KR102610700B1 - Method for Aligning the Avalanche Photodiode to an Optimal Position for Detecting Photons - Google Patents

Abstract

A method of aligning an avalanche photo diode to an optimal position for detecting photons is disclosed.
According to one aspect of the present embodiment, it is possible to operate as both a single photon detection device operated by a SPAD (Single Photon Avalanche Diode) and a single photon detection device operated by an NFAD (Negative Feedback Avalanche Diode), but operates selectively with either one. In the method of aligning the avalanche photodiode to a position to receive photons incident on its center as an NFAD, the avalanche photodiode operates as a SPAD in a first operation process and the avalanche photodiode operates as a SPAD. A measurement process of adjusting the position and measuring the avalanche signal at each position, and adjusting the position of the avalanche photo diode to the position where the largest avalanche signal among the avalanche signals measured in the measurement process occurred. An avalanche photodiode position alignment method is provided, comprising an adjustment process and a second operation process in which the avalanche photodiode operates as an NFAD.

Description

Method for Aligning the Avalanche Photodiode to an Optimal Position for Detecting Photons}

This embodiment relates to a method of aligning an avalanche photo diode operating as an NFAD to an optimal position for detecting photons.

The content described in this section simply provides background information for this embodiment and does not constitute prior art.

With the development of information and communication technology, the importance of single photon detectors that can detect weak optical signals at the single photon level in quantum cryptography communication is emerging.

The single photon detection device is suitable for the long-distance communication wavelength band of 1.3㎛ to 1.5㎛, and is particularly effective in detecting light signals of weak intensity such as single photons. This single-photon detection device mainly uses an InGaAs/InP type APD (Avalanche Photo Diode) as a light receiving element.

APD operates above the breakdown voltage to detect a single photon, which is called Geiger Mode. In Geiger mode, a large reverse voltage is applied to the junction area (PN Junction) of the APD, and as a result, a large electric field is formed in the junction area. At this time, an electron-hole pair is created in the junction area by a photon incident on the junction area. Electron-hole pairs that acquire energy by the strong electromagnetic field applied to the junction region are accelerated in turn, creating new electron-hole pairs. The cumulative occurrence of this phenomenon is called the avalanche phenomenon.

The Geiger mode is again a gated Geiger mode that detects a single photon above the breakdown voltage by the gate signal when a gate signal in the form of a pulse or sine wave is applied to the APD, and direct current power above the breakdown voltage is continuously applied to the APD. It is applied as a quenching mode and is classified into a free running mode that continuously detects a single photon by quenching it using a quenching resistance.

Single photon detection devices that typically operate in free running mode are used as sensors to detect photons that are always incident. For continuous detection of photons, a resistor is placed in the single-photon detection device to quickly quench the avalanche signal after it is generated, and this resistance causes a drop in the avalanche signal.

At this time, the single photon detection device must be aligned to the optimal position where the photon is incident and detect the photon. However, due to the drop in the avalanche signal described above, the single photon detection device operating in free running mode determines the optimal position. This poses a difficult problem.

The purpose of one embodiment of the present invention is to provide a method for aligning the position of a single-photon detection device that operates as an NFAD, capable of aligning the single-photon detection device to an optimal position.

According to one aspect of the present invention, it is possible to operate both a single photon detection device operated by a SPAD (Single Photon Avalanche Diode) and a single photon detection device operated by an NFAD (Negative Feedback Avalanche Diode), but selectively operates with either one. In a method in which a Balanch photo diode is aligned to a position to receive photons incident on its center as an NFAD, a first operation process in which the single photon detection device operates as a SPAD and a position of the single photon detection device operating as a SPAD are adjusted. A measurement process of adjusting and measuring the avalanche signal at each position, an adjustment process of adjusting the position of the single photon detection device to the location where the largest avalanche signal among the avalanche signals measured in the measurement process occurred, and A method for positioning a single-photon detection device is provided, including a second operation process in which the single-photon detection device operates as an NFAD.

