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Degenerated Spontaneous Parametric Down Conversion in Semiconductor Waveguide with -43m Crystal Symmetry

Eleonora De Luca, Marcin Świłło

Published Jan 1, 2019• 0 citations
OpenAlex

Abstract

In this paper, a configuration consisting in a pump propagating in an orthogonal direction with respect to the surface of a nanowaveguide is studied. It is possible to show that the generation by spontaneous parametric down-conversion of a signal and an idler photons inside the nanowaveguide is strongly dependent on the waveguide thickness, because the high refractive index of the waveguide core creates also an optical cavity for the pump field. Furthermore, it was evaluated the best condition for photon-pair generation in case of a nanowaveguide in gallium indium phosphide, which has a −43m symmetry.For the same waveguide geometry, but orientation parallel to the [110] plane, it is possible to use spontaneous parametric down-conversion to generate counter-propagating photon-pair with the same polarization. When the efficiency of the generated photon-pairs in TM0 and TE0 modes is the same, then it is possible to obtain polarization entangled photons, by using this configuration. Furthermore, by adding a mirror at one of the end of the waveguide, the system can be used to produce a squeezed-state.

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•Jan 1, 2026•0 citations
In this paper, a configuration consisting in a pump propagating in an orthogonal direction with respect to the surface of a nanowaveguide is studied. It is possible to show that the generation by spontaneous parametric down-conversion of a signal and an idler photons inside the nanowaveguide is strongly dependent on the waveguide thickness, because the high refractive index of the waveguide core creates also an optical cavity for the pump field. Furthermore, it was evaluated the best condition for photon-pair generation in case of a nanowaveguide in gallium indium phosphide, which has a −43m symmetry.For the same waveguide geometry, but orientation parallel to the [110] plane, it is possible to use spontaneous parametric down-conversion to generate counter-propagating photon-pair with the same polarization. When the efficiency of the generated photon-pairs in TM0 and TE0 modes is the same, then it is possible to obtain polarization entangled photons, by using this configuration. Furthermore, by adding a mirror at one of the end of the waveguide, the system can be used to produce a squeezed-state.
Generation of entangled photon pairs at telecom wavelength has been garnering a growing interest in the context of quantum communications and quantum computing. Several generation techniques have been proposed, including spontaneous Four-Wave Mixing in resonators or Spontaneous Parametric Down Conversion (SPDC) in Periodically Polled Lithium Niobate (PPLN) waveguides. Large photon pair efficiencies have been demonstrated in particular in PPLN on insulator [3]. However, polarization entangled photon pair generation (Type II phase matching configuration) suffers from a less favourable non-linear coefficient and optical mode birefringence in PPLN.
We present an optical configuration for the generation of degenerate counterpropagating photon pairs via spontaneous-parametric down-conversion in subwavelength thin waveguides with 4 ¯ 3 m symmetry. The generated photon pairs exhibit orthogonal polarizations and excite TE- and TM-like modes. Compensation of the momentum mismatch between the excited modes by pump tilting enables tunable degenerate emission across the S , C , and L bands (1400 to 1600 nm). Experimental verification confirms an efficiency of ≈ 10 − 5 photon pairs per pump photon with an expected linewidth of 0.3 nm in 2-mm-long Ga 0.51 In 0.49 P waveguides. Published by the American Physical Society 2024
In this paper, we show that the polarization-entangled photon pairs can be generated using spontaneous parametric down conversion in a dual periodically poled planar waveguide. The proposed configuration is shown to have efficiencies higher than in the case of bulk crystals with the possibility of ease of collection, like in channel waveguides, with the additional feature of wavelength tunability. We also show that the planar waveguide configuration permits the generation of hyperentanglement in polarization and path degree of freedom, which is not possible in case of channel waveguide. The proposed design should find applications in quantum information processing using integrated quantum optics.
