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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

AlGaAs Bragg Reflection Waveguides as Single and Entangled Photon Pair Source

Akriti Raj, Tobias Bauer, David Lindler, Quankui K. Yang, T. Passow, Christoph Becher

Published Jun 23, 2025• 0 citations
Publisher

Abstract

AlGaAs Bragg reflection waveguides are promising systems for the generation of single and entangled photons through the process of spontaneous parametric down-conversion (SPDC) [1]. We use a type II SPDC process where the downconverted photons are orthogonally polarized. The produced photons are inherently polarization-entangled eliminating the need for any additional entanglement setup. The material AlGaAs is our preferred choice as a nonlinear medium because it features a high nonlinear coefficient allowing for room temperature operation and has the advantage of being a non-birefringent material. Further, the material platform allows for the direct integration of a pump laser into the same chip.

DOI
10.1109/cleo/europe-eqec65582.2025.11111258

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AlGaAs Bragg reflection waveguides are promising systems for the generation of single and entangled photons through the process of spontaneous parametric down-conversion (SPDC) [1]. We use a type II SPDC process where the downconverted photons are orthogonally polarized. The produced photons are inherently polarization-entangled eliminating the need for any additional entanglement setup. The material AlGaAs is our preferred choice as a nonlinear medium because it features a high nonlinear coefficient allowing for room temperature operation and has the advantage of being a non-birefringent material. Further, the material platform allows for the direct integration of a pump laser into the same chip.
Integrated photonics is playing a key role in the development of quantum technologies covering applications ranging from quantum communication to computing and from simulations to sensing. In this context, material platforms enabling the chip-scale integration of quantum components are a key issue on the way towards real-world and large-scale technological implementations. In this paper, we review our last achievements on AlGaAs Bragg reflection waveguides emitting nonclassical states of light by spontaneous parametric down conversion. The choice of this platform combines the advantages of a mature fabrication technology, room temperature operation, emission in the telecom C-Band and compliance with electrical injection. We demonstrate the ability of these devices to generate a large variety of quantum states spanning from biphoton frequency combs to broadband polarization entanglement enabling promising applications in quantum processing as well as flexible quantum networks.
We demonstrate efficient photon pair generation for quantum communication using an all-semiconductor approach. In an AlGaAs Bragg-reflection waveguide we employ spontaneous parametric down-conversion to produce photon pairs at telecommunication wavelengths. The various phase-matching solutions present in our device can be used to create timebin or polarization entanglement. This approach can to lead to a fully integrated photon pair source with the pump laser, active and passive optical devices all on a single semiconductor chip.
In this paper, we present Bragg reflection waveguides as a novel universal platform for reaching the phasematching of spontaneous parametric downconversion process in semiconductor materials. We have designed two different waveguide structures. The first one is based on AlGaN and it is able to produce spectrally uncorrelated photon pairs. The second one is based on AlGaAs and it allows us to generate entangled photon pairs with ultra-broad spectra. Spontaneous-parametric-downconversion and second-harmonic-generation experiments are presented.
We report the observation of polarization entangled photon pairs generated by means of type-II spontaneous parametric down-conversion (SPDC) within an Al x Ga 1-x As Bragg reflection waveguide (BRW).Even though SPDC in BRW had been observed before, the photons detected were not entangled in the polarization degree of freedom.As a necessary previous step, we also characterized the phasematching properties of the waveguides designed by means of the nonlinear process of second-harmonic generation (SHG).
Quantum states of photons such as entangled and single photons are indispensable components for applications in optical quantum information processing. Being able to generate and manipulate quantum states of photons on a chip is a crucial step towards realizing real-world quantum information processing systems such as an optical quantum computer. In this thesis, theoretical and experimental research was carried out for on-chip generation of quantum states of photons via the nonlinear process of spontaneous parametric down-conversion (SPDC), including polarization entangled photons, hyperentangled photons and heralded pure single photons. A majority of the study was based on III-V semiconductor AlGaAs, which could lead to monolithic integration of pump lasers and enable electrically pump sources operating at room temperature. The generation of cross-polarized entangled photons via a type-II SPDC in an AlGaAs Bragg reflection waveguide (BRW) was first investigated. The lack of material birefringence enables the direct generation of wavelength-multiplexed polarization entangled photons with a concurrence of at least 0.77 in a bandwidth of 95 nm. Second, a technique using concurrent type-0 and type-I processes on an AlGaAs chip to generate polarization entangled photon was developed. This technique allows the generation of both co-polarized and cross-polarized entangled photons on the same chip without the need of off-chip compensation, interferometer and bandpass filter. Third, a technique of generating hyperentangled photons on an AlGaAs chip was developed by utilizing spatial modes of different guiding mechanisms. High quality entanglement could be achieved with bandpass filtering of a few nanometers without off-chip phase compensation. Four, a generic technique using nonlinear photonic nanowires to engineer two-photon quantum states was proposed. Via dispersion engineering which controls the group velocity of each mode, maximally entangled polarization entangled photons and pure heralded single photons can be generated on-chip. Design examples were applied to III-V semiconductor and ferroelectric materials. Last, a strategy to enhance the bandwidths of wavelength conversion and SPDC spectrum was developed by tapering the waveguides. Combined with further integration of pump lasers, photonic circuits and detectors, the techniques developed in this thesis provides a viable route to achieve fully integrated generation and manipulations of photonic quantum qubits.