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SPIE Conference on Nonlinear Optics and its Applications

Correlated photon pair generation based on spontaneous four-wave-mixing in ultra-silicon-rich nitride waveguides (Conference Presentation)

Ju Won Choi, Byoung‐Uk Sohn, George F. R. Chen, Doris K. T. Ng, Dawn T. H. Tan

Published May 23, 2018• 0 citations
Publisher

Abstract

Correlated single photons provide a means to drive applications such as quantum computing and quantum communications. Correlated single photons can be generated via parametric down conversion in second–order nonlinear media or spontaneous four–wave mixing in third–order nonlinear media. In particular, complementary metal–oxide–semiconductor (CMOS) technology allows for seamless integration with electronics, providing the potential for a completely on-chip solution for quantum information processing. Ultra–silicon–rich nitride platform is a backend CMOS compatible platform, that has already been used to obtain high gain optical parametric amplification, wideband supercontinuum and enhanced nonlinearity in photonic crystal waveguides due to its large nonlinearity. In this work, we demonstrate correlated photon pair generation based on spontaneous four–wave mixing using ultra-silicon-rich nitride waveguides for the application in CMOS–based optical quantum technologies. A CW pump at a wavelength of 1555.747nm amplified using an EDFA is filtered through five wavelength division multiplexers (WDM) with a bandwidth of 1.2nm, providing 175dB suppression of EDFA induced pump sideband noise. The filtered quasi–TE pump, adjusted using a fiber polarization controller, is coupled into an ultra–silicon–rich nitride waveguide using a lensed fiber. A SiO2 cladded waveguide with a width of 550nm and height of 300nm possesses a high nonlinear parameter of 530W^-1/m with anomalous dispersion necessary for spontaneous four-wave mixing. The waveguide output is coupled into a lensed fiber and 7 cascaded WDMs are used to provide 245dB of residual pump filtration. The pump–suppressed output is spectrally separated into signal/idler part using WDMs. We refer to lower (higher) frequency photon as the signal (idler). The spontaneously generated signal and idler photons are filtered using cascaded tunable band pass filters (OTF) centered at 1571.24nm and cascaded WDMs centered at 1540.56nm, respectively. The bandwidth of the tunable OTF and WDM is 0.5nm and 1.2nm, therefore the correlated signal/idler photons are observed within the bandwidth window of 0.5nm induced by the OTF. The signal and idler photons are measured using InGaAs/InP avalanche photodetectors. The time correlation between signal and idler photons is obtained using a time interval analyzer with a detection efficiency of 20% and dead time of 15μs.The time bin is set to 81ps and the photon collection time is 240s. The coincidence peak is located ~11ns in the time–bin histogram due to the optical-path difference between the tunable OTF and WDM at respective signal and idler sides. The experimental raw coincidence counts (Hz), calculated by subtracting the accidental rate from the coincidence peak, show a quadratic increase with respect to coupled pump power. At the maximum coupled power of 5mW, the raw coincidence count is ~1Hz. We achieve a raw coincidence–to–accidental ratio (CAR) of up to 3. Therefore, we succeeded to observe correlated photon pair generation based on spontaneous four–wave mixing using the ultra–silicon–rich-nitride waveguide as a CMOS compatible platform, for future applications in quantum technologies.

