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 technology]

[0002] The communication quality of an optical transmission line deteriorates due to various causes such as reflections in the optical transmission line, equipment failures, and a drop in the received light power, and measures are required for each of these. When multiple reflections occur in the optical transmission line, the signal quality after demodulation deteriorates. To prevent this, a technique is generally known that uses an OTDR (Optical Time Domain Reflectometer) to check for the presence or absence of reflections in advance. However, after the inspection, the OTDR is removed and another device or optical patch cable is connected, so this method cannot detect new reflection points (for example, reflections caused by gaps due to poor connection to an optical receiver, etc.) that occur when connecting a device after the inspection. Therefore, it is desirable to implement a function to detect reflections in the optical receiver, which is the final stage that demodulates the signal, so that the presence or absence of reflections in the system can be determined even after the system is constructed.

[0003] As an example of implementing a function for detecting reflections in an optical receiver or the like, for example, there is a configuration as shown in the following document. Patent Document 1 discloses a technology for detecting and notifying reflected light generated inside an optical signal processing device configured by combining multiple optical components. In this technology, an optical switching device is provided with multiple 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 by utilizing the reflection monitor function, the reflection position in the path of the reflected light is identified.

[0004] Patent Document 2 discloses a technique for monitoring abnormalities such as the mating of an optical connector in an optical subscriber accommodating device that accommodates a plurality of optical subscriber devices in a passive double star configuration. In this technique, a transmission signal processing unit of the optical subscriber accommodating device generates a downstream signal to be sent to the optical subscriber device, and an electrical / optical conversion unit transmits the downstream optical signal from an optical coupler to the optical subscriber device via an optical fiber transmission line. An optical signal branched from the optical coupler is converted to an electrical signal by an optical / electrical conversion unit and sent to a reception signal processing unit and a reflected signal detection unit. The reflected signal detection unit detects whether an optical signal is received at a timing that is not normally received, and outputs an alarm signal if an optical signal is received at an abnormal timing. The optical signal transmitted from the optical subscriber accommodating device detects a reflected signal at the optical connector of the optical subscriber accommodating device, the optical branching unit, and the optical subscriber device, and outputs an alarm signal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4676099 specification [Patent Document 2] JP 2000-304647 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the technology described in Patent Document 1, reflection is detected by adding an optical device, so additional optical components are required. However, since the demand for optical components is generally limited compared to electrical components, cost reductions through mass production cannot be expected. For this reason, the structure of Patent Document 1 results in a significant increase in device costs due to the addition of functions.

[0007] Furthermore, in Patent Document 2, reflections are detected electrically, so there is a possibility that the device costs can be reduced compared to Patent Document 1. However, although there is no problem when the distance between multiple reflection points is sufficiently long, in order to deal with cases where multiple reflections occur over a very short distance (for example, when reflections occur 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 the cost of the device, it is necessary to implement a reflection detection function that does not require additional optical components or a high-speed ADC.

[0009] The present invention has been made in consideration of the above 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]

[0010] (1) In order to achieve the above object, the present invention provides the following means: That is, the reflected light detection device of the present invention is a reflected light detection device that detects reflected light in an optical transmission path, and is characterized by comprising an optical / electrical signal conversion functional unit that converts an optical signal acquired from the optical transmission path into an electrical signal, an RF (Radio Frequency) power detection functional unit that detects the power of an RF (Radio Frequency) component of the electrical signal, a reflected light determination functional 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 reflection notification functional unit that notifies the outside of the presence of reflected light when the reflected light determination functional unit determines that reflected light is present.

[0011] This configuration makes it possible to determine the presence or absence of reflected light based on the RF power, which eliminates the need for additional optical components or a high-speed ADC, making it possible to reduce costs.

