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Applied Optics and Photonics China (AOPC)

Integrated spatially multiplexed single-photon sources in a bidirectionally pumped spiral waveguide

Fanjie Ruan, Haoran Ma, Li’ao Ye, DongHui Chen, Denghui Wang, Yuehai Wang, Jianyi Yang

Published Dec 13, 2024• 0 citations
Publisher

Abstract

Silicon-based integrated spiral waveguides are extensively used as on-chip single-photon sources. However, inherent uncertainties and limitations in single-photon fidelity pose significant theoretical performance bottlenecks. These challenges often necessitate the multiplexing of multiple sources. In this paper, we propose a novel scheme for spatial multiplexing using bidirectional spirals. By pumping a spiral waveguide bidirectionally, photon pairs are generated in both clockwise (cw) and counterclockwise (ccw) directions, each producing signal-idler photon pairs in a two-mode squeezed state. Consequently, a single spiral waveguide can function as two spatially multiplexed sources. Using CMOS fabrication technology, we constructed a bidirectional spiral waveguide structure. We measured the coincidence count rates, heralded second-order correlation function, and coincidence to accidental ratio (CAR) as functions of pump power, both before and after multiplexing. Our experimental results demonstrated a 1.67-fold increase in performance post-multiplexing. This finding underscores the potential of bidirectional spirals as spatially multiplexed sources, paving the way for the largescale integration of future photonic quantum chips.

DOI
10.1117/12.3048112

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Silicon-based integrated spiral waveguides are extensively used as on-chip single-photon sources. However, inherent uncertainties and limitations in single-photon fidelity pose significant theoretical performance bottlenecks. These challenges often necessitate the multiplexing of multiple sources. In this paper, we propose a novel scheme for spatial multiplexing using bidirectional spirals. By pumping a spiral waveguide bidirectionally, photon pairs are generated in both clockwise (cw) and counterclockwise (ccw) directions, each producing signal-idler photon pairs in a two-mode squeezed state. Consequently, a single spiral waveguide can function as two spatially multiplexed sources. Using CMOS fabrication technology, we constructed a bidirectional spiral waveguide structure. We measured the coincidence count rates, heralded second-order correlation function, and coincidence to accidental ratio (CAR) as functions of pump power, both before and after multiplexing. Our experimental results demonstrated a 1.67-fold increase in performance post-multiplexing. This finding underscores the potential of bidirectional spirals as spatially multiplexed sources, paving the way for the largescale integration of future photonic quantum chips.
Large-scale quantum photonic circuits require integrating multiple single-photon sources, which are typically based on spontaneous four-wave mixing (SFWM) in spiral waveguides or microring resonators (MRRs). Photons can be generated in both clockwise (CW) and counterclockwise (CCW) orientations from a single source in a Sagnac configuration, showing promise for improving scalability. In this work, we propose a fully integrable scheme for bidirectional creation and usage of single photons. This concept is based on two asymmetric Mach-Zehnder interferometers (AMZIs) integrated within the Sagnac loop. As a proof of concept, we fabricated a device with a spiral waveguide on a silicon chip and demonstrated its application as a quantum splitter and two multi-wavelength quantum light sources.
We demonstrate integrated spatial multiplexing of heralded single photons generated from a single 96 μm long silicon photonic crystal waveguide in a bidirectional pump configuration. By using a low-loss fiber-coupled opto-ceramic switch, the multiplexing technique enhances the brightness of the single photon source by 51.2±4.0% while maintaining the coincidence-to-accidental ratio. Compared with the demonstration of multiplexing two individual sources, the bidirectional pump scheme represents a twofold reduction in the footprint of nonlinear devices for future large-scale integration of on-chip single photon sources. The 51.2±4.0% gain will make any quantum operation requiring n photons 1.5(n) times faster.
The non-deterministic nature of photon sources poses a fundamental challenge to scaling single-photon quantum processors. While multiplexing in space, time, and frequency can enhance heralding efficiency, key bottlenecks remain in the efficiency of the on-chip resource unit and the speed of the external control system. Here, we demonstrate a high-count-rate, spatially multiplexed single-photon source on a silicon chip. By implementing a bidirectional pumping scheme, our architecture halves the number of required photon sources, creating a compact, optimized unit for future large-scale multiplexing sources. In addition, we implement a control system based on a Random-Access Memory First-In-First-Out module to improve the count rate limitation. Experimental results demonstrate a coincidence count rate gain of 1.67 under both pulsed and continuous-wave pumping regimes in our system. This work provides a scalable unit design and a robust control strategy for high-rate quantum photonic circuits.
Integrated silicon micro-ring resonator (MRR) has been widely used as on-chip single photon source. In this paper, we introduce an approach to generate frequency-degenerate photons by bidirectionally pumping an add-drop micro-ring resonator (MRR) within a Sagnac loop configuration. This scheme facilitates the concurrent generation of photon pairs from both clockwise (CW) and counterclockwise (CCW) directions, transforming a single MRR into a dual-source system. Through CMOS fabrication techniques, we realized the proposed device and conducted measurements of key parameters including the single side count rate (SSCR), coincidence count rate (CCR), and coincidence-to-accidental coincidence ratio (CAR) for both directional outputs. Notably, the CCRs exhibit remarkable similarity between the two sources, reaching approximately 550 Hz at an waveguide power of 0.59 mW. Furthermore, we observed a differential CAR, with the CCW direction yielding a lower value compared to the CW direction, with estimated maxima of 161 and 387, respectively. These findings underscore the viability of utilizing a singular MRR as a dual-source entity. Additionally, we outline the design of an on-chip structure for heralded Hong-Ou-Mandel (HOM) interference, necessitating 4-fold coincidences.Our work holds the promise of advancing the realm of large-scale integrated quantum photonic chips.
The non-deterministic nature of photon sources is a key limitation for single-photon quantum processors. Spatial multiplexing overcomes this by enhancing the heralded single-photon yield without enhancing the output noise. Here the intrinsic statistical limit of an individual source is surpassed by spatially multiplexing two monolithic silicon-based correlated photon pair sources in the telecommunications band, demonstrating a 62.4% increase in the heralded single-photon output without an increase in unwanted multipair generation. We further demonstrate the scalability of this scheme by multiplexing photons generated in two waveguides pumped via an integrated coupler with a 63.1% increase in the heralded photon rate. This demonstration paves the way for a scalable architecture for multiplexing many photon sources in a compact integrated platform and achieving efficient two-photon interference, required at the core of optical quantum computing and quantum communication protocols. Photonic quantum technologies will require efficient single-photon sources and spatial multiplexing has been explored as a route to achieve this. Here, the authors present a scheme to integrate several single-photon sources using spatial multiplexing for on-chip applications at telecommunications wavelengths.