WO2014003221A1

WO2014003221A1 - Photon detection device and method

Info

Publication number: WO2014003221A1
Application number: PCT/KR2012/005144
Authority: WO
Inventors: 한상욱; 문성욱; 보우지드압세타; 이민수; 우민기; 김일영
Original assignee: 한국과학기술연구원
Priority date: 2012-06-28
Filing date: 2012-06-28
Publication date: 2014-01-03
Also published as: KR101331790B1

Abstract

The photon detection device includes: a photon detecting element that outputs an electrical signal according to an input periodic signal and a signal generated by an incident photon; an integrator that integrates the electrical signal output from the photon detecting element; and a comparator that outputs a signal which distinguishes the magnitudes of the integrated signals output from the integrator from each other. The device can detect a photon even if a weak avalanche signal is generated.

Description

Photon detection device and method

A device and method for detecting photons.

The single photon detection device is a very important configuration in many fields such as quantum cryptography system, optical network inspection equipment or semiconductor device analysis. Fibers are the most suitable for long distance communication because they exhibit minimal loss and low dispersion at 1.55μm. At this 1.55μm wavelength, the most common single photon detection device is based on InGaAs / InP Avalanche Photodiode. InGaAs / InP avalanche photodiodes have advantages such as small size and low driving voltage.

To detect single photons, InGaAs / InP avalanche photodiodes typically operate above the breakdown voltage, which is called Geiger mode. In Geiger mode, the avalanche photodiode has a large reverse voltage applied to its junction, resulting in a large electric field. Photons incident on the junction region then generate electron-hole pairs. The electron-hole pairs generated in the junction region are accelerated by the strong electromagnetic field applied to the junction region. The electron-hole pairs, which have been given sufficient energy by the electromagnetic field, are in turn accelerated and create new electron-hole pairs. This phenomenon is called avalanche.

While avalanches occur, some of the carriers (electrons or electrons) generated by the avalanche process remain trapped in the multiplication layer of the avalanche photodiode. If the remaining carrier starts to move at the time the avalanche photodiode operates (De-trapping), it can cause a new avalanche. This avalanche phenomenon is called an afterpulse. This after pulse is one of the important causes of error in photon detection.

In order to reduce the after-pulse at the time of photon detection, there is a method of sufficiently setting the time for extinguishing the remaining carriers. The time for dissipating the remaining carriers is called dead time. The longer the dead time is, the more suitable for dissipation of the remaining carriers, the longer the photon detection time is.

The present invention provides a single photon detection apparatus and method that are robust to after pulse noise.

Photon detection device according to an aspect of the present invention includes a photon detection element for outputting an electrical signal in accordance with the input signal and the signal of the incident photon; An integrator which integrates an electrical signal output from the photon detection element; And a comparator for outputting a signal for distinguishing an integrated signal output from the integrator and a threshold voltage magnitude.

In addition, the photon detection method according to an aspect of the present invention includes the steps of outputting an electrical signal in accordance with the input signal and the signal by the incident photon, integrating the electrical signal; And outputting a signal that distinguishes the magnitude of the integrated signal from a threshold voltage.

Photons can be detected by integrating the electrical signal output from the photon detection element and dividing the magnitude of the integrated signal. The structure and detection method proposed in the present invention can detect an electrical signal of a significantly smaller size than the conventional invention, thereby reducing the magnitude of the avalanche current generated by a single photon, which is a trapped carrier. ) Can be reduced. As a result, after-pulse noise can be reduced, making a single photon detection device robust to after-pulse noise.

1 is a block diagram according to an embodiment of the present invention.

2 is a block diagram according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating input and output signals of the photon detection element illustrated in FIG. 2.

4 is a circuit diagram according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a signal of the circuit diagram shown in FIG. 4.

6 is a flowchart according to an embodiment of the present invention.

Hereinafter, with reference to the drawings will be described embodiments of the present invention;

1 is a block diagram according to an embodiment of the present invention. Referring to FIG. 1, the photon detection apparatus 100 includes a photon detection element 110, an integrator 120, and a comparator 130. In the photon detecting apparatus 100 shown in FIG. 1, only components related to the present exemplary embodiment are shown. Accordingly, it will be understood by those skilled in the art that other general purpose components may be further included in addition to the components shown in FIG. 1. For example, a count that counts a signal output from the comparator 130 and counts photons may be connected to an output terminal of the comparator 130.