[0012] (2) Also, a reflected light detection device of the present invention is a reflected light detection device that detects reflected light in an optical transmission path, and is characterized in comprising an optical / electrical signal conversion functional 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 of a lower frequency band from one of the branched electrical signals, a first RF power detection functional unit that detects the power of an RF (Radio Frequency) component of the electrical signal of the lower frequency band, a band-pass filter unit that extracts an electrical signal of a specific band from the other branched electrical signal, a second RF power detection functional unit that detects the power of the RF component of the electrical signal of the specific band, a reflected light determination functional unit that compares the power of the RF component detected by the first RF power detection functional unit with the power of the RF component detected by the second RF power detection functional unit to determine whether or not reflected light is present, and a reflection notification functional unit that notifies the outside of the presence of reflected light when the reflected light determination functional unit determines that reflected light is present.

[0013] This configuration makes it possible to determine the presence or absence of reflected light based on two RF powers, one in the low frequency band and the other in the other frequency bands. As a result, it is not necessary to set a reference value for determining the presence of reflected light, and it is also not necessary to provide a separate photodetector or high-speed ADC, which allows for cost reduction.

[0014] (3) Furthermore, the reflected light detection device of the present invention is a reflected light detection device that detects reflected light in an optical transmission path, and is characterized in comprising: an optical / electrical signal conversion functional unit that converts an optical signal acquired from the optical transmission path into an electrical signal; a DC power detection functional unit that detects the power of a DC (Direct Current) component of the electrical signal; an RF power detection functional unit that detects the power of an RF (Radio Frequency) component of the electrical signal; a reflected light determination functional 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, while, if the power of the DC component exceeds the second reference value, compares the power of the detected RF component with a first reference value and determines whether or not reflected light is present; and a reflection notification functional unit that notifies the outside of the presence of reflected light when the reflected light determination functional unit determines that reflected light is present.

[0015] With this configuration, if the power of the DC component is less than the second reference value, the presence or absence of reflected light is not determined, making it possible to suppress erroneous recognition. On the other hand, if the power of the DC component exceeds the second reference value, the power of the detected RF component is compared with the first reference value to make it possible to determine whether or not reflected light is present. As a result, there is no need to provide additional optical components or a high-speed ADC, making it possible to reduce costs.

[0016] (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 including at least the steps of converting an optical signal acquired from the optical transmission path into an electrical signal, detecting the power of an RF (Radio Frequency) component of the electrical signal, comparing the power of the detected RF component with a first reference value to determine whether or not reflected light is present, and, if the determination results in the presence of reflected light, notifying the outside of the presence of reflected light.

[0017] This configuration makes it possible to determine the presence or absence of reflected light based on the RF power, which eliminates the need for additional optical components or a high-speed ADC, making it possible to reduce costs.

[0018] (5) Furthermore, a 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 including 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 of a lower frequency band from one of the branched electrical signals, detecting the power of an RF (Radio Frequency) component of the electrical signal of the lower frequency band, extracting an electrical signal of a specific band from the other branched electrical signal, detecting the power of the RF component of the electrical signal of the specific band, comparing the power of the RF component of the electrical signal of the lower frequency band with the power of the RF component of the electrical signal of the specific band to determine whether or not reflected light is present, and, if the determination results in the presence of reflected light, 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 powers, one in the low frequency band and the other in the other frequency bands. As a result, it is not necessary to set a reference value for determining the presence of reflected light, and it is also not necessary to provide a separate photodetector or high-speed ADC, which allows for cost reduction.

[0020] (6) Furthermore, a 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 including at least the steps of: converting an optical signal acquired from the optical transmission path into an electrical signal; detecting the power of a DC (Direct Current) component of the electrical signal; detecting the power of an 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 power of the detected RF component with a first reference value to determine whether or not reflected light is present; and, if the determination results in the presence of reflected light, notifying the outside of the presence of reflected light.

