Fiber optical parametric oscillators are being busily investigated as sources of classical light, but are comparatively neglected as potential quantum light sources. Squeezed light is a crucial resource for emerging quantum technologies for computing, communications, and measurement. The direct generation of squeezed light inside optical fiber is of particular interest due to minimal material loss, desirable mode properties and compatibility with long-distance optical networks. Here, we describe a novel all-fiber continuous-wave optical parametric oscillator developed with the aim of generating squeezed light. Our device is based on a 10 cm Fabry-Perot cavity formed by two high-reflectivity fiber Bragg gratings written directly into a single section of photonic crystal fiber. This enables low-loss optical feedback and strongly resonance-enhanced four-wave mixing, with a cavity finesse of up to 400. We observe resonance-enhanced four-wave mixing in these devices, demonstrating a step towards their application as quantum light sources.
Fiber optical parametric oscillators are being busily investigated as sources of classical light, but are comparatively neglected as potential quantum light sources. Squeezed light is a crucial resource for emerging quantum technologies for computing, communications, and measurement. The direct generation of squeezed light inside optical fiber is of particular interest due to minimal material loss, desirable mode properties and compatibility with long-distance optical networks. Here, we describe a novel all-fiber continuous-wave optical parametric oscillator developed with the aim of generating squeezed light. Our device is based on a 10 cm Fabry-Perot cavity formed by two high-reflectivity fiber Bragg gratings written directly into a single section of photonic crystal fiber. This enables low-loss optical feedback and strongly resonance-enhanced four-wave mixing, with a cavity finesse of up to 400. We observe resonance-enhanced four-wave mixing in these devices, demonstrating a step towards their application as quantum light sources.
Squeezed light sources are crucial components of emerging quantum technologies for computing, communications, and measurement. The direct generation of squeezed light inside optical fibre is of particular interest due to minimal material loss, desirable mode properties and compatibility with long-distance optical networks. Squeezing of bright coherent-state laser pulses in fibre is regularly achieved via the Kerr effect, but this is not readily extensible to the continuous-wave (CW) and null-mean field regimes, and the maximum measurable squeezing is degraded by various noise processes around the common pump/signal wavelength [1].
Photonic crystal fibers (PCFs) offer a high degree of design flexibility, particularly in terms of dispersion control, making them ideal for nonlinear optical processes. These fibers have found applications in various photonic fields, including fiber lasers [1] and single-photon generation [2]. Dispersion control allows for efficient four-wave mixing at desired wavelengths, which can be used in quantum optical sources. These processes require or are enhanced by the use of fiber Bragg gratings (FBGs) in the fiber. For example, in PCF-based FWM heralded single photon sources, FBGs can be used to filter out unwanted noise contributions, such as Raman noise. However, current filtering methods are lossy [3], making it desirable to integrate filters into the fibers themselves. Additionally, specially designed PCFs with FBGs can be used for in-fiber OPOs to generate squeezed light.
Engineering non-classical states of the electromagnetic field is a central quest for quantum optics(1,2). Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems(3). We focus here on the use of a continuous-wave optical parametric oscillator(3,4). This system is based on a non-linear χ(2) crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states(5). Generating directly such states is a difficult task and would require strong χ(3) non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.
Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems3. We focus here on the use of a continuous-wave optical parametric oscillator3,4. This system is based on a non-linear χ2 crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states5. Generating directly such states is a difficult task and would require strong χ3 non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.
ABSTRACT Optical parametric oscillators are among the best‐developed quantum light sources, having already been adopted in precision measurement and underpinning various quantum computing and communication paradigms. Meanwhile, progress in photonic structures such as Bragg gratings has enabled distributed feedback oscillators to become widely established as classical laser sources with desirable properties, as well as enabling a new generation of precision optical sensors. Recent work in fabricating and processing photonic structures in nonlinear media opens the path to combining these two programs to realize distributed feedback parametric oscillators. Such devices have great potential as sources of quantum light, especially for squeezed vacuum, a crucial resource state in emerging quantum technologies. We present an analytic and fully quantum‐mechanical model of the dynamics of such devices. This approach yields the key properties of these sources, such as the parametric oscillation threshold, intracavity mode, tunability, and quantum statistics (including entanglement) of the output modes. We also discuss the application of these devices as quantum‐enhanced sensors. These results underpin future work on a versatile class of next‐generation quantum light sources.
The focus of this thesis is to investigate and fabricate a platform that can facilitate the enhancement of light-matter interactions. By tightly confining the photons and atoms to the same region of space, the probability of interaction is drastically increased as compared to free space interactions. Specifically, we focus on forming an optical cavity (or resonator) incorporated into a hollow-core photonic crystal fiber (HCPCF) using two distinct types of reflective mirrors along the axis of the fiber while still permitting atoms to be loaded into the region of high field confinement. \n \nOne means of pursuing this goal that we explored was to propose and numerically simulate two methods for implementing Bragg gratings in a HCPCF. These two methods leave the hollow-core unobstructed and are both based on controlled selective injection of photosensitive polymers into the photonic-crystal region of the hollow-core fiber, followed by interference photolithography. We report the results of numerical simulations for the hollow core fiber with Bragg gratings formed by the two methods. We find that a reflectivity of > 99.99% should be achievable from such fiber-integrated mirrors. Such a device could support high cooperativity and strong coupling regimes to be achieved. \n \nWe also demonstrate a fiber-integrated Fabry-Pérot cavity formed by attaching a pair of dielectric metasurfaces to the ends of a hollow-core photonic-crystal fiber segment. The metasurfaces consist of perforated membranes designed as photonic-crystal slabs that act as planar mirrors but can potentially allow injection of gases through their holes into the hollow core of the fiber. We have so far observed cavities with finesse of 11 and Q-factors of ~ 4.5 × 10^5, but much higher values should be achievable with improved fabrication procedures. We expect this device to enable the advancement of new fiber lasers, enhanced gas spectroscopy, and studies of fundamental light-matter interactions and nonlinear optics. These mirrors can be designed to be polarization dichroic — transparent for one polarization and reflective for another. This unique property can be exploited to allow for all signals to be directed along the high optical depth axis of the cavity and may provide a excellent platform for applications such as optical switching. \n \nFinally, we develop a novel protocol for a single photon all-optical transistor and how it may be implemented in the above mentioned fiber cavity systems. This unique scheme utilizes a far off-resonant vacuum cavity mode to stimulate a Raman absorption process of a source photon which may be switched off by the insertion of a single gate photon into the cavity mode. Relatively high switching contrasts and ratios for the source photon transmission can be obtained in our system.