The photon detection device 100 is a device for determining whether to detect photons. In other words, when the photon is incident, the photon detecting apparatus 100 determines whether the photon is detected by integrating an electrical signal generated by the incident photon. Since the photon detection device 100 determines whether to detect photons using a threshold value for distinguishing the magnitude of the integrated signal of the output of the photon detection element 110 changed by the signal generated by the avalanche, the weak avalanche Even if is detected, it is possible to determine whether to detect photons.

The photon detecting device 110 is a light receiving device that generates an electric signal when photons are incident. The photon detection device 110 determines an operation time according to an input signal. In other words, in the case of a periodic signal in which an input signal is repeated on-off, the photon detection element 110 also operates according to the input signal. The photon detection element 110 responds to incident photons only during the operation time. The operation of the photon detection element 110 will be described in detail below with reference to FIG. 3.

For example, the photon detection element 110 may be an avalanche photodiode. The gate signal is applied to the avalanche photodiode. When a gate signal is applied to the avalanche photodiode, a capacitive response inherent to the avalanche photodiode occurs. In general, the capacitive response signal of the avalanche photodiode has the form of a vibrating sine wave. Accordingly, when a photon is incident on the avalanche photodiode to generate an avalanche signal, the avalanche photodiode outputs an electrical signal in which the capacitive response and the avalanche signal are combined to the integrator 120.

The integrator 120 integrates the electrical signal input from the photon detection element 110 and outputs the integrated signal to the comparator. The integrator 120 integrates only an electrical signal based on a capacitive response when no avalanche signal is generated, and integrates an electrical signal obtained by combining the capacitive response and avalanche signal when an avalanche signal occurs. Therefore, the magnitude of the integrated signal integrated in the integrator 120 varies depending on whether the avalanche signal is generated. The integrator 120 outputs the integrated signal to the comparator 130.

The comparator 130 compares an integrated signal input from the integrator 120 with a threshold value and outputs a comparison result. The threshold is a value for distinguishing whether or not an avalanche signal is generated. In other words, the threshold value is set to distinguish the integral signal when the avalanche signal has occurred and the integral signal when the avalanche signal has not occurred. The comparator 130 outputs a comparison result. For example, the comparator 130 may output a signal indicating 1 or 0 to indicate whether an avalanche signal is generated. In other words, according to the output value of the comparator 130, it is determined whether photons are detected.

As described above, the photon detection device 100 integrates the electrical signal output from the photon detection element 110 by using the integrator 120, and distinguishes the magnitude of the integrated signal by using a threshold value, so that a weak avalanche is achieved. When generated, it is possible to determine whether to detect photons. A method of determining whether the photon detection device 100 detects photons will be described in detail below.

2 is a block diagram according to an embodiment of the present invention. Referring to FIG. 2, the photon detection apparatus 100 includes a synthesizer 140, a photon detection element 110, an integrator 120, and a comparator 130. FIG. 2 is a circuit diagram showing an example of the photon detection device 100 shown in FIG. 1. Referring to FIG. 2, the components of the photon detecting apparatus 100 shown in FIG. 1 are illustrated in a circuit diagram. Therefore, even if omitted below, the above description of the photon detection apparatus 100 may also be applied to the photon detection apparatus according to the embodiment of FIG. 2.

The synthesizer 140 synthesizes the gate signal 21 and the DC bias voltage 22 and outputs the synthesized signal to the photon detection element 110. The synthesized signal may be a signal obtained by moving the gate signal 21 vertically by the DC bias voltage 22. The gate signal 21 is a periodic signal having a predetermined period. For example, the gate signal 21 may be any one of a square wave signal, a sine wave signal, or a bipolar gate signal, and other types of signals may be used. Do. The DC bias voltage 22 is a DC voltage having a predetermined magnitude and may be a voltage lower than the breakdown voltage of the photon detection device 110. The synthesized signal changes from a voltage lower than the breakdown voltage of the photon detection element 110 to a voltage higher than the breakdown voltage of the photon detection element 110. In other words, the maximum value of the synthesized signal is greater than the breakdown voltage of the photon detection element 110, and the minimum value of the synthesized signal is less than the breakdown voltage of the photon detection element 110. Accordingly, while the synthesized signal is applied with a voltage greater than the breakdown voltage of the photon detection element 110, the photon detection element 110 operates to generate an avalanche signal by the incident photons. On the contrary, since the photon detection element 110 does not operate during the time when the synthesized signal is smaller than the breakdown voltage of the photon detection element 110, the avalanche signal does not occur even when photons are incident.

