KR101244868B1 - Optical receiver, Optical line terminal and recovery method for receiving signal - Google Patents

Abstract

An optical receiver applicable to a wavelength division multiplexing passive optical subscriber network based on a reflection type semiconductor optical amplifier of a wavelength recycling method, comprising: a photodiode for converting an optical signal into an electrical signal and outputting the optical signal; A preamplifier for linearly amplifying the converted electrical signal and converting the converted electrical signal into a voltage signal; A gain amplifier capable of gain control, converting the voltage signal converted by the preamplifier into a signal having a constant output level, and performing a threshold threshold control of the converted signal; And an offset voltage generator configured to generate a preset offset voltage to control the decision threshold of the post amplification unit and to provide the post amplification unit to the post amplification unit. In the semiconductor optical amplifier-based wavelength division multiplexing passive optical subscriber network, the extinction ratio of the downlink optical signal can be increased to a certain level, and at the same time, the optical power incident to the reflective semiconductor optical amplifier located at the subscriber terminal is reduced below a certain level. It is possible to improve downlink and uplink optical signal transmission quality.

Description

Optical receiver, optical line terminal and recovery method for receiving signal

The present invention relates to an optical receiver, and more particularly, to an optical receiver applicable to a wavelength division multiplexing passive optical subscriber network based on a reflection type semiconductor optical amplifier using a wavelength recycling method.

The present invention is derived from the research conducted as part of the IT growth engine technology development project of the Ministry of Knowledge Economy and the Ministry of Information and Telecommunication Research and Development. [Task management number: 2007-S-014-02, Title: Metro-access all-optical integrated network Development]

In a wavelength division multiplexing passive optical network (PON) using a reflective semiconductor optical amplifier as a light source of a central base station or a subscriber station terminal, the reflective semiconductor optical amplifier is a light source having no wavelength dependency. This is of increasing interest due to the advantage that the inventory level of the optical transceiver module can be solved at the system level.

In a passive optical subscriber network using such a reflective semiconductor optical amplifier as a light source, various up / down optical signal transmission techniques exist. Among them, a technique for transmitting downlink optical signals as uplink optical signals of the same wavelength is a system. And because of the economic advantages due to the simplification of parts has already reached the commercialization stage.

As a related technology, a passive optical subscriber network related technology has been proposed to improve economic efficiency and bandwidth utilization by using a reflective semiconductor optical amplifier capable of compensating optical loss due to an optical link. This is a technology for recycling the downlink light signal, there is an advantage in terms of simplicity and economics of the technology. However, the extinction ratio of the downlink signal must be kept below a certain level, and when the downlink optical signal is remodulated and transmitted as an uplink optical signal, a residual transmission signal component included in the uplink signal may have a certain level of transmission penalty. There is this.

In addition, in order to maintain the transmission quality of the uplink signal using the gain saturation performance of the semiconductor optical amplifier and to receive the downlink optical signal having a low extinction ratio, the power level of the downlink optical signal input to the subscriber station where the reflective semiconductor optical amplifier is located is at a predetermined level. It should be ideal.

In addition, there is a disadvantage in that the optical power penalty due to bit intensity noise generated in a single optical fiber bidirectional transmission has both the up and down signal transmission. In addition, optical power penalty due to the increase in relative light intensity noise generated when using a broadband light source based on an erbium-doped optical amplifier spectral sliced with seed light has also been pointed out as a problem.

An alternative method to solve this problem is to improve optical power penalty through dynamic current injection into a semiconductor optical amplifier-based optical transmitter located in a subscriber terminal. This method relates to an electric drive device that effectively injects a downlink optical signal into an uplink optical signal by injecting an appropriate dynamic current into the semiconductor optical amplifier according to the type of the downlink optical signal input, and a semiconductor optical amplifier structure suitable for wavelength recycling. It is mainly for improving the problem in terms of an optical transmitter. As a result, there is an effect that the optical power penalty is improved, but there is a limit to being proposed as a fundamental solution for solving the problems of the existing technology described above.

The present invention has been derived from such a background, and it is possible to increase the extinction ratio of the downlink optical signal to a predetermined level or more in a passive optical subscriber network system based on a reflective semiconductor optical amplifier that recycles the downlink optical signal. An object of the present invention is to provide an optical receiver that enables communication even if the optical power of the injected downlink optical signal is reduced to a predetermined level or less.

