WO2021118411A1 - Single-proton detector - Google Patents

Abstract

The present technical solution relates to the field of measurement technology, in particular to a single-photon detector (SPD), used in the field of quantum cryptography. The technical result is to reduce the probability of noise pickup and to raise quantum efficiency. The claimed SPD construction comprises a housing in which are mounted: a signal board comprising a strobe oscillator, an output pulse generator, a bias voltage source of an avalanche photodiode and a dead-time generator; a controller board comprising a temperature regulator and a control system; a cooling circuit comprising a temperature sensor and a thermoelectric transducer; a flexible board arranged within the cooling circuit and comprising an avalanche photodiode and at least one signal amplification cascade of the avalanche photodiode.

Description

SINGLE PHOTON DETECTOR

FIELD OF TECHNOLOGY

[0001] The present technical solution relates to the field of measurement technology, in particular, to the design of a single photon detector (DOP) used in the field of quantum cryptography.

LEVEL OF TECHNOLOGY

s у stems/produets/id210/1. Модель ДОФ ID210-SMF-C при частоте стробирования 100 МГц имеет темновой счет 6 Гц при 10% эффективности детектирования и 30 Гц при 25%. [0002] The most widely known in the art are DOPs from ID Quantique. DOF series ID210 is designed to work in near infrared light in gated phoion mode

s at stems / produets / id210 / 1. The DOP model ID210-SMF-C at 100 MHz sampling rate has a dark count of 6 Hz at 10% detection efficiency and 30 Hz at 25%.

[0003] DOPs from Princeton Lightwave PGA-600 are also known, which have a dark counting frequency of 100 Hz with 20% detection efficiency. At the same time, this value corresponds to a 20 MHz sampling frequency, which does not allow using the PGA-600 for operation at high frequencies.

[0004] The main significant disadvantage of the known solutions is their weight and size, as well as their efficiency. The weight and overall dimensions of the well-known DOF do not allow their use in standard equipment racks for conventional telecommunication fiber-optic networks.

[0005] Superconducting DOPs, as a rule, require special equipment and its regular maintenance. In particular, the turbomolecular and foreline pumps used to evacuate the volume in which the working fluid of the NbN-based superconductor is located, require servicing. In terms of dimensions, such equipment exceeds the dimensions of a standard telecommunication rack or cabinet. According to the available information, there are no regularly operated quantum communication lines with superconducting detectors both in Russia and abroad. maintaining such an infrastructure is costly.

[0006] According to research tests, the developed detector under the same test conditions has a dark count of 5 Hz at 10% efficiency and 30 Hz at 25% efficiency. DISCLOSURE OF THE INVENTION

[0007] The claimed DOP is developed on the basis of a semiconductor device, namely an avalanche photodiode, which allows the development and implementation of a new technology of quantum key distribution for conventional telecommunication fiber-optic networks, which also provides the compactness of the final device with the required efficiency of its operation. The claimed device is intended for installation in a conventional rack or cabinet to accommodate standard telecommunications equipment. At the same time, a DOF based on an avalanche photodiode does not require service and does not require special qualifications from operators for its operation, which simplifies its operation and subsequent service.

[0008] The claimed solution provides a solution to the technical problem of creating a DOP with reduced weight and dimensions while ensuring efficient operation.

[0009] The technical result is to reduce the likelihood of noise triggering and increase the quantum efficiency.

[0010] The claimed design of the DOP contains a housing in which are installed: a signal board containing a strobe generator, an output pulse shaper, an avalanche photodiode bias voltage source and a dead time shaper; a controller board containing a temperature controller and a control system; a cooling loop containing a temperature sensor and a thermoelectric converter; a flexible board located inside the cooling circuit and containing the avalanche photodiode and at least one stage for amplifying the avalanche photodiode signals.

[OOP] In one embodiment of the device, the avalanche photodiode is made of a compound selected from the group: InGaAs, InAlAs, or Si.

[0012] In another embodiment of the device, the photodiode comprises a substrate made of an InGaAs-InP indium phosphide compound.

[0013] In another embodiment, the signal board further comprises at least one filter stage.

[0014] In another embodiment of the device, the thermoelectric converter comprises at least one Peltier element. BRIEF DESCRIPTION OF DRAWINGS

[0015] FIG. 1 illustrates the functional diagram of the claimed DOP.

CARRYING OUT THE INVENTION

[0016] As shown in FIG. 1, the declared DOF (10) contains a radiator housing (100), inside which a signal board (software), a controller board (120), a cooling circuit (130) and a flexible board (140) are installed. The radiator housing (100) ensures the integrity of the structure, as well as the thermal mode of operation of the detector (10). It contains all the necessary signal input-output connectors, both optical and electrical. The following can be used as connectors: a power connector, connectors for connecting fans, holes for the output of these connectors are also made in the case (100) to provide external connection. An optical FC-FC connector is mounted directly on the housing cover (100).

[0017] The signal board (110) contains the main functionality, while it houses a strobe generator (111), an avalanche photodiode bias voltage source (112), an input for a flexible diode output board, amplifying stages for obtaining an avalanche response of a diode of an acceptable amplitude ( 143), an output pulse shaper (113), which forms a calibrated counting signal of the desired logic level and duration, and a dead time shaper (114). The signal board can additionally contain at least one filtering stage (142), which reduces the influence of the parasitic harmonics of the strobe on the useful signal of the avalanche response.

