Device for detecting photons

Abstract

The invention relates to a device for detecting photons comprising: an avalanche photodiode (APD) configured to receive a flux of incident photons and to deliver a photodiode output signal (Se) containing information relating to detection of an incident photon (PI) on detection of an incident photon, the avalanche photodiode having a breakdown voltage, the avalanche photodiode further being configured to receive a synchronisation signal (S1), the avalanche photodiode being capable of detecting an incident photon during a length of time when the voltage of the synchronisation signal is above the breakdown voltage; and a control unit (UC), the control unit being configured to deliver the synchronisation signal (S1) to the avalanche photodiode, the synchronisation signal being such that the length of time during which the voltage of the synchronisation signal is above the breakdown voltage is synchronised with the time range during which an incident photon issuing from the flux of incident photons is received by the avalanche photodiode, and / or to deliver the synchronisation signal (S1) with a determined power.

Description

Description Photon detection device Scope of the invention

[0001] The invention relates to photon detection devices, and in particular devices comprising an avalanche photodiode. State of the art

[0002] Single-photon detectors are used in various applications that require low-light detection. These applications include quantum communication networks such as quantum key distribution (QKD), quantum information networks (QIN), light-wave detection in the atmosphere (LIDAR), laser ranging, optical tracking of space debris and satellites (SSA) in orbit, navigation (gyroscopes), optical fiber detection such as time-domain optical reflectometry (OTDR), and life sciences (time-correlated single-photon counting TCSPC, fluorescence lifetime imaging microscopy FLIM).

[0003] Current single-photon detectors include superconducting nanowire single-photon detectors (SNSPDs). These detectors have high photon detection efficiency. However, they require cryogenic cooling, which is bulky and maintenance-intensive, making their deployment on an industrial scale extremely difficult, if not impossible.

[0004] Another solution involves single-photon avalanche photodiodes (SPADs) operating in Geiger mode. An avalanche photodiode, by definition, has a breakdown voltage. When an avalanche photodiode receives an electrical signal (called a trigger signal) with a voltage above this breakdown voltage, it can detect a photon. In Geiger mode, a trigger signal with a voltage slightly above the photodiode's breakdown voltage is supplied to the avalanche photodiode. However, SPAD avalanche photodiodes operating in Geiger mode face a significant limitation in photon detection rates, primarily due to the undesirable effect of afterpulses.

[0005] The afterpulse is the most limiting factor on the photon detection rate of an avalanche photodiode (i.e., the number of photons detected per unit of time). The afterpulse is noise that occurs for a period of time when the photodiode detects an event. This noise interferes with the detection of other photons during that period. It is possible to limit the period during which the noise occurs by reducing the overvoltage of the photodiode's trigger signal, i.e., the voltage above the breakdown voltage. However, it is difficult to detect a photon when the overvoltage of the trigger signal is low.

[0006] When operating an avalanche photodiode in Geiger mode using a trigger signal well above the breakdown voltage, the probability of an afterpulse in the 0 to 100 ns following detection is very high. Consequently, it is impossible to detect photons at a high detection rate while maintaining an acceptable noise level. Therefore, the counting rate of photon detectors is generally limited to around ten MHz.

[0007] Therefore, it is important to find solutions to minimize the probability of afterpulse and to operate photon detectors at higher speeds. Summary of the invention

[0008] In order to overcome the aforementioned drawbacks of photon detection devices, the invention proposes a photon detection device in which the probability of afterpulse is limited.

[0009] To this end, the invention relates to a photon detection device comprising an avalanche photodiode configured to receive a stream of incident photons and to provide a photodiode output signal containing information about the detection of an incident photon. Upon detection of an incident photon, the avalanche photodiode, having a breakdown voltage, is further configured to receive a synchronization signal, the synchronization signal being a signal having a voltage that varies above and below the breakdown voltage of the avalanche photodiode. The avalanche photodiode is capable of detecting an incident photon for a duration during which the voltage of the synchronization signal is above the breakdown voltage.The photon detection device further includes a control unit, the control unit being configured to provide the synchronization signal to the avalanche photodiode, the synchronization signal being such that the duration for which the voltage of the synchronization signal above the breakdown voltage is synchronized with the time range for which an incident photon from the incident photon flux is received by the avalanche photodiode and / or to provide the synchronization signal with a determined power.

[0010] The invention therefore makes it possible to limit the probability of afterpulse and to obtain a higher detection rate. Thus, the device is capable of detecting photons efficiently and / or stably regardless of the phase and power of an initial trigger signal.

[0011] Furthermore, the invention makes it possible to obtain a device that is compact, fast and maintenance-free.

[0012] Optionally, photons from the incident photon stream are emitted at given times of a photon emission frequency, the control unit being further configured to, from the photon emission frequency, synchronize the duration for which the synchronization signal voltage is above the breakdown voltage with the time range for which an incident photon from the incident photon stream is received by the avalanche photodiode.

[0013] Optionally, the control unit is configured to provide the avalanche photodiode with a synchronization signal whose phase is determined from the number of photons detected by the avalanche photodiode over a determined period of time.

