JP2009244163A - Device and method for measuring ratio of light signal to noise - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a ratio of light signal to noise (light SNR) of signal light amplified by an optical amplifier without performing light spectrum measurement. <P>SOLUTION: A device is provided for measuring the light SNR. The device includes an light power detecting means for converting light into an electric signal and detecting light power, a signal light power detecting means for detecting the signal light power from the electric signal corresponding to signal light included in the light, a subtracting means for subtracting the signal light power from the light power and determining noise light power included in the light, and a dividing means for dividing the signal light power and the noise light power. The output of the dividing means corresponds to the light SNR, so that the light SNR can be measured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an apparatus and method for measuring a signal-to-noise ratio of signal light.

  In a long-distance optical transmission system, in order to compensate for a loss of an optical fiber that is a transmission path, optical amplifiers are arranged every several tens of kilometers to amplify attenuated signal light. When the signal light is amplified by the optical amplifier, spontaneous emission light is also generated at the same time, and amplified spontaneous emission (ASE) light, which is amplified in the optical amplifier, is superimposed on the signal light. To do. Since this ASE light is superimposed by each optical amplifier connected to the transmission line in multiple stages, the ASE light increases cumulatively every time the signal light is amplified by the optical amplifier.

Since the ASE light becomes a noise component with respect to the signal light, the ratio of the signal light to the ASE light determines the optical signal-to-noise ratio (optical SNR). On the other hand, in order to obtain transmission characteristics required in an optical transmission system (for example, a bit error rate of 10 ⁻¹² or less), an optical SNR of a certain value or more is required. Therefore, in the operation of the optical transmission system, it is necessary to monitor the optical SNR and control individual devices incorporated in the optical transmission system so as to obtain a sufficient optical SNR.

  FIG. 7 shows the spectrum of the signal light amplified by the optical amplifier. This figure shows the optical spectrum when 11 wavelength signal lights multiplexed in wavelength are amplified. ASE light is superimposed on the signal light when amplified by an optical amplifier. FIG. 8 is a diagram for explaining the optical SNR measurement method of the signal light on which the ASE light is superimposed as described above, in which the vicinity of 1548 nm of the optical spectrum shown in FIG. 7 is enlarged.

  The ratio between the signal light power and the ASE level indicated by the arrow in FIG. 8 is the optical SNR of this signal light. Therefore, in order to measure the optical SNR, the signal light power and the ASE level near the signal light wavelength are required. For this reason, the optical SNR measurement requires an optical spectrum analyzer that measures the optical spectrum (Patent Document 1).

Japanese Patent No. 3569217 (for example, [Prior Art] column) Shintoku, et al., “Method for flattening transmission characteristics of AWG using higher-order modes”, 2002 IEICE General Conference, C-3-66, pp. 11-29. 198

  However, when an optical spectrum analyzer is provided in an optical SNR measurement apparatus, there is a problem in terms of downsizing and cost reduction of the apparatus. That is, in order to measure the signal light power and the ASE level in the vicinity thereof, an optical spectrum analyzer with good wavelength resolution is required. Therefore, the prior art has a limit to realize such an optical spectrum analyzer in a small size and at a low cost.

  In a small and low-cost optical spectrum analyzer, even though there is sufficient wavelength resolution to demultiplex the wavelength-multiplexed signal light for each wavelength to measure the optical power of the signal light, It may be insufficient to measure the ASE level near each wavelength. On the other hand, an optical spectrum analyzer having sufficient wavelength resolution to measure the ASE level increases the size and cost, which is a problem in mounting on an optical SNR measurement apparatus.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a technique for performing optical SNR measurement of signal light amplified by an optical amplifier without performing optical spectrum measurement. It is in.

  In order to achieve the above object, the present invention provides an apparatus for measuring an optical signal-to-noise ratio, wherein the first detection is performed by converting light into an electric signal. Means, a second detection means for detecting an electrical signal corresponding to the signal light included in the light, and a subtraction for subtracting the detection value at the second detection means from the detection value at the first detection means Means, and a dividing means for dividing the detected value of the first detecting means and the subtracted value of the subtracting means.

  The invention according to claim 2 is an apparatus for measuring an optical signal-to-noise ratio of wavelength division multiplexed light, wherein the wavelength division multiplexed light is demultiplexed into light of each wavelength, and the demultiplexed. First detection means for converting the detected light into an electrical signal and detecting it, second detection means for detecting an electrical signal corresponding to the signal light contained in the demultiplexed light, and the first detection means Subtracting means for subtracting the detection value at the second detection means from the detection value at the time, and dividing means for dividing the detection value at the first detection means and the subtraction value at the subtraction means. It is characterized by.

