Reflected light detection device and reflected light detection method

Abstract

To detect reflected light in an optical transmission line without requiring an additional optical component and a high-speed ADC.SOLUTION: A reflected light detection device for detecting reflected light in an optical transmission line includes: an optical / electrical signal conversion function section 11 that converts an optical signal obtained from the optical transmission line into an electrical signal; an RF (Radio Frequency) power detection function section 31 which detects power of an RF component of the electrical signal; a reflected light determination function section 41 which compares the detected power of the RF component with a first reference value and determines whether the reflected light is present; and a reflected light notification function section 51 which, if the reflected light determination function section 41 determines that the reflected light is present, notifies the outside of the presence of the reflected light.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a reflected light detection device and a reflected light detection method for detecting reflected light in an optical transmission line.

Background Art

[0002] The communication quality of an optical transmission line deteriorates due to various causes such as reflection in the optical transmission line, device failure, and reduction of received optical power, and countermeasures are required for each. Among these, when multiple reflections occur in the optical transmission line, the signal quality after demodulation deteriorates. Therefore, in order to prevent this, a technique for pre-checking the presence or absence of reflection using an OTDR (Optical Time Domain Reflectometer) is generally known. However, after the inspection, the OTDR is removed and another device or optical patch cable is connected. Therefore, with this method, it is not possible to detect newly generated reflection points (for example, gaps occur due to loose connections to an optical receiver or the like, resulting in reflections) by connecting a device after the inspection. Therefore, it is desirable to implement a function for detecting reflection in an optical receiver, which is the final stage of signal demodulation, so that the presence or absence of reflection in the system can be determined even after the system is constructed.

[0003] As an example of implementing a function for detecting reflection in an optical receiver or the like, a configuration such as the following document can be cited. Patent Document 1 discloses a technique for detecting and notifying reflected light generated inside an optical signal processing device configured by combining a plurality of optical components. In this technique, an optical switching device includes a plurality of reflection monitor units having a reflection monitor function, and the reflection monitor units detect reflected light in a certain path of an optical signal input to the optical switching device, and identify the reflection position in the path of the reflected light by using the reflection monitor function.

[0004] Furthermore, Patent Document 2 discloses a technology for monitoring abnormalities such as the mating of optical connectors in an optical subscriber accommodation device that accommodates multiple optical subscriber devices in a passive double star configuration. In this technology, the transmission signal processing unit of the optical subscriber accommodation device generates a downlink signal to be sent to the optical subscriber device, and the electrical / optical conversion unit sends it as a downlink optical signal to the optical subscriber device via the optical fiber transmission path from the optical coupler. The optical signal branched from the optical coupler is converted into an electrical signal by the optical / electrical conversion unit and sent to the reception signal processing unit and the reflected signal detection unit. The reflected signal detection unit detects whether or not an optical signal is received at a timing that would not normally be received, and outputs an alarm signal if an optical signal is received at an abnormal timing. The optical signal transmitted from the optical subscriber accommodation device is detected as a reflected signal in the optical subscriber accommodation device, optical brancher, and optical connectors of the optical subscriber device, and an alarm signal is output. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 4676099 specification [Patent Document 2] Japanese Patent Publication No. 2000-304647 [Overview of the project] [Problems that the invention aims to solve]

[0006] The technology described in Patent Document 1 detects reflection by adding an optical device, thus requiring additional optical components. However, since the demand for optical components is generally limited compared to electrical components, cost reductions due to economies of scale cannot be expected. Therefore, in the structure described in Patent Document 1, the cost of the device increases significantly due to the addition of functionality.

[0007] Furthermore, since Patent Document 2 detects reflection electrically, it may be possible to reduce the equipment cost compared to Patent Document 1. However, while this is not a problem when the distance between multiple reflection points is sufficiently long, in order to deal with cases where multiple reflections occur at very short distances (for example, when reflection occurs due to air gaps), it is necessary to prepare a very high-speed and expensive ADC (Analog-to-Digital Converter).

[0008] Therefore, in order to reduce equipment costs, it is necessary to implement a reflection detection function that does not require additional optical components or high-speed ADCs.