[0014] Optionally, the control unit is further configured to adjust the phase and / or power of the synchronization signal supplied to the avalanche photodiode.

[0015] According to this characteristic, phase adjustment allows synchronization of the duration for which the synchronizing signal voltage is above the breakdown voltage with the time range at which an incident photon from the incident photon flux is received by the avalanche photodiode. Furthermore, adjusting the synchronizing signal power ensures stability in the photon detection probability.

[0016] Optionally, the device further includes a signal generator configured to generate an initial trigger signal, the initial trigger signal being supplied to the control unit to form the synchronization signal.

[0017] Optionally, the control unit is configured to modify the phase of the initial trigger signal to form the synchronization signal, so as to synchronize the duration for which the voltage of the synchronization signal is above the breakdown voltage with the time range for which an incident photon is received by the avalanche photodiode.

[0018] Optionally, the control unit is configured to determine the power of the initial trigger signal and to modify the power of the initial trigger signal to a given power to form the synchronization signal.

[0019] Optionally, the device further includes a coupler configured to connect a measuring device, the measuring device being configured to measure the power, frequency, phase and / or waveform of the synchronization signal.

[0020] Based on this characteristic, the coupler allows for the measurement of the phase of the synchronization signal. The measuring device ensures that the synchronization signal is correctly synchronized with the arrival of incident photons on the avalanche photodiode. Furthermore, the coupler allows for the measurement of the synchronization signal power.

[0021] Optionally, the device further includes a processing unit configured to perform processing of the photodiode output signal supplied by the avalanche photodiode.

[0022] Thus, the processing performed by the processing unit makes it possible to extract the useful electrical signal corresponding to the detected incident photon.

[0023] Optionally, the processing unit is configured to extract a useful signal from the photodiode output signal provided by the avalanche photodiode.

[0024] Optionally, the processing unit includes a frequency electrical filter.

[0025] Optionally, the processing unit also includes an amplifier.

[0026] Optionally, the processing unit also includes a comparator configured to compare a useful signal to a predetermined threshold value.

[0027] Optionally, the device also includes a counting unit configured to count the number of photons detected by the avalanche photodiode over a specified period of time.

[0028] Based on this characteristic, the counting unit makes it possible to determine the rate and number of photons detected by the avalanche photodiode.

[0029] Optionally, the control unit is configured to receive the number of photons detected by the avalanche photodiode over a period of time determined by the counting unit and to provide the avalanche photodiode with a synchronization signal whose phase is further determined from the number of photons detected.

[0030] Optionally, the synchronization signal is a periodic signal, and preferably a sinusoidal signal.

[0031] According to this characteristic, the voltage of the periodic signal can be adjusted to be above and below the breakdown voltage.

[0032] Optionally, the avalanche photodiode is configured to detect at least one incident photon having a wavelength in the visible or infrared range.

[0033] Optionally, the device also includes a temperature controller configured to control the temperature of the avalanche photodiode.

[0034] According to this characteristic, temperature control allows the avalanche photodiode to operate optimally and avoids breakdown voltage variations. Furthermore, temperature control allows the avalanche photodiode to operate at lower temperatures, thus reducing dark current caused by thermal noise.

[0035] Optionally, the device further includes a power supply device, the power supply device being configured to generate a continuous electrical signal supplied to the control unit.

[0036] According to this characteristic, the synchronization signal is formed in particular from the initial trigger signal and the continuous electrical signal, thus allowing the overshoot of the synchronization signal voltage to be adjusted above the breakdown voltage of the avalanche photodiode.

[0037] Optionally, the initial trigger signal is generated from a reference signal provided by a reference clock.

[0038] Optionally, the synchronization signal has a frequency lower than the cutoff frequency of the avalanche photodiode.

[0039] Optionally, the synchronization signal has a frequency of approximately 1.25 GHz.

[0040] Optionally, the reference signal has a frequency of approximately 10 MHz.

[0041] Optionally, the reference clock is an oscillator.

[0042] The following description presents several embodiments of the device of the invention; these examples are not limiting to the scope of the invention. These embodiments illustrate both the essential features of the invention and additional features related to the embodiments considered. Brief description of the drawings

[0043] The invention will be better understood and other advantages will become apparent upon reading the following description, which is given by way of non-limiting example, and through the figures, among which:

[0044] FIG. 1 illustrates a schematic diagram of an example of a photon detection device according to the invention;

[0045] FIG. 2 illustrates a functional diagram of a photon detection device according to the invention illustrated in figure 1;

[0046] FIG. 3 schematically illustrates an example of synchronization performed by the control unit;

[0047] FIG. 4 illustrates a particular embodiment of the photon detection device according to the invention, in which the device includes a signal generator;

[0048] FIG. 5a illustrates a particular embodiment of the photon detection device according to the invention, in which the device comprises an operating unit of the avalanche photodiode;

[0049] FIG. 5b illustrates a particular embodiment of the control unit according to the invention;

[0050] FIG. 6 illustrates a particular embodiment of the photon detection device according to the invention, in which the device includes a coupler;

[0051] FIG. 7a illustrates a particular embodiment of the photon detection device according to the invention, in which the device includes a processing unit;

[0052] FIG. 7b illustrates a particular embodiment of the processing unit;

[0053] FIG. 8a illustrates a particular embodiment of the photon detection device according to the invention, in which the device comprises a processing unit and a counting unit;

[0054] FIG. 8b illustrates a particular embodiment of the counting unit; and

[0055] FIG. 9 illustrates another particular embodiment of the control unit in the photon detection device according to the invention. Of course, the embodiments described in these figures can be combined. Detailed description

[0056] The present invention relates to a photon detection device, and in particular a single photon detection device.