  The invention described in claim 3 is the apparatus described in claim 2, characterized in that the demultiplexing means has a flat transmission spectrum characteristic.

  According to a fourth aspect of the present invention, there is provided the apparatus according to any one of the first to third aspects, further comprising a filter unit that transmits an electric signal corresponding to the signal light.

  The invention according to claim 5 is a method for measuring an optical signal-to-noise ratio, wherein the light is converted into an electric signal and detected, and an electric signal corresponding to the signal light included in the light is detected. Detecting a signal, subtracting a value obtained by detecting an electric signal corresponding to the signal light from a value detected by converting the light into an electric signal, and a value detected by converting the light into an electric signal. And dividing the subtracted value.

  The invention according to claim 6 is a method for measuring an optical signal-to-noise ratio of wavelength multiplexed light, wherein the wavelength multiplexed light is demultiplexed into light of each wavelength, and the demultiplexed. Detecting the converted light into an electrical signal, detecting an electrical signal corresponding to the signal light included in the demultiplexed light, and detecting the converted light into an electrical signal Subtracting the detected value of the electrical signal corresponding to the signal light from the measured value, and dividing the detected value by converting the demultiplexed light into an electrical signal. It is characterized by.

  The invention according to claim 7 is the method according to claim 5 or 6, further comprising selectively transmitting an electric signal corresponding to the signal light.

  The optical SNR measurement apparatus according to the present invention can perform optical SNR measurement of signal light amplified by an optical amplifier without using an optical spectrum analyzer. Therefore, the optical SNR measurement can be realized with small size and low cost.

(First embodiment)
FIG. 1 is a block diagram showing an example of an optical SNR measurement apparatus according to the first embodiment of the present invention. The optical SNR measuring apparatus 100 includes a photodiode (PD) 102 that receives signal light superimposed with ASE light, a distributor 104 that distributes the received electric signal, and a high-frequency amplifier that amplifies one of the distributed electric signals. 106, a band pass filter (BPF) 108 for filtering the amplified electric signal, and a detector 110 for detecting the filtered electric signal. The optical SNR measurement apparatus 100 also includes a distributor 112 that distributes the signal detected by the detector 110, a subtractor circuit 114 that subtracts the other of the electrical signals distributed by the distributor 104 from one of the distributed detection signals, and a subtraction. And a division circuit 116 that divides the detected signal by the other of the detection signals distributed by the distributor 112.

  When the signal light on which the ASE light is superimposed enters the photodiode 102, a current corresponding to the sum of the signal light power and the ASE light power is generated. This current is converted into a voltage and then distributed in two directions by the distributor 104. One of the signals is amplified by an amplifier (not shown) as necessary, and then input to the subtraction circuit 114. The input to the subtracting circuit 114 corresponds to the total optical power value of the signal light and the ASE light.

  On the other hand, the other signal distributed by the distributor 104 is amplified by the high frequency amplifier 106. The high-frequency amplifier 106 has an amplification band that can sufficiently amplify the frequency component of the modulation bit rate value of the signal light. The output of the high frequency amplifier 106 transmits the same frequency component as the bit rate value of the signal light by the band pass filter 108, and the power of the frequency component is detected by the RF power detector 110. The band pass filter 108 may be replaced with a high pass filter (high pass filter) that transmits the same frequency component as the bit rate value of the signal light. When a high-pass filter is used, a frequency component that is an integral multiple of the bit rate value of the signal light is mainly transmitted. The RF power detected here is a value uniquely determined with respect to the signal light power, and becomes a signal light power value by applying an appropriate coefficient.

  The output signal of the RF power detector 110 is distributed by the distributor 112, and one is input to the other input terminal of the subtracting circuit 114 described above. The two inputs to the subtracting circuit 114 correspond to the total optical power value and signal optical power value of the signal light and the ASE light, respectively. For this reason, the output of the subtracting circuit 114 corresponds to the ASE optical power. Therefore, by calculating the ratio between the output of the subtracting circuit 114 and the other output of the distributor 112 by the dividing circuit 116, a voltage corresponding to the optical SNR value can be obtained as an output. Note that the present invention is limited to the configuration of the present embodiment as long as the power of the signal light is detected by using an electric signal having the same frequency component as the bit rate value of the signal light and the optical SNR is measured by this. Not.

