High-speed single-photon superconductor detector

FIELD: fiber-optic communications, data protection, telecommunications, large-scale integrated circuit diagnosing and testing, single molecule spectrometry, astronomy, and medicine.

SUBSTANCE: proposed device has substrate carrying contact pads, One strip is made of superconductor in the form of meander and its ends are connected to contact pads. Other, additional, semiconductor strip is connected in parallel with above-mentioned strip made in the form of meander. Additional strip is made of superconductor whose kinetic inductance is lower than that of strip made in the form of meander.

EFFECT: enhanced speed, sensitivity, and bandwidth of detector.

9 cl, 2 dwg

 

The invention relates to a device for detecting a single photon of visible and infrared ranges and can be used in optical fibre communication over large distances, telecommunications technologies, systems, information security using quantum cryptography systems, diagnostics and testing of large scale integrated circuits (LSIS) in electronics and spectroscopy of single molecules, the analysis of the emission of quantum dots in semiconductor nanostructures, astronomy, and medicine.

The known device is a superconducting bolometers, in which the sensitive element is made of a superconducting strip in the form of a meander (USSR Author's certificate No. 747370, 01L 40/00, publ. 23.09.1982, USSR author's certificate No. 1032959, 01L 39/14, publ. 15.05.1989).

The use of superconducting strips in the form of a meander allows to increase the sensitivity of the bolometer. Limitation of bolometers is that they are large sensitive element (the width of the strips 1 μm, the total size of the meander 8×8 mm2), which makes it impossible for his work in single-photon mode, and the device operates in the integral mode. The output signal of the integrating detector is a linear function of the average energy of the absorbed radiation. To ensure operation of the bolometer is a need for the fast application of an external magnetic field, perpendicular to the plane of arrangement of the sensing element.

The closest is a superconducting single photon detector with anti-reflective coating containing substrate pads provided on the substrate, strip-shaped meander of the superconductor, located on the substrate between the pads and the ends of which are connected to contact pads (U.S. Patent No. 6812464, 01L 39/00, publ. 02.11.2004).

The advantage of this device before bolometers is that quantum detector provides sufficient signal when the absorption of one photon.

This device uses a mirror as the quanta of radiation can be registered only after the passage of radiation through the substrate. The sensing element in the known device is a narrow strip length 500 μm of the thin film superconductor, curved in the form of a meander and fill the rectangular space. The film thickness of the selected order of the coherence length and the width of the strips is less than the depth of penetration of the magnetic field. The use of strip-shaped meander of the superconductor, allows to increase the sensitivity of the device. In addition, in another embodiment, the device used a straight strip of superconductor that can improve would be rodasta device, but significantly reduces its sensitivity.

Limitations of the known superconducting detector with anti-reflective coating are:

- the possibility of achieving high sensitivity when using the strips, made in the form of a meander, only to quanta of radiation in a narrow wavelength range;

- performance superconducting strips in the form of a meander is characterized by a significant amount of kinetic inductance, which limits the performance of the detector.

Solved by the invention to improve technical and operational characteristics of the detector.

The technical result that can be obtained when performing the claimed device, the enhancement of sensitivity, speed and bandwidth.

To solve the problem with the achievement of the technical result in the known superconducting single-photon detector containing substrate pads provided on the substrate, strip-shaped meander of the superconductor, located on the substrate between the pads and the ends of which are connected to contact pads, according to the invention introduced an additional strip, made of a superconductor with a kinetic inductance, smaller than the kinetic inductance strips done is authorized in the form of a meander, additional strip is located on the substrate between the pads, its ends connected to the contact pads, and it is connected electrically parallel to the strips, made in the form of a meander.

Possible additional embodiments of the device in which it is advisable to:

- dimensions of the strips, made in the form of a meander, and additional strips were inscribed in a square of side 10 microns;

- the width of the strips, made in the form of a meander, and additional strips was chosen in the range of 80÷120 nm, while the size of the gaps inside of meander between creating his stripes and between the edge of the meander, addressed to the additional strip and edge were performed in the range 120÷80 nm;

- the width of the strips, made in the form of a meander, and additional strips was the same;

the strip is made in the form of a meander, was performed with the factor k fill more than 0.75, which is determined by the formula

k=a/b,

where a is the width of the strip meander,

b - period of the meander;

- additional strip was made straight;

- additional strip was made in the form of a meander.

For the last variant of execution of the invention it is advisable to

- additional strip was made with a number of bands in its meander in the range from 3 to N-3, where N is the number of the voice in the meander mentioned strips, made in the form of a meander;

- additional strip was performed with factor k fill more than 0.75, which is determined by the formula

k=a/b,

where a is the width of the additional strips meander,

b - period of the square wave.