The photon detection element 110 outputs an electrical signal according to a signal input from the synthesizer 140 or a signal by an incident photon. The photon detection element 110 outputs an electrical signal based on a signal input from the synthesizer 140 when no photons are incident. In other words, the photon detection element 110 outputs only the capacitive response. In addition, when there are incident photons, the photon detecting element 110 outputs an electrical signal based on a signal input from the synthesizer 140 and an electrical signal by the incident photons. In other words, the photon detection element 110 outputs an electrical signal including a capacitive response and an avalanche signal.

The integrator 120 integrates the electrical signal input from the photon detection element 110 with time, and outputs the integrated signal to the comparator 130. Therefore, the size of the signal output from the integrator 120 varies according to the input electrical signal. For example, when the electrical signal input to the integrator 120 includes an electrical signal by an incident photon, the integrator 120 outputs 1V, and the electrical signal input to the integrator 120 is incident to the photon incident. Integrator 120 may output 3V if it does not include the electrical signal. The signal output from the integrator 120 is not limited to the above example.

The comparator 130 compares the signal input from the integrator 120 with a threshold and outputs a comparison result. The threshold value is preset to distinguish electrical signals output from integrator 120. V _REF 26 represents an example of a threshold input to the comparator. For example, when the signal input from the integrator 120 is 1V or 3V as in the above case, the threshold value may be set to any one of values between 1V and 3V. The comparator 130 compares the signal input from the integrator 120 with a threshold value, and outputs a signal representing 1 when the threshold is large, and outputs a signal representing 0 when the threshold is small. The photon detecting apparatus 100 may determine whether photons are detected by the photon detecting element 110 through a signal output from the comparator 130. For example, when the signal output from the comparator 130 is a signal indicating 1, the photon detecting apparatus 100 determines that a photon is detected, and when the signal indicating 0 indicates that a photon is not detected. Can be. It will be appreciated by those skilled in the art that, depending on the integrator 120, thresholds, and the like, the signal indicative of the detection of photons may vary.

In addition, the resistor 23 included in the photon detection device 110 of FIG. 2 may have a size of 50 Ω and the resistor 25 may have a size of 5 nF, but the resistor 25 may have a size of 5 nF. The size is not limited to this.

FIG. 3 is a diagram illustrating input and output signals of the photon detection element illustrated in FIG. 2. FIG. 3A is a diagram illustrating an example of an input signal input to the input terminal S1 of the photon detection element 110, and FIG. 3B is an output terminal S2 of the photon detection element 110. A diagram showing an example of an output signal (APD Output Signal) output from the).

Referring to Figure 3 (a), V1 is a voltage that represents the maximum value of the input signal value, V _BR represents the breakdown voltage (Breakdown Voltage) of a photon detection element (110), V _DC indicates the input signals a minimum value . V _DC is a voltage value corresponding to the DC bias voltage 22 in FIG. 2. For example, the input signal is a signal having a constant period, and maintains the voltage of V1 for a predetermined time.

Referring to Figure 3 (b), the output signal has a waveform according to the signal by the input signal and photons. If no avalanche signal is present (31), the output signal has a waveform that increases or decreases or decreases and increases at the edge of the input signal. If an avalanche signal is present 32, the output signal has a waveform that increases at the moment the avalanche occurs. Therefore, depending on the presence of the avalanche signal, the waveform of the output signal is different, the integral signal obtained by integrating the output signal of the waveform of different forms in the integrator 120 is also different. For example, the value integrating the output signal when the avalanche signal is present is larger than the value integrating the output signal when the avalanche signal is not present. The photon detection apparatus 100 may determine whether an avalanche signal is present, that is, whether a photon is detected by distinguishing different integrated signals.