According to one aspect of the present invention, the single photon detection device includes a cathode terminal receiving a first direct current power supply, a gate power supply, or a second direct current power supply, a ground terminal, and a device that outputs an avalanche signal as a SPAD when a photon is incident. It is characterized by comprising an anode stage and a second anode stage that outputs an avalanche signal as NFAD when a photon is incident.

According to one aspect of the present invention, when the single photon detection device operates as a SPAD, the cathode terminal, the ground terminal, and the first anode terminal are connected.

According to one aspect of the present invention, a first detection resistor is connected to the first anode terminal, and the generated avalanche signal is detected.

According to one aspect of the present invention, when the single photon detection device operates as an NFAD, the cathode terminal, the ground terminal, and the second anode terminal are connected.

According to one aspect of the present invention, when the single photon detection device operates as an NFAD, a quenching resistor is connected to the second anode terminal.

According to one aspect of the present invention, the quenching resistor is characterized in that it generates a drop in the avalanche signal.

As described above, according to one aspect of the present invention, even if the single photon detection device operates as an NFAD, there is an advantage in that the single photon detection device can be aligned at the optimal position where photons are incident.

Figure 1 is a diagram showing an implementation of a single photon detection device according to an embodiment of the present invention.
Figure 2 is a diagram showing the configuration of a single-photon detection system including a single-photon detection device according to an embodiment of the present invention.
Figure 3 is a graph showing the waveforms of direct current power and gate power applied to the single photon detection device according to an embodiment of the present invention.
Figure 4 is a graph showing the waveform of direct current power applied to a single photon detection device according to an embodiment of the present invention.
Figure 5 is a graph showing the relationship between the position of the light-receiving area of a photo diode in a single-photon detection device serving as a SPAD according to an embodiment of the present invention and the photocurrent generated in the APD.
Figure 6 is a graph showing the relationship between the position of the light-receiving area of a photo diode in a single-photon detection device serving as an NFAD according to an embodiment of the present invention and the photocurrent generated in the APD.
Figure 7 is a diagram showing how the single photon detection device according to an embodiment of the present invention is aligned to the optimal position where photons are incident when functioning as an NFAD.

Since the present invention can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention. While describing each drawing, similar reference numerals are used for similar components.

Terms such as first, second, A, and B may be used to describe various components, but the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, a first component may be named a second component, and similarly, the second component may also be named a first component without departing from the scope of the present invention. The term and/or includes any of a plurality of related stated items or a combination of a plurality of related stated items.

When a component is said to be "connected" or "connected" to another component, it is understood that it may be directly connected to or connected to the other component, but that other components may exist in between. It should be. On the other hand, when it is mentioned that a component is “directly connected” or “directly connected” to another component, it should be understood that there are no other components in between.

The terms used in this application are only used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as "include" or "have" should be understood as not precluding the existence or addition possibility of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification. .

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by a person of ordinary skill in the technical field to which the present invention pertains.

Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and unless explicitly defined in the present application, should not be interpreted in an ideal or excessively formal sense. No.

Additionally, each configuration, process, process, or method included in each embodiment of the present invention may be shared within the scope of not being technically contradictory to each other.

Figure 1 is a diagram showing an implementation of a single-photon detection device according to an embodiment of the present invention, and Figure 2 shows the configuration of a single-photon detection system including a single-photon detection device according to an embodiment of the present invention. It is a drawing.

Referring to Figures 1 and 2, the single photon detection system 200 according to an embodiment of the present invention includes a single photon detection device 110, a direct current power source 120, and a gate power source 125.

The single photon detection device 110 receives power and detects incoming photons. The single photon detection device 110 includes a cathode stage (C) that receives power, a photo diode 210 that receives photons and generates an avalanche signal (photocurrent), and an avalanche signal generated from the photo diode is output. Includes an anode stage (A).