[0057] The objective of the present invention is to detect a maximum number of photons, particularly single photons, from an incident photon stream emitted by a photon source, the incident photons being received by an avalanche photodiode. Figure 1 illustrates a schematic diagram of an example of a photon detection device according to the invention.

[0058] According to one exemplary embodiment, the SPD photon detection device may include a detection unit UD that is configured to receive an incident photon stream PI and an initial trigger signal S0.

[0059] In this description, it will be understood that an incident photon is a photon that is directed towards the avalanche photodiode for the purpose of its detection.

[0060] The incident photon flux is directed towards the avalanche photodiode by an optical fiber or free-space optical components.

[0061] The UD detection unit includes an avalanche photodiode.

[0062] The SPD device is suitable for connection to a photon source, such as a laser or a single-photon source, which emits a stream of incident photons. The incident photons emitted by the source are received by the avalanche photodiode.

[0063] The avalanche photodiode APD provides a photodiode output signal Se. The photodiode output signal Se may contain information relating to the detection of an incident photon PI when an incident photon is detected.

[0064] The initial trigger signal S0 is a periodic electrical signal, notably sinusoidal, which can have an adjustable frequency.

[0065] For each detected incident photon PI, the avalanche photodiode emits a photodiode output signal Se containing information about the detected incident photon PI. This photodiode output signal Se can then be transmitted to a processing unit to analyze the information and extract a useful signal.

[0066] Figure 2 illustrates a functional diagram of a photon SPD detection device, in particular of single photons, illustrated in Figure 1 according to the invention.

[0067] The SDP device includes an APD avalanche photodiode. Avalanche photodiodes offer a cost-effective solution, are compact, consume little energy, and require little maintenance, compared to SNSPD-type photodetectors which require bulky cryogenic cooling.

[0068] By definition, an avalanche photodiode (APD) has a breakdown voltage. When the photodiode receives an electrical signal with a voltage higher than its breakdown voltage, it can detect one or more incident photons (PI) for as long as the signal voltage exceeds the breakdown voltage. Conversely, when the photodiode receives an electrical signal with a voltage lower than its breakdown voltage, it does not detect any photons.

[0069] In one example, the APD avalanche photodiode can operate in Geiger mode.

[0070] In one example, the avalanche photodiode (APD) can be configured to detect incident photons with wavelengths in the infrared range. For instance, the APD could be a photodiode made from gallium-indium arsenide and indium phosphide (InGaAs / InP), germanium (Ge), or mercury-cadmium telluride (HgCdTe). Alternatively, the avalanche photodiode can be configured to detect incident photons with wavelengths in the visible range. For example, the APD could be a photodiode made from silicon (Si).

[0071] The APD avalanche photodiode is configured to receive a stream of incident photons and to provide a photodiode output signal containing information relating to the detection of an incident photon when an incident photon is detected.

[0072] The incident photon PI originates from a photon source SP emitting a flux of incident photons. The photon source SP is notably a pulsed laser with a predetermined photon emission frequency.

[0073] From the predetermined photon emission frequency, the time range during which the photodiode is likely to receive a photon can be determined.

[0074] The SP photon source can emit photons with wavelengths in the infrared range. Advantageously, the SPD device can be used in telecommunications and quantum communications applications. Alternatively, the SP photon source can emit photons in the visible range.

[0075] The avalanche photodiode APD is further configured to receive a timing signal SL. The timing signal SI is an electrical signal with a variable voltage. Specifically, the timing signal SL has a voltage that varies above and below the breakdown voltage of the avalanche photodiode APD. Thus, when the timing signal SI voltage is above the breakdown voltage, the avalanche photodiode APD can detect an incident photon PI from the incident photon flux if an incident photon is received while the timing signal SI voltage is above the breakdown voltage. Conversely, when the timing signal SI voltage is below the breakdown voltage, the avalanche photodiode APD cannot detect an incident photon PI.

[0076] In other words, the avalanche photodiode APD is configured to detect an incident photon PI, for example a single incident photon, over a period of time during which the timing signal voltage SI is above the breakdown voltage.