DOI
10.1117/12.2306492

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Correlated single photons provide a means to drive applications such as quantum computing and quantum communications. Correlated single photons can be generated via parametric down conversion in second–order nonlinear media or spontaneous four–wave mixing in third–order nonlinear media. In particular, complementary metal–oxide–semiconductor (CMOS) technology allows for seamless integration with electronics, providing the potential for a completely on-chip solution for quantum information processing. Ultra–silicon–rich nitride platform is a backend CMOS compatible platform, that has already been used to obtain high gain optical parametric amplification, wideband supercontinuum and enhanced nonlinearity in photonic crystal waveguides due to its large nonlinearity. In this work, we demonstrate correlated photon pair generation based on spontaneous four–wave mixing using ultra-silicon-rich nitride waveguides for the application in CMOS–based optical quantum technologies. A CW pump at a wavelength of 1555.747nm amplified using an EDFA is filtered through five wavelength division multiplexers (WDM) with a bandwidth of 1.2nm, providing 175dB suppression of EDFA induced pump sideband noise. The filtered quasi–TE pump, adjusted using a fiber polarization controller, is coupled into an ultra–silicon–rich nitride waveguide using a lensed fiber. A SiO2 cladded waveguide with a width of 550nm and height of 300nm possesses a high nonlinear parameter of 530W^-1/m with anomalous dispersion necessary for spontaneous four-wave mixing. The waveguide output is coupled into a lensed fiber and 7 cascaded WDMs are used to provide 245dB of residual pump filtration. The pump–suppressed output is spectrally separated into signal/idler part using WDMs. We refer to lower (higher) frequency photon as the signal (idler). The spontaneously generated signal and idler photons are filtered using cascaded tunable band pass filters (OTF) centered at 1571.24nm and cascaded WDMs centered at 1540.56nm, respectively. The bandwidth of the tunable OTF and WDM is 0.5nm and 1.2nm, therefore the correlated signal/idler photons are observed within the bandwidth window of 0.5nm induced by the OTF. The signal and idler photons are measured using InGaAs/InP avalanche photodetectors. The time correlation between signal and idler photons is obtained using a time interval analyzer with a detection efficiency of 20% and dead time of 15μs.The time bin is set to 81ps and the photon collection time is 240s. The coincidence peak is located ~11ns in the time–bin histogram due to the optical-path difference between the tunable OTF and WDM at respective signal and idler sides. The experimental raw coincidence counts (Hz), calculated by subtracting the accidental rate from the coincidence peak, show a quadratic increase with respect to coupled pump power. At the maximum coupled power of 5mW, the raw coincidence count is ~1Hz. We achieve a raw coincidence–to–accidental ratio (CAR) of up to 3. Therefore, we succeeded to observe correlated photon pair generation based on spontaneous four–wave mixing using the ultra–silicon–rich-nitride waveguide as a CMOS compatible platform, for future applications in quantum technologies.
In this talk, I will discuss two applications of nonlinear quantum photonics in silicon nanowires: correlated photon pair sources and a single-photon wavelength converter. Correlated photon pairs can be generated in a nonlinear silicon waveguide through the spontaneous four-wave mixing (SFWM) process, where two photons from a bright pump laser are annihilated, and a two photons are spontaneously created at different wavelengths (the signal and idler). However, indistinguishable photon pairs are of particular interest for two-photon interference experiments, meaning that the signal and idler should have the same wavelength and be entirely identical to each other. Indistinguishable pairs can be generated with the SFWM process. where two pump lasers create a degenerate signal and idler at the frequency mid-way between them. Since the two photons are indistinguishable, it is not trivial to divide them into separate waveguides so as to manipulate them individually. I will present recent results concerning a silicon quantum splitter, where degenerate pairs are created in a ring resonator which is pumped in both directions. The ring is coupled to a sagnac loop interferometer, which combines the two directions at a 50 : 50 coupler. Here, a quantum interference effect (reverse-Hong Ou Mandel interference) splits the photons to two output waveguides. This device is ultra-compact and the use of a sagnac loop means that the phase is automatically set correctly for the interference. I will also discuss progress on single photon wavelength conversion in silicon nanowires using the four-wave mixing Bragg scattering (FWMBS) process. Here, two intense pump beams are used to modulate a weak signal, causing it to shift to the idler by the frequency difference between the pumps. In principle, this can allow coherent, noiseless frequency conversion of single photon signals. Fig. 1(b) shows output spectra from a 6mm silicon nanowire when the frequency shift is varied 100 GHz to 400 GHz. Multiple peaks are visible, corresponding to up-conversion and down-conversion of the input signal.
