) pair and an eight-channel electrooptic phase shifter array. The monolithic fabrication process includes anisotropic reactive ion etching and planarizing hydride-vapor-phase-epitaxy lateral regrowth to realize buried hetero-waveguide structures in AWGs and phase shifters. Electrooptical modulation in the phase shifter arrays in the encoder chip achieved Walsh-code-based optical code-division multiple access (O-CDMA) encoding and decoding. The matched-code encoding-decoding operation resulted in error-free performance in the presence of an interferer, indicating good potential for O-CDMA network applications

10-GHz Device for Optical Arbitrary Waveform Generation

Abstract GaInAsP / GaInAsP multi quantum well (MQW) structures with 1% compressive strain in the wells and a bandgap wavelenght of 1.55 μm have been grown by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). Photoluminescence (PL) measurements at 300 and 4 K together with X-ray diffraction analysis reveal a strong dependency of the material quality on the MOVPE growth conditions. The photoluminescence intensity could be increased by more than a factor of 3 by optimizing reactor pressure and temperature. Under properly chosen pressure and temperature in the reactor, we found a greatly reduced sensitivity of the material quality to other parameters such as growth interruptions or barrier composition. When utilizing strain-compensating barriers, the number of strained quantum wells could be increased up to 32, without any indication for material degradation due to strain relaxation. Utilizing those findings, distributed feedback (DFB) laser structures employing 8 compressive strained wells with lattice-matched as well as strain-compensating barriers have been grown. The processed lasers showed excellent static and high-frequency characteristics with threshold currents as low as 3.3. mA and a 3dB modulation frequency of 21.7 GHz, which is among the highest values ever reported for DFB lasers.