The single-photon detection device 110 may be implemented as an InGaAs/InP type APD (Avalanche Photo Diode), but is not necessarily limited thereto. The single photon detection device 110 receives direct current power or direct current power and a gate signal (gate power) at the cathode end (C), thereby generating a reverse bias voltage (described later with reference to FIG. 3 or 4) greater than the breakdown voltage (V _B ). It operates in Geiger mode to perform light detection at V _gh or V _g2 ). Here, the Geiger mode refers to an operation in which the single photon detection device 110 performs photodetection under reverse bias conditions (V _gh or V _g2 ) greater than the breakdown voltage (V _B ). That is, the single-photon detection device 110 operates in Geiger mode by the gate signal GS, and as photons are received from the outside, the avalanche phenomenon (or amplification of carriers) occurs inside the single-photon detection device 110. , amplification) occurs. To be more specific, when the single photon detection device 110 is biased in the reverse direction by the gate signal GS, the single photon detection device 110 is detected by the bias voltage (V _gh or V _g2 ) of the applied gate signal GS. A high electric field is formed at the PN junction surface of (110). At this time, when the carrier generated by absorption of photons is injected into the amplification layer of the single-photon detection device 110, it goes through continuous avalanche amplification (Avalanche Impact Ionization) and is converted to current inside the single-photon detection device 110. An amplified electronic avalanche phenomenon (Avalanche Breakdown) occurs. Accordingly, the single photon detection device 110 outputs an avalanche signal (photocurrent).

The single photon detection device 110 is an anode stage (A), which is a first anode that outputs an avalanche signal when operating in gated Geiger mode to serve as a SPAD (Single Photon Avalanche Diode). It includes a stage (A ₁ ) and a second anode stage (A ₂ ) that outputs an avalanche signal when operating in free running mode to serve as a negative feedback avalanche diode (NFAD). Here, the first anode stage and the second anode stage may be implemented as different terminals, as shown in FIG. 1, or may be formed by branching from one terminal. The operating mode of the single photon detection device 110 is determined depending on which anode terminal, along with the cathode terminal (C), is connected to an external device (for example, a photon receiving device or a communication device, etc.). Furthermore, in some cases, in addition to the avalanche signal when the first anode stage (A ₁ ) operates in gated Geiger mode, a photo diode (described later with reference to FIG. 2) is operated in linear mode. The output value during operation may be output.

When the single photon detection device 110 operates in gated Geiger mode, the direct current power 120 and the gate power 125 as the gate signal GS are applied to the cathode terminal (C), The first anode end (A ₁ ) is connected to an external device (not shown) to form a closed circuit, and the second anode end (A ₂ ) is terminated. The waveforms of the direct current power supply 120 and the gate power supply 125 applied to the cathode terminal (C) are shown in FIG. 3.

Figure 3 is a graph showing the waveforms of direct current power and gate power applied to the APD according to an embodiment of the present invention.

Referring to FIG. 3, generally, the gate signal GS is maintained at a first bias voltage (V _g1 ) that is smaller than the breakdown voltage (V _B ) during the gate-off (T _na ) period, and the gate on ( During the gate-on, T _a ) period, the second bias voltage (V _gh ) is maintained at a level greater than the first bias voltage (V _g1 ). Here, the first bias voltage (V _g1 ) may be the same voltage as the bias voltage (V _dc ) generated from the DC power supply 120 .

The amplitude (V _G ) of the gate signal (GS) can be expressed as the difference between the second bias voltage (V _gh ) and the first bias voltage (V _g1 ), and the period (T _g ) is when the gate on (T _a ) starts. It means from the point to the point where the next gate on (T _a ) begins. The difference voltage (ΔV ₁ , or the absolute value of the difference voltage) between the breakdown voltage (V _B ) and the second bias voltage (V _gh ) of the gate signal (GS) means the over bias voltage. The gate signal GS may have a frequency of tens of megahertz (MHz) to several gigahertz (GHz).

In Figure 3, the gate power is shown as a pulse waveform, but it is not necessarily limited to this and may be implemented as a sine waveform.