We explore how III-V semiconductor microring resonators can efficiently generate photon pairs and squeezed vacuum states via spontaneous parametric down-conversion by utilizing their built-in quasi-phase-matching and modal dispersion. We present an analytic expression for the biphoton wave function of photon pairs generated by weak pump pulses and characterize the squeezed states that result under stronger pumping conditions. Our model includes loss and captures the statistics of the scattered photons. A detailed sample calculation shows that for low pump power conversion efficiencies of ${10}^{\ensuremath{-}5}$, corresponding to a rate of 39 MHz for a pump power of $1\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{W}$, are attainable for rudimentary structures such as a simple microring coupled to a waveguide, in both the continuous-wave and pulsed-excitation regimes. Our results suggest that high levels of squeezing and pump depletion are attainable, possibly leading to the deterministic generation of non-Gaussian states.
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.
Entangled photons have acted as a workhorse in many quantum technologies, including cryptography, imaging, sensing, and computation. With the growing demands of quantum technology, the entangled photon pair sources are required to be compact and integrable. For the last few years, the field of quantum optics in the nanoscale has demonstrated photon pair generation in ’flat’ optics such as thin layers, Van der Waals crystals, micro-, nano-antennas, and metasurfaces. The word ’flat’ is used because such optical platforms have sub-wavelength thicknesses. Due to the short travel length inside the sources, they can possess multiple functions that their bulky counterparts cannot have. This doctoral thesis addresses photon pair generation in ’flat’ optics via second- and third-order nonlinear processes, which are spontaneous parametric down-conversion (SPDC) and spontaneous four-wave mixing (SFWM). The main aims of the thesis are to understand how the photon pair generation is realized via SPDC and SFWM on subwavelength-scale platforms, and to make a bridge between photon pair generation via two nonlinear processes under the presence of optical resonances. The thesis covers two experimental parts related to SPDC and SFWM, and one future expectation of the SFWM in metamaterials. The first part of the thesis addresses one of the multi-functionalities that has recently been reported: the emission direction control of the photon pairs. A 150 nm-thick gallium phosphide (GaP) metasurface is used as a source. The metasurface supports a quasi-bound state in the continuum (quasi-BIC) resonance, enhancing the electric field inside the material. I generate the entangled photons through the SPDC process. The generated photons are in two different wavelengths under the given pump wavelength: signal photon at the resonance, and idler photon out of the resonance. The photon pair generation rate is enhanced by 66 times compared to the unpatterned GaP slab since the vacuum field in the signal mode is enhanced by the resonance. The generated photons obey the transmission spectrum of the metasurface. As a result, the signal photons at resonance are mostly reflected, and the idler photons are transmitted after generation. This result is the first work of photon demultiplexing by a metasurface. The second part of the thesis covers the photon pair generation through SFWM in thin nonlinear films. Silicon-rich silicon nitride (SiN) layers are selected as the sources. The layers have an intriguing characteristic that the third-order nonlinear susceptibility (chi-3) differs with the nitrogen doping rate. I generate the photon pairs through chi-3 variant SiN layers. The thicknesses of the samples are all sub-wavelength level, having a few hundred nanometers. Time-energy correlation measurements are conducted for all samples, and the second-order correlation functions (g(2)(0)) are calculated. The maximum g(2)(0) of the samples exceeds 2. Interestingly, I observed two-photon interference effects between photon pairs generated in the layers and the fused-silica substrate, which allows me to estimate the chi-3 values of the samples by knowing the reference: chi-3 value of the substrate. The last part of the thesis introduces designs of metasurfaces and possible experimental schemes for photon pair generation through SFWM. Yet, due to its weak light-matter interaction in third-order nonlinear processes, the photon pair generation through SFWM has not been observed in metasurfaces. However, it is fairly possible to enhance the vacuum fields at the output photon modes and generate photon pairs because preliminary work in unpatterned slabs has already been observed in this thesis. Finally, I introduce a fabricated metasurface. It needs improvements, but it is quite promising for the ongoing project.