[0021] With this configuration, if the power of the DC component is less than the second reference value, the presence or absence of reflected light is not determined, making it possible to suppress erroneous recognition. On the other hand, if the power of the DC component exceeds the second reference value, the power of the detected RF component is compared with the first reference value to make it possible to determine whether or not reflected light is present. As a result, there is no need to provide additional optical components or a high-speed ADC, making it possible to reduce costs. Effect of the Invention

[0022] According to the present invention, it is possible to determine the presence or absence of reflected light based on RF power. As a result, there is no need to provide additional optical components or a high-speed ADC, which makes it possible to reduce costs. [Brief description of the drawings]

[0023] [Figure 1] 1 is a block diagram showing a configuration of an optical receiver with a reflection detection function in a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a schematic configuration of an optical transmission line. [Diagram 3] FIG. 13 is a diagram illustrating an example of a spectrum when multiple reflection occurs in an optical transmission line. [Figure 4] FIG. 11 is a block diagram showing a configuration of an optical receiver with a reflection detection function in a second embodiment. [Diagram 5] FIG. 2 is a diagram illustrating a frequency band of an electrical signal. [Figure 6] FIG. 11 is a block diagram showing a configuration of an optical receiver with a reflection detection function according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The inventors noticed that when reflection occurs in the optical transmission path, unnecessary power is detected in the RF (radio frequency) region of the electrical signal output from the optical / electrical signal conversion function unit, and discovered that the presence or absence of reflected light can be determined from the magnitude of the power of the RF component, resulting in the present invention.

[0025] That is, the reflected light detection device of the present invention is a reflected light detection device that detects reflected light in an optical transmission path, and is characterized by comprising an optical / electrical signal conversion functional unit that converts an optical signal acquired from the optical transmission path into an electrical signal, an RF power detection functional unit that detects the power of an RF (Radio Frequency) component of the electrical signal, a reflected light determination functional 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 reflection notification functional unit that notifies the outside of the presence of reflected light when the reflected light determination functional unit determines that reflected light is present.

[0026] This allows the inventors to determine the presence or absence of reflected light based on RF power. As a result, it is no longer necessary to provide additional optical components or a high-speed ADC, making it possible to reduce costs. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. To facilitate understanding of the description, the same reference numbers are used for the same components in each drawing, and duplicate descriptions will be omitted.

[0027] [First embodiment] (composition) 1 is a block diagram showing the configuration of an optical receiver with reflection detection function according to the first embodiment. The optical receiver with reflection detection function according to the first embodiment is composed of an optical / electrical signal conversion function unit 11 and a reflection detection function unit 20a. The reflection detection function unit 20a is composed 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 function unit 11 has a function of converting an optical signal into an RF electric signal, and can be realized by, for example, a photodiode and a DC block.

[0029] The reflection detection unit 20a includes a branching unit 21 having a function of branching an RF electrical signal, an RF power detection function unit 31 having a function of detecting RF power, a reflection determination function unit 41 having a function of determining the presence or absence of reflection from the detection result, and a reflection notification function unit 51 having a function of notifying the presence or absence of reflection. Next, the details of each element constituting the reflection detection unit 20a will be described.

[0030] The branching unit 21 has a function of branching a part or the whole of an RF electrical signal supplied to a subsequent circuit (e.g., a signal processing function such as an ADC) not shown, and supplying the branched signal to an RF power detection function unit 31 described later. The branching unit 21 can be realized by, for example, a divider, a directional coupler, or a switch.

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

[0032] The reflection determination function unit 41 has a function of comparing the output signal of the RF power detection function unit 31 with a reference value, determining that a reflection is occurring when the output signal is equal to or greater than a reference value (first reference value) or equal to or less than the reference value (first reference value), 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 41 can be realized by, for example, an analog circuit such as a comparator, or a digital circuit such as a microcomputer or FPGA.

[0033] The reflection notification function unit 51 has a function of notifying the presence or absence of reflection to the outside based on the output signal of the reflection determination function unit 41. As a notification method, for example, an indicator such as an LED (Light Emitting Diode) that changes color or blinks depending on the presence or absence of reflection may be implemented, or the presence or absence of reflection may be notified to another device via digital communication at regular intervals, or the presence or absence of reflection may be notified when a command or the like is given from another device via digital communication, or a combination of these may be used.

