On-chip Beam Splitter Research Articles

Harpoon-shaped topological photonic crystal for on-chip beam splitter

Harpoon-shaped topological photonic crystal for on-chip beam splitter

On-Chip Hong–Ou–Mandel Interference from Separate Quantum Dot Emitters in an Integrated Circuit

Scalable quantum photonic technologies require the low-loss integration of many identical single-photon sources with photonic circuitry on a chip. Relatively complex quantum photonic circuits have already been demonstrated; however, sources used so far relied on parametric down-conversion which has a probabilistic nature that intrinsically limits its efficiency and scalability. Quantum emitter-based single-photon sources are free of this limitation, but frequency matching of multiple emitters within a single circuit remains challenging. In this work, we demonstrate a key component in this regard in the form of a fully monolithic GaAs circuit combining two frequency-matched quantum dot single-photon sources interconnected with a low-loss on-chip beamsplitter connected via single-mode ridge waveguides. This device enabled us to perform a two-photon interference experiment on-chip with a visibility reaching 66%. Our device could be further scaled up, providing a clear path to increasing the complexity of quantum circuits toward fully scalable integrated quantum technologies.

Cavity-enhanced linear dichroism in a van der Waals antiferromagnet

Optical birefringence is a fundamental optical property of crystals widely used for filtering and beam splitting of photons. Birefringent crystals concurrently possess the property of linear dichroism (LD), which allows asymmetric propagation or attenuation of light with two different polarizations. This property of LD has been widely studied from small molecules to polymers and crystals but has rarely been engineered on demand. Here we use the newly discovered spin-charge coupling in the van der Waals antiferromagnetic insulator FePS3 to induce large in-plane optical anisotropy and consequently LD. We report that the LD in this antiferromagnetic insulator is tunable both spectrally and in terms of its magnitude as a function of the cavity coupling. We demonstrate near-unity LD in the visible–near-infrared range in cavity-coupled FePS3 crystals and derive its dispersion as a function of the cavity length and FePS3 thickness. Our results hold wide implications for the use of cavity-tuned LD as a diagnostic probe for strongly correlated quantum materials and offer new opportunities for miniaturized, on-chip beamsplitters and tunable filters. Researchers use spin-charge coupling and FePS3 crystals to induce large in-plane optical anisotropy and near-unity linear dichroism in the visible–near-infrared range.

Integration of quantum dots with lithium niobate photonics

The integration of quantum emitters with integrated photonics enables complex quantum photonic circuits that are necessary for photonic implementation of quantum simulators, computers, and networks. Thin-film lithium niobate is an ideal material substrate for quantum photonics because it can tightly confine light in small waveguides and has a strong electro-optic effect that can switch and modulate single photons at low power and high speed. However, lithium niobate lacks efficient single-photon emitters, which are essential for scalable quantum photonic circuits. We demonstrate deterministic coupling of single-photon emitters with a lithium niobate photonic chip. The emitters are composed of InAs quantum dots embedded in an InP nanobeam, which we transfer to a lithium niobate waveguide with nanoscale accuracy using a pick-and-place approach. An adiabatic taper transfers single photons emitted into the nanobeam to the lithium niobate waveguide with high efficiency. We verify the single photon nature of the emission using photon correlation measurements performed with an on-chip beamsplitter. Our results demonstrate an important step toward fast, reconfigurable quantum photonic circuits for quantum information processing.

Tunable on-chip optical beam splitter

Optical Devices Integrated optical approaches potentially offer a robust and compact platform to develop quantum-enhanced sensing and metrology technology. Bishop et al. describe an on-chip beam splitter in which the emission mode can be selected by electromechanically tuning the coupling of two suspended gallium arsenide waveguides. Using a quantum dot as a source of single photons pumped into the input arm of the waveguide, they show that the output port for the emitted photons can be selected by applying a small actuation voltage. Being compact, versatile, and scalable, the technique can be applied to tune other optical components, providing a powerful platform for the fabrication of on-chip quantum optical circuits. Opt. Lett. 43 , 2142 (2018).

On-chip coherent conversion of photonic quantum entanglement between different degrees of freedom.

