RU176010U1 - Fiber-optic superconducting single-photon detector - Google Patents

Abstract

Usage: for optical radiation detectors with high quantum efficiency. The essence of the utility model is that the superconducting single-photon detector is an optical module based on an FC optical socket and includes a cryogenic preamplifier and a replaceable module with a segment of an optical ferule with a single-mode fiber, while gold contact pads are formed on the side surfaces of the module, and on the optical core fibers, sensitive layers of a superconductor are formed in the form of a meander structure, the meander structure being two meanders oriented by It is parallel to each other and separated by a dielectric layer with a thickness equal to a quarter of the wavelength. Effect: providing the possibility of increasing the overall efficiency of SSPD without complicating its design. 4 ill.

Description

Technical field

The utility model relates to the field of single-photon detectors and can find application in the creation of quantum cryptography systems and networks with a quantum key distribution. Also, the claimed device can find application in other devices for recording optical radiation, requiring high resolution and high quantum efficiency.

State of the art

The device relates to superconducting single photon detectors (SSPDs) having a meander structure (Goltsman G., Okunev O., Chulkova G. et al. // Appl. Phys. Lett. 2001. V. 79.P. 705. and Gol'tsman GN, Smirnov K., Kouminov P. et al. // IEEE Trans., Appl. Supercond. 2003. V. 13. P. 192.).

Such detectors (US 6,812,464 B1 Superconducting single photon detector, 2004-11-02) typically consist of a semiconductor substrate (e.g., Si) coated with a dielectric layer (e.g., SiO2) over which a film of superconducting material (e.g., NbN) is sprayed with topology in the form of a meander and conductive (Au, Nb, Pd) contact pads, providing bias current to the detector and signal pickup.

The overall effectiveness of SSPDs is determined by a combination of several indicators.

One of such important indicators is quantum efficiency, and the other is the accuracy of combining the optical beam with the SSPD recording zone, which is small in size and realizes effective cooling without loss of functionality.

The small quantum efficiency of SSPD, that is, the ratio of the number of detected photons to the total number of photons incident on the detector, is limited by several factors. Firstly, it is the fill factor k = a / b, where a is the width of the superconducting strip, b is the period of the structure. This value characterizes the absorption region of the incident radiation. The limit of the filling factor for a simple single meander, known to the authors is 75% (RU 2300825 C1 High-speed superconducting single-photon detector, 2007-10-06).

A second factor affecting the efficiency of the superconducting detector is the absorption of the incident radiation by the substance of the NbN detector. So, for a thickness of 4 nm, optical absorption reaches about 30% at a wavelength of 1.55 μm. The detection efficiency at such a thickness and wavelength (for a duty cycle of 75%), in theory, cannot exceed 20-25%) due to the small thickness of the NbN layer with normal radiation incidence. In view of the impossibility of realizing an optimal filling factor (close to unity) for the effective absorption of incident radiation by the detector material, a method was proposed for increasing light absorption by creating resonator structures using a reflective metal layer and a dielectric coating of a quarter wavelength thickness. A quarter-wave resonator was located on the surface of the photosensitive element. The light incident on the detector substance from the substrate side and not absorbed by it passes through the dielectric layer, is reflected from the metal layer with a phase change in pi, and is added in antiphase with light reflected from the dielectric-superconducting film interface.

Another possible approach is to combine multiple NbN layers to achieve a fill factor close to unity (US 9240539 B2 Efficient Polarization Independent Single Photon Detector, 2016-01-19 and US 9490112 B2 System and method for characterizing ions using a superconducting transmission line detector, 2016 -11-08) and their location one above the other, and so that these meanders will be perpendicular to each other. This allows us to achieve a quantum efficiency of about 85%. At the same time, such solutions (in particular, US 9240539 B2 Efficient Polarization Independent Single Photon Detector, 2016-01-19) have an ineffective layout when the quarter-wave SiO2 resonator is located after both layers of meanders, which increases the dimensions, increases the overall fragility and is very significant complicates the installation of the detector on the base of a standard FC-optical outlet.

The main difficulty with precise combination is to provide both broad capabilities (including measuring the polarization of photons) with constructive simplicity and cooling difficulties. Thus, a solution is known (US 2014353476 Al Fiber optical superconducting nanowire single photon detector, 2014-12-04) for the detection of single photons, the essence of which is to create an SSPD detector directly at the end of the fiber. The entire manufacturing process takes place on the upper edge of the zirconium oxide ferrule tip, from a standard polished fiber connector (FC optical socket) containing a single-mode fiber. The disadvantages of this solution are the technological complexity of manufacturing and operation, the inability to determine the polarization of optical radiation.

Another important problem in creating photonic detectors is their effective cooling. So, when heating the elements of the detector, spurious thermal radiation and the corresponding noise of the detector occur, which significantly reduce the overall efficiency. In the technical solution mentioned above (US 2014353476 A1), cooling efficiency is another weakness.

Based on the set of common features, the solution for the detection of single photons was selected as the prototype (US 2014353476 A1 Fiber optical superconducting nanowire single photon detector, 2014-12-04).