[0077] The SI synchronization signal, due to its voltage varying above and below the breakdown voltage of the avalanche photodiode (APD), allows operation in a so-called "triggered, sinusoidal, fast" (or "Gigahertz sine wave gated") mode. This means the APD operates by alternating periods of possible photon detection with periods of impossible photon detection. Thus, the APD remains in detection mode for only a short duration, reducing noise associated with incident photon detection (i.e., the afterpulse). The SI synchronization signal voltage can remain above the breakdown voltage for a few hundred picoseconds, enabling the detection of a single photon.

[0078] The device according to the invention reduces the probability of afterpulse and consequently reduces the dead time. In particular, when the avalanche photodiode (APD) detects a photon, the afterpulse phenomenon occurs, consisting of noise generated by the APD that disrupts photon detection for a specific period. A dead time limits the probability of afterpulse in the APD to a sufficiently low level. Specifically, the invention has the advantage of creating avalanches with low electrical charges, resulting in a low probability of afterpulse and a high detection rate.

[0079] In one particular embodiment, a continuous electrical signal with a voltage slightly lower than the breakdown voltage is generated. This continuous electrical signal is used, in particular, to form the SI synchronization signal at the input of the avalanche photodiode. This signal is then applied to the avalanche photodiode (APD), causing it to periodically exceed the breakdown voltage, thus enabling the detection of single photons.

[0080] According to another embodiment, the continuous electrical signal is added to the initial trigger signal S0.

[0081] In one example, the synchronization signal SI can be a periodic signal. For example, the synchronization signal SI can have a period of approximately 1 ns. For example, the synchronization signal SI can be sinusoidal, triangular, or rectangular. Thus, for example, the duration for which the synchronization signal SI is above the breakdown voltage can be synchronized with the time range at which an incident photon PI from the incident photon flux is received by the avalanche photodiode APD.

[0082] In addition, the SDP device includes a UC control unit.

[0083] According to a particular embodiment, the control unit UC is configured to provide the synchronization signal SI to the avalanche photodiode APD. The synchronization signal is such that the duration for which the voltage of the synchronization signal above the breakdown voltage is synchronized with the time range at which an incident photon PI from the incident photon flux is received by the avalanche photodiode.

[0084] In particular, the UC control unit phases the initial trigger signal S0 with the photon emission frequency.

[0085] In one particular embodiment, phasing is achieved based on the number of photons detected by the avalanche photodiode over a predetermined time period. In another particular embodiment, the number of photons is determined by a counting unit.

[0086] According to another embodiment, to achieve phasing, it is determined, in particular by the control unit UC, whether the duration for which the voltage of the synchronization signal above the breakdown voltage is synchronized with the time range during which the avalanche photodiode is likely to receive an incident photon, the duration being determined from the photon emission frequency.

[0087] If this is the case, the synchronization is correct and the phase of the synchronization signal SI will have the same phase as the initial trigger signal S0. Otherwise, the initial trigger signal S0 is modified by the control unit UC to form the synchronization signal SI supplied to the avalanche photodiode APD.

[0088] It should be noted that the photon emission frequency can be on the order of a multiple or a submultiple of the synchronization signal frequency.

[0089] The device of the present invention is such that it allows the synchronization signal voltage to be controlled so that it remains above the breakdown voltage upon the reception of an incident photon PI by the avalanche photodiode APD. It is possible that the synchronization signal voltage may be above the breakdown voltage outside the time range of the reception of an incident photon by the avalanche photodiode APD. However, the device of the present invention allows the synchronization signal voltage to be controlled so that it remains above the breakdown voltage upon the potential reception of an incident photon PI by the avalanche photodiode APD, in order to detect a maximum number of incident photons from the incident photon flux.

[0090] To this end, and in accordance with a first aspect of the invention, the control unit UC can modify the initial trigger signal S0 to form the synchronization signal SI such that the duration for which the voltage of the synchronization signal SI is above the breakdown voltage is synchronized with the time range at which an incident photon PI is likely to be received by the avalanche photodiode APD. In particular, this modification is achieved by modifying the emission frequency and phase of the incident photon flux.

[0091] Figure 3 schematically illustrates an example of synchronization performed by the control unit UC. This figure shows the trigger signal S0, the continuous electrical signal SC, and the synchronization signal SI. For illustrative purposes, an intermediate signal SI is artificially represented, which represents the sum of the voltage of the trigger signal SO and the voltage of the continuous electrical signal SC.

[0092] As illustrated in Figure 3i), in this example, the intermediate signal voltage SI varies periodically above and below the breakdown voltage. The photon source SP emits photons at a predetermined photon emission frequency as shown in Figure 3ii). The photons are emitted at times within this photon emission frequency. Initially, as illustrated in Figure 3ii), the incident photons (i.e., the arrival of photons at the avalanche photodiode) are either not synchronized or poorly synchronized with the times during which the intermediate signal voltage SI is above the breakdown voltage. In other words, when the incident photons arrive at the avalanche photodiode APD, the intermediate signal voltage SI is below the breakdown voltage. In this case, the avalanche photodiode APD does not detect the incident photons.