[0018] The controller board (120) provides the possibility of external control and monitoring of such parameters of the DOP operation as: temperature, bias voltage, gating signal amplitude and parameters of the cooling system (stabilization temperature, PID controller coefficients, conditions for enabling emergency modes). For example, a 70 V bias voltage, a 6 V p-p gating signal amplitude, and an avalanche photodiode temperature of -45 degrees Celsius. External control is provided using the USB interface when connected to an external computing device such as a computer.

[0019] The cooling circuit (130) is designed to provide the avalanche photodiode (141) with optimal operation in terms of the likelihood of noise triggers. The cooling circuit (130) contains a temperature sensor (131) and a thermoelectric converter (132), made in the form of one or more Peltier elements. The temperature sensor (131) can be made in the form of a platinum thermistor.

[0020] The cooling circuit (130) can be made of a foam box, in which a photodiode (141) is placed in a special copper holder, and a thermoelectric converter (132). The contour (130) is fixed on the body-radiator (100) to provide heat removal from the thermoelectric converter (132).

[0021] The flexible board (140) is located inside the cooling circuit (130), contains an avalanche photodiode (141) installed on it and is designed to reduce the heat losses inevitable when the avalanche photodiode (141) communicates with the external environment through its contact with the signal board ( 110). The avalanche photodiode (141) can be made on the basis of known technologies, for example, from such compounds as: InGaAs, InAlAs, or Si. Also, the photodiode (141) may contain a substrate made of an InGaAs-InP indium phosphide compound.

[0022] The presence of the flexible board (140) avoids direct contact of the legs of the photodiode (141) and the temperature sensor (131) with the external environment, which greatly improves the performance of the circuit (130) and avoids the formation of condensation on the legs of the photodiode (141) and increases the reliability measuring the temperature inside the cooling loop (130). In this case, the flexible board (140) can contain one or several stages (143) for amplifying the signal of the photodiode (141), which makes it possible to reduce the influence of interference and time resolution, which has a positive effect on reducing the noise triggering of the DOP (10). Due to the installation of the amplifier stage on the flexible board (140) in the immediate vicinity of the diode (141), a good parameter of the temporal resolution of the detector is obtained.

[0023] The DOP elements (10) are installed in the housing (100) ensuring structural and functional unity and are connected by means of a different spectrum of standardized assembly operations, in particular, by soldering, welding, riveting, joining, and other type of structural fixation of elements suitable for use in the art.

[0024] DOP (10) operates as follows. The bias voltage source (112) generates a constant bias voltage of the avalanche photodiode (141) to enable the formation of an avalanche photocurrent. The strobe generator (111) generates a harmonic signal, synchronous with respect to the external synchronization signal, to ensure the sensitivity of the avalanche photodiode (141) only in the vicinity of the maximum of the strobe signal and insensitivity during the rest of the time. This is achieved by keeping the bias voltage, gate signal amplitude, and temperature of the avalanche photodiode (141) stable.

[0025] The temperature controller (122) maintains a constant temperature by controlling the voltage on the thermoelectric converter (132) and measuring the temperature of the photodiode (141) using the sensor (131).

[0026] An external signal in the form of a single photon of the required spectral range is fed to the input of the detector (10) via a fiber-optic communication line. Getting into the active zone of the avalanche photodiode (141), the photon is absorbed and causes the avalanche photocurrent to flow through the photodiode (141). As a consequence of the flow of the photocurrent across the load resistor, a voltage pulse is formed, which is amplified to the level of a few volts, filtered from the strobe signal using a filter (142) and goes to the output pulse shaper (113) and the dead time shaper

(114).

[0027] The output pulse shaper (113) provides the formation of a pulse with a duration of 85 ns and an amplitude of 3 V, at a load of 50 Ohms. This pulse is transmitted to external equipment for further processing, through the corresponding output of the detector (10). The dead time generator (114) temporarily reduces the bias voltage of the photodetector by a predetermined time interval (for example, 3, 5, 6 μs, etc.), thereby eliminating any triggering of the avalanche photodiode (141) during the dead time. This control mode excludes the formation of afterpulses. Afterpulses are noise alarms, the probability of which sharply increases for some time after the photodiode is triggered (141). The declared DOP (10) is gated at a frequency of 312.5 MHz and is designed to register single photons in the near infrared range.

[0028] The main technical characteristics of the claimed DOP (10) are presented in Table 1.

Table 1. Specifications

Claims

FORMULA 1. A detector of single photons, containing a housing in which are installed: a signal board containing a strobe generator, an output pulse shaper, an avalanche photodiode bias voltage source and a dead time shaper; a controller board containing a temperature controller and a control system; a cooling loop containing a temperature sensor and a thermoelectric converter; a flexible board located inside the cooling circuit and containing the avalanche photodiode and at least one stage for amplifying the avalanche photodiode signals. 2. The detector according to claim 1, characterized in that the avalanche photodiode is made of a compound selected from the group: InGaAs, InAlAs, or Si. 3. The detector according to claim 2, characterized in that the photodiode comprises a substrate made of an InGaAs-InP indium phosphide compound. 4. The detector of claim 1, wherein the signal board further comprises at least one filter stage. 5. The detector according to i. 1, characterized in that the thermoelectric converter contains at least one Peltier element.