[0009] This invention has been made in view of these circumstances, and aims to provide a reflected light detection device and a reflected light detection method that can detect reflected light in an optical transmission path without requiring additional optical components or a high-speed ADC. [Means for solving the problem]

[0012] (1) Furthermore, the reflected light detection device of the present invention is a reflected light detection device for detecting reflected light in an optical transmission path, and is characterized by comprising: an optical / electrical signal conversion function unit that converts an optical signal acquired from the optical transmission path into an electrical signal; a branching unit that branches the electrical signal in two directions; a low-pass filter unit that extracts an electrical signal in the low-frequency band from one of the branched electrical signals; a first RF power detection function unit that detects the power of the RF (Radio Frequency) component of the electrical signal in the low-frequency band; a band-pass filter unit that extracts an electrical signal in a specific band from the other branched electrical signal; a second RF power detection function unit that detects the power of the RF component of the electrical signal in the specific band; a reflected light determination function unit that compares the power of the RF component detected by the first RF power detection function unit with the power of the RF component detected by the second RF power detection function unit to determine whether or not reflected light exists; and a reflected light notification function unit that, if the reflected light determination function unit determines that reflected light exists, notifies the outside of the presence of reflected light.

[0013] This configuration makes it possible to determine the presence or absence of reflected light based on two RF power values, one in the low-frequency band and one in the other frequency bands. As a result, it becomes unnecessary to set a reference value for determining the presence of reflected light, and it is also possible to reduce costs by eliminating the need for a separate photodetector or high-speed ADC.

[0014] (2) Furthermore, the reflected light detection device of the present invention is a reflected light detection device for detecting reflected light in an optical transmission path, and is characterized by comprising: an optical / electrical signal conversion function unit that converts an optical signal acquired from the optical transmission path into an electrical signal; a DC power detection function unit that detects the power of the DC (Direct Current) component of the electrical signal; an RF power detection function unit that detects the power of the RF (Radio Frequency) component of the electrical signal; a reflected light determination function unit that compares the power of the DC component with a second reference value, and if the power of the DC component is less than the second reference value, does not determine whether or not reflected light is present, but if the power of the DC component exceeds the second reference value, compares the detected RF component power with a first reference value and determines whether or not reflected light is present; and a reflected light notification function unit that notifies the outside of the presence of reflected light when the reflected light determination function unit determines that reflected light is present.

[0015] This configuration prevents misrecognition because, when the power of the DC component is below the second reference value, the system does not determine whether or not reflected light is present. On the other hand, when the power of the DC component exceeds the second reference value, the system compares the detected power of the RF component with the first reference value to determine whether or not reflected light is present. As a result, it becomes unnecessary to provide separate optical components or a high-speed ADC, thus reducing costs.

[0018] (3)Furthermore, the reflected light detection method of the present invention is a reflected light detection method for detecting reflected light in an optical transmission path, and is characterized by comprising at least the steps of: converting an optical signal acquired from the optical transmission path into an electrical signal; branching the electrical signal in two directions; extracting an electrical signal in the low-frequency band from one of the branched electrical signals; detecting the power of the RF (Radio Frequency) component of the electrical signal in the low-frequency band; extracting an electrical signal in a specific band from the other branched electrical signal; detecting the power of the RF component of the electrical signal in the specific band; comparing the power of the RF component of the electrical signal in the low-frequency band with the power of the RF component of the electrical signal in the specific band to determine whether or not reflected light exists; and, if the determination shows that reflected light exists, notifying the outside of the presence of reflected light.

[0019] This configuration makes it possible to determine the presence or absence of reflected light based on two RF power values, one in the low-frequency band and one in the other frequency bands. As a result, it becomes unnecessary to set a reference value for determining the presence of reflected light, and it is also possible to reduce costs by eliminating the need for a separate photodetector or high-speed ADC.