Another object of the present invention is to provide an optical receiver capable of improving optical power penalty due to an increase in relative light intensity noise generated when using an erbium-doped optical amplifier based on spectral sliced stiff light.

In addition, the present invention aims at an optical receiver capable of improving optical power penalty due to light intensity noise associated with reflection and Rayleigh backscattering occurring in a single optical fiber bidirectional transmission.

The technical problem is to convert the optical signal into an electrical signal and output a photodiode; A preamplifier for linearly amplifying the converted electrical signal and converting the converted electrical signal into a voltage signal; A gain amplifier capable of gain control, converting the voltage signal converted by the preamplifier into a signal having a constant output level, and performing a threshold threshold control of the converted signal; And an offset voltage generator configured to generate a preset offset voltage to control the decision threshold of the post amplification unit and provide the preset offset voltage to the post amplification unit.

By applying an optical receiver having a decision threshold variable function according to an embodiment of the present invention, an extinction ratio of a downlink optical signal in a wavelength division multiplexing passive optical subscriber network based on a reflective semiconductor optical amplifier that recycles a downlink optical wavelength signal is reduced. Can be increased to a certain level, it is possible to improve the downlink optical signal transmission quality.

In addition, since the input optical power operating region of the reflective semiconductor optical amplifier can be lowered below the gain saturation input optical power level, the link power budget can be improved.

In addition, it is possible not only to improve the phase downlink transmission penalty caused by retro-reflection related light intensity noise generated in a single optical fiber bidirectional transmission, but also to improve the uplink signal transmission quality due to the increased extinction ratio of the downlink signal. In addition, there is an effect of improving the transmission quality of the phase-down signal generated by the increase in the relative light intensity noise generated by using an erbium-doped optical amplifier spectral sliced with seed light.

The foregoing and further aspects of the present invention will become more apparent through the preferred embodiments described with reference to the accompanying drawings. Hereinafter, the present invention will be described in detail so that those skilled in the art can easily understand and reproduce the present invention through these embodiments.

1 is a diagram of a received signal in a typical optical receiver. As shown in FIG. 1, noise components generated due to the conventional problems are mainly located at the "1" level of the optical signal. It can be seen visually that the thickness of the "1" level present on the eye diagram has become considerably thicker than the thickness of the "0" level due to the remodulation of the downlink optical signal. That is, although the extinction ratio of the downlink optical signal appears to be greatly reduced due to gain compression, which is one of the characteristics of the reflective semiconductor optical amplifier itself, more than a certain amount remains.

When applying a conventional photodiode, an optical receiver including a preamplifier and a post amplifier, most decision thresholds are fixed at values corresponding to the average of magnitudes of the "1" level and the "0" level (Fig. 1) 11) This is a cause of increasing bit error rate in digital signal demodulation if the thickness of the " 1 " level is thick because it is not variable.

In addition, the re-modulation of the downlink optical signal not only increases the thickness of the "1" level, but also increases the rise and fall time of the digital modulated signal due to the slow frequency response characteristic, which is one of the characteristics of the reflective semiconductor optical amplifier itself. Will increase. This can be converted into timing jitter on a system and when conventional optical receivers are used, timing jitter is known to be one of the biggest causes of power penalty in optical signal transmission.

The optical receiver according to an embodiment of the present invention applies an optical receiver having a decision threshold variable function, thereby reducing the downlink optical signal in a wavelength division multiplexing passive optical subscriber network based on a reflective semiconductor optical amplifier that recycles the downlink optical wavelength signal. Extinction ratio can be increased to a certain level, thereby improving downlink and uplink optical signal transmission quality.

2 is a diagram illustrating a configuration of an optical receiver according to an embodiment of the present invention.

The optical receiver according to the embodiment of the present invention includes a photodiode 20, a preamplifier 22, a post amplifier 25, and an offset voltage generator 28.

The photodiode 20 is interpreted to cover both the PIN type or the balanced type. In this embodiment, the photodiode 20 converts the incident optical signal into an electrical signal in the form of a current.

