Single-crystal diamond combines exceptional optical, thermal, and mechanical properties while hosting optically addressable and spin-coherent colour centres, making it a promising platform for integrated quantum and nonlinear photonics. However, practical post-fabrication mechanisms for dynamically controlling and tuning monolithic diamond photonic circuits remain limited. Here, we demonstrate all-optical modulation and long-lived tuning of suspended diamond Fabry--Perot nanobeam cavities containing nitrogen-vacancy centres. Under 532~nm illumination, the infrared (1000 to 1100~nm) cavity response is governed by two competing contributions: a well-understood thermo-optic red-shift, and a novel charge-mediated blue-shift that we attribute to the free-carrier plasma dispersion effect. With 10~mW of 20~kHz-modulated green light, we achieve an infrared modulation depth of approximately 45\% of the available reflection contrast. Green illumination also produces quasi-permanent photo-refractive resonance blue-shifts, with a maximum observed tuning of 3.15~nm (0.87~THz), without measurable degradation of the cavity linewidth or contrast. Achieving the same cavity shift in a lithium-niobate Pockels modulator would require 200 to 500~V across a \(5~μ\mathrm{m}\) electrode gap. These results establish a monolithic diamond nanophotonic platform combining agile and reversible modulation with long-lived optical reconfiguration, two key ingredients in photonic technologies.
Single-crystal diamond combines exceptional optical, thermal, and mechanical properties while hosting optically addressable and spin-coherent colour centres, making it a promising platform for integrated quantum and nonlinear photonics. However, practical post-fabrication mechanisms for dynamically controlling and tuning monolithic diamond photonic circuits remain limited. Here, we demonstrate all-optical modulation and long-lived tuning of suspended diamond Fabry--Perot nanobeam cavities containing nitrogen-vacancy centres. Under 532nm illumination, the infrared (1000 to 1100nm) cavity response is governed by two competing contributions: a well-understood thermo-optic red-shift, and a novel charge-mediated blue-shift that we attribute to the free-carrier plasma dispersion effect. With 10mW of 20kHz-modulated green light, we achieve an infrared modulation depth of approximately 45% of the available reflection contrast. Green illumination also produces quasi-permanent photo-refractive resonance blue-shifts, with a maximum observed tuning of 3.15nm (0.87THz), without measurable degradation of the cavity linewidth or contrast. Achieving the same cavity shift in a lithium-niobate Pockels modulator would require 200 to 500V across a (5μ\mathrm{m}) electrode gap. These results establish a monolithic diamond nanophotonic platform combining agile and reversible modulation with long-lived optical reconfiguration, two key ingredients in photonic technologies.
Diamond constitutes a promising material platform for a myriad of photonic applications. In this work, we demonstrate several novel nonlinear optical phenomena in fibre-taper coupled diamond micro and nanocavities. Central to these observations are ensembles of nitrogen-vacancy (NV) centres native to the diamond devices. We first show photoinduced modifications of second-harmonic generation (SHG) from a microdisk, and demonstrate, for the first time, that the strength of the SHG strongly depends on the charge state of the NV centres. Illuminating the microdisk with a green laser quenches the SHG signal. Removing the green laser recovers the original SHG signal, allowing for deterministic optical switching of the device’s χ(2). We next show strong photorefractive blue-shifting of the resonance frequency in a diamond photonic crystal cavity. The total frequency shift exceeds the intrinsic linewidth, corresponding to a fractional change in refractive index of ∼ −10−4.
Single-crystal diamond nanocavities have tremendous potential for use in quantum and nonlinear optical technologies. The ability to precisely control their resonant frequencies is essential for many applications, and in situ tuning is particularly desirable. In this work, we demonstrate deterministic resonance tuning of a diamond nanocavity. We observed a photorefractive effect in concert with the generation of third-harmonic light within the device. This effect blue-shifted the cavity resonance frequency by 20.2 (2) GHz, exceeding the cavity linewidth. The shift corresponded to a fractional change in refractive index of −1.05(1)×10 −4 , and its relaxation occurred over several tens of hours. Although photorefraction is a second-order nonlinear effect and has previously not been observed in diamond owing to its vanishing χ (2) , the observed behavior is consistent with the generation of non-zero χ (2) by electric fields from charged crystal defects. In addition to allowing tuning of diamond cavities for resonant nonlinear and quantum photonics applications, this observation could enable the realization of diamond frequency converters and electro-optical modulators that rely on second-order nonlinearity.
Diamond is a leading quantum photonics platform due to its ability to host qubits based on crystal defects such as nitrogen-vacancy centres. Fabricating nanophotonic devices from defect-rich diamond, which underpins many quantum sensing technologies, promises enhanced performance and integrability of diamond quantum sensors. Here we demonstrate microdisk cavities fabricated from defect-rich diamond that support optical modes with high quality factor (Q∼7×104 at 1042nm) and show that they exhibit saturable absorption. Power-dependent spectroscopy measurements spanning 979nm to 1604nm are used to observe intensity-dependent cavity loss and extract wavelength-dependent absorption coefficients and saturation intensities. At 1047nm, we observe saturation and measure a saturation intensity of 2.1(8)MW/cm2 and an absorption coefficient of 0.53(2)cm−1. These results provide insight into defect-mediated optical loss in diamond nanophotonics and suggest strategies to harness defect-induced nonlinearities in future diamond photonic devices.
