Engineering topics

Das, Utpal

Publications and source records attributed to Das, Utpal.

3 records

NASA NTRS1987

Nonlinear effects in coplanar GaAs/InGaAs strained-layer superlattice directional couplers

The performance characteristics of InGaAs/GaAs strained-layer superlattice coplanar ridge-type directional couplers realized by molecular beam epitaxy are reported. The measured power transfer characteristics with 1.15 micron incident photoexcitation demonstrate nonlinear coupling due to absorption associated with the tails of the excitonic resonances in the quantum wells. From a theoretical fit of the measured data, the nonlinear refractive index coefficient, n2, of the multiquantum well is found to be 2.25 x 10 to the -7th sq cm/W. This agrees very well with a value of n2 = 1.9 x 10 to the-7th sq cm/W obtained independently on the same material from interferometric measurents.

Das, Utpal↗

NASA NTRS1987

Performance characteristics of InGaAs/GaAs and GaAs/InGaAlAs coherently strained superlattice photodiodes

The properties of In(0.24)Ga(0.76)As/GaAs and GaAs/In(0.05)Ga(0.58)Al(0.37)As superlattice photodiodes grown by molecular beam epitaxy have been investigated. From the temporal response characteristics, deconvolved rise times about 60-100 ps are obtained. The measured responsivities of the photodiodes with dark currents of 5-10 nA at 10 V are about 0.4 A/W, which correspond to peak external quantum efficiencies of about 60 percent. These results indicate that very high performance photodiodes can be realized with strained layers.

Das, Utpal↗

NASA NTRS1987

InGaAs/GaAs multiquantum-well electroabsorption modulator with integrated waveguide

A monolithically integrated guided-wave modulator has been realized by using molecular-beam epitaxial regrowth and ion-milling techniques. The guiding and modulating regions consist, respectively, of In-doped GaAs and GaAs/In(0.34)Ga(0.66)As strained-layer multiquantum wells. Modulation is achieved by field-enhanced electroabsorption in the multiquantum wells. The insertion loss of the modulator is 0.9 dB, and the transmission loss in the guides is less than or equal to 1 dB/cm. The temporal response of similar GaAs/InGaAs as-grown photodiodes to pulsed laser excitation is characterized by a rise time of 115 psec.

Das, Utpal↗