RU2848145C1 - Single photon source - Google Patents

Abstract

FIELD: optical communication systems.

SUBSTANCE: invention relates to single-photon sources of optical radiation. The single-photon source contains a pulsed periodic UV excitation source and a carbon nanotube or fullerene molecule containing an iodine atom and an oxygen molecule located in the cavity of a quartz optical fibre, with the carbon nanotube located between Bragg gratings forming a resonator in the quartz light guide.

EFFECT: creation of an effective source of single photons in the spectral region of transparency of quartz light guides and the Earth's atmosphere.

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Description

AREA OF TECHNOLOGY

The invention relates to the field of optical communication systems, namely to single-photon sources of optical radiation, and can be used to create highly secure information transmission systems based on the principle of quantum cryptography and the implementation of a quantum key distribution protocol through free space and fiber-optic networks, as well as in metrology for testing single-photon detectors.

PRIOR ART

Russian Federation Patent for Invention No. RU 2722133, "Educational Setup for Performing Experiments in Quantum Optics for the Purpose of Studying Quantum Cryptography Protocols," describes a quasi-single-photon source used in most existing cryptographic systems, which utilize a laser pulse attenuated to a single-photon state. The main drawback of this source is that it is not a true single-photon source; the number of photons in a pulse obeys Poisson statistics, and the average number of photons in a pulse can only be controlled using attenuators.

Russian Federation Patent for Invention No. RU 2746870 "Single-Photon Radiation Source" The source comprises an optical pumping channel with an excitation radiation source, a luminescence channel with a single-photon generation element based on a diamond nanocrystal, a magnification system with a multiplicity of M and a scanning system, a receiving channel and a dichroic mirror providing the ability to direct the excitation radiation into the luminescence channel, and the generated photons into the receiving channel, characterized in that the said generation element is realized in the form of a diamond single crystal with luminescence growth centers of concentration N, and confocal modules with pinholes are installed in the optical pumping channel and the receiving channel. A disadvantage of such a source is the complexity of manufacturing and aligning the structure containing nanocrystals with vacancy centers. The creation and control of such structures requires specialized technologies. In addition, this device does not have an optimal spectrum for information transmission in fiber-optic networks and in the atmosphere.

International Patent Application No. WO 2018/015738, "SCALABLE QUANTUM DEVICE," is a low-dimensional (zero- or one-dimensional) structure consisting of a layer of two-dimensional material placed on a pointed protrusion formed on the surface of a solid substrate. However, a significant drawback of this implementation of a single-photon source is the lack of precise control over the spatial profile and magnitude of local deformation of the two-dimensional material and, consequently, the lack of control over the optical properties of the resulting single-photon sources.

Chinese Patent for Invention No. CN 103532010 "Single-Photon Emitter and Manufacturing Method Based on a High-Refractive Index Contrast Grating Structure." The source design is based on a structure fabricated on a GaAs substrate and consisting of a GaAs buffer layer, distributed upper and lower GaAs/AlxGal-xAs Bragg mirrors, and an array of InAs quantum dots (QDs) in the active region. A disadvantage of the proposed single-photon emitter design is the complexity of fabrication and the difficulty of monitoring the source's state.

US Patent 2007295977, "OPTICAL SEMICONDUCTOR DEVICE AND METHOD FOR FABRICATION THEREOF." In this design, all parts of the structure are doped, and electrical contacts are formed on the backside of the doped GaAs substrate and on the top of the structure. A mesa structure containing at least one QD is formed to collect the radiation. A disadvantage of the proposed single-photon emitter design is the complexity of fabrication and the difficulty of monitoring the source.

Chinese Patent for Invention No. 106299066 "Single-photon source based on quantum dots and the method of its fabrication" The design of a diode-pumped single-photon radiation source based on semiconductor QDs, which includes a GaAs substrate on which a Bragg mirror is formed by alternating GaAs/ _{Al0.95Ga0.05As} layers. This is followed by an active region consisting of InAs QDs, an _In0.4Ga0.6As wetting layer and _{In0.8 - xAl0.2GaxAs} and _{In0.71- xAl0.29GaxAs} capping _layers . A _SiO2 layer is deposited on the surface, in which a microresonator structure is _formed . This single-photon radiation source design utilizes intracavity electrical contacts, which reduces optical losses associated with free-carrier absorption. Russian Federation Patent No. 2611555, "Vertical-Cavity Semiconductor Laser with Intracavity Contacts," includes a semi-insulating GaAs substrate, a GaAs buffer layer, a lower undoped distributed Bragg reflector (DBR), an n-type contact layer, an n-type electrical contact, an n-type composite grating, and an undoped optical resonator. The optical resonator comprises an active region based on quantum wells, a p-type composite grating, a p-type contact layer, a p-type phase-correcting contact layer, a p-type electrical contact, and an upper dielectric DBR. The composite grating comprises at least one oxide current aperture. However, the disadvantages of this design include the complex and expensive technology for forming a sparse array of QDs, as well as the complex design of the microresonator structure, which is formed inside the dielectric layer deposited on top.