4 is a circuit diagram according to an embodiment of the present invention. Referring to FIG. 4, the buffer 400 provides V _{APD_out} to the integrating circuit 410 using the first amplifier 401. The integrating circuit 410 integrates the input V _{APD_out} and outputs it to the comparing circuit 420. The comparison circuit 420 outputs a result of comparing the threshold value with the signal input from the integration circuit 410. The function of each circuit will be described in detail. FIG. 4 is a circuit diagram showing an example of the photon detection device 100 shown in FIG. 1. Referring to FIG. 4, the components of the photon detection apparatus 100 shown in FIG. 1 are shown in a circuit diagram. Therefore, even if omitted below, the above description of the photon detection apparatus 100 may be applied to the photon detection apparatus according to the embodiment of FIG. 4.

The buffer 400 provides the input signal V _{APD_out} to the integrating circuit 410. For example, V _{APD_out} may be the output signal of FIG. 3 (b). The buffer 400 outputs V _{APD_out} input through the (+) terminal of the first amplifier 401 through the (−) terminal.

The integration circuit 410 includes a first switch 411, a second switch 412, a capacitor 413, and a second amplifier 414. The first switch 411 controls the period and integration time that the integration circuit 410 integrates. In other words, since the integrating circuit 410 receives the input signal V _{APD_out} only when the first switch 411 is closed, the first switch 411 can control the period and time that the integrating circuit 410 integrates. Can be. For example, the period in which the first switch 411 is opened and closed is the same as the period of the input signal S1 of FIG. 3A, and the time when the first switch 411 is closed is the input of FIG. 3A. It may be equal to the time when V1 of the signal S1 is maintained. The second switch 412 removes the electrical signal accumulated in the integrator 120. The second switch 412 is connected in parallel with the capacitor 413. When the second switch 412 is closed, the charge accumulated in the capacitor 413 is removed. Accordingly, the second switch 412 is closed and opened before the integrating circuit 410 integrates the input signal, thereby removing the previous input signal and integrating only the newly input input signal. Capacitor 413 accumulates charges input to integrating circuit 410. The second amplifier 414 receives V _REF1 at the (+) terminal and maintains the voltage V _{int_in at} the (−) terminal as V _REF1 . The output voltage V _{int_out} of the integrating circuit 410 represents a voltage obtained by adding the voltage accumulated in the capacitor 413 to V _{int_in} .

The comparison circuit 420 includes a third switch 421, a fourth switch 422, and a third amplifier 423. The third switch 421 controls the input of V _{int_out} to the comparison circuit 420. When the third switch 421 is closed, V _{int_out} is input to the comparison circuit 420 and compared with V _REF2 . The fourth switch 422 controls the input of V _DD to the comparison circuit 420. When the fourth switch 422 is closed, V _DD is input to the comparison circuit 420 and compared with V _REF2 . Therefore, the third switch 421 and the fourth switch 422 are not closed at the same time. When the third switch 421 is closed, the fourth switch 422 is opened, and when the third switch 421 is opened, the fourth switch 422 is closed. Thus, the third and

fourth switches

421 and 422 are controlled so that the comparison circuit 420 can compare V _REF2 and V _{int_out} or V _REF2 and V _DD .

FIG. 5 is a diagram illustrating a signal of the circuit diagram shown in FIG. 4. The first switch 411 is periodically closed. For example, the period of the first switch 411 may be the same as the period of the signal input to the photon detection element (110). In addition, the time when the first switch 411 is closed may be the same as the time when the photon detection element 110 operates.

V _{APD_out} is an output signal of the photon detection element 110 and has different waveforms depending on whether an avalanche signal is generated. For example, as shown in FIG. 5, when the avalanche signal does not occur, V _{APD_out} may be in the form of a vibrating sine wave. On the contrary, when the avalanche signal is generated, the avalanche signal is added to the sine wave and _thus may have the same shape as the first detection signal of the signal of V _{APD_out} of FIG. 5. The form of V _{APD_out} of FIG. 5 is expressed for better understanding of the invention, and the waveform of V _{APD_out} is not limited to the waveform of FIG. 5.