[0034] (Detection method) Fig. 2 is a diagram showing a schematic configuration of an optical transmission line. As shown in Fig. 2, when multiple reflection occurs on the optical transmission line due to factors such as dirt on the end of an optical connector or gaps between optical connectors, direct light from the light source and multiple reflected light are input to the optical / electrical signal conversion functional unit 11. Since the optical / electrical signal conversion functional unit 11 outputs a component proportional to the square component of the electric field, the optical / electrical signal conversion functional unit 11 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 in addition to the component obtained by converting the optical signal of the direct light into an electrical signal and the component obtained by converting the optical signal of the multiple reflected light into an electrical signal.

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

[0036] In this case, if a device (such as a log detector) in which the signal value that can be identified by the reflection determination function increases as the RF power increases is used as the RF power detection function unit 31, the output of the RF power detection function unit 31 will also clearly increase, and it can be determined that reflection has occurred when the output exceeds a predetermined reference value (a first reference value, for example, specified according to the amount of reflection to be tolerated). Note that, if a device (a device in which the voltage drops inversely proportional to the RF power) in which the signal value that can be identified by the reflection determination function decreases as the RF power increases is used, it is determined that reflection has occurred when the output falls below the reference value (first reference value). The above procedure makes it possible to detect the presence or absence of reflection.

[0037] [Second embodiment] (composition) 4 is a block diagram showing the configuration of an optical receiver with reflection detection function in the second embodiment. In the second embodiment, a method of generating a reference value for a reflection determination function unit 42 is shown. Configurations that perform the same or similar operations as those in the first embodiment are given the same or similar reference symbols and descriptions thereof are omitted. The optical receiver with reflection detection function according to the second embodiment is composed 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 having a function of branching an RF electrical signal, a second branching unit 23 having a function of branching the branched electrical signal, a low-pass filter unit 61 having a function of extracting low-frequency components from the electrical signal, a band-pass filter unit 62 having a 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 having a function of detecting the RF power of each extracted signal, a reflection determination function unit 42 having a function of comparing the detection results to determine the presence or absence of reflection, and a reflection notification function unit 51 having a function of notifying the presence or absence of reflection. Next, the details of each element constituting the reflection detection unit will be described.

[0039] The first branching unit 22 has a function of branching a part or the whole of an RF electrical signal supplied to a subsequent circuit (e.g., a signal processing function such as an ADC) not shown, and supplying the branched signal to an RF power detection function unit described later. The first branching unit 22 can be realized by, for example, a divider, a splitter, a directional coupler, a switch, or the like.

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

[0041] As shown in FIG. 5, the low-pass filter unit 61 has a 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 a 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 a reflection determination function described later. As shown in FIG. 5, the band-pass filter unit 62 has a function of extracting components with a bandwidth fA from any frequency equal to or greater than the frequency fA of the electrical signal. The band-pass filter unit can be realized by, for example, a band-pass filter. Also, for example, when the band of the optical / electrical signal conversion function unit 11 is 2×fA and a high-pass filter with a cut-off frequency of fA is used, a high-pass filter may be used instead of a band-pass filter because the band of the optical / electrical signal conversion function unit and the high-pass filter play the role of a band-pass filter.

[0042] The second RF power detection function unit 33 has a 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 a reflection determination function described later. The reflection determination function unit 42 has a function of comparing the outputs of the first RF power detection function unit 32 and the second RF power detection function unit 33, determining that a reflection is occurring when the output of the first RF power detection function unit 32 is higher or lower than the output of the second RF power detection function unit 33, and converting the determination result into a signal that can be identified by a reflection notification function unit 51 described later. The reflection determination function unit 42 can be realized by, for example, an analog circuit such as a comparator, or a digital circuit such as a microcomputer or FPGA.