The closest model in technical essence and achievable technical result (prototype) is a single-photon source emitting directly into an optical waveguide. International Patent Application No. WO 2006/135789, "FIBER-COUPLED SINGLE PHOTON SOURCE," describes the source as a semiconductor nanowire placed in a cavity etched into the substrate material. The cavity is shaped to accommodate recesses for subsequent connection to the waveguide.

ESSENCE OF THE INVENTION

The technical objective of this invention is to create a source of single photons in the transparency region of quartz light guides and the Earth's atmosphere, capable of operating at temperatures above 210 K, and having a fairly simple and reliable design.

The technical result is achieved by placing an iodine atom and an oxygen molecule inside a carbon nanotube. The carbon nanotube itself is placed in a microcavity in the quartz fiber core. Bragg gratings are formed on both sides of the cavity, forming a resonator. In the resonator, one mirror is fully reflective at a wavelength of 1.315 µm, while the other is translucent, with a retroreflectivity of over 5%. The cavity can be filled with freon to increase the efficiency of the single-photon source. The photon source operates as follows: when the carbon nanotube is pulsed with UV radiation, the UV radiation is absorbed by the walls of the carbon nanotube and transfers excitation to the oxygen molecule upon interaction. And the oxygen molecule, which after a collision with the walls of the nanotube excited by UV radiation, finds itself in an excited state, forms singlet oxygen ¹ Δ _g O ₂ , which resonantly transfers its excitation to the iodine atom, exciting it to the state 5 ² I* _1/2 . From the iodine atom, in the state 5 ² I* _1/2 of which then occurs the emission of a photon with a wavelength of λ = 1.315 μm during the transition 5 ² I* _1/2 → 5 ² I _3/2 .

An embodiment of the invention is a single-photon source comprising a pulse-periodic UV excitation source and a fullerene molecule containing an iodine atom and an oxygen molecule, located in a cavity of a quartz fiber. The fullerene molecule is positioned between Bragg gratings forming a resonator in the quartz fiber. The cavity can be filled with freon.

BRIEF DESCRIPTION OF DRAWINGS

The essence of the invention is explained in Fig. 1. Fig. 1 schematically shows an example of a cross-section of a single-mode quartz fiber, in which 1 - a carbon nanotube is placed in a microcavity - 2, realized in a quartz fiber - 3 in the region of the core - 4, while Bragg gratings - 5 and 6 are formed on both sides of the cavity, forming a resonator, where one mirror is completely reflective at a wavelength of 1.315 μm (6), and the second is semi-transparent (5), with a retroreflection coefficient of more than 5%; 7 - a pulsed UV radiation source, with the help of which excitation of a source of single photons is carried out.

IMPLEMENTATION OF THE INVENTION

The device operates as follows: when a UV pulse from the source (7) hits a carbon nanotube containing oxygen molecules and an iodine atom, the radiation is absorbed by the walls of the carbon nanotube and the oxygen molecule is resonantly excited. After a collision with the walls of the nanotube excited by UV radiation, the oxygen molecule finds itself in an excited state, forming singlet oxygen ¹ Δ _g O ₂ , which resonantly transfers its excitation to the iodine atom, exciting it to the state 5 ² I* _1/2 , from which a photon with a wavelength of λ = 1.315 μm is then emitted during the transition 5 ² I* _1/2 → 5 ² I* _3/2 (Grenishin A.S. et al. // Optics and Spectroscopy. - 2010. - Vol. 108. - No. 1. - Pp. 148-155.). An excited iodine atom, located in a resonator formed by Bragg gratings (5) and (6), will, due to the Purcell effect, preferentially emit a photon with a wavelength of 1.315 µm into the core (4) of a quartz fiber (3). The pulse repetition rate will be determined by the excitation transfer time from the walls to the oxygen, and then to the iodine atom, which depends on the temperature, which can be controlled, and the pulse repetition rate of the UV source.

Thus, the invention makes it possible to create a source of single photons in a spectral range that is important for telecommunications applications, namely at a wavelength of 1.315 µm. At this wavelength, quartz fibers and the Earth's atmosphere have low absorption, and this range is optimal for transmitting information using single photons.

The use of the single-photon source described in the invention allows for a significant reduction in costs and, with the same economic outlay, a manifold increase in the functional capabilities of quantum communications, quantum sensorics, and metrology systems.

Claims (4)

1. A single-photon source containing a pulse-periodic UV excitation source and a carbon nanotube containing an iodine atom and an oxygen molecule located in the cavity of a quartz light guide, wherein the carbon nanotube is located between Bragg gratings that form a resonator in the quartz light guide. 2. A source of single photons according to paragraph 1, characterized in that the cavity is filled with freon. 3. A source of single photons containing a pulse-periodic UV excitation source and a fullerene molecule containing an iodine atom and an oxygen molecule, located in the cavity of a quartz light guide, wherein the fullerene molecule is located between Bragg gratings that form a resonator in the quartz light guide. 4. A source of single photons according to paragraph 3, characterized in that the cavity is filled with freon.