(Second Embodiment)
FIG. 2 is a block diagram showing a configuration example of an optical SNR measurement apparatus according to the second embodiment of the present invention. In this configuration example, the optical SNRs of a plurality of wavelength-multiplexed signal lights can be measured for each wavelength by using the plurality of optical SNR measurement apparatuses according to the first embodiment of the present invention. In this configuration example, an optical fiber for transmission 202, an optical coupler 204 that branches signal light from the optical fiber 202, an optical demultiplexer 206 that demultiplexes the branched signal light, and a signal of each wavelength that has been demultiplexed. It comprises N optical SNR measuring devices 100-1 to 100-N that perform optical SNR measurement of light.

  In the present embodiment, the wavelength-multiplexed signal light propagating through the optical fiber 202 is branched by the optical coupler 204. The branched signal light demultiplexes the signal light wavelength-multiplexed by the demultiplexer 206 into N signal lights for each wavelength. For example, 40-wavelength wavelength-multiplexed signal light is input to the input port of the optical demultiplexer 206, and 40-wave signal light is demultiplexed and output from the output port.

  FIG. 3 shows the transmission spectrum shape at one output port (center wavelength 1550 nm) of the optical demultiplexer 206. The center wavelength of the transmission spectrum matches the center wavelength of the signal light transmitted through the port, and the 3 dB bandwidth of the transmission spectrum is about 0.45 nm. At this time, when the signal light on which the ASE light is superimposed is incident, the signal light having a wavelength of 1550 nm and the ASE light having a bandwidth of about 0.45 nm in the vicinity thereof pass through the port of the demultiplexer and enter the optical SNR measuring device. To do. Note that output ports of other wavelengths have similar transmission spectrum shapes.

  FIG. 4 shows the result of measuring the optical SNR of the signal light having a different optical SNR and having a wavelength of 1550 nm using the optical SNR measurement apparatus of the present invention. The optical SNR of the signal light having a wavelength of 1550 nm is measured by an optical spectrum analyzer before being input to the optical SNR measuring apparatus, and the value is plotted on the horizontal axis of FIG. 4 with the optical SNR measured by the optical SNR measuring apparatus of the present invention. Is shown on the vertical axis. When the optical SNR measured by the optical spectrum analyzer matches the optical SNR measured by the optical SNR measuring apparatus of the present invention, the measurement point is on the straight line shown in FIG.

  From FIG. 4, it can be seen that the optical SNR measured by the optical SNR measuring apparatus of the present invention substantially matches the optical SNR of the input signal light. It can also be seen that the optical SNR can be measured with an error of 0.7 dB or less by the optical SNR measuring apparatus of the present invention. Similarly, it was confirmed that the optical SNR measurement apparatus of the present invention was able to measure the optical SNR with an error of 0.7 dB or less at the output ports of other wavelengths.

  As described above, the optical SNR measurement apparatus according to the present invention can measure the optical SNR of the signal light on which the ASE light is superimposed without performing optical spectrum measurement.

(Third embodiment)
The configuration example of the optical SNR measurement apparatus according to the third embodiment of the present invention is the same as that of the second embodiment shown in FIG. 2, but the transmission spectrum shape of the duplexer 206 is different. FIG. 5 shows a transmission spectrum shape at one output port (center wavelength 1550 nm) of the duplexer in the present embodiment. Unlike the duplexer used in the second embodiment, this transmission spectrum shape has a small wavelength dependency near the transmittance peak and is flat. As such a duplexer, a method using a method of deforming the incident waveguide shape, a method of cascading AWG and MZI, a method using a higher-order mode, or the like is known (see Non-Patent Document 1).

  In the optical SNR measurement apparatus according to the second embodiment, if the transmission spectrum shape of the duplexer is close to Gaussian and the signal light wavelength is slightly deviated from the transmittance peak wavelength, excessive transmission loss is added. For this reason, the detected value of the signal light power becomes small, and as a result, an error occurs in the optical SNR measurement. On the other hand, the duplexer used in the optical SNR measurement apparatus of the present embodiment has a transmission spectrum shape that is flat in the vicinity of the peak over approximately ± 0.2 nm (0.4 nm). Therefore, even if the signal light wavelength is deviated from the center wavelength by about ± 0.2 nm, an excessive error does not occur in the optical SNR measurement.

  FIG. 6 shows the optical SNR measurement apparatus according to the present embodiment and the optical SNR measurement apparatus according to the second embodiment for the change in the optical SNR measurement error with respect to the wavelength shift of the signal light (when shifted to the longer wavelength side from the center wavelength). The result is shown. In the optical SNR measurement apparatus according to the second embodiment, the optical SNR measurement error suddenly increased with respect to the wavelength shift of the signal light. However, in the optical SNR measurement apparatus according to the present embodiment, the signal light wavelength shift is almost 0.2 nm. A constant optical SNR measurement error was obtained. The optical SNR measurement error due to the signal light wavelength shift was the same when the signal light wavelength shifted to the short wavelength side.