The preamplifier 22 converts a current signal input from the photodiode 20 into a voltage signal using a transimpedance amplifier and amplifies it. In the present embodiment, the preamplifier 22 may be implemented as a preamplifier for a continuous mode in a specific frequency band or less in an application field for receiving a continuous mode signal according to an application field. In addition, an application receiving a burst mode may be implemented as a preamplifier for a burst mode below a specific frequency band.

In detail, the post amplifier 25 includes a first post amplifier 24 and a second post amplifier 26. The first post amplifier 24 is implemented as a post amplifier having an automatic gain control function. The first post amplifier 24 maintains the output voltage at a constant level according to the input optical power in the dynamic input region of the optical receiver.

The second post amplifier 26 outputs a signal having an appropriate intersection point on an output diagram when an appropriate DC offset voltage value is input to configure a decision threshold value suitable for noise distribution of a signal input to the optical receiver. Perform the function. The DC offset voltage for the decision threshold control is input from the offset voltage generator 28 for the decision threshold control. In the present embodiment, the first post amplifier amplification unit 24 and the second post amplifier amplification unit 26 may be implemented in one configuration, it may be implemented in a physically separate configuration.

The offset voltage generator 28 includes a constant voltage source having excellent power supply safety and a voltage distribution circuit for changing the output of the constant voltage source to a value suitable for a purpose. In the present embodiment, the load resistance of the voltage divider circuit may be implemented as a variable resistor for convenience.

According to the wavelength recycling method, the asymmetric noise components generated during the remodulation process of the same wavelength optical signal and the asymmetric noise components generated by transmitting the same wavelength optical signal to both optical fibers are mainly distributed in the "1" level of the optical signal. do. This can be seen with reference to FIG. 1. The optical signal of the shape shown in FIG. 1 is input to a photodiode and converted into an electrical signal.

In this process, the asymmetric noise component of the optical signal is converted into an electrical signal in the form of a current signal while maintaining most shapes and shapes without any change or distortion. In this case, the photodiode 20 used may be determined by carefully considering the power budget of the link itself to be applied and the optical path penalty due to wavelength recycling.

Specifically, for example, when the transmission distance is long and the optical path penalty is large, it is preferable to use an avalanche-type photodiode having excellent reception sensitivity performance. Since the balanced photodiode requires a high bias driving voltage, an appropriate high bias voltage generator must be additionally implemented. In addition, since most breakdown type photodiodes have a characteristic in which the breakdown voltage changes depending on the operating temperature, a temperature compensation circuit that can apply a bias voltage is required to compensate for this.

In addition, for example, when designing an optical receiver for short-range transmission with low link power budget, it is preferable to use a PIN type photodiode because it is economical and simplifies the implementation circuit.

The preamplifier 22 converts the electrical signal converted by the photodiode 20 into a signal format in which a voltage is changed to have a reception level characteristic suitable for a digital communication system. In this embodiment, the preamplifier 22 may be implemented as a transimpedance amplifier most widely used to convert a current signal into a voltage signal. It is also desirable to implement an amplifier with automatic gain control whenever possible, but when a low input optical power level near the receiver sensitivity is input, the output level to the input is greatly reduced or the output voltage is proportional to the input optical power reduction. This tends to shrink.

That is, even if the preamplifier 22 is provided with an automatic gain control function, there is a limitation that it does not always provide a constant output characteristic in the total input dynamic range.

3 is a graph showing the change performance of the output voltage level with respect to the input optical power for three kinds of preamplifiers. All three types of preamplifiers used an avalanche type as the photodiode. As shown in FIG. 3, most of the preamplifiers show that the peak-to-peak output voltage level decreases rapidly when the input optical power decreases near the reception sensitivity. As can be seen in such a situation, it is impossible to output a constant voltage signal only with a preamplifier capable of automatic gain control. This problem can be solved through the first post-amplification unit 24 capable of automatic gain control according to an embodiment of the present invention.

4 to 6 are diagrams showing the change of the decision threshold value according to the change of the output voltage level with respect to the input optical power.

