AlGaAs Bragg-reflection waveguides offer the potential for on-chip entangled photon sources which integrate the entangled photon source and the pump source in the same chip. We designed and experimentally realized an AlGaAs Bragg-reflection waveguide structure in which the effective refractive indices for TE and TM polarized down converted photons are the same to improve the degree of entanglement without external compensation. This was realized by appropriate choice of the ridge width of 1.8 μm, which offers lateral optical confinement. The difference in effective refractive indices has been reduced by more than a factor of 10 compared to waveguides of several micron width. Photon generation rates of 9,200,000 cps (single rates) and 1,700,000 cps (coincidence rate) and a coincidence accidence ratio of about 60 were determined for these waveguides for 5 mW pump power.
Quantum sensing and quantum communication systems rely on high-performance single- or entangled-photon sources and single-photon detectors enabling experiments based on the quantum nature of single photons. In this contribution, we discuss the development of an entangled-photon source delivering entangled photon pairs with wavelengths of about 1550 nm alongside with single-photon avalanche detectors (SPADs) for the short-wave infrared (SWIR) and for the extended SWIR (eSWIR) spectral range. The fabrication processes of such quantum-enabling technologies is highlighted. The entangled-photon source is based on AlGaAs Bragg-reflection waveguides. Very low difference in effective refractive index of TE and TM polarized photons – important for high polarization entanglement without external compensation – as well as high single and coincidence count rates were achieved. For the fabrication of InGaAs/InP SWIR SPADs, the key technology is the planar process technology via zinc diffusion to produce spatially confined p-type regions. For the zinc-diffusion process, a novel method of selective epitaxial overgrowth was developed, achieving the intended double-well diffusion profile. Experimental data of thus fabricated InGaAs/InP SPADs show the expected dark-current, photo-current, and multiplication-gain characteristics in linear-mode operation as well as breakthrough behavior in Geiger-mode operation at 240 K, which is a typical operating temperature for InGaAs/InP SPADs achievable by thermoelectric cooling. GaSb-based SPADs for the eSWIR are fabricated in a mesa approach showing the expected dark current behavior as well. All three different devices are linked by enabling quantum technologies in the (e)SWIR as well as by using our III/V-semiconductor technology facilities.
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