[0093] In such a situation, the intermediate signal SI can be modified or adjusted using the control unit UC to obtain a synchronization signal SI that is synchronized, or in phase, with the duration during which the avalanche photodiode APD is likely to receive an incident photon PI from the incident photon flux. This duration is determined, in particular, from the photon emission frequency. After synchronization, as illustrated in Figure 3i), the durations (or at least one of them) during which the synchronization signal voltage is above the breakdown voltage are correctly synchronized with the potential arrival of incident photons at the APD (illustrated by the vertical lines in Figure 3ii). Indeed, when the incident photons arrive at the avalanche photodiode APD, the synchronization signal voltage SI is above the breakdown voltage.The incident photons can therefore be detected by the avalanche photodiode APD.

[0094] To achieve this, the control unit (CU) can adjust the phase of the synchronization signal (SI) supplied to the avalanche photodiode (APD). Phase adjustment synchronizes the phase of the synchronization signal (SI) with the arrival of incident photons (PI) at the avalanche photodiode (APD). For example, the maximum amplitude of the synchronization signal can be aligned with the arrival of the incident photon (PI) at the APD. The control unit (CU) may include a phase shifter or a delay line for this purpose.

[0095] Thus, due to the synchronization performed by the control unit (CU) between the arrival of incident photons and the time periods during which incident photon detection by the avalanche photodiode (APD) is possible, the SPD device has a high incident photon detection rate. Advantageously, this ensures that the durations during which the avalanche photodiode can detect incident photons are synchronized with the arrival of incident photons at the avalanche photodiode.

[0096] In addition or alternatively, and according to a second aspect of the invention, the control unit UC is configured to provide a synchronization signal SI to the avalanche photodiode at a predetermined power. Thus, the control unit UC can be configured to control the power of the synchronization signal SI, thereby controlling the detection efficiency (i.e., the probability of detecting an incident photon). Power control therefore enables repeatable and / or reproducible measurements. As a result, the probability of detecting incident photons by the avalanche photodiode APD is stable. To this end, the control unit UC includes, among other things, an amplifier and a power controller.

[0097] For example, the power can be constant, or nearly constant. In other words, the amplitude of the SI synchronization signal can be constant. Maintaining a constant power of the SI synchronization signal ensures a stable and reproducible probability of photon detection, regardless of any variations in the initial trigger signal supplied to the control unit, such as variations in amplitude, noise, or time drift.

[0098] In particular, the constancy of the synchronization signal power ensures that the overvoltage applied to the avalanche photodiode during phases where the voltage exceeds the breakdown voltage is controlled and identical over time, which makes it possible to reduce the variability of the avalanche gain, to limit the statistical dispersion of the charges generated during avalanches and, consequently, to control the probability of post-pulse.

[0099] Furthermore, the constant power of the synchronization signal allows the adjustment of the avalanche photodiode's detection efficiency to be decoupled from the shape and amplitude of the synchronization signal. Thus, the detection efficiency can be adjusted, for example, by superimposing a continuous electrical signal onto the synchronization signal, without altering the power of the synchronization signal, thereby contributing to the overall stability of the device.

[0100] Thanks to this constant power, the device according to the invention makes it possible to carry out repeatable and comparable measurements over time, to improve the stability of detection performance, and to facilitate the operation of the device in applications requiring high reliability, particularly in the fields of quantum communications, fast photon detection and embedded or distributed systems.

[0101] Thus, thanks to synchronization and / or power control, the SPD device makes it possible to detect photons efficiently, and in particular with a very high photon counting rate, for example up to 200 MHz and a minimum dead time of 5 ns.

[0102] Thus, the SPD device optimizes the detection of incident PI photons from a photon flux with a high photon emission frequency.

[0103] Furthermore, the invention makes it possible to obtain a device that is both compact and maintenance-free since it does not require cryogenic cooling.

[0104] It is noted that when operating a state-of-the-art avalanche photodiode (APD) (such as an indium gallium arsenide / indium phosphide In-GaAs / InP photodiode) in Geiger mode, the probability of an afterpulse is very high. Consequently, it is impossible to detect two consecutive incident photons whose arrival time difference is less than the dead time. Thus, only approximately one photon per 100 nanoseconds can be detected. Advantageously, in the present invention, the avalanche photodiode operates in "gigahertz sine wave gated" mode, allowing it to remain in Geiger mode for only a short period and with a low overvoltage, thereby increasing the speed and detection rate.

[0105] In one example, as illustrated in Figure 4, the SPD device may further include a signal generator GS configured to generate an initial trigger signal S0. In another embodiment, the signal generator GS is an external device connected to the SPD device. In this case, the external signal generator can be connected to an input port of the SPD device to provide the initial trigger signal S0 to the control unit UC.

[0106] The GS signal generator can generate an initial trigger signal S0, which is a periodic signal, preferably sinusoidal, multi-sinusoidal, rectangular, or triangular. The frequency and amplitude of the periodic signal are adjustable. Furthermore, the duty cycle of the initial trigger signal S0 is also adjustable.

[0107] The initial trigger signal S0 can have a power of, for example, 0 dBm.