Specifically, FIG. 4 illustrates a situation that occurs when the decision threshold is fixed to an arbitrary value while the output voltage level changes with respect to the input optical power. It can be seen that as the input optical power level input to the optical receiver decreases in the order of 40-> 42-> 44, the noise included in the "1" level gradually increases the probability of causing an error in signal discrimination. In this case, as shown in FIG. 5, it can be seen that the decision threshold level should be automatically changed according to the change of the input optical power level. That is, when the optical power level gradually decreases as 52-> 54-> 56, the decision threshold is 52 (a)-> 54 (a)-> 56 (a for accurate reception of this reduced input signal. It can be seen that it should be adjusted downward gradually.

On the other hand, even if any preamplifier is used, the above-described error can be solved when the first post amplification unit 24 having the buffer type automatic gain control function is used. The post amplifier generally linearly amplifies the preamplifier's output signal to any level that can be digitally identified. In addition to this function, when the automatic gain controlled output level is provided to the second post-amplifier 26 at the rear end, it is possible to provide an output signal level having the same magnitude even near the reception sensitivity. Accordingly, as described above, even if the noise component remaining at the "1" level is large, the output is provided regardless of the input optical power level. Therefore, a change in the decision threshold value should be arbitrarily induced as shown in FIG. There is no need to do it. That is, even if a fixed decision threshold is applied, consistent reception sensitivity performance can be maintained in the dynamic input region of the entire light receiver.

FIG. 6 illustrates a case in which reception sensitivity performance is maintained, and since the signal level input to the second post amplification unit 26 always maintains a constant value even when the input optical power is reduced as in 62, 64, and 66. It is not necessary to adjust the decision threshold according to the input optical power. However, when the decision threshold value is slightly lower than the existing decision threshold level, a better eye opening can be obtained, thereby ensuring improved light reception performance.

7A to 7C are output eye diagrams of offset input voltage values of a second post-amplification unit capable of controlling a decision threshold according to an embodiment of the present invention.

In the present exemplary embodiment, the second post amplifier 26 may be implemented as a limiting amplifier. When a specific voltage level is applied to the DC offset input terminal of the limiting amplifier, a cross point change on the output diagram is possible. This change in intersection can be seen as a direct reflection of the change in decision threshold. This decision threshold value change can lead to an improvement in reception characteristics of the optical signal.

FIG. 7A illustrates that an arbitrary voltage level is applied to the DC offset input terminal of the second post amplifier 26 so that the intersection point on the output diagram of the second post amplifier 26 is about 20% in terms of "0" level and magnitude. It shows the results made in the location. In this case, the decision threshold in the clock data recovery block is at the 20% intersection on the diagram.

FIG. 7B illustrates a result of making an intersection point on the output postgram of the second post amplifier 26 by about 50% by applying another voltage value to the DC offset input terminal of the second post amplifier 26. It can be seen that the optical receiver applied to the conventional optical communication system that does not have a variable function of the decision threshold is generally provided. The decision threshold for this case is the 50% intersection point on the diagram as in the case described above.

FIG. 7C illustrates a result of making the intersection point on the output diagram by 80% through the decision threshold value change of the second post amplifier 26. Such output diagrams may arbitrarily set the decision threshold level near the "0" level when there is more noise included in the "1" level compared to the noise included in the "0" level, similar to the application of the present invention. This feature is equivalent to the case where it is reduced to. It is characterized by the fact that the intersection point rises near the "1" level on the output diagram.

On the other hand, when the noise included in the "0" level is more than the noise included in the "1" level, as shown in FIG. 7A, the decision threshold level is used to be raised upward. In the output diagram, the intersection looks like it's falling near the "0" level.

8 is a diagram illustrating a configuration of an offset voltage generator according to an embodiment of the present invention.

As shown, the offset voltage generator 28 includes a constant voltage source 80 and a voltage divider 82. The voltage divider 82 of the offset voltage generator 28 outputs a part of the constant voltage output from the constant voltage source according to the magnitude of R1 and R2. In this case, in order to variably control the output voltage, R2 is implemented with a variable resistor. desirable.

9 to 10 are graphs of transmission test performance results in an optical receiver according to an embodiment of the present invention.

Specifically, FIG. 9 is a graph of received signal characteristics when the downlink optical signal extinction ratio is fixed.

9 (a) shows an uplink light measured using a conventional optical receiver while varying the optical power incident to a reflective semiconductor optical amplifier based optical transmitter located at a subscriber terminal after fixing the extinction ratio of the downlink optical signal to 6 dB. Transmission test results for the signal. As the input optical power decreases and the gain compression decreases, the residual extinction ratio component of the downlink optical signal increases, resulting in deterioration of uplink transmission characteristics.