Efficient interfaces between optical photons and quantum bits are fundamental building blocks for quantum networks and large-scale quantum computers. We demonstrate an integrated platform for scalable quantum optics based on color centers coupled to diamond nanodevices. First, we incorporate nitrogen-vacancy (NV) centers in diamond into hybrid nanophotonic crystal cavities. Despite our progress towards coupling the NV to cavity photons, we find that the NV-cavity interface is limited by the imperfections of the color center's properties and its local environment. We approach this challenge first by characterizing and modifying the diamond surface to reduce the environmental noise affecting the NV optical transition. Subsequently, we develop a new approach that makes use of a quantum emitter with intrinsic protection from this noise: the silicon-vacancy (SiV) center in diamond. We demonstrate that SiV centers introduced through ion implantation feature highly coherent optical transitions, even inside nanostructures. By placing SiV centers inside all-diamond photonic crystal cavities, we achieve strong SiV-photon coupling with a cooperativity of greater than 20. Using this platform, we realize a quantum-optical switch controlled by the spin degree of freedom of a single SiV. By measuring intensity correlations of indistinguishable Raman photons emitted into a single waveguide, we observe a quantum interference effect resulting from the superradiant emission of two probabilistically entangled SiV centers. Finally, we demonstrate controllable photon-mediated interactions between the spin degrees of freedom of two cavity-coupled SiV centers. When the optical transitions of the two SiV centers are tuned into resonance, the coupling of each SiV to the common cavity mode results in a coherent interaction between the two SiVs, leading to the observation of super- and sub-radiant two-SiV states.
Weak optical nonlinear interactions can be greatly enhanced by tight confinement and recirculation of light in an optical resonator. In this work, we demonstrated cavity-enhanced strong green third-harmonic generation from a single-crystal diamond photonic crystal nanocavity. Furthermore, we observe a novel photorefractive resonance blue-shift of the cavity, arising from charge excitation by intense IR pump photons and generated third-harmonic photons. The resulting photorefractive blue-shift greatly exceeds the cold cavity linewidth.
Luminescent lattice defects (so called “color centers”) in diamond provide a robust, solid-state architecture for exploring quantum optics, with many facilitating direct access to highly coherent electron and nuclear spins. The past two decades have seen tremendous advances in our ability to prepare and control the quantum states of these atom-like systems. For instance, demonstrations that leverage the diamond nitrogen vacancy (NV–) center as a spin-photon interface have included the generation of indistinguishable photons, a quantum bit memory exceeding 1 second, entanglement of two distance solid-state qubits, and deterministic long distance quantum teleportation. While diamond color centers are an attractive platform for scalable quantum information processing, the diamond solid-state matrix, by its very nature, inhibits efficient photon collection into either free-space or fiber-optical systems. Due to its large refractive index, emitted photons are inevitably trapped within the diamond crystal by total internal reflection, limiting count rates and overall scalability of information processing via quantum optical protocols. To this end, there has been significant progress towards integrating individual diamond color centers within well-defined radiation channels: namely, those provided by monolithic diamond nanophotonic networks. Currently, on-chip low loss (~ few db/cm) diamond waveguide networks are available, as well as key passive photonic elements like micron scale ring and disk resonators and photonic crystal cavities, with high optical quality (Q) factors. Specifically, we recently demonstrated a scalable ‘angled-etching’ nanofabrication method for realizing nanophotonic networks starting from bulk single-crystal diamond substrates (MJ Burek et al., Nano Letters 2012, MJ Burek et al., Nat Comm. 2014). Angled-etching employs anisotropic oxygen-based plasma etching at an oblique angle to the substrate surface, resulting in suspended optical structures with triangular cross-sections. Using this approach, we demonstrated high Q-factor (> 10^5) optical nanocavities fabricated in bulk single-crystal diamond, operating over a wide wavelength range (visible to telecom). Beyond isolated photonic devices, we have further developed free-standing angled-etched waveguides which efficiently route photons between diamond optical nanocavities, while maintaining physical support through attachment to the bulk substrate. Although on-chip diamond nanophotonics realized by angled-etching continue to mature, efficient off-chip optical coupling schemes which provide near seamless transition of photons on-chip into commercial optical fibers remain an outstanding challenge. This is especially pertinent in applications involving single photons, such as quantum optics with diamond color centers. Herein, we demonstrate a high efficiency fiber-optical interface with aforementioned on-chip diamond nanophotonic networks, achieving > 90% power coupling at both telecom and visible wavelengths. The coupling scheme utilizes a single mode optical fiber, with one end fabricated into a conical taper, to adiabatically transition guided light between on-chip tapered diamond waveguides and off-chip optical fiber networks. Additionally, we develop techniques to robustly pigtail single-mode fibers with diamond waveguide couplers, yielding a packaged technology that may potentially enable deployment in harsh environments, including vacuum, sub-Kelvin cryogenics, or even liquid/biological environments. With these newly developed optical integration schemes, single-crystal diamond is now a viable integrated nanophotonics platform, servicing a range of applications, from non-linear optics and chemical sensing, to quantum science and cavity optomechanics.