[0043] In addition, in cases where, for example, the second branching unit 23 cannot distribute the power equally or there are individual differences between the first RF power detection function unit 32 and the second RF power detection function unit 33, the comparison of the outputs of the first RF power detection function unit 32 and the second RF power detection function unit 33 is not performed as expected, and thus it is possible to prevent a mistaken determination that a reflection has occurred when no reflection has actually occurred. In this case, the reflection determination function unit 42 may have a function of correcting the value.

[0044] (Detection method) As shown in Fig. 5, the noise floor, which is usually determined by thermal noise, noise figure, etc., becomes a constant value regardless of frequency when averaged. Here, for simplicity of explanation, it is assumed to be N (W / Hz). When the bandwidths of the low-pass filter section 61 and the band-pass filter section 62 are equal as in this example, 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 x fA (W). 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] It should be noted that there is a possibility that the outputs of the first RF power detection function unit 32 and the second RF power detection function unit 33 may not match when the second branching unit 23 cannot distribute the power equally or when there is an individual difference between the first RF power detection function unit 32 and the second RF power detection function unit 33. Therefore, it is necessary to appropriately correct the value of the reflection determination function unit 42 so that, for example, when an optical signal is input in a state where no reflection occurs, it is appropriately determined that no reflection occurs.

[0046] 3, when reflection occurs, the RF power in the region extracted by the low-pass filter unit 61 becomes higher than the RF power extracted by the band-pass filter unit 62. In this case, if a log detector or the like is used for 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. When using a device in which the signal value that can be identified by the reflection determination function decreases as the RF power increases, it is 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 the above procedure, the presence or absence of reflected light can be detected without setting a reference value.

[0048] [Third embodiment] (composition) 6 is a block diagram showing the configuration of an optical receiver with reflection detection function in the third embodiment. In the third embodiment, a method for preventing erroneous detection due to insufficient optical receiving power is shown. The configurations performing the same or similar operations as those in the first and second embodiments are given the same or similar reference numerals and the description thereof is 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 a function of converting an optical signal into a DC and an RF electric signal. The optical / electrical signal conversion function unit 12 can be realized by, for example, a photodiode and a bias T.

[0050] The reflection detection unit 20c includes a DC power detection function unit 71 having a function of detecting DC power, a branching unit 21 having a function of branching an RF electrical signal, an RF power detection function unit 31 having a function of detecting RF power, a reflection determination function unit 43 having a function of determining the presence or absence of reflection from the detection results of DC and RF, and a reflection notification function unit 52 having a function of notifying the presence or absence of reflection. Next, the details of each element constituting the reflection detection unit 20c will be described.

[0051] The DC power detection function unit 71 has a function of detecting the power of a DC electric signal and converting it into a signal that can be identified by the reflection determination function unit 43 described later. The reflection determination function unit 43 has a function of judging that it is not possible to judge whether or not reflection has occurred 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 judgment result into a signal that can be identified by the reflection notification function unit 52 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 is equal to or less than the reference value (first reference value), the reflection determination function unit 43 has a function of judging that reflection has occurred and converting the judgment result into a signal that can be identified by the reflection notification function unit 52 described later.

[0052] The reflection notification function unit 52 has a function of notifying the outside whether or not a reflection can be determined and whether or not a reflection exists, based on the output signal of the reflection determination function unit 43. As a notification method, for example, an indicator that changes color depending on whether or not a reflection can be determined and blinks depending on whether or not a reflection exists, or notifying another device of whether or not a reflection can be determined and whether or not a reflection exists via digital communication at regular intervals, or notifying whether or not a reflection can be determined and whether or not a reflection exists when a command or the like is given from another device via digital communication, or a combination of these can be used.

[0053] (Detection method) As shown in Fig. 3, when multiple reflections occur on the optical transmission line, the optical / electrical signal conversion functional unit outputs a 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. On the other hand, since the RF component of the electrical signal output from the optical / electrical signal conversion functional unit 12 depends on the strength of the electric field (optical reception power) input to the optical / electrical signal conversion functional unit 12, when the optical reception power is low, even if multiple reflections occur on the optical transmission line, it may be determined that no reflection occurs because the RF power is low.

