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IPC classes for russian patent Method of filtering background infrared radiation (RU 2510056):
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 / 2346357
 / 2300825
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FIELD: physics.
SUBSTANCE: method of filtering background infrared radiation incident on a superconductor single-photon detector involves transmitting infrared radiation with wavelength of 0.4-1.8 mcm to the superconductor single-photon detector using a single-mode fibre which is partially at temperature of 4.0-4.4 K, wherein the length of the cooled section of the single-mode fibre is 0.2-3.5 m.
EFFECT: high reliability of operation of photon detectors.
3 cl
The invention relates to methods for reducing the intensity of radiation in the infrared range and can be used in optical fibre communication over large distances, in telecommunications technologies, systems, information security using quantum cryptography systems, diagnostics and testing of large scale integrated circuits, electronics, spectroscopy of single molecules, the analysis of the emission of quantum dots in semiconductor nanostructures, astronomy and medicine.
The invention according to patent RU 2300825, publ. 10.06.2007, there is excessive heating of the fiber, which leads to unexpected positives superconducting single photon detector, up to 10 times, which adversely affects the reliability of the device.
Known cryostat Cryo-Cycle company Canberra (see ). The unit is intended for cooling detectors of ionizing radiation. The system uses a cooling technology with liquid nitrogen and using an electric cooling. This device has limited capabilities, the device does not allow you to cool the fiber to a temperature of less than 10 K.
The objective of the invention is to increase the reliability of the photon detectors.
The technical result of the invention when executed, is to reduce the number of the positives and the photon detector background radiation of interest, at ambient temperature 20-28°C.
The specified task and the technical result is achieved by the fact that the filtering method of the background radiation in the infrared range, incident on a superconducting single photon detector, includes the transmission of radiation with a wavelength of 0.8 to 1.8 micrometers superconducting single-photon detector using single-mode fiber, partially at a temperature of 4.0-4.4, the length of the cooled area single-mode fiber is 0.2 to 3.5 m
Cooling area single-mode fiber is produced by immersing it in liquid helium.
Preferably, if a single-mode fiber installed close to the detector, which helps minimize losses to the incident radiation.
Experimentally determined that to reduce the number of positives superconducting single-photon detector to 5-7 times per second on the background radiation of objects stored at a temperature of 300 K, it is necessary to increase the length of the cooled fiber up to 2.5 m and more, and to reduce the number of activations of the single-photon detector to 1 times per second we need to increase the length of the cooled fiber up to 3.5 meters.
To reduce the length of the cooled fiber and while maintaining an acceptable level of background radiation falling on the detector, the prob is should change the spatial distribution of the cooled part of the single-mode fiber to create conditions increasing losses in the fiber outside of the strip passing it.
Singlemode fiber is inherently band-pass filter with the long border approximately 1.8 micrometers. In addition, it is known that the maximum of the background radiation of objects that are at a temperature close to the room, falls on the wavelength range of 8-10 micrometers. Increasing the length of the fiber leads to greater attenuation (attenuation) radiation outside the bandwidth of the fiber, and the cooling of the fiber reduces the power level emitted by the fiber, also outside the bandwidth of the fiber. Thus, increasing the length of the fiber at low temperature, leads to a significant decrease in the spectral power of radiation outside the bandwidth and thereby reduce the integral power background radiation transmitted through the fiber.
The proposed method filters as background radiation of the fiber by the method of maximum cooling, and various filters radiation from the premises (daylight, devices) method of increasing the length of the cooled fibers.
The choice of the length range of radiation in the infrared range from 0.4 to 1.8 micrometers due to the fact that the use of fibers at other wavelengths leads to a strong attenuation in them. In the range of the e length of the cooled areas singlemode fiber of 0.2-3.5 m can be effectively changing the level of background illumination, depending on the tasks. Unused fiber length of less than 0.2 m is connected with the peculiarities of the measuring units, the fiber may not reach from the detector to the exit, where light starts. When the fiber length of more than 3.5 may decline to background illumination. Upon cooling of the detector to a temperature of less than 4.0 To increasing background illumination, cooling over 4.4 To no appreciable effect.
The proposed method of filtering background-infrared radiation incident on a superconducting single photon detector as follows.
Work item superconducting single-photon detector is combined with one end of the single-mode fiber in such a way as to make him the maximum of the incident radiation. Typically, the detector with the scheme removal of an electrical signal and an optical fiber located in a special metal holder, which allows to securely fix all of the sites with the possibility of its placement in the Dewar vessel with liquid helium at a temperature approximately equal to 4.2 K. Thus, there is a cooling of all nodes to the temperature of liquid helium. On the other end of the single-mode fiber located outside the Dewar vessel kept at room temperature 300 K, served investigated optical radiation. Depending on what wavelength are of erenia (0.4 to 1.8 micrometers), selected special type of single-mode fiber, which minimized losses at this wavelength. As a rule, they differ in the size of the core, which applies radiation, and the type of material. Thus, along the fiber is formed by a gradient of temperature from 4.2 K To 300 K. Through a part of the fiber, the temperature of which lies near 300 K, inevitably comes in addition to the analyzed signal and even background illumination, due to the fact that all hot bodies radiate electromagnetic waves, whose wavelength is determined by the temperature of a radiating body through the Wien displacement law
where T is the temperature of the black body, expressed in degrees Kelvin, λmax- wavelength (in cm)at which the emissivity of the black body to the maximum. In our case, all emitting body are not completely black, as are gray, but the law of Wine can be used for approximate estimates. The calculation shows that the range of wavelengths when the background illumination is 8-10 microns at temperatures in the range 290-360 K. Since single-mode fiber optimized for wavelengths of 0.4 to 1.8 μm, the radiation outside this range will weaken the I when passing through it. On the other hand, the attenuation of the radiation depends on the thickness of the layer through which it passes. Therefore, the increase of the length of the fiber (layer thickness) leads to greater attenuation of the radiation in the range of 8-10 microns, while the attenuation at the operating wavelength of 0.4 to 1.8 μm is very weakly dependent on the length of the fiber. To eliminate the background illumination caused by the fiber, it is advisable to cool to the lower temperature, because the spectral radiation power of the body decreases with decreasing temperature. It is thus proposed that a large part of the long fibers to be placed in the most cool place Dewar vessel: partly in the helium, partly from its surface.
The invention can find wide application in industry, such as may be used in optical fibre communication, telecommunication technologies, systems, information security using quantum cryptography systems, diagnostics and testing of large scale integrated circuits, electronics, spectroscopy of single molecules, the analysis of the emission of quantum dots in semiconductor nanostructures, astronomy and medicine.
1. How to filter background-infrared radiation incident on a superconducting single photon detector, includes the transmission of infrared radiation di is the range with a wavelength of 0.4 to 1.8 micrometers superconducting single-photon detector using single-mode fiber, partially at a temperature of 4.0-4.4, the length of the cooled area single-mode fiber is 0.2 to 3.5 m
2. How to filter background radiation according to claim 1, characterized in that the cooling area single-mode fiber is produced by immersing it in liquid helium.
3. How to filter background radiation according to claim 1, characterized in that the single-mode fiber installed close to the detector.
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