We demonstrate room temperature heralded single photon generation in a CMOS-compatible silicon nanophotonic device. The strong modal confinement and slow group velocity provided by a coupled resonator optical waveguide produced a large four-wave-mixing nonlinearity coefficient γeff≈4100 W−1 m−1 at telecommunications wavelengths. Spontaneous four-wave-mixing using a degenerate pump beam at 1549.6 nm created photon pairs at 1529.5 nm and 1570.5 nm with a coincidence-to-accidental ratio exceeding 20. A photon correlation measurement of the signal (1529.5 nm) photons heralded by the detection of the idler (1570.5 nm) photons showed antibunching with g(2)(0)=0.19±0.03. The demonstration of a single photon source within a silicon platform holds promise for future integrated quantum photonic circuits.
Abstract Broadband frequency-correlated photon-pair sources could enable the realization of various quantum information technologies especially WDM-QKD (wavelength division multiplexed quantum key distribution) accommodating multiple users with enhanced data transmission rates. The wide transparency window, negligible nonlinear losses, and con- siderable refractive index contrast of silicon nitride (SiN) on insulator (SiO2) platform makes it an ideal material system for designing CMOS- compatible integrated photon sources based on spontaneous four-wave mixing (SFWM). We propose simple rectangular cross-section, few- cm long SiN waveguide designs capable of generating ultra-broadband frequency-correlated photon pairs via SFWM, exceeding an octave in bandwidth spanning the visible-to-telecom wavelengths (∼700-1700nm for ∼1-μm pump) with a spectral brightness of >2.5×104 photon pairs/s/nm/mW2. Such compact sources, spanning the entire telecom spectrum (across O, E, S, C, L, and U bands) on one side and cover- ing most of the major atomic transitions used in ultracold gases and solid-state based quantum memories on the other side, could poten- tially be employed in large-scale multi channel hybrid (free space + fiber) quantum networking schemes in addition to the heralding of telecom single photons by utilizing high efficiency visible detectors.
Abstract The third-order nonlinearity of silicon gives rise to a spontaneous four-wave mixing process in which correlated photon pairs are generated. Sources based on this effect can be used for quantum computation and cryptography, and can in principle be integrated with standard CMOS fabrication technology and components. However, one of the major challenges is the on-chip demultiplexing of the photons, and in particular the filtering of the pump power, which is many orders of magnitude larger than that of the signal and idler photons. Here, we propose a photonic crystal coupled-cavity system designed so that the coupling of the pump mode to the output channel is strictly zero due to symmetry. We further analyze this effect in the presence of fabrication disorder and find that, even then, a pump suppression of close to 40 dB can be achieved in state-of-the-art systems. Due to the small mode volumes and high quality factors, our system is also expected to have a generation efficiency much higher than in standard micro-ring systems. Those two considerations make a strong case for the integration of our proposed design in future on-chip quantum technologies.
Correlated photon pairs are a fundamental building block of quantum photonic systems. While pair sources have previously been integrated on silicon chips built using customized photonics manufacturing processes, these often take advantage of only a small fraction of the established techniques for microelectronics fabrication and have yet to be integrated in a process which also supports electronics. Here we report the first demonstration of quantum-correlated photon pair generation in a device fabricated in an unmodified advanced (sub-100nm) complementary metal-oxide-semiconductor (CMOS) process, alongside millions of working transistors. The microring resonator photon pair source is formed in the transistor layer structure, with the resonator core formed by the silicon layer typically used for the transistor body. With ultra-low continuous-wave on-chip pump powers ranging from 5 μμμW to 400 μμμW, we demonstrate pair generation rates between 165 Hz and 332 kHz using >80% efficient WSi superconducting nanowire single photon detectors. Coincidences-to-accidentals ratios consistently exceeding 40 were measured with a maximum of 55. In the process of characterizing this source we also accurately predict pair generation rates from the results of classical four-wave mixing measurements. This proof-of-principle device demonstrates the potential of commercial CMOS microelectronics as an advanced quantum photonics platform with capability of large volume, pristine process control, and where state-of-the-art high-speed digital circuits could interact with quantum photonic circuits.
Correlated photon pairs at 1.5μm are generated in a silicon wire waveguide (SWW) with a length of only 1.6mm. Experimental results show that the single-side count rates on both sides increase quadratically with pump light, indicating that photons are generated from the spontaneous four-wave mixing (SFWM) processes. The quantum correlation property of the generated photons is demonstrated by the ratio between coincident and accidental coincident count rates. The highest ratio measured at room temperature is to be about 19, showing that generated photon pairs have strong quantum correlation property and low noise. What is more, the wavelength correlation property of the coincident count is also measured to demonstrate the correlated photon pair generation. The experimental results demonstrate that SWWs have great potential in on-chip integrated low-noise correlated photon pair sources at 1.5 μm.