V _{APD_out} exists only for a predetermined time every predetermined period. For example, V _{APD_out} may only be present while photon detection element 110 is operating. In addition, V _{APD_out} exists every predetermined period, but the period of V _{APD_out} and the present time may be determined depending on the gate signal 21 of FIG. 2.

The first switch 411 controls the time for the integrator 120 to perform the integration operation. That is, the integrator performs the integration operation only during the time when the first switch 411 is closed.

The second switch 412 resets the signal stored in the integrator 120. The second switch 412 operates before the integrator 120 performs the integration so that only the signal input after the integrator 120 is reset can be integrated.

V _{int_in} holds V _REF1 . Therefore, V _{int_out} has a value by integrating the V _{APD_out} relative to the V _{int_in.} The value of V _{int_in} may be set to a value smaller than V _DD .

V _{int_out} represents a value obtained by integrating the V _{APD_out} relative to the V _{int_in.} In other words, V _{int_out} has a value obtained by adding a value obtained by integrating the value of V in V _{APD_out} _{int_in.} V _{int_out} illustrated in FIG. 5 will be described with time. First, V _{int_out} holds V _REF1 when there is no V _{APD_out} . The first input V _{APD_out} is when an avalanche signal occurs. When the first V _{APD_out} is input, V _{int_out} is decreased by the value obtained by the integration circuit 410 integrating V _{APD_out} to become V _avalanche . V _{int_out} maintains V _avalanche until it is reset by the second switch 412 and again becomes V _REF1 when it is reset by the second switch 412. When V _{int_out} becomes V _REF1 at V _avalanche , some time delay may occur. The second input V _{APD_out} is a case where no avalanche signal occurs. After the second V _{APD_out} is input, the V _{int_out} increases or decreases as the integration circuit 410 integrates the value V _{APD_out.} In FIG. 5, the case where V _{int_out} increases and decreases to V _REF1 has been described as an example. However, V _{int_out} may be larger or smaller than V _REF1 according to V _{APD_out} . In general, when there is no avalanche signal, V _{aPD_out, which} is a capacitive response of the avalanche photodiode, is a sinusoidal wave form, and V _{int_out} has a value closer to V _REF1 than V _avalanche .

The third switch 421 is controlled to close for a predetermined time after the integration of the integration circuit 410 is completed so that V _{int_out} can be input to the comparison circuit 420. The fourth switch 422 is opened for a predetermined time after the integration of the integration circuit 410 is completed. The third switch 421 operates opposite to the fourth switch 422.

V _{comp_in} represents a voltage input to the comparison circuit 420. V _{comp_in} maintains V _DD because the fourth switch 422 is closed when the third switch 421 is open. V _{comp_in} is opened and the fourth switch 422 in a state that the third switch 421 is closed, indicates a voltage equal to V _{int_out.}

V _{comp_out} represents a voltage output to the comparison circuit 420. V _{comp_out} compares V _{comp_in} and V _REF2 and outputs the result. For example, when an avalanche signal is input, V _REF2 becomes _greater than V _{comp_in} , and V _{comp_out} outputs a constant voltage to indicate that photons are detected. On the other hand, in the case where the avalanche signal is not input, the V _REF2 is smaller than V _{comp_in,} V _{comp_out} does not output the voltage.

As shown in FIG. 5, V _REF1 is set to a value smaller than V _DD , and V _REF2 is set to have a size between V _REF1 and V _avalanche . Accordingly, the photon detecting apparatus 100 may determine whether photons are detected by comparing the magnitudes of V _{comp_in} and V _REF2 .

6 is a flowchart according to an embodiment of the present invention. FIG. 6 is a flowchart illustrating a method of detecting photons by the photon detecting apparatus 100 of FIG. 1. Therefore, even if omitted below, the above description of the photon detection apparatus 100 may be applied to the photon detection method according to the embodiment of FIG. 6.

6 is a flowchart of a method for detecting photons according to an embodiment of the present invention. Referring to FIG. 6, the method of detecting photons according to the present exemplary embodiment includes steps that are processed in time series in the photon detecting apparatus 100 illustrated in FIG. 1. Therefore, even if omitted below, the above description of the photon detection apparatus 100 is applied to the method of detecting photons according to the present embodiment. The method for detecting photons using the integrator 120 in the photon detecting apparatus 100 is composed of the following steps.