[0020] (4) Furthermore, the reflected light detection method of the present invention is a reflected light detection method for detecting reflected light in an optical transmission path, and is characterized by comprising at least the steps of: converting an optical signal acquired from the optical transmission path into an electrical signal; detecting the power of the DC (Direct Current) component of the electrical signal; detecting the power of the RF (Radio Frequency) component of the electrical signal; comparing the power of the DC component with a second reference value, and if the power of the DC component is less than the second reference value, not determining whether or not reflected light is present, while if the power of the DC component exceeds the second reference value, comparing the detected power of the RF component with a first reference value to determine whether or not reflected light is present; and if, as a result of the determination, reflected light is present, notifying the outside of the presence of reflected light.

[0021] With this configuration, when the power of the DC component is less than the second reference value, it is not determined whether there is reflected light, so misrecognition can be suppressed. On the other hand, when the power of the DC component exceeds the second reference value, it is possible to compare the power of the detected RF component with the first reference value and determine whether there is reflected light. As a result, there is no need to separately provide optical components or a high-speed ADC, so cost reduction can be achieved.

Effects of the Invention

[0022] According to the present invention, it is possible to determine the presence or absence of reflected light based on the RF power. As a result, there is no need to separately provide optical components or a high-speed ADC, so cost reduction can be achieved.

Brief Description of the Drawings

[0023] [Figure 1] It is a block diagram showing the configuration of an optical receiver with a reflection detection function in the first embodiment. [Figure 2] It is a diagram showing a schematic configuration of an optical transmission line. [Figure 3] It is a diagram showing an example of a spectrum when multiple reflections occur in an optical transmission line. [Figure 4] It is a block diagram showing the configuration of an optical receiver with a reflection detection function in the second embodiment. [Figure 5] It is a diagram showing the frequency band of an electrical signal. [Figure 6] It is a block diagram showing the configuration of an optical receiver with a reflection detection function in the third embodiment.

Modes for Carrying Out the Invention

[0024] The inventors of the present invention focused on the fact that when reflection occurs in an optical transmission path, unwanted power is detected in the RF (Radio Frequency) region of the electrical signal output from the optical / electrical signal conversion function unit. They discovered that the presence or absence of reflected light can be determined by the magnitude of the power of the RF component, leading to the present invention.

[0025] In other words, the reflected light detection device of the present invention is a reflected light detection device for detecting reflected light in an optical transmission path, and is characterized by comprising: an optical / electrical signal conversion function unit that converts an optical signal acquired from the optical transmission path into an electrical signal; an RF power detection function unit that detects the power of the RF (Radio Frequency) component of the electrical signal; a reflected light determination function unit that compares the power of the detected RF component with a first reference value and determines whether or not reflected light is present; and a reflected light notification function unit that, if the reflected light determination function unit determines that reflected light is present, notifies the outside of the presence of reflected light.

[0026] This enables the inventors to determine the presence or absence of reflected light based on RF power. As a result, it becomes unnecessary to provide separate optical components or high-speed ADCs, thus enabling cost reduction. Embodiments of the present invention will be described in detail below with reference to the drawings. To facilitate understanding of the explanation, the same reference numerals are used for identical components in each drawing, and redundant explanations are omitted.

[0027] [First Embodiment] (composition) Figure 1 is a block diagram showing the configuration of an optical receiver with a reflection detection function in the first embodiment. The optical receiver with a reflection detection function according to the first embodiment consists of an optical / electrical signal conversion function unit 11 and a reflection detection unit 20a. The reflection detection unit 20a consists of a branching unit 21, an RF power detection function unit 31, a reflection determination function unit 41, and a reflection notification function unit 51, which will be described later.

[0028] The optical / electrical signal conversion unit 11 has the function of converting an optical signal into an RF electrical signal. The optical / electrical signal conversion unit 11 can be realized, for example, by a photodiode and a DC block.

[0029] The reflection detection unit 20a includes a branching unit 21 that has the function of branching the RF electrical signal, an RF power detection function unit 31 that has the function of detecting RF power, a reflection determination function unit 41 that has the function of determining whether or not reflection is present based on the detection result, and a reflection notification function unit 51 that has the function of notifying whether or not reflection is present. Next, the details of each element constituting the reflection detection unit 20a will be described.

[0030] The branching section 21 has the function of branching off part or all of the RF electrical signal supplied to a downstream circuit (e.g., a signal processing function such as an ADC) and supplying it to the RF power detection function section 31, which will be described later. The branching section 21 can be implemented, for example, by a divider, a directional coupler, or a switch.

