On-chip near 100 dB pump filtering using silicon ion implantation
Akhil Varri, Daniel Wendland, Ravi Pradip, Shabnam Taherinia, Zhe Zhao, Emma Lomonte, Francesco Lenzini, Frank Brückerhoff‐Plückelmann, Wolfram H. P. Pernice
Integrated photonics is an exciting platform for quantum communication, computing, and sensing due to its inherent stability and scalability. However, full monolithic or hybrid photonic quantum technology demonstrations remain limited owing to performance and integration challenges. One of the main challenges is the filtering the high-power classical pump light from the generated photons in spontaneous parametric down-conversion sources. Here, we report what we believe to be a novel optical filtering technique based on silicon ion implantation in silicon nitride (SiN) waveguides. Our approach effectively introduces selective absorption of near-visible light, achieving nearly 100 dB suppression of the pump light at 775 nm. On the contrary, the insertion loss for light in the telecom C-band near 1550 nm is just around 4 dB with a scope of significant reduction. This result paves the way for practical and efficient integration of quantum sources, filters, and detectors on-chip, advancing the field toward scalable quantum photonic systems.
Integrated photonics is an exciting platform for quantum communication, computing, and sensing due to its inherent stability and scalability. However, full monolithic or hybrid photonic quantum technology demonstrations remain limited owing to performance and integration challenges. One of the main challenges is the filtering the high-power classical pump light from the generated photons in spontaneous parametric down-conversion sources. Here, we report what we believe to be a novel optical filtering technique based on silicon ion implantation in silicon nitride (SiN) waveguides. Our approach effectively introduces selective absorption of near-visible light, achieving nearly 100 dB suppression of the pump light at 775 nm. On the contrary, the insertion loss for light in the telecom C-band near 1550 nm is just around 4 dB with a scope of significant reduction. This result paves the way for practical and efficient integration of quantum sources, filters, and detectors on-chip, advancing the field toward scalable quantum photonic systems.
Quantum technologies hold the promise of revolutionizing computing, communication, and sensing, and integrated photonics stands as a key enabler in this realm. Silicon nitride, with its unique combination of low loss, remarkable non-linear performance, and compatibility with existing semiconductor technologies, has emerged as a promising candidate for the implementation of quantum photonic circuits. Alternately, Lithium-Niobate-OnInsulator (LNOI), a material platform well known for its high electro-optic coefficient, has also turned out to be an attractive choice for quantum integrated circuits with the development of low-loss fabrication processes. Moreover, the integration of on-chip photon sources and superconducting nanowire single-photon detectors (SNSPDs) on these platforms has paved the for scalable quantum circuits minimizing the footprint and eliminating the need for lossy interconnects. However, the integration of these components on a single material platform is often hindered by background photons from the strong classical pump light used for processes such as spontaneous parametric down-conversion (SPDC). Here, we propose silicon-implanted SiN and LNOI waveguides as a novel material platform that acts as a passive filter at visible wavelengths while imparting negligible losses in the telecom band. The implantation process can be selectively patterned with manometer precision enabling enhanced tunability of the process. Furthermore, transmission electron microscopy (TEM) results provide a thorough understanding of the material dynamics at the atomic scale allowing accurate modelling of the mode profiles. This breakthrough advances the scalability of quantum photonic technologies where the source, filters, circuits, and detectors can be integrated on a single platform.
Integrated quantum photonic chips are promising for scalable, photonic based quantum information processing. Although on-chip quantum photon sources and single photon detectors have been demostrated separately, the full integration of these components on single chip is hindered by the background photons from the strong classical pump light. Here we design and fabricate an on-chip long-pass filter which can provide 70 dB attenuation for visible light near 775 nm with less than 3 dB insertion loss for light in the telecom C-band near 1550 nm. The adiabatic design makes this device broadband and robust against fabrication errors as well as working conditions. Combined with the previously demonstrated non-classical on-chip source based on spontaneous parametric down conversion on the same material system, this platform could enable 100 dB suppression of pump light and holds promise in realizing fully integrated quantum photonic chips where the sources, filters and detectors are monolithically integrated.
