Columnar quantum dashes for an active region in polarization independent semiconductor optical amplifiers at 1.55μm

Abstract

Here comes a report on the optical properties of InP based InAs columnar quantum dashes, which are proposed as an alternative for columnar quantum dots in semiconductor optical amplifiers construction since they offer convenient spectral tuning over 1.55μm together with a very broad and high gain. Electronic structure details are investigated by photoreflectance and photoluminescence and analyzed by comparison with effective mass calculations. Columnar quantum dash emission from the cleaved edge is examined by polarization resolved photoluminescence showing a transition of the dominant polarization from transverse electric to transverse magnetic with an increase in the quantum dash vertical dimension.

Orientation dependent emission properties of columnar quantum dash laser structures

“…The PL emission is TE dominated in this low energy part of the spectrum that originates from the "true" ͑i.e., three dimensionally confined͒ CQDash states. 13 This is due to the fact, that for this orientation the polarization is determined by the elongated extension of the CQDashes, 13 which is much larger than the vertical dimensions ͑about 300 nm length compared to ϳ10 nm height͒.…”

“…Due to the reduced CQDash gain in this geometry the lasing wavelength is significantly blueshifted to 1550 nm ͑see Fig. 2͒, which thus constitutes lasing of the quantum well such as immersion layer 13 with the polarization of the laser emission being also TE in this case.…”

“…This spectral part is almost unpolarized as it is dominated by transitions of the more quantum well-like states of the slightly tensile strained immersion layer. 13 So the reason why lasing does not start in TM polarization on the CQDash states is because the gain of the immersion layer is slightly higher than the gain of the CQDashes for this orientation. Nevertheless, the polarization of the CQDash emission itself was changed from TE to TM dominated by changing the geometrical orientation of the dashes.…”

Carrier relaxation dynamics in InAs/InGaAlAs quantum dashes

“…The active region consists of four sheets of 5 monolayer InAs dashes, each embedded within a 7.6 nm thick compressively strained In 0.64 Ga 0.16 Al 0.2 As quantum well [8] with a thickness of 50 nm of tensile strained In 0.50 Ga 0.32 Al 0.18 As barrier. The Q-dash structures have an average height of 3.2 nm, average width of 18 nm, and length varied from 20 to hundreds of nm.…”

“…Among the variety of such materials the quantum dashes (strongly elongated quantum dots) are of growing interest now due to perspectives in optoelectronic applications, especially in telecommunication lasers operating at 1.55 mm and longer wavelengths [7][8][9]. Size distribution of quantum dash (Q-dash) structures results in a broad gain profile and wide tunable emission (from 1.5 to 2 mm) [7].…”