These advantages, and features of the present invention are explained better options run the device with reference to the accompanying drawings:

figure 1 depicts an external view of the substrate with the claimed device, when performing additional strips straightforward; figure 2 - topology device, when performing additional strips in the form of a meander.

Superconducting single photon detector (figure 1) contains the substrate 1 and the pad 2 is placed on the substrate 1. The strip 3 is made in the form of a meander of the superconductor, is located on the substrate 1 between pads 2 and the ends of the strips 3 are connected to contact pads 2.

Introduced an additional strip 4 made of a superconductor, which is located on the substrate 1 between the contact pads 2, the ends of which are connected to the pads 2. Additional strip 4 is electrically connected in parallel to the mentioned strip 3. Additional strip 4 made of a superconductor has a lower kinetic inductance than the strip-shaped meander.

The dimensions of the floor of the ski 3 and additional strips 4 to increase performance can be inscribed in a square of side 10 microns.

The width of the strips 3 and additional strips 4 can be selected in the range of 80÷120 nm, while the size of the gaps inside of meander between creating his stripes and between the edge of the meander, addressed to the additional strip 4 and its region was performed in the range of 80÷120 nm.

The width of the strips 3 and additional strips 4 may be the same.

To increase the sensitivity strip of 3 (figure 2), made in the form of a meander, performed with factor k fill more than 0.75, which is determined by the formula

k=a/b,

where a is the width of the strip meander,

b - period of the square wave.

To ensure maximum performance additional strip 4 can be made straight (figure 1).

Additional strip 4 can be made in the form of a meander (figure 2).

To ensure that the kinetic inductance additional strips 4 less than the kinetic inductance of the strip 3, with the additional strips 4 in the form of a meander additional strip 4 is made with a number of bands in its meander in the range from 3 to N-3, where N is the number of bands in the meander mentioned strips 3.

In addition, to increase the sensitivity without significant reduction in performance additional strip 4 can be performed with the factor k fill more than 0.75, which is determined by the formula

k=a/b,

where a is the width additionally, the strips 4 meander,

b - period of the square wave.

Works superconducting single photon detector (figure 1 and 2), as follows.

Absorption of superconductor photon is destroyed Cooper pairs. Superconductivity for a short time is suppressed in small compared with the width of the side strips 3 and forms a "hot spot". This region has a resistance value which corresponds to the resistance of the film from which the strip 3 and the additional strip 4 in the normal state. If at this time through the strip 3 and the additional strip 4 is missing from the current close to the critical current of steaming, it redistribution by remaining in the superconducting part of the film, and the magnitude of the current density in the superconducting region begins to exceed critical. As a result, all the cross-section of the strip enters the normal state and in the detector's electrical resistance, which is accompanied by a voltage pulse.

In operating mode, the detector has a temperature below the superconducting transition temperature (for example, the temperature of liquid helium). Through the strip 3 and the additional strip 4 is skipped transport current is close to critical. The voltage pulse occurring at the time of absorption of a photon enters the registration.

As in the near anal is gay, to obtain high sensitivity in the visible and infrared wavebands sensitive element is a strip 3 made of a thin film superconductor, curved in the form of a meander and fill the rectangular space. The thickness of the film strips 3 are of the order of the coherence length and the width of the strips is less than the depth of penetration of the magnetic field. You could increase the performance of the detector, reducing the number of strips in the meander strips 3, however, rapidly deteriorating the sensitivity. To speed up parallel to the sensitive element - strip 3 - connecting additional strip of 4, performing shunting function. Additional strip has a kinetic inductance smaller than the kinetic inductance of the strip 3. The film strips 3 and additional strips 4 is temperatures below the critical temperature, and electric current is close to critical.

To increase performance dimensions additional strips 4 can be selected with the value of its kinetic inductance 50 times smaller than the kinetic inductance of the strip 3, which is the shortest amount of additional strips 4 on the distance between the pads 2, in the case of performing additional strips 4 straight (figure 1). Or kinetic is Kai inductance additional strips 4 is chosen 10 times smaller than the kinetic inductance of the strip 3, which is achieved by performing additional strips 4 in the form of a meander, with the number of bands in the meander additional strips 4 in the interval from 3 to N-3, where N is the number of bands in the meander mentioned strips 3, originally made in the shape of a meander.