The photon detection apparatus 100 outputs an electrical signal according to an input periodic signal and a signal of an incident photon, integrates the output electrical signal according to the periodic signal, and outputs a signal that distinguishes the magnitude of the integrated signal. Steps.

The photon detection device 100 integrates the electrical signal for a predetermined time for each cycle of the periodic signal. In other words, the photon detection device 100 integrates the electrical signal at predetermined intervals and integrates only for a predetermined time. The periodic signal is a signal obtained by combining the gate signal and the DC bias voltage. For example, the gate signal may be a pulse signal having a certain period. The DC bias voltage is a DC voltage having a constant magnitude of voltage. The predetermined time is determined according to the periodic signal. The photon detection apparatus 100 outputs an integrated signal by adding an integrated value of an electrical signal to a predetermined first reference value, and outputs a result of comparing the integrated signal with a second reference value set for distinguishing the magnitude of the integrated signal. At this time, the second reference value is set to a value between the first reference value and the integrated signal when the photon is incident. Therefore, the photon detection apparatus 100 compares the integrated signal with the second reference value and outputs different signals depending on whether the integrated signal is large or small, thereby indicating whether the photons are detected. The DC bias voltage is set such that the minimum value of the periodic signal is smaller than the breakdown voltage of the photon detection element, and the maximum value of the periodic signal is greater than the breakdown voltage.

As described above, the photon detecting apparatus 100 may detect the avalanche signal having an amplitude smaller than the amplitude of the capacitive response of the photon detecting element 110 using the integrator 120. In other words, the photon detecting apparatus 100 integrates the avalanche signal generated together with the capacitive response by using the integrator 120 and compares the integral signal with a predetermined threshold value to determine whether the avalanche signal is generated. The determination may determine whether photons are detected.

Claims

A photon detection element for outputting an electrical signal according to the input periodic signal and the signal of the incident photon;

An integrator which integrates an electrical signal output from the photon detection element; And

And a comparator for outputting a signal for discriminating the magnitude of the integrated signal output from the integrator.
The method of claim 1,

And the integrator integrates the electrical signal for a predetermined time every period of the periodic signal.
The method of claim 2,

And said predetermined time is determined in accordance with said periodic signal input to said photon detection element.
The method of claim 1,

The integrator outputs an integral signal obtained by adding a value obtained by integrating an electrical signal output from the photon detection element to a predetermined first reference value,

And the comparator outputs a comparison result of comparing the integrated signal with a second reference value set to distinguish the magnitude of the integrated signal.
The method of claim 4, wherein

And the second reference value is set to a value between the first reference value and an integrated signal output from the integrator when photons are incident.
The method of claim 1,

A signal generator for outputting a gate signal,

And the periodic signal is a signal obtained by combining a gate signal and a direct current bias voltage.
The method of claim 6,

And the DC bias voltage is set such that the minimum value of the periodic signal is smaller than the breakdown voltage of the photon detection element and the maximum value of the periodic signal is greater than the breakdown voltage.
The method of claim 7, wherein

And the photon detection element is an avalanche photodiode.
Outputting an electrical signal in accordance with the input periodic signal and the signal by the incident photons;

Integrating the electrical signal; And

And outputting a signal for discriminating the magnitude of the integrated signal.
The method of claim 9,

And the integrating step integrates the electrical signal for a predetermined time for each period of the periodic signal.
The method of claim 10,

And said predetermined time is determined in accordance with said periodic signal.
The method of claim 9,

The integrating may include adding an integrated value of the electrical signal to a first predetermined reference value and outputting an integrated signal.

And outputting a signal for discriminating the magnitude of the integrated signal outputs a result of comparing the integrated signal with a second reference value set to distinguish the magnitude of the integrated signal.
The method of claim 12,

And the second reference value is set to a value between the first reference value and the integrated signal when photons are incident.
The method of claim 13,

And the periodic signal is a signal obtained by combining a gate signal and a direct current bias voltage.
The method of claim 14,

And the DC bias voltage is set such that the minimum value of the periodic signal is smaller than the breakdown voltage of the photon detection element and the maximum value of the periodic signal is greater than the breakdown voltage.