  Furthermore, in the optical SNR measurement apparatus according to the present embodiment, since the transmission spectrum shape of the duplexer is flat near the peak, more ASE light near the signal light wavelength is detected, and as a result, the optical SNR The measurable range could be expanded by about 2 dB compared with the optical SNR measurement apparatus of the second embodiment.

  The present invention has been described above with respect to several embodiments. However, in view of the many possible embodiments to which the principles of the present invention can be applied, the embodiments described herein are merely illustrative, It is not intended to limit the scope of the invention. The configuration and details of the embodiment exemplified here can be changed without departing from the spirit of the present invention. Further, the illustrative components and procedures may be changed, supplemented, or changed in order without departing from the spirit of the invention.

It is a block diagram which shows an example of the optical SNR measuring apparatus by the 1st Embodiment of this invention. It is a block diagram which shows the structural example of the optical SNR measuring apparatus by the 2nd Embodiment of this invention. It is a figure which shows the transmission spectrum shape in one output port of the optical demultiplexer by the 2nd Embodiment of this invention. It is a figure which shows the result of having measured optical SNR using the optical SNR measuring apparatus by the 2nd Embodiment of this invention. It is a figure which shows the transmission spectrum shape in one output port of the optical demultiplexer by the 3rd Embodiment of this invention. It is a figure which shows the optical SNR measurement error with respect to the wavelength shift of the signal light at the time of using the optical SNR measurement apparatus by the 2nd Embodiment of this invention, and the optical SNR measurement apparatus by 3rd Embodiment. The spectrum of the signal light amplified by the optical amplifier and superimposed with the ASE light is shown. It is a figure for demonstrating the method to measure the optical SNR of the signal light on which the ASE light was superimposed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100,100-1-100-N Optical SNR measuring apparatus 102 Photodiode 104 Divider 106 Amplifier 108 Band pass filter 110 Detector 112 Divider 114 Subtraction circuit 116 Dividing circuit 202 Optical fiber 204 Optical coupler 206 Optical demultiplexer

Claims (7)

An apparatus for measuring an optical signal-to-noise ratio,
First detection means for detecting light by converting it into an electrical signal;
Second detection means for detecting an electrical signal corresponding to the signal light included in the light;
Subtracting means for subtracting the detection value at the second detection means from the detection value at the first detection means;
An apparatus comprising: a division unit that divides a detection value obtained by the first detection unit and a subtraction value obtained by the subtraction unit. An apparatus for measuring an optical signal-to-noise ratio of wavelength multiplexed light,
Demultiplexing means for demultiplexing the wavelength-multiplexed light into light of each wavelength;
First detecting means for detecting the converted light by converting it into an electrical signal;
Second detection means for detecting an electrical signal corresponding to the signal light included in the demultiplexed light;
Subtracting means for subtracting the detection value at the second detection means from the detection value at the first detection means;
An apparatus comprising: a division unit that divides a detection value obtained by the first detection unit and a subtraction value obtained by the subtraction unit. The apparatus of claim 2, comprising:
The demultiplexing means has a flat transmission spectrum characteristic. The apparatus according to any one of claims 1 to 3,
The apparatus further comprises filter means for transmitting an electrical signal corresponding to the signal light. A method for measuring an optical signal to noise ratio comprising:
Detecting light by converting it into an electrical signal;
Detecting an electrical signal corresponding to the signal light included in the light;
Subtracting a value obtained by detecting an electric signal corresponding to the signal light from a value detected by converting the light into an electric signal;
Dividing the detected value by converting the light into an electrical signal and the subtracted value. A method for measuring an optical signal-to-noise ratio of wavelength multiplexed light, comprising:
Demultiplexing the wavelength-multiplexed light into light of each wavelength;
Detecting the demultiplexed light by converting it into an electrical signal;
Detecting an electrical signal corresponding to the signal light included in the demultiplexed light;
Subtracting the detected value of the electrical signal corresponding to the signal light from the value detected by converting the demultiplexed light into an electrical signal;
Dividing the value detected by converting the demultiplexed light into an electrical signal and the subtracted value. The method according to claim 5 or 6, comprising:
The method further comprises selectively transmitting an electrical signal corresponding to the signal light.

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