Referring again to FIGS. 1 and 2, this gate signal GS is transmitted to the cathode stage C, and the single photon detection device 110 operates in gated Geiger mode by the gate signal GS. At this time, photons are input to the photo diode 210 in the single-photon detection device 110, and the gate signal GS is incident on the activation period (T _a ) maintained at the second bias voltage (V _gh ). set it to As the gate signal GS is applied to the single photon detection device 110, the photo diode 210 detects photons during the activation period (T _a ). When a photon is detected, the photo diode 210 produces an avalanche signal (photocurrent) and outputs it directly to the first anode terminal (A ₁ ). The output avalanche signal passes through the first detection resistor (R _O1 ) and is detected in the form of a voltage between both ends of the first detection resistor.

On the other hand, when the single photon detection device 110 operates in free running mode, only the DC power supply 120 is applied to the cathode terminal (C) as the gate signal (GS), and the second anode terminal ( A ₂ ) is connected to an external device (not shown) to form a closed circuit, and the first anode end (A ₁ ) is terminated. The waveform of the direct current power supply 120 applied to the cathode terminal (C) is shown in FIG. 4.

Figure 4 is a graph showing the waveform of direct current power applied to the APD according to an embodiment of the present invention.

Referring to FIG. 4, a bias voltage (V _{g2 ) greater than the breakdown voltage (V B} ) is applied to the cathode terminal (C) of the single photon detection device 110 by the DC power supply ₁₂₀ . Because DC power greater than the breakdown voltage is applied, the single photon detection device 110 can continuously operate in Geiger mode regardless of time from the time the power is applied.

Referring again to FIGS. 1 and 2, such direct current power 120 (V _gh ) (only) is applied to the cathode stage (C), and the single photon detection device 110 operates in free running mode.

A quenching resistance (R _Q ) is disposed at the anode end (A ₂ ) of the single photon detection device 110. When DC power 120 above the breakdown voltage (V _B ) is applied, photons can be detected by the photo diode 210 at any time after application. When a photon is detected, an avalanche signal is generated in the photo diode 210. While the avalanche signal is being generated, photons may be additionally incident on the photo diode 210. If an additional photon is incident while the avalanche signal is being generated, it is unclear whether the avalanche signal generated in the photo diode 210 is caused by a previously incident photon or an additionally incident photon, so the detection result is Problems with inaccuracy may arise. To prevent this problem, a quenching resistance (R _Q ) is disposed at the anode end (A ₂ ) of the single photon detection device 110. The quenching resistance (R _Q ) rapidly reduces the avalanche signal due to photon detection and stabilizes the photodiode 210. Accordingly, even if photons are incident successively at regular intervals, the photodiode 210 in the single-photon detection device 110 operating in free running mode can detect all photons. To improve quenching efficiency, the quenching resistance (R _Q ) may have a resistance value in the range of 0.1 to 1.5 MΩ, and more specifically, may have a resistance value of 0.5 MΩ.

The avalanche signal output through the quenching resistor passes through the second detection resistor (R _O2 ) and is detected in the form of a voltage between both ends of the second detection resistor.

The cathode end (C) and the first anode end (A ₁ ) of the single-photon detection device 110 can be connected to an external device (not shown) and operate in gated Geiger mode, and during the gate-on (T _a ) time. It functions as a SPAD to detect photons. Conversely, the cathode end (C) and the second anode end (A ₂ ) of the single photon detection device 200 can be connected to an external device (not shown) and operate in free running mode, detecting photons regardless of time. It plays the role of NFAD.

Figure 5 is a graph showing the relationship between the position of the light-receiving area of a photo diode in a single-photon detection device serving as a SPAD according to an embodiment of the present invention and the photocurrent generated in the APD, and Figure 6 is an embodiment of the present invention. This is a graph showing the relationship between the position of the light-receiving area of the photo diode in the single-photon detection device that acts as an NFAD and the photocurrent generated by the APD.

The photodiode 210 receives photons and generates an avalanche signal (photocurrent), and the size of the generated signal varies depending on the position where the photons are incident. When a photon is incident on the center of the light-receiving area of the photo diode 210, a signal with the largest size is generated, and the size decreases as the incident position of the photon moves away from the center.

