Understanding photoluminescence in semiconductor Bragg-reflection waveguides: Towards an integrated, GHz-rate telecom photon pair source

TL;DR

This paper investigates photoluminescence in semiconductor Bragg-reflection waveguides used for telecom photon pair sources, identifying causes and proposing wavelength shifts and material adjustments to enhance performance at high repetition rates.

Contribution

It reveals the origin of broadband photoluminescence in BRWs and suggests practical modifications to improve integrated photon pair sources for GHz-rate applications.

Findings

Photoluminescence mainly results from impurity-related radiative recombination.

Shifting operation to the L-band reduces photoluminescence significantly.

Material adjustments enable higher pump powers and multi-GHz pair rates.

Abstract

Compared to traditional nonlinear optical crystals, like BaB$_2$O$_4$, KTiOPO$_4$ or LiNbO$_3$, semiconductor integrated sources of photon pairs may operate at pump wavelengths much closer to the bandgap of the materials. This is also the case for Bragg-reflection waveguides (BRW) targeting parametric down-conversion (PDC) to the telecom C-band. The large nonlinear coefficient of the AlGaAs alloy and the strong confinement of the light enable extremely bright integrated photon pair sources. However, under certain circumstances, a significant amount of detrimental broadband photoluminescence has been observed in BRWs. We show that this is mainly a result of linear absorption near the core and subsequent radiative recombination of electron-hole pairs at deep impurity levels in the semiconductor. For PDC with BRWs, we conclude that devices operating near the long wavelength end of the S-band or the short C-band require temporal filtering shorter than 1 ns. We predict that shifting the operating wavelengths to the L-band and making small adjustments in the material composition will reduce the amount of photoluminescence to negligible values. Such measures enable us to increase the average pump power and/or the repetition rate, which makes integrated photon pair sources with on-chip multi-gigahertz pair rates feasible.