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

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

[0056] As described above, according to the embodiments of the present invention, after an optical signal is converted 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 determination function (e.g., a comparator or a microcomputer), which are readily available and relatively inexpensive electronic components. This eliminates the need to prepare optical components or a high-speed ADC for reflection detection, and is expected to reduce device costs compared to conventional technologies.

[0057] In addition, the present invention can be applied to detecting reflections in optical transmission lines during operation without connecting a device such as an OTDR. For example, when the present invention is applied to optical communications using a time division duplex (TDD) method (e.g., radio over optical fiber), the presence or absence of reflections can be determined by measuring the power when no signal is being transmitted. This eliminates the need to prepare an OTDR or similar device when it becomes necessary to isolate the cause of degradation of signal quality during operation, for example, and thus reduces the man-hours required to isolate the cause. [Explanation of symbols]

[0058] 11 Optical / electrical signal conversion function section 12 Optical / electrical signal conversion function section 20a Reflection detection unit 20b Reflection detection unit 20c Reflection detection unit 21 Branch 31 RF power detection function 31 RF power detection function 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

Claims

1. A reflected light detection device for detecting reflected light in an optical transmission line, comprising: an optical / electrical signal conversion functional unit that converts an optical signal acquired from the optical transmission line into an electrical signal; an RF power detection function unit that detects the power of an 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; a reflection notification function unit that notifies an outside device 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 line, comprising: an optical / electrical signal conversion functional unit that converts an optical signal acquired from the optical transmission line into an electrical signal; A branching unit that branches the electrical signal into two directions; a low-pass filter unit that extracts an electrical signal in a low-frequency band from one of the branched electrical signals; a first RF power detection function unit that detects the power of an 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 function unit that detects the power of an 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 and determines whether or not reflected light exists; a reflection notification function unit that notifies an outside device of the presence of reflected light when the reflected light determination function unit determines that reflected light is present.

3. A reflected light detection device for detecting reflected light in an optical transmission line, comprising: an optical / electrical signal conversion functional unit that converts an optical signal acquired from the optical transmission line into an electrical signal; A DC power detection function unit that detects the power of a DC (Direct Current) component of the electrical signal; an RF power detection function unit that detects the power of an 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 when the power of the DC component is less than the second reference value, does not determine whether or not reflected light exists, and when the power of the DC component exceeds the second reference value, compares the power of the detected RF component with a first reference value to determine whether or not reflected light exists; a reflection notification function unit that notifies an outside device of the presence of reflected light when the reflected light determination function unit determines that reflected light is present.

4. A reflected light detection method for detecting reflected light in an optical transmission line, comprising the steps of: converting an optical signal acquired from the optical transmission line into an electrical signal; detecting the power of an RF (Radio Frequency) component of the electrical signal; comparing the power of the detected RF component with a first reference value to determine whether reflected light is present; and if the determination result indicates that reflected light is present, notifying an outside party of the presence of reflected light.

5. A reflected light detection method for detecting reflected light in an optical transmission line, comprising the steps of: converting an optical signal acquired from the optical transmission line into an electrical signal; splitting the electrical signal into two directions; extracting an electrical signal in a low frequency band from one of the branched electrical signals; detecting the power of an RF (Radio Frequency) component of the electrical signal in the low frequency band; extracting an electrical signal of a specific band from the other branched electrical signal; detecting the power of an 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 is present; and if the determination result indicates that reflected light is present, notifying an outside party of the presence of reflected light.

6. A reflected light detection method for detecting reflected light in an optical transmission line, comprising the steps of: converting an optical signal acquired from the optical transmission line into an electrical signal; detecting a power of a direct current (DC) component of the electrical signal; detecting the power of an 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, whereas if the power of the DC component exceeds the second reference value, comparing the power of the detected RF component with a first reference value to determine whether or not reflected light is present; and if the determination result indicates that reflected light is present, notifying an outside party of the presence of reflected light.

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