When the input optical power is reduced to -24dBm compared to the case where the input optical power is -16dBm, the optical power penalty can be confirmed up to 8.5dB. On the other hand, Figure 9 (b) is applied to the optical receiver according to the present invention, the optical power penalty can be reduced to 3.5dB can see the improvement of about 5dB.

10 is a graph of received signal characteristics when the size of the optical power incident on the optical transmitter is fixed.

Specifically, the optical power incident to the reflective semiconductor optical amplifier based optical transmitter located at the subscriber terminal is fixed to -15 dB, and the extinction ratio of the downlink optical signal is changed to 6 to 10 dB.

(a) is a result measured using a conventional optical receiver, and even if the extinction ratio of the downlink optical signal reaches 8 dB, it can be seen that an error floor occurs and transmission is impossible. Similarly, as the extinction ratio of the downlink optical signal is gradually increased, gain squeezing is not sufficient, so that the residual extinction ratio component of the downlink optical signal is increased to deteriorate the uplink transmission characteristic. On the other hand, Figure 10 (b) shows the measurement results in the optical receiver according to an embodiment of the present invention, it can be seen that even if the maximum down extinction ratio reaches 9dB has a power penalty of about 2dB and good transmission characteristics are maintained. have.

That is, through the graphs shown in FIGS. 9 and 10, when using the optical receiver according to the exemplary embodiment of the present invention, it is possible to transmit the uplink signal even if the extinction ratio of the downlink signal is increased to a predetermined level or more. In addition, it is possible to re-modulate the downlink optical signal and significantly reduce a transmission penalty of a predetermined level or more when transmitting the uplink optical signal. In addition, it can be confirmed that transmission is possible even if the size of the downlink optical signal input to the subscriber terminal falls below a certain level.

11 and 12 are graphs of transmission test performance results in an optical receiver according to an embodiment of the present invention.

Specifically, the results of transmission test performance according to the improvement of optical power penalty caused by reflection and Rayleigh backscattering in bidirectional transmission are shown. Specifically, when an optical receiver according to an embodiment of the present invention is used in an uplink optical signal receiver of a passive optical subscriber network based on a reflection type semiconductor optical amplifier that recycles a downlink optical signal, the optical receiver may reflect and Transmission test performance results are shown to improve optical power penalty due to bit-intensity noise caused by Rayleigh inverse scattering.

As can be seen from FIG. 11, it can be seen that the thickness of the "1" level on the optical signal eye pattern has been substantially increased by the retroreflection. This is the result of bit strength noise as described above.

12 illustrates a result of improving a transmission penalty caused by retroreflective noise due to the application of an optical receiver according to an embodiment of the present invention. When there is a retroreflection, it seems to have this reception sensitivity characteristic regardless of the amount of reflection when the optical receiver according to an embodiment of the present invention is used. Even when the floor is mass-produced and there is no reflection, it can be seen that the optical power penalty is up to about 5 dB compared with the conventional optical receiver according to the present invention.

13 is a block diagram of an optical line terminal according to an embodiment of the present invention.

As shown, the optical line terminal according to the exemplary embodiment of the present invention includes the above-described optical receiver and the signal processor 30.

The signal processor 30 analyzes an output signal whose decision threshold is controlled from the optical receiver and performs necessary processing. For example, a process of generating a downlink may be performed to transmit the restored signal to another optical line terminal or to transmit the restored signal to the optical network terminator. According to the present invention, it is possible to more accurately recover the received signal, thereby further improving the reliability of signal processing in the optical communication network.

14 is a flowchart of a method for recovering a received signal according to an embodiment of the present invention.

First, the photodiode converts the received optical signal into an electrical signal (S400). In addition, the electrical signal in the form of the converted current is amplified linearly and converted into a voltage signal (S410). Thereafter, the converted voltage signal is amplified into a signal having a constant output level (S420).

The decision threshold value of the amplified output signal is controlled based on the preset data. In this case, the preset data for the decision threshold value control may be setting data input from the user (S430). The offset voltage for the decision threshold value control is generated and provided according to the input setting data (S440). In the present embodiment, providing the offset voltage can be made by varying the variable resistor included in the voltage divider circuit for voltage division of the constant voltage supplied from the constant voltage source. However, the present invention is not limited thereto.