[0031] The RF power detection unit 31 has the function of detecting the power of the RF electrical signal branched at the branching unit 21 and converting it into a signal that can be identified by the reflection determination unit 41, which will be described later. The RF power detection unit 31 can be implemented, for example, by an RF power detector or a low-speed ADC.

[0032] The reflection detection function unit 41 compares the output signal of the RF power detection function unit 31 with a reference value and determines that a reflection has occurred if the output signal is greater than or equal to the reference value (first reference value) or less than or equal to the reference value (first reference value). It has the function of converting the determination result into a signal that can be identified by the reflection notification function unit 51, which will be described later. The reflection detection function unit 41 can be implemented by analog circuits such as comparators, or by digital circuits such as microcontrollers or FPGAs.

[0033] The reflection notification function unit 51 has the function of notifying an external party of the presence or absence of reflection based on the output signal of the reflection determination function unit 41. Notification methods include, for example, implementing an indicator such as an LED (Light Emitting Diode) whose color or blinking changes depending on the presence or absence of reflection, notifying another device of the presence or absence of reflection via digital communication at regular intervals, notifying the presence or absence of reflection when a command is given from another device via digital communication, or a combination of these methods.

[0034] (Detection method) Figure 2 shows a schematic configuration of an optical transmission path. As shown in Figure 2, if multiple reflections occur on the optical transmission path due to factors such as dirt on the optical connector end or air gaps between optical connectors, the optical / electrical signal conversion function unit 11 receives both direct light from the light source and multiple reflected light. Since the optical / electrical signal conversion function unit 11 outputs a component proportional to the square component of the electric field, in addition to the component obtained by converting the direct light signal into an electrical signal and the component obtained by converting the multiple reflected light signal into an electrical signal, the optical / electrical signal conversion function unit 11 also outputs an electrical signal (beat component) at a frequency corresponding to the absolute value of the difference between the frequency of the direct light and the frequency of the multiple reflected light.

[0035] Figure 3 shows an example of a spectrum when multiple reflections occur in an optical transmission path. Because the center frequency of the light source is always slightly fluctuating, as shown in Figure 3, the beat component is output at a position away from DC, i.e., as RF power. Therefore, when reflection occurs, the RF power is clearly higher.

[0036] In this case, if the RF power detection unit 31 is a device (for example, a log detector) whose signal value can be identified by the reflection detection function increases as the RF power increases, the output of the RF power detection unit 31 will also increase significantly. Therefore, if the output exceeds a predetermined reference value (a first reference value, defined, for example, according to the allowable amount of reflection), it can be determined that reflection has occurred. If a device is used in which the signal value that can be identified by the reflection detection function decreases as the RF power increases (a device whose voltage decreases inversely proportional to the RF power), it is determined that reflection has occurred if the value falls below the reference value (a first reference value). The presence or absence of reflection can be detected by following the above procedure.

[0037] [Second Embodiment] (composition) Figure 4 is a block diagram showing the configuration of an optical receiver with a reflection detection function in the second embodiment. The second embodiment shows the method for generating the reference value of the reflection determination function unit 42. Components that perform the same or similar operations as in the first embodiment are denoted by the same or similar reference numerals and their description is omitted. The optical receiver with a reflection detection function according to the second embodiment consists of an optical / electrical signal conversion function unit 11 and a reflection detection unit 20b.

[0038] The reflection detection unit 20b includes a first branching unit 22 that has the function of branching the RF electrical signal, a second branching unit 23 that has the function of branching the branched electrical signal, a low-pass filter unit 61 that has the function of extracting low-frequency components from the electrical signal, a band-pass filter unit 62 that has the function of extracting a specific band from the electrical signal, a first RF power detection function unit 32 and a second RF power detection function unit 33 that have the function of detecting the RF power of each extracted signal, a reflection determination function unit 42 that has the function of comparing the detection results to determine whether or not there is a reflection, and a reflection notification function unit 51 that has the function of notifying whether or not there is a reflection. Next, the details of each element constituting the reflection detection unit will be described.