In the quantum world, a single particle can have various degrees of freedom to encode quantum information. Controlling multiple degrees of freedom simultaneously is necessary to describe a particle fully and, therefore, to use it more efficiently. Here we introduce the transverse waveguide-mode degree of freedom to quantum photonic integrated circuits, and demonstrate the coherent conversion of a photonic quantum state between path, polarization and transverse waveguide-mode degrees of freedom on a single chip. The preservation of quantum coherence in these conversion processes is proven by single-photon and two-photon quantum interference using a fibre beam splitter or on-chip beam splitters. These results provide us with the ability to control and convert multiple degrees of freedom of photons for quantum photonic integrated circuit-based quantum information process.

Generation, guiding and splitting of triggered single photons from a resonantly excited quantum dot in a photonic circuit.

We demonstrate resonance fluorescence from single In-GaAs/GaAs quantum dots embedded in a rib waveguide beamsplitter structure operated under pulsed laser excitation. A systematic study on the excitation laser pulse duration depicts that a sufficiently small laser linewidth enables a substantial improved single-photon-to-laser-background ratio inside a waveguide chip. This manifests in the observation of clear Rabi oscillations over two periods of the quantum dot emission as a function of laser excitation power. A photon cross-correlation measurement between the two output arms of an on-chip beamsplitter results in a g(2)(0)=0.18, demonstrating the generation, guiding and splitting of triggered single photons under resonant excitation in an on-chip device. The present results open new perspectives for the implementation of photonic quantum circuits with integrated quantum dots as resonantly-pumped deterministic single-photon sources.

Directional couplers with integrated carbon nanotube incandescent light emitters.

We combine on-chip single-walled carbon nanotubes (SWNTs) emitters with directional coupling devices as fundamental building blocks for carbon photonic systems. These devices are essential for studying the emission properties of SWNTs in the few photon regime for future applications in on-chip quantum photonics. The combination of SWNTs with on-chip beam splitters herein provides the basis for correlation measurements as necessary for nanoscale source characterization. The employed fabrication methods are fully scalable and thus allow for implementing a multitude of functional and active circuits in a single fabrication run. Our metallic SWNT emitters are broadband and cover both visible and near-infrared wavelengths, thus holding promise for emerging hybrid optoelectronic devices with fast reconfiguration times.

Publisher's Note: “On-chip beamsplitter operation on single photons from quasi-resonantly excited quantum dots embedded in GaAs rib waveguides” [Appl. Phys. Lett. 107, 021101 (2015)

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On-chip beamsplitter operation on single photons from quasi-resonantly excited quantum dots embedded in GaAs rib waveguides

We present an on-chip beamsplitter operating on a single-photon level by means of a quasi-resonantly driven InGaAs/GaAs quantum dot. The single photons are guided by rib waveguides and split into two arms by an evanescent field coupler. Although the waveguides themselves support the fundamental TE and TM modes, the measured degree of polarization (∼90%) reveals the main excitation and propagation of the TE mode. We observe the preserved single-photon nature of a quasi-resonantly excited quantum dot by performing a cross-correlation measurement on the two output arms of the beamsplitter. Additionally, the same quantum dot is investigated under resonant excitation, where the same splitting ratio is observed. An autocorrelation measurement with an off-chip beamsplitter on a single output arm reveal the single-photon nature after evanescent coupling inside the on-chip splitter. Due to their robustness, adjustable splitting ratio, and their easy implementation, rib waveguide beamsplitters with embedded quantum dots provide a promising step towards fully integrated quantum circuits.

Beam splitter and combiner based on Bloch oscillation in a spatially modulated waveguide array

We theoretically and numerically investigate light beam propagation in a periodic waveguide array that is spatially modulated with a certain structure which brings novel functionalities to the array. We find that a light beam may split, coalesce, deflect, and be localized during propagation in a simply modulated waveguide array. The phenomena described originate from the Bloch oscillation and supply a convenient method for fabricating on-chip beam splitters and beam combiners.

Monolithic integration of a quantum emitter with a compact on-chip beam-splitter

A fundamental component of an integrated quantum optical circuit is an on-chip beam-splitter operating at the single-photon level. Here, we demonstrate the monolithic integration of an on-demand quantum emitter in the form of a single self-assembled InGaAs quantum dot (QD) with a compact (>10 μm), air clad, free standing directional coupler acting as a beam-splitter for anti-bunched light. The device was tested by using single photons emitted by a QD embedded in one of the input arms of the device. We verified the single-photon nature of the QD signal by performing Hanbury Brown-Twiss measurements and demonstrated single-photon beam splitting by cross-correlating the signal from the separate output ports of the directional coupler.