At this time, when the single photon detection device 110 operates in gated Geiger mode (SPAD), the differential voltage (ΔV ₁ ) is formed relatively large and there is no quenching resistance at the anode end (A ₁ ). In that, the size of the generated avalanche signal (photocurrent) is clearly distinguished depending on the position of the light receiving area of the photo diode 210, as shown in the graph shown in FIG. 5. As shown in Figure 5, assuming that 510 is the position where the photo diode 210 can receive photons at the center of its light-receiving area, when the photo diode 210 is placed at 510, the largest avalanche signal is It is generated, and as the distance from 510 increases, the size of the signal gradually decreases.

On the other hand, when the single photon detection device 110 operates in free running mode (NFAD), the anode terminal (A ₂ ) is blocked when a current of a certain size or more flows due to the presence of the quenching resistance (R _Q ). , a drop in the avalanche signal occurs due to resistance, as shown in the graph shown in FIG. 6. The size of the avalanche signal increases as it approaches 510 at a certain distance away from the 510, but within a preset radius from the 510, the avalanche signal is saturated regardless of the distance difference from the 510 and becomes a signal of similar size. An avalanche signal is generated.

These characteristics can lead to the following results: In a situation where the NFAD needs to be placed at a location to detect photons, if the NFAD is placed at that location, the photo diode 210 accurately receives photons within the light receiving area due to saturation of the avalanche signal generated from the NFAD. The probability of being accurately placed in the possible position 510 is extremely low. On the other hand, the single photon detection device 110 can perform both the NFAD role and the SPAD role, so even in a situation where the NFAD device 110 needs to be deployed, the device 110 performs the SPAD role first to detect the photo. The optimal position 510 where the diode 210 can receive photons can be found, and a device placed at that position can perform the role of an NFAD. Since the role that the single photon detection device 110 performs may vary if only the terminal (or terminated terminal) connected to an external device (not shown) changes, the single photon detection device 110 needs to perform the role of an NFAD. Even in a situation where there is, the optimal position 510 can be easily found by prioritizing the role of the SPAD in aligning to the position 510.

Finding the optimal location for photon detection or not can lead to the following differences.

When the device 110 operating as an NFAD is aligned directly, the detection efficiency of the single photon detection device is reduced by 8 to 12% compared to when the SPAD is aligned first. The decrease in detection efficiency can be more evident when the quenching resistance increases. When the size of the quenching resistor increases, the detection efficiency decreases by 12 to 15%.

Since the single photon detection device 110 can operate as both SPAD and NFAD, photon detection efficiency can be improved by more accurate alignment.

However, it is not necessarily limited to this. In order for the single photon detection device 110 to operate as a SPAD, it must operate in a relatively strictly restricted environment. Accordingly, when operating as an NFAD, the single photon detection device 110, especially the photo diode 210, may preferentially operate in a linear mode instead of a SPAD when aligning to an optimal position. A voltage of an appropriate size is applied to the cathode terminal (C) of the single photon detection device 110 so that a voltage of a size that allows the photo diode 210 to operate in a linear mode is applied to both ends of the photo diode 210. When the photo diode 210 operates in linear mode, the second anode terminal A ₂ may be terminated or open. When the second anode stage is terminated or open, the photocurrent generated by the photo diode is output to the first anode stage (A ₁ ). When the photo diode 210 operates in linear mode, the largest signal is detected at the position where photons are accurately received at the first anode terminal (A ₁ ), like the output when operating as a SPAD. Accordingly, the single photon detection device 110 can find the optimal position 510 for receiving photons.

FIG. 7 is a diagram illustrating how the single photon detection device according to an embodiment of the present invention is aligned to the optimal position where photons are incident when operating as an NFAD.