[0039] The first branching section 22 has the function of branching off part or all of the RF electrical signal supplied to a subsequent circuit (e.g., a signal processing function such as an ADC) and supplying it to the RF power detection function section described later. The first branching section 22 can be implemented, for example, by a divider, splitter, directional coupler, or switch.

[0040] The second branching section 23 has the function of branching and supplying electrical signals to the low-pass filter section and the band-pass filter section, which will be described later. The second branching section 23 can be implemented, for example, by a divider or a splitter.

[0041] As shown in Figure 5, the low-pass filter unit 61 has the function of extracting components with a frequency of fA or less (for example, 3 GHz or less) from the electrical signal. The first RF power detection function unit 32 has the function of detecting the power of the RF electrical signal extracted by the low-pass filter unit and converting it into a signal that can be identified by the reflection determination function described later. As shown in Figure 5, the band-pass filter unit 62 has the function of extracting components with a bandwidth of fA from any frequency of the electrical signal above the frequency fA. The band-pass filter unit can be realized by, for example, a band-pass filter. Also, for example, if the bandwidth of the optical / electrical signal conversion function unit 11 is 2 × fA and a high-pass filter with a cutoff frequency of fA is used, the bandwidth of the optical / electrical signal conversion function unit and the high-pass filter will act as a band-pass filter, so a high-pass filter may be used instead of a band-pass filter.

[0042] The second RF power detection unit 33 has the function of detecting the power of the RF electrical signal extracted by the bandpass filter unit and converting it into a signal that can be identified by the reflection determination function described later. The reflection determination function unit 42 has the function of comparing the outputs of the first RF power detection unit 32 and the second RF power detection unit 33, determining that reflection has occurred if the output of the first RF power detection unit 32 is higher than or lower than the output of the second RF power detection unit 33, and converting the determination result into a signal that can be identified by the reflection notification function unit 51 described later. The reflection determination function unit 42 can be implemented by analog circuits such as comparators, or by digital circuits such as microcontrollers or FPGAs.

[0043] Furthermore, in cases where, for example, the second branching unit 23 cannot equally distribute power, or where there are individual differences between the first RF power detection unit 32 and the second RF power detection unit 33, the comparison of the outputs of the first RF power detection unit 32 and the second RF power detection unit 33 may not be performed as expected, and in order to prevent a misjudgment that a reflection is occurring when no reflection is occurring, the reflection judgment unit 42 may be provided with a function to correct the value.

[0044] (Detection method) As shown in Figure 5, the noise floor, which is usually determined by thermal noise and noise figure, becomes a constant value regardless of frequency when averaged. Here, for the sake of simplicity, we will use N (W / Hz). In this case, where the bandwidths of the low-pass filter section 61 and the band-pass filter section 62 are equal, the power input to the first RF power detection function section 32 and the second RF power detection function section 33 when no reflection occurs is ideally N × fA (W) in both cases. Therefore, the outputs of the first RF power detection function section 32 and the second RF power detection function section 33 are the same.

[0045] Furthermore, if the second branching unit 23 cannot equally distribute the power, or if there are individual differences between the first RF power detection unit 32 and the second RF power detection unit 33, the outputs of the first RF power detection unit 32 and the second RF power detection unit 33 may not match. Therefore, it is necessary to appropriately correct the value of the reflection detection unit 42 so that, for example, when an optical signal is input while no reflection is occurring, it is appropriately determined that no reflection is occurring.

[0046] On the other hand, as shown in Figure 3, if reflection occurs, the RF power in the region extracted by the low-pass filter unit 61 will be higher than the RF power extracted by the band-pass filter unit 62. In this case, if log detectors or the like are used in the first RF power detection function unit 32 and the second RF power detection function unit 33, it can be determined that reflection has occurred when the output of the first RF power detection function unit 32 exceeds the output of the second RF power detection function unit 33. Note that if a device is used in which the value of the signal that can be identified by the reflection detection function decreases as the RF power increases, it can be determined that reflection has occurred when the output of the first RF power detection function unit 32 falls below the output of the second RF power detection function unit 33.

[0047] By following the above procedure, it is possible to detect the presence or absence of reflected light without setting a reference value.