Utility Model Essence

The objective of this utility model was to create a high-performance SSPD without complicating its design and without losing functionality.

The technical result is to increase the overall efficiency of SSPD without complicating its design.

The problem is solved by solving the non-trivial problem of combining the latest achievements in this field and eliminating their common shortcomings.

According to this utility model, a superconducting single-photon detector is an optical module based on a standard FC optical socket and includes a cryogenic preamplifier and a replaceable module with a single-mode fiber segment of an optical ferula. Gold contact pads are formed on the lateral surfaces of the module, and sensitive layers of a superconductor in the form of a meander structure are formed on the cortex of the optical fiber, the meander structure being two meanders oriented orthogonally to each other and separated by a dielectric layer with a thickness equal to a quarter of the wavelength.

Brief Description of the Drawings

The claimed utility model is illustrated by drawings, in which:

FIG. 1 is an image of a meander structure.

FIG. 2 - general view of the detector.

FIG. 3 is a fiber side view of the detector.

FIG. 4 - view of the detector in profile. Detailed description of the utility model.

In FIG. Figure 1 schematically shows the meander structure of a single-photon superconductor detector in which the sensitive element is located simultaneously in two or more spatially separated planes separated by a dielectric layer.

Here, the numbers denote 1 and 3 — corresponding sensitive layers made, for example, of NbN in the form of meanders, 2 — an intermediate layer of a dielectric, for example, Si02.

The meanders 1 and 3 are rotated perpendicular to each other, which significantly increases the filling factor and, as a result, the overall efficiency of the detector.

The dielectric layer 2 has a thickness equal to a quarter of the wavelength and acts as a quarter-wave plate of the resonator with reflective surfaces, one of which is the boundary of the upper meander and silicon oxide (SiO2), and the second is the interface between silicon oxide and lower meander. This further enhances the detection efficiency. Moreover, due to the fact that the plate 2 is located between the sensitive layers 1 and 3, there is no increase in the size of the entire module and the efficiency of using the available space increases. This allows the detector to be implemented on the basis of a standard FC optical socket.

Such a sensitive module operates as follows. The optical radiation of the source falls on the meander structure of the first layer. The result of the absorption of optical radiation is recorded by the upper layer of a superconducting single-photon detector. If radiation absorption did not occur in the structure of the first layer, the photon passes through the dielectric layer and enters the second layer of the detector, where it can be absorbed, penetrate further, or be reflected in the direction of the first detector, etc.

Sensitive elements of NbN preferably have a thickness of the order of 3.5-5 nm.

In FIG. 2 shows a detector based on an FC optical receptacle assembly. The detector contains a receiving module 6 based on an FC socket with a cryogenic preamplifier 5 attached to it with an interchangeable optically coupled module for a superconducting detector 4, consisting of a section of a cylindrical optical ferula 7 polished from two ends and glued with a single-mode fiber 8, on which core 9 is sprayed films niobium nitride (NbN) with a topology in the form of meanders 10 and gold (Au) contact pads 11, which provide the bias current to the detector and pick up the RF signal. In addition, there is an optical quarter-wave resonator, the cavity of which is a layer of silicon oxide (SiO2) of the corresponding thickness, and reflecting surfaces: one is the outer surface of silicon oxide (SiO2), the second is the interface between silicon oxide (SiO2) and niobium nitride (NbN), which has been described in detail above with reference to FIG. one.

Since the sensitive element is a structure with formed meanders 10 oriented orthogonally on opposite ends of the optical module 4, each of the meanders 10 is a structure sensitive to the orientation of the plane of polarization of the optical radiation. It has been experimentally shown that optical radiation, the electric field vector of which is directed along the meander bands, is absorbed by such a sensitive element with a probability 10 times higher than the sensitive element, in which the direction of the meander bands is perpendicular to the direction of the electric field vector. If the electric field vector is directed at an angle ϕ to the direction of the bands of the meander 10, then the signal recorded by this meander will be proportional to cosϕ. And the signal recorded by this second meander will be proportional to sinϕ. Thus, the orientation of the polarization plane of the detected optical radiation relative to the direction of the meander bands can be determined from the ratio of the signals recorded by the sensitive elements 10 formed at the opposite ends of the optical module 4.

Flat faces are made on the cylindrical surface of the optical module 4, on which the gold contacts 11 are applied to output the signal, which will provide additional protection for the working surface of the detector from mechanical damage during transportation and installation of the detectors in the receiving module 6 using protective caps.

The module works as follows. The optical radiation of the source passes through the fiber and in the optical outlet 6 enters the optical registration module 4 along the cortex 9 of the optical fiber 8 and then to the meander structure 10.

Claims (1)

The superconducting single-photon detector is an optical module based on an FC optical socket and includes a cryogenic preamplifier and a replaceable module with a segment of an optical ferula with a single-mode fiber, while gold contact pads are formed on the side surfaces of the module and sensitive layers of the superconductor are formed in the form of a superconductor in the form a meander structure, the meander structure being two meanders oriented orthogonally to each other and separated by a dielectric layer ika thickness equal to a quarter of the wavelength.

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