Integrated photonic circuits have become an attractive platform for the quantum information processing, paving the way for quantum information management with scalable device. In this context, silicon photonics represents the most mature technology to implement the quantum system functionalities, due to its large scalability and compatibility with CMOS technology. Efficient photon-pairs sources based on Spontaneous Four-Wave Mixing (SFWM) and high-performance photodetector have been already demonstrated. The efficient detection of photon-pairs requires a pump filter at the photodetector, preserving the signal-idler pair. Thus, filters with high Extinction Ratio (ER), low Insertion Loss (IL) and narrow rejection Bandwidth (BW) are needed. Here, we propose the design of an ultra-high-performance rejection filter, based on a silicon dual-loaded single input/output Mach-Zehnder Interferometer (MZI), with one branch coupled to a Ring Resonator (RR) and the other to three serially coupled RRs forming a Coupled Optical Resonator Waveguide (CROW). Very high performance (ER = 150.55 dB, IL = 0.104 dB, BW = 0.243 nm), within a footprint of 60 µm × 160 µm, has been calculated, demonstrating its suitability for an efficient suppression of the pump signal. The filter response is also thermo-optically tuneable in a 6 MHz range, with a reconfigurability time of about 8 µs.
In this work, we design and fabricate a telecom band quantum light source (QLS) on a silicon photonic chip, which integrates a piece of a long silicon waveguide as the nonlinear medium for spontaneous four-wave mixing (SFWM) and five narrow FSR-free bandpass filters based on a grating-assisted contra-directional coupler (GACDC). Two optical filtering functions of the silicon integrated QLS have been demonstrated. First, the QLS supports two tunable outputs of photon pair generations by four GACDC filters. A wavelength tunable range of 6 nm is demonstrated. Second, one GACDC bandpass filter is designed as an on-chip pump filter before the silicon waveguide. The performances of the QLSs with and without the on-chip pump filter are measured and compared. It shows that the on-chip pump filter has the effect to enhance the performance of the QLS by suppressing the Raman noise photons generated when a pump light propagated in optical fibers before it is injected into the chip. These results show that FSR-free filters would play important roles in developing silicon integrated QLSs.
Integration of quantum optical technique on-chip is crucial for large scale applications of quantum technology, which were proven in a free space environment to be superior to the corresponding classical technology. Squeezed states of light can be used for enhancing the sensitivity of quantum sensors and for fault-tolerant quantum computing. Although chip-based squeezed light generation has advanced significantly, practical impact remains limited because coupling losses between the chip and off-chip detectors destroy delicate quantum correlations, restricting the amount of observed squeezing. Here, we overcome this limitation by implementing the idea of on-chip quantum measurement with the aid of a parametric amplifier and applying it to the squeezed state generated by a silicon nitride (SiN) microring resonator. In our scheme, two matched SiN micro-rings are sequentially constructed. The first ring generates a squeezed state, whereas the second ring acts as a high-gain parametric amplifier (PA) that measures the squeezed state before the light experiences significant off-chip loss. This architecture is inherently loss-tolerant: the amplifier elevates the quantum noise well above the vacuum level, making the measurement insensitive to downstream losses. We directly observe a quantum noise reduction of 4.6 dB from the first ring, despite a chip-to-fiber coupling loss exceeding 5 dB. This work also demonstrates the first monolithic SU(1,1) interferometer with an estimated 5 dB signal-to-noise enhancement compared to traditional linear interferometers, and thus establishes a practical pathway for chip-based quantum sensors.
We propose silicon nitride (Si3N4) nanowaveguide-based CMOS-compatible integrated sources of spectrally pure visible-telecom photon pairs. Our designs are intrinsically devoid of spectral correlations, eradicating the need for narrow-band filtering that reduces the source brightness. Further, the signal photons lie in the visible--near-infrared (vis-NIR) band, which can provide increased heralding efficiency of the idler photon in the telecom band using high-efficiency single-photon detectors. For example, a rectangular-cross-section silica-clad Si3N4 nanowaveguide with dimensions $680\text{~nm}\ifmmode\times\else\texttimes\fi{}840\text{~nm}$ and length 7 cm provides a heralded single-photon purity of approximately $91\mathrm{%}$ for a pump wavelength of 956.8 nm and a pump bandwidth of 1200 GHz, with the signal and idler lying in the visible and telecom bands at approximately 701 nm and approximately 1505 nm, respectively, demonstrating a peak spectral brightness of approximately $1.2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ photon pairs/s/nm/mW2 for a linear propagation loss of 0.5 dB/cm. The effect of propagation losses on the purity is also studied for such source designs. We also propose some designs capable of generating high-purity photon pairs to address various specific vis-NIR quantum memory transitions with telecom-band interfacing for long-distance hybrid quantum networks. Such compact on-chip sources could have potential applications in various quantum technologies, such as sensing, simulation, computing, communication, and networking.