[0048] [Third Embodiment] (composition) Figure 6 is a block diagram showing the configuration of an optical receiver with reflection detection function in the third embodiment. The third embodiment shows a method for preventing false detection due to insufficient optical reception power. Components that perform the same or similar operations as in the first and second embodiments are denoted by the same or similar reference numerals and their descriptions are omitted.

[0049] The optical receiver with reflection detection function according to the third embodiment is composed of an optical / electrical signal conversion function unit 12 and a reflection detection unit 20c. The optical / electrical signal conversion function unit 12 has the function of converting an optical signal into DC and RF electrical signals. The optical / electrical signal conversion function unit 12 can be realized, for example, by a photodiode and a bias T.

[0050] The reflection detection unit 20c includes a DC power detection function unit 71 that has the function of detecting DC power, a branching unit 21 that has the function of branching RF electrical signals, an RF power detection function unit 31 that has the function of detecting RF power, a reflection determination function unit 43 that has the function of determining whether or not reflection is present based on the DC and RF detection results, and a reflection notification function unit 52 that has the function of notifying whether or not reflection is present. Next, the details of each element constituting the reflection detection unit 20c will be described.

[0051] The DC power detection function unit 71 has the function of detecting the power of a DC electrical signal and converting it into a signal that can be identified by the reflection determination function unit 43, which will be described later. The reflection determination function unit 43 has the function of determining whether or not reflection is occurring when the output signal of the DC power detection function unit 71 is less than a reference value for DC power (second reference value), and converting the determination result into a signal that can be identified by the reflection notification function unit 52, which will be described later. In addition, when the output signal of the DC power detection function unit 71 is equal to or greater than the reference value for DC power (second reference value), and the output signal of the RF power detection function unit 31 is equal to or greater than the reference value (first reference value), or less than or equal to the reference value (first reference value), the reflection determination function unit 43 has the function of determining whether or not reflection is occurring and converting the determination result into a signal that can be identified by the reflection notification function unit 52, which will be described later.

[0052] The reflection notification function unit 52 has the function of notifying an external party whether reflection can be determined and whether or not reflection is present, based on the output signal of the reflection determination function unit 43. Notification methods include, for example, implementing an indicator whose color changes depending on whether or not reflection can be determined and which blinks depending on whether or not reflection is present, notifying another device of whether or not reflection can be determined and whether or not reflection is present via digital communication at regular intervals, notifying whether or not reflection can be determined and whether or not reflection is present when a command is given from another device via digital communication, or a combination of these methods.

[0053] (Detection method) As shown in Figure 3, when multiple reflections occur on the optical transmission path, the optical / electrical signal conversion function outputs a beat component at a frequency corresponding to the absolute difference between the frequency of the direct light and the frequency of the multiple reflected light. On the other hand, the RF component of the electrical signal output from the optical / electrical signal conversion function 12 depends on the strength of the electric field (optical received power) input to the optical / electrical signal conversion function 12. Therefore, if the optical received power is low, even if multiple reflections occur on the optical transmission path, the low RF power may cause it to be determined that no reflections have occurred.

[0054] Therefore, in the third embodiment, a function is added to detect the DC power, which changes output depending on the optical reception power, and if it falls below a reference value for DC power, it is determined that it is not possible to determine whether or not reflection is occurring. If it is above the reference value, the determination function described in the first embodiment is performed.

[0055] By following the above procedure, it is possible to detect the presence or absence of reflection while preventing the false determination that no reflection is occurring when the received light power is low.

[0056] As described above, according to the embodiments of the present invention, after converting an optical signal into an electrical signal, reflection can be detected simply by combining an RF power detection function (e.g., an RF power detector or a low-speed ADC) and a reflection detection function (e.g., a comparator or a microcontroller), which are readily available and relatively inexpensive electronic components. Therefore, there is no need to prepare optical components or high-speed ADCs for reflection detection, and equipment costs can be expected to be reduced compared to conventional technology.