[0108] In one example, as noted above, the control unit UC can be configured to control the power of the initial trigger signal S0 and, if necessary, adjust the power of the initial trigger signal S0 to form a synchronization signal SI having a determined (i.e., approximately constant) power which is then supplied to the avalanche photodiode APD.

[0109] In one example, the GS signal generator may include a phase-locked loop (PLL) to form the initial trigger signal S0.

[0110] In one example, the control unit UC may include an amplifier, thus amplifying the initial trigger signal S0 and forming the synchronization signal SL

[0111] In one example, the SI synchronization signal can be a periodic signal. For example, the SI synchronization signal can be a sinusoidal, multi-sinusoidal, rectangular, or triangular wave. The duty cycle of the SI synchronization signal can be adjustable. In one example, the SI synchronization signal can have a frequency of approximately 1.25 GHz. In another example, the SI synchronization signal can have a frequency lower than the cutoff frequency of the avalanche photodiode (APD).

[0112] In one example, as also illustrated in Figure 4, the initial trigger signal S0 can be generated from a reference signal provided by a reference clock H. The reference clock H can be a clock that is part of the photon detection SPD device. Alternatively, the reference clock H can be external to the SPD device. In one particular embodiment, the reference clock H is an oscillator, for example, a quartz oscillator. In one example, the reference signal might have a frequency of approximately 10 MHz. However, other frequencies, including higher ones, can be used (for example, 100 MHz). The frequency of the synchronization signal is synthesized from this reference signal, for example, using a phase-locked loop (PLL).

[0113] In one example, as illustrated in Figure 5a, the SPD device includes an avalanche photodiode operating unit (UFAPD) connected to an avalanche photodiode (APD). The UFAPD operating unit may include a temperature controller (TT) configured to control the temperature of the APD. This temperature control prevents variations in the breakdown voltage of the APD. The TT can control the temperature of the APD and, consequently, the dark noise produced by the photodiode, since the latter is proportional to the APD temperature. The TT thus allows the avalanche photodiode to operate optimally. To achieve this, the TT may include a Peltier element and temperature probes for controlling the temperature of the APD.

[0114] In one example, the operating unit of the UFAPD avalanche photodiode may further include a power supply unit, configured to generate a continuous electrical signal SC supplied to the control unit UC. The continuous electrical signal may also be supplied to the avalanche photodiode APD. The continuous electrical signal SC may be on the order of a few tens of volts. The voltage of the continuous electrical signal SC is slightly lower than the breakdown voltage of the photodiode APD.

[0115] Alternatively, the power supply unit can be in a separate unit from the operating unit of the UFAPD avalanche photodiode.

[0116] According to another embodiment, the continuous electrical signal SC serves as an offset signal to the initial trigger signal S0.

[0117] In one example, the continuous electrical signal SC can be amplitude adjustable in order to control the quantum efficiency of the avalanche photodiode APD.

[0118] Figure 5b illustrates a particular embodiment of the control unit UC. In this example, the control unit UC comprises a phase control unit Ph, a power modification unit MP, a power controller CP and an addition unit S.

[0119] The control unit UC receives the initial trigger signal S0.

[0120] The phase control unit Ph modifies the phase of the initial trigger signal S0. For example, the phase control unit Ph can receive the incident photon detection rate PI from the photon stream by the avalanche photodiode APD to determine if its phase is synchronized with the arrival of incident photons at the avalanche photodiode APD. Additionally, or alternatively, the phase control unit Ph can receive the photon emission frequency PI from the incident photon stream to determine if its phase is synchronized with the arrival of incident photons at the avalanche photodiode APD. If the phase of the initial trigger signal S0 is not synchronized with the arrival of incident photons at the avalanche photodiode APD, the phase control unit Ph adjusts the phase of the initial trigger signal S0 so that its maximum amplitude is aligned with the arrival of incident photons at the avalanche photodiode APD.For example, the phase control unit Ph may include a phase shifter.

[0121] The MP power modification unit amplifies or attenuates the initial trigger signal S0. For example, the MP power modification unit might include an amplifier and / or an attenuator. The amplified or attenuated signal is transmitted to the CP power controller. The CP power controller measures the power of the amplified or attenuated signal. If the amplified or attenuated signal is higher (or lower) than a predetermined power value, the CP power controller transmits information to the MP power modification unit, which then adjusts the signal power again, specifically by amplifying or attenuating it.

[0122] The MP power modification unit provides a modified initial trigger signal S0' whose phase and power are modified relative to the initial trigger signal S0.

[0123] The modified initial trigger signal S0' is transmitted to the addition unit S. The addition unit S receives the continuous electrical signal SC from the control unit UC via the operating unit of the avalanche photodiode UFAPD. The addition unit S adds the modified initial trigger signal S0' and the continuous electrical signal SC. The addition unit S provides the synchronization signal SI to the avalanche photodiode APD, the synchronization signal SI being the sum of the modified trigger signal S0' and the continuous electrical signal SC.

[0124] In an alternative embodiment, the control unit UC may include the phase control unit Ph and the addition unit S. In another alternative embodiment, the control unit UC may include the power modification unit MP and the power controller CP and the addition unit S.