The inventive device is characterized by the presence of new characteristics: significantly greater performance due to the presence of additional strips 4 that performs a bridging function. In addition, due to the lack of antireflection coating device does not have a pronounced spectral selectivity, allows the registration of photons impinging directly on the substrate 1, instead of passing through it, which allows for the registration of falling on the sensitive elements of the strip 3 and an additional strip of 4 - photons in the wavelength range of 0.4-4 μm. The detector has great performance while maintaining high sensitivity in all the stated wavelength range, the choice of the factor k fill more than 0.75. In addition, as shown by experimental studies, the sensitivity of the choice of the factor k fill more than 0.75 is increased by 5÷7% compared with the closest analogue that is due to the fact that the additional strip of 4, in addition to the shunt function, also performs the function of the sensing element, as the strip 3.

The size of the strips 3, made in the shape of a meander, and additional strips 4 with the specified factor k can be inscribed in an imaginary rectangle, for example, 20×10 μm, or 10 square×10 μm, or 20 square×20 μm in accordance with the technology described in the nearest equivalent.

The strip 3 and the additional strip 4 may be made of NbN film thickness of 4 nm, deposited on a substrate 1 of sapphire. The primary sensing element - strip 3 is performed with a width of 80÷120 nm, curved in the form of a meander with the distance between the strips on the inside of meander about 100 nm, for example, also in the range of 80÷120 nm, and fill the square with a side of 10 μm. Shunt section is an optional strip of 4, for example, of the same width as the strip 3 meander, and a length of 10 μm (figure 1). Pads 2 made of NbN and are coated with gold to improve electrical contact.

The detector operates at temperatures below 10 K (the approximate temperature of the superconducting transition for thin films of NbN), for example 4,2K. When the specified size of the strips 3, 4 the critical current Iwithapproximately 30 μa at a temperature of 4,2K. The magnitude of the transport current is 0.8-0.9 from Ic. As in the near equivalent, the device connects to the DC power source and the RF path through the adapter offset. Microwave tract to depict the place of a coaxial cable and a chain of microwave amplifiers. After amplification, the voltage pulses appearing at the detector when the absorption of photons arrive at the registration apparatus. The main characteristics of the detectors (figure 1 and 2) shown in the following table:

High-speed superconducting detector
The operating range of wavelengths λ0.4 to 4 microns
The quantum efficiency at the wavelength of 1.26 μm at a temperature of 4,2K20%
Dynamic range109
The level of a dark account<0.1 s-1
Temporary instability of the signal20 PS
Quantum efficiency is defined as the ratio of the number of photons detected per unit time to the number of photons that fell on his sensitive element.

The inclusion of additional strips 4 that performs a bridging function, improved performance in 7-12 times. Thus the quantum efficiency increases by 7%.

Most successfully stated a superconducting single photon detector of industrial application for the registration of individual photons of visible and infrared ranges in systems optical fiber communications, telecommunications t is hnology, systems information security using quantum cryptography systems, electronics for diagnostics and testing of large scale integrated circuits (LSI), in spectroscopy of single molecules, the analysis of the emission of quantum dots in semiconductor nanostructures, astronomy and medicine.

1. Superconducting single-photon detector containing substrate pads provided on the substrate, strip-shaped meander of the superconductor, located on the substrate between the pads and the ends of which are connected to contact pads, wherein the additional strip is made of a superconductor with a kinetic inductance, the smaller the kinetic inductance of a strip, made in the form of a meander, the additional strip is located on the substrate between the pads, its ends connected to the contact pads and is connected electrically parallel to the strips, made in the form of a meander.

2. Superconducting single photon detector according to claim 1, characterized in that the dimensions of the strips, made in the form of a meander, and additional strips inscribed in a square of side 10 microns.

3. Superconducting single photon detector according to claim 1, characterized in that the width of the strips, made in the form of a meander, and will complement the school strips selected in the range of 80-120 nm, while the magnitude of the gaps inside of meander between creating his stripes and between the edge of the meander, addressed to the additional strip, and its edge, performed in the range of 80÷120 nm.

4. Superconducting single photon detector according to claim 1, characterized in that the width of the strips, made in the form of a meander, and additional strips are the same.

5. Superconducting single photon detector according to claim 1, characterized in that the strip-shaped meander performed with factor k fill more than 0.75, which is determined by the formula

k=a/b,

where a is the width of the strip meander,

b - period of the square wave.

6. Superconducting single photon detector according to claim 1, characterized in that the additional strip is made straightforward.

7. Superconducting single photon detector according to claim 1, characterized in that the additional strip is made in the form of a meander.

8. Superconducting single photon detector according to claim 6, characterized in that the additional strip is made with a number of bands in its meander in the range from 3 to N-3, where N is the number of bands in the meander mentioned strips, made in the form of a meander.

9. Superconducting single photon detector according to claim 6, characterized in that the additional strip executed with factor k fill more than 0.75, which is determined by the formula

k=a/b,

where a is the width of more is more strips meander,

b - period of the square wave.



 

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