[0057] Furthermore, one application of this invention is the ability to detect reflections in an optical transmission path during operation without connecting something like an OTDR. For example, when applying this invention to time-division duplexing (TDD) optical communication (e.g., optical fiber wireless), the presence or absence of reflection can be determined by measuring the power at times when no signal is being transmitted. This eliminates the need to prepare an OTDR or similar device when troubleshooting is required, for example, if signal quality deteriorates during operation, thus reducing the effort required for troubleshooting. [Explanation of symbols]

[0058] 11 Optical / Electrical Signal Conversion Function Unit 12 Optical / Electrical Signal Conversion Function Unit 20a Reflection detection unit 20b Reflection detection unit 20c Reflection detection unit 21 Branching point 31 RF Power Detection Function Unit 31 RF Power Detection Function Unit 41 Reflection judgment function section 42 Reflection judgment function section 43 Reflection judgment function section 51 Reflection notification function section 52 Reflection notification function section 61 Low-pass filter section 62 Bandpass filter section 71 DC Power Detection Function Unit

Claims

1. A reflected light detection device for detecting reflected light in an optical transmission path, An optical / electrical signal conversion function unit that converts optical signals acquired from the optical transmission path into electrical signals, A branching section that branches the aforementioned electrical signal in two directions, A low-pass filter unit that extracts the electrical signal in the low-frequency band from one of the branched electrical signals, A first RF power detection function unit detects the power of the RF (Radio Frequency) component of the electrical signal in the low-frequency band, A bandpass filter unit that extracts an electrical signal of a specific band from the other branched electrical signal, A second RF power detection unit that detects the power of the RF component of an electrical signal in the aforementioned specific band, A reflected light determination function unit compares the power of the RF component detected by the first RF power detection function unit with the power of the RF component detected by the second RF power detection function unit and determines whether or not reflected light is present. A reflected light detection device characterized by comprising: a reflected light detection function unit that notifies the outside of the presence of reflected light when the reflected light determination function unit determines that reflected light is present.

2. A reflected light detection device for detecting reflected light in an optical transmission path, An optical / electrical signal conversion function unit that converts optical signals acquired from the optical transmission path into electrical signals, A DC power detection function unit that detects the power of the DC (Direct Current) component of the aforementioned electrical signal, An RF power detection function unit that detects the power of the RF (Radio Frequency) component of the aforementioned electrical signal, A reflected light determination function unit compares the power of the DC component with a second reference value, and if the power of the DC component is less than the second reference value, it does not determine whether reflected light is present or not, while if the power of the DC component exceeds the second reference value, it compares the detected power of the RF component with a first reference value and determines whether reflected light is present or not. A reflected light detection device characterized by comprising: a reflected light detection function unit that notifies the outside of the presence of reflected light when the reflected light determination function unit determines that reflected light is present.

3. A method for detecting reflected light in an optical transmission path, The steps include converting an optical signal acquired from the optical transmission path into an electrical signal, The steps include: branching the aforementioned electrical signal in two directions, The steps include extracting an electrical signal in the lower frequency band from one of the branched electrical signals, The steps include detecting the power of the RF (Radio Frequency) component of the electrical signal in the low-frequency band, The steps include extracting an electrical signal of a specific frequency band from the other branched electrical signal, The steps include detecting the power of the RF component of the electrical signal in the specified frequency band, The steps include comparing the power of the RF component of the electrical signal in the low-frequency band with the power of the RF component of the electrical signal in the specific band to determine whether or not reflected light is present, A method for detecting reflected light, characterized by comprising at least the step of notifying the outside of the presence of reflected light if, as a result of the above determination, reflected light is present.

4. A method for detecting reflected light in an optical transmission path, The steps include converting an optical signal acquired from the optical transmission path into an electrical signal, The steps include detecting the power of the DC (Direct Current) component of the aforementioned electrical signal, The steps include detecting the power of the RF (Radio Frequency) component of the electrical signal, The power of the DC component is compared with a second reference value. If the power of the DC component is less than the second reference value, no determination is made as to whether or not reflected light is present. However, if the power of the DC component exceeds the second reference value, the power of the detected RF component is compared with a first reference value to determine whether or not reflected light is present. A method for detecting reflected light, characterized by comprising at least the step of notifying the outside of the presence of reflected light if, as a result of the above determination, reflected light is present.

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