[0125] In one example, as illustrated in Figure 6, the SPD device may further include a coupler C configured to connect a measurement device DM to the SPD device, the measurement device DM being configured for sampling and measuring the power, frequency, phase, and / or waveform of the synchronization signal SL

[0126] In one example, the measurement device DM could be an oscilloscope, a spectrum analyzer, a power meter, or a frequency counter.

[0127] The output signal of photodiode Se from the avalanche photodiode APD contains information about the detection of an incident photon PI. Specifically, this information indicates that the avalanche photodiode detected an incident photon. This signal can therefore be processed to extract this information. In an example, as illustrated in Figure 7a, the SPD device may further include a processing unit UT configured to process the output signal of photodiode Se provided by the avalanche photodiode APD. Thus, the processing performed by the processing unit UT allows the extraction of information about the detected incident photon PI.

[0128] In one example, the processing unit UT may include a frequency electrical filter. For example, the frequency-dependent electrical filter can be a planar filter using a cascade of resonators or a cavity filter. A frequency-tunable frequency-dependent electrical filter can also be used.

[0129] A plurality of frequency electrical filters can be used in series in any type of combination.

[0130] In particular, and for example, the planar frequency electrical filter makes it possible to obtain a rejection rate greater than 70 dB, while having an inexpensive and compact device.

[0131] In a specific example, a frequency-domain electrical filter used can be a band-stop filter (single-band or multi-band) or a low-pass filter. Thus, the frequency-domain electrical filter allows the removal of harmonics that would have been generated by the non-linear response of the avalanche photodiode (APD), and therefore the extraction of the signal representing the detected photon (i.e., an electrical pulse representing a detected photon).

[0132] In addition, the UT processing unit can also be configured to amplify the useful signal from the filter.

[0133] The processing unit (PU) can also be configured to compare the voltage of the amplified signal to a reference voltage. For example, when the voltage of the amplified useful signal is greater than the reference voltage, then it is determined that the voltage of the amplified useful signal represents a photon.

[0134] Figure 7b illustrates a particular embodiment of the processing unit. In this example, the processing unit UT comprises a frequency-domain electrical filter F, an amplifier Amp, and a comparator Comp. The processing unit UT receives the output signal from the photodiode Se. The frequency-domain electrical filter F includes, for example, a planar frequency-domain electrical filter that filters out harmonics that would have been generated by the nonlinear response of the avalanche photodiode APD. The amplifier Amp then amplifies the filtered electrical signal. Finally, the comparator Comp includes a predetermined threshold voltage value. The filtered and amplified electrical signal is compared to the predetermined threshold voltage value.The comparator Comp can be configured to determine the presence of a pulse of the filtered and amplified electrical signal which is greater than the predetermined threshold value and thus to confirm the detection of an incident photon by the avalanche photodiode by generating an electrical pulse, in particular a digital one (for example, signals of type LVTTL, ECL or CML).

[0135] In one example, as illustrated in Figure 8a, the SPD device may further include a counting unit UCDT configured to count a number of events. In particular, the counting unit UCDT may be configured to count the number of events from the comparator, essentially including photons detected by the avalanche photodiode (APD) over a specified time period. Specifically, in one embodiment, the counting unit UCDT is configured to count the number of photons detected by the avalanche photodiode over a specified time period. For example, the counting unit UCDT can determine the rate of photons detected by the avalanche photodiode (APD). The counting unit UCDT outputs a detection signal Sd. The detection signal Sd is, for example, a digital signal (e.g., an LVTTL, ECL, or CML type signal).

[0136] In addition, the UCDT counting unit can be configured to set a dead time value for the APD avalanche photodiode.

[0137] Figure 8b illustrates a specific example of the UCDT counting unit. In this example, the UCDT includes a dead time unit (DT) that allows for the definition of a dead time. For example, the dead time can be set between 0 and 100 ns. Additionally, the UCDT may include a pulse width adjustment unit (PS). Specifically, when a photon is detected, the useful signal (Su) comprises an electrical pulse representing a photon. The pulse width adjustment unit (PS) allows for adjusting the temporal width of the pulse, thus enabling the pulse to be used later in the SPD device application. Finally, the UCDT may include an event counting unit (CE) to determine the number of events detected over a specified time period.

[0138] In one example, as illustrated in Figure 9, the control unit (CU) can be configured to receive the number of photons detected by the avalanche photodiode (APD) over a time period determined by the counting unit and to adjust the phase of the synchronization signal supplied to the avalanche photodiode based on the number of photons detected by the avalanche photodiode over a specified time period. Specifically, the control unit is configured to provide the avalanche photodiode with a synchronization signal whose phase is determined from the number of photons detected by the avalanche photodiode over a specified time period.

