Abstract Fabry‐Pérot (F‐P) cavities are highly desirable for atom cooling and narrow‐linewidth generation. However, there are few studies on integrated F‐P cavities with high‐quality factors in the visible and near‐visible wavelength ranges, particularly at 780 nm, which corresponds to the energy transition of rubidium atoms. In this work, an integrated F‐P cavity design based on silicon nitride is demonstrated achieving an intrinsic quality factor of 6.1 × 105 at 780 nm without thermal annealing, along with a broad operating bandwidth of 500 nm and high fabrication tolerance. To the best of the knowledge, this quality factor represents the highest reported value in these wavelength ranges, accompanied by the largest operating bandwidth. These results offer significant potential for advancing on‐chip atom cooling and contribute to the broader development of photonic integrated circuits and quantum optics.
CMOS-compatible photonic chips are highly desirable for real-world quantum optics devices due to their scalability, robustness, and integration with electronics. Despite impressive advances using Silicon nanostructures, challenges remain in reducing their linear and nonlinear losses and in creating narrowband photons necessary for interfacing with quantum memories. Here we demonstrate the potential of the silicon nitride (Si3N4) platform by realizing an ultracompact, bright, entangled photon-pair source with selectable photon bandwidths down to 30 MHz, which is unprecedented for an integrated source. Leveraging Si3N4's moderate thermal expansion, simple temperature control of the chip enables precise wavelength stabilization and tunability without active control. Single-mode photon pairs at 1550 nm are generated at rates exceeding 107 s-1 with mW's of pump power and are used to produce time-bin entanglement. Moreover, Si3N4 allows for operation from the visible to the mid-IR, which make it highly promising for a wide range of integrated quantum photonics applications.
Multi-wavelength quantum light sources, especially at telecom band, are extremely desired in quantum information technology. Despite recent impressive advances, such a quantum light source with high quality remains challenging. Here we demonstrate a multi-wavelength quantum light source using a silicon nitride micro-ring with a free spectral range of 200 GHz. The generation of eight pairs of correlated photons is ensured in a wavelength range of 25.6 nm. With device optimization and noise-rejecting filters, our source enables the generation of heralded single-photons - at a rate of 62 kHz with
gh(2)(0)=0.014±0.001, and the generation of energy-time entangled photons - with a visibility of
99.39±0.45% in the Franson interferometer. These results, at room temperature and telecom wavelength, in a CMOS compatible platform, represent an important step towards integrated quantum light devices for the quantum networks.
Open Fabry-Perot microcavities represent a promising route for achieving a quantum electrodynamics (cavity-QED) platform with diamond-based emitters. In particular, they offer the opportunity to introduce high-purity, minimally fabricated material into a tunable, high quality factor optical resonator. Here, we demonstrate a fiber-based microcavity incorporating a thick ($>10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\text{m}$) diamond membrane with a finesse of 17 000, corresponding to a quality factor $Q\ensuremath{\sim}{10}^{6}$. Such minimally fabricated thick samples can contain optically stable emitters similar to those found in bulk diamond. We observe modified microcavity spectra in the presence of the membrane, and we develop analytic and numerical models to describe the effect of the membrane on cavity modes, including loss and coupling to higher-order transverse modes. We estimate that a Purcell enhancement of approximately 20 should be possible for emitters within the diamond in this device, and we provide evidence that better diamond surface treatments and mirror coatings could increase this value to 200 in a realistic system.
The field of photonic integrated circuits (PIC) has flourished in the past two decades, fueling numerous cutting-edge applications across sensing, networking, data interconnect, and quantum information processing. As a guiding material for PIC, Si
3N
4 has seen extensive use for its ultra-low loss, broad transparency, and diversity in implementation across both thin and thick films. Although the standard, traditional silicon dioxide (SiO
2) on silicon (Si) substrates that underpin the majority of Si
3N
4 photonics face drawbacks in the form of long-wavelength transparency limited by SiO
2, high-stress deposition for anomalous dispersion thick-film Si
3N
4, and leakage loss to the Si layer for low-confinement thin-film Si
3N
4. Featuring increased long-wavelength transparency into the mid-infrared, low-stress deposition of Si
3N
4, and a low index, this work investigates sapphire substrates as alternate hosts for Si
3N
4 photonics with greater spectral coverage and reduced fabrication complexity. This work presents a robust method of fabricating ultra-low loss photonic integrated circuits on a 500-nm-thick Si
3N
4-on-sapphire platform, exhibiting record-low losses below
0.1dB/cm. Implemented using this process are high-Q microrings with intrinsic quality factors in excess of
4.5×106 and coupled-ring photonic molecules to support nonlinear gain. Leveraging the achievable low loss and high-Q, this work further reports the first demonstration of Kerr-comb and soliton generation on the Si
3N
4-on-sapphire platform. These advances in loss, quality factor, and soliton generation on this versatile, broad-transparency platform pave the way for future work in spectroscopy and quantum-enhanced sensing across previously prohibited spectral regions for Si
3N
4 photonics with reduced fabrication complexity.