Thereafter, the decision threshold value is restored (S450). Accordingly, more accurate recovery of the received signal is possible.

Meanwhile, the above-described received signal restoration method can be created by a computer program. The program may also be embodied by being stored in a computer readable media and being read and executed by a computer. The storage medium includes a magnetic recording medium, an optical recording medium and the like.

So far I looked at the preferred embodiments of the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is shown in the claims, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

1 is a diagram of a received signal in a conventional optical receiver,

2 is a view showing the configuration of an optical receiver according to an embodiment of the present invention;

3 is a graph showing the change performance of the output voltage level with respect to the input optical power for three kinds of preamplifiers,

4 to 6 are diagrams illustrating changes of a decision threshold value according to a change of an output voltage level with respect to an input optical power;

7 is an output eye diagram of an offset input voltage value of a second post-amplification unit capable of controlling a decision threshold according to an embodiment of the present invention;

8 is a diagram illustrating a configuration of an offset voltage generator according to an embodiment of the present invention;

9 to 10 are graphs of transmission test performance results in an optical receiver according to an embodiment of the present invention;

11 and 12 are graphs of transmission test performance results in an optical receiver according to an embodiment of the present invention;

13 is a block diagram of an optical line terminal according to an embodiment of the present invention;

14 is a flowchart illustrating a method of recovering a received signal according to an embodiment of the present invention.

Claims (12)

A photo diode converting an optical signal into an electrical signal and outputting the converted optical signal; A preamplifier for linearly amplifying the converted electrical signal and converting the converted electrical signal into a voltage signal; A first post amplifier for outputting a voltage signal converted by the preamplifier through an automatic gain control as a signal having a constant output level irrespective of an input optical power level; A second post amplification unit configured to control a decision threshold value of an output signal output from the first post amplification unit; And And an offset voltage generator configured to generate a preset offset voltage to control the decision threshold of the second post amplifier, and provide the preset offset voltage to the second post amplifier. delete The method of claim 1, And the preamplifier is a preamplifier for continuous mode. The method of claim 1, And the preamplifier is a preamplifier for a burst mode. The method of claim 1, wherein the offset voltage generating unit A constant voltage source for outputting a constant voltage; and And a voltage divider for outputting at least a portion of the constant voltage output from the constant voltage source as an output voltage. 6. The method of claim 5, And the voltage divider includes a variable resistor capable of varying a resistance value. An optical line terminal in a wavelength division multiplexing passive optical subscriber network based on a reflection type semiconductor optical amplifier using a wavelength recycling method, A photodiode for converting optical signals received from a plurality of optical network terminals or optical network units into electrical signals and outputting the electrical signals; A preamplifier for linearly amplifying the converted electrical signal into a voltage signal; A first post amplifier for outputting a voltage signal converted by the preamplifier through an automatic gain control as a signal having a constant output level irrespective of an input optical power level; A second post amplification unit configured to control a decision threshold value of an output signal output from the first post amplification unit; A signal processor configured to analyze and process a signal output from the second post amplifier; And And an offset voltage generator configured to generate a preset offset voltage to control the decision threshold of the second post amplifier, and provide the preset offset voltage to the second post amplifier. delete The method of claim 1, wherein the offset voltage generating unit A constant voltage source for outputting a constant voltage; and And a voltage divider configured to output at least a part of the constant voltage output from the constant voltage source as an output voltage. The method of claim 9, And the voltage divider includes a variable resistor capable of varying a resistance value. A method for recovering a received signal in a wavelength division multiplexing passive optical subscriber network based on a reflection type semiconductor optical amplifier using a wavelength recycling method, Converting the received optical signal into an electrical signal; Linearly amplifying the converted electrical signal and converting the converted electrical signal into a voltage signal; Amplifying the converted voltage signal into a signal having a constant output level regardless of an input optical power level through automatic gain control; Receiving setting data for controlling a decision threshold value of the signal amplified to the constant output level; Generating an offset voltage for decision threshold control according to the input setting data; And And controlling the decision threshold value of the signal amplified to the constant output level using the generated offset voltage. delete

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