[0139] Specifically, the control unit (CU) can communicate with, or be connected to, the counting unit (UCDT). The control unit can then receive the detection rate from the UCDT, which is the number of photons received per unit of time. Based on this detection rate, the control unit (UC) can adjust the phase of the synchronization signal (SI) so that the maximum amplitude of the SI is synchronized with the arrival of photons at the photodiode (APD). Thus, the control unit (UC) can perform synchronization using the detection rate value.In particular, from the detection rate, the control unit UC can adjust the phase of the synchronization signal SI, so that the voltage of the synchronization signal above the breakdown voltage is synchronized with the time range during which an incident photon from the incident photon flux is likely to be received by the avalanche photodiode.

[0140] This configuration allows the implementation of a feedback loop in which the phase of the synchronization signal is adjusted to optimize the synchronization between the arrival times of the incident photons and the durations during which the voltage of the synchronization signal is above the breakdown voltage.

[0141] In particular, adjusting the phase from the number of detected photons makes it possible to maximize the detection rate and / or the detection efficiency of the avalanche photodiode, by aligning the phase of the synchronization signal with the arrival times of the photons for which the probability of detection is maximum.

[0142] Furthermore, this phase control based on the number of detected photons allows for automatic compensation of delay or phase variations linked, for example, to time drifts, optical propagation variations, environmental fluctuations or system configuration changes, without manual intervention.

[0143] Thus, the invention makes it possible to obtain a photon detection device exhibiting increased robustness, stability of performance over time and dynamic adaptation to operating conditions, while maintaining a high detection rate.

[0144] Although the invention has been illustrated and described in detail using a preferred embodiment, the invention is not limited to the disclosed examples. Other variations can be deduced by a person skilled in the art without departing from the scope of protection of the claimed invention.

Claims

Demands

1. A photon detection device (SPD) comprising: - an avalanche photodiode (APD) configured to receive a flux of incident photons and to provide a photodiode output signal (Se) containing information relating to the detection of an incident photon (PI) upon detection of an incident photon, the avalanche photodiode having a breakdown voltage, the avalanche photodiode being further configured to receive a synchronization signal (SI), the synchronization signal being a signal having a voltage varying above and below the breakdown voltage of the avalanche photodiode; the avalanche photodiode being capable of detecting an incident photon for a duration during which the synchronization signal voltage is above the breakdown voltage; and - a control unit (CU), the control unit being configured - to provide the synchronization signal (SI) to the avalanche photodiode, the synchronization signal being such that the duration for which the voltage of the synchronization signal above the breakdown voltage is synchronized with the time range for which an incident photon from the incident photon flux is received by the avalanche photodiode and / or - to provide the synchronization signal (SI) with a determined power.

2. Device according to claim 1, wherein photons from the incident photon flux are emitted at given times of a photon emission frequency, the control unit being configured to, from the photon emission frequency, synchronize the duration for which the synchronization signal voltage is above the breakdown voltage with the time range for which an incident photon from the incident photon flux is received by the avalanche photodiode.

3. Device according to any one of the preceding claims, wherein the control unit (CU) is further configured to provide the avalanche photodiode with a synchronization signal whose phase is determined from the number of photons detected by the avalanche photodiode over a determined period of time.

4. Device according to any one of the preceding claims, wherein the control unit is further configured to adjust the phase and / or power of the synchronization signal supplied to the avalanche photodiode.

5. A device according to any one of the preceding claims, the device further comprising a signal generator (SG) configured to generate an initial trigger signal (TS), the initial trigger signal being supplied to the control unit to form the synchronization signal (S).

6. A device according to claim 5, wherein the control unit is configured to modify the phase of the initial trigger signal (TS) to form the synchronization signal (S), so as to synchronize the duration for which the voltage of the synchronization signal is above the breakdown voltage with the time range for which an incident photon is received by the avalanche photodiode.

7. A device according to claim 5 or 6, wherein the control unit is configured to determine the power of the initial trigger signal (SO) and to modify the power of the initial trigger signal (SO) to a given power to form the synchronization signal (SI).

8. A device according to any one of the preceding claims, the device further comprising a coupler (C) configured to connect a measuring device (DM), the measuring device being configured to measure the power, frequency, phase, and / or waveform of the synchronization signal.

9. Device according to any one of the preceding claims, the device further comprising a processing unit (PU) configured to perform processing of the photodiode output signal (Se) supplied by the avalanche photodiode.

10. Device according to the preceding claim, wherein the processing unit is configured to extract a useful signal (Su) from the photodiode output signal supplied by the avalanche photodiode.

11. Device according to any one of claims 9 or 10, wherein the processing unit comprises a frequency electrical filter (F).

12. Device according to any one of claims 9 to 11, wherein the processing unit further comprises an amplifier (Amp).

13. Device according to any one of claims 9 to 12, wherein the processing unit further comprises a comparator (Comp) configured to compare a useful signal to a predetermined threshold value.

14. Device according to any one of the preceding claims, the device further comprising a counting unit (UCDT) configured to count the number of photons detected by the avalanche photodiode over a determined period of time.

15. Device according to claim 14, wherein the control unit (CU) is configured to receive the number of photons detected by the avalanche photodiode over a period of time determined by the counting unit and to provide the avalanche photodiode with a synchronization signal whose phase is further determined from the number of photons detected.

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