The single photon detection device 110 operates as a SPAD (S710). Before operating as an NFAD, the single photon detection device 110 first operates in gated Geiger mode and operates as a SPAD. However, as described above, the single photon detection device 110 is not necessarily limited to operating as a SPAD, and may operate in a linear mode.

The single photon detection device 110 adjusts its position and measures the amount of photocurrent at each position (S720). In order to align the photon to a position where it can enter its center, the single photon detection device 110 adjusts the position within an adjustable range and measures the size of the avalanche signal (photocurrent) at each position. do.

The single photon detection device 110 adjusts its position to the position where the largest photocurrent occurs (S730). The single photon detection device 110 operates as a SPAD and adjusts its position to the location where the largest photocurrent occurs. Since the single photon detection device 110 operates as a SPAD, it can accurately align the photon to a position where it can enter its center.

The single photon detection device 110 operates as an NFAD at the corresponding location (S740).

In Figure 7, each process is described as being sequentially executed, but this is merely an illustrative explanation of the technical idea of an embodiment of the present invention. In other words, a person skilled in the art to which an embodiment of the present invention pertains can change the order depicted in each drawing or perform one or more of the processes without departing from the essential characteristics of an embodiment of the present invention. Since various modifications and variations can be applied by executing in parallel, FIG. 7 is not limited to a time series order.

Meanwhile, the processes shown in FIG. 7 can be implemented as computer-readable codes on a computer-readable recording medium. Computer-readable recording media include all types of recording devices that store data that can be read by a computer system. That is, computer-readable recording media include storage media such as magnetic storage media (eg, ROM, floppy disk, hard disk, etc.) and optical read media (eg, CD-ROM, DVD, etc.). Additionally, computer-readable recording media can be distributed across networked computer systems so that computer-readable code can be stored and executed in a distributed manner.

The above description is merely an illustrative explanation of the technical idea of the present embodiment, and those skilled in the art will be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Accordingly, the present embodiments are not intended to limit the technical idea of the present embodiment, but rather to explain it, and the scope of the technical idea of the present embodiment is not limited by these examples. The scope of protection of this embodiment should be interpreted in accordance with the claims below, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of rights of this embodiment.

110: Single photon detection device
120: DC power
125: gate power
200: Single photon detection system

Claims (7)

It can be operated as both a single photon detection device operated by SPAD (Single Photon Avalanche Diode) and a single photon detection device operated by NFAD (Negative Feedback Avalanche Diode), but an avalanche photo diode that selectively operates as an NFAD is a photon detection device. In the method of arranging the position to receive employment with its center,
A first operation process in which the avalanche photo diode operates as a SPAD;
A measurement process in which an avalanche photo diode operating as a SPAD adjusts its position and measures the avalanche signal at each position;
An adjustment process of adjusting the position of the avalanche photo diode to a position where the largest avalanche signal among the avalanche signals measured in the measurement process occurred; and
Second operation process in which the avalanche photodiode operates as an NFAD
Avalanche photodiode position alignment method comprising: According to paragraph 1,
The avalanche photodiode is,
A cathode terminal receiving the first direct current power and gate power or a second direct current power supply, a ground terminal, a first anode terminal outputting an avalanche signal as a SPAD when a photon is incident, and an avalanche terminal as an NFAD when a photon is incident. An avalanche photodiode position alignment method comprising a second anode stage that outputs a value signal. According to paragraph 2,
When the avalanche photo diode operates as a SPAD, the cathode terminal, the ground terminal, and the first anode terminal are connected. According to paragraph 3,
An avalanche photo diode position alignment method, characterized in that a first detection resistor is connected to the first anode terminal, and the generated avalanche signal is detected. According to paragraph 2,
When the avalanche photo diode operates as an NFAD, the avalanche photo diode position alignment method is characterized in that the cathode terminal, the ground terminal, and the second anode terminal are connected. According to clause 5,
When the avalanche photo diode operates as an NFAD, a quenching resistor is connected to the second anode terminal. According to clause 6,
The above ??quenching resistance is,
An avalanche photodiode position alignment